id
stringlengths 6
14
| issn
stringclasses 15
values | title
stringlengths 4
1.08k
| fpage
stringlengths 1
4
| lpage
stringlengths 1
8
| year
int64 1.67k
1.92k
| volume
int64 1
220
| journal
stringclasses 12
values | author
stringlengths 3
395
⌀ | type
stringclasses 26
values | corpusBuild
stringclasses 1
value | doiLink
stringlengths 40
40
⌀ | language
stringclasses 4
values | jrnl
stringclasses 10
values | decade
int64 1.66k
1.92k
| period
int64 1.65k
1.9k
| century
int64 1.6k
1.9k
| pages
int64 1
1.38k
| sentences
int64 1
15.5k
| tokens
int64 10
255k
| visualizationLink
stringlengths 66
74
| doi
stringlengths 22
22
⌀ | jstorLink
stringlengths 34
36
⌀ | hasAbstract
float64 110k
113k
⌀ | isAbstractOf
float64 107k
112k
⌀ | primaryTopic
stringclasses 30
values | primaryTopicPercentage
float64 16
99.9
| secondaryTopic
stringclasses 30
values | secondaryTopicPercentage
float64 0.01
49.6
| category
stringclasses 24
values | tsne_embedding
sequencelengths 2
2
| text
stringlengths 44
1.01M
|
|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|
rspa_1912_0004 | 0950-1207 | The mechanics of the water molecule. | 102 | 105 | 1,912 | 86 | Proceedings of the Royal Society of London. Series A, Containing Papers of a Mathematical and Physical Character | R. A. Houstoun, M. A., Ph. D., D. Sc.|Prof. A. Gray, F. R. S. | article | 6.0.4 | http://dx.doi.org/10.1098/rspa.1912.0004 | en | rspa | 1,910 | 1,900 | 1,900 | 5 | 63 | 1,154 | http://corpora.clarin-d.uni-saarland.de/surprisal/6.0.3/?id=rspa_1912_0004 | 10.1098/rspa.1912.0004 | null | null | null | Atomic Physics | 48.77517 | Tables | 22.820621 | Atomic Physics | [
10.617203712463379,
-35.36957550048828
] | ]\gt ; 1 .
02 The Mechanics of the Molccnle .
By B. A. HOUSTOUN , M.A. , Ph. D. , D.Sc .
, Lecturer in Physical tics in the University of Glasgow .
( Communicated by Prof. A. Gray , F.R.S. Received November 6 , 1911 , \mdash ; Read January 11 , 1912 .
) In the ultra-violet and visible spectrum water is very transparent .
In the infra-red it absorbs very strongly .
E. Aschkinass*has ated its absorption in the infra-red , and has represented his results in tables , giving a constant in terms of being defined by the equation where and I are the intensities before and after traversing a layer cm .
thick .
I have calculated into the more useful constant being the dielectric constant , and have plotted the result in the curve .
The two constants snd are connected by the relation CTRUU or WATER From the curve it is evident that water has two great maxima at and respectively .
These occur also in water vapour ; they do not occur in oxygen or hydrogen .
It seems therefore plausible to ) nect them with the linkings of the oxygen and hydrogen atoms .
A system of three atoms should , of course , have two periods .
' Ann. .
Phys 189 vol. 56 , p. 401 .
According to W. W. Coblentz watel ' becomes more opaque again in the region between and ; while , according to Rubens and Aschkinass , water apour is relatively transparent in region .
The , Ilechanics of the Water , Molecvle .
Let the figure represent an oxygen atom of mass and two hydrogen atoms each of mass .
The first hydrogen atom has lost one electron bo the second , and the second has lost two electrons to the oxygen atom .
We cannot connect the two hydrogen atoms directly to the oxygen atom , since from chemical considerations they are not situated in the same way with regard to the latter .
Let be respectively the co-ordinates of the three atoms , the number of water molecules per cubic centimetre , and X the component of the electric intensity in the light wave .
Then , by the theory of dispersion , If we write for , the right-hand side becomes since .
Substitute for for , and the equation finally becomes Now consider the equations of motion of the three atoms .
Since all equations in optics are linear , the forces between the atoms must be linear functions of the distances .
We can look upon the inverse-square-law pull as balanced by the structure of t , he atoms , or , better still , we can regard the three lines of force as acting like three equally strong spiral , a line of force being probably a more fundamental thing than the inverse square law .
If we suppose that there is no friction , the equations of motion are then Combine the first and second and the second and third of these equations , write and , and we obtain , ( 2 ) .
( 3 ) Let the transmitted radiation be of type , assume that the vibrations are forced , solve ( 2 ) and ( 3 ) and substitute in ( 1 ) .
Then we obtain , omitting the ntermediate steps .
' .
( 4 ) Now write for in ( 4 ) .
This is equivalent to writing equations ( 2 ) and ( 3 ) in the form The Mechanics of the ?
Molecule .
to the introduction of dissipative forces of a special kind .
On equating the imaginary parts of side , ( 4 ) then ives It can easily be shown that in through an absorption band the maximum change in is equal to half the maximum value of , and hence ( cf. curve ) must be ] than .
Assume that has the constant value the of absorption .
Then The positions of the two absorption bands are given by and .
The ratio of their wave-lengths is therefore The actual value should be Let be the maximum value of for an absorption band , the wavelength of the for which has half its maximum value , and the value of .
We have respectively for the first and second bands , and .
We shall the values for each band to calculate the value of For the first batld , If be easured in electromagnetic units cuts out .
Write except in the factor .
Then , for the other band we obtain On substituting for , and , we obtain from the first band and from the second .
As denotes the elementary Active of of electricity divided by the mass of the hydrogen atom it should be about 9660 .
The model has thus been tested numerically on three independent points .
It yives 2 for the ratio of the wave-lengths instead of , and it gives 7110 or 1550 for the value of instead of 9660 , according as we use tlIe first second band .
If we consider the simplicity of the assumptions made , and the room there for modification .
making different for the different ) , the agreement must be arded as ratifying .
The other maxima in the absorption spectrum are possibly due to mole complex lecules .
This is incidentally the first time that chemical bonds have been connected mathematically with absorption bands .
oscopic IConnectio with the Active fication of .
II .
of lements Compounds excited by the Nitrogen .
By the Hon. R. J. STRUTT , M.A. , F.R.S. , Professor of Physics , and A. , Assistant Professor of Physics , of Science and Technology , South tono .
( Received November 13 , \mdash ; Read November 23 , 1911 .
) [ PLATE 6 .
] Introductor ?
y. In continuation of previous accounts of the active modification of nitrogen , * and of the spectrum of the afterglow which is associated with it , the present paper ives further details of the spectra which are developed when various elements and compounds are inlroduced into the glowing gas .
investigations of the spectra were made by direct observation , and with a small quartz spectrograph , and greater resolving power was required a larger quartz raph and an instrument of the Littrow type were used .
The arrangements for producing the afterglow were as described in the previous papers .
By means of a mechanical pump a stream of purified * B. J. Strutt , Bakerian Lecture , ' Roy .
Soc. Proc 1911 , , vol. 85 , p. 219 .
A. and R. J. Strutt , ' Roy .
Soc. Proc 1911 , , vol. 85 , p.
|
rspa_1912_0005 | 0950-1207 | Spectroscopic investigations in connection with the active modification of nitrogen. II\#x2015;Spectra of elements and compounds excited by the nitrogen. | 105 | 117 | 1,912 | 86 | Proceedings of the Royal Society of London. Series A, Containing Papers of a Mathematical and Physical Character | Hon. R. J. Strutt, M. A., F. R. S.|A. Fowler, F. R. S. | article | 6.0.4 | http://dx.doi.org/10.1098/rspa.1912.0005 | en | rspa | 1,910 | 1,900 | 1,900 | 8 | 257 | 6,698 | http://corpora.clarin-d.uni-saarland.de/surprisal/6.0.3/?id=rspa_1912_0005 | 10.1098/rspa.1912.0005 | null | null | null | Atomic Physics | 83.79516 | Chemistry 2 | 10.527956 | Atomic Physics | [
0.49140670895576477,
-46.38688659667969
] | Active Modification of Nitrogen .
105 of electricity divided by the mass of the hydrogen atom it should be about 9660 .
The model has thus been tested numerically on three independent points .
It gives 2*32 for the ratio of the wave-lengths instead of 2*00 , and it gives 7110 or 1550 for the value of cjm instead of 9660 , according as we p.se the first or second band .
If we consider the simplicity of the assumptions made , and the room there is for modification ( c.g. making k different for the different linkings ) , the agreement must be regarded as gratifying .
The other maxima in the absorption spectrum are possibly due to more complex molecules .
This is incidentally the first time that chemical bonds have been connected mathematically with absorption bands .
Spectroscopic Investigations in Connection with the Active Modification of Nitrogen .
II.\#151 ; Spectra of Elements and Compounds excited ; by the Nitrogen .
By the Hon. R. J. Strutt , M.A. , F.R.S. , Professor of Physics , and A. Fowler , F.R.S. , Assistant Professor of Physics , Imperial College of Science and Technology , South Kensington .
( Received November 13 , \#151 ; Read November 23 , 1911 .
) [ Plate 6 .
] Introductory .
In continuation of previous accounts of the active modification of nitrogen , * and of the spectrum of the afterglow which is associated with it , f the present paper gives further details of the spectra which are developed when various elements and compounds are introduced into the glowing gas .
Preliminary investigations of the spectra were made by direct observation , and with a small quartz spectrograph , and when greater resolving power was required a larger quartz spectrograph and an instrument of the Littrow type were used .
The arrangements for producing the afterglow were as described in the previous papers .
By means of a mechanical pump a stream of purified * R. J. Strutt , Bakerian Lecture , 4 Roy .
Soc. Proc. , ?
1911 , A , vol. 85 , p. 219 .
t A. Fowler and R , J. Strutt , 'Roy .
Soc. Proc. , ' 1911 , A , vol. 85 , p. 377 .
Hon. R. J. Strutt and Mr. A. Fowler .
[ Nov. 13 , nitrogen at low pressure was passed through the discharge tube , and the afterglow was observed in a side tube , into which the various substances were introduced as required .
It will be remembered that a discharge with condenser and spark gap is necessary to develop the afterglow with maximum intensity .
Later experiments have shown that the afterglow is also generated by the ring discharge produced by electromagnetic induction when the pressure of the nitrogen is appropriately adjusted .
The spectrum of the exciting discharge is identical with that of the condensed discharge which has already been described ; that is , the first positive bands of nitrogen are feeble , the second positive bands very intense ( giving a bluish colour to the ring ) , the third positive group absent , and the fourth positive bands present .
We mentioned in our previous paper ( p. 377 ) that the deep yellow afterglow was destroyed by a small amount of oxygen in the nitrogen employed , and that only a bluish-white luminosity was then visible .
This is due , as we have since ascertained , to the formation of a small quantity of nitric oxide by combination of oxygen and nitrogen in the discharge ; for the same effect is produced if a very small quantity of ready made nitric oxide is introduced into the stream after it has passed the discharge tube .
Larger quantities introduce a different phenomenon\#151 ; the yellow-green flame with continuous spectrum.* The effect of a small nitric oxide admixture is to suppress the a-group of afterglow bands , leaving the rest of the afterglow spectrum untouched .
Metallic Elements .
Sodium.\#151 ; It has already been pointed out by one of us that when sodium is heated a little above its melting point in the presence of active nitrogen , the sodium spectrum is developed with great brilliancy ; when heated more strongly , the vapour close to the metal becomes visibly green , and in this region the D lines almost vanish , while the pair of green lines about 5685f is shown very strongly .
Other lines of the subordinate series are also very bright , and lines of potassium appear as impurities .
As regards the principal series , the photographs suggest that the suppression of the D lines does not so much indicate a tendency towards the extinction of this series as a change in the position of maximum intensity to the next pair of lines in the series near 3303 , which is the strongest in the whole spectrum ; other lines of the principal series at 2853 and 2680 are also well visible .
In the first subordinate series the greatest intensity is towards the red * R. J. Strutt , ' Roy .
Soc. Proc. , ' in corirse of publication , t Wrongly referred to in the Bakerian Lecture as the E line .
1911 .
] Active Modification of Nitrogen .
end , and the colour of the glowing vapour indicates that the maximum occurs at the green pair 5685 .
The second subordinate series is relatively very weak .
Apart from the redistribution of intensity in the principal series , however , the spectrum approximates very closely to that given by sodium in the oxy-hydrogen flame or electric arc .
The suppression of the I ) lines recalls an experiment described many years ago by Lockyer , * in which a similar result was obtained .
In this case an electric discharge was passed through a capillary tube which was in connection with a wider tube containing heated metallic sodium , the platinum electrode nearest to the metal being a few inches above it .
There was no obstruction between the electrode and the sodium , and the only gas present was the hydrogen given off by the metal .
The similar results obtained in hydrogen and nitrogen suggested that in both cases the effect might be due to the production of the spectrum under reduced pressure .
We have not , however , been able to produce the same phenomenon by passing a discharge through sodium vapour in a vacuum tube , although the lines of the subordinate series were well displayed under these conditions .
Potassium.\#151 ; The photographed spectrum was rather faint , but it showed very clearly the lines of the principal series at 4046 , 3447 , 3217 , and 3102 , the first named being by far the strongest .
Several lines belonging to the two subordinate series were shown faintly , and there were feeble indications of a band fading to the violet , with its head about 460 .
Magnesium.\#151 ; The spectrum of this metal was only observed with difficulty , and the photograph obtained was not very strong .
Nevertheless it sufficed to show that the spectrum did not contain any of the characteristic spark lines , such as that at 4481*3 .
The characteristic flame line at 4571 appeared faintly , while the adjacent line at 4703 , which is a much stronger line in the arc spectrum , did not appear .
The spectrum thus approximates closely to that given by the flame , but it tends to be intermediate between the liame and the arc .
The lines photographed are shown in the following table :\#151 ; Wave-length .
Intensify in glow .
4571 -33 1 3838 '44 10 3336 -83 1 3097 -06 3 2852 -22 2 2779 -94 3 Remarks .
Characteristic flame line .
1st line of triplet , 1st subordinate series .
a f ) 2nd " , , jj a a a it a 1\#174 ; ^ a a Arc line , not included in series .
J.he b group was observed visually , but was not photographed .
* 1 Roy .
Soc. Proc. , ' 1879 , vol. 29 , p. 266 .
Hon. R. J. Strutt and Mr. A. Fowler .
[ Nov. 13 , Mercury.\#151 ; The mercury line spectrum is well developed in active nitrogen , and the photograph shows all the stronger lines of the arc spectrum which are given by Kayser and Eunge .
With the exception of the pair 5790 , 5769 , and the line 4078 , all the lines photographed belong to the two triplet series , and include numbers 4 and 5 of the first subordinate series , and numbers 3 and 4 of the second subordinate series .
The relative intensities of the lines are not notably different from those of the arc spectrum .
Comparisons with the spectrum of a mercury lamp revealed no distinct difference .
Thallium.\#151 ; The chloride of the metal was employed in this experiment , but no bands special to the compound were observed or photographed .
The glow produced was bright green , and the spectrum consisted of numerous sharply defined lines .
With the exception of two probable impurity-lines at 3239 , 3220 , the lines agree very closely with those of the arc spectrum , as regards their relative intensities , but there are indications that the second subordinate series is somewhat weaker than in the arc .
Nickel.\#151 ; Nickel chloride was used , but the only bands observed were afterwards found to be identical with* those given by cuprous chloride , and they may therefore be referred to an impurity of copper in the substance employed .
Some of the lines of copper were also shown in the photographs .
In addition , between 20 and 30 lines due to nickel itself were photographed , and these are identical with the strongest arc lines of the metal , so far as they can be identified with the small dispersion employed .
The lines were most distinct in the ultra-violet region , 3620 to 2900 , where there were no copper bands to mask them .
The Halogens .
Iodine.\#151 ; The vapour given off by iodine at ordinary temperatures readily generates a characteristic bright blue glow when it comes in contact with active nitrogen .
The spectrum shows a broad faint band in the green , and a number of ill-defined bands in the blue and ultra-violet , of which one at about 3430 is by far the most prominent ( Plate 6 , fig. 1 ) .
In addition , there is an apparently continuous background , which is feeble on the less refrangible side of a band at 4770 , but is quite strong from that wave-length to the most refrangible part of the spectrum shown on the photographs .
The bands as a whole do not appear to have been previously recorded , but the strongest band has been noted by Konen , * who describes it as extending from 3430 to 3340 .
We have found , however , that the vacuum tube shows all the bands of the glow spectrum in the region compared ( 3200 to 5900 ) , * ' Wied .
Ann. , ' 1898 , vol. 65 , p. 269 .
1911 .
] Active Modification of Nitrogen .
109 but the vacuum tube differs from the glow in showing greater luminosity in the less refrangible parts of the spectrum .
Also , while the most intense band in the vacuum-tube is at 4310 , that in the glow is at 3430 .
Details relating to the bands of the glow spectrum are given in the appended table .
Wave-lengths of Iodine Bands .
\#151 ; r Approx , wave-lengfcli : Intensity .
Approx , wave-length .
Intensity .
4770 5 2890 3 4620 3 2835 2 4310 5 2775 2 3890 2 2720 1 3535 1 2480 2 3495 1 2430 1 3430 10 2380 1 3270 2 2075 5 The last on the list , at 2075 , is a strong sharp line , quite unlike the others in appearance , but there seems to be no reason to assign it to any impurity , as it has not been found in mercury or any other substance likely to be present .
The band at 4770 was photographed with the Littrow spectrograph , but there were no signs of resolution into fine lines in a spectrum of purity 3000 in that region .
It should be noted that the flutings shown in fig. 1 , which only occupy the upper half of the spectrum , are due to nitrogen .
Bromine.\#151 ; The luminosity in this case was very feeble , and the photograph of the spectrum shows only one band which can be attributed to bromine .
This is a broad symmetrical band , having ill-defined edges about 2930 and 2890 .
A band in the orange , dominating the colour of the glow , was observed visually .
[ Note added Deeeinber 5.\#151 ; This band is not identical with the yellow-green band recorded in the vacuum tube spectrum by Eder and Valenta .
With moderate dispersion it was found to consist of eight narrow bands extending from about 5875 to 6070 , at nearly equal distances of 28 tenth-metres .
] Lines of aluminium were well seen in this spectrum , the metal having been carried forward into the glowing gas , probably in the form of a volatile bromide .
Chlorine.\#151 ; The spectrum of chlorine excited by active nitrogen was similar to that of bromine , but the single broad band shown on the photograph occurs in a more refrangible part of the spectrum , namely , 2600 to 2540 .
No lines of chlorine were recorded on the photograph .
no Hon. II .
J. Strutt and Mr. A. Fowler .
[ Nov. 13 , Compounds of Metals .
Cuprous Chloride.\#151 ; The blue-green glow developed by cuprous chloride gives a spectrum which is generally similar to that of the same substance when volatilised in the Bunsen flame .
The afterglow , however , produces a greater number of lines of copper , and the band spectrum of the chloride is more completely developed .
The chloride bands are also better visible in the glow than in the flame , in consequence of the absence of overlying continuous spectrum : A series of bands which is either absent from the flame , or is very weak , is a conspicuous feature in the glow spectrum .
These bands are more refrangible than those which occur in the flame , their approximate wave-lengths being 4150 , 4080 , 4010 , 3945 , 3885 , 3835 , 3785 , 3740 .
The intervals between the bands suggest that they form a connected series which is related to those in which the flame bands have been arranged by Kien.* Chlorides of Tin.\#151 ; Stannous and stannic chlorides produce a brilliant blue glow .
The most striking feature shown on a photograph of the spectrum of stannic chloride is an intense band in the blue , extending from about 4000 to 5000 ; with small dispersion , the band shows no signs of any maxima , and fades off gradually in both directions ( Plate 6 , fig. 2 ) .
In addition there are seven lines of tin between 3262 and 2706 , which are identical with the strongest lines of the arc spectrum in this region .
There are other faint lines at the approximate positions 3855 , 3780 , 3748 , 3480 , and 3474 , which have not yet been identified .
A photograph of the blue band , taken with the Littrow spectrograph , shows that it is not perfectly continuous .
Superposed on the continuous background , there are several symmetrical but ill-defined bands , 4 or 5 tenth-metres broad , which show no further signs of resolution in a spectrum of a purity of about 4000 in the region where the bands occur .
Accurate measures of these bands cannot be obtained , and it will suffice to state that there are 15 bands between 4768 and 4430 , at nearly equal distances of 24 tenth-metres .
Some of the bands are double .
The bands are very similar in appearance to those which occur in fluorescence spectra , as , for example , that of uranium phosphate .
An experiment was accordingly made in order to ascertain if a fluorescence could be obtained by the action of ultraviolet light on stannic chloride . .
A small quantity of stannic chloride was placed in a quartz tube , 2 cm .
in diameter , which was exhausted and sealed , the liquid chloride being frozen with liquid air during this operation .
The quartz tube was then * ' Zeit .
fiir Wiss .
Pliotog .
, ' 1908 , vol. 6 , p. 337 .
1911 .
] A ctive Modification of Nitrogen .
Ill examined in a concentrated beam from an electric lantern with quartz condensers , with and without a deep violet glass .
But no fluorescence could be observed , either at the ordinary temperature or when the tube was warmed .
Experiments on the vacuum-tube discharge through the vapour of stannic chloride showed that the discharge was generally similar in colour to the glow produced in active nitrogen , but was not so perfect a blue .
The vacuum-tube spectrum , however , showed the same strong blue band as the glow , but there was also a fairly bright continuous , or nearly continuous , spectrum extending from the blue band to the red .
Lines of tin were also more prominent in the vacuum-tube than in the glow .
Mercuric Iodide.\#151 ; This substance yields a violet glow , and the spectrum shows bands which appear to be characteristic of the compound , together with a feeble band which coincides with the principal band of iodine about 3430 .
Mercury was only represented by the line 2536*7 , which was no stronger than in other spectra obtained in the same manner when mercury was only accidentally present .
The strongest band begins at about 4455 .
It is very intense from that point to 4390 , after which it fades off rather rapidly to the neighbourhood of 3700 .
With the small resolving power employed , the band is a nearly continuous one , but there are indications of numerous ill-defined maxima .
The spectrum , as a whole , is similar to that described by Jones , * and afterwards by Lohmeyer , f as occurring in mercuric iodide rendered luminous in a vacuum tube .
For the brightest band the wave-length of the beginning is given by Jones as 4396 , but from the description there can be no doubt that it is the same band as that found in the glow .
Lohmeyer 's wave-lengths , giving the brightest parts of the band as lying between 4456 and 4393 , confirm this .
The remaining ( faint ) bands agree with those tabulated by Jones .
Sulph ur and its Compounds .
Sulphur.\#151 ; When sufficiently heated in the glowing nitrogen , sulphur gives a blue glow .
The spectrum consists of a succession of bands , degraded to the red , and very evenly distributed .
Between 4700 and 2800 there are about 30 principal bands , some of which are complex groups or doublets .
There was little or no continuous spectrum .
The spectrum has nothing in common with that of sulphur in a vacuum tube , but it is closely related to that given by the flame of carbon disulphide burning in air .
In the * 4 Ann. d. Physik .
, ' 1897 , vol. 42 , p. 50 .
t 4 Zeit .
fiir Wiss .
Photog .
, ' vol. 4 , p. 376 .
Hon. R. J. Strutt and Mr. A. Fowler .
[ Nov. 13 , flame , however , the bands are superposed on a moderately strong continuous spectrum , and those which are more refrangible than 3400 are only very feebly displayed.* When the flame was supported by oxygen , it was found that the bands were barely visible , while another group in the region 3000 to 3200 ( seen also in the flame of burning sulphur ) was introduced .
Sulphuretted Hydrogen,.\#151 ; The spectrum obtained when sulphuretted hydrogen was introduced into active nitrogen was identical with that given by sulphur in the nitrogen .
Carbon Disulphide.\#151 ; The spectrum given by carbon disulphide in nitrogen showed the bands already described as occurring with sulphur , but the bands were only well developed on the less refrangible side of 3700 .
The cyanogen band 3883 and the carbon line 2478 were shown feebly .
In the ultra-violet there was an additional series of well-marked bands , degraded to the red , having their heads about 2550 , 2592 , 2620 , 2665 , 2700 , 2745 , 2785 , 2830 , 2920 .
These bands were also present , in an ill-developed form , and superposed on continuous spectrum , in the carbon disulphide flame .
They appeared also in the spectrum of impure sulphurous anhydride in a vacuum tube , while the less refrangible group previously described was absent .
Further investigations will be undertaken to determine whether the different groups of bands represent different compounds of sulphur , or sulphur in different molecular states .
Compounds of Carbon .
The introduction of many of the compounds of carbon into the nitrogen afterglow results in the development of the spectrum of cyanogen , and direct chemical evidence of the formation of cyanogen has been obtained.f The cyanogen spectrum was strongly developed in cyanogen , ethyl iodide , chloroform , carbon tetrachloride , and acetylene , and it was also seen , with less intensity , in methane , pentane , ethylene , alcohol , ether , and benzol .
An investigation of the spectra thus obtained , however , has revealed some interesting peculiarities .
The cyanogen spectrum , as given by the flame of the burning gas , has long been recognised as consisting of two principal sets of bands .
One of them occupies the red , yellow , and green parts of the spectrum , and the flutings composing the bands are degraded to the red .
The other consists of groups of flutings in the violet and ultra-violet , degraded to the violet , which * The chief bands of the CS2 flame spectrum are about 3370 , 3420 , 3500 , 3557 , 3590 , 3645 , 3680 , 3740 , 3835 , 3940 , 4050 , 4080 , 4160 , 4200 , 4275 , 4310 , 4440 , 4480 .
t R. J. Strutt , loc. cit. , p. 228 .
Active Modification of Nitrogen .
1911 .
] are especially well known in consequence of their great brilliance in the spectrum of the carbon arc .
For convenience of reference , these two sets of bands may be distinguished as the red and violet groups respectively .
In addition , there are four groups of fainter flutings in the ultra-violet , degraded to the red , which have been regarded as the probable " tails " of the violet bands.* The different compounds of carbon do not all behave in the same way when in contact with active nitrogen .
In most cases , the " flame " produced was of a lilac tint , very similar to that of the cyanogen flame , but in the case of carbon tetrachloride , or chloroform , the flame was orange in colour and more luminous , and the red spectrum of cyanogen was more strongly developed in relation to the violet .
The " Red " Bands.\#151 ; In carbon tetrachloride ( Plate 6 , fig. 3 ) and chloroform the red spectrum is very brilliant , and is particularly free from contamination with other spectra .
The photographs give only feeble indications of the stronger of the second positive bands of nitrogen , and they show no traces of carbonic oxide , or of the Swan bands of carbon .
Moreover , the system of bands can be traced clearly into the blue-green and blue , where there are several easily visible bands which are not seen , or only seen with difficulty , in the ordinary flame or vacuum-tube spectrum .
This method of producing the spectrum accordingly offers special advantages for the study of the regularity of the bands , and it has been utilised by Messrs. Fowler and Shaw in a separate investigation of the red cyanogen spectrum as obtained from different sources.f Previous accounts of this spectrum have been very incomplete , and only roughly approximate wave-lengths of the bands have been available .
In the small scale photograph reproduced in fig. 3 , and in visual observations , the bands appear to follow each other at nearly equal intervals and to show no marked discontinuity as regards their intensities .
Other photographs taken with shorter exposures , however , show that the principal bands occur in groups of three , of which the middle one is the brightest in each case .
It has been found that all the bands can be arranged in seven regular series , similar to those which constitute the first positive band .spectrum of nitrogen .
The Violet Bands.\#151 ; The familiar cyanogen bands in the violet and ultraviolet are greatly modified in all the carbon compounds which produce a visible luminosity when they are brought in contact with active nitrogen .
* King , 4 Astrophys .
Journ. , ' 1902 , vol. 14 , p. 323 ; Jungbluth , 4 Astrophys .
Journ.,5 1904 , vol. 20 , p. 237 .
t 'Roy .
Soc. Proc. , ' this vol. , p. 118 .
VOL. LXXXVI.\#151 ; A. I Hon. R. J. Strutt and Mr. A. Fowler .
[ Nov. 13 , Considerable resolving power is necessary to show the character of the changes clearly , and the Littrow spectrograph was utilised in obtaining the comparative spectra which are reproduced on an enlarged scale in Plate 6 , figs. 4 and 5 .
It will be seen that the details of the violet groups are very different in the glow as compared with the carbon arc .
Taking the 4216 band of the glow spectrum as a typical case , there is a modified development of the structure lines proceeding from the first and third heads ( counting from red to violet , or right to left ) , and a partial suppression of the second and fourth heads .
The structure lines emanating from the first head are identical with lines in the corresponding part of the arc band , but there is a conspicuous interruption of the sequence at a short distance from the head , after which the lines became stronger and overrun the second head , which itself appears to be rather weak .
A similar effect is observed in the case of the third head , the structure lines of which overrun the fourth , but the third head is not nearly so strong as the first .
These effects are apparently identical with the variations in the negative band of nitrogen 3914 , and in the cyanogen band 3883 , which have been observed by Deslandres* as the pressure was reduced from one atmosphere to a few millimetres .
We have confirmed this observation in the case of the first heads of the cyanogen bands 4216 and 3883 , and the differences between the glow and arc bands , to which reference has so far been made , are therefore probably due , either directly or indirectly , to the fact that the cyanogen bands in the glow were produced at a relatively low pressure ( 5 to 10 mm. ) .
A still more striking difference between the glow and arc bands occurs in the most refrangible part of each of the violet groups .
There is a special increase of intensity in this region , which may possibly be due to a local intensification of some of the series of structure lines , or to the introduction of entirely new bands .
Until still greater resolving power can be employed , it will be difficult to determine the exact nature of the difference , but the development of new bands offers the simplest explanation .
In favour of this view is the observation that the structure lines of the glow bands do not all occur in the bands of the arc , and also the fact that in some of the photographs ( e.g. in cyanogen , Plate 6 , fig. 6a ) the supposed new bands are far stronger than the first heads of the groups .
Assuming that new bands are developed , their less refrangible edges would be about 4495 ( in the 4606 group ) , 4153 ( in the 4216 group ) , and 3850 ( in the 3883 group ) .
Each band must then be supposed to consist of a group of close lines extending over about 9 tenth-metres , this group being followed by a gap of * 4 Comptes Rendus , ' 1904 , vol. 139 , p. 1179 .
1911 .
] Active Modification of Nitrogen .
115 about 3 tenth-metres , and this again by another group of lines extending over about 10 tenth-metres .
The " new " bands are especially intense in ethyl iodide , cyanogen , and acetylene ; they are also well marked in ethylene and chloroform , but are not nearly so pronounced in carbon tetrachloride .
Stimulation of cyanogen by the nitrogen afterglow is not the only means of producing these new bands , a\amp ; they also appear on the photographs of the spectrum produced by the phosphorescent combustion of cyanogen in ozone.* We have not yet succeeded in obtaining the new bands clearly in vacuum-tube discharges through cyanogen , but there were feeble indications of their presence when wide discharge tubes were employed .
Special care has been taken to show that the spectrum given by cyanogen itself in the nitrogen afterglow has the same peculiarities as that produced from other carbon compounds .
When the cyanogen from mercuric cyanide is merely passed through a phosphorus pentoxide drying tube , the removal of water vapour is not complete , and the hydrocarbon band 4315 usually appeared in the spectrum obtained .
It seemed possible , therefore , that the modifications of the violet bands in this case might result from the presencer of hydrocarbons formed by interaction of water vapour with cyanogen .
An experiment was accordingly made in which the cyanogen introduced into the afterglow had been kept in contact with the drying agent for five days .
In this case ( fig. 6a ) the hydrocarbon band did not appear , but the violet cyanogen bands presented the same appearances as before .
Hence , the stimulation of ready-made cyanogen by active nitrogen produces the same modifications of the violet bands as are observed when the gas is produced by the interaction of nitrogen with other carbon compounds which give luminous effects .
The modified bands therefore do not represent cyanogen in course of formation , as might , perhaps , have been supposed .
As previously suggested , ]- it would seem that cyanogen is immediately produced by admixture of the carbon compounds with active nitrogen , and that the observed spectrum is due to the subsequent stimulation of the gas by the peculiar conditions existing in the afterglow.^ The Cyanogen " Tail " Bands.\#151 ; The ultra-violet groups of flutings , fading * R. J. Strutt , 4 Phys. Soc. Proc. ' The 44 unknown " bands mentioned in this paper as occurring at 431 and 415 appear to be respectively the hydrocarbon band 4315 and the new band of cyanogen 4153 .
The cyanogen band 4606 is also represented by a band about 450 , which would correspond with another of the new cyanogen bands .
+ R. J. Strutt , 4 Roy .
Soc. Proc. , ' vol. 85 , p. 228 .
X It should be mentioned that the photographs of the spectrum generated by the specially dried cyanogen in the afterglow of nitrogen show two of the bands ( 4679 and 4365 ) of the 44 high pressure " spectrum observed in carbon monoxide by Fowler I 2 116 Hon. R. J. Strutt and Mr. A. Fowler .
[ Nov. 13 , towards the red , which have been regarded as tails of the violet groups , are also very considerably modified in the glow cyanogen as compared with their appearances in the carbon arc ( Plate 6 , fig. 6 , where the bands in the arc are indicated by black dots ) .
So far as can be determined from the photographs available , including some taken with the Littrow spectrograph , the bands are changed in the glow .in the same manner as the first heads of the 4216 and 3883 groups ; that is , there is an intensification of the structure lines near the head of each band , a conspicuous break in the sequence of the lines at a short distance from the head , and a greater development of the lines immediately following the break .
It is probable that a complete investigation of the structure of these bands , in relation to the modified violet bands , would throw additional light on the supposed connection of the two groups , but it would be a laborious piece of work , and cannot at present be undertaken .
In addition to the bands noted by King at 3910 , 3945 , 3985 , there is evidently one near 3883 , and another about 4030 .
The Hydrocarbon Band 4315.\#151 ; The hydrocarbon band 4315 appeared in the glow spectrum in the case of carbon compounds which contain hydrogen , and in cyanogen which had not been completely freed from water vapour .
Like the cyanogen bands , this also shows very considerable modifications as compared with the bands obtained from flames .
This will be seen from Plate 6 , fig. 7 , in which the band given by the oxy-coal-gas flame is compared with that given by acetylene in nitrogen .
No new lines appear in the glow band , but there are great differences in the relative intensities of the structure lines in the two spectra .
Particularly striking is the concentration of luminosity about the head of the band at 4315 .
This is followed by a dark space about 5 tenth-metres broad , on the more refrangible side , after which there is a special intensification of the first half-dozen structure lines .
On the less refrangible side , the flame line 4324 almost disappears in the glow , and the more refrangible members of the group lying between 4335 and 4390 are especially developed .
The character of the change corresponds generally with that of the violet cyanogen bands , and of the negative band of nitrogen 3914 , under reduced pressure , and the variations are possibly to be accounted for in the same manner .
( 'Monthly Notices R.A.S. , ' vol. 70 , p. 490 ) .
These bands had not.then been observed in any other compound of carbon and were provisionally attributed to carbon monoxide ; their presence in cyanogen may have been due to an impurity , or the real origin of the bands may be carbon .
The bands in question are generally similar in structure to the new cyanogen bands 4495 , etc. , and it is remarkable that they occupy positions with respect to the bands of the Swan spectrum corresponding to those which the new cyanogen bands occupy with respect to the violet bands 460 , 421 , and 388 .
\#151 ; J o -J o cr u I- L*~ .
\lt ; z Ld ci\gt ; o O ' t z z O Ui Q_ O _i Ld \gt ; Ld O \lt ; cc h* o U Q_ CO ( Ni Nh r-\gt ; VO 1911 .
] Active Modification of Nitrogen .
Summary and Conclusions .
( 1 ) The spectra generated by the nitrogen afterglow do not differ fundamentally from those , which can be produced by other means of excitation .
In many cases , however , band spectra are better displayed in the glow , and the more refrangible parts of the spectrum are more completely developed .
The method therefore adds to our resources for the production of spectra .
( 2 ) The spectra of metallic substances approximate to those obtained in the electric arc , or are intermediate between arc and flame spectra .
In the case of sodium , when sufficiently heated , the maximum intensity in the principal series is at \ 3303 , the D lines being nearly extinguished .
( 3 ) The spectra given by iodine , chloride of tin , and mercuric iodide are very similar to those obtained from vacuum tubes .
There is , however , a greater development of the more refrangible parts of the spectrum in the case of the glow .
( 4 ) The band spectrum of cuprous chloride is more completely developed in the glow than in the Bunsen flame .
It shows an additional series of bands in the ultra-violet which is probably related to the series which constitute the flame spectrum .
( 5 ) The spectra exhibited by sulphur , sulphuretted hydrogen , and carbon disulphide consist of bands which are quite distinct from those given by sulphur in a vacuum tube , but resemble the bands of the carbon disulphide flame in air .
( 6 ) The cyanogen spectrum which is developed in the glow by cyanogen and certain other compounds of carbon differs in several respects from that observed in the cyanogen flame or carbon arc .
Some of the differences appear to be due to the production of the spectrum at a relatively low pressure in the glow .
A new set of bands , occupying positions near the more refrangible edges of the violet groups , occurs in the glow spectrum , and has also been observed during the phosphorescent combustion of cyanogen in ozone .
DESCRIPTION OF PLATE .
( 1 ) Spectrum of iodine in afterglow .
( 2 ) Spectrum of stannic chloride in afterglow .
( 3 ) Spectrum of cyanogen produced by carbon tetrachloride in afterglow .
( 4 ) , ( 5 ) The cyanogen bands 4216 and 3883 ; ( a ) as given by carbon arc in air ; ( b ) as given by acetylene in the afterglow .
( 6 ) A group of " tail " bands of cyanogen ; ( a ) and ( c ) as given by cyanogen and carbon tetrachloride respectively in the afterglow ; ( b ) as given by the carbon arc in air .
The marked heads are 3910 , 3945 , 3985 , 4030 .
The greater development of the new bands 4153 , 3850 , by cyanogen , as compared with carbon tetrachloride , is also shown .
( 7 ) The hydrocarbon band 4315 ; ( a ) as given by the oxy-coal-gas flame ; ( b ) as given by acetylene in the afterglow .
|
rspa_1912_0006 | 0950-1207 | The less refrangible spectrum of cyanogen, and its occurrence in the carbon arc. | 118 | 130 | 1,912 | 86 | Proceedings of the Royal Society of London. Series A, Containing Papers of a Mathematical and Physical Character | A. Fowler, A. R. C. S., F. R. S.|H. Shaw, A. R. C. S., F. R. A. S. | article | 6.0.4 | http://dx.doi.org/10.1098/rspa.1912.0006 | en | rspa | 1,910 | 1,900 | 1,900 | 2 | 5 | 84 | http://corpora.clarin-d.uni-saarland.de/surprisal/6.0.3/?id=rspa_1912_0006 | 10.1098/rspa.1912.0006 | null | null | null | Atomic Physics | 44.469436 | Tables | 41.292327 | Atomic Physics | [
16.475114822387695,
-49.11394500732422
] | ]\gt ; , etc. 123 .
we consider , say , the vertical series , it is clear that the equation manner fifferent series tepresented bpplicable temainder bmere Hence , all the bands may be included in Table II.\mdash ; Regularity of Cyanogen Bands ( oscillation frequencies in vacuo ) .
-lu 2047 14098 l$6S 2042 15786 2014 13772 * Phil. ffig , [ 6 ] , vol. 3 , p. 348 .
* .
Bend 1902 , vol. 134 , p. 747 .
|
rspa_1912_0007 | 0950-1207 | A high-speed fatigue-tester, and the endurance of metals under alternating stresses of high frequency. | 131 | 149 | 1,912 | 86 | Proceedings of the Royal Society of London. Series A, Containing Papers of a Mathematical and Physical Character | Bertram Hopkinson, F. R. S. | article | 6.0.4 | http://dx.doi.org/10.1098/rspa.1912.0007 | en | rspa | 1,910 | 1,900 | 1,900 | 9 | 335 | 8,698 | http://corpora.clarin-d.uni-saarland.de/surprisal/6.0.3/?id=rspa_1912_0007 | 10.1098/rspa.1912.0007 | null | null | null | Measurement | 54.052804 | Tables | 18.302929 | Measurement | [
47.1900520324707,
-62.457881927490234
] | 131 A High-Speed Fatigue-Tester , and the Endurance of Metals under Alternating Stresses of High Frequency .
By Bertram JIopkinsox , F.R.S. ( Received November 20 , \#151 ; Read November 23 , 1911 .
) The deterioration of metals under the action of stress varying rapidly between fixed limits has been the subject of much experimental investigation .
It is found that the important factor in the rate at which this " fatigue " goes on is the algebraic difference of the limits between which the stress varies , usually called the " range of stress " ; and that the absolute position of these limits matters little , provided , of course , that the mean stress is not too large .
The number of applications of a given range of stress required to fracture the piece increases as the range is diminished , the general nature of the relation between the two being as shown in the curve ( fig. 1 ) , which represents the results of a series of tests -S * $ -a 1 " EgJL . ?
Test on , mild Steel bars by Dr. Stanton , i ~ 1IOO r.ft .
7TL 'Tension , ZzmzZ = / .
09 times comfiression limit .
Jtrobatble vatue of hrruZing range 24'5 tonsfier sq.in , .
3 * s \amp ; 7 Jlever\amp ; aZs , hundreds of thous-ccnds made by Dr. Stanton on mild steel .
In these observations the stress alternated between compression and tension , the ratio of the compression and tension limits being 1*09 .
The form of the curve suggests that a range of stress not much below 25 tons , which in an average specimen would just cause fracture after a million reversals , could never break the bar , however often applied .
One of the chief objects of the fatigue tests hitherto made has been to discover this " limiting range .
" At an early stage in these investigations the question was raised whether K 2 Mr. B. Hopkinson .
[ Nov. 20 , the endurance by the material of a given cycle of stress is affected by the rate of repetition of the cycle .
Besides its intrinsic interest , this question is of importance because on the answer to it depends the possibility of reducing the excessive amount of time taken to carry out fatigue tests .
The determination within a few per cent , of the limiting range requires several separate tests in which the cycle is repeated at least a million times , and even that number is not always sufficient to give a reasonably close approximation .
Wohler worked with 60 to 80 reversals per minute , and he found that the same wrought iron which could just sustain a million applications of a range of 23 tons broke after 19 million repetitions of a range of 17| tons .
The more recent machines have been run at much higher speeds , and there is now a machine of the Wohler type at the National Physical Laboratory which gives 2000 cycles of bending stress per minute .
Even at this speed , which I believe is the highest yet reached under conditions admitting of accurate measurement , it takes eight hours to do a million reversals .
Within these limits it does not appear that frequency of application has much effect on endurance , that is , it takes the same number of repetitions of stress alternating between given limits to rupture a bar whether they be performed fast or slow .
It is true that the experiments of Keynolds and Smith* suggested that endurance was less at high speeds , but this has not been confirmed by more recent work.f The weight of evidence seems to favour the conclusion that speed is without effect on endurance , at any rate up to 2000 applications per minute .
Eor reasons which I discuss in detail below I think that this independence of endurance and speed is to be expected a priori so long as the speed does not exceed a certain limit , but that if that limit be passed the number of repetitions of a given range required to produce fracture will begin to increase , and it seemed probable that the increase might become noticeable if the speed were so high as 7000 per minute .
It was mainly with the object of testing this point that I constructed the machine described in this paper , which gives alternations of stress at the rate of over 7000 per minute , or three times as fast as the highest speed hitherto attained .
I may say at once that , in the case of the mild steel which has been examined , the endurance is undoubtedly greater at the higher speed , not only in number of reversals , but also in the actual time taken to produce fracture .
Hence the machine does not , as I thought it might ( if the speed effect * ' Phil. Trans./ A , vol , 199 , p. 265 .
t See " The Endurance of Metals , '5 by Messrs. Eden , Eose , and Cunningham , Institution of Mechanical Engineers , October 20 , 1911 .
1911 .
] A High-Speed Fatigue-Tester , etc. 133 revealed were zero or small ) , serve the practical purpose of reducing the time required for fatigue tests .
It seems rather to open anew field for investigation , which differs from that covered by the older slow-speed machines .
Description of the Machine .
The apparatus ( which is shown semi-diagrammatically in fig. 2 ) is designed to give alternations of direct stress between any desired limits of tension and compression at the rate of 100 complete cycles per second , or more .
The test-piece A is fixed at the lower end , by means of a nut B , to the screwed pillar C , which again is fixed into a massive block of cast-iron D , forming part of the base .
The base is bolted to a concrete foundation .
At its upper end the test-piece carries an iron weight E ( about 180 lbs. ) , to the upper side of which is fixed the laminated armature F by means of yokes Gr .
An electro-magnet H is carried by the pillars and cross-pieces I , above and independently of the armature , so as to leave a small air-space across which the magnetic pull acts .
The magnet is excited by alternating current in the winding H ' and exerts a periodically varying pull along the axis of the piece , whose frequency is twice that of the current.* * When the experiments described in this paper were practically complete I learnt that Prof. Kapp had also \amp ; 134 Mr. B. Hopkinson .
[ Nov. 20 , The test-piece behaves as a spring , the lower end of which is held fixed by the inertia of the masses to which it is attached , while the upper end carries the mass E. The adjustments are such that the natural period of vertical oscillations of this system is nearly equal to the period of the varying magnetic pull .
The latter then sets up large forced oscillations of its own period .
If the two periods are so far different that the dissipative forces have not much effect , the amplitude of the range of pull experienced by the piece is to the range of pull exerted by the magnet approximately in the ratio 1/ ( 1 \#151 ; n2 ) , where n is the ratio of the two periods .
The range of stress in the piece can be adjusted coarsely by variation of the frequency of the magnet current , and more finely by changing the E.M.F. applied to the coils .
By means of wire guys Y the weight is constrained to move parallel to the axis of the piece .
Owing to the smallness of this movement the wires exert no appreciable pull in a vertical direction .
The weight is carefully balanced so that its centre of gravity is in the axis of the test-piece .
The extension of the piece is measured by means of a pair of extenso-meters L , which are shown in greater detail in fig. 3 .
The concave mirror of each of these instruments casts on to a transparent scale an image of a horizontal lamp filament .
When the instrument is in action the line image is drawn out into a band , whose ends are sharply defined , and whose length measures the range of extension in the piece .
The extensometer readings are calibrated by means of the micrometer screws 0 ( fig. 3 ) , and were checked when the machine was in action by observing , with microscopes , the movement of needle points attached to the blocks P , P. The extensometer always agreed with the microscopes within 3/ 10,000 inch , or 3 per cent , of the range , and the measurements of extension are certainly correct within that amount .
The form of test-piece used is shown in fig. 3 with the extensometers attached .
The section is 0*049 square inch .
Current is supplied to the machine from a 4-pole rotary converter , which takes continuous current at 100 volts from a storage battery .
Constant frequency in the supply of alternating current is , of course , of vital importance , and this is perfectly secured if the converter is driven from a battery which is not being charged or doing other work .
The converter has a weak field , and is therefore largely self-compensating as regards speed , a drop in battery voltage producing a constructed a fatigue-tester , in which direct stress was produced by the pull of an electromagnet excited by alternating current .
The principle of resonance is not , however , used in this machine .
A description of Prof. Kapp5s machine appeared in the ' Zeitschrift des Yereines Deutscher Ingenieure , ' Aug. 26 , 1911 .
1911 .
] A High-Speed Fatigue-Tester , etc. Mr. B. Hopkinson .
[ Nov. 20 , corresponding drop in the field current .
It is found that , once set going , the machine will continue to run for several hours , giving a constant stress within 2 per cent. , without being touched in any way .
The converter takes about 10 amperes at 100 volts when the machine is in action .
Test-coils of 100 turns each of fine wire placed round the magnet poles , just above the air-gap , are connected to an electrostatic voltmeter , and serve to measure the flux density , whence the magnetic pull can be calculated .
Typical curves showing the relation between frequency of supply current and the corresponding stress for a given magnetic pull are given in fig. 4 .
The pressure of supply was raised in each case in proportion to the frequency , Relation , behcreen frequency and sh Tflagnehc fudl constant for each curve:-Tbr Dj Sc 113 , 0 4 Ions fuzr scy .
ui td n " " " / J^requertcy x\gt ; f fwJJL , cycles fier second .
so that the flux density , and therefore the range of pull applied by the magnet , remained constant .
The frequency was accurately measured by counting the beats between the notes produced by the machine and by a standard tuning fork .
In one case ( Di ) the maximum pull produced in the piece at the point of resonance was about 75 times , and in another ( UB ) ( taken under similar conditions ) 35 times the magnetic pull .
The ratio between these quantities at the resonance point depends mainly on the rate of dissipation of energy by elastic hysteresis in the test-piece and its attachments , and by vibrations communicated to the ground .
A bar of steel subjected to alternations of stress at the rate of 100 cycles or more per second in this machine gets perceptibly warm even when the stress is apparently within 1911 .
] A High-Speed Fatigue-Tester , etc. 137 the elastic limit .
It was observed that much more heat was developed in the bar UB than in Di ( which was of a different brand of steel ) , and it is probable that the difference between the two curves is mainly due to this cause .
When these trials were made the machine was bolted to a very heavy block of concrete , and it is improbable that much energy was dissipated by vibration .
When the third curve ( D2 ) was taken , the machine had been shifted on to a lighter foundation .
The vibration in the surrounding floor was then perceptibly greater , and this is probably the cause of the smaller magnification of pull observed in this case ( about 17 times ) .
It will be observed that the resonance point is much less marked , the curve having a flatter maximum .
This is in practice an advantage , though more power is taken to drive the machine , because the stress is less affected by slight alterations of speed .
The pull of the magnet varies between zero and a maximum value , and is always such as to give tension in the piece .
The mean value of this pull is half the maximum value or range of pull , and ( in consequence of the magnification by resonance ) is small compared with the total range of stress .
Such as it is , it is more or less counteracted by the weight of the mass E , so that in the normal working of the machine the mean stress is almost zero , and the limits of stress are nearly equal in tension and compression .
The machine has been used in this way throughout the experiments described in this paper .
It is easy to apply any desired steady tension by means of a screw and spring balance ( see fig. 2 ) , and thus to alter the ratio of the tension and compression limits .
Measurement of Stress .
As already indicated , the quantity directly measured in this machine is the change of length of the piece in inches .
By applying a static pull to the same piece in a testing machine the relation between pull in pounds and extension in inches can be directly determined , and the stress can then be calculated from a measurement of the section of the reduced portion of the bar on the assumption that Young 's modulus is the same for the rapid ' alternating stress as for the steady pull .
The experiments of Sears on the longitudinal impact of rods* justify this assumption completely if the stresses are within the elastic limit .
In the present instance the stresses may be rather outside that limit , and the fact that fatigue , resulting ultimately in fracture , occurs , shows that at each application there must be a small extra-elastic extension or compression .
Bairstow , f measuring the * ' Camb .
Phil. Soc. Proc. , ' vol. 14 , p. 257 .
t 'Phil .
Trans. , ' A , vol. 210 , p. 35 .
Mr. B. Hopkinson .
[ Nov. 20 strain in a piece subjected to cycles of stress slowly performed ( about two per minute ) , and rather outside the limiting range , so that fracture would ultimately result , found that the range of strain , which was at first that corresponding elastically to the stress , slowly increased , owing to the formation of a hysteresis loop of the type shown in fig. 5 .
It consists of the two parallel elastic portions AB and CD which correspond to the normal Young 's modulus of the material and the curved portions BC and DA .
The error committed in calculating the stress from the strain on the assumption of perfect elasticity is represented very approximately by LM .
After a good many thousand reversals this loop settled down to a constant form which apparently persisted till fracture .
The extra-elastic strains at YAjifiarent 'Range , caLculalecL from strain -h m\#151 ; True Range of Stress-----------------\#151 ; *J .
these slow speeds are considerable ; for instance , in a steel whose7 limiting range was probably about \#177 ; 13 tons , the application of a range of \#177 ; 14 tons gave ultimately a hysteresis loop whose width ( LM ) was about lJ5t'ns\gt ; or 10 per cent , of the range .
It is , however , quite certain that the non-elastic portion of the strain in the high-speed machine is nothing like so great , because , if it were , the magnification of the pull at the resonance point would be much less than is actually found .
The magnetic pull , by its action on the moving weight , provides all the energy dissipated mechanically in the system , whether by defective elasticity of the piece , vibrations of the floor , or other causes .
The work done per cycle is easily calculated from the range of pull P and the movement of the weight d ; it is , in fact , \irVd if the frequency corresponds 1911 .
] A High-Speed Fatigue-Tester , etc. 139 ' to maximum resonance .
This sets an upper limit to the area of the hysteresis loop , and thus to the amount of extra-elastic strain .
It is not difficult to show that , even if the whole work done by the magnet is accounted for by hysteresis in the piece , the range of stress differs from the value corresponding to perfect elasticity by an amount not exceeding about 2 P* For instance , in the curves Di and UB ( fig. 4 ) , the error in measuring the stress must have been less than 0*8 ton per square inch , and was probably a good deal less .
In D2 , which was exactly the same steel as Di , the magnetic pull is much greater , but this , as has already been explained , is due to the greater vibration of the floor .
These considerations seemed to justify the view that , while the stress calculated from the change of length of the piece in this machine must be rather too high , the error could not be important , so long as the magnetic pull was but a small fraction of the range of stress .
It was , however , thought desirable to determine the acceleration of the moving mass , and thus to obtain a direct measurement of the pull exerted by it .
For this purpose a needle was fixed horizontally at a convenient point on the mass E , and a microscope , magnifying about 60 diameters , was sighted on the reflection , in the surface of the needle , of an electric lamp .
By properly adjusting the position of the lamp , a very sharp line could be obtained , whose position , when the machine was at rest , could be defined within 1/ 10,000th of an inch .
With the machine in action , this line was drawn out vertically into a band , whose length could be measured against a transparent scale in the field of the microscope correct to about l/ 5000th of an inch .
The microscope was supported for this purpose , with its axis horizontal , on a table loaded with iron plates , and resting on thick blocks of rubber placed on the heavy block of concrete to which the machine was bolted .
In this way movement of the microscope itself was completely eliminated , and the apparent movement of the needle in its field corresponded to the actual motion of the weight .
The wire guys V , being stretched fairly taut , prevent any angular motion of the weight , so that the movement of its centre of gravity is equal to that of the needle , wherever the latter be attached .
The sufficiency of this constraint was proved by attaching a mirror to the weight and observing through a telescope the reflection of a distant lamp filament .
Not the slightest tremor could be seen when the supply of current to the machine was suddenly * If d !
be the change of length of the piece in a cycle , and P ' the amount ( LM in fig. 5 ) by which the apparent stress calculated from the strain exceeds the true stress , the area of the hysteresis loop is greater than \ Hence ^7rPd ( work done by magnetic pull P per cycle ) is greater than JP 'd ' .
Now in this particular machine d is about %d\ hence P ' must be less than 2P .
Mr. B. Hopkinson .
[ Nov. 20 , thrown on , though an angular movement , giving a displacement of the needle ( relative to the centre of gravity ) of l/ 5000th of an inch , would \#166 ; certainly have been detected .
Having thus obtained the range of movement a of the weight , its acceleration / at each end of its travel can be calculated from the formula / = p1a , where 27r/ p is the periodic time of the cycle .
It is here assumed that the motion of the weight is simple harmonic .
The mechanical conditions of the problem are such as to justify this assumption .
We are dealing in effect with a weight attached to a spring , the other end of which is fixed , and this simple system has practically only one degree of freedom , so that its natural small oscillations will be nearly ^simple harmonic .
Further , the wave form of the alternating E.M.F. supplied is nearly simple harmonic , and the corresponding magnetic pull , which depends only on the flux , will be of a similar character , and will force approximately simple harmonic vibrations in the mass of a period equal to its own period .
Finally , under normal circumstances , the frequencies are adjusted so that the natural period of the mass is approximately equal to that of the force , and the selective action of resonance has the effect of accentuating that type of motion of the weight whose period corresponds with the fundamental period of the applied force .
A record of the extension of the piece in terms of the time was taken by causing one of the extensometer mirrors to throw a spot of light on to a revolving drum .
The curve so traced showed no appreciable departure from a sine wave .
It must , however , be remembered that in consequence of the increased importance in the acceleration of high frequency terms in the displacement , a departure from simple harmonic motion which could not be detected on the record might produce a considerable change in the acceleration .
The justification of the assumption that for this purpose the motion may be treated as simple harmonic therefore rests mainly on the theoretical considerations mentioned above .
The photographic records , however , were useful as showing the very regular character of the cycle of stress produced in the machine .
The forces acting on the weight are the pull in the bar and the pull of the magnet .
At the point of resonance these two forces will differ in phase by a quarter of a period , and consequently at the two ends of the travel of the weight , when its acceleration is a maximum , the pull exerted by the magnet will be zero .
At these points therefore the mass multiplied by the acceleration is equal to the pull in the rod , and the range of pull in pounds may therefore be taken as equal to 2 Map2/ g , where 2a is the range of movement of the weight observed in the microscope .
If the frequency of the magnet pull differs from the natural frequency by such an amount as considerably to 1911 .
] A High-Speed Fatigue-Tester , etc. 141 reduce the movement of the weight , the magnetic pull comes nearly into phase with the pull in the bar , the relation .
of signs being such that if the force frequency is the greater the magnetic pull assists the pull in the rod to accelerate the weight , while if the natural frequency be the greater these pulls are in opposite directions .
Thus in the first case the range of pull calculated from the movement of the mass should exceed , and in the second should fall short of , that shown by the extensometer by an amount equal to the range of pull exerted by the magnet .
The following table gives one complete set of observations made with the object of comparing the different methods of getting the stress .
The material used in this trial and in the endurance tests described below was a mild steel containing 018 per cent , of carbon , with a breaking stress of about 30 tons per square inch .
Frequency of stress cycle , per sec 100 .
j 100 .
116 .
120 .
134 .
Range of extension in piece :\#151 ; Extensometer A ( thousandths of an inch ) 1 *6 2 5 8*6 9*1 0*9 " B ( " " ) 1-5 2-5 8*2 8*9 1 *1 Microscope A ( , , " ) 1 *6 2*5 8*6 9*1 1 -o Mean 1 *6 2-5 8-4 9-0 1 *0 Stress calculated from extension ( tons per sq .
in .
) ... 5 5 8 *5 28-7 30 -7 3-4 Magnetic Rail :\#151 ; Volts on test-coil ( 100 turns ) 47 *5 58 *5 46 49 48 Maximum flux density ( kilo-lines per sq .
cm .
) 4-4 5*4 3*6 3*8 3*3 ( 1 ) Range of magnetic pull ( tons per sq .
in .
) 1 *5 2-3 1 -1 1-1 0-9 Acceleration Pull:\#151 ; Movement of mass observed in microscope 2 -4 3*6 12 -1 12 -7 1 *6 ( thousandths of an inch ) ( 2 ) Corresponding range of stress ( tons per sq .
in .
) 4'0 6-0 27 -3 30 -6 4-8 Sum or difference of ( 1 ) and ( 2 ) 5 .5 8-3 ( 28 -4 ) \#151 ; 3-9 i Range of stress calculated from frequency ( assuming that resonance occurs at frequency 119 ) 5*1 7-9 ( 29 0 ) 3 3 The point of resonance in this case was probably very near 119 periods per second .
At 100 periods and at 134 periods the magnetic pull would be very nearly in phase with the pull in the piece .
It will be seen that at the first of these frequencies the sum and at the second the difference of the magnetic pull and the acceleration pull agrees closely with the tension in the piece .
The frequency of 116 is near to but is certainly below the resonance frequency .
There will be a considerable difference of phase in this case , but not so much as 90 ' .
Consequently the stress in the piece should exceed that required to accelerate the weight by something less than the magnetic pull of IT tons per square inch .
In fact , it appears to exceed it by 1*4 tons per square inch .
At 120 periods we are very close to the resonance point , but probably rather past it .
Here the difference of phase 142 Mr. B. Hopkinson .
[ Nov. 20 , will be nearly 90 ' , and it will be seen that the stress required for acceleration is very near to that calculated from the extension .
The last line of the table gives the stress calculated from the magnetic pull P by the formula P/ ( l\#151 ; n2 ) , where n is the ratio of the forced to the free period .
This is , of course , not applicable to frequencies near the resonance point , when the amplitude is controlled largely by the dissipative forces , but it gives results in fair agreement with the observations at lower or higher frequencies .
A great number of comparisons of the stress estimated from the acceleration and that estimated from the extension have been made on different pieces of the same steel , at or near the point of resonance , and with a range .of stress of 30 to 32 tons per square inch .
These observations , taken altogether , reveal a systematic difference between the two ; the stress calculated from the extension being higher by perhaps f ton per square inch on the average .
It seems probable that this is mainly due to defective elasticity , which becomes apparent in this particular steel when the true stress exceeds 30 tons per square inch .
The endurance tests which follow were made on the same steel .
It may be observed here that the phenomenon of increasing hysteresis .under the influence of alternating stress which was observed by Bairstow at low speeds is completely reproduced at the high speed of this machine.* If the true stress , as shown by the movement of the weight , be maintained .constant at a fairly high value , the strain shown by the extensometer slowly increases , reaching a steady value after the lapse of some thousands of reversals .
At the same time the magnetic pull has to be quite noticeably increased in order to maintain the stress .
The piece also gets considerably hotter .
Comparison of Endurance at Different Speeds .
Some systematic endurance tests were then carried out on the same steel with the object of finding whether the high speed had any effect on resistance to fatigue .
Dr. Glazebrook kindly arranged that a series of trials of the material should be made at the National Physical Laboratory in the direct stress machine designed by Dr. Stanton , f whom I must thank for the great interest he has shown in the tests and the trouble which he has taken * Bairstow , ' Phil. Trans. , ' A , vol. 210 , p. 42 .
The increase of hysteresis under alternating stress has also been observed by Turner , who noticed the rise of temperature of a tube subjected to a Wohler test , 'Engineering , ' Sept. 4 , 1911 .
t Stanton and Bairstow , ' Inst. Civ .
Eng. Proc. , ' vol. 166 , p. 78 .
The first machine on these lines was made by Messrs. Reynolds and Smith ( see 'Phil .
Trans. , ' A , vol. 199 , p. 265 ) .
1911 .
] A High-Speed Fatigue-Tester , etc. 143 in carrying out this part of the work .
The steel contains 0T8 per cent , of carbon and 07 per cent , manganese and was supplied in the form of bright drawn bars of 1 inch or inch diameter .
The cold drawing to which these bars are subjected has the effect of raising the elastic limit of the bar as a whole , but that this change is not serious is apparent from the tensile tests given below , and anyhow it is of little consequence in a comparative trial .
Three bars of this steel in all were used in the test , two being of 1 inch in diameter , and the other ( D ) 1 ] inch .
These bars are referred to as .C , D , and E respectively .
Tensile tests were made on two specimens cut from bar D with the following average results:\#151 ; Elastic limit in tension ... ... . .
19'3 tons per sq .
in .
" compression ... ... .
13'4 " Maximum stress ... ... ... ... ... ... .
29 " Elongation on 8 in ... ... ... ... ... 16 per cent. Reduction in area ... ... ... ... ... .
60 " For the tension test the bar was turned down to a diameter of f inch , and for the compression to 1 inch .
The elastic limits correspond to the load at which permanent set first becomes distinctly apparent in a Ewing extensometer ; that for compression is not well defined .
A series of seven pieces cut from bar C and tested in the direct stress machine at the National Physical Laboratory gave the following results , which have been plotted in fig. 1 N.P.L. No. of specimen .
Mark .
Reversals per minute .
Range of stress , in tons per sq .
in .
Reversals to fracture .
Total duration of test ( hours ) .
216 C VI 1351 38 *8 , 6,613 0*08 217 C IV 1351 34 *9 7,633 0*09 220 C V 1246 29 *65 44,244 0*59 219 C I 1104 26 -45 197,761 3*0 218 C III 1063 17 *7 1,017,337* 15 *9 218 C III 1283 25 *7 150,981 1 '96 221 C II 1092 22-8 1,113,484* 17 *2 221 C II 1125 25 *5 1,003,610* 14 *9 225 C VII 1076 24 *6 326,550 5*0 * Unbroken .
Pieces of another bar ( D ) of the same material were tested in the direct-stress reciprocating machine and also in a high-speed Wohler machine with the following results :\#151 ; Mr. B. Hopkinson .
[ Nov. 20 , .
N.P.L. No. of specimen .
Mark .
Reversals per minute .
Range of stress , in tons per sq .
in .
Reversals to fracture .
Total duration of test ( hours ) .
Direct Stress Machine .
222 D I 1084 27 -7 120,000 1 *8 223 D II 1084 27 -7 119,200 1 *8 224 D J 1084 - 24 -6 326,560 5*0 Wohler Machine .
77 D J 2200 27 -0 1,637,500 12 *5 105 D J 2200 25 -5 7,000,000* 53 *0 # Unbroken .
The endurance tests on the new high-speed machine were carried out on pieces of the same bars .
It may be noted that the diameter of the test-piece\#151 ; \ inch\#151 ; is the same as that of the piece used in the direct stress machine at the National Physical Laboratory , so that exactly the same portion of the bar was tested .
The trials were net all continuous , but were split up into periods separated by intervals of rest ranging from a few minutes to several hours .
But most of the continuous runs covered at least a million cycles , and if a piece was not broken in one day , the trial was usually continued on the next , and so on , until fracture occurred .
In all the trials the piece got perceptibly warm , and if it reached a temperature ( judged by the hand ) of 60 ' or 70 ' C. at the centre , a jacket of blotting paper was applied and kept soaked with water .
It does not appear that the rise of temperature materially affected the endurance , for the pieces seemed to break indifferently at the centre or near the ends , where of course the temperature was by conduction kept nearly atmospheric .
Continuous observation was kept of the extensometer reading during a trial .
After the first few minutes this settled down to a constant value , , and very little adjustment was then required .
The " apparent stress " given in the second column of the following tables is that calculated from the extension on the assumption of perfect elasticity .
In the first series of trials , which were made on the " C " bar the strain was kept at rather a high value , and there must have been considerable departure from elasticity .
The true stress is , therefore , uncertain except in the one case C7 where the movement of the mass was measured .
Continuous observation was , however , kept of the E.M.F. on the test-coil and as pointed out in the last section the " apparent stress " cannot exceed the true stress by more than twice the range of magnetic pull calculated from these observations .
This is the basis of the assertion ( in cases other than C7 ) that the stress in the following series of trials never fell short of 3ft tons per square inch .
1911 .
] A High-Speed Fatigue-Tester , etc. No. of bar .
Range of stress ( tons per sq .
in .
) .
Time ( hours ) .
Millions of Remarks .
By extensometer ( apparent ) .
True stress .
reversals to fracture .
Co 32\#151 ; 34 Exceeded 30 15 6*0 Four periods .
6 C5 34\#151 ; 35 Exceeded 30 15* 6*2 Three periods , one of 12 hrs .
continuous .
c6 33\#151 ; 34 Exceeded 30 29 11 '5 Four periods , one of 14 hrs .
C- 31\#151 ; 33 30\#151 ; 32 ( by movement of mass ) 7 2*8 Three periods .
C8 32\#151 ; 33 Exceeded 30 8* 3*4 Two periods .
In most of these tests the piece heated to such an extent that it was necessary to jacket it with wet blotting paper .
Further trials were made in two pieces cut from another bar of the same material ( D ) .
Piece Di was the same as that used in the comparisons of different methods of getting the stress which have been described above , in the course of which the stress varied , rising sometimes to 31 tons per square inch .
On the conclusion of these experiments .it was put through a steady endurance test at an " apparent " range of stress of 30*5 tons per square inch , calculated from extensometer .
It broke after 10 million cycles taking about five periods of five hours each on consecutive days ( total , 25 hours ) .
As the piece kept cool ( it was not necessary to jacket it ) it may be inferred that the elasticity was nearly perfect to the end of the test , and that the estimate of stress derived from the extensometer was not far wrong .
Allowing liberally for all possible errors , it may be asserted that the stress exceeded 29 tons per square inch throughout this test .
The treatment of piece D2 was as follows:\#151 ; Range of stress ( tons per sq .
in .
) .
Total time ( hours ) .
Total reversals ( millions ) .
Remarks .
By extensometer .
By acceleration .
28 *2 26 *8 32 12*8 | Four periods , about 8 hrs .
each .
Four weeks ' rest .
29 *0 I 28*8 | I 15 1 6*0 | Three periods , about 5 hrs .
each .
Two days ' rest .
30 -0 28*2 14 5*6 Three periods , one of 12 hrs .
continuous .
31 *0 30 *0 15 -8 6*3 The piece was perceptibly hotter .
32 *0 29 *0 5*0 2*0 Two periods .
Broke .
vol. lxxxvi.\#151 ; A. L Mr. B. Hopkinson .
[ Nov. 20 , Until the last period of five hours the piece was only slightly warm , and the elasticity must have been nearly perfect .
During the last period it got very hot , and had to be jacketed .
It is probable that the stress did not fall short of 29 tons during the last 50 hours and 20 million reversals\#151 ; certain that it did not fall short of 28 tons .
Finally , a piece Ei , cut from another bar of the same material , was subjected to the following treatment:\#151 ; Range of stress ( tons per sq .
in .
) .
Total time Reversals By extensometer .
By acceleration .
( hours ) .
\#187 ; ( millions ) .
31 32 Not less than 30 Not less than 31 6 7 2-5 | 2*7 1 *0 ( broke ) Each of the runs was continuous , and they took place on successive days .
In each continuous observation was kept of the movement of the weight , and care was taken that the true stress ( calculated from the movement ) should never fall short of 30 tons and 31 tons per square inch respectively .
Deference to the curve ( fig. 1 ) on which the observations with the slow-speed machine ( 1100 revolutions per minute ) are plotted , shows that the probable life of this material under a range of 28 tons per square inch at that speed is about 100,000 reversals and one and a-half hours of time ; and with a range of 30 tons about half as much .
In the Wohler machine ( at 2000 revolutions per minute ) the endurance is apparently a little greater , but neither the number of observations nor the amount of the difference is sufficient ground on which to base an inference as to the effect of speed .
But at the higher speed of 7000 alternations per minute the evidence seems to be conclusive that the endurance is greater .
Not only is the number of reversals of a given range of stress required to break the piece greatly increased , but the actual time during which it must be subjected to alternating stresses is also increased .
It is not , however , proved that the limiting range of stress , namely , the maximum range which will not cause breakdown however often it be repeated , is greater at the higher speed .
Though the observations suggest that conclusion , it is quite possible that sufficiently prolonged vibration at a range of stress of 27 tons per square inch would ultimately have ruptured the material .
Since , however , it takes 10 million reversals and some 25 hours of time to break the piece with a range which certainly exceeds 29 tons , it would appear probable that the number of reversals and the time required with a range of 27 tons would be very great indeed , perhaps so great that for practical 1911 .
] A High-Speed Fatigue-Tester , etc. 147 purposes the piece might be regarded as unbreakable by this load if it be applied and removed sufficiently rapidly .
Probable Causes of Speed-effect .
In the hysteresis loop ( fig. 5 ) into which the stress-strain curve of a metal undergoing fatigue apparently always develops , the straight portions AB and CD correspond to perfect elasticity , but during the curved parts BC and DA the material is flowing or taking permanent set .
There seems to be little doubt that fatigue is the cumulative effect of the internal slips which accompany this flow , and that the rate of fatigue is determined mainly by the amount of the extra-elastic strain occurring in a cycle ( BD in fig. 5 ) which Bairstow has called the " cyclical permanent set .
" Accepting that view , there are two ways in which speed may be expected to affect endurance .
First , if the speed be high enough there may not be time for the full amount of flow corresponding to BO and DA to take place at each reversal .
The amount of flow , and therefore of damage to the material , occurring at each cycle will then be reduced .
So far as this factor is concerned , therefore , increased speed will make for greater endurance , provided that the speed is sufficient materially to affect the stress-strain relation .
Second , there is the phenomenon of recovery .
Any over-strained material tends to recover its elasticity with time .
This tendency must be supposed to be continually at work during the progress of a fatigue test , repairing the ravages of the successive over-strains .
Obviously , so far as it goes , its operation will be relatively more effective at slow speeds .
Hence the effect of this second factor is to associate greater endurance with slower speed , and is opposite to ' that of the first .
The combined effect of the two would be to cause the endurance ( always reckoned as the number of stress-cycles to fracture ) to diminish at first as the speed is increased , then to reach a minimum value and increase again .
But if the influence of recovery on the progress of a continuous fatigue test is small , then the minimum of the curve connecting speed and endurance becomes very flat and we shall get approximately constant endurance until the speed reaches a certain limit , after which the endurance increases .
The conclusion expressed in the last sentence is in accord with the facts , and the inference that recovery is not an important factor is at least probable .
It may be , however , that the opposed actions of recovery and of time-change in the stress-strain relation happen to cancel each other pretty accurately over the fiat part of the curve .
Finally , to settle the point it would be necessary to carry out comparative tests in which the speed is the same but the rate of recovery different .
The most obvious way would be to A High-Speed Fatigue-Tester , etc. try the effect upon endurance of raising the temperature of the piece , which is known to accelerate recovery .
Such an experiment would give very useful information .
As pointed out above , there is some evidence in the experiments with tire high-speed machine that the rate of fatigue , at that speed at any rate , is not much affected by temperature ; but the observations were not directed especially to this point , and the evidence is not conclusive.* The direct determination of the other factor\#151 ; the effect of speed on extra-elastic stress-strain relations\#151 ; also requires much more experimental study than it has yet received .
It is certain , however , that if the cycle of stress be completed in 1/ 100 second or less , the effect must be large .
The greater endurance at high speeds found in the present research is perhaps sufficient evidence for this assertion , but there is independent confirmation of it in the results of experiments which have been made on the extension of a wire under the action of a blow.f The wire ( stretched vertically ) was stressed by the blow of a weight falling against a stop at its lower end .
Measurement of the momentary extension , and calculation from the mass of the weight and the height of fall , alike showed that the average stress over the top 20 inches of the wire must have reached a maximum value exceeding by 50 per cent , the static elastic limit , and sufficient if long continued to break the wire .
Yet it was found that 11 such blows in succession extended the part of the wire under measurement by less than 1/ 2000 part of its length , and the wire was almost perfectly elastic up to the maximum stress applied by the blow .
The stress was outside the elastic limit for about 1/ 1000 second at each blow , which is of the same order as the time during which the over-stress lasts in each cycle in the high-speed machine .
The arguments here used would lead to the conclusion that though the rate of fatigue under the action of stress which ultimately ruptures the piece will be lower at high speeds of reversal , yet the limiting range of stress which the piece will sustain indefinitely without breaking will be independent of speed .
For if a single reversal produces any permanent effect whatever it is to be expected that a sufficient number must ultimately fracture the piece , and it is difficult to believe that time can be a factor determining whether or no such permanent effect shall exist , though it may affect its amount .
It is quite possible , however , that as the time occupied by each cycle is diminished the effect produced may diminish in greater \#166 ; * Some experiments on the effect of temperature on fatigue have been made by XJnwin , who found that the endurances of mild steel was slightly increased at a temperature of about 200 ' C. , 'Inst .
Civ .
Eng. Proc./ vol. 166 , p. 117 .
t Hopkinson , 6 Roy .
Soc. Proc. , ' vol. 74 , p. 498 .
Mechanism of the Semi-permeable etc. 149 proportion .
And the ultimate result may be that for practical purposes the limiting range is raised on account of the great length of time required to cause fracture .
Further , it is noted that when the rate of fatigue is very slow the property of recovery becomes relatively more important , and it is at least conceivable that it may be more than competent to overcome the fatigue altogether and so really raise the limiting range .
The observations described in this paper were for the most part taken and reduced by my assistant , Mr. H. Quinney , whom I must thank for the zeal and ability with which he has carried out the work .
I wish also to acknowledge valuable assistance given at various stages by Mr. C. Trevor-Williams , advanced student in the University of Cambridge , and by my brother , Mr. R. C. Hopkinson , Trinity College .
The Mechanism of the Semi-permeable Membrane , and a Netv Method of Determining Osmotic .
By Prof. F. T. Troutgn , F.R.S. ( Received November 14 , 1911 , \#151 ; Read January 11 , 1912 .
) Introduction .
For the theoretic exposition of osmotic pressure , no further attention need be paid to the membrane than to postulate its semi-permeability .
It is , however , desirable that the physical properties of the membrane should not be lost sight of , especially from the experimental point of view .
Leaving out of ' account for the moment the mechanical requirements of a rigid membrane , let us imagine a system in which we have a solution separated from the pure solvent by a thick layer of another liquid which can take up or dissolve the solvent , but not the solute .
Such a system might be sufficiently realised by means of an aqueous solution of cane sugar , ether , and water , since sugar is insoluble in ether , while ether dissolves a small quantity of water .
Both water and sugar solution take up some ether , but that is of no immediate interest in the present considerations .
This complication will be , however , dealt with later on .
If it is desired to imagine the necessities of gravity complied with , the sugar solution and the water can be supposed to be placed side by side in a vessel and kept from mixing by an impervious vertical partition reaching to
|
rspa_1912_0008 | 0950-1207 | The mechanism of the semi-permeable membrane, and a new method of determining osmotic pressure. | 149 | 154 | 1,912 | 86 | Proceedings of the Royal Society of London. Series A, Containing Papers of a Mathematical and Physical Character | Prof. F. T. Trouton, F. R. S. | article | 6.0.4 | http://dx.doi.org/10.1098/rspa.1912.0008 | en | rspa | 1,910 | 1,900 | 1,900 | 5 | 90 | 2,551 | http://corpora.clarin-d.uni-saarland.de/surprisal/6.0.3/?id=rspa_1912_0008 | 10.1098/rspa.1912.0008 | null | null | null | Thermodynamics | 39.291853 | Biochemistry | 34.872044 | Thermodynamics | [
-19.68837547302246,
-29.22296905517578
] | Mechanism of the Semi-permeable etc. 149 proportion .
And the ultimate result may be that for practical purposes the limiting range is raised on account of the great length of time required to cause fracture .
Further , it is noted that when the rate of fatigue is very slow the property of recovery becomes relatively more important , and it is at least conceivable that it may be more than competent to overcome the fatigue altogether and so really raise the limiting range .
The observations described in this paper were for the most part taken and reduced by my assistant , Mr. H. Quinney , whom I must thank for the zeal and ability with which he has carried out the work .
I wish also to acknowledge valuable assistance given at various stages by Mr. C. Trevor-Williams , advanced student in the University of Cambridge , and by my brother , Mr. R. C. Hopkinson , Trinity College .
The Mechanism of the Semi-permeable Membrane , and a Netv Method of Determining Osmotic .
By Prof. F. T. Troutgn , F.R.S. ( Received November 14 , 1911 , \#151 ; Read January 11 , 1912 .
) Introduction .
For the theoretic exposition of osmotic pressure , no further attention need be paid to the membrane than to postulate its semi-permeability .
It is , however , desirable that the physical properties of the membrane should not be lost sight of , especially from the experimental point of view .
Leaving out of ' account for the moment the mechanical requirements of a rigid membrane , let us imagine a system in which we have a solution separated from the pure solvent by a thick layer of another liquid which can take up or dissolve the solvent , but not the solute .
Such a system might be sufficiently realised by means of an aqueous solution of cane sugar , ether , and water , since sugar is insoluble in ether , while ether dissolves a small quantity of water .
Both water and sugar solution take up some ether , but that is of no immediate interest in the present considerations .
This complication will be , however , dealt with later on .
If it is desired to imagine the necessities of gravity complied with , the sugar solution and the water can be supposed to be placed side by side in a vessel and kept from mixing by an impervious vertical partition reaching to Prof. F. T. Trouton .
[ Nov. 14 , a certain height ; then ether poured in , so as to cover all and to act the part of a semi-permeable membrane separating the solution from the water .
Ether takes up about 1*05 per cent , of water when placed in contact with it , but takes up less than this from sugar solution , the amount depending upon the concentration of the solution .
For equilibrium at the water-ether surface the ether must thus contain 1'05 per cent , of water , while at the solution-ether surface a less quantity is necessary for equilibrium to exist there .
Diffusion through the ether prevents this equilibrium existing , so that water will pass across from the water side to the solution side.* If the ether could rigidly maintain its position so as to prevent the volume of the solution increasing , the hydrostatic pressure of the solution would go up owing to water passing into it .
This process , we must suppose , would , under such circumstances , come to an end when , owing to the increase of pressure , the amount of water taken up by the ether from the sugar solution reached the amount taken up from water at the ordinary pressure .
A practical equivalent to the assumed rigidity might be provided in our supposed experiment by having the level on the solution side lower than on the water side , the difference in levels depending upon the strength of the solution used .
By making the column of ether sufficiently high , the necessary pressure could obviously always be provided to enable the amount of water held by the ether at the solution-ether surface to equal that held near the water-ether surface .
The pressure competent to bring about this state of equilibrium in the ether w^ould thus appear , from the above considerations , to be the osmotic pressure of the sugar solution .
The complication above alluded to , arising from the solution of our " membrane " in both the solution and solvent , introduces probably only an apparent and not a real difficulty , and is met , it would seem , in the case of sugar solution , ether , and water , by the amount of ether held by the solution when under the equilibrium or osmotic pressure being equal in amount to that held by water at the normal pressure .
It is well known that the presence of a salt in water causes a reduction in the amount of ether taken up when ether is placed in contact with the solution , but this amount rises with the pressure .
No accurate quantitative determinations have been obtained as to the amount of this , but some qualitative observations bear out the above assumption , in which case the solvent would simply be a solution of ether-water instead of pure water .
We could under these circumstances infer that in order to determine the * A small correction may be required to allow for the equilibrium distribution of concentration depending upon the gradient of pressure in the ether .
1911 .
] Mechanism of the Semi-permeable Membrane , etc. osmotic pressure of a given solution it is only necessary to find the pressure to which a suitable liquid , say ether , must be subjected when in contact with the solution , in order that the liquid may take up as much water from the solution as the liquid takes up from water at the ordinary pressure .
Method of Experiment .
In order to determine osmotic pressures on this principle an apparatus was constructed in which the solution in contact with ether , or other suitable liquid , could be subjected to hydrostatic pressure of any desired amount .
It consisted of a copper U-tube strong enough to stand high pressures , and closed by taps on each side .
A gauge was attached for reading the pressures .
In this apparatus any pressure up to somewhere over a hundred -atmospheres could be obtained .
To charge the apparatus : first , enough solution is introduced to half fill the tube .
Then ether is sucked in on the side marked A and the tap closed .
By means of a screw coupling B connection is made with a pressure pump and air forced in till the requisite pressure is indicated on the attached gauge when the tap B is closed .
After sufficient time has elapsed for the ether to take up its full complement of water from the solution , the tap A is opened , when the compressed air in the other limb drives the ether out , which is collected and its water content determined .
By shaking the tube the length of time required for equilibrium to be reached can be reduced , but care must be taken to keep the ether on the A side .
The strength of the solution with which the experiments described in this paper were carried out was 600 grm. of sugar per litre of solution .
The curve shows the amount of water , in grammes per 100 grm. of the examined ether , found to be taken up from this solution at various pressures ranging from atmospheric up to over 100 atmospheres .
It was found in this ' way that at about 79 atmospheres the amount of water taken up from this strength solution had risen to the amount taken up by ether from water at 1 atmosphere .
This amount is indicated on the diagram by the dotted horizontal line .
This , according to the above considerations , should be the osmotic pressure of solutions of the particular molecular strength used .
This result may be compared with Lord Berkeley 's and Mr. Hartley's* * 4 Phil. Trans. , ' A , vol. 206 , p. 481 .
Prof. F. T. Trouton .
[ Nov. 14 , determinations of osmotic pressure made with a semi-permeable membrane of ferrocyanide of copper on porcelain .
They plot a curve from their results obtained with cane sugar , from which we can scale off the value of the osmotic pressure for a solution of 600 grm. per litre .
This is about 81 atmospheres , and is , within the limits of error , practically the same as the value given by the ether experiments .
press : in atm ?
After trying various plans , the one finally adopted for determining the amount of water taken up by the ether was to pass the ether in the form of vapour through calcium chloride drying tubes .
The ether was slowly evaporated in a flask placed in warm water .
The vapour was led through several drying tubes so as to secure that all the water was absorbed .
The escaping ether could be collected and saved when so desired .
The drying tubes were kept at 40 ' C. by placing them in a bath at that temperature .
This was sufficiently warm to prevent ether condensing in the tubes , and yet was found not to be too high for substantially absorbing all the water .
Before weighing the tubes dry air was run through them , in order to sweep out all ether vapour .
The following table gives the data from which the curve has been plotted . .
The second column gives the weight of water held by 100 grm. of the ether-water solution in equilibrium with the sugar solution at the corresponding pressure .
The corrected weights given in the last column were calculated for convenience of plotting the curve by grouping the observations .
This was done for the pressures given in the third column by taking the tangents found from a preliminary curve as giving the rate of change of the weight with pressure , and then taking the mean of the weights so found .
1911 .
] Mechanism of the Semi-permeable Membrane , etc. Table I. Pressure in atmospheres .
Weight held by 100 grm. Pressure .
Corrected weight .
1 0*935 1 0*953 1 0-941 1 0 *938 1 0*926 1 0*939 30 0*965 30 0*973 30 0 *953 30 0*948 30 0*974 30 0*962 38 *1 0*979 38 *1 0*979 40 0 *964 40 0*997 40 0*997 40 0*986 57 1 *007 56 *5 1 *024 57 *1 1 *015 57*8 1 *002 57 *8 1 *035 57 1*016 73 *1 1 *040 73 *5 1 *056 72 *8 1 *028 73 1 *039 80 1 *047 81 *5 1 *056 78 *9 1 *053 80 1 *051 93 *9 1 *103 92*5 1*093 92 *5 1*089 92 *5 1 *098 91 *8 1 *077 92 1 *090 107 *5 1 *130 107 *5 1 *130 110 *5 1 *143 110 *5 1 *143 The value assumed for the weight of water taken up by ether at atmospheric pressure when in contact with water is the mean of the following 10 experiments:\#151 ; Table IL 1 *060 1 *032 1 -040 1 *052 1 '048 1 -063 1 *054 1 *045 1 *087 1*064 j* Mean 1 *0545 In the determination of osmotic pressure by the semi-permeable membrane method , the difficulty of finding a suitable membrane for most salts becomes very great when high pressures are resorted to , so that it has been found practicable to work with only a limited range of substances .
The method here described opens up a wider field , for less exacting conditions have to be complied with in the working material selected , namely , that it should be a substance which takes up the solvent but does not take up the solute .
154 Dr. A. F. Kovarik .
Mobility of the Positive and [ Nov. 14 , while , in the case of the material needed for making a semi-permeable membrane , in addition to taking up the solvent but not the solute , it must be either rigid itself or be capable of being mounted on a rigid support .
These determinations were carried out by my assistant , Mr. Burgess , for whose care and accuracy I wish here to acknowledge my thanks .
Mobility of the Positive and Negative Ions in Gases at High Pressures .
By Alois F. Kovarik , Ph. D. , John Harling Besearch Fellow in Physics , The Victoria University of Manchester .
( Communicated by Prof. E. Rutherford , F.R.S. Received November 14 , 1911 , \#151 ; Read January 11 , 1912 .
) Introduction and Purpose .
The velocity of ions in gases at reduced pressures was first investigated by Rutherford* and by Langevin.f Recently the author and others have carried out similar investigations .
The results of these investigations show that for the negative ions in air the product of the mobility and the pressure is constant for pressures ranging from 760 mm. to 200 mm. of mercury , but with further reduction the product increases with the reduction of pressure , this increase becoming very great at low pressures.* For the positive ions in air the product of the mobility and pressure is constant for pressures investigated between 760 mm. and 3 mm. of mercury .
S Similar results were obtained for the mobilities of the ions in other gases .
The results show that if the ion is an aggregation of molecules , this aggregation becomes , at low pressures , less complex in the case of the negative ion , while in the case of the positive ion it persists down to 3 mm. of mercury .
The purpose of the present research was the study of the mobilities of both kinds of ions in gases at high pressures .
The method of investigation is based on the mathematical expression , developed by Prof. Rutherford , || for the current between two plates , assuming that a very intense ionisation exists near the surface of one of the electrodes .
* Rutherford , E. , 'Camb .
Phil. Soc. Proc. , ' 1898 , vol. 9 , p. 401 .
t Langevin , N. P. , 4 Ann. de Chim .
et de Phys. , ' 1903 , vol. 28 , p. 289 .
J Kovarik , Alois F. , 'Phys .
Rev. , ' 1910 , vol. 30 ( 4 ) , p. 415 .
S Todd , G. W. , 'Camb .
Phil. Soc. Proc. , ' 1910 , vol. 16 , p. 21 .
1| Rutherford , E. , 'Phil .
Mag. , ' 1901 , vol. 2 , p. 210 .
|
rspa_1912_0009 | 0950-1207 | Mobility of the positive and negative ions in gases at high pressure. | 154 | 162 | 1,912 | 86 | Proceedings of the Royal Society of London. Series A, Containing Papers of a Mathematical and Physical Character | Alois F. Kovarik|Prof. E. Rutherford, F. R. S. | article | 6.0.4 | http://dx.doi.org/10.1098/rspa.1912.0009 | en | rspa | 1,910 | 1,900 | 1,900 | 3 | 197 | 3,912 | http://corpora.clarin-d.uni-saarland.de/surprisal/6.0.3/?id=rspa_1912_0009 | 10.1098/rspa.1912.0009 | null | null | null | Thermodynamics | 37.021367 | Electricity | 31.766088 | Thermodynamics | [
6.046012878417969,
-69.36425018310547
] | 154 Dr. A. F. Kovarik .
Mobility of the Positive and [ Nov. 14 , while , in the case of the material needed for making a semi-permeable membrane , in addition to taking up the solvent but not the solute , it must be either rigid itself or be capable of being mounted on a rigid support .
These determinations were carried out by my assistant , Mr. Burgess , for whose care and accuracy I wish here to acknowledge my thanks .
Mobility of the Positive and Negative Ions in Gases at High Pressures .
By Alois F. Kovarik , Ph. D. , John Harling Besearch Fellow in Physics , The Victoria University of Manchester .
( Communicated by Prof. E. Rutherford , F.R.S. Received November 14 , 1911 , \#151 ; Read January 11 , 1912 .
) Introduction and Purpose .
The velocity of ions in gases at reduced pressures was first investigated by Rutherford* and by Langevin.f Recently the author and others have carried out similar investigations .
The results of these investigations show that for the negative ions in air the product of the mobility and the pressure is constant for pressures ranging from 760 mm. to 200 mm. of mercury , but with further reduction the product increases with the reduction of pressure , this increase becoming very great at low pressures.* For the positive ions in air the product of the mobility and pressure is constant for pressures investigated between 760 mm. and 3 mm. of mercury .
S Similar results were obtained for the mobilities of the ions in other gases .
The results show that if the ion is an aggregation of molecules , this aggregation becomes , at low pressures , less complex in the case of the negative ion , while in the case of the positive ion it persists down to 3 mm. of mercury .
The purpose of the present research was the study of the mobilities of both kinds of ions in gases at high pressures .
The method of investigation is based on the mathematical expression , developed by Prof. Rutherford , || for the current between two plates , assuming that a very intense ionisation exists near the surface of one of the electrodes .
* Rutherford , E. , 'Camb .
Phil. Soc. Proc. , ' 1898 , vol. 9 , p. 401 .
t Langevin , N. P. , 4 Ann. de Chim .
et de Phys. , ' 1903 , vol. 28 , p. 289 .
J Kovarik , Alois F. , 'Phys .
Rev. , ' 1910 , vol. 30 ( 4 ) , p. 415 .
S Todd , G. W. , 'Camb .
Phil. Soc. Proc. , ' 1910 , vol. 16 , p. 21 .
1| Rutherford , E. , 'Phil .
Mag. , ' 1901 , vol. 2 , p. 210 .
1911 .
] Negative Ions in Gases at High Pressures .
The expression developed is i = 9V2K/ 32ttcP .
where i is the current per square centimetre through the gas , K the mobility of the ions , V the potential difference , and d the distance between the plates .
Rutherford* verified this equation experimentally , using for the intense surface ionisation , ionisation produced by a heated platinum plate .
C. 1 ) .
Child , f who developed the same equation independently , utilised it for the measurement of the velocity of ions drawn from tame gases .
In the present work this equation was again tested experimentally , and was utilised for the purpose of measuring the mobility of the ions in gases at high pressures .
The intense surface ionisation was obtained by using a preparation of ioniumj at one of the plates and reducing the range of the a-partieles by using the gas at high pressures .
Since ionium is separated with thorium , some / 3- and 7-rays due to thorium were present .
With the specimen used this volume ionisation was not found to be of importance .
If / 3-rays are present in abundance , their volume ionisation superposed on the surface ionisation due to a-particles at high pressure is very noticeable , as was found in an experiment where freshly prepared polonium was used , the polonium containing a considerable amount of radium E , which emits / 3-rays .
Electrometer M Apparatus .
The apparatus used was a cylinder 8 cm .
in diameter and 12 cm .
deep , made especially for high pressure work , and shown in fig. 1 .
The upper electrode in most of the experiments was 1*054 cm .
in radius , and was encircled by a guard ring .
The insulation was amber .
The lower electrode was held in position by ebonite fastened at the bottom of the cylinder , and was connected with the battery .
The gas passed into the cylinder through a valve at the lower part of the cylinder , and its pressure was measured by an attached calibrated gauge .
The ionium was spread as a very thin layer over a plate 6 cm .
in diameter , and this plate served as the lower * Rutherford , E. , 'Phys .
Rev./ 1901 , vol. 13 ( 6 ) , p. 321 .
+ Child , C. 1 ) .
, 'Phys .
Rev. , ' 1901 , vol. 12 ( 3 ) , p. 137 .
+ I his material was part of the ionium separated by Prof. Boltwood from the radioactive residues loaned by the Royal Society to Prof. Rutherford ( 'Roy .
Soc. Proc. , ' 1911 , A , vol. 85 , p. 77 ) .
Battery Fig. 1 .
156 Dr. A. F. Kovarik .
Mobility of the Positive and [ Nov. 14 , electrode .
In order to protect the ionium from sudden gusts of gas , a cylinder of ebonite was placed round the wall inside the cylinder .
By means of keys the lower plate could be brought to a positive or negative potential .
An electrometer with condensers of suitable capacities was used to measure the current between the electrodes .
Test of the Equation .
Experiments were first carried out to test the equation .
In order to find out if the equation is applicable to the present problem , it was necessary to show:\#151 ; ( 1 ) That the current varies as the square of the potential difference. .
( 2 ) That the current varies inversely as the cube of the distance .
( 3 ) That the ionisation produced by the a-particles of the ionium used was sufficiently great , so that any increase in the ionisation had no effect on the current for a given potential difference and a given distance .
These experiments were carried out in air .
The air was first compressed into a large cylinder to 120 atmospheres by means of a liquid air compressor .
The amount of moisture present at this pressure must be small .
From this cylinder it was passed very slowly into the apparatus so as not to scatter the active material .
When a desired pressure was reached it was necessary to wait some time before taking measurements on account of the motion and the changing temperature of the gas .
The method of taking readings was to measure the time of deflection of the spot of light over a definite calibrated portion of a scale .
This was done for both positive and negative currents for every potential .
Readings for a given potential difference were taken often in each set and were used as a check .
Table I gives the results of an experiment when the pressure of the air was 59*5 atmospheres , and the distance between the plates was 2*81 cm .
The potential difference is given in volts and the current per centimetre in E.S.U. These results are shown graphically in fig. 2 .
If the currents are plotted against the square of the potential difference , a straight line passing through the origin is obtained for the first 80 volts .
Above 80 volts , there is a deviation from the square of the potential difference law .
The range of voltage for which the current is proportional to the square of the potential difference varies for different pressures and also for different distances , being greater for higher pressures and greater for greater distances .
It is within this range of potential difference , where the law holds , that the current must be determined for the calculation of the mobility of the ions .
This was done in all cases by obtaining a set of 1911 .
] Negative Ions in Gases at High Pressures .
] 57 readings similar to those oi ' Table I , plotting the currents against the square of the potential difference and then selecting some convenient value for the potential difference and measuring the value of the current on the graph .
Table I.\#151 ; Air .
Pressure = 59'5 atmospheres , d = 2'81 cm .
T = 19 ' C. P.D. , in volts .
Square of P.D. Current in E.S.U. per cm.2 .
Positive .
Negative .
6 36 2 *3 x 10-5 1 *48 x 10~5 10 100 3*8 4*98 14 196 7*0 9*4 20 400 13*0 18 *2 26 676 20 -6 32 -0 32 1024 32 *6 46 *5 41 1681 49 -5 68 *6 51 2601 77 -2 108 61 3721 112 161 71 5041 142 206 82 6724 187 263 123 356 410 164 509 564 205 630 646 287 748 807 492 966 1040 0 1000 2000 square 3000 of 4000 p d 5000 6000 7000 Fia .
2 .
158 Dr. A. F. Kovarik .
Mobility of the Positive and [ Nov. 14 , In testing the equation for distance , measurements were made for current foi a potential difference of oO volts for different distances .
The pressures were all above 30 atmospheres , and the current , which , as will be seen , varies inversely with the pressure ( in air ) , was reduced to the value for the mean pressure of all the experiments , viz. , 50 atmospheres .
The product of the current per square centimetre thus obtained and the cube of the distance between the plates is given in Table II for the various distances used .
Table II.\#151 ; Various Distances between Electrodes .
Air at 50 atmospheres .
P.D. = 30 volts = 0*1 E.S.U. T = 19 ' C. i x d3 .
Distance , in cm .
d\ i in E.S.U. per cm.2 ; d in cm .
1 Positive .
Negative .
0-805 0*52 8 -3 x 10-s 10 *4 x 10-3 1 -36 2* 52 7 -4 9-7 1 -53 3-58 7'6 10 *2 1 -76 5-45 7-7 10 *3 2*31 12 -33 7 '6 10*1 2-81 22 *2 7'3 10 *2 3*27 35 -0 7-0 9*3 3*78 54 -0 7 -2 9'4 4-27 77 *8 6-8 8*9 It will be noticed that the values of this product are reasonably constant although the cube of the distance changed in the ratio of 1 to 150 .
With the greater distances , the values are somewhat lower , due , no doubt , to the fact that the field became less uniform .
On the whole , however , the results may be considered fairly satisfactory in proving that , for the distances used , the current varies inversely as the cube of the distance between the plates .
After a series of experiments the amount of ionium was considerably increased , the layer still being extremely thin .
The current for a definite potential difference and distance between the plates , and for a definite pressure , did not change , which shows that the surface ionisation was intense enough , and that the current was independent of further increase in the intensity of the ionisation .
Experiments with Air .
In the experiments to determine the mobility of the ions at various pressures , care had to be taken in the choice of the distance between the plates for the following reasons : At lower pressures the range of the a-particle becomes greater and the correction for this range becomes appreciable for small distances .
The correction for the range of the 1911 .
] Negative Ions in Gases at High Pressures .
159 a-particles consisted in decreasing the distance between the electrodes by one half of the range at the particular pressure used .
With great distances between the plates the field could not be made uniform on account of the small dimensions of the apparatus .
With distances between 2 and 3 cm .
, however , the field appeared to be quite uniform and the correction for the range was small for the high pressures .
The results obtained for the various pressures in air are given in Table ILL The actual mobilities in centimetres per second per volt per centimetre for the two kinds of ions , as deduced from Eutherford 's equation , are given , and also the products of the mobility and the pressure in atmospheres .
It will be noticed from the results that the velocity varies inversely with the pressure up to 75 atmospheres .
The mean values for the product of the mobility and pressure in atmospheres for pressures above 30 atmospheres at a temperature of 19 ' C. are T89 and 1-346 for the negative and the positive ions respectively , with a ratio of T405 .
The values obtained by Zeleny* at atmospheric pressure , and at a temperature of 13-5 ' C. , are respectively 1-87 and 1-36 , giving a ratio of 1'375 .
i Table III.\#151 ; Air .
Mobility at various Pressures .
d = 2-81 cm .
T = 19 ' C. Pressure , in atmospheres .
Mobility , in cm./ sec. per volt/ cm .
Mobility x Pressure .
; Ratio of Positive .
Negative .
Positive .
Negative .
mobilities .
74 *6 0 *0187 0 *0262 1 *39 1 -96 1 *41 70 *6 0 *0192 0 *0270 1 -36 1 -91 1 *40 59 *5 0 *0226 0 *0318 1 *34 1 -89 1 *41 53 *0 0 *0258 0 -0366 1 *37 1 *94 1 -41 50 *6 0 *0261 0 -0366 1-32 1*85 1 *40 47 *6 0 *0272 0 *0392 1 -30 1 -86 1 *43 41 -7 0 *0317 0 *0449 1 -32 1-87 1 -42 36 -8 0 *0373 0 *0506 1 *37 1 -87 1 *37 31 *2 0 *0433 0 -0600 1 -35 1 -87 1 *39 21 *1 0 *0615 0 *0830 1 -30 1 -75 1 *35 13 -3 0-103 0-138 1 *37 1 *84 1 *40 Mean 1 *346 1 -89 1 *405 Experiments with Carbon Dioxide .
In these experiments a cylinder of carbon dioxide was used .
The gas was found to be saturated with moisture , and to contain about 0-3 per cent , of air , a trace of HC1 , and a slight trace of alcohol .
On letting the gas into the * Zeleny , J. , 'Phil .
Trans. , ' 1900 , A , vol. 195 , p. 193 .
160 Dr. A. F. Kovarik .
Mobility of the Positive and [ Nov. 14 , apparatus , the insulation generally broke down .
Attempts were made to dry the gas partially by placing calcium chloride into the apparatus and letting the apparatus stand for a day .
The insulation never broke down in this case , and the negative ions were found to have a greater velocity than the positive ions , but consistent results could not be obtained for some reason .
As arrangements were not made to dry the gas previous to passing it into the apparatus , the only results included are those for the moist gas .
These results are given in Table IV .
It will be noticed that the product of the mobility and the pressure is practically constant up to a pressure of 40 atmospheres , but that it decreases considerably as the gas approaches the liquid state .
The mobility of the positive ions in moist carbon dioxide is greater than the mobility of the negative ions , as was also observed by Zeleny and others , the ratio of mobilities being 095 for pressures up to 40 atmospheres and unity for pressures above 50 atmospheres .
The mean values of the product of the mobility and pressure in atmospheres taken for pressures up to 40 atmospheres and 19 ' C. are 0-705 and 067 for the positive and negative ions respectively .
Zeleny 's values at atmospheric pressure and 17 ' C. are 082 and 075 respectively , giving a ratio of 0'92 .
Table IV.\#151 ; Carbon Dioxide ( moist ) .
Mobility at various Pressures .
d = 2-31 cm .
T = 19 ' C. Pressure , in atmospheres .
Mobility in cm./ sec. per volt/ cm .
Mobility x Pressure .
Ratio of mobilities .
Positive .
Negative .
Positive .
Negative .
57-0 0 *0091 0 *0091 0-52 0-52 1-00 52 *4 0 *0116 0 *0116 0-61 0-61 1 -oo 46 *7 0 *0137 0 *0136 0-64 0-63 0-98 41 *8 0 *0160 0 *0148 0 67 0-62 0-93 36 *7 0 -0187 0 *0181 0-69 0-66 0-96 31 *5 0 *0234 0 *0225 0-74 0-71 0*96 26 *0 0 *0264 0 *0254 0-69 0-66 0*96 21 -1 0 *0355 0*0340 0-75 0*72 0-95 15 *3 0 *0465 0 -0427 0-71 0-65 0*92 10 -2 0 *0732 0 *0679 0-75 0*69 0*93 Mean for values for pressure up to 40 atmos .
... 0-705 0-67 0-94 Experiments with Hydrogen .
The hydrogen used in these experiments contained 0-7 per cent , nitrogen and very little moisture ( about 0 02 per cent. ) .
The range of the a-particles in hydrogen is four times that in air , consequently greater pressures were necessary to realise the condition of surface ionisation .
The results of the 1911 .
] Negative Ions in Gases at 161 experiments are given in Table V. It will be noticed that the mobility varies inversely as the pressure up to 72'5 atmospheres\#151 ; the highest pressure used in the experiments .
The mean values of the product of the mobility and pressure in atmospheres at 20 ' C. are 8T9 and 6'20 for the negative and the positive ions respectively , giving a ratio of mobilities equal to T32 .
The mobilities for the negative and positive ions in hydrogen at atmospheric pressure and 20 ' C. , as found by Zeleny , are 7'95 and 6'70 respectively , giving a ratio of mobilities equal to 1T9 .
Table V.\#151 ; Hydrogen .
Mobility at various Pressures .
d = 2-31 cm .
T = 20 ' C. Pressure , in atmospheres .
Mobility , in cm./ sec. per yolt/ cm .
Mobility x Pressure .
Ratio of mobilities .
Positive .
Negative .
Positive .
Negative .
72 *5 0*084 0-110 6*10 8-00 1 *31 68 -4 0*090 0-120 6-15 8-25 1 -34 62 7 0-096 0 126 6-01 7*90 1 -31 58 *1 0-105 0*139 6-10 8-08 1 -32 52 -8 0 116 0 *153 6*14 8-10 1 -32 47 *3 0 *132 0-175 6 25 8-29 1 *32 41 -9 0-146 0-198 6-11 8*30 1 -36 36 *7 0-170 0-228 6-25 8-38 1 -34 31 -5 0*201 0-267 6-34 8*41 1 *33 25 -7 0-248 0-322 6-38 8-28 1 '30 20 -8 0*305 0*388 6*35 8*08 1 -27 Mean 6-20 8-19 1 -32 Summary .
The mobilities of the positive and negative ions in dry air , dry hydrogen , and moist carbon dioxide were measured .
The method of measurements is based on Eutherford 's equation for the velocity of ions between two plates , the assumption in the theory being that a strong surface ionisation exists at one of the plates .
This assumption was satisfied experimentally by using the a-particles from ionium as the ionising agent , and reducing their range by using the gases at high pressure .
The equation was tested experimentally .
The results for the mobilities of the ions in these gases are as follows .
: In dry air and dry hydrogen the mobility varies inversely as the pressure up to 75 atmospheres , the highest pressure used .
In moist carbon dioxide the product of the mobility and pressure is constant for pressures up to VOL. LXXXVI.\#151 ; A. M 162 Dr. A. 0 .
Rankine .
On the [ Nov. 22 , 40 atmospheres , but for higher pressures the product decreases as the gas approaches the liquid state .
The mean values for the products of the mobility and pressure in atmospheres , for the range of pressures for which the product was constant , are , for the negative and positive ions respectively , in dry air , 1*89 and 1*346 ; in dry hydrogen 8*19 and 6*20 , and moist carbon dioxide 0*67 and 0*705 cm .
per second for a potential gradient of 1 volt per centimetre .
In conclusion , I take great pleasure in expressing my best thanks to Prof. Rutherford for suggesting this research , and for the valuable advice given by him during the progress of the experiments .
On the Viscosities of Gaseous Chlorine and Bromine .
By A. O. Rankine , D.Sc .
, Assistant in the Department of Physics , University College , London .
( Communicated by Prof. F. T. Trouton , F.R.S. Received November 22 , 1911 , \#151 ; Read January 25 , 1912 .
) Introduction .
The object of the experiments about to be described was to determine the viscosities , at various temperatures , of gaseous chlorine , bromine , and iodine , by comparison with air .
The 'apparatus , however , proved unsuitable in several respects for working at the higher temperatures required .
It has , nevertheless , yielded satisfactory results at the lower temperatures ; and the viscosity of chlorine at atmospheric temperature and at 100 ' C. , and that of bromine at the latter temperature only , have been measured by means of it .
These values are now published , pending the extension of the investigation on the lines indicated , with a new form of apparatus which promises to be entirely adequate for the purpose .
The chief difficulty which presents itself in working with the halogen gases is the readiness with which they attack mercury .
On this account , the method I have previously used* for viscosity determinations was rendered unsuitable ; but it has been found possible to retain one of its most desirable features , viz. , the mercury pellet , which serves the double purpose of creating a constant pressure difference , and of measuring the volume of * ' Roy .
Soc. Proc.,5 A , vol. 83 , pp. 265 and 516 .
|
rspa_1912_0011 | 0950-1207 | On the relation between current, voltage, pressure, and the length of the dark space in different gases. | 168 | 180 | 1,912 | 86 | Proceedings of the Royal Society of London. Series A, Containing Papers of a Mathematical and Physical Character | F. W. Aston, B. Sc.|H. E. Watson, B.Sc.|Sir J. J. Thomson, F. R. S. | article | 6.0.4 | http://dx.doi.org/10.1098/rspa.1912.0011 | en | rspa | 1,910 | 1,900 | 1,900 | 11 | 224 | 5,997 | http://corpora.clarin-d.uni-saarland.de/surprisal/6.0.3/?id=rspa_1912_0011 | 10.1098/rspa.1912.0011 | null | null | null | Thermodynamics | 39.789447 | Electricity | 20.515611 | Thermodynamics | [
1.427568793296814,
-51.18661117553711
] | 168 Messrs. Aston and Watson .
On [ Dec. 7 , case of chlorine and bromine at one pair of corresponding temperatures only , and although this does not prove that a similar rule holds at the critical temperatures , the probability is that the extension of the investigation will show this to be the case .
On the Relation between Current , Voltage , Pressure , and the Length of the Dark Space in Different Gases .
By F. W. Aston , B.Sc. , Trinity College , Cambridge , and H. E. Watson , B.Sc. , 1851 Exhibition Scholar , Trinity College , Cambridge .
( Communicated by Sir J. J. Thomson , F.R.S. Received December 7 , 1911 , \#151 ; Read January 25 , 1912 .
) In a previous communication by one of us* the results of a number of experiments on the relation between current , voltage , pressure , and the length of the dark space were given for the gases hydrogen , nitrogen , oxygen , and air .
The first part of the present paper consists of a continuation of that communication giving the results obtained with carbon monoxide , argon , and helium , together with some constants for these and the gases previously mentioned which were not published at the time .
The second part deals with a systematic investigation of the behaviour of the inactive gases when in a state of great purity .
Part I.\#151 ; For detailed description of the apparatus and method employed the reader is referred to the above-mentioned paper .
It will be sufficient to state here that the discharge took place between aluminium discs , 10 cm .
in diameter and about 17 cm .
apart , the cathode being of the guard-ring type to ensure accurate measurements of the current density .
The case of carbon monoxide is particularly interesting as it is the only compound gas yet experimented on which allows the passage of a continuous current without very serious decomposition .
In its behaviour it resembles exactly the active elementary gases .
Its dark space is sharp and well defined , but if the current density is increased beyond a certain limit ( about half the maximum used for the other gases ) , the discharge strikes back behind the cathode , and consequently the values of constants obtained are not very accurate .
The argon used was certainly impure , for it showed no signs of the primary * F. W. A. , 'Roy .
Soc. Proc. , ' A , 1907 , vol. 79 , p. 80 .
1911 .
] Dark Space in Different Gases .
dark space* exhibited by the pure specimen used in the later experiments .
The helium also probably contained sufficient impurity to make it behave more or less the same as the active gases and obey approximately the two empirical equations I ) A P B y/ C ' Table I gives the values obtained for the constants A , B , E , and F , and for the expression CPD3/ V2 ; f D , the Crookes dark space , is measured in centimetres ; P , the pressure , in hundredths of a millimetre of mercury ; C , the current density , in tenths of a milliampere per square centimetre of the cathode .
In the sixth column are given the values of the pressure Pi at which the dark space is 1 cm .
with unit current density , and in the seventh the voltage Vi between the electrodes under these conditions .
Table I. A. B. E. F x 10~2 .
CPD^IO5/ ?2 .
Pi- v , .
Hydrogen 26 -5 0-43 144 57 -3 57 -5 46 -8 266 Helium 36 0-49 255* 100 38 -8 70 -6 395 Carbon monoxide ... 10 0-42 255 41 -5 5 -75 17 5 489 Nitrogen 6-8 0-40 230 23 -6 5*75 11-3 434 Air 6-5 0-42 255 23 *0 5-70 11 -3 457 Oxygen 5-7 0-49 290 17 -6 5 -55 11 -4 444 Argon 5-4 0 34 240* 29 -4 2-37 8-2 594 * The high values given here should not be compared directly with the values of E in Table II , as they are obtained by extrapolation of a different part of the curve .
Part IT.\#151 ; The general method of conducting the experiments was the same as before , but some different measuring instruments were used .
The discharge tube was of the same type , being a large cylindrical bottle 12 cm .
in diameter , provided with a plane glass window at one side for observing the dark space .
The anode and cathode were parallel aluminium discs 9 cm .
apart , closely fitting the tube , the latter being of the guard-ring type previously described .
The area of the centre portion was 6'90 cm .
The length of the dark space was measured by a sighting arrangement similar to that used in the former experiments .
The potential fall across the tube was determined by means of a Weston voltmeter .
The pressure of the gas was measured by means of a McLeod gauge constructed with tubing 2'5 mm. in diameter in order to minimise the effects * F. W. A. , ' Roy .
Soc. Proc. , ' A , 1907 , vol. 80 , p. 45 .
t Loc .
cit. , also F. W. A. , ' Roy .
Soc. Proc. , ' A , 1911 , vol. 84 , p. 526 .
Messrs. Aston and Watson .
On the [ Dec. 7 , of capillarity .
It was usually cut off from the discharge tube by a tap to prevent access of mercury vapour , but the two vessels were always allowed to remain in communication for three or four minutes before measuring the pressure .
In making a series of experiments the gas was always admitted at the highest pressure required .
The pressure was then reduced by means of a Topler pump .
The ratio of the volume of gas removed at each stroke to that of the whole apparatus was determined , sufficient time being allowed for equilibrium to be established , and this afforded a means of checking the pressure given by the gauge .
The two values were found to be in good agreement .
The current was obtained from a battery of 500 small lead accumulators , and passed through two large water resistances in parallel .
Before taking a reading it was adjusted to a fixed value by means of a null method , the connections of which may be seen from the annexed diagram .
The current from an accumulator A passes through two resistances of 200 O and 5 fl in series .
In parallel with the latter is connected a current divider consisting of 100 20 D coils in series , and a sliding contact connecting with the terminals of any coil .
In this way the potential difference between the wires D and F could be set at 101 different voltages , rising by equal increments from 0 to about 1/ 20 volt .
The main current through the centre portion of the cathode of the discharge tube passed through a 50 XI shunt C to earth .
In making a measurement , the sliding contact of the current divider was moved to a fixed point , and the liquid resistances K adjusted until the potential difference across the shunt C exactly balanced that between D and F , the galvanometer G- being used to indicate the equilibrium point .
The apparatus was calibrated by passing known currents and simultaneously measuring the E.M.F. of the accumulator A. Since the current necessary 1911 .
] Dark Space in Different Gases .
to produce equilibrium is proportional to this E.M.F. the voltage of A was tested from day to day , although it remained very constant .
The maximum current measured was very nearly 1 milliampere , corresponding to 100 coils of the current divider between D and F , and the other fixed currents adopted corresponded to 81 coils , 64 , 49 , 36 , 25 , 16 , 9 , 4 , and sometimes 1 , these values being chosen because the square roots and inverse square roots of the current were the functions considered .
An adjustable resistance H was inserted between the guard ring of the cathode and the earth connection , for by varying this until the difference in potential between the two parts of the cathode ( indicated by a galvanometer not shown in the diagram ) was zero , the ratio of the currents through the two portions could be determined .
The extreme variation of this ratio was about 15 per cent. , and considering the small size of the centre portion of the cathode , it seems probable that the current density over its surface was uniform within the limits of experimental error .
Before starting the experiments the discharge tube was repeatedly filled with oxygen at low pressure and a current passed , the tube being evacuated with charcoal in liquid air , as soon as the yellow colour of the oxygen turned grey from contamination by carbon compounds .
After 10 days the rate of production of the latter gases became very slow , and experiments were then started with the inactive gases .
After a few preliminary difficulties had been overcome , it was seen that these gases were very similar to one another in their manner of conducting the discharge , but at the same time they differed considerably from the active gases , in that the two equations given on p. 169 did not hold with any degree of accuracy .
The first of them , connecting the length of the dark space with the current density , was true for high current densities , but the second , connecting voltage and current density , seemed to be in no way applicable .
If , however , P be eliminated from the equations , the result is V \#151 ; G = KD^/ C where G = E \#151 ; BF/ A and K = F/ A , and this relation was found to agree remarkably well with the experimental results .
One noticeable feature is common to the gases of the helium group , this being that they all exhibit the primary dark space close to the cathode discovered by one of us in helium and hydrogen.* In argon and krypton it is not very obvious , but in the other three gases it is exceedingly striking , especially at low current densities .
The conditions of experiment were , unfortunately , not suitable for accurate measurements of the very small length d of this dark space , but from some rough results obtained , the values of the expression die / D , which appeared to be fairly constant , * F. W. A. , ' Roy .
Soc. Proc. , ' A , 1907 , vol. 80 , p. 45 .
Messrs. Aston and Watson .
On [ Dec. 7 , were found to be approximately 10 volts for neon , 12 for argon , 15 for krypton , and 20 for xenon , the figures previously obtained for hydrogen and helium being 10 and 20 respectively .
Neon was the first gas investigated .
It had been prepared originally by fractionation from a mixture with helium , and was repurified by means of charcoal in liquid air before use .
Two samples were examined , one of which probably contained a little helium , but no difference could be detected between them .
The boundary of the dark space was not as sharp as in oxygen , especially at low current densities , and its position was rather difficult to determine owing to the large amount of light in the dark space itself .
The colour of the latter was rather redder than that of the negative glow , which was orange , but there was no obvious spectroscopic difference .
The first experiments made appeared to indicate that the above-mentioned equations held good in the case of neon as well as for the active gases , but after about 20 series of readings at various pressures it was found that the relation between Y and ^/ Gat constant pressure tended to deviate from the linear type and become hyperbolic , the curve rising fairly steeply at first , OVc OZ 0-4 0-6 0-8 10 I-Z Fig. 2.\#151 ; Neon\#151 ; Relation between Current and Voltage .
1911 .
] Dark Space in Different Gases .
and then turning over and becoming nearly horizontal .
After continuing the experiments for some time , fresh gas being used for each series , the bend in the curve became much sharper , but finally a constant state was reached .
Some of these curves are shown in fig. 2 .
The lowest one and the fourth from the top were obtained with one sample of gas and the rest with the same after undergoing another fractionation to remove possible traces of helium .
Several weeks elapsed between the two series of experiments , and other gases were introduced into the discharge tube in the interval .
It will be observed that there is a slight tendency for the curves to bend upwards at high current densities , especially at low pressure .
This appears to be a real effect , but at the same time it is very difficult to keep the current constant under these conditions , and the rise in voltage may be exaggerated .
With regard to the shape of the curves at low current densities it is possible that the limiting voltage for zero current is the same for all pressures , but the curves hardly bear extrapolation to one point , and at low pressures the truth cannot be ascertained by means of the apparatus used , because if the current is reduced below a certain limit , the discharge suddenly ceases to pass .
At high pressures , however , the curves tend to become horizontal with small currents and the limiting voltage is that which persists when the current is insufficient to cover the cathode .
For the sake of uniformity , all measurements were made as the currents were increased .
If the reverse procedure was followed , the voltages obtained were a few volts lower .
This is probably due to a combination of effects , such as the presence of mercury vapour , and tiring of the electrodes , which cannot be investigated conveniently in a tube of large dimensions .
It seems likely , however , that the real voltages at high current densities are slightly higher than those given .
This applies also to the other gases .
With regard to the relation between dark space and current density , the equation D = A/ P + B/ ^/ C appeared to hold for high current densities , but at low ones D was much smaller than the calculated value .
Moreover in the measurements with diatomic gases , B was found to be very constant , while in the case of neon it varied more than in any other gas , being 0*41 at high pressures and 0'81 at low ones .
Fig. 3 shows some typical curves obtained , and corresponding to those in fig. 2 .
Krypton was the next gas investigated .
Before its introduction the discharge tube was evacuated as completely as possible and rinsed first with oxygen and then with the gas itself .
The colour of the discharge was greenish , there being a considerable amount of light in the dark space .
The gas first used contained sufficient 174 Messrs. Aston and Watson .
On the [ Dec. 7 , argon to be visible spectroscopically , but the results were not appreciably affected when this gas was sparked with oxygen which was then removed with phosphorus , the residue condensed in liquid air , and a small heavy fraction which appeared to be very pure krypton taken .
When using krypton an unexpected difficulty was encountered .
The anode , which was a plane disc parallel to the cathode , had been used Fig. 3.\#151 ; Neon\#151 ; Relation between Dark Space and Current Density .
previously for other experiments , and had three small holes pierced in it near the edge .
When the gas was at a fairly high pressure , a small secondary discharge frequently passed through one or more of these holes , and often assumed beautiful shapes and colours .
Its behaviour appeared to be quite erratic , and , as the difference of potential across the tube only fell by 5 volts when it was passing , it was considered more advisable to allow for its presence than to cut down and rebuild the wThole discharge tube .
Another restriction when using krypton was the fact that if the current density exceeded about 0T0 milliampere , the discharge passed from the back of the cathode as well as from the front , as in the case of carbon monoxide .
This change in the nature of the discharge appeared to be independent of the pressure .
The edge of the dark space was difficult to locate owing to small contrast , but the curves connecting the length of the dark space and the reciprocal of the square root of the current density were very similar to those for neon , that is to say , straight lines at high current densities .
These lines were , however , very nearly parallel , therein differing from the neon lines .
The Y^/ C curves were also of the same type as those in fig. 2 , but the bend was even more sudden .
In fact , each curve could be well represented 1911 .
] Dark Space in Different Gases .
by two straight lines .
The bend occurred at approximately the same current density as that in neon .
The case of xenon was similar .
The gas was frozen in liquid air , and foreign gases removed by pumping , until a high vacuum was obtained .
The residue appeared to be very pure xenon .
The apparatus was thoroughly rinsed before the experiments were started .
The appearance of the discharge was very beautiful .
Starting from the cathode , there was first a very dark and well-marked primary dark space , Current 81 6\#177 ; 49 36 Dark 05 space ro Pig .
4 .
The above diagram shows the relation between the length of the dark space and the voltage in the case of krypton .
The concurrent straight lines are drawn in such a way that the crosses representing the experimental results obtained would lie upon them if the relation V \#151 ; G = KD^/ C were rigidly true , each line being the locus of points for which the current is constant .
Before drawing them , the position of the point at which they meet was determined by extrapolation .
The lines crossing this pencil are the loci of points for which the pressures are equal , the actual pressures drawn being , starting from the bottom , 17'6 , 14-2 , 11*6 , 9*2 , 7*5 , 6*3 , and 5*2 , hundredths of a millimetre , and then a bright olive green glow , becoming deeper green with increased distance from the cathode .
This constituted the Crookes dark space .
The negative glow was bluish-white , merging into orange , and the boundary of the dark space , though fairly sharp , was very difficult to measure owing to lack of contrast .
Messrs. Aston and Watson .
On the [ Dec. 7 , The same phenomenon of discharge through the anode as in krypton was noted , and the current density at which the discharge started from the back of the cathode was rather less than half that in the former case , so that high current densities could not be investigated .
The forms of the curves connecting the length of the dark space , the current density , and the voltage were very similar to those in the case of krypton , but the bend in the Y , \lt ; yG , curves was not so marked .
The results given by argon were similar to those from neon .
Owing to the presence of mercury vapour which could not be removed entirely by freezing a side tube connected with the apparatus in liquid air , the spectrum of the negative glow showed only mercury lines except at the boundary of the dark space where the glow was white , and argon lines showed as well .
The dark space itself was red , and showed the argon spectrum with a few very faint mercury lines .
At lower pressures the dark space became bluer , and argon lines appeared in the negative glow .
The curves connecting the length of the dark space with the current density were of the usual type , but the Y , ^/ C , ones were much straighter than in the case of neon .
There was , however , a slight bend at the same current density as in the other gases , and the curves were similar to those yielded by neon in the early experiments .
It is very probable that this was due to a slight trace of oxygen , for although the argon was treated with phosphorus and subsequently distilled , it is quite likely that all the oxygen was not removed .
The phenomena occurring in helium were very complicated and difficult to investigate , as there appeared to be two forms of discharge .
The changes were most marked when observations of the current and voltage were made at constant pressure .
Usually on taking readings after a change in pressure , values were obtained such that the relation between Y and C was approximately linear .
Before the voltages for the highest current densities could be measured , however , there was almost invariably a sudden drop in voltage , amounting often to 400 volts for the same current , and as more readings were taken the voltage would gradually decrease a little more , until what was apparently a minimum was reached .
Very often before this was attained the voltage rose again .
Sometimes the reverse was the case , and a series of low readings was first obtained until , without warning , the voltage would increase beyond the limits of measurement .
The following account of a particularly erratic specimen of gas at a pressure of 1*5 mm. is taken from the original notes:\#151 ; A series of readings for which the relation between V and y/ C was linear was obtained .
When the current through the tube was 0'81 milliampere the voltage was 368 .
This dropped to 185 , and then rose at once to 392 .
1911 .
] Dark Space in Different Gases .
The current was next increased to 1 milliampere .
The voltage dropped to 200 , and in about 15 seconds rose to 450 , after which it fell slowly to 425 , and then again fell to 200 .
This occurred several times .
When at the low voltage , the current was cut off and restarted with the intensity of 0-36 milliampere only .
The initial voltage was 240 , which rose to 284 .
A side tube connected to the discharge tube was next immersed in liquid air , and a heavy current run .
On reducing to the previous value of 0-36 milliampere the voltage was found to be 170 , which rose shortly to 255 .
At 0-81 milliampere the voltage dropped from 350 to 200 twice .
The actual voltage changes in this example were not very great , but at low pressures they increased largely .
At the same time it was increasingly difficult on lowering the pressure to obtain the low values for the voltage .
The cause of these two kinds of discharge is difficult to determine .
It seems probable , however , that what may be termed the low voltage discharge is the normal one corresponding to the discharge in the other monatomic gases , while the high voltage discharge is abnormal , and its occurrence favoured by the presence of an impurity , which is probably carbon dioxide .
It would appear , moreover , that this impurity acts catalytically , firstly because the current-voltage curves obtained were quite regular and definite at different pressures , although the amount of impurity cannot have been constant , and , secondly , because , as already mentioned , the discharge rapidly altered from one type to the other , whereas it can hardly be imagined that at constant current the gas should first become more pure and then grow impure again .
There is at present no actual proof that the high voltage discharge is caused by impurity at all , but it was usually possible to obtain the low voltage discharge by cooling a portion of the apparatus for some time in liquid air , while cooling in solid carbon dioxide had no effect .
On removing the liquid air the voltage would usually rise , but these simple effects were largely masked by the production and possible absorption of impurity when the current was running .
There was also the effect of mercury vapour to be guarded against .
Unfortunately the apparatus had not been constructed so as to remove this gas completely , and it appeared that there was a small rise in the voltage when much mercury vapour was present , but the main phenomenon of changing voltage was apparently not due to its presence , for its spectral lines appeared relatively as strongly in both forms of To the eye there was a distinct difference between the two types .
The low voltage one was characterised by the edge of the dark space being very blurry and almost invisible at low current densities owing to lack of contrast .
discharge .
VOL. lxxxvi.\#151 ; A. N 178 Messrs. Aston and Watson .
the [ Dec. 7 , The dark space itself was a deep emerald green , and the negative glow a slightly paler green , except at high current densities , when it became whitish .
With the high voltage discharge the negative glow was almost white ( possibly owing to the greater transference of energy ) , and the boundary very sharp .
There was no obvious spectroscopic difference between the two forms .
As far as it was possible to judge , the curves connecting length of dark space , current , and voltage were similar in type to those of the other gases .
The Y , y/ C , curves were , however , when not quite irregular , fairly straight , and , moreover , all of them extrapolated very closely to the same point for zero current .
Upon the completion of these experiments , a series was performed with oxygen for comparison with results previously obtained , and the agreement was found to be good .
It will thus be seen that , apart from small individual peculiarities , the behaviour of each of the five inactive gases is very much of the same nature , provided the experiments are conducted at constant pressure .
Thus , the 1/ ^/ C , D , curves are almost identical , and the V , ^/ C , curves very similar to each other .
The only marked difference in making the experiments is that the range of pressures over which they can be carried out in order to obtain similar values for the length of the dark space and the voltage is widely different , varying regularly from 1'5 \#151 ; 02 mm. in the case of helium to 03\#151 ; 006 mm. in the case of xenon .
Owing to these facts , little information is to be gained from a cursory inspection of the characteristic curves for each gas , and consequently one curve only of each type has been reproduced .
Some idea of the relative behaviour of the gases may , however , be obtained by examining the approximate values for the constants in the equations D=| + -^ , V = E + ^ , V-G = KDV'C , which may be deduced from these curves .
Of the above equations , the first holds good only at high current densities , and A is by no means constant .
In the second equation E can be found , since the Y , \/ G , curves extrapolate approximately to one point where C = 0 , but F is meaningless .
The third equation , however , is much more accurate , and fairly close values can be obtained both for G and K. Table II gives the values of these quantities .
The seventh and eighth columns show the pressure and voltage for unit dark space and unit current density , the units being those given on p. 169 .
1911 .
] Dark Space Di fferent Gases .
Table II .
A. B. E. a. K. Pi .
Vi .
PxlOVVi2 .
PjlC^/ Vi2 x at .
wt. Helium ... 38 PO-27 137 25 380 52 '5 412 31 124 f eon | 5 -0\#151 ; 8 -0 0 *41\#151 ; 0 -82 170\#151 ; 220 90 445 18*6 545 6*25 125 !
rornn l 4 0 0 -32\#151 ; 0 -41 190 60 530 8'3 610 2'25 89 Ll gVIA | [ rypton ... j 3 '8\#151 ; 5 -4 0 -37\#151 ; 0 -45 225\#151 ; 325 100 630 8'3 745 1 '50 125 tenon ... 4 *0\#151 ; 6 '0 0 -23\#151 ; 0 '40 245 120 890 5'9 1025 0 *60 78 )xygen ... 6 1 0'48 292 135 318 11 '5 460 5'45 82 The expression CPD3/ V2 , which has been shown by one of us to be proportional to the velocities of the positive ions , when certain assumptions are made , * is by no means constant for the inactive gases , but a rough comparison for the different gases may be made by considering its value under certain conditions .
Column 9 shows the values for unit current and unit dark space .
These appear to be approximately inversely proportional to the atomic weight , as may be seen from Column 10 , which gives the product of Pi/ Vi2 and the atomic weight .
It seems unlikely that the agreement in the case of helium , neon , and krypton is fortuitous .
It will , however , be noticed that the figures for argon and xenon differ considerably from the others .
It is possible , as mentioned before , that the argon contained a trace of oxygen , which might easily vitiate the results , whilst with xenon , the values of Pi and Vi are only obtained by a wide extrapolation , as the maximum current which could be measured was only half the unit current adopted .
Actually , the value of 0*75 for CPD3105/ V2 was obtained for the highest current densities used in a series of experiments , and the variation with current density and pressure was very slight , so that it is quite possible that the extrapolated figure is too low .
With regard to the other quantities given in the tables , it is somewhat remarkable that B has very similar values for all gases .
K and Vj increase regularly with rise in atomic weight of the gas , whilst Pi decreases , but there appears to be no simple connection between any of these quantities .
The values in the table are all determined graphically from the characteristic curves of the gas , and it will be seen that the sum of Gr and K is approximately Vi , as it should be if the third equation on p. 178 were rigidly exact .
At present , it seems useless to evolve a theoretical discussion of the general results obtained , since our knowledge of the whole mechanism of discharge is very limited , and the data so far available insufficient .
Further experiments with cathodes of different shapes are , however , in progress , and it is hoped that by this means further light may be thrown on the subject * 'Roy .
Soc. Proc. , ' A , 1907 , vol. 79 , p. 85 ; and 1911 , vol. 84 , p. 534 .
N 2 Mr. G. A. Shakespeare .
A Method of [ Nov. 21 , and an explanation found for the results just given .
In the meantime , the present paper must remain as a statement of facts .
In conclusion , we wish to express our best thanks to Sir J. J. Thomson for the great interest he has taken in this work , which was carried out in the Cavendish Laboratory , and also to Sir William Ramsay for the loan of the krypton and xenon , which alone made the research possible .
A New Method of Determining the Radiation Constant .
By G. A. Shakespeare , M.A. , B.Sc. ( Communicated by Prof. J. H. Pointing , F.R.S. Received November 21 , 1911 , \#151 ; Read January 8 , 1912 .
) According to Stefan 's law the rate of radiation of energy from a full radiator in surroundings at a temperature of absolute zero is \lt ; r04 ergs per cm.2 per sec. , where 6 is the absolute temperature of the radiator .
If the radiator be in surroundings which are themselves full radiators , but at absolute temperature 6\ , the rate of loss of energy by radiation is taken to be o-^4-# !
4 ) .
The classical determination of the constant a is due to Kurlbaum , * who used a surface bolometer with a platinum-black surface .
The rise of temperature of the bolometer when exposed to the radiation from an approximately full radiator or " black body " was observed .
The radiation was then cut off , and an equal rise of temperature was produced by increasing the main current in the bolometer .
It was assumed that the energy received per second from the radiator in the first case was equal to the energy received per second from the increase of current in the second case .
The resulting value of cr was 5*33 x 10~5 ergs per cm.2 per sec. per deg.4 , or 5'33 x 10~12 watts per cm 2 per deg.4 .
Kurlbaum gives a summary of previous measurements of cr , and there appears little doubt that his method was a great advance on those of earlier workers , and that it was carried out with such a high degree of experimental skill as to justify confidence in the result .
Later work , however , has suggested that Kurlbaum 's value is too low .
Feryj* in particular , using an entirely different method , in which he employed * ' Ann , d. Phys. , ' 1898 , vol. 65 , p. 746 .
t 'Compt .
Kend .
, ' April 5 , 1909 .
|
rspa_1912_0015 | 0950-1207 | The testing of plane surfaces. | 227 | 234 | 1,912 | 86 | Proceedings of the Royal Society of London. Series A, Containing Papers of a Mathematical and Physical Character | P. E. Shaw, B. A., D. Sc.|Prof. J. H. Poynting, F. R. S. | article | 6.0.4 | http://dx.doi.org/10.1098/rspa.1912.0015 | en | rspa | 1,910 | 1,900 | 1,900 | 7 | 136 | 3,096 | http://corpora.clarin-d.uni-saarland.de/surprisal/6.0.3/?id=rspa_1912_0015 | 10.1098/rspa.1912.0015 | null | null | null | Measurement | 82.690481 | Tables | 11.230611 | Measurement | [
35.02159118652344,
-11.942281723022461
] | 227 The Testing of Plane Surfaces .
By P. E. Shaw , B.A. , D.Sc .
( Communicated by Prof. J. H. Pointing , F.R.S. Received December 9 , 1911\#151 ; Read January 25 , 1912 .
) There is only one way of originating a true plane , viz. , to make it in triplicate and to work all three surfaces so as to obtain a " fit " between them .
In engineering trade practice this is done when a standard plate is required , and any one of the three plates thus obtained can be used as being truly plane ( within the limits of the " raddle " process ) for the making of further surface-plates .
In many modern exact apparatus , e.g.y a standard measuring machine or a Michelson 's interferometer , accuracy of measurement directly depends on the truth of the plane " ways " of the bed along which the various parts of the apparatus slide .
These ways are made either by scraping or lapping , and it is of importance to know what errors occur from place to place along the bed due to defective workmanship .
The bed generally has three worked planes all inclined to one another , and the movable parts rest on these by five contact points , thus allowing only one degree of freedom .
These five feet bear on the surfaces below by small areas , and amongst other considerations it is important to know how far these feet rise and fall in and out of the scraping marks if the surfaces have been made by scraping .
Any such rise and fall produces a rocking motion in a movable part as it slides along the bed .
In a badly made surface such pits would be wide and deep and the attendant rocking motion considerable .
But any surface , whether scraped or lapped , is liable to have constant or variable curvature over a large area due to defective workmanship or due to warping subsequent to manufacture .
It is convenient for present purposes to denote the small local irregularities as ripples ( only found on scraped surfaces ) and the large changes in curvature as waves .
Any tool used to test for ripples must have small feet , whereas for waves one would need an appliance with feet of such large area as would not fall into scrape marks .
The object of this paper is to indicate ways of measuring these errors in surface-plates .
The writer recently had a measuring machine made .
Its purpose 'was to apply to end-standards of length very severe tests as to length and figure ; and for this purpose one must be sure that errors of the first order , due to inequalities in the bed , will not enter the results .
In the Dr. P. E. Shaw .
[ Dec. 9r making of the bed more than usual care was taken in casting the bed and in \#171 ; a"eing " it with repeated planing and finally with various stages of scraping .
The principal headstock of the machine has a long base ( 18 inches ) .
Suppose this headstock is placed on the bed and a sensitive spirit level mounted on it ; if it be moved along the bed , then , supposing the three cardinal planes of the bed are true planes , it will move along without rocking and the spirit level will remain at rest .
But any error , whether ripple or wave , in the bed would be shown by the level .
Very sensitive spirit levels can be made , but exact quantitative results are required , and it would not be easy to calibrate such a device , besides which , if it is sensitive , it must have a very limited range .
Moreover it could only be used or a level surface and would not be generally applicable to testing plane surfaces which are often inclined in situ to the horizon .
So a spirit level device will not serve our purpose .
Vain a spherometer will not do .
as we have to test a surface which has considerable length but small breadth .
In short , there is no apparatus or method in use suitable for the purpose , so one must be invented .
Surface-tester No. 1.\#151 ; The first device adopted is shown m fig. .
_ bar , 20 inches long , of teak is fitted with ( 1 ) a micrometer screw m the centre and with ( 2 ) two feet , half an inch apart set in a line across the foot which has been worked which ig akin to a spherometer , micrometer screw being , IP binding screw attached to , d rest stably on and telephone " rjned to Te binding screw and the surface-plate .
By working 1911 .
] The Testing of Plane Surfaces .
the micrometer " out " electric contact is made when the screw point reaches the surface-plate , and the micrometer is read when the telephone sounds .
Calling the three cardinal surfaces of the bed ay b , c , the following measurements were taken at equal intervals along the length of the bed .
The units are 1/ 10000 inch .
a. b. c. 144 143 144 144 146 142 143 144 142 142 144 144 144 145 144 144 144 144 140 144 144 Means ... . .
143 144 *3 143 -5 Mean of means . .
143*6 These surfaces agree , therefore , throughout , to 4/ 10000 inch for measured lengths of about 16 inches .
The rounded mean reading is 143*6 .
But we have no method , with surface-tester No. 1 , of finding the true zero reading .
The above surfaces may be all convex or all concave , or the mean reading may be nearly true zero .
The surface-tester was then tried on a new , well-made , scraped surface-plate , the readings being 140 142 140 139 141 142 142 140 140 Mean ... ... ... .
140 *7 If we could assume this plate to be very good , we might take the reading 140*7 to be true zero ( i.e. the reading which a geometrical plane surface would give ) , in which case the mean error of the surfaces a , b , c , would be 3/ 10000 inch in a length of 16 inches .
But it is not permissible to assume the truth of any " standard/ ' so the following modification of the above apparatus was made to determine true zero reading .
Surface-tester No. 2.\#151 ; A stout bar of iron ( fig. 2 ) with a deep vertical web Fig. 2 .
VOL. LXXXVI.--A .
R Dr. P. E. Shaw .
[ Dec. 9 , lias let into its lower face two hardened steel studs with true flat feet of \ inch diameter .
These studs are 12 inches apart .
Midway between them is fixed in the bar a Brown and Sharp micrometer screw , whose working end is another true flat surface \ inch diameter .
The studs are bushed , and a binding-screw is let into the bar to enable a circuit to be made just as in tester No. 1 .
Great care must be taken , when using the testers , that no shocks are received by micrometer and studs .
Guards are shown , one on each side of the micrometer .
Also , when not in use , the testers are packed away carefully .
This instrument is made in duplicate .
Call the two testers A and B. Place A on the surface to be tested .
If the micrometer screw is " in , " A would rest stably on a flat surface , the end feet touching the latter at places , say d and e. On screwing in the micrometer , contact is made when the latter reaches the surface .
Lift the tester from the surface and place it , feet upwards , on a suitable cradle ( see fig. 2 ) .
Next take the tester B and place it on the surface , its feet resting on places d and e ; adjust the micrometer to contact .
Take a reading of B ; call it Bi .
Place B on A as shown in fig. o. If the centre feet of A and B just meet in the above position , Bx is true zero reading and the surface is a true plane , at least as regards places d , and the place on the surface midway between them .
If , on the other hand , the micrometer of B has to he screwed in or out to just meet the screw of A , giving reading B2 , we have J ( Bx-B2 ) as the error of the three places 1911 .
] The Testing of Plane Surfaces .
231 from a straight line .
Screwing in shows convexity , and screwing out concavity of the surface .
True zero reading is + \ ( Bi \#151 ; B2 ) .
The process used is akin to the three-surface method mentioned at the beginning of the paper .
A small flexure of the tester occurs , due to its own weight .
To avoid this , the supporting blocks under A in the cradle are placed at the Airy points along the bar as shown .
Before B rests on A , this arrangement would leave A slightly concave upwards , but when B is placed on A this concavity would be reduced to zero by the weight of B. For tester No. 2 mechanical contact is simplest , but for tester No. 1 electric contact is more accurate .
In order to obtain true zero reading , we have had to resort to micrometry with flat faces ( tester No. 1 would obviously not serve ) .
One great disadvantage of employing flat faces in micrometry is that the errors in truth of these faces enter into the results directly .
Surface-tester No. 2 will be of small service unless the highest possible mechanical skill is put into the setting of its three feet in one plane for true zero .
Mr. A. Jenkiuson , of the National Physical Laboratory , Teddington , an experienced micrometer maker , undertook to make the two testers No. 2 to meet my requirements , and his work proved very satisfactory .
He proceeded as follows :\#151 ; Castings were made and were machined and bored roughly to remove casting strains .
They were then left for a period in a vibrational place to settle .
Machining was repeated .
The bottom was scraped true , then clamped to a lathe face-plate and the hole for the micrometer bored out .
The holes for the other two feet were reamered to size through a true jig plate .
The studs were turned and hardened and were settled in boiling water ; they were then pressed into place with bushes .
The micrometer was then put into its place and the two other feet lapped by hand till they were true with the micrometer foot .
This last process took considerable time and trouble , as on it hangs the accuracy of results .
As examples of the use of the surface-testers the following cases are given :\#151 ; I. Hexagon Surface-Plate ( 2 feet diameter).\#151 ; Using tester No. 2 , nine positions were taken symmetrically round the centre of the plate .
In some cases repetition was made to ascertain whether any change due to temperature occurred as the measurements proceeded .
Dr. P. E. Shaw .
[ Dec. 9 , Reading Beading Zero reading Error Position .
Bl B2 .
Bj + i ( Bj\#151 ; Bj ) .
i(B1-B3 ) .
1 17 14 15 *5 1*5 2 17 13 *5 15 *3 1-8 3 17 14 15 *5 1 5 4 18 13 *5 15 *7 2*2 5 18 14 16 2 6 18 13 5 15*7 2*2 7 18 *5 14 16 *2 2*2 8 17 *5 13 *5 15 *5 2 9 17 *5 13 5 15 5 2 7 18 14 16 2 1 17 14 15*5 1*5 Mean ... 15*7 Mean ... 1 *9 ( convex ) As before the unit is 1/ 10000 inch .
This plate is consistently convex at regions about the centre , the error on a length of 12 inches being on the average about 1/ 5000 inch .
A set of readings like the above establishes an accurate true zero reading ( 15-7 in this case ) .
The divergence from this value is at most 0-4/ 10000 in the table above .
This irregularity may be due to defects in the testers or to the impossibility of placing both testers on the same places exactly , or to both causes .
Having discovered true zero for B we need not use A further , for the reading B , together with true zero , gives the error of the surface .
A set of readings taken round the edge of the above surface plate gives us results as below :\#151 ; B !
... ... ... ... .
17-5 18 17 16 16-5 16 17 18 16 16 Error , B , -15-7 ... 1 -8 2'3 1*3 0'3 0'8 0-3 1 3 2'3 0'3 0-3 ( convex ) Thus the mean error near the edge of the plate is less than near its centre , but the plate is more irregular .
Having ascertained the general contour of the surface by tester No. 2 we look for ripples near the centre of the plate by tester No. 1 and obtain readings:\#151 ; 172 172 172 171-6 171-6 171'6 171-6 172 172-4 Mean ... ... 171 '9 The units are again 1/ 10000 inch .
The extreme readings here differ from the mean reading by about the same amount as when the tester No. 2 was used .
So the ripples are a negligible quantity in this plate .
In some plates , however , one finds ripples in evidence .
II .
Two small surface-plates ( 10 inches by 8 inches ) , one lapped and one scraped , were very carefully made , and were tested soon after manufacture .
As is seen below they are so good that errors of observation by the micrometer are of the same order as errors of the surface .
Probably at present The Testing of Plane Surfaces .
1911 .
] surface-plates are not required and cannot be made as a commercial proposition to higher accuracy .
But if such should ever be the case the surface-testers would have to be made more sensitive .
This could be done by having a larger divided drum on the micrometer and by using electric contact .
Ten places are chosen and readings repeated at each for each of the above surfaces .
True zero for tester A is 56 and for B is 62*7 .
For the lapped surface both A and B were employed ; for the scraped surface A only , further trial being unnecessary .
Results :\#151 ; Position .
Lapped plate .
Scraped plate .
Tester A. Tester B. Tester A. 1 56 56 62 62 -5 56 5 57 2 56 55 *5 62 62 *5 56 *5 56 3 56 *5 56 62 *5 62 *5 56 56 4 56 56 62 *5 63 56 *5 56 5 56 56 62 63 56 56 6 56 55 *5 62 62 *5 56 56 7 56 55 *5 62 62 *5 57 56 8 55 *5 56 62 62 *5 56 55 *5 9 55 5 55 5 62 *5 63 56 56 '5 10 55 *5 55 5 62 *5 62 *5 56 *5 56 *5 Mean error 0 *1 M[ean error 0 *3 Mean error 0*2 The readings on any surface differ by 1/ 10000 inch only , and the mean errors are only 1/ 100000 inch , 3/ 100000 inch , and 2/ 100000 inch .
The mean error in the lapped plate is a convexity and in the scraped plate a concavity .
The above plates are too small for observation by tester No. 1 .
III .
Experiments on Plate Glass.\#151 ; Of all cheap commercial articles this has plane faces with the nearest approach to truth .
As regards small areas the two surfaces are so nearly plane that reflection and refraction at them appears , by ordinary tests , to be regular .
It is of interest to discover how nearly the surfaces taken on large areas approach truth .
# Surface-tester No. 2 is used .
Four specimens , taken from the stock of one of the largest manufacturers of plate glass , gave results shown in the following table .
A length of plate was placed on two narrow wooden strips so that when the tester rested on the glass its feet would lie vertically over the strips .
The strips would take up the weight of the tester and prevent flexure of the plate .
The Testing of Plane Surfaces .
Beading A1# Beading A2 .
Zero .
Mean plate error .
I Front Back 239 242 300 298 296 294 267 -51 268 j j- Mean 267 '7 27 *2 concave 31 convex II Front Back 273 272 253 253 4 *5 convex 15 concave III Front Back 295 294 249 246 26 *5 convex 20 *5 concave IY Front Back 272 271 263 264 3 *5 convex 4 *5 concave Thus the errors vary from 30/ 10000 to 3/ 10000 for these specimens .
The fourth specimen has an accuracy which compares well with that of a surface-plate .
When once the zero reading ( 267'7 here ) has been found , it is an easy matter to test the plates quickly and pick out a good one .
In all cases the plates are curved as a whole , one side being convex , the other concave .
I am glad to acknowledge that the cost of the apparatus was defrayed by a Government grant from the Royal Society .
|
rspa_1912_0017 | 0950-1207 | The effect of temperature upon radioactive disintegration. | 240 | 253 | 1,912 | 86 | Proceedings of the Royal Society of London. Series A, Containing Papers of a Mathematical and Physical Character | Alexander S. Russell, M. A., B. Sc.|Prof. E. Rutherford, F. R. S. | article | 6.0.4 | http://dx.doi.org/10.1098/rspa.1912.0017 | en | rspa | 1,910 | 1,900 | 1,900 | 6 | 302 | 6,990 | http://corpora.clarin-d.uni-saarland.de/surprisal/6.0.3/?id=rspa_1912_0017 | 10.1098/rspa.1912.0017 | null | null | null | Thermodynamics | 41.935178 | Atomic Physics | 31.814963 | Thermodynamics | [
3.9911768436431885,
-80.54322052001953
] | 240 Mr. A. S. Russell .
The Effect of [ Dec. 19 origin .
This is also in agreement with the equation , since the tangent at the point of inflection cuts the X axis at the point \#151 ; \#177 ; n0 , a quantity which is independent of the specific properties of the scattering material .
From similar considerations to those given above , it is possible to calculate the scattering of a-particles in gases , and to deduce the scattering coefficients .
This question is of interest , since for substances of atomic weight comparable with that of the a-particle , the amount of scattering may not be proportional to the atomic weight , a relation which seems to hold fairly well for the heavier atoms so far examined .
A discussion of this will , however , be postponed until the necessary experiments have been carried out .
I take this opportunity of expressing my thanks to Prof. Eutherford for many helpful suggestions .
The Effect of Temperature upon Radioactive Disintegration .
By Alexander S. Eussell , M.A. , B.Sc. , Carnegie Eesearch Fellow of the University of Glasgow .
( Communicated by Prof. E. Eutherford , F.E.S. Eeceived December 19 , 1911 , \#151 ; Eead January 25 , 1912 .
) 1 .
Introduction .
Within the last few years the influence of high temperature on the activity of radium emanation , of the active deposit , and of radium C has been examined in detail by several authors .
The conclusions arrived at have been conflicting , some workers affirming a positive effect of temperature , others denying it .
This lack of agreement is due , however , to a difference in the method of measurement of the active matter under investigation .
Those workers who measured the activity by 7-rays are all agreed that temperature has no effect whatever , while those who measuied by / 3-rays found always an effect of some kind , in many cases of considerable magnitude , and often , indeed , of a very surprising nature .
While , however , the fact that there is a / 3-ray effect is admitted by all , there is still a lack of agreement between the results of the experiments of different workers , and even of different experiments of the same worker , which is hardly to be expected if the effects were due to a definite change in the properties of the disintegrating atoms at high temperatures .
In view , therefore , of the uncertainty which has arisen on a point of such Temperature upon Radioactive Disintegration .
great theoretical importance , a systematic investigation was necessary to obtain definite results , whether positive or negative .
This the author , at the request of Prof. Rutherford , has carried out .
Work on ( 3-Rays.\#151 ; The original experiments of Curie and Danne* showed that the rate of decay of radium C could be altered by subjecting it to temperatures above 630 ' .
Bronson , however , foundf that the more volatile radium B had a longer period of change than radium C , instead of the contrary as previously supposed , and showed that , when this fact is taken into consideration , the anomalies in question are capable of a complete explanation .
Makower , } working with radium emanation inside tubes of sealed quartz , found , however , that the / 3-radiation from radium C was reduced in intensity from 4 to 15 per cent , by heating the tube to temperatures over 1000 ' , the measurements being conducted in the cold .
The effect was temporary only , the normal activity of the tube being reached again after it had been left for an hour at room temperature .
In later experiments with RussS the same author found that , while the / 3-activity of the emanation was distinctly lower at high temperatures than at room temperature , it decayed at 1100 ' at the normal rate .
The / 3-activity of the active deposit on a wire inside a sealed quartz tube showed also a somewhat irregular diminution of from 3 to 15 per cent , for temperatures between 900 ' and 1500 ' .
As a result , measurement of the decay of the active deposit , with the tube at first cold , and subsequently subjected to a high temperature , showed an apparent increase in the rate of _ decay , and vice versed .
Engler , || working on the same lines as Makower and Russ , measured the / 3-activity both of the emanation and of the active deposit during heating and cooling , as well as when a steady temperature had been reached .
With the emanation itself in the quartz tube , a rapid increase in the activity was always observed on heating .
Cooling brought the activity at first below the room temperature value , but after an hour in the cold the activity regained its original value .
In some experiments , cooling did not cause a decrease of the activity below the normal value at all .
Heating the active deposit to 1100 ' or 1200 ' caused a decay more rapid than the normal , which gradually became normal as the heating was maintained .
On cooling , the decay was at first less than , but later increased to , the normal .
* ' Count .
Bond .
, ' 1904 , vol. 138 , pp. 748\#151 ; 751 .
+ 'Phil .
Mag. , ' 1906 , vol. 11 , p. 810 .
I 'Boy .
Soc. Proc. , ' 1906 , A , vol. 77 , p. 241 .
S 'Boy .
Soc. Proc. , ' 1907 , A , vol. 79 , p. 158 .
|| ' Anil .
Physik , ' 1908 , vol. 26 , p. 518 .
Mr. A. S. Bussell .
Effect of [ Dec. 19 Schmidt and Cermack , * * * S using radium itself as a source of / 3-ray activity showed that , while there is no permanent effect of high temperature on the / 3-radiation , the rays show a somewhat complex sequence of variations of activity , which is explained as being due to changes in their absorption by the preparation itself , ( a ) The first effect of heating to 1000 ' is to liberate the occluded emanation and to volatilise the products radium A , B , and C from the preparation , causing a lessened absorption and consequent sudden increase of / 3-radiation .
( b ) On cooling , the products , all except the emanation , are suddenly absorbed again by the preparation , with a consequent sudden return of the / 3-radiation to its initial value , ( c ) Three hours afterwards a new set of products is produced on the walls of the containing tube from the liberated emanation , which causes the ^-radiation gradually to return to the higher value .
( d)Then over a period of three weeks the liberated emanation decays , while fresh emanation is produced within the solid preparation , producing a gradual decay of the / 3-rays to their initial value .
The explanation ( b ) seems , however , very unlikely , and it will be shown later that the effect described in ( 5 ) and part of the effect described in ( a ) may be obtained in a sealed tube in which no solid matter whatever is present .
Work on y-ltays.\#151 ; The experiments of Bronsonf on the 7-rays from a source of radium , of EnglerJ and of SchmidtS on the 7-rays from radium emanation , from the active deposit and from radium C itself , show conclusively that there is no detectable effect of high temperatures on the intensity or nature of 7-rays .
Eutherford and Petavel|| showed also that the 7-radiation from radium emanation exposed momentarily to a pressure of about 1200 atmospheres and a temperature not lower than 2500 ' , produced by an explosion of cordite , was not altered at the moment of explosion .
A 9 per cent , temporary reduction of the activity found after the explosion was due to a change of distribution of radium C inside the bomb , caused by its volatilisation and subsequent condensation , and was of the amount to be expected theoretically .
It is seen that the point at issue concerns itself entirely with the / 3-rays .
The one abnormality , upon which all experimenters are agreed , is that a temporary increase or decrease of activity takes place at high temperatures , * 'Phys .
Zeit .
, ' 1910 , vol. 11 , p. 793 .
t ' Roy .
Soc , Proc. , ' 1907 , A , vol. 78 , p. 494 .
{ Loc .
cit. S 'Phys .
Zeit .
, ' 1908 , vol. 9 , p. 113 .
|| 'Brit .
Assoc. Report , ' 1907 , Section A , p. 456 .
1911 .
] Temperature upon Radioactive Disintegration .
243 the departures from the normal activity disappearing entirely after the source has been kept at room temperature for three hours .
The results of this paper show that this effect is due to a change of distribution of the active matter in the tube .
The conclusion is reached that neither the / 3- nor the 7-ray activities of radium C , of the active deposit , or of the emanation , suffer any change , either in amount of activity or in rate of decay , at high temperatures .
The author has succeeded in obtaining all of the abnormal effects of the workers whose experiments he has repeated .
They can be completely explained by taking into consideration the change in average path of the / 3-rays through the quartz tube containing the active source caused by :\#151 ; ( 1 ) Changes of distribution of radium C inside the tube , arising from the volatilisation of radium C and radium B from the hotter to the cooler part , at all temperatures greater than 300 ' , and especially from 650 ' upwards .
( 2 ) A change with temperature in the partition of radium C between the walls of the quartz tube and the volume enclosed .
2 .
Experimental Disposition .
The electroscope used was of lead , 7*5 cm .
cube , and of 0*3 cm .
wall thickness .
One side , through which the rays passed , was of aluminium , 0*01 cm .
thick .
For 7-ray measurements a thick plate of lead ( 1*8 cm .
) or of iron ( 0*6 cm .
) was placed against this aluminium window .
The furnace consisted of a silica tube 12*5 cm .
long , 2*2 cm .
inside diameter , open at both ends , round which was wound a platinum wire , the whole being jacketed with kieselguhr for thermal insulation .
Temperatures were measured with a Ft\#151 ; Pt-Kh thermo-couple .
Measurements were not carried usually beyond 1150 ' C. , which was reached without any difficulty .
The active material under investigation was in tubes of sealed quartz and mounted centrally in the furnace by means of thin nickel wire .
When thus mounted , there was an unintercepted path between every point of the tube and the electroscope .
Their distance apart was 40 to 60 cm .
3 .
Experiments on Radium C. Pure radium C was deposited on nickel by v. Lerchs method , and the nickel sealed in a thin quartz tube .
The decay of the radiations over a period of three hours was measured , the tube being kept at a temperature of 1150 ' for the first 90 minutes , and at room temperatures for the second .
The / 3-rays were measured over the whole period , the 7-rays only at the high temperatures .
The radiations , whether / 3 or 7 , at high temperatures and 244 Mr. A. S. Russell .
The Effect of [ Dec. 19 low temperatures alike , decayed exponentially , falling to half value in about 19*4 minutes .
In a second experiment the decay of the / 3-rays was measured for 65 minutes at a temperature of 1220 ' , but no difference in the value of the half-value period was obtained .
Neither the / 3- nor the 7-rays of radium C are thus affected by high temperatures .
4 .
Experiments on the Active Deposit .
Purified emanation was forced into a little quartz bulb 0*3 cm .
outside diameter , 0*25 mm. wall thickness , left there four hours , and then pumped out and the bulb sealed off .
Measurements of 7-rays were started after 20 minutes , and continued at intervals for three hours .
Measurements of / 3-rays were started after 85 minutes , and continued for five hours after sealing off .
All the 7-ray observations lie on a continuous curve , the points at high temperatures being in no case abnormal .
Of the 33 points observed , 29 agree with the theoretical values within 1 per cent. , and the other 4 within per cent. The theoretical curve was plotted on the assumption that 11 per cent , of the 7-radiation , capable of penetrating the iron plate 0*6 cm .
thick placed before the electroscope , comes from radium B. This result was kindly supplied me by Messrs. Moseley and Makower , who have been investigating the 7-radiation of radium B in detail .
The radium B 7-rays affect chiefly the initial part of the curve , over which no measurements were taken .
The / 3-ray activity also decays at the theoretical rate at high temperatures ( 1150 ' ) and low temperatures ( 200 ' ) alike , and the amount of activity is unaltered with temperature .
Of the 35 points observed , 2 are within 3 per cent. , 2 within 2 , and the rest within 1 per cent , of the theoretical values .
The rest of this paper deals with the behaviour of the active deposit inside sealed tubes containing radium emanation .
5 .
Volatilisation of Radium C inside Quartz Tubes .
A tube of clear quartz , 7*2 cm .
long , diameter of section 0*5 cm .
, and wall thickness 0*04 cm .
, was filled with about 25 millicuries of emanation at a pressure of 20 cm .
of mercury .
It gave a very uniform fluorescence on a zinc sulphide screen , which could be seen even in a fully lighted room when the screen was held in the shadow of the observer .
The tube was then inserted in the furnace , so that one end was just inside , while the other end was in the centre .
The hotter end was at 700 ' , and the cooler about 500 ' .
After live minutes the tube was r* j|P| - . .
1911 .
] Temperature upon Radioactive Disintegration . .
... ' .
' taken out , and its fluorescence on the screen again examined .
The fluorescence was now almost entirely concentrated as a bright green spot not more than a couple of millimetres in diameter at the cooler end , while that from the rest of the tube could only just be seen in the dark room .
The tube was then replaced in the same position as before , but reversed .
After five minutes the whole of the fluorescence was now at the other ( the cooler ) end .
The wrapping of 0-5 mm. lead round the tube did not effect any change in the position of maximum fluorescence .
It must therefore be concluded that radium C is capable of complete volatilisation inside the tube at 700 ' .
This experiment has been repeated with the hotter end of the tube at different temperatures varying from 15 ' to 1000 ' .
With increasing temperatures from 320 ' , the radium C shifts more or less completely to the cooler end of the tube , and the higher the temperature the more quickly is this accomplished .
An exposure for half an hour at 320 ' is sufficient to produce the maximum change .
Below this temperature the fluorescence is not continuous , but consists of bright and dark patches , the cooler half of the tube being always more fluorescent than the other .
The time required to produce a marked change in the fluorescence at these low temperatures is from two to three hours , and therefore makes it difficult to prove whether the radium C is itself volatilised , or whether it is produced in situ by volatilised radium B. Quantitative results were also obtained by means of y-ray measurements .
Let A be the leak in divisions per minute when the cooler ( and therefore more active ) end is nearer the electroscope , B the leak when the activity has been driven by heat to the other end , so as to be about 7 cm .
farther away from the electroscope , then the ratio A/ B serves as a measure of the amount of radium C capable of volatilisation at a given temperature .
For each temperature the leaks A and B were determined twice , so that the radium C was moved bodily along the whole length of tube four times .
In the experiments , the results of which are summarised below , the tube was 22 cm .
from the electroscope , and the side of the electroscope consisted of lead T8 cm .
thick .
Temperature of hotter end ... 1000 ' 800 ' 700 ' 650 ' 600 ' 500 ' 450 ' 320 ' 15 ' " cooler end ... 800 ' 600 ' 525 ' 400 ' 320 ' 260 ' 230 ' 150 ' -80 ' Ratio A/ B ( 7-rays ) 1 *70 1-72 1 -71 1-72 1 *62 1 -49 1 -42 1 -26 1 '06 Time required for maximum 5 5 5 10 ' 15 20 20 30 ISO effect ( minutes ) It was found experimentally that a shift of a point source of radium through a distance of 7*2 cm .
( the length of the tube ) under the conditions YOL .
LXXXYI.\#151 ; A. s 246 Mr. A. S. Russell .
The Effect of [ Dec. 19 of experiment gave a value of 1-71 for A/ B. Between 450 ' and 600 ' therefore , a large and increasing percentage of radium C can be volatilised while from 650 ' upwards the volatilisation is complete .
The ratio A/ B for / 3-rays at 650 ' is 6-6 , a result to be expected when it is considered that in addition to a mere distribution change , there is a large effect due to a change in the average path of the rays through the quartz .
The y-ray activity of the tube with the radium C concentrated at one end ( the nearer , let us say ) , measured over a period of three hours in the cold , falls to the normal value to be expected if radium A , radium B , and radium C are iu equilibrium at one end , and the rest of the tube contains emanation only .
Experiments have also demonstrated clearly that from 450 ' onwards the radium C itself is volatilised and not merely grown from radium B. It thus appears that at 650 ' radium B and radium C , and very probably radium A , are completely volatilised in quartz tubes .
Radium B commences to volatilise at room temperature .
Results of a similar character have been obtained with tubes Nos. 1 and 2 : described in the next section .
For the former the ratio A/ B ( / 3-rays ) at 700 ' was 2-78 , at 500 ' 219 , and at 350 ' 118 .
At 700 ' the ratio A/ B for y-rays corresponded to a total shift of the active matter from one end of the tube to the other .
For the latter tube A/ B ( / 3-rays ) was F29 at 700 ' although from its size and shape ( it was a sphere , outer diameter 3 mm. , of uniform wall thickness ) so large a distribution effect is at first sight unexpected .
These results on volatilisation are entirely at variance with those of previous authors , who found that at temperatures of about 900 ' , 600 ' , and 1200 ' , radium A , B , and C respectively are completely removed from a platinum wire .
No explanation of these discordant results need be attempted here , but the lack of agreement between the two sets of experiments is probably due to differences in pressure , and to the shape and nature of the surface on which the active material is deposited .
6 .
Experiments with Emanation .
A series*of experiments on the activity of the radium emanation at high temperatures , made in the beginning of the investigation , will now be described .
Two shapes of tubes were used .
They are shown in fig. 1 as they appear after being sealed up .
No. 1 was conical in shape , made of clear quartz , 1 cm .
long , sectional diameter of narrow end 0T cm .
, and of wider 05 cm .
, wall thickness 0'03 cm .
No. 2 was made of quartz , spherical in shape , of outer diameter 0'3 cm .
, and wall thickness 0'025 cm .
Both tubes gave essentially the same results .
1911 .
] Temperature upon Radioactive Disintegration .
Tube No. 1 , containing about 30 millicuries of emanation at a pressure of 16 cm .
mercury , was mounted in the centre of the furnace , the broader end AB being nearer to the electroscope .
The furnace was heated slowly , so that after one and a-half hours the maximum temperature ( 1150 ' ) was Fig. 1 .
reached .
It was then kept at this temperature half an hour , cooled to 300 ' over an interval of 45 minutes , and then from 300 ' to 15 ' in about three hours .
The / 3-ray activity was measured every minute .
It was found that the / 3-ray activity increased continuously from room temperature to 600 ' no less than 25 per cent. , decreased sharply between 600 ' and 700 ' to a value 9 per cent , greater than at 15 ' , and remained unchanged from 700 ' to 1100 ' , no matter how long the heating was continued .
The tube was then cooled slowly in the furnace .
The activity remained constant till 700 ' , increased rapidly between 700 ' and 600 ' to its old value 25 per cent , greater than at 15 ' , remained there till 300 ' was reached , and then fell slowly in the course of three hours to the room temperature value .
These processes of heating and cooling were repeated several times .
It was estimated that the critical temperature at which the sudden change in activity occurred was 650 ' .
Measurements of 7-rays in a similar experiment lasting live hours were also carried out .
Details of the heating and cooling , with values of the leaks , are tabulated in Table I. Table I. Leak in divisions per minute .
Temperature of the tube .
f A A Mean .
Highest .
Lowest .
Heated from 15 ' to 1000 ' in 1 hour ... . .
43 *9 44 *1 43 *8 Cooled from 1000 ' to 300 ' in 20 minutes ... 43 *9 44 *2 43 *6 Heated from 300 ' to 1000 ' in 20 minutes ... 43 *7 44*0 43 *6 Maintained at 1000 ' for 1 hour 43 -8 44 *0 43 *6 Cooled from 1000 ' to 100 ' in 1 hour 43*6 44 *2 43 *4 Maintained at 500 ' for 1 hour 44 *0 44 *2 43 *6 Cooled from 500 ' to 15 ' 43 *8 44*2 43 *4 The leaks are corrected , of course , for the decay of the emanation at room temperature during the period of measurement ( 075 per cent , per hour ) .
These results show that the 7-ray activity is not affected by temperature to any appreciable extent .
248 Mr. A. S. Russell .
The Effect of [ Dec. 19 , The emanation tube ( AB nearer the electroscope ) was next supported exactly in the centre of the cross-section of the furnace tube and near one end of it .
It was then heated for an hour at the highest temperature attainable at that point , and cooled slowly over an hour to 250 ' or 300 ' , / 3-ray measurements being made every two or three minutes .
The whole furnace was then turned round , the part C D of the emanation tube being now nearer the electroscope , and the experiment repeated .
The tube was then pushed down the furnace cylinder , and the whole procedure given above ' exactly repeated .
This was done for ten points along the furnace tube .
Let a be the leak with the tube cold , b when the tube attains 300 ' after cooling from the highest temperature , and c when the highest temperature has been reached , then for different distances along the furnace tube ( 12*5 cm .
long ) the following results were obtained , the origin of length being the end of the furnace tube to which the broader end of the emanation tube is nearer , and a being put at 100 throughout .
Distance ( cm .
) 3-7 5*0 Table II .
6-0 6 3 7*5 7-7 8*0 8*5 9-3 10 *5 AB nearest electroscope\#151 ; a 100 100 100 100 100 100 100 100 100 100 1 167 141 143 125 108 108 102 102 84 75 c 121 111 110 109 108 108 107 106 95 93 Temperature at which c is 850 ' 1080 ' 1100 ' 1120 ' 1120 ' 1120 ' 1120 ' 1000 ' 1000 ' 800Q measured CD nearest electroscope\#151 ; a \#151 ; \#151 ; 100 100 \#151 ; \#151 ; 100 \#151 ; \#151 ; \#151 ; b 100 100 96 81 100 100 110 100 100 100 c 130 122 102 102 100 100 103 88 85 83 It was not convenient to measure all the a1s , as this necessitated waiting three hours for the distribution to become normal again at 15 ' .
When no measurement of a was made , b has been put at 100 .
Consider just now only the Vs and c9s .
At 7*5 and 7*7 cm .
b = c , whether AB or CD is nearer the electroscope .
Bor distances greater than 7*7 , % b\lt ; cwith AB nearer , b\gt ; cwith CD nearer .
For distances less than 7*5 , b\gt ; c with AB nearer , .
b\lt ; c with CD nearer .
Leaks other than a , b , or c are not discussed , as experiment showed that their values depend entirely on the magnitude of a , b , and The temperatures at various points along the furnace tube were next measured , when the hottest part in the centre was kept at various tern1911 .
] Temperature upon Radioactive Disintegration .
peratures , from 200 ' to 1100 ' .
The results showed that the hottest part of the furnace from 200 ' to 1100 ' was not in the centre ( i.e. at 6*3 cm .
) , but at a point 7*5 cm .
, identical with the point at which b = c in Table II .
At 1100'* 2 cm .
on either side of this point had a very constant temperature , but this 4 cm .
of very constant temperature decreased to 1 cm .
as the temperature fell to 300 ' .
If , therefore , the centre of the active tube were not situated at this point , but , say , at 0*5 cm .
on either side of it , it would have a constant temperature at 1100 ' .
As this temperature is reduced , however , one end would tend to become hotter than the other , though the differences in temperature would be only of the order of 10 degrees .
When the tube is-placed at greater distances than 2 cm .
from the centre , the difference in temperature between the ends , when the tube has been heated a long time at 1100 ' , is much smaller than it is when it has been cooled to 300 ' , owing to the way in which the furnace cools .
Now it is a fact that radium C concentrates in the cooler end of a tube between 320 ' and 1100 ' , and the more easily the greater the temperature difference between the two ends* The results , therefore , for b and c of Table I receive a full explanation when this volatility is taken into account .
Two examples are discussed:\#151 ; ( 1 ) Distance 6*0 cm .
, AB nearer .
AB is cooler than CD at 300 ' ... ... . .
( b ) But has same temperature at 1000 ' ... .
( c ) Therefore b \gt ; c. With CD now nearer , CD is hotter than AB at 300 ' ... ... . .
( 6 ) But has same temperature at 1000 ... .
( c ) Therefore b \lt ; c. ( 2 ) Distance 10*5 cm .
, AB nearer .
AB is throughout hotter .
The difference in temperature between AB and CD is less at 1000 ' than at 500 ' .
Therefore b \lt ; c. With CD now nearer , same consideration applies as above , CD is cooler .
Therefore b \gt ; c. It is still conceivable , however , that a real change of / 3-ray activity exists at high temperatures , but that it is masked by this relatively large distribution change .
At points 7*5 and 7*7 cm .
, however , b = c no matter in which direction the emanation tube points towards the electroscope , so this supposition is entirely excluded .
We therefore conclude that , between 300 ' and 1100 ' , there is no effect of temperature upon the / 3-radiation of the emanation .
In general , the order of results whether ct^\gt ; b , b^\gt ; c , etc. , depends not only on the length of the tube , and how it is placed in the furnace , but also on 250 Mr. A. S. Russell .
The Effect of [ Dec. 19 , the winding of the furnace , and whether it is heated quickly or slowly .
It is not at all difficult , even with the tube near the centre of the furnace , to obtain conditions whereby , on heating to 1100 ' and cooling to room temperature , the activity passes through two maxima and minima .
The author has been able to repeat all of the abnormalities in the activity of the emanation found by Engler , and to obtain even some which Engler himself could not repeat .
Moreover , for every experiment in which the activity apparently increases when subjected to a temperature change , an experiment may be devised in which the activity decreases , and vice versa .
7 .
Partition of Homogeneously Distributed Activity .
It still remains to explain why the leaks a and c of Table II differ , which correspond to the / 3-ray activities of the emanation tube at 15 ' and 1100 ' respectively .
It may be seen from Table II that , when the tube is near the centre of the furnace , the leaks differ by a constant amount ( 8 per cent , approximately when AB points towards the electroscope , and about 3 per cent , when CD does ) .
These differences may be explained by a consideration of the partition of radium C inside the tube between the walls and the contained volume .
When an emanation tube has stood at room temperature for three hours , the partition of radium C has attained a steady state .
The larger part of the active material is known to be on the walls , but a small part must be distributed throughout the volume of the tube .
This partition gives the ionisation denoted by a. Heating the tube uniformly beyond 650 ' volatilises radium B and C , so that the partition of radium C is changed .
Prolonged heating at 1100 ' cannot effect the partition further .
This gives the ionisation c. If , now , the tube be suddenly cooled to room temperature , by tipping it out of the furnace on to a cold porcelain plate , the volatilised products are precipitated entirely on the walls , and quite uniformly , as there is no reason , if the tube be properly cooled , why the products should concentrate at one end rather than at another .
7-ray measurements confirm this .
This gives a third partition of radium C ; let it be called d. Each of these partitions gives a different ionisation effect due to / 3-rays , because , under ordinary conditions , the average path of the / 3-rays through the quartz depends upon the character of the partition .
Consider , for example , these types of partition inside a sphere of uniform wall thickness ( 0*025 cm .
, say ) , and internal radius r ( say , 3 mm. ) , mounted symmetrically with regard to the electroscope 30 cm .
away .
We are concerned only with the passage of rays through the hemisphere facing the electroscope .
In partition d , the particles of radium C lie on a sphere of radius r. 1911 .
] Temperature upon Radioactive Disintegration .
251 Partition c , in which the radium C is distributed uniformly throughout the volume , may be approximately represented by a uniform distribution of particles of radium C on an ellipsoid of revolution about a major axis 2 r , the minor axes of length 2 r " lying in a horizontal plane at right angles to the side of the electroscope through which the / 3-rays enter .
Partition a may be represented by a distribution of radium C on a similar ellipsoid with minor axes 2 r ' ( r\gt ; / \gt ; r " ) .
If a section be now cut at right angles to the major axis , and the average distances through the quartz of lines joining all points for the circle and for the two ellipses to the electroscope respectively measured , it is found that the lines from the circle make the largest average intercept on the quartz and those from the ellipse corresponding to the ellipsoid of minor axis 2 r " the least .
Now what C E Fig. 2 .
D applies to this section applies to any section parallel to it , and therefore to the whole sphere .
Thus , the particles of partition d are intercepted most by the quartz , and those of partition c least .
From this it follows that for tube 2 ionisation c is the greatest of the three , and d the least .
In fig. 2 this is shown more clearly .
AOB represents a horizontal section of the sphere through the centre , CD ( mid-point E ) the electroscope .
The circles inside the sphere a , c , and d , represent the three partitions respectively .
For convenience of making calculations the active matter is supposed concentrated on the circumference of the circle at 12 equidistant points .
In the figure the inner diameter of the section is 3 mm. , the wall thickness 0-25 mm. , and the diameters of circles a , e , and are 2'2 mm. , 252 Mr. A. S. Russell .
The Effect of [ Dec. 19 1-5 mm. , and 3'0 mm. respectively .
CD at its distance from 0 corresponds to the breadth of the electroscope ( 7'5 cm .
) at a distance of 30 cm .
From the point 1 of circle d , three lines are drawn to C , E , and D respectively , and the distance intercepted by the quartz in each case measured .
This is done for all the points of one circle and for all three circles .
Putting now the sum of the 36 distances intercepted by the quartz as 100 for circle a , we get 83 for circle c , and 145 for circle d. This graphical method of solution is , of course , only rough .
It takes no account , for instance , of scattering of the rays by the quartz , which must be not inconsiderable , but it serves to bring out the main result that the average path through the quartz is greatest for the particles on circle d , and least for those on circle c , and to give an idea of the magnitude of these differences .
As regards tube 1 , a change of partition can only effect the ionisation when the axis of the tube points towards the electroscope , and here also When the axis of the tube is at right angles to the line joining the tube to the electroscope , it follows from geometrical observations that ionisations a , c , and d should be equal .
This is what is found by experiment .
Eepetition of the experiment by which ionisation d is obtained does not alter the value of d. Now , if the difference between a and d were due to an atomic change , one would expect that the difference would be proportional to the number of times the experiment had been carried out .
If the tube be heated to temperatures below the volatilisation point of radium C ( 650 ' ) instead of to 1000 ' , the difference between d and a is reduced .
This is simply because partition d is the result of the precipitation on the walls of the tube of completely volatilised radium C. If the tube at 1000 ' be cooled , the partition c is not affected until temperatures of about 300 ' are reached , though probably all of the radium O is solidified at this temperature .
From 300 ' to 15 ' it commences to settle on the walls , and partition results For tube 1 ( parallel to its axis , AB nearer to the electroscope ) a : c : d =100 : 108 : 90 , and for tube 2 a : d = 100 : 84 .
These results explain why Makower and Buss found that , although the activity of the emanation was less at high temperatures than at low , it decayed at the same rate .
They were simply measuring the decay of the particles in partition d in one case and in partition a in the other .
Both partitions are perfectly definite for any one tube , and therefore afford consistent results .
They explain also the result of Schmidt and Cermack ( mentioned above , 1911 .
] Temperature upon Radioactive Disintegration .
253 ' p. 242 ) , that , when the volatilised products were cooled quickly , the / 3-ray activity suddenly diminished .
They attributed this to a sudden absorption of the products by the radium itself .
It is due , however , to their precipitation on the walls of the containing tube and consequent alteration of the partition of radium C. Summary .
( a ) The effect of temperature upon the rate of decay , and the amount of / 3- and 7-ray activity , of radium emanation , active deposit , and radium C have been investigated .
The results are entirely negative .
( b ) Radium B and radium C , and very probably radium A , may be completely volatilised inside sealed quartz tubes at a temperature of 650 ' .
Radium B commences to volatilise at room temperatures .
( 1c ) All abnormalities of activity of / 3-rays obtained by previous authors , and by the author in this paper , can be completely explained on two simple grounds , a change of distribution and a change of partition , of radium C inside quartz tubes , produced by changes of temperature .
I take the opportunity of expressing my indebtedness to Prof. Rutherford for all he has done for me throughout the work .
vol. lxxxvi.\#151 ; a. T
|
rspa_1912_0019 | 0950-1207 | The spectrum of comet brooks (1911 c). | 258 | 262 | 1,912 | 86 | Proceedings of the Royal Society of London. Series A, Containing Papers of a Mathematical and Physical Character | Sir Norman Lockyer, K. C. B., F. R. S. | article | 6.0.4 | http://dx.doi.org/10.1098/rspa.1912.0019 | en | rspa | 1,910 | 1,900 | 1,900 | 8 | 100 | 2,415 | http://corpora.clarin-d.uni-saarland.de/surprisal/6.0.3/?id=rspa_1912_0019 | 10.1098/rspa.1912.0019 | null | null | null | Atomic Physics | 77.505282 | Astronomy | 11.948954 | Atomic Physics | [
24.322010040283203,
-37.60490798950195
] | The Spectrum of Comet Brooks ( 1911 c ) .
By Sir Norman Lockyer , K.C.B. , F.R.S. ( Received December 14 , 1911 , \#151 ; Read February 8 , 1912 .
) [ Plate 8 .
] On July 23 a Kiel telegram announced that the comet discovered by Brooks was of the tenth magnitude .
During the next few weeks its faintness , combined with the bad state of the sky at Kensington , made it impossible to obtain any satisfactory observations .
On August 30\#151 ; the comet having got considerably brighter by this time\#151 ; an attempt was made to photograph its spectrum with the calcite prismatic camera .
No trace of spectrum could be found on the plate .
On August 31 an exposure of three hours was given , and two lines , evidently the carbon radiations X3883 and X 4737 , wTere feebly shown .
Every available opportunity has since been taken of getting a photographic record with the same instrument .
More or less successful photographs\#151 ; the degree of success depending on the state of the sky on the various evenings\#151 ; h^ve been obtained on the nights of September 6 , 11 , 16 , 20 , 26 , 28 , and 30 , October 4 .
9 , and 31 .
Between October 9 and October 31 the comet was not available , having changed in the interim from an evening object to a morning one .
The lines in the various photographs are all very broad and diffuse , and the reduced wave-lengths of the lines are probably only approximately correct .
On September 6 two weak radiations were found far in the ultra-violet region of the spectrum .
The positions of these were approximately obtained by constructing a curve from the series of hydrogen lines in an excellent photograph of the a-Cygni spectrum taken with the same instrument .
As the comet lines fall beyond this hydrogen series their wave-lengths had to be estimated by extrapolation .
In some of the later photographs these lines are much better shown , and other lines are seen when the sky conditions have been favourable .
Thus a line whose position was at first estimated to be X3183 is well seen in the photograph of September 30 between the two ultra-violet lines previousl ) mentioned .
The values obtained from the curve for the latter lines were X 3126 and X 3369 .
The Spectrum of Comet Brooks ( 1911 c ) .
Subsidiary Bands between the Bright Radiations X3883 and X4737 .
Whenever the cometary spectrum was photographed with any degree of success , three subsidiary bands were shown between the lines at X 3883 and X 4737 .
Their intensities are comparatively low and the lines are of such a diffuse nature that it is impossible to determine the wave-length of the middle of the lines with any great accuracy , especially as the lines are practically lost if any magnification is brought to bear on the spectra .
The estimated wave-lengths , obtained by comparing the cometary spectrum with that of an iron arc photographed with the same instrument , are XX 405 , 421 , and 436 .
With regard to the middle one of these it is very likely identical with the carbon band whose main head is at X4216 .
In a paper* on the spectrum of Comet 1907 d ( Daniel ) , Prof. Campbell gives a reproduction of the spectrum and a tabular list of lines which occur in it .
There is a bunch of bright lines extending from X 4020 to X4074 , the mean position of the group being about X 4047 .
There is little doubt that the broad diffuse line of the Kensington photograph is identical with the bunch of lines in Campbell 's slit spectrum .
Another well-marked , isolated , and sharply defined line in Campbell 's spectrum is X4216 , and this is probably the same line as is seen in the Kensington photograph , though in the latter it is of a very diffuse nature .
The third line , approximately at X 436 , also appears to agree in position with another well-marked bunch of lines in Campbell 's photograph .
The strongest radiations in the latter are the carbon groups , XX 3883 , 4737 , and these are the outstanding lines in the Kensington photographs .
Thus , allowing for the difference in dispersion between the Lick and Kensington spectra , and for the fact that one was taken with a slit spectroscope , while the other was photographed with an objective prism , there seems little doubt that the spectrum of Comet Daniel , at the time Campbell photographed it , was practically of the same nature as that of Brooks ' Comet during September and October .
Wave-lengths of the Ultra-violet Lines .
Assuming the middle of the strong radiation near X 388 to be X 3883 , which is the head of the so-called cyanogen group , a comparison of the comet 's spectrum with an arc spectrum of iron taken with the same instrument shows that the two stronger ultra-violet bands fall respectively on the iron r qi a a , .
f 3369-62 lines X3100 and 13370-87 as nearly as can be estimated .
The mean values of the previous estimates of the cometary wave-lengths as obtained * 'Lick Observatory Bulletin , ' No. 135 .
260 Sir N. Lockyer .
[ Dec. 14 ( 1 ) from an extrapolation curve , ( 2 ) by calculation from Hartmann 's formula , were X 3104 and X 3359 .
The position of the faint line between these two which comes in in the best photograph ( September 30 ) has been estimated by comparison with the iron spectrum to be X316 .
The mean of the previous estimates was X 3164 .
The uncertainty of setting the middle of the strong diffuse line near X 388 on its exact position amongst the iron lines in the comparison spectrum , combined with the very diffuse nature and comparative weakness of the ultra-violet lines , makes it impossible to give the wave-lengths of the latter with any great accuracy , and it will be well to adopt only three figures in the wave-lengths and refer to them as the lines X 310 , X 316 , and X 337 respectively .
In order to determine , if possible , the origin of the ultra-violet bands , a series of comparison spectra was taken with the ealcite spectrograph provided with a collimator .
Long exposures on the spectrum of C02 have been made , but this has not given any clue to the origin of the cometary lines .
Other modifications of carbon are now being tried .
Lines shown in the Various Photographs .
The following statement gives the approximate wave-lengths of the lines seen in the Kensington photographs:\#151 ; Date .
w. 1911 .
August 31 3883 4737 September 6 310 337 3883 405 4737 " 11 ?
337 3883 405 4737 " 16 310 337 3883 405 421 436 4737 5165 " 20 310 337 3883 405 421 436 4737 5165 " 26 310 337 3883 405 421 436 4737 5165 5635 " 28 310 337 3883 405 421 436 4737 5165 " 30 310 316 337 3883 405 421 436 4737 5165 5635 October 4 ?
337 3883 405 421 436 4737 5165 5635 " 9 ( Poor photograph ) 3883 4737 " 31 310 337 3883 405 421 436 4737 5165 5635 Amongst the photographs obtained from August 31 to October 9 inclusive no definite changes in relative intensity of the cometary lines were noticed .
The difference in sky conditions on the various nights probably accounts for the fact that more lines were detected in some photographs than in others .
On the other hand , the photograph of October 31 , the first one taken after the comet had become a morning object , shows most decided changes in the 1911 .
] The Spectrum of Comet Brooks ( 1911 c ) .
relative intensity of some of the lines .
Of the three subsidiary bands* A 405 , \ 421 , \436 , the middle one was , in the series of spectra taken between September 16 and October 4 ( the only spectra in which it was visible while the comet was an evening object ) , invariably the weakest of the three .
In the spectrum of October 31 , however , it is the strongest of the three .
Another notable change was in the relative intensities of lines A , 3883 , A 4737 .
In the first series these two were of about equal intensity .
In the later photograph A 3883 is decidedly stronger than A 4737 .
The ultra-violet lines A 310 and A 337 , which are visible in nearly all the spectra taken when the comet was an evening object , are not seen in the spectrum of October 31 .
The changes mentioned can be seen by reference to the plate at the end of the paper .
Probable Origin of the Cometary Lines .
The identity of the cometary lines AA3883 , 4737 , 5165 , and 5635 with lines of carbon or its compounds has previously been well established .
With the object of determining the origin of the remaining lines , reference has been made to published records of laboratory spectra , especially those appertaining to carbon .
No success has attended this search .
The series of laboratory spectra recently taken here with the same object in view appears to throw no light on this point .
With regard to the origin of line A 337 , it may be said that there is a line at A 336 given under the head of cyanogen by Living and Dewar , Eder and Valenta , and by Deslandres , but as the equally strong cyanogen band , the head of which is at A 359 , is apparently entirely lacking in the cometary spectra , it cannot be claimed that the identity of A 336 with the cyanogen line of nearly corresponding wave-length has been established .
The reduction to wave-lengths and the discussion of the lines in the various cometary spectra has been undertaken by Mr. F. E. Baxandall , who has also taken part in the preparation of the paper .
The series of photographs of laboratory spectra for comparison with the cometary spectra was taken by Mr. C. P. Butler .
The wave-lengths of the ultra-violet lines were separately estimated both from an extrapolation curve and from Hartmann 's formula by Mr. T. F. Connolly .
The photographs of the comet 's spectrum were taken with the 2-inch quartz-calcite prismatic camera by Messrs. W. Moss and T. F. Connolly .
[ Dec. 21 , Hon. R. J. Strutt .
A Chemically DESCRIPTION OF PLATE .
The Kensington photographs shown on the Plate have been directly enlarged from the original negatives , the magnification being five-fold .
The upper illustration shows a comparison of the spectrum of September 30 , when the comet was an evening object , and that of October 31 , when it was a morning object .
The chief differences between the two are referred to in the paper .
The lower illustration is a comparison of a portion of the Kensington spectrum of Comet Brooks , and the Lick spectrum of Comet Daniel* ( 1907 d\ the latter having been taken with a slit spectrograph .
There can be little doubt that the two spectra are nearly identical , bunches of individual lines in the Lick spectrum being represented in the Kensington spectrum by wide and diffuse lines .
* 'Lick Bulletin , ' No. 135 .
A Chemically Active Modification of Nitrogen , Produced by the Electric Discharge.\#151 ; III.# By the Hon. R. J. Strutt , F.R.S. , Professor of Physics , Imperial College of Science , South Kensington .
( Received December 21 , 1911 , \#151 ; Read February 8 , 1912 .
) S 1 .
Effect of Temperature on the Duration of Active Nitrogen .
In the first paper ( S 2 ) it was mentioned that a stream of glowing nitrogen led through a tube cooled in liquid air glowed out with increased brilliancy , and then became extinguished .
There is some ambiguity in the interpretation of this experiment , since the density of the gas is locally increased by cooling ; and increased density may ( and does ) make the nitrogen expend its glowing power more quickly .
A hermetically sealed bulb containing rarefied nitrogen was excited by the electrodeless discharge .
Allowed to expend itself at room temperature , the glow in this bulb was conspicuous for more than a minute .
But if the bulb was immersed completely in liquid air immediately after excitation , and after 15 seconds withdrawn and examined , it was found to be quite dark .
The glow was very brilliant as seen under the surface of the liquid air .
This experiment proves that the glow-transformation really occurs more quickly the lower the temperature , apart from changes of density .
The same experiment was repeated , substituting boiling water for liquid air .
Again the life of the glow was shortened , but this time its brilliancy * Part I , 'Boy .
Soc. Proc. , ' 1911 , A , vol. ' 85 , p. 219 ; Part II , 'Boy .
Soc. Proc. , ' 1911 , A , vol. 86 , p. 56 .
Lockyer .
Roy .
Soc. Proc. , A 86 , Plate 8 .
\#163 ; \#163 ; 9\#163 ; - \#163 ; 919- zez-H 9C+1-9 I2V\#163 ; 0-tr- \#163 ; 999- zee- r4 CO \lt ; 3 o o o o CO 0\gt ; a cl CD QQ o r\#151 ; I go w 'S a a3 a ?
Oh go 99V- 9I2V- 90V- 9999- tH OQ A O ft *55 .
G r^S \lt ; D 3s f\#151 ; H is 13 S 1 Sh vS PQ A \#166 ; s 'S a a o o O O H ( M* 019-1 1907 d ) , Licl
|
rspa_1912_0020 | 0950-1207 | A chemically active modification of nitrogen, produced by the electric discharge.\#x2014;III. | 262 | 269 | 1,912 | 86 | Proceedings of the Royal Society of London. Series A, Containing Papers of a Mathematical and Physical Character | Hon. R. J. Strutt, F. R. S. | article | 6.0.4 | http://dx.doi.org/10.1098/rspa.1912.0020 | en | rspa | 1,910 | 1,900 | 1,900 | 3 | 166 | 3,573 | http://corpora.clarin-d.uni-saarland.de/surprisal/6.0.3/?id=rspa_1912_0020 | 10.1098/rspa.1912.0020 | null | null | null | Thermodynamics | 45.100119 | Atomic Physics | 31.16199 | Thermodynamics | [
26.529733657836914,
-36.45079040527344
] | 262 [ Dec. 21 , Hon. R. J. Strutt .
A Chemically DESCRIPTION OF PLATE .
The Kensington photographs shown on the Plate have been directly enlarged from the original negatives , the magnification being five-fold .
The upper illustration shows a comparison of the spectrum of September 30 , when the comet was an evening object , and that of October 31 , when it was a morning object .
The chief differences between the two are referred to in the paper .
The lower illustration is a comparison of a portion of the Kensington spectrum of Comet Brooks , and the Lick spectrum of Comet Daniel* ( 1907 d\ the latter having been taken with a slit spectrograph .
There can be little doubt that the two spectra are nearly identical , bunches of individual lines in the Lick spectrum being represented in the Kensington spectrum by wide and diffuse lines .
* 'Lick Bulletin , ' No. 135 .
A Chemically Active Modification ofi Nitrogen , Produced by the Electric Discharge.\#151 ; III.# By the Hon. R. J. Strutt , F.R.S. , Professor of Physics , Imperial College of Science , South Kensington .
( Received December 21 , 1911 , \#151 ; Read February 8 , 1912 .
) S 1 .
Effect of Temperature on the Duration of Active Nitrogen .
In the first paper ( S 2 ) it was mentioned that a stream of glowing nitrogen led through a tube cooled in liquid air glowed out with increased brilliancy , and then became extinguished .
There is some ambiguity in the interpretation of this experiment , since the density of the gas is locally increased by cooling ; and increased density may ( and does ) make the nitrogen expend its glowing power more quickly .
A hermetically sealed bulb containing rarefied nitrogen was excited by the electrodeless discharge .
Allowed to expend itself at room temperature , the glow in this bulb was conspicuous for more than a minute .
But if the bulb was immersed completely in liquid air immediately after excitation , and after 15 seconds withdrawn and examined , it was found to be quite dark .
The glow was very brilliant as seen under the surface of the liquid air .
This experiment proves that the glow-transformation really occurs more quickly the lower the temperature , apart from changes of density .
The same experiment was repeated , substituting boiling water for liquid air .
Again the life of the glow was shortened , but this time its brilliancy * Part I , 'Boy .
Soc. Proc. , ' 1911 , A , vol. ' 85 , p. 219 ; Part II , 'Boy .
Soc. Proc. , ' 1911 , A , vol. 86 , p. 56 .
1911 .
] Active Modification of Nitrogen .
while it lasted was judged to be less than at ordinary temperatures .
This corresponds very well with the results formerly obtained by the flow method .
But now I feel able to offer more of an interpretation than was then possible .
There are two phenomena to be reckoned with .
One of these is a direct temperature effect on the glow-transformation .
The other is a destructive effect of the walls of the vessel on the glow , also variable with temperature .
There are various reasons for believing in the existence of the latter effect:\#151 ; 1 .
Certain substances , copper oxide , for instance , have been shown to be directly and immediately fatal to the glow , without themselves experiencing any change.* There is every probability that other solid surfaces , such as the glass walls , should , in a less degree , show the same effect .
2 .
When two similar glass bulbs are so thoroughly exhausted that no electrodeless discharge can pass , and then charged simultaneously with rarefied nitrogen and sealed off , the afterglow is about equally bright in each immediately after excitation .
When a few seconds have elapsed , there is almost always a marked difference in luminosity between the bulbs .
It is , in fact , impossible to get two bulbs which give the same rate of decay .
As the initial intensity of glow is the same in each , this is .most easily explained by supposing that the difference lies , not in the gas , but in the more unfavourable influence of the walls in the one case than in the other .
3 .
An ' experiment was made in which the glowing gas produced in one vessel was allowed to diffuse into two others , which were then shut off by a trap of sulphuric acid .
The glow was initially of the same intensity in each vessel .
The walls of one were wet with sulphuric acid , while those of the other were dry glass .
The decay in the latter was much the more rapid .
It cannot be doubted , therefore , that glass walls exercise some destructive action on the glow which sulphuric acid does not exert\#151 ; at all events , in the same degree .
Admitting , then , that the walls produce a destructive effect on the active nitrogen analogous to that produced by cupric oxide , it is allowable to assume , as a working hypothesis , that this is increased by rise of temperature .
The effect of cupric oxide , at all events , varies in that sense .
We are now in a position to interpret the observed effect of temperature on glowing nitrogen contained in a glass bulb .
When cooled to -180 ' C. , the effect of the walls in destroying the active nitrogen is , it is true , somewhat checked ; on the other hand , the glow-transformation in the gas occurs more rapidly at that temperature , and the glow is given out in greater intensity and for a briefer period .
* 'Roy .
Soc. Proc. , ' 1911 , A , vol. 85 , p. 226 .
264 Hon. R J. Strutt .
A Chemically [ Dec. 21 When the bulb is heated to 100 ' C. , the destructive effect of the walls is Fig. 1 .
The electrodeless discharge passes i almost immediately into the tube B. increased , and this prevents the glow lasting so long as at ordinary temperatures , in spite of the fact that the glow-transformation is retarded .
In the absence of the walls , the latter effect would make the glow feebler , but of increased duration .
This , however , is not experimentally realisable .
We have it on the authority of iSTernst* that no exception has been known to the rule that chemical change is accelerated by increase of temperature .
The change from active towards inert nitrogen which is going on in the afterglow seems , therefore , to be unique in contradicting this rule.f S 2 .
Effect of Density , Experiments on the duration of the glow with various densities of gas in the discharge vessel are difficult of interpretation , for two things are altered simultaneously\#151 ; the conditions of discharge and the conditions of afterglow . .
The effect of changed density can be examined to better advantage if the change is made when the gas is already glowing .
The apparatus shown in fig. 1 was used to effect this , n the vessel A. The afterglow diffuses The mercury column C , covered with * 'Theoretical Chemistry/ 1911 ed. , p. 679 .
t I desire to withdraw the too hasty suggestion made in Part I that the recombination of dissociated substances behaves in this way , and that this is a valid reason for regarding the active nitrogen as dissociated .
It is necessary to distinguish between the effect of temperature in changing the rate of reaction and its effect in changing the condition of equilibrium to which the reaction tends ( see Nernst , passim ) .
1911 .
] Active Modification of Nitrogen .
265 sulphuric acid* at D , can be raised so as to cut off the tube B from the rest of the vessel .
The gas in B can be made to glow more brightly when compressed .
In this condition it is more rapidly exhausted .
If , after compression , the volume is kept constant , the glow gradually fades out .
If it is wholly extinguished nothing is gained by compressing it further .
But if any faint luminosity remains , it may be greatly increased by further compression .
In this way the brilliance may be repeatedly restored by successive compressions .
The process has been traced up to pressures of 4 cm .
of mercury .
If , after compression to small bulk , the gas is again expanded , the luminosity is found to have disappeared , and tube B is now quite dark , though luminosity survives in the rest of the apparatus .
If communication between B and A is again opened , a fresh supply of faintly luminous gas quickly diffuses in , and can be made to glow brightly by a second compression .
This can be repeated several times without fresh excitation of the gas by discharge .
An alternative method of showing the effect of compression is more readily carried out , though less well adapted to a detailed study of the phenomena .
In this case gas instead of liquid is admitted to drive the active nitrogen up to one end of the vessel .
Fig. 2 .
I he electrodeless discharge passes in the vessel a ( fig. 2 ) , a bulb of 300 c.c. capacity .
The afterglow is developed , and may be allowed to die down to a very low intensity .
About 1 c.c. of nitrogen is then admitted * ^hen mercury was used uncovered , the glow was destroyed so soon as an attempt was made to compress it .
1 his must be due to a destructive action of the mercury surface .
I found formerly ( loc. cit. , p. 225 ) that a mercury surface at rest had no effect on the glow .
There must be some thin protective film on the surface of apparently clean mercury , which is broken up when it is moved .
266 Hon. R. J. Strutt .
A Chemically [ Dec. 21 from the space between the stopcocks and c. This enters a and compresses the still glowing gas to the end d. A bright flash of luminosity is seen , due to the compression of the faintly glowing nitrogen already in the bulb .
To repeat the experiment , communication may be opened to the cooled charcoal in e , which quickly restores the degree of vacuum desired .
The space between b and c is replenished from / .
The flash on compression is still more striking if cl is immersed in an unsilvered vacuum vessel containing liquid air .
In this way the intensity is increased by cooling as well as by compression .
In this form of experiment the nitrogen admitted merely acts as a piston compressing the glowing nitrogen , but not mixing appreciably with it .
If the increase of pressure is made in such a way as not to cause a concentration of the glowing gas , no increased brightness is obtained .
This may be realised in practice by gently admitting more nitrogen into a spherical bulb in which the glow has been generated , by means of a tube which projects into the centre , and is then provided with several jet-holes to distribute the entering gas uniformly in all directions .
The phenomena described are consistent with the following hypothesis :\#151 ; Active nitrogen may revert to the normal condition in two ways\#151 ; either by the action of the solid walls of the vessel , in which process no glow is emitted , or by its own spontaneous change , which is accompanied by the glow .
This is analogous to what is known to happen in other gaseous reactions\#151 ; the combination of oxygen and hydrogen , for instance .
The change may be a volume one , with luminosity , as when the mixture is exploded ; or it may occur at the surface of a solid catalyst , without luminosity , at comparatively low temperature.* Although no quantitative measurements have been made , the experiments suggest that , with definite conditions of excitation , and if the effect of the walls could be eliminated , the time-integral of the intensity of the glow would be constant , unaffected by changes in temperature and density of the gas after excitation .
The intensity of the glow is greatly dependent on these conditions , being increased by cooling or compression .
But it is only increased at the expense of the duration .
S 3 .
Theoretical Inferences .
, It may be assumed that , where the action of the walls may be neglected , the visual intensity of the glow is a measure of the rate at which transformation is occurring .
On this hypothesis , the compression phenomena described can give us valuable information as to the nature of the reaction from a * See Bone and Wheeler 'Phil .
Trans. , ' 1906 , A , vol. 206 , p. 1 .
1911 .
] Active Modification of Nitrogen .
267 molecular standpoint .
If it is monomolecular , and the luminosity results from changes which can originate from a single molecule of modified nitrogen , then the rate of reaction will be proportional to the number of such systems in unit volume .
The intrinsic luminosity should therefore increase on compression .
But , if partial* decay is allowed to occur at small volume , and the volume then restored , the amount of modified nitrogen remaining will be the same , and the glow will have the same brilliancy as it would have had after the same time interval , if no change of volume had been made at all .
This is clear , without calculation , from the simple consideration that the transformation of each molecule of modified nitrogen is ( on this hypothesis ) independent , and that the number remaining after a given time cannot depend on whether the molecules have been brought close together or separated in the meanwhile .
We have seen , however , that this is not what is , in fact , observed .
More rapid transformation occurs at high concentrations , and , on restoring the volume after considerable compression , the glow is found to have ceased , showing transformation to be nearly complete .
The observations , therefore , contradict the hypothesis of a monomolecular reaction .
If we assume that the collision of two molecules of modified nitrogen is necessary to the reaction , then all is explained .
Compression makes such collisions more frequent , and a given mass of modified nitrogen is more quickly transformed at small volume .
The number of collisions is proportional to the square of the concentration ; we may expect , therefore , very rapid increase of brightness when the volume is diminished beyond a certain point , by a piston moving with uniform velocity in a cylinder , as in the experimental arrangement .
Since the active nitrogen is quickly used up at small volume , the luminosity will attain a maximum at a certain volume , the value of which depends on the velocity of the piston .
On expansion after extreme compression , luminosity will be no longer visible .
The present experiments do not in themselves decide whether two or more than two molecules are concerned in the reaction .
To do so , quantitative measurements of the law of decay would be necessary , and for this the action of the walls , which intervene in some way to cause a transformation without glow , would have to be eliminated .
This action does not obscure the main features of the phenomenon , but it stands in the way of close quantitative scrutiny .
On general grounds , however , the reaction would naturally be regarded as bimolecular , in the absence of evidence that it is more complex .
268 Hon. R. J. Strutt .
A Chemically [ Dec. 21 S 4 .
Comparison with Prof. H. F. Experiments .
Some very interesting experiments were described by Prof. H. F. Newall* in which he obtained brilliant luminosity from a sample of rarefied gas by compression after discharge .
It was the study of his paper which led me to many of the above experiments , and any merit there may be in them must be largely credited to inspiration from this source .
Prof. Newall was not able to specify precisely the nature of the gas with which his effect was obtained , or to reproduce it with certainty .
He says : " I can only say that oxygen , with traces of nitrogen and S02 , is the mixture I should begin with , if I wished to recover the conditions . . . .
" The spectrum given out on compression he identified with the negative glow spectrum of oxygen .
Prof. Newall kindly came to see my experiments , and , while agreeing that the effect was one of the same class as that which he discovered , was unable to admit their identity .
He is confident that his gas gave an afterglow with continuous spectrum , and that a discontinuous one was only developed on compression .
It seems best to state what I feel to be a difficulty .
In my experiments compression has the effect of making the gas give out more quickly radiation which it will give out in any case .
This is in sharp contrast with Prof. Newall 's view of his effect .
Again , my effect only occurs in pure nitrogen .
Prof. Newall 's effect , if it is really analogous , and gives an oxygen spectrum , should occur in pure oxygen .
Many careful , experiments with oxygen spectroscopically pure have convinced me that it does not develop a band spectrum-when compressed after discharge .
The spectroscopic test of purity in the case of oxygen is a severe one , for oxygen lines are easily outshone by impurities .
I cannot help thinking that something of the following kind may account for Prof. Newall 's result .
Suppose that he had nitrogen with some oxygen to begin with\#151 ; such a mixture would give an afterglow with continuous spectrum .
Passing the discharge undoubtedly sometimes causes an absorption of oxygen in such cases , as I have myself seen , f and the nitrogen remaining would show the peculiar afterglow spectrum , which would shine out brightly on compression .
It seems to me that this spectrum might easily be mistaken for the negative glow of oxygen , particularly as the observations had to be made quickly , and the nitrogen afterglow spectrum * ' Camb .
Phil. Soc. Proc. , ' 1895 , vol. 9 , p. 295 .
t This may be due to formation of oxides of nitrogen and their absorption by alkaline matter on or in the glass surface .
1911 .
] Active Modification of Nitrogen .
had not been described at the time .
The bands of these spectra in the visual region are in the following positions :\#151 ; Oxygen negative glow ... ... ... .
5985 , 5870 , 5592 , 5248 .
Nitrogen afterglow ... ... ... . .
6252 , 5804 , 5407 , 5054 .
Certainly no other known gaseous spectrum would give so close a general resemblance to the nitrogen afterglow spectrum .
It may be added that many attempts to produce Prof. Newall 's effect with different gaseous mixtures containing oxygen have failed .
There is , indeed , a brightening of the nitric oxide afterglow by compression to one end of the tube , but the spectrum remains continuous .
S 5 .
Summary .
( 1 ) Active nitrogen emits its energy more quickly , and reverts sooner to ordinary nitrogen , if it is cooled .
This is apparently a unique instance of a chemical change accelerated by cooling .
( 2 ) If the glowing gas is compressed to small volume , it flashes out with great brilliance , and exhausts itself in so doing .
This proves that the glow-transformation is polymolecular , i.e. that more than one molecule must take part in it .
( 3 ) Active nitrogen may revert to ordinary nitrogen in two distinct ways .
One of those is a volume change , accompanied by glow , the other a surface action of the walls of the vessel , without glow .
This is analogous to the behaviour of oxy-hydrogen gas in its transformation to water , which may be a surface or volume effect , according to circumstances .
vol. lxxxvi.\#151 ; A. u
|
rspa_1912_0022 | 0950-1207 | An optical determination of the variation of stress in a thin rectangular plate subjected to shear. | 291 | 319 | 1,912 | 86 | Proceedings of the Royal Society of London. Series A, Containing Papers of a Mathematical and Physical Character | E. G. Coker, M. A., D. Sc.|Prof. Karl Pearson, F. R. S. | article | 6.0.4 | http://dx.doi.org/10.1098/rspa.1912.0022 | en | rspa | 1,910 | 1,900 | 1,900 | 18 | 195 | 6,740 | http://corpora.clarin-d.uni-saarland.de/surprisal/6.0.3/?id=rspa_1912_0022 | 10.1098/rspa.1912.0022 | null | null | null | Measurement | 60.431111 | Tables | 27.024832 | Measurement | [
51.77033615112305,
-55.459693908691406
] | ]\gt ; An Determination of the Variation of Stress in a Thin Rectangular Plate Subjected to Shear .
By E. G. COKER , M.A. , D.Sc .
, Professor of Mechanical ineering in the City and Guilds of London Technical College , Finsbury .
( Communicated by Prof. Karl Pearson , F.R.S. Received December 28 , 1911 , \mdash ; Read February 8 , 1912 .
) Introduction.\mdash ; The determination of the distribution of shear stress in a body subjected to the action of an arbitrary set of forces applied to its bounding surfaces is often of great importance in constructional work .
In most cases mathematical difficulties do not allow of an exact solution , while the simplifying assumptions which are often made to reduce these difficulties lead to formulae which are probably not correct even to a first approximation .
It is important , therefore , to have experimental determinations to compare with the values calculated by approximate methods to determine to what extent the assumptions are correct , and also , if possible , to afford data for better approximations in cases which do not allow of mathematically exact solutions .
The shear stresses in riveted joints , the stiffened webs of plate girders and such like structures , afford examples of practical problems of extreme complexity from the mathematical standpoint , which are dealt with in practice by rough approximations , using large factors of safety fixed by experience of the behaviour of similar structures , in order to allow for contingencies due to ignorance of the actual stresses and accidental overloading .
The experimental determination of the state of stress in a body as inferred by measurements of the strains produced at its surface affords a means , which has been used by various investigators , to determine the condition of stress in a body subjected to the action of forces applied at its boundary .
In shear problems , with which the present paper deals , this ] involves the measurement of angular displacements , but these strains are so minute for the materials of construction at ordinary working stresses that it is usually found necessary to make experiments on other materials like indiarubber , plasticine and the like , which afford strains sufficiently large for accurate measurement , while their elastic properties are such that they may be considered to behave like more intractable materials with fair accuracy .
Another possible method of attack is to use a material possessing optical properties which depend on the applied stresses , and by measuring the change in optical property to infer the stress in the material .
For this Prof E. G. Coker .
Optical Determination of purpose glass possesses very many advantages , in that its action on light depends on the stress in the material and , to a first a linear law expresses the relation between the stress and the effect produced .
Glass can be obtained in a very perfectly elastic condition , and the strain relations resemble those of steel and wrought iron very Unfortunately , measurements of the optical effects produced usually stresses in the neighbourhood of fracture , and this , coupled difficulty of shaping the material into other than the simplest prevented its use becoming general for this kind of investigation .
At the present time other transparent bodies may be used which do offer this kind of objection , and in the investigation to be described commercial form of transparent nitro-cellulose is employed which has , a high degree , most of the desirable properties of glass and few of disadvantages .
If a beam of plane polarised light is passed through a plate of glass , or like transparent material , it is found that the relative retardation duced between the ordinary and extraordinary rays depends on difference between the principal stresses and , at any point , also on the thickness of the material .
We may express the relation the formula where is a constant .
This retardation is easily measurable , and the of may be inferred in a simple manner by a mechanical measure4 meant to be described .
The distribution of the shear stress in the cross section of a dam has , late years , been the subject of many experimental and theoretical tions , and one of the outstanding difficulties of this problem is the distribution of the shear stress in the horizontal secrions of a dam .
At the suggestion of Prof. Karl Pearson some experiments were made , the autumn of 1910 , on the related and more simple problem of distribution of shear stress in a rectangular plate , by an optical method being used by the author in another investigation .
These earlier experiments on a small model gave promise of accurate quantitative results with a large experimental apparatus , and , a preliminary to the more difficult problem of the shear stress in a an apparatus for experimental work was constructed on what appeared to a sufficiently large scale , and it was set up in the engineering of the City and Guilds of London Technical College , Finsbury .
1911 .
] of Stress in a Thin Rectangu lar Plate .
Description of the Apparatus the Method of Experiment.\mdash ; A small tension testing machine of the simple lever type was available for applying stress to a plate .
It was capable of exerting a maximum pull of and it had a clear gap between the end shackles of 20 inches .
In order to adapt the machine for the purpose of applying shear stresses a steel frame was constructed to give a symmetrical double shear to a plate of the transparent material .
The arrangement adopted is shown in the accompanying sketch ( fig. 1 ) , in which , are eye-bolts provided with nuts having spherical ends fitting into the shackles , of the testing machine .
When these latter are separated by the action of the machine the lin pull passes through the centres of the pins , to which the frame proper is secured .
This frame consists of pairs of vertical planished steel bars of 2 inches by 9/ 16 inch rectangular cross-section , the outer pairs being pin-connected above to a pair of cross- bars , 3 inches by 5/ 8 inch in cross-section , and below to a similar but lighter set K. Each gripping is slightly undercut for the greater part of its width , leaving faces on each side , so that when the plate to be stressed is placed in position and the bolts adjusted in the holes provided , the bars grip the plate along its whole length on each side .
The extent of the gripping surfaces is indicated by dotted lines in fig. 1 and by the accompanying cross-section .
The central bars are constructed in the same manner , and when a pull is applied by the testing machine the free parts , of the plate are subjected to a nearly pure shear .
The maximum length of plate which can be accommodated in the apparatus is 14 inches , and horizontal cross-bars are provided to permit free widths of*inoh , 1 inch , and 2 inches respectively .
The general arrangements of the testing machi1le and frame are shown in fig. 2 , in which a simple lever A pivoted at supports the stressing frame on a spherical bearing , and the lower shackle engages with a siniilar bearing .
The load is applied by a wire attached to a spring balance hanging from the outer end of the lever .
The wire passes over a pulley to a frame provided with a nut threaded on a screw , which latter is turned by a hand-wheel J. Prof E. G. Coker .
Optical of This arrangement has some advantages over an alternative employed at an early stage of using dead weights at the outer end of testing machine lever .
This necessitated the lifting and frequent of masses of as much as 150 lbs. weight in some experiments , involving much labour and waste of time .
The same load can be applied with ease by a few turns of the hand-wheel and changed for a new load a few seconds without shock or jar .
It is , however , open to the that a spring balance is hardly ever quite accurate , and that its vary slightly from time to time owing to changes in temperature and like .
These objections are to a great extent removed by careful and these were carried out at intervals and the observations corrected from .
The differences proved to be very small , and were practically negligible .
At the commencement of an experiment the machine balanced by adjusting the position of the weight on the screw load was put on the specimen by turning the hand-wheel until the balance registered a definite pull .
The distances between the on the main lever were such that the pull on the speoimen was 20 the pull shown on the balance , while the weight of the central pair of and shackles always added a load of 15 lbs. to the plate under shear , which due account was taken .
Arrangemxnt of the Optical Apparatus.\mdash ; In the earlier experiments consisted of a pair of Nicol prisms and suitable focussing lenses 1911 .
] iation of Stress in Thin lar Plate .
producing a parallel beam of light from an arc lamp .
The field of view with such an arrangement was very small , and with the apparatus available the maximum area under observation at any one time was practically a circle of about 1S inches diameter .
To examine the optical effects produced over a long length of plnte the apparatus was supported on an optical bench and carried by a rising and falling table , which latter could be adjusted by screws to any part of the plate under observation .
This caused much waste of time due to the frequent changes of position required and the numerous minor adjustments of the optical apparatus .
The arrangement was ultimately replaced by a much more convenient apparatus designed for me by Prof. Silvanus Thompson , , which enabled a plate 10 inches in length to be examined in detail without any change in the adjustments of the optical apparatus except an alteration in height of the Nicol prism used as an eyepiece .
This new apparatus consisted of a black glass plate 24 inches by 12 inches , set at a suitable angle for polarising the light obtained from a number of glow glamps , and diffused through tissue paper screens .
Quarter wave plates of mica were also constructed about one square foot in area for obtaining circularly polarised light .
This apparatus was set up in the neighbourhood of the stressed plate , and the colours due to double refraction were observed by the aid of a Nicol prism , which when set at close range enabled any point to be examined in detail , while the whole plate could be viewed from a distant position at one time .
The positions of any stress maxima or minima could therefore be approximately determined from the colours by a qualitative examination , and any stress variations due to imperfect adjustments could be localised .
For quantitative work it is most convenient to determine the stress produced by reference to a colour scale , and this may be either a calibrating member stressed in the same way as the plate under experiment until the colour effects are identical , or an optical wedge might be arranged to give a graduated retardation of any fraction of a wave-length of light to correspond to that given by the stressed plate .
In the present experiments , however , the most obvious method was to take advantage of the fact that a pure shear is equivalent to a pair of equal strains at angles and equally inclined to the direction of slide , one a stretch and the other a squeeze .
If a tension member cut from the same plate is stressed in the direction of the compression stress the retardation produced by the one is annulled by the other for a definite pull on the calibration member .
Let the tension member be subjected to a stress , then the strain in Prof. E. G. Coker .
Optical of the direction of its length is given by , where is modulus ; the lateral contraction produced in the breadth of the is , where is the stretch-squeeze ratio .
These strains are equivalent to a slide and an all round stretch point , and we may express the relations between them by from which we obtain and .
Now , since the shear stress , where is the coefficient of rigidity the material , we obtain or T. The shear at any point may therefore be determined from the stress in a tension member set along the direction of compression and stressed to give total extinction at the point considered .
The tension stress in the calibration member also produces a change in the thickness of the material of an amount expressed by Experiments*have shown that the value of Young 's modulus for this material is approximately 300,000 , measured in pounds and inches , and that is .
The change in thickness er 1000 lbs. of stress intensity is therefore .
The highest stress recorded in any experiment is 4730 lbs. per square inch , corresponding to a diminution of rather less than of the thickness of the material .
In the majority of the experiments the stress rarely exceeded .
per square inch , and the joint correction for the calibration member and the shear specimen is therefore so small that it is well within the limits of error of the determinations , and no corrections have been applied .
It is necessary to determine the directions of the principal stresses at points in the plate where measurements are to be taken , and these can be mapped with considerable accuracy if the plate is examined by aid of a pair of Nicol prisms , with their principal planes at right angles .
At any point where the directions of principal stress correspond to the principal planes of the crossed Nicol prisms no light can pass to the eye , and all points in the field of view for which this condition obtains are mapped by a black band or black area , which , in general , alters in position when the prisms are rotated .
An examination of the stressed plate shows that the directions principal stress are inclined at to the line of pull of the frame 'Phil .
Mag October , 1910 .
1911 .
] Variation of Stress in a Thin Plate .
at the ends , where the directions change somewhat rapidly .
The observed changes in angular position for one end of a plate having a length of 4 inches and a breadth of 1 inch are shown in fig. 3 , from which it will be observed that for the centre line all these variations occur within inch from the edge .
Hence , if measurements are made along the centre line of this plate the tension member must be set at an angle of to the line of pull for all positions not very close to the ends .
This is also evident from a map of the lines of principal stress obtained from the curves of observation , and shown by fig. 4 .
The breadth of the plate influences the distribution at the ends , and the disturbing effect upon the positions of the lines of principal stress appears to be approximately proportional to the breadth , as appears from fig. 5 , which shows the lines of equal inclination corresponding to a plate Prof. E. G. Coker .
Optical of 2 inches in breadth and 4 inches in length .
For this breadth , of the shear stress were taken along the central line , and also along parallel thereto , and inch away from the sides .
The lines of stress and equal inclination at one end of this plate are shown in fig. from which it appears that along the central line no correction is unless the distance is less than inch from one end , while along a parallel and inch away from the central line a correction will required for this width of plate if t'ne distance is less than inch one end .
For applying load to a calibrating member set along the direction compression stress in the plate a miniature lever testing machine constructed ( fig. 7 ) , so that the specimen could be ad.iusted in position .
This consists of a right-angled frame , supported on a swivel pin carried by a , which latter slides on a vertical rod D. Clamping screws are provided to fix the block in any position along the vertical rod and to adjust the angular position of the frame .
One end of the specimen is carried by a , and the other by a similar knife-edge , in a lever , which latter is pivoted about a knife-edge , secured in the frame .
A pull on the specimen is obtained by a spring balance , one end which is attached to the outer end of the main lever , and the other through a hole in the frame , and is secured by an adjusting nut regulating the pull .
1911 .
] Variation of Str.ess in a Thin lar In order to obtain a uniform tension stress in the specimen each end is drilled , and steel rings are inserted in the holes so made to receive the , which latter pass through the rings , and are supported on each side of the specimen by cheek plates .
The weight of the inclined lever and spring balance produces a total pull on the specimen of lbs. , and the lever multiplies the pull of the balance by five , so that if the dimensions of the cross-section of the caliration member are determined the stress on the material can be calculated .
In all cases the calibration specimen was cut from a part in close proximity to the plate used as the specimen under shear stress .
Method of Experiment.\mdash ; A plate of material , of approximately the required size , was first cut from the sheet , and examined for flaws between crossed Nicol prisms .
If it proved satisfactory , the plate was afterwards drilled for clamping in the frame , and finished to the required size .
It was then covered with a network of reference squares by marking with a fine needle point , and , before setting in place , it was again examined , to make sure that the shaping processes had caused no injury to the material .
With the specimen clamped in position , the maximum load was applied , and a further optical examination was made , to discover if there were any signs of local stresses due to unequal tightening of the bolts , or due to direct pressure of a bolt on circumference of the holes .
This examination was easily carried out by observing the appearance of the plate from a considerable distance by aid of a Nicol prism set to give total extinction at no load .
If the colours indicated local stresses , the gripping forces of the bolts were adjusted until - these colours disappeared and similarly disposed colour effects were observed on both free widths under shear .
The colour indications were very sensitive to the slight adjustments which were usually found necessary at the commeneement of each experiment , and the application of stress by the gripping surfaces was probably very uniform , and a close approximation to an evenly distributed shear stress along the vertical sides .
The central arrangement of the applied loads , and the construction of the stressing frame , ensured that both lengths of the plate were loaded in exactly the same manner .
The gripping surfaces were maintained at the same distance apart by large turned bolts , fitting exactly into holes in the cross-bars\mdash ; these holes were reamered to ensure an accurate fit , and were probably true to one thousandth of an inch .
During the experiments , no tilt of the frame was observed which would tend to make the outside vertical members approaob one another , and , as a large tilt would be required to oause a very small horizontal displacement , it was assumed that the arrangement of the frame effectually held the bars at the correct distance apart at all Prof. E. G. Coker .
Optical Determination of loads .
This is an important matter , because a central load applied frame produces shear in the material , and , if the outer plates are approach each other , an unbalanced bending moment is produced .
however , as in the present instance , the tendency to bend is resisted by frame , we obtain a practically pure stress in the material .
earlier experiments , the same result was obtained on a single plate held rigidly in a support , and loaded by a weight , by supplying opposing couple of amount .
This was accomplished by using a bell-crank lever EOE'D , pivoted at , and connected to the outer plates by equal links .
A pull at was furnished by a balance , which was adjusted to give a moment of the required about the fixed centre O. Observations of material in both frames gave similar indications , while effect of an unbalanced bending moment could also be observed in arrangement .
A point-to-point examination of the stress distribution made by aid of the calibration member , which was adjusted to any height , with its line of direction at an angle of to the frame .
in this tension member was first adjusted until the colour effect at the 1911 .
] Variation of Stress in Thin Rectangular under observation was extinguished and a dark field obtained .
The mean value obtained by first slightly passing the stress at which extinction was observed , and then afterwards lowering the stress until this position was again passed , was taken as the measure of the shear stress in the plate under ervation .
Analytical Theory.\mdash ; The mathematical theory of the distribution of stress due to shear in a rectangular section may be considered with reference to the case of a cantilever joist , fig. 9 , loaded by a weight at its outer end , the term joist denoting that the length is many times the depth , and that the thickness is small compared with the depth .
At any cross section distant from the origin there is a couple and a shear , both of which are balanced by the stresses and set up in the interior of the beam .
The couple can be balanced if the stresses where is the distance from the central plane , while the stress must -satisfy the general equations of equilibrium , , and the stresses being taken as averages throughout the thickness of the plate .
In addition , the sum of the shear stresses taken over the vertical section must have the same total magnitude as the shear load , and the value of must be zero at the upper and lower surfaces of the beam .
These conditions are fulfilled if provided that the terminal load is distributed over the end section according to this parabolic law .
In general the accurate distribution of the load over the terminal section is of no importance in practical applications to beams , since they are usually of considerable length compared with their Love , ' Mathematical Theory of Elasticity , ' p. 137 .
VOL. LXXXVI.\mdash ; A. Prof. .
G. Coker .
Optical Determination of [ Dec. depth , but it has often been assumed that the shear stress in any section is distributed according to this parabolic Iaw , even in such cases as that of the section of a reservoir wall or a dam , where the of the application of the load and the dimensions of the section are different from those assumed in the simple theory .
In the case of a plate of rectal ) gular section subjected to uniformly shear stresses over the edges , there appears to be no good for the assumption that the shear distribution follows a parabolic law , the width of the plate is comparable with the depth .
If the plate is long compared with its width , and the distribution is uniformly applied over the vertical edges , it would also appear from general considerations that the shear stress must be very uniform over a considerable length .
For if we imagine the vertical shear stresses equilibrated by shear stresses of the same intensity applied along the two horizontal ends , the condition of the plate becomes one of uniform shear throughout , and it seems improbable , if these latter applied forces be removed , that any considerable variation in shear stress can be caused thereby except near the ends .
Andrade*has considered the case of a rectangular block of length and breadth with the upper and lower faces subjected to uniform shifts in their own planes in opposite directions , all the remaining faces being free , and he obtains for the distribution of shear stress the form where A and are complex and the summation is for all values of ; and is the distance from the central plane of the block .
This gives maximum values near the ends and some maxima and minima of much less importance distributed along the central length .
Experimental Results.\mdash ; The general method of experiment having described , we now turn to the values obtained .
One of the early experi .
ments with the shear apparatus above was made on a plate which had thickness of 1/ 16 inch and a free width of 1 inch .
A length of 10 was chosen as the most convenient maximum , as all the experiments then be made without altering the adjustments of the polarising apparatu The plate was subjected to a pull of 100 lbs. per inch run , and of the testing machine showed that 99 lbs. per inch run was applied , the remaining 1 per cent. being accounted for by errors in balance and frictional resistance of knife-edges .
The weight of the ' ' The Distribution of Slide in a Right Six Face subject to Pure Shear ' Roy .
Proc , vol. 85 , 1911 .
1911 .
] of Stress in Thin Plate .
maximum value .
From this point there is a slight decline in the stress intensity until in the bourhood of the centre of the plate a minimum value is reached ; and , as we proceed in the same direction , there is a gradual recovery to a maximum value at a distance from the lower edge of the plate which corresponds very well with the position of the upper maximum , the stress finally falling to zero at the lower edge .
The general accuracy of the experimental work may be tested by a determination of the mean value of the tension stress from a summation of the area of this diagram .
If this value is compared with the mean intensity of the applied shear we ought to find that this latter is one-half the numerical value of the tensional stress , provided we may assume that the optical effect has a linear relation to both tension and shear .
In the present example this ratio was found to be In order to discover the effect of an alteration in the ratio of length to breadth , the same plate was cut to a length of 6 inches by removing equal portions from each end .
The applied load was maintained at nearly the same mean intensity , and readings similar to those of the previous experiment were obtained , as shown in the annexed table .
A slight increase of the shear stress was observable over the middle portion of the length , with maxima spaced nearly as before .
The ratio of tension to shear in this case was found to be .
In the same manner a length of 3 inches was also examined , which gave more pronounced maxima , nearly symmetrical ] spaced ; the ratio of the stresses was The shear distribution in the 2-inch length , however , underwent a it no longer had a double maximum , but increased in value from the to the centre .
The principal result of this change in the distribution was to raise the maximum stress by a considerable amount , as the diagram shows , and a still further reduction in length to 1 inch gave a similar distribution curve which approximated to a parabolic form with a further increase of stress intensity .
These experiments show fairly well the general features of the distribution , which are characterised by a fairly uniform distribution of stress over the greater part of a long length , rising slightly to a maximum near the ends and falling rapidly to zero at the edges .
As the tithe diminishes the maximum values approach one another , until they finally merge into a maximum value at the centre for some ratio of length to breadth , which the experiments show to be in the neighbourhood of two .
A measure of the accuracy of the values contained in Table I is afforded by the accompanying Table II , from which it will be observed that the percentage differences between the experimental and calculated values range Prof. E. G. Coker .
Optical of between and per cent. , and they indicate that the measured stresses are in defect , a result which may be due to inaccuracies in observations or imperfections in the material , or both .
These percent differences are given for each set of experimental values .
Experiments were also made on a similar plate 12 inch in free and having a length of 8 inches .
The loads imposed were slightly from those of the previous case , owing to the dead weight of the middle being allowed for in the application of the load , which latter was maintain at a uniform amount of 100 lbs. per inch run of plate , corresponding a mean stress of 1584 lbs. per square inch on the specimen when due is taken of friction and other errors .
The curves of equal inclination that the principal stresses were equally inclined to the central line distances up to within 1/ 16 inch from the ends .
This plate yielded which agree very well with those described above as shown by Table 1II the accompanying fig. 11 .
Commenclng with the full length , we have same characteristic distribution as in the former case , and this is repeat with a length of 4 inches , except that the intermediate stress is slightly than before .
Further reductions in the length of the specimen to 2 and inches respectively show somewhat similar stress distributions maxima closer ether and a general increase in numerical while for a length of 1 inch we obtain a single central maximum corresponding to a stress intensity in the calibration member of 4150 per square inch .
The final length of 12 inch , for which the plate a square form , also gives a very symmetrical shear curve with a very increase in the stress .
It is interesting to compare the stresses at the of this length with that on the 8-inch length under the same mean per unit of length .
The former gives a shear stress of .
per inch as compared with .
per square inch on the longer length or of 36 per cent. in the intensity of the stress .
Variation of Stress in a Thin lar Table As the fol.egoing experiments at a high working stress could not be completed to the buckling of the thin plate , it was considered advisable to study the stress distribution at low loads , and a sheet of transparent material was therefore obtained of the greatest thickness procurable , inch , and from this three plates were cut and ruled , as described above .
They were each 10 inches in length and of 12 inch , 1 inch , and 2 inches width respectively .
The applied load was in all cases proportional to the length of the plate , and for convenience it was fixed at 15 lbs. on the spring balance reading per inch length of plate .
Allowing for all error in defect of 1 per cent. , as already mentioned , this amounted to an actual load of lbs. per inch run .
The procedure was much the same as in the earlier experiments , but the -experience of former work showed , among other details , that it was of primary importance to have all the bolts very accurately adjusted to give equal intensities of grip on the plate to avoid local stresses and consequent error of measurement .
Although the applied stress was much lower than before , the increased thickness of plate multiplied the optical effect so considerably that no difficulty was experienced in making the required measurements .
The plate of 5 inch width , when under test , showed all the principal features brought out by previous experiments .
The numerical values obtained are shown in the accompanying Table , and these values are plotted in fig. 12 .
Prof. E. G. Coker .
Optical Determination of plate in all cases except that of the full length .
The change to the with a maximum at the centre is not complete for a length of 2 but becomes so for a length of inches , a result which agrees positions of the other maxima in all but the full length , but is not agreement with other determinations .
The minimum values are very defined , and are practically at the centre in every case where they This set of experiments shows a much closer approach to the standard , as will be observed by the results collected in Table which it appears that the percentage differences are with one very small and negative .
The experiments made on a plate of 2 inches width were directed to determine the stress distribution not only along the central section , but also at sections midway between this and the sides of the gripping bars .
The results obtained ( Table IX ) show that the distribution near the sides is very similar to that of the central section , for some distance remote from the ends , and in most cases the differences are within the limits of experimental error .
At the ends , however , there are considerable changes ( fig. 14 ) , especially as the length of the specimen is diminished , and the change in the directions of the lines of principal stress becomes an increasingly important factor .
Except close to the ends , however , the general features of the distribution are shown to remain unchanged ; figs. 6 and 7 indicate that the observations on each side of the central line require correction for distances within inch from the ends .
This slightly affects few values at a distance of S inch from the ends , where the lines of principal stress are inclined at approximately and to the central line .
Subsequen measurements on another specimen , when the calibration member was in accordance with the angles indicated above , showed that these correction amounted to approximately 4 per cent. , and the curves of shear stress 1911 .
] Variation of Stress in a Thin Plate .
observation and setting are somewhat variable , and are greater at longer lengths .
This latter circumstance may be partly accounted for by the want of uniformity in the application of ] at the ends of the full length .
The rapid change in the intensity of the shear at tho ends of the shear plates , and the apparent rity of these portions of the curves for different lengths , is one 01 considerable interest , and it is ) tant to enquire if the distributions { ollow the same law for all lengths .
methods of experiment adopted for the general snrvey of a long plate do not adapt themselves very well for a very detailed examination of small areas , but the ) ental values recorded afford some opportunity of .
the character of the end distril ) ution curves , and it appears that the observations for a plate in which ratio of length to readth is the hbourhood of unity follow a law approximately .
may be shown by comparing the ) rved values with the corresponding values of a trne parabola , and this has been carried out for a thick plate by applying Simpsoll'S rules to obtain the of the experimental shear curves .
this way the mean average values of the sheal stress been found along the central lines of } ) lates of square form , inch , 1 inch , and 2 inches side respectively .
values are mately 1413 lbs. , , and 1556 lbs. respectively , and correspond to parabolic distributions with maximum ordinates of ) average values .
True parabolic curves were plotted and compared with the experimental values , and one is shown in the accompanying fig. 11 from which it appears that the correspondence is a fairly close one .
The accompanying Table XI , showing approximately the percentage difference from a parabolic distribution , indicates a very fair agreement , with the exception of two observations at points close to the edges of the plate .
VOL. LXXXVI.\mdash ; A. 1911 .
] Variation of Stress in Thin Plate .
general distribution of the shear stress that there is any want of uniformity in the results .
It is shown that the shear stress in a long thin plate , subjected to a uniform shear load applied to the long parallel edges , rises rapidly from a zero value at each end to a maximum value , which latter is usually attained at a distance rather less than the free breadth of the plate ; the stress then decreases in value until it reaches a minimum at the centre .
As the length of the plate is diminished , the maximum and minimum stresses become more pronounced , and when the ratio of the length of the plate to the free width is in the neighbourhood of two the distribution changes in such a manner that there is a maximum at the centre and a rapid fall to the ends .
The experiments show that a parabolic distribution of shear is probably only true within narrow limits .
The distribution of shear stress over a long rectangular section may be nately represented by a lmiform shear over the central section with a rapid fall towards the ends .
For rough approximations the shear stress over a long ular section may be taken as uniform throughout .
The experiments appeal to show that the tion is of the sam cter for the same ratio of length to width .
In sion the author desires to express his warmest thanks to Prof. Karl Pearson , his valuable advice and assistance during the progress of the work , and also to Prof. Silvanus Thompson , F.B.S. , for much help in optical matters .
|
rspa_1912_0023 | 0950-1207 | Spectroscopic observations : lithium and c\#x153;sium. | 320 | 329 | 1,912 | 86 | Proceedings of the Royal Society of London. Series A, Containing Papers of a Mathematical and Physical Character | P. V. Bevan, Sc. D.|Sir J. J. Thomson, F. R. S. | article | 6.0.4 | http://dx.doi.org/10.1098/rspa.1912.0023 | en | rspa | 1,910 | 1,900 | 1,900 | 8 | 166 | 3,942 | http://corpora.clarin-d.uni-saarland.de/surprisal/6.0.3/?id=rspa_1912_0023 | 10.1098/rspa.1912.0023 | null | null | null | Atomic Physics | 48.328215 | Tables | 47.792268 | Atomic Physics | [
8.671096801757812,
-48.31635284423828
] | ]\gt ; Spectroscopic and By P. .
BEVAN , Sc. D. , Royal Holloway College .
Communicated by Sir J. J. Thomson , F.R.S. Received January 4 , \mdash ; Read February 8 , 1912 .
[ PLATE 9 .
] The present communication deals with a further study of the absorption spectra of the vapours of lithium and caesium .
These spectra were investi , ated , ) results communicated at the beginning of last to the Royal Society .
* The present account deals with an extension of the principal series lines for the two metals , and a more detailed examination of the expression of the wave-lengths by a formula , as well as an investigation of the broadening effect in a } ) of lines with increase of density of the vapoul of sium .
We shall deal first of all with the lithium spectrum .
As has remarked before , lithium vaponr presents some difficulties , because of the .
temperature required ) the action of the vapour in this condition on the material of the containing vessel , but this difficulty can be surmounted by the use of a double steel tube and a quantity of lithium .
With the tube at a bright red heat , a dense vapouu : is produced to show in transmitted light a large number of the principal series lines ; the number that can be observed depends , I convinced , only on the resolving power of the spectrograph used to investigate them .
With the instrumen6 at my disposal , I have been able to measure 41 of these lines , and I think in this case the resolution has been pushed as far as is practicable , the lasb few lines being separated only about ngstrom unit .
Fig. 1 , Plate 9 , shows the absorption lines up to No. 25 .
The finer lines after this do not appear in the reproduction .
The following table gives the results of measuremenbs .
In the column is the number of the line in the series .
The second column gives wave-length in Iriternational units founded on the absolute measurements the red cadmium line .
The next column contains an estimate of the errors in the individual .
The fourth column gives " " oscillation frequencies\ldquo ; in number wave-lengths per timetre ; and the last column the rences , observed\mdash ; calculated the calculated values being those obtained from a Hicks formula discussed later .
' Roy .
Soc. Proc , vol. 85 , p. 54 .
Spectroscopic : Lithium Ctesium .
Table I.\mdash ; Lithium .
The measurements for the lines 1\mdash ; 7 are by Kayser and Run , and 9 easured by Living and Dewar , but were remeasured ; 10\mdash ; 27 were given in my former paper aheady referred to ; new .
The errot .
S indicated as possible are probI ) in nearly all cases mnch outside the limits .
They have been increased for the lines 10\mdash ; 27 , owing to the fact -that the uncertainties in the measurements of lines and in ] ) tions of wave-lengths were ) Jated .
To begin with , there is some considerable uncertainty in the values of the wave-lengths of the cadmium lines .
For example , the values of the possil ) errors given by Kayser and unge for the lines , and are , and , and when the cadmium spark is used as the sonrce of light these are 1nuch -exposed in , so their positions calmot bo determined with any boreat raCy .
Then is some uncertainty in the Rowland on which the lleasurements of the lines are based .
At } ) resent , Kayser has not extended the third order stamdards into this region , so that we have only the secoud order stan dards of Fabry and Buisson to go , but there llay easily be ular errors of some hundredths of an strom uniu in the old Rowland standards .
As far as my actual 1lleasuremens are concerned there should not be , in the case of lines not very near to cadmium lines in wave-le errors of more than a hundredths of an ngstroln uuit for lives near the Dr. P. V. Bevan .
[ Jan. 4 , end of the series , even when possible unsymmetrical broadening and other effects are taken into account .
Taking all sources of error into consideration , I have put the possible errors high ; the diHerences are due to the uncertainty when an absorption line is near an emission line , so that the true centre of each is difficult to determine .
After the 25th line the measurements are expressed to hundredths of an Angstrom unit , because , although the possible error is much above this order , yet , as a rule , the errors will affect lines almost equally , in so far as they are produced by uncertainty in the measurements of the position of the cadmium reference lines .
The difference of between successive lines is thus much more accurately determined than the actual values .
In reducing the measurements to the International scale , the values of iron lines as determined by abry and Buisson were used ; a table of the necessary corrections has been published by Birge*which gives practically the corrections used for Table I. The reduction to vacuo for the oscillation frequency was obtained from the ] of corrections published in Watts ' Index and the temperature corrections in the same volume .
The formula on which the last column of Table I is based is that due to Hicks ' where is the oscillation frequency , universal Rydberg constant , and takes the values 1 , 2 , 3 , etc. , for the different lines of the series , and being constants for the particular substance .
Using the oscillation frequencies based on the International scale , we have to use a different value of N. The value has been calculated by Birge in the paper referred to from the wavelengths of five hydrogen lines .
This value is instead of the value 109675 .
Using the first three lines of the series to calculate we obtain and these values are used for the last column of Table I. The possible errors work out to be practically the same as those given by Hicks for for , for If we take a higher member of the series to determine with approximate values of and , the method I have used before and adopted by Birge , we obtain a higher value of ; for example , from the lines 25 , 30 , 35 , 40 , we obtain the numbers , but in each case a * B. T. Birge , ' Astrophys .
Jour vol. 32 , p. 113 .
'Phil .
Trans , vol. 210 , p. 96 .
'Roy .
Soc. Proc , vol. 83 , p. 425 .
1912 .
] Spectroscopic Observations : Lithium nd .
323 possible error .
This method does not give us such close limits as the method of taking the first three lines of the series if the limits of error are reliable .
A slightly higher value of A would make the numbers in the colmnn look better , but the agreement would not be so good in the earlier members of the series , and in view of the larger possible errors in my own measurements , which quite possibly may all be too small , it is preferable to rely on the Kayser and Rung measnrements for the earlier lines .
The only line for which there is not agreement between the calculated and observed values is 4 , for which the limit of error is givetl by Kayser and Rung as and the difference appears as .
This , probably , is to be explained by an error in the determined wave-length owing to errors in the old standards .
It is quite possible that an error of may be introduced owing to this .
The agreement in the other lines is fairly complete .
In former measurements of the absorption lines of caesinm the absorption at1nosphere was obtained by , caesium chloride with metallic sodium or potassium .
Sufficient was set free to give a vapour which showed 24 of the absorption lines belonging to the principal series , but owing to the comparatively easy volatilisation of the sodium or potassium the spectrum was complicated by the presence of the sodium or potassium absorption spectrum .
A method of obtaining caesium by heating the anhydrous chloride in with metallic calcium was given by Hackspill .
* This method I found not very satisfactory for my purpose , as it was difficult to control the rate of formation of caesium .
A more suitable method was found in heating the anhydrous chloride with metallic lithium .
The lithium volatilises with difficulty , and a steady atmosphere of caesium vapotlr of sufficient dellsity can easily be maintained .
With this method the sel'ies lines were photographed up to the thirtyfirst of the principal series , and again the limit is only imposed by the resolving power of the instrument .
The principal series for all the alkali metals , with the exception of lithium , consist of pairs of lines , the separation of corresponding pairs being as we go from sodium to caesium .
The lines are not equally intense in all cases , the line of greater wave-length in a pair being the less intense .
There are , in fact , bwo series , , in the notation of Rydberg .
It is only the cases of rubidium and caesium that we could expect to be able to distinguish the pairs for more than a few members of the series , as , on the assumption that the ' Comptes Rendus , ' 1905 , vol. 141 , p. 106 .
Dr. P. V. Bevan .
two series have the same limit , the pairs become so close together they cannot be separated .
But in the case of caesium especially separation is considerable , and so the pairs of lines can be more distinguished .
The later members in all these series belong to -this becomes clear from the cases of idium and caesium , where intensity of the P2 lines falls oif with higher order in the series until line cannot be observed , although its position assuming an formula should be quite easily distinguishable from the corresponding .
The lines of P2 cannot be out by increase of density of the vapour , as this produces .
of the lines , which spread over the position of the P2 lines in the photograph .
This disappearance of P2 lines has led to some errors in applying formulae to the series .
has calculated constants for the Ritz formula for the alkali metals and has found that the formula is inapplicable in the case of caesium , but the explanation is that the first four membels he ] ) used lines\mdash ; those of the pairs with greater wave-length\mdash ; while the rest of the wave-lengths are of lines .
The wave-lengths used by him for the higher members have not much accuracy , but the formula would give very much better results if the four lines of less wave-length were used .
The same remark applies to of Birge 's calculations\mdash ; he has used the lines where they are observed , while after the lirst few members it is the lines which are measured .
This makes very little difference in the case of sodium , where the pairs are very close together after the first three\mdash ; the only ones which have been observed .
In the case of potassium also five pairs have been observed and for later pairs the differences would be hardly greater than the errors in the experimental numbers .
For rubidium the diflerences are greater , and again this accounts for the bad fit for the numbers calculated by from the Ritz formula .
In Table II are given the wave-lengths on the International scale .
The first column gives number in the series , the second the wave-lengths , the third the possible error , the fourth the oscillation frequency in vacuo , and the the values of observed-calculated wave-lengths , to be dealt with later .
In Table II the wave-lengths for the first pair are measured by Lehmann .
There are no measurements which give a check on his values , but judging from his measurements of other lines in this infra-red region we can accept them as being reliable .
The measurements for the second pair are by Kayser and Rung , and the values agree with those of Ramage and Exner and Haschek .
The rest of the lines are my own For my value agrees with Kayser and Runge 's ( reduced to InIernational units ) \mdash ; but their valne for the other one of the .
is 387659 , with a possible error of .
Ramage gives , which agrees better with my own value , and would give better yreentent with the calculated values .
I have kept my own value , as it seems certain that the Kayser and value is too .
For yser and 's values are ; corrected to international units gives ; ayser and 's limits of error are given as and respectively .
For my own measurements the line of greater wave-length was very no , the breadth being about ; the other line was broader , about unit .
It seems probable that Kayser and 's value for P2 ( 4 ) is too low .
Ramage for gives ) , and for lines , .3314 , .
The line has no error attached to it , as it is practically coincident with a rubidium line which ppeared in the photographq , the two lines appearing together sinlply as one .
It is doubtful therefore what this measurement represents .
For the determination of the constants , of the Hicks mula ' the method adopted was to take a fairly high order of line for , 15 , which with nate values of and determines A. Then from early lines and can be redetermined .
Successive approxilnations give Dr. P. .
Bevan .
very quickly the constants required .
P2 the sixth line was used the first two .
The work of approximation is , of course , slower than but not much arithmetic is involved .
The possible errors in the are determined as by Hicks , and it easily appears that the best are obtained by usin , the first two lines .
We obtain , for the 1 , 2 , and 15 , 3 , and 15 we obtain .
For we obtain , using 1 , 2 , and 6 , The two values of A for , come out the same , which is in with the assumption that the two series have the same limit .
I think , the best evidence for this relation between the pairs that we at present .
The column O-C in Table Il gives the differences observed and calculated values of the wave-lengths derived from these of the constants .
The agreen ) is everywhere within the limits of error except for .
A permissible change in A would this inside the limits , but in any case it is not a very reliable it is the last of the series visible , and so a very faint linle , difficult to out and .
Perhaps a greater error should have been allowed in case , but , as is hardly necessary to say , the possible errors were allotted the calculated values were obtained .
The values of the constants and enable us to make more complete investigation with regard to the relations they exhibit the series the alkali metals .
For this purpose I have recalculated the constants of series for sodium , potassium , and rubidium , the wavethe International scale and to .
The reduction is not very as for the infra-red we have to extrapolate , but it seemed worth make the aGtempt to get as near the right values as possible .
The table gives the values of and with limits of error for the four metals , Rb , Cs , for the Na Bb Cs , 1912 .
] Spectroscopic Observations : Lithium Coesium .
327 These numbers were calculated from the lines 1 , 2 , and 35 for sodium , with a slight increase in possible errors owing to uncertainty in the old Rowland standards\mdash ; an increase of this kind has been made in all cases . .
potassium the lines 1 , 2 , and 22 were used , and for ) idium 1 , 2 , and 25 .
The hmits are on the whole narrower than those given by Hicks .
In the case of sodium the limits are wider owing to the fact that the publishPd possible errors have been increased for the reason mentioned above .
It follows at once from these numbers that the relations*for , and are not we have in fact the following:\mdash ; Na 2 Bb 5 Na 2 Rb .
5 Cs We see in the values of a regular decrease with increasing atomic weight , but clearly the fraction is not constant .
In the values of , however , there is no apparent relation to the atomic weights .
It also appears that it is impossible to make the fraction when is different from 1 a constant multiplied by the rn mbers 2 , 4 , 5 , 6 .
An expression of the form is giveu by Hicks which applies to Na , , and Bb , and to Cs if the term is dropped .
This expression also is not exact within the limits ibed .
It rees for the independent of for Na , , and ) but the part reptesenting is outside the limits for Bb , and the numbers when the term in is dropped .
be made to agree with and for caesiu1n .
These relations then cannot be considered as exact , they are very and provide fairly good approximations to the actual lines .
We can therefore only regard the formula based on them as approxima .
It would doubtless not be difficult to add other ternls to the Hicks expressions on the atomic weights or other properties of the * Hicks , , p. .
so .
Dr. P. V. Bevan .
metals and thus obtain expressions correct within the limits prescribed , but there seems little point in attempting this at the present stage , as Hicks ' own expressions are so near the actual values that new terms would be so small and the possible errors so that we could conclude nothing as to their real correspondence with the actual state of affairs and they would be mere interpolation terms .
dening of with of Density of Vapour.\mdash ; Absorption lines are never quite as sharp as good emission lines , though in some cases their apparent breadth can be certainly less than .
U. , and therefore there is some doubt in measurements of wave-lengths by means of absorption , as errors may be introduced owing to the broadening of the line not being symmetrical .
It seemed worth while therefore to examine a typical case with some care to see the effect firstly on the determination of ] cvth , and secondly for the interest of the asymmetry of the broadening itself .
It is observed in all cases these irlcipal series lines the broad line obtained by using dense vapour behaves in the same way .
The line broadens unsymmetrically , extending much further on the more yible side than on the other .
As all the lines I have observed behave in a similar way a careful examination of one pair was made , and for this purpose the second pair in the caesium series was investigated .
The advantages of taking this pair were that it occurs in a visible part of the spectrum , so that ordinary glass for lenses and prisms could be used , and also that the effect on each line could be studied , as the two lines are separated by a nsiderable interval .
To get more dispersion for this case a small Thorpe grating mounted on a prism to form a direct vision spectrograph was used .
The effective aperture was somewhat less than 2 cm .
This was mounted on an ordinary laboratory spectrometer and the telescope aCed by a camera .
The mounting of the apparatus left a reat deal to be desired in the way of rigidity , but some satisfactory raphs were obtained .
Fig. 2 of the plate shows enlargements of the photographs obtained : ( 1 ) shows the absorption using a white source of Nernst lamp ; ( 2 ) has the iron arc photographed in addition to the absorption spectrum .
With the apparatus used it was very difficult to keep the adjustment when changing from the absorption spectrum to the comparison spectrum . .
However , as the series of photographs shows , with a certain number of failures there were obtained some good results .
a glance at the figure the asymmetry of the effect can at once be seen .
Measurements were made of the edges of the lines\mdash ; the edge of the line is of course somewhat indefinite as there is no abrupt change , but measurements of the two edges are probably fairly comparable , as , 1912 .
] Spectroscopic Observations : Lithium and Coesium .
at any rate until the line becomes very broad , the aspect of the two is practically the same .
The following table gives a set of measurements of the two edges of these lines:\mdash ; 4555.26 .
4593.16 .
4555 .
4555.78 4593 .
57 .
92 .
92 .
94.20 59 .
92 .
53 .
95.74 95.59 The wave ] were determined from the iron lines The second of these was not a good line , and there may easily be in some of these an error of A-U .
from this ) in any case it is clear that the broadening is very lnuchulOl'e on the side of greater wave .
The narrowest lines of ave were considerably broader than ] used in -length determinations .
dening effect is eater in the earlier members of the series , and the lines after the first few of the early members relnain very fine , except in the case of very dense vapour .
For example , in the one of the raphs from which was determined , the breadth of the line was less than .
In all of lines used for eluent the eadth of the lines was not greater than and in most cases not rreater than .
From the above table it is clear centle 1Jf the will give too tlreat a , but the is ] for account to be taken of it with the accuracy available for ments .
|
rspa_1912_0024 | 0950-1207 | The so-called thermoid effect and the question of superheating of a plantinum-silver resistance used in continuous-flow calorimetry. | 330 | 332 | 1,912 | 86 | Proceedings of the Royal Society of London. Series A, Containing Papers of a Mathematical and Physical Character | Howard T. Barnes, D. Sc., F. R. S. | article | 6.0.4 | http://dx.doi.org/10.1098/rspa.1912.0024 | en | rspa | 1,910 | 1,900 | 1,900 | 2 | 69 | 1,337 | http://corpora.clarin-d.uni-saarland.de/surprisal/6.0.3/?id=rspa_1912_0024 | 10.1098/rspa.1912.0024 | null | null | null | Electricity | 37.379956 | Thermodynamics | 37.175172 | Electricity | [
16.321372985839844,
-64.0694808959961
] | 330 The So-called ThermoidEffect and the Question of Superheating of a Platinum-Silver Resistance Used in Continuous-flow Calorimetry .
By Howard T. Barnes , D.Sc , F.E.S. , Macdonald Professor of Physics McGill University , Montreal .
( Received January 29 , \#151 ; Read February 8 , 1912 .
) In a recent paper by Glazebrook , Bousfield , and Smith* some doubt has been cast on the accuracy of my absolute measurements of the specific heat of water by the continuous-flow calorimeter .
It is stated that an error of as much as 6 parts in 10,000 might have occurred in the superheating of the oil-stirred platinum-silver resistances from which the values of the electric heating current were obtained .
On the other hand , it is also stated that this error might have been as small as 2*5 parts in 10,000 .
It was with some surprise that I read this statement , inasmuch as the authors could not have been aware of the rapidity of oil circulation which I used .
It has been shown by Osborne Reynolds and others that the heat loss from a surface immersed in a liquid moving in turbulent motion is directly proportional to the velocity of How .
The degree of superheating of a wire immersed in oil will depend then directly on the rate of circulation .
Fully realising this fact , the resistances which I used were designed by Prof. Callendar and myself to be immersed in oil which could be circulated with great rapidity .
These resistances are described in our papers , f where the illustration shows approximately to scale the relative sizes of the stirrer and resistances .
The paddle was rotated at a high speed by a powerful water motor , and the oil was thrown down with such force that a considerable depression was made in the surface .
The oil , thrown sideways , passed up around the bare wires , which wTere wound loosely on the mica frames .
I do not know by what standard Glazebrook , Bousfield , and Smith decide what is " normal stirring " or " very vigorous stirring,1 " but it was evident to me at once that I must have had much more rapid circulation than anything used by these authors .
In testing the accuracy of my experiments special attention was taken of possible superheating , and tests of stirring were made at the time .
The good agreement of the various determinations of the specific heat , made with such different values for the heating current and flow of water , make * 'Roy .
Soc. Proc. , ' 1911 , vol. 85 , p. 541 .
t 'Phil .
Trans. , ' 1902 , A , vol. 199 , p. 55 and p. 149 .
Superheating in Continuous-flow Calorimetry .
331 it evident that no large superheating error could have existed without being detected .
In spite of this , however , I have thought it worth while to test my resistances for superheating again .
I have accordingly made up a platinum-silver resistance out of wire 0*06 cm .
in diameter , rolled into a Hat ribbon about 2*5 mm. wide and 0*0075 cm .
in thickness .
Four ribbons of this thin metal strip were taken , connected in parallel on an ebonite frame , and immersed in an oil bath with stirrer , the mounting being similar to the specific heat resistances .
These ribbon strips were each approximately 150 cm .
long .
Hence the total cooling surface in contact with the oil was 75 sq .
cm .
per strip , giving a total of 300 sq .
cm .
and a resistance of approximately 1 ohm .
The old mica resistances consisted of two 1-ohm coils in parallel .
For this comparison one coil ( No. 2 ) was disconnected and No. 1 connected in series with the ribbon-strip resistance .
Each of the old coils was made of four wires 100 cm .
long and 0*04 cm .
in diameter .
Hence each wire had a cooling surface of 12*56 sq .
cm .
or a total surface of 50 sq .
cm .
fora resistance of 1 ohm .
Thus it will be seen that the ribbon coil has six times as much cooling surface as coil No. 1 .
The oil in both boxes was circulated at the same speed from the same water motor , and this circulation was the same as that employed during the specific heat measurements .
A steady heating current was passed through the coils and the temperature of the oil maintained steady in both boxes by means of coils of tube through which cold tap water was flowing .
The drops of potential across the coils were compared on our Kelvin-Varley slide potentiometer .
Both readings came very nearly at the same part of the slide .
The errors of this potentiometer have recently been redetermined for me by Mr. A. N. Shaw , M.Sc .
, for his work on the absolute measurements of the Weston cell , and the constancy of the instrument is a matter of great interest and satisfaction.* The galvanometer used was the Broca type , from the Cambridge Scientific Instrument Company , with 1000-ohm coils , and gave a sensitiveness from 17 to 40 divisions of scale to one division of the vernier slide .
The comparison could , therefore , be made withi an accuracy of one or two parts in 100,000 with all the heating currents .
The following table gives the value of the ribbon coil calculated by assuming the correctness of coil No. 1 for all heating currents .
The resistance of coil No. 1 was obtained by reference to the resistance temperature chart which was obtained with great care for the specific heat experiments .
* The results of this comparison will be published later .
Superheating in Continuous-j Calorimetry .
Heating current .
Temp , of oil .
Ribbon resistance .
Ribbon resistance .
Ribbon resistance reduced to 10 ' .
Difference in parts per 10,000 .
amps .
1 *5 9*9 1 -07604 1 -07607 0 2*5 9*9 1 -07601 1 -07604 0 *3 3*5 10 *2 1 -07609 1 -07604 0 3 4*5 11 T 1 -07622 1 -07595 1 *2 5*5 11 *7 1 -07640 1 -07598 0*9 The last two values of the ribbon resistance in Column 4 show the existence of a small superheating of coil No. 1 over the ribbon resistance , but are for heating currents in excess of the greatest used in the specific heat experiments .
The calculations made by Glazebrook , Bousfield , and Smith for my coils were for the maximum current used , which was 8 amperes divided between the two .
This gives 4 amperes for each coil , or 1 ampere for each wire conductor .
Since the ribbon resistances have a cooling surface six times as great as the standard we should expect a difference between the two coils of 5 parts in 10,000 were the Teddington method of stirring followed , while according to the Hendon stirring this should have been 2 parts in 10,000 for a heating current of 4 amperes .
With the method of stirring we used the actual difference is seen to be not over 1 part in 10,000 for a development of heat twice as great .
Taking the probable value for a current of 4 amperes the difference is only 5 parts in 100,000 .
Quite apart from the close agreement of the individual observations of the specific heat of water for widely different heating currents , these comparisons justify me in concluding that the error due to superheating in my platinum-silver resistances is certainly not more and probably less than 1 part in 10,000 , and therefore beyond the limits of error of the method of continuous calorimetry .
|
rspa_1912_0026 | 0950-1207 | On the velocities of ions in dried gases. | 349 | 357 | 1,912 | 86 | Proceedings of the Royal Society of London. Series A, Containing Papers of a Mathematical and Physical Character | Robert Tabor Lattey, M. A.|Henry Thomas Tizard, M. A|J. S. Townsend, F. R. S. | article | 6.0.4 | http://dx.doi.org/10.1098/rspa.1912.0026 | en | rspa | 1,910 | 1,900 | 1,900 | 2 | 6 | 79 | http://corpora.clarin-d.uni-saarland.de/surprisal/6.0.3/?id=rspa_1912_0026 | 10.1098/rspa.1912.0026 | null | null | null | Electricity | 44.853977 | Thermodynamics | 41.739507 | Electricity | [
1.925041913986206,
-69.03311920166016
] | ]\gt ; Velocities of Negative Ions in Dried Hydrogen .
Series .
Imperfectly Dried .
p. These results were obtained with the first filling of gas , after washing out the appalatus several times , and are possibly affected by minute traces of .
They are given here to show the extraordinary effect of small braces of impurity\mdash ; less than 1 in 1000 probably .
The following results were obtained with several different samples of dried hydrogen:\mdash ;
|
rspa_1912_0027 | 0950-1207 | Short index to reports of physical observations (electric, magnetic, meteorological, seismological) made at Kew observatory. | 358 | 359 | 1,912 | 86 | Proceedings of the Royal Society of London. Series A, Containing Papers of a Mathematical and Physical Character | Dr. C. Chree, F. R. S. | article | 6.0.4 | http://dx.doi.org/10.1098/rspa.1912.0027 | en | rspa | 1,910 | 1,900 | 1,900 | 1 | 28 | 676 | http://corpora.clarin-d.uni-saarland.de/surprisal/6.0.3/?id=rspa_1912_0027 | 10.1098/rspa.1912.0027 | null | null | null | Meteorology | 68.510051 | Biography | 18.951566 | Meteorology | [
47.607234954833984,
14.801177978515625
] | 358 Short Index to Reports of Physical Observations ( Electric , Magnetic Meteorological , Seismological ) made at Kew Observatory .
Communicated by Dr. C. Chkee , F.E.S. , by request of the G-assiot Committee .
( Received January 25 , \#151 ; Read February 22 , 1912 .
) A summary of observational data obtained at Kew Observatory used to be given in an Annual Report , which was printed in the Royal Society 's 4 Proceedings ' up to the year 1900 .
From 1901 to 1909 these data were published in the Annual Report of the National Physical Laboratory , of which Kew Observatory then formed a department .
The data for 1910 have been published by the Meteorological Office , which came into occupation of the Observatory on July 1 , 1910 .
As the Reports of the National Physical Laboratory are not unlikely to be overlooked by those whose primary interest is in observational work , the Gassiot Committee decided , in October , 1911 , that it was desirable that a short list of their observational contents should be published in the Royal Society 's ' Proceedings/ The descriptions of the data , which appeared in tabular form in the Annual Reports , are arranged below according to the subject ; when there is no specific statement to the contrary , they refer to Kew Observatory .
References to some of the more outstanding phenomena \#151 ; especially the magnetic storms\#151 ; will be found in the text of the Annual Reports .
Electrical .
Mean hourly values of the absolute potential of the Kelvin " water-dropper " for each month , from 10 quiet days , and , based thereon , mean diurnal inequalities of the potential gradient in the open for the 12 months , three seasons , and the year .
In 1907 , 1908 , and 1909 mean monthly values of " dissipation " of positive and negative electrical charges obtained with an Elster and Geitel apparatus .
Magnetic .
Mean hourly values of declination and horizontal force for each month , from the Astronomer Royal 's " quiet " days , and diurnal inequalities deduced from these hourly means for two seasons ( " summer " and " winter " ) and the-year .
Mean monthly values of inclination and vertical force .
Mean annual values of declination , inclination , horizontal force , an Physical Observations made at Kew Observatory .
359 " vertical force , from all observatories contributing these data to the Kew Observatory .
In 1901 and 1903 , mean hourly values of Falmouth declination and horizontal force , from the Astronomer Royal 's " quiet " days , for 1901 , 1902r and 1903\#151 ; the latter two years in the 1903 volume\#151 ; and diurnal inequalities ( analogous to the Kew ones ) based thereon .
For the same three years particulars of the Falmouth dip observations , and mean monthly values of horizontal and vertical force .
Since 1904 , mean hourly values of Falmouth declination , inclination , , horizontal and vertical force , from the Astronomer Royal 's " quiet " days , and diurnal inequalities of these elements for the year , " summer " and " winter .
" ' ( The 1904 Report also included Falmouth vertical force and inclination hourly means , and inequalities for the year 1903 .
) Since 1903 , results of absolute observations at Valencia Observatory , and monthly and annual means based thereon .
Meteorological .
Monthly mean values and extremes of air temperature and pressure .
Monthly mean values or totals of vapour pressure , cloud , wind velocity , rainfall , duration of bright sunshine .
Information as to prevalence of wind directions and different kinds of weather .
In 1908 and 1909 , earth temperatures at 1 and 4 feet , and measurements of solar radiation with an Angstrom pyrheliometer .
Seismological .
Particulars of the principal movements recorded by a Milne seismograph .
|
rspa_1912_0028 | 0950-1207 | The transmission of cathode rays through matter. | 360 | 370 | 1,912 | 86 | Proceedings of the Royal Society of London. Series A, Containing Papers of a Mathematical and Physical Character | R. Whiddington, M. A.|Sir J. J. Thomson, F. R. S. | article | 6.0.4 | http://dx.doi.org/10.1098/rspa.1912.0028 | en | rspa | 1,910 | 1,900 | 1,900 | 1 | 17 | 410 | http://corpora.clarin-d.uni-saarland.de/surprisal/6.0.3/?id=rspa_1912_0028 | 10.1098/rspa.1912.0028 | null | null | null | Atomic Physics | 26.892467 | Thermodynamics | 23.076171 | Atomic Physics | [
8.632450103759766,
-74.63811492919922
] | ]\gt ; Cathode rays produced within a discharge tube were first led out into the open air successfully by Lenard , who observed that after escaping through a thin aluminium window , they were able to penetrate several millimetres of air at ordinary pressures .
Lenard observed the of his rays in air by making use of the fact that their track was luminous ; in the apparatus indicated in fig. 2 , the range of the rays is deduced from the ionisation they FIG. 2 .
produce .
It is assumed that a cathode particle may be regarded as having been reduced to rest when it has lost the power of ionising , an assumption perfectly legitimate for the present purpose .
* This is more the next paper .
The outside of the chamber and A were charged to a potential of 100 volts , while the collecting electrode was connected to earth through the galvanometer .
From a knowledge of the thickness of the window and the velocity of the incident beam , the velocity of the speediest rays entering the ionisation chamber can be calculated from 3 ) .
It is clear that it is this maximum speed which determines in 4 ) .
The apparatus shown in the figure is capable of being used in two distinct ways .
We can either alter the distance between the plates and note when further increase of at constant pressure produces no increase in ionisation , we keep the distance between the plates constant and determine the lowest pressure necessary to yield the greatest possible ionisation .
The latter method was adopted on account of its greater simplicity .
If is this pressure above which the ionisation is independent of the pressure and is the normal atmospheric pressure , then where is the actual distance between the plates .
Unfortunately , it is impossible to construct rqally satisfactory pressureionisation curves ( as Beatty has done , using secondary cathode rays ) from which to determine with accuracy , the reason being that it.is not possible to keep everything steady long enough to go over the whole curve .
The method finally adopted was to start with the pressur high enough to oompletely absorb the rays and then to exhaust the chamber very gradually .
The galvanometer deflection remains constant until the pressure is ?
when it commenoes to diminish .
By taking the mean of a number of
|
rspa_1912_0029 | 0950-1207 | The velocity of the secondary cathode particles ejected by the characteristic R\#xF6;ntgen rays. | 370 | 378 | 1,912 | 86 | Proceedings of the Royal Society of London. Series A, Containing Papers of a Mathematical and Physical Character | R. Whiddington, M. A.|Sir J. J. Thomson, F. R. S. | article | 6.0.4 | http://dx.doi.org/10.1098/rspa.1912.0029 | en | rspa | 1,910 | 1,900 | 1,900 | 1 | 6 | 67 | http://corpora.clarin-d.uni-saarland.de/surprisal/6.0.3/?id=rspa_1912_0029 | 10.1098/rspa.1912.0029 | null | null | null | Tables | 52.580812 | Atomic Physics | 40.637466 | Tables | [
16.422372817993164,
-83.28237915039062
] | ]\gt ; .
flg .
2 the experimental curves ( Beatty ) for the Fe , , and Sn cathode * are plotted together on the same scale .
It is obvious that all the points - close to a common curve .
therefore , legitimate to assume that .
( 5 ) :blning 4 ) and 5 ) , we have constant , ( 6 )
|
rspa_1912_0030 | 0950-1207 | The emission of electricity from carbon at high temperatures. | 379 | 396 | 1,912 | 86 | Proceedings of the Royal Society of London. Series A, Containing Papers of a Mathematical and Physical Character | J. A. Harker, D. Sc., F. R. S.|G. W. C. Kaye, B. A., D. Sc. | article | 6.0.4 | http://dx.doi.org/10.1098/rspa.1912.0030 | en | rspa | 1,910 | 1,900 | 1,900 | 12 | 312 | 7,357 | http://corpora.clarin-d.uni-saarland.de/surprisal/6.0.3/?id=rspa_1912_0030 | 10.1098/rspa.1912.0030 | null | null | null | Electricity | 40.662146 | Thermodynamics | 33.636644 | Electricity | [
6.530250072479248,
-62.41331481933594
] | 379 The Emission of Electricity from Carbon at High Temperatures .
By J. A. Hakker , D.Sc .
, F.R.S. , and G. W. C. Kaye , B.A. , D.Sc .
( Received January 30 , \#151 ; Read February 8 , 1912 .
) ( From the National Physical Laboratory .
) Introductory .
This paper is a first communication of the results of some experiments conducted in electric furnaces at atmospheric pressure , and mostly at very high temperatures .
The investigation came about originally in an attempt to explain some contamination phenomena which were encountered when short tubes of extremely refractory rare earths were baked in various types of carbon-tube resistance furnaces at temperatures from 1500 ' C. upwards .
An examination of the refractory tubes after baking showed that , in certain circumstances , the outer surface of each tube , instead of having the white and hard appearance of the rest , was carburised and crumbly .
The action was not merely a surface one , but extended to an appreciable depth .
On the other hand , the inner surface of the tube was comparatively unaffected , although it was freely open to the furnace gases , nor did the blackening occur if the tube was shielded .
An explanation which at once suggests itself is that the blackening was produced by particles\#151 ; possibly electrified\#151 ; shot off from the carbon walls of the furnace with sufficient velocity to penetrate the material of the refractory tubes some millimetres ( 4 to 7 ) away .
The circumstances pointed to the desirability of a general study of the electrical properties of the atmospheres of such furnaces .
Historical .
Negative Electricity.\#151 ; So far as we know , practically no experiments have been conducted with carbon at pressures approaching atmospheric , but at low pressures the emission of negative electricity from hot carbon has been investigated systematically by 0 .
W. Richardson ( 1903 , H. A. Wilson ( 1904 ) , f Deininger ( 1907 ) , t and very recently by Pring and Parker ( 1912).S The ionisation currents have been generally attributed to the liberation of corpuscles from the hot carbon ; the magnitude of the * * * S * Richardson , ' Phil. Trans. , ' 1903 , A , vol. 201 , p. 497 ; 1908 , vol. 207 , p. 1 .
t Wilson , ' Phil. Trans. , ' 1904 , A , vol. 202 , p. 243 .
} Deininger , ' Deutsch .
Physik .
Gesell .
, ' 1907 , vol. 9 , p. 674 .
S Pring and Parker , ' Phil. Mag. , ' Jan. , 1912 .
Drs. Harker and Kaye .
The Emission of [ Jan 3fJ effect is largely influenced by the pressure and nature of the residual ga\lt ; Richardson obtained from a carbon filament at low pressures currents from 10-8 to 2 amperes per square centimetre .
He found that the relatioi between ionisation and temperature for carbon ( as well as for some othe bodies ) could be expressed by the formula* i = a where i is the saturated ionisation current , 6 is the absolute temperature and a and b are constants for the substance .
( For carbon , a = 1034 ant b = 98,000 .
) Wilson and Deininger each subscribed to Richardson 's formula ; but Pring and Parker , as the result of experiments on purified carbon at extremely low pressures , impeach the truth of the formula , and affirm that the large ionisation currents obtained by previous observers are due to the emission of corpuscles not from the carbon itself , but rather from some high-temperature reaction between the carbon ( or its contained impurities ) and the residual gas .
Their results show that the negative ionisation from heated carbon falls off continuously both with reduction of pressure and with progressive purification of the carbon .
Positive Electricity.\#151 ; So far as we know , a similar emission of positive electricity has not been detected with carbon at atmospheric pressure . !
But in the case of incandescent metals at atmospheric pressure , Guthrie , !
as far back as 1873 , referred to an experiment which , according to modern views , shows that an iron ball in air at atmospheric pressure emits positive electricity when red hot , and negative electricity when white hot\#151 ; a result now well known .
Elster and Geitel ( 1883 , seqf got much the same sort of effect with a platinum wire at atmospheric pressure ; the ionisation currents were of electrometer magnitude , and their direction and amount were considerably affected by the nature of the surrounding gas .
" Sputtering"\#151 ; The various phenomena are further complicated by the vaporising or " sputtering ' ' of the hot metal or carbon\#151 ; an actual transport of material , which is more marked wrhen the substance is negativel } charged and the pressure is reduced .
The nature of the surrounding gas * Richardson 's formula , though deduced from theoretical considerations , is of the type which was used by Kirchlioff , Rankine , and Dupre to connect vapour pressure ( p ) wit flibsolutc temperature logp = A + B log This latter formula , it may be noted , is elastic and allows considerable latitude in the relative values of the constants without impairing its efficiency .
+ J. J. Thomson ( ' Phil. Mag. , ' 1899 , vol. 48 , p. 547 ) found that a carbon lamp hlamen gave a positive leak so long as occluded gas was being expelled . .
+ See J. J. Thomson 's ' Conduction of Electricity through Gases , ' 2nd edit .
, p. 1 .
a complete bibliography .
1912 .
] Electricity from Carbon at High Temperatures .
381 ilso affects the disintegration considerably .
The carriers appear to consist \gt ; f small molecular aggregates.* In the case of cathodic sputtering , they are legatively charged .
Thus the electrification produced by an incandescent solid is depends on :\#151 ; * 1 .
The nature and temperature of the solid .
2 .
The nature and pressure of the surrounding gas ; and it is evident that the phenomena under the conditions of the present experiment will not be of a simple character .
Experimental .
The type of electric furnace employed in nearly all the present experiments consisted of a straight carbon tube heated by alternating current .
Some of the details of a small furnace of this type are shown in fig. 1 .
A J A r Fig. 1 .
Small model Straight Carbon-tube Furnace , with Pyrometer Sighting Tube and movable Electrode in position for Determination of Potential-current Curves .
* The sputtering of iridium at .temperatures from 1400 ' upwards is notorious , and Fieboul and de Bollemont ( ' Count .
Bend .
, ' Mar. 20 and Oct. 2,1911 ) have recently shown that both copper and silver , when heated in a furnace at temperatures from 500 to 1000 ' C. , give a sputtered image having the outline of the emitting metal on screens up to 2 mm. away in air at atmospheric pressure .
No potential was applied .
The amount of the deposit increases with the temperature and varies with the surrounding gas .
They pu t forward the view that the sputtering is associated with the known emission of positive electricity when these metals are heated .
VOL. LXXXVI.\#151 ; A. 2 D Drs. Harker and Kaye .
The Emission of [ Jan. 30 , second form was made up of a graphite spiral heater having an insulated liner-tube of carbon similar to the conductor used in the first type 0f furnace .
This is illustrated in fig. 2 .
In both furnaces the heater was surrounded by very pure lamp black , with an outer lagging of magnesia brick .
The graphite used in the experiments was the usual grade of Acheson graphite made at Niagara .
In one instance , analysis showed it to be of a purity of about 99-8 per cent , carbon .
The graphite tubes were drilled from solid rods and after a little experience the heating spirals of the second type of furnace were easily cut from the solid to any dimensions by the use GRAPHITE SPIRALLAMP BLACK WATER TUBES CABLES WEIGHTS Fig. 2.\#151 ; Carbon Spiral Furnace , for temperatures up to 2500 ' C. of an appropriate lathe ; graphite , unlike amorphous carbon , is an extremel ) tractable material to machine .
^ ^ The carbon tubes were supplied by the General Electric Company 's Witton Works , Birmingham , and were of a purity higher than the average , but usually contained a little under 1 per cent , of foreign matter ( iron , silica , and alumina ) .
A good deal of this , however , was usually removed previous to use in the experiments by heating for some time to a very high temperature in a current of nitrogen .
The experiments were carried out in the Thermometry Department of t e National Physical Laboratory , where a newly installed plant , specialty designed for electric furnace work , was to hand .
The power supp ies available are a 100 volt D.C. circuit , giving currents up to 600 amperes , an 1912 .
] Electricity from Carbon at High Temperatures .
383 t motor alternator of 15 kilowatts capacity with extra large range of regulation and capable of giving voltages up to 500 and frequencies from 3o"to 200 .
Low-frequency alternating current up to 250 amperes at 30 to 30 cycles at a fixed voltage of about 70 can be got from slip-rings on the motor .
By means of a transformer having a number of variable ratios , alternating current can be obtained up to 250 amperes at 20 volts or 2000 ampeies at 2 volts .
The regulating devices are such that any temperature attainable in a furnace can be kept constant as long as desired.* Many of the details of this unusually complete equipment are due to Mr. C. G. Eden , now of the Aeronautics Division of the National Physical Laboratory .
We wish to acknowledge our great indebtedness to him , not only for his work in this connection , but also for his active co-operation in the earlier experiments .
Potential-current Curves .
The initial experiments were directed to a determination of the current-voltage curves for two insulated carbon rod electrodes projecting within the furnace one from each end , and in alignment , as shown in fig. 1 .
The distance between them could be varied as desired .
By means of copper clips and low resistance leads they were connected at their outer endsf with a battery of variable E.M.F. and a current-measuring device of many overlapping ranges capable of reading from a micro-ampere to 50 amperes .
One electrode was hollow and through it was sighted a Siemens optical pyrometer , suitable for the measurement of temperatures up to 3000 ' C. Access of air to the interior of the furnace was prevented by thin mica windows , and a current of any required gas , in most cases nitrogen , could be .passed through when desired.^ In all the experiments dealt with in this paper , the pressure remained atmospheric .
With small potentials ( up to 6 or 8 volts ) applied to the electrodes , no appreciable current could be detected at temperatures below about 1400 ' C. , but as the temperature rose the current became measurable and rapidly increased until at about 2000 ' it reached a value of several amperes .
The * A detailed description of the furnaces and other electro-technical equipment used in this research is being prepared for publication elsewhere , and to this source reference must be made for further details .
+ The outer ends of the electrodes remained perfectly cool and there was no question of any thermo-electric disturbances between the carbons and the copper leads .
% The passage of a current of gas was absolutely necessary while temperature measurements above 1800 ' were being made , in order to remove the slight fog which always accumulates in the sighting tube if any impurities are present in the carbon .
Drs. Harker and Kaye .
The Emission of [ Jan. 3( highest current recorded was 10 amperes .
Fig. 3 will give a notion of 8om of the curves obtained at different temperatures for electrodes 1 cm .
apart At the lower temperatures the ionisation currents attain\#151 ; curiously enou\lt ; \gt ; ) for such a high pressure and currents of this magnitude\#151 ; what appear to H saturation values with quite small applied voltages .
As far as the experi ments go , the curves at the higher temperatures show the same eharacte 0 volts 2468 Fig. 3.\#151 ; Relation between Ionisation-current and applied Potential for a 1-cm .
gap between the electrodes .
with higher potentials ; with small voltages , there is a linear ielation between potential and current , as will be seen.* Ionisation and Temperature .
The continuous curve of fig. 4 shows a relation between ionisation-current and temperature for an applied potential of 2 volts on a l-cin .
gap betwee * This experiment was shown by Mr. Eden and one of us at the Royal Squety Conversazione of May , 1911 .
1912 .
] Electricity from Carbon at High .
385 the electrodes .
As will be seen , the curve is exponential in character , * but as the currents make no pretence of being saturated , the actual numbers have no great quantitative interest .
Ihe points indicated ( by small ciicles ) were not all obtained in the one experiment but on different days with the same apparatus .
The dotted straight line was obtained by plotting the logarithm of the current against temperature .
2300'C .
-Fig .
4.\#151 ; The full-line curve shows a relation between ionisation-current and temperature for an applied potential of 2 volts on a 1-cm .
gap between the electrodes .
The dotted straight line is plotted from log .
of the current and temperature .
Ionisation Current and Length of Gap .
The table adjoining indicates how the current varies with the distance between the electrodes for an applied potential of 2 volts .
The results are set out in fig. 5 .
The full-line curves are plotted to the left-hand scale of current ; the dotted lines to the right-hand scale .
It will be noticed that the effective resistance of the gap increases , but not very much , with the distance between the electrodes .
The explanation of this is given later , on p. 388 .
* The curve is very fairly represented by \#151 ; 1-55 x 10-se ' , ##M*e , where i is the current in amperes and 6 the temperature on the centigrade scale . .
Drs. Harker and Kaye .
The Emission of [ Jan. 30 APPLIED DISTANCE BETWEEN ELECTRODES h- 2 : U_J ctr id o S p \lt ; M 2 : O l*"iCr .
5.\#151 ; Relation between Ionisation-current and Distance between Electrodes for an applied Potential of 2 volts .
The full-line curves are plotted to the left-hand scale of current ; the dotted lines to the right-hand scale .
Table I.\#151 ; Applied Potential , 2 volts .
Distance between electrodes .
1440 ' C. 1650 ' .
1800 ' .
1850 ' .
1940 ' .
2080 ' .
milli - milli- milli- milli .
millimillicm .
ampere .
amperes .
amperes .
amperes .
amperes .
amperes .
1 0-22 3-40 16 -0 30 -6 96 -2 301 2 0-21 3 T8 14 -8 28 -2 89 -5 278 3 0-19 2-92 13 -6 25 -9 82 -5 261 4 0-18 2-59 12-5 22 -7 72 -5 234 5 0T6 2-20 10 -9 19 -9 65 -2 214 6 0-13 1-75 9-0 16 -5 54 -0 180 2110 ' .
j milli* amperes .
The Magnitude of the Ionisation .
The magnitude of the ionisation currents indicated that , although the pressure was atmospheric , the atmosphere of the furnace was ionised to an unusual degree at high temperatures .
The possibility of some sort o leakage and rectification-effect from the alternating heating current was tested and dismissed , as it was found that the ionisation currents persist 1912 .
] Electricity from Carbon at High Temperatures .
387 when the furnace current was temporarily shut off .
Before testing the effect of temperature in the absence of an external source of potential , we were led to try an experiment in which the furnace tube was heated by direct instead of alternating current .
In these circumstances , we found a decided asymmetry in the amount of the ionisation current , depending on the direction of the external potential ( which amounted to 2 volts ) .
When the potential was such as to tend to send the current between the electrodes in the same direction as the heating current in the furnace tube , the resulting ionisation current was some four or five times bigger than when the external E.M.F. was reversed ; in some cases the inequality was even more marked .
Hot only that , but the reading of the current-measurer was always in the same direction , no matter which way the outside battery was connected , i.e.the potential collected by the electrodes from the furnace was greater than the applied voltage .
The outside battery was accordingly cut out , and the galvanometer now revealed currents of from 8 milli-amperes with a furnace temperature of 1660 ' to 34 milliamperes at 1770 ' .
The explanation is , doubtless , the greater electrical emissivity of the negative end of the furnace tube as compared with the positive end .
The electrode within the negative end of the furnace becomes negatively charged with respect to the other electrode , and the resulting potential difference assists or retards the applied E.M.F. in a way which agrees with that actually found .
Hot and Cold Electrodes .
The next step was to try the effect of temperature alone in the absence of any directive influence of the heating current .
Accordingly , one of the two insulated carbon electrodes was mounted as before within the central hot region of the alternating current furnace , while the other was arranged on a sliding carriage , so that ( with a travel of about 6 inches ) it could , at will , be placed either near the fixed electrode or some distance away , in the cooler part of the furnace tube .
Thus , each time the movable electrode was shifted a large difference of temperature ' existed temporarily between the electrodes , and this manifested itself in the ammeter in the circuit as a transient current , which at 1400 ' amounted to 2 milliamp\amp ; res , and increased to nearly 2 amperes at 2500 ' C. When the movable electrode was pushed in , the current attained its maximum value pretty rapidly and died away as the two electrodes assumed the same temperature .
The direction of the current was such that the cooler inserted electrode was positive with respect to the hotter fixed electrode .
When the movable electrode was withdrawn into a cooler part of the furnace a current was again generated , but in the reverse direction .
Such a reversal would / Drs. Harker and Kaye .
Emission of [ Jan. 30 , .
naturally not follow if the electrodes alone were concerned , but is easily explained if the furnace tube is taken into account .
For the radial distance between the electrodes and the furnace tube was only some 8 mm. ; so that , when the electrodes were separated , the easier path for the ionisation current was to bridge the two gaps between the electrodes and the furnace tube rather than cross the gas separating the electrodes .
The hot fixed electrode remained at the same temperature ( and potential ) as the surrounding furnace tube and played no direct part in generating the current , but the hot movable electrode after being moved outward would emit negative electricity to the colder furnace tube , resulting in a reverse ionisation current as found.* Similar results were obtained when the movable electrode was made the fixed , and vice versa , and there was little difference in behaviour if graphite electrodes were substituted for carbon .
In view of the above explanation we carried out a pair of experiments , in \#166 ; one of which the inner ends of the carbon electrodes were inserted into carbon blocks of larger diameter , so that the distance between the electrodes and the furnace walls was reduced from about 8 mm. to 3 mm. In the other experiment the blocks were removed .
Keeping the same distance between the electrodes , we found , as we expected , a larger ionisation current when the blocks were present than when they were absent .
The currents were also of much longer duration owing to the extra time the blocks took to heat up and cool down .
The part the furnace tube plays in these experiments explains the comparatively small variation of the resistance of the gap between the electrodes with its length ( see p. 385 ) .
The foregoing experiments were simplified by making a " poker of a closed hollow carbon ( or graphite ) tube with an insulated co-axial rod of the same material inside it .
When this was inserted into the furnace the outer sheath became hot first and a current passed across the intervening gas in the usual direction , from the cold rod to the hotter tube .
In several of these poker experiments we noticed a small initial " reverse current , which soon died away and changed into a large current in the usual direction .
This reverse current is doubtless due to positive ions which were emitted at the lower stages of the heating .
The effect was not always obtained , and our experience up to now in these and further experiments has been that it is most marked with new carbon and diminishes with repeated heating .
This is also the experience of workers with other substances than carbon ; many experimenters , indeed , maintain an intimate connection * By means of a device giving a suitable periodic movement to one electrode , a ciuitnt generator constructed on this principle was shown at the reading of the papei .
I9i2 J Elccti'icity from Cavbon cti Hic/ h 389 between the emission of positive electricity and the evolution of absorbed " ases , such as CO. In the case of carbon it may be related to the expulsion of some of the gaseous or more volatile impurities .
Non-electric Heating .
We felt that it would be of distinct interest to try to get some of the results put out above by methods of heating other than electric .
The poker experiment last referred to was accordingly repeated , using a M4ker gas furnace giving a temperature of about 1600 ' C. The largest negative* current obtained was 10 milliamperes .
Positive currents as large as 20 milliamperes were also recorded , but owing to the oxidising nature of the atmosphere some combustion of the outer carbon tube occurred , and the results were at times a little obscure .
A second arrangement was tried in which the outside of a small poker ( constructed essentially as before ) was subjected to the flame of an oxy-acetylene burner .
This has a temperature of some 2400 ' C. at the tip of the inner cone and is the hottest of all known flames .
The heating was uneven and the currents obtained were unsteady ; the highest value was about 1 milliampere in the usual direction , with occasional small " positive " currents . !
IPciter-cooled Electrodes .
We were now naturally desirous of converting the transient currents of the above experiments into steady currents , and to this end the following new arrangement was employed .
An insulated brass tube , through which was sent a rapid current of water , was arranged along the axis of the furnace , and formed a cold electrode .
The hot electrode was a surrounding co-axial insulated carbon tube , which received its heat from the furnace .
The radial distance between the electrodes , both of which were stationary , was about 5 mm. and into this space hydrogen was continually passed , as it is known that this gas facilitates the passage of ions .
As before , the electrodes were connected externally through a current-measurer and no potential was applied .
The observations for a steadily rising temperature are shown in fig. G. The carbon electrode was new and the first current recorded by the galvanometer was one which would be produced by positive ions crossing from the hot to * l.e. , in the usual direction , from the cold electrode to the hot across the gap .
+ We have since found that Dubs tried a similar experiment as long ago as 1888 ( Jentralblatt .
f. Elektrotechnik , ' vol. 10 , p. 749 ) .
He played a blowpipe flame on the lower of two carbon plates , one above the other and 1 mm. apart , and found ( by the use of a " galvanoscope " ) that a weak current flowed from the cold to the hot plate across the gap .
The effect was less with copper plates and was not detectable with iron .
Drs. Harker and Kaye .
The Emission of [ Jan. 30 .
the cold electrode ( see p. 388 ) .
Afterwards the current reversed , attained maximum in 17 minutes , and then dropped considerably .
From 22 minute onwards the current progressively increased with temperature and was in tin neighbourhood of 0'4 milliampbre for the last five minutes of the run , wind had to be terminated owing to overheating of the furnace transformer , wliid at this stage was being greatly overloaded .
On taking down the apparatus , tht brass tube was found to be coated over most of its length with a deposit 0 carbon thick and coherent enough to be slid off in short lengths .
Towards ont NEW CARBON ELECTRODE DISTANCE BETWEEN ELECTRODES5mm .
q : 200 \lt ; zlOO 5 min s. 10 15 20 25 30 35 TIME Fig. 6.\#151 ; Relation between Ionisation current and Time with a steadily rising Temperature .
The " cold " electrode was water-cooled ; the " hot " electrode was of new carbon .
No potential was applied .
end of the tube the deposit was rarer and whitish\#151 ; presumably silica .
T his evidence of the distillation of both silica and carbon at atmospheric pressure is important .
We associate the maximum negative current shown in fig. 7 with the passage of silicon and other impurities which are volatilised at about 2000 ' C. out of the carbon electrode .
On a second heating , the maximum does not occur , and the ionisation current increases steadily with temperature .
The transference of carbon from the hot electrode to the cold may pio\e to be a complete explanation not only of the contamination phenomena men tioned on p. 379 , but also of the comparatively Vge accompanying currents .
The point is being worked at and , should it appear that the ionisation currents 1912 .
] Electricity from Carbon at High Temperatures .
391 are due almost wholly to carbon vaporised or sputtered in this way , the experiment could probably be modified so as to yield an average value of the ratio of the charge to the mass for the carriers concerned .
It was apparent that the comparative smallness of the ionisation currents in the last experiment was due to insufficient temperature-difference between the electrodes , and steps were taken to remedy this .
The furnace tube was taken out , and thinned over a short central region so as to render the heat , with the power available , more local and intense .
The transformer was fitted with an air blast arrangement to keep it cool .
The walls of the outer carbon electrode ( which were rather thick ) were also thinned considerably over the central region .
In the new run , neither positive rays nor a " negative " maximum was detected , but there was a general increase in the negative ionisation , the highest steady value being about 20 milliamp\amp ; res with the furnace near its upper limiting temperature of about 3000 ' C. A copious supply of hydrogen was found to be beneficial ; the flow required nice adjustment , as too much gas cooled the furnace and was as bad as too little .
The Gas between the Electrodes.\#151 ; Some interesting results came to light when the gas between the electrodes was varied .
The following figures are abstracted from the note book Eough value of temperature of hot electrode.* Atmosphere .
Hydrogen .
Nitrogen .
Residualf furnace gas .
'c .
2000 ?
milliamperes , 10 milliamperes .
9 milliamperes .
6 2300 ?
17 12 10 2400 ?
19 14 12 2500 ?
20 13 15 * In this particular arrangement , temperature measurements of any sort were very uncertain , and the figures given above must be considered only as the roughest estimates , t Neither H2 nor N2 was supplied .
So far as these experiments go , there is not much difference between nitrogen and hydrogen at the lower temperatures ; there is more at higher temperatures .
But perhaps the most interesting feature of the observations is the large momentary increase in the ionisation that was obtained when a new gas was admitted into the space between the electrodes , e.g. , when hydrogen was admitted the current would leap up momentarily to half as much again as its ultimate steady value .
The same thing occurred when nitrogen was the new gas .
Now it is well known that acetylene , cyanogen , Drs. Harker and Kaye .
The Emission of [ Jan. 30 , methane , etc. , can be synthesised at such temperatures , and it seems probable that on the entry of a new gas into the furnace momentary synthesis occurs when the proportions of the components are favourable , and that this production of C2H2 , CH4 , C2N2 , 1sTH3 , or the like , is evidenced by an increase in the ionisation of the atmosphere .
We hope to investigate this point further .
This particular experiment terminated eventfully in the fusion of the brass tube electrode .
It was interesting to note that most of the water which streamed into the furnace ( which was then at about 3000 ' C. ) was immediately dissociated into hydrogen and oxygen , which burnt at one end of the furnace in a large blue flame , 2 feet long , coloured green at times with the vapour of brass .
Later Experiments .
In order to enhance the effect still further we have tried various modifications of the apparatus .
To augment the electrode difference of temperature the hot electrode was removed , as we found that with alternating heating current the furnace tube could without prejudice be used as the hot electrode , provided , of course , that the " ionisation circuit " was carefully insulated .
The brass water-cooled tube was sheathed with a larger carbon tube which served as the cold electrode , the whole being mounted as before along the axis of the furnace .
The general cooling of the furnace was reduced in consequence , and with this arrangement we have obtained in different experiments steady currents of as much as 0*8 ampere for a few minutes , 0*2 ampere for half an hour , and 0T ampere for over an hour .
Tig .
7 illustrates one run obtained in a nitrogen atmosphere with new carbon electrodes .
As the temperature rose , an initial small positive current of a few micro-amperes was succeeded by a large negative maximum amounting to 0'8 ampere .
This diminished afterwards to about 0'1 ampeie , and at this stage the furnace temperature was steadied , and a constant ionisation current was obtained for over an hour , in fact , until the experiment was arrested .
The potential difference which developed between the electrodes during this time amounted to 1*8 volts .
While the large negative maximum was being recorded we noted that the blue flame of the escaping gases from the furnace tube was tinged yellowish\#151 ; an effect attributed to silica vapour which was carried along with the stream of gas .
The yellow colour disappeared when the current dropped to its steady value .
On a second run with the same apparatus neither positive lays no a negative maximum was observed .
1912 .
] Electricity from Carbon at High Temperatures .
20mins .
40 60 80 100 120 TIME Fig. 7.\#151 ; Relation between Ionisation current and Time for two new Carbon Electrodes , one hot , the other water-cooled .
No potential was applied .
The temperature was rising for the first 50 minutes and was afterwards steady .
Discussion .
Although we have not as yet any definite knowledge of the nature of the carriers of electricity concerned in the foregoing experiments , we should like to offer a few comments on the results .
It may be that these carriers are almost wholly sputtered solid matter and that corpuscles do not play a great part in the phenomena as they do at low pressures .
According to Richardson , the ionisation currents obtained with carbon in high vacua are due solely to the emission of corpuscles ; the only part the surrounding gas plays is to become ionised by collision and so augment the current .
In some of the present experiments no potential was applied to the electrodes , and if the corpuscles owe their velocity of emission only to the temperature , such velocity at 3000 ' C. , for example , is about 3 x 107 cm .
per second* ( assuming with J. J. Thomson the applicability of the gas laws and the kinetic theory to the unattached electrons which are disseminated through solids ) .
This speed is a very slow one : corpuscles liberated by ultra-violet light are more than 10 times , cathode rays over 100 times and some / 8-rays nearly 1000 times as fast .
In gases at atmospheric pressure the free path of such * Equivalent to a potential fall of about \#163 ; volt .
394 Drs. Harker and Kaye .
The Emission of [ Jan\gt ; 3o unencumbered electrons would be very small indeed , and their ability to ionise by collision would be negligible according to present theory .
\ye have , of course , to remember that a rise of temperature produces a fall 0f density , with a corresponding increase in the free path , e.g. , at 2000 ' C. the " effective " pressure is reduced to about l/ 8th ; at 3000 ' C. to 1 / 11th Experiments with a vacuum furnace would probably throw much light on the matter , and such experiments are now in progress in a furnace in which the prevailing pressure can be adjusted to any desired value .
As we have remarked elsewhere , our largest ionisation currents appear to be associated with the expulsion of impurities in the carbon , and probably the magnitude of the effects wTould be modified if impurities were wholly absent .
Carbon has the faculty of holding tenaciously enormous amounts of foreign matter , particularly occluded gases , and if the evolution of these impurities* goes hand in hand with the emission of negative electricity some ultimate steady fatiguing of the carbon should be found .
Our experience does not enable us to say whether this is so ; up to now we have noticed nothing of the kind .
Much the same ideas have been expressed by Messrs. Pring and Parker in their paper already referred to .
In this connection reference should be made to an important paper by W. C. Arsem in vol. 20 of the ' Transactions of the American Electrochemical Society , ' in which the relation between the rate of graphitisation of carbon and its contained impurities is thoroughly studied .
The view hitherto held that graphitisation of carbon is generally accelerated by the presence of impurities such as iron oxide derives no support from his experiments .
Apropos of the effect of impurities , the large currents obtained by Pdchardson with an over-run carbon glow-lamp may be largely due to the ejection at such a high temperature of the various impurities contained in the carbon and binding material of the filament .
It is well known that , in lamp practice , it is only of recent years that it has become customary to heat carbon filaments either before or after mounting ( except during the flashing process ) to much more than about 1700 ' C. , at which temperature some of the possible contained impurities are only slightly volatile .
We hope to repeat all the present experiments with spectroscopically pure carbon and graphite .
In considering the chemical side of the phenomena described in this paper , it should be remembered that the relative activity of various gases * Cunningham ( 'Phil .
Mag. , ' 1905 , vol. 9 , p. 193 ) found that an electric discharge at low pressures was transmitted more easily by nitrogen freshly expelled from cat bon than by ordinary nitrogen .
1912 .
] Electricity from Carbon at High Temperatures .
395 changes rapidly with temperature .
For example , C02 at 2500 ' behaves as an energetic supporter of combustion , and acts on carbon not very differently from oxygen at low temperatures .
Nitrogen , which at ordinary temperatures is regarded as inactive , becomes , at high temperature , an agent of attack for many metals and other substances .
Many compounds , such as steam , cannot exist at really high temperatures , and are probably completely dissociated .
It may be noticed , in passing , that the experiments set out above , in which no potential was applied , afford an interesting example of the Thomson effect for a vapour .
The currents brought about by the potential gradient flow in the direction opposite to the heat flow .
In the case of carbon " vapour " this agrees with what is known for the solid .
It is worth recording that the atmosphere of the furnace appeared , as far as could be seen , to be perfectly clear when the carbon " vapour " was crossing the space between the electrodes .
It would at once occur to anyone who had been occupied with considerations such as have been detailed in this paper that it might be possible to construct on some such lines a generator of electricity which would depend directly upon combustion at high temperatures ; and , naturally , this is an aspect of the question of which we have not lost sight .
Summary .
An investigation into the electrical properties of the atmospheres of carbon-tube resistance furnaces has been undertaken at temperatures from 1500 ' to 3000 ' C. , and at atmospheric pressure .
( 1 ) Potential-current curves have been derived by the use of two exploring electrodes of carbon or graphite .
At high temperatures , currents up to 10 amperes were obtained with the application of quite small potential differences ( up to 8 volts ) between the electrodes .
The ionisation increases exponentially with the temperature .
( 2 ) In the absence of any applied potential a reversible transient electric current was obtained by keeping one of the electrodes fixed in the furnace and heating or cooling the other electrode by moving it in or out of the hot region of the furnace .
The highest current thus obtained was nearly 2 amperes .
The production of an alternating current was thus rendered possible by the use of a suitable periodic device .
( 3 ) If both electrodes are stationary in the furnace and one is kept permanently hot and the other ( by water-cooling ) permanently cold , a continuous current can be maintained without applying potential , e.g. , a steady current of 0'8 ampere has been obtained for a few minutes , and 0T ampere for over an Mr. F.B. Pidduck .
[ Feb. l , hour .
These are " negative " currents , they flow from the cold to the ho electrode across the gap .
Their magnitude is somewhat greater in hydros !
than in nitrogen .
( 4 ) These large negative currents appear to be intimately associated with the transit across the electrode gap , first of the impurities in the carbon , anc afterwards of the carbon itself .
( 5 ) Small " positive " currents of a few micro-amperes have been detected with new ( but not with old ) carbon electrodes at the lower stages of the heating .
( 6 ) Some of these effects have also been obtained from non-electric sources of heat .
The Wave-Problem of Cauchy and Poisson for Finite Depth and slightly Compressible Fluid .
By F. B. Pidduck , M.A. , Fellow of Queen 's College , Oxford .
( Communicated by Prof. A. E. H. Love , F.R.S. Received February 1 , \#151 ; Read February 22 , 1912 .
) 1 .
Introduction .
The present paper is in some respects a completion of a former paper* on water waves resulting from a given disturbance .
The following article is devoted to a numerical discussion of a solution , previously given , of the normal Cauchy-Poisson problem for finite constant depth of fluid .
The last part of the paper contains a detailed treatment of compressible fluids , with a view to elucidating the initial stages of the spreading out of a disturbance initially confined to a limited region of the fluid .
It is found that a very general case of propagation is capable of formal solution .
2 .
Numerical Discussion of the Cauchy-Poisson Problem for Finite .
The serial solution given in the previous paper lends itself to a certain extent to numerical treatment , though not so well as for the case of infinite depth , which has been so completely discussed by Lamb.f In the general case there does not seem to be any general transformation to facilitate the calculation , so that we have to rely on the direct use of the series .
The solution referred to may be briefly recapitulated as follows:\#151 ; * ' Roy .
Soc. Proc. , ' A , 1910 , vol. 83 , p. 347 .
t H. Lamb , 'Proc .
Lond. Math. SocSeries 2 , 1904 , vol. 2 , p. 371 .
|
rspa_1912_0032 | 0950-1207 | On the devitrification of silica glass. | 406 | 408 | 1,912 | 86 | Proceedings of the Royal Society of London. Series A, Containing Papers of a Mathematical and Physical Character | Sir William Crookes, O. M., For. Sec. R. S. | article | 6.0.4 | http://dx.doi.org/10.1098/rspa.1912.0032 | en | rspa | 1,910 | 1,900 | 1,900 | 3 | 44 | 1,021 | http://corpora.clarin-d.uni-saarland.de/surprisal/6.0.3/?id=rspa_1912_0032 | 10.1098/rspa.1912.0032 | null | null | null | Thermodynamics | 80.004486 | Optics | 8.932327 | Thermodynamics | [
-4.74544620513916,
-49.69612503051758
] | 406 On the Devitrification of Silica Glass .
By Sir William Crookes , O.M. , For .
Sec. R.S. ( Received February 15 , \#151 ; Read March 7 , 1912 .
) The use of apparatus blown and worked from melted quartz is now almost universal in chemical laboratories , especially where temperatures are required above the heat at which glass softens .
When working at fairly high temperatures , I was inconvenienced by the leakage of air through silica glass.* The apparatus ( fig. 1 ) was in the form of a perfectly clear and transparent tube , 1 cm .
diameter and 20 cm .
long , with a bulb cm .
diameter blown on the end .
The other end of the silica tube was drawn out for connecting with the pump and sealing .
It was exhausted to a high vacuum and heated to near redness along its whole length to remove any gas that might be condensed od the walls\#151 ; it was then sealed off .
Fig. 1 .
The tube was placed bulb uppermost in an electric resistance furnace in such a position that the bulb would be at the point of greatest heat , the lower part of the tube remaining comparatively cool ; it was kept at a temperature of 1300 ' for 20 hours , at the end of which time the silica tube was removed from the furnace .
The long continued high temperature 1 , * Jaquerod and Perrot have shown that fused silica is permeable to helium and hydrogen at a low red heat ( 'Oomptes Rendus , ' Nov. , 1904 , vol. 139 .
p. 789 ; and Jan. 1907 , vol. 144 , p. 135 ) .
On the Devitrification of Silica Glass .
caused the bulb and the upper part of the tube to devitrify , and become white and translucent like frosted glass .
The sealed-off end was carefully opened , and it was apparent that the inrush of air was by no means so strong as it would have been had the vacuum been as perfect as it was when the tube was sealed up .
This looked as if there had been a considerable amount of leakage through the devitrified bulb , and I tried a test experiment .
The tube was again attached to the Sprengel pump , and exhausted to as high a point as possible .
During the progress of exhaustion , when the pump was rattling with the characteristic sound of a high vacuum , a large and powerful Bunsen flame was used to heat the bulb .
Not the least difference in the sound could be distinguished .
When the vacuum was at its highest the tube was sealed off ; it was put into the electric furnace , and kept at a temperature of 1300 ' for 11 hours .
After cooling , the end of the tube was broken off under mercury .
The mercury rose , but did not fill the bulb .
The amount that entered was measured , and found to be 17*75 c.c. Afterwards the tube and bulb were completely filled with mercury , the whole again measured , and the capacity of the tube and bulb was found to be 19*25 c.c. , showing that 1*5 c.c. of gas , or 7*79 per cent , of the tube 's capacity , had leaked through the devitrified silica in 11 hours at 1300 ' .
To ascertain if air would leak through the devitrified silica at the ordinary temperature a facsimile of tube and bulb was made in glass , and the two tubes were simultaneously exhausted on the pump .
They were both heated , allowed to cool , and sealed off at the same time .
The silica and glass tubes were put in the balance case and kept there for some time .
When they were both at uniform temperature the silica tube was weighed .
The tube and weights not being moved in the meantime , weighings were taken hourly , the balance being untouched during the intervals .
In 18 hours the weight increased 0*048 grain .
After the silica and glass tubes had been at rest for some days , they were opened simultaneously under mercury .
The glass tube filled at once , only a microscopic bubble of air remained at the top .
The silica tube , on the contrary , only partially filled , and , on measuring the mercury that entered , it amounted to 10*15 c.c. , the capacity of the tube being 19 c.c. Therefore , in a few days , air to the amount of 46*58 per cent , of the total capacity of the apparatus had leaked in .
A micro-photograph was taken of the surface of the devitrified silica bulb ( fig. 2 ) .
It showed a surface cracked all over into the appearance of cells , and , on closer examination , many of the cells showed decided hexagonal outline .
On the Devitrification of Silica Glass .
Fig. 2 .
Fig. 3 .
I observed a similar appearance a few years ago , when a silica dish , originally clear and transparent as glass , was used for evaporating down about 100 mgrm .
of pure radium bromide .
Patches appeared on the bottom having a dull , roughened appearance , and , on examination under the microscope , the appearance was very similar to the surface of the devitrified silica bulb just described ( fig. 3 ) .
The appearances are so alike that it is legitimate to assume that the same cause had been at work , and that devitrification of the surface is produced both by exposure to a very high and long continued temperature and to the contact with a radium salt at a temperature of boiling water .
I have not seen this effect on the surface of glass or silica bottles in which radium salts have been kept in the cold for some years .
|
rspa_1912_0033 | 0950-1207 | Experimental work on a new standard of light. | 409 | 410 | 1,912 | 86 | Proceedings of the Royal Society of London. Series A, Containing Papers of a Mathematical and Physical Character | W. A. Harwood|J. E. Petavel, F. R. S. | experiment | 6.0.4 | http://dx.doi.org/10.1098/rspa.1912.0033 | en | rspa | 1,910 | 1,900 | 1,900 | 1 | 34 | 989 | http://corpora.clarin-d.uni-saarland.de/surprisal/6.0.3/?id=rspa_1912_0033 | 10.1098/rspa.1912.0033 | null | null | null | Thermodynamics | 22.894581 | Biography | 17.386679 | Thermodynamics | [
8.190852165222168,
-19.946958541870117
] | 409 Experimental Work on a New Standard of Light .
By W. A. Hakwood and J. E. Petavel , F.E.S. ( Received January 10 , 1911 , \#151 ; Read March 21 , 1912 .
) The competition between flame and incandescent standards of light , which has existed almost since the necessity for a standard began to be realised , has resolved itself for the time being into a compromise , so that , while Europe continues to employ the flame standard and America the electric glow-lamp , the relation of these two has been accurately determined , and they are now expressible in terms of the accepted International standard candle.* This state of affairs , however , can hardly be considered as final , and effort has not altogether ceased to be directed towards finding some standard free from the defects of those at present in use .
The following is an account of the results of an examination of an incandescent standard proposed some years ago.f In bringing forward the original proposal , a review of the state of the / subject led to the following conclusions :\#151 ; ( 1 ) The Violle molten platinum standard is satisfactory as an absolute standard of reference .
( 2 ) The flame standards are the most convenient for general use , and are of sufficient accuracy for commercial purposes .
( 3 ) The secondary standard , intended to serve as a go-between from the absolute to the commercial standards , are in the least satisfactory state of the three .
The sets of Fleming large-bulb glow-lamps , which are now so largely used , are subject to a gradual decay and to the multiplication of photometric errors by successive inter-comparison .
The suggested new standard was intended to fill the gap , by providing a single apparatus , which should be free from the above defects .
The principle upon which it was based consisted in taking the quality of the radiation itself as the criterion by which the temperature of the radiator was regulated .
The sensitiveness and accuracy of the spectrophotometer and spectro-bolometer proved to be insufficient for this purpose , and the analysis of the radiation was obtained by making use of the selective absorption of black fluorspar and water , the former of which transmits essentially radiation of long wave-length , to which the latter is nearly opaque .
The method used may be described as follows : The electric radiator consists of a wide strip of metal placed behind a water-cooled diaphragm .
Two thermopiles , connected in opposition , are placed on the right and left of * ' Phil. Mag. , ' August , 1909 , vol. 18 , p. 263 .
t ' Electrician , ' April 10 , 1903 , vol. 50 , p. 1012 .
410 Experimental Work on a New Standard of Light .
the axis of the photometer , and receive respectively the radiation passing through a plate of black fluorspar and through a water-trough .
As the temperature of the radiating strip increases , the percentage of the total radiation which penetrates the water will increase , and the percentage which penetrates the fluorspar will decrease .
At some temperature the two will be equal , and the electromotive force in the galvanometer circuit will therefore fall to zero .
This zero point may be used to fix the standard temperature .
The choice of a suitable material for the radiator offered some difficulty .
The emissivity of the oxides of the rare earths alters under prolonged heating , and only the metals of the platinum group will withstand exposure to air when at a high temperature .
Iridium disintegrates rapidly at temperatures above 1600 ' C. , a continuous stream of black smoke arising from the surface of the metal .
The loss of weight measured on various occasions amounted to about 4 mgrm .
per square centimetre per hour .
The evaporation of platinum is about 10 times slower , but , unless the metal is chemically pure , a gradual change in the texture of the surface produces a variation in the intensity of the light emitted .
After a long series of experiments , chemically pure platinum was chosen as the radiating substance .
The apparatus was first set up , and subjected to tests extending over several months .
The experience thus gained resulted in the construction of a self-contained instrument , the cost of which was defrayed by the Government Grant Committee of the Royal Society .
The platinum strip , 7 x 12 cm .
and about 005 mm. thick , was stretched between two water-cooled clips connected to a low-tension battery through a variable resistance .
The strip was enclosed in a cylindrical water-cooled casing having three apertures .
The light , passing through a diaphragm , was directed on the photometer head , and the radiation emitted from the other side of the same portion of the strip reached the two thermopiles , which were placed at 30 ' to the axis of the photometer .
Careful tests proved that , with suitable precautions , the variations in intensity of the light emitted by such an apparatus will not exceed + 0'5 per cent. , and in this respect the result of the work can be considered entirely successful .
On the other hand , this form of standard is not portable , the intensity of the light emitted is low , its colour unsatisfactory , and , finally , much skill and care is required in the adjustment of the very sensitive thermo-electric circuit .
From a practical point of view , these defects are probably sufficient to outweigh the advantage gained with regard to accuracy , and it is therefore thought unnecessary to give a detailed account of the experimental work .
|
rspa_1912_0035 | 0950-1207 | A critical study of spectral series. Part II.\#x2014;The \lt;italic\gt;p\lt;/italic\gt; and \lt;italic\gt;s\lt;/italic\gt; sequences and the atomic volume term. | 413 | 413 | 1,912 | 86 | Proceedings of the Royal Society of London. Series A, Containing Papers of a Mathematical and Physical Character | W. M. Hicks, Sc. D., F. R. S. | abstract | 6.0.4 | http://dx.doi.org/10.1098/rspa.1912.0035 | en | rspa | 1,910 | 1,900 | 1,900 | 1 | 16 | 417 | http://corpora.clarin-d.uni-saarland.de/surprisal/6.0.3/?id=rspa_1912_0035 | 10.1098/rspa.1912.0035 | null | null | null | Atomic Physics | 47.104032 | Tables | 44.341578 | Atomic Physics | [
22.58838653564453,
-78.17436981201172
] | 413 A Critical Study of Spectral Series .
Part II.\#151 ; The p and s Sequences and the Atomic Volume Term .
By W. M. Hicks , Sc. D. , F.RS .
( Received January 24 , \#151 ; Read March 7 , 1912 .
) ( Abstract .
) This is a sequel to a paper on the same subject published in the ' Philosophical Transactions/ vol. 210 ( 1910 ) .
The sequences which give the principal and the sharp series are discussed as they occur in the second and third groups of the periodic table of the elements , and it is found that the sequences , or types of formulae , which in the alkalies give the principal and sharp series , here give the sharp and principal .
In order to prevent confusion the notation P and S sequence is changed to p and s sequence , the letters P , S , being reserved for principal and sharp series .
Additional evidence is afforded to show that these sequences depend on the atomic volumes of elements in a quite definite way .
An attempt is made to allot the S and D series of europium and of radium .
The spectrum of Eu affords evidence that the element fills the gap between Cd and Hg , and from the series formulae of both elements regarded as functions of their atomic volumes probable values of their densities are obtained , viz. , 12*58 for Eu and either 5*10 or 6*12 for Ra .
Further , the result obtained in Part I , that if the denominator of the p sequence be thrown into the form m + 1\#151 ; W(l\#151 ; m~r ) + fi \#151 ; am"1 the ratio a/ /x , is a constant ( 0*21520 with uncertainty in the last two digits ) , is confirmed for elements of second and third groups .
A comparison of denominators of corresponding orders of P series , and of these with those of S series , gives relations which can be used as tests for their proper allocation in doubtful cases .
In consequence slight modifications are suggested in Paschen 's lists of upper lines of HgP and CaP .
Two appendices are added , one dealing with the S and D series of Eu and Ra , the other giving lists of the S and P series lines treated of , with some historical notes .
VOL. LXXXVL\#151 ; A.
|
rspa_1912_0037 | 0950-1207 | The passage of homogeneous R\#xF6;ntgen rays through gases. | 426 | 439 | 1,912 | 86 | Proceedings of the Royal Society of London. Series A, Containing Papers of a Mathematical and Physical Character | E. A. Owen, B. Sc.|Prof. Sir J. J. Thomson, F. R. S. | article | 6.0.4 | http://dx.doi.org/10.1098/rspa.1912.0037 | en | rspa | 1,910 | 1,900 | 1,900 | 7 | 254 | 5,653 | http://corpora.clarin-d.uni-saarland.de/surprisal/6.0.3/?id=rspa_1912_0037 | 10.1098/rspa.1912.0037 | null | null | null | Atomic Physics | 39.653193 | Thermodynamics | 27.643773 | Atomic Physics | [
45.90694046020508,
-59.97991943359375
] | 426 Mr. E. A. Owen .
The Passage of [ Mar. 11 , These diagrams are shown in order to indicate the possibilities of the instrument .
It is proposed to make a series of tests on the various kinds of metals used in the industries particularly with the object of investigating the region immediately beyond the elastic limit and the effect of suddenly applied loads and loads applied very gradually .
The characteristic of the method of applying the load in all the diagrams shown is that the rate at which the extension of the specimen increases is approximately constant , because the pressure is applied to the straining cylinder of the testing-machine by a ram driven in at a nearly constant rate .
The rate at which the load is applied is therefore variable , as will be understood from fig. 8 .
The scale of the extension can in the particular instrument described be magnified conveniently about eight times , so that it is only suitable for investigations outside the true elastic region .
The author hopes to communicate a paper shortly giving the description of a similar instrument for obtaining automatic diagrams within the elastic region .
The Passage of Homogeneous Rays through Gases .
By E. A. Owen , B.Sc. , 1851 Exhibition Scholar of the University College of North Wales , Trinity College , Cambridge .
( Communicated by Prof. Sir J. J. Thomson , F.R.S. Received February 8 , and in revised form March 11 , \#151 ; Read March 21 , 1912 .
) Introduction .
The phenomena attending the passage of Rontgen rays through gases has been examined by several experimenters .
The relative ionisation produced in different gases was investigated early in the history of Rontgen rays by Perrin* and Rutherford , f and later by Sir J. J. Thomson , J Strutt , S McClung , || Eve,1T Barkla , ** and Crowther.ff Some of these experimenters * Perrin , ' Ann. de Chimie etde Phys./ 1897 , vol. 11 , p. 496 .
t Butherford , 'Phil .
Mag./ 1897 , vol. 43 , p. 241 .
X J. J. Thomson , ' Camb .
Phil Soc. Proc./ 1900 , vol. 10 , p. 10 .
S Strutt , 'Boy .
Soc. Proc./ 1903 , vol. 72 , p. 209 .
|| McClung , ' Phil. Mag./ 1904 , vol. 8 , p. 357 .
IT Eve , ' Phil. Mag./ 1904 , vol. 8 , p. 610 .
** Barkla , 'Camb .
Phil. Soc. Proc./ 1909 , vol. 15 , p. 257 ; 'Phil .
Mag./ 1910 , vol. 20 , p. 370 .
ft Crowfher , ' Boy .
Soc. Proc./ 1908 , vol. 82 , p. 103 .
1912 .
] Homogeneous Rontgen Rays through Gases .
427 allowed the rays to strike the electrodes and the walls of the ionisation chambers ; this gave rise to corpuscular radiation which was totally absorbed in the gas , so that the ionisation observed was higher than the true value , and consequently the apparent relative ionisation was smaller than it should be for those gases in which the ionisation is greater than in air .
Sir J. J. Thomson , McClung , and Crowther took precautions against this source of error , but in every case rays direct from a Eontgen bulb were used , and these rays were necessarily heterogeneous , and the heterogeneity was different in the various bulbs .
In experiments on the relative ionisation in gases by Rontgen rays , not only rays of exactly the same hardness and the same intensity should be used to ionise each gas , but in order to obtain quite definite results it is necessary to use rays of quite a distinct hardness .
Barkla 's discovery of homogeneous rays emitted by different metals when Rontgen rays fall upon them makes it possible to use rays of a definite hardness .
Such homogeneous rays have been used by Barkla to investigate the amount of ionisation relative to air produced in different gases and vapours .
The main object of the following research is to investigate more fully the various phenomena observed when homogeneous rays pass through gases composed of elements in the group in which no appreciable homogeneous radiation has been detected for rays of penetrating power within the range of that of those homogeneous beams emitted by metals of atomic weight from iron to silver .
The gases used are air , carbon dioxide , and sulphur dioxide .
The investigation may be divided into three parts\#151 ; ( 1 ) The absorption of homogeneous rays .
( 2 ) The variation of ionisation with pressure .
( 3 ) The ionisation , relative to air , produced in a gas by rays of different hardnesses . .
Apparatus .
In the present work we deal with narrow pencils of homogeneous Rontgen rays .
It was found very difficult to obtain a sufficiently intense pencil by placing a piece of metal in the path of the rays from an ordinary type of bulb ; in this case only a small solid angle of rays emanating from the anticathode could be utilised to produce a secondary homogeneous beam , and in addition the rays had to traverse the glass wall of the tube and a certain column of air before they fell on the radiator , so that their intensity was greatly diminished .
The problem therefore is to construct a bulb which will allow the primary rays to strike the radiator immediately after they leave the anticathode , and consequently reduce the size of the radiator , Mr. E. A. Owen .
The Passage of [ Mar. 11 , which would still envelop a greater solid angle of rays than would be the case in an ordinary bulb with a much larger radiator .
The following is an account of an attempt made to construct such a bulb which could be used with the same ease as an ordinary type of bulb:\#151 ; The bulb is designed to have the anticathode on the surface .
Since it is to be permanent and capable of being run for any reasonable length of time it is essential that no wax joints be used in its construction .
A glass-metal air-tight joint had therefore to be used .
The joint adopted was that used by Roebuck* in experiments on " The Bursting Strength of Glass Tubing .
" The principle of the method is as follows:\#151 ; A thick glass tube , diameter about 2*5 cm .
, is taken and the outside carefully cleaned .
A coating of platinum is spluttered over this tube for about 5 cm .
of its length .
This is done by brushing over the glass with a water solution of platinum chloride and dextrin containing 1 to 2 per cent , of each ; the tube is then gently heated until the solution dries up , and afterwards it is incinerated in a Bunsen flame .
After this process a thin conducting semi-transparent film of platinum is left on the glass .
To secure a perfectly continuous layer all over the surface , two or three coatings of platinum are added in a similar way .
It is essential to get a continuous layer of platinum on the glass tube , and to get it the glass surface must be very clean ; distilled water should also be used to make up the solution of platinum chloride and dextrin .
The next step is to deposit electrolytically a thick layer of copper on the platinum .
The deposit should be very fine , so as to obtain a smooth surface on the copper .
A very small current is therefore sent through the voltameter .
A layer of copper , about 1 mm. thick , is deposited in this way .
The glass tube is now ready to be soldered on to any metal tube which fits over it .
Preliminary experiments on this method showed that the joint was quite air-tight , even when the metal tube was simply soldered round its edge to the copper layer on the glass .
A large distilling flask , about 20 cm .
in diameter , is taken and a wide piece of thick glass tubing , about 8 cm .
in length , fused to it diametrically opposite to its neck and in line with it .
Over about 5 cm .
of this tube is deposited a thick layer of copper by the above described process .
A brass cap B ( fig. la ) is now put over the end of the tube , the brass tube T fitting over the copper deposit .
The edge of the tube T is carefully soldered on to the deposit on the glass .
The other part of the cap B is a thick circular brass disc having a circular hole , 1 cm .
in diameter , bored at its centre , and which is soldered to the other end of the tube T. Over this hole is soldered a piece of silver foil , thick enough to stop all cathode particles travelling * Roebuck , i Phys. Review , ' 1909 , vol. 28 , p. 264 .
1912 .
] Homogeneous Rontgen Rays through Gases .
429 with a velocity corresponding to an equivalent spark gap of 4 to 5 cm .
The collar W allows cold water to circulate round the tube , thus keeping the joint cool .
This glass-metal joint proved very satisfactory ; no trouble at all was experienced in obtaining it air-tight .
The cathode is slightly concave , so as to tend to bring the rays to a focus on the silver window .
The beam of Rontgen rays emerging from the window can be made very intense , and a very large solid angle of the rays-can be utilised to produce secondary beams .
A silver anticathode is used because a beam of Rontgen rays is required which is sufficiently hard to stimulate the homogeneous beams of metals of atomic weight lower than silver .
It was also preferred to platinum because the latter occludes hydrogen very rapidly when heated , and would therefore be unsuitable for this purpose .
Silver , however , occludes oxygen , but the amount it occludes is inappreciable at the temperature to which the anticathode is raised .
Platinum was not actually tried ; possibly , with good cooling arrangements , it may be used .
The bulb is fitted with a palladium softener and is permanently connected to a Topler pump and charcoal tube .
The equivalent spark gap can be kept quite constant by manipulating the palladium softener and charcoal tube , or , when liquid air is not available , the Topler pump .
The equivalent spark gap was kept at 4*5 cm .
and the coil worked with a Cox mechanical interrupter , which is much more satisfactory than any form of mercury break tried , in that it gives a much steadier discharge .
The bulb was fixed up in a lead box .
The radiators were placed over the silver anticathode , as shown in fig. 1 , and were held always in the same position by a little aluminium frame , which was rigidly fixed to the lead box .
The dimensions of the aperture S in the lead box were 1*5 cm .
by 4*7 cm .
, and the centre of the radiator was about 7 cm .
from it .
A small lead collar , 0*5 cm .
high , was placed 1 cm .
from the centre of the window , to stop any rays direct from the bulb from passing through the aperture S. The beams sent out by the radiators were tested for their homogeneity before the rest of the apparatus was set up .
This was done in the ordinary way , by putting an electroscope in the path of the rays and finding the percentage absorption produced by successive sheets of aluminium placed in front of it .
The required homogeneity was detected .
A standardising ionisation chamber A , with central rod electrode , was placed in the direction of the rays at a distance of about 30 cm .
from the aperture S. The inner surface of the chamber , together with the surface of the electrode , was covered with layers of filter paper , and the rays passed into the chamber through a parchment window .
The electrode was carefully VOL. LXXXVI.\#151 ; A. 2 G 430 Mr. E. A. Owen .
Passage of [ Mar. li } insulated from the chamber and was connected through an earthing key to a Wilson tilted electroscope , the needle of the earthing key being connected to a potential divider .
A second ionisation chamber B , which contained the gases under investigaTo electroscope \amp ; , potential divider r ... .
To dr Fig. 1 .
tion , was placed parallel to the rays and at the same distance from the aperture S as the standardising chamber A. This chamber was 25 cm .
long and contained two parallel aluminium electrodes at a distance of about 4| cm .
apart .
One of these , act , 24 cm .
by 6 cm .
, was raised to a high potential , and the other , 18 cm .
by 6 cm .
, connected through an earthing key to the potential divider and a second Wilson electroscope .
The second of these electrodes was guarded at its ends by two plates of the same width and in the same plane as the electrode , and each 3 cm .
long ; the gap between the plates and the electrode was about 3 mm. wide .
The plates were soldered to the ends of the chamber , which was earthed .
The guard ring served to sweep away all the ions produced by the corpuscular radiation emitted from the ends of the chamber when the rays strike it , and the ions produced in the gas by the Rontgen rays , before coming to the region between the electrodes , aa and bb .
The electrodes , guard plates , and the surface of the chamber were covered with layers of filter paper .
The window through which the rays entered was of parchment , supported by two very thin crosspieces of aluminium .
A lead screen was placed in front of the chamber , having a rectangular aperture in it measuring T8 cm .
square .
A pencil of 1912 .
] Homogeneous Rontg Rays through Gases .
rays from the aperture S would then pass between the electrodes without touching them .
Both of the chambers were made air-tight ; the chamber B was permanently connected to a Topler pump and gauge .
The same specimen of dried air was kept in the standardising chamber throughout the experiment ; the other chamber was filled with the different gases examined , which were carefully dried and purified .
It was found that a potential of about 300 volts was ample to ensure saturation currents in the gases used .
The electroscopes were worked at a sensitiveness of about 60 and 30 divisions per volt respectively .
The readings could be taken very quickly .
A certain fixed deflection was taken in the standardising electroscope in each case , and the corresponding deflection in the other electroscope observed .
The rise of the potential of each leaf was immediately determined with the potential divider ; in this case the error introduced is only that due to the fluctuation of the zero during the interval this potential was determined .
This interval , however , was very short , and the leaves as a rule were very steady .
Absorption Experiments .
The first set of experiments were carried out to determine the absorption coefficient for different homogeneous beams in the three gases , air , carbon dioxide and sulphur dioxide .
A wide brass cylinder , exactly 20 cm .
long , with parchment windows at its ends , was placed directly in front of the chamber B and parallel to the rays coming from the radiators .
It was made air-tight and connected to a gauge and a mercury pump .
A lead screen with a small aperture in it was placed in front of the cylinder , so that only a narrow beam of rays passed through it .
In the case of air and carbon dioxide the absorption of the rays was measured at atmospheric pressure .
The determination of the ionisation in B when the cylinder was evacuated , and afterwards when it was filled with the gas , sufficed to find the coefficient of absorption .
The first reading gives a measure of the initial intensity I0 , and the second , the intensity I after passing through a column of gas 20 cm .
long .
Hence from the formula I = Io6_m , X , the coefficient of absorption in the gas ( at that temperature and pressure ) for the particular type of rays used is directly calculated .
With sulphur dioxide at atmospheric pressure it was found that the absorption was very great for the softest rays used\#151 ; so great that the ionisation produced in the chamber B was almost inappreciable when bulb was run for about one minute .
Readings were consequently taken with diminished pressures in the cylinder .
Plotting the logarithm of the observed Mr. E. A. Owen .
Passage of [ Mar. 11 , ionisation in the chamber B against the pressure of the gas in the absorbing chamber , we get straight lines for all the homogeneous beams used .
These curves are shown in fig. 2 .
60 cm.\#151 ; -p Fig. 2 .
Hence the law of absorption for homogeneous beams in a gas becomes I = I0e-**\gt ; */ * , when p is the pressure of the gas , and r the atmospheric pressure .
From the curves in fig. 2 the absorption coefficient of the rays at atmospheric pressure can be obtained .
The values of the coefficients of absorption , defined in this way , of the respective rays by the different gases at 0 ' C. and 760 mm. are given in Table I ; the mass absorption coefficients are also tabulated for convenience .
Fig. 3 shows the relation existing between the atomic weights of the radiators giving out the homogeneous rays and the mass absorption coefficients of the different rays for any individual gas .
The logarithm of the atomic weight of the radiator is plotted against the logarithm of the mass absorption coefficient .
For each gas , the points lie on straight lines within the limits of experimental error , and these straight lines are parallel to each other .
Hence the absorption coefficients of the different homogeneous 1912 .
] Homogeneous Rontgen Rays through Gases .
433 Table I. Radiator .
Atomic weight of radiator .
tv .
Air .
co2 .
S02 .
A/ p.* A. \/ P. A. A/ p. A. A/ p. c. Mg .
Al .
Fe 55 -9 0 *0254 19 *72 0 *0456 23 *04 0 *2673 91 *2 10 *1 80 88 *5 Ni 58 -7 0 *0186 14 *39 0 *0319 16 *10 0 *1691 57 *73 6*58 51 *8 59*1 Cu 63 -6 0 *0130 10 *08 0 *0227 11 *48 0 *1404 47 *90 5*22 41 *4 47 *7 Zn 65-7 0 *0108 8*41 0 *0184 9*29 0 *1040 35 *49 4*26 34 *7 39 *4 As 75 -0 0 *00592 4*59 0 *00988 4*99 0 *0548 18*69 2*49 19*3 22*5 Se 79 -2 0 *00442 3*43 0 *00782 3*95 0 *0449 15*31 2*04 15 *7 18 *9 Sr 87 '6 0 *00258 2*00 0 *00420 2*12 0 *0272 9*29 \#151 ; \#151 ; \#151 ; Mo 96-0 0 *00166f 1 *29 0 *00281 1 *42 0 *0170 5*81 \#151 ; \#151 ; \#151 ; # Taken from Barkla and Sadler , ' Phil. Mag./ May , 1909 , p. 749 .
f Deduced from the curve .
radiations in air are proportional to the absorption coefficients of those radiations in carbon dioxide or sulphur dioxide .
Barkla and Sadler* found the same proportionality between the absorption coefficients of primary radiation by two elements , provided the primary radiation was not hard enough to excite the characteristic radiation of those elements .
* Barkla and Sadler , 4 Phil. Mag , ' 1909 , p. 739 .
Mr. E. A. Owen .
The Passage of [ Mar. 11 , Hence , generally , if x^a denote the coefficient of absorption of a certain " radiation X in a substance A , whether elementary or compound ( using the notation adopted by Barkla and Sadler ) , xAv _ yAv __ Z^A X^B Y^B Z^B provided the radiations X , Y , Z do not excite the characteristic radiations of the substances A and B. ( When A and B are compounds the law does not hold if the rays excite the characteristic radiation of any one of the elements present .
) The straight lines in fig. 3 incline to the axis of abscissa along which logw is measured , at an angle tan-1 ( \#151 ; 5 ) approximately , so that A/ p = curb ( approximately ) , where c is a constant depending upon the nature of the absorbing medium .
Hence the coefficient of absorption of homogeneous Bontgen radiation in any of the gases investigated is approximately inversely proportional to the fifth power of the atomic weight of the element emitting the characteristic radiation .
It is possible that the absorption of these rays follows the same law universally , whatever the absorbing medium may be .
Taking , for example , the values given by Barkla and Sadler for A/ p in carbon , magnesium , and aluminium for the different rays , w^e find that the same law approximately holds also for these elements in the case of rays of penetrating power from iron to strontium radiation .
It is desirable , however , that rays of a wider range of penetrating power be used before a general conclusion be arrived at , but , for the range of rays examined in the present work , the above relation undoubtedly approximately holds .
Ionisation and Pressure .
When a beam of Bontgen radiation passes through a gas it gives rise to both secondary Bontgen radiation and corpuscular radiation .
With the pressures used in the experiment the corpuscular rays are totally absorbed , but this is not the case with the secondary Bontgen rays .
The amount of secondary radiation produced in these light gases is , however , very small .
Barkla finds that the energy of the secondary radiation proceeding from 1 cm .
length of primary beam passing through air at atmospheric pressure and about 15 ' C. is 0*00024 of the energy of the primary radiation passing through .
Consequently , the amount of ionisation produced by these secondary rays in the chamber is negligible compared with the whole amount of ionisation produced in the chamber .
The only way by which these secondary rays -can give rise to an appreciable amount of ionisation is by the production of 1912 .
] Homogeneous Rontgen Rays through Gases .
435 corpuscular radiation if the rays were allowed to strike the metal electrodes and walls of the chamber .
To avoid this , the electrodes and the walls of the chamber are covered with layers of filter paper .
With this arrangement the amount of ionisation produced by the corpuscular radiation from the electrodes and the walls will be negligible , because the amount of corpuscular radiation sent out from the filter paper is of the same order as the corpuscular radiation produced in the gas , and , further , the corpuscular radiation sent out by the walls on account of the secondary rays penetrating the paper will be totally absorbed in the paper , and therefox*e not allowed to produce any ionisation in the gas .
In each gas there is a correction to be applied to the observed value of the ionisation due to the absorption of the rays in the gas before they reach the central plate electrode , and in the volume of gas under investigation between the electrodes .
These corrections were rather small in air and carbon dioxide , but much larger in sulphur dioxide .
Some of the corrected results obtained with air and carbon dioxide are represented graphically in fig. 4 .
All the curves are straight lines through the origin .
In the case of SO2 the method of procedure was somewhat different .
12 Ionisation Fio .
4 .
Mr. E. A. Owen .
TAe Passage of [ Mar. 11 , On the assumption that the ionisation is proportional to the pressure , it is very easy to calculate what the ionisation should be at any pressure , knowing the dimensions of the electrodes and guard ring and the coefficient of absorption of the rays in the gas .
Suppose a is the distance from the middle of the first gap to the parchment window , and b that of the second gap .
Let I0 be the intensity of the rays on the inner side of the parchment window , and let be the pressure of the gas in the chamber .
If is the coefficient of absorption of the rays in the gas at the given temperature and 760 mm. pressure , The intensity of the radiation at a distance x from the end = I\lt ; )e~Xxpl , r , Ionisation produced at x in small layer dx =2 .
AI TT where A is the ionisation produced by rays of unit intensity in travelling through a unit distance in the gas at atmospheric pressure .
Ionisation produced between the plates = ^AI0 f J a ( g-hap/ it g-Mp/ n'j \#166 ; X i.e. , say , \#166 ; z , where z = \#151 ; g-ASp/ w ( 1 ) The quantity AI0/ X. is a constant for the same gas for any particular type of rays used .
All the quantities in the expression z are accurately determined .
With the aid of these the value of z can be calculated for any pressure .
These calculated values of z , multiplied by a constant , are in very close agreement with the observed values of the ionisation for all the pressures taken .
Some of the curves obtained are shown in fig. 5 .
The agreement which exists between the calculated and observed values justifies the assumption that the ionisation in the gas is proportional to the pressure .
Relative Ionisation .
The ionisations in carbon dioxide and sulphur dioxide are calculated relative to air as a standard .
The chamber B is initially filled with dry air and the ionisation produced in it by each of the homogeneous beams is measured .
Dry carbon dioxide is then substituted for the air , and another series of observations taken with the gas at atmospheric pressure .
In the case of sulphur dioxide , four sets of readings were taken with the gas at different pressures .
For any one definite type of rays we have by equation ( 1 ) for any gas y = z , and for air ya \#151 ; \#151 ; za .
A. Xfl 1912 .
] Homogeneous Rontgen Rays through Gases .
Hence A/ Aa , the ionisation in the gas relative to air for that certain radiation , is equal to y\za/ ya\az , where y and ya are the observed ionisations in the gas and air respectively , X and Xa , the coefficients of absorptions of the rays in the gas and air respectively at the given temperature and 760 mm. pressure .
z and za are expressions defined by equation ( 1 ) .
o ... Observed .
x ... Calculaled .
Fig. 5 .
The calculated values of the relative ionisation for all the different rays are tabulated in Table II .
Within the limits of experimental error , the relative ionisation is constant in the same gas for the range of rays employed .
Knowing the coefficient of absorption of all the rays in the different gases , we can find the relative total ionisation .
For the total ionisation produced in a gas at pressure = ^AI0 f " e-W'dx = 7T J 0 A where A ' is calculated from the values of A given in Table I , allowing for scattering .
Hence T , the relative total ionisation = A A'a/ Aa A ' .
438 Passage of Homogeneous Rontgen Rays through Gases .
Table II .
Relative ionisation in Relative total ionisation in Radiator .
co2 .
so2 .
CO. , .
S02 .
Fe 1 -581 11*34 0*90 1 *07 m 1 *546 11 *57 0*88 1 *25 Cu 1 *552 11 *84 0*89 1*08 Zn 1-538 11 *52 0*91 1*18 As 1 *510 11 *73 0*91 1 *22 Se 1 *533 11 *76 0*86 1 *11 Sr 1 *527 11 *81 0*94 1*04 Mo 1 *541 11 *45 0*92 1*00 Table II gives the values of T calculated from this formula .
It is observed that for the same gas the relative total ionisation is approximately constant for the range of rays used .
There is a very great difference between the values of the relative ionisation in the two gases , but the difference between the relative total ionisation is comparatively small .
It appears , therefore , that for these light gases\#151 ; the characteristic radiation of whose constituent elements has not been detected\#151 ; the total number of ions produced by homogeneous beams of equal intensity is approximately the same in each gas for any particular type of rays .
Summary .
( 1 ) The absorption of the different homogeneous radiations in a light gas , such as CO2 or SO2 , is proportional to the absorption of those radiations in air .
( 2 ) The absorption of homogeneous radiation in a gas is proportional to the pressure of that gas .
( 3 ) For the homogeneous rays emitted by metals of atomic weight ranging from that of iron to that of molybdenum , the coefficient of absorption in the gases investigated is approximately inversely proportional to the fifth power of the atomic weight of the radiator which emits that characteristic radiation , i.e. A , oc w~5 .
( 4 ) The amount of ionisation produced in a thin layer of a gas is directly proportional to the pressure of the gas .
( 5 ) The ionisation relative to air is approximately constant in the same gas for the different homogeneous rays .
( 6 ) The total number of ions produced by homogeneous beams of equal Fluorescent Rontgen Radiation .
439 intensity is approximately the same in each gas for any particular type of rays .
In conclusion , I wish to acknowledge my indebtedness to Prof. Sir J. J. Thomson for his kindly interest and helpful suggestions throughout the course of the investigation .
Fluorescent Rontgen Radiation from Elements of High Atomic Weight .
By J. Crosby Chapman , B.Sc. , Layton Research Scholar of the University of London , King 's College ; Research Student of Gonville and Cains College , Cambridge .
( Communicated by Prof. Sir J. J. Thomson , F.R.S. Received February 8 , \#151 ; Read March 21 , 1912 .
) A considerable amount of work has been done by various experimenters* showing that , when an element of higher atomic weight than calcium is subjected to a suitable primary beam of X-rays , the rays which leave the radiator consist of two types : firstly , the purely scattered radiation , which is almost exactly similar to the incident beam , and , secondly , a characteristic homogeneous radiation .
The scattered radiation which in the case of a primary beam from an X-ray bulb is heterogeneous , is , with elements of low atomic weight , quite small in intensity when compared with the intensity of the homogeneous radiation which is emitted simultaneously .
Owing to this fact , it is comparatively easy to prove that the elements with atomic weights between that of calcium and cerium give off when stimulated with X-rays homogeneous beams , and the hardness of the characteristic radiation from each of these elements has been measured by determining the absorption in aluminium .
The radiations are usually defined by the value of their absorption coefficients , that is , by X/ p where I = I0e"Ax ; p = density of aluminium .
Using the values obtained , it is possible to plot a curve showing the relation between atomic weight and X/ p for the elements which emit a characteristic radiation , taking atomic weight as abscissa and X/ p for ordinates .
If this is done , it will be found that the elements with atomic weights between that * Barkla and Sadler , 'Phil .
Mag. , ' Oct. , 1908 ; Chapman , 'Phil .
Mag. , ' April , 1911 ; Barkla , ' Phil. Mag. , ' Aug. 1910 .
|
rspa_1912_0038 | 0950-1207 | Fluorescent r\#xF6;ntgen radiation from elements of high atomic weight. | 439 | 451 | 1,912 | 86 | Proceedings of the Royal Society of London. Series A, Containing Papers of a Mathematical and Physical Character | J. Crosby Chapman, B. Sc.|Prof. Sir. J. J. Thomson, F. R. S. | article | 6.0.4 | http://dx.doi.org/10.1098/rspa.1912.0038 | en | rspa | 1,910 | 1,900 | 1,900 | 12 | 195 | 4,491 | http://corpora.clarin-d.uni-saarland.de/surprisal/6.0.3/?id=rspa_1912_0038 | 10.1098/rspa.1912.0038 | null | null | null | Atomic Physics | 71.967638 | Tables | 17.460522 | Atomic Physics | [
10.968870162963867,
-77.40115356445312
] | Fluorescent Rontgen Radiation .
439 intensity is approximately the same in each gas for any particular type of rays .
In conclusion , I wish to acknowledge my indebtedness to Prof. Sir J. J. Thomson for his kindly interest and helpful suggestions throughout the course of the investigation .
Fluorescent Rontgen Radiation from Elements of High Atomic Weight .
By J. Crosby Chapman , B.Sc. , Layton Research Scholar of the University of London , King 's College ; Research Student of Gonville and Cains College , Cambridge .
( Communicated by Prof. Sir J. J. Thomson , F.R.S. Received February 8 , \#151 ; Read March 21 , 1912 .
) A considerable amount of work has been done by various experimenters* showing that , when an element of higher atomic weight than calcium is subjected to a suitable primary beam of X-rays , the rays which leave the radiator consist of two types : firstly , the purely scattered radiation , which is almost exactly similar to the incident beam , and , secondly , a characteristic homogeneous radiation .
The scattered radiation which in the case of a primary beam from an X-ray bulb is heterogeneous , is , with elements of low atomic weight , quite small in intensity when compared with the intensity of the homogeneous radiation which is emitted simultaneously .
Owing to this fact , it is comparatively easy to prove that the elements with atomic weights between that of calcium and cerium give off when stimulated with X-rays homogeneous beams , and the hardness of the characteristic radiation from each of these elements has been measured by determining the absorption in aluminium .
The radiations are usually defined by the value of their absorption coefficients , that is , by X/ p where I = I0e"Ax ; p = density of aluminium .
Using the values obtained , it is possible to plot a curve showing the relation between atomic weight and X/ p for the elements which emit a characteristic radiation , taking atomic weight as abscissa and X/ p for ordinates .
If this is done , it will be found that the elements with atomic weights between that * Barkla and Sadler , 'Phil .
Mag. , ' Oct. , 1908 ; Chapman , 'Phil .
Mag. , ' April , 1911 ; Barkla , ' Phil. Mag. , ' Aug. 1910 .
440 Mr. J. C. Chapman .
Fluorescent Rontgen [ Feb. 8 , of calcium and cerium lie on an approximately smooth curve ( Group K ) .
When , however , the elements with higher atomic weight than silver are examined under suitable conditions , it is found that , with these elements , there are two distinct types of radiation : one , a hard characteristic radiation such as belongs to Group K , and superposed on this a very soft radiation .
Prof. Barkla and Mr. Nicol* have investigated the soft radiations from the elements silver , antimony , iodine , and barium , and have shown that these elements , in addition to the usual characteristic radiation , emit another very soft radiation , which is also characteristic of the element .
The values of the \/ p for these elements have been determined , and it has been shown , as far as it is possible with such soft rays , that they are homogeneous .
If these values are plotted on the same diagram as that mentioned above , a second short curve is obtained , which can be continued to the X axis ; when this is done , if this second curve resembles in shape the curve for Group K , it will pass before it reaches the X axis through the region of atomic weights between 184 and 238 , which contains tungsten , gold , platinum , lead , bismuth , thorium , and uranium .
This second series of elements has been designated Group L. Up to the present it has been impossible to draw this curve with any accuracy , as none of the elements between tungsten and uranium have been investigated as regards their X-ray properties .
The following experiments were performed in order to see\#151 ; ( 1 ) Whether the radiations emitted by these elements when the scattered radiation was allowed for , were as homogeneous as those emitted by the elements of Group K. ( 2 ) To investigate whether the same absorption phenomena are found with the elements of Group L as with Group K. .
( 3 ) To investigate whether there is an empirical relation between atomic weights of different elements emitting characteristic radiations of the same penetrating power as tested by the absorption coefficient .
The chief difficulty which has to be met , when examining the X-radiation from the elements in the second group ( Group L ) , is the magnitude of the scattered radiation , this being heterogeneous , depending on the primary beam ; it is , unless special precautions are taken , impossible to distinguish it from the supposed homogeneous radiation which it accompanies .
With elements of atomic weight jsuch as copper , the intensity of the scattered radiation is so small ( sometimes less than O'5 per cent , of the total radiation ) that it can for all practical purposes be neglected , but , as the atomic weight rises , the intensity of the scattered radiation increases , for two reasons : firstly , for the same number of atoms present , there is a greater mass of * 'Lond .
Phys. Soc. Proc. , ' Dec. , 1911 , vol. 24 , part 1 .
1912 .
] Radiation from Elements of High Atomic Weight .
441 scattering material ; and , secondly , sufficient evidence has been obtained to show that the ordinary law of scattering of mass for mass the same , which has been shown to hold for all elements up to sulphur , ceases to be true when the heavier elements are considered .
In a recent paper , Prof. Barkla* estimated that copper scatters about twice as much radiation as an equal mass of one of the lighter elements , such as sulphur , while it would appear that silver is six times as efficient a scatterer as sulphur , mass for mass .
This difficulty , which begins to enter , even in Group K , with silver , will , with elements of atomic weight of the order of 200 , enter to such an extent that if the radiation from an element of high atomic weight such as platinum was examined in the ordinary way , the great increase of scattered radiation would mask , if it did not completely swamp , any characteristic radiation which might be present .
The method of attacking this difficulty was to so arrange the experiment that the intensity of the purely scattered radiation could be measured and subtracted .
A description of the apparatus will serve to show the manner in which the correction for the scattered radiation was made .
X-rays from the anticathode 0 passed through the slit L in the lead box * Barkla , ' Phil. Mag. , ' Sept. , 1911 .
442 Mr. J. C. Chapman .
Fluorescent Rontgen [ Feb. 8 , on to the radiator in the position P. The radiation leaving the plate P passed through another adjustable slit in the lead screen KK , into the two electroscopes A and S. In front of the electroscope A was placed a stand in which the absorbing sheets were placed when the radiation was tested .
The electroscope S simply served to standardise the intensity of the secondary radiation from the plate P. In order to limit the primary beam so that it fell almost wholly on the radiator P , the rays from the bulb were made to pass through a narrow lead tunnel , and at the end of this tunnel at T sheets of thick aluminium were placed so as to cut off all but the very hard radiation which is present in the beam .
A factor which enabled the scattered radiation to be minimised , and which has perhaps not received the importance it should , is the advantage derived from using thin radiators .
For , generally speaking , the homogeneous radiation , owing to its low penetrating power , comes only from a small depth .
Any greater thickness than this depth does not serve to increase the intensity of the homogeneous radiation but merely increases the scattered radiation which is able to come from deeper layers .
In these experiments very thin radiators were used but they were in all cases of sufficient thickness as to be considered of infinite depth from the point of view of the homogeneous radiation .
The ordinary method of determining the successive absorptions was used .
The deflection in the electroscope A was first determined while the standardising electroscope underwent a certain deflection ; a sheet was then placed in the stand H so as to absorb a portion of the rays passing into A , and the leak in A while the standardising electroscope suffered the same deflection was measured .
From these values the percentage absorption of the radiation by each sheet was measured .
The method of subtracting the merely scattered radiation was as follows:\#151 ; The bulb was worked until it was exceedingly hard with an equivalent spark gap of 5 or 6 inches .
In addition to this the primary beam was made to pass through a thick sheet of aluminium ( 02 cm .
) placed in the path of the beam at T ; in this way all but the hardest constituent of the beam was stopped by the aluminium , thus a beam of X-rays of very great hardness was obtained .
This penetrating primary when it fell on the radiator at P made it emit a radiation which consisted of ( 1 ) the supposed homogeneous constituent , ( 2 ) the superposed scattered radiation .
This heterogeneous beam was then examined in the usual way ; the effect of placing the sheets of aluminium in front of the electroscope A was to cut down the supposed homogeneous radiation , which was , of course , soft when compared with the scattered radiation for the elements experimented on in Group L. On the other hand , owing to its great penetrating power , the scattered radiation was 1912 .
] Radiation from Elements of High Atomic Weight .
443 not cut down to any great extent ; in the case of gold , aluminium of thickness sufficient to cut off 99'9 per cent , of the homogeneous radiation , did not cut down the scattered radiation more than 10 per cent. When these successive absorptions had been taken , a thickness of aluminium ( 0T3 cm .
) was placed in the stand H ; this cut off , for all practical purposes , the whole of the homogeneous radiation .
At the same time almost the whole of the hard scattered radiation still reached the electroscope .
With this arrangement the amount of the superposed scattered radiation was measured by allowing the standardising electroscope to suffer the same deflection as in the previous absorption experiments , and noticing the deflection which the leak , due to the scattered radiation , produces in the electroscope A. From these values the total intensity of the scattered radiation can be readily found .
If this constant factor is subtracted from the previous values , results are left which give not the absorption of the whole beam consisting both of scattered and homogeneous rays , but now only the absorption of the supposed homogeneous radiation .
A typical account of this scattering correction is given in detail for the platinum radiation , for the other elements a correction of the same order has been made and the final results are stated .
Correction for the Scattered Radiation from Platinum .
The first column in the table below shows the number of sheets in front of the electroscope A , the second column the intensity of the total radiation ( i.e. , scattered and homogeneous ) after each successive absorption .
The third column represents the intensity of the total radiation minus the scattered radiation , obtained by subtracting the scattered radiation as shown below:\#151 ; No. of absorbing sheets , each 0 *0067 cm .
Intensity of total radiation ( scattered + homogeneous ) .
Intensity of homogeneous radiation ( total \#151 ; scattered radiation ) .
0 .
54 *6 50 *1 1 38 *3 33 *8 2 27 *5 23 *0 3 20 *1 15*6 4 15 *2 10 *7 5 11 *7 7*2 Intensity of the scattered radiation as measured by passing the beam from the platinum radiator through O'13 cm .
of aluminium , which absorbs 99'9 per cent , of the homogeneous radiation and only 9'8 per cent , of the scattered radiation = 4'1 .
Adding to 4'1 the 10 per cent , of the scattered radiation which is absorbed in the aluminium , Total intensity of scattered radiation = 4'5 .
Mr. J. C. Chapman .
Fluorescent Rontgen [ Feb. 8 , Subtracting this as a constant factor from the values in Column 2 , Column 3 is obtained .
If , now , log ( I0/ I ) for the total radiation from Column 2 and log ( I0/ I ) for ( total radiation\#151 ; scattered radiation ) from Column 3 be plotted against thickness of aluminium absorbing , fig. 1 is obtained .
It will be seen that the curVe which represents the absorption of the total radiation becomes a straight line when the scattered rays are allowed for .
That is , when the superposed scattered radiation is subtracted , there is left a homogeneous beam .
Results showing the Homogeneity of the Radiations .
To measure the homogeneity of the rays from the various elements they were passed through plates of aluminium of different thicknesses and the percentage absorption of the emergent rays measured by a sheet of aluminium .
In the tables below , the first column gives the percentage absorption of the rays by the different plates of aluminium ; the second , the value of the percentage absorption of the emergent rays by aluminium ( 0*0067 cm .
) .
Tungsten , Radiator ... ... .
Powdered tungsten metal .
Percentage absorption of rays by different plates of Al .
Percentage absorption of the emergent rays by Al ( 0*0067 cm .
) .
43*8 41*9 39*9 38*0 39*9 Mean value .
\/ p = 30*0 .
40*7 1912 .
] Radiation from Elements of High Atomic Weight .
445 Platinum .
Eadiator ... . .
Percentage absorption of rays by different plates of Al .
Pure platinum foil .
Percentage absorption of the emergent rays by Al ( 0*0067 cm .
) .
32*5 31*9 32*2 32*2 32*7 Mean value ... ... ... ... .
32 3 X/ p = 22*2 .
Gold .
Eadiator ... Percentage absorption of rays by different plates of Al .
Pure gold plate .
Percentage absorption of the emergent rays by Al ( 0*0067 cm .
) .
31*3 33*2 31*5 29*9 31*6 Mean value ... ... ... ... . .
31*5 X/ p = 21*6 .
Lead .
Eadiator ... .
Percentage absorption of rays by different plates of Al .
Pure lead foil .
Percentage absorption of the emergent rays by Al ( 0*0067 cm .
) .
25*6 26*3 25*8 25*8 27*8 .
26*0 26*0 Mean value ... ... ... ... . .
26*2 X/ p = 17*4 .
Bismuth .
Eadiator ... ... .
Powdered bismuth metal .
Percentage absorption of rays by Percentage absorption of the emergent different plates of Al .
rays by Al ( 0*0067 cm .
) .
10 23*7 32 24*2 * 49 24*5 24*5 24*3 25*0 Mean value ... ... ... . .
24*4 X/ p = 16*1 .
VOL. LXXXVI.\#151 ; JL .
2 II Mr. J. C. Chapman .
Fluorescent Rontgen [ Feb. 8 , Thorium .
Badiator ... ... .
Powdered thorium oxide .
Percentage absorption of rays by Percentage absorption of the emergent different plates of Al .
rays by Al ( 0-0134 cm .
) .
24*6 25*7 24*4 25*1 25*5 Mean value ... ... ... ... 24*3 A/ p = 80 .
Uranium .
Badiator ... ... Powdered uranium oxide .
Percentage absorption of rays by different plates of Al .
Percentage absorption of the emergent rays by Al ( 0*0134 cm .
) .
24*9 22*6 23-2 23*1 23*1 Mean value ... ... ... ... 23*1 A Ip = 7*5 .
The relation between the thickness of aluminium absorbing and log ( I/ Io ) at each successive absorption is plotted in fig. 2 for the whole series of radiations , from the tables just given .
The straight lines obtained indicate the almost exact homogeneity when the scattered radiation is subtracted .
\#151 ; Thickness oF Al x 0067cms .
1912 .
] Radiation from Elements of High Atomic Weight .
447 Relation between the Atomic Weights of Elements Emitting same Characteristic Radiation .
If a curve be plotted with A/ p for ordinate and atomic weight as abscissa for these elements , it will be seen that the points so obtained lie on an approximately smooth curve .
The determination of the values of X/ p for so many elements in Group L has revealed an interesting relation , similar to that pointed out by Whiddington , * between the atomic weights of two elements which , though belonging to different groups , can be caused to emit the same characteristic radiation .
If WL represents the atomic weight of an element in Group L that gives out a radiation having a certain penetrating power as measured by the X/ p in aluminium , and WK is the atomic weight of an element in the first group ( K ) , which , if it existed , would give out the same radiation ( this is obtained from the curve mentioned at the commencement of the paper ) , then it will be found that in all cases the relation between WL and WK is expressed almost exactly by the empirical formula\#151 ; WK = KWl-48 ) .
This is shown for all elements from tungsten to uranium in the following table , which explains itself :\#151 ; Element in second group ( Group L ) .
A/ p. Atomic weight of element in Group L , WL .
Atomic weight of element in Group K , which , if it existed , would emit the same characteristic radiation .
Value from curve , experimental .
Value calculated from formula WK = J(Wl-48 ) .
Tungsten 30 0 184 *0 ' 69-7 68 *2 Platinum 22 -2 195 -0 75 -2 73 *5 Gold 21 -6 197 *2 75 *5 74 *6 Lead 17 *4 207 *0 79 -8 79 *5 Bismuth 16 T 208 *5 80 *7 80 *2 Thorium 8*0 232 *0 91 *4 92 *0 Uranium 7*5 238 *0 93 *2 .
95 -0 It is impossible , at present , to state what is the physical significance of this formula , but it is most useful in determining the absorption coefficients of elements directly from their atomic weights .
Selective Absorption by Elements of Group L. The elements belonging to Group K exhibit another leading characteristic .
This is that any particular element in Group K shows a selective absorption * 'Nature , ' November 30 , 1911 .
448 Mr. J. C. Chapman .
Fluorescent Rontgen [ Feb. 8 , for radiations which have a penetrating power just greater than its own .
Thus if the coefficient of absorption of an element X in Group K , such as copper , be measured for the various homogeneous beams from calcium to cerium , when the radiation absorbed is soft the absorption in X is considerable , but as the radiation is made more penetrating the absorption in aluminium and in the element X diminishes proportionately .
When , however , the radiation which is being absorbed is made more penetrating than the secondary characteristic of the metal X , the absorption in X first ceases to diminish as rapidly as the absorption in aluminium , then it increases , and it is at this point of increase that the characteristic radiation of the element X is excited .
As the primary beam becomes still more penetrating , the absorption in the element X begins to diminish , and eventually the absorptions in aluminium and the metal X diminish proportionately .
In order to show that the same phenomena take place with the elements of Group L , the absorption of thin layers* of lead oxide and bismuth carbonate for a series of homogeneous beams belonging to Group K was measured .
The percentage absorptions by the thin layers of the two salts were determined for the characteristic radiations from copper , zinc , arsenic , selenium , bromine , strontium , molybdenum , silver , and tin .
It was impossible to use the pure elements lead and bismuth , owing to the difficulties of obtaining thin enough layers for absorbing sheets .
On this account only relative values of the absorption coefficients have been determined , but these serve to show all that is necessary .
In the following tables the first column shows the radiation absorbed , the Absorption by Lead Oxide .
Secondary radiator .
Absorption in Al .
Absolute \/ p. Absorption in Pb .
k ( A/ p ) .
Absorption in Pb Absorption in Al ' \#166 ; = Jc~l times value below .
Copper 47*7 269 5*6 Zinc 39 *4 224 5*7 Arsenic 22 *5 140 6 2 Selenium 18 *9 129 6*9 Bromine 16 *3 126 7 7 Strontium 13*0 161 12 *4 Molybdenum 4*7 143 30 -0 Silver 2*5 84 34 *0 Tin 1*57 63 40 *0 / c is of the order unity .
* These layers were made by mixing the salt in question with a small amount of pure gum ; the absorption of a thin layer of the paint so formed was then measured .
In this way it was impossible to obtain exactly even thicknesses of the salt , so that an error is 1912 .
] Radiation from Elements of High Atomic Weight .
449 Absorption by Bismuth Carbonate .
Secondary radiator .
Absorption in Al .
Absolute A/ p. Absorption in Bi , relative .
v ( A/ p)- Absorption in Bi Absorption in Al ' = Jc'~l times value below .
Copper 47 *7 277 5*8 Zinc 39 *4 238 6*0 Arsenic 22 *5 152 6*8 Selenium 18 *9 134 7*0 Bromine 16 *8 117 7*0 Strontium 13 *0 165 12 *7 Molvbdenum 4*7 147 31 -3 Silver 2*5 87 34 *9 Tin 1-57 66 42*0 Jc ' is of the order unity .
second the absorption in aluminium for this radiation , the third the relative absorption in the salt .
The two following curves show graphically the relation between absorption in aluminium and the relative absorption in lead and bismuth .
The *o 160 \#151 ; ( in Al ) for absorbed radiations introduced in the determination of A/ p. Owing to this , no correction has been applied for any slight lack of homogeneity of the rays from the several elements which served as radiators .
450 Mr. J. C. Chapman .
Fluorescent Rontgen [ Feb. 8 , o ' O 120 w 80 Fig. 4 .
\#151 ; ( in Al ) for absorbed radiations absorption by the light elements in the two salts is practically negligible when the relation between the relative masses and the absorption coefficients of the light and heavy elements are considered , so that the values obtained show within the limits of error of the experiment the absorption in lead and bismuth .
It will be seen that the shape of both curves is similar in its general features to that obtained for elements of Group K. In these curves the dotted lines show the point at wnich the characteristic radiation is excited .
This can be found directly from the known values of X/ p for the homogeneous radiations from lead and bismuth , or it can be calculated from the empirical formula .
The results demonstrate that the lead radiation ( X/ p = 17*4 ) is excited between the elements selenium ( X/ p = 18*5 ) and bromine ( X/ p = 16*4 ) , whereas bismuth ( X/ p = 16*1 ) is excited between bromine ( X/ p = 16*3 ) and strontium ( X/ p = 13 ) .
Thus these elements of Group L exhibit the same absorption phenomena as elements of Group K , in so far as they need a more penetrating radiation than themselves to be the exciting source .
1912 .
] Radiation from Elements of High Atomic Weight .
451 Summary .
The results of these experiments show that there is a whole group of elements ( Group L ) , containing tungsten , gold , platinum , bismuth , and the radioactive elements thorium and uranium , which emit when suitably excited secondary homogeneous Rontgen radiations similar in type to those emitted by the elements of the ordinary Group K. Their homogeneity has been demonstrated by a method which allows the scattered radiation to be subtracted .
The values of the absorption coefficients in aluminium have been determined .
An empirical relation exists between atomic weights ( W ) of two elements which are in different groups , but which give out the same characteristic radiation .
It is expressed by the formula WK = KWl-48 ) .
This relation holds for all the elements in Group L within the limits of experimental error .
It has also been shown that the elements of Group L exhibit the same selective absorption phenomena in the neighbourhood of an absorption band .
The values given are for lead and bismuth .
These results would go to show that the mechanism of production and the type of the radiations of both groups are the same , but further experiments are still necessary to show that there is an exact similarity .
In conclusion my best thanks are due to Prof. Sir J. J. Thomson for his kind interest in these experiments .
|
rspa_1912_0040 | 0950-1207 | The volatility of metals of the platinum group. | 461 | 477 | 1,912 | 86 | Proceedings of the Royal Society of London. Series A, Containing Papers of a Mathematical and Physical Character | Sir William Crookes, O. M., For. Sec. R. S. | article | 6.0.4 | http://dx.doi.org/10.1098/rspa.1912.0040 | en | rspa | 1,910 | 1,900 | 1,900 | 15 | 254 | 6,240 | http://corpora.clarin-d.uni-saarland.de/surprisal/6.0.3/?id=rspa_1912_0040 | 10.1098/rspa.1912.0040 | null | null | null | Thermodynamics | 49.386869 | Chemistry 1 | 18.205372 | Thermodynamics | [
-6.633551597595215,
-51.357513427734375
] | The Volatility of Metals of the Platinum Group .
461 In the present uncertainty with regard to the mechanism of conduction in solids it would be premature to attempt a theory of the potential effect on these lines .
But , on the other hand , the simple relation between voltage and resistance specified above may furnish some guidance in a future choice among theories of conduction .
In conclusion , I have to thank Prof. Pointing for offering me ample facilities in conducting this investigation , and Prof. T. Turner for some valuable hints regarding the distillation of metals and the treatment of thin conducting films .
The Volatility of Metals of the Platinum Group .
By Sir William Ckookes , O.M. , For .
Sec. R.S. ( Received February 15 , \#151 ; Read March 7 , 1912 .
) For the last two years I have been using an electric furnace , and some facts which came under my notice on the occasion of a breakdown of the heating arrangement led me to suspect that platinum was not so entirely fixed at temperatures well below its melting-point as has been universally accepted by chemists and physicists .
The electric resistance furnace used ( fig. 1 ) is on the Heraeus system .
It A , Wires from thermo-junction .
B , Platinum platinum-rhodium junction .
C , D , Terminals of platinum strip .
E , Crucible .
E , Porcelain supporting tube .
G , Platinum strip .
Fig. 1 .
consists of a highly refractory porcelain tube , around which is coiled a ribbon of platinum foil , 11 mm. wide , 2*8 metres long , and 0*01 mm. thick , VOL. LXXXVI.\#151 ; A. o T Sir W. Crookes .
[ Feb. 15 , each convolution almost , but not quite , touching its neighbour .
The ribbon closely enwraps the tube , practically covering the surface to be heated , so that the heat produced by the passage of the electric current is immediately transmitted to the tube .
The tube is 4 cm .
internal diameter ; the object to be heated stands on a porcelain rod fixed upright in the middle of the tube .
The body of the furnace is made to slide up and down by means of a windlass , so as to allow the crucible to be properly adjusted .
The temperature of the furnace is measured by a Le Chatelier platinum and platinum-rhodium thermo-couple .
Although the melting-point of platinum is 1753 ' , * it is not safe to use the furnace at higher temperatures than about 1500 ' , as a temporary variation in the voltage of the current for a few minutes , or a reduction of the resistance , may easily make a difference of one or two hundred degrees .
After a certain time the platinum ribbon coil gets thinner and melts at the weakest part , and the furnace becomes useless until a new porcelain tube and platinum ribbon coil are supplied .
During the two years I have had the furnace in use this breakdown has happened three times .
On examining the point of rupture I was struck by the appearance of a fine glistening dust on the porcelain tube .
I carefully removed particles to the slide of a microscope , and found the dust to consist of beautifully-formed hexagonal plates with a brilliant metallic lustre and perfect crystalline form .
The amount at my disposal was infinitesimal\#151 ; not more than a few milligrammes\#151 ; and careful chemical examination showed me that the crystals were almost entirely platinum .
A control examination by Messrs. Johnson and Matthey confirmed my observation .
When the furnace was taken to pieces more crystalline deposits of platinum were found , especially inside the outer tube facing the platinum spiral .
Fig. 2 shows some of these crystals .
At first sight it might seem superfluous to try experiments to see if platinum volatilised at all when strongly heated , considering how many generations of chemists have been daily igniting and weighing platinum crucibles .
But it is customary among chemists to cleanse their crucibles between each using , and in some cases they are scoured with fine sand .
It therefore seemed of interest to subject a platinum crucible to a temperature approaching that to which the platinum resistance coil had been exposed As an appreciable amount of platinum had sublimed and deposited in the form of crystals in the furnace it was possible that a carefully weighed platinum crucible exposed to a high temperature , after a 'certain number of hours , might show a detectable diminution in weight .
* Waidner and Burgess , 'Bulletin of the Bureau of Standards , Washington , 1907 , vol. 3 , p. 208 .
1912 .
] The Volatility of Metals of the Platinum Group .
463 I assumed that the loss of weight in a platinum crucible by sublimation , at temperatures not much above those available in chemical laboratories , would be very small , and would require the balance to be in the best condition to enable its indications to be relied on .
The balance\#151 ; a very delicate chemical one\#151 ; I employed for this research was put into accurate adjustment , and not used for any other purpose .
It was kept in a dry room at nearly constant temperature , and was locked when not actually in use .
The grain* weights used were made for me in 1864 by Johnson and Matthey , and were turned out of bars of melted , cast , and well hammered platinum .
They were adjusted by the method I described in the ' Chemical Fig. 2 .
News ' for April 19 , 1867 , and ' Phil. Trans. Roy .
Soc. , ' 1873 , p. 288 , and have been in use ever since .
In 1895 Mr. Chaney , Superintendent of Weights and Measures , tested my 1000-grain platinum weight against their absolute standards , with the result that it was shown to be 3'9858 grains light .
This made no difference to previous work with the weights , as in chemical operations the object is not to ascertain the absolute weight of a substance in terms of a grain or gramme , but to determine its relative weight in comparison with that which it possessed at some other time before submission to certain analytical or synthetical operations .
If the weighings are performed with * My results are given in grains , not grammes .
I have used my standard platinum grain weights for nearly fifty years , and they are too valuable to discard in favour of gramme weights , which would demand many months ' work on them to bring them to the state of accuracy into which I have now got the grain weights .
Sir W. Crookes .
[ Feb. 15 , the same weights it does not matter whether they are absolutely of the value they profess to be\#151 ; but it is of vital importance that they should bear a known proportion to each other .
On receiving Mr. Chaney 's result I adjusted the 1000-grain weight by melting a bead of pure gold on it of the exact weight required , viz. , 3*9858 grains , and then readjusted the whole series in the same way so as to get them absolutely as well as relatively accurate .
In 1897 , the readjustment being complete , I again asked Mr. Chaney to tell me the absolute weight of my platinum 1000 grains , and he returned it in a few days , saying that in air at 62 ' F. and pressure of 30 inches , my 1000-grain weight weighed 999'99574 grains , and in vacuo it weighed 999*90300 grains .
Comparisons made last year showed that their values have remained absolutely unaltered , and I have the satisfaction of knowing they are as near perfection as can reasonably be expected .
By taking all precautions and using Gauss 's method of interchanges , the balance will clearly indicate a difference of O'OOOl of a grain when loaded with 1000 grains in each pan .
In the course of the research it was seen that this extreme delicacy was not needed , and , as weighing to such minute accuracy is very tedious , I have not , as a rule , gone beyond three places of decimals .
Platinum at 1300 ' .
A platinum crucible in good condition was ignited , cooled in a desiccator , and , an hour after , transferred to the balance .
It weighed 150*487 grains .
It was put into the electric furnace at 1300 ' C. , and kept at that temperature for two hours .
It was then removed , allowed to cool in a desiccator , .and after another hour in the balance room it was found to weigh 150*458 grains , showing a loss of no less than 0*029 grain .
It was now put into the furnace for another two hours , and the temperature kept at 1300 ' ( a white heat ) .
On cooling an hour in the balance case its weight was found to be 150*427 grains .
Table I shows the losses by sublimation when exposed to a temperature of 1300 ' for two hours at a time \#151 ; being cooled and weighed between each heating .
These results are shown plotted as a curve in fig. 3 .
After this heating , and loss of 0*245 per cent , of its weight , the platinum crucible was not appreciably different in appearance from the time it was first put into the electric furnace .
I examined its surface under the micro-tscope , expecting to find the re-crystallisation described by Mr. Rosenheim* * ' Roy .
Soc. Prod , ' vol. 70 , p. 252 .
1912 .
] The Volatility of Metals of the Platinum Group .
Table I. Grains .
Loss .
Grains .
Per cent. Original weight of platinum 150 -487 After 2 hours at 1300 ' weighed 150 *458 0*029 0*019 4 j , ^ \gt ; \#187 ; j ) 150 *427 0*060 0*040 , , 6 , , , , 150 *394 0*093 0*062 )\#187 ; 8 i ) )\gt ; 150 -365 0*122 0*081 " 10 " " 150 *344 0*143 0*095 " 12 " " 150*316 0*171 0*114 } } 44 Ji } ) 150 *295 0*192 0*128 )i 46 } ) }\gt ; 150 *266 0*221 0U47 jj 48 , , " 150 *233 0*254 0*169 " 20 " " 150 *209 0*278 0*185 22 " " 150*194 0*293 0*195 " 24 " " 150 *180 0*307 0*204 " 26 " " 150*159 0*328 0*218 j ) 28 , , , , 150 *140 0 *347- 0*231 ) ) 60 , , , , 150 *118 0*369 0*245 PLATINUM 2 4 6 8 10 12 14 16 18 20 22 24 262S 30 HOURS AT 1300 C Fig. 3 .
I was unable to detect any appearance resembling the photograph given in his paper .
Probably the heating in his case was extended much beyond the 30 hours to which my crucible was exposed .
The action known as " air washing " ( particles from a white-hot semi-molten surface being mechanically carried away by a current of impinging air ) could not be active in the case of this experiment , for the tube of the furnace was closed at the top , nearly closed at the place where the crucible Sir W. Crookes .
[ Feb. 15 , stood , and almost completely obstructed at the lower end .
Therefore the platinum was in almost perfectly still air .
Palladium at 1300 ' .
Having with platinum obtained such unexpected results I tested palladium in similar conditions .
The metal used was pure , in the form of thick plate , bright and polished on both sides .
In the following table it will be seen that , like platinum , palladium loses weight when exposed to a temperature of 1300 ' for two hours at a time , cooling and weighing at each interval:\#151 ; Table II .
Grains .
Loss .
Grains .
Per cent. 1 Original weight of palladium 58 -007 i After 2 hours at 1300 ' , weighed 57 -939 0*068 0*117 ij 4 j ) j\gt ; 57 88.3 0*124 0*214 jj 6 )t jj 57 -825 0*182 0*314 )\gt ; 8 jj j ) 57 -808 0*199 0*343 ) ) 10 ) ) ff 57 -761 0*246 0*424 ) ) 12 , , i ) 57 -735 0*272 0*469 \#187 ; 14 \gt ; \gt ; a 57 -720 0*287 0*495 n 16 j ) jj 57 -702 0*305 0*526 57 *674 0*333 0*574 " 20 " 57 '656 0*351 0*605 jj 22 , , jj 57 -642 0*365 0*629 3 , 24 , , jj 57 -624 0*383 0*660 jj 26 " jj 57 -607 0*400 0*690 jj 28 , , jj 57 -591 0*416 0*717 jj 60 , , jj 57 -575 0*432 0*745 The curve plotted from these data is shown in fig. 4 .
PALLADIUM 1300 " 2 4 6 8 10 1214 1618 202224262836 Fig. 4 .
1912 .
] The Volatility of Metals of the Platinum Group .
467 Moissan* says that " palladium is more easily fused than platinum , but is apparently less volatile .
, , From the foregoing data it appears that at temperatures much below its melting-point palladium is three times as volatile as platinum .
At the end of the series the plate of metal had curved into an arc of about 60 ' , and its concave surface showed raised blisters .
These blisters appeared after the first few heatings , and were due evidently to the liberation of occluded gas ; further heating did not seem to increase the blisters .
On examining the plotted curve the two-hourly loss of weight is seen to be greater in the earlier stages , diminishing up to 10 hours , and then pretty regular in a straight line .
This agrees with the supposition that gas was given off during the earlier heatings , and the extra loss at these stages was due to the weight of gas liberated .
From the above data the loss due to occluded gas would be about 0T5 of a grain , and supposing it were hydrogen it would measure about 111 c.c. The bulk of 58 grains of palladium would be about 0*34 c.c. , and as palladium will absorb more than 600 times its volume of hydrogen , the amount it could have held is 204 c.c. As the heatings at 1300 ' progressed there was a gradual change in the surface of the metal from smooth to crystalline , and at the end of the 30 hours the surface had a crystalline moire appearance , similar to that shown by iridium after similar heating , but not so marked , the crystals being smaller .
The metallic appearance was unimpaired and no oxidation was detected on the surface .
Iridium at 1300 ' .
In May , 1908 , f I suggested to chemists the great advantages of using crucibles of pure iridium instead of platinum in laboratory work .
An iridium crucible is hard as steel ; it may be heated for hours over a smoky Bunsen burner without injury .
It will stand hours of boiling in aqua regia without appreciable attack ; lead and zinc can be melted in it and boiled at a full red heat ; likewise nickel , copper , gold , and iron can be melted in an iridium crucible , and poured out without injury .
I used an iridium crucible for more than a year in the scandium research , and did not notice any appreciable diminution in weight .
Any slight loss I attributed to mechanical abrasion during the cleaning and burnishing with sand , sometimes rendered necessary after an experiment .
Subsequent observations , however , led me to suspect that iridium was not altogether fixed at high temperatures ; looking into the literature of the * 'Comptes Rendus , ' January 22 , 1906 , vol. 143 .
t 'Roy .
Soc. Proc. , ' A , vol. 80 , p. 535 .
Sir W. Crookes .
[ Feb. 15 , subject I met with several references to the supposed volatility of this metal .
Accordingly , I commenced experiments to see if I could detect loss of weight in iridium at 1300 ' , a temperature at which I had found platinum to be slightly volatile .
An iridium crucible was heated for a few minutes in the electric furnace , and then cooled in a desiccator .
It was taken to the balance room , put near the balance for an hour , and then placed on the pan .
In an hour 's time it was weighed and found to be 145*726 grains .
This therefore was taken as the original weight from which to calculate the loss , if any , after long exposure to the high temperature of the furnace .
The crucible was put into the hot electric furnace , standing on an iridium plate , and kept at 1300 ' for two hours .
It was then removed , allowed to cool with all precautions , when its weight was found to be 144*520 grains , showing a loss of 1*206 grains or about 0*8 per cent. The experiment was repeated until the iridium had been exposed to this temperature for a total of 22 hours .
The following table shows how in the above circumstances iridium loses weight , the data being plotted as a curve in fig. 5:\#151 ; Table III .
Grains .
Loss .
Grains .
Per cent. Original weight of iridium 145 -726 After 2 hours at 1300 ' , weighed 144 -520 1-206 0*828 jj 4 33 jj 143 -430 2-296 1 -576 jj 6 J ) jj 142 -208 3-518 2-414 " 8 33 33 ... ... 141 -379 4*347 2-983 " io 33 jj 140 -354 5*372 3-686 , j 12 3/ 33 ... ... 139 -577 6-149 4*220 j , 14 33 jj 138 -605 7 *121 4*887 " 16 33 \gt ; \gt ; 137 '878 7 -848 * 5-385 " 18 33 33 ... *. .
137 -151 8 -575 5*884 " 20 136 151 9*575 6-571 j , 22 33 135 -092 10 *634 7*297 Before the crucible was exposed to long continued heating to 1300 ' it was bright and polished .
After four hours ' heating it had a slightly crystalline look , which increased each time until , after 22 hours , the surface had assumed a beautiful moire appearance .
After the iridium crucible had been heated in the electric furnace in the above experiments until it had lost 7*297 per cent , of its weight , it was submitted to further experiments to see if loss of weight was proportional to 1912 .
] The Volatility of Metals of the Platinum Group .
HOURS AT 1300 Fig. 5 .
the temperature .
After the last experiment at 1300 ' the crucible was exposed for two hours at a time to temperatures rising from 1000 ' to 1400 ' , with the following results :\#151 ; Table IY .
G-rains .
Loss .
Grains .
Per cent. Weight of iridium at starting 135 *092 __ After 2 hours at 1000 ' 134 927 0*165 0*122 After 2 additional hours at 1100 ' 134 *509 0*583 0*432 " " " 1200 ' 133 -746 1*346 0*996 " " " 1275 ' 132 -395 2*697 1*996 " " " 1320 ' 131 *367 3*725 2*757 \#187 ; " 1400 ' 129 *996 5*096 3*772 The curve , fig. 6 , is plotted from the above data , and shows conclusively that the loss of weight for equal periods of time is proportional to the temperature .
IRIDIUM 1 2 hours temperature rising Fig. 6 .
Sir W. Crookes .
[ Feb. 15 , -After this severe treatment the crucible , which had taken on a crystalline appearance over the whole surface when the series commenced , began to show approaching disintegration along its edges ( fig. 7 ) , and after several more heatings of two hours pieces began to crumble when touched with the forceps .
Fig. 7 .
The disintegration of iridium has been examined by Messrs. Holborn and Austin , * who found that at high temperatures ( 1670 ' ) a narrow strip disintegrated about ten times as rapidly in the air as platinum .
Rhodium at 1300 ' .
I next tried rhodium , a metal intermediate in fusibility between platinum and iridium , and similar to iridium in its resistance to chemical agents which attack platinum .
In my paper above quotedf I suggested the use of rhodium for crucibles in the laboratory .
Its low density ( 11 as against iridium 22 ) would be a great advantage in quantitative operations , as the weight of a rhodium orucible would be only half that of one made of platinum , and its cost would not be excessive .
The following table shows the losses in weight when metallic rhodium is exposed to ajtemperature of 1300 ' for two hours at a time for 30 hours in an * ' Phil. Mag. , ' Ser. 6 , vol. 7 , p. 388 .
t ' Roy .
Soc. Proc. , ' A , vol. 80 , p. 535 .
1912 .
] The Volatility of Metals of the Platinum Group .
electric furnace , the rhodium being cooled and weighed at intervals of two hours:\#151 ; Table Y. Grains .
Loss .
Grains .
Per cent. Original weight of rhodium 32 -774 After 4 hours at 1300 ' , weighed 32 -767 0*007 0 '021 \#187 ; \gt ; 6 " , , 32 -765 0*009 0*027 , , 8 , , , , ... ... 32 -763 0*011 0*034 \#187 ; , , , , 32 -760 0*014 0*043 \#187 ; 12 , , " 32 -758 0*016 0*049 \#187 ; 14 \#187 ; \#187 ; 32 -755 0*019 0*058 \gt ; \#187 ; 1^ a a ... ... 32 -752 0*022 0*067 n I\#174 ; \gt ; \gt ; jj 32 -749 0*025 0*076 , , 20 " 32 '746 0*028 0*085 22 " " 32 -743 0*031 0*095 n 24 \#187 ; \#187 ; 32 -739 0*035 0*107 \#187 ; 26 \#187 ; a ... ... 32 -734 0*040 0*122 tt 60 " " 32 -731 0*043 0*131 Fig. 8 shows the curve plotted from these data .
RHODIUM 0 2 4 0 S 10 12 1416 IS 20 22 2426 2S 30 HOURS A1 1300 ' Fig. 8 .
After the above heating the rhodium did not appear much changed .
It was a little darker , as if with a slight tarnish , but showed no crystalline structure .
Ruthenium at 1300 ' .
Ruthenium does not lend itself to such experiments as the foregoing owing to the formation of a volatile oxide .
A piece of the pure metal , in the form of a highly polished plate , exposed in the furnace to a temperature of 1300 ' for eight hours , lost 25 per cent , of its weight .
After this heating the ruthenium was of a dull black and was covered with a coating of oxide having a fused appearance .
Sir W. Crookes .
[ Feb. 15 , The diagram ( fig. 9 ) shows the loss per cent , in weight of the metals platinum , palladium , iridium , rhodium and ruthenium on the same scale when exposed to a temperature of 1300 ' for two-hourly periods .
O 2 4 6 8 1012 14 16 18 2022 2426 28 30 HOURi *T i300 ' C Fig. 9 .
Having obtained such unexpected results at 1300 ' it was of interest to see how these metals would behave at a temperature sometimes employed in an analytical laboratory .
* Platinum at 900 ' .
I therefore arranged a large M4ker burner , with fused silica triangle and a surrounding clay cylinder to obstruct radiation , and with it heated an almost new platinum crucible .
The thermo-couple showed a temperature of about 900 ' in the centre of the hot crucible .
After being heated to this temperature for 10 minutes the crucible was cooled and transferred to the ' balance .
It weighed 121*059 grains .
It was now subjected to 10 successive heatings of two hours each to 900 ' , weighing each time .
The original weight of 121*059 grains was not found to vary in the slightest degree , and the same experiment tried with other platinum crucibles gave a similar result .
A 1912 .
] The Volatility of Metals of the Platinum Group .
473 temperature of 900 ' is a full orange heat , and , unless a blowpipe is used , is higher than platinum crucibles are usually subjected to in the laboratory .
Palladium at 900 ' .
Palladium was next tried at a temperature of 900 ' under the same conditions to which platinum was subjected .
The following table shows the diminution in weight:\#151 ; Table VI .
Grains .
Loss .
Grains .
Per cent. Original weight of palladium 56 *579 After 2 hours at 900 ' , weighed 56 *570 0-009 0-0159 , ) 4 , ) , , 56 *560 0-019 0 *0336 , , 0 , , ... ... 56 -550 0*029 O -0513 , , 8 , , , , ... ... 56 -535 0-044 0 *0778 , , 10 , , , , ... ... 56 *527 0*052 0 -0919 jj 12 " " 56 *521 0-058 0-1025 j\gt ; 14 , , , , 56*512 0-067 0-1184 " 16 " " 56 -505 0*074 0-1308 " 18 " " 56 -500 0*079 0-1396 \#187 ; 20 " , , 56 -491 0-088 0 -1555 " 22 " " 56 -487 0-092 0 -1626 " 24 " " 56 -481 0-098 0 1732 26 " " 56 -478 0-101 0-1785 \#187 ; 28 , , , , 56 -477 0-102 0 -1803 \#187 ; so " \#187 ; .
.* ... .
56 *476 0-103 0-1827 The palladium scarcely altered during these heatings .
Beyond a faint pink tinge no signs of superficial oxidation could be detected , and the surface , with the exception of a few more blisters , presented practically the same appearance as it had after the 1300 ' series .
Iridium at 900 ' .
Having found platinum to be absolutely fixed at 900 ' , it was of interest to see how iridium would behave at that temperature .
Another iridium crucible was taken , and its original weight , after good ignition , was found to be 175*374 grains .
Heating to 900 ' over a Meker gas burner in air for 2 hours 25 minutes reduced the weight to 175*322 .
In Table VII is shown the gradual diminution in weight with the duration of heating .
After these successive heatings to 900 ' , the iridium crucible was a little darker than it was originally , but it had no crystalline moire appearance , like the other one after having been heated for 22 hours to 1300 ' .
Sir W. Crookes , [ Feb. 15 , Table VII .
Grains .
Loss .
Grains .
Per cent. OriginaJ weight of iridium 175-374 After 2 h. 25 m. at 900 ' , weighed ... 175 -322 0*052 0*030 " 4 h. 40 m. j\gt ; jj ... 175 -297 0*077 0*044 " 6 h. 40 m. jj jj ... 175 -289 0*085 0*048 " 8 h. 40 in .
jj jj ... 175 -268 0*106 0*060 " 11 h. 40 m. jj jj ... 175 -244 0*130 0*074 " 14 h. jj \#187 ; j ... 175 -241 0*133 0*076 " 16 h. jj jj ... 175 -221 0*153 0*087 " 18 h. jj jj ... 175-219 0*155 0*088 " 20 h. jj jj ... 175 -215 0*159 0*091 " 22 h. jj jj ... 175 -213 0 *161 0*092 Rhodium at 900 ' .
* Experiments were now instituted to see if a temperature of 900 ' continued for many hours would have any effect on metallic rhodium .
Table VIII .
Original weight of rhodium ... ... ... ... .
32*731 grains .
After 2 hours at 900 ' , weighed ... ... ... 32*731 " j ) 4 " " 32*732 " \#187 ; 6 jj jj \#163 ; 2*731 " jj 8 \#187 ; \#187 ; 32*731 " jj 10 5\gt ; \#187 ; 32*732 " The weight remains almost exactly the same .
The differences , amounting to 0*001 grain , equal to a difference of 0*003 per cent. , are due probably to slight superficial oxidation to RhO , and reduction of the oxide to the metallic state in a reducing atmosphere .
I have plotted these curves on one diagram ( fig. 10 ) so that the volatility of *20t PALLADIUM 8c IRIDIUM *18 " .id 900 " *12 H*io \#163 ; *08 S*06 *04 2 4 6 8 10 12 14 16 18202224262830 Fig. 10 .
1912 .
] The Volatility of Metals of the Platinum Group .
475 the metals at 900 ' can be compared one withi the other , and also with the corresponding curve of metals at 1300 ' .
The horizontal scale of hours is the same in each , but to render the curves at 900 ' distinct I have been obliged to make the vertical scale of percentage loss 10 times as large as it is in the 1300 ' curves .
Summary .
These results bear two explanations:\#151 ; ( 1 ) The metal is volatile per se at these high temperatures , or ( 2 ) the metal unites with oxygen at a certain temperature , forming a volatile oxide , which may either volatilise unchanged , , or may decompose at a higher temperature with deposition of the metal , the oxygen acting in this case as the temporary carrier of the metal .
It is .
probable that each of these causes is active in one or other of the metals experimented with .
I will take the case of the metal first tried , viz. , platinum .
The universal experience of chemists is against the supposition that platinum forms a volatile oxide below 1300 ' .
Deville and Debray , who worked long and thoroughly on the platinum metals , agree that " platinum is distinguished from all the metals which accompany it in the mineral , by the fact that it does not unite direct with oxygen in whatever condition the two bodies are placed."* The mode of occurrence of the beautiful crystals of platinum is against the supposition that they are a product of the decomposition of an oxide , for the crystals deposit on a part of the apparatus that is at a slightly lower temperature than the bulk of the metal , and it is inconceivable that platinum should unite with oxygen to form a volatile oxide at one definite temperature , and part with this oxygen and come down in metallic crystals at a little lower temperature .
The boiling-point of platinum is put by Kaye and Laby at about 2450 ' .
f Moissan 's electric furnace , in which the arc is used , is said by him to give with ease a temperature of 3500 ' , and here platinum enters into fusion in a few minutes , and soon volatilises .
The metallic platinum collects in small brilliant globules and in powder on the cooler parts of the electrodes , or on the surface of the lower brick some centimetres from the crucible . !
No. mention is made of the metal condensing in crystals .
I must therefore come to the conclusion that platinum is absolutely non-volatile at 900 ' , a temperature easily attainable in an analytical laboratory , and that the formation of crystals of the metal in the electric furnace is a true case of sublimation .
* 'Comptes Rendus , ' 1878 , vol. 87 , p. 441 .
+ 'Physical Constants , ' 1911 , p. 49 , Longmans .
+ Moissan , ' Le Four Electrique , ' p. 43 .
Sir W. Crookes .
[ Feb. 15 , The next metal , iridium , under experiment behaves differently to platinum .
It is admitted that iridium is volatile at a high temperature .
Thus , Mendenhall and Ingersoll* speak of melting iridium into a globule , and then re-melting it two or three times , before it entirely sublimed .
This at a temperature above its melting-point , which these authors put at between 2300 ' and 2400 ' .
Waidner and Burgess , f describing an " iridium furnace , " of which the essential part is an iridium tube 25 cm .
long , 2 cm .
in diameter , and 0-25 mm. wall thickness , state that , to avoid evaporation of the iridium , it was coated with Nernst 's refractory earth mixture .
These illustrations , however , are taken from observations of experimentalists who were working with iridium at or near its melting-point .
At high temperatures below 1000 ' iridium oxidises , forming an oxide , lr203 , which is volatile .
Deville and Debray consider the alleged volatility of the metal is due to the formation of this volatile oxide .
They say : " Above 1000 ' all volatilisation becomes impossible in our atmosphere , because the oxide of iridium ceases to exist , and the metal is at least as fixed as platinum .
" !
In my experiments the cold iridium was put into the furnace , previously heated to 1300 ' or thereabouts , and the metal quickly became hot .
While it was rising to 1000 ' it oxidised superficially , and the oxide rapidly volatilised , accounting for the loss of weight .
I devised an experiment to see if iridium would volatilise at a high temperature in a vacuum .
A fused silica tube , 1 cm .
diameter and 20 cm .
long , had a bulb 2\ cm .
diameter blown on the end ( fig. 11 ) .
In the bulb was put 27'619 grains of clean iridium , and the other end of the silica tube was drawn out for connecting with the pump and sealing .
It was exhausted to a high vacuum and heated to near redness along its whole length , till all moisture and occluded gases had been removed ; it was then sealed off .
The tube was placed bulb uppermost in the furnace in such a position that the iridium would be at the point of greatest heat , the lower part of the tube remaining comparatively cool .
The bulb was kept at a temperature of 1300 ' for 30 hours .
On examining the silica tube when cold , it was seen that the long-continued high temperature had caused the bulb and the upper part of the tube to devitrify , and become white and translucent , and that it had an irregular black deposit on the lower part , which , on examination , proved to be metallic iridium .
The iridium removed from the bulb was now found to weigh 27'600 grains , showing a total loss of 0 019 grain , or 0069 per cent. , in 30 hours .
* ' Physical Review , ' vol. 25 , p. 13 .
t 'Bulletin of the Bureau of Standards , Washington , ' vol. 3 , p. 183 .
J ' Comptes Rendus , ' vol. 87 , p. 445 .
The Volatility of Metals of the Platinum Group .
The presence of a deposit of iridium in the cooler end of the silica tube may thus be accounted for : during the heating of the bulb containing the iridium , a little air leaked in , and the oxide of iridium formed before the temperature became high enough to decompose it volatilised and deposited on Fig. 11 .
the cooler part of the tube .
There the oxide remained until the heat rose to the decomposing-point\#151 ; somewhere about 1000 ' .
I must not conclude this paper without expressing my thanks to the firm of Johnson and Matthey , to whom I am indebted for many specimens of the pure metals used in this research .
vol. lxxxvi.\#151 ; A.
|
rspa_1912_0041 | 0950-1207 | On the distribution of the scattered R\#xF6;ntgen radiation. | 478 | 494 | 1,912 | 86 | Proceedings of the Royal Society of London. Series A, Containing Papers of a Mathematical and Physical Character | J. A. Crowther, M. A.|Prof. Sir. J. J. Thomson | article | 6.0.4 | http://dx.doi.org/10.1098/rspa.1912.0041 | en | rspa | 1,910 | 1,900 | 1,900 | 13 | 271 | 5,935 | http://corpora.clarin-d.uni-saarland.de/surprisal/6.0.3/?id=rspa_1912_0041 | 10.1098/rspa.1912.0041 | null | null | null | Atomic Physics | 39.541314 | Tables | 37.917638 | Atomic Physics | [
11.722373962402344,
-74.86072540283203
] | ]\gt ; On the Distribu tion of the Scattered Rontgen By J. A. CROWTHER , , Fellow of St. John's- College , Cambridge .
( Communicated by Prof. .
J. Thomson .
Receiwed February 15 , \mdash ; Read March 21 , 1912 .
) Introduction .
The fact that a substance through which Rontgen rays from a focus tube are passing becomes itself a source of secondary Rontgen rays has long been known .
The most probable explanation was given by Prof. Sir J. J. Thomson .
If a Rontgen pulse is due to the acceleration of a charged electron , then if the electrons in the atom are to move under the action of the electromagnetic forces in the wave front of the primary ntgen pulse , their motion will be accelerated during the passage of the latter through the atom , and they will themselves become sources of secondary Rontgen radiation .
Considering only a single electron , the intensity of the secondary radiation at any angle with the direction of motion will be proportional to If the primary beam is unpolarised , the motion of the eIectron may have any direction in the plane at right angles to the primary beam .
The intensity of the scattered radiation in the direction with the primary beam is thus the mean of all the values of for that direction .
It can easily be shown that this is proportional to .
If is the intensity of the scattered radiation in the direction , we thus have .
( 1 ) This expression gives a distribution symmetrical about the primary beam and about a plane through the radiator at right angles to the primary beam .
There is a minimum of radiation in this plane , and a maximum , equal to twice the minimum , at right angles to this plane , both in the forward and backward direction .
Prof. C. G. Barkla some time ago found that the radiation coming back from a radiator in directions close to the primary beam was nearly twice as great as that in a direction at right angles to it , and thus obtained evidence in favour of the theory .
In the course of some experiments on the energy of the scattered radiatio was found necessary to know the actual distribution of the radiation round the radiator , and experiments were made to determine it .
narrow pencil of Bontgen rays was allowed to fall on a suitable radiator , * J. A. Crowther , ' Proc. Camb .
Phil. Soc November , 1910 ; 'Roy .
Soc. Proc 1911 , , vol. 85 , p. 29 .
On the Distribution the ttered Rontgen Radiation .
mounted on the axis of a wheel an ionisation chamber .
By turning the wheel , the latter could be placed at different angles with the radiator , and the intensity of the scattered radiation measured at different angles with the imary beam .
It was found that the theoretical expression did not exactly represent the experimental results .
The distribution of the radiation which came back from the radiator agreed closely with predicted by the theory , but , at any given angle with the primary beam , there was alwa .
more radiation scattered in the forward direction than in the vard .
This dissymmetry between the two sides of the radiator increased as the direction of the primary beam was more nearly approached .
Thus for an aluminium radiator there was , at an angle of with the primary beam , nearly three times as much scattered radiation in the forward as in the reverse direction .
The actual distribution in this case is shown in fig. 1 .
The value of the intensity of the scattered radiation in any direction is represented by the length of the vector drawn in that direction from the centre .
The full curve shows the distribution actually observed .
The inner broken curve represents the theoretical distribution .
For the return radiation , the two curves are practically coincident .
Somewhat later Prof. C. G. Barkla*published an account of a similar series of experiments .
He only observed dissymmetry at angles of less than with the primary beam , but Owen , who repeated my experiments in the Cavendish Laboratory , confirmed the results I had obtained .
He also found that the dissymmetry decreased as the primary rays became harder .
We shall return to this lesnlt later .
The fact that the distribution of the return radiation agreed so closely with that predicted by the theory of scattering naturally suggested that the excess of secondary radiation on the forward side of the radiator be due to some other cause of secondary radiation .
Experiments made on the absorption of the scattered radiation in the forward and backward directions failed to reveal any sppreciable difference in the character of the rays in the two directions .
The coefficient of absorption was in each case very nearly the same as that of the primary beam .
It was ested that a possible source of this excess radiation might be Barkla aAyres , Owen , Proc CPhil S ' 1912 .
] Distribution of the Scattered Rontgen possibility of the dissymmetry in the scattered radiation being due to irregular refractions if we could assume that only a small fraction of the pl.imary Rontgen rays were thus affected .
Only a small fraction of the encounters between the Rontgen rays and the atoms result in ionisation .
If we suppose that in.a similar way only a small fraction of the collisions result in any appreciable deflection of the primary ray it might be possible to explain the results obtained .
I am indebted for this suggestion to Prof. Sir J. J. Thomson , to whom I wish to express my best thanks .
Let us assume , however , for the present that the excess of the forward over the returned scattered radiation is due to some effect other than the symmetrical scattering of the primary beam .
It seemed desirable that further and more accurate experiments should be made to determine its exact distribution and its variation with the hardness of the primary rays .
tal Details .
A brief description of the apparatus may be desirable , as it differs in some respects from that described in the previous papers .
The radiator ( fig. 2 ) is carl'ied on an alnminium frame , the different parts of the framework being well out of the path of the primary rays .
The framework , which carried a pointel moving over a circular scale , could rotate about the axis , and the radiator could thus be set at any desired angle with the primary beam .
The primary beam from the focus tube was confined to a narrow rectangular pencil , by means of the lead , rectangular in Mr. J. A. Crowther .
On the shape .
It was found experimentally that there was very little radiation outside the geometrical cross-section of the beam as so defined .
Two equal and similar ionisation chambers , were fitted up with aluminium leaf electrodes as described in the previous papers .
They were mounted on carriers running on a circular geometrical slide , the centre of which was immediately beneath the axis of the radiator .
Each of the chambers was connected to a separate tilted electroscope in the way previously described , so that it could be moved freely round the circular slide without disturbing the connections .
Each ionisation chamber had an aperture of cm .
in width , and was placed 15 cm .
from the centre of the radiator B. The angle subtended at the radiator by the aperture was therefore about .
The ratio of the ionisation currents in the two chambers for equal intensities of radiation entering them was determined experimentally by placing them at equal angles with the primary beam , and on opposite sides of it .
The ratio was found to be constant for all angles .
The distribution of the scattered radiation is thus symmetrical on each side of the primary beam .
In performing the experiments , one of the two chambers , say , was placed at an angle of with the direction of the beam .
The other chamber was moved round to the angle at which it was desired to measure the intensity of the scattered radiation .
The radiator was then turned so that its normal bisected the angle between the secondary beams entering the two chambers , that is to say the angle in the figure .
It can easily be seen that in this position the lengths of path in the radiator of the two secondary beams are the same .
The two beams therefore undergo the same relative absorption , and no further account need be taken of this factor .
This adds considerably to the convenience and accuracy of the experiment , as it is difficult to keep the hardness of the focus tube quite constant over a series of experiments .
Let be the intensity of the scattered radiation entering the ionisation chamber when its axis is inclined at an angle with theprimary beam .
The ratio of the two ionisation currents ( corrected for the small difference between the two chambers when subject to the same intensity of radiation , as explained above ) gives the value of the ratio of .
Since the areas of the apertures of the two chambers are the same , this ratio is also a measure of the intensity of the secondary radiation per unit area in the two directions .
There is a certain amount of ionisation in the two chambers in the absence of the radiator ; this can be measured separately , and allowed for .
It is principally due to the scattered Rontgen radiation from the air traversed 1912 .
] of the Scattered Rontgen by the primary beam , and is only very appreciable at very small angles with the primary rays .
The first experiments were made with a radiator of alunninium foil .
Subsequently , radiators made by soaking best Swedish filter paper in paraffin wax were employed .
These have a much smaller coefficient of absorption for the rays than the aluminium , and it is possible , therefore , to obtain far more secondary radiation from them than from aluminium .
They were therefore principally employed in the ations which follow .
Rcsnlts .
In Table I are given the results obtained with a radiator of filter paper cm .
in thickness .
The first column gives the direction with the primary beam at which intensity was measured .
The columns give the value of the ratio at those angles for primary rays of different hardness .
The hardness of the primary beam is fixed by the th of the spark-gap ( measured between two brass spheres ) which is just sufficient to extinguish the focus tube when connected across its terminals .
The length of this spark-gap in centimetres stands at the head of the column to which it refers in the table .
The last column of the table gives the value of the ratio of the intensity per unit area of the scattered radiation in the direction to that at angles to the primary beam , deduced from equation ( 1 ) , p. 478 .
For brevity , we shall refer to this as the theoretical value .
It is , of course , independent of the hardness of the primary rays .
Table II gives the results of experiments made with filter-paper radiators of different thicknesses .
In these experiments the two ionisation chambers were fixed at angles of and respectively , and the hardness of the bulb was kept as constant as possible , with an equivalent spark-gap of about cm .
The first column gives thickness of the radiator in centimetres , Mr. J. A. Crowther .
On the the second the corresponding values of the to .
It will be seen that , within the limits of the experimental error , the ratio is independent of the thickness of the radiator .
I have shown in a previous paper* that the intensity of the radiation scattered at an angle of with the primary beam is simply proportional to the thickness of the radiator .
It follows , therefore .
that the intensity of the radiation at an angle of with the primary beam , and therefore also the intensity of what we have called the excess radiation , is also proportional to the thickness of the radiator .
Table II.\mdash ; Variation in the Ratio Table \mdash ; Aluminium Badiator .
for Filter-paper Badiators of Different Spark Gap cm .
Thickness .
Equivalent Spark Gap cm .
The , figures in Table I give directly the intensity of the scattered Bontgen radiation across an aperture of fixed area , placed so that the line joining its centre to the radiator makes an angle with the direction oi the primary beam .
If the primary rays are unpolarised , the intensity of the scattered radiation at an angle with the primary beam is independent of the plane in which it is measured .
The rays from most focus tubes show a certain amount of polarisation ; for the bulb used in these experiments it amounted to about 8 per cent. In order to reduce the effect as far as possible , the focus tube was placed so that the stream of cathode rays in it was at right angles to the plane in which the measul.ements were made .
In this position the effect of the admixed polarised rays would be to add to both numerator and denominator of the ratio to a small constant fraction depending on the quantity of polarised radiation present , and thus to reduce slightly the theoretical value .
The maximum correction for the bulb used did not amount to more than 4 per cent. .
A. Crowther , ' Proc. Camb .
Phil. Soc , vol. 16 , p. 366 .
1912 .
] bution of the ttered Rontgen Allowing , therefore , when necessary for the polarisation , we can now proceed to calculate from our results the whole intensity of the Bontgen radiation scattered by the radiator at an angle with the primary beam .
Let be the energy of the scattered radiation included within a cone of angle and increment .
We will call the whole intensity of the radiation in the direction .
The area swept out by this cone on a sphere of radius passing through the windows of the two ionisation chambers is Now if is the area of the window of the ionisation chamber , supposed small enough to be included in this ] , the intensity of the rays entering the ionisation chamber is equal to But , the area of the window , is constant , and is constant .
We may write , therefore , constant ) .
To obtain from the readings in Table I , we must multiply by the corresponding values of In the same way if we denote by the whole of the true scattered radiation ( i.e. the radiation scattered in accordance with the theory ) included in the hollow cone of angle and increment , we have constant ) , where is the intensity of this radiation entering the ionisation chamber in the direction .
In order to find therefore , we have to multiply the values given in the last column of Table I by the corresponding value of The difference between the values of and for any ooiven angle gives the amount of the secondary radiation which has still to be explained .
Let us denote the intensity of this excess radiation in the direction .
Then The various stages of the calculation for the case of a radiator of filter paper of thickness cm .
and for an equivalent of cm .
are given in Table III .
The first column of this table gives the angle at which the measurements of were made .
The second column gives the corresponding value of in terms of , the radiation at right to the primary beam , taken from Table I. The third column contains the values of .
As we have shown above this is proportional to .
The fourth column gives the corresponding value of deduced from ( 1 ) .
The difference between them , given in the fifth column of the table , gives the magnitude of the effect which remains to be explained .
In other words , assuming that the Mr. J. A. Crowther .
On the [ Feb. 15 , distribution of the scattered radiation is that given by ( 1 ) , p. 478 , the fifth column of Table III gives the distribution of the secondary radiation whose origin is still to be explained .
Table III.\mdash ; Filter-paper Radiator .
Equivalent Spark Gap cm .
I. Angle of measurement of scattered radiation .
II .
Values of III .
multiplied by to obtain the lvhole radiation between and IV .
Value of same quantity on simple theory of scattering .
V. Difference between Columns III and IV , giving excess radiation .
VI .
Value of , where VII .
Ratio of Columns V and VI .
These operations are represented graphically in fig. 3 .
Th lower unbroken curve gives the relation between , the intensity of the scattered radiation on the theory of scattering , and .
The upper unbroken curve represents the experimental curve for the measured radiation .
The difference between the ordinates of these two curves is therefore the value of the excess radiation for the angle at which the ordinates are drawn .
This difference is represented on three times the vertical scale of the other by the broken curve in the figure .
This broken curve therefore represents the distribution of the excess radiation .
It will be seen that it rises rapidly at first to a sharp maximum at an angle of about with the direction of the primary beam , and then falls , at first rapidly and then more slowly , to a value which approaches zero as approaches We have , of course , tacitly assumed , in making our calculations , that the intensity of the excess radiation is inappreciable at angles of and more with the primary beam .
That this is practically the case is shown by the fact that all the experiments have proved that the distribution of the scattered radiation at angles of and above is very closely in agreement with the distribution calculated from equation ( 1 ) . .
J. A. Crowther .
On the [ Feb. 15 , are all very similar in shape .
As the rays get harder , however , two changes occur : ( 1 ) the whole area of the curve gets less , that is to say the total amount of the excess radiation decreases , and ( 2 ) the maximum of the curve gets nearer and nearer to the primary beam .
These curves enable us to explain the results obtained by Owen for hard rays .
With his apparatus , he was unable to make experiments at angles less than with the primary beam .
Drawing an ordinate at it will be seen that the of the ordinate , which measures the excess radiation over the theoretical value and therefore the dissymmetry in the position , rapidly diminishes as the hardness of the rays increases .
For rays of an equivalent spark-gap of 4 cm .
it is already almost inappreciable , and thus , for primary lays of this hardness , the distribution of the radiation at angles greater than would be that of the simple scattered radiation .
There would be no appreciable dissymmetry .
The more complete curve given in fig. 4 shows that there is , even for rays of this hardness , a considerable amount of excess radiation , but the maximum is close to the primary beam .
The actual dissymmetry observed at any therefore depends upon two factors:\mdash ; ( a ) The whole area of the curve , and ( b ) The position of the maximum of the curve .
Measurements made at an angle of or less would show an actual increase in the dissymmetry as the hardness of the rays increased .
Distribution of the Excess diation .
We must now proceed to consider the shape of these distribution curves more closely .
It may be noted in that as these curves represent the difference of two curves their accuracy diminishes very rapidly when this difference becomes small compared with either of the curves .
Owing to the small amount of scattered radiation entering the ionisation chambers under the conditions of the experiment , and the difficulty of keeping the conditions quite constant during the experiments , it would be futile to expect an accuracy of more than about 2 per cent. or 3 per cent. in the measurements of the intensity of radiation .
An error of this amount in the measurement at an angle of would introduce an error of as much as 20 per cent. in the difference we are measuring .
We shall therefore confine our attention to angles of less than , where the difference to be measured is relatively greater and the proportionate error correspondingly less .
Considering the curves of fig. 4 in detail , one may note their general resemblance to the curves representing the distribution of a parallel pencil of 1912 .
] Distribution of the Scattered Rontgen diation .
-rays after passing through a thin sheet of matter .
The author has shown that this case may be represented closely by the expressions given on p. 480 , based on the theorem of Lord Rayleigh on random displacements .
If the present curves are to be of this form , the intensity of the excess radiation must be expressible in the form , ( 3 ) where has been written for , and is a constant .
It is evident that is the ratio of the whole of the excess radiation round the radiator to the intensity , , of the scattered radiation entering the ionisation chamber at right angles to the primary beam .
Writing for the expression we see that if ( 3 ) expresses the actual experimental distribution of the excess radiation we must have , a constant for all values of In order to determine the value of for a given experimental curve it is most convenient to consider the position of the maximum .
with respect to and to zero , we have , so that .
( 4 ) The value of for which the excess radiation reaches a maximum can be found from the experimental curves .
Taking the case represented in this maximum occurs at an angle of or radian ; the value of is , therefore , .
Substituting in the formula we obtain the values of given in Column 6 of Table III .
The last column of this table contains the values of , or K. We have shown that if our experimental curves are expressible by equation ( 3 ) this ratio must be constant .
Similarly if this ratio is constant we may assume that the distribution of the excess radiation is represented by this expression .
The last column of Iable III shows how nearly this is the case : The agreement is , on the whole , satisfactory .
There is no systematic variation from the mean value as increases , and the fiuctuations from the mean are not greater than might have been reasonably expected from tlIe nature of the experiments .
The calculations from the othel .
sets of observntions showed a similar agreement .
Similar experiments and calculations were also made for an aluminium radiator .
The results are given in Table .
The angle of maximum radiation is much greater for the filter-paper radiators , and the whole area of the curve is much larger .
The agreement between the experimental and theoretical curves is , , equally satisfactory .
We may conclude then that the distribution curves for the excess radiation have the form we have suggested for them , and that the intensity of the excess radiation at an angle can be represented by equation ( 3 ) .
Mr. J. A. Crowther .
the [ Feb. 15 , Constants of the Curves .
values of the various constants of this expression depend upon ( 1 ) the nature of the radiator , and ( 2 ) the hardness of the exciting rays .
So far as they have been determined they are given in Table I. Equivalent spark gap of focus tube .
II . .
the angle at which reaches its maximum value .
II1 .
Corresponding value of oonstant .
IV .
Corresponding value of constant K. V. Ratio of whoie excess radiation to whole scattered radiation .
VI .
Coefflcient of excess radiation see p. 491 ) .
The first part of the table deals with the radiators of waxed filter paper ; the last row refers to a ladiator of aluminium .
The first column of the table gives the equivalent spark-gap of the } tube with which the experiments were made .
The second gives the angle at which the excess radiation reached its maximum value , and the third the corresponding value of the constant It will be seen that , as the spark-gap increased , the maximum of the excess radiation moved in towards the direction of the primary beam , and the value of in consequence diminished .
Comparing the results for filter paper and aluminium it will be seen that the maximum occurs much further out for aluminium than for filter paper .
Taking the case of incident rays of equal hardness , it may be noticed that the ratio of the values of for aluminium and filter paper is or .
This is very nearly the ratio of the densities of the two radiators .
The value of , which is proportional to the whole energy of the excess radiation , is given in the fourth column of Table V. It will be seen that ,1912 .
] Distribution of the Scattered Rontgen diation .
it decreases as the primary get harder .
It will be noticed also that the value for aluminium is more than ten times that for the filter paper .
Experiments with other radiators of higher atomic weight are very desirable .
Owing to their high coefficients of absorption , and to the presence of fluorescent radiation in such large amounts as to mask almost completely the radiation we wish to measure , it is difficult to make the measurements required with any degree of accuracy .
Our experiments show that the excess radiation is not proportional to the density , the emission per unit mass four times as great for aluminium as for filter paper .
of the The secondary Rontgen radiation round a radiator ( in the absence of the homogeneous secondary radiation which is distributed , as we have previously shown , uniformly round the radiator ) can thus be represented as the sum of two radiations , the scattered radiation distributed in accordance with ( 1 ) , p. 478 , and the excess radiation given by equation ( 3 ) .
We can calculate from our results the intensities of these two radiations relative to each other and to the .
primary beam .
Let and be the whole intensities of the excess and scattered radiations respectively given out by the radiator .
From p. 489 we have We have seen that we may regard the intensity as due almost entirely to the true scattered radiation .
Calling 2S the angle subtended at the centre of the radiator by the window of the ionisation chamber ( radian in these experiments ) we have on evaluating the integrals .
Thus KS .
The values of are iven in the fourth column of Table , the corresponding values of in the fifth column of the same table .
For filter paper the energy of the excess radiation is only a small fraction of that of the scattered radiation .
It is much more important in the case of aluminium .
The ratio decreases as the primary rays become harder .
of the Scattered Radiation .
In order to calculate this it is necessary to know the ionisation produced by the primary beam falling upon the radiator in terms of the intensity entering the standard chamber .
This can be done directly by turnin the chamber until its angle with the primary beam is zero ; the primary Mr. J. A. Crowther .
On the [ Feb. 15 , then pass directly down the chamber .
Tt is , of course , necessary that the window of the chamber should be large enough to include the whole cross-section of the primary beam .
The greater intensity of the primary rays necessilates the addition of a large capacity to the primary electroscope system .
The ratio of the capacities of the two systems can be obtained by the method described by Norman Campbell .
Let be the capacities of the primary and secondary systems , and the ratio of their rates of charging up .
Then if is the intensity of the primary radiation , It must be noted that is not the whole scattered radiation between the angles , and , as the aperture of the ionisation chamber does not completely surround the primary beam .
If is the angle subtended at the radiator by the length of the apertul.e ( at right angles to the plane of measurement ) , the whole intensity of the radiation scattered between these angles is greater than in .
the ratio In order to eliminate the correction for absorption of the rays the radiator was inclined to the primary beam at an angle of .
The paths of the primary and secondary beams were then equal in the radiator .
The effective thickness of the radiator ( waxed filter paper ) in this position was cm .
The intensity of the scattered radiation has been shown to be proportional to the thickness of material traversed by the primary rays .
We may therefore write where is a constant which we may call the coefficient of scattering .
Substituting from above we have , For the present experiments we have radians , cm .
Inserting these values in the equation we obtain for the coefficient of scattering , , the value As the density of the filter-paper radiators is almost exactly unity , this value of is also the value of the coefficient of scattering per unit mass .
It has been thought that the mass coefficient should be independent of the nature of the radiator .
Recent experiments of the author have shown that this is not the case .
The amount of radiation scattered increases with the 1912 .
] Distribution of the Scattered Rontgen Radiation .
atomic weight of the radiator .
Thus , the mass coefficient of the scattering being for filter paper , for aluminium it is , for copper and nickel about , and for tin as as o , more than five times as great as for filter paper .
Ihese results have important bearings on the constitution of the atom .
of Excess Radiation .
Knowing the intensity of the scattered radiation we can calculate that of the excess radiation in terms of the primary radiation .
We have shown in Table II that the ratio of the excess radiation to the scattered radiation was independent of the thickness of the radiator .
We have already seen that we can write in the form , where is a constant .
It follows , therefore , that we may also write the whole intensity of the excess radiation in the form where may be called the coefficient of the excess radiation .
We can then write The value of the latter ratio is }iven in Table .
The corresponding values of the coefficient are given in the last column of that table .
Unlike the coefficient of scattering , it is not independent of the hardness of the primary rays , but decreases as the primary rays get harder .
With the ionisation chamber in the position , the coefficient of absorption of the primary rays in the substance of the radiator can be found by interposing different thicknesses of the substance in the path of the primary beam .
The coefficient of absorption for rays with an equivalent spark-gap of cm .
in the waxed paper is cm .
The secondary ontgen radiation round a radiator , in the absence of any homogeneous secondary radiation , has been shown to be divisible into two parts : the scattered radiation distributed in accordance with the expressions deduced from the usual theory of scattering , and ( 2 ) an additional or excess radiation of the same quality .
An expression has been deduced for the ibution of this excess radiation , and the constants of the expression determined for different radiators and different qualities of the primary rays .
Experiments have also been made to determine the energy of each type of radiation in terms of that of the other and of the primary beam .
VOL. LXXXTI.\mdash ; A. 2 On .
the .
Distribution of the Scattered Rontgen diation , It would perhaps lie premature to put forward at the present moment , any suggestion as to the nature and origin of the excess radiation .
We have already noted that there is a possibility of explaining it as being due to deflection suffered by a small fraction of the primary Rontgen pulses ' encounters of a special type with the atoms of the radiator .
Of the nature of such collisions we have at present no information .
On the other hand , the similarity of the distribution curves to those.for a parallel beam of -rays ests that possibly the cathode particles which are given off in quantity when Bontgen rays fall upon a radiator may play some part in the production of what we have called the excess radiation .
From this point of view , the excessradiation would be due to the retransformation into rays of some fraction of this secondary cathodic radiation .
That some such transformation must take place seems certain .
Furthe.r examination of the hypothesis , however , shows that , in order to make it fit the curves , further assumptions must be made , for which there is at present little evidence .
Experiments in progress to test these points .
Pending their completion , it is , perhaps , not desirable to develop the suggestion further .
In conclnsion , I have pleasure in expressing to Prof. Sir J. J. Thotnson my thanks for his interest in these experiments .
|
rspa_1912_0042 | 0950-1207 | Contributions to the study of flicker. -Paper III. | 495 | 513 | 1,912 | 86 | Proceedings of the Royal Society of London. Series A, Containing Papers of a Mathematical and Physical Character | T. C. Porter, M. A., D. Sc.|Lord Rayleigh, O. M., F. R. S. | article | 6.0.4 | http://dx.doi.org/10.1098/rspa.1912.0042 | en | rspa | 1,910 | 1,900 | 1,900 | 16 | 180 | 7,273 | http://corpora.clarin-d.uni-saarland.de/surprisal/6.0.3/?id=rspa_1912_0042 | 10.1098/rspa.1912.0042 | null | null | null | Optics | 65.419813 | Tables | 24.570532 | Optics | [
14.972870826721191,
-13.926175117492676
] | ]\gt ; Contributions to the Study of Flicker . .
III .
By T. C. PORTER , M.A. , D.Sc .
( Communicated by Lord Rayleigh , O.M. , F.R.S. Received January 2 , \mdash ; Read April 25 , 1912 .
) Since the last papers*the research has been continued at intervals through the nine years .
Some numerical errors on pp. 325 ) in the last paper have been detected by the author , but nothing ] in the least degree alters the main results of that paper , viz. , that the number of revolutions per second which a disc having a white sector , and a black sector must make in order that the flicker may just vanish , under an illumination I , iven by an equation of the form , being a constant , and of the form , where and are constants .
If the disc is considered to be under unit illumination when lighted by a standard stearine candle , burning .
of stearine per hour , at a distance of 4 metres ; that is , if I is taken to 1 under these conditions , then , from the combination of the series of observations described in Papers I and II , with many others made since , it follows that the numerical value of is deternlined with a very fair degree of accuracy to wilhin at most three revolutions per second , and generally within one , from the equations , for discs half white , half black , and , when the of the white sector is These two equations hold only for illuminations above , i.e. that given by the candle at 2 metres distance .
For illuminations below , the two corresponding equations to be used are , for the disc , and for discs with a white sector , other than , the equation gives satisfactory values for white sectors larger than , but not so consistent 'Roy .
Soc. Proc vol. 63 , p. 347 , and vol. 70 , p. 313 .
VOL. LXXXVI.\mdash ; A. 2 Dr. T. C. Porter .
[ Jan. 2 , with experimental results in the case of smaller white sectors .
A number of careful experiments were made to determine whether the suspected sudden change in the slope of the straight line expressing the variation of with I was real or not ( the break is shown in Paper II , fig. 2 ) , with the that it is fully confirmed , the line being certainly broken , apparently sharply , at very approximately illumination 4 , i.e. of the candle at 2 metres .
This shows well in of the present paper , the details for the various new points being given , without omissions , in the accompanying table .
The made with the axis of X by the upper part of the line , given as in Paper II , seems to be more accurately represented as , whilst that by the lower , conjectured from few readings made for Paper II to be , is found to be very nearly .
The experimental details and precautions observed were the same as those already described .
To produce the lower illuminations , a single thickness of filter paper was placed in front of the standard candle , so as to cut off part of its light , and the brightness of the residual light was found to be , the paper at 647 mm. distance giving the same illumination as another standard candle at 2500 mm. The lowest value of at which flicker on a half-white disc was observed to disappear was 5 , in a room almost completely dark , and after 1912 .
] Contributions to the Study of Flicker : more than an hour , and then by The cause of the above-mentioned remarkable discontinuity can only , at present , be conjectured in the light of experiments to be presently dib It cannot well be due to the cessation of the expansion of the of the eye as the illumination falls , for it is evident that this expansion tends to keep the retina better illuminated , and therefore to make fall more slowly ; that is , if the pupil ceased to expand , would fall more rapidly with decreasing illumination , whereas , whatever be the cause of the change in the line , it is one which makes ?
fall more slowly .
Experiments to determine the law connecting the of the pupil with the illumination have been begun ; it seemed desirable to fix , if possible , the limit to the expansion ; to this end the eyes to be examined were kept in Paper II , p. 31 1912 .
] Contributions to the Study Flicker .
powder 's constituents , or from the little heap of conbustible having a tail which prolongs the " " exposure Seven different pairs of eyes were tried , with the result that the ratio of the diameter of the iris 's outer circle to that of the pupil varied from nearly four-thirds to three-halves .
The last mentioned will be found to be that in .
Attempts were made at first to measure this ratio under various degrees of illumination with a telescope and micrometer eyepiece , but the results were unsatisfactory .
At low illuminations the limit of the dark pupil was very hard to see , and made almost invisible by the necessary artificial illumination of the spider lines , and , at higher values of I , the pupil was never steady enough , not only moving slightly .
as a whole , whilst measurements were being taken , but also constantly changing its diameter slightly , now , now contracting .
The flash-light method is free from these objections ; the eyes can be fixed on the white disc while they are , the flash made well to the side of the disc .
The measurements taken so far only show that it is unlikely that the variation of the pupil 's size at illuminations less than 16 any considerable part in the form or dimensions of the curves given .
The sectors of white and black on a disc may be arranged symmetrically or not .
If there be only one sector of each sort , it may now be said that we know the rate at which the disc must be rotated under a given illumination in order that flicker may just vanish , for all possible values of the two sectors .
How is this rate affected if there are more than two sectors ?
A definite answer can be given for one class of disc , viz. , that in which there are the same number of sectors of white and black , and all of these of the same angle .
Take , for example , a disc with four sectors of alternately white and black .
It is clear that , at any rate of rotation , such a disc presents to the eye exactly the same stimulus and rest periods as a disc half white , half black , if the .-sector disc be made to go round at half the speed of the other ; consequently , if it require , say , 40 revolutions per second to make a " " half-and-half\ldquo ; disc 's flicker vanish under a given illumination , it will require exactly 20 revolutions per second to make the disc in quarters show no flicker at the same illumination .
Experiment shows that this is exactly true ; under all illuminations , a disc in qnarters becomes flickerless at exactly half the speed necessary for a disc halves .
A disc of six sectors , three white and three black , is flickerless at one-third the speed of the half-and-half when the latter is just fiickerless ( the illunlination being the same ) .
The following is a typical experiment : A disc was divided into three concentric rings , the innermost made of white and 18 black ; the next , with sectors , alternately white and black ; whilst Dr. T. C. Porter .
[ Jan. 2 , outermost ring was divided into 12 equal sectors , six white , six black .
The disc had 24 holes in its rim , and the notes it gave were : ( a ) For disappearance of flicker in the innermost ring A above ( b ) For the middle ring : A below ( c ) For the outelmos6 ring above all three notes sounded very exactly .
Another experiment was made with a white disc with two concentric rings , the inner a half white , half black ; whilst the outer was divided into 24 equal sectors , alternately white and black .
On rotating this under a certain illumination , the flicker for the inner circle vanished at above , or vibrations per second , whilst the flicker for the outer ring vanished at below ( vibrations per second ) .
Now The number of revolutions per second necessary for flicker just to vanish under a given illumination is therefore in all perfectly symmetrical discs inversely proportional to the number of sectors .
This fact has proved very useful in the present research , for when examining the rotation necessary for a half-and-half disc under high illuminations , the speed of rotation of the disc is very great , and if the disc has , say , 12 holes , the pitch of the note emitted is high .
This means that any error in judging the pitch of the sound makes a large error in the value of inferred .
If the number of holes in the syren is diminished , the sound it gives is too much enfeebled .
The pitch of a note is most correctly estimated when it lies within the register of the experimenter 's own voice , The remedy for this difficulty with high speeds is to use a disc with two or three times as many sectors ; flickel .
will then disappear at a half or a third the speed necessary for the half-and-half disc , and then , by the above law , we can calculate the speed of the latter .
The law for perfectly symmetrical discs is also useful if the flicker disc is used to measure bright illuminations such as obtain out of doors in summer weather .
These can be estimated , with a near approach to accuracy , and without requiring any great speed ( though it must be even ) , if a disc with sectors be used , alternately white and black .
Asymmetric , with four or more \mdash ; The exact general law connecting and the number and distribution of the sectors has not yet been found , but the following facts have been proved:\mdash ; ( a ) The flicker on the asymmetric disc always vanishes at a higher rate of rotation than on the perfectly symmetrical disc of the same number of sectors , and the same sum of the white sectors ' angles .
a disc was made up of the four following sectors taken clockwise in 1912 .
] to the Study of Flicke , order round the disc , 12 black , white , black , and white , whilst the central part of the disc was a circle with four equal sectors of alternately black and white .
The rates of rotation for flicker to vanish in these two arrangements were as 3 to 2 , the asymmetrical the higher speed .
Another asymmetric disc consisted of four white sectors of , whilst between these white sectors came , in order , black sectors of , and respectively .
The corresponding symmetrical disc , occupying the central portion of the other , is a1145o sectors , alternately black and white .
The relative rates of rotation of these two arrangements were also , as 3 : 2 , and also just half the rates necessary for the corresponding discs in the last experiment The reason for this last fact is , obviously , that the corresponding discs in the two experiments are similar , but have twice as many sectors in the second case .
( b ) The direction of rotation makes no difference to with an asymmetric disc .
To ascertain this it is necessary to make the conditions of illumination , etc. , exactly the same in the two cases , and this is very difficult to do in practice , and so the device shown in fig. 3 was resorted to .
The inner circle , going round it dockwise , shows white , 12 black , white , black ; the outer circle , going round it in the clirection , shows black , white , black , 12 white , which is the order of the sectors of the inner circle taken in the reverse direction , so that by rotating this disc we get , under exactly the same conditions , the effect of rotating the asymmetric disc first way , and then the other , under similar conditions .
result of the experiment is that , until flicker vanishes , the " " oppositely rotating\ldquo ; arrangements present a strikingly different but each becomes flickerless at the same moment , and at that llolnent of precisely the same even grey , the same grey as that of auy other disc which is , on the whole , half white and half black , and under same illumination .
At this of the enquiry it was considered to verify tally that a disc , half black , half white , rotating fl ) under illumination 2 , looks precisely the same grey as a wholly white disc ( made of the same material ) under illumina The two discs were arranged at the proper calculated distances from the source of illumination , and viewed so that the nearer overlapped the more distant , and also so that the background to both the discs was black ( so that any contrast effects might be the same for both ) .
The two discs seemed like Dr. T. C. Porter .
[ Jan. 2 , one , and when viewed through a tube which cut off the background , it was impossible for the observer to tell where one disc began and the other ended .
In the same way it was experimentally shown that the grey of a blackand-white disc , when flickerless under illumination I , appears always to match the all-white disc under an illumination , where is the sum of the angles of the white sectors .
It follows from this that the apparent luminosity of all black-and-white discs under the same illumination is the same , if is the same ; but the converse not true , the apparent luminosity of two flickerless discs under the same illumination may be precisely the same , and yet the angle of the black sector may be different in the two discs ; indeed one disc may be entirely white , and the other may have a black sector by no means small under some conditions of illumination , and yet these two may , to the eye , form a perfect match , when flickerless .
The next experiments were , therefore , undertaken to measure the magnitude of the black sector which could be placed in a white disc , rotating so fast as to be quite flickerless , without producing any appreciable difference to the htness ( albedo ) of the disc .
For the sake of brevity such a black sector will be referred to as a vanishing sector , and its magnitude in degrees as .
A white disc was prepared with a concentric broad black ring upon it , and this was dovetailed , after Maxwell 's plan , with another wholly white disc made from the same cardboard ; thus a variable sector of black could produced with white on each side of it .
If the black sector were greater than could completely vanish on swiftly rotating the disc , the appearance presented was of a more or less dark tOTey ring on a white ground ; when , however , the breadth of the black sector was below a certain ynitude , no such grey ring could be seen , the disc appeared of uniform brightness .
It was manifestly of great interest to see whether Weber 's law would hold in this case , .
to find out whether the width of the vanishing black sector would be 1 per cent. of the total stimulus given by the white of the disc .
This would mean that , at all illuminations , a white disc would not be rendered appreciably darker by a sector of of absolute black .
On a bright day in a well lit room , of Indian ink ( which had been proved to reflect per cent. of white light ) just vanished ; whilst at metres from a powerful arc light , of this same black disappeared\mdash ; so that for ordinary daylight illuminations , Weber 's law may be said to hold good , but it was soon found that as the illumination of the disc is lowered below these , the magnituule of the vanishing black sector grows .
If be the ular magnitude of the black sector , I the illumination , and and constants , the equation connecting them was found to be , I. 1912 .
] Contributions to the Study Flicker .
Several very careful determinations of the value of for different illuminations were made ; the results of three typical ones can be seen in fig. 4 .
The points marked 1 were made by a observer , who , however , took no very special precautions to secure a steady state of the retina : only ( i ) avoiding looking at the disc except when ( ii ) never looking at the illuminant ; ( iii ) shutting his eyes and covering his head with black velvet cloth when a moderate was used in the room for the purpose of reading the distance of the disc from the illuminant .
It will be seen that the readings are very consistent , and are all greater than in the other two cases .
The points in marked 3 were obtained , on the other hand , every precaution experience has suggested for securing extreme sensitiveness of the retina , and also for it constant .
The observer , after more than an hour in a very feeble light , spent half an hour in total darkness , and except when he inspected the very faintly illuminated disc , each time fainter still , he remained in total darkness .
About seven minntes elapsed between each The results again are very consistent , and the line expressing growth of the black sector with the diminishing arithm of the illumination is very nearly parallel to the first line .
The points marked 2 are typical of the results obtain in an experiment where for the higher illuminations the observer has had no Dr. T. C. Porter .
[ Jan. 2 , preliminary rest , has taken the readings rather rapidly , used the black cloth for the lower illuminations , but has looked accidentally at a feeble flame once twice .
The points lie between the other two sets , but they diverge much more from lineal arrangement .
Unit illumination for these experiments is the same which has been used throughout the whole research , namely , that of the standard candle 4 metres off , and the lowest illumination , whose logarithm is , is to that of the candle at a distance of metres .
By using an illumination much lower than this , it was found possible to witness quite certainly the vanishing of a sector of of black .
In this case the eyes had been in darkness more than two hours .
except for looking at very feebly illuminated discs for a minute or two at a time .
The grey reappears with a very slight rise in the illumination .
Whilst watching this ring on the disc , if the illumination of the disc is cut off completely and , the ring appears to expand outwards and inwards over the white on both sides of it , and so to render the disc black and invisible .
The feebly illuminated disc itself , much more the grey ring on it , was quite invisible to another observer , whose eyes , though fairly rested , had not been in complete darkness , so that the line of points 1 on fig. 4 must come to an end far above the end of the line for the points 3 , and also the disturbance of the retina by the brightness of the disc at higher illuminations must in practice the line 3 to an end before it has extended far upwards .
( N.B.\mdash ; In this and many other cases the observer was not the writer , and had no idea of the purpose for which he was observing ; he had in every case normal and very keen sight , and was generally between 17 and 19 years of age .
) The full dattt for these observations will be found in the table on the opposite The oing experiment seems to the writer of considerable importance , not only on account of the light it throws on flicker phenomena , but also because it ives a numerical measure of the power of perceiving contrast at varying ( a ) It accounts for the small amount of detail in a landscape under feeble light , e.g. moonlight , and it gives a reason for the wonderful amount of detail visible in clear air under brilliant sunshine .
There are , in general , two ways of making an object clear to the eye : one is to make the object appear large , either by constructing it large , or bringing it near to the eye ; the other , which is very useful in exhibiting small objects to a large number of people at ones , to illuminate it brightly .
( b ) The law also applies to any photometer , in which the relative brightnesses 912 .
] Contributions to the Study of Flicker .
N.B.\mdash ; In fig. 4 there is probably a shalT turn here in the region Illumination 10 because for all much greater illuminations seems to be almost .
the hopes to examine point .
of two sources of light are compared by comparing ( i ) the brightnesses of two surfaces lit up by these sources at a distance from the illuminants , or ( ii ) the depth of two shadows cast by the illuminants on a screen .
The experiments prove that the eye incapa.ble of disti u contrasts which lie between certain limits , these limits growing wider apart as the logarithm of the illumination diminishes .
Thus , taking the photometer used in these experiments and described in Paper II , p. 316 , fig. 1 , where the from each of the sources to be compared passes through one side of each of two right-angled prisms respectively , and thence to the hypotenuse , whence it is reflected ' totally\ldquo ; on to the third side of each prism , side is finely evenly ground , \mdash ; if the illumiuants are low in power , or if the photometer is far from them , the on the scale when the eye the illumination of the two prism faces to be equal must partly depend upon the in which the photometer has been moved to strike the balance .
Thns , in , let and be the sources of the } ) hotometer ; the1l if be Dr. T. C. Porter .
[ Jan. 2 , moved from left to right only , and A is the point where the faces of first seem equally bright , ( the left face ) will still in reality be brighter ( the right prism 's face ) by an amount , say , which is the same fraction of the apparent brightness of the faces of that the vanishing black sector is of the whole of the white disc which looks as bright as P. Similarly , if is moved only from right to left till the balance is again struck , say first at the point , then at will be brighter than by the same amount .
Thus the il]uminations of and within the space AB , which may with reason be called the " " blind space are comparable with the various invisible differences of albedo of a rotating flickerless white disc with a black sector of any nitude from to and since we know that becomes large for low illuminations , the space AB must increase with the fall of illumination and in accordance with the logarithmic law given in this paper .
Having found the points A and in any particular experiment , we can find the true ratio of the two illuminants , for if I and I ' be the intrinsic brightness of the two illuminants at and , then At A illumination of by I is therefore At A illumination of by I ' is Similarly At illumination of by I ' is ' therefore At illumination of by I is ' whence ; and since the quantities on the right side of this equation are known , is determined .
Also if is the point of true equality of illumination , and , then from which can be found .
When using the photometer thus , and moving it up to , or , always in the same direction , it is necessary to close and rest the eyes before deciding whether it has been moved far enough , because , to take for example the determination of , as has always been brighter than during this motion , the retinal fatigue caused by will be greater than that caused by , and it will be found that , after resting the eyes , has to be 1912 .
] Contributions to the Study of Flicke : advanced a little more .
If great accuracy is required , the eyes should be rested approximately equally when the other position , , is being found .
With higher illuminations of the photometer faces , the interval is found , as it should be , to be much smaller , and more difficult to trace .
The retinal fatigue is then greater , and by far the more serious source of error .
To give the results of one of several experiments:\mdash ; Two very small gas flames were used , run from a wide branched tube , so that any possible change in pressure should affe , ct both flames equally ( the measuring scale was 60 inches long , and was graduated from zero on the left , this zero was inches from I , the true zero , and inches from I ' .
from left to right .
28.31 Moving from right to left .
30.51 27.36 I.e. , AB inches .
The left flame , measured against a standard candle , gave its intrinsic brightness as .
Therefore I ' by method given ) and the point , fig. 5 , is then found to ) , i.e. to the of , and inch to the left of B. Now the illumination of .
at A is and , , , , , , The difference between these , multiplied by 2 ( because not only does the of diminish in moviog from A to , but that of increases in nearly the same ratio , since I and I ' are not very unequal ) , is the imperceptible decrease of uination at illumination .
As apercentage of this last illumination this is equal to Now the illumination given by the standard caodle at 4 metres is the unit brightness of the disc , and the brightness of a white disc at point Dr. T. C. Porter .
[ Jan. 2 , in the photometer experiment is found to be , the logarithm of which is .
On referring to fig. 4 , we find the of the vanishing black sector at this illumination , for well rested eyes , about , or corrected for 5 per cent. of white light in the black pigment used , , which , as a percentage of the all-white disc , is .
This tallies well with the result of the photometer experiment , when we remember that the apparent illumination of the photometer face is a little greater than that of the white cardboard at the same distance from the gas flame .
It appears from the facts expressed in fig. 4 that it is possible , and not very difficult , to express numericalty the state of the retina as regards excitability by finding the magnitude of , and further , that it is by no means impossible to keep the state of the retina fairly constant , even allowing for some brief but considerable changes in the illumination of the room the observer is in , that the state required is not that of exceeding sensitiveness ; to maintain this last , very little variation can be permitted , and that must be followed by several minutes ' complete rest .
To return to The equation which best represents the line 1 is where is the angular width of the black sector in degrees , and I is the illumination measured in terms of the illumination given by the standard candle before described , at a distance of 4 metres .
To make plain the connection between and ( the number of revolutions per second which must be iven to a disc so that it may just become flickerless ) , suppose a white disc , with one black sector , to rotate very slowly before the eye .
If it turn slowly enough , the excitation of the retina afforded by the white of the white sector will rise to its maximum ( measured by I , the illumination the disc is under ) , say from A to fig. , measured vertically ; whilst the black sector passes , the excitation , which for brevity 's sake will be called , falls completely , to its first level , as BC .
If the disc 's rate of rotation be gradually quickened , it is certain that soon neither sinks so low , nor rises so } .
This can be proved by comparing the apparent white and black of the respective sectors as they pass , with the white and black of a second similar disc , kept at rest , and placed near the rotating disc so as to be under the same illumination ; the rences are plain to any observer , and , as the rate of rotation is increased , become plainer still .
Thus it is certain that the curve expressing the variations of roughly resembles fig. , and the oscillations eventually tako place about the line which expresses the final 1912 .
] Contributions to tloe Study of Flicker .
value of .
In fig. , drawn for a " " half-and-half\ldquo ; disc , the final value of is half its value for the all-whire disc ( proved already ) .
In fig. we have the similar curve for a disc with one white sector of , the final value of being one quarter its maximum value .
In every case , so soon the rise and fall of become equal to the rise and ] caused by , the vanishing sector on an otherwise white disc for the particular value of brightness shown by the first-mentioned disc at the moment , \mdash ; then flicker vanishes .
For example , \mdash ; for the half-black , half-white disc iu fig. 6 pose that KL is the alnplitude of the variation of ( shown enlarged out of proportion in fig. ) , when flicker just yanishes , then , if the disc is kept turning at this rate , the imperceptible variations will continue of the same magnitude as long as the disc seems of the same brightness , and if its apparent diminishes from retinal fatigue or any othel cause , then , since the value of the black sectol the brightness falls , the flicker will manil.estly be further from visibility .
In other words , if a disc is once flickerless , provided that its illulnination be not raised , nor the rate of rotation slackened , it will flickerless .
This is consistent with experience .
Gazing at a flicker ] disc makes the flicker reappear , and it is plain that in judging whether a disc is flickerless or not , it is well to be as quick as possible .
The total excitation caused by the passage of the white sector when flicker just vanishes is expressed in fig. by , the actual rise by , and the fall by , for when flicker just vanishes ( not necessarily at other speed ) the rise and fall of must be equal , for if either were the greater , the effect would be cumulative , and the disc must apparently brighter or Dr. T. C. Porter .
[ Jan. 2 , darker , whereas as a fact it remains of the same apparent brightness , namely , OQ .
Thus , if the white and black sectors are of equal magnitude , the mean rate of rise of must be equal to the mean rate of fall of during the passage of the white and black sectors respectively , and if the white and black sectors are of unequal magnitude then , at the rate of rotation for which flicker just vanishes ( not necessarily at any other rate ) , the rate o of ( whilst the white sector passes ) must be to the of fall of ( whilst the black sector passes ) as the time the black sector takes to pass is to the time the white sector takes to pass , that is as the angular magnitude of the black sector is to the angular magnitude of the white sector .
Now KL fig. is to the apparent brightness of the disc ( OQ ) as , the magnitude of the vanishin , .
sector in degrees , is to , or , since is indistinguishable from 36 in brightness , to Thus , if we know and , and , the rate of rotation for flicker just to vanish , we can find the rate of rise and rate of fall of , when the mean value of is of the highest value the disc can give , i.e. , 360 .
Now these quantities have been measured during this investigation , and equations connecting them have been established .
We can find the three above-mentioned quantities for every , say , of increase of the white sector under a given constant illumination , and therefore we can find the rate of rise and fall of when it is just reaching these mean values .
lf we that the rwte of rise and fall of " " \ldquo ; at a given value of " " when " " \ldquo ; is not approaching a tirniting value , is proportional to these rates found for series of limiting values , we can also arrive at a definite idea of the curve which expresses the rise of the excitation of the retina with time , when we look at a flickerless rotating or , equally well , the same white disc , or any other equally white surface , at rest .
It is necessary first , however , to find by experiment the size of for discs of a variable black sector .
For example , if a disc , half white , half black , is rotating under , say , unit illumination , and therefore appearing as bright as a wholly white disc under illumination 2 , will the value of be the same for the two discs , and , if not , how will it differ ?
We can see that it cannot be the same , for in one case is half its value in the other , and the apparent brightness depends on as well as on the illumination , so that a black sector of given breadth must have twice as darkening an effect on the half-and-half disc as on the other .
This leads to the conclusion that must be the same fraction of ths white sector in all cases ( I being constant ) .
To test this lsion , half a disc was painted black , and an additional black sector of was added symmetrically , as shown in fig. 7 .
1912 .
] ibutlons to the Study of Flicker .
This additional sector was found by experiment to vanish completely under an illumination of a candle of standard candle power at a distance of metres .
If we calculate what value must have with an all-white disc to vanish at the same illumination ) using the equation given for line 1 , fig. 4 , we find it to be almost exactly ; i.e. , for the white disc must be halved for the half-and-half disc which looks as bright .
If , then , is the value of the vanishing black sector for an otherwise all-white disc , then is its value for a disc of white sector ; e.g. , suppose on an otherwise white disc , then on a disc with white and 27 black , an additional of black will vanish .
On a disc with four sectors of each , two white , two black , will vanish , and so on , if the illuminations are such that the apparent brightnesses of all the three discs when flickerless are the same .
We can now deduce the form of the curve expressing the rise and fall of the retinal excitation , or , perhaps , more correctly , of the apparent brightness of a white surface , illuminated to a given degree , and suddenly presented to the eye , previously in a feeble illumination ( because in the particular cases for which formulae have been given , the eyes of the observers had not been rested in complete darkness ) , the fall of the excitation happening when the surface is suddenly made to disappear into the same almost complete darkness .
For the illumination of the surface , take that of the standard candle at a distance of 87 cm .
, so that I and From the equation connecting I and , we find From the equation connecting , and , calculate the values of for the various values of , from , etc. , up to In each case the actual rise of ( not the total rise ) , when the critical speed of rotation is reached , is , as we have proved , To find the rate of rise of , divide the rise of in each case by the time in seconds the white sector takes to pass , i.e. , .
Thus the rate required , which To find the rate of fall of at the same value of : we have already proved that the rate of fall is to the rate of rise as is to , so that the rate of fall rate of rise .
The curve thus obtained is seen in fig. 8 .
The unit of time is the second , The equation actually uaed here was .
VOL. LXXXVL\mdash ; A 2 The Nature of the excited by 513 and two of the paper divisions the axis of X go to one second , whilst five units of retinal excitenlent , or apparent brightness , go to every degree along the axis of .
It is therefore evident that , if the curve is to represent the actual rate of rise and fall of retinal excitation when one looks at a white surface of the albedo stated , and which is afterwards made to disappear , the time scale must be different from that just mentioned .
From rather rough experients made with a photographic shutter by the writer , it would appear that the whole of the rise from to 36 takes about half a second : if this be true , and the assumption mentioned above ( in italics ) be correct , we must consider each of the paper divisions , of which every other one is marked in black along the axis of X , to represent one twentieth part of one second .
The data for the construction of the curve are given in the foregoing table .
The .
the excited by -Rays .
By J. A. GRAY , B.Sc. , lS51 Exhibition Scholar , niversity of Melbourne ; Hon. Research Fellow , University of Manchester .
( Communicated by Prof. E. Rutherford , F.R.S. Received February 24 , \mdash ; Read Iarch21 , 1912 .
) In a previous pape was shown ] the -rays of radium excited -rays in different materials , the amount increasing with the atomic weight of the substance used .
It found that the -radiation was increased when the -rays fell on a lead screen suitably placed , as the active material , radium , was mixed with lead sulphate confined in a small space , it was obvious that some , if not all , of the -radiation from the mixture was due to -rays excited by -rays in the lead impurity .
It thus seemed possible that no primary -rays were emitted by radium E. By using a more suitable source , in which the active material was spread in a thin layer over filter paper , it has been found that a primary -radiation is emitted from the active matter .
This radiation , however , is much soitel than that excited by the -rays in lead .
A more detailed account of these primary rays win be given later .
The main object of the present investigation was to examine carefully the question whether the -ray excited by a -ray travels in the direction of the * Gray , ' Roy .
Soc. Proc 1911 , , vol. 85 , p. 131 .
In the paper mentioned , the term secondary -rays was given to -rays excited by -rays .
To distinguish , however , another phenomenon , described later , the term " " exoited\ldquo ; -rays is now nsed .
|
rspa_1912_0043 | 0950-1207 | The nature of the \#x3D2;-rays excited by \#x3B2;-rays. | 513 | 529 | 1,912 | 86 | Proceedings of the Royal Society of London. Series A, Containing Papers of a Mathematical and Physical Character | J. A. Gray, B. Sc.|Prof. E. Rutherford, F. R. S. | article | 6.0.4 | http://dx.doi.org/10.1098/rspa.1912.0043 | en | rspa | 1,910 | 1,900 | 1,900 | 1 | 35 | 801 | http://corpora.clarin-d.uni-saarland.de/surprisal/6.0.3/?id=rspa_1912_0043 | 10.1098/rspa.1912.0043 | null | null | null | Atomic Physics | 57.863091 | Thermodynamics | 11.796241 | Atomic Physics | [
9.475500106811523,
-77.20401763916016
] | ]\gt ; tli$b the -rays of radium , the chance of a -ray ( if it spends its range a radiator ) making a -ray is roughly proportional to the atomic weight of the radiator .
Somewhat similar results to those obtained above have been found by Kaye*for the production of -rays by cathode rays in radiators of the order of cm .
in thiokness .
He found that the emergent -radiation was greater in amount ' the incident radiation , and also more penetrating .
An analysis similar to that made above is impossible , but the main explanation of the results must be that the -radiation tends to move in the same direction as the cathode radiation exciting it .
Theoret at The result that the -radiation excited in " " thin\ldquo ; sheets is practically all emergent shows that , in general , such radiation , in any amount , is not formed by small deflections of the -rays .
Let us suppose AOB ( fig. 5 ) represents the path of a -ray suddenly deflected at , through a right angle , giving X FIG. 6 .
FIG. 6 .
rise to -radiation .
It is clear that such radiation , if due to the acceleration of the particle near , will not move in any one definite direction , and , even if it did , that direction would probably be OX .
Such comparatively small deflections cannot therefore be the cause of the -rays , or , at least , of any large amount of such radiation .
It is seen from this that -radiation is most likely to be produced when the -ray is suddenly stopped .
We will , therefore , assume that the -ray only arises when the -ray is suddenly stopped or loses a great part of its energy , and try to explain results on the theory of Sir J. J. Thomson , which seems , of theories akin to the ordinary pulse theory , the most suitable .
'Camb .
Phil. Soc. Proc November , 1909 , , p. 269 .
It is considered that the -ray stops if it forms a -ray in the way supposed by Brag , as well as by loss of speed .
PhiL Mag February , 1910 , vol. 19 , p. 301 .
VOL LXXXVI.\mdash ; A. 2 same material the thinner the radiator , for radiators of different materials thick enough to stop the -rays , the lower the atomic weight .
( 3 ) Results obtained point to the conclusion that the ray is an entity , the direction of which is nearly that of the -ray it .
( 4 ) For -rays of the speed used , the chance of a -ray making a -ray is roughly proportional to the atomic weight of the radiator , provided the spends its range in the radiator .
In conclusion , the writer has much pleasure in expressing his best thanks to Prof. Rutherford for his very helpful interest in this research , and for the use of the active preparation of radium necessary .
The After-luminosity of Electric Discharge in , observed by Hertz .
By the Hon. B. J. STRUTT , F.B.S. , Professor of Physics , Imperial College of Science , South Kensington .
( Received March l , \mdash ; Read lsiarch 21 , 1912 .
) In previous papers I have examined certain striking cases of afterluminosity in gases through which the electric discharge has been passed .
The cases dealt with fall under two heads , those due to ozone , and those due to active nitrogen .
I wish now to pass.to a case in which neither of these substances is concerned .
Hertz* described a phenomenon of after-luminosity which he had observed in hydrogen .
The method of investigation was somewhat special .
A series of jar discharges was passed through a small discharge tube , with an open end , a1ranged inside a bell jar .
It was then observed that at each discharge a stream of luminous gas was squirted from the end of the small discharge tube into the bell jar .
This is apparently due to a kind of explosive action of the spark-.the same , probably , as that described by De La Rue and Muller The method is well adapted to show the afterglow in other gases , nitrogen or air , for instance , but the immediate concern is with hydrogen .
With this gas , Hertz sometimes observed ajet of blue luminosity , which was best developed at a pressure of * Wied .
Ann 1883 , vol. 19 , p. 78 . .
' Phil. Trans 1880 , vol. 171 , p. 86 .
|
rspa_1912_0044 | 0950-1207 | The after-luminosity of electric discharge in hydrogen, observed by Hertz. | 529 | 533 | 1,912 | 86 | Proceedings of the Royal Society of London. Series A, Containing Papers of a Mathematical and Physical Character | Hon. R. J. Strutt, F. R. S. | article | 6.0.4 | http://dx.doi.org/10.1098/rspa.1912.0044 | en | rspa | 1,910 | 1,900 | 1,900 | 4 | 95 | 2,071 | http://corpora.clarin-d.uni-saarland.de/surprisal/6.0.3/?id=rspa_1912_0044 | 10.1098/rspa.1912.0044 | null | null | null | Atomic Physics | 45.475594 | Thermodynamics | 33.413701 | Atomic Physics | [
5.898366451263428,
-55.39868927001953
] | The After-luminosity of Electric Discharge in Hydrogen .
529 ( 2 ) The ratio of emergent to incident 7-radiation is greater , for radiators of the same material , the thinner the radiator , for radiators of different materials thick enough to stop the / 3-rays , the lower the atomic weight .
( 3 ) Results obtained point to the conclusion that the ray is an entity , the direction of which is nearly that of the / 3-ray exciting it .
( 4 ) For / 3-rays of the speed used , the chance of a / 3-ray making a 7-ray is roughly proportional to the atomic weight of the radiator , provided the / 3-ray spends its range in the radiator .
In conclusion , the writer has much pleasure in expressing his best thanks to Prof. Kutherford for his very helpful interest in this research , and for the use of the very active preparation of radium D necessary .
The After-luminosity of Electric Discharge in Hydrogen , observed by Hertz .
By the Hon. R. J. Strutt , F.R.S. , Professor of Physics , Imperial College of Science , South Kensington .
( Received March 1 , \#151 ; Read March 21 , 1912 .
) In previous papers I have examined certain striking cases of afterluminosity in gases through which the electric discharge has been passed .
The cases dealt with fall under two heads , those due to ozone , and those due to active nitrogen .
I wish now to pass.to a case in which neither of these substances is concerned .
Hertz* described a phenomenon of after-luminosity which he had observed in hydrogen .
The method of investigation was somewhat special .
A series of jar discharges was passed through a small discharge tube , with an open end , arranged inside a bell jar .
It was then observed that at each discharge a stream of luminous gas was squirted from the end of the small discharge tube into the bell jar .
This is apparently due to a kind of explosive action of the spark\#151 ; the same , probably , as that described by De La Rue and Muller.f The method is well adapted to show the afterglow in other gases , nitrogen or air , for instance , but the immediate concern is with hydrogen .
With this gas , Hertz sometimes observed a jet of blue luminosity , which was best developed at a pressure of * 4 Wied .
Ann. , ' 1883 , vol. 19 , p. 78 .
t ' Phil. Trans. , ' 1880 , vol. 171 , p. 86 .
Hon. R. J. Strutt .
The After-luminosity of [ Mar. ] , 100 mm. He considered that he had good evidence that this luminosity showed the hydrogen spectrum , but he found an unaccountable capriciousness of the effect , which sometimes refused to appear at all .
He did not succeed in tracing the cause of this uncertainty .
Goldstein* made similar experiments ; he states that the spectrum consists of at least 10 bands , from the green to the ultra-violet , totally unrelated to the recognised hydrogen spectrum .
But he believed that the glow was due to pure hydrogen .
This glow is of very short duration .
I have not been able to observe it , either by the use of a rapid stream of gas , as in the former investigations , or by the simple method of looking at the vessel immediately after the discharge is stopped .
Hertz 's method is much more searching for detecting a glow of very short life .
The form of discharge vessel used in my experiments is shown in fig. 1 , which scarcely needs detailed explanation .
Jar discharges take place between the electrodes a , \amp ; , which have a spark-gap in series with them .
The glowing Fig. 1 .
gas is squirted into the large bulb e , and the glow remains continuously visible in this bulb , in a state of turbulent motion , as long as the induction coil is in action .
On admitting commercial hydrogen from a cylinder of the compressed gas to a pressure of about 50 mm. , the blue glow described by Hertz was brilliantly developed .
I never failed to obtain it in this way , and to maintain it as long as desired .
The first object was to photograph the spectrum , which was readily done by means of a small quartz spectrograph , through a quartz window ( not shown ) in the side of the bulb c. The spectrum is reproduced * * Verhand .
d. Phys. Gesellsch .
, ' 1883 , vol. 2 , p. 16 .
Electric Discharge in Hydrogen .
1912 .
] in fig. 2 , and was at once recognised as identical with the spectrum obtained when active nitrogen is passed over heated sulphur.* A photograph of the latter taken with the same instrument was an exact facsimile of that of the hydrogen afterglow here reproduced .
The same bands occur in the flame of carbon disulphide , but obscured to some extent by a continuous background .
Fig. 2 .
The Hjg line which appears in the photograph is , no doubt , due to stray reflected light from the discharge .
The sodium line was put on for reference .
The blue glow of hydrogen , then , is connected with the presence of sulphur as an impurity in the gas .
On cooling the annexe d of the vessel in liquid air , so as to condense out sulphuretted hydrogen ( or any other sulphur compound ) , the glow disappears completely in one or two minutes .
On removing the liquid air , and allowing the glass to warm up , it is restored to its full brilliancy .
This is a striking experiment , and can readily be shown to a large audience . .
In another experiment , after removing sulphuretted hydrogen by condensation , so as to get rid of the glow , a fresh quantity of that gas was admitted , amounting by volume to about one-twentieth pnrt of the hydrogen present .
The blue glow at once reasserted itself .
There was some deposition of sulphur on the walls of the discharge tube , and it was found impossible now to get rid of the glow by condensation .
Evidently fresh sulphur enters into combination with hydrogen under these conditions , and continually replaces what has beerf removed .
It is ' clear that the quantity of sulphuretted hydrogen admitted was enormously in excess of what was necessary in order to bring in the blue glow in full intensity .
The formation of this glow seems , in fact , to be an exceedingly sensitive test for the presence of sulphur in hydrogen\#151 ; a test that might with advantage be made use of by anyone requiring the purest hydrogen lor determination of physical constants .
The commercial bottled hydrogen above mentioned was found incapable of discolouring moistened lead test- * Strutt and Fowler , 'Roy .
Soc. Proc. , ' 1912 , A , vol. 86 , p. 112 .
532 Hon. R. J. Strutt .
The After-luminosity of [ Mar. 1 ?
paper , even when passed over it for an hour in a rapid stream .
Yet this hydrogen gave the blue glow in full brilliance .
Again , a discharge vessel which had been washed out with sulphuric acid , and afterwards with water , gave the glow persistently , in spite of the treatment with liquid air , which is so successful in removing it from a new tube .
Probably continual supplies of sulphur were afforded by a slight deposit of sulphate on the aluminium electrodes .
It has been mentioned that the spectrum of the blue glow is identical with that of sulphur in active nitrogen , or of carbon disulphide burning in air .
Conceivably , in both these cases , the spectrum might be due to a compound of nitrogen and sulphur .
It became important , therefore , to test whether nitrogen as well as sulphur was necessary to the formation of the blue glow in hydrogen .
Some charcoal was placed in the lower part ( d , fig. 1 ) of the discharge vessel , and a small fragment of sulphur fused on to the glass in the upper part , near where the discharge passes .
The charcoal was immersed in liquid air , and hydrogen admitted until the charcoal was saturated at a pressure of 50 mm. of mercury .
The tube was then sealed off , keeping the charcoal cooled .
The blue glow remained in full intensity for an hour , after which the experiment was discontinued .
If any trace of nitrogen had been initially present in the hydrogen used ( and none wTas visible spectroscopically ) it could not have failed to be removed by this prolonged exposure to cooled charcoal .
Sulphuretted hydrogen was , no doubt , removed too , but its loss was made good from the solid sulphur intentionally introduced , as in one of the experiments previously described .
I conclude , therefore , that the spectrum of the blue glow is essentially a spectrum of the element sulphur .
It may occur in the absence of hydrogen , as when developed by active nitrogen , and in the absence of nitrogen , as in the above experiment .
I have not succeeded in obtaining the well developed blue^glow in sulphur vapour alone .
It seems , therefore , that the glow must be dependent on a combination of sulphur and hydrogen with luminosity after they have left * the discharge .
For this to occur , one or other of the substances must be in a special condition of chemical activity , analogous , perhaps , to ozone or to active nitrogen .
I have not been able to devise an experiment to decide which of the elements concerned possesses this peculiarity .
The extreme shortness of its duration makes it impossible to apply the synthetic methods ' which have been so successful in the cases of ozone or active nitrogen .
But on general grounds it is perhaps more likely7 that the sulphur is in a peculiar state .
1912 .
] Electric Discharge in Hydrogen .
[ Addition , March 26.\#151 ; Selenium and tellurium , the elements most kindred to sulphur , give similar effects .
A fragment of tellurium was placed in a discharge vessel like fig. 1 , where it could get heated by the spark , and hydrogen was admitted to 50 mm. pressure .
The deep blue glow due to sulphur was at first visible , but as the tellurium got heated up it was replaced by a greenish-blue afterglow , quite distinct from the former .
At the same time the walls of the globe acquired an opaque deposit of tellurium .
The glow showed a spectrum of narrow uniformly spaced bands from the red to the blue .
With selenium very similar effects were observed .
The general colour of the glow was nearly the same as with tellurium , but not bright enough to make spectroscopic observation easy .
Arsenic was tried in the same way , as forming a gaseous compound with hydrogen .
No glow was observed due to arsenic , and the glow of sulphur , originally present in the hydrogen used , was quickly destroyed .
Probably the sulphur reacted with arsenic vapour and was thus removed .
] Pure hydrogen gives no afterglow whatever .
In this respect it resembles pure oxygen , * and differs strikingly from pure nitrogen.f In conclusion , I wish to express my best thanks to my colleague , Prof. A. Fowler , F.R.S. , for help most kindly given in preparing for publication the photograph reproduced in fig. 2 , and for advice on the spectroscopic side of the work generally .
* 4 Phys. Soc. Proc. , ' 1911 , vol. 24 , p. 4 .
t 'Roy .
Soc. Proc.,5 1911 , A , vol. 85 , p. 219 .
|
rspa_1912_0045 | 0950-1207 | On the changes in the dimensions of a steel wire when twisted, and on the pressure of distortional waves in steel. | 534 | 561 | 1,912 | 86 | Proceedings of the Royal Society of London. Series A, Containing Papers of a Mathematical and Physical Character | J. H. Poynting, F. R. S. | article | 6.0.4 | http://dx.doi.org/10.1098/rspa.1912.0045 | en | rspa | 1,910 | 1,900 | 1,900 | 7 | 87 | 2,458 | http://corpora.clarin-d.uni-saarland.de/surprisal/6.0.3/?id=rspa_1912_0045 | 10.1098/rspa.1912.0045 | null | null | null | Fluid Dynamics | 37.317466 | Measurement | 25.48153 | Fluid Dynamics | [
41.15327453613281,
-58.54136276245117
] | ]\gt ; unisted , etc. fall on twisting and a rise on untwisting of about diyision .
The actual change observed on twisting through one turn was about division .
If then the heat or cold only slowly spread from the wire , or again if it were rapidly shared with the water in the wire tube but only slowly spread thence , the measurements would be seriously affected .
But it is obvious that there must , in reality , be a rapid adjustment of temperature between the wire tube and the outer water jacket , and it was important to find out how rapidly the adjustment progressed .
Fortunately the wire was insulated from the tube where it passed through the washer , so that it was easy to pass an electric through it by connecting the terminals of a battery , one to the bracket , the other to the wire tube .
Heating currents of the order of 1 to 2 amperes were thus passed along the wire .
The current was put on for 2 seconds , the meniscus rushing up meanwhile fairly uniformly , and the point to which it rose was read on the micrometer .
Then , 15 seconds after the cut off , the position of the meniscus was read and the mean of a number of determinations showed that after 15 seconds only of the original rise remained .
The original rise varied from 7 to 18 divisions with different currents .
If the twisting were made instantaneously and the reading of the fall in the tube were made 15 seconds later , about of the fall would be due to the cooling on twisting .
But this is a very considerable over-estimate .
The twisting was usually begun 25 seconds before reading and ended more than 15 seconds before .
The effect of temperature change may , I.think , be estimated at less than 1/ 300 of the whole .
It was impossible to assign even an approximate value to it and as it proved to small it was neglected .
The effect would have been reduced altogether beyond consideration if the readings had been taken at intervals of one minute , but this would have introduced errors , probably much worse , through irregularities in the temperature march .
In the experiments on Poisson 's ratio the adiabatic change of temperature on adding a load which stretches length by is where is the change in Young 's modulus per degree .
The value of steel is about 1/ 4000 .
This gives the heat for a stretch of 10 as about calories .
With uniform temperature of steel and water in the wire tube the water would have about 7 calories , and its effect VOL. LXXXVI .
On comparing the results for Wires I and II we see that side contraction - elongation is very nearly the same both .
The theory given below makes both and proportional to the square of the radius for wires of the same material undergoing the same twist .
But as far as these two wires are concerned they are very nearly proportional to radius ) .
I do not think the discrepancy is to be ascribed to experimental error .
Perhaps the theory is inadequate , but I think that it is more probable that slight differences in the material not greatly affecting the ordinary elastic moduli may produce very considerable changes in what we may term the secondary moduli , which , in the theory below , are denoted by and I should like to have taken observations on several more steel wires with a wider range of diameters , but I am not able to continue the work at present .
Veriffiation of a Reciprocal In the 'Philosophical Magazine ' for November , 1911 , vol. 22 , p. 740 , Dr. B. A. Houstoun has expressed the reciprocal relation between the stretching and twisting of a wire ( confined within limits of reversibility ) in the form const . .
( 1 ) where is the end pull and the increase in length , the torque , and the twist on the wire ( I use letters for length and torque differing from Dr. Houstoun 's ) .
As the apparatus only needed small modification it appeared to be worth while to see how nearly this relation was verified , and Wire II was used for the purpose .
Incidentally , the value of the rigidity was obtained by the statical torque method .
When the observations needed are worked out it is found that they are identical , as of course was to be expected , with those needed to verify the relation ' ( 2 ) which is the more direct expression of the Conservation of Energy these phenomena .
Taking equation ( 1 ) we require to know on the left the extra twist which must be put upon the wire to keep the same when a load is added .
For this purpose the wire was initially loaded with kgrm .
, and .
This is given by , where whence , on substituting for from ( 3 ) , we get , and .
( 4 ) Taking the right hand of equation , we reqmre to know the lowering for a ohange in the torque under constant load .
We get the lowering from the equation giving Also .
Them and ( 5 ) , we ought to find .
( 6 ) Substituting the known values on the right , viz. , we get The observed value of is given as on p. 548 , showing as close an agreement as could be expected , considering the errors of observation .
Taking the second reciprocal relation ( 2 ) , to find must twist through and observe , and then calculate what load must be removed to restore the original length .
We have , and Then where is a constant to that order .
If we reverse becomes equal to , so that we have or We can only assume that there is no pressure or tension perpendicular to the plane of the figure , if we neglect .
Going to the second order , we have to allow the possibility of a pressure of that order , which we may put as where if is negative the force is a tension .
FIG. 2 .
FIG. 3 .
Considering the equilibrium of the wedge ABC , , with AC in the direction of greatest elongation and BC in that of { yeatest contraction , I showed that the tangential stress along AB is , to the second order , and that a pressure is required perpendicular to AB given by The analysis stopped here and was incomplete , as no account was taken of the stresses on the plane , fig. 3 , perpendicular to AB .
It requires to be supplemented.as follows:\mdash ; Considering the equilibrium of the wedge CDB , let us suppose that on CD there is a tangential stress along , and a pressure perpendicular to it .
Resolving all the forces on CDB parallel to DB , .
CB .
CB .
CB whence ; ' perpendicular to the plane of the figure .
Through the tension on every face we get an extension in all directions , where is the bulk modulus .
The tensions on AB and CD and the pressures Sn on AD and BC constitute a shear stress giving elongation parallel to BC 4 , and a contraction parallel to AB also 4 The tensions perpendicular to the plane of the figure give an elongation perpendicular to that plane , and contractions at right angles , viz. , along AB and AD , , where is Young 's modulus and is Poisson 's ratio .
Collecting the results , we have secondary , strains accompanying the shear as follows:\mdash ; An elongation parallel to BC , perpendicular to the plane As in the experiments described above and were determined directly , it will be convenient to replace from the equation , and the secondary strains become Changes in the Dimensions of a Wire Subject to a Torque .
I am indebted to Sir Joseph Larmor for his kindness in dicating how the following equations should be formed and solved .
Let us assume that we put on to a wire of length and radius a pure shear stress proportional to the distance from the axis , and twisting length through angle .
Then in addition to the shear , this stress would produce in an element unconstrained by noighbouring material what we may term " " free strains\ldquo ; co-ordinates , , and The diflerences between these actual strains and the ' free strains viz. , imply " " secondary stresses\ldquo ; in the wire due to adjustment of strain in neighbouring elements .
Let these be denoted by , W. To find , and , we treat , as if they vrere strains in an inqependent system .
Putting , the equations are , ( 3 ) where K-Sn and ) .
The forces , and must form a system in equilibrium , there being no external forces to balance .
Considering the equilibnum ) the elekent ABCD , fig. 5 , , whence .
( 4 ) .
( 6 ) By putting , we easily find the solution where and and are arbitrary constants to be determined by the boundary conditiona If the wire is unstrained in all parts before twisting , the solution applies with the same constants for all parts .
In order that when , we must have , so that .
( 8 ) When Substituting from S in the value of in ( 3 ) , and putting when , we get From equation ( 5 ) we obtain another relation between and , when we substitute for from ( 8 ) in from ( 3 ) and rate from to viz. , and from ( 9 ) and ( 10 ) we can find and Since A is a linear function of , and , and each of these is proportional to and are proportional to .
Substituting for in ( 8 ) , is also proportional to .
The theory , then , es the parabolic law for the twisting of a wire initially unstrained both for lengthening and for side contraction .
It also gives the lengthening and side contraction and for different wires of the same material as proportional to So far the theory does not , of course , give any account of the fact that the wires examined are always unsymmetrical , that the effects always date from a point , on the counter-clockwise side in the wires examined , being different for and .
This want of symmetry implies initial internal strain , probably , in reality , very complicated .
Let us examine a simple case in which there is a core , radius , twisted initially against a sheath , outer radius , and let the opposing twists be respectively and .
When we put a twist from outside on to the core as a whole the core is twisted through , and the sheath through .
For the core and sheath respectively we have Steet Wire when Twisted , etc. .
twist , which We take as one turn , or as in leugth cm .
We ako know and , since and Substituting for , and we can determine A in terms of and Then from equations ( 9 ) and ( 10 ) we can find and in terms of and Equating to the observed value of ( which is negative , and to the observed value of , we have two linear equations in and The arithmetic is straightforward , though lengthy , and may be omitted .
I have used a slide rule .
in the calculations .
Using the of the elastic constants and from Table II , and the values of and , on p. 548 , I find for Wire I so that the force perpendicular to the plane of the figure in fig. 4 is a tension and not a pressure .
in the Direction of Propagation in Distortional Waves and the Longiterdinal Waves Pr.oduced by the Pressure .
If we had a train of waves purely distortional , that is , a train in which the strain could be represented by a pure shear , there would be a pressure in the direction of propagation ( Snp ) .
But as varies from point to point in the train , the pressure due to the shear strain varies , and there must be longitudinal disturbance , longitudinal waves , accompanying the distortional waves .
The longitudinal strain implies that the material yields under the pressure , and the pressure will , in general , have a different value from that in a pure shear .
Let us represent the distortional train by where and is the amplitude of the shear .
If is the longitudinal displacement at the point where the shear is is the elongation of the element about the point .
Now if we shear a cube , and remove the pressure ) , the cube elongates in that direction , and if the dimensions in the two directions at right angles are maintained the same , the removal of the pressure produces elongation This we may term the ' free elongation\ldquo ; in the direction of propagation on the supposition that there is no change of length at right angles to it .
VOL LXXXVL\mdash ; k 2 If we put the energy per cubic centimetre in the longitudinal waves as , we find that so that the ratio is proportional to and therefore in any actual waves it is very small .
The pressuoes at right angles to the line of propagation will not produce any disturbance in a wave front where is constant .
Round the edges of the wave front , however , where is diminishing as we go outwards , they may have effects , and it appears likely that they may give rise to disturbances ated sideways .
I have much pleasure in recording my hearty thanks to Mr. .
O. Harrison , mechanic in the laboratory workshop , for his great help in planning the apparatus used in the experiments described in this paper , for his skill in constructing it , and for his assistance in making the observations .
|
rspa_1912_0046 | 0950-1207 | On the self-induction of electric currents in a thin anchor-ring. | 562 | 571 | 1,912 | 86 | Proceedings of the Royal Society of London. Series A, Containing Papers of a Mathematical and Physical Character | Lord Rayleigh, O. M., F. R. S. | article | 6.0.4 | http://dx.doi.org/10.1098/rspa.1912.0046 | en | rspa | 1,910 | 1,900 | 1,900 | 3 | 78 | 1,730 | http://corpora.clarin-d.uni-saarland.de/surprisal/6.0.3/?id=rspa_1912_0046 | 10.1098/rspa.1912.0046 | null | null | null | Fluid Dynamics | 37.330253 | Tables | 28.468708 | Fluid Dynamics | [
51.119850158691406,
-45.63936233520508
] | ]\gt ; discrepancy in the formula given by myself and by M. for tlm induction of a coil of ciroular cross section over whioh tk uIltnt : uniformly .
With omission of , repoesentative of Ue nuznber windings , my formula was where is the radius of the seotion and that of th9 oircular axis .
first two terms were given long before by Kirchhoff .
In place oTUe fourth term within the bracket , viz. , aeund In either case a correction would be neoessary in practice to take account'of the space occupied by the insulation .
Without , so far as I see , giving a reason , Rosa and Cohen express a preference for number .
difference is of no great importance .
but I have thought it worth while to repeat the calculation and I obtain the same result as in 1881 .
A confirmation after 30 years , and without reference to notes , is perhaps almost as good as if it were independent .
I propose to exhibit the main steps of the calculation and to make extension to some related problems .
The starting point is the expression given by for the mutual .
induction between two neighbouring co-axial circuits .
For the present .
purpose this requires transformation , so as to express the in terms of the situation of the elementary circuits relatively to the circularaxis .
In the figure , is the centre of the circular axis , the centre of .
a section through the axis of symmetry , and the posi of any of the section is given by polar -ordinates relatively to A. , by *'Bulletin of the Bureau tandards , Wuhing vol. No. 1 . .
Soa Proc. , ' 1881 , vol. p. 104 ; cientiAo P 'Ann .
\amp ; ' lS94 , bS p. ; it would did by angle PAC ) .
, be the co-ordinates of two points of the section , P2 , the mutual induction between the two circular circuits represented by , P2 is ately .
, ( 2 ) in which , the distance between and , is given by .
Further details will be found in Wien 's memoir ; do not repeat them because I am in complete agreement so far .
For the problem of a current uniformly distributed we are to integrate ( 2 ) twice over the area of the section .
'Taking first the integrations with respect to , let us express , ( 4 ) of which we can also make another application .
The integration of the terms which do not inYolve is elementary .
For those which do involve we may conveniently replace by , where and take first the integration with respect to being constant .
Subsequently we integrate with respect to It is evident that the terms in ( 2 ) which involve the first power of vanish in the integration .
For a change of , into respectively reverses and it leaves unaltered .
The definite integrals required for the other terms are* * Todhunter 's ' Int. Odc SS287 , 289 .
fflectric Currents in Thin Anchor-Ring .
Thus altogether the terms in ( 2 ) of the second .
order involving yield in ( 4 ) [ greater of and ] smaller of and .
( 15 ) The complete value of ( 4 ) to this order of approximation is found by addition of ( 8 ) , ( 10 ) , and ( 15 ) .
By making and equal we obtain at once for the self-induction of a current hmited to the circumference of an anchor-ring , and uniformly dis- tributed over that circumference , , ( 16 ) being the radius of the circular section .
The value of for this case , when is neglected , was virtually given by Maxwell .
* When th6 current is uniformly distributed over the area of the section we have to integrate again with respect to and between the limits and in each case .
For the more important terms we have from ( 8 ) [ -greater of and ] .
( 17 ) A similar operation performed upon ( 10 ) gives .
( 18 ) In like manner , the first part of ( 15 ) yields .
For the second part we have [ smaller of ] ; thus ether from ( 15 ) .
( 19 ) The terms of the second order are accordingly , by addition of ( 18 ) and ( 19 ) , .
( 20 ) 'Electricity and Nagnetism , ' SS692 , 706 .
{ -greater of and } .
( 26 ) The first part of this is , and the second is The additional terms are accordingly These multiplied by aoe to be added to ( 1 ) .
We thus obtain ( 28 ) for the self-induction of the solid ring when currents are slowly generated in it by uniform magnetic forces palallel to the axis of symmetry .
In Wien 's result for this case there appears an additional term within the bracket equal to A more interesting problem is that which arises when the alternations in the magnetic field are rapid instead of slow .
Ultimately the distribution of current becomes independent of renstance , and is determined by induction alone .
A leading feature is that the currents are superficial , although the ring itself may be solid .
They remain , of course , symmetrical with respect to the straight axis , and to the plane ich contains the circular axis .
The magnetic field may be supposed to be due to a current in a circuit at a distance , and the whole energy of the field may be represented by , etc. , being currents in other circuits where no independent electromotive force acts .
If be regarded as given , the corresponding values of , are to be found by making a minimum .
Thus ( 30 ) and so on , are the equations by which , etc. , are to be found in terms of What we require is the corresponding value of , formed from by omission of the terms containing only the leading term need be retained .
The ratio of to is to be found by elimination of between ( 35 ) .
( 36 ) .
We get .
( 38 ) Substituting this in ( 34 ) , we find as the coefficient of self-induction .
( 39 ) The approximate value of in terms of is .
( 40 ) A closer approximation can be found by elimination of between ( 35 ) , ( 36 ) .
In ( 39 ) the currents are supposed to be induced by the variation ( in time ) of an unlimited uniform magnetic field .
A problem , simpler the theoretical point of view , arises if we suppose the uniform field to be limited to a cylindrical space co-axial with the ring , and of diameter less than the smallest diameter of the ring .
Such a field may be supposed to be due to a cylindrical current sheet , the length of the cylinder being infinite .
The ring currents to be investigated are those arising from the instantaneous abolition of the current sheet and its conductor .
If be the area of the cylinder , ( 33 ) is replaced simply by .
( 41 ) The expression ( 34 ) remains unaltered and the equations replacing ( 35 ) , ( 36 ) , are thus .
( 42 ) .
( 43 ) The introduction of ( 43 ) into 34 ) gives for the coefficient of self-induction in this case\mdash ; .
( 44 ) It will be observed that the sign of is different in ( 38 ) and ( 43 ) . .
If the density be unity , the kinetic energy of the motion has .
the ( 46 ) having th6 value given in ( 44 ) .
P.S. , March 4.\mdash ; Sir W. D. Niven , who in 1881 verified some other results for self-induction\mdash ; those numbered ( 11 ) , ( 12 ) in the paper referred to\mdash ; has been good enough to confirm the formulae ( 1 ) , ( 28 ) of the present communica- tion , in which I differ from M. Wien .
The Diffusion and Mobility of Ions in Magrtetic Field .
By JOHN S. TOWNSEND , F.R.S. , Wykeham Professor of Physics , Oxford .
Received March ll , \mdash ; Read Apri125 , 1912 .
) 1 .
When the motion of ions in a gas takes place in a magnetic field the rates of diffusion and the velocities due to an electric force may be determined by methods similar to those given in a previous paper .
* The effect of the magnetic field may be determined by considering the motion of each ion between collisions with molecules .
The magnetic force causes the ions to be deflected in their free paths , and when no electric force is acting the paths are spirals , the axes being along the direction of the magnetio force .
If be the intensity of the magnetic field , the charge , and the mass of an ion , then the radius of the spiral is being the velocity in the direction perpendicular to H. The distance that the ion travels in the interval between two collisions in a direction normal to the magnetic force is a chord of the circle of radius .
The average lengths of these chords may be reduced to any fraction of the projection of the mean free path in the direction of the magnetic force , so that the rate of diffusion of ions in the directions perpendicular to the magnetic force is less than the rate of diffusion in the direction of the force .
In the previous paper it has been shown that the coefficient of diffusion is a measure of the rate of increase of the mean square the distance of any distribution from any being equal to Since Fbbuary , 1918 , vol. 86 .
|
rspa_1912_0047 | 0950-1207 | The diffusion and mobility of ions in a magnetic field. | 571 | 577 | 1,912 | 86 | Proceedings of the Royal Society of London. Series A, Containing Papers of a Mathematical and Physical Character | John S. Townsend, F. R. S. | article | 6.0.4 | http://dx.doi.org/10.1098/rspa.1912.0047 | en | rspa | 1,910 | 1,900 | 1,900 | 2 | 51 | 1,545 | http://corpora.clarin-d.uni-saarland.de/surprisal/6.0.3/?id=rspa_1912_0047 | 10.1098/rspa.1912.0047 | null | null | null | Fluid Dynamics | 56.857682 | Tables | 20.639536 | Fluid Dynamics | [
7.777341842651367,
-69.04838562011719
] | ]\gt ; .
If the density be unity , the kinetic energy of the motion has .
the ( 46 ) having th6 value given in ( 44 ) .
P.S. , March 4.\mdash ; Sir W. D. Niven , who in 1881 verified some other results for self-induction\mdash ; those numbered ( 11 ) , ( 12 ) in the paper referred to\mdash ; has been good enough to confirm the formulae ( 1 ) , ( 28 ) of the present communica- tion , in which I differ from M. Wien .
The Diffusion and Mobility of Ions in Magrtetic Field .
By JOHN S. TOWNSEND , F.R.S. , Wykeham Professor of Physics , Oxford .
Received March ll , \mdash ; Read Apri125 , 1912 .
) 1 .
When the motion of ions in a gas takes place in a magnetic field the rates of diffusion and the velocities due to an electric force may be determined by methods similar to those given in a previous paper .
* The effect of the magnetic field may be determined by considering the motion of each ion between collisions with molecules .
The magnetic force causes the ions to be deflected in their free paths , and when no electric force is acting the paths are spirals , the axes being along the direction of the magnetio force .
If be the intensity of the magnetic field , the charge , and the mass of an ion , then the radius of the spiral is being the velocity in the direction perpendicular to H. The distance that the ion travels in the interval between two collisions in a direction normal to the magnetic force is a chord of the circle of radius .
The average lengths of these chords may be reduced to any fraction of the projection of the mean free path in the direction of the magnetic force , so that the rate of diffusion of ions in the directions perpendicular to the magnetic force is less than the rate of diffusion in the direction of the force .
In the previous paper it has been shown that the coefficient of diffusion is a measure of the rate of increase of the mean square the distance of any distribution from any being equal to Since Fbbuary , 1918 , vol. 86 .
of diffusion along , which is unaltered by the fiel\amp ; .
As phenomena are of special interest in connection with negative ionr in the electronic state when magnetic fields produce large , the with molecules may be supposed to affect the motion of the ions irt the same .
way as the motion of small bodies is affected by colliding with comparatively large particles .
All directions of motion of an ion after collision with molecules may therefore be supposed to 9qually probable , so .
that Ae mean values of the velocities of the ions after colliding be zero .
Since the magnetic field only alters the direction of motion , the number of collisions that an ion makes per second is not affected , and the intervals between the collisions will be distributed as in the ordinary case , pnd will have the same value T. The number of intervals that exceed the time out of a total number will be In the following investigations two expressions occur which may be found in terms of the mean time between collisions .
These are the series of cosines : .
; and the series of sines : , etc. , being intervals between a large number of consecutive collisions that an ion makes with molecules .
The number of intervals that lie between the values and is ' so that the series of cosines may be expressed as the integral This expression may be integrated by parts and its value is Similarly , the series of sines will be found to equal to 2 .
The rate of increase of the mean square of the diSt1}e of any distribution from the axis of , may be determine , by the motion of an ion parallel to the plane of Let and be the ates of an ion at any time after a ion .
he equations of motion are\mdash ; He ' and the and given by equations of the : .
: so that ) and } : Nobitity of Ions in .
a Magnetie Field .
578 Let be the ities at the beginning of the first interval , and let the first collision occur in a time the velocities after the first collision , and the interval between the first and second collision , etc. In the first interval , the distances and traversed by the ions are and Let be the initial position of the ion , then after the time NT , the position will be and and the square of the distance from the axis will have increased by the amount The latter terms are zero , since , on the average , the sum of the cosines of the angles which any path makes with the consecutive paths vanishes .
Hence , for any ion , the square of the distance changes by the amount For alarge number of ions starting from the point , the average values of and vanish , since the ions are free to move in all directions .
Hence the rate of change in the mean square of the distance of the distribution from the axis is Substituting for and their values , the quantity becomes .
The velocities are independent of the times , so that the mean value of may be substituted for in this expression .
Also , since is the velocity in the plane , the mean value of is being the mean velocity of agitation of the ions ; and , since the series of cosines , is equal to , the above expression reduces to The rate of sion K along the direction of the magnetic force is .
Hence 3 .
The motion of the ions may therefore be expressed in the usual form by the equations plane and collide with molecules on the side opposite to B. There will .
therefore .
be no tendency for the ions to move across the plane and the only effect of the netic force is to cause the ions to move in circular paths , and so shorten their effective mean free paths along the direction of the axes of and .
Hence when .
Apparently , therefore , the original equations which lead to an expression for involving cannot be correct .
4 .
When ions are moving in an electric field and a magnetic force is applied adong the axis of , the motion iu that direction is unchanged , but in the directions and the velocities are altered .
Taking the axis of as the direction of the electric force X , the equations of motion become so that the velocities and are given by the equations and the velocities at the beginning of the path being A and -Acos Let , etc. , , etc. , be the velocities after a number of consecutive collisions of an ion with molecules of the gas .
The distances that an ion travels in the first interval are and The distances traversed in the time NT are he terms independent of X obviously vanish in estrimating the mean displaoements of a group of ions starting from the origin , and the velocities and along the axes become VOL LXXXVI.\mdash ; A. 2 : In this case the arc of the circle described between two collisions is large compared with the radius .
The velocities of ions under an electric force in gases at low pressures may thus be easily determined by producing a small deflection of a stream with a magnetic force , since when is small .
Also the theory may be tested by observing the effect of a magnetic force on the diffusion of a narrow stream moving under an electric force .
In this case when the magnetic force coincides with the electric force , the motion arising from diffusion in directions normal to the force is reduced in the proportion , so that the ions are kept together in a narrower stream .
There are several well known phenomena connected with magnetic rays that occur in discharge tubes , in which remarkable effects are obtained by magnetic forces .
The erved effects are qualitatively in accordance with the above theory , but the conditions under which they are obtained and the system of forces that is called into play are so complicated that an accurate comparison with the theory would not be possible .
A New Treatment of Aberration .
By B. A. SAMPSON , F.B.S. ( Received March 15 , \mdash ; Read May 23 , 1912 .
) ( Abstract .
) A method is developed by which Gauss 's method of relating original and emergent rays in a coaxial optical system by means of a transformation , where may be applied so as to include the aberrations of the third order .
|
rspa_1912_0048 | 0950-1207 | A new treatment of optical aberration. | 577 | 578 | 1,912 | 86 | Proceedings of the Royal Society of London. Series A, Containing Papers of a Mathematical and Physical Character | R. A. Sampson, F. R. S. | abstract | 6.0.4 | http://dx.doi.org/10.1098/rspa.1912.0048 | en | rspa | 1,910 | 1,900 | 1,900 | 4 | 29 | 839 | http://corpora.clarin-d.uni-saarland.de/surprisal/6.0.3/?id=rspa_1912_0048 | 10.1098/rspa.1912.0048 | null | null | null | Tables | 20.86486 | Formulae | 20.454744 | Tables | [
34.17139434814453,
-41.38792037963867
] | A New Treatment of Optical Aberration .
When 0 is large the velocity in the direction of the force becomes Xe m Xm H2eT ' so that tan 6 = HeT m HUE / In this case the arc of the circle described between two collisions is large compared with the radius .
The velocities of ions U under an electric force in gases at low pressures may thus be easily determined by producing a small deflection of a stream with a magnetic force , since U = UA when 0 is small .
Also the theory may be tested by observing the effect of a magnetic force on the diffusion of a narrow stream moving under an electric force .
In this case when the magnetic force coincides with the electric force , the motion arising from diffusion in directions normal to the force is reduced in the proportion K/ t/ K , so that the ions are kept together in a narrower stream .
There are several well known phenomena connected with the magnetic rays that occur in discharge tubes , in which remarkable effects are obtained by magnetic forces .
The observed effects are qualitatively in accordance with the above theory , but the conditions under which they are obtained and the system of forces that is called into play are so complicated that an accurate comparison with the theory would not be possible .
A New Treatment of Optical Aberration .
By R. A. Sampson , F.R.S. ( Received March 15 , \#151 ; Read May 23 , 1912 .
) ( Abstract .
) A method is developed by which Gauss 's method of relating original and emergent rays in a coaxial optical system y = y ' = \#163 ; V + Z/ , o z = yx + c , J = by means of a transformation , V = G\amp ; + H/ 3 , / 3 ' = K6+L/ 3 , = Gc + Hy , = Kc + Lie , where GL-HK = = N , may be applied so as to include the aberrations of the third order .
A New Treatment of Optical Aberration .
Using SG , for the added terms for a single surface , of curvature B , with both origins at the tangent plane , G -f- 8G = 1 A\#174 ; , H + SH = w/ B , Iv-|-81C -\#151 ; ( 1 \#151 ; N)B-pB(t|t\#151 ; ew ) , L + SL = N + -v|r\#151 ; \amp ; ) , where \#171 ; = |(l-N)B2(J2 + c2 ) , ^ 0S'2 + 7'2-/ 32-72 ) , and e is a term which is unity for the sphere and zero for the paraboloid .
It is shown how to build up the values resulting from any series of such aberrations and to obtain finally the aberrational increments SG , ... , in the forms SG = !
{ SiGK\amp ; 2-f c2 ) + 2S2G(\amp ; /3 + c7 ) + S3G(/ 32 + 72 ) } , SH = etc. , 8K = etc. , SL = etc. The twelve coefficients , SiG , ... , are then shown to obey seven relations , namely , .
s2g-S !
H _ s3G-a3H _ s2K\#151 ; SiL _ s3k-s2l _ aa G H K L V* where ^9 = yasr-i-1 ) Bar , and is in fact Petzval 's expression , the vanishing of which is known as the condition for flatness of field in stigmatic systems , and SxN = G81L + LS1G-Ha1K-KS1L = K ?
hT , a2N = ... = KLN , 83N = ... = ( L2\#151 ; 1)N .
These lead to Abbe 's sine condition , and both throw light on the general relationships of these two well known conditions .
The geometrical interpretation of the presence of the coefficients SjG , ... , at any numerical values , is followed out .
The formulae are then applied , as a numerical illustration , to the calculation of the celebrated Fraunhofer heliometer objective described by Bessel , and calculated with great completeness by A. Steinheil* In this portion the whole numerical work is given , and it is shown to amount to a mere fraction of that requisite for the trigonometrical calculation as employed , e.g. , by Steinheil .
Comparison is made with the whole of Steinheil 's results , for rays which meet and which do not meet the axis ; the numbers are shown to agree within a few units in the last places , and this discrepancy is probably to be attributed to the large number of operations requisite for the trigonometrical calculation .
Thus the method is adequate for the numerical calculation of telescopic objectives , and offers a remarkable economy in the work hitherto necessary .
* 1 Munich .
Akad .
Math. Pliys .
Class .
Sitzungsber .
, ' vol , 19 , Part 3 .
|
rspa_1912_0049 | 0950-1207 | Obituary notices of fellows deceased. | i | lv | 1,912 | 86 | Proceedings of the Royal Society of London. Series A, Containing Papers of a Mathematical and Physical Character | F. W. D. | article | 6.0.4 | http://dx.doi.org/10.1098/rspa.1912.0049 | en | rspa | 1,910 | 1,900 | 1,900 | 3 | 1,034 | 31,168 | http://corpora.clarin-d.uni-saarland.de/surprisal/6.0.3/?id=rspa_1912_0049 | 10.1098/rspa.1912.0049 | null | null | null | Biography | 55.415015 | Atomic Physics | 16.586728 | Biography | [
34.499149322509766,
79.3836898803711
] | OBITUARY NOTICES FELLOWS DECEASED VOL. LNXXVI.\#151 ; A. CONTENTS , Page Sir William Huggins , O.M. , K.C.B. ( With portrait ) ... ... ... ... . .
i George Johnstone Stony .
( With portrait ) ... ... ... ... ... ._ ... . .
xx SIR WILLIAM HUGGINS , O.M. , K.C.B. , 1824\#151 ; 1910 .
By the death of Sir William Huggins on May 13 , 1910 , the Royal Society lost a past President and one of its oldest and most distinguished Fellows .
He was one of the earliest to apply the spectroscope to the analysis of the light of the stars .
From the importance and diversity of the discoveries which he made and the methods which he originated , he may with justice be called the founder of Astrophysics .
It was his good fortune to assist in and follow the progress of this branch of knowledge for nearly half a century .
William Huggins was born in London on February 7 , 1824 , his father being in business in the City .
He was entered at the City of London School in the first term of 1837 , and stayed there till Christmas , 1843 .
In the school records it is stated that he gave the German Declamation in praise of the founder , John Carpenter , on Friday , July 28 , 1843 .
After leaving school he continued his studies under private tutors , paying attention to classics , modern languages , and Hebrew .
After a few years in business he was able to retire and devote his life to scientific pursuits .
In an autobiographical article in the 'Nineteenth Century/ for June , 1897 , entitled " The New Astronomy : A Personal Retrospect , " he tells us that it was with some hesitation that he decided to give his chief attention to Observational Astronomy .
He was strongly under the spell of the rapid discoveries which were then taking place in microscopical research in j- connection with physiology .
He joined the Royal Microscopical Society in 1852 , and it was not till 1854 that he became a Fellow of the Royal Astronomical Society .
He purchased a house at Tulse Hill , which was then a little distance out of London , and in 1856 built an observatoryNn his garden , reached by a passage from the house .
The observatory consisted of a dome , 12 feet in diameter , and a transit room .
A 5-inch telescope by Dollond , equatorially mounted , and a small transit were the instrumental equipment .
At that time a 5-inch refractor was considered a large rather than a small instrument .
With the 5-inch equatorial Huggins made observations and drawings of the planets .
His earliest published paper contains drawings of Jupiter for October 14 and 15 , 1856 , and of Mars for April 28 and May 19 .
In 1858 he purchased from Mr. Dawes an object glass of 8 inches diameter made by Alvan Clark , the famous founder of the American firm which in later years made the great telescopes for Washington , Lick , and Yerkes .
This object glass had met with high approval from Dawes , and no one was more competent to judge than that distinguished observer of double stars , who obtained the name of " eagle-eyed " by reason of the acuteness of his vision .
Huggins thus became the possessor of a very VOL. lxxxvi.\#151 ; a. i ii Obituary Notices of Fellows deceased .
fine telescope , which he mounted equatorially and provided with slow motions .
He tells us that he soon became dissatisfied with the routine character of ordinary astronomical work .
The belief that the most important and interesting discoveries in astronomy had been made , and that details only required to be filled in , was prevalent in the middle of last century .
That this view was entirely erroneous has been proved* as regards Dynamical Astronomy by the work of Delaunay , Hill , and others , and as regards Stellar Astronomy by the recent cosmical developments which have their foundation in the accurate measures of the positions of stars .
But neither of these main branches of the astronomy of the period was quite suited to the genius and tastes of Huggins .
" Just at this time , " he tells us , " when a vague longing after newer methods of observation for attacking many of the problems of the heavenly bodies filled my mind , the news reached me of KirchhofTs great discovery of the true nature and the chemical composition of the sun from the interpretation of the Fraunhofer lilies .
This news was to me like the coming upon a spring of water in a dry and thirsty land .
Here at last presented itself the very order of work for which in an indefinite way I was longing\#151 ; namely , to extend his novel methods of research upon the sun to the other heavenly bodies .
" Kirchhoff 's memoir , in which he demonstrated with full experimental verification the relationship of the dark lines in the solar spectrum to the bright line spectra of the elements obtained in his laboratory , was published in 1859 .
In the following year , in conjunction with Bunsen , he showed that the sun contained many elements known to exist on the earth .
Although the theoretical ideas of Kirchhoff were not so novel as he had thought , having been to some extent largely anticipated as regards the main principles by Stokes and Balfour Stewart , spectroscopy as an important method of research dates from this paper of 1859 .
Huggins relates in the 'Nineteenth Century ' how , on January 15 , 1862 , he attended a soirde of the Pharmaceutical Society , and met his friend and neighbour , W. A. Miller , Professor of Chemistry at King 's College , London , and Treasurer of the Eoyal Society from 1860 to 1871 .
After the soiree the two friends drove back to Tulse Hill together , and Huggins asked Miller to join him in his proposed attempt to apply the method of " prismatic analysis , " employed by Kirchhoff and Bunsen , to the stars .
Miller at first hesitated , as the small amount of light from a star rendered the success of the experiment doubtful , but finally agreed to co-operate .
Kirchhoff and Bunsen had compared in their spectroscope , simultaneously , the light of the sun with light from various terrestrial sources .
But the total light received from one of the brightest of the stars is less than the fraction 10~10 of that received from the sun .
All the light which falls from a star on an object glass can , however , be concentrated into one point , the telescopic image .
A spectroscope had therefore to be designed and applied Sir William Hugginsi ii ] in such a manner that the whole of this light could be utilised .
It was accordingly mounted firmly on the telescope , with the slit at the focus ; and the terrestrial light with which comparison had to be made was obtained from the sparks of an induction coil , and was bent round into the tube of the spectroscope by means of a reflecting prism placed over half of the slit .
The spectrum of a star obtained in this way was , however , a mere line , too narrow for the eye to detect any lines crossing it .
To broaden it a cylindrical lens\#151 ; an optical appliance then seldom used\#151 ; was obtained and placed within the focus of the telescope , thus lengthening the point of light on the slit into a short line , and giving the necessary breadth to the spectrum .
By the end of 1862 a stellar spectroscope had been constructed of sufficient dispersive and defining power to resolve such lines as D and b of the solar spectrum , and competent to reveal the finer lines in the spectra of the stars if these should be found to resemble those in the solar spectrum This spectroscope utilised two dense flint glass prisms of 60 ' angle .
The collimating lens had a diameter of 0'6 inch and a focal length of 4^ inches , the ratio of aperture to focal length enabling the whole of the light from the linear image of the star on the slit to fall upon the collimating lens .
The viewing telescope had an aperture of 0*8 inch and a focal length of 6'75 inches ; it was carried by a micrometer screw which turned it so that different parts of the spectrum could be examined , and the relative positions of the lines in the spectrum accurately measured .
Particular pains were taken to ensure accuracy in the relative positions of the stellar and comparison spectra .
Owing to flexure of the spectroscope the absolute reading of the micrometer was not the same for the same spectrum line for stars at different altitudes .
Therefore for each star a preliminary observation was made , which secured coincidence of the comparison spectrum of sodium with that obtained from a small alcohol lamp saturated with sodium chloride placed close to the centre of the object glass of the telescope .
It was verified that when this adjustment had been made , lines from other parts of the two spectra also coincided .
Thus when for any star the presence of the double line corresponding to D had been satisfactorily determined , it was only necessary in further comparisons so to adjust the spark that the sodium lines from it agreed with these lines from the star .
Besides the points of difficulty which were thus successfully surmounted in the construction of a stellar spectroscope , an additional one arose from the want of convenient maps of the spectra of terrestrial elements .
Huggins devoted a large part of the year 1863 to mapping , with a train of six prisms , the spectra of the elements , using as a standard of reference the spark spectrum of air obtained by the discharge of a large induction coil fed by a condenser consisting of nine Leyden jars .
In this way maps and tables extending through the whole length of the visible spectrum were made for no less than 24 elements .
A brief note in which diagrams of the spectra of Aldebaran , a Orionis , and b 2 iv Obituary Notices of Fellows deceased .
Sirius are described had been communicated to the Eoyal Society in February , 1863 , but it was not until April , 1864 , that complete results were communicated .
In this important paper ( 'Phil .
Trans. , ' 1864 , vol. 154 , pp. 413\#151 ; 435 ) the authors state that they have investigated the spectra of fifty stars to a greater or less extent , but have concentrated their efforts in the complete examination of two or three stars .
The spectrum of Aldebaran , for example , was compared directly with the spectra of sixteen terrestrial elements , and the existence of sodium , magnesium , hydrogen , calcium , iron , bismuth , tellurium , antimony , and mercury in this star was announced .
In Betelgeux they found sodium , magnesium , calcium , iron , and bismuth .
The presence of some of these metals has not been confirmed by later work ; but these remarkably accurate pioneer researches established beyond question the authors ' conclusions that " the stars , while differing the one from the other in the kinds of matter of which they consist , are all constructed'upon the same plan as our Sun , and are composed of matter identical at least in part with the materials of our system .
" Simultaneously with the appearance of the first announcement by Huggins and Miller of their preliminary results , Eutherfurd published , in the ' American Journal of Science , ' an account of a study by very similar methods of the spectra of the Moon , Jupiter , Mars , and several of the fixed stars .
He did not , however , pursue this line of research , but turned his thoughts to astronomical photography .
The work of Secchi , carried on contemporaneously with that of Huggins and Miller , was complementary to their studies .
He investigated and classified the spectra of 600 and later of 4000 stars by the use of a prism placed in front of the object glass of his telescope .
This method had been employed by Fraunhofer in very delicate work , before , however , the meaning of the dark lines in stellar spectra named after him was understood ; and later , Donati used the imperfect method of a slitless spectroscope .
The use of a prism in front of the object glass avoided the observational difficulties with which Huggins and Miller had to contend , and was suitable for the important work of a survey of a large number of stars .
The disadvantage of the method is the absence of the fiducial lines which are obtained by the comparison spectrum when a slit spectroscope is used .
To interpret stellar spectra with certainty the more laborious method of Huggins and Miller was necessary , more especially in the early stages of the science .
Owing to pressure of other duties , Miller was obliged to discontinue his co-operation with Huggins when their researches had reached this stage .
They had worked together from January , 1862 , to April , 1864 , and in that period had laid the foundations of the methods to be applied in the spectroscopic study of the stars .
From this time till his marriage , ten years later , Huggins pursued his researches single-handed .
On August 29 , 1864 , Huggins made a discovery of cardinal importance .
Having pointed his telescope on a planetary nebula in Draco , described in Sir John Herschel 's Catalogue as " very bright , pretty small , suddenly Sir William Huggins .
\gt ; v brighter in the middle , very small nucleus/ ' he found that the light of the nebula , " unlike any extra-terrestrial light which I have previously subjected to prismatic analysis , is not composed of light of different refrangibilities , and therefore does not form a spectrum .
A great part of the light of this nebula is monochromatic , and , after passing through the prisms , remains concentrated in a bright line , occupying in the instrument the position of the part of the spectrum to which its light corresponds in refrangibility .
" A narrower slit showed two fainter lines in addition .
The bright line was found to agree in position with the brightest of the air lines , viz. , the strongest line in the spectrum of nitrogen ; the faintest of the three lines coincided with the F line of hydrogen , while the third line did not coincide with any known line , but its position was identified by its proximity to a line of barium .
This historic observation proved that the nebula in Draco is not an incandescent solid or liquid transmitting light of all refrangibilities through an atmosphere which intercepts some of them\#151 ; not a body of the type of our Sun\#151 ; but is a widely extended mass of luminous vapour .
In a moment a definite answer had thus been given to the question whether all nebulae were aggregations of stars too distant to be resolved into separate units by the telescope , or were , in Sir William Herschel 's words : " A shining fluid fit to produce a star by its condensation .
" By the middle of the nineteenth century many nebulae had already been resolved into multitudes of stars by the large telescopes which had been directed to them , and it was matter of speculation whether all might not be resolvable with still larger telescopes .
Huggins ' spectroscope showed that this was not the case , and left tenable the view that nebulae were " the early stages of long processions of cosmical events which correspond broadly to those required by the nebular hypothesis .
" The researches on nebulae were pursued by Huggins with characteristic thoroughness .
Eight other bodies were found to give spectra which indicated their gaseous nature .
In all of these the same bright line was found coincident in position with the line of nitrogen , while generally the two fainter lines seen in the Draco nebula were also seen .
Six of these bodies were small and comparatively bright objects , designated as " planetary " nebulae by Herschel .
The other two were the ring nebula in Lyra and the nebula in Yulpecula .
But the great nebula in Andromeda , and the bright condensation associated with it , did not give a gaseous spectrum like the other nebulae examined ; they gave a continuous one , similar to that shown by a star , though , on account of its faintness , dark lines could not be seen crossing it .
In the following winter the great nebula in Orion was examined , and the same three bright lines found in the spectrum of all parts of that nebula .
Its gaseous constitution was therefore established .
Observations of Lord Boss and Prof. Bond were thought to have resolved the great nebula , as well as the ring nebula , into discrete points .
If so , these nebulae must be vi Obituary Notices of Fellows deceased .
considered not as simple masses of gas , but as systems formed from the aggregations of such masses around centres of condensation .
The four bright stars in the centre of the Orion nebula were also examined ; they showed continuous spectra with no indication of absorption lines , and it was noted that the continuous spectrum of the stars in the neighbourhood of the green nebula line was brighter than this line in the adjacent nebula .
The existence of the same three bright lines in all nebulae , indicating an identical gaseous constitution , appeared to show that the nebulae possessed " a structure and purpose in relation to the Universe , altogether of a distinct and of another order from the great group of cosmical bodies to which our sun and the fixed stars belong .
" Huggins soon afterwards adopted the view that the gaseous nebulae were to be regarded as precursors of the stars in the course of evolution of the Stellar Universe .
Leaving on one side speculative questions , he made a more complete examination of the nebulae and clusters , comparing his results with the telescopic observations made with Lord Rosse 's great reflector .
By August , 1866 , he had examined the spectra of more than 60 nebulae and clusters .
About one-third of these were found to give spectra consisting of bright lines , indicating their gaseous constitution .
None of the bodies showing bright line spectra had been resolved into stars by Lord Rosse .
On the other hand , all the true clusters , which could be resolved into distinct bright points , gave spectra which were apparently continuous , and , in addition , many nebulae , of which the great nebula in Andromeda is a striking example , gave spectra of a similar character .
At this stage , subjects for investigation crowded themselves upon Huggins ' attention .
The regular fluctuation in the brightness of variable stars might be elucidated by'spectroscopic examination .
If physical changes occurred , they would be shown by changes in the spectra .
Again , if diminution of brightness were caused by the interposition of a dark companion , additional lines of absorption might be shown in the spectrum .
Observations of Betelgeux at its maximum brightness in February , 1866 , showed that a group of lines was missing which had been seen and mapped two years previously .
While these observations were in progress a new star appeared in the sky .
Such bodies may be considered as extreme types of variable stars .
They flash up suddenly and slowly fade .
One of these rare phenomena was opportunely observed on May 12 , 1866 , by Mr. Birmingham , of Tuam , County Galway .
He immediately communicated to Mr. Huggins his discovery of a new star of the second magnitude in the constellation of Corona .
When the news was received on May 16 the star was of the third magnitude ; it was still a bright star and suited to spectroscopic examination .
Huggins sent a messenger to Miller and they directed the spectroscope to the new star .
_ Jaj Examination showed the spectrum to be different from any previously examined ; and , as described in the 'Proceedings ' ( vol. 15 , p. 146 ) : " The light of the star is compound and has emanated from two different sources .
' Sir William Huggins .
, un Each light forms its own spectrum .
In the instrument these spectra appear superposed .
The principal spectrum is analogous to that of the sun , and is evidently formed by the light of an incandescent solid or liquid photosphere which has suffered absorption by the vapours of an envelope cooler than itself .
The second spectrum consists of a few bright lines , which indicate that the light by which it is formed was emitted by matter in the state of luminous gas .
" The two principal bright lines were in the positions F and C of the solar spectrum , and showed that the luminous gas consisted in part of hydrogen .
Their great brightness was taken as an indication that the gas was hotter than the liquid or solid photosphere of the star .
In conjunction with the sudden outburst of the star and its rapid decline in 12 days from the second to the eighth magnitude , these facts suggested that the star had become suddenly enwrapt in the flames of burning hydrogen .
The early researches of Huggins are of such general character as to make an appeal to all who are interested in physical science as well as to astronomers .
The observations of the new star astonished a still wider circle , which did not hesitate to conclude that , " from afar astronomers had seen a world on fire go out in dust and ashes .
" The new star drew attention in a sensational manner to the possibilities of the new science of which Huggins was laying the foundations .
The structure of comets is a subject marked out for elucidation by prismatic analysis .
In 1864 Donati found that the comet of that year had a spectrum consisting of bright lines .
Huggins examined faint comets which appeared in 1866 and 1867 , and was able to detect a very faint continuous spectrum from the coma , from which he inferred that its light was probably reflected sunlight .
In the middle of this faint spectrum a bright point was seen , showing that the nucleus of the comet was self-luminous and gaseous .
This bright point appeared to coincide with the principal bright line in the spectra of nebulse , and at first Huggins supposed the lines might have the same origin .
Early in 1868 he observed the spectrum of Brorsen 's comet , and found it to consist of three bright bands .
The transverse length of the bands showed that they did not arise solely from the nucleus of the comet but from the brighter parts of the coma .
When the slit of the spectroscope was narrowed the bands did not become sharp , and in that respect differed from the spectra of nebulse .
The positions of the bands were determined by micrometric measurements , and by comparison with various terrestrial spectra .
It happens , curiously , that this earliest obtained spectrum of a comet 's head is not of the character usually found in these bodies ; but it has recently been pointed out that the spectrum of the tail of Morehouse 's comet of 1908 resembles that found by Huggins in the head of Brorsen 's comet .
On June 13 , 1868 , a comet was discovered by Winnecke , with a coma very bright at the centre and suitable for spectroscopic observation .
Huggins examined it with a spectroscope containing two 60 ' prisms , and found that the light was resolved into three bright bands .
These bands were brightest viii Obituary Notices of Fellows deceased .
on their less refrangible sides , where they commenced sharply , and gradually faded away on their more refrangible sides .
They could not be resolved into lines even when a spectroscope of greater dispersion was employed .
On the following day the spectrum as drawn and measured was compared with various terrestrial spectra .
The positions of the bands , and their general character , resembled the spectrum obtained when a spark is passed through olefiant gas .
The next evening a direct comparison was made between the spectra of the comet and of olefiant gas , and the bands were found to agree exactly in position .
Later observations have shown that this spectrum of the three bands found in hydrocarbons is characteristic of the heads of comets .
Huggins delivered at the British Association at Nottingham on August 24 , 1866 , a " Discourse on Spectrum Analysis applied to the Heavenly Bodies .
" He concludes the lecture by summing up the knowledge which had been gained by the method .
This summary serves to show the great discoveries he had made in the few years from 1862 to 1866 and the state of Astrophysics at the time .
1 .
All the brighter stars , at least , have a structure analogous to that of the Sun .
2 .
The stars contain material elements common to the Sun and Earth .
3 .
The colours of the stars have their origin in the chemical constitution of the atmospheres which surround them .
4 .
The changes of brightness of some of the variable stars are attended by changes in the lines of absorption of their spectra .
5 .
The phenomena of the star in Corona appear to show that in this object at least great physical changes are in operation .
6 .
There exist in the heavens true nebulae .
These objects consist of luminous gas .
7 .
The material of comets is very similar to the matter of gaseous nebulae and may be identical with it .
8 .
The bright points of the star clusters may not be in all cases stars of the same order as the separate bright stars .
Observations made later , in 1868 , showed the incorrectness of the view ( 7 ) that cometary matter was similar to that of the nebulae .
The explanation of the colours of stars cannot now be accepted as complete .
With these exceptions the conclusions of this lecture all hold , and are a statement of the important and fundamental knowledge then obtained by the spectroscopic study of the stars .
At the time when he was making simultaneous comparisons of stellar and terrestrial spectra for the determination of the chemical constitution of the stars , Huggins realised that such comparisons might serve to determine the motions of the stars in the line of sight .
If the stars were moving to or from the Earth , their motion compounded with the Earth 's motion would alter to an observer on the Earth the wave-length of the light emitted by them , and consequently the lines of terrestrial substances would no longer coincide in IX Sir WjUictm Huggins .
, position in the spectrum with the dark lines produced by the absorption of the vapours of the same substances in the stars .
The two-prism spectroscope he employed was sufficient to show that no displacement in any of the stars he examined was so great as the interval between the two D lines , and thus to obtain the important conclusion that none of these stars had velocities to or from the earth amounting to 196 miles per second .
From the velocities of the few stars wThose parallax was sufficiently well known , it was seen that the order of the quantity to be sought was in their case only a fraction of the interval between the I ) lines .
He therefore designed and had constructed a spectroscope of much greater dispersion , equivalent in power to 6-|- prisms of 60 ' .
At the same time he experimented in different ways with a view to making the comparison spectrum more trustworthy and more convenient .
Two pieces of silvered glass were fixed before the slit at an angle of 45 ' , leaving an opening of one-tenth of an inch between them for the passage of the star 's light from the object glass of the telescope .
The light from an induction-spark whose position relatively to the telescope was kept fixed by careful precautions , was reflected into the spectroscope by these pieces of glass .
The star 's spectrum was therefore seen accompanied by two comparison spectra , one on each side of it .
In the winter of 1867 lie made observations on Sirius , a star which was suitable on account of its brilliancy and of the great intensity of its hydrogen lines .
He compared the line at F with the corresponding hydrogen line .
At first hydrogen at atmospheric pressure was used , but as the width of the line obtained in this way was greater than the corresponding dark line in the spectrum of Sirius , a vacuum tube fixed in front of the object glass was substituted .
The line thus obtained was about one-fifth of the width of the broad line in the spectrum of Sirius , and was seen distinctly as a bright line on the dark line .
It was clearly seen not to coincide with the middle of the line , and the distance from the middle was estimated in terms of the micrometer screw .
It was found that the displacement towards the red was 1'09 tenth-metres , giving a velocity of separation of Sirius from the Earth of 41'4 miles per second .
Allowing 12 miles for the recession of the Earth from Sirius owing to its orbital motion , there remained a movement of recession of 29'4 miles per second of Sirius from the solar system .
The importance of these researches and their extreme delicacy made it desirable that they should be pursued with greater optical power .
The President of the lloyal Society , in his address for 1869 , stated that " the Council have resolved to provide a telescope of the highest power that is conveniently available for spectroscopy and its kindred inquiries . . . .
The instrument will be entrusted to such persons as , in their opinion , are the most likely to use it to the best advantage for the extension of this branch of science ; and in the first instance there can be but one opinion that the person so selected should be Mr. Huggins .
" The Oliveira bequest of \#163 ; 1350 to the Society facilitated this project , and \#166 ; a tender from Mr. Grubb was accepted in April , 1869 , for the construction of x Obituary Notices of Fellows deceased .
an object glass of 15 inches aperture and of 15 feet focal length , on an equatorial which could be easily worked by an observer without an assistant .
In order that observations on the heat of the stars , which had already been attempted by Huggins , might be pursued , the equatorial , at the suggestion of de la Rue , was also provided with an 18-inch reflector which could be substituted for the 15-inch refractor .
A drum of 18 feet diameter was erected in 1869-70 , instead of the 12 feet dome , to house the new equatorial .
By February , 1871 , the instrument was installed and found to work admirably .
Spectroscopes specially adapted for the instrument were constructed suitable for the observation of stars , nebuke , and the sun .
With this new instrument the determination of velocities in the line of sight was immediately continued .
The best means of introducing the comparison spectrum were again considered .
Although the reflection from a silvered surface in front of the slit worked well , some troublesome adjustments and a liability to displacement were avoided by a plan adopted instead of it .
Holes were drilled in the telescope tube 2 feet 6 inches from the focus , and tubes carrying the vacuum tubes or electrodes were inserted .
The spark was in this way brought right into the axis of the telescope .
The following paragraph from a paper presented to the Royal Society in 1872 , in which the results of observation of thirty stars are given , may be quoted as showing the great difficulties of these observations and the care bestowed on them by Huggins :\#151 ; " It may be well to state some circumstances connected with these comparisons which necessarily make the numerical estimations , given farther on , less accurate than I could wish .
Even when spectroscope C , containing four compound prisms , and a magnifying power of 16 diameters are used , the amount of the change of refrangibility to be observed appears very small .
The probable error of these estimations is therefore large , as a shift corresponding to 5 miles per second ( about 1/ 40 of the distance of Hi to D2 ) , or even a somewhat greater velocity , could not be certainly observed .
The difficulty arising from the apparent smallness of the change of refrangibility is greatly increased by some other circumstances .
The star 's light is faint when a narrow slit is used , and the lines , except on very fine nights , cannot be steadily seen , in consequence of the movements in our atmosphere .
Further , when the slit is narrow , the clock 's motion is not uniform enough to keep the spectrum steadily in view ; for these reasons I found it necessary to adopt the method of estimation by comparing the shift wTith a wire of known thickness , or with the interval between a pair of close lines .
I found that , under the circumstances , the use of a micrometer would have given the appearance only of greater accuracy .
I wish it therefore to be understood that I regard the following estimations as provisional only , as I hope , by means of apparatus now being constructed , to be able to get more accurate determinations of the velocity of the motions .
" Sir William . .
xi Comparison with later measurements has shown , as is not surprising when it is considered that all the apparatus had to be improvised , that the velocities obtained for these thirty stars are , when regarded as standard determinations , of but small weight .
Nevertheless , the result of the efforts which Huggins made to determine precise values for the velocities in the line of sight must be considered as a great step in the progress of Astronomy .
He attempted a practical problem so novel and difficult that only his appreciation of its great importance could have sustained him in his effort .
After the publication of Huggins ' paper , line of sight determinations were taken up at Greenwich , and observations were carried on for many years by Mr. Maunder .
But it was not till the years 1888 to 1892 , when photography was applied by Yogel and Schemer , that a reliable procedure was evolved.* Huggins had the good fortune to witness that immense development of this branch of Astronomy , in which he was the pioneer , which has been made possible by the great light-gathering power of large telescopes combined with spectroscopes of high resolving power and sensitive modern photographic plates .
The large spectroscope which he had installed in 1867 enabled Huggins to prosecute researches on the Sun .
A comparison of the spectrum of the Sun near its limb with that at its centre , and of the spectra of sunspots with the solar spectrum , engaged his attention .
He also endeavoured to obtain in direct sunlight by increased prismatic dispersion the spectrum of the prominences which are visible during total eclipses on the limb of the Sun , and in the Report of his Observatory to the Royal Astronomical Society in February , 1868 , described fully and definitely the method of observation .
In the detection of the spectrum of the prominences he was , however , anticipated by Janssen and by Lockyer .
But he had priority a few months later in a new application of the principle that was involved ; he succeeded in making an image of a solar prominence visible in each bright line by the simple method of widening the slit of the spectroscope .
In 1875 Dr. Huggins married Miss Margaret Lindsay Murray , in whom he found , to quote his own words , in addition to an inspiring helpmate , an able and enthusiastic assistant .
Her name is associated with that of her husband in the authorship of most of the work after this date .
From 1876 to 1880 Huggins was engaged on the application of photography to stellar spectroscopy.- So early as 1863 he had obtained a spectrum of Sirius on a wet collodion plate , but did not prosecute researches in this direction , as the plates were not sufficiently sensitive , and their use involved numerous practical difficulties .
He saw that the gelatine dry plate , from the convenience attending its use and its great sensitiveness , was well adapted for spectroscopic research .
Its reaction to ultra-violet light made it possible for spectra of stars to be obtained in this hitherto unexplored * H. C. Vogel , " On the Progress made in the Last Decade in the Determination of Stellar Motions in the Line of Sight , " ' Astrophys .
Journ. , ' vol. 11 , p. 373 .
xii Obituary Notices of Fellows deceased .
region .
But , owing to the great absorption by glass of light of wave-length shorter than the violet , a refracting telescope and glass prisms are unsuitable for work on this part of the spectrum .
Huggins therefore decided to use the 18-inch speculum mirror of''his Cassegrain telescope and to fit it with a suitable spectroscope .
This he constructed of a single 60 ' prism of Iceland spar , with collimator and camera lenses of quartz .
He removed the small convex mirror of his telescope and mounted the spectroscope with its slit at the focus of the 18-inch speculum , 13 feet distant from the eye-end of the telescope .
To enable him to bring the star to be observed on the slit , and to keep it exactly there during an exposure which might be of an hour 's duration or more , he made the jaws of the slit of speculum metal and maintained the adjustment by watching the reflection of the star-image from the jaws by means of a small telescope mounted in the central hole of the large speculum .
With this instrument he obtained in 1876 , with the assistance of Mrs. Huggins , a spectrum of Yega showing seven strong lines , two of which were known to be due to hydrogen , and the remaining five were continuations hitherto unobserved of the same series of hydrogen lines , which afterwards became classical as the subject of Balmer 's law { infra ) .
With some minor improvements , observations on the brighter stars were continued in this manner till 1879 , when the results were communicated to the Boyal Society in a paper on " The Photographic Spectra of Stars " ( ' Phil. Trans. , ' 1880 , Part II , p. 669 ) .
Maps and tables of wave-lengths of the lines are given for the white stars Sirius , Yega , 7 Cygni , 7 Yirginis , rj Ursse Majoris , 7 Aquike , and ( a star of different type ) Arcturus , extending from Hy , X 4340 , to X 3300 .
The spectra of these white stars were found to possess a remarkable similarity .
The photographs showed 12 very strong lines .
The first three of these were the hydrogen lines , Hy , Hg , He .
The remaining nine were not coincident with any strong lines in the solar spectrum , but the symmetrical appearance of the whole group suggested at once that all belonged to the spectrum of the same substance .
These lines were afterwards obtained in the spectrum of terrestrial hydrogen by Cornu .
In 1885 Balmer showed that all were embraced with great exactness in the simple formula X = 3645'6 m2/ ( m2\#151 ; 4 ) by giving m in succession the values 3 , 4 , 5 , etc. Huggins afterwards obtained spectrographs of stars showing 31 lines belonging to this series with the same exactness ; and thus the discovery of the hydrogen series in the spectra of the stars provided the stimulus for the subsequent sorting out of the lines of the spectra of other elements into series which has been effected by Kayser and Bunge , Bydberg , Bitz , and other physicists .
Huggins directs attention to three characteristics in these stellar spectra : ( i ) the differences in width and diffuseness of the hydrogen lines ; ( ii ) the absence or presence of the K line due to calcium and its intensity relatively to the hydrogen lines ; and ( iii ) the number and distinctness of other lines .
These features served as a basis for a classification of the stars .
In an Sir William Huggins .
, XUl addendum to the paper , in which spectra of Capella , Aldebaran , and Betelgeux obtained by him in January , 1880 , are also considered , he arranges the stars in an order substantially the same as that given by Vogel a few years previously , as indicating successive stages in the evolution of these bodies .
The appearance of a fairly bright comet , in 1881 , presented an opportunity for pushing researches on cometary spectra into the ultra-violet region .
The spectrum was photographed with the spectroscope he had used for stars , and revealed two strong bright lines at 3883 and 3870 , which were identified with two cyanogen lines found by Profs .
Liveing and Dewar .
There was also a continuous spectrum , in which the Fraunhofer lines were visible , showing that a part of the comet 's light was reflected solar light .
In the following year he photographed the spectrum of Comet Wells , and found it to be entirely different from the comet of 1881 .
It consisted of five bright bands , whose positions he measured , but he did not succeed in determining their chemical origin .
In this year he also obtained a photograph of the spectrum of the Orion nebula , and found , in addition to the lines he had observed visually long-before , an extremely strong line in the ultra-violet at the approximate wavelength 3730 .
In the years 1882 to 1885 a good deal of attention was given by Huggins to the problem of photographing the sun 's corona without an eclipse .
The photograph of the spectrum of the corona taken by Prof. Schuster in Egypt during the eclipse of May 17,1882 , had shown the coronal light to be strongest in the part of the spectrum from G to H. By the use of screens of coloured glass or liquid Huggins limited the light to this range of wave-length in the hope that this would enable the coronal light to hold its own against the atmospheric glare .
He thus obtained photographs which in their general features resembled the corona , and he , as well as other experts to whom the photographs were submitted , thought that a successful start had been made .
A resemblance between photographs taken in England near the time of the eclipse of May 6 , 1883 , and those taken by the eclipse observers in Caroline Island were held to lead to the conclusion that to a distance of 8 ' from the Sun 's limb the appearances on Huggins ' plates were genuine pictures of the corona .
A committee was appointed by the Eoyal Society for the purpose of carrying on experiments under the more favourable conditions provided by high elevation .
Mr. Woods , an observer at the 1883 eclipse , was sent to the Eiffel Alp at an altitude of 8,500 feet in July , 1884 , and took a large number of photographs .
Fine matter in the air\#151 ; due , in Huggins ' opinion , possibly to the Krakatoa explosion or else to ice spicules\#151 ; was always present , and produced sufficient stray light to prevent the experiment being successful .
Photographs taken subsequently at the Cape also gave negative results .
A final test of the method was made at the eclipse of August , 1886 , during the partial phase .
In a letter to ' The Times ' Huggins says : " The partial phases of this eclipse furnished conditions which would put the success of the method xiv Obituary Notices of Fellows deceased .
beyond doubt , if the plates showed the corona cut off partially by the Moon during its approach to and passage over the Sun .
As the telegrams received state that this partial cutting off of the corona by the Moon is not shown on the plates , I wish to be the first to record this untoward result .
I greatly regret that the method which seemed to promise much new knowledge of the .corona would seem to have failed .
" This problem had called for an attack , and the failure of an observer so skilful and persevering shows that a successful result can only be looked for under exceptional atmospheric conditions .
His attention was withdrawn from stellar researches for several years while he was experimenting on the photography of the corona without an eclipse .
Some repairs of his instrument were also required .
A number of alterations were made , of which the most important was the modification of his equatorial by which it was made to carry both the refractor and reflector instead of only one of them .
In addition he constructed a new and more rigid spectroscope for visual observations .
In 1888 he resumed observations , both visual and photographic , of the spectrum of the Orion nebula .
The visual observations , which were continued to 1890 , were concerned with the wave-length and identification of the principal nebular line .
The following summary of the history of this line is given by Keeler in the 'Lick Observatory Publications , ' vol. 3:\#151 ; " In 1864 Huggins found that this line coincided in position with the brightest air line , a coarse double , the mean position of which is A , 5003 .
He then considered that it was probably due to nitrogen ; in 1872 with his more powerful spectroscope he gave the wave-length as 5005 , and was still disposed to regard it as due to nitrogen , ascribing its displacement to recession of the nebula from the Sun .
In 1874 he found that the line was apparently coincident with the less refrangible of the nitrogen lines .
He appears by this time to have abandoned his view of the chemical origin of the line .
He also discovered a very convenient comparison line in the spectrum of lead .
In 1887 Prof. Lockyer , in connection with the ' meteoric hypothesis , ' suggested that the nebular line is coincident with the magnesium fluting at A 5006*4 .
This rendered the exact determination of the position of the line a matter of great interest .
In 1889 Dr. and Mrs. Huggins compared the nebular line with the magnesium fluting , using a very high dispersion .
They found the line to be more refrangible than the edge of the magnesium fluting , and to be fine and sharp like the hydrogen lines .
They also concluded that neither visual nor photographic observations afforded any evidence of the presence of magnesium in the nebula .
In 1890 Prof. Lockyer , from a review of previous observations and his own in that year , maintained that the chief nebular line is a remnant of the magnesium fluting .
Dr. and Mrs. Huggins repeated their observations , and confirmed their result that the nebular line is more refrangible than the head of the magnesium fluting .
" At the request of Dr. Huggins the position of the line was determined by Prof. Keeler , at the Lick Observatory , who found the nebular line to be at A 5007*0 , the head of the magnesium fluting at A 5007*5 , and the two Sir William Huggins .
, xv nitrogen lines at X 5001'0 and X 500o-3 .
These observations of Keeler showed conclusively that the nebular line is not a remnant of the magnesium fluting , and its chemical origin is still unknown .
In the ' Proceedings * ( 1889 , vol. 46 , p. 40 ) , an account is given of a remarkable photograph of the ultra-violet spectrum of the Orion nebula taken on February 5 , 1888 .
The photograph shows the strong line X 3727 .
As the slit was set so that two bright stars in the centre of the nebula fell upon it , the photograph shows the continuous spectrum of these stars as well as the bright line spectrum of the nebula .
Four groups of faint lines can be seen extending across the continuous spectra of the stars into the nebula .
As the stars have these lines in common with the nebula , the conclusion is drawn that they are not merely in the same direction as seen from the Earth , but are physically connected with it .
The photograph was too faint to be reproduced , but was shown to several eminent spectroscopists , who agreed that the appearances on the negative were real lines .
In particular , Prof. Hale , in 1894 , examined the photograph and verified the existence of the faint lines , and stated that the increase in width and brightness of the lines where they crossed the spectra of the stars was most striking .
In the year 1890 the two lines and in the hydrogen series were discovered in the spectrum of the Orion nebula , as well as a line X 3868 .
In the same year , on a very clear night in September , Huggins obtained photographs of the spectrum of Vega to determine the point at which the star 's light is extinguished by the absorption of the earth 's atmosphere .
The light was found to be abruptly weakened at X 3000 , but to be faintly seen to X 2970 .
Similar results were found from observations of the Sun 's spectrum .
In 1890 he discovered a series of six broad lines in the spectrum of Sirius in the extreme ultra-violet from X 3338 to X 3199 .
In the same year he made visual observations of the positions of the bright band in the blue in Wolf-Payet stars , confirming observations of Vogel 's , that this band did not coincide with the blue band due to carbon which is seen in a spirit lamp flame .
The appearance of Nova Aurigse in 1892 naturally attracted the attention of Dr. and Mrs. Huggins .
They observed the remarkable phenomenon that the bright hydrogen lines and some others were doubled by a dark line of absorption on the blue side , and they estimated the relative shift to be 550 miles a second , a result in accord with the estimates of other observers .
They also saw in the spectrum the double line of sodium .
By comparison with suitable spectra they found that , at this stage of the star 's history , there was no sign of the nebular line , and no relationship with cometary spectra .
With the ultra-violet spectroscope they obtained a photograph of the spectrum up to the extreme limit which the absorption of the atmosphere permits .
It shows the hydrogen series in bright lines , with accompanying absorption lines on the blue side , as well as a large number of other lines .
They were unable to examine the spectrum very completely after its xvi Obituary Notices of Fellows deceased .
remarkable change into that of a planetary nebula in August , announced by Campbell , owing to alterations which were being made in .
their telescope .
A few observations on the character of the bright bands in the positions of the principal and second nebular lines were made by them in February , 1893 , and they laid some stress on the difference between these bands and the sharp lines in the spectra of nebulae .
Huggins favoured some connection between the later stages of new stars and planetary nebulae .
Referring to Nova Persei , the new star of 1901 , in his Presidential Address to the Royal Society in that year , he says : " A remarkable phenomenon occurred in Nova Cygni and in Nova Aurigae , namely , that at a certain stage of cooling , the bright lines peculiar to the gaseous nebulae ( and which are probably due to an undiscovered light substance we may call nebulum ) made their appearance , and , together with the lines of helium and hydrogen , which are common to the nebulae and early white stars , remained to constitute the latest stage of their spectra .
" At the very commencement of his spectroscopic work , the Observatory at Tulse Hill was a meeting place where terrestrial chemistry was brought into direct touch with celestial changes .
When the spectra of the elements in 1863 were required in order to determine the position of the stellar lines with accuracy , the necessary observations were made by Huggins .
In 1870 the spectra of erbia and other earths were examined by him .
In 1880 the flame spectrum of hydrogen burning in air was photographed and mapped .
Huggins tells us that in the early sixties his observatory had very much the appearance of a chemical and physical laboratory .
Throughout his life he excelled in the laboratory experiments which interpret astronomical observations .
In 1897 he published a paper " On the Relative Behaviour of the H and K Lines of the Spectrum of Calcium .
" He wished to elucidate a problem of great interest\#151 ; why , although in the general spectrum of the Sun there are no fewer than 70 lines attributed to the element calcium , there are only two\#151 ; the lines H and K\#151 ; in the spectrum of the chromosphere and in the spectra of some stars .
His conclusions were that this was simply due to differences in the density of the calcium in the source from which the light originated .
In 1903 he published in the ' Astrophysical Journal ' the results of experiments on the modifications in the appearance of the magnesium line \ 4481 under different laboratory conditions of spark discharge , with a view to the interpretation of its appearance in stellar spectra .
Still later , when over 80 years of age , he pursued very delicate investigations on the spontaneous luminosity of radium , showing that it was due to phosphorescence of the nitrogen of the air .
The conclusions at which Huggins arrived on the subject of stellar evolution are given in * An Atlas of Representative Stellar Spectra , published in 1899 .
Lady Huggins is associated with Sir William in the authorship of this beautiful volume , and she has enriched it with initial letters and othei drawings , which recall the decoration of the works of the old astronomeis .
A short history is given of the pioneer researches carried out at Tulse Hill , Sir William Huggins . .
xvn and a description of the various instruments employed .
These have been already referred to , with exception of the new ultra-violet spectroscope constructed in 1896 .
The small spectroscope with its slit in the principal focus of the 18-inch speculum was dismounted and the convex speculum was replaced , restoring the original Cassegrain telescope .
The new spectroscope was mounted with its collimator passing through the hole in the large speculum to such a distance that the slit was at the focus of the Cassegrain .
The spectroscope consisted of two 60 ' prisms of Iceland spar , the smaller having a length of 2\ inches and height of If inches .
The collimator and camera lenses were of quartz , the latter having a focal length of 15 inches .
The ' Atlas ' consists of a series of plates reproduced from spectra photographed with this instrument , extending from A , 4870 to A , 3300 .
They are of special value as giving many typical spectra over a very long range of wave-lengths .
Very little work has been done elsewhere on the ultra-violet spectra of the stars .
The text contains a discussion of the " Evolutional Order of the Stars and the Interpretation of their Spectra .
" In 1879 Huggins had selected as a natural criterion , indicating successive changes of density and temperature , the gradual increase of strength of the calcium line K , taken together with the diminution in strength of the lines of hydrogen and the simultaneous incoming and strengthening of the metallic lines .
He thus obtains an order , essentially the same as Vogel 's of date 1874 , and regards the white stars , such as Sirius , to represent the early adult and persistent stage of stellar life , stars like the Sun and Capella , the condition of maturity and commencing age , while in the orange and red stars , such as Aldebaran and Betelgeux , he saw the setting in and advance of old age .
This classification is , in the main , adhered to in 1899 .
An important addition is the separation of the helium stars from other white stars .
From their association with nebulae they are naturally placed first in the order of evolution .
From them the change is continuous to the Sirian stars , from the Sirian to the Solar , and from the Solar to the Red stars .
Sir William and Lady Huggins attach more importance to density than to temperature in causing spectral changes , and they point out how large a part is played by the increase of gravity at the surface which accompanies the contraction of a star .
They determine the relative temperature of the stars by the comparative intensities of the ultra-violet and blue portions of their continuous spectra .
These delicate observations led to the conclusion that temperatures of stars increase till they have reached the stage of the Sun , and then decrease .
Here they are at variance with the conclusions favoured by other astronomers , which make the white stars hotter than those of solar types .
The ' Atlas of Representative Spectra ' forms vol. 1 of the ' Publications of the Tulse Hill Observatory .
' It was followed in 1909 by vol. 2 , containing a collection of Huggins ' scientific papers , edited by Sir W. and Lady Huggins , reprinted from the ' Transactions ' and ' Proceedings ' of the Royal Society and other scientific journals .
The Address to the British Association at vol. lxxxvi.\#151 ; A. c xviii Obituary Notices of Fellows deceased .
Nottingham and the Presidential Address at Cardiff , are also included .
The volume contains a reproduction of the portrait of Huggins , painted by the Hon. John Collier during the term of his Presidency , which hangs in the rooms of the Royal Society ; it has also a photograph of Lady Huggins .
The papers are arranged according to the subjects with which they deal they present a contemporary record of the growth of Astrophysics in its different branches .
In the preface Sir William Huggins says : " Looking back , with the knowledge of the more efficient and perfectly adapted instruments and methods of work which have been gradually introduced during the last forty years , no one can be more conscious than I am of the inevitable shortcomings of my pioneer instruments and methods of work which had to be created under circumstances of no little difficulty .
These shortcomings prevented the attainment of accurate results in some single oases , but time has shown that they did not affect the fundamental general correctness of my early work .
" Huggins witnessed a great advance in Astrophysics .
But he saw no departure from the methods he employed .
The development was due mainly to an increase in light-grasping power , brought about by large telescopes and sensitive dry photographic plates .
Huggins realised clearly what problems could be solved by prismatic analysis , and he showed the right way to set to work .
His attack combined a splendid audacity with great judgment .
This collection of his papers rounded off the main work of his long scientific life .
He relinquished in 1908 the charge of the telescopes and spectroscope which had been placed in his care by the Royal Society in 1871 .
These were given by the Royal Society on his advice to the Astrophysical Department of the University of Cambridge , and were erected there during his lifetime .
Arrangements had been made , at the time of his death , for him to visit Cambridge , to inaugurate the , completion of this installation .
Sir William Huggins received many marks of distinction in recognition of his scientific achievements .
He was elected a Fellow of the Royal Society in 1865 , and received a Royal Medal in the following year .
The Rumford Medal was awarded to him , most appropriately , in 1880 , and the Copley Medal , the crowning honour at the disposal of the Society , in 1898 .
The Gold Medal of the Royal Astronomical Society was awarded to him along with Prof. Miller in 1867 , and to him alone a second time in 1885 .
In 1869 he was Rede Lecturer at Cambridge , and he received the honorary degree of LL. D. from that University in 1870 .
Oxford conferred on him the degree of D.C.L. in 1871 , Edinburgh the LL. D. in 1871 , Dublin the LL. D. in 1886 , and St. Andrews the LL. D. in 1893 , and he received degrees from various Foreign and Colonial Universities , including Leyden and Heidelberg .
The Paris Academy of Sciences awarded him the Lalande Prize in 1872 , and elected him a Corresponding Member in 1874 ; he also received the Yalz Prize in 1883 , and the Janssen Gold Medal in 1888 .
In 1901 he received the Henry Draper Gold Medal from the National Academy of Sciences of Washington .
He was enrolled as honorary or foreign member of most of the principal Sir William Huggins .
\gt ; xix national learned societies , including the Institute of France , Reale Accademia dei Lincei , the Royal Academies of Sciences of Berlin and Gottingen , the Royal Society of Sweden , the Royal Society of Denmark , the Royal Society of Holland , the ( American ) National Academy of Sciences , the American Philosophical Society of Philadelphia , and the American Academy of Arts and Sciences of Boston , the Royal Irish Academy and the Royal Society of Edinburgh .
He was created K.C.B. in 1887 , on the occasion of the Diamond Jubilee of Queen Victoria .
In 1902 , when the Order of Merit was instituted by King Edward , Sir William was chosen as one of the twelve who originally constituted the Order .
Sir William Huggins served repeatedly on the Council of the Royal Society .
He was three times Vice-President , and in 1900 was chosen to succeed Lord Lister as President .
He filled this very important office for five years with marked dignity and distinction .
At the suggestion of his colleagues , selections of four of his Presidential Addresses , which treat of subjects of general interest , were published by him in book form .
In these he discusses the value of science in education as compared with humanistic studies , considering them as equally essential , and indeed complementary of each other .
He also gives an account of the great work that science , as represented by the Royal Society , has done and is doing for the nation .
In 1891 he was President of the British Association at Cardiff .
He served on the Council of the Royal Astronomical Society continuously from 1864 to 1910 .
He was Secretary from 1867 to 1870 , Vice-President from 1870 to 1873 , President from 1876 to 1878 , and Foreign Secretary from 1873 to 1875 and from 1883 to 1910 .
Sir William Huggins gave ungrudging service in all these capacities .
Only a week before his death he took part in a meeting of a joint committee of the Royal and Royal Astronomical Societies , for making arrangements for the publication of a collected edition of Sir William Herschel 's papers , an undertaking due largely to his initiative .
His scientific eminence naturally brought him a great deal of correspondence , to which he gave generously of his time and thought .
His unfailing good health enabled him to do this in the midst of his own researches .
In the last year of his life he worked for some hours daily in the physical laboratory , spent the afternoon in the study , and wrote in the evening .
His death , at the age of 86 , took place in a nursing home in London on May 12 , 1910 , unexpectedly , after one day 's illness .
F. W. D. XX GEOEGE JOHNSTONE STONEY , 1826\#151 ; 1911 .
The family from which George Johnstone Stoney was derived , on his father 's side , settled in Ireland in the seventeenth century , coming from Yorkshire .
From the marriage of George Stoney of Oakley Park , King 's County , with Anne , daughter of Bindon Blood , D.L. , of Cranagher and Bockforest , County Clare , was born in February , 1826 , George Johnstone Stoney , eldest son and third child .
One other son also was born , Bindon Blood Stoney .
The latter , a distinguished engineer , and a Fellow of the Eoyal Society , died early in 1909 .
A sister of the late George Johnstone Stoney married her cousin the Eev .
William FitzGerald , Bishop of Killaloe , a union which gave rise to the late George Francis FitzGerald , whose remarkable genius , especially in physical science , is known to all .
Other distinguished relatives are to be found in William Bindon Blood ( mother 's brother ) , who was a professor of engineering and author of professional papers ; in General Sir Bindon Blood , G.C.B. ( son of mother 's brother ) , Commander of the Forces in the Punjab and distinguished in the Chitral Expedition and in the Boer War ; and in Maurice FitzGerald , lately Professor of Civil Engineering in Queen 's University , Belfast .
The Stoneys ' country property in Ireland was of considerable value during the early years of the last century .
Those were times of large profits to agricultural undertakings , the Napoleonic Wars conferring an artificial value on home produce .
Irish property fell in value when the wars ceased , and country gentlemen found that encumbrances incurred during the more prosperous times , and as the result of lavish hospitality , were not so easily met as in the good times .
Poverty fell upon them and* the terrible times of the Irish Famine ( 1846\#151 ; 48 ) , intensified by the monstrous policy of that day which decreed the local raising of the Poor Law rate just where the famine was most severe , completed the ruin of many Irish families in those districts where the unfortunate tenants stood most in need of the landlord 's assistance .
The Stoneys ' property had to be sold ; it fetched about eight years ' purchase of the reduced rental , and Johnstone Stoney 's widowed mother and her children had no other means .
Many county families who had similarly lost their landed property flocked to Dublin and turned to professional careers in order to make their way in the world .
It was a strenuous time in this younger society of Dublin , and one of much mutual helpfulness .
Johnstone Stoney and his brother Bindon entered Trinity College , earning the expense of their fees by " grinding , " or in English phraseology " coaching .
" Although unable to afford such assistance for themselves , both brothers had distinguished college careers , Johnstone never failing to obtain a place amongst the first three in the First Class honour lists , and taking a Second Senior Moderatorship in Mathematics and Physics in the Final , the first place going to the George Johnstone xxidistinguished mathematician Mr. Morgan Crofton , F.R.S. In those days scholarships all went to classical men .
When Johnstone Stoney left college Lord Rosse made him his first* regular ; astronomical assistant at Parsonstown , a post subsequently filled by ' Robert Ball and by other young men who later on made a distinguished mark in science .
Stoney read for the Trinity College Fellowship while at Parsonstown .
He entered for it in 1852 and took second place , winning* thereby the Madden Prize , which is worth about \#163 ; 300 .
It was the last examination conducted in Latin , and a wide range of subjects was included in the course , the cumulative marks deciding .
Although not so severe an examination as it has since become , the ordeal was a severe one .
Stoney was examined in Hebrew , chronology , metaphysics , and classics , besides his own'1 special subjects of mathematics and physics .
The range of subjects , the method of cumulative marking , and the encumbrance of Latin as a medium of expression , would handicap any science student .
It was , too , an examina- !
tion in which brilliant originality of mind counted practically for nothing .
Stoney is one of many distinguished men whom Trinity College has lost as the result of the exclusively examinational mode of entry to Fellowships .
Johnstone Stoney could not afford to try for the Fellowship again , and Lord Rosse , who was always a true friend to him , used his influence to have him appointed to the Chair of Natural Philosophy in Queen 's College , Galway .
Stoney remained five years in Galway and then became Secretary to the Queen 's University , which brought him back to Dublin and to the wider life of a great University city , a change keenly appreciated by him .
For many years after this Stoney devoted himself enthusiastically to the ' work of solving the problem of the provincial university , in other words to 1 securing to the local university the same beneficent influence which the ' greater central universities exert upon those more wealthy students who can afford the cost of residence away from home .
The problem was then a new one , for although the older universities have in past centuries gone through times of mere provincial importance , the conditions of their growth and development were different from those which affect a recent institution .
' The latter has to face at once the rivalry of the older institutions , with their ' greater prestige , and the facilities of modern modes of travel .
In Ireland the whole question is complicated by differences in views as to the mental standpoint of the university , differences founded upon religious principles which seem impervious to argument .
In the midst of these labours , which continued till 1882 , when the Queen 's 1 University was dissolved , other chances came to Johnstone Stoney , but his devotion to what he hoped would have been his life 's work prevented his considering them , though some of these offers would have benefited him i pecuniarily and others would have given him greater leisure for research , the \#166 ; latter a condition far outweighing the former in his estimation .
" The office of the Queen 's University %as then situated in Dublin Castlei , and Stoney 's conversancy with educational matters led to his beingj xxii Obituary Notices of Fellows deceased .
frequently consulted by both political parties .
He was frequently brought over to the House of Commons , so as to be at hand to give information to the Chief Secretary of the day when Irish educational matters were in question .
He wrote many reports on educational subjects , more especially for Sir Thomas Larcom .
When Sir Thomas retired , he was anxious that Stoney should succeed him as Permanent Secretary in Ireland .
Lord Mayo , then Lord-Lieutenant , sounded him on the subject ; however , Stoney frankly told him he approved of Mr. Gladstone 's Irish Church Disestablishment Bill as the healthiest policy for the Church itself .
This closed the matter , as Lord Mayo was a Conservative and opposed to Mr. Gladstone 's policy .
At the request of the Civil Service Commissioners , Stoney added to his other duties those of Superintendent of the Civil Service Examinations in Ireland .
The double duties added much to his already heavy office work , and sorely curtailed what leisure he had for scientific work .
In 1882 the dissolution of the Queen 's University fell as a crushing blow upon Stoney .
" At a stroke of the pen , I beheld the labour of nearly thirty years of my life annulled"\#151 ; in such words he described the event to the present writer .
There is no doubt that the policy of dissolution was a most questionable one .
The University was dissolved just when becoming most successful .
In its stead an examining University was installed , and the several colleges of the old Queen 's University became feeders to this institution , which had the power of conferring degrees on purely examinational tests , degrees bearing the same status as those conferred upon students who were not in residence in the colleges .
The evils arising , and developing with the lapse of years , in the new Royal University found little defence when , many years later , the latter became the subject of enquiry by the Irish University Commission of 1901 .
The Commissioners reported that , in addition to defects of organisation , the Royal University " has seriously impaired the value of the University education which was previously in existence .
On this side its influence has been one of positive destruction ; since it came into being , the growth of the Queen 's Colleges has been arrested .
" In the end , the Royal University , which had supplanted the Queen 's , was in turn swept away , and , the present National University of Ireland and the Queen 's University of Belfast installed in its place , the purely examinational system being , it is to be hoped , banished for good .
It was during this long period of residence in Dublin that Stoney 's influence made itself felt in the policy of the Royal Dublin Society .
This Society is unique among voluntary institutions in the United Kingdom\#151 ; unique in organisation , and , it may be said , unique in the influence it has exerted upon almost every factor tending towards advance of civilisation and national prosperity .
Originating in the efforts of a few enthusiasts to better the arts and industries of Ireland , it was founded in 1731 , having its first home in Trinity College .
Developing year by year , it fostered not only industries but science , and to its inception are due^the Royal Botanic Gardens of Dublin , the Royal College of Science , the National Library , the National Museums George Johnstone xxiii of Art , Archaeology , and Natural Science , and the National Art Gallery of Ireland .
In this Society Stoney served as Honorary Secretary for over twenty years , and afterwards as Vice-President , until he left Dublin for London , on his retirement from official life , in 1893 .
During his tenure of office the Society went through great and fundamental changes , exacting much extra work from its officers .
The Society used to be the channel through which the Government administered grants in Ireland to Agriculture , Science , and Art .
The time came when the Treasury felt that it was anomalous for public grants to be administered by a private , voluntary society and out of the direct control of a Public Department .
The Royal Dublin Society , in Stoney 's time of office as Honorary Secretary , handed over its great collections to the Government , receiving an allotment of capital for the pursuance of its scientific functions , and for enlarging and amplifying its agricultural shows and otherwise helping Irish agriculture .
The premises at Ball 's Bridge were acquired at this time , and an era of advance in the magnitude and influence of its shows initiated , which has resulted in making them of international importance .
Towards the close of his personal influence in the Royal Dublin Society , Stoney induced the Council to inaugurate concerts directed to the performance of the best chamber music by proficients brought from various parts of the world ; these concerts soon became a permanent part of the Society 's work , attracting many members to the Society , and undoubtedly doing much for the advance of musical culture in Dublin .
It would be impossible here to estimate adequately Stoney 's influence upon the Ro}ral Dublin Society .
The work of reorganisation arising in its constitutional changes was enormous .
One who , like the writer , served in the secretaryship during more settled times , can realise what it must have been .
The Council is a complex body , sitting together as a Council , working apart as three great Committees of Agriculture , of Science and its Industrial Applications , of General Purposes .
There are two secretaryships , which generally are regarded as respectively apportioned to Agriculture and to Science .
The latter was filled by Stony , but the secretaries ' work is by no means limited by this subdivision .
They enter alike into all the questions of public policy continually arising , and into the Financial Committee 's supervision of ways and means .
Additional to his general work for the Society Stony worked wholeheartedly for the advancement of its scientific functions .
For many years his own research work was communicated almost exclusively to the Society , and published in its ' Proceedings ' and ' Transactions ' : his aim being to confer upon its publications something more than a local prestige .
His gifted relative , George Francis FitzGerald , ably assisted him in this endeavour .
The younger men , feeling the advantages of discussions in which men of such critical ability participated , gladly brought their work to the Society , and for many years the evening meetings were characterised by debates of the highest scientific interest .
Although the Society still xxiv Obituary Notices of Fellows deceased .
does invaluable work for science , there is no doubt that in the untimely death of FitzGerald , and the loss of Stony upon his departure to London , the science meetings lost much of their high standing .
The close of his official work in Dublin meant for Stony a time of leisure ; but it came too late for the publication of much of the scientific work he had done .
He was then nearly 68 years of age , with health impaired by the long and heavy strain of official work .
His life in London was largely devoted to the completion and publication of original work begun in earlier years ; but this could only be slowly accomplished , and he died before it was completed according to his wishes .
Stoney 's scientific work needs no apology on the score of diversity or of prolificness ; but the amount of it conveys but a small idea of his life 's work , and , indeed , forms but a small part of it .
Only an over-mastering scientific enthusiasm could have elicited such a body of work from a man harassed for the best years of his life by strenuous duties continually leading his thoughts into other channels .
Yet a major part of his work was accomplished during those years of official toil .
He was a remarkable instance of the resistless power of a great intellectual development ; of its relentless pertinacity and resolution .
His power of accomplishment was linked with an unusual degree of self-centred devotedness to the immediate subject of his thoughts and speculations .
Around this subject the interests of his intellectual life appeared to be gathered and concentrated for the time .
With this very conspicuous quality of mind it is the more remarkable that he worked as a devoted and successful official during years of considerable scientific fertility .
It must have been a heavy exaction even from one with his high-minded sense of duty .
The final facts of his success in both spheres of his work demonstrate at once his intellectual force and his splendid devotion to his aims and to his duties .
One of Stoney 's earliest papers was a geometrical examination of the conditions of propagation of undulations of plane waves in media ( ' Trans. Roy .
Irish Acad. , ' vol. 24 , 1861 ) .
The reasoning is mainly directed to explaining why an undulation of the kind considered , when once established , continues to propagate itself in one direction only .
Analytical reasoning is not used .
Indeed , throughout a major part of his writings Stony prefers geometrical to analytical reasoning .
In a later paper he states his preference for the former : " The chief value of the geometrical form of proof is that it gives us a more continuous view of what is going , on in nature , inasmuch as the stages of the geometrical proof of a physical problem keep throughout their whole progress in close proximity to what actually takes place , whereas a symbolical proof is in contact with nature only at its commencement and at its close " ( " On a New Theorem in Wave Propagation , " ' Phil. Mag. , ' April , 1897 ) .
After the appearance of his optical paper of 1861 the subject of geometrical optics does not appear to have enjoyed Stoney 's attention till the appearance of the " Monograph on Microscopic Vision " ( ' Phil.iMag .
, ' October , November , XXV .
George Johnstone and December , 1896 ) , that is , till after his official life was closed and he had leisure to work up material which , as in this case , had probably been by him for many years .
The study of microscopic vision is based upon a method of resolution into flat wavelets . .
Stony shows that the method is one of wide generality , and a series of propositions occupy a large part of the paper , establishing and analysing the fundamental proposition that " however complex the contents of the objective field . . .
the light which emanates from it may be resolved into undulations , each of which consists of uniform plane waves , " or wavelets , which do not undergo change as they advance^ On this basis the causes of the phenomena presented by microscopic vision are sought in a paper ingenious in reasoning and laborious in its scope .
The proof of the fundamental proposition given in the first paper did not , however , satisfy Stony , and several subsequent papers appeared , one criticising an insecure proof advanced by Thomas Preston , " On a Supposed Proof of a Theorem in Wave-Motion " ( 'Phil .
Mag. , ' May , 1897 ) ; also , on this subject , see 'Phil .
Mag. ' for February , April , July , and August , 1897 , and July , 1898 .
A proof of the theorem by the principle of reversal is given in a paper published at p. 570 of the ' Report of the British Association ' for 1901 ; and Stony returns to the matter again in the ' Philosophical Magazine ' of February , 1903 , this time partly with a view to welcome an analytical proof of the resolution into flat wavelets by E. T. Whittaker .
This paper , entitled " How to Apply the Resolution of Light into Uniform Undulations of Flat Wavelets to the Investigation of Optical Phenomena , " contains several theorems not contained in earlier papers .
All this work was written in ignorance of the fact that Stokes , in one of his earlier papers ( 1845 ) , had enunciated the same fundamental proposition from which Stoney 's work takes origin\#151 ; but without offering any proof .
In a paper contributed to the * Philosophical Magazine ' in April , 1905 ( " Flat-Wavelet Resolution , Part III " ) , Johnstone Stony announces his discovery of Stokes ' priority .
It is probable that Sir George Stokes considered it almost self-evident as a general statement " . . .
for we may represent an arbitrary disturbance in the medium as the aggregate of series of plane waves propagated in all directions .
" In an appendix to this paper of April , 1905 , Stony again considers the proof of the theorem , and from a manuscript note inserted in his " Monograph on Microscopic Vision " it would appear that the last mode of regarding the matter was that which he preferred .
Stoney 's last published scientific papers were on telescopic vision ( ' Phil. Mag. , ' August , November , and December , 1908 ) , and these are now referred to because they are a continuation of the subject to which Stony directed his attention early in life\#151 ; consideration of wave-propagation and the formation of images .
In treating of telescopic vision Stony resolves the light before it enters the telescope into a somewhat special system of undulations of spherical wavelets , i.e. into spherical undulations , the centres of which shall be the several points of a plane perpendicular to the optic axis and situated close in front of the objective , and by the interference of xxvi Obituary Notices of Fellows .
which ( in the usual manner ) , at the principal focus , the image is formed ; the papers are of the same character\#151 ; at once ingenious and laborious\#151 ; as that upon microscopic vision .
It is a surprising reflection that Stony was in his eighty-third year when these elaborate and painstaking papers were penned .
The papers alluded to above represent important work , and are characteristic of Stoney 's manner of dealing with investigations of similar description .
Their inception dates from the beginning of his scientific career , and they have , therefore , been placed in the forefront of this brief review of his work , but they are by no means the most important part of his work .
His investigations in various departments of molecular physics distinctly claim that place .
Stoney 's work in molecular physics began in 1860 , when , on the basis of Maxwell 's estimate of the average length of the free path of the molecules of a gas , he made an estimate of the number of molecules present in unit volume .
This was , of course , led up to also by the work of Clausius , and was an early contribution to a great subject , then only beginning to be a subject of research .
Waterston 's memoir had been submitted fifteen years earlier ( 1845 ) , and , not being published , the advent of the new ideas had to wait for Clausius ' papers of the later years of the forties .
For the first time the kinetic theory then received publication , and it was recognised that planetary conditions as regards freedom of motion might attend the movement of a gaseous atom between its encounters .
Stony showed a clear and vivid appreciation of the new molecular science , and from this time forward the application and exposition of its laws occupied him at intervals throughout his life .
We gather some idea of the state of the subject by perusing a paper by Stony appearing in the 'Proc .
Roy .
Irish Acad. , ' vol. 7 , 1858 .
This appears to be his earliest contribution to the subject .
We find him demonstrating that the law of Boyle is contrary to the view that the particles of a gas are at rest , or that it can be a continuous homogeneous substance .
Ten years later , writing in the ' Philosophical Magazine ' " On the Internal Motions of Gases Compared with the Motions of Waves of Light " ( 'Phil .
Mag. , ' August , 1868 ) , we find him complaining that the dynamical theory of gases had not met with the general attention and acceptance which it deserved .
In this latter paper a vivid appreciation of the relative magnitudes is shown , and Stony pictures the source of the light waves as existing in the " from fifty to one hundred thousand of these little orbital revolutions " which the molecules are able to execute between successive encounters .
Such thoughts were more fully elaborated later .
He closes his review of the subject with his estimate of molecular numbers in a gas at standard pressure and temperature , concluding that in 1 cubic mm. there are 1018 molecules . . .
Arising out of his interest in the kinetic theory of gases are his series of papers on the conditions limiting planetary atmospheres .
He first touches George Johnstone Stony .
XXVll -on the subject in his paper " On the Physical Constitution of the Sun and Stars , " which appeared in the * Proceedings ' of the Royal Society in 1868 .
In this he infers that a complex atmosphere will , near its outward quiescent boundaries , cease to be homogeneous , the lighter constituents extending further into space .
Towards the close of 1870 , in a discourse delivered before the Royal Dublin Society , the subject of the absence of atmosphere from the moon is discussed , the conclusion being that the gravitation on the moon will not suffice to retain a free molecule moving in a radial , or even outward , direction , with a velocity of 2'38 kilometres per second .
Molecules which occasionally reach this speed may be , accordingly , lost to the moon .
A full account of his views is given in his paper " On Atmospheres of Planets and Satellites " ( ' Trans. Roy .
Soc. Dub .
, ' vol. 6 , 1897 ) .
Stony contends that on the earth hydrogen and helium are scarce or absent because of their leakage from the atmosphere ; water molecules , on the other hand , cannot attain so great an excess over the velocity of mean square as is required for their escape .
The theory has been called in question on deductive reasoning ( see papers by S. R. Cook , ' Astrophys .
Journ. , ' vol. 11 , Jan. , 1900 : and by G. H. Bryan , ' Phil. Trans. , ' A , vol. 196 , March , 1900 ) .
Stoney 's argument rests , as he admits , on inductive reasoning , based on the observed facts of the absence of atmosphere from the moon , and the scarcity of helium and hydrogen on the earth , and he meets the deductive objections by questioning the adequacy of the mathematical theory to include all the events which may lead to excessive velocities of isolated molecules in the upper atmosphere .
The discussion is too long to enter upon here .
In the limit we must accept as true that a small asteroid could not retain an atmosphere by its gravitational attraction ; and the view , held by some , of an asteroidal origin of our earth would appear to meet considerable difficulty here , more especially with regard to the existence of the terrestrial hydrosphere .
There is no doubt that Stoney 's theory removes difficulties in explaining the absence of a lunar atmosphere .
It has been applied , too , to the condition apparently obtaining on Mars .
However , it must be admitted that other causes may exist to account for the condition obtaining in those bodies .
The discovery by Crookes that a blackened vane suspended in a high vacuum is repelled by radiant heat or by light led to various suggestions as to the cause of the phenomenon .
Stony offered an explanation in harmony with the various experimental conditions which have to be fulfilled in order for the Crookes force to be developed .
The theory of Stony is \#171 ; given , in a somewhat crude state , in the * Phil. Mag. ' for March and April , 1876 .
Stoney 's view may be summarised in the statement that for a certain distance in front of the heated vane , and reaching from it to the glass envelope , when the vessel is not too large , the molecular motions of the rarefied gas are polarised by the thermal conditions , and interpenetrate one another in a degree greater than prevails elsewhere in the gas .
The greater molecular interpenetration in the line xxviii Obituary Notices of Fellows deceased .
between glass and vane involves nothing of the nature of a wind , but determines a greater stress in the direction of polarisation .
Errors in the earlier statements of his views are corrected in his paper in the ' Trans. Roy .
Soc. Dub ; , ' 1878 , and republished in the 'Phil .
Mag. ' of December , 1878 ; and a mathematical expression for the Crookes stress is given , based upon an investigation of Clausius of the stress across a layer of gas conducting heat normal to a heater and cooler .
FitzGerald took a part in the discussion ( c/ .
his 'Collected Papers ' ) by showing that the stress parallel to the heater and cooler Could not be the same as the perpendicular stress\#151 ; -or , in other words , a polarisation stress must exist ( ' Nature , ' vol. 17 , p. 514)\#151 ; and by a mathematical discussion of the subject in the 'Trans .
Roy .
Soc* Dub .
, ' 1878 .
In 1874 , in a paper * On the Physical Units of Nature , ' read before the Belfast meeting of the British Association , Stony pointed out that , on the basis of Faraday 's law of electrolysis , an absolute unit of quantity of electricity exists in that amount of it which attends each chemical bond or valency .
This paper was printed afterwards in the ' Phil. Mag. ' for May , 1882 .
He suggests that this might be made the unit quantity of electricity .
He subsequently suggested the name electron for this small quantity .
Yon Helmholtz , in 1881 , independently , drew attention to the existence of such definite elementary charges , which behave-like atoms of electricity.1 Stony estimated the magnitude of the electron in 1874 , finding it to be equal to the unit ( then the amp\amp ; re ) x 10-20 .
This is the same as 1 C.G.S. : electrostatic unit x 3 x 10-11 .
In this estimate he avails himself of his determination of the number of molecules present in 1 cubic mm. of a gas at standard temperature and pressure , viz. , 1018 .
That the result should suffer from the errors in the then available data detracts nothing from the merit of Stoney 's performance .
It was pioneer work in an obscure and difficult line of research .
The conception of one or more unit charges of electricity within the atom was soon applied by Stony to the phenomena of spectral dispersion .
Maxwell 's ideas on the electromagnetic nature of light were first published in 1862 and 1866 , but the final statement of his theory only appeared with his great work on 'Electricity and Magnetism ' in 1873 .
In Stoney 's first paper , which deals with the " Internal Motions of Gases compared with the Motions of Waves of Light , " which appeared in the ' Philosophical Magazine ' for August , 1868 , no reference to Maxwell 's views is made , nor is there , of course , any suggestion of the electronic origin of light waves .
The aim of the paper is to point out that there must be periodic motions within the " molecule " to occasion the spectral lines , motions distinct from those translatory ones which are affected by the temperature of the gas .
The latter are irregular , the former are in general regular , save at the instant of collision\#151 ; an instant short in comparison with the time occupied in describing the mean free path .
The causes of continuous and band spectra are referred to .
The nature of the internal motions must differ in different gases .
A George Johnstone xxix further step is taken in his paper of January , 1871 ( ' Proc. Roy .
Irish Acad. ' ) .
The internal atomic motion is a complex periodic motion which , however , is resolvable into harmonics .
If we assume the undulation arising in the .ether to consist of periodic plane waves , then , whatever its form , it may be regarded as formed by the superposition of simple pendulum vibrations , one of which has the full periodic time , while the others are harmonics of this vibration , which may be developed by Fourier 's theorem .
While these .component vibrations are superimposed in free ether , on entering a dispersive medium the several vibrations no longer keep together , and a physical resolution is effected in the spectrum .
Hence simply harmonic sequences of .spectral lines would arise from the distinct motions in the molecule of the gas , for there may be several such motions , each producing its own series of harmonics .
Applying these views to the case of the ordinary hydrogen spectrum , Stony finds that the lines h , F , and C are nearly the 32nd , 27th , .and 20th harmonics of a fundamental vibration whose wave-length in vacuo is 0*13127714 of a millimetre , this agreeing closely with Angstrom 's measurements .
A few months later , Stony , in conjunction with Emerson Reynolds , advances yet further , finding a serial relationship , of the kind referred to above , in a large number of lines in the absorption spectrum of chlorochromic anhydride .
But the general result as to the existence of simple harmonic relations was challenged by Schuster and others , on the ground of the theory of probabilities , the instances being held to be too few to establish a .case .
It was some years later that the observations of Huggins upon stellar .spectra led to an extension of the hydrogen spectrum , as this had been observed in solar light ; and in 1885 Balmer showed that a comprehensive law for the whole system of hydrogen lines was expressible in a single formula of quite different type ; and a train of ideas was thus introduced , which has led to much subsequent work directed to the sorting out of related .series in the lines of a spectrum .
Stony , in his principal paper on this subject ( ' Trans. Roy .
Soc. Dub .
, ' vol. 4 , May , 1891 ) , states his electronic theory of the origin of the complex ether vibrations which proceed from a molecule emitting light .
The paper is " On the Cause of Double Lines and of Equidistant Satellites in the Spectra of 'Oases .
" His theory is based on the electromagnetic theory of light , and refers a series of spectral lines to the periodic motion of an electron in the atom or molecule , the elliptic partials into which this motion may be resolved by Fourier 's theorem accounting for the several lines .
If perturbing forces exist an apsidal motion may affect the elliptic partials , and Stony shows that , while the undisturbed orbit will in general be such as to give rise to a definite series of single lines in the spectrum , the consequences of an .apsidal motion affecting some , or all , of its partials is to cause the corresponding lines of the series to become double .
He deduces , on these views , the result that the double D lines of sodium in the solar spectrum might be accounted for by the motion in each molecule of an electron in an elliptic orbit having an axial ratio lying between 11 to 1 and 13 to 1 , round which xxx Obituary Notices of Fellows deceased .
ellipse the electron revolves 169,637 times in a " jot " of time , the ellipsebeing slowly shifted round with an apsidal motion which carries it once-round while the electron performs 1984 revolutions .
Similarly , precessional motion will occasion triple lines .
The " jot " of time is the time light takes to* traverse one-tenth of a millimetre in vacuo .
A very large amount of work has been done by mathematical physicists , within recent years on theories of atomic structures involving the electron in motion ; and , again , the importance of the electron in views on the phenomena , of the vacuum tube , and on radioactivity , is known to all .
Atomistic ideas as to the nature of electricity were , of course , held before Stoney 's views were expressed , but there was a period when the continuous theory had largely displaced the atomistic view .
This seems to have arisen mainly from Maxwell 's teaching .
The more recent and , it must now be admitted , more-helpful atomistic theory , in its modern development , dates back to the finding of the electron in Faraday 's law of electrolysis by Stony and Helmholtz ; and Stoney 's use of the electron in a light-giving atom is one of the earliest developments , showing the availability of the conception of a small discrete particle of electricity .
This , in the present writer 's opinion , is Stoney 's most important -work for science .
It may be that a very different conception of intra-atomic structure will , ultimately prevail , but the moving electron as a constituent part has not as-yet found a good substitute .
The phenomena of radioactivity have strongly confirmed it .
The early work of Thomas Preston on the Zeeman effect also* confirms it .
Such recent views as those of Iiitz , on atomic structure and the explanation of the Zeeman phenomena , assume , indeed , other sources of ' action and reaction within the atom , but the electron still remains as generator of electromagnetic waves .
And even if the electron ultimately yields place to new conceptions it has helped to forward investigation in .
many lines of research , and those who first gave it to theoretical science have taken a worthy part in the advance of man 's knowledge of Nature .
The early date of Stoney 's work and the clearness and the fullness with which he urged his views certainly entitle him to a leading place among ; those pioneers .
Stony gave much time and thought to the subject of the units of physical science and their nomenclature .
He served upon the Committee of the British Association for the selection and nomenclature of dynamical and electrical units in 1873\#151 ; a committee whose recommendations have been very generally accepted .
His paper " On the Physical Units of Nature , " ' which was read before the Belfast meeting of 1874 , has already been referred to .
In it he urges the claims of " the single definite quantity of electricity " observed in electrolysis as a unit of electrical quantity .
The paper is printed in the ' Proceedings ' of the Poyal Dublin Society , 1881 .
Several other papers relating to the subject of units came from his pen , and throughout his ; many papers bearing on other subjects he frequently suggests new departures I in nomenclature .
Indeed , it may be said that his desire for the perfection* j George Johnstone Stony .
XXXI of brevity and reasonableness introduces some difficulties in the study of his papers , seeing that in some cases an unwonted nomenclature has to be first acquired .
His services to the subject of physical mensuration have , however , been great ; and till quite late in his life he laboured to facilitate the introduction of the metric system into this country .
The circumstances of Stoney 's early life led , as has been mentioned , to his .
appointment as observer to Lord Rosse at Parsonstown .
The interest in astronomy then aroused remained with him throughout life .
He wrote both on the instrumental equipment of observatories and on the objects of the heavens .
Thus there are papers " On Collimators for Adjusting Newtonian Telescopes " ( ' B. A. , ' 1869 ) ; " On the Equipment of the Astrophysical Observatory of the Future " ( ' Monthly Notices , ' 1896 ) ; " On the Mounting of the Specula of Reflecting Telescopes " ( 'Proc .
Roy .
Soc. Dub .
, ' 1894). .
His other papers are principally upon the Leonids .
In one of them , a discourse before the Royal Institution ( 1879 ) , the idea of comets capturing meteorites in virtue of the retardation experienced by the latter when passing through the gaseous substance of the comet is put forward ( see also .
* Monthly Notices , ' June , 1867 ) .
Other papers are upon the physics of the-solar atmosphere ; one of them has already been referred to , another was published in the * Philosophical Magazine ' of December , 1868 .
In 1888 Stony entered upon a study of the numerical relations of the atomic weights .
An outline of his results appears in the * Proceedings ' of the Royal Society , April , 1888 .
The full paper has not been published .
The leading idea is that if a succession of spheres be taken whose volumes , are proportional to the atomic weights ( " atomic spheres " ) , and the radii of these spheres are plotted on a diagram as ordinates , and a series of integers as abscissse , a logarithmic curve , y \#151 ; K log ( qx ) , is developed which , in the belief of the investigator , shows that the atomic weights follow laws which can be represented as the intersection of two definite mathematical curves ; , implying that two definite laws of nature have to be coincidently fulfilled for an atom to come into existence .
The curve so represented passes nearly through the positions given by observations .
The discussion as to how ta reconcile the curve with the slight perturbations , and why neighbouring logarithmic curves pursuing courses close to the observed positions are excluded , occupies several sections of the paper .
He also gives a polar diagram in which the radii of the atomic spheres are used as radii vectores .
This diagram suggested to him , in the first instance , the logarithmic spiral .
The diagram is of much interest , and finds publication in the ' Phil. Mag. , ' September , 1902 .
The quadrants of the figure are alternately found to include electro-positive and electro-negative elements .
An unoccupied sesqui-radius appears in the diagram at a place where alone an abrupt transition from the electro-positive to the electro-negative character is observed .
The inert gases discovered some years later now occupy this radius .
In the ' Phil. Mag. ' of September , 1902 , Stony suggests that the unusual chemical behaviour of these new elements is a consequence of their xxxii Obituary Notices of Fellows deceased .
occupying a position between the halogen radius , in which the electronegative condition attains its greatest intensity , and the radius containing lithium , sodium , potassium , rubidium , and caesium , which are the most electro-positive of the elements .
The prediction of missing elements on the indications of the logarithmic law is notified specially by Stony in a letter to the 'Phil .
Mag./ October , 1902 .
He suggests here that the new elements will possess the greatest atomic volumes among the elements in the solid state .
The specific gravity in the solid state of these bodies has not as yet been determined .
There is no doubt that the logarithmic curve given by Stony is suggestive in the highest degree , and is a most interesting contribution to this subject .
Stony had the matter very much at heart , and the non-appearance of his full paper evidently caused him much pain .
Stony believed that a mistaken view was taken of what he really aimed at , this belief being supported by a note of Sir George Gabriel Stokes appearing in ' Stokes ' Scientific Correspondence/ vol. 1 , p. 219 .
In the month of March , 1911 , Stony , then upon his death-bed and already worn with many months of illness , dictated a memorandum on the mathematical principles which influenced him in his work upon the logarithmic law of the elements .
There is no sign of failing power in this memorandum .
Extracts from the original manuscript were in consequence made by Lord Eayleigh , and were communicated by him and published in the ' Proceedings ' of the Eoyal Society ( A , vol. 85 , p. 471 , July , 1911 ) .
In these extracts the spiral curve is again reproduced .
A considerable number of scientific subjects , additional to those already referred to , engaged Stoney 's attention at various times .
They range over a wide field of scientific enquiry and often show much originality .
In the * Phil. Mag. ' for April , 1890 , he suggests that bacteria may derive a part of their life-energy by relations towards the faster moving molecules in the surrounding medium , of a selective nature , so that they escape the second law of thermodynamics much as the Maxwell demon might have done .
A very different topic is " The Magnetic Effect of the Sun or Moon on Instruments at the Earth 's Surface " ( ' Phil. Mag./ October , 1861 ) ; also " On the Energy Expended in Driving a Bicycle , " in conjunction with his son , Mr. G. Gerald Stony , E.E.S. ( ' Trans. Eoy .
Dub .
Soc. , ' 1883 ) ; Address to the Mathematical and Physical Section of the British Association , 1879 : " On Denudation and Deposition " ( 'Phil .
Mag./ April and June , 1899 ) , etc. Johnstone Stony served on several Committees of the British Association .
His name appears in Eeports on Solar Eadiation , Catalogue of Spectral Eays , on papers connected with Spectrum Analysis , 1881 ; and he acted as reporter of a lengthy compilation of the Oscillation-frequencies of Solar Eays , 1878 .
The subject of Ontology engaged his attention for a considerable time : a paper " On the Eelation between Natural Science and Ontology " was George Johnstone Stony .
xxxiii communicated by him to the ' Proceedings ' of the Royal Dublin Society in 1890 .
This paper is in the highest degree characteristic at once of Stoney 's mental attitude towards Nature , his methods of logical analysis , and the tendency he so often shows of a desire to build up a subject in its entirety and from first principles , framing for the purpose new words and new definitions .
As already remarked , the tendency to revising the ordinary use of language so as to give it more direct significance and more convenient form often imposes some labour upon his readers .
The ontology paper is a really profound and exhaustive review of the subject , and indicative of keen introspection , but it is difficult reading on account of the large amount of definition which the writer deems essential .
A second part of the essay was published in 1903 by the American Philosophical Society .
An earlier allied essay is " On how Thought presents itself among the Phenomena of Nature , " being a discourse delivered before the Royal Institution , February , 1885 .
A few papers on what may be called abstract physics may be mentioned here : " Survey of that Part of the Range of Nature 's Operations which Man is Competent to Study " ( * Proc. Roy .
Soc. Dub .
, ' 1899 ) ; " On Texture in Media and on the Non-existence of Density in the Elemental Ether " ( 'Proc .
Roy .
Soc. , ' 1890 ) ; " Curious Consequences of a well-known Dynamical Law " ( ' Proc. Roy .
Soc. Dub .
, ' 1887 ) , etc. Stony was keenly alive to the charm and refining influence of music , and , as already stated , did much for the study of music under the auspices of the Royal Dublin Society .
He wrote a paper " On Musical Shorthand , " and in the same volume ( 1882 ) of the ' Proceedings ' of the Royal Dublin Society is one on methods of dealing with echoes in rooms .
In 1883 he suggests , in the same journal , a mode of prolonging the tones of a pianoforte .
Enough has now been said with reference to his scientific work to show how wide in scope it was .
Stony wrote on other subjects , however : " On the Demand for a Catholic University " ( ' Nineteenth Century , ' February , 1902 ) : and in the interests of his University , he writes upon the subject of its reform in 1874 , and speaks in its defence against the legislation which threatened it in 1907 .
As late as 1910 he printed a thoughtful pamphlet on " The Danger which in our Time threatens British Liberty .
" No man ever lived more completely and devotedly for his ideas than did Johnstone Stony .
He was the type of the philosopher .
Nothing could check his ardour for research ; no labour was too great for him to undertake in the pursuit of his ideas .
In spite of heavy office-work which afforded none of the long-vacation leisure of university life , in spite of the absence of that stimulus which comes from a professional scientific life , Stony published two or three papers each year .
Through his middle life he rose at five o'clock in order to get in some scientific work before starting for his office .
He was never a very strong man , and this necessitated much restraint as to evening society functions .
His Sundays were largely devoted VOL. lxxxvi.\#151 ; a d xxxiv Obituary Notices of Fellows deceased .
to experiments or writing .
His annual holiday was usually lor the ten days of vigorous intellectual life of a British Association meeting .
At all times he greatly grudged the time and labour of writing down and putting through the press work which had been a pure delight to carry out .
Of the moral attributes of Johnstone Stony it is impossible to speak without a feeling of profound respect .
His fearless love of truth was bound up with an ideal rectitude of life .
He stood above all creed that could not appeal to the rationality of man and that denied the continuity of Nature 's laws .
Intellectually superior to most men , he was yet at once too great and too benevolent to criticise the littleness of the many , the shallowness of their minds , and the fallacies of their tenets .
This did not arise in abstraction from the struggle of life and its troubles , for no more sympathetic and kindly man ever breathed .
He championed every earnest effort , more especially endeavouring to forward the interests of the younger scientific men with whom he came in contact , in this respect meting to others that same treatment which he himself received at the hands of his early and life-long friend , the Earl of Boss .
Stoney 's word was a law to him : what he promised he performed .
This is a moral quality which soon gets known , and confers a just influence upon its possessor , not only with those who also possess it , but again with those deficient in it .
When Stony left Dublin , and the occasion was taken by the Boyal Dublin Society to present him with a memento of his work for the Society , and again when he received their Boyle Medal , the recognition of his high moral qualities was in the minds of all , and could not be kept out of analyses which were intended to embrace only his social and scientific work .
George Johnstone Stony received many distinctions during his long and laborious life .
Probably the one he most highly valued was the receipt of the first Boyle Medal from the Boyal Dublin Society .
The medal had just been founded to commemorate the great Irishman who had so large a share iu the initiation of the parent scientific society of this country .
It was felt by the Council of the Boyal Dublin Society that Stony , above every other Irishman then living , merited the distinction of having his name placed first upon the roll .
It was conferred upon him in 1899 .
He was a Foreign Member of the Academy of Science at Washington , and of the Philosophical Society of America founded by Franklin .
He was a corresponding member of Sci. di Lettere ed Arti di Benevento .
He was President of Section A at the meeting of the British Association in 1879 .
He served as Vice-President of the Boyal Society under Lord Lister , and also served upon the Council , 1898\#151 ; 1900 , Stony married his cousin Margaret Stony .
He leaves two sons and three daughters .
His eldest son has risen to distinction as an engineer , having been collaborator in the development of the steam turbine with the Hon. Sir Charles Parsons , K.C.B. , F.B.S. , and is now manager in the Parsons Turbine Works .
One daughter is a Lecturer at the London School of Medicine for Women , and another daughter is a London physician .
George Johnstone George Johnstone Stony .
xxxv Stony died in the eighty-sixth year of his age , on July 5 , 1911 , after a long illness .
His body was cremated , and his ashes buripd in the graveyard of the little suburban town of Dundrum , Co. Dublin .
" In stature , he was tall ; in bearing , dignified ; and his features and expression revealed at once his intellectual power , his nobility of character , and his kindly and sympathetic disposition .
The portrait prefixed to this memoir was taken in the year 1910 , in the eighty-fifth year of his age .
It is in every way faithful and excellent .
J. J. / OBITUARY NOTICES OF FELLOWS DECEASED .
CONTENTS Page Giovanni Virginio Schiaparelli ... ... ... ... ... ... ... xxxvii Jacobus Henrictjs ya n't Hoff ... ... ... ... ... ... ... . .
xxxix John Attfield ... ... ... ... ... ... ... ... ... ... ... ... ... ... xliv Nevil Story-Maskelyne ... ... ... ... ... ... ... ... ... ... xlvii XXXV11 GIOVANNI VIRGINIO SCHIAPARELLI , 1835\#151 ; 1910 .
Giovanni Virginio Schiaparelli was born at Savigliano , in Piedmont , on March 14 , 1835 : he graduated at the University of Turin in 1854 , and studied the practice of astronomy at Berlin Observatory between the years 1856 and 1859 , when Encke was the Director .
After spending a short time at Pulkowa under W. and 0 .
Struve , he returned to Italy in 1860 to take up the position of assistant to Carlini in the Royal Brera Observatory of Milan , where he spent the remaining years of his life , succeeding Carlini as Director in 1862 .
He held this position for thirty-eight years , and wa ?
succeeded on his retirement in 1900 by Prof. Celoria .
Schiaparelli early proved his mettle by discovering the minor planet Hesperia in 1861 , when such a discovery was still something of an event but his first great work was the recognition that meteors were distributed along definite orbits , and that these orbits coincided with those of known comets .
He observed that the meteors which occur in greater or less force annually from August 6 to 12 , radiated principally from points in the constellation Perseus , and that those which did so possessed a distinctive character of their own , showing that they belonged to a single family .
Such a fact is geometrically sufficient to determine the plane and perihelion of their orbit if the eccentricity or period of revolution is assumed , and this determination showed an agreement which could not be accidental with the orbit of the comet I of 1862 .
A more signal instance was supplied in 1866 , the year of the great shower which radiates from 7 Leonis .
This orbit proved to be identical with that of Tempel 's Comet II of the same year .
For this striking discovery the Paris Academy of Sciences awarded the Lalande Prize to Schiaparelli in 1868 , and the Royal Astronomical Society its Gold Medal in 1872 .
The Brera Observatory was provided with an 8-inch equatorial telescope by Merz , \#151 ; the same aperture as that which Dawes had used for his valuable maps of Mars in 1864 .
A comparison of what we owe to that keen-sighted observer with what Schiaparelli afterwards accomplished with equal optical aid is a searching test and proof of the latter 's skill .
When he turned his attention to the surface of Mars , he completely transformed our knowledge of the face of that planet .
Beginning with the opposition of 1877 , he followed it on successive occasions up to 1890 , producing more and more detailed maps and masses of observation .
The later ones were made with a more powerful telescope , by the same maker , of 19 inches aperture .
The whole series of measures and observations are wonderfully voluminous as well as delicate , and they are eminentty reliable .
It may be said that all that Schiaparelli delineated has been in one way or another confirmed .
On Proctor 's map , which was based upon Dawes ' observations , a few long dark bands leading from the " seas " were shown and were named by him VOL. lxxxvi.\#151 ; A. / xxxviii Obituary Notices of Fellows deceased .
" inlets .
" Schiaparelli added a host of finer ones , making an irregular mesh-work over the whole of the " continents .
" In describing them he translated inlet " by " canal , " and so introduced , apparently by accident , a term whose artificial implications have served as the channel of so much speculation as to the state of Mars .
He showed further that the " canals " and other delicate features were not fixed like the features of the moon , but were subject to fluctuations relatively - to one another , and independently of the conditions of vision .
Sometimes they were strongly marked , sometimes invisible , sometimes narrow and dark , sometimes broad , sometimes doubled .
Schiaparelli always guarded himself carefully from countenancing any theoretical conclusion as to the nature of these markings .
In his latest memoir but one he speaks of them as " the lines ( or so-called canals ) , " and refers to an earlier statement where he tentatively attributes the duplication to some unknown atmospheric cause .
Schiaparelli turned his attention to the surface of Mercury in 1882 , and to that of Venus in 1890 , and came to the conclusion\#151 ; as to the former planet , one now generally accepted\#151 ; that each rotated as the moon does about the earth , so that it always turned the same face to the sun .
He was also an excellent and very industrious observer of double stars .
He published in 1903 , after his retirement , a work entitled " L'Astronomia nell ' Antico Testamento , " in which he showed the same industry and acuteness that he brought to observation , coupled with a singular wealth of learning .
It has been translated into English and German .
He was elected a Foreign Member of the Koyal Society in 1896 .
He died on July 4 , 1910 .
E. A. S. XXXIX JACOBUS HENRICUS YAN'T HOFF , 1852\#151 ; 1911 .
Jacobus Henkicus va n't Hoff was born at Rotterdam on August 30 , 1852 , his father being a physician of that city .
After having received his school education in Rotterdam , he entered the Polytechnikum at Delft in 1869 , where he completed the ordinary three years ' course in technology in two years .
In 1871 he entered the University of Leiden , passing the " Kandi-datsexamen " of that university in 1872 .
Attracted by the fame of Kekule , he went to Bonn in the same year to study organic chemistry .
During these " Wanderjahre " he also spent a short time in the laboratory of Wurtz in Paris .
Returning to Utrecht to continue synthetical organic work under Mulder , he obtained on December 22 , 1874 , the degree of " Doktor der Wis-en Natuurkunde , " with a research on cyanacetic and malonic acids .
But already in September , 1874 , va n't Hoff had laid the foundation of his reputation by the publication of a short pamphlet in Dutch , in which he unfolded his views on the extension of structural chemical formulae to three-dimensional space , and on the relation between optical activity and chemical constitution .
The time was ripe for such a development .
Pasteur , in 1861 , in his classical 'Lemons sir la Dissymetrie Moldculaire , ' had shown the connection between optical activity and hemihedral crystalline form , and had perceived that , in the two isomeric optically active forms , the molecules must possess an asymmetric structure similar to that of object and mirror-image .
In fact , Pasteur had suggested that the atoms surrounding the carbon atom might possess a tetrahedral arrangement in space .
But it was the work of Wislicenus on the lactic acids which chiefly influenced va n't Hoff .
The fundamental discovery of the latter lay in the recognition of the part played by the so-called " asymmetric carbon atom , " that is , a carbon atom united by its four valencies to four different groups or atoms .
Ya n't Hoff showed that optical activity , and the existence of two optically active isomers , differing merely in the sign of their rotations , only occurred when such an asymmetric carbon atom was present .
Yery similar ideas were published by J. A. Le Bel , quite independently of va n't Hoff , two months later , namely , in November , 1874 ; but va n't Hoff discussed the " geometrical " isomerism in the case of unsaturated compounds more fully than Le Bel .
In 1875 he published a much enlarged French edition of his original pamphlet , with the title ' La Chimie dans l'Espace , ' whilst a German edition , with a preface by J. Wislicenus , appeared under the title * Die Lagerung der Atom im Raume ' in 1877 .
Ya n't Hoff 's views were violently attacked by Kolbe , then Professor of Chemistry at Leipzig .
But , in spite of much early opposition and neglect , the new point of view gradually triumphed .
The warm support of Wislicenus , and the work of himself and his school , largely contributed to this consummation .
Thus was born the now flourishing science of Stereochemistry .
f 2 xl Obituary Notices of Fellows deceased .
In 1876 va n't Hoff was appointed to the post of Docent in Physics in the State Veterinary School at Utrecht .
During this period he occupied himself with a number of problems in organic chemistry , many of them relating to points connected with his new theory .
As a result of his studies on the nature of the carbon atom and its compounds , there appeared ( 1878 and 1881 ) his highly original ' Ansichten liber die organische Chemie , ' in which he strove after a systematic arrangement of carbon compounds according to their structure , and emphasised the importance of studying chemical reactions from a kinetic point of view .
Although preceded here by such pioneers as Harcourt and Esson , and Guldberg and Waage , he developed in the ' Ansichten ' the fundamental equations of chemical kinetics and equilibrium on the basis of the law of mass-action .
In 1878 va n't Hoff was appointed Professor of Chemistry , Mineralogy , and Geology in the newly created University of Amsterdam .
Together with a number of pupils , he now began to develop with extraordinary insight and experimental skill the field of research already indicated in the ' Ansichten .
' Starting with the object , " connaitre les grandeurs precises et caract^ristiques n4eessaires pour comparer les propri4t\#163 ; s chimiques d'un corps avec sa formule de constitution/ ' he was led step by step to a complete and precise formulation of the velocity and course of chemical reactions and the influence of temperature thereon .
At the same time , he applied the laws of thermodynamics with great success to the problems of chemical equilibrium and affinity .
The first fruits of these labours appeared in book form in his classical ' fitudes de dynamique chimique ' ( 1884 ) .
In the first section , va n't Hoff gives a systematic account of the principles of chemical kinetics , with many new applications to special problems , and a new and important method of determining the number of molecules taking part in the reaction which controls the speed .
The second section deals with the application of thermodynamics- to chemical equilibria .
The notion of " condensed systems " ( in which none of the phases possesses variable composition ) and the corresponding equilibria at definite temperatures ( transition-points ) are here clearly enunciated and experimentally treated .
The distinguishing feature of this part is , perhaps , the clear and simple exposition of the relation between the change of internal energy of a reaction and the variation of the equilibrium-constant with temperature .
This led va n't Hoff to his " Principe de l'lilquilibrie Mobile/ ' which states that a rise ( or fall ) of temperature will displace the equilibrium in such a way as to favour that system whose formation is attended with an absorption ( or evolution ) of heat .
This theorem may be regarded as a special case of a more general principle developed by Le Chatelier in the same year ( 1884 ) .
In his discussion of these matters , va n't Hoff showed in a masterly manner how the approximate validity and real practical value of Berthelot 's principle could be reconciled with the accurate deductions of thermodynamics .
The third and perhaps most original part of the * Etudes deals with the definition and measurement of chemical affinity .
Va n't Hoff proposed to Jacobus Henricusva n't Hoff .
xli i * measure the affinity with which substances combine or react by means of the ( maximum ) work obtainable when the reaction is conducted isothermally and reversibly .
He showed how this work could be calculated not only from measurements of osmotic and gaseous pressures , but also from the electromotive force of reversible galvanic cells , thus , together with Helmholtz , laying the practical foundations of the newest chapter of modern electro-chemistry , namely , the electrometric measurement of the affinity of ehemical reactions .
In 1896 the 'Etudes ' was published in a revised and much extended form by E. Cohen , one of va n't Hoff 's most distinguished pupils , under the title ' Studien sir Chemischen Dynamik .
' Already in 1884 va n't Hoff 's mind was busy with the idea of osmotic pressure .
As he has himself related , his attention was drawn to the osmotic measurements of Pfeffer by his colleague , de Vries , Professor of Botany at Amsterdam .
It occurred to va n't Hoff that by the use of semi-permeable u osmotic " pistons he could apply the methods of Carnot to solutions .
The important question then arose as to how the osmotic pressure was related to the temperature and concentration of the solution .
The data of Pfeffer showed that for dilute solutions of cane sugar the osmotic pressure was very approximately equal to the pressure which the cane sugar would have exerted if it could have occupied as a gas the same volume at the same temperature .
Such was the origin of va n't Hoff 's famous " Theory of Solutions " ( 1886 ) .
But in order to include electrolytes he was obliged to introduce certain coefficients ( i ) , the general equation taking the form PV = HIT .
As is well known , these ^-coefficients have received , in the case of dilute solutions , an interpretation by means of Arrhenius ' theory of electrolytic dissociation .
In this way va n't Hoff was enabled to work out a simple method of applying the laws of thermodynamics to many important problems , such as the relations between the freezing-point and boiling-point of dilute solutions and the corresponding molecular concentrations , the law of chemical equilibrium and its variation with temperature , the variation of solubility with temperature , etc. These investigations not only provided a sure basis for the methods of determining molecular weights in solution , but gave a great impetus to the study of chemical reactions and chemical equilibrium in ( dilute ) solutions .
Va n't Hoff 's work was of the greatest influence in the development of the theory of electrolytic dissociation and modern electrochemistry .
Although preceded here by Gribbs and Helmholtz , he worked out the fundamental relationship between the equilibrium-constant of a chemical reaction and the electromotive force and concentrations of the constituents in a reversible galvanic cell in which the same reaction occurs .
During the period 1887\#151 ; 1895 va n't Hoff published a considerable number .of papers dealing with various points connected with his theory of solutions and its relation to the then rapidly developing theory of electrolytic dissociation .
One of the most interesting and original of these , entitled \#166 ; " Uber feste Losunge i und Molekulargewichtsbestimmung an festen Korpern " xlii Obituary Notices of Fellows deceased .
( 1890 ) , opened up a new field of research .
During the same period va n't Hoff , , together with a number of his pupils , was actively engaged in the investigation of the conditions determining the formation and decomposition of double salts .
These researches were published in collected^form in 1897 with the title 'Yorlesungen fiber Bildung und Spaltung von Doppelsalzen .
' His-treatment of the subject is characterised from the theoretical side by the application of thermodynamics , and from the experimental side by the elegant methods\#151 ; microscopic , thermometric , dilatometric , tensimetric , and electrical \#151 ; which he and his pupils worked out for the determination of the transition-points of the systems investigated .
As may be judged from the foregoing very brief survey , the eighteen years , from 1878 to 1896 , during which va n't Hoff held the Professorship of Chemistry at Amsterdam , were years of fertile and many-sided research .
After having refused several other calls , he accepted , in 1895 , an invitation from the Prussian Academy of Sciences , who had elected him a member , to go to Berlin and establish a research laboratory there .
He went to Berlin in 1896 , becoming at the same time a Professor of the University .
There , in collaboration with his old pupil , Meyerhoffer , and assisted by a small number of research students , he began that great series of investigations on the formation of oceanic salt deposits ( with special reference to the salt beds at Stassfurt ) which occupied him for more than ten years and inaugurated a new era in the study of experimental mineralogy .
These researches were a logical outcome of the theoretical and experimental methods summarised in the ' Bildung und Spaltung von Doppelsalzen .
' Ya n't Hoffs method consisted in determining the fundamental non-variant equilibria ( consisting of vapour , solution , and three solid phases ) which characterise a four-component s}7stem at each particular temperature .
In this way he succeeded in systematically mapping out the whole region of investigation , so that the amount and nature , of the various substances which can crystallise out under given conditions could be deduced .
The results of these investigations were published in collected form with the modest title * Sir Bildung der Ozeanischen Salzablagerungen * ( in two volumes , 1905 and 1909 ) .
The last few years of va n't Hoff 's life were clouded with illness , his lungs having become affected .
But in spite of weakness due to the progress of the disease , and of enforced rests in sanatoria , he continued his scientific work .
In his last laboratory , set amongst the pine trees of the royal demesne of Dahlem , between Berlin and Potsdam , he had planned and already begun an investigation of the action of enzymes , when death overtook him .
He died at Steglitz on March 1 , 1911 .
During his residence in Berlin va n't Hoff found time to publish in book form the lectures which he delivered at the University , with the title 'Yorlesungen fiber Theoretische und Physikalische Chemie .
' The short series of lectures which he delivered in 1901 at the University of Chicago , on the occasion of the decennial celebrations of its foundation , were published Jacobus Henricus Hoff .
xliii with the title 'Acht Vortrage iiber Physikalische Chemie ' ( 1902 ) .
Both these works are characterised by remarkable breadth of outlook , combined with extreme conciseness of statement and close relation of theory to experimental results .
During his lifetime va n't Hoff was the recipient of scientific and academic honours from all parts of the world .
In 1888 he was elected an honorary Foreign Member of the Chemical Society of London .
A similar honour was conferred on him by the Royal Society in 1897 , and by the Physical Society in 1911 .
In 1889 the German Chemical Society , and in 1895 the German Bunsen Society elected him to honorary membership .
He was the recipient of the Davy and Helmholtz medals , and of the Nobel prize for chemistry ( 1901 ) .
The Emperor of Germany conferred on him the Order " Pour le merit , " whilst honorary degrees were received from the universities of Cambridge , Chicago , Greifswald , Heidelberg , Manchester , and Utrecht .
The thirty-first volume ( 1899 ) of the ' Zeitschrift fur physikalische Chemie ' ( of which journal he had been joint editor since its foundation in 1887 ) was dedicated to him by his pupils in honour of the twenty-fifth anniversary of his promotion to the degree of Doctor .
In 1878 va n't Hoff married Miss Jenny Mees , of Rotterdam , who survives him .
By her he had two sons and two daughters , all of whom are living .
In his manner va n't Hoff was simple and homely .
To those who had the privilege of working with him he was endeared by the unaffected friendliness and sincerity of his nature .
As a lecturer he made no pretence of oratorical brilliance .
He was content to give his hearers an unadorned though profound and fundamental account of the development of chemical facts and theories .
As an investigator he will ever be remembered as a great and outstanding genius .
Although preceded by many great pioneers , such as Harcourt and Esson , Guldberg and Waage , Horstmann , Gibbs , Kirchhoff , Kelvin , Helmholtz , etc. , it was va n't Hoff who so developed and systematised chemical dynamics and thermodynamics , that he may well be regarded as one of the chief founders , if not the chief founder , of modern physical chemistry .
Regarding nature with the delicate and finely attuned perception of genius , , he saw in chemical reactions phenomena whose course was subject to exact , law , and whose limits were controlled by the play of affinities that could be measured and compared .
The influence of his work extends far beyond the ordinary bounds of chemistry .
Physiology and biology , dealing with the mysterious mechanism of living matter , in which dilute solutions , semi-permeable membranes and subtle chemical affinities play an important part , have received a powerful stimulus .
A new vista of possibilities has been disclosed to geology and mineralogy .
Everywhere the influence of va n't Hoff 's , work has led to advance in the direction of quantitative relationship , to a profounder perception of causality in the sequence and balance of chemical phenomena .
E. G. D. xliv JOHN ATTFIELD , 1835\#151 ; 1911 .
John Attfield was born in August , 1835 , near Barnet , in Hertfordshire , the son of John Attfield , surveyor , of Whetstone .
The name\#151 ; originally At the-fields , and later Atte Field or Atefeld\#151 ; is purely English , and it is therefore easy to trace the descent of John Attfield from the John Atefeld who flourished in " the Ville of Staundon " ( now Standon , eight miles north-east of Hertford ) as far back as 1361 .
Attfield was educated at the school of the Bev .
Alexander Stuart , then of Barnet , where he developed a taste for scientific pursuits as a direct result of the teaching he received .
Having expressed a desire to be allowed to continue his studies in chemistry and physics , he was apprenticed , at the age of 14 , for five years to Mr. William Frederick Smith , a pharmacist of Walworth .
During the last year of his apprenticeship , 1854 , he attended the School of Pharmacy of the Pharmaceutical Society in Bloomsbury Square , and obtained the first prizes or medals in all subjects\#151 ; namely , chemistry , pharmacy , materia medica , and botany .
He passed the Minor or qualifying examination of the Society in the same year , and offered himself as a candidate for the Major examination , but was refused admission , as he was not of age .
In September , 1854 , he obtained the position of junior assistant to Dr. Stenhouse , F.R.S. , lecturer on chemistry in the medical school at St. Bartholomew 's Hospital , and subsequently became demonstrator of chemistry at the same hospital .
Stenhouse was succeeded by Dr. ( afterwards Sir Edward ) Frankland , and Attfield remained with the latter as demonstrator , assisting him in research work , besides lecturing at the Addiscombe Military College , until 1862 , when he was appointed director of the laboratories of the School of Pharmacy of the Pharmaceutical Society , and afterwards Professor of Practical Chemistry , which subject was given up by Prof. Redwood so that he might devote all his attention to the teaching of theoretical chemistry and pharmacy .
Shortly after his appointment Attfield went to Tubingen , where he obtained the degree of Doctor of Philosophy , presenting as his thesis a paper on " The Spectrum of Carbon , " read before the Royal Society in June , 1862 .
Attfield remained Professor of Practical Chemistry at Bloomsbury Square till his retirement from public life in 1896 .
He was elected a Fellow of the Chemical Society in 1862 , and was a member of Council during the period 1874-8 ; was a Fellow , one of the founders of , and for several years a member of Council of the Institute of Chemistry ; was elected a Fellow of the Royal Society in 1880 ; was an honorary member of the Pharmaceutical Society of Great Britain , and of some twenty other pharmaceutical colleges and societies all over the world .
Attfield was no less active in private than in public life ; he took a keen interest in educational , philanthropic , social , and recreative movements in John At xlv general , and was one of the leading spirits in the Herts Natural History Society and in the Watford Fieldpath Association .
He retired practically from all public work in 1896 ; and , although suffering under rather severe physical disabilities , he was able to enjoy life in a very quiet way , his garden and his books being specially a great solace to him .
He died at Ashlands , Watford , on Saturday , March 18,1911 .
Attfield 's published work deals almost exclusively with scientific pharmacy .
During the time he was at St. Bartholomew 's Hospital he wrote most of the chemical articles in ' Brand 's Dictionary of Art , Science , and Literature , ' and in the Arts and Science Division of the ' English Cyclopaedia , ' and he also found time to revise and extend the chemical portion of the fourth edition of Clegg 's work on ' The Manufacture and Distribution of Coal Gas .
' His first original paper , " On the Solubility of Mercurial Precipitates in Alkaline Salts , " was read in November , 1859 , to the Chemical Discussion Association of the Pharmaceutical Society , and was published in the ' Chemical News ' for 1860 .
From that time till 1897 , he contributed between seventy and eighty papers to pharmaceutical and scientific literature .
In 1867 appeared the first edition of Attfield 's ' Manual of Chemistry : General , Medical , and Pharmaceutical , ' the basis of the work being some manuscript notes which the author had prepared for the students at St. Bartholomew 's Hospital .
The book has now reached its nineteenth edition .
Undoubtedly the greatest work of Attfield was in connection with the ' British Pharmacopoeia .
' It is interesting to note that the name Johannes Attfield appeared in the prefatory pages of the ' Pharmacopoeia ' of 1677 , and of the reprints of 1678 and 1682 , as one of the Fellows of the College of Physicians responsible for the production of the volumes , and he appears to have belonged to one and the same family as the editor of the 1898 ' Pharmacopoeia .
' On the appearance of the 1864 edition of the ' Pharmacopoeia , ' lectures were given at Bloomsbury Square by Profs .
Bentley , Eedwood , and Attfield , which with other criticisms aided in the suppression of the book and the appointment by the General Medical Council of Prof. Bedwood and Mr. Warrington to edit a new edition .
Redwood was also asked to edit the 1885 edition , but declined , and Attfield and Bentley became associated with him , and on the completion of the work Attfield was appointed Reporter in Pharmacy to the Pharmacopoeia Committee and Editor of an Addendum to the ' Pharmacopoeia .
' In carrying out this work Attfield succeeded in bringing about the recognised co-operation of the General Medical Council and the Pharmaceutical Society and the imperialisation of the \#166 ; 'Pharmacopoeia , ' as evidenced by the publication , under his exclusive editorship , of the 1898 edition and the Indian and Colonial Addendum , his success being largely due to the nine Annual Reports ( 1886-94 ) " On the Progress of Pharmacy in Relation to the 1885 British Pharmacopoeia , " prepared by him for the General Medical Council .
The reports , which aptly illustrate Attfield 's method and thoroughness , show how much the medical profession was xlvi Obituary Notices of Fellows deceased .
indebted to pharmacists for their voluntary efforts to make the ' Pharmacopoeia ' a better book .
Attfield received the thanks of the General Medical Council " for all that he had done to make the ' Pharmacopoeia ' complete and accurate .
" One of the principal projects in which Attfield was interested , and of which he was one of the founders , was the British Pharmaceutical Conference , which has for its object the promotion of pharmaceutical research and of good fellowship among its members .
The annual meetings of the Conference , inaugurated at Newcastle in 1863 , have always been very successful , owing largely to Attfield 's influence , in appreciation of which the members presented him with 500 volumes of general literature in 1880 on his retirement from official connection with the Conference as its Honorary Secretary .
In addition , this Association has ever since its foundation published a ' Year-Book of Pharmacy/ containing not only a full report of its meetings , but a digest of the scientific work bearing on Pharmacy published in other countries .
The editorship of this publication was entrusted to Attfield and retained by him for many years .
Attfield 's views on education were always of the broadest type .
He had a high opinion of the value of chemistry as a means of culture , considering that it taught the student\#151 ; to quote his own words\#151 ; " to observe accurately , reflect accurately , and describe accurately on all and any matters in general life .
" He was a strong advocate of a curriculum of study , regarding the acquisition of knowledge merely for examination purposes as pernicious ; hence ho questioned any method of examining candidates which did not take note of the quality of the educational course which had been gone through .
As a teacher he was pre-eminently kind and sympathetic , and the esteem in which he was held by his students may be gauged from the following extract from an address presented to Attfield in July , 1897 , together with a silver tray and silver tea and coffee service , by his old pupils and friends :\#151 ; " During the whole of this long tenure of his important office Prof. Attfield not only won and retained the respect of successive generations of students by the lucidity , accuracy , and thoroughness of his teaching , but he also-endeared himself to them by his unfailing tact , kindness , and urbanity .
Not .
less successfully did he serve pharmacists and medical practitioners , and through them the public , by his versatile ability , untiring energy , and power of organisation as an editor of the ' Pharmacopoeia , ' and author of a manual of chemistry , and generally as a worker who unceasingly applied th\amp ; resources of the great science of chemistry to the demands of the great art of healing .
" A. C. xlvii NEVIL STORY-MASKELYNE , 1823\#151 ; 1911 .
In view of the near approach of the 250th Anniversary of the Royal Society , it is worthy of remark that the death of Mervyn Herbert Nevil Story-Maskelyne removes from the roll of living Fellows the name of one whose father and grandfather were Fellows before him .
With a short break between 1811 and 1823 these three generations held the Fellowship from 1758 to 1911 , that is , for 140 out of 153 consecutive years , or for more than half the whole period during which the Society has existed .
The Maskelyne family can be traced back as landowners in Wiltshire to 1435 .
Though the returns for the borough of Cricklade ( 1625 ) are missing , Brown Willis states that Edmund Maskelyne ( 1564\#151 ; 1629 ) was M.F. for Cricklade in that year , and the same constituency was also represented by his son , Nevill Maskelyne , in 1660 , and again ( both before and after its conversion into the Cricklade Division of Wiltshire ) by the late Mr. Story-Maskelyne from 1880 to 1892 .
The introduction of the name Nevill or Nevil into the family arose from the fact that the wife of Edmund Maskelyne was grand-daughter of Mary Neville , sister of Lord Abergavenny .
It was borne by many of Edmund 's descendants , among whom was the celebrated Astronomer Royal .
It is unnecessary to recapitulate here the claims to distinction of this well-known Copley Medallist .
His only child , Margaret Maskelyne , married in 1819 Mr. Anthony Mervyn Reeve Story , who had taken a Double First at Oxford at the early age of 19 , and was elected a Fellow of the Royal Society in 1823 .
Subsequently , Mr. Story , as owner of the Maskelyne estates in right of his wife , took the name of Story-Maskelyne , by which his descendants were thenceforth known .
His eldest son , the subject of this memoir , was born on September 3 , 1823 ; was educated at Bruton Grammar School , in Somersetshire ; entered Wadham College , Oxford , in 1842 ; and took his Degree with a Second Class in Mathematics in 1845 .
It is probable that his taste for experiment prevented his attaining higher honours , for , as an undergraduate , he had taken to the study of chemistry , which he himself sarcastically described as " an absolutely useless or rather harmful study , as distracting the mind from the degree subjects of the Schools .
" He had been intended by his father for the Bar , and , after leaving Oxford spent his time between Basset Down , the family place in Wiltshire , and the Temple .
The story of how science ultimately captured him is a sufficiently good illustration of the difficulties with which students of science had to contend in the forties and early fifties of the last century to be worth telling in some detail .
About two years before he went to Oxford Story-Maskelyne had become known to Dr. Buckland , who visited Basset Down to collect fossils in the xlviii Obituary Notices of Fellows deceased .
great cutting in the Kimmeridge clay made between Swindon and " Wootton Bassett during the construction of the Great Western Bailway .
By him the young man , shortly after his arrival in Oxford , was introduced to Dr. Daubeny , and thus was welcomed to the meetings of the Ashmolean Society , to which , as he believed , he was the only undergraduate then admitted .
His impressions of these meetings were described by him in an autobiographical note which he wrote in November , 1908 , in response to a letter from Mrs. Gordon , a daughter of Dean Buckland " The discussions , " he said , " were sometimes interesting , often not very interesting , to me at least , but as I felt even then , and have always felt since , these gentlemen held up the lamp of learning in natural science that had been lit more than a century and a half before by Boyle and Wren and other founders of the Boyal Society .
The lamp was flickering , but it has since burnt more brightly under the new conditions of its feeding .
" During his undergraduate days , as has been already stated , he studied chemistry , attending Dr. Daubeny 's lectures in that subject , Buckland 's in mineralogy , and experimenting both in his own rooms and later in a laboratory which he established at Basset Down .
He also formed an early intimacy with Fox-Talbot , a Wiltshire neighbour , whom he frequently visited , and who was attracted by the fact that Maskelyne himself was among the first to practise the art of photography in its then stage of development .
At the meeting of the British Association held in Oxford in 1847 the latter read a short paper on some of his results , and he used to relate that he showed the method of developing a photograph to Faraday , who had never seen the operation performed before .
At a later period Maskelyne was recognised as an authority on the early history of photography .
An anonymous article on " The Present State of Photography , " which appeared in the ' National Beview .
in April , 1859 ( No. 16 , pp. 365\#151 ; 392 , Chapman and Hall ) , was written by him , and he was Secretary to a Committee which reported to the British Association on the same subject in the same year ( ' Bep./ 1859 , pp. 103-\#151 ; 110 ) .
To return , however , to the " forties , " Dr. Buckland was made Dean of Westminster in 1845 , the year that Story-Maskelyne took his degree .
While reading at the Temple the youth was a frequent visitor at the Deanery , where he met many well-known men , among whom was Sir David Brewster .
How favourable the impression he produced must have been is shown by the fact that Brewster , then Principal of the University of St. Andrews , invited him to become a candidate for a Professorship there , but as the recipient of the compliment ambiguously said , " guided by parental wisdom , or in obedience to its authority , I continued my studies in a conveyancer 's chambers .
" But neither wisdom nor authority could for much longer restrain the young chemist from yielding to his natural bent .
At the meeting of the British Association already referred to ( 1847 ) he met Benjamin Brodie , who had just returned to London after completing the Giessen course under Nevil Story-Mask xlix Liebig .
This new friend , who offered the hesitating recruit an opportunity of working at chemistry in his own laboratory , induced him to give up law and to throw in his lot with science , a decision which was doubtless strengthened by his growing friendship with Faraday .
Only three years later , in 1850 , Dean Buckland became unable to carry on his work at Oxford , and , to his great surprise , Story-Maskelyne was asked if he would undertake the lectures on Mineralogy which had been delivered by his old friend .
With becoming modesty he suggested that Brodie should have been invited in preference to himself , but when Brodie refused the invitation he consulted Faraday as to his own course of action .
" I told him , " he afterwards wrote to Mrs. Gordon , " that I had collected minerals at one time and had only superficially studied them , but had no fear as regards the subject of mineralogy alone ; but that crystallography was essential as the most important part of the subject , and with that I had only the slight acquaintance that the ordinary chemist was equipped with .
Faraday 's answer was , 'Accept the offer , and , as you have several months before you , come here ( to the Royal Institution ) on such evenings as you may have [ free ] .
You shall have a room and light , and I will get from the library any books you may need .
' A noble offer , need I say that I accepted it ?
" Flis acceptance of the Oxford post was , however , subject to the condition that a laboratory should be assigned to him where he could teach Mineralogical Analysis and Chemistry in general .
In answer to this request a suite of rooms was allotted to him , situate under the Ashmolean Museum and comprising six living rooms and offices , a laboratory , and a small theatre .
There he lived from 1851 to 1858 .
Previous to the opening of his laboratory , chemical manipulation had not been taught in the University of Oxford , and great interest was excited by the opportunity of learning what sort of thing modern chemistry might be .
The first applicant for admission was Thompson , afterwards Archbishop of York , and he was followed by Henry Stephen Smith ( afterwards the well-known Savilian Professor of Geometry ) , Richard Congreve , Charles Pearson , and many others .
During his residence in Oxford Story-Maskelyne served as Secretary of the Ashmolean Society , and published various papers , among which may be mentioned that " On the Oxidation of Chinese Wax"('Chem .
Soc. Journ. , ' vol. 5 , 1853 , pp. 24\#151 ; 26 ) , and an " Investigation on the Vegetable Tallow from a Chinese Plant ( Stillingia sebifera ) " ( ' Chem. Soc. Journ. , ' vol. 7 , 1856 , pp. 1\#151 ; 13 ; Erdmann 's 'Journ .
Prakt .
Chemie , ' vol. 65 , 1855 , pp. 287\#151 ; 296 ) .
In addition to his scientific work Story-Maskelyne took an active part in the historic struggle for the erection of a museum in Oxford .
" There were two Delegacies , " he wrote , " to which the museum question was entrusted .
I was Secretary to the first Delegacy , Charles Conybeare , of Christ Church , an excellent man and an ardent supporter of the cause , was Secretary to the second Delegacy .
I had collected in London a quantity of Obituary Notices of Fellows deceased .
suggestions for the mode of lighting , size of rooms , etc. , at the desire of the Delegacy , and the general scheme was sketched out sufficiently for a further step in discussing the actual [ erection of the building ] .
This matter went before Convocation , and a big meeting was held in the theatre . . .
[ but ] the proposal was thrown out . . . .
Much unpleasant feeling was produced , and I think some who were in opposition became convinced they had made a mistake .
" This defeat was the precursor of ultimate victory , but it is needless to tell again the tale of how , under the leadership of Sir Henry Acland , that victory was won .
In 1855 ( a date wrongly given as 1865 in the new edition of the 'Encyclo-psedia Britannica , ' p. 625 ) Sir Benjamin Brodie was appointed Professor of Chemistry at Oxford , and Story-Maskelyne , who was successively Deputy Beader , Header , and Professor of Mineralogy , held also for a short time the title of Assistant Professor of Chemistry .
By Brodie 's appointment , however , as Maskelyne hipaself said , his own Chemical Laboratory became " redundant " as a University Institution .
The difficulty was soon solved , for within the next two years he was appointed to the newly-established post of Keeper of the Minerals at the British Museum , in which , perhaps , the chief work of his life was done . .
He continued to hold the Chair of Mineralogy at Oxford , and by inviting the most promising of his pupils to work with him in London he extended the usefulness of both offices , and trained the next generation of British mineralogists .
Among the best known of these are W , J. Lewis , the Professor of Mineralogy at Cambridge ; Lazarus Fletcher , who succeeded him as Keeper of the Minerals , and is now Director of the Natural History Museum at South Kensington ; and Sir Henry Miers , who followed him as Professor at Oxford , and is now Principal of the University of London .
To these may be added Dr. Viktor von Lang , who , after studying for two years in the British Museum , was successively Professor of Physics at Gratz and Vienna , and was associated with Joseph Grailich in a series of Memoirs on " Crystallography , " published in the ' Sitzungsberichte ' of the Academy of Vienna .
On settling in London Mr. Maskelyne married a lady who was herself a member of a scientific family , being grand-daughter of Dillwyn , the well-known botanist , and daughter of Mr. John Llewelyn , of Penllergare , Swansea , who was a Fellow of the Royal Society .
For six years previous to 1857 there had been no one at the British Museum who took any special interest in Mineralogy , and it was only in that year that the special Department of Mineralogy was instituted , and Story-Maskelyne was appointed Keeper .
For five years he had only one assistant , the late Mr. Thomas Davies , who came without any special training , but , fortunately , developed an extraordinary capacity for museum work , acquired an unrivalled eye-knowledge of minerals , and became a most valuable scientific assistant .
Nevil Story-Mask li Maskelyne undertook the whole rearrangement of the collection according to the crystallo-chemical system of Bose .
He busied himself much with the acquisition of specimens , and , under his direction , the collection was -enormously increased and improved .
He was quick to see the importance of making as complete a collection of meteorites as possible , and devoted a great deal of his time and energy to their study .
There was at that time no laboratory or equipment for scientific research .
Gas was not allowed in the building , and it was therefore extremely difficult to conduct any real scientific investigation .
Maskelyne 's work was during these years very largely confined to what could be done with the microscope and goniometer .
He was one of the first to investigate thin sections of rocks and minerals with the aid of polarised light , and was actually using a microscope , with a revolving stage and eyepiece micrometer , for the study of thin sections of meteorites , about the year 1861 .
His goniometer work was carried on with great difiiculty without the assistance of proper artificial light , and he always attributed the deterioration of his eyesight to the strain of this work .
That he , nevertheless , managed to carry out difficult and minute crystal determinations either at the Museum or at home , is shown by the remarkable measurements made on almost microscopic crystals of Connellite , and on those of Asmanite .
By 1867 he had made it clear to the authorities that scientific research \#166 ; could not be carried on without a chemical laboratory , and in that year Dr. Flight was appointed as assistant , and the laboratory was fitted up in a house outside the Museum .
Maskelyne held the office of Keeper of Minerals from 1857 to 1880 , and , during that period , was able not only to maintain and develop the collections , so that they became the largest and best arranged series of minerals and meteorites in existence , but also to issue , with the help of his assistants , an important series of scientific memoirs .
Among these especially noteworthy are the series of ' Mineralogical Notes ' published in 1863-4 , in conjunction with von Lang , and the ' Mineralogical Notices ' published in 1871-4 , in conjunction with Flight .
It is stated in an obituary notice in the ' Mineralogical Magazine ' that , \#166 ; during Maskelyne 's tenure of the Keepership , no less than 43,000 specimens were added to the collection .
These included , among others , the well-known Koksharov Collection acquired in 1865 , in connection with which Maskelyne paid a visit to Eussia , in order to negotiate the purchase , and the Allan-Greg Collection ( 1880 ) , which included a fine series of British minerals well catalogued .
A survey of Maskelyne 's published papers shows that , up to 1855 , he was chiefly interested in chemical problems , that the study of meteorites engaged his attention as soon as he went to the British Museum , and that the period of his greatest scientific activity , as a mineralogist , judged by the published papers on minerals and meteorites , ranged from 1860 to 1880 .
Among the more important of the papers on meteorites may be mentioned lii Obituary Notices of Fellows deceased .
the investigations on the Parnallee , Nellore , Breitenbach , Manegaum , Bnsti , Shalka , and Bowton meteorites ; among mineral researches , those upon Langite , Melaconite , Tenorite , Andrewsite , Connellite , Chalkosiderite , and Ludlamifce .
New minerals described by him were Andrewsite , Langite , Liskeardite , and Waringtonite , and the following constituents of meteoric stones were first isolated and determined by him : Asmanite , described in 1871 as an orthorhombic variety of silica from the Breitenbach meteorite isomorphous with Brookite , but now generally regarded as identical with the mineral Tridymite , described by vom Rath in 1868 ; Oldhamite , a calcium sulphide , described in 1862 , from the Busti meteorite ; and Osbornite , described in 1870 , from the same stone .
He was also the first to recognise the presence of Enstatite in meteorites .
He was always much interested in the history of the diamond , and , in a paper published in 'Nature ' in 1891 , returned to the history of the Koh-i-noor , on which he had first written in 1860 .
There was considerable stir about 1880 , just before he left the Museum , concerning the artificial production of the diamond ; Maskelyne proved that the supposed diamonds which had been manufactured by Mactear were in reality a crystallised silicate .
The mode of occurrence of the diamond in South Africa also occupied his attention , and he described the Enstatite rock , which is associated with it in that part of the world .
Maskelyne 's views on Crystallography were first made public in a series of lectures delivered before the Chemical Society in 1874 , and more fully in his well-known text-book , ' The Morphology of Crystals , ' which was published in 1895 .
In this , as in his University lectures , the attention of students was especially called to the important subject of symmetry .
From his early days this had particularly engaged Maskelyne 's attention , and many of his views are no doubt the result of discussions between him and Yiktor von Lang at the time when the latter was Assistant in the Mineral Department , from 1862-4 .
Yon Lang 's book , which was published in 1866 , treated the subject of crystal symmetry in a novel and original manner , and Maskelyne 's publications were devoted to the development of this subject on somewhat similar lines .
His ' Morphology of Crystals ' was published at so late a date that other methods of treatment , and another nomenclature , had become somewhat firmly established before it appeared .
Had it been published when first written , it would have attracted much attention as a highly original work .
Some of the proof-sheets were in the hands of his pupils for very many years before the book ultimately appeared ; his views had been made known to them throughout the whole period of his professional career , and profoundly influenced their own teaching .
The chief feature of this book is the investigation of the geometrical relations of a crystalloid system of planes , that is to say , planes obeying the law of rational indices , and the most important and original part of the investigation is that which deals with the varieties of symmetry possible in Nevil Story-Maskelyne .
liii such a system .
The subject is developed by a study of the symmetry planes inherent in the system ; the important proof concerning the number of symmetry planes possible in a crystalloid system and their mutual inclinations was , as is stated by Prof. Lewis in his ' Crystallography/ given in a course of lectures by Prof. Maskelyne as far back as 1869 .
The whole treatment of the subject is elegant and lucid , and the new and expressive nomenclature employed invests these chapters with a certain charm , but by the time the book appeared other investigators had begun to approach the subject of crystal symmetry from another point of view .
The independent operation of axes and planes of symmetry , and the application of these operations to homogeneous molecular structures , had been adopted as a less arbitrary and more fundamental treatment .
Maskelyne contemplated a second volume , which was to deal with the physical properties of crystals , and had this been written he would doubtless have elaborated and criticised the newer methods .
Some portions of this book were for several years actually in print , but he never found himself sufficiently free to complete the work .
In his mathematical , as in his scientific , writings Maskelyne 's work was characterised by a remarkable distinction and charm of style , which was , indeed , part of his character , and prevailed in everything that he undertook .
In all his scientific work the mind and sympathies of an artist declared themselves , and were as well known to his pupils as to his personal friends .
It was therefore characteristic that his devotion to his work as Keeper of Minerals did not lead him to narrow the range of his interests to mere specialism , but to extend it to a kindred subject .
A good deal of his scientific work brought him into contact with ancient art , for which he always had a great fondness , and which was fostered by his opportunities in the British Museum .
In his own words " Antique gems and Greek art got hold of me as I went continually through the galleries of the British Museum on my way to my own .
" But though favourable circumstances undoubtedly stimulated him , his taste was shown both before and long after he was connected with the Museum .
As far back as 1869 , for example , he was discussing at the Society of Antiquaries the nature of the Murrhine vases of the ancients , which he believed to be composed of heated sard , in opposition to Westrop , who thought Pliny 's Murrhina to be fluor .
As late as 1894 he was lecturing in Wiltshire upon the subject of Greek art .
In the intervening years he not only formed a very valuable private collection of antique gems , but , at the request of the Duke , produced the well-known catalogue of the engraved gems belonging to the Duke of Marlborough 's collection .
A great change took place in Maskelyne 's life on the death of his father in 1879 .
Henceforth he became an active country gentleman , though he continued to hold his office of Professor of Mineralogy at Oxford .
At that date funds were not available for securing the whole time of a resident VOL. lxxxvi.\#151 ; A. g liv Obituary Notices of Fellows .
professor , and it was in the interests of the University itself that he retained office while waiting for the adequate endowment of his Chair , So soon as .
this was secured , by attaching the professorship to the Waynflete foundation at Magdalen College , he retired .
In 1880 he was elected in the Liberal interest as Member for Cricklade , .
and thereafter sat in three Parliaments , i.e. until 1892 .
Though he could hardly be called a conspicuous , he was unquestionably an active Member of Parliament .
He was one of the Liberals who refused to follow Mr. Gladstone in his Home Rule policy , and without any doubt or hesitation ranged himself from the first among those who threw out the Bill of 1886 .
His constituency , nevertheless , returned him again to Parliament in the General Election which followed .
It is not too much to say that the maintenance of the Union and of the efficiency of the Navy .were two of the leading ; articles of his political creed .
He served on several Committees , such as that concerned with the subsidences in Cheshire due to salt workings , and as a Member of the Committee on Electric Lighting he always opposed what he believed to be the harmful obstacles then thrown in the way of the development of the nascent industry .
He was one of the members who-supported the Commons Preservation Society , and this led to his Chairmanship .
of the Committee that dealt with the Thames Preservation Bill .
His-interest in politics did not flag after his defeat in the election of 1892r and : was enhanced by the career of his son-in-law , the late Mr. Arnold-Forster .
He also took an active part ill county matters , was a Member of the Wiltshire County Council from its foundation till he was over eighty years-of age , and was for many years Chairman of the Agricultural Committee .
He was an active Member of the Bath and West of England Agricultural Society , the presidency of which he declined , on account of his advanced years , when the meeting was held in Swindon .
It was at his suggestion that the first itinerant dairy scliool was established .
In 1904 Mr. Maskelyne underwent a severe operation , and from that time till his death in 1911 he was always more of less of an invalid .
His old ago was , however , brightened by his intense mental activity and by his interest , in the progress of science .
In 1904 , when his life was in great danger , he-exclaimed : " I must live , I want to know more about radium .
" He was a good scholar , and was one of the few scientific men who read Homer till late in life .
The variety of his interests had brought him into contact with many of the most distinguished minds of two generations .
He knew the bearers of all the best known Oxford names .
He helped to entertain Liebig when he visited that University .
He .
was the intimate friend of Charles Mansfield , the chemist , who died too young to have achieved a great popular name , but whose heroic end in a laboratory accident he could not recall without emotion .
With him he worked in the social movement associated with the names of Kingslfey and Maurice , and frequently lectured at / the Working Men 's College .
At the British Nevil Story-Maskelyxie .
lv Museum he was visited by many foreign mineralogists and collectors of minerals and gems .
As a Member of Parliament he was on terms of friendship with Mr. Chamberlain and many other politicians .
His wide knowledge of men and things , his memories of a long distant past , and his keen attention to th*e problems which are interesting the youth of to-day , made him a delightful companion to young and old .
To use his own words , " the twilight of his departing day " was cheered by the consciousness of having lived through a great age and by the pleasure of having " known , in different degrees , so very many of the vigorous men to whom that era is indebted for its splendour .
" Mr. Story-Maskelyne was the recipient of many testimonies to his scientific worth .
He was an Honorary Fellow of Wadham College , and received in 1902 the Honorary Degree of Doctor of Science from the University of Oxford .
He became a Fellow of the Eoyal Society in 1870 , served twice on the Council , and was Vice-President from 1897 to 1899 .
He was Corresponding or Honorary Member of the Imperial Mineralogical Society of St. Petersburg , of the Society of Natural History of Boston , of the Eoyal Academy of Bavaria , and of the Academy of Natural Sciences in Philadelphia .
Mrs. Maskelyne and his three daughters survive him .
One of the latter married the late Eight Hon. H. 0 .
Arnold-Forster , some time Secretary of State for War , and another is the wife of Sir Arthur Eficker .
A. W. E. H. A. M.
|
rspa_1912_0050 | 0950-1207 | The critical constants and orthobaric densities of xenon. | 579 | 590 | 1,912 | 86 | Proceedings of the Royal Society of London. Series A, Containing Papers of a Mathematical and Physical Character | Hubert Sutton Patterson, B. Sc.|Richard Stafford Cripps|Robert Whytlaw-Gray|Sir W. Ramsay, K.C.B., F. R. S. | article | 6.0.4 | http://dx.doi.org/10.1098/rspa.1912.0050 | en | rspa | 1,910 | 1,900 | 1,900 | 1 | 189 | 5,333 | http://corpora.clarin-d.uni-saarland.de/surprisal/6.0.3/?id=rspa_1912_0050 | 10.1098/rspa.1912.0050 | null | null | null | Thermodynamics | 76.317277 | Tables | 14.114573 | Thermodynamics | [
-3.247427463531494,
-43.605194091796875
] | 579 The Critical Constants and Orthobaric Densities of Xenon .
By Hubert Sutton Patterson , B.Sc. , Richard Stafford Crtpps and Robert Whytlaw-Gray .
( Communicated by Sir W. Ramsay , K.C.B. , F.R.S. Received March 4 , \#151 ; Read March 21 , 1912 .
) Rudorf , in a paper on the rare gases and the equation of state , * has drawn attention to the high value found by Ramsay and Travers for the density of liquid xenon at its boiling point , f As is well known the atomic volume in any group of elements in the periodic table either increases regularly with rise of atomic weight or remains approximately constant , so that it is to be expected that the atomic volume of xenon would be greater than that of krypton , since the value for krypton exceeds that of argon .
If Rudorfs calculated value for the density of neon is taken into account , this anomaly becomes more striking , as is shown from the following table taken from his paper :\#151 ; Neon .
Argon .
Krypton .
Xenon .
Density 1 *24 1 *404 2*196 3-58 Atomic volume 16 T 28 *4 37 *8 36 -6 According to Rudorf the density of xenon near its boiling point should be 2*68 , which would lead to an atomic volume of 48*8 , but this question can only be settled by fresh experimental evidence .
For other reasons a study of the densities of liquid xenon and its saturated vapour appeared to us of interest , for the critical volume of this substance has never been determined , and at the commencement of this work the validity of Cailletet and Mathias 's law of rectilinear diameters had never been tested with any of the argon series of gases .
It might be expected that these gases on account of the simple structure and non-valent character of their molecules would approximate closely in behaviour to the requirements of the kinetic theory of gases and would follow the equation of van der Waals .
This equation gives for the ratio of critical density to theoretical density at critical point the value 2*667 , and D. Berthelot has calculated* from Ramsay and Travers ' densities of liquefied argon that the ratio for this * ' Ann. des Phys. , ' 1909 , vol. 29 , p. 751 .
t 4 Phil. Trans.,5 1901 , A , vol. 197 , p. 74 .
J 4 Journ. de Phys. , ' Ill , 1901 , vol. 10 , p. 611 .
VOL. LXXXVI.\#151 ; A. 2 S 580 Messrs. Patterson , Cripps , and Whytlaw-Gray .
[ Mar. 4 , element lies between 2*62 and 2*71 .
Rudorf , however , by the use of the data of Baly and Donnan for the liquid densities* deduced the value 2*95 , which although slightly greater than the theoretical , is much lower than the corresponding value for gases such as C02 , N20 , S02 , which possess a ratio approximating to 3*6 .
Sydney Youngf has shown that for a large number of organic liquids this ratio is nearly constant and differs only slightly from 3*77 , and regards this number as characteristic of normal non-associated substances .
If , however , it should prove that this ratio for the monatomic gases is markedly lower than that for polyatomic gases and vapours , an interesting light would be thrown on the question of molecular association in the liquid state and it would lend support to the view which has often been -expressed that all normal liquids are partially associated .
These considerations made us anxious to revise the critical constants of xenon and to determine its orthobaric densities ; and the kindness of Sir William Ramsay in willingly placing at our disposal the whole of his stock of this very precious gas has enabled us to carry out the measurements with highly purified material and with quantities sufficient to ensure a fair degree of accuracy in the results .
Experimental.\#151 ; The original determinations of the density and critical constants were carried out by Ramsay and Travers with only about 3 c.c. of gas measured at normal temperature and pressure , and this quantity when liquefied yielded a volume of liquid in the neighbourhood of its boiling point of only 6 cu .
mm. In consequence the xenon could not be effectively purified by fractionation and in their paper the authors claim for their measurements no high degree of accuracy .
The specimen of gas investigated by us was originally obtained by Ramsay and Moore* from the residues of about 120 tons of liquid air presented to them by M. Claude , of Paris .
The gas after careful fractionation was employed by MooreS in the determination of the exact atomic weight of xenon .
The xenon , which was of a volume of about 120 c.c. at normal temperature and pressure , was , when it came into our hands , in a high state of purity , but in order to obtain a specimen completely free from possible traces of krypton and air , the whole amount was first solidified in a bulb of small volume and a small amount of uncondensable gas which was present was removed by means of a mercury pump .
The remaining gas was surrounded by a bath of cooled pentane , * * * S * 4 Journ. Chem. Soc. , ' 1902 , vol. 81 , p. 907 .
t 4 Phil. Mag. , ' 1900 .
{ 4 Roy .
Soc. Proc. , ' 1908 , vol. 81 , p. 195 .
S 4 Trans. Chem. Soc.,5 1908 , vol. 93 , p. 2182 .
1912 .
] Critical Constants and Ortliobaric Densities of Xenon .
581 the liquid xenon allowed to boil away , and the last fraction , consisting of about 20 c.c. , was collected for these measurements .
The densities of liquid and vapour were measured in a graduated capillary tube A of approximately 1 mm. internal diameter closed at one end and sealed at the other on to a wider tube B which served as a reservoir for the gas .
The capillary carried a nut C by means of which the tube could be screwed into position on a modified Andrews apparatus .
The capillary was very carefully calibrated by means of mercury before it was sealed up and the end where the readings of the liquid were taken was specially studied .
The form of the tube and the method of filling is best followed from the diagram .
The solid xenon , contained in a small fractionating vessel ( not shown ) , was allowed to flow into the perfectly dry and air-free experimental tube AB and was re-condensed again , thus washing out the calibrated tube and its connections .
This washing was repeated many times before each filling .
In order to fill the tube , the end A was cooled by immersion in liquid air until sufficient xenon had solidified in it , and a very complete exhaustion was then carried out with the Topler pump .
At the end of this operation , the solid xenon in the capillary was allowed to liquefy and some allowed to boil away into the pump , whence it could afterwards be collected .
Finally , A was again cooled , the reservoir B completely filled with mercury to a point E on the capillary , and the mercury thread was frozen by surrounding the tube below E with a paper vessel filled with solid C02 .
The nut and experimental tube were then disconnected at the rubber connection D from the rest of the apparatus and transferred to the compression apparatus .
We found all these precautions were absolutely necessary in order to fill the tube with gas which should afterwards liquefy 2 s 2 582 Messrs. Patterson , Cripps , and Whytlaw-Gray .
[ Mar. 4 , completely at constant pressure .
After the measurements of density had been made , the mercury was again frozen at E , the tube detached from the Andrews apparatus and re-connected with the filling apparatus .
The gas was pumped off and introduced into the point burette K where its volume was measured .
The actual method of reading the volumes of liquid and vapour in the experimental tube was that used by Sydney Young.* At each temperature , readings of the liquid and vapour were taken at four different volumes , and from these data the volumes of vapour yielded by a given volume of liquid were calculated .
The constancy of these ratios was taken as a criterion of the purity of the gas and of the accuracy of the measurements .
From these ratios and the known volume of gas in the experimental tube the densities of liquid and vapour were afterwards calculated .
In determining the orthobaric volumes by this method it is essential that the volume of the experimental tube containing liquid and vapour shall remain constant for a long enough interval to ensure the attainment of equilibrium between the liquid and gaseous phases and between the temperature of the tube and the bath in which it is immersed .
In order to obviate slow changes in volume produced by the change of temperature of the mercury in the Andrews apparatus , we adopted the expedient of keeping the mercury in the capillary tube frozen at E during the readings .
Since four readings were made at each temperature , this procedure necessitated thawing and re-freezing the mercury each time the volume was changed , but this disadvantage was more than compensated by the increased accuracy of the readings .
Measurements were made at temperatures ranging from 16 ' to \#151 ; 66 ' C. Above 0 ' the tube was immersed in water contained in a silvered Dewar vacuum vessel , and the temperature was adjusted from time to time by the addition of small fragments of ice .
The bath was stirred by means of a stream of air which had previously been cooled , and no difficulty was experienced in keeping the temperature constant to within 0*02 ' .
Below 0 ' a bath of alcohol cooled by the addition of small pieces of solid carbon dioxide was used .
The higher temperatures were read by means of a standard mercury thermometer , and for temperatures below \#151 ; 20 ' a pentane thermometer graduated in tenths of a degree , which had been compared with a pentane thermometer standardised at the National Physical Laboratory , and kindly lent us by Prof. Trouton , was employed .
The difficulty of maintaining the temperature of the bath constant when working below \#151 ; 30 ' was overcome by stirring with a stream of air cooled by a mixture of solid carbon dioxide and alcohol .
The uncertainty of these temperature * 'Trans .
Chem. Soc. , ' 1893 , vol. 63 , p. 1199 .
1912 .
] Critical Constants and Orthobanc Densities of Xenon .
583 readings did not exceed 0*1 ' C. The results which are given in the following table refer to two separate fillings of the tube , which yielded , however , for the densities at 0 ' values falling within the limits of experimental error .
The total volume of xenon used measured at normal temperature and pressure 16*79 c.c. and 8*752 c.c. in the two cases .
The densities of liquid and vapour are expressed in grammes per cubic centimetre , and are therefore in terms of the density of water at 4 ' .
In calculating the results , corrections were applied for the errors of the thermometers , the variation of the volume of the tube with temperature , and for the forms of the meniscus of liquid and mercury .
Orthobaric Densities of Xenon .
Temperature .
Yapour density .
Liquid density .
Mean density observed .
Liquid and vapour calculated .
A x 1000 obs .
\#151 ; calc .
o 16 grm. per c.c. 0*844 grm. per c.c. 1 *468 1 *156 1T56 0 15 0*779 1 *528 1 *158 1 *159 -1 14 0*740 1*592 1 *166 1 *162 + 4 12 10 *662 1 *677 1 *169 1T68 +1 10 0*602 1*750 1 *176 1T74 + 2 5 0*501 1 *879 1T90 1 *190 0 0 0*421 1 *987 1 *204 1 *205 -1 -5 0*363 2*074 1*219 1 *220 -1 -10 0*313 2*169 1 *241 1 *236 + 5 -20 *25 0*235 2*297 1*266 1 *267 -1 -30 *3 0T80 2*411 1*296 1 *298 -2 -39 *3 0*139 2*506 1*323 1 *325 -2 -49 *2 0*103 2*605 1 *354 1 *355 -1 -69 -3 0*078 2*694 1 *386 1 *386 0 -66 *8 0*059 2*763 1*411 1*409 + 2 The observed mean densities of liquid and saturated vapour when plotted against the temperature were found to lie very nearly on a straight line .
Taking a mean value of all the data , the equation to this straight line is expressed by the formula D t = 1-205-0-003055* , when D* is the mean density and t is the temperature in degrees centigrade .
Hence , between these limits of temperature , xenon follows Cailletet and Mathias 's law of rectilinear diameters .
Critical Temperature and Pressure.\#151 ; Direct readings of the critical temperature were made on several samples of the gas in the compression apparatus , using the method of Sydney Young .
The value finally obtained , and which has been confirmed by later measurements , was 16*6 ' .
This is distinctly higher than the original value of Eamsay and Travers , viz. , 14*75 ' .
For the critical pressure , readings were taken on the critical isothermal , and 584 Messrs. Patterson , Cripps , and Whytlaw-Gray .
[ Mar. 4 , the pressures observed were plotted on a diagram against the volumes .
The point at which the flexure of the curve changes its sign was taken as corresponding to the critical pressure .
The value found was 44*27 metres or 58*2 atmospheres .
Critical Volume.\#151 ; Knowing the critical temperature , the critical density was calculated by means of the equation already cited , on the assumption that the diameter was strictly rectilinear .
It proved to be 1*155 grm. per cubic centimetre , corresponding to a critical volume of 0*866 c.c. per gramme .
Xenon has therefore a smaller critical volume and a greater critical density than any other substance so far investigated .
Immediately above the critical temperature gaseous xenon is heavier than water .
Vapour Pressures.\#151 ; A few measurements of the vapour pressures of the liquefied gas were made , but the complete vapour pressure curve has not been determined .
Experiments on this point are in progress .
The results obtained are:\#151 ; Temperature .
Yapour pressure .
o metres .
10 38 *702 0 31*360 -10 25 *246 -20 19 *056 From these data the boiling point of xenon has been calculated by the method of Ramsay and Young .
The ratios of the temperatures at which xenon and methyl alcohol have the same vapour pressure were plotted against the corresponding temperatures of methyl alcohol .
The four points were found to lie nearly on a straight line , and by extrapolation the value of the ratio at the boiling-point of methyl alcohol was obtained , and the boiling-point of xenon calculated from it .
The value found for the boiling-point was \#151 ; 106*9 ' C. , which , like the critical point , is higher than the value \#151 ; 109*1 ' found by Kamsay and Travers , but on account of the somewhat large extrapolation and the small number of points , we regard this figure as only approximately correct .
The mean density at the boiling point of liquefied xenon can be calculated approximately if , as seems probable , the diameter is straight between \#151 ; 66*8 ' and \#151 ; 106*9 ' .
The value so obtained is 1*538 .
The density of the saturated vapour , given with sufficient accuracy by assuming the normal coefficient of expansion is 0*013 .
Hence the liquid density at the boiling point = 1*538x2 \#151 ; 0*013 = 3*063 grm. per cubic centimetre , and the atomic volume of xenon = 130*7/ 3*063 = 42*7 .
1912 .
] Critical Constants and Orthobanc Densities of Xenon .
585 Although these values are somewhat different than those calculated by Rudorf for this element , they show that in the argon series there is not only a steady increase in liquid density , but also a progressive rise in atomic volume , with rise in atomic weight , as can be seen in fig. 2 .
A study of the equation of the rectilinear diameter shows that the variation Atomic weight .
Fig. 2 .
in the mean density of liquid and saturated vapour with change of temperature is for xenon remarkably large .
For most substances the angular coefficient lies between \#151 ; 0 0023 and \#151 ; -0-0005.* Recently , Kamerlingh Onnes and Crommelin have drawn attention to the singularly large coefficient possessed by argon , f viz. , \#151 ; 0*003050 .
The correspondence between this number and our own is striking .
The diameters of argon and xenon have not only an almost identical slope , but the slope is greater than that of nearly every substance so far investigated .
The angular coefficient of the helium diameter has been deduced by Onnes from his experiments at very low temperatures on the liquefied gas , and found to be \#151 ; 0*0033 , a number not very far removed from that of xenon or argon .
A large angular coefficient would appear to be a characteristic of the rectilinear diameters of the rare gases .
Mathias has pointed outj that , if van der Waals ' law of corresponding * Mathias , ' Le Point Critique des Corps Purse ,5 pp. 9 and 10 .
t ' Proc. Roy .
Acad. Amsterdam , ' 1911 , vol. 13 , p. 1020 .
X ' Memoires de la Societe Royale des Sciences de Liege , ' 1899 , 3rd ser. , vol. 2 .
586 Messrs. Patterson , Cripps , and Whytlaw-Gray .
[ Mar. 4 , states were strictly true for the orthobaric densities of liquid and vapour , the expression \#151 ; Oa/ A\#151 ; a , where 6 = critical temperature in degrees abs .
, A = critical density , a = angular coefficient of inclination of the diameter a \#151 ; constant , should be the same for all substances .
In reality , a is not a constant , but varies for different substances from 068 in the case of nitrogen to T09 in the case of ethylene .
For argon , Onnes and Crommelin found a = 0-9027 ; our results for xenon give a = 0-766 ; so that , viewed from this standpoint , the inactive gases show no greater regularity than the common gases .
The ratio RT k/ pkVkor so-called critical coefficient for xenon , calculated from our data , is 3-605 , and is hence considerably greater than the value 8/ 3 = 2 667 , which is required by van der Waals ' equation.* This ratio appears to depend on the weight of the molecule , and also on the critical temperature ; for substances of low critical point and small molecular-weight the critical coefficient is small , whilst Young found that , for the majority of organic liquids he investigated , the ratio approximated to 3-77 .
If liquefied xenon does not appreciably differ from the majority of liquids in molecular complexity , one would expect its coefficient to exceed that possessed by other gases of smaller molecular weight , as long as their critical temperatures were not far removed from each other .
This is exactly what we find , as the following data show:\#151 ; 6 .
KTjJptY* .
Ethylene o 284 3 *42 Carbon dioxide 304 *3 3 *59 *Ethane 305 3 -55 Xenon 289 *6 3'60 # Kuenen and Robson , ' Phil. Mag./ 1902 , vol. 3 , p. 622 .
For helium and argon , Kamerlingh Onnes has recently found the values Helium , 3*13 ; Argon , 3*283 ; whilst for oxygen the value 3*346 was obtained .
This constant therefore furnishes no evidence that the elements of the argon series in liquid state are less associated or are simpler in molecular aggregation than any other normal liquids .
Appendix.\#151 ; The value of these experiments depends mainly on the degree of purity of the xenon , and , before concluding , we wish to draw attention to some curious effects noticed during the research , and which led us at first to * Kuenen , 4 Die Zustandsgleichung/ p. 60 .
1912 .
] Critical Constants and Orthobaric Densities of Xenon .
587 suspect that the gas was slightly contaminated .
The first specimen of xenon with which the densities were determined was purified in the manner described already .
The gas , when compressed in the Andrews apparatus below its critical temperature , liquefied completely without measurable rise of pressure , and , on increasing the volume again , a given volume of liquid always yielded the same volume of vapour , provided the temperature remained constant .
The xenon behaved , in fact , like a very pure liquid free from uncondensable gas .
Before filling the tube a second time , the gas was passed over heated copper oxide , and then over hot lead chromate , and finally treated with solid caustic potash , with the object of removing possible traces of organic impurities .
On liquefaction , unsatisfactory results were obtained , and , when the total space confining the two phases was changed , the volume of vapour yielded by a given volume of liquid was found to vary in different points of the tube .
The xenon was next sparked with oxygen , treated with solid caustic potash , and solidified by cooling to the temperature of liquid air .
The oxygen was then removed by pumping , and the gas introduced into the compression tube again .
The results obtained were even less satisfactory than before , although no trace of uncondensable gas could be detected .
Much time was spent in trying to find an explanation of this behaviour ; the experimental tube was re-calibrated , the constant temperature bath was carefully tested , but no source of error could be discovered .
The old experimental tube was then replaced by a new carefully calibrated tube , without any change in the results .
Experiments were next undertaken to see if the density of xenon at pressures in the neighbourhood of atmospheric was altered by treatment with oxygen .
It seemed just possible that a compound between oxygen and the gas might be formed , which at high pressure condensed along with the xenon itself in the experimental tube , and which was the cause of the discrepant results .
A large number of experiments were made , with the object of detecting this possible combination , but no convincing evidence of the existence of an oxide was obtained .
The method employed was as follows : A mixture of oxygen and xenon was treated in various ways , viz. , sparked at ordinary temperatures , submitted to the silent electric discharge , sparked at a low temperature , etc. The xenon was then solidified by means of liquid air , and the oxygen , which under these conditions remains in the gaseous state , was removed by careful and prolonged evacuation with the Topler pump .
The xenon was finally allowed to gasify , and its density determined in a bulb of about 7 c.c. capacity .
588 Messrs. Patterson , Cripps , and Whytlaw-Gray .
[ Mar. 4 , Appended is a short summary of the results we obtained :\#151 ; Experiment .
Weight of 1 c.c. of gas at 0 ' and 760 mm. I Xe and 02 submitted to silent electric grm. 0 *00564 discharge and afterwards cooled to -80 ' II Xe and 02 sparked at ordinary tem- 0 *00573 Mean of three results .
peratures III Large quantity of mixture Xe and 0 *00573 ( 1st fraction ) .
02 sparked and xenon afterwards fractionated 0 *00567 ( 8th fraction ) .
IY 02 liquefied and agitated with solid 0 *00581 xenon .
Oxygen then pumped off as before V Xe and 02 sparked at \#151 ; 80 ' in special bulb .
Xe solidified , oxygen pumped off and density of remaining gas taken at \#151 ; 80 ' 0 00597resuifcs are corrected | from -80c C. to 0 ' C. , y and hence are not strictly Xenon alone subjected to same treatment 0 *00592 !
comparable with fore-j going .
Since in these experiments the total volume of gas weighed hardly exceeded 7 c.c. it seemed important to check the method by determining the density of pure xenon in the same apparatus .
To obtain the pure gas the xenon was mixed with a small quantity of pure hydrogen obtained from palladium , sparked , dried , condensed , and the hydrogen removed by pumping . .
Three density determinations were made , and the values agreed within the limits of experimental error with the value found by Moore :\#151 ; Experiment .
Weight of 1 c.c. at 0 ' and 760 mm. I 0 *00585 II 0 *00585 III 0*00586 Mean 0 *005854 Moore 's value 0*005842 It is hence apparent that the density of xenon is normal after sparking with hydrogen , but in every case after sparking with oxygen , with the exception of Experiment Y , too low a density was obtained .
Tt is to be especially noted that Experiment IY , in which the oxygen was merely liquefied and not sparked with the xenon , yielded a nearly normal result .
The low values might be caused by the incomplete removal of oxygen from the mixture , but in nearly all the experiments a considerable proportion of the xenon was allowed to escape after the oxygen had been pumped away and before the density was taken .
1912 .
] Critical Constants and Orthobaric Densities of Xenon .
589 It is difficult to believe that the solidified gas after this treatment retained as much as 4 to 5 per cent , of free oxygen .
Moreover , Experiment IY demonstrates that the mixed gases can be satisfactorily separated by this treatment if the sparking is omitted .
Further , in Experiment III , where the mixture was fractionated after sparking , the eighth fraction was distinctly less dense than the first fraction .
The presence of small quantities of ozone in the gas would also account for the low densities , but the precaution was taken of always passing the gas over mercury after sparking and before it was solidified .
Moreover , liquid ozone has a deep blue colour , and small traces would be sufficient to tint the solidified xenon .
In all the experiments the solid xenon was perfectly white in colour .
On the other hand , it was repeatedly noticed that when the xenon which had been used for the density measurements was collected through the pump and re-solidified it did not completely re-condense , and small quantities of nearly pure oxygen could be pumped off it .
It was never found possible , however , by repeated condensations and evacuation bo obtain a gas which behaved normally when compressed in the Andrews apparatus .
We frequently re-condensed the gas five times , and finally solidified it in the end of the experimental tube , the Topler pump being kept in constant operation , without obtaining a satisfactory filling .
When , however , xenon which had been sparked with hydrogen underwent the same treatment , the gas on compression gave fairly consistent and normal results , as the following figures for the volume of vapour yielded by unit volume of liquid at 0 ' show:\#151 ; After sparking with oxygen ... ... 4*66 , 4*76 , 4*91 .
Mean , 4*78 " " hydrogen ... - 4*58 , 4*60 , 4*63 .
Mean , 4*60 It will be noticed that after sparking with oxygen , the greatest variation is 2*7 per cent , of mean value , whilst the variation after sparking with hydrogen is only 0*65 per cent. It is also noticeable that the mean value is different in the two cases .
A similar difference was also observed in the critical temperatures of the two specimens of gas .
The oxygenated samples became critical at temperatures varying from 16*9 ' to 17*2 ' , whilst the pure gas had a constant critical temperature of 16*6 ' .
We think it must be admitted that the presence of a small quantity of free oxygen in the xenon would not explain the results .
The supposition that small amounts of ozone were present seems at first sight more likely , but does not bear examination , for , apart from the reasons given already , it is hard to see how ozone could have escaped decomposition on standing for 590 Critical Constants and Orthobaric Densities of Xenon .
days together at high pressure in the presence of mercury in the Andrews apparatus .
On the other hand , if we suppose that an oxide is formed , it is clear that it must be a compound of great instability , and from Experiment Y it appears to be more readily formed at low than at high temperature .
By sparking at ordinary temperatures , a small percentage of oxide might be produced , which might decompose again fairly rapidly on standing , and by cooling its velocity of decomposition might be greatly diminished as well as its velocity of formation .
Since xenon is monatomic , the density of any possible oxide must exceed that of the pure gas , and on this hypothesis the decomposition of the greater part of the oxide during the manipulations involved in a determination would be regarded as the cause of the low densities .
It is not improbable , however , that we have here to do with an association of two elements which is essentially physical rather than chemical , and is more allied to absorption or solution than to chemical combination .
Such a view is supported by the well-known fact that the inactive gases are slowly absorbed by the electrodes in a Pliicker tube when the discharge is passed for a long period , and also by the recent experiments of Claude , * and Ramsay and Collie , who found that on passing a discharge between copper electrodes in an atmosphere of helium and neon , the volatilised metal deposited in the tube contained a large quantity of helium together with a little neon .
Although the experiments just described yielded no definite results they show how oxygen can associate itself with xenon in such a way that the presence of the less condensable gas almost escapes detection .
Also these observations showed how the pure gas could be obtained and furnish additional proof of the homogeneity of the xenon employed for the critical constants and orthobaric densities .
* 'Comptes Reudus , ' 1911 , vol. 153 , p. 713 .
|
rspa_1912_0051 | 0950-1207 | On the observed variations in the temperature coefficients of a precision balance. | 591 | 600 | 1,912 | 86 | Proceedings of the Royal Society of London. Series A, Containing Papers of a Mathematical and Physical Character | J. J. Manley, Hon. M. A. Oxon.|Prof. E. B. Elliott, F. R. S. | article | 6.0.4 | http://dx.doi.org/10.1098/rspa.1912.0051 | en | rspa | 1,910 | 1,900 | 1,900 | 3 | 143 | 4,389 | http://corpora.clarin-d.uni-saarland.de/surprisal/6.0.3/?id=rspa_1912_0051 | 10.1098/rspa.1912.0051 | null | null | null | Measurement | 38.63006 | Tables | 31.537839 | Measurement | [
2.705444574356079,
-25.02057456970215
] | 591 On the Observed Variations in the Temperature Coefficients of a Precision Balance .
By J. J. Manley , Hon. M.A. Oxon .
, Daubeny Curator , Magdalen College , Oxford .
( Communicated by Prof. E. B. Elliott , F.R.S. Received March 8 , \#151 ; Read April 25 , 1912 .
) Introductory.\#151 ; In a former paper* communicated to the Royal Society , the apparent abnormal behaviour of certain precision balances was described and discussed .
One of the most important points therein considered was that dealing with the displacement of the resting-point , R.P. , of a beam , consequent upon a uniform rise or fall in the temperature of the instrument .
The magnitude of the displacement of the resting-point , R.P. , for a change of 1 ' C. was termed the temperature coefficient of a balance .
The variations in the R.Ps .
of the balances tested were observed within a somewhat limited range of temperature only .
Within those limits they were found to be regular and expressible by an equation of the form R t \#151 ; Rs { 1 i \lt ; *t i ftt2 } , in which Rs and R* are the R.Ps .
at some standard temperature and t ' respectively , and \#171 ; and ft experimentally determined constants for a given balance and particular load .
In this present communication the author would direct attention to the hitherto unrecorded changes which may occur in the temperature coefficients of delicate balances , and offer some further remarks upon the subject in general .
, Description of Balance.\#151 ; The balance used during this investigation was obtained new , direct from the makers , Messrs. A. Gallenkamp and Co. , about three years ago .
The beam is cantilever in type and enclosed by an inner protecting case , as recommended in my former paper .
As the result of prolonged testing , I conclude that the balance fully merits the distinction which the makers claim for it , namely , a practically constant sensibility for all loads varying from 0 to 200 grm. , this latter being the maximum load for which the balance was built .
The sensibility of the balance was , with advantage , set somewhat high , and equal to 45 divisions per 1 mgrm .
; its value was kept unchanged throughout .
The equality of the temperature of the beam could at any time be tested by means of a differential bolometer * 'Phil .
Trans.\gt ; A , vol. 210 , p. 387 .
592 Mr. J. J. Manley .
Observed Variations in the [ Mar. 8 , placed within the beam case , and capable of indicating so small a difference as 1/ 10,000 ' C. As the bolometer was fully described in my former paper an account of it here is unnecessary .
Experimental Work.\#151 ; The temperature coefficient was , in the first instance , calculated from data obtained during March , 1909 , the range in the temperature during the observations being from 10 ' to 16 ' C. The accompanying graphs ( fig. 1 ) illustrate the variations which at that time occurred in the E.P. as the temperature , or load , or both were altered .
O- ( i m.fmrt or t Cantilever Beam March 1909 .
o-4 .
x 0-3 * Cf 02 \#171 ; v^y *0 ' ! .
0 nr ir n ' it H9 ip i6'C .
Fig. 1 .
As the variations in the R.P. with changes in the temperature and load were found within the above-named limits of temperature to be both definite and regular , the conclusion was drawn that for a small additional range , the application of the method of extrapolation might be resorted to with a sufficient degree of safety .
This course was therefore adopted for reducing to a standard temperature a series of weighings , some of which had been 1912 .
] Temperature Coefficients of a Precision Balance .
593 carried out when the temperature of the balance room approached 18 ' C. It was then seen that , whilst the weighings at temperatures up to and including those at 16 ' C. were , when reduced , very concordant , those made when the temperature approximated 18 ' C. gave , when corrected and compared with the values obtained at the lower temperatures , inharmonious and variable values .
With the object of elucidating the cause of these discordant values , each pan of the balance was loaded with 130 grm. , this load being practically equal to that of the substances which were being weighed when the discrepancies were detected .
Taking the precautions shown to be necessary and described in my former paper , a number of observations of the R.P. were made at temperatures ranging from 16 ' to 21*6 ' C. , during August 1 , 3 , and 4 , 1910 .
The different values then found for the E.P. are plotted against the corresponding temperatures and shown graphically in fig. 2 .
H - 0-3 .
Cantilever Beam Loac/ =/ 30 grms. 5=45 0 2 . .
4 .
o\#177 ; .
/ - 4 , 1910 .
0 / 6 ' it / 8 ' 19 ' 20* 21 ' 22'C Fig. 2 .
Here it may be seen that the regularity which exists in the temperature coefficient curve up to 16*7 ' C. , or thereabout , suddenly disappears ; between that temperature and 19*0 ' C. the beam is , with reference to its temperature coefficient , in a state of unstable equilibrium .
We have here a well-marked example of what I venture to term a critical temperature range for this particular balance and load .
Referring again to the curve ( fig. 2 ) we observe that for temperatures above 19*0 ' C. the coefficient k again becomes well defined and regular ; but its former positive value has now given place to another and negative value .
594 Mr. J. J. Manley .
Observed Variations the [ Mar. 8 , Therefore , if an object is weighed when the temperature is below 16 ' C. , its weight will appear to increase as the temperature of the balance approaches the limit , 16 ' C. Similarly , there will be an apparent decrease in the mass of the same body when it is weighed after the temperature has passed beyond the upper limit , 19-0 ' C. All weighings taken when the temperature falls within those two limits will yield more or less uncertain values .
Having completed the observations just described , the balance was rested for two months , and then a new series of determinations of the R.P. was commenced .
These were conducted at intervals during October 4 to 8 inclusive , the temperature of the balance varying within the limits 14-7 ' and 206 ' C. The results obtained upon this occasion are represented in graph No. I* ( fig. 3 ) .
The beam was now given the more prolonged rest of 23 weeks , after Cantilever Beam Load=130 grms. S -4 Fig. 3 .
which a third series of observations was undertaken .
These were commenced on March 22 , and concluded on March 24,1911 .
During that time the temperature of the balance varied within the limits 12'9 ' and 19 9 ' C * The portion a ... / 3 was obtained by extrapolating .
1912 .
] Temperature Coefficients of a Precision Balance .
595 Graph No. 2 ( fig. 3 ) was plotted from the data secured during this last series of experiments .
Although the characteristics of the two curves are similar , it will be observed that the slope of No. II is less marked than that of No. I. Comparing these two curves with those given in fig. 1 , we also observe that the change from a positive to a negative value is accompanied by a decided simplification in the nature of the curve ; and that , wdiereas formerly the type of the temperature coefficient k was represented by the equation k = 1 +at\#151 ; fit2 , it has now , within the experimental limits , become expressible as a straight line equation , namely , k = 1 \#151 ; oij .
Since the completion of the third and last series of determinations from which the present value of k was calculated , a very large number of weighings of different objects have been carried out with this balance ; the temperature has been allowed to vary quite freely ; the maximum temperature was as high as 23*4 ' C. in August , and the minimum as low as 10*4 ' C. in October , 1911 .
During the past ten months the temperature coefficient k appears to have remained strictly constant ; the values obtained from numerous weighings of the several bodies at different temperatures having shown , when reduced to a standard temperature of 16 ' C. , a remarkable degree of concordance .
With the balance adjusted to so high a degree of sensibility as that already named , it is believed that any further change in k could scarcely have escaped detection .
Discussion.\#151 ; On a previous occasion* an attempt was made to explain why certain precision balances exhibited a behaviour which was termed anomalous , and the opinion was expressed that the observed and correlated variations in the temperature and E.P. of a beam were primarily due to very small inequalities in the movements of the several groups of screws , together with their associated knife-edge blocks .
The additional evidence secured during this and another research not yet concluded , tends to confirm and strengthen this opinion .
The probability of the correctness of such a view will , it is believed , be apparent from the following theoretical considerations .
If , when the temperature of the beam is varied , the nature and sum of all the resultant movements of the screws forming one group are precisely equal both with regard to the nature and sum of all the movements of the corresponding screws of an opposed similar group , there will result a small but perfectly symmetrical movement .
Such a movement may either lengthen or shorten the two arms of the beam , but will leave the ratio of their lengths unaffected .
Therefore , under these conditions , provided the masses of the disturbed parts are strictly equal , the E.P. of the beam will experience no change and the temperature coefficient k = 0 .
* ' Phil. Trans. , ' A , vol. 210 , p. 398 .
VOL. LXXXVI.\#151 ; A. 596 Mr. J. J. Manley .
Observed Variations in the [ Mar. 8 , If , however , the total movement of two opposed groups of screws is unsymmetrical , the final result will be a more or less distinct differential displacement of the one group with reference to the other , and the greater the change in the temperature , the larger will be the differential displacement .
Now any perceptible movement of this nature will at once affect the ratio of the two arms and thus cause a shifting of the E.P. This shifting , when it proceeds with uniformity as the temperature increases or decreases , may be determined and its value per 1 ' C. calculated .
A definite expression for the temperature coefficient k is thus obtained ; k may be either positive or negative according to the direction in which the E.P. moves as the temperature increases or decreases .
If this mode of accounting for the presence or absence of the temperature coefficient of a balance be rejected then it would appear that there still remain two alternatives .
1 .
It may be suggested that the variations in the E.P. are caused by slight differences in the flexure of the two arms as the temperature varies .
In my former paper it was shown that this view is incorrect , for in no investigated case was there found any measurable difference in the flexure of the two arms when the temperature or load , or both , are varied .
Further , the balance used during this present research maintained an unchanged sensibility for all loads ; this would have been an impossibility had the beam suffered either equal or differential flexures .
2 .
The remaining alternative assumes the possession by the beam of distinctly different coefficients of expansion for the two arms .
It is , however , well known that in the case of first-class precision balances , very great care is exercised both in preparing and selecting only such alloys , the physical characteristics of which suggest a highly homogeneous whole ; and , therefore , any conclusion based upon the assumption of the presence of irregularities in the coefficient of expansion of the beam would appear to be not only unwarranted but also untenable .
If these views be accepted , we meet with no insuperable difficulty in accounting for the observed transformation of a positive temperature coefficient into one which possesses a negative and distinctly different value .
We proceed to consider this point .
The transient nature of the instability observed in the E.P. of the cantilever beam as the balance was made to pass through the critical temperature range , may to some appear not a little remarkable .
But in the authors opinion this behaviour of the beam should cause no surprise .
We are here dealing with a balance which had been in use for a comparatively short period ; and , therefore , the conditions as to load and temperature had 1912 .
] Temperature Coefficients of a Precision Balance .
597 not been sufficiently varied to enable the knife-edges and their kindred parts to take up truly normal positions .
For the purpose of removing some slight abnormal strains it was imperative that the beam should be subjected to the combined influences of a certain minimum load and a range of temperature approximately equal to 3 ' C. above 16*7 ' C. As soon as those conditions were fulfilled , it appears that some one or more of the parts secured to the beam proper moved into other and slightly different positions ; these new positions they still retain .
Such slight readjustments in the relative positions of the several screw groups might readily be accompanied by a transference of a major strain from one group to another , and thus , in a perfectly natural manner , bring about the changes observed both in the sign and value of k as cited in the experimental section of this paper and shown graphically in fig. 2 .
Some may dissent from the views and conclusions expressed above , but few , if any , will deny the importance of the experimental results which have been obtained during this present research .
We therefore pass from points of theoretical interest to a consideration of the manner in which , according to our view , the beam must be " aged/ ' On the " Ageing " of a Beam.\#151 ; The marked changes noted in both the character and value of the temperature coefficient of the cantilever beam almost inevitably lead us to conclude that , before a new , or even comparatively new , precision balance can be safely used for securing trustworthy values of the highest order of accuracy , the instrument must be suitably " aged .
" In making this suggestion nothing novel or unusual is proposed .
Every physicist is familiar with the fact that many precision instruments* ( such as standard resistance coils and thermometers ) are incapable of yielding really reliable values before they have been subjected to an " ageing , r process of some kind . .
It is fortunate that in the case of a balance beam , the ageing can be so* conveniently effected .
If the single instance already described can be accepted as a safe criterion , it will appear that the ageing of the beam maybe brought about as follows:\#151 ; The balance should be first placed in a room having a somewhat lower temperature than that likely to be encountered during the subsequent research ; the pans must then be suitably loaded and the beam released .
( Possibly the load should be the maximum for which the instrument is* built ; but experiment alone can enable us to determine this .
) After a time the temperature of the room should be gradually increased until it has passed beyond that which is known to be the upper temperature limit .
If the R.P. be determined at intervals during the slowly increasing 598 Mr. J. J. Manley .
Observed Variations in the [ Mar. 8 , temperature , we at the same time obtain the necessary data for calculating temperature coefficient k of the beam .
By repeating both the process and the observations , we may acquire all the evidence we need for a critical examination of the behaviour of the beam during the whole treatment , and thus be able to determine whether a further ageing of the beam is desirable .
It is quite possible , indeed , we think it is highly probable , that some balances may have to be " aged " for the particular loads they are to carry during the subsequent research .
It is conceivable that under the influence of a given stress , one group of screw 's may manifest , relatively , a large degree of freedom ; the application of a totally different stress may cause the larger degree of freedom to be transposed to another group .
But it is to be hoped that further experiments will show that such tactics on the part of a balance are the exception rather than the rule .
By referring to the numerous papers dealing with atomic weight and other determinations involving very accurate weighting , we find that investigators have frequently made a special point of securing a new balance for their research .
Viewed in the light of the facts we have given , it would appear that this plan might in some cases be productive of uncertain and misleading data .
We believe that the most reliable instrument for highly refined weighings is a well-cared-for balance that has been regularly and freely used for at least twTo or three years .
Under those conditions there will be a tendency for the balance to become aged in a perfectly natural manner .
The author does not commit himself to the extent of asserting that the artificial ageing process advocated by him is thus rendered wholly unnecessary ; on the contrary , he is of opinion that whenever very refined weighings are to be undertaken , the safe plan is to resort to the device for ageing the beam , prior to the inauguration of the research .
In this way alone can it be determined whether or not the balance merits that large degree of confidence which wre at times are apt to repose in it .
Effects Produced by Sudden Changes in the Temperature of a Balance Shelf\#151 ; During the concluding stage of another research , a new and hitherto unobserved disturbing factor recently asserted itself ; this factor assumed the form of a diurnal variation in the R.P. On certain days the values of the reduced R.Ps .
increased very slightly but steadily as the day advanced ; generally , the value attained a maximum by 2 p.m. and then remained , within the limits of experimental error , invariable throughout the afternoon and evening .
The cause of this shifting in the R.P. was not at once apparent ; but ultimately it was suspected to be due to a minute tilting of the shelf upon which the balance rested , the disturbing element of the tilt being in a direction parallel 1912 .
] Temperature Coefficients of a Precision Balance .
599 to the length of the beam .
Any tilt imparted to the shelf will obviously be correspondingly shared by the central pillar which supports the beam ; and as the summit of the pillar will , for a given tilt , describe a larger arc than the base , it follows that ( other conditions remaining constant ) , the pointer will suffer a lateral displacement with regard to the scale placed behind it ; but the actual angular position of the free beam , when referred to a vertical line , will remain unaffected .
That this hypothesis was correct was proved in the following way .
A stout-walled glass tube , having a diameter of 25 mm. , was chosen ; by grinding , one end was adjusted until its plane was very approximately at right angles to the tube 's axis ; the other end was softened and drawn out , so as to form a short , rigid , capillary tube .
A pendulum , consisting of a small brass sphere suspended by a very fine platinum wire , was then introduced , the free end of the wire being passed up through the capillary at the top , and there secured by means of a plug and cement .
Immediately behind the wire , and just above the bob , was fixed a strip of Bristol board , with a thin but well-defined vertical index line drawn upon it .
The distance from the point of suspension to one end of the index line was practically equal to the distance from the central knife-edge of the balance to the lowest extremity of the pointer .
The tube , with its enclosed pendulum , was then set up upon the plate glass slab , upon which the balance stood , and there fastened with a little cement .
For the purpose of measuring the distance between the pendulum wire and the index line , use was made of a reading-telescope , placed at a distance of 2 metres , and fitted with a micrometer eye-piece , capable of indicating 0*01 mm. This apparatus afforded all that was required for detecting and measuring those minute lateral displacements of the balance pointer that might be produced when the shelf was tilted .
As the balance pointer and the tilt-detecting pendulum were of equal length , by measuring the side displacement of the latter we discover the corresponding movement of the former .
In these experiments no attempt was made to measure any lateral displacements that were less than 0*01 mm. ; this was sufficiently small for our purpose , and was therefore accepted as a minor limit .
It may be mentioned that a lateral displacement of the pointer amounting to 0*01 mm. was approximately equivalent to 0*002 mgrm .
Experimenting with the above described apparatus , conclusive proof was soon obtained that the daily growth observed in the R.P. was due to slight vertical movements at one or both ends of the balance shelf .
These vertical movements never equalled 0*2 mm. ; generally , they varied within the limits 0*05 \#151 ; 0*15 mm. Other experiments revealed the cause .
It was found that 600 On the Temperature Coefficients of a Precision Balance .
the disturbances occurred only when the room temperature was varied somewhat suddenly .
When care was taken to slowly vary the temperature , there was no measurable displacement of the pendulum , and reduced R.Ps .
were quite normal .
From the evidence here given in brief , it will probably be gathered that , in the author 's opinion , the balance shelf possessed a temperature lag sufficient under the given conditions to develop a deformation which was manifested in the manner already described .
We were now in a position to control the disturbing element , and the necessary measures for its complete suppression were accordingly taken .
By weighing only after the room temperature had remained nearly constant for some considerable time , all difficulties arising from the cause discussed above have been successfully avoided .
In connection with highly refined weighings , constant use is now made of the tilt indicator .
The instrument is permanently placed upon and near one end of the balance shelf , and from the indications which it offers we at once know whether a weighing may be advantageously proceeded with or not .
Appendix .
Since the publication of my former paper , Mr. L. Southerns , of the Cavendish Laboratory , Cambridge , has drawn my attention to some experiments land observations of his own .
In a paper on the " Dependence of Gravity on Temperature , " * he shows that soon after heating the contents of the calorimeter , which was suspended from one arm of his balance , an apparent increase in weight was noted ; this apparent increase is attributed to a decrease in the buoyancy of the air immediately surrounding the calorimeter .
This view , although correct as far as it goes , is nevertheless incomplete .
The ascending warm air would certainly lengthen the balance arm from which the calorimeter was suspended , and therefore the apparent increase in weight was due to the joint effects produced by the decrease in the density of the enveloping air and the change in the ratio of the arms of the beam .
Such effects are , as I have already shown , quite distinct from those which properly appertain to and are restricted to the temperature coefficient of a balance .
The changes observed by Mr. Southerns could be demonstrated with any precision balance , but with some balances it would be difficult , if not impossible , to render the possession of a temperature coefficient evident .
* 'Roy .
Soc. Proe .
, ' A , vol. 78 , p. 393 .
|
rspa_1912_0052 | 0950-1207 | The general theory of colloidal solutions. | 601 | 610 | 1,912 | 86 | Proceedings of the Royal Society of London. Series A, Containing Papers of a Mathematical and Physical Character | W. B. Hardy, F. R. S. | article | 6.0.4 | http://dx.doi.org/10.1098/rspa.1912.0052 | en | rspa | 1,910 | 1,900 | 1,900 | 11 | 148 | 4,516 | http://corpora.clarin-d.uni-saarland.de/surprisal/6.0.3/?id=rspa_1912_0052 | 10.1098/rspa.1912.0052 | null | null | null | Fluid Dynamics | 55.021873 | Biochemistry | 16.675718 | Fluid Dynamics | [
-34.59110641479492,
-34.57390594482422
] | ]\gt ; The General Theory of Colloidal Solutions .
By W. B. HARDY , F.R.S. ( Received March 13 , \mdash ; Read IsIay 16 , 1912 .
) A large } ) of observations upon the filterability and the optical properties of colloidal solutions prove that they are coarse grained and consist of particles dispersed throughout a continuous fluid phase .
For this reason these solutions are commonly described as multiphase systems in which the dispersed particles form one of the phases .
This description is wrong unless it be qualified by the further statement that the particles do not constitute a phase in esse , but only a phase in po lise .
Consider a heterogeneous fluid such as is described above in contact with its own vapour , and let the components be two , e.g. elatine and water .
If the fluid really consisted of two phases there would , with the vapour , be three phases .
Let us distinguish the vapour phase by and the exterior and interior fluid ( or solid ) masses by and ' respectiyely .
Then , since the surface enclosing the interior fluid ( or solid ) masses is curved , we have The variables , therefore , are the two components , temperature , and two pressures , or five in all .
Since by hypothesis there are three phases , the system has two degrees of freedom .
Therefore , in order completely to define the system , it will be necessary to fix the temperature and one of the pressures , or the composition of the phases .
But on this hypothesis the two fluid phases are separated by a curved surface , and this introduces a difficulty ; for if the surface be freely permeable by the components the potentials and pressures in the two phases must be the same , and , as neither component is confined to the interior phase or to the interface , that phase is unstable .
* The phase rule is applicable only to contiguous masses which are thoroughly stable , whereas the stability of the interior masses in colloidal solutions is open to question .
From the fact that the state of the solution at any instant is determined not only by temperature , pressure , and composition , but also by previous history , we may conclude that neither the exterior nor the interior fluid masses conform to Gibbs ' criterion of stability , namely , that the value of the expression when , are respectively intrinsic energy , entropy , volume , and mass , and , and constants , * Gibbs , ' Trans. Conn. Acad vol. 3 , p. 406 .
In order to obtain comparable results for osmotic pressure or viscosity , it is necessar ) to start the system from a fixed point and allow it to proceed along a particular path .
Mr. W. R Hardy .
[ Mar. 13 , shall be zero for the particular phase and either zero or positive for any other phase of the same composition .
" " If equilibrium subsists ( in such systems ) without passive resistance to change it must be in virtue of properties which are peculiar to small masses surrounded by masses of different nature and which are not indicated by the fundamental equation.\ldquo ; * There is no intention at this stage of attempting to elaborate a complete theory , and enough has been said in support of the contention that it is almost .
as erroneous to speak of colloidal fluids as multiphase systems without qualification as it would be to ignore their heterogeneity altogether .
The nature of the problem and the particular questions which need investigation may be brought out by considering a simplified diagrammatic scheme of a system consisting of a heterogeneous fluid in contact with its own vapour .
Let it be supposed that a solution of A in is homogeneous and forms a simple phase when the concentration of A is sufficiently small , but becomes eous by the separation of small globules rich in A and poor in when the concentration rises above a point defined by temperature and pressure .
It would obviously be possible to produce the required concentration by compressing the mass in a cylinder with a piston permeable only to the solvent B. Let this be carried out and let the system now consist of vapour of , pure , and a heterogeneous fluid consisting of a weak solution of A in , with globules of solution rich in A dispersed through it , and let us agree to distinguish the vapour phase by , the pure solvent by the globules by ' and the external solution by ' ' .
The piston which separates solvent from the complex solution is maintained in position by a force which is obviously equal to the osmotic pressure of the solution .
Call this pressure Let the volume of the space under the piston be , and let there be only one globule present .
For a small compression which expels of solvent and causes the globule to increase by we have , ( 1 ) and , if be the mass and the potential of the solvent , and and the mass and potential of the solute , and the tension and the area of the surface of the globule , we have for the thermodynamic potential \mdash ; p'dv ' ( 2 ) * Gibbs , , p. 169 .
For the limitation of this supposition in connection with infinitesimal changes of state see Gibbs , pp. 1912 .
] The General Theory of Solutions .
an equation which is true only if the specific volumes of the components be reckoned the same throughout the fluid parts of the system .
But if the piston is completely permeable to the solvent , and the surface of the globule is completely permeabie to both solvent and solute , have ; ( 3 ) nd since and , ( 4 ) all the terms including these quantities disappear .
Also , if be the pressure on the piston\mdash ; that is the osmotic pressure\mdash ; and be the excess pressure in the interior of the lobule due to the tension of the surface , then and Equation ( 2 ) now reduces to ( ta ) .
Dividing through by , and remembering that , we get ( ta : ) , and from ( 5 ) , - In colloidal solutions there is usually a difference of electric potential between the and the exterior fluid due to polarisation of the interface .
The electric density must be a function of the chemical nature and density of the matter on each side of the interface , since the polarisation is due to chemical and osmotic forces acting across it .
Therefore , if the globule be so large as to contain in its interior a phase fully formed ( that is if the radius be greater than the effective range of any of the molecules there present ) electric density will be sensibly independent of the size of the globule , being , like the pressures and potentials of the interfacial film , fixed by the phases on each side supposed constant .
But when the radius is less than the range of molecular action the composition and physical properties of the globule will vary , and therefore the density of the charge on the surface will also vary .
An expression for the energy of an interfacial layer expressed in terms of * The latter part of this assumption probably is not of actual colloidal systems , for if any degree of mechanical stability be iml , arted to the interface by , e.g. , an eIectric charge , the great difference in diffusibility between solute and solvent ( leading to great differences in the rate of transference across the interface ) will operate in finite time as though the surface were only partially permeable to the solute .
Mr. W. B. Hardy .
[ Mar. 18 , tensions may be got by the method of Dupre* : " " If denote the interfacial tension , the energy corresponding to unit of area of the interface also as we see by considering the introduction ( through a fine tube ) of one body into the interior of the other .
A comparison with another method of generating the interface similar to that previously employed when but one body was in question will now allow us to evaluate " " The work required to cleave asunder the parts of the first fluid which lie on the two sides of an ideal plane passing through the interior is , per unit of area , , and the free sur.ace produced is two units in area .
So for the second fluid the corresponding work is .
This having been effected , let us now suppose that each of the units of area of free surface of fluid ( 1 ) is allowed to approach normally a unit area of ( 2 ) until contact is established .
In this process work is gained which we may denote by for each pair .
On the whole , then , the work expended in producing two units of interface is , and this , as we have seen , may be equated to 2 Hence ( 7 ) Experiments with plane surfaces ( see next paper ) suggest that the term consists mainly of the electric energy per unit area of interface due to electric polarisation .
But as this is not established it will be well to proceed in a more general way .
Let represent the tension which the interface would have if no polarisation occurred , then putting as the electric density on the surface of the globule , we have for the actual tension , ( 8 ) a relation which implies that the total energy per unit area of interface fixed by the mass of the components and the temperature .
From ( 6 ) and ( 8 ) we get .
( 9 ) As an approximation , the electric displacement at the interface may be represented by two concentric shells , each infinitely thin , and with electric density and .
The radius of the inner shell being the radius of the globule , and the distance between the shells , the energy due to polarisation is then given by .
* Lord Rayleigh , ' Phil. Mag 1890 , 5 ) , vol. 30 , p. 461 .
Equation ( is rigorously true , for , if account be of any gained or expended in the formation or condensation of vapour , the balance of such work is zero , if Dalton 's law be assumed .
1912 .
] The Theory of Colloidal Solutions .
Putting OIlstant , we have .
( 10 ) If the solute A were an electrolyte , account would have to be taken of the electric work or lost in phases ' and ' 'during the compression .
* Equations ( 9 ) and ( 10 ) show the osmotic pressure of schematir colloidal solution such as we are considering depends upon the functions and When exceeds the range of molecular action , the globule contains in its interior a phase ( the interior phase ) fully formed , but under a pressure greater than the pressure of the external phase by the quantity .
Let us make the probable assumption that , when the lobule has grown to this size , so as to constitute a phase in mass , the pressure has fallen so low as to cease to affect sensibly the composition or properties of the internal phase .
Since the pressure and potentials of the layer of transition between phases ' and ''are fixed when those phases are fixed , and become equal to zero , and the equation becomes .
( 9 ) The point where is equal to the extreme range of nlutual action of any of the molecules present is therefore one of great importance .
Three things therefore need discussion : they are the forms of the functions and and the range of molecular action .
The Surface Tension of the Globul \mdash ; Lord Rayleigh has shown that , according to the Young-Laplace theory of capillarity , the tension of a very thin film of matter should increase as the film thickens , according to the square of the thickness .
Experiment with actual films has failed to confirm this generalisation .
The experiments of Reinold and and of JohannotS prove that , for soap lilms in air , the curve connecting tension and thickness shows a series of maxima and minima ( fig. 1 ) .
The tension in the case under consideration is that of a drop of liquid forming in the interior of a mass of liquid .
It is therefore that of a fluidfluid interface .
If , however , the function has maxima and minima , * In order to simphfy the problem , any kinetic energy which the globule may possess , owing to progressive motion , has been neglected .
This quantity has been experimentally investigated by Perrin for certain suspensions .
'Phil .
Mag 1892 , [ 5 ] , vol. 33 , p. 468 .
'Phil .
Trans 1886 , vol. 17 p. 679 .
S 'Phil .
Mag 1899 , [ 5 ] , vol. 47 , p. 501 .
Mr. W. B. Hardy .
[ Mar. 13 , certain important conclusions follow .
For let phase ' ' be supersaturated with respect to phase ' : by raising the osmotic pressure to , the result would be the formation of a globule of tension and radius .
But if the system contains globules of radius , and the osmotic pressure be reduced by admitting solvent , globules of tension T2 and radius will be iormed .
FIG. 1 .
At pressure , globules of radius can -exist , but those of radius and will probably be unstable .
According to the accepted theory , the of a film is constant so long as the thickness is greater than twice the range of molecular action .
That portion of the curve in the figure which lies between and relates to a system whose globules are so small that the radius is less than the range of molecular attraction .
It follows , therefore , that so long as the globule substance has not the properties of a phase in mass , i.e. so long as , a state in which the interior mass is present as globules is stable , and the globules l1lay be of different radii , also the osmotic pressure of the solution will not be fixed by fixing the ratio of the masses of the components and the temperature .
These are the characteristics of a oolloidal solution , and it is obvious that a determination of the form of the function is of fundamental importance in the theory of such solutions .
The evidence that in certain films tension varies discontinuously with thickness is complete .
Reinold and cker determined the thickness of the black area in a soap film to be about 12 , and found that at the edge of the area the film thickened abruptly to or more .
Since the tension of a horizontal film must be everywhere the same , the tension of the film thick is also that of the thicker film .
The abruptness of the transition between thin and thick regions can only mean that films 1912 .
] The General Theory of Colloidal Solutions .
of intermediate thickness are unstable , that between certain thicknesses tension increases as thickness diminishes .
Johannot 's experiments make it probable that when the tension of the film is considered as a function of the thickness there is more than one maximum .
It is comnlonly held by physicists that these results obtained by the study of films of fluid immersed in air can be applied to variations of the tension of a globule of fluid immersed in its own vapour .
The likelihood of this being true depends upon the view that is taken of the significance of these maxima and minima .
If they are due to something fundamental and fixed in the nature of the field of force about an atom or a molecule , they will appear in all expressions for the of a mass or layer of matter whose dimensions are less than the range of the force .
showed that if the mutual attraction between the molecules of a fluid changes to a repulsion when the distance separating the molecules is less than a certain quantity , the tension of a film would begin to increase with decreasing thickness when the thickness was equal to this quantity , and Reinold and RuckerS suggest that the increase of tension which they found in the films 50 thick is due to this cause .
J. J. Thomson finds in the corpuscle theory of atomic structures justification for the view that the extra atomic field of force has zones of attraction and repulsion .
It is obvious on this theory that the field must be complex , for consider the simplest model of an atom\mdash ; a central core of stationary electrons surrounded by a plane ring of rotating electrons .
There will be a field due to the stationary electrons in which the electric intensity will vary inversely with the square of the distance from the centre of the atom .
And there will also be an electromagnetic field due to the rotating ring in which the 'intensity varies that radius which is at right angles to the plane of the rin inversely with the cube of the radius .
On purely theoretical grounds , therefore , Boscovich 's conception of a field of force about an atom whose sign changes as the distance from the centre of the field increases has some justification , and , as is well known , Kelvinl applied this conception to capillary phenomena .
The assumption * Reinold and Rucker , too .
Thomson , ' Conduction of Electricity through Gases , ' 2nd EditioI ] , p. 183 ; Thomson and Pointing , ' Properties of Matter , ' p. 168 .
' Encyc .
Brit art .
" " Capillarity S , p. 681 .
The Corpuscular Theory of Matter , ' London , 1907 , p. 158 .
'Mathematical and Physical Papers , ' vol. 3 , pp. 398 and 409 Mr. W. B. Hardy .
[ Mar. 13 , that maxima and minima occur in the variation of the tension with the radius of a drop of fluid adso offers a singularly simple and direct explanation of the influence of electrically charged nuclei upon the condensation of supersaturated vapour , , as we have seen , it would furnish an equally direct interpretation of the peculiarities of many colloidal systems .
Unfortunately much may be urged against the view that these maxima and minima in the tension of a soap film have any direct relation to the field about an atom or molecule .
It must be borne in mind at the outset that a drop of water immersed in its own vapour is a system composed of one component , and that variations in the tension of the drop with the radius can , therefore , be due only to the nature of the field of force between the molocules of water .
That is to say , it depends solely upon the form of the function in the Young-Laplace theory of capillarity .
But the soap films with which Reinold and Rucker and Johannot worked contained two components at least , and were composed of colloidal solution , that is , of a peculiarly complex type of fluid .
If maxima and minima did exist in the tension of a drop of pure water of radius less than the range of the mutual attraction of the molecules , it should be possible to form films of pure water just as it is possible to form films of soap solution .
This is not so .
A film of water breaks with very great rapidity ; in fact , it behaves as it should if tension decreased very rapidly wiffi the thickness of the film .
The repulsion suggested by Maxwell , and needed to account for the peculiarities of soap films , can perhaps be found in quite another direction .
In a previous paper I described the existence of a remarkable potential difference between a film of impurity , such as an oil , on the surface of water and the subjacent water .
It occurred to me , when conducting the exlJerimenCs , that if such a surface were lifted up to form a free film , as it can be lifted up by slowly a solid frame from the fluid , it would consist of three layers , two outer ones at a potential higher or lower , as the case may be , than the interior layer .
The arrangement would be such as is shown in the diagram ( fig. 2 ) .
' FIG. 2 .
J. J. Thomson , ' Conduction of Electricity through Gases , ' loc. 'Roy .
Soc. Proc 1911 , , vol. 84 , p. 220 ; compare also Beinold and Rucker , 'Phi .
Trans 1893 , , vol. 184 , p. 527 .
1912 .
] The Theory of Colloidal utions .
, are films of oil which may be from to thick , and at the interfaces , a constant difference of potential is found due to polarisation of the matter 011 either side .
Let the fluid drain away .
The positively charged portion of the fluid on either side is of finite thickness , owing to molecular movements .
When has drained away so that the extreme oscillations of the positively molecules at are into the electric field about the positive molecules at , there will be a lepulsion .
If the film thin further it must first entirely reconstruct itself The first state may be that of soap film showing Newtonian colours ; the second , that is after reconstruction , may be that of a black film .
This theory finds justification in a study of the actual filma The experiments and apparatus will be described llore fully in a later paper .
For the present it will be sufficient tu refer briefly to two typical cases .
A film , 1 ) , of soap , starch , or saponin solution in water , with air on each side , was so arranged that it could be inspected under the microscope while a constant current was pasf ; ed through it .
dust , or specially prepared French chaIk , was dusted on to the film , and also immersed in it , and it was noticed that the unimmersed particles moved in the electric field in a direction opposite to that of the immersed Measuring movement in the divisions of a micrometer eyepiece covered in five minutes , I found:\mdash ; Distance .
Saponin-water film\mdash ; Unwetted particles on the surface \mdash ; Middle of the film -- 12 Starch-water film\mdash ; Unwetted on surface Immersed That is to say , it was possible to observe particles at different levels in the film moving in opposite directions at the same time , the direction of the movement of each particle being reversed on reversing the direction of the electric current .
These observations can , I think , mean only one thing , namely , that such films are composed of layers between which there is a contact difference of potential .
Let us agree to call the various surfaces of such composite films interior and exterior surfaces .
Ihere will then be in the case of a film of fluid in air two exterior and two interior surfaces , and in the case of a film of one fluid on the surface of a mass of another fluid two surfaces , one interior and Mr. W. B. Hardy .
[ Mar. 18 , one exterior .
In the same way there will be in the former case one interior two exterior layers , and in the latter an exterior layer and an interior mass .
When all the layers have a thickness exceeding twice the range of action of any molecules present in the layers , the sum of the tension of the layers and the electric density at the interfaces will be constant and independent a variation in thickness of any or all the layers .
When the thickness of all or of any one layer is less than this magnitude the tension and the electric density vary , and may be considered functions of the thickness .
It of importance , therefore , first of all to determine whether the range of molecular action is a fixed value or whether it is dependent upon the chemical nature of the molecules concerned .
The question is considered in the next paper .
The Tension of Composite Fluiol Surfaces and the Stability of Films of Fluid .
By W. B. , F.R.S. ( Received March 13 , \mdash ; Read May 16 , 1912 .
) The tension of a composite surface composed of a fully separated layer one fluid ( say oil ) spread over a mass of another fluid ( say water ) is given by the equation , ( 1 ) where A and denote respectively the oil layer ( exterior layer ) and the water ( interior mass ) .
If be the depth of the exterior layer , then , for a given temperature the quantity will reach a constant value when is either twice the range of action of the oil molecules on each other , or the sum of two values , namely , the range of action of oil molecuIes on each other , and of the oil molecules on the water molecules .
Let be the lowest value of for which is constant : is equal to the greater of two quantities , the range of action of the molecules of oil , or the mean of this value plus the range of action of these molecules upon the molecules of water .
The attractive force between two molecules in the theory of capillarity is a force which decreases rapidly as the distance between the molecules increases .
Young assumed the force to be negative , that is to say ,
|
rspa_1912_0053 | 0950-1207 | The tension of composite fluid surfaces and the mechanical stability of films of fluid. | 610 | 635 | 1,912 | 86 | Proceedings of the Royal Society of London. Series A, Containing Papers of a Mathematical and Physical Character | W. B. Hardy, F. R. S. | article | 6.0.4 | http://dx.doi.org/10.1098/rspa.1912.0053 | en | rspa | 1,910 | 1,900 | 1,900 | 28 | 418 | 10,935 | http://corpora.clarin-d.uni-saarland.de/surprisal/6.0.3/?id=rspa_1912_0053 | 10.1098/rspa.1912.0053 | null | null | null | Fluid Dynamics | 35.462077 | Tables | 13.46962 | Fluid Dynamics | [
-2.8348379135131836,
-32.512351989746094
] | ]\gt ; Mr. W. B. Hardy .
[ Mar. 18 , one exterior .
In the same way there will be in the former case one interior two exterior layers , and in the latter an exterior layer and an interior mass .
When all the layers have a thickness exceeding twice the range of action of any molecules present in the layers , the sum of the tension of the layers and the electric density at the interfaces will be constant and independent a variation in thickness of any or all the layers .
When the thickness of all or of any one layer is less than this magnitude the tension and the electric density vary , and may be considered functions of the thickness .
It of importance , therefore , first of all to determine whether the range of molecular action is a fixed value or whether it is dependent upon the chemical nature of the molecules concerned .
The question is considered in the next paper .
The Tension of Composite Fluiol Surfaces and the Stability of Films of Fluid .
By W. B. , F.R.S. ( Received March 13 , \mdash ; Read May 16 , 1912 .
) The tension of a composite surface composed of a fully separated layer one fluid ( say oil ) spread over a mass of another fluid ( say water ) is given by the equation , ( 1 ) where A and denote respectively the oil layer ( exterior layer ) and the water ( interior mass ) .
If be the depth of the exterior layer , then , for a given temperature the quantity will reach a constant value when is either twice the range of action of the oil molecules on each other , or the sum of two values , namely , the range of action of oil molecuIes on each other , and of the oil molecules on the water molecules .
Let be the lowest value of for which is constant : is equal to the greater of two quantities , the range of action of the molecules of oil , or the mean of this value plus the range of action of these molecules upon the molecules of water .
The attractive force between two molecules in the theory of capillarity is a force which decreases rapidly as the distance between the molecules increases .
Young assumed the force to be negative , that is to say , 1912 .
] The Tension of Composite Fluid Surfaces , etc. repulsion , over a very small distance , positive beyond this distance , and constant until it vanished at a distance large in relation to the depth of the zone of repulsion , but very small relatively to distances directly appreciable by our senses .
Maxwell assumed the force to vary inversely with the fifth power of the distance .
Whatever the form of the function may be , that which is measured when tension is taken as an index of the range is not necessarily the absolute limit of the field of force about a moJecule , but the limit of its sensible action .
It can be proved that , ( 2 ) the term being the work ained per unit area when a surface of is allowed to approach normally a surface of The full ession for the tension of a double surface is therefore .
( 3 ) This expression , and the equation , are the values of for the limits and respectively , and it should be possible to pass from one to the other without a break by gradual increments of the fluid A. For all thicknesses of is constant , therefore it would appear that could be determined by measuring the minimal of A for which is constant .
Obviously A must be a pure substance , for if it contained an impurity whose molecular relations to were such that it reduced the tension of more effectively than pure , the tension would be constant and lminimal only when the mass of the external layer ( Aa ) per unit area was great enough to saturate the interface with The conditions which determine the spreading of one fluid over another , or rather between two others , one of which is air , may be stated as follows:\mdash ; Denoting the third fluid , air , by , then at the of a flat drop of A three forces have to be resolved due to the three ions .
" " If the three fluids can remain in contact with one another , the sum of any two of the [ tensions ] must exceed the third , and by Neunlann 's rule the directions of the interfaces at the common edge must be parallel to the sides .
a triangle , taken proportional to .
If the above-mentioned condition be not satisfied , the is inary , and the three fluids camlot rest in contact , the two weaker tensions , even if acting in full COIlcer , being incapable of the strongest .
For instance , if the second fluid spreads itself indefi1litely upon the interface of the first and * See the preceding paper , p. 604 ; also Lord Bayleigh , ' Phil. Mag 1890 , [ 5 ] , vol. 30 , p. 460 .
VOL LXXXVI.\mdash ; A. 2 Mr. W. B. Hardy .
[ Mar. 13 , third flnids .
" " The experimenters who have dealt with this question\mdash ; Marangoni , van der Mensbrugghe , Quincke\mdash ; have all arrived at results inconsistent with the reality of Neumann 's triangle .
Three pure bodies ( of which one may be air ) cannot accordingly remain in contact .
If a drop of oil stands in lenticular form upon a surface of water , it is because the water-surface is already contaminated with yreasy film * Further , the Young-Laplace theory of capillarity leads , according to Lord Rayleigh , " " to the important conclusion , so far as I am aware hitherto unnoticed , that , according to this hypothesis , Neumann 's triangle is necessarily imaginary that one of three fluids will always spread upon the interface of the other two The preceding pages present what I believe to be the current theory of the tension of composite surfaces ; my own experiments prove that it is too narrow for the facts .
When some ricinolic acid ( Kahlbaum ) is placed upon a clean surface of water the quantity first added spreads with great rapidity , but when the film is somewhere about thick , any further quantity added refuses to spread , but remains permanently gathered into a lens .
When more acid is added to the lens it enlarges until the whole surface is covered with a layer of the oil which has been forced over it by gravity .
Clearly , therefore , whereas the first added oil spreads because it lowers the tension , the sign of the effect changes at a certain stage in the thickening of the layer further the tension .
The spreading of the oil is therefore resisted , and a lens is formed .
With some substances ( olive oil , cymene , heavy oil ) , before the stage is reached at which a drop refuses to spread , small lenses , just visible to the naked eye , appear dotted all over the surface .
In the case of cyrnene these tiny lenses are just visible when the film A is of an average thickness of 100 , calculated on the assumption that its density is that of cymene in mass .
The phenomena can be followed in detail by adding successive drops of ' heavy at the same spot .
The result is a patch which is bounded by rings .
Each drop allows the one last added to contract to a ring .
The rings are of the same breadth when the drops are of equal size .
The outermost ring of all\mdash ; very visible when heavy oil is used\mdash ; is the contracted field of contamination on the surface before the oil is added .
The colour of the rings slowly changes .
A drop of heavy oil spreads first to a patch of superb blue , then changes to purple with a defined yellow edge , 1 mm. wide , the patch being say ) 5 cm .
across .
The patch , up now uniform , begins to become mottled , the red gives way to a beautiful pattern of peacock green , steel blue , and bronze yellow , the various Lord Rayleigh , loc. cit. , p. 463 .
Distilled from Price 's " " Motorine A see later .
1912 .
] The Tension of Composite Fluid , etc. colours being sharply marked off from one another even under considerable magnification .
In the centre of each blue patch , which in an undisturbed surface is accurately circular , is a small lens of oil , appearing as a point only to the naked eye .
The mode of formation of these lenses is clear .
Each is a droplet of oil condsnsed about some nucleus , for the most part solid , much more rarely a tiny bubble of gas .
They appear on a surface of distilled water with the heavy oil when the average thickness of the film is ] .
The surface except at first is therefore highly complex\mdash ; coloured areas and lenses being in tensile equilibrium .
In these cases when the general surface is nearly saturated with oil , that is , when the minimum of surface energy is nearly reached , condensation occurs on any nuclei which may be present .
The ultimate relation is the same as that found for ricinolic acid , or , indeed , for all the substances experimented with ( olive oil , castor oil , croton oil , ricinoleic acid , benzyl cyanide , " " heavy\ldquo ; oil , cymene and benzene ) : a uniform sheet of a third fluid in mass*can only be inserted between the fluids air and water by the operation of an externalforce , namely It is obvious from equation ( 1 ) that must have a minimal value unless the rate of decrease of TAB is equal to the rate of increase of .
For , let it be supposed that oil could be spread evenly and continuously on water until it reached the thickness at which it forms a separate phase , the first oil spread on the surface causes the tension TB to fall , but the last of the oil added is tension to rise , and the may more than compensate for any further fall in .
An approximate equation for the surface may be got as follows .
Consider a large lens of oil , say 10 cm .
in diameter and about a millimetre in thickness .
Such a can readily be formed .
Its surface is sensibly flat , but at the edges it curves down to meet the general surface of the fluid , which is also depressed at the edge .
Let the tonsions of the flat surfaces be denoted by , T2 , .
Then .
( 4 ) Let be the area of a horizontal section of the lens , the height of the upper surface above the mean level of the fluid , the depth of the lower * That is a sheet whose depth is , so that the substance is present as a full } .
separated phase .
614 Mr. W. B. Hardy .
[ Mar. 13 , plane surface below the mean level , and the density of of B. Then for the potential energy of the drop we have , if the effects of curvature at the edge be neglected , All the terms in this equation are constant , except , and , which are related variables .
* We may therefore put , ( 6 ) and .
and are very small quantities , so that the whole of the last term may be neglected .
From ( 6 ) , and ( 7 ) we get in which the term upon gravity is written for brevity .
The tension of the gas may certainly be neglected , and probably , which represents the energy per unit area of the gas or vapour condensed on to the surface of the lens .
There remains and the term in brackets is equal to If were equal to then , that is to say the lens is maintained against the action of gravity solely by the tension of its air surface , that is by the tension of the oil itself .
But there is no necessary equality between and .
They refer to essentially different things .
is the potential per unit area of a " " film of discontinuity to use Gibbs ' phrase , between water and air whose tension is reduced by a concentration per unit area of a component A. on the other hand refers to a surface of discontinuity between A and both in mass .
In the application of theory to the solution of the equilibrium of three fluids it is usual to consider the tensions as forces which meet at a point .
The theorem known as Neumann 's triangle may be quoted as an instance .
The method seems to me open to grave objections .
It is true , as Gibbs has shown , that the energy of a surface layer may be equated to a strain limited to a appears only in the term relating to gravity , and may be taken as constant over that range in which this term has a sensible value .
1912 .
] The Tension of Composite Fluid Surfaces , etc. mathematical surface , the " " surface of tension and , therefore , at the meeting place of three fluids these surfaces will intersect in a line , but since the range of action of molecular forces is finite the tensions of the surfaces cannot be the same for a finite distance from the line of intersection , the distance being the greatest distance at which any of the molecules present act upon one another .
The alternative assumption is absurd , namely , that there is no mutual attraction between the material composing the three films right up to the mathematical intersection of the " " surfaces of tension At the edge of the lens there is equilibrium , so that ; ( 9 ) but , and must not be identified with , and All interfaces which I happen to have observed have been highly polarised , the work T'AB , therefore , in those cases must include at least two terms , one for the work per unit area needed to produce electrification of density and , and another for the work due to simple molecular attraction .
If the sum of all the molecular forces which contribute to the self-attraction of the matter be included in the phrase " " molecular attraction the electric energy ceases to be a separate term .
But if any attempt be made to distinguish between the kind of attractions , e.g. chemical or physical , two terms must be employed .
The actual phenomena are undoubtedly better represented by two terms .
Consider the tension T2 , which is equal to .
We have , as before , In forming this surface , by allowing unit areas of surfaces A and to approach normally , let the work be gained in two steps , that is to say , when the surfaces come into contact , let work be first gained by the operation of the mutual attraction of unchanged molecules of A and ; call this work per unit area .
The molecules then proceed to alter one another so that polarisation occurs and work per unit area is done equal to .
Since the necessary condition of equilibrium of a film of discontinuity is that the tension shall be " " less than that of any other film which can exist between the same homogeneous masses , \ldquo ; * we may conclude that the effect of polarisation is to make the tension less .
We have , therefore , the relation ( 10 ) and .
( 11 ) Owing to molecular movements , the polarised molecules occul layers of finite thickness , but we may with Helmholtz consider the two electricities as * Gibbs , , p. 403 .
Mr. W. B. Hardy .
[ Mar. 13 , distributed on two parallel surfaces as in a condenser , the plates of which are separated by a very small distance and have an area .
Polarisation will be complete , that is , the electric density will be maximal , only when the film of A shall have reached a certain thickness , which may or may not be the same as the extreme range of attraction of the molecules of A and B. In other words , and and , therefore , the electric energy of the surface , are functions of the mass of A per unit area .
and , with ( 8 ) and ( 11 ) we have It is important to realise distinctly the meaning of the terms and .
The former is that fraction of the work gained when unit area of a surface of pure A approaches normally unit area of a surface of pure due to the Laplacian attraction of molecules of pure , say oil , for pure , say water .
On the corpuscular theory of matter , it is the term which expresses the work gained from the mutual influence of the external or stray fields of the molecules .
The latter term , , is that portion of the work , assumed to be expended entirely in producing polarisation , which is due to chemical action between the molecules .
It is the term which expresses the sum of the change in the internal fields of force of the molecules .
If A does not react chemically with at the interface , , and is equal to the work gained by simple Laplacian attraction .
This distinction may seem artificial , but it will be seen that it is needed in order to explain the actual phenomena .
It must also be made in any.complete specification of the intrinsic energy of some fluids .
Consider , for instance , benzene and water .
In the former , selfattraction , so far as we know , is entirely due to the stray field of the stable ring of atoms which forms the molecule .
In the latter , a fraction of the total self-attraction , a Yery small fraction it is true , is due to dissociated moleeules , that is , to the opening out of the internal molecular fields .
It must be borne in mind in considering the polarisation of an interface between such bodies as oil and water that the phenomena may be partly due to electrolytes present as " " impuribies Celtainly they cannot be without influence , and equally certainly they cannot be wholly excluded ( e.g. the carbonic acid of the air ) .
But in colloidal solutions the charge on the colloid masses is always greatest when the concentration of electrolytes is least , and I have found that a slight leakage of zinc sulphate from the non-polarised electrodes iuto the observation chamber completely arrests any migration at an interface .
According to our present knowledge such interfaces are discharged , not charged , by soluble electrolytes , but further experiment is both needed and difficult .
1912 .
] Tension of Composite , etc. Methods.\mdash ; The tension was determined in two ways .
In the first , usually called Wilhelmj 's method , the needed to balance tlJe pull exerted by the fluid on a thin blade hung vertically is measured by a balance ; in.the second , the weight needed to detach a flat plate from the surface is measured .
Five glass blades , each mm. thick , were mounted in a light frame so that they were parallel to each other and 1 cm .
apart .
The frame and blades were suspended from one arm of a balance and the level adjusted by means of a fine screw so that the lower of the blades was as nearly as possible at the mean level of the fluid when the pointer of the balance stood at zero .
If be the total of the blades , the needed to balance the pull , the tension is given by .
This formula assumes that the angle of contact of fluid and ylass is zero .
The assumption is sensibly true clean water and nearly true for a contaminated surface .
The factor to correct for the angle is its cosine , and , as this decreases in very slowly for angles , the correction is small .
But , though small , it must not be lost sight of .
The effect of ignoring this correction is to make the calculated values of the tension too low when the water surface is much contaminated .
The formula cannot be used to obtain the tension of a double surface A and AB , for the angle of contact of the AB surface with the glass seems in all cases to be considerable .
In prolonged experiments , it is very necessary to inspect the blades from time to time with a hand lens , to see that no " " beading\ldquo ; has taken place to impurity condensing on to the surface of the glass from the air .
The formula usually given for the plate method also assumes the angle of contact between fluid and plate to be zero at the moment of breaking .
The formula is at best an approximation , and the error may be considerable .
As the best ion , I used the following , , and the weight was taken as the mean of the weight which the surface would just hold , and the weight which broke the plate away .
The plate method has this advantage , that it can be applied when onJy a small quantity of fluid is .
It was therefore used only to obtain an approximate value for the tension of the substances used to fornl the on the water .
The thickness of the film was varied either by Miss Pockel 's lletho which the mass of the film is constant and the area varied , or by gradually thickening a film by increments of material , the surface being constant .
ordinates of the curves in all cases are tension in dynes per ' Nature , ' 1891 , vol. 43 , p. 437 ; also Lord Rayleigh , 'Phil .
Mag 1899 , [ 5 ] , vol. 48 , p. 331 .
Mr. W. B. Hardy .
[ Mar. 13 , centimetre , the abscissae are the thickness of the film calculated from the weight of material placed on the surface , and the area of the surface , the density of the film being taken as that of the substance in mass .
I did not succeed in weighing the minute quantities of croton oil used , and Ihe abscissae for this curve are therefore on an arbitrary scale , the unit 1 being probably much less than 1 Except when the contrary is stated , freshly distilled water from a silver still was used .
The , which was of tin plate , measured cm .
The most satisfactory barriers were made of tin plate cm .
wide , with a vertical strip of plate slightly less than 10 cm .
long , and about cm .
deep , soldered ( with tin ) to the middle .
Each blade in transverse section was thus -shaped .
Two blades were always used , and kept about half a centimetre apart or ] , so as to obviate leakage from a contracted film .
Direct leakage was , I think , practically absent\mdash ; at any rate , lycopodium dusted on to the cleaned surface just near the blade failed to reveal it .
But , of course , the contracted and the cleaned surfaces are in communication with the mass of the liquid , and , if the substance used to contaminate the surface is at all miscible with water , solution from the contracted surface and condensation on to the clean surface will go on .
The vertical strips on the blades were placed there to " " wire-draw\ldquo ; any diffusion stream .
The influence of solubility on the equilibrium of a surface needs careful consideration ; for the present , it may probably be owing to the extreme insolubility in water of the substances experimented with .
The water surface was cleaned by sweeping any contamination to one end with ' one of the blades It was then got rid of by a quick jerk , which threw the surface out of the trough .
Lord Bayleigh* has measured the tension of clean and contaminated surfaces of water by the ripple method and by the blade method .
The values obtained are more divergent the greater the degree of contamination:\mdash ; Owing , however , to the hysteresis of the surface , the ripple method itself cannot be relied upon to erive oorrect results .
The sources of error in the blade method are of contrary sign , and should , therefore , to a certain extent neutralise one another .
As contamination 'Phil .
Mag 1890 , [ 5 ] , , p. 398 .
1912 .
] The Tension of Surfaces , etc. increases three changes have to be considered , ( l ) an increase in the angle of contact of the surface with the blades , ( 2 ) a thickening of the edge of the film of fluid on the , which may result in " " beading and ( 3 ) any change in the tension of the fluid where it wets the blades owing to an attraction of the solid for the oil .
( 1 ) would give the relation from ( 2 ) , and from ( 3 ) .
So as there is no sign of beading or irregularity when the blades are inspected by a lens , and the angle of contact appears to be nearly zero , .
is probably not far removed from .
In order to centre attention on the main point , namely , the relation of tension to chemical constitution , the hysteresis of co1nposite surfaces is accepted throughout this paper without criticism .
There is no doubt in my mind that it is a real phenomenon of the surface and nob merely an effect of adjustments at t , he blades , since it appears when the layer of contamination is excessively thin : also Reinold and Bucker found the properties of a film to depend upon its age .
It will be well here briefly to recapitulate Lord Rayleigh 's results .
The theory of the movements of camphor on the surface of water , due to van der Mensbrugghe , innplies that they will take place so long as the tension of the surface is than that of a saturated solution of camphor .
At a certain tension , therefore , which Lord Rayleigh found by the blade method to be that of a pure water surface , the } ) movements cease .
* To this particular tension he gives the } " " camphor point On the assumption that the density .
a film of oliye oil is the same as that of the oil in Lord Rayleigh found the thickness of the film at the camphor point to be Using castor oil , not olive oil , to form the film , Lord Rayleigh measured the tension when the thickness of the film was varied by Miss Pockel 's method .
His curves show that up to a thickness of about 1 the oil scarcely alters the tension , then a fall sets in until the film becomes about 2 thick .
Further addition of oil has only a slight effect on the tension .
The most important and the most quoted conclusion which Lord draws from these curves is that " " if we be by supposing the number of molecules of oil upon a water surface to be small enough not only will every molecule be able to approach the water as closely as it desires , but any repulsion between molecules will have exhausted itself .
Under these conditions there is nothing to oppose the contraction of the surface\mdash ; the tension is that of pure water " " The next question for consideration is\mdash ; at what point will an opposition 'Phil .
Mag 1899 , [ 5 ] , vol. 48 , 'Roy .
Soc. Proc 1890 , vol. 47 , p. 365 .
Mr. W. B. Hardy .
[ Mar. 13 ; to contraction*arise ?
The answer must depend upon the forces supposed to operate between the molecules of oil .
If they behave like the smooth rigid spheres cf gaseous theory , no forces will be called into play until they are closely locked .
According to this view the tension would remain constant up to the point where a double layer commences to form .
It would then suddenly change , to remain constant at new value until a second layer is complete . .
If we accept this view as substantially true , we conclude that the first drop in tension corresponds to a complete layer one molecule thick , and that the diameter of a molecule of oil is about The first comment to be made on these conclusions is that the oils with which Lord Rayleigh experimented are quite exceptional in their power of reducing the tension of water , and a similar train of reasoning applied to other substances seems to lead to impossible conclusions .
The molecules of heavy oil and of cymene would have a diameter of 20 to 40 .
Or , taking the camphor points given in the table as the measure of a layer two molecules thick , we should have to accord diameters of from 200 to to their molecules .
CastoCrotoSubstan.nsity .
Thick Olive oil Benzene Benzene spread on a clean water surface , but a flat lens 1/ 10 mm. in average has no observable effect upon the movements of catnphor .
To give this result , however , the benzene must be carefully purffied by distillation and crystallisation .
Impure benzene behaves very differently .
* In one sense of the word contraction it may be said that the clean surface of water does not contract at all .
When the blades are moved so as to diminish the area of a surface , motes iloating on it do not move at all .
This is the best test I know of the cleanliness of a surface .
There is therefore no tangential contraction of the surface such as occurs and is readily seen when any " " skin\ldquo ; of impurity is present .
The diminution of area is effected solely by movement of the surface layer normal to itself .
So long as ffiis kind of adjustment can take place and only so long is there no hysteresis .
All the elements of the surface ( cf. Gibbs , p. 468 ) are in complete equilibrium with one another throughout any changes of area .
'Phil .
Mag 1899 , [ 5 ] , vol. 48 , p. 336 .
The Tension of mposite Fluid Surfaces , etc. Camphor is quite " " dead\ldquo ; upon pure benzene in mass , but still active upon a water surface carefully saturated with this substance .
A surface of Cambridge tap water is very slightly contaminated .
The surface must be contracted to one-tenth its area in order to produce a readable difference of tension .
On such a surface of 700 sq .
cm .
area , 4 .
of benzene poured on to it forms lenses 3 to 4 cm .
in diameter .
These lenses show expansions and contractions , and smaller lenses , that is those of less diameter , move across the surface and fuse with ones .
The expansions and contractions of the lenses are due to the tension altelnately falling below and rising above that of the plane surface in the process of adjustment of the tension by horizontal spreading of a sheet of benzene from a lens and its removal by evaporation .
The explanation of the pulsations ) erefore is the same as that which accounts for the " " tears\ldquo ; of wine .
A touch of ether ( redistilled ) caused the benzene-water film to contract , owing to its tension being greater than that of the ether-water film .
This is the more remarkable when it is remembered that ether is fairly soluble in water ( 1 in 12 ) , and that , therefore , a large part of the ether added must be removed from the surface to pass into solution .
After the addition of ether the small lenses of benzene behave differently .
They move as before towards the large lenses but union seems to be impossible .
When only a short distance separates small from large the former , the nearest point of the large lens being at the same time deeply indented .
The of the small lens is , therefore , accompanied by a local and lowering of tension .
If an " " active\ldquo ; substance be one which lowers the tension of water when a film less than 2 thick is spread on the surface , they fall into two groups which , in order of activity , are Active .
Relatively inactive .
Croton oil .
Benzene .
Castor oil .
Cymene .
Olive oil .
oil .
The first group contains bodies of characteristic chemical instability , namely , the esters .
They are salts of unsaturated fatty acids and glycerine .
Castor oil , for instance , consists mainly of the glyceride of ricinoleic acid .
The " " inactive\ldquo ; group are as characteristically stable , the heavy oil being composed of paraffin , while cymene is a benzene derivative .
Benzene , the least active , has a very stable ; structure .
The simple paraffins are at least as stable as benzene and the relatively large activity of the heavy oil may , therefore , be due to the presence of the\ldquo ; active\ldquo ; impurity .
The " " heavy oil\ldquo ; was obtained by distilling Price 's ' air cooled oil \ldquo ; in a vacuum .
Mr. W. B. Hardy .
[ Mar. 13 , fraction which boils at about 40 was used and denoted by the term oil Since the entire Price 's oil A actively reduces tension this fraction may well contain a trace of active substance .
In cymene the benzene ring is no longer simple , as the formula shows , and all such modifications of the benzene ring decrease its stability .
CH CH CH CH Benzene .
Cymene .
The chemical stability of benzene is associated with a remarkably slight influence on the tension of water .
The molecules of the " " active\ldquo ; substances , being organic salts , might be expected to polarise readily under an axial stress such as must be exerted at the AB surface .
Castor Oil and Croton Oil .
The curves ( figs. 2 , castor oil , and 3 , croton oil ) differ from those obtained by Lord Bayleigh in the sharp points of inflection .
In order to settle whether the inflection is really as abrupt as it appears to be , the first part of the Mr. W. B. Hardy .
[ Mar. 13 , deep , and adjustment by horizontal diffusion or spreading will be slow and difficult .
In this region contraction of the surface caused a rise of tension , for instance:\mdash ; Croton Oil , a trace . .
Tension .
74.17 74.27 74.17 Successive positions of the barriers are given in centimetres from that end of the trough at which the tension was being measured , and it will be noticed that , with slow contraction , the tension at 31 rose to , but , with rapid contraction , the barriers being moved quickly from 68 to 31 , it rose only to The part BC appears to be accurately a straight line .
In curve 4 it is seen to be made up of two straight lines , which are not continuous , but are joined by a cluster of points .
The explanation brings out the most interesting property of these surfaces .
Owing to the hysteresis , it is obvious that any accidental expansion while one is mapping a curve of contraction will displace the curve\mdash ; the subsequent values belong , in point of fact , to quite another curve ( compare , for instance , figs. 5 and 6 ) .
The nebulae of points therefore represent attempts which I made to return to the original curve when I had accidentally left it .
The part of the curve CD slopes very slightly downward , but , as the formula for the tension is probably far from exact in the region , the particular form of the curve is here not of great importance .
Cymene.\mdash ; I am indebted to my friend , Dr. Ruhemann , for a sample of this hydrocarbon .
By ordinary tests it is insoluble in water .
The sample was of ordinary chemical purity , probably sufficiently so to give the true value for a water-cymene-air surface .
Fig. 5 needs some explanation .
The curves are plotted to two distinct scales of thickness of film .
The upper curves are plotted to the upper scale of , the lower to the scale of 0-2000 .
Three sets of measurements are recorded : the simple dots were obtained by contracting or a surface with blades , the ringed dots and crosses by adding known quantities of cymene to a surface of constant area .
The agreement between the results proves that solubility of cymene in water does not produce a sensible effect , at any rate , over the first part of the 1912 .
] The Tension of Composite Fluid Surfaces , etc. curve , for the used contained 1S litres of water , while for the measurements with constant area of surface only 70 cm .
of water was used .
The slight divergence in the later parts of the curves may be due to the difference in the mass of water employed or to the different type of surface produced by moving a barrier so as to contract the area to what is formed when successive additions of cymene are made to a surface of constant area .
It has been pointed out already that a surface in contracting follows a curve different to that of an extending surface\mdash ; the figure of hysteresis for cymene illustrates the point .
Now , in Miss Pockel 's method , a surface starts from an arbitrary point , and thenceforward is a pure contraction surface .
But , when a second drop of cymene or any other substance is added , it is rapidly extended by tho already existing surface , and then , after a few oscillations , comes to rest .
The surface , as formed , is thenceforward composite , being partly a surface of expansion , partly a surface of contraction .
Cymene is a relatively inactive substance .
With the diminished activity , the sharp points of inflection on the curve disappear , and a curve of gradually 'changing slope is obtained .
The hysteresis is seen in the curve of expansion which follows on and is continuous with the curve of contraction .
Heavy Oil.\mdash ; From its source may be regarded as being mainly composed of paraffins .
The curves for the heavy oil are those characteristic of .an inactive substance .
The slope is gradual throughout .
The initial rise of tension is well marked .
A surface of clean distilled water reased by four drops of the oil applied at intervals of 10 minutes .
The surface was then allowed to remain quiet for 70 minutes in order , if possible , to attain eqnilibrium .
In all , cu .
mm. was spread on a surface of 68,000 sq .
mm. area .
The result was lower the tension to the first point indicated by a ringed dot ) .
The Mr. W. B. Hardy .
[ Mar. 13 , crossed points refer to an entirely different experiment , in which the disc method was used .
The surface was contracted slowly , and the curve AC represents the results .
At it was found that the tension rose when the surface was allowed to remain quiet , and reached a stable point at ; it was then extended rapidly , the points measured being indicated by the ringed dots .
It was again contracted , this time rapidly , and now followed curve rising again to , and again extended slowly , the curve being DE .
The whole time occupied in plotting curve DE was 100 minutes , and no sign of variation of tension with time was noticed at any point .
The surface was then expanded along .
It will be noticed that changes of direction appear at exactly corresponding points in the curve of slow contraction and slow expansion .
The four drops of oil spread on ths surface do no.t fuse .
The last added drop , after 70 minutes , could be seen by reflected light to form a large patch with sharply defined edges .
The surface is therefore composite , and the breaks in the curves may provisionally be referred to this .
The question arises whether the curve of contraction AC would not be identical with the curve ED if time were allowed for the surface to adjust itself after each phase of contraction\mdash ; expansion of the surface is , so to speak , dead-beat , as is shown by the ringed dots lying on the curve DE of relatively slow expansion .
The evidence ayailable does not suffice to settle the point .
This , like the many other questions raised , must be made the subject of separate experiment .
It may be noticed , however , that the curve of rapid extension of the heavy oil surface coincides with that of slow The Tension of Composite Fluid , etc. lsion .
Also the curve of very rapid contraction , which was taken Gly in four rapid , and secondly in one jump , i.e. in about four lies above and not below curve , which was taken quite slowly , time occupied in the contraction being about one hour .
comparison of these results shows that the influence of a substance the tension of a water surface is remarkably independent of its own or viscosity .
Cymene , a ] spirit , has much the same type of curve that iven by an oil so viscous that it will scarcely flow .
Benzene , with a tension , has relatively little influence on the tension of water .
Croton oil , with about the same tension , is incredibly potent .
All physical have an influence which is insignificant compared to that exerted the chemical nature of the substance .
Organic salts , that is to say the esters , intensely active , and have sharply inflected .
Stable substances , and benzene derivatives , have given curves only htly inflected , their activity is relatively slight .
The different portions\mdash ; AB , \mdash ; of the sharply inflected curves I interpret as follows : is the which the layer A is discontinuous .
The surface is unstable , and the tension rises above that of pure water the surface is contracted .
In BC the tension is rapidly falling , owing perhaps mainly to the development of a difference of potential between the film A and the water B. That is to say , we may picture partial hydrolysis and ionisation of the ester taking place at the interface .
The second inflection at marks the point at which polarisatiou is maximal , and from onwards the tension falls gradually to a minimum .
Measurements of tension , however , fail to give the real relation in this region owing to the formation of lenses by condensation of oil on to solid particles .
The conclusion that tension falls to a minimum and theu ises again is probable from considerations already advanced , and is supported in a remarkable way by the study of the mechauical ility of composite films .
The curves for relatively inactive substances are sharply distinct in type .
There is an absence of shar } ) inflections , and the second iniiection may be absent .
The curve for the heavy oil suggests that the whole efl.ect in tension may be due to an impuriCy ( see p. 632 ) , bulk of the oil being not relatively but absolutely inactive .
The slow decrease in tetlsion increase in concentration of the substance on surface of the water ascribe to the feebleness or absence of chemical reaction at the interface .
The Mechanical ability of Surfaces.\mdash ; When a bubble of air is to rise in a fluid the lface is lifted and a film is formed which to thin owing to the fluid drained away by its own weight .
a certain time the film becomes so thin as to be ruptured by the VOL. LXXXVI.\mdash ; A. 2 X Mr. W. B. Hardy .
tension .
The time of persistence of the film obviously will depend upon viscous resistance to the flow of fluid which thins it , and the speed which adjustment of tension can be effected by tangential diffusion of components .
* These factors also determine the durability of a flat Without attempting precisely to analyse what it means , let us agree to of the mechanical stability of a film and to regard the time which between formation and rupture as a direct measure of this property .
Bubbles of the same size were formed as nearly as possible at the distance cm .
below the surface in a trough , and their persistence on surface measured by a stop-watch .
The thickness of the film calculated , and the tension measured by the blade method .
For each the duration of at least 10 bubbles was recorded and the mean taken .
the bursting of bubbles on a surface almost invariably raises the tension , was measured before and after each set of 10 , and the mean taken as tension corresponding to the mean duration .
The rise of tension due to bursting of 10 bubbles corresponds on the ayerage to about .
in balance pan .
Castor Oil-Water.\mdash ; The upper curve ( fig. 7 ) is the curve of tension , the scale of the ordinates appears to the left .
The lower curve shows changes in mechanical stability with changes in thickness of the film .
ordinates for ) curve denote seconds and the scale appears to the The abscissae for both curves are to the same scale of .
The zero time scale is the time taken to bursC by a bubble formed on a clean of water .
It is as nearly as can be measured of a second .
At the * Gibbs , , p. 475 .
Tension of Composite Surfaces , etc. in the curve the duration of the bubbles is even less than this ; I unable even to estimate it and entered it in my notes simply as The lower curve shows a remarkable series of oscillations over a corresponds to a composite surface whose tension is varying very decrease in the amplitude of the oscillations is It is obvious that oscillations must occur in the means of any series of numbers , for not only is the tension of the surface with variations in the thickness of the film , but also it is subject to hysteresis eifects .
Therefore , the durability of a film formed from the surface will vary with variations in , e.g. , the velocity of ascent of the bubl ) , the distribution of solid nnclei in the film , etc. The oscillations may , therefore , be a of the means rathel than an indication of a real variation in the mechanical of the face .
Their larity and the orderly decrease in amplitude , however , are most remarkable , and as precisely the same oscillations are foumd in the times and in the means of the longest and shortest times for each set it is , on the whole , probable that they are not merely llumerical .
Similar oscillatiol ) appear in measurements of the mechanical stability of composite surfaces of water with cymene or benzyl cyanide .
In the region of the first oscillation bubbles have sometimes persisted for as long as 70 seconds .
It is possible , therefore , that an apex earlier than the one found may be present .
C'ymene-Water.\mdash ; The ation of the bubbles in seconds as ordinates are plotted directly against tension ( abscissae ) in the curve ( fig. 8 ) .
Fewer points Mr. W. B. Hardy .
[ Mar. were taken , and therefore the true form of the curve probably does appear .
The oscillations are obvious .
In both cases there is a stage mechanical stability is that of a pure surface .
It lasts until the tension of mixed surface begins to fall , with increase in the depth of the layer A. after the first inflection of the curve of tension and thickness a film acquires very great mechanical stability because when it thins , owing draining away of the fluid , the thinning of layer , which must also occur , once raises the tension .
When a surface is brought as nearly as possible the point where mechanical stability appears the record of persistence bubbles is very remarkable .
Tension .
Duration of a series of bubbles in seconds .
1050 552023 221120 2211 In the first series a few bubbles , so to speak , make films with an order stability which rightly belongs to the next series .
If those bubbles exceptional structure be arded the curve may be said to rise from the base line to the maximum of mechanical stability .
When the surface of croton or castor oil and water is near this bubbles which burst as rapidly as possib ] give way when the moved 1 mm. to bubbles which persist for 20 seconds or more and play of Newtonian colours .
It will be noticed that there are two points at which the stability of the surface is minimal , one when the tension is sensibly clean water , and another when it is heavily contaminated .
The minimum occurs when the thickness of the layer of castor oil is 13 , and of cymene is of the order of 2000 .
The line AA in fig. 8 a thickness of .
Beyond this I have no measurements .
Bubbles of the composite surface at the second minimum seem to even more apidly than do those on a clean water surface .
In my notes have simply entered the time as .
At both minima , and there only , bubbles burst with a sharp crackle strongly esting an electric Some active liberation of energy is needed to account for the rapidity of rupture at the second minimum .
It is not the rate of bursting of in , e.g. , pure castor oil , for that oil is a very viscous fluid .
It is a minimum and beyond it the curve rises again .
For instance , a surface oiled with a large excess of castor oil and the mean duration of the rose to seconds .
The Tension of Composite Flnid Surfaces , etc. 6.31 The existence of the second minimum of mechanical stability confirms the already arrived at that between the values of a clean surface and of a double surface there is at least one minimal value of less than either .
For let the curves of tension have the form shown in fig. 9 .
A to the tension of a free film decreases the thickness diminishes , and therefore it is unstable .
Also the tension of a free film formed from the composite surface at would increase with both increase and decrease in thickness ; that is to say rupture would occur even more rapidly than in the region AB .
But , frolu considerations already anced , the extrenle range of action of the llolecular forces at the surface must be equal to at least half the thickness of the film when is minimal , and the method adopted for calculating this thickness , which itself ives minimal values , would fix it as 9 for castor oil , and some hundreds of millimicrons for cymene or heavy oil .
Are we to conclude from this that the range of the -Laplacian attraction really extends to 100 or more ?
The answer depends entirely upon what is meant by the range of molecular action .
If by it is meant the radius of the sphere of influence of a molecule of , say , a then I think the experiments are compatible with the view that this has an extremely small value , not much oreater than the diameter of the molecule itself .
Quite another kind of range of molecular action is possible in close packed structures such as fluids and solids , namely a strain transmitted from molecule to molecule .
At the interface AB , which has sensible thickness owing to the kinetic energy of the molecules , the matter present has to a certain extent the properties of a solid .
The stresses are not isotropic , but there is a component the normal to the snrface probably of very great magnitude .
This may , as we have seen , produce chemical effects , that is to ) , it may the intra-molecular fields of force , it will also strain the extrafields .
The strains on the intra-molecular fields appear as a ionisation of esters , or partial hydrolysis .
Looked at from a purely standpoint , we may egard these modified molecules as reacting with Mr. W. B. Hardy .
molecules on boih sides , and the effect so transmitted from molecule lno]ecule on each side of the mathematical interface .
From the standpoint we may consider the give and take between these molecules and those further away from the interface which must occur the course of their vibrations .
Molecules using out of the zone are to normal ] ecules , those diffusing in are abnormal , just as at an interface between water and water vapour , molecules the zone on the average become polymerised to molecules , while molecules leaving it to enter the yapour must on the be in process of depolymcrisation .
Tb is this irradiation of strain in a packed structure may extend so deeply as to modify the state of a skin solle hundreds of microns in depth .
\mdash ; After the foregoing paper was completed , certain new came to light which make it possible to extend and confirm the al.rived at .
As will be remembered , a suspicion was expressed that effect of the oil called heavy oil\ldquo ; upon the tension of water might be to the presence in it of some active impurity .
I wrote to Messrs. Patent Candle Co. asking them for information as to the chemical of the oil " " Motorine A and especially whether the distillate I under the name " " heavy oil\ldquo ; might be taken to be composed entirely paraffins .
I did so because , as the simple paraffins are more stable en , the chemical theory of the tension of composite surfaces that the effect of parnffins upon the tension of water should be even than that of pure benzene .
The courteous letter which I received from Messrs. Price informed me the Motorine A contains glycerides , which would account for its further , that my distillate also might contain glycerides , that is esters , products of the decomposition of bolycerides .
Messrs. Price sent to me sample of a paraffin oil about as heavy as , and about th same time I came , by accident , across another sample of an oil chiefly paraffins .
Ihese oils I will call and respectively .
Both of refuse completely to spread upon pure water .
The statement is upon the most rigorous tests I could devise .
One experiment follows : trough and blades were scrubbed with strong caustic and left in running tap water for one hour .
The trough was then out with water freshly distilled in a silver stil ] , filled with water , the surface scraped at intervals for an hour .
It was now not to detect any contraction of surface by the movement of motes .
fully cleaned blades were inserted , and the tension found to be The Tension of Composite Fluid , etc. the surface was contracted as much as possible .
The barriers were at the extreme end of the ough .
A very few grains of lycopodium then dusted on to one spot\mdash ; very few in order to avoid of While the position of a particular cluster of grains was being observed along a fixed line of sight a small drop of oil was placed on the surface 1 cm .
distant from the cluster .
The cluster did not move at and the tension did not vary .
A tiny drop of oil was then placed away from the cluster , again with no result .
Each drop floated on surface as a tiny lens .
The barriers were now moved , and the surface contracted as much as possible , with no effect upon the tension .
In con the surface it was noticed that the lenses of oil did not move until were impelled forward by the upward slope of the surface to That is to say , the surface was so pure as to be " " non-contractile.\ldquo ; were driven in this way up to the blades .
Both bal.riers were lifted out .
without any of expansion of a " " skin and placed one another in the middle of the length of the trough .
They were rapidly moved apart to each end and on to the fresh surface so formed few grains of lycopodium were placed , and oil beside them , all as as possible .
The oil did not spread at all .
The great chemical stability of the paraffins makes chemical interaction with water impossible , and with the absence of chemical action at the interface the term in equation ( 11 ) vanishes , and the term in brackets reduces to .
Some degree of chemical action , therefore , would seem to be necessary to make one fluid spread as a film between two others ( air and water ) .
This leads to a purely chemical theory of the miscibility of iiuids , for fluids mix when is negative , and given the relation occurs when , that is , when the energy of chemical per unit area of interface is sufficient to satisfy the condition Oil is completely colourless and transparent .
The contour of the cdge the lens and the nature of the oil-water face can thClefore be followed ease .
Careful examination of the lens shows that the water-air is drawn umder its edge .
The contour of a lens , 3 cm .
in diameter , is somewhat as shown in fig. 10 .
The sign ificance Mr. W. B. Hardy .
of this is obvious , namely , that , for , if the relation be one of the angle must be 10 in order to satisfy the relation , when put a relation which is certainly sufficiently exact to prove the From this point two possibilities nfront us : either that at the edge fluids do actually exis in contact , in which case Marangoni , Quincke , Lord Bayleigh are wrong in .
that Neumann 's triangle is sarily illusory ; or that , in which case the lens of touch but is separated by a pellicle of air .
The choice between these alternatives must be based upon a study of the optical properties of surface .
The general appearance of the AB surface does not suggest presence of a pellicle of air at all .
It is interesting to note that the second alternative may imply a of A for B. This viously follows from the relation if the quantities due to air be ignored and be put respectively to .
The quantity must then necessarily be negative .
The corpuscular theory of matter traces all material forces to the tion or repulsion of foci of strain of two opposite types .
All systems these foci which have been considered would possess an unsymmetncal field\mdash ; equipotential surfaces would not be disposed about the system concentric shells .
If the stray field of a molecule , that is of a of these atomic systems , be unsymmetrical , the surface layer of fluids solids , which are close packed states of matter , must differ from the mass in the orientation of the axes of the fields with respect to the to the surface , and so form a skin on the surface of a pure substance all the molecules oriented in the same way instead of purely in random The result would be the polarisation of the surface , and the surfaces of different fluids would attract or repel one another according to the sign their surfaces .
The statement , so commonly made , that a drop of oil fluid refuses spread on the surface of another only when the latter is contaminated film of impurity is remarkably far from the truth unless the in question be the air\mdash ; an interpretation not usually included in the meant .
I have found lenses of oil on pure water unohanged after 24 the edge still being tucked in .
The lens , however , at once flattens if the Quincke 's value for the tension of paraffin is 30 .
My own measurements of tension of oil give at The Tension of Composite Fluid surface be slightly oiled with an acGive substance such as castor oil , and the edge takes the form shown in fig. 1 .
Castor oil reduces the quantity TBC , and therefore the result is at first sight paradoxical .
The explanation is simple\mdash ; I owe it entirely to an observation made by Mr. Stevens .
When a coloured body such as impure dibronlricinolic acid is used to contaminate the water surface it may be seen to be drawn in as a fllm under the lens .
The quantity TAB is therefore also reduced in value .
An instance of the fact that spreading is made possible , not prevented , by a film of impurity , which must not be too thick , is furnished by oil , which spreads slowly on tap water but refuses to spread if the surface has been first thoroughly scraped .
When a lens of fluid A stands on a surface of water which is coated with a film of , it is possible that the layer of discontinuity AB of the general surface is continued under the lens .
In that case the composite surface between lens and waver would be composed of two surfaces of discontinuity of different molecular structure , namely , the surface of mixed oil and water , which is an extension of the }eneral surface , and the surface of the oil .
|
rspa_1912_0054 | 0950-1207 | On the torque produced by a beam of light in oblique refraction through a glass plate. | 1 | 16 | 1,912 | 87 | Proceedings of the Royal Society of London. Series A, Containing Papers of a Mathematical and Physical Character | Guy Barlow, D. Sc.|Prof. J. H. Poynting, F. R. S. | article | 6.0.4 | http://dx.doi.org/10.1098/rspa.1912.0054 | en | rspa | 1,910 | 1,900 | 1,900 | 15 | 267 | 5,725 | http://corpora.clarin-d.uni-saarland.de/surprisal/6.0.3/?id=rspa_1912_0054 | 10.1098/rspa.1912.0054 | null | null | null | Optics | 27.959208 | Measurement | 23.127438 | Optics | [
34.650787353515625,
-39.607627868652344
] | ]\gt ; PROCEEDINGS OF THE ROYAL SOCIETY .
SECTION ]ATEEMA TAND PE YSICAL SCIE the Torqne produced by a Beam of Liqht Oblique Refraction through Glass By BAItLOW , D.Sc .
( Commumicated ) Prof. J. H. Pointing , F.R.S. Received March 27 , \mdash ; Read Apri125 , 1912 .
) In the Presidential Address to the Physical Society in 1905* Prof. Pointing developed the idea that a beam of light must be yarded as containing a stream of momentum , and he showed that this principle may be used to solve with great ease the various cases in which a beam of light is absorbed , reflected , or refracted at a surface .
This method is particularly powerful and convenient , for , once havin made the assumption that light carries with it a stream of momentum , the forces can be calculated by the ordinary mechanical laws without any further appeal to the theory of wave disturbance of which we suppose light to consist .
When a beam falls normally on a perfectly absorbing surface the force exerted is the momentum received per second , and it is therefore equal to the momentum in a length of the beam , where is the velocity of light .
But the pressure exerted is equal to the energy density of the beam\mdash ; the law first deduced by Maxwell from his electromagnetic theory and now well established by the experiments of Lebedew and Nichols and Hull .
It follows then that the density of the momentum in the beam must equal The particular case which concerns us in the present paper is that in which ' Phil. Mag April , 1905 .
VOL. LXXXVII.\mdash ; A. Dr. G. Barlow .
Torque produced by a of [ Mar. 27 , a parallel beam of light is displaced parallel to itself by means of some optical system .
Such a displacement may be produced by oblique of the beam through a glass plate .
If the reaction is on the matter through which the light is passing , the molnentum principle shows at once that the material system must experience a torque of magnitude , where is the per unit length of the beam , and is the lateral shift .
This case is analysed by Prof. Poynting , who shows that when a beam is refracted at a surface there will always be an outward pull ( i.e. from the denser medium ) along the , and it follows that when a beam of light passes obliquely through a parallel plate there is a normal pull outwards both at incidence and at emergence , and these two pulls constitute the torque .
The result must be slightly modified when we take into account the fact that some of the light will be reflected at the surfaces and will give rise to additional forces normal to the surfaces .
In the same paper a brief account was given of some experiments carried out by Prof. Poynting and the writer with the object of showing the outward pull at oblique refraction .
* Two glass prisms , each with refracting angle , were arranged 3 cm .
apart at the ends of a torsion arm suspended at its middle point from a quartz fibre .
The air pressure was reduced to about 15 mm. .
The lateral displacement of the beam of light sent t , hrough the system was about cm .
The observed torque agreed within a few per cent. with that calculated from the energ of the beam .
The experiment was repeated with a pair of smaller prisms with the hope of obtaining more accurate results .
Unfortunately this lighter system was not so satisfactory as we expected .
The results were not concordant , and in some cases the observed torque was 50 per cent. greater than the theoretical value .
Although it seemed impossible to doubt that these experiments indicated a real agreement with theory , it was felt that a fuller experimental investigation of this case of refraction would not be without value .
With this object the experiment described in the present paper was planned some years ago , but other work has prevented its being carried out until recently .
The arrangement in the earlier experiments appeared to possess several defects .
Thus , in spite of the presumably small absorption of heat by the prisms , the disturbing action of the gas was quite evident .
This action was probably mainly due to the somewhat complicated form of the suspended system , since experience gained later with various forms of pressure of apparatus has shown that simplicity and symmetry in the suspended system greatly reduce .
also " " The Pressure of Light by J. H. Poynting , ' Romance of Science ' Serie* 1912 .
] Light in Obliqne through Plate .
the gas action .
Another objection is that , owing to the considerable distance between the prisms , there must have bee , n appreciable dispersion in the beam during its passage .
Also a very large correction had to be applied to allow for the four reflections in the system , and this correction was calculated by assuming the Fresnel formulae for the reflection coefficients .
Finally , it is now known that much greater accuracy could be obtained by hydrogen instead of air as the residual gas in the case .
IIIethod .
The desirability of doing away with the internal air space between the two } prisms , and necessity for symmetry , suggested to the author that the best form to adopt would be a perfect cube .
Let ABCD ( fig. 1 ) be the cube seen FIG. 1 .
FIG. 2 .
in plan , and let a uniform and parallel beam of hght fall on the one half AE of the face AB at such an angle of incidence that after refraction through the cube it emerges from the half ] of the opposite face .
The cube should then experience a torque in the direction shown by the arrow .
It is evident that the portions of the cube , AEG , CFH , correspond to the two prisms used in the earlier experiments This oement has the following advantages:\mdash ; ( 1 ) There is perfect symmetry .
It is easy to make the faces all truly vertical .
( 3 ) The optical path in the system is short .
( 4 ) There are only two primary reflections .
This correction is ooreatly reduced and can .
be calculated with more certainty than before .
( 5 ) By rotation all four faces may be used for incidence .
Any errors due to slight want of verticality will then be eliminated .
Dr. G. Barlow .
Torque oduced by of [ Mar. 27 , ( 6 ) No is required , as the faces of the cube can be used for observing the deflections .
This is an , as the attachment of even a small mirror will introduce a certain amount of dissymmetry , and therefore increase the sensibility of the apparatus to gas disturbance .
Description of the Apparatus .
A cube of crown glass was obtained from Messrs. .
Its were all 1 cm .
with an error of less than 1/ 100 mm. Four of the faces were optically worked , but the top and bottom surfaces were left rough ground .
The method of suspension is shown in fig. 2 .
An aluminium disc , of 1 cm .
diameter , was to the end of the axial brass rod B. Both disc and rod were accurately turned by a watchmaker .
The cube was then cemented to the disc by a small amount of shellac .
The upper end of the suspension rod was filed down so that the quart fibre could be soldered to it axially .
The experimental case , a gunmetal casting cm .
see was provided with plate glass windows on front and back , and with smaller windows A and at the ends of two lateral tubes .
The beam of light , entered by one of these tubes and left by the other .
Owing to the considerable length ( 20 cm .
) of the tubes , it was expected that any gas action due to warming of the windows by the the beam would be very greatly reduced .
The vertical tube was closed by a ground stopper to which was fixed a suspension rod for the attachment of the quartz fibre .
The stopper also carried an index so that angles of rotation could be measured on the divided circle E. The source of was an Ediswan -volt focus lamp\ldquo ; which was fed from accumulators .
By means of adjustable resistances in series with the lamp the was maintained at 60 volts to vithin1/ 10 volt , the lamp then taking a current of ) amperes .
A lens of focal length 15 cm .
formed an image of the lamp filament on an achromatic lens which had a focal length of 19 cm .
In front of was placed a specially constructed rectangular provided with regulating screws so tlJat all its edges could be independently adjusted .
The lens formed an image of this in a plane through the centre of the cube .
As the depth of focus was considerable the cross-section of the beam could be fairly well regarded as uniform through a distance of 1 cm .
the thickness of the cube ) .
In the ideal case the beam of light should be strictly parallel , whereas in the experiment the light formed a htly converging cone .
A circular diaphragm ( radius cm .
) at limited the semi-angle of the cone to less than .
The errors introduced by this effect and also by the 1912 .
] Light in Oblique Refraction through dispersion at refraction are evidently very small and therefore have not been taken into account .
The experimental case was first set up on a pier built up from the floor .
Much inconvenience was caused by the slight pendulum motion of the cube produced by vibrations in the building .
For the " " critical measurements\ldquo ; ( referred to in Table ) the apparatus was reset up on a very massive brick pier built up directly from the ground and separated from the floor by a narrow trench .
The observing telescope was clamped to the pier , and the deflections were read on a millimetre scale at a distance of 250 cm .
The definition was so good that 1/ 10 scale division could be estimated with certainty .
In the experiments in which the cube was rotated slight adjustments of the telescope were sometimes required , but the scale was nsver moved .
Some metal screens , not represented in fig. 3 , protected the case extraneous radiation .
Dr. G. Barlow .
Torque produced by Beam of [ Mar. 27 , Optical ustments .
In adjusting the beam of light three conditions have to be fulfilled : ( 1 ) The image of the diaphragm formed by the lens L2 must be in the plane containing the axis of the cube .
( 2 ) The cube must be set so that the beam falls on it at the required angle of incidence .
( 3 ) The beam must be adjusted to cover exactly one half face at incidence .
These adjustments were made as follows:\mdash ; ( 1 ) An auxiliary achromatic lens ( fig. 3 ) was placed behind the exit tube , so that an enlarged image of the cube was projected on a screen at J. The lens was then moved until the image of the diaphragm opened fully so that it could be seen above and below the cube ) was also in focus at J. During this operation the cube was strongly illuminated .
( 2 ) The cube was first set so that one face was perpendicular to the axis of the incident beam .
To do this a vertical slit of width 2 mm. was placed over the diaphragm , and a half-silvered plate was set obliquely in the path of the beam .
When the face of the cube was perpendicular to the light , the reflected beam passed back again ohrough the slit and was easily observed by placing the eye at , and looking into the half-silvered plate .
When the cube was the torsion head was until the instants of the illumination of the slit occurred at equal intel.vals of time .
After allowing the cube to come to rest a more exact adjustment was effected if necessary .
The reading of the torsion head was then observed and the head was rotated through , the required of incidence .
( 3 ) The slides of lihe adjustable were now slowly closed in until the image of the diaphragm illuminated exactly one half the face of the cube .
This adjustment was carried out with great ease and accuracy by observing the image formed on the screen , and also the images formed by the lenses and on the screens and R The top and bottom slides were first adjusted by looking at the image or ) J. For the laGeral adjustment , which is particularly important , use was made of the fact that when the beam was too wide an internal reflection in the cube rise to a bnght patch on the screen , and refraction at another face gave rise to a second bright patch on the screen J. The slides were closed in until these two patches of illumination just vanished .
The screen then showed only a single rectangular patch of brilliant illumination\mdash ; the image of the half face of the cube through which the beam emerged .
The actual deflection of the cube produced by the was less than and the amplitude of oscillation was generally of this order .
Hence the beam could be regarded as being always incident at sensibly the same angle , and therefore the torque exerted by the light could be taken as constant .
1912 .
] Light in Oblique Refraction through In fact observations of the deflections for various amplitudes of swing showed that no appreciable error could be attributed to any variation of couple with displacement .
The Gas Action .
It is well known that the disturbance , or " " gas action in air is generally at a minimum for a pressure of about 1 or 2 cm .
Hg .
The existence of this favourable pressure region taken advantagefof by Nichols and Hull in their experiments .
Below this pressure the gas action rapidly increases , and is then due almost entirely to the radiometer effect .
But above this critical pressure it has been shown by Ghat convection plays the chief and he proved that the action then depended very greatly on the inclination of the receiving surface to the vertical .
In the writer has observed a similar minimum of the gas action , which occurs also at the pressure of 1 or 2 cm .
Hg .
But in this gas the disturbance due to convection is always very much less than in air .
This fact , which does not appear to be widely known , that in all experiments where use is made of a delicate torsion balance it will be found of great advantage to work in hydrogen at a reduced pressure .
The exceptional behavionr of this gas is probably due to its great thermal conductivity .
In the experiments the range of gas pressure extended from atmospheric pressure down to cm .
Hg .
As had been anticipated , the apparatus proved to be remarkably free from the effects of convection , especially when hydrogen was used .
In this gas only minute changes in the centre of swing took place during any set of observations at a favourable pressure .
It was not until the pressure exceeded about 40 cm .
Hg that any appreciable disturbances occurred , and even then they were not very serious .
The radiometer action being always a pressure back on the surface heated , it follows that in the present experiment ( and also in the earlier experiments with prisms ) any radiometer action will tend to deflect the system in the opposite direction to the torque due to the light .
This will be seen by reference to fig. 1 , since the radiometer pressures on the areas AE and which we must suppose warmed by the passage of the beam , will produce a torque on the cube in the direction opposite to the arrow .
The actual observations confirmed this supposition .
For example , in hydrogen he deflection was nearly constant for pressures from 76 cm .
down to about 10 cm .
Hg , and the value of the deflection agreed closely with that expected from the pressure of light .
But below 10 cm .
the 'Phys .
Review , ' 1905 , vol. 20 , p. 292 .
Dr. G. Barlow .
Torque oduced by of [ Mar. 27 , deflection fell off , at first slowly , and finally very rapidly , as the gas pressure was reduced , until at the lowest pressure available ( about cm .
Hg the deflection had fallen to 1/ 40 of its original value , .
the radiometer action had almost compensated the torque due to the light .
There seemed no doubt that a further reduction in the gas pressure would have resulted in a reversal of the deflection .
Unfortunately , the apparatus was not suitable for .
at lower pressures , so the reversal could not be obtained .
The general behaviour in air was similar to that in hydrogen , but the measurements were not nearly so consistent .
Hence hydrogen was used in most of the experiments .
A curve showing the variation of the observed deflection with gas pressure in the case of hydrogen is given in fig. 4 ( see also Table I ) .
It 1o so FIG. 4 .
will be noticed that even up to such high pressures as 20 or 30 cm .
Hg the radiometer action was still sensible , as evidenced by the cvht slope of the curve .
The slope continues at higher pressures but the observations are not reliable in this region on account of convection .
It , therefore , appeared a little difficult to determi1le what value of the deflection should be taken as representing the action of light pressure alone .
But an inspection of the curve suggested that the radiometer effect was inversely proportional to the gas pressure over the range used .
This same law is also given by theory .
* Hence the deflection and the pressure should be related by the equation where is the required deflection due to light pressure alone , and is some constant .
* Osborne Reynolds , " " On Certain Dimensional Properties of Matter in the Gaseous State ' Phil. Trans 1879 .
1912 .
] Light in Oblique Refraction a The above relation was tested by plotting the product as ordinate against as abscissa .
This should give a line ( since not passing through the origin , and the slope of the line determines .
The resulting graph for the observations made in ( see fig. 5 , which is obtained from the critical determinations given in Table II ) showed so little deviation from a straight line that we may regard the relation as satisfactorily established .
The value of is best obtained phically by the slope of the line , but it can be calculated from any pair of deflections observed at , respectively , by means of the expression Both these methods have been used .
Measurement of the Deflections .
The observations were made on the following plan : apparatus was first exhausted as completely as possible , and dry gas was then admitted Below 3 cm .
Hg the gas pressure was determined by a small mercury Dr. G. Barlow .
Torque produced by Beam of [ Mar. 27 , manometer inside the experimental case , but the greater pressures were measured on an external manometer immediately before closing the stopcock of the case .
The process of admitting or pumping out , in order to change the pressure , generally caused the cube to vibrate with a considerable amplitude .
After allowing the oscillations to die down to a convenient amplitude , the " " damping ratio wing ) : ( swing ) , was determined by observing about fifteen successive turning-points .
In hydrogen was about , in air about , but the value varied ) htly with the pressure , so that it was necessary to determine it for each pressure used .
Knowing , the centre of swing can be determined from any two consecutive turning-points , , by the relation .
The centre of swing was thus calculated for every pair of successive turning-points for both " " on\ldquo ; and " " light off This method is particularly convenient in such cases as the present , where the value of is known very accurately , and where it is of importance to estimate the centre of in as short a time as possible , so that any ressive change 1Jlay be detected .
At each pressure a set of observations was taken as follows:\mdash ; ( l ) Light off ; three -points observed , two values of the centre of swing .
( 2 ) on for three turning-points .
( 3 ) Light off for three turning- points , and so on for four or exposures .
The conditions were varied as much as possible .
The was put on ( or cut off ) sometimes just before a turning-point and sometimes just after one .
lso in some cases the exposures were made for only two , and in other cases for more than three , turning-points .
Care was taken to avoid up a large amplitude of swing .
The mean centre was taken for each of the groups ( 1 ) , ( 2 ) , ( 3 ) , etc. , and the deflection for each exposure then calculated as the difference between the mean centre for the light on , and the mean centre for the two groups , with light off , on either side .
A few observations were made with exposures lasting for seven or eight turning-points ( i.e. over six minutes ) , but in no case was there noticed any appreciable influence of time of exposure on the deflection .
Also a few deflections were calculated by observing the first swing of the cube from rest when the beam was suddenly put on .
These were in close agreement with the other values .
The turning-points were read with certainty to of a millimetre scale division .
The error in the calculated centre of swing was then probably not more than of a division , and in .
the mean of a number of observations the error should be still less .
On this account the final values of the deflections are given to of a scale division , but this last figure is uncertain .
An inspection of the tables appears to show that the 1912 .
] Light in Oblique Refraction through Glass uncertainty in this figure does not amount to more than one or two units for the determinations at favourable gas pres , sures .
Therefore the deflection , which is of the order of 5 mm. , can be regarded as measured to within 1 per cent. But differences greater than 1 per cent. were sometimes found when the observations were separated by several hours , and it seemed probable that slight changes in the intensity of the light may have affected the deflections .
Calculation of the Cube , ( iorrections for the Reflections .
Let edge of cube cm .
mean refractive index for white light angle of incidence angle of refraction The condition for the symmetrical transmission of the beam is that .
This ives r , and is then found from : The numerical values are given above .
Let total energy per unit of the incident beam measured in .
First , suppose that is transmitted without loss by reflections .
We have then a single torque on the system , and the arm of this torque is equal to the perpendicular distance of from the ray incident at the point ( see fig. 1 ) .
Hence Arm cm .
Torque When we take reflections into account , it is convenient to regard separately all the beams , incident , reflected , and transmitted , and to calculate the moment of each about the axis .
We have then ( see which shows the course of the central ) FIG. 6 .
Dr. G. Barlow .
Torque prodnced by a Beam of [ Mar. 27 , ( 1 ) The incident beam on the face .
The moment due to its reception is , where denotes half the arm given above .
( 2 ) A beam reflected from AE at incidence .
It can be shown that this will have arm , and gives a moment ( 3 ) A beam is internally reflected from .
It then falls on BC , is totally reflected at this face , and finally issues as a slightly diminished beam , , from the face .
Its direction is parallel , but opposite to that of the original beam , and it will have the same arm as that last considered .
Hence the moment due to it is ( 4 ) The transmitted beam of intensity .
This gives a moment Adding all these four effects together , we have the total torque on the cube given by The small fraction of the original beam is internally reflected at , but this may be left out of account .
A calculation showed that , even if this beam followed the theoretical path , it would not affect the total torque by more than per cent. Owing to imperfect parallelism in the beam , and the consequent scattering , its actual effect must be even less .
In the above calculation , it is assumed that there is no rption of by the cube .
In the experiment the ption was probably very small , since the beam had previously passed through a thickness of several centimetres of glass .
It may be noticed , however , that complete absorption would only reduce the torque to about half its value , so that , even if the absorption of energy were 1 per cent. of the whole , the error produced in the torque would be much less .
The coefficients , were calculated from Fresnel 's formulae for reflection .
The partial polarisation produced in the successive reflections was taken into account .
The following values were found:\mdash ; cm .
, , ; and subQtitution in the above expression gave Torque This is 10 per cent. less than the value given above for the ideal case of transmission without reflection .
In expressing the results of the experiments the method followed has been to compare the observed scale deflection ( corrected for radiometer action 1912 .
] Light in Oblique Refraction through Plate .
as explained above ) with the scale deflection which should theoretically be given by the beam .
The value of is calculated from the relation where scale distance , 2500 mm. dyne-cm .
, the torsion couple per radian for the fibre .
The constant was calculated in the usual way from the period , sec. , of the cube and the moment of inertia , .
cm.2 , of the system .
To obtain the last quantity the moment of inertia of the cube itself was calculated from its mass and dimensions , and to this was added the moment of inertia of the suspension rod , which was determined experimentally .
Determ of the EnerrJy of the The method is essentially the same as that adopted by Nichols and Hull and since used by Prof. Pointing and the writer in other experiments on the pressure of light .
The beam was allowed to fall on a blackened disc of pure silver diameter , thick ) , and the initial rate of rise of temperature of the disc was observed by means of a constantan-silver thermo-junction soldered to the back .
A Rubens " " Panzer\ldquo ; galvanotneter was used ; this was adjusted to have a period of about two seconds , and was then made dead beat .
The transit of each scale division across the spider line of the telescope was recorded on the drum of an electricallydriven chronograph .
A separate pen actuated by the laboratory clock simultaneously recorded seconds on the drum .
It was then possible by means of a graphical representation of the chronograph record to calculate , the rate of change of galvanometer deflection .
The number of microvolts per scale division of the galvanometer was determined with a cadmium cell and standard resistances .
The thermo-electric power of the couple was known from a separate investigation .
energy in unit length of the beam was then calculated from where is the thermal capacity of the disc , is the " " mechanical equivalent is the velocity of light , and is the fraction of the incident light not absorbed by the disc .
The optical system ( see was mounted firmly on a base which could be rotated in order to direct the beam on to the silver disc .
Measurements of the energy were made at the end of each complete set of readings Dr. G. Barlow .
Torque produced by a of [ Mar. 27 , of the cube deflections .
The mean of several consecutive energy determinations was always taken .
The silver disc was placed in a very massive cylinder of iron which served as a constant temperature enclosure .
The beam was admitted through a window of glass cut from the same sheet as the window of the experimental case .
Before the disc to the beam the rate of of galvanometer deflection was observed , but it was generally so small that it could be entirely neglected .
Some uncertainty in the determination of the energy is due to the absorption coefficient , , of the platinum black surface of the silver disc .
This coefficient has been assumed to have the value for the quality of the light used .
This is not likely to be far from the truth , but an error of 1 or 2 per cent. may possibly exist .
Experiments with an improved form of receiver are bein undertaken .
The Results .
A summary of the final results is given in Iable .
It will oe seen that there is a general tendency for the observed deflection to be slightly greater than the value calculated from the energy .
The difference is from 1 to 2 per cent. in the hydrogen experiments , and considering the difliculties in determining the absolute value of the energy this agreement may be considered satisfactory .
The experiments in ai show reater deviations , but the measurements were obviously much less reliable than those in hydrogen , so that no great weight must be attached to them .
Fuller details of some of the series of observations are given in Tables I , II , and III .
The values in Table I are also represented graphically in fig. 4 .
Table III contains a set of observations in which all four faces of the cube were used in turn for incidence , and it is seen that the mean deflection for any face does not differ by more than 1 per cent. from the mean for the four faces .
Except in the two series A and , the same face ( that denoted Table I.\mdash ; Variation of Deflection with Gas Pressure in .
( Series B. ) The value of is the mean of 3 to 6 determinations .
cm .
Hg .
cm .
Hg .
cm .
Hg .
cm .
Hg .
in scale divs .
3.44 0.55 to 0.1 From these results the raphical method gives 1912 .
] Light in Oblique Refraction through Glass by ( 1 ) in Table III ) was used for incidence in all experiments .
face , at least for the higher gas pressures , generally gave a deflection about 1 per cent. in excess of the mean .
On this account the values of for the and in Table should perhaps be reduced by about 1 per cent. , and this correction is in the right direction to bring about closer agreement .
Table II.\mdash ; Variation of Deflection with Gas Pressure in Hydrogen .
( Series E. ) From these results the graphical method.gives Torque produced by Light in Oblique Refraction .
Table III.\mdash ; Deflections in using the Four Faces of the Cube .
( Series F. ) From these two values of the formula ives ) ) ) .
Table cRange * This value has been corrected for radiometer action by applying a factor obtained from the later series .
" " Critical determinations\ldquo ; made after the apparatus had been re-set up .
We may therefore conclude that the oblique passage of a beam of light through a plate of refracting material produces on the matter of the plate a torque which has the magnitude deduced from the transfer of momentum in the beam .
|
rspa_1912_0055 | 0950-1207 | The transformations of the active deposit of thorium. | 17 | 29 | 1,912 | 87 | Proceedings of the Royal Society of London. Series A, Containing Papers of a Mathematical and Physical Character | E. Marsden, M. Sc.|C. G. Darwin, B. A.|Prof. E. Rutherford, F. R. S. | article | 6.0.4 | http://dx.doi.org/10.1098/rspa.1912.0055 | en | rspa | 1,910 | 1,900 | 1,900 | 10 | 180 | 4,540 | http://corpora.clarin-d.uni-saarland.de/surprisal/6.0.3/?id=rspa_1912_0055 | 10.1098/rspa.1912.0055 | null | null | null | Atomic Physics | 56.108016 | Tables | 18.411391 | Atomic Physics | [
1.880496859550476,
-80.0666732788086
] | ]\gt ; The Transformations of the Active Deposit of Thorium .
By E. MARSDEN , M.Sc .
, John Harling Fellow , and C. G. DARWIN , B.A. , leader in Mathematical Physics , University of Manchester .
Communicated by Prof. E. Rutherford , F.RS .
Received Apri12 , \mdash ; Read May 9 , 1912 .
) The present paper is concerned with a series of experiments undertaken with a view to discovering the genetic arrangement of various products of the active deposit of thorium .
The main part of the paper deals with the nature of the transformations which take place in the product or products generally included under the name thorium C. These transformations are of unusual interest and importance , for it will be seen that there is undoubted evidence in this case that the atoms of a single kin of matter have two distinct modes of disintegration .
The nomenclature adopted will be based on that given by Rutherford an Geige is as follows:\mdash ; Product . .
Th Em .
\mdash ; Th \mdash ; Th \mdash ; \mdash ; Th Radiation. .
and As a result of our experiments , however , we find that of the atoms of thorium , some , which we shall denote by , give -particles of range ' cm .
; and some , which we denote by , give -rays .
Further , our results suggest that the atoms rise on disintegration to the -ray product generally known as thorium , while the atoms disintegrate into a very short-lived -ray product thorium Thus our corresponds to the product given above as , while our corresponds to the parent of suggested by Marsden and Barratt , and called in their paper .
In what follows , when we speak of thorium , we shall mean the combined and .
Thorium will also generally include , owing to the very short period of the latter .
In the active deposit of thorium the doubtful question has been the relationship of the two -ray products and .
That one is not the parent of the other is shown by the recoil experiments of Hahn and MeitnerI who proved that if this were the case the second of the products must have 'Phil .
Mag 1911 , vol. 22 , p. 621 .
'Marsden and Barratt , .
Soc. Proc , vol. 24 , p. 50 ; 'Phys .
Zeitschr 1912 , , p. 19\amp ; Hehn and Meitner , ' Deutsok Phys. Ges 1909 , p. 55 .
VOL LXXXVn .
Messrs. E. Marsden and C. G. Darwin .
[ Apr. 2 , a period less than a few seconds , and the experiments of one of us in conjunction with Geiger and Barratt , *which showed that the second product could not have a very short period .
Comparing the number of -particles from the active deposit with that from the emanation , and Geiger and showed that the latter ives twice as many as the former .
As the emanation includes a second product , the short-lived thorium , this allows only one -particle for the active deposit .
Barratt and one of us found that for every short range -particle thorium there occur of long range ( thorium cm As the simple disintegration theory requires that successive products give the same number of -part.icles , this result indicates a branch point in the family in which 35 per cent. of the atoms -particles of cm .
range , and 65 per cent. give parti-cles of cm .
range .
The experiments we have undertaken were designed to elucidate how this branch occurs .
They may be divided as follows:\mdash ; ( 1 ) Examination of magnetic spectrum of the -particles from thorium active deposit .
2 ) Attempts to separate thorium and thorium ( 3 ) Examination of the origin of the and -rays emitted by the active deposit .
( 1 ) nation of Magnetic Spectrum .
A wire was made active by exposing it to the emanation from a strong source of meso-thorium .
The -particles from this wire after passing through a thin sheet of mica to in , crease the ratio of their emergent velocities and ough a fine slit placed parallel to the wire , were deflected in a strong magnetic field and fell on .
zinc-sulphide screen , the whole apparatus being evacuated .
Countings of the numbers of scintillations were made at different points of the screen .
The resulting curve of distribution for a parti.cular experiment is shown in fig. 1 , where A represents the Bronson , ' Phil. Mag 1908 , vol. , p. 291 .
Geiger } Marsden , ' Phys. Zeitschr 1910 , vol. 12 , p. 7 .
Messrs. E. Marsden and C. G. Darwin .
[ Apr. 2 , Von Lerch* has shown that the various products of the active deposit of thorium can be separated by electrolysis or by dipping plates of nickel , etc. , into the solution of the active deposit .
Von Hevesy has recently extended these results , and has shown that when a metal plate is dipped into a solution of the active deposit the relative amounts of the products which are deposited on it depends on its electro-chemical potential with oegard to the solution .
Thus nickel deposits practically pure thorium in acid solution , while zinc , being strongly electro-positive , becomes coated in neutral solution with thorium , together with only about 20 per cent. of its equilibrium amount of thorium C. Other metals , such as copper and cadmium , give intermediate ratios of the two products .
If thorium exists , we might therefore expect to separate it from thorium by plates of various electro-chemical potentials in solutions of the active deposit , and comparing the ratio of the numbers of -particles emitted of ranges and cm .
To make this comparison we employed the same method as was used in the comparison of the rise curves , i.e. by comparing the leaks in an -ray electroscope when the source was covered with tinfoil sufficient to stop the cm .
range particles , and when the source was bare .
The ratio was in every case the same , and equal to that for ordinary thorium active deposit .
Again , the rate of decay of the activity of a nickel plate , dipped in a solution of the active deposit , was the same bare and covered , while the rise curves of the activity of a zinc plate were exactly similar .
We have also obtained thorium by recoil from the -ray product , thorium , and found that the ratio of the numbers of -particles with the different ranges was the same as for the ordinary active deposit in equilibrium .
No separation of and could be obtained in experiments in which the active deposit was heated to various temperatures up to 100 C. , this temperature being higher than the volatilisation points of either thorium or thorium C. ( 3 ) Examination of and -rays .
The foregoing ents having entirely failed to separate the -ray products , an investigation of the -rays was made .
Assuming the rule of Geiger and Nuttall to hold good , we have seen that it is necessary to assume the existence of a parent for thorium which we have denoted by .
This hypothetical substance cannot emit -rays , and we therefore tested for -rays .
The -rays of thorium active deposit have been shown by various investi- * Von Lerch , ' Wien .
Ber 1906 , vol. 114 , p. 18 .
Von Hevesy , ' Phil. Mag 1912 , vol. TransfOrmations of the Active osit of Thorium .
gators* to .
consist of two sets , slow -rays from thorium and relatively hard swift -rays generally attributed to thorium D. We need only consider the latter in testing for rays from thorium Ce , and we have , therefore , compared the absorption curve of the -rays from thorium with those from pure thorium D. Thorium was obtained by von .
Lerch 's method , a nickel plate being dipped in a hot hydrochloric acid solution of the active deposit .
In these conditions with carefully polished plates we were able to obtain pure with practically no thorium B. Before taking the absorption curves a sufficient time was allowed to elapse after taking the plate from the solution for the thorium and to attain equilibrium .
Pure thorium was obtained by recoil from a plate coated with the active deposit .
In comparing -ray absorption curves we used exactly similar conditions , the active plates being similar circular discs of nickel .
The base of the -ray electroscope was covered with aluminium foil equal in stopping power of -rays to about 9 cm .
of air , so that the -particles could not penetrate into the electroscope .
Aluminium foils for determining the absorption of the -rays were placed in a frame beneath the electroscope in such a way that their positions could be rapidly and exactly reproduced .
The active plates fitted into a special slot almost directly beneath the aluminium foils .
In calculating the absorption curves alowance for decay of the source was made by taking alternate readings with different foils and afterwards correcting by means of logarithmic curves .
The rates of leak were corrected for natural leak and also for -rays , which were determined by placing lead over the source sufficient to stop all the -rays .
he results are plotted in curves and ( D ) shown in , the absorption curve of the -rays from the whole active deposit being also given for comparison .
It is apparent from an inspection of the curves that the rays from thorium are more penetrating than those from thorium esting that thorium may exist and emit -rays still more penetrating .
In any case the results show that penetrating -rays must be attributed to thorium C. We will now consider the growth of thorium , from thorium C. In the experiments of von Lereh and Wartburg , in which thorium was separated by electrolysis or on nickel with an exposure for a very short period , it was found that the -ray activity rose with time for about 10 minutes before * Won Lerch , ibchr 1906 , vol. 7 , p. 913 ; Hahu and Meitner , 'Phys .
Zoibhr , ' 1908 , vol. 9 , ; A. F. Kovarik , 'Phil .
Mag 1910 , vol. 20 , p. 849 ; H. iger and A. F. Kovarik , ' Phil Mag 1911 , , p. 604 .
Von Urch and Wartburg , Yien .
Rr 1909 , vol. , p. 1675 .
the nickel plate and if thorium does not give -rays .
Von Lerch assumed .
as seemed very reasonable , that some thorium was deposited on the plate along with the tholium but in less quantity than the equilibrium amount .
In view of our experiments , however , it is possible that the initial activity may be partly or wholly due to -rays from thorium Q. If this is the case , and if the -rays of thorium are harder than those of thorium , we should expect that when the rise in activity is measured through a fairly thick layer of aluminium foil there should be a smaller rise than in the ordinary case , owing to the more penetrating.rays becoming a more important factor .
We have therefore made these experi ents , a nickel plate being .
in a 1912 .
] Transformations of the Active Deposit of Thorium .
23 solution of thorium active deposit for about half a minute ( i.e. sufficient time to get a reasonable activity ) and rapidly transferred to the electroscope for measurement .
The rise in activity in a particular experiment is shown in fig. 3 , readings being taken alternately with no absorption foils ( ) and with absorption foils equal to cm .
aluminium .
It will be seen from the curves that our assumptions are justified .
We have mentioned above that , in deducing the absorption curves of thorium and thorium , we corrected for the -ray leaks .
It was uoticed that , while the -ray effect in the case of was only per cent. of the -ray effect , yet in the case of thorium it was per cent. * This suggests that thorium gives more -radiation than thorium C. We have therefore repeated the above experiments with -rays , the variation of -ray activity with time being observed for a nickel plate dipped in active deposit solution for half a minute .
A difficulty was experienced in the small amount of activity obtainable , a specially large -ray electroscope being necessary .
The result of a particular experiment is shown in fig. ( ) , and it will be seen that the -ray activity rises from a very small initial value , indicating that practically the whole of the -radiation comes from thorium , and that very little thorium is deposited on the plate along with the thorium C. The foregoing rise curves by and -rays were analysed , and expressed , where amount of iouisation at time and * It nlAy be of interest to note that for pure radium the ratio under the was per cenh See Rutherford , ' Radioaclivity , ' 2nd Edition , p. 330 Messrs. E. Marsden and C. G. Darwin .
are constants , and and are the transformation constants of thorium and thorium respectively .
An inspection of the equation will show that , if the whole effeot were due to thorium would be equal to 1 , while , if the whole activity were due to would be infinite .
Intermediately , the larger is , the smaller the fraction to be attributed to D. Table I gives the values of in several experiments .
The values taken for and are and respectively .
During the course of the various experiments , we have made a large number of measurements of the periods of .thoriumB , , and D. The mean values found are hours , and minutes respectively .
These values are in good agreement with those of other observers , and are probably correct to less than 1 per cent. It will be noticed that the values vary slightly in different experiments .
Apart from the errors of measurement , this is probably due to variations in the electro-chemical potential of the nickel plates , although considerable care was taken in the polishing before each experiment .
Thus , in different experiments , there would be variations in the small amount of initially present .
Thorium seems to be electro-chemically very similar to thorium B. Cases in which was found to be present on the nickel plates were also cases in which the curves rose from a somewhat high initial value , while we were able to deposit thorium on a zinc plate from a solution of , and this is an electro-chemical property of thorium B. Recoil of Thorium from Thorium Before considering more fully the deductions to be made from the above experiments , it will be convenient to describe some experiments on the recoil efficiency of thorium from thorium C. A metal plate was aotivated with the active deposit by exposure to the emanation .
The recoil thorium was obtained from this plate on a second plate , placed about 1 mm. from it in air , and at a negative potential of 200 volts .
It was found that , measuring by -rays , 31 per cent. the activity of the souroe could be 1912 .
] mations of the Active Deposit of Thorium .
25 transferred to the oecoil plate , while measured by -rays the ratio was only per cent. , which was equal to per cent. when corrected for the soft -rays of thorium B. Special ments showed that no appreciable radiation comes from thorium , and , assuming that thorium does not give -rays , it can easily be calculated from these ratios that thorium must give about times as much -radiation as the thorium in equilibrium with it .
The importance of this ratio ( below called ) will appear later .
Interpr.etation of Results .
To interpret the results so obtained we must proceed by a more accurate analysis .
The evidence of the -particles proves conclusively that tbere is a branch at thorium and prescribes a ratio 65 : 35 for its two members .
It is clearly reasonable to suppose that thorium comes from either one or other or both of these branches , while the same applies to the -rays of C. Let us then suppose that a fraction of thorium gives -rays and a fraction ultimately becomes thorium , where and may have any of the values , or .
Considering the foregoing rise curves of thorium from thorium the amounts of the products present at any time are given by the equations ; The nickel plate sometimes takes a certain amount of thorium out of solution .
Let this be a fraction of the equilibrium amount , that is for every atom of there is of thorium initially on the plate .
time then No Let be the -ray ionisation effect in the electroscope of a single disintegrating atom of thorium , and let be the corresponding quantity for that fraction of thorium which gives -rays .
Then the curve that will be observed in the electroscope is The quantity above called is thus whence Messrs. E. Marsden and C. G. Darwin .
[ Apr. 2 , In exactly the same way for the -rays , Taking corresponding selected values of from Table I , we obtain in the case of -rays , by substituting ; Supposing to be the same in the -ray experiments we can now substitute its extreme values and and , putting in the value of , we get lies between and This ratio being known within fairly narrow limits , it is a very simple matter to deduce the absorption curve of pure thorium from those of and D. The curve is shown in fig. 2 .
The absorption coefficients corresponding to the curves , and are and c respectively .
Geiger and Kovarik* give a value for , the difference being probably due to experimental arrangement .
Assuming the values to be proportional , the absorption coefficients of thorium and thorium under their standard conditions would be and c aluminium respectively .
We now consider the deductions to be derived from the value of .
An estimate of this ratio may also be obtained , as will be seen above , from recoil efficiency of and -rays .
The best value from the combined experiments appears to us to be about .
We must determine what are the best values bo choose for and .
Lt us assume that an atom of thorium gives the same number ( probably one ) of -particles as the -radiating atoms of thorium C. The rays from thorium are distinctly harder than those from thorium , and we might therefore expect to be somewhat less than unity .
Prof. Butherford has kindly informed us that , as the result of some unpublished calculations , he finds that the ionisation produced by equal numbers of -particles varies with the coefficient between the square and cube root .
Taking the 2/ 5 power , should be and may have any of the three values , , or and of the nine possible combinations two give results near the observed .
These are , which gives , and , which gives .
The latter value agrees best with the experimental result , , and also leads to more simplicity in interpretation .
Thus , of the atoms of thorium .
cit. Marsden and Barratt , 1912 .
] Transformations of the Active Deposit of Thorium .
35 per cent. give -rays of range cm .
, and ecome atoms of thorium D. The remaining 66 per cent. of the atoms give very penetrating -rays , and become atoms of thorium .
If our assumptions are justified , the following equivalent schemes show the process diagrammatically.* In the second scheme and do not denote different substances , but the same substance breaking down in two different ways .
This arrangement satisfies all the and -ray conditions .
It , satisfies the conditions of Geiger and Nuttall 's empirical rule .
It also } satisfies the experiments of Geiger and Kovarik on the numbers of -particles from the various products , for there are as many -radiating atoms as -radiating atoms in thorium , and their results can explained by assuming that and give one -particle each per disintegrating atom .
With regard to the final products , they are probably inactive .
A plate .
was exposed for two weeks to the emanation from the strong meso-thorium preparation .
At the present time , after a period of six months , there is no detectable activity on the plate .
The atomic weight of thorium is *Note added , 1912.\mdash ; In a recent number of the 'Physikalische Zeitschrift ( 1912 , vol. 13 , p. 264 ) , Baeyer , Hahn , and Meitner have given details of the magnetic spectrum of the -rays of the various thorium products .
They show that givea some very slow -rays with velocities and the velocity of light , the rays giving -defined lines in the spectrum .
Prof. Rutherford has shown that hne spectra of -rays are generally associated with -rays ( ' Manchester Lit. and Phil. Soc 1912 ) , that these slow -rays probably oome from Th D. In the above experiments these slow -rays would be totally absorbed by the foils required to cut off the -rays , and they would not produce ionisation in the electroscope .
Hence , if there are a considerable fraction of such -rays , our conclusions on the ratio found for may require slight modification .
Geiger and Kovarik , 100 .
, ' Phil. Mag 1911 , vol. 22 , 28 The sformations of the Active Deposit of Thorium .
and subtraeting six times the atomic weight of helium from this number for the -particles from thorium , radio-thorium , thorium X , thorium emanation , thorium , and thorium we obtain a number very near to the atomic weight of bismuth .
There appears to be little chemical evidence , however , for assuming bismuth to be a final product .
With regard to the and -radiations it is very remarkable the very penetrating -rays of thorium are not accompanied by -radiation , while the relatively soft -rays of thorium accompany an intense radiation , which is the most penetrating known .
It can be calculated that there is probably more than six times as much energy in the -rays of thorium :as in its -rays .
It is possible to regard the branching in two different ways , and this may ultimately throw light on the fundamental nature of radioactive change .
In ordinary processes the characteristic quantity measured is the transformation constant .
The most significant way of regarding this constant is as the chance that an atom will break down in any second .
Now in the present case there are two modes of transformation .
It is possible to suppose that the fundamental fact is the breakdown of the atom , for which there is a probability , and that this breakdown is succeeded by a secondary effect , the expulsion of a particle either or ; or we may ( suppose that there is a chance that any atom shall emit an -particle and thereby break down , and an independent chance that the atom gives particle causing a breakdown .
It would require and ; and the two ways of regarding the matter could not be tdistinguished by any experiment .
However , the two conceptions lead to different values of the transformation constant of the atoms which give the -particles , namely , and .
If the empirical relation between range and transformation constant given by Geiger and Nuttall can be established accurately , and if it can be regarded as holding for the above type of disintegration , it should be possible to predict the transformation constant corresponding to a range cm .
If this comes to then the basal fact radioactivity is the atomic breakdown and the radiation is secondary , but if it comes to then the emission of a particle actually is the fundamental event in radioactive change .
The ranges of the -particles of the thorium products are , however , not yet known with sufficient accuracy for purpose , as we should require them within about one third of a millimetre .
*Cf .
Soddy , ' Phil. Mag 1909 , vol. 18 , p. 739 .
On the Formation of a Reversible Get .
Summary .
1 .
By magnetic deflection of the -particles from thorium active deposit the result of Marsden and Barratt , that the -particles of cm .
and cm .
range do not occur in equal numbers , has been confirmed .
2 .
Chemical , physical and recoil experiments alike failed to separate the atoms giving the -particles of the two different ranges .
3 .
The experiments show that thorium emits very penetrating -rays practically unaccompanied by -rays , while thorium gives relatively soft -rays with intense penetrating -rays .
4 .
The results suggest that of the atoms of thorium , 35 per cent. emit particles of range cm .
and become converted into atoms of rium .
while the remaining 65 per cent. emit -particles and disintegrate into atoms of a very short-lived -ray product thorium ( range cm We wish to our indebtedness to Prof. Rutherford for his ever ready advice and encouragement .
On the Formation of Heat-Reversible Gel .
By W. B. HARDY , F.B.S. ( Received April ll , \mdash ; Read May 16 , 1912 .
) In the course of his study of the cyclic ketonic compounds , ) .
Ruhemann has discovered a substance which is , I think , destined to play an important part in the development of the theory of gelation .
The substance is 5-dimethylaminoanilo-3 : 4 diphenylcyclopentene-l : 2 dione , * the formula being It is a solid at ordinary temperature , and occurs either as orange-coloured needles or as small dark red plates ; the separate from dilute solutions , the latter from ooncentrated solutions in absolute alcohol .
' If a little water is added to the hot alcoholic solution , no crystals mann and Naunton , Chem. Soc. Trans 1912 , vol. 101 , p. 42 .
|
rspa_1912_0056 | 0950-1207 | On the formation of a heat-reversible gel. | 29 | 37 | 1,912 | 87 | Proceedings of the Royal Society of London. Series A, Containing Papers of a Mathematical and Physical Character | W. B. Hardy, F. R. S. | article | 6.0.4 | http://dx.doi.org/10.1098/rspa.1912.0056 | en | rspa | 1,910 | 1,900 | 1,900 | 10 | 190 | 4,576 | http://corpora.clarin-d.uni-saarland.de/surprisal/6.0.3/?id=rspa_1912_0056 | 10.1098/rspa.1912.0056 | null | null | null | Biochemistry | 35.882644 | Chemistry 2 | 21.407696 | Biochemistry | [
2.121429443359375,
-79.12830352783203
] | On the Formation of a Heat-Reversible Gel .
Summary .
1 .
By magnetic deflection of the a-particles from thorium active deposit the result of Marsden and Barratt , that the a-particles of 4'8 cm .
and 8'6 cm .
range do not occur in equal numbers , has been confirmed .
2 .
Chemical , physical and recoil experiments alike failed to separate the-atoms giving the a-particles of the two different ranges .
3 .
The experiments show that thorium C emits very penetrating / 3-rays ( / 1 = 13*5 cm.-1 Al ) practically unaccompanied by 7-rays , while thorium I\gt ; gives relatively soft / 3-rays ( / / .
= 2P5 ) with intense penetrating 7-rays .
4 .
The results suggest that of the atoms of thorium C , 35 per cent , emit a-particles of range 4'8 cm .
and become converted into atoms of thorium Dr while the remaining 65 per cent , emit / 3-particles and disintegrate into atoms , of a very short-lived a-ray product thorium C2 ( range 8-6 cm .
) .
We wish to acknowledge our indebtedness to Prof. Butherford for his ever ready advice and encouragement .
On the Formation of a Heat-Reversible Gel .
By W. B. Hardy , F.R.S. ( Received April 11 , \#151 ; Read May 16 , 1912 .
) In the course of his study of the cyclic ketonic compounds , I)r .
Ruhemann has discovered a substance which is , I think , destined to play an important part in the development of the theory of gelation .
The substance is 5-dimethylaminoanilo-3 :4 diphenylcyclopentene-1 : 2 dione , * the formula , being c6h5c\#151 ; c : nc6h4n(ch3)2 c6h5c CO \o It is a solid at ordinary temperature , and occurs either as orange-coloured needles or as small dark red plates ; the former separate from dilute solutions , the latter from concentrated solutions in absolute alcohol .
" If a little water is added to the hot alcoholic solution , no crystals * Ruhemann and Naunton , 'Chem .
Soc. Trans. , ' 1912 , vol. 101 , p. 42 .
[ Apr. 11 , Mr. W. B. Hardy .
separate on cooling , but the whole sets to a transparent jelly , which , according to concentration , is yellow or yellowish-red .
This gel , when kept at the ordinary temperature , gradually liquefies , and in the course of one or two days completely disappears , with separation from the resulting solution of the azomethine in orange needles .
" Dr. Ruhemann has therefore furnished us with a substance which offers special facilities for studying the relations between the crystalline and the colloidal state .
The colloidal characters do not appear in any of the substitution products of the azomethine which have been prepared .
They completely disappear when a single hydrogen atom is displaced by , e.g. , bromine .
Why so small a .change in the molecule should cause the complete disappearance of such striking physical characters is an important problem , which I understand Dr. Ruhemann is investigating .
I have to thank Dr. Euhemann for his kindness in providing me with a small quantity of the azomethine , and for allowing me the opportunity of examining the remarkable changes of state .
In the following pages is given an account of a purely qualitative study .
Influence of the Solvent.\#151 ; The action of water in promoting the change of solutions in alcohol to the colloidal state ( and I may also add solutions in aldehyde and glacial acetic acid ) led the authors to suggest that the phenomenon is accompanied by the formation of a hydrate , which spontaneously loses water , and so yields the original compound in the crystalline form .
My own experiments prove that , if water be necessary for the .change , the most minute traces are sufficient .
I found it easy to obtain a gel at 10 ' with a good sample of absolute alcohol , provided the solutions , made at the boiling point of the alcohol , were sufficiently concentrated .
Wrater lowers the concentration of solute needed for gelation .
It was immaterial whether red or orange crystals were used for making the solution .
The substance is completely insoluble in water , which , therefore , may be said to act by lowering the degree of super-saturation needed for gelation , which occurs only in solutions supersaturated with respect to crystals .
In unit volume the added water displaces so much alcohol , and combines with some of the alcohol actually present , and so in both ways increases the mass ratio of solute to alcohol .
Water also delays crystallisation , and thereby alters the time relation in such a way as to make it easier to reach the limit of overcooling , at which gelation occurs without deposition of crystals .
This is especially seen when ether is the solvent .
More rigorous experiments to eliminate water are the following:\#151 ; Absolute alcohol , prepared by standing on calcium chloride for a week , and prolonged boiling with calcium chloride under a vertical condenser , and 1912 .
] On the Formation o f a Heat-Reversible Gel .
subsequent distillation , was again kept over a large quantity of freshly fused chloride for a week .
It was then distilled slowly , the first quantity to come over being rejected , and the middle portion received directly , with exclusion of air as far as possible , into a quartz test-tube , which had been strongly heated , and allowed to cool in a desiccator .
Crystals of azomethine which had been exposed to an air current for four hours at 120 ' were at once added , and a solution made by heat , but without boiling .
In three minutes the solution was poured off the remaining crystals into another dry quartz tube , and placed in a freezing mixture of ice and salt .
It at once set to a firm gel .
Ethylicether made anhydrous by distillation from sodium and exposure to a large surface of sodium for a week was then tried in a similar way , but as the substance is only slightly soluble in ether it was necessary to concentrate by rapid boiling .
When the solution saturated at the boiling point of ether had been concentrated to one-third its volume it was placed in the freezing mixture and gelation occurred .
Carbon tetrachloride is a very good solvent for the substance and deep orange-red solutions are readily obtained .
This solvent is immiscible with water .
A solution made in a dry quartz tube of red crystals with solvent which had stood for 48 hours over a large excess of freshly fused calcium chloride gave a firm gel in a freezing mixture .
The most probable conclusion from these and similar experiments with other solvents is that water is not necessary .
With the help of a freezing mixture a gel has been obtained from solutions in ethylic alcohol , ethylic ether , aldehyde , acetone , carbon tetrachloride , carbon bisulphide and glacial acetic acid , and , doubtfully , in chloroform and benzine .
The substance is insoluble in the paraffins ( petroleum ether ) and in water .
Some of the solvents which give gels are associating liquids , that is to say the liquid molecule is a complex of simple molecules , * others are not .
Gelation occurs at least as readily in carbon tetrachloride , which does not associate , as it does in alcohol , w'hich is an associating liquid .
An important negative conclusion follows , namely , that gelation is not founded upon an intrinsic tendency of the solvent molecules to form complexes amongst themselves .
Nor , if the view of the mechanism of solution put forward by Walden and Abeggf be accepted can gelation be traced to the association of solute molecules with molecules of solvent , for , according to this view , such associations occur only in solvents which themselves associate and do not occur in non-associating solvents .
From whatever point of view it be regarded the slight influence exerted by the molecular state of the solvent is remarkable * Ramsay and Shields , ' Phil. Trans. , ' 1893 , p. 647 .
t ' Zeits .
f. An.org .
Chem. , ' 1904 , vol. 29 , p. 330 .
Mr. W. B. Hardy .
[ Apr. 11 , and unexpected .
The process of gelation and the curious structural features of the gels are the same in solvents of both types .
All the gels examined liquefy on standing with deposition of crystals .
The change occurs at room temperature ( 15 ' ) in a few minutes from an ether gel , a few hours from gels of absolute alcohol or aldehyde , and in some days from a carbon tetrachloride gel .
The presence of water delays the liquefaction of the gel , that is it stabilises the gel state so that gels of aldehyde water and alcohol water may persist for days .
Sooner or later at about 15 ' the gel liquefies ; it is , therefore , at this temperature labile to the system saturated solution-crystals .
At temperatures below say +5 ' the gels change very slowly .
At higher temperatures the gel melts and will set again on cooling .
If it remains melted crystallisation rapidly occurs .
Above a certain temperature gelation will not occur at all , but crystallisation occurs direct .
The limiting temperature rises as concentration of solute increases .
For instance , , alcohol 97'5 per cent , ( by specific gravity ) as solvent , a strong solution supposed to be saturated at the boiling point set to a gel at 32 ' , but deposited crystals only at 36 ' .
On again testing after further boiling with crystals it now formed a gel at 35*17 ' which completely liquefied with deposition of crystals-in three minutes , the temperature rising to 35*55 ' in this process .
At this temperature the borderland between gel and crystals is as narrow as it is with ether at temperatures about the freezing point .
The temperature range of solutions in alcohol may , therefore , be divided into an upper region above about 35 ' in which gelation does not take place , a middle region in which the gel is .
labile to crystals , and a lower region below about +5 ' in which the gel persists for so long a time as to be sensibly stable .
The azomethine is , so far as I know , unique in the wide range of solvents which it will convert into gels .
It is true that Graham described gels of silica and alcohol or silica and sulphuric acid , etc. , but these were obtained by displacing the water of an already formed hydrogel by diffusion\#151 ; a process probably akin to the replacement of one fluid in the interstices of a sponge of solid by another .
Euhemann 's substance seems capable of forming gels directly with any solvent .
The Structure of the Gel.\#151 ; Whatever the molecular process underlying gelation may be , it in many most remarkable features resembles crystallisation .
To this I now turn .
When a strong solution is cooled , it becomes supersaturated with respect to crystals and to gel .
One characteristic of over-cooling is that , if the fall of temperature below the point of change be sufficiently great , the appearance of the new phase is prevented.* ' In this sense a solution may be over-cooled with respect to gelation .
When a * Cf H. A. Wilson , \#163 ; Phil. Mag. ' 1912 .
] On the Formation of a Heat-Reversible Gel .
solution in 97-5-per-cent , alcohol was rapidly cooled in ice , it remained fluid , but set to a gel when allowed to warm to room temperature , or at once on rapid shaking .
I have observed the same feature of over-cooling in solutions of gelatine in water rapidly brought to the freezing point ; and Garrett , working under Quincke , found that the changes in a cooled solution of gelatine in water were hastened by sowing with already formed gel\#151 ; an observation which clearly points to a similar state of affairs * An overcooled and therefore supersaturated solution contains a quantity of heat Hi which must be dissipated before gelation can occur , and a further quantity , H2 , which is dissipated when the gel liquefies with separation of crystals , and , from what has been already said , the ratio Hi/ H2 must be regarded as varying with temperature , and becoming equal to zero at some temperature about 359 for solutions in strong alcohol .
Since the gels of this type , that is heat-reversible gels , are liquefied by a rise of temperature , gelation may be .taken to be an exothermic change .
Attempts were made to measure the heat given off or absorbed , but the experimental difficulties proved to be considerable , and the results were not satisfactory .
They will be renewed with a new form of calorimeter .
Gelation of the opposite type , namely , that which is not reversed by warming but produces a gel which shrinks on warming , occurs with absorption of heat .
For instance , when allowance is made for the heat of mixing of the solvent with chloroform , it is easily possible to prove experimentally that the gelation of a solution of celloidin in absolute alcohol and ether , which is caused by chloroform , is accompanied by a small absorption of heat .
Nuclei , as is well known , favour crystallisation , and nuclei seem necessary for gelation .
The gel starts always at distinct points on the wall of the vessel which holds the solution .
I failed to discover the nature of the nuclei , but their influence is unmistakable and profound .
If a test-tube of glass or quartz containing a solution about to gel be tilted , the gel may be watched rapidly forming at a number of points on the wall .
Each mass grows rapidly until it meets neighbouring masses , on which it seems to press .
The result is that a fully formed gel , though it appear transparent and homogeneous , has in reality a remarkable structure determined by the number and nature of the nuclei .
It is composed of masses more or less imperfectly joined together and of very various sizes in alcohol gels , and very uniform in size in carbon tetrachloride gels .
The formation of these masses may be readily followed , and they are easily obtained isolated , either by pouring away the fluid from a partially formed gel or by disintegrating a gel with careful shaking .
* Dissertation , Heidelberg , 1903 .
VOL. LXXXVII.\#151 ; A. D Mr. W. B. Hardy .
[ Apr. 11 , For example:\#151 ; 130 c.c. of a 0'7-per-cent .
solution was made in 97'5-percent .
alcohol , and allowed to cool slowly by standing on the laboratory bench .
It set to a continuous , firm , transparent gel the colour of amber .
At the end of an hour about 0'5 c.c. of fluid separated and floated on top of the gel .
In the fluid were fine crystals .
Seen by transmitted light the gel was seen to be composed of facetted masses , the base of each where it abutted on the glass being a regular hexagon .
A sketch , the actual size , is given in fig. 1 , and the arrangement is shown diagrammatically in fig. 2 , \gt ; Fig. 1 .
which is an optical and horizontal section of part of the gel .
Sections cut with the free hand of a gel show , under the microscope , polygonal areas , and in the centre of some of these a confused mass appears , from which darker lines radiate regularly to the periphery ( fig. 3 ) .
This figure was drawn from a gel entirely free from true crystals .
These masses have all the appearance of crystals .
They are not crystals , however .
They are singly refractive , and when they form in free fluid the surface is rounded and not at all facetted .
In fact , each nucleus is the centre of a sphere of gelation which continues as a sphere until it meets neighbouring masses , when mutual pressure produces a polygon .
The true crystals of the azomethine are doubly refractive .
The appearance of radiating lines reproduced in fig. 3 puzzled me greatly until I came to study gels of carbon tetrachloride and carbon bisulphide .
In these gels the gel masses are easily studied , for they are always very distinct , giving to the gel a curious cloudy opaque appearance .
The following description applies to gels of tetrachloride .
The gel is seen by a hand lens of good power to be composed of spheres , very uniformly 0T4 mm. in diameter .
These spheres hang together to form a framework , and there is fluid between them .
I described gels 1912 .
] On the Formation of a Heat-Reversible Gel .
with similar structures many years ago.* Each sphere is opaque and cloudy , and the cause of this is found when a sphere is examined under a higher magnification ( Oc .
4 , Ob .
D ) .
Each sphere is then seen to be built of close packed smaller masses , which are polygonal owing to the close packing , and are very uniform in size , an axis being 10 The smaller masses are arranged in a pattern which radiates outward from the centre of the larger sphere .
They are singly refractive , and at the free surface the facetted type seems to give place to a spherical type\#151 ; to globuliten , in fact .
The gels of azomethine are thus built up of at least two orders of structure , and the air surface of a transparent and apparently homogeneous alcohol gel exhibits by reflected light a pattern of large hexagons .
The further history of a gel can be followed under the microscope .
The gel never changes directly into crystals .
The true gel is completely stable with respect to crystals , but the component large masses melt at their surfaces only , and the fluid so formed deposits crystals .
These facts concerning the gels of azomethine , together with what is known of gelation in aqueous solutions , lead to the following account of the process in heat-reversible gels .
The over-cooled fluid solution changes to a solid solution by a process which , starting about some nuclei , spreads equally through the fluid , so that spherical masses of solid are formed .
Each solid mass is isotropic , and it may be compared to a glass .
The foundation of gelation , therefore , is a formation of masses of glass , which start from independent centres .
The process has many points of resemblance to crystallisation , but the masses are not crystals unless the sphere be admitted as a crystalline form .
To the masses the old term globuliten fitly applies , and the change may be called vitrification .
The particular glass of azomethine gel is a solid solution Plut the globuliten which appear in a cooling colloidal solution may be at first fluid , and continue fluid over a determinate range of temperature , just as ordinary glass will melt to a viscous fluid .
This appears very conclusively from Garrett 's investigation of the viscosity of solutions of gelatine at various temperatures .
The temperature range divides itself into three parts : ( 1 ) from 100 ' to about 25 ' the viscosity of a 2-per-cent , solution of gelatine does not change with time ; ( 2 ) a middle region , between about 25 ' and 21 ' , in which viscosity rises with time to a maximum\#151 ; in this region , although the viscosity is high , gelation does not occur ; and ( 3 ) below 21 ' , in which viscosity continually rises with time , until it becomes infinite when the state of a solid gel is reached .
The existence of the middle region may , * ' Journ. Physiol. , ' 1899 , vol. 24 , p. 167 ; 'Roy .
Soc. Proc. , ' 1900 .
D 2 Mr. W. B. Hardy .
[ Apr. 11 , without doubt , be traced to the separation of a colloid rich phase , which is fluid , as Garrett himself points out .
It is the region in which vitrification is incomplete , a fluid glass separating .
Vitrification may involve all the solution , or a portion of fluid may persist , in which case two phases result .
Both conditions are readily obtained and studied in carbon tetrachloride gels of azomethine .
The phase which separates on cooling as spheres is not always the colloid rich phase .
Thus , when gelatine is dissolved in 40-percent .
alcohol , if the percentage by weight is less than about 25 , spheres of a solid solution rich in gelatine separate , and adhere together in anastomosing lines , so as to form a brittle framework of solid .
But when the concentration of gelatine lies between about 25 and 36 , spheres of fluid poor in gelatine , and uniformly 10 yu .
in diameter , may be seen to separate at 20 ' , and the remainder vitrifies as a continuous solid mass .
I succeeded in pushing the concentration of gelatine to 40 per cent. ; the mixture now melted at 70 ' and set at 35 ' to a milky gel with the remarkable feature that increasing the concentration of the colloid increases the volume of the spheres of fluid\#151 ; some being 25 g in diameter.* Agar water containing 1 to 2 per cent , of agar unquestionably vitrifies incompletely .
The colloid poor phase can be expressed from the gel with the utmost readiness either by centrifuging , by squeezing the gel in one 's hands , or by gravity , as e.g. if a hole is made in a mass of such gel it rapidly fills with fluid .
Why do not the masses of the colloid rich phase fuse completely ?
I suggested in an earlier paperf that the " passive resistance to change\#151 ; introduced by the formation of a solid phase " would account for it .
The influence of this resistance is undeniable ; once the solid state is reached , progress to complete equilibrium between the phases will take place mainly by slow interchange due to diffusion\#151 ; mixing by convection becomes impossible .
Difficulties in the way of dissipation of surface energy will also play their part\#151 ; electrification of the surface of the spheres would , for instance , delay or prevent the diminution of surface which follows fusion .
All these features have been already insisted upon , | but the azomethine series of gels afford convincing evidence that the distinct vitreous masses which start from the nuclei , although they may and do adhere to one another , still do not fuse in the sense of losing their individuality .
Each continues to persist as a quasi-independent system of molecules grouped about and related to its own nucleus , and each , when the mass changes , changes independently of the others at its own rate .
Whether the mass would be annealed to a truly * Hardy , loc. t ' Roy .
Soc. Proc. , ' 1900 .
I Loc .
tit .
1912 .
] On the Formation of a Heat-Reversible Gel .
continuous glass by very slow cooling is a matter for speculation , but it may be some such process of slow annealing , that is the adjustment of the individual vitreous masses of different size and nature to a common level , which accounts for the slow change in vapour tension and elasticity which reversible gels are known to exhibit .
If gels of the azomethine are typical of all reversible gels , then these are the glass state of solutions supersaturated with respect to crystals .
Why therefore , do not gels of gelatine or agar slowly liquefy and deposit crystals ?
It is not because of the large size of the chemical molecules , for many proteins can be obtained in the crystalline form .
The answer lies , I think , in the fact that , in the case of solutions of azomethine , between the region of concentration and temperature in which the gel is permanent , and the region of simple saturated solutions , there is interposed a region in which the glass melts to a true fluid which is supersaturated with respect to crystals .
In the case of solutions of gelatine or agar , this intervening region does not exist ; instead , we have the glass softening to a viscous fluid , which passes insensibly to colloidal solution .
That solutions of azomethine are not singular in the fact that gelation starts from centres , and only slowly involves the whole mass , is proved by an observation made by me many years ago .
A solution of silicic acid was dialysed for some days against running tap-water until it formed a firm gel in the dialysing tubes .
The gel was then removed from the tubes , broken up , and centrifuged for three hours , with the result that a small quantity of fluid separated at the top of the gel .
This was pipetted off and , on adding a trace of magnesium sulphate , it at once set to a firm gel .
Vitrification proceeding from nuclei in the solution of silicic acid had therefore not yet had time to involve the whole mass of the solution .
A stage in which a melted viscous " glass " separated was directly observed by me in a solution of 55 parts by weight of gelatine in equal parts by volume of absolute alcohol and water .
When sufficiently heated , this forms a fluid which appears homogeneous under a magnification of 450 diameters .
On cooling , it may be seen to separate into two fluids , one of which , as the temperature continues to fall , becomes solid .
[ \#166 ; Postscript added May 20.\#151 ; The gels described in the preceding pages behave like ordinary watery gels in the fact that dyes such as eosine and methylene blue diffuse into them from alcoholic solution and " stain " the substance of the gel .
]
|
rspa_1912_0057 | 0950-1207 | On the ultimate lines, and the quantities of the elements producing these lines, in spectra of the oxyhydrogen flame and spark. | 38 | 48 | 1,912 | 87 | Proceedings of the Royal Society of London. Series A, Containing Papers of a Mathematical and Physical Character | Sir Walter Noel Hartley, F. R. S.|Henry Webster Moss, A. R. C. Sc. I., A. I. C. | article | 6.0.4 | http://dx.doi.org/10.1098/rspa.1912.0057 | en | rspa | 1,910 | 1,900 | 1,900 | 5 | 206 | 4,380 | http://corpora.clarin-d.uni-saarland.de/surprisal/6.0.3/?id=rspa_1912_0057 | 10.1098/rspa.1912.0057 | null | null | null | Atomic Physics | 60.675082 | Electricity | 13.295602 | Atomic Physics | [
7.863296985626221,
-43.92789077758789
] | 38 On the Ultimate Lines , and the Quantities of the Elements Producing these Lines , in Spectra of the Flame and Spark .
By Sir Walter Noel Hartley , F.R.S. , and Henry Webster Moss , A.R.C.Sc .
I. , A.I.C. ( Received April 15 , \#151 ; Read May 9 , 1912 .
) In a paper recently published by one of us , on some mineral constituents of a dusty atmosphere* as determined both by flame and spark spectra , the lines most commonly occurring were described as either the ultimate groups or simply the ultimate lines of calcium , magnesium , aluminium , lead , manganese , copper , and nickel .
A brief account was given of the method employed in determining the weights of matter necessary to give the calcium and copper lines in the spark , and it was shown that the tests for lead , manganese , and magnesium are more delicate than those for calcium and copper , and these again are more sensitive than either the yellow flame or the spark spectrum for sodium .
M. de Gramont has given a list of the ultimate lines of some of the elements* !
* and remarks that the ultimate rays are generally the same for spectra taken from the condensed spark , with or without self-inductance , for the spark without condenser , for the arc , and for flames at high temperatures when the reaction is a very sensitive one .
There are , however , so many important exceptions that it is necessary to ascertain the ultimate lines of the same elements when the spectra are produced in different ways .
The wave-length of the ultimate line observed in any spectrum depends upon whether the observations are made with the eye only , or by photography , and when by photography , it depends upon the sensitiveness of the photographic plate .
In the oxyhydrogen flame spectra , which seldom extend beyond X 3000 when photographed , the ultimate lines are , as a rule , found to be in a region of less refrangibility than when , with the same element , condensed sparks are employed .
Thus in flame spectra , with the Mecke burner , or oxyhydrogen flame , the ultimate line of calcium is that in the blue , 4226*9 ; in spark spectra , the ultimate line is X 3933*8 , the penultimate line is 3968*9 .
In flame spectra observed by the eye , the ultimate line of lithium is in the red , X 6708 ; by * Hartley , 'Roy .
Soc. Proc. , ' 1911 , vol. 85 , p. 271 .
t 'Compt .
Rend .
, ' 1907 , vol. 144 , p. 1101 .
Ultimate Lines in Oxyhydrogen Flame and Spark Spectra .
39 photography , it is in the blue , \4603 , but by using panchromatic plates it is again in the red .
The actual quantities of matter which render the ultimate lines in various spectra are of great importance , as they differ widely .
The differences are due to the emissive intensity of the rays , and to the volatility of the elements in the flame or spark .
The delicacy of the spectrum reaction of flames , though dependent on the volatility of a substance and the intensity of action , chemical or physical , of the emitted rays and the sensitiveness of the plate , is not increased in proportion to the increase of temperature in the flame .
Thus , though the temperature of the acetylene and oxygen blow-pipe flame is higher than that of the oxyhydrogen flame , yet the efficiency of the latter is greater than that of the former , by reason of the greater facility with which it effects the chemical reduction of oxides and oxy-salts.* The Ultimate Lines in the Oxyhydrogen Flame Spectra of Solid Substances Volatilised in the Flame , with the Quantities of the Elements which render the Lines .
X. X. X. Mgrm .
Lithium 6708 4603 *07 4-0 3 ) 6708 1-0 Potassium 4047 -39 4044-33 1-2 33 4047 -39 0 -0008 Rubidium 4215 -68 4202-04 0*01 Caesium 4593 *3 4555 -46 o-oi Calcium 4226 -9 o-i 33 4226 *9 fairly strong .
1 *0 Strontium 4608 o-oi Barium 5536 1 -o Copper 3274 3247 -7 10 Silver 3383 -5 3280 -8 o-i Gold* 3975 3652 50 -0 Gallium 4172 -214 4033 -125 0-01 Indium 4511 4102 0 " 01 Thallium 5351 3776 o-i 33 * 3776 o-oi Tin Feeble bands , 5000 to 3250 100 -o Lead 4058 3682 -9 3639 -2 1 -o 33 4058 01 Manganese 4034 -5 4033 -2 4031 *0 o-ooi Nickel 3618 -5 3609 -8 3571 -2 l-o 33 3433-0 3425 3415 * The gold spectrum shows the edges or heads of very strong bands , which correspond with the lines in the spark spectrum , \ 3976 -8 diffuse and \ 3650 -9 sharp , as measured and described by Eder and Valenta .
* Hartley , " The Thermochemistry of Flame Spectra at High Temperatures , " 'Roy .
Soc. Proc , ' 1907 , A , vol. 79 .
40 Sir W. N. Hartley and Mr. H. W. Moss .
Ultimate [ Apr. 15 , The quantities of the elements which render the ultimate lines in the oxyhydrogen flame have been carefully determined ( see table on p. 39 ) .
The foregoing numbers have been applied to the quantitative analysis of minerals , also to slag and flue dust , the by-products of metallurgical operations .
The method of ascertaining the ultimate lines and quantities of matter volatilised in the spark when dry electrodes are used , is somewhat different and requires to be fully described .
Method of Photographing the Ultimate Lines in Spark Spectra of the Elements Obtained from Dry Electrodes .
Attempts were made to ascertain the ultimate line or lines by exposing the plate in the spectrograph to the light from the spark for very short periods , which were regulated by means of a Goerz sector shutter placed immediately in front of the slit of the spectrograph .
It was found , however , that although the shutter measured very accurate intervals of time , yet , owing to the intermittent nature of the spark discharge , it was quite impossible to obtain consistent results .
For example , if the shutter were set to give an exposure of 1/ 20 sec. duration , the plate might receive the light of from one to five discharges the number depending upon the speed of the " hammer " break of the induction coil , and upon the instant of release of the shutter .
In order to obviate these disadvantages an arrangement was made whereby either a single discharge or a definite number of discharges could be obtained .
The contacts of the hammer break of the coil were insulated from each other by a piece of ebonite , and were connected by wires to a switch , which consisted of a copper contact pivoted so that it could be immersed in a mercury cup .
The copper contact and the mercury of the cup were connected to the terminals of the switch , and the copper contact was controlled by a spring in order that the circuit , when completed , might be rapidly broken .
In such an arrangement , each rapid release of the switch causes a discharge at the spark-gap , and the photographic plate can , in this way , be exposed to the spectra produced by any desired number of discharges .
The procedure adopted in most cases was to expose each plate to a number of discharges , descending from 20 or 30 to 1 , and thus eliminate all but the most persistent lines .
In some cases , the effect of inserting a Hemsalech inductance in the secondary circuit was examined with a small number of discharges .
Its effect in such cases was to weaken the whole spectrum 1912 .
] Lines inOxyhydrogen Flame and Spark Spectra .
without making any notable change in its character , other than the removal of the air lines XX 4035*3 and 3995*3 .
These are the only lines of air ( nitrogen ) which appear in the spectrum given by a small number of discharges .
It is an interesting fact that , while these air lines appear in the case of some metals with the least number of discharges necessary to give the spectrum of the metal , with other metals there may be no trace of them for an even greater number of discharges .
A possible cause of this may be that the nitrogen combines with the metal .
Determinations of the smallest weight of material necessary to yield the ultimate lines of the elements were made in the following manner from dry electrodes:\#151 ; SparJc Spectra.\#151 ; With metallic calcium it was found that the loss of weight from both electrodes was 3-4 mgrm .
in passing the spark for .10 minutes , the number of discharges per second being 50-70 .
Taking the mean weight of calcium volatilised at 3*5 mgrm .
in 10 minutes , and the number of discharges as 60 per second , the quantity volatilised in one minute is 0*35 mgrm .
By further experiments it was found that , from the two electrodes of calcium , 0*004 grm. was volatilised in 10 minutes , this being the average of several weighings , which showed very small variations .
Therefore 0*0004 grm. is the weight volatilised in 60 seconds , or 0*00007 grm. is volatilised per second .
From 50 to 70 discharges occur per second , therefore the weight of calcium volatilised at each discharge from both electrodes is 0*00010-0*00014 mgrm .
From the negative electrode only , the weight volatilised in 10 minutes is 0*0026 grm. , and at each discharge 0*00006-0*00010 mgrm .
The lines in the calcium spectrum photographed were exclusively the following:\#151 ; X ( Eder and Valenta ) .
3968*6 3933*8 3737*2 3706*2 3179-4 3159*1 Intensity .
10 Very feeble .
10 10 The Preparation of Pure Manganese.\#151 ; This element was specially prepared , as all other specimens obtainable contained considerable quantities of impurities .
The metal was obtained by electrolysing a saturated solution of pure manganous chloride , employing a cathode of mercury weighing 1| kgrm .
42 Sir W. N. Hartley and Mr. H. W. Moss .
Ultimate [ Apr. 15 , and a platinum anode .
A current from 4 to 5 amperes passed for about five hours was sufficient to convert the cathode into a stiff amalgam .
This was washed , and freed from an excess of mercury by pressure .
The metallic manganese was isolated by distilling off the mercury in a quartz tube filled with hydrogen , and fusing the residue by means of an oxy-coal-gas flame applied to the tube .
Solid points of the metal were submitted to the condensed spark .
The following list gives the very large number of 27 lines , which are rendered by only one spark discharge .
It includes three well-marked groups , each containing three lines:\#151 ; X. X. 4030*8 2889*5 4018*3 2719*0 3610*4 2701*7 n 3570*2 2672*8 3548*2 2663*3 3532*1 2632*5 ?
3497*7 2625*7 3494*2-1 2618*2 3483*0 ?
Group I. 2594*0 3474*2 J 2576*2 .
3460*5 2452*6*1 .
| 2949*31 2438*2 [ Group III .
2939*4 2933*1 J ^ Group II .
2428*0 J 1 Groups I , II , and III are very well marked .
Group II is the strongest .
Several relatively strong lines occur between 2701*7 and 2576*2 , notably 2576*2 , 2594 , and 2618*2 , but the whole of the manganese lines situated between XA2701*7 and 2576*2 , which are indicated by a bracket , occur feebly .
The ultimate lines , and the quantity of manganese volatilised which is required to render them , was determined as follows:\#151 ; The condensed sparks were from 3 to 4 mm. long , without self-inductance .
The average weight of manganese volatilised from the two electrodes during 60 seconds was 0*00025 grm. , and per second 0*000004 grm. The number of discharges per second was from 50 to 70 , therefore the weight of manganese volatilised by one discharge lies between the limits of 0*00008 and 0*00006 mgrm .
The average weight volatilised from the negative electrode only , per 60 seconds , was 0*0002 grm. , and per second 0*000003 grm. ; at each discharge the quantity is 0*00006 to 0*00004 mgrm .
1912 .
] Lines inOxyhydrogen Flame and Spark Spectra .
43 Determination of the Ultimate Lines of Manganese by Means of Manganese Amalgam .
When freed from excess of mercury by pressure the composition of the amalgam was determined by distilling in an atmosphere of hydrogen at a temperature below redness , whereby the mercury was entirely separated , and the manganese left as a metallic sponge .
Two determinations gave the percentage of manganese in the amalgam as 340 exactly .
Assuming the quantity of manganese volatilised in each discharge to be proportional to the concentration in the amalgam , we ascertain from previous experiments that when the amalgam is submitted to the spark about 0,000002 mgrm .
of manganese are volatilised at each discharge .
This quantity gives the group of three lines with wave-lengths 2949'3 , 29394 and 29334 , which are therefore the ultimate lines ; they are identical with Group II on the previous list .
They appear to be very feeble , but 2949-3 is the most distinct , and therefore the ultimate line .
With two discharges taken from the amalgam four groups of lines appear .
The following lines were measured :\#151 ; Manganese .
X. 2949-31 2939-4 \gt ; Group III .
2933-1 J 2605-8 -j 2594-0 l Group IV .
2576-2 J Groups III and IV are the strongest and most characteristic .
These groups differ somewhat from those taken from the solid metal by one spark discharge .
Determination of the Ultimate Lines of Mercury , as Photographed from the Spark passed betioeen Poles of the Solid Amalgam .
Mercury ( from manganese amalgam).\#151 ; With one discharge the following lines were photographed\#151 ; XX 4358-6 , 4046'8 , 3650-3 , 3131-9 , 3125-8 , 2980-8 , 29674 , 2847*9 .
The line 3650-3 and the pair 3131*9 and 3125*8 are distinct and characteristic ; the other lines are very faint .
X. 3570-2 -j 3548-2 V Group I. 3497-7 3494-2 3483-0 -j 3472*2 l Group II .
3460-5 J 44 Sir W. N. Hartley and Mr. H. W. Moss .
Ultimate [ Apr. 15 , The Ultimate Lines of the Metals taken directly from Condensed Spark Discharges passing between Dry Electrodes without Self-Inductance , with the Quantities of the Metals in the Spark lost by the Negative Electrode .
The Alkali Metals\#151 ; * Lithium.\#151 ; With five spark discharges the following lines appear:\#151 ; 4602*4 , 4132-4 , 3232-8 .
The two former are stronger than 3232-8 .
With one spark no line is visible .
Sodium.\#151 ; With five spark discharges the yellow lines are rendered , the mean wave-length of which is 5893-2 ; also a pair in the ultra-violet , 3301-1 and 3302-5 , which appear much stronger than the lines in the yellow .
With one spark there are no lines , and the quantity of metal volatilised is variable , between 0-000165 and 0*000275 mgrm .
in each discharge .
Potassium.\#151 ; With five spark discharges the following lines are photographed\#151 ; \\ 4308 , 4186-3 , 4047-4 , 4044*3 , and 4001-2 .
With one spark , 4047*4 and 4044-3 .
With the condensed spark the quantity of metal volatilised cannot be determined with any degree of certainty , because particles , either solid or liquid , of lithium , potassium , and sodium are projected from the electrodes .
Oxidation also takes place .
Heavy Metals\#151 ; Lead.\#151 ; With one spark discharge = 0-000187 mgrm .
4387-3 ( 4 ) 3740-1 ( 1 ) 3572-9 ( 1 ) 4058-0 ( 5 ) 3683-6 ( 2 ) 2802-1 ( 1 ) 4045-2 ( 5 ) 3639-7 ( 1 ) 2614-.3 ( 1 ) The relative intensites of the lines are represented by the numbers in brackets , the larger values representing greater intensities .
The ultimate lines are 4045-2 and 4058*0 .
Silver.\#151 ; With five discharges = 0*000165 mgrm .
XX 3383-0(1 ) , 3280-8 ( 2 ) , 2447*9 ( 3 ) , 2437*8 ( 1 ) , and 2413-3 ( 2 ) .
The lines 2447*9 and 2413-3 appear with one spark discharge = 0-000033 mgrm .
Of these 2447'9 is the stronger and the ultimate line .
Copper.\#151 ; With 10 spark discharges , the lines 3274*1 ( 1 ) and 3247*5 ( 2 ) appear .
With five sparks = 0-000272 mgrm .
, the line 3247'5 alone appears .
It is very feeble and the ultimate line .
* To prevent the metals taking fire , they were surrounded by an atmosphere of hydrogen .
1912 .
] Lines inOxyhydrogen Flame and Spark Spectra .
45 Cadmium.\#151 ; With five spark discharges = 0-000275 mgrm .
X. 3613-01 / on 3610*7 J 3 3467*81 / o\ 3460-3 J 3403-7 ( 1 ) X. 2748-7 ( 5 ) 2573-1 ( 3 ) 2313-0 ( 1 ) 2265-0 ( 1 ) With one discharge pairs of lines 0-000055 mgrm .
2748-7 is faint , but distinct , but the X. x. 3613n and 3467,8 \gt ; 3610-7 J 3460-0 J are very faint .
Under these conditions 2748-7 is the ultimate line .
In the case of solutions , the ultimate line is at X 2265-0 , the penultimate lines are much the same as with dry electrodes above , except that a line with X 2288-1 occurs .
The results thus differ from those obtained with dry electrodes .
Bismuth.\#151 ; With one spark discharge = 0*000358 mgrm .
XX 4259-9 ( 9 ) , 3793'0 ( 8 ) , 36956 ( 10 ) .
The ultimate line is at X3793 .
Aluminium.\#151 ; With five spark discharges = 0*00018 mgrm .
XX 3944-3 ( 3 ) , 3587*0 ( 5 ) , 3092*8 ( 4 ) , 3082*3 ( 3 ) , 2816*4 ( 4 ) .
With one spark discharge = 0*000036 mgrm .
, the line 3587 is quite distinct , it is the ultimate line .
N.B.\#151 ; The calcium line X 3933*8 appears in this spectrum with five discharges .
It undoubtedly comes from dust in the air .
Titanium.\#151 ; With one spark discharge = 0*000105 mgrm .
XX 3822-2 ( 5 ) , 3491-2 ( 10 ) , 3477*4 , 3461*7 ( 15 ) .
The last three lines are the ultimate group .
Thallium.\#151 ; With one spark discharge = 0*000187 mgrm .
XX 3775-9 , 3529-6 , 3519-4 , 3091*9 and 2768 0 .
Of these , 3775*9 and 3519*4 are the strongest lines , and the stronger of these , 3519*4 , is the ultimate line .
Zinc.\#151 ; With five spark discharges = 0*000405 mgrm .
XX 3345*5 1 3345-l } ( 3 ) , 3303-0(2 ) , 3282-4 ( 1 ) , 2558-0 ( 5 ) , 2502-1 ( 2 ) .
With one discharge = 0*000081 mgrm .
XX 3345-5 -i 3345-1 } ' 3303''\gt ; 2558-0 , and 2502 1 .
Of these , 2558 is the strongest and the ultimate line .
The lines 3303*0 and 2502-1 are very feeble .
46 Sir W. N. Hartley and Mr. H. W. Moss .
Ultimate [ Apr. 15 , Gold*\#151 ; With 10 spark discharges = 0*00017 mgrm .
XX 4437-37 , 4041-07 , 3122-88 , 2913'63 , 2802*3 , 2667-08 , 2428*06 .
With five discharges = 0*000085 mgrm .
, the line A , 4437*37 disappears , the latter six lines remain , and of these 3122*9 and 2676*1 are the ultimate lines , the former being the most distinct .
With one discharge there are no lines .
Uranium.\#151 ; With five spark discharges = 0*001375 mgrm , all the lines in this spectrum from X. 4627*3 to about 2698 appear faintly , and they are so numerous that they give almost a continuous spectrum .
According to Exner and Haschek 's table of wave-lengths the lines number 4300 .
With one discharge = 0*000275 mgrm .
, a group of three lines appears faintly ; the approximate wave-lengths are XX 3019 , 3102 , and 3090 , they are all of equal intensity .
Uranium metal , owing to its brittle and friable nature , is very apt to lose comparatively large particles when the spark passes .
A number of determinations yielded the mean quantity given .
Iridium.\#151 ; With five spark discharges = 0*00022 mgrm .
, X 3437*2 and a nebulous line of approximately X 3327 are visible .
Platinum.\#151 ; With 10 discharges = 0*00028 mgrm .
, the following lines are rendered:\#151 ; XX 3064*8 , 3036*6 , 2794*3 .
Of these , X 2794*3 is the strongest line .
With five discharges , no line appears .
Iron.\#151 ; With three spark discharges = 0*000315 mgrm .
, there appear 10 lines in three ultimate groups ; the first group of 6 lines is very characteristic .
X. 2628-4 }Group II .
2625*8 J F * These are the most distinct lines .
The quantity of the metal volatilised from the negative electrode by one discharge = 0*000105 mgrm .
It is interesting to compare with the above , lines rendered by the oxy-hydrogen flame and by solutions , thus:\#151 ; X. 2753*4 *2749*4 *2747*1 *2746*6 2743*2 | 2739*6 J l-Oroup I. * Eder and Valenta 's wave-lengths .
1912 .
] Lines in Oxyliydrogen Flame and Spark .
47 Oxyhydrogen flame\#151 ; X. X. 3886-41 3749-61 3860-0 i 45-7 / 3824-5 J 3735-01 33-41 3722-61 20-0 J The last six lines are very feeble.* Solution containing O'Ol A solution of gold chloride per cent , of iron .
containing iron.t Condensed spark with Condensed spark with self-inductance .
self-inductance .
X. X. 3737-3 1 2755*8 ' 35-0 J 2749-4 3722-71 2747*6 \gt ; * 20-1 J 2743-2 3021-21 2739-6 \gt ; 20-81 2767-6 2755-8 1 39-6 J 2631-41 28*4 J 2625*8 2599-31 98-5 J 4 2562-0 The quantity of iron present in the gold chloride was not known .
In each case the lines were measured on small photographs , and the wavelengths ascertained from interpolation curves , quite independently , by different observers .
Cobalt.\#151 ; Four spark discharges = 0'000748 mgrm .
, render the following lines , very feebly :\#151 ; XX 3587*3 , 3569-5 , 3529'9 , 3502-4 , 3453'6 , 3412-8 , 34053 , 2587-2 , 2582-3 , 2580-4 , 2564'2 .
With the exception of the lines 2582*3 and 2580"4 , which are slightly more prominent than the others , all the lines are feeble .
In the case of the four elements following , quantities are omitted:\#151 ; Antimony.\#151 ; With five spark discharges the following lines appear feebly\#151 ; XX 3637-9 , 3504-8 , 3267'6 , 3241-3 , 2790-6 , 2528*6 .
With two discharges 3241*3 and 2790-6 are visible but very faintly so ; with one discharge there are no lines .
* Hartley and Ramage , 'Roy .
Soc. Proc. , ' 1901 , vol. 68 , pp. 98-109 .
t Pollok and Leonard , 'Sci .
Proc. Roy .
Dublin Soc. , ' 1907 , vol. 11 ( N.S. ) .
Dr. P. Phillips .
[ Apr. 18 , Arsenic.\#151 ; Five discharges rendered the lines W 28605 , 2780-3 , and 2745-1 ; with four discharges the line 2780-3 is alone visible and very feeble .
Carbon.\#151 ; Pure Ceylon graphite was taken for the electrodes .
With five discharges only one line , X 24787 , appears .
Vanadium,.\#151 ; With one spark discharge the following lines appear distinctly :\#151 ; X X 3723-5 q *2926-5 3718-3 J 2920-5 *3280-0 2893-5 3190-8 2702-3 3102-4 2382-6 2371 2 * This is a distinct line at X 3280 , and a distinct pair , XX 2926*5 , 2920'5 , constitute with it a group .
The Viscosity of Qarbon Dioxide .
By P. Phillips , D.Sc .
, B.A. ( Communicated by Prof. F. T. Trouton , F.R.S. Received April 18 , \#151 ; Read May 23 , 1912 .
) The viscosity of carbon dioxide was determined under considerable variation of \#166 ; temperature and pressure by Warburg and Babo* in 1882 , but their results are rather incomplete .
They determined a few viscosity-pressure isothermals at temperatures above the critical temperature , one such isothermal for the liquid at 25 ' C. , and a few values of the viscosity of the liquid under the pressure of its saturated vapour at different temperatures .
Recently E. N. da C. Andrade , working at University College , began to determine the viscosity of carbon dioxide at different temperatures under the critical pressure by a continuous flow method .
This involved the use of large quantities of CO2 , which he obtained in the usual trade cylinders , and which he kept at the critical pressure by immersing the cylinder in a bath at the critical temperature .
The cylinder communicated with the capillary tube , which was surrounded by water at any desired temperature , and through which the C02 was slowly allowed to escape into weighed potash bulbs .
The mass of C02 absorbed in a certain time gave the quantity of C02 flowing through the capillary tube per second , and a manometer gave * Warburg and Babo , ' Annalen der Physik und Chemie , ' 1882 , vol. 17 , p. 390 .
|
rspa_1912_0058 | 0950-1207 | The viscosity of carbon dioxide. | 48 | 61 | 1,912 | 87 | Proceedings of the Royal Society of London. Series A, Containing Papers of a Mathematical and Physical Character | P. Phillips, D. Sc., B. A.|Prof. F. T. Trouton, F. R. S. | article | 6.0.4 | http://dx.doi.org/10.1098/rspa.1912.0058 | en | rspa | 1,910 | 1,900 | 1,900 | 15 | 160 | 3,698 | http://corpora.clarin-d.uni-saarland.de/surprisal/6.0.3/?id=rspa_1912_0058 | 10.1098/rspa.1912.0058 | null | null | null | Thermodynamics | 64.194026 | Measurement | 17.899139 | Thermodynamics | [
-8.662735939025879,
-35.0759162902832
] | ]\gt ; Dr. P. Phillips .
[ Apr. 18 , \mdash ; Five discharges rendered the lines , and ; with four discharges the line 27803 is alone visible and very feeble .
Carbon.\mdash ; Pure Ceylon graphite was taken for the electrodes .
With five discharges only one line , , appears .
Vanadium.\mdash ; With one spark discharge the following lines appear distinctly : \mdash ; 2893.5 3190.8 3102.4 2371.2 * This is a distinct line at 3280 , and a distinct pair , , constitute with it a group .
The Viscosity of Qarbon Dioxide .
By P. PHILLIPS , D.Sc .
, B.A. ( Communicated by Prof. F. T. Trouton , F.R.S. Received April Read May 23 , 1912 .
) The viscosity of carbon dioxide was determined under considerable variation of temperature and pressure by Warburg and Babo*in 1882 , but their results are rather incomplete .
They determined a few viscosity-pressure isothermals at temperatures above the critical temperature , one such isothermal for the liquid at C. , and a few values of the viscosity of the liquid under the ) ressure of its saturated vapour at different temperatures .
Recently E. N. da C. Andrade , working at University College , began to determine the viscosity of carbon dioxide at different temperatures under the critical pressure by a continuous flow method .
This involved the use of large quantities of , which he obtained in the usual trade cylinders , and which he kept at the critical pressure by immersing the cylinder in a bath at the critical temperature .
The cylinder communicated with the capmary tube , which was surrounded by water at any desired temperature , and through which the was slowly allowed to escape into weighed potash bulbs .
The mass of absorbed in a certain time gave the quantity of flowing through the capillary tube per second , and a manometer gave * Warburg and Babo , ' Annalen der Physik und Chemie , ' 1882 , vol. 17 , p. 390 .
1912 .
] The Viscosity of Carbon Dioxide .
the difference of pressure at the two ends of the capillary .
The weakest point in the method was the use of from the ordinary cylinders , for it contains a considerable amount of moisture , which has a effect on the viscosity , especially near the critical point .
Andrade obtained a number of results*but they were very irregular , and he had to leave the work unfinished at a point where he had decided that the apparatus would need to be almost entirely remodelled .
His results are in as good agreement with the corresponding results in this paper as their irregularity will allow .
These are the only experiments on the viscosity of at high pressures of which I am aware . .
O. Rankine 's device*for , the viscosity of small quantities of a gas suggested a convenient form of apparatus and led the author to determine some viscosity-pressure isothermals both above and below the cntical temperature .
Appxratus.\mdash ; The essential part of the apparatus\mdash ; an adaptation for use at high pressures of Rankine 's apparatus\mdash ; is shown in fig. 1 .
The weight of a pellet of mercury contained in a glass drives the liquid or gas through fine capillary tube , and the time which the pellet takes to fall between two marks is determined .
The two tubes and are connected together at each end by passages bored in mild steel blocks and , and are fixed into the blocks by means of stuffing boxes , S. These stuffing boxes gave some considerable trouble at first by leaking .
washers were not used at first because indiarubber absorbs carbon dioxide and allows it to diffuse through .
Other packings which were tried had to be screwed up so tightly , and became so hard , that they broke the tubes before they were air-tight .
In the end indiarubber packing was tried and was found to be admirable , the absorption of carbon dioxide proving to be a great advantage , for the indiarubber swelled up and made a ectly t joint .
The diffusion of the carbon dioxide through it was so slow that no leak was detected for several weeks .
Into the upper steel block another steel block was screwed , and this contained two pin valves and , and had attached to it a pressure gauge reading to 150 atmospheres .
The valve served to separate the pressure gauge from the lower part of the apparatus , while .
separates this apparatus from the arrangement for evacuating and .
The screwed connection to the evacuating and filling apparatus stands out from the plane of the paper , and is indicated by the dotted circle at A. The mercury pellet was introduced at by unscrewing the small nut , and it ran into the passage * A. O. Rankine , ' Roy .
Soc. Proc 1910 , , vol. 83 , p. 266 .
VOL Dr. P. Phillips .
[ Apr. 18 , remaining there while the apparatus was being filled .
The ivory scale fixed on to the tube by clips , served to measure the height of fall of the FIG. 1 .
mercury pellet and the length of the pellet itself .
After the apparatus was filled it was placed in a large water-tight copper-lined box cm .
1912 .
] The Viscosity of Dioxide .
inside ) , with the pressure gauge and the two valve spindles , and projecting , and with the connection A communicating with the exterior by means of rubber tubing .
The box was supported on two pivots so that it could be rotated about an axis perpendicular to and about in the centre of fig. 1 .
A plate glass window in one side of the box allowed a complete view of the tube , and of the pellet and scale .
The box was filled with water , which was heated to the desired temperature by means of a hot water geyser , and the final adjustment of the temperature was made by introducing small quantities of cold or hot water and with the main bulk of the water .
The mixing was very effectually done by turning the box on its pivot .
The temperature of the large mass of water remained constant to within one-tenth of a degree for quite a considerable time\mdash ; quite long enough to time the fall of the pellet several times\mdash ; and , therefore , the temperature adjustment was very simple and accurate .
The carbon dioxide was prepared by the action of hydrochloric acid on pieces of marble , and was washed by being passed through water , and dried by being passed through calcium chloride and phosphorus pentoxide drying tubes .
It was temporarily stored over water in a aspirator of 9litres capacity .
In order that no air might be introduced into the gas , all the water was boiled before used .
On absorbing a volume of the gas in strong caustic soda solution the residue was less than a thousandth part of the original volume , and therefore the was very free from air .
The gas was introduced into the apparatus in fig. 1 by means of the arrangement in fig. 2 .
A and are two steel cylinders , A of 1800 .
capacity , and of 2000 .
They were mounted on a board in the relative position shown in the figure , and were connected by a steel tube with a pin valve The cylinder was filled with mercury up to the gauge tube , which was fixed into a stuffing box on the top of the cylinder .
Above , and fixed to it by another stuffing box , was a connection to a compression pump which would compress to 200 atmospheres , if desired .
Above the cylinder A were a gauge tube and two steel valve blocks with valves and .
The lower valve block was connected by a steel tube to the connection A in fig. 1 , and the valve served to shut off the cylinder A from the apparatus in fig. 1 .
The valve served to cut off the aspirator and the evacuating pump from the cylinder A. In order to fill the apparatus the valve and the tap of the aspirator were closed , the valves , and were opened , and the whole apparatus , with the connecting tubes and drying tubes , was evacuated to about 1 mm. pressure .
The aspirator tap was then turned on a very little so as to slowly fill the apparatus with through the drying tubes .
In order Dr. P. Phillips .
[ Apr. 18 , to get rid of the last traces of air from the apparatus the evacuating and filling with was repeated .
The valve was then closed , was opened , and the compression pump was started .
This forced the mercury from into , and so compressed the into the essential part of the apparatus .
When the mercury appeared in the gauge tube , , the valve was closed the compression pump was stopped , and the pressure in released .
Some FIG. 2 .
of the mercury in A then ran back into until the pressure of the small quantity of gas in A became less than atmospheric pressure , and then the valve was opened , allowing the to enter , and allowing the mercury to fill the cylinder .
The valve was then closed and the compression repeated .
The with and compressing it into the essential part of the apparatus was repeated until the desired pressure was reached .
The valve was then closed and the apparatus in fig. 1 was disconnected and placed in its box ready for the actual determination of the time of fall of the pellet .
The capillary tube was calibrated by a slight variation of 1912 .
] The Viscosity of Dioxide .
the method of W. J. Fisher , the value of for the equivalent uniform tube .
The length of the tube cm .
The volume between the two marks on the wide tube was found by filling the tube with mercury and running out the mercury between these two marks and weighing it .
In the earlier part of the experiment the marks were cm .
apart and the volume between them was found to be .
Later , in order to increase the time of fall , the distance was increased to 20 cm .
and the volume between these was found to be Errors and Corrections.\mdash ; The chief correction which had to be made was for the reduction in the pressure of the pellet due to capillarity .
When the mercury is moving , the front surface has a smaller radius of curvature than the rear surface , and there is , therefore , a back pressure due to this difference of curvature .
The ideal thing would have been to take a number of observations with different lengths of pellet at each temperature and pressure and thus evaluate the correction for each reading in the same way as Rankine did .
This would have been very troublesome with the apparatus adapted for high pressures , and , since a large number of values of the viscosity had to be found , would have meant prolonging the experiment enormously .
Consequently the correction was found under a few conditions , and the mean value was used throughout the calculation .
The length of the pellet was varied by running parts of it above the valve ( fig. 1 ) and then closing the valve and repeating the observation of the time of fall .
The correction decreases with rise of temperature and with increase of density of the , as is shown by the following four values which were chosen because they represent the widest changes in temperature and density:\mdash ; A few other determinations of the correction were made at odd times , and it was never found to be below and never higher than 0.36 .
The largest error introduced by taking the mean value was therefore cm .
or about per cent. 'Phys .
Rev Feb. , 1909 .
Dr. P. Phillips .
[ Apr. 18 , A small correction is needed for the rounded ends of the mercury pellet .
Assuming that the two ends were hemispherical while the length was being measured , the volume of the two hemispherical ends was , whereas if the ends had been cylindrical the volume would have been .
There is , therefore , a reduction in the effective length of , i.e. of cm .
cm .
The total reduction of pressure due to these two causes was , therefore , cm .
of Hg dynes per cm.2 .
There will also be an error due to the momentum of the fluid in the capillary tube .
This will probably be very small , as the two ends of the capillary tube are similar , and would be zero if we could assume stream-line motion at both ends .
The author has , however , been unable to evaluate it either experimentally or by calculation .
of -Bjsults.\mdash ; Pankine has shown in the same paper that the calculation of the coefficient of viscosity for a gas is just the same as for a liquid , i.e. where coefficient of viscosity ; radius of capillary tube ; ence of pressure on the two sides of the mercury pellet ; length of capillary tube ; volume swept out by the pellet ; time of fall .
When the pressure is low , the obeys the gas laws , and therefore the formula is exact .
When the pressure is high , is such a very small fraction of the total pressure that the formula is true whatever the law relating the volume and the pressure .
In this experiment dynes/ cm.2 , where 136density of mercury ; density of the length of pellet ; .
when of fall was cm .
, Therefore when height of fall cm .
or , , , , As a sample of the calculation , take the values obtained at 83 atmospheres and C. 1912 .
] The Viscosity of Carbon Dioxide . .
Length of pellet .
Height of fall .
The density of , calculated from Amagat , Method of Observation.\mdash ; After the apparatus had been filled , placed in its box , and surrounded by water at the desired temperature , it was placed in the horizontal position , the pressure was read , and the valve was closed .
It was then turned into the vertical position , so that the mercury pellet ran into the space in fig. 1 .
The box was then rotated gently in the clockwise direction , looking at the apparatus as in fig. 1 , until it was inverted .
This caused the mercury pellet to run into the glass tube G. The times of fall in the inverted and upright positions of the box were then determined four times , and the mean of the times calculated .
In no case did the times differ between themselves by more than one-fifth of a second .
The box was then placed in the horizontal position , and the length of the pellet observed by means of the ivory scale .
This could be done accurately to a quarter of a millimetre , the scale being divided into half millimetres .
The temperature was observed during the timing .
The box was then turned into the upright position again , and the pellet run into the space , and kept there while the temperature of the water was altered , or while the pressure of the was reduced , by allowing a little to escape through the valve ( fig. 1 ) .
The observations were then repeated , and so on for all the variations of temperature and pressure .
The Results .
Viscosity-pressure isothermals were determined at , and C. , and the values are given in the five tables below .
Dr. P. Phillips .
[ Apr. 18 , Temperature C. Temperature C. 1912 .
] The Viscosity of Carbon Dioxide .
Temperature C. Temperature C. The observations in the above five tables are plotted in figs. 3 and 4 , the former giving the viscosity-pressure isothermals , and the latter the kinematic viscosity-pressure isothermals .
At the lower pressures the values are only plotted for , and , in order to avoid confusion .
For the same reason , in fig. 4 , the and the isothermals are left out entirely .
The minimum values of the kinematic viscosity at , and are nearly equal , the value being .
The critical value of the kinematic viscosity will , therefore , also be 0 .
, and since the critical density is , the critical viscosity will be Putting this value into fig. 3 , it would seem that a law of rectilinear diameters holds here , as is shown by the dotted line .
Ths uncertainty as to the exact position of the points and would quite account for the slight divergence that exists , but as there are only two pairs of points from which to construct the diameter , and , as one of these pairs is a little uncertain , Dr. P. Phillips .
[ Apr. 18 , oo Pres 1912 .
] The Viscosity of Carbon Dioxide .
very little emphasis must be placed on this point .
The form of the viscosity-pressure isothermals is very similar to that of the densitypressure isothermals , but the former cross one another , whereas the latter do not .
They must necessarily cross , since the viscosity of a gas increases with rise of temperature , whereas the viscosity of a liquid decreases .
It is noticeable that the curves cross before the gas is liquefied , thus showing that it is beginning to act like a liquid as regards viscosity before condensation takes place .
Whether this would happen further from the critical temperature is , of course , doubtful ; the crossing might then happen in the passage from the liquid to the gas .
At the only two temperatures at which liquefaction takes place in this experiment , the kinematic viscosities of the liquid and gas seem to be equal at the point of condensation .
This means that in fig. 4 there is no discontinuity of position in the curves .
There is , apparently , a discontinuity of curvature .
At and atmospheres the kinematic viscosity of the liquid is , while that of the gas is FIG. 6 .
Dr. P. Phillips .
[ Apr. 18 , At and 71 atmospheres the kinematic viscosity of the liquid is , and that of the gas .
Here again there are only two pairs of such values , and therefore too much weight must not be given to this point .
If the viscosity-pressure isothermals , as their form seems to suggest , are represented by a van der Waals or Clausius equation , then the parts of a curve representing the gaseous and liquid states must be connected by a Square of Density FIG. 6 .
continuous curve as indicated by the dotted line in fig. 3 .
The portions AB , , will represent the viscosity of the superheated liquid , and the parts , the viscosity of the supercooled vapour .
These would be represented in fig. 4 by loops of some sort , such as those indicated by the dotted loops , and these would shrink to zero at the critical point .
In figs. 5 and 6 the density and the square of the density of the are plotted respectively against the viscosity .
It will be noticed from these that in the greater part of the range of the experiment the viscosity seems to 1912 .
] The Viscosity of Dioxide .
depend almost entirely on the density , for the points corresponding to different temperatures are all confused together about the same line .
The change in temperature is not great , whereas the change in density is large , so that any effect due to slightly different velocity of molecules is probably quite masked by the effect due to the great alteration of their distance apart in the critical region .
At very low densities the scale is too small to show the fact that the viscosity is independent of the density , while at the highest densities it will be noticed that the different temperatures are beginning to get separated .
Fig. 6 shows that between densities of about and the viscosity is a linear function of the square of the density .
This would mean that in this region of very rapid alteration of density with temperature or pressure , the change in viscosity is due almost entirely to the change in attraction between two adjacent layers of the fluid , for this would be proportional to the square of the density .
In other words , the viscosity in this region depends almost entirely on the term in the van der Waals equation .
At higher densities it is probable that the alteration in kinetic energy of the molecule begins to play a larger part , whereas at low densities the attraction between the molecules becomes quite negligible .
In conclusion , I wish to thank Prof. Trouton for his kindly interest throughout the experiment , which was carried out in University College Physical Laboratory , and to thank Assistant Prof. Porter for some useful suggestions .
I also wish to acknowledge the Government Grant , which defrayed most of the cost of the experiment .
|
rspa_1912_0059 | 0950-1207 | Theory of a new form of the chamber crank chain. | 62 | 69 | 1,912 | 87 | Proceedings of the Royal Society of London. Series A, Containing Papers of a Mathematical and Physical Character | Dr. H. S. Hele-Shaw, F. R. S. | article | 6.0.4 | http://dx.doi.org/10.1098/rspa.1912.0059 | en | rspa | 1,910 | 1,900 | 1,900 | 7 | 97 | 2,760 | http://corpora.clarin-d.uni-saarland.de/surprisal/6.0.3/?id=rspa_1912_0059 | 10.1098/rspa.1912.0059 | null | null | null | Measurement | 42.240357 | Tables | 19.885001 | Measurement | [
43.24235916137695,
-15.552371978759766
] | ]\gt ; Theory of New Form of the Charnber Crank Chain .
By DR. H. S. HELE-SHAW , F.B.S. ( Received May 7 , \mdash ; Read May 23 , 1912 .
) This particular crank mechanism in which the crank itself is fixed and the two arms rotate about the fixed crank ends , named by Reuleaux the " " rotating slider crank\ldquo ; rotirende kurbelschiefe and by Kennedy the " " turning block has been , as Reuleaux pointed out , basis of more attempted applications than any other mechanisnL Notwithstanding all these attempts it has had little if any practical success , at any rate for rotary pumps or motors .
The reason for this want of success is largely due to the difficulty of making running joints for holding the pressure of fluids with any device except lower pairs of either the revolute or the cylindrical prism form .
The following note gives the theory of a new modification of this mechanism , which , apart from any useful practical application it may have , appears to be of some scientific interest .
The great theoretical of this type of mechanism is that the parts revolve about two fixed centres and very nearly balanced mechanism results .
There is another advantage which is not even pointed out by Reuleaux and certainly was not applied in any of the examples given by him , namely , that the crank being fixed , it is possible conveniently to vary its stroke whilst the mechanism is in operation , and consequently to vary by a continuous process the volume of fluid taken in and discharged in each cycle of the machine .
In recent years attempts have been made to take adyantage of this property such as in the interesting mechanism of Rigg , but all the proposals hitherto suggested differ in various ways from the particular device which is the subject of this communication .
In order to see what difficulties have to be overcome when a mechanism of this type is employed to deal with a fluid so as to vary the volume in each cycle , the mechanism itself and the changes given to it must be analysed .
Fig. 1 , in which the lettering and rotation of Reuleaux is adopted , shows in certain positions the best known form of the chamber crank chain .
and are four cases in which not only the volume but the direction of flow is changed , Case being one in which no volume is discharged at all .
It is quite clear that these changes are difficult to effect as the crank is actually turning .
In Fig. 2 the crank is fixed , the same lettering being 'Theoretische Kinematik , ' 1st edit .
, vol. 2 , p. 359 .
Theory of New Form of the Crank Chain .
retained , and it will be evident that it is now possible to vary the stroke , and with it the volume of discharge whilst rotation is taking place .
With a single chamber the volume , if the fluid is incompressible , would , of course , be of an intermittent character .
Fig. 3 shows how by multiplying the fundamental mechanism this intermittency can be reduced to any required extent , and a uniform flow secured which can be varied as required .
The formula of the mechanism in fig. 3 is 4 showing that it is driven by the link which has four arms in one piece , the cylinders having a certain amount of angular motion relative to each other .
This device constitutes the fundamental mechanism of Rigg 's rine .
In this case the difficulty of the valve action ( of which not one of Reuleaux 's examples gives a practical form ) is surmounted by inverting the cylinders , so that the pressure comes on the inner instead of the outer side of the pistons , thus making it possible to use a central valve system .
Instead of having the various cylinders with relative angular motion , it may be more convenient to have the cylinders in one piece , and the coupler or connecting rod jointed .
This further modification is shown in fig. 4 , in which the formula has changed to 4 , since the mechanism is now driven by the revolving cylinder body instead of by the coupler .
If a central valve is required with this modification , a serious difficulty arises with regard to the operation of the rods ; in fact , the coupler rods themselves in this particular form could not be practically employed .
Thus in the Gnome engine , used for aeroplanes , separate valves are placed ab the end of the cylinders , the fluid being on the outside instead of the inner side of the piston .
In order to get over the difficulty of the coupler rods and obtain a central valve , the next step shown in fig. 5 must be taken .
Here the path of the pistons is maintained by providing a circular guiding surface , so that their movement is exactly the same as it would be under the action of the couplers .
In fig. 5 the guide blocks shown are used instead of the couplers , to compel the pistons to travel in the required path .
The formula , it will be observed , remains the same , notwithstanding the changed appearance of the mechanism , since nothing more than the common device , of an element , has taken place .
Although kinematically the effect is the same , a very serious practical difficulty has resulted , since the friction in the guide blocks , especially with a high speed of rotation and a high pressure of the working fluid , renders such a mechanism useless .
In order to get over this difficulty , instead of using guide blocks , rollers or wheels traversing the circular path may be provided , but such a modification will only be of Dr. H. S. Heal .Shaw .
[ May 7 , \mdash ; Fiq .
{ .
Fig. 5 .
ellccf .
Fig. 5 .
le effcc ' / Fig. Fig. 4 .
FIg .
6 .
Infigs .
4 and 5 the coeflcient 4 has been accidentauy omitted before the expression in brackets .
Theory of a New Form of the Chamber Crank .
65 use in the case of low pressures and low speeds .
For practical purposes , when high speed and high pressure are usually required , some other modification is necessary .
Suppose , instead of to use rollers , the guide blocks themselves are retained , and the ring or guide forming the path of the guide blocks allowed itself to revolve , being carried about its proper centre on ball or roller bearings , then instead of the slippers or guides rubbing in frictional contact round the whole circular path , they carry round with them their own guide .
The circular revolving guide may be termed \ldquo ; floating guide ring or , more shortly , " " floating ring There must , of course , be a certain relative sliding in this floating ring because of the relative angular velocity of the respective coupler rods , whose effect may still be supposed , although they have themselves actually disappeared .
This relative angular movement , however , is dependent entirely on the throw of the crank ; if the crank stroke is reduced this relative movement .
be correspondingly reduced , and hence the sliding movement of the slippers may be reduced to as small an amount as desired .
The importance of the new mechailism is evident when it is remembered bhat at high pressures the stroke itself usually becomes very small indeed ; hence the friction is not only reduced on account of the actual movement , but also very largely reduced because the viscous friction of the material of the slippers is a function of relative velocity of the surfaces in contact .
This , however , is not the only result which arises from this device .
The chief practical use of a variable stroke is the transmission of power , oil being used as the working fluid , and in a contrivan ce of the kind the working parts usually revolve in oil , which fills the outer case and ensures complete lubrication .
Now the action of this oil , whether the case is completely full or not , although not very important at low speeds , is very serious at high speeds , and the turbulent motion of the oil is capable of absorbing and thereby wasting a large proportion of the available energy of the machine .
If , however , the rotating guide ring shown in fig. 5 is made to form a rotating case , the oil is carried round with the revolving portion , the outer cover being kept empty , and the churning action entirely avoided .
Analysis of the two cases reveals their difference .
In fig. eccentricity of guide ring , radius of centre of guide pin , radius of slipper path ( i.e. rubbing surface ) , pressure on each plunger , centrifugal force on plnngers , number of plungers , VOL. LXXXVII.\mdash ; A. Dr. H. S. Hele-Shaw .
[ May 7 , In fig. constant for machine , angular velocity , coefficient of friction , frictional loss per revolution due to rubbing , loss per revolution due to resistance of fluid ( i.e. churning ) .
Then Case I ( with fixed guide ring ) , Case II ( with floating guide ring ) , approx. , approx. , This analysis of the work lost in the two cases reveals at once how gleat is the saving effected by the floating guide ring .
This is clear from the fact that not only are and much greater than when is at its maximum value , but because beyond this is continually reduced as the stroke is decreased and the pressure increased .
The combined ratio but the expression is not very simple or one which enables the ratio of losses to be easily seen .
The gain is , however , at once evident by comparing separately the losses due respectively to slipper friction and ( b ) churning .
Thus ( b ) In sn example of which experimental results are afterwards given , if , then Case ( a ) , Q. \ldquo ; ( ) , , , 1912 .
] Theory of Form of the Charnber Crank .
67 Fig. 7 .
ROKE Fig. 9 .
Fig. 8 .
SQ .
N STROKC Fi .
IO .
Theory of a New Form of the Chain .
As a matter of fact , these expressions do not take into account a certain amount of friction which is common to both systems , that is the fi'iction of the pistons and the friction of the fluid in the passages and ports .
In addition to these , there is the comparatively small amount of friction of the roller or ball bearing on which the floating ring revolves , though the last-mentioned friction is almost negligible .
A general expression may be obtained without much difficulty which would approximately represent the ratio of the loss with and without the rino , but this result has been more satisfactorily arrived at by actually testilg the input of the work from an electric motor and by measuring the discharge of an actual pump at different pressures , the pump having a floating guide ring , which could be either fixed or allowed to revolve freely , and in which either slippers or rollers could be used .
The pump with which the experiments were made was similar to the one which will be exhibited at the May Soiree of the Society by the kind permission of the Compayne Company .
This shows the actual details by which the floating of the guide ring is eflected , but which details are not dealt with in this note .
The results of the experiments are shown plotted in figs. 7 , 8 , 9 , and 10 .
Figs. 7 and 9 give the input and output under the different conditions for full stroke and half stroke respectively .
Figs. 8 and 10 show.the same results put in the form of efficiency curves .
The results are so clearly indicated by these diagrams that no further comment is necessary .
It is clear that as the stroke is diminished the relative effect is llagnified until at last when there is a very small stroke ( and that is the case where the greatest pressures are likely to be in operation ) we have , in the one without the floating ring , nearly all the work absorbed in friction , and the friction losses at their maximum , whereas in the case of the ring the friction is reduced to a minimum .
This effect is indicated in a striking way by the fact that whereas in fig. 7 , with the floating ring , the curve of input is parallel to the curve of output , without the floating , the curve diverges from it as the are increased , and the divergence becomes much more marked in the case of the diagram representing the effect with the smaller strokes , that is to say in fig. 9 .
Comparing the two mechanisms in which slippers are used , the diagrams show thab it requires more than twice as much power to operate a chamber crank chain of this kind to produce a given discharge of liquid at a given pressure without the floating ring than with it .
To put it another way , the efficiency at the best , without the floating ring , is not , at a reasonable working pressure , higher than 40 per cent. in one case , rising to 83 per cent. in the other , while with the stroke and pressure reduced , the efficiency without the floating ring may fall , even under working Influence of Condenseron Working of Ruh.mkorff Coil .
69 conditions , as low as 10 per cent. , a loss of nine-tenths of the whole energy available .
The thanks of the author are due to Mr. T. E. Beacham , B.Sc. , for his assistance in connection with this paper .
An Experimental of the Influence of the Condcnser on the Working of a hmkorff Coil , together a Practical Outcome thereof By WILLIAM HAMILTON WILSON .
( Communicated by Sir Oliver Lodge , F.R.S. Received March 8 , \mdash ; Read June 27 , 1912 .
) The opinion most generally held the action of the condenser in a Ruhmkorff coil seems to have been that the condenser is by the falling netic field immediately after interruption , and discharges back through the primary winding , setting up oscillations which cause the netism to fall very rapidly .
The subject has been dealt with matheatically by Prof. Colley and others .
* Lord Rayleigh has shown that very long secondary sparks can be obtained without the use of a condenser , by interrupting the primary current with great rapidity , such as by the severing of a wire with a rifle bullet .
Walter used a cathode ray deflected by the magnetic field to show that the primary current is with a frequency depending upon the condenser capacity , and that the best results are obtained by adjusting the condenser capacity to a certain critical value .
Oscillograph curves of primary current and secondary E.M.F. have been obtained by Armagnat and others .
An oscillograph method of such culves is described by Wittmann , S and Zenneck describes a method using a Braun tube To completely understand what takes place it is necessary to have curves of secondary E.M.F. and of the currents in all parts of the primary system , with ' Wied .
Ann 1891 , vol. 44 , p. 109 .
' Ann. der Phys 1897 , vol. 62 .
Kellyon , ' The Induction ) ' S 'Ann .
der Phys 1904 , vol. 12 .
' Ann der Phys ] , vol. 13 .
|
rspa_1912_0060 | 0950-1207 | An experimental investigation of the influence of the condenser on the working of a ruhmkorff coil, together with a practical outcome thereof. | 69 | 78 | 1,912 | 87 | Proceedings of the Royal Society of London. Series A, Containing Papers of a Mathematical and Physical Character | William Hamilton Wilson|Sir Oliver Lodge, F. R. S. | article | 6.0.4 | http://dx.doi.org/10.1098/rspa.1912.0060 | en | rspa | 1,910 | 1,900 | 1,900 | 5 | 124 | 3,442 | http://corpora.clarin-d.uni-saarland.de/surprisal/6.0.3/?id=rspa_1912_0060 | 10.1098/rspa.1912.0060 | null | null | null | Electricity | 84.485366 | Tables | 9.842546 | Electricity | [
21.803104400634766,
-67.00480651855469
] | Influence of Condenser on Working of Coil .
69 conditions , as low as 10 per cent. , representing a loss of nine-tenths of the whole energy available .
The thanks of the author are due to Mr. T. E. Beacham , B.Sc. , for his assistance in connection with this paper .
An Experimental Investigation of the Influence of the Condenser on the Working of a Ruhmkorff , together a Practical Outcome thereof By William Hamilton Wilson .
( Communicated by Sir Oliver Lodge , F.R.S. Received March 8 , \#151 ; Read June 27 , 1912 .
) The opinion most generally held regarding the action of the condenser in a Ruhmkorff coil seems to have been that the condenser is charged by the falling magnetic field immediately after interruption , and discharges back through the primary winding , setting up oscillations which cause the magnetism to fall very rapidly .
The subject has been dealt with mathematically by Prof. Colley and others.* Lord Rayleigh has shown that very long secondary sparks can be obtained without the use of a condenser , by interrupting the primary current with great rapidity , such as by the severing of a wire with a rifle bullet .
Walter used a cathode ray deflected by the magnetic field to show that the primary current is oscillating , with a frequency depending upon the condenser capacity , and that the best results are obtained by adjusting the condenser capacity to a certain critical value.f Oscillograph curves of primary current and secondary E.M.F. have been obtained by Armagnat and others.\#163 ; An oscillograph method of obtaining such curves is described by Wittmann , S and Zenneck describes a method using a Braun tube.|| To completely understand what takes place it is necessary to have curves of secondary E.M.F. and of the currents in all parts of the primary system , with * ' Wied .
Ann. , ' 1891 , vol. 44 , p. 109 .
t 'Ann .
der Phys. , ' 1897 , vol. 62 .
+ Kenyon , The Induction Ooil .
' S ' Ann. der Phys. , ' 1904 , vol. 12 .
|| 'Ann der Phys. , ' 1904 , vol. 13 .
[ Mar. 8 , Mr. W. H. Wilson .
Influence of information as to relative phases and amplitudes , and the following research , commenced on February 27 , 1909 , was undertaken with the object of ascertaining the exact function fulfilled by the condenser .
Joubert 's method was adopted for obtaining the curves , using a Kelvin quadrant electrometer and a contact-maker rigidly attached to a motor-driven shaft , carrying an interrupter immersed in oil .
The interrupter^ was a disc of ebonite with a copper contact let into its edge ; a springy copper brush rubbed on the edge of the disc , and made contact once in each revolution .
The contact was connected to a slip-ring from which a brush carried the current to the coil .
The potential differences for operating the electrometer were obtained by resistance strips placed in each of the three parts of the primary circuit , a search coil of a few turns wound round the outside of the secondary at the middle , and a non-inductive reducing ratio placed across the interrupter terminals .
The curves obtained for the P.D. across the interrupter were found to be so closely the same as those for the secondary search coil that observation of them was not continued .
The diagram of connections generally adopted is shown in fig. 1 .
Fig. 1.\#151 ; Diagram of connections used in the investigation.\#151 ; 1 , primary of coil ; 2 , secondary ; 3 , exploring secondary ; 4 , battery ; 5 , condenser ; 6 , interrupter ; 7 , 8 , and 9 , resistance strips ; 10 , reducing ratio ; 11 , multiple-way switch ; 12 , contact-maker ; 13 , reversing switch ; 14 , condenser ; 15 , quadrant electrometer .
One coil experimented with , made by a well-known maker , was rated to give a 6-inch spark .
The primary resistance was 0'29 ohm , inductance 0'0114 henry .
The condenser capacity was P43 microfarads .
The secondary resistance was 8023 ohms .
The above described interrupter was substituted 1912 .
] Condenser on Working of Ruhmkorff .
for the ordinary platinum contact hammer interrupter .
For other experiments special coils were constructed , having iron cores 13\#163 ; inches long , If inch diameter , of good quality annealed charcoal iron wire , No. 28 S.W.G. well soaked in paraffin wax .
Primaries of No. 14 S.W.G. silk covered copper wire were wound on the cores in layers of 138 turns each , so arranged that the layers could be connected in series or used singly .
Experimental secondaries of No. 35 S.W.G. silk covered copper wire were wound by a special method in Hat helical sections to go over the primaries , with ebonite insulation between .
Condensers of various capacities were made up of tinfoil sheets and paraffined paper .
Where it is not otherwise stated the tests were made on coils constructed as described above .
The magnetisation curve for one of the cores obtained by means of a ballistic galvanometer test , showed that this was practically a straight line up to the point where saturation begins .
This knowledge is of great assistance in examining the results obtained , since the self-induction of the primary can be assumed constant up to the limit of core magnetisation advisable in well designed apparatus .
The curves of rising current in the primary , and secondary E.M.F. , when the battery circuit is closed , were first studied .
These showed that when the secondary winding is absent the current in the primary rises strictly according to Helmholtz 's equation c = E/ R .
[ 1 \#151 ; g~E\lt ; /L ] , when the magnetisation of the core is not carried beyond the point where saturation begins .
When the usual secondary winding is in place , however , the primary current no longer strictly obeys this equation .
During the initial stages of its rise there is an oscillating current superposed on the magnetising current .
This oscillating current seems to be due to the reaction of capacity currents in the secondary set up by the sudden E.M.F. generated in it at " make , " which surge to and fro and gradually die out .
Walter has shown that a high supply voltage is necessary to secure a reasonable frequency of interruptions of the primary current , while maintaining the full spark length of a coil having a given primary self-induction .
It can be shown , however , that the energy -fLC2 stored in the magnetic field can be made large even if the supply voltage is low , and the frequency of interruptions is high , if the self-induction of the primary is made small ; since the time constant of the circuit and the energy vary only directly with L , while the energy varies as C2 .
The curves in fig. 2 show that when the magnetising current is interrupted , the current persisting in the primary winding , after metallic contact is broken , divides into two distinct parts , one of which passes across the interrupter contacts in the form of a spark , while the other charges the Mr. W. H. Wilson .
of [ Mar. 8 , condenser and oscillates to and fro , with decreasing amplitude .
The secondary E.M.F. starts to rise as soon as interruption begins , and reaches its maximum value about the instant when the current in the primary is passing through zero , if the interrupter spark has died out .
This result is confirmed by observations obtained in a number of tests .
foIt in t turn 2 A mperes Interruption begins .
C. \ A .00083 Second Fig. 2.\#151 ; Curves of secondary E.M.F. ( A ) , primary current ( B ) , condenser ( C ; , and interrupter ( D ) currents at " break .
" Secondary not sparking .
C and D shown negative for clearness .
It does not appear , therefore , that the condenser demagnetises the iron core by discharging back through the primary .
The magnetism of the core must be substantially zero when the primary current is zero , since at this instant the condenser E.M.F. is equal and opposite to the E.M.F. induced in the primary by the changing magnetic field .
The secondary E.M.F. will be at its maximum , since the rate of change of the field is greatest when changing sign .
The energy ^LC2 , originally stored in the magnetic field before interruption began , has been transferred to the condenser , after making due allowance for the energy lost in the spark at the interrupter , and in damping caused by C2R in the primary and connections , eddy currents and hysteresis .
The maximum E.M.F. on the secondary terminals is equal to the voltage to which the condenser is charged multiplied by the ratio of transformation of the coil .
1912 .
] Condenser on Working of Ru 73 The following figures are calculated from curves obtained , and confirm the above remarks:\#151 ; Joule per cycle .
Energy supplied by battery 0-0642 55 lost in extra resistance of shunts 00383 55 supplied to coil 0*0259 55 lost in OR in primary 0*00453 = 17*5 percent , of input .
55 stored in magnetic field before inter- 0-0205 = 79-5 55 55 ruption 0-00728 = 28 55 lost in spark at interrupter 55 55 55 lost in hysteresis and eddy currents 0-00253 = 9-8 55 55 55 stored in condenser at maximum 0-0116 = 45 55 55 voltage These figures show that the efficiency of this coil , under the conditions of the test , with the secondary just able to spark across the gap , must be lower than 45 per cent. , since when the spark passes further losses must occur in the primary , core , and secondary .
It will be noted from fig. 2 that the secondary E.M.F. is an oscillating one , with considerable inverse half-waves when no spark passes ; and that the first half-wave is longer than succeeding ones when the oscillation settles down , practically 90 ' out of phase , to the natural periodic time of the primary oscillating current .
If the secondary is only just able to send a spark across the gap , it is clear that the energy of the spark is produced by the discharge of the condenser through the primary ; while if the spark gap is shortened the energy will be produced partly by the falling magnetic field and partly by the discharge of the condenser .
When the spark is very short the secondary discharge becomes practically unidirectional , if the magnetic leakage between primary and secondary is small , and the total resistance of the secondary circuit is not too high .
Fig. 3 shows that , under these conditions , the primary current and the condenser current increase in frequency due to the reaction of the secondary current .
In these tests the current across the interrupter was a steady leak , as the resistance of the shunts inserted for the tests damped out the oscillations which were found under normal conditions to take place across the interrupter .
By suitable adjustment of the self-induction of the circuit through the interrupter it was possible to obtain curves of these oscillations , but under normal circumstances their frequency is too high for them to be detected by a contact maker method .
The adjustment of a circuit inductively coupled with the interrupter leads till maximum resonance was obtained , indicated that with normal conditions the frequency is several ^hundreds 74 Mr. W. H. Wilson .
Influence of [ Mar. 8 , of thousands per second .
Other investigators have observed these oscillations.* It was found that much longer sparks could be obtained from the coil when these oscillations were present , and any resistance or inductance placed -Amperes Interruption \ -.00083 Second Fig. 3.\#151 ; Curves showing currents in primary ( A ) , condenser ( B ) , and across interrupter ( C ) when secondary was sparking 5/ 32 inch .
Six-inch coil .
in their path at once decreased the secondary spark .
For this reason the connection of the condenser directly across the primary , which would be desirable to eliminate the supply source from the path of the charging current to the condenser , will not in most cases give good results .
Fig. 4 shows the reduction in the periodic time of the secondary E.M.F. and increase in amplitude when the capacity of the condenser is reduced .
If the periodic time is decreased too far , either by decrease of the condenser capacity or of the self-induction of the primary , the secondary E.M.F. falls off .
This is due partly to the increased loss in the interrupter spark and partly to increased eddy current loss in the primary and core .
Tests showed that when the frequency of the oscillations much exceeds 1000 per second , eddy current losses become very considerable .
Curve E in fig. 4 shows that the action of the condenser in storing the energy of the magnetic field is the same , whether placed across the primary * ' Electrician , ' 1909 , vol. 63 , p. 720 .
Secondary E.M.F with condenser \ across primary winding 138 turns .
Secondary E.M.Fwith condenser / across secondary of equal number of turns .
i Interruption begins / ^ Curve E U-v00033 second\#151 ; J Fig. 4.\#151 ; Three curves of secondary E.M.F. with different condenser capacities , and one curve with condenser across a secondary , secon ary E.M.F. , with smaller capacity condenser , primary inductance 0*00396 henry ; B , secondary pr'mary inductance 0 00396 henry ; C , secondary E.M.F. with greater capacity in condenser , 00396 henry ; D , current in primary winding with 1'88 mfd .
condenser .
AVs.-Thia is positive , but shown 1912 .
] Con denser on Working of Ruhmkorff Coil .
Mr. W. H. Wilson .
Influence of [ Mar. 8 , winding or across a secondary of similar number of turns , when the magnetic leakage is small .
It was noted that when the energy in the magnetic field was so small as to cause no appreciable spark at the interrupter , a longer secondary spark could be obtained without a condenser on the primary than with one .
The conclusions drawn from the investigation are as follows:\#151 ; A low primary self-induction is desirable to enable considerable energy to be dealt with when only low supply voltages are available , but tends towards bad sparking at the interrupter , and , if obtained by reducing the primary turns , to serious inverse E.M.F. at " make .
" The condenser acts normally ( a ) by limiting the maximum voltage across the interrupter contacts ; ( b ) by limiting the rate at which that voltage rises as the contacts are separated ; ( c ) by producing high frequency oscillations across the interrupter which delay the loss of energy that would otherwise occur ; ( d)by limiting eddy current losses in the primary and core .
Sparking at the interrupter may be made as small as desired by sufficiently increasing the periodic time of the primary oscillating circuit , but this necessitates a considerable increase in the ratio of transformation of the coil for a given spark length .
To obtain long sparks with reasonable dimensions of the secondary a small periodic time is required .
To avoid serious inverse E.M.F. at " break , " magnetic leakage between primary and secondary must be as small as possible .
A number of arrangements were devised whereby magnetising turns of low self induction could be combined with an oscillating circuit of long periodic time , which periodic time could be reduced to any desired extent after interruption of the battery current , thus giving long sparks with few secondary turns and a small amount of inverse E.M.F. Fig. 5.\#151 ; -1 , primary of coil ; 2 , secondary of coil ; 3 , magnetising turns on inductance ; 4 , extra turns on inductance ; 5 , condenser ; 6 , interrupter j 7 , slip-ring brush ; 8 , mains brush ; 9 , inductance short-circuiting brush ; 10 , battery .
primary current , coil sparking ^ 19 cm .
between points .
primary current , coiI net sparking .
Second .
E.M.F. in 1 turn , coi !
not sparking .
\Secondary E.M.Fcoil sparking 1 F9 cm .
between points .
i* Secondary E.M.F \0*\ i f \ primary current .
Inductance unshortcircuited Inductance short- \ -circuited \ ( Inductance shortcircuited Fig. 6.\#151 ; 10-inch spark coil operated according to fig. 5 .
1912 .
] Condenser on Working of Ruhmkorff Coil .
77 The most suitable arrangement arrived at is shown in fig. 5 .
The magnetising turns are on a separate iron core to the primary and 78 Influence of Condenser on Working of Ruhmkorff Coil .
secondary windings of the coil , and have in series with them a sufficient number of turns to give the long periodic time for satisfactory interruption of the supply current .
Tapping points on this inductance , or autotransformer , enable the magnetising turns to be adjusted to suit the supply voltage .
Fig. 6 shows curves of primary current and secondary E.M.F. obtained with this arrangement .
At " make " the supply voltage charges the condenser , by transformer action , to a voltage depending on the ratio of the total turns on the inductance to the magnetising turns .
The charging current passes through the primary of the coil , inducing in the secondary an oscillating E.M.F. of small amplitude , the first half-wave of which is a direct , and not an inverse one .
This E.M.F. can be entirely suppressed by a modification in connections , or by providing a brush which short-circuits the primary at " make .
" The supply also magnetises the inductance core , and at " break " the condenser discharges back through the inductance , building its magnetic field up still slightly higher .
The magnetic field then falls and charges the condenser in the reverse direction .
The time taken to do this is normally made so long that the interrupter contacts are separated by about 1 inch before the condenser is fully charged , and since the voltage between them is determined by the supply voltage and the ratio of transformation of the auto-transformer , sparkless opening of the interrupter can be obtained without the use of oil or gas .
When the condenser is fully charged the necessary reduction in the periodic time of the oscillating circuit is obtained by short-circuiting the inductance .
The condenser then discharges with great rapidity through the primary of the coil , and induces a very high E.M.F. in its secondary .
If the secondary circuit is open too wide for a spark to pass , the E.M.F. is an oscillating one ; but immediately a spark passes the condenser discharge becomes almost entirely unidirectional , owing to the reaction of the secondary current .
This is well shown in the curves obtained with the coil sparking , but the coil used in this experiment had only a partially closed magnetic circuit .
The best results are obtained by using a completely closed core transformer in which the magnetic leakage can be made very small .
The early part of this work was carried out at King 's College , London , and the author wishes to acknowledge his indebtedness to Prof. Ernest Wilson for affording him facilities for carrying it out .
He further wishes to thank Messrs. F. S. Eobertson , E. E. Shawcross , H. W. Franks , A. E. O'Dell , and G. F. O'Dell , for help received , also Mr. F. W. Wright , who took great pains in constructing most of the apparatus experimented with .
|
rspa_1912_0061 | 0950-1207 | On the diurnal variations of the electric waves occurring in nature, and on the propagation of electric waves round the bend of the earth. | 79 | 99 | 1,912 | 87 | Proceedings of the Royal Society of London. Series A, Containing Papers of a Mathematical and Physical Character | W. H. Eccles, D. Sc., A. R. C. Sc.|Sir Arthur W. R\#xFC;cker, F. R. S. | article | 6.0.4 | http://dx.doi.org/10.1098/rspa.1912.0061 | en | rspa | 1,910 | 1,900 | 1,900 | 21 | 315 | 9,928 | http://corpora.clarin-d.uni-saarland.de/surprisal/6.0.3/?id=rspa_1912_0061 | 10.1098/rspa.1912.0061 | null | null | null | Fluid Dynamics | 30.31595 | Meteorology | 18.86245 | Fluid Dynamics | [
39.46500778198242,
-0.8338354229927063
] | ]\gt ; On , Diurnal Variations of the Etectric Waves Occurring in , and on the of Electric Waves Round the Bend of the , Earth .
By W. H. , D.Sc .
, A.R.C.Sc .
( Communicated by Sir Arthur W. Rucker , F.R.S. Received March 5 , \mdash ; Received in revised form June 5 , \mdash ; Read June 27 , 1912 .
) Since the earliest days of electric wave telegraphy it has been known that there exist natural electric waves which frequently affect the apparatus at a wireless telegraph station more powerfully than do the message-bearing waves .
In the telephonic method of receiving nals , where the apparatus is so arranged that the effect of a of waves is .to cause a pulse of electric current to pass from the " " detector\ldquo ; through the telephones , the natural electric waves make themselves evident as clicks , or as rattling noises , in the telephones .
They are easily distinguished from signals , for the sounds produced by the latter are more ular , and , in fact , are often musical in character .
The natural electric waves are doubtless due to electric discharges taking place between masses of electrified air , or between such masses and the earth .
Till recently it was not knowu whether the discharges affecting any particular station were taking place at distances of hundreds of miles or at distances of thousands of miles from the station ; but it is now certain that for stations in gland the distances concerned must usually be reckoned in thousands of miles .
This point was settled by tracing and identifying individual natural wave trains at two receiving stations , one in London and the other in Newcast]e .
* It was found that about 70 per cent. of the natural wave trains perceived at one station could be identified with those perceived at the other , and , further , that more than half of these were of much the same intensity at both stations\mdash ; from which it may fairly be inferred that the distance of the discharge is great compared with the distance between the stations .
The number of natural wave trains , or ' strays\ldquo ; as they are commonly called for brevity , received at any station varies in general from hour to hour .
In these variations are most pronounced during the summer months , principally on account of the frequency of local lightning storms during these months .
( The word local is here intended to mean within a * Eccles and Airy , ' Roy .
Soc. Proc 1911 , , vol. 85 .
In all that follows it is assumed that the sources of the wave trains are not extraterrestrial .
VOL. .
W. H. Eccles .
riations of the [ June 5 , radius of two or three hundred miles of the station .
) During the winter months , on the contrary , the number and intensity of the strays are elatively regular .
The study of the phenomena to the strays of distant origin may clearly be more favourably pursued in the winter than in summer , since the confusing feature of local lightning discharge is absent in winter .
Besides the seasonal variations in the number and the intensity of the strays there is at every station a well-marked diurnal variation .
Leaving out the irregularities due to local storms , we may say that the strays are in eneral more frequent and numerous the night hours than during the day hours .
The variations may be represented graphically as a curve in any of the methods indicated below and then they appeal ' as shown in fig. 1 , which may be regarded as a typica124 hours ' continuous record of the integral of number and intensity .
These diurnal FIG. -four hours ' Continuous Record of Integral Intensity of Strays , November 14 and 16 , 1910 .
variations have not yet been investigated .
The author haslnot been able to find any account of observations in which the effects of local storms have been eliminated .
From what has been said it is plain that the most interesting parts of the diurnal curve are those at which day and night conditions meet and change one into the other .
To investigate these important parts of the curve the ordinary apparatus of a wireless telegraph station may be utilised .
The apparatus employed by the author consisted of an antenna of 12 wires sloping from south to north at an angle of about from a height of 170 feet , connected at the bottom to a coil of variable inductance , which was in turn 1912 .
] Electric TVaves Occurring in Nature .
connected to an earth plate .
The inductance was usually about cm .
, and the natural period of the antenna was about 50,000 per corresponds to a wave-length of about 6000 metres .
This frequency was selected merely because it was of the same order of nitude as that of the Marconi Transatlantic stations , signals from which were also being measured from time to time .
The antenna inductance engaged inductively with another coil forming part of a secondary circuit that could be tuned to the antenna by aid of a variable condenser in it .
A detector and telephone were connected with the circuit in the ordinary way .
The Pickard zincite-chalcopyrite detector was used .
With such apparatus several ways of making and recording observations present themselves .
The easiest and most obvious method consistsinlistening at sumrise and sunset to the noises made in the telephone by the natural wave trains ; other methods involve the use of a galvanometer in place of a telephone receiver .
The observations in this paper were practically made with the hone .
A careful listener ill find that on a typical the following phenomena appear :First , to listen about half an hour before sunrise , the strays heard in the telephone are loud and numerous and much as they have been all night ; then about 15 minutes before sunrise a sets in , the strays get weaker and fewer rather quickly , till at about 10 minutes before sunrise a distinct lull occurs , of perhaps a minute 's duration .
At this period there is sometimes complete silence .
Then the strays begin to appear again , and within 10 minutes of the lull they have settled down to the steady stream proper to the daytime .
These day strays are weaker and fewer than the night strays , except on rare occasions .
The lull is sometimes very pronounced , and at other times there is no lull at all .
It is usually more marked at sunset than at sunrise .
The simplest way of representing these events , just as they are heard in the telephone , is by a hand-written record of the sounds .
With practice , it becomes easy to make pencil marks on paper ruled in convenient units of time in such a way that the height of the mark represents the intensity of the sound , and the eneral shape of the mark the duration and character of the sound .
Some of the records that have been obtained in this way are reproduced in figs. 2 to 5 .
These are selected out of a large number of records as examples of the different kinds of minima obtained at both sunnse and sunset .
It will be noticed that at sunset the minimum is about 10 minutes after the calendar time of setting .
Records such as these can be made to yield quantitative results of sufficient accuracy for the discussion of so irregular a phenomenon , by plotting rough estimates of the time integral of the intensity of the strays , that is , by estimating the Dr. W. H. Eccles .
Variations of the [ June 5 , aggregate area of the representative marks in any convenient intervals of time .
The of this time integral taken over , say , two minutes , is treated as the ordinate corresponding to the middle moment of the interval , which is taken as abscissa and a smooth curve drawn .
But an even rougher method , consisting of counting the number of marks in each two minutes ' interval , ) using these numbers as ordinates corresponding I. FIG. 2.\mdash ; Strays , November 14 , 1909 .
Sun rises at 7.17 FIG. 3.\mdash ; Strays , November 13 , 1911 .
Sun sets at 4.13 FIG. 4.\mdash ; Strays , November 23 , 1911 .
Sun sets at 4.0 P.lf .
A. FIG. 5.\mdash ; Strays .
December 9 , 1911 .
Sun sets at.3.50 to the mid-times , may suffice in many cases .
Of course , a theoretically more perfect procedure would be to pass the detector currents through a sensitive galyanometer a heavy moving system .
A time record of the deflections indicated by the instrument would , at first sight , give a better quantitative result the hand-made record just described ; but actual trials show that there is an increase of accuracy only when the strays are very numerous , more numerous , in fact , than on the average occasion .
Adopting , then , the method already ibed , we obtain curves such as that of fig. 6 .
These observations were made at the author 's laboratory in London .
The scientific value or importance of an olated result like the present one FIG. 6 .
\mdash ; Integral Intensity Curve , Sunset , December 9 , 1911 .
1912 .
] Electric in Nature .
8 $ may be regarded as very small in itself .
But , in the present case , the result , is so completely inexplicable by the ordinary conceptions of the propagation of electric waves through the atmosphere , that we are compelled by its refusal to fit into the accepted scheme of things to attempt an extension of that scheme .
Now , in searching for an explanation of these twilight minima , we have to notice that there are two main alternative possibilities .
In the first place , the atmospheric that produce the strays may themselves , for some reason , become infrequent at twilight ; and , in the second place , the space which the waves travel may become temporarily less easily traversed in twilight .
The former alternative , when taken in conjunction with the author 's experience over nearly of itude that it is the receiving station 's local time which is concerned , implies that the bulk of the strays received at a given station are produced by atmospheric discharges occurring in regions of the atmosphere that have the same sunset and sunrise as that station ; or , in other words , implies that the strays observed have their origin at places on ( roughly ) the meridian of the receiving station .
Evidence has been already quoted , however , to show that the larger proportion of the strays observed at any station usually originate at a great distance from the station ; hence the alternative under discussion leads to the unlikely conclusion that every station receives its strays from atmospheric a great distance along its own meridian , and from that place solely .
We turn , therefore , to the other alternatiye , that the propagation of electric waves towalds any place is hindered by some unknown effect of That this latter alternative is really the correct one is strongly indicated by observations ( to be described later ) on artificial electric waves from considerable distances .
Electric waves travelling near the earth 's surface might conceivably affected by the presence or absence of the sun at a point of observation in two obvious ways : First , light may ionise the air locally in sufficient degree to cause considerable absorption of the energy of the waves ; and , secondly , sunlight might affect the electrical resistance of the ground within , say , 50 miles lound the antenna , and thus have an effect on the absorption of the waves when they run over this region .
Considering the former hypothesis first , the atmospheric absorption by ionisation due to solar radiation must , if it exists , be greater in strong sunshine than during twilight , which is contrary to observation .
In point of fact , the absorption arrived at in this manner is , as will be shown incidentally later , much too small at any time of day to produce the effects actually observed .
Moreover , it has long been known that the propagation of electric waves over short distances is Dr. W. H. Eccles .
Variations of the [ June 5 , practically as perfect in strong sunlight as in the dark .
On all these counts , therefore , the supposition that the minima phenomena under discussion can be explained by ionisation of the lower layers of the atmosphere must be discarded as untenable .
We must turn to the possibility of alterations in the resistance of the ground round the antenna , alterations of such a nature that the waves are absorbed much more freely during a certain few minutes of twilight than before or after .
Here we may at the same time consider a subordinate possibility , namely , that the resistance of the ground within a few yards of the earth plates of the antenna yary through a minimum value during .
If this really happened there would be extra dissipation near the earth plate of the of the oscillations excited on the antenna by the incoming waves .
Both of these views have been negatived by the author 's observations on signals coming from short distances , which show that signals originating at distances of less than 50 miles do not undergo appreciable diminution in strength , even on days when the stray minimum is well marked .
But , to make certain of the non-existence of the subordinate possibility just referred to , a series of minations was made , during the past autumn , of the high-frequency resistance of the antenna and its earth connection at various frequencies and at various times of the day ; and especially at the twilight periods .
These measurements were carried out by two distinct and trustworthy methods .
The details of the determinations need not be given here ; it is sufficient to that the results leave no doubt that the local earth resistance does not vary in the rapid manner , nor to the wide extent , that is required to explain the twilight minim of the strays .
Another point that supports the view that the stray minimum is not produced by strictly local causes may be stated here .
It is very noticeable that the twilight minima are easier to observe when the receiving apparatus is adjusted for long waves ( say 6000 metres ) than when it is adjusted for short waves ( say 1000 metres ) .
This is of obvious significance when taken with the fact that signal waves of great length are most suitable for communication over great distances .
Now the most striking difference between signals received from long and from short distances is that in the case the curvature of the earth may exert appreciable , perhaps very grcat , influence on the signal This immediately raises the question of the manner of propagation of long electric waves round the earth .
The fact is now thoroughly established that signal-bearing waves can travel a quarter of the way round the globe and still be easily perceptible .
That this is not a manifestation of ordinary 1912 .
] Electric Occurring Nature .
diffraction has been thoroughly settled by the investigations of Poincare , Macdonald , Nicholson , and others , whose work has shown irrefutably that the energy propagated round a quarter of the globe by the process of diffraction would be utterly inappreciable .
Heaviside has suggested that , in the type of waves used in wireless aphy , the Faraday lines of electric force are attached , as it were , to the earth , and slide its surface , and that therefore they cannot leave it ; but this view , in fact , rows us back on the diffract , ion result .
Again , in 1906 , Zenneck added to this suggestion a consideration based on a well-known illustration of Poynting 's theorem .
In his original memoir*on the propagation of energy in the electromagnetic field , Pointing gives as an illustration of the theorem the case of a wire possessing resistance and carrying an electric current .
Heaviside , referring to this illustration , showed that the moving electric field cannot be purely radial ; other words , the Faraday lines ging to { he flowing electricity must lean forward as they move along the wire\mdash ; so that the energy vector shall have a component perpendicular to the surface of the wire .
This particular case has been worked out in great detail since the date of the memoir , but Zenneck 's application was to the simple case of the propagation of a plane wave over a badly conducting solid , such as the earth , with a plane boundary .
His suggestion is , briefly , that the tilting forward of the wave fronts near the conductor will lead to a general slow turning downward of the waves towards the earth , so that a large proportion of the energy of the waves will be deflected round the bend of the earth instead of being propagated linearly into space .
This suggestion does not in reality assist the pure diffraction theory at all .
Another hypothesis was put forward by Heaviside in 1900 , when he suggested that the attenuated gases of the upper atmosphere might provide a conducting surface concentric with the earth , between which and the surface of the earth itself the waves might spread with two-dimensional divergence .
This hypothesis has not yet been supported or denied by any trustworthy experiments or observations .
Such experiments or observations will necessarily have to be made on waves that have travelled long distances , for the upper layers of the atmosphere cannot be greatly concerned in shortdistance transmission .
But it will be perceived , from the remarks already made on the minima of natural electnc waves , that this upper conducting layer might supply the explanation of the phenomenon , and thereby gain some support .
On examination , however , it appears that the phenomenon cannot be explained by means of the bare hypothesis , and still less can the EJectrical Papers , Phil. Trans. Dr. W. H. Eccles .
of the [ June 5 , other recorded facts of long-distance transmission be explained .
The writer has therefore investigated another , and closely related , possibility , which , it turns out , throws light on the causes of the stray minimum , as well as on many of the facts of long-distance transmission .
To these new considerations we now turn .
The hypothesis to be introduced is based on the influence of the ionisation of the air on the propagation of electric waves through it .
It is well known that , under normal conditions , the air at the sea-level is only slightly ionised even in strong sunshine , and that at a height of a few miles above the earth 's surface the ionisation is , according to observations from balloons , sometimes 20 times as great as at the surface .
Higher still the ionisation doubtless increases further , on account of the more and more intense ionising action of the solar radiation , which , it is plain , must be greater in these higher and rarer regions than in the dense regions below .
No law can be legitimately assigned for the computation of this gradual transition from low conductivity to high conductivity , yet , for the purpose in hand , it is necessary to form idea of the effect of this heterogeneity on the propagation of electric waves .
It is first necessary to examine the effect of charged ions of molecular mass on the velocity of the waves , and here we may follow , with suitable modifications , the standard methods applied to the study of optical dispersion in media containing electrons .
Let be the charge , the mass , of each ion , and let be the number of ions per cubic centimetre at a point whose co-ordinates are , referred to a right-handed rectangular frame of axes with the axis of vertical .
Suppose that electric waves are advancing .
through the medium in the positive direction of the axis , and with electric force , magnetic force , at the point .
Then if be the permeability of the medium and the dielectric constant of the unionised air , and where indicates the displacement of each ion from its original position produced by the waves .
The equation of motion of an ion is where is a frictional constant of viscous type .
If the time factor in be , this equation becomes 1912 .
] Electric Waves in Eliminating and among these three equations , we have There is a solution of the form for waves of frequency , if the velocity and the absorption factor Here has been put for the quantity , it will be shown , is usually smaller than unity .
In addition , the quantity is usually very small compared with unity , hence , approximately , ; or the absorption coefficient per wave-length is mp It should be mentioned that , in formin the equations , it has been implicitly assumed that the ions are so heavy that they acquire only small locities and make very small excursions under the action of the waves .
That is to say , the ions are supposed to be collections of molecules , or , at the smallest , single molecules .
The absorption in the case of very small ions , that is , electrons , has been worked out by J. J. Thomson , different considerations from those appropriate here .
ough estimates of the various magnitudes involved in the last equations may be obtained by using the results of laboratory experiments on ionised gases , though , unfortunately , there are as yet but very few data available on the ionisation of air by solar radiation .
First notice that the friction coefficient can be estimated from experiments on the terminal velocities of ions in various gases .
From the equation of motion of an ion we see that its terminal velocity under a steadily applied electric field is 'Phil .
Mag August , 1902 , p. 253 .
Dr. W. H. Eccles .
of the [ June 5 , In air under standard conditions cm . .
in a field having a gradient of 1 volt per centimetre .
Take in electromagnetic units , then , roughly .
Again taking and in grammes , then ? .
Thus waves of the order of frequency 1,000,000 per second , the two terms in the denominator of the quantity are of about the same order of importance at low levels in the atmosphere .
For waves of lower frequency the term is much more important than the term , which may then be neglected in the denominator of .
At levels , on the , the term probably becomes ible in comparison with since the value of is known to fall off much faster than that of as the rarefaction increases .
Thus , at high levels , we have , approximately .
At low levels the value of works out as with the numbers already assumed .
The number of ions per cubic centimetre at sea level is often given as between 1000 and 10,000 .
Thus is quite ible compared with unity if this estimale of and that of are valid .
At high levels , the last equation , we find for ( corresponding to a wave-length of nearly 200 metres ) and for ( corre( to a wave-length of neal.ly 2000 metres in ordinary air ) .
It is more than probable , however , that at moderately high levels , where the air is rather rarefied\mdash ; for example , at a of 20 miles the pressure is , on the theory of convective equilibrium , about 1/ 100 of the pressure at sea level\mdash ; the ion is of much smaller mass , say 100 times smaller , than is assumed above , and this would make the last figure become for For convenience in discussion , the portion of the atmosphere below the permanently conducting layer and throughout which the equation holds good , that is the portion of the atmosphere which is ionised strongly and directly by the sun , will be called the middle atmosphere .
The part below this will be called the lower atmosphere , and here the equation is probably appropriate while has low values .
Of the middle atmosphere and of the upper atmosphere we know nothing directly .
Perhaps the best information available is that contained in the memoirs of P. Lenard and C. Ramsauer , * who showed that the ultra-violet light of the sun will produce in air two effects of interest in the present connection .
One effect is that the ultra-violet light , and possibly the cathode rays , of the sun produce carriers of 'Heidelberger Akademie Sitzungsber 1910\mdash ; 11 .
1912 .
] Electric Waves Nature .
molecular size , and the other is that these same agencies also produce , by direct action on the gases of the atmosphere , condensation nuclei consisting of solid or liquid compounds which are not electrically charged when first formed .
Evidently , the condensation nuclei can have only slight influence on the value of the quantity as compared with the electrical carriers of molecular size .
These heavy ions , or condensation nuclei , doubtless frequently become by attaching one or more of the light ions , which has the effect of putting such ions out of action for our purposes .
The lighter ions are probably in a majority in the higher parts of the middle atmosphere , and the heavy ions in a majority in the lower parts , and also in the lower atmosphere .
It may be mentioned that the heavier ions found in the lower atmosphere , whether consequences of solar radiation or not , escape counted by the kind of apparatus usually used in measurements of atmospheric electricity , on account of their immobility .
So far as the quantity is concerned the principal difference between day and night conditions , and between the conditions at different times of the day , is due to the variations of the number of ions per cubic centimetre provided by solar radiation .
It is not possible to be precise on this matter , even in the lower .
But , broadly , it is clear that the value of in the lower and middle atmospheres must vary considerably with the obliquity of the sun 's rays at the place , that is to say , with the season and the of day , and also must vary profoundly from daylight to darkness .
About the time of sunrise at any particular place the process of ionisation by the solar radiation will be occurring at all heights of the atmosphere over an area many miles to east and west of the place ; at sunset recombination of the ions will occur through a similar space .
Of course the layers nearest the earth will be least disturbed in electrical constitution , mainly for the reason that the sum 's rays must have been robbed of much of their ionising powers by the time they reach low levels ; but it is known from direct observations at various levels up to heights of several miles that the influence of the sun is quite perceptible .
But , in fact , it is easily seen from the formula deduced above for the absorption per wave-length , that the normal ionisation observed in the lower atmosphere produces inappreciable absorption of the waves at any time of day over terrestrial distances .
Our knowledge of the conditions ruling in the hours of darkness is even less precise than that of the day conditions .
The very rapid rate of recolubination of ions when the ionising agent is removed points to the possibility of the middle atmosphere being perfectly free from ions during darkness .
But it is probable that there occurs during the day a great sifting of oppositely charged ions under the operation of the earth 's vertical electric field , Dr. W. H. Eccles .
Diurnal Variations of the [ June 5 , ions moving up and negative ions moving down , with the result that some parts of the middle atmosphere may remain ionised after the sun has set .
If we suppose , however , that the ions do for the most part recombine , then the effect of the change from day to night is to remove a veil , as it were , of ionised air from between the upper conducting layer and the earth .
Since the velocity of the waves in the sunlit middle atmosphere is greater the higher the level at which they are travelling , a ray of electric radiation from a point of the earth 's surface in a direction inclined upward will pursue a straight path in the lower atmosphere and a slightly bent path , with its concavity downwards , in the middle atmosphere , thus following to a greater or less extent the curvature of the earth .
If its curvature in the middle atmosphere is on the average greater than that of the earth\mdash ; and not otherwise\mdash ; the ray will be turned down the lower atmosphere and will traverse a straight line .
In other words , the wave-fronts will be tilted forward as they tlavel , in a manner quite analogous to the refraction of sound in air when the temperature varies upward .
This bending of the rays may be given for shortness the name ionic refraction ; it would be very rapid in layers where approached unity .
Thus the radiations diverging in all directions from a lightning stroke or from a wireless telegraph antenna become confined in the day between the conducting surface of the earth and a certain level in the middle atmosphere .
Even the rays that start horizontally from a placi on the earth 's surface must , owing to the earth 's curvature , reach , within 300 miles of the source , to heights where the air may be expected to be strongly ionised , and must then suffer refraction downwards .
Since the quantity is inversely proportional to the frequency of the transmitted waves , the limiting height of penetration of the waves is smaller the lower the frequency , and therefore low-frequency waves become concentrated nearer to the earth 's surface than do higher frequency waves .
The curvature of the trajectory of waves travelling at a height is , being the velocity at the place .
But when is small , and therefore the curvature is approximately .
If we assume a condition of things in which the radius of curvature of rays at all heights is , where is the radius of the earth , and that at we find , approximately .
Ihough , in fact , the bending of rays in the lower atmosphele is probably not so great as this , the equation indicates that the order of magnitude of required in the middle atmosphere at , say , a height of 20 miles is about 1912 .
] Etectric Occnrnng in .
This in turn indicates that the number of ions per cubic centimetre should be about 160,000 when the wave-length is 2000 metres , and about 16,000 when the wave-length is 6000 metres .
Such ionic concentrations are not improbable .
It may be objected that there has as yet been no experimental corroboration of this concentration of the energy of the waves into a comparatively thin stratum near the surface of the earth .
But as a fact no measurements have as yet been carried out over great distances on the variation of intensity of signals with distance and under unvarying atmospheric conditions ; and clearly the measurements that have been made over short distances\mdash ; which all support the inverse square law as was to be expected\mdash ; cannot have any bearing on refractions that take place in high layers .
When measurements of intensity over distances of 1000 to 2000 miles become it may be expected that the inverse square law will hold for a distance three or four hundred miles , and after that a law indicating rather less divergence may hold for several hundred miles more , if the frequency is low enough for the ionic refraction to produce bending at least as great as the convexity of the globe .
* We now proceed to the explanation of the stray minima described earlier .
In the first place it is evident that if the surfaces of equal ionisation in a * Since the above was written , an account by L. W. Austin ( ' Washington Bureau of ndards Bulletin , ' October , 1911 ) of some new measurements of the intensity of signals has come to hand , which appears to strengthen the author 's position greatly , so far as the measurements go .
The inverse square law for the divergence of energy shows that I , where I is the intensity of the current received on an antenna , and is the distance of the sending station .
If the waves were in free space of electrical constitution like that of our lower atmosphere , the absorption would demand a formula of the type where is independent of the wave-length .
Also it has been shown above that if the waves were travelling in free space filled with air highly ionised , the absorption would require a formula of the type where is again independent of the wave-length .
Now , the observations quoted support an empirical formula very different from either of these , namely , A Formula involving the wave-length in this manner is not suggeste , and cannot even be accounted for , by absorption in an ionised atmosphere or in a badly surface such as that of land or sea ; but it is clearly in rough general accord with the law , developed in this paper , that the desired bending of the rays is better with long waves than with short waves ; or , to put it in another way , the loss of radiation by failure to turn the curve of the earth is greater with short waves than with long .
The measurements made up to the present by Austin and his collaborators have extended to distances of only 900 miles , involving only very slight bending , and , besides , have not been very numerous .
Dr. W. H. Eccles .
Diurnal Variations of the [ June 5 , still atmosphere be drawn round the globe they will be nearest the earth at places where the sun is on the meridian , and will rise away from the earth somewhat sharply at places where the sun is or setting .
The ions in which the change from the day level to the night level takes place form a great circular band round the globe and inclined to the meridians at an depending on the season .
This region of the atmosphere , since it is perpetually moving with the sun , will be in a highly disturbed electrical condition .
Formation of ions is actively proceeding in one half of the great circle and recombination in the other , and these processes doubtless take place somewhat irregularly even in a still atmosphere\mdash ; with the result that patches or banks of ionised air , analogous to the banks of met at sea\mdash ; will transiently constitute this band in the middle atmosphere .
The effect of such patches of variously ionised air on electric waves propagated through the oion is , in view of the connection between the velocity of the waves and the concentration of the ions , certain to be difficult .
The scattering by repeated refractions will tend to make the impenetrable to waves directed through it .
Hence it may be expected that the ularity of the propagation through the steadily ionised horizontal strata of the daytime will be greatly disturbed by the twilight transitional banks and patches , with the ultimate consequence that the sounds heard in the receiving apparatus will be greatly weakened .
The author 's experience up to the present indicates that the existence or stence of clouds in the vicinity of the receiving station has but iittle influence on the intensity and character of the stray minima , or , for that matter ( provided the day is not brilliantly clear ) , on signals received from any distance and any point of the compass .
Whence we may conclude that the irregularly ionised band is situated above the ordinary cloud level .
The transitional region may therefore be arded as a sort of curtain enringing the earth and occupying the middle atmosphere and not the lower .
Thus it can affect only the trajectories of waves travelling from great distances .
The weakening of such long-distance waves will probably be greater or less according as they have to penetrate the curtain more or less obliquely .
In the case of the natural electric waves received by an antenna in England during the autumn and winter the of the waves must in general lie to the south .
It is reasonable to suppose that tropical Africa will supply most of them .
In that case , the twilight tra , nsitional band must have a very great and a relatively short-lived influence on the intensity of the strays heard in the telephones , for the of the waves from the suggested source to the receiving station is nearly coincident with the twilight band .
These suppositions accord precisely with the observed facts .
The minimum 1912 .
] Electric Occurring in Nature .
is sometimes a complete zero for only two minutes or less .
Assuming that in this case the source of the natural electric waves and the receiving station lie both on the great circle of , we deduce that the twilight band is at least 30 miles wide , this the distance the earth rotates eastward in two minutes .
In addition , the same assumption would indicate that the principal source of the strays during November , 1909 and 1911 , lay in the direction of the eastern portion of the Atlas Mountains .
Again , the observations have shown that the chief twilight minima occur about 10 minutes before sunrise and about 10 minutes after sunset during the same periods .
This fact is accounted for by the consideration that the time of sunrise in the middle atmosphere is a little earlier and the time of sunset a little later than at the surface of the earth .
In this connection it should be noticed that the electrically effective sunrise at a point in the nliddle atmosphere , as measured by the ionising power of the sunlight reaching the point , is not coincident in time with the sunrise at the same point as indicated by mere luminosity , that is , with the geometrical sunrise .
The rays heralding the sunrise in the latter and ordinary sense must possess very little ionising power , for the reason that in passing the earth tangentially they have traversed so long a path in the lower atmosphere as to have lost their ionisin radiation .
Thus an observation of the time interval of the stray minimum before geometrical sunrise and after sunset does not determine the height of the electrically disturbed regions .
Besides this , the exact time of the stray minimum will be affected to some extent by the obliquity of the ionic curtain to the line of ation of the waves .
During the day the electric waves travel in the relatively narrow shell of dielectric between some stratum in the middle atmosphere and the surface of the earth .
At they travel in the much wider shell of dielectric between the assumed high conducting layer and the earth .
In England , in winter , the strays are much weaker than the night strays .
From this we might conclude either that the aggregate absorption in the thin shell of dielectric is greater than in the deeper night shell , or that the ionisation of the middle atmosphere during the day is sufficiently non-uniform to hinder the tion of the waves .
But another factor must be recognised .
The electric disturbance produced by a lightning discharge is doubtless impulsive in character , and is probably either a solitary wave or a very short train of waves .
The study of the refraction of such disturbances leads to some wellknown theoretical difficulties , but if we assume that the wave dispersion during its progress through the ionised middle atmosphere , then the disturbance arriving at a given receiving station should exhibit a fairly definite frequency , and that arriving at a station at a different distance should Dr. W. H. Eccles .
Diurnal Variations of the [ June 5 , exhibit a different frequency ; or , in other words , there should be a distinct best frequency at which to adjust the receiving apparatus at each of these stations .
This is on account of the difference of trajectory that difference of frequency brings .
There is but little experimental evidence bearing on this point , though what there is favours the assumptions ; but clearly if dispersion do occur in the sunlit middle atmosphere , and do not occur at night , the weakness of the day strays is fully accounted for without invoking the assistance of absorption .
Though the hypothesis of propagation round the earth by refraction in the ionised middle atmospherehas now been applied to the problem that prompted it , namely , the explanation of the minimum phenomenon of natural electric waves , yet it seems desirable to enquire how the hypothesis comports itself towards the known lracts and properties of the artificial electric waves used in signalling .
The two assumptions on which the discussion has so far been built are , first , that there exists in the atmosphere a permanently conducting upper layer which is somewhat sharply defined , and which therefore reflects waves of every frequency\mdash ; we may call it Heaviside 's layer ; and , second , that in the day ( and only to a slight and erratic extent in the night ) the atmosphere below this reflecting layer is ionised in nearly horizontal strata , the ionisation diminishing as the surface is approached , with the result that electric waves are given a bent trajectory and the Heaviside layer put out of action .
In using these assumptions in what follows , the atmosphere will be supposed at rest .
One of the most important of the facts known concerning the transmission of artificial waves is the difference between day and night signals discovered by Marconi* in 1902 during a from England to New York .
He found that there was little difference between day and signals at distances less than 500 miles from the station , but that the day signals were unreadable at distances of 800 miles and more , while the night nals were readable up to distances of 2000 miles .
This is possibly due to the same causes as the weakening of the day strays relatively to the night strays , but is most probably due to the failure of the heterogeneously ionised air to bend the waves sufficiently to fit the convexity of the earth .
Thus , in the daylight effect observed first by Marconi in 1902 , it is only necessary to suppose that the relatively short waves then in use travelled to great heights in the atmosphere on account of the smallness of the curvature of their trajectory , and were not refracted sufficiently to *Marconi , 'Roy .
Soc. Proc June , 1902 .
1912 .
] Electric Waves Occurring in reach the earth in appreciable amount .
This would probably not have happened with waves .
As for the night nals , both long and short waves are through the lower and middle atmosphere in straight lines to great and reflected at the Heaviside layer , and then they descend to earth again , having suffered comparatively little absorption .
The waves may be imagined to creep round this electrical vault of the atmosphere in a manner somewhat analogous to the creeping of sound round a whispering gallery , being plentifully scattered downward in their progress by the ularities in the reflecting surface , or , to put it another way , we may imagine that a transmitting station " " lights up the sky in an electrical sense , for many degrees below its horizon .
Since in the observations quoted the daylight signals wele percept at 700 miles , where the horizontal plane of the sender crosses the observer 's ertical at a height of 60 miles , we may conclude that the trajectory of the radiation directed horizontally from the sender does not reach higher than 30 miles in the daytime .
It may be mentioned at this point that Marconi originally ested that the phenomenon might be due to a possible discharging action of on the sending antenna , and J. J. Thomson considered it rather due to the absorption of energy by the ionised air in the immediate neighbourhood of the antenna , but both these explanations ought to make the contrast between day and night signals the same for short distances as for long , which is not the case .
The above considerations suggest that there should exist a best frequency for signalling over great distances .
Now the radiation from a Hertzian oscillator is most intense in its equatorial plane , and therefore , from a vertical linear earthed antenna , is most intense in the horizontal plane of the sending station .
Hence we conclude that the best frequency is that for which , in a given ionic condition of the atmosphere , the trajectory of the radiation which starts nearly zontally retu1ns to the earth 's surface near the receiving station .
Marconi has stated* that a wave-length of 5000 metres is almost always better than one of 4000 metres for Transatlantic signalling\mdash ; though , he remarks , the shorter wave-length is better than the occasionally .
In this connection it may be pointed out that , if the trans- mission of signals be attempted with an exceedingly long wave-length , the aggregate curvature produced by the ionic refraction in the day might be sharper than the curvature of the earth .
This would cause the nearly horizontal radiation to be turned down to the earth within a relatively short distance from the radiator .
In that case reception at a distance would be * Nobel Lecture , December , 1909 .
VOL. LXXXVIL\mdash ; A. Dr. W. H. Eccles .
Variations of the [ June 5 , carried on with radiation that had started at considerable upward inclination , and would therefore be accomplished with difficulty .
The wave-fronts arliving at the station would also be tilted forward considerably , and consequently the horizontal component of the electric field of the waves might approach the magnitude of the vertical component .
In this case an inclined antenna would be a better receiver than a vertical one .
In various parts of the world it has been found that stations on the opposite sides of a mountain chain can communicate in the night with ease , though only with great difficulty , if at all , in the day .
This is especially the case if a short wave is in use , and such a pair of stations can sometimes establish day communication by adopting a longer wave-length .
It is , in fact , now common knowledge that for communication across hilly country in the daytime , a wave\mdash ; a thousand metres or more\mdash ; should be used .
The explanation is obvious on the hypotheses developed above .
The rays , starting with sufficient elevation from a sending station in the plains , travel in lines through the lower atmosphere past the mountain tops , and then , reaching the middle atmosphere , are deflected downward by refraction in the ionised air .
Short waves are refracted much less than long waves , and are therefore not bent so fully into the lower atmosphere as are the long waves .
Indeed , the short waves may be entirely lost , and the long waves be bent down abundantly and come to earth again on the far side of the mountains .
In the night , however , the ionisation of the middle atmosphere has disappeared , the Heaviside layel is open , and waves of all frequencies are reflected down to earth Another fact that emphasises the existence of elevated trajectories is afforded by the experiences of the Alpine receiving stations .
These stations commonly receive signals from great distances in all directions\mdash ; from stations in all parts of Europe and from ships on the Atlantic\mdash ; so that it has been said that " " the Alps attract signals Stations in the plains do not these distant signals nearly so often .
The fact is that the high mountain stations have , of course , a much better chance of lying on the trajectories of the waves , or , as suggested by Larmor , in a slightly different connection , of " " tapping a stronger stratum of radiation Recently , in an evening discourse at the Boyal Institution , Marconi has described* the striking effects of sunrise and sunset on the strength of signals received from across the Atlantic Ocean .
He stated that the intensity of the signals received at Clifden , Ireland , from Glace Bay , Canada , remains fairly steady during the day , but shortly after sunset at Clifden it becomes gradually weaker , and reaches a minimum in about * June 2 , 1911 .
1912 .
] Electric Waves Occurring in Nature .
two hours .
It then to strengthen , and finally reaches a maximum\mdash ; sometimes a very high one\mdash ; at the time of sunset at Glace Bay .
During the night the signals are very variable in strength , varying from very weak to very .
Shortly before sunrise at Clifden the signals grow and reach a high maximum shortly after sunrise ; they now dwindle to a marked minimum about two hours after , and then they return gradually to their normal day strength .
The ratio of the intensity of the cvnals during the twilight maximum to the average intensity throughout the day is mucb greater for a wave 5000 metres long ( frequency 60,000 per second ) than for a wave 7000 metres ( frequency 43,000 per second ) , and the long wave signals are uniformly stronger during the day than those of the shorter wave .
Some of these observed facts can be understood by the aid of the hypothesis of ionic refraction .
We have only to lay down the principle that the aggregate curvature of the trajectory of the longer waves is nearer to the curvature of the earth than that of the shorter waves , or , in other words , that the daylight trajectory of the longer waves is more suited than that of the shorter waves to the distance between the Irish and Canadian slations .
Again , the minimum that occurs at about two hours after sunset at Clifden is readily explained by the conception , already discussed , that in the twilight regions the recombination of ions has consequences equivalent to a somewhat opaque curtain ring from the top to the bottom of the middle atmosphere .
Moreover , at two hours after sunset at Clifden the sun is at a place between the stations about 650 miles from Glace Bay .
At this place the horizontal plane of Glace Bay passes between and 60 miles overhead .
If now we assume that the of the curtain of irregularly ionised air is of the order 50 miles , thus making no allowance whatever for the bending of the rays from Glace Bay in their progress below that level , we see that the signals transmitted to Clifden are weakest when the curtain comes on the horizon of the sending station .
If , on the other hand , we allow for the likelihood of the rays following considerably bent paths even in the lower middle atmosphere , we must take Marconi 's results as showing that the ionic curtain reaches effectively to much lower atmospheric levels than 50 miles .
All of this applies , mutatis mutandis , to the morning minimum produced by the sunrise belt passing between the stations .
In regard to the remaining point quoted from Dr. Marconi , namely , the strong maximum in signals to Clifden at about sunset at Glace Bay , and before sunrise at Clifden , there is n1ore difficulty in finding an explanation .
It would seem that the heterogeneous ionisation following the twilight Dr. W. H. Eccles .
Variations of the [ June 5 , through the atmosphere can .
rise to regular reflections , so that when it passes over and behind the sending station it changes from being a hindrance to a help in .
This view contains nothing that is fundamentally inadmissible .
But the reflecting process was observed to be better with short waves than with long ; perhaps the following considerations may in some yrec account for this .
First , it is known from general electron ) etic principles that when a wave crosses layers of hanging refractive index there is a reflected wave propagated backwards , and this reflected wave is the more intense the greater the change in index .
, let us assume that the surfaces of equal ionisation rise from the day level to the level in a slope extending over , perhaps , hundred miles from east to west twilight belt , being rather broken of course , by ularities in the ionisation .
On account of the broken character of the belt reflection from the sloping surfaces will be irregular .
But it will be more irregular for the more refrangible radiation , that is to say , will ] ) more irregular for waves of low frequency than for waves of higher frequency .
Perhaps with this may be conjoined the fact that the frictional absorption suffered by the wave is greater than that suffered by the shorter .
The phenomena just discussed are to some extent noticeable over relatively short distances .
The following curves are drawn from observations of the intensity of signals from Clifden as at the author 's laboratory in London , the measurements being made by balancin the intensity of the ifden signals against the adjustable intensity of locally produced artificial signals of about the same acoustic frequency .
On the curves the intensities are plotted in arbitrary units as with the times of measurement as abscissae .
The observation had to be snatched , so to speak , at the moments when the station happened to despatch a messa , and the points of observation are therefore often rather irregularly distributed .
Fig. 7 shows two remarkable minima , which are produced , presumably , by the presence of the ionic curtain between the stations .
Of these two minima , FIG. 7.\mdash ; Intensity of Signals reaching London from Clifden , January 12 , 1912 .
1912 .
] Electric .
Occurring in Nature .
the one that occurs most commonly\mdash ; the phenomena vary ) reatly from to day\mdash ; is that one appearing when the sun is at a place about half-way between the stations .
The minimum is fairly well marked in the sumrise curve shown in .
The reflections that are so pronounced a feature of Marconi 's -distance observations are not nearly so evident over short distances , according to the author 's experience .
) fig. 9 shows FIG. 8.\mdash ; Intensity of Signals , FIG. InteI ) sity of Signals , January 25 , 1912 .
January 20 , 1912 .
a case variations soon after sunset at Clifden were very decided .
The curve does not do full justice to the phenomena , however .
As a matter of fact the chief variations were so rapid and so wide that there was not time to measure them ; indeed , on occasion , the changes in intensity are startling in their amplitude and swiftness .
It will be noticed that all the lrves exhibit a great difference between the strength of the night signals and that of the day signals , although the distance is only 440 miles .
Yet it is known that the same signals are heard at Glace Bay as strongly in the day as in the night .
We gather from this that the daytime trajectory of the radiation passes well above places relatively near to the sending station and descends , after overtaking the curvature of the earth , at the greater distance .
It is well to recall here that in his recent experiments on the reception of signals from Clifden at distttnces up to 6000 miles , Marconi found the nals readable only at night at greater distances than 4000 miles\mdash ; which seems to indicate that the trajectories of the rays in the daytime are such as to bring down within the distance named p1actically all the radiation starting , at all elevations , from the antenna .
The author desires to tender his thanks to the Government Grant Committee of the Royal Society for a grant in aid of the observations described in this communication .
|
rspa_1912_0062 | 0950-1207 | On the \#x3B2;-particles reflected by sheets of matter of different thicknesses. | 100 | 108 | 1,912 | 87 | Proceedings of the Royal Society of London. Series A, Containing Papers of a Mathematical and Physical Character | W. Wilson, M. Sc.|J. J. Thomson, F. R. S. | article | 6.0.4 | http://dx.doi.org/10.1098/rspa.1912.0062 | en | rspa | 1,910 | 1,900 | 1,900 | 8 | 120 | 2,828 | http://corpora.clarin-d.uni-saarland.de/surprisal/6.0.3/?id=rspa_1912_0062 | 10.1098/rspa.1912.0062 | null | null | null | Atomic Physics | 39.155238 | Optics | 33.455692 | Atomic Physics | [
8.325325012207031,
-77.9520492553711
] | ]\gt ; On the rticles Reflected by Sheets of Matter of Different Thicknesses .
By W. WILSON , M.Sc .
, Exhibition Scholar of the University of Manchester , Wollaston Student of Gonville and Caius College , Cambridge .
( Communicated by Sir J. J. Thomson , F.R.S. Received March 27 , \mdash ; Read May 9 , 1912 Int roduction .
The properties of the rays reflected when a beam of -particles strikes an object in its path have been the subject of a large number of ations .
It has been found by many observers , Eve , * S. J. Allen , Schmidt , McClelland , S and Kovarik that the scattered radiation is more easily absorbed than the primary .
concluded from considerations of the distribution of the scattered radiation that it consists of two parts , which he considered to be real secondary and reflected primary rays .
Schmidt , the other hand , has advocated the view thab all the phenomena observed can be explained by mere scattering or reflection of the primary beam .
The following experiments were undertaken in order to determine how the absorbability of the reflected rays depends on the thickness of the reflector , the primary beam one is absorbed by matter to an exponential law .
Experimental Details .
The primary rays used those given out by uranium X , and had an absorption coefficient of 14 cm . .
A very strong source of radiation was obtained from 50 kgrm .
of uranium nitrate by a method devised by Prof. H. W. Schmidt .
The uranium X thus obtained was contained in a brass capsule and was spread out in a thin layer over an area of about 1 sq .
cm .
The layer was so thin that there was very little absorption of the radiation inside it .
It was covered with a thin sheet of mica which protected it from the air and absorbed Che slow groups of rays ( absorption coefficients 500 and 300 c ) which are given out by uranium X and uranium * Eve , ' Phil. Mag 1904 , vol. 6 , p. 8 .
S. J. Allen , ' Phys. Rev 1906 , vol. 23 .
H. W. Schmidt , ' Phys. Zeit 1907 , vol. 8 .
S McClelland , ' Dublin Trans 1905 , vol. 8 .
Kovarik , 'Phil .
Mag November , 1910 .
T McClelland , ' Roy .
Soc. Proc 1908 , , vol. 80 .
Schmidt , ' Ann. der Phys 1907 , ( 4 ) , vol. 23 .
-Particles Reflected by Sheets oj .
Different Thicknesses .
101 The apparatus used is shown diagrammatically in fig. 1 .
The capsule A containing the uranium X stood on a lead block which prevented the -rays from the ionisation vessel and electroscope .
The -particles struck a screen and were scattered by it , some entering the ionisation vessel , whose central electrode was.connected through an amber plug to the gold leaf electroscope .
The top of the ionisation vessel was closed by a thin sheet of ninium leaf of thickness cm .
The primary beam was prevented from entering the ionisation vessel by the small lead screen F. By measuring the ionisation in when sheets of aluminium of various thicknesses were placed on the top of it , the rate of absorption of the rays reflected by the screens could be determined .
Now the ionisation in the electroscope is due not only to the particles scattered back by the reflector , but also to the -rays , the -particles scattered back by the air above the oscope , and those set up when the -rays strike the reflector .
The quantities not required can be eliminated as follows : was found that the ionisations in the vessel were substantially the same when sheets of lead were placed directly on the uranium X or on the vessel , which shows that the amount of -radiation set up in the reflectors by the -rays is negligible .
By a separate experiment it was found that the -radiation scattered by the air came mostly from the region between the source of radiation and the reflecting screen , and further that this radiation was very easily absorbed , .
almost negligible compared with the radiation scattered by the thicker screens after passing thr.ough about of aluminium .
Mr. W. Wilson .
On rticles Reflected by [ Mar. 27 , Thus , when the reflector was in position , the ionisation in the electroscope was due to the -rays scattered by the screen , those scattered by the air , and the -rays .
When the reflector was absent the ionisation was due to the two latter only and the intensity of the rays reflected by the screen was given by the difference of the two readings .
Results .
Experiments were made with aluminium , copper , and lead as reflectors .
The results obtained for aluminium are shown in fig. 2 , where the intensity sThickness .bsorbing s cm FIG. 2 .
of the reflected radiation is plotted against the thickness of matter traversed for the rays reflected from screens of different thicknesses .
The curves correspond to reflectors , and mm. respectively .
It will be seen that on the whole the rays reflected by thin layers are much more easily absorbed than those reflected by thick ones .
The results are also shown in fig. 3 , where the logarithm of the ionisation is plotted against the thickness of the absorbing screen .
From these curves it will be seen that the reflected radiation can be roughly divided into two parts , an easily absorbed radiation and a more penetrating one .
The coefficient of absorption of the latter is seen to vary with the thickness of the reflector , reater for thin sheets than for thick ones .
The proportion of the penetrating radiation to the whole increases , as would be expected , with the thickness of the reflector .
Similar results were found for lead and copper .
proportion of the penetrating radiation in the whole beam reflected from a thick screen was found to be ooreatest for lead and least for aluminium , while the absorption coefficient of the reflected radiation was greatest for aluminium and least for lead .
12 .
] Sheets of Matter of Different Thicknesses .
The absorption curves for the rays reflected from thick sheets of lead and copper are also shown in fig. 3 , curves and The values of the final absorption coefficients in aluminium of the reflected rays from the three substances examined are given in Table Table I. Experiments were also made , using very thin sheets of aluminium as reflectors and absorbers , to obtain an approximate value for the absorption coefficient of the slow group of reflected rays .
In each case the final straight line of the arithmic curve was produced backwards , and from it Mr. W. Wilson .
On -Particles Reflected by [ Mar. 27 , the ionisation due to the penetrating rays found by extrapolation .
On subtracting the thus found from the ionisation due to the whole beam , we obtain the ionisation due to the slow group of -particles alone .
results are shown in fig. 4 , the curves given being obtained with FIG. 4 .
reflectors and mm. thick respectively .
Owing to the small amount of radiation of this type , results could not be obtained to any great degree of accuracy .
The mean absorption coefficient found was 235 c The fact that the radiation scattered back by sheets of aluminium is apparently of two distinct types seems at first sight to support the view of McClelland that the radiation sent back by a screen consists of a real secondary radiation set up in the screen by the impact of and of a scattered beam whose velocity is only slightly less than that of the primary rays .
The rays given out by uranium X are , however , heterogeneous , and this explanation is not a necessary consequence of the experimental data .
The splitting up of the reflected radiation into two types may be merely arbitrary , the reflected rays to the slower portion of the primary beam being more easily absorbed than those corresponding to 1912 .
] Sheets of Matter Different Thicknesses .
the more portion .
Furbher experiments to test this point are now in progress at the Cavendish Laboratory .
That both types of rays are due to the group of uranium X rays an absorption coefficient 14 cm .
, and not to the slower groups , was shown by placing screens of aluminium over the capsule containing the uranium X. The results obtained with a piece of aluminium mm. thick over the uranium X were exactly the same as when the preparation was uncovered except for the mica .
A series of experiments was made on the absorption of the rays reflected from the air above the electroscope .
The rays were mostly of a very absorbable type , whose coefficient of absorption was 300 c approximately .
There was also a small amount of a more penetrating radiation , whose absorption coefficient was approximately 70 cm .
Variation of Intensity of Reflected Radiation with thickness of Reflector .
In theory for the reflection of -particles which are absorbed according to an exponential law there is a large discrepancy between the calculated and experimental results for elements .
Thus in the case of aluminium for thin sheets a discrepancy of as much as 50 per cent. is found .
Schmidt assumed that the absorption coefficients of the reflected and incident radiations were the same , whereas we ave seen not only that is this not so , but that in the case of light elements a considerable proportion of the reflected radiation is of a very absorbable type .
With the small amount of data at our disposal regarding the reflection of particles of different penetrating powers it is impossible to construct a theory which like that of Schmidt takes account of the boundary conditions , but an expression can be worked out , using simple assumptions , which agrees almost exactly with experiment .
From the fact that the -rays from uranium X are absorbed by matter according to an exponential law it follows that the properties of the rays falling on any thin layer as regards absorption and reflection must be the same no matter what the position of the layer in the material .
Now the rays passing through any layer in the direction of the primary beam are made up of rays which have come straight through the matter and rays which have been scattered by the material they have traversed .
As is found by experiment , however , the intensity of the whole beam decreases according to an exponential law with the thickness of matter traversed , and , usin this fact , we take into consideration not only the rays which have gone straight through the material but also those which have been reflected across * H. W. Schmidt , 'Ann .
der Phys 1907 , 4 , vol. 23 .
Mr. W. Wilson .
On -Particles Reflected by [ Mar. 27 , the layer any number of times .
This , of course , is not rigidly true near the boundaries .
Now , since the rays falling on all layers have identical properties , we can assume that the amount of radiation scattered back by any thin layer is proportional to the intensity of the radiation falling on that layer .
Thus , if is the intensity of the radiation incident on a reflector , the amount of radiation scattered back by a layer of thickness at a distance from the surface is where is a constant and the coefficient of absorption of the rays .
From the foregoing experiments , however , we have seen that the reflected radiation can be considered as consisting of two parts with different absorption coefficients .
We can thus write for the amount of radiation scattered back by the layer under consideration where and are constants .
If and are the coefficients of absorption of these two types of rays in the reflector , the amount of this scattered radiation reaching the front surface will be or , if is the amount of radiation reflected by a screen of thickness which may be written .
For a thick layer Now Schmidt has determined the variation of with the thickness of the reflecting scleens , and , putting his value for the amount of radiation reflected from a thick layer , we have for aluminium Now A and are the maximum amounts of the two types of radiation reflected and their ratio can be easily determined from our absorption curve for the particles reflected by a thick sheet of .
aluminium .
The ratio of to A is found to be .
Hence The value of , as found by various observers , is 14 cm . .
The value of varies from 34 for a thick reflector to 44 for a very thin one .
The value for a sheet of thickness sufficient to reflect half the maximum amount of 1912 .
] Sheets of Matter of Di.fferent Thicknesses .
radiation is about c , and this is used in plotting the theoretical ourve .
The value of is 235 cm .
Using these values , we can calculate the value of for any thickness of the reflector .
The results obtained are shown raphically in .
The Thickness of reflecCor .
theoretical curve is drawn , and points obtained from Schmidt 's experimental curve are marked .
The agreement is seen to be very good .
Unfortunately , results were not obtained for the absorption by lead of the rays reflected from lead .
However , Borodowsky*has shown that , for a large 1lumber of substances , the rate of absorption of different types of -particles in those substances is proportional to that in aluminium .
Applying this to the values obtained for the absorption coefficients of the rays reflected by lead in aluminium , and taking the value of in lead to be 103 c , the values of and are found to be 149 cm .
and 1100 cm .
respectively .
The results obtained , using these values , are also plotted in fig. 5 , and the agreement with experiment is again seen to be good .
It has been shown by McClelland ( loc. cit. ) that the amount of reflected radiation obtained varies with the angle of incidence of the primary beam .
In the experiments described above , the incidence was more or less normal , but the pencil of rays was so diffuse that we may consider the results obtained as representing an average effect .
* Borodowsky , ( Phil. Mag April , 1910 .
108 -Particles Reflected by Sheets of Diferent Thicknesses .
( 1 ) The radiation reflected when the -particles from uranium X strike a screen can be split up into two parts , one with a very large coefficient of absorption , and the other with absorption coefficient of the same order as that of the primary beam .
( 2 ) The absorption coefficient of the more penetrating part of the reflected beam decreases with increasing thickness of the reflector .
( 3 ) The final absorption coefficients of the rays reflected from thick sheets of aluminium , copper , and lead are , and c respectively .
( 4 ) The coefficient of absorption of the easily absorbed part of the radiation reflected by aluminium is about 235 c .
The absorption coefficients of the corresponding reflected from copper , lead , and air have not been determined with any degree of accuracy , but are of the same order of magnitude as that of the rays reflected by aluminium .
( 5 ) An expression has been obtained for the variation of the amount of reflected radiation with the thickness of the reflector , and has been shown to be in good agreement with the results obtained experimentally by Schmidt .
These experiments were carried out in the Physical Laboratories of the University of Giessen , and I wish to express my best thanks to Prof. JConig for placing the resources of the laboratory at my disposal .
I also wish to express my best thanks to Prof. H. W. Schmidt for the great help he gave me in the separation of the uranium X , and for the kind interest he showed in the work while it was in progress .
|
rspa_1912_0063 | 0950-1207 | On a form of the solution of Laplace's equation suitable for problems relating to two spheres. | 109 | 120 | 1,912 | 87 | Proceedings of the Royal Society of London. Series A, Containing Papers of a Mathematical and Physical Character | G. B. Jeffery|Prof. L. N. G. Filon, F. R. S. | article | 6.0.4 | http://dx.doi.org/10.1098/rspa.1912.0063 | en | rspa | 1,910 | 1,900 | 1,900 | 12 | 100 | 2,332 | http://corpora.clarin-d.uni-saarland.de/surprisal/6.0.3/?id=rspa_1912_0063 | 10.1098/rspa.1912.0063 | null | null | null | Formulae | 60.277867 | Fluid Dynamics | 21.952 | Mathematics | [
53.73210906982422,
-34.39073944091797
] | ]\gt ; On a Form of the Solution of Laptace 's Equation for Problems Relating to Spheres .
By G. B. JEFFEBY , University , London .
( Communicated by Prof. L. N. G. Filon , F.R.S. Received April 11 , and in reyised form June 10 , \mdash ; Read June 13 , 1912 .
) S1 .
Introduction .
The problems presented by the motion of two solid spheres in a perfect fluid have been attacked by various writers .
* In each case the method has been that of approximation by successive images , and it appears that no gerieral analytical method of solution has been developed as in the case of the analogous problems for the sphere , ellipsoid and .
In this paper a general solution of Laplace 's equation is obtained in a form suitable for problems in which the boundary conditions are given over any two spherical surfaces .
A similar solution is obtained of the differential equation of Stokes ' current function .
With the aid of these results it is theoretically possible to determine completely a potential function when its value is specified over any two spheres .
The method is illustrated by an application to the electrostatic field of two charged conducting spheres .
In this case the method leads to a simple expression for the capacity of either of the spheres .
The co-ordinates employed are defined by rotating about the axis the system of circles , in any plane , through two fixed points on the axis and the orthogonal system of circles .
Thus , if , are the Cartesian co-ordinates and , and the distance between the fixed points is , we have a system of orthogonal curvilinear co-ordinates , where .
( 1 ) The surfaces constant will then be a series of coaxal spheres having a common radical plane .
It is obvious that the and the value of can be so chosen that any two given spheres will be included in the system .
These co-ordinates are similar to those employed by Hicks in his memoir on " " Toroidal Functions , \ldquo ; the difference being that in the present * R. A. Herman , " " On the Motion of Two Spheres in a Fluid ' Quart .
Journ. of Maths 1887 , vol. 22 ; W. M. Hicks , " " On the Motion of Two Spheres in a Fluid ' Phil. Trans 1880 ; A. B. Basset , " " On the Motion of Two Spheres in a Liquid 'Proc .
Lond. Math. Soc 1887 .
' Phil. Trans 1881 , p. 609 .
Mr. G. B. Jeffery .
Solution 's [ June 10 , case the circles are rotated about the line the li1niting points instead of about their common radical axis .
Further , in one case the surface conditions are given over spheres , while in the other they are given over " " tores\ldquo ; or anchor-rings .
For these reasons , although that part of Hicks ' paper which deals with the eneral theory of curvilinear co-ordinates has been of very considerable help to the present writer , the functions obtained and methods suitable for their applications are very different in the two cases .
The following results will be of use ; they are easily obtained from ( 1 ) and are set down here for reference:\mdash ; .
( 2 ) .
( 3 ) If denote the lengths of elements of the curves constant and ( 4 ) If be the radius of any sphere of the system , and the distance of its centre from the origin , .
( 5 ) S2 .
Solution of It is well known that if , be any system of orthogonal co-ordinates Laplace 's equation may be written in the form , ( 6 ) where In the present case , conjugate functions of and if 1912 .
] Equation for Problems Retating to Two Spheres .
Substituting these values in ( 6 ) , we have , as the form taken by Laplace 's equation in co-ordinates , .
( 7 ) In order to solve this equation , write .
We obtain which becomes , in virtue of equations ( 2 ) and ) , .
( 8 ) After the usual manner we will seek a solution of the type where , are functions of , respectively .
Substituting in ( 8 ) we at once obtain const .
, say .
Hence and Put and we obtain ally , , we have the solution of which is well known to be , where being the Legendre function of order is the corresponding functiun of " " second kind Hence and a particular solution of ( 7 ) may be expressed in the form We shall find that for physical applications it is sufficient to confine our VOL. LXXXVII.\mdash ; A. Mr. G. B. Jeffery .
Solution of 's [ June 10 , attention to integral values of .
Moreover , the solution corresponding to is identical in form with that corresponding to .
It will , therefore , be sufficient to consider only positive values of , and since by the nature of the function , , we may write the solution of ( 7 ) in the form .
( 9 ) S3 .
Properties of the Function The function and its first differential coefficients must be finite and continuous at all points of the field except those which correspond to some special physical condition such as a source or charge .
is finite and continuous for all real values of , but becomes infinite when or , and hence cannot occur in an expression for which is to hold throughout a region including any part of the axis of .
It is to such cases that we confine our attention in the present paper .
At the limiting points of the system becomes infinite , and hence the forms of appropriate to regions including the points are respectively It will be convenient for reference to have the general value of with respect to we have , omitting the terms , .
Applying the recurrence relation , we have , after further reduction , , ( 10 ) provided that ( 9 ) may be differentiated term by term and rearranged .
1912 .
] Equation for Relating to Two Spheres .
The coefficients in the function are not in all cases identical in the two regions into which the field is divided by the plane .
Let ( 9 ) be the expl.ession for in that part of the field for which while a similar expression with accented coefficients holds throughout the other half of the field .
In order that may be continuous across the plane while , in order that may be continuous , we must have ( provided that is given by ( 10 ) ) where and if .
Writing ) .
This relation holds for all values of such that .
Hence if which at once leads to the result These forms occur whenever the field includes both limiting points together with any part of the plane , for any expression for of the form ( 9 ) which is finite at one of these points becomes infinite at the other .
For a unit at the points the potential is riven by Thus , as in the case of spherical harmonics , the harmonic of zero order corresponds to a point charge .
The analogy , however , extends no further ; the nth harmonic does not correspond to a charge of the nth order .
It may be shown that , if be the radius vector from the pole where is the ordinary binomial coefficient .
Mr. G. B. Jeffery .
Solution of 's [ June 10 , S4 .
of Symmetry an Axis ; Stokes ' Current Function .
When the field is symmetrical about the axis of , we obtain the form of the function by putting in ( 9 ) .
( 11 ) Many physical problems are more easily interpreted by means of " " lines of force or " " lines of flow than by the potential .
In the symmetrical case there exists a function corresponding to Stokes ' current function , such that the su1faces constant are orthogonal to the equipotential surfaces , and which is connected with by the following relations* ; Transforming to co-ordinates , , By a well-known property of conjugate functions and Hence Hence , since ; .
( 12 ) When a potential exists , and is continuous , we may write .
( 13 ) Substituting from ( 12 ) , we obtain the differential equation satisfied by an equation which is somewhat similar in form to Laplace 's equation and * Lamb , ' Hydrodynitmics , ' p. 117 .
1912 .
] Equation for Problems to Two Spheres .
which yields to an mode of treatment .
Writing , we have which becomes in the case under consideration Assuming , as before , a solution of the form constant Hence In order to solve for , substitute .
We obtain Now write and the equation becomes the general solution of which is As for the function , it is only necessary to consider itive i values of , and the solution of ( 13 ) which is finite on the axis is .
( 14 ) S5 .
Properties of the Function It is obvious that the remarks made in S3 on the continuity of the function apply equally to the function .
Differentiating ( 14 ) with respect to and applying the recurrence relation we have .
( 15 ) Mr. G. B. Jeffery .
Solution 's [ June 10 , As for the coefficients must be the same on both sides of the plane , while to secure the continuity of the potential gradient we must have provided that ( 14 ) may be differentiated term by term , where , 2 , 3 , , , and adding , we have where is a constant .
Multiplying by and again putting , 2 , , , we obtain on adding or A simple example of this form is afforded by the case of a uniform field parallel to the axis of in which Relations betwethe Coefficients in and Let siuh , be functions specifying the same field .
The coefficients will be related in such a way as to satisfy equations ( 12 ) , which for our present purpose may be written in the form .
( 16 ) Differentiating the expression for with respect to and applying the well-known recurrence relations we obtain Identifying this expression with the value of given by ( 15 ) , we have ( 17 ) 1912 .
] Equation for Problems to ) It is easily verified that these are also the relations necessary and sufficient to satisfy the second of equations ( 12 ) .
, 2 , 3 , , , and adding , we obtain ( 17 ) S6 .
The Potcntial and of two Sphcri Condmctors .
We will conclude the present paper by an application of this method to a classical electrostatic problem .
Let be any two spheres such that but is unrestricted .
The potential is constant over each of these spheres , and we can without loss of generality suppose it to be zero over the surface and over the surface .
It is obvious that will be of the form , from which we have .
The left-hand side may be written since Equating the coefficients of , we obtain the value of , and the potential function becomes If denote surface densities of the charges on the spheres respectively , we have , by Coulomb 's theorem , , .
Using Maxwell 's notation we will denote the coefficients of capacity by Mr. G. B. Jeffery .
Solution of 's [ June 10 , and the coefficient of induction by .
To obtain these we put and integrate the surface density over the appropriate sphere .
The following integrals will be required , and ' if From considerations of symmetry it is clear that we should obtain for the third coefficient These expressions are not those obtained by Maxwell ( ' Electricity and Magnetism 3rd ed. , vol. 1 , p. 271 ) , but it is possible to transform them into the forms there given , e.g. \mdash ; Since the double series is absolutely convergent , and we may interchange the order of summation which is Maxwell 's form .
1912 .
] for Problems to Two When one sphere is enclosed within the other and there are slight differences in the coefficients due to the different forms taken by the rals in these circumstances .
We obtain For two equal spheres cosech In the case of a sphere in the presence of an infinite plane , We have tabulated below some of the more important of these functions .
Table I.\mdash ; Capacity of Two Equal Spheres .
120 Laplace 's Equation for Problems Relating to Two Spheres .
Table II.\mdash ; Capacity of a Sphere in the Presence of an Infinite Conducting Plane .
In a future paper we will show how the method can be applied to the problems of the motion of two spheres in a perfect fluid .
In conclusion , I wish to express my deep sense of obligation to Dr. L. N. G. Filon , F.R.S. , and Mr. E. Cunningham , M.A. , for the valuable assistance they have given me , and to .
A. W. Porter , li .
R.S. , for his helpful interest and encouragement throughout the preparation of this paper .
|
rspa_1912_0064 | 0950-1207 | On changes in the absorption spectra of \#x201C;didymium\#x201D; salts. | 121 | 137 | 1,912 | 87 | Proceedings of the Royal Society of London. Series A, Containing Papers of a Mathematical and Physical Character | Walter C. Ball, M. A.|V. H. Veley, F. R. S. | article | 6.0.4 | http://dx.doi.org/10.1098/rspa.1912.0064 | en | rspa | 1,910 | 1,900 | 1,900 | 15 | 353 | 8,626 | http://corpora.clarin-d.uni-saarland.de/surprisal/6.0.3/?id=rspa_1912_0064 | 10.1098/rspa.1912.0064 | null | null | null | Atomic Physics | 51.617952 | Chemistry 2 | 27.485546 | Atomic Physics | [
9.073627471923828,
-40.184974670410156
] | 121 On Changes in the Absorption Spectra " Salts .
By Walter C. Ball , M.A. ( Communicated by Y. H. Yeley , F.R.S. Received April 17 , \#151 ; Read May 23 , 1912 .
) [ Plate 1 .
] There is a large amount of literature dealing with the changes produced by various agents in the absorption spectra of the rare-earth metals , amongst the most important contributions being those of de Boisbaudran , * Becquerel , f Crookes , \ Muthmann and Stiitzel , S Living , || and recent papers by H. C. Jones , with various collaborators.1T Living examined the effects of changes of temperature , and of concentration , on the chlorides and nitrates of erbium and " didymium."** He investigated the spectra of solutions in alcohol and in glycerol ; of an ammoniacal solution of didymium tartrate ( rather similar to that of an alkaline solution of didymium containing sucrose , of which the photograph is given below\#151 ; photograph 10a ) , of acidified solutions , and also of borax glass containing didymium .
He made an extensive series of photographs of these spectra , and many of the shifts of lines and bands discussed in this paper are to be seen in them , but he states that the plates had to be moved between the exposures " so that no reliance can be placed on the appearance of a shift in such photographs when the amount of such displacement is small .
" In the present series of photographs , some of which are shown in the illustration appended , I have endeavoured to make the shifts of lines and bands more obvious and more easily measurable by photographing the modified spectrum in juxtaposition to that of a standard solution of didymium nitrate , and superposing the helium lines on both .
Muthmann and Stiitzel examined the spectrum of the acetate , and also that of the hydrogen carbonate , and concluded that Bunsen 's suggestion , that the character ot the absorption spectrum depends upon the molecular weight of the didymium compound , is incorrect .
( This is rendered even more obvious * ' Comptes Rendus , ' vol. 88 , p. 1167 .
t 'Comptes Eendus , ' vol. 104 , pp. 777 and 1691 .
f ' Journ. Chem. Soc. Trans. , ' 1889 , p. 255 .
S 4 Berichte , ' 1899 , vol. 32 , p. 2653 .
|| 4 Carab .
Phil. Soc. Trans. , ' 1900 , vol. 18 , p. 298 .
IT 4 Amer .
Chem. Journ. , ' 1907 , et seq. ** For convenience , throughout the following paper , the latter is referred to simply as didymium , although it can be resolved into neodymium and praseodymium .
Mr. W. C. Ball .
On Changes in the [ Apr. 17 , by a comparison of the spectra of the acetate and trichloracetate with that of the nitrate ( see Plate 1 , photographs 1 and 9 ) .
) H. C. Jones , with various collaborators , has examined the absorption spectra given by solutions in various pure solvents , and also in mixed solvents .
Liveing concludes " that the absence of any diminution of intensity of either the erbium or didymium bands by addition of acid , taken with the fact that rise of temperature does not increase their intensity , go a long way to negative the supposition that these bands are produced by metallic ions .
" He remarks , however , that the substantial identity of the spectra of very dilute solutions of the chloride , nitrate , and sulphate points apparently in the other direction .
Of the other workers on the subject , some have reached the conclusion that ionisation will explain the facts , whereas others hold that combination of the salt , or of its ions , with the solvent is the principal factor to be considered .
For the experiments described below , I used didymium salts obtained from two sources .
One sample of the nitrate contained much lead nitrate , which was almost completely removed by one extraction with absolute alcohol , which dissolved the didymium , but not the lead salt .
The measurements of the lines and bands gave results agreeing very closely with those obtained by Crookes , Liveing , and other workers on the subject .
In the course of some experiments on the action of reducing agents on didymium salts , made in the hope of obtaining compounds of the metal ( or rather of the neodymium and praseodymium of which the didymium consists ) in a lower state of oxidation , I observed that a very marked change in the spectrum occurred on the addition of sodium hyposulphite , bra2S204 ( the so-called hydrosulphite ) .
As seen with a pocket spectroscope , this alteration consisted chiefly in a great increase in breadth and intensity of the absorption band near D , the broadening being almost wholly towards the red .
In addition , others of the bands could be seen to have shifted slightly towards the red .
So noticeable is the effect on the band near D , that a didymium solution diluted until its absorption spectrum is no longer visible regains this band on the addition of a little of the hyposulphite .
So far as could be ascertained by eye observations , the intensity of this band is approximately trebled by this treatment .
Many other reducing agents were used in place of the hyposulphite , such as zinc , magnesium , and other metals with various acids , hydroxylamine salts , titanous chloride , sulphites , etc. , but in no case was any similar effect observed .
As didymium salts can be fractionated into neodymium and praseodymium salts , specimens of the nitrates of these metals were obtained , and the action of hyposulphite on them examined also .
In spite of the fact that other reducing agents did not produce these changes , it seemed possible , hyposulphites being very powerful reducing 1912 .
] Absorption Spectra of " " Salts .
substances , that the changes might be due to a reduction of the didymium ( or possibly of the contained neodymium only , for no shift of a praseodymium line could be detected with certainty in the not very satisfactory photographs obtained ) , but on further examination there was no evidence that this was the case .
On the other hand , it was found that similar changes in the absorption spectra could be effected by adding the sodium or potassium salts of weak acids , such as acetic or nitrous .
As sodium hyposulphite is the salt of a weak acid , it seemed probable that its action was an example of a general action of such salts , rather than a case of reduction by one particular reducing agent .
In order to investigate the matter more fully , a series of photographs of the absorption spectra of didymium under various conditions was made , the strengths of the acid combined with the metal , the solvent , and the concentration all being varied ( Plate 1 , photographs 1 to 10 ) .
'Experiments made it evident that , in order to render the photographs of such a series comparable among themselves , it would be necessary to maintain definite conditions of concentration of the didymium , * thickness of absorbing layer , f etc. , for increase in the amount of didymium , due either to increase in concentration or in thickness of absorbing layer , causes a broadening of the bands , generally greater towards the red than towards the violet end of the spectrum .
This effect is , however , not very marked unless the differences between two solutions are large ; for example , photographs given by equal thicknesses of solutions of didymium nitrate , one containing 3 per cent , and the other 4 per cent , of Di , would appear very similar .
Again , although the spectra given by a 10-cm .
layer of didymium nitrate solution containing 1 per cent Di is almost identical with that given by a 1-cm .
layer of a solution containing 10 per cent. Di , the only readily observable differences being that the absorption bands are wider and more hazy at their edges in the case of the stronger solution , yet , when the differences of concentration are very great , the positions of some of the lines are no longer the same in the two solutions ( photographs 7 and 8 show this * All concentrations mentioned refer to grams per 100 c.c. , thus the 4-per-cent , solution contained 4 grm. of Di per 100 c.c. t In many cases , when two spectra were to be photographed together for comparison , it was useless to give equal exposures , particularly when very dilierent thicknesses were to be examined .
In such cases the exposures were judged approximately from the relative illuminations on the camera screen , and if the resulting photographs were of very different densities , the experiment was repeated with suitably arranged exposures , as this appeared to be the only satisfactory means of obtaining comparable results .
The plates were all developed for equal times , six minutes , and the other conditions were likewise uniform ( cf. Living , ' Camb .
Phil. Soc. Trans. , ' 1900 , vol. 18 , p. 298 et seq. ) .
Mr. W. C. Ball .
On Changes in the [ Apr. 17 , effect for concentration ratios 1:300 and 1:400 , the amounts of Di in each layer being the same ) .
For the above reasons , the conditions in taking the appended series of photographs have been kept constant as far as possible , and are given in full .
Methods Used in Photograp the Spectra .
The source of light was a Nernst filament , the light from which was concentrated on the slit by means of an achromatic condenser .
A transmission grating of 14,400 lines to the inch was used .
The camera lens consisted of an achromatic telephoto combination of about 100 cm .
focal length .
When two photographs were to be compared , the tanks containing the absorbing solutions were placed successively in front of the slit , one half or the other of the slit being obscured by moving a screen , in which holes of the requisite size had been cut .
The helium lines were then superposed on the entire photograph by the replacement of the Nernst filament by a helium tube .
In this way the helium lines occupied the same position on each photograph , so that the positions and possible shifts of any absorption bands could be accurately measured .
This arrangement was found to answer better than the employment of two similar sources of light , one beam passing directly to the slit , and the other after reflection by a right-angled prism attached to the slit , as , with this latter arrangement , it was not easy to obtain equality of illumination in the two photographs , which were therefore less comparable with one another .
In order to render the shifts of the lines more obvious , and as an additional check in the subsequent measurements made on the plates , most of the photographs were taken against similar standard solutions of didymium nitrate .
The various absorbing solutions were contained in parallel-sided glass cells , made so as to contain various accurately measured thicknesses of liquid .
In most cases these cells were fixed together with sealing-wax , and then rendered watertight with paraffin-wax .
Two pairs of photographs were generally obtained on the same plate by cutting off the light when one pair had been taken , and then raising or lowering the plate .
Any slight shaking of the camera during this operation was unimportant , as the helium lines were subsequently superposed on the second pair of photographs .
Panchromatic plates were used in all cases .
Eye observations were made with a telescope having a micrometer eyepiece with two moving cross-wires , and reading to 02 of an Angstrom unit .
These observations were often more useful than photographs , especially when gradual changes , produced by the addition of successive small quantities of some substance , had to be made .
Absorption Spectra of"Salts .
Measurement of the Absorption Bands and Lines .
Nine of the absorption bands and lines in the didymium spectrum were measured , beginning with the large band near the D lines , and ending with that in the violet , near the helium line of wave-length 3889 A.U. The other bands , especially the groups in the red , were generally too faint or too diffuse to measure accurately .
These groups in the red were often absent in the photographs , and were always difficult to see , even when considerable thicknesses of concentrated solutions were used .
The bands and lines measured are shown and numbered in photograph No. 1 , and they fall conveniently into three groups , 1 , 2 , and 3 , lying between the yellow helium line , D3 , wavelength 5875*6 , and the green helium line 5015*7 ; 4 , 5 , and 6 between the green helium line and the blue 4471'5 ; and 7 , 8 , and 9 between this line and the violet helium line 3889 .
The distances between these four helium lines were measured for each plate and the number of Angstrom units per centimetre thus determined for the three sections into which the spectrum was divided .
The position of any particular line or band was then calculated using the value found from the helium lines between which it lay .
The positions of the centres of the maxima of absorption have been measured , and these are not in general the same as the half-way distance between the two edges .
The edges of a line or band are often more or less hazy , and cannot be measured so accurately as the maximum of absorption .
Line 8 , especially in very dilute solution , is extraordinarily sharp and narrow , its width in a solution containing 0*0625 per cent. Di ( as nitrate ) was found to be four Angstroms , and it was , in reality , probably less ; in consequence , it can be measured with more accuracy than the others .
The mean value for its centre from eight measurements was , for solutions containing 4 per cent. Di ( as nitrate ) , X 4274*3 A.U. , and from four other photographs , taken last , and with some further precautions suggested during the course of experiments , the mean was 4274*0 .
Most of the other values given are means , and these should be correct to + or \#151 ; an Angstrom unit .
Tables I , II , and III ( see pp. 128 , 132 , etc. ) give the positions and shifts of the lines for several varieties of the didymium spectrum .
All shifts towards the red are denoted by + , and those towards the violet \#151 ; ; similarly , the edge of a line or band which is nearer towards the red is described as the + edge , that nearer the violet the \#151 ; edge .
Causes of the Alterations in the Spectra .
If the changes in the didymium spectrum produced by the addition of sodium or potassium acetate ( see photographs 1 , 2 , 3 , and 4 ) are due to a Mr. W. C. Ball .
On Changes in the [ Apr. 17 , diminution in the ionisation of the didymium salt , it would be expected that the addition of sodium or potassium salts of other weak acids would produce similar effects , for they should also reduce the ionisation .
Photographs of the spectrum of didymium nitrate , before and after the addition of sodium nitrite , azide and similar salts showed that this was the case , the solid salts being added to the didymium nitrate solution ( 4 per cent. Di ) so that the concentration of the didymium should be altered as little as possible .
These effects are produced by salts of weak inorganic acids as well as by those of weak organic , acids .
Again , the use of other solvents than water should entail similar effects , for the ionisation produced is generally less than that in aqueous solutions of the same strength .
Photographs 5 and 6 give the spectra of solutions of anhydrous didymium nitrate ( 4 per cent. Di ) in very carefully dried ethyl alcohol and acetone .
These and other photographs of solutions in glycerol and in pyridine show that the spectra in these different solvents are very similar to one another , and that they all differ in certain respects from that given by aqueous solutions .
The most important of these changes are\#151 ; ( a ) A shift of the bands and lines towards the red , the \#151 ; edges being moved less than the -f edges .
Line 5 is the only exception , it exhibits a \#151 ; displacement .
( b ) A fusion of lines 5 and 6 ( apparently due to their shifts in opposite directions , which brings them nearer together ) into a broad band with two rather indistinct maxima .
( c ) The two* maxima in band 2 , wave-lengths 5225 and 5203 ( these are \#166 ; their positions in the standard didymium nitrate solution , 4 per cent. Di ) , are replaced by a single band , centre about 5231 .
Table II ( p. 132 ) shows that these changes are approximately equal for the solvents used , and also that the spectra thus modified are very similar to those given by crystalline didymium nitrate and by the fused salt ( that is , by the ordinary salt Di(N03)3,6H20 fused in its own water of crystallisation ) .
Further , it should be possible to produce similar changes by altering the concentration of an aqueous solution of a didymium salt : for a highly concentrated solution should be less ionised than a more dilute one , and so its spectrum should alter in the same direction as those given by solutions in alcohol , acetone , etc. , and by the solid nitrate .
It was not found easy to show this satisfactorily until very different concentrations were used , for the differences * In some plates this band showed another faint maximum at 5253 , and also traces of a division of the maximum with centre at 5225 into two parts with centres at 5231 and 1912 .
] Absorption Spectra of " Salts .
between photographs of the spectra given by 1 cm .
thickness of a nitrate^ solution containing 10 per cent. Di and 20 cm .
of one containing 0'5 per cent Di were very slight .
When , however , the concentration ratio was altered to 1:400 , 0'1-cm .
and 40-cm .
layers of solutions containing 25 per cent , and 00625 per cent. Di respectively being employed , the effect was well shown ( see photographs 7 and 8 ) .
The narrowness and sharpness of definition of the bands and lines in the case of the very dilute solution , and the increase in breadth and decrease in intensity and definition and also the slight + shift in the case of the very concentrated solution , can be easily seen with lines 2 and 8 , photograph 8 .
Line 5 appears much more intense in dilute than in concentrated solution ; and in very concentrated solution is practically absent ( see photographs 7 and 8).* There is a curious point with regard to band 2 ; in the dilute solution the two maxima in this band at 5215 and 5201 are of about equal intensity and differ little in breadth ( 13 and 11 A.XJ .
respectively ) , but in the concentrated solution the maximum at 5215 has increased greatly in breadth towrards the red , its centre now being at 5224 , whereas the other maximum at 5201 has become very faint , but has not altered perceptibly in position .
An exactly similar effect is produced by the gradual addition of sodium ( or potassium ) acetate , and can be followed by eye observation , when it is seen that the maximum in band 2 ( A , 5215 in the dilute solution ) nearest the red gradually moves towards the red , at the same time increasing in width , whilst the other maximum retains its position but becomes fainter until it entirely disappears , the original double band becoming single ( see photographs 3 and 4 ) .
finally , if these effects are due to ionisation , on comparing the spectra of solutions of didymium salts , each containing the same amount of didymium , but combined with acids of different degrees of strength , similar changes should occur ; the salt of the strongest acid giving a spectrum most like that given by the nitrate of didymium , whereas the salt with the weakest acid should yield a spectrum similar to that produced by the addition of sodium acetate , nitrite , etc. , by the use of other solvents than water , or by the solid salt .
Ihis is shown in photograph 9 , which is that of didymium triehloracetate , dichloracetate , monochloracetate , and acetate , each containing 4 per cent. Di .
The trichloracetate , being the salt of an acid of the same order of strength as nitric acid , gives a spectrum exactly similar to that given by the nitrate ( see Table I for measurements ) .
The dichloracetate spectrum is very similar , but there is a slight + shift of some of the lines , seen best with * In the three photographs which were taken of an almost saturated solution of the nitrate in water ( 42-3 per cent , of Di ) , line 5 appeared to be replaced by a wide , faint band , having three almost indistinguishable maxima of absorption .
VOL. LXXXVII.\#151 ; A. K Mr. W. C. Ball .
On Changes in the [ Apr. 17 , line 8 .
The monochloracetate , which is the salt of a weak acid , shows greater changes in the same direction , band 2 being now single , and in the case of the acetate , the salt of a very weak acid , the alterations are very obvious .
Even in the case of the acetate , however , the change to the altered spectrum does not appear to be complete , as the lines are less shifted and signs of fusion of lines 5 and 6 are only faintly seen .
This was to be expected , for measurements of the conductivity of the acetate show that part of the didymium must be present in an ionised condition , the change to the non-ionised condition being therefore incomplete .
The analogous spectra given by the propionate , butyrate , and lactate were also examined , but only that of the propionate , the salt of an acid still weaker than acetic , was photographed .
The formate appeared to be little soluble in water .
The electrical resistances of these solutions were next determined to discover whether they altered pari passu with the changes in the spectrum , and , as can be seen from the appended figures , this is approximately the case .
Table I. Solutions containing 4 per cent Di .
Relative resistance in ohms .
Position of line 8 .
Shift of line 8 from 4274 -0 .
Acetate 118 -4 4282 + 8 From these figures it can be Monochloracetate 62 -3 4277 -6 + 3-6 seen that the resistance and Dichloracetate 29 -2 4275 + 1 the shift of line 8 alter nearly Trichloracetate 17 -9 4273 -5 \#151 ; in the same ratio .
Propionate 167 -5 4283 + 9 Nitrate 22 -9 4274 -0 \#151 ; The figures for the resistances are only comparative , and are those given by the various solutions actually used in the spectroscopic work , when placed in a small , specially constructed electrolytic cell , with fixed electrodes .
The altered spectrum produced by the addition of sodium acetate to a solution of didymium nitrate , which appears to be essentially the spectrum of a compound , and not the spectrum of ionic didymium , reverts at once to the ordinary condition on the addition of a strong acid ; these changes can be repeated at pleasure by further alternate additions of the acetate and strong acid .
Addition of potassium or sodium nitrate to didymium nitrate solution also alters the spectrum in the same manner , but the effect is very much more feeble than with the acetate .
The addition of strong nitric acid brings about similar changes .
Finally , a non-electrolyte , such as cane-sugar , may be added to an aqueous solution of didymium nitrate until the liquid becomes a thick syrup , and yet 1912 .
] Absorption Spectra of " Didymium " Salts .
129 the spectrum remains unaltered ; a very small addition of the acetate will now produce the altered spectrum .
Incidentally , this shows that viscosity and refractive index have little to do with the alterations described .
There would , therefore , appear to be two distinct classes of didymium spectra .
( a ) The ionic spectrum , that is the spectrum of the didymium ion , given by the didymium salts of strong acids , such as nitric , hydrochloric , trichloracetic , and sulphuric , especially in very dilute solution .
This spectrum is shown in photographs 7 and 8 .
The spectrum given by a 4-per-cent .
Di solution of these salts differs but little from that given by a very dilute solution , the stronger solution giving rather broader lines and bands , with less well defined edges , and very small + shifts .
( b ) The non-ionised spectrum , which , being in every case the spectrum of a compound , shows slight variations from compound to compound , but has a definite character .
Such spectra are those produced by adding the sodium or potassium salt of a weak acid to the didymium salt of a strong acid ( photographs 1 , 2 , 3 , and 4 ) , those given by the didymium salt of a weak acid ( photographs 9 , C and D ) , those given by solutions of didymium salts in certain solvents , such as ethyl alcohol , etc. ( photographs 5 and 6 ) , and those given by the nitrate , either crystalline or melted ( photograph 11 ) .
These spectra are characterised by the great increase in breadth and in intensity of band 1 ; disappearance of the maximum 5203 in band 2 ( it appears , however , in the crystal spectrum ) ; similar changes in band 3 ; the fusion of lines 5 and 6 , and a general shift of bands and lines towards the red ( line 5 , which has an opposite shift , excepted ) .
The fusion of lines 5 and 6 does not appear to be so constant as the other effects , and is absent in the spectrum produced Die the addition of sodium hyposulphite ( photographs 1 and 2 ) , which is probably essentially that of lion-ionised didymium hyposulphite.* Although these " non-ionised " spectra are similar to one another in general character , they show many minor differences , especially in the positions of the maxima in band 1 ( these cannot easily be seen in the photographs , but have been examined by eye ) , and in the positions of the edges of this band .
Although alkalis at once precipitate the hydroxide from solutions of didymium salts , yet , by the addition of sucrose , it is possible to prevent this precipitation and to obtain the spectrum of didymium in alkaline solution ( see * Some attempts were made to obtain the spectrum of a didymium salt in a non-lonising solvent , but without much success , as the salts used proved to be nearly insoluble in such solvents .
However , the trichloracetate was slightly soluble in chloroform , and in 20 cm .
thickness of this solution bands 1 and 2 could be observed .
They were rather amuse , and consequently difficult to measure , but showed + shifts of about 15 .
Mr. W. C. Ball .
On Changes in [ Apr. 17 photograph 10 ) .
This spectrum presents quite exceptional characters , some of the lines being enormously shifted .
Possibly in this case the didymium is contained in the negative ion .
The same remarks apply to the very similar photographs given by didymium glass .
Liveing states that the anhydrous chloride , DiCl3 , is insoluble in absolute alcohol , but samples of the nitrate which I heated to 170'\#151 ; 180 ' C. , until there was no further change in weight ( they lost very slightly more than the theoretical amount of water for the formula Di(lSr03)3,6H20 ) , dissolved almost completely in very dry alcohol , dried over lime for some weeks , and then over metallic calcium : they were also soluble in pure acetone.* These solutions gave spectra similar to those produced by dissolving the hydrated salt in alcohol and in acetone respectively .
These spectra again differ so little from that of the crystalline nitrate , that it seems possible that the absorbing constituent in all is the same , and that they are all essentially the spectra of non-ionised Di(ISr03)3 .
Tfie spectra of these solutions in alcohol or acetone rapidly revert to that of an aqueous solution , on the addition of water , so that the spectrum of didymium nitrate in a mixture containing 50 per cent , ethyl alcohol and 50 per cent , water is practically that of an aqueous solution .
On comparing very concentrated solutions of didymium salts in water with very dilute ones , it appears that the chief alterations in the spectra take place on passing from a very high concentration to one rather lower , and that further dilution produces only trifling changes in the spectrum , although ionisation , judging from the conductivity changes , is by no means complete .
Thus the changes in the spectrum between a solution of the nitrate containing 42 per cent. Di and one containing 4 per cent. Di are much greater than those between concentrations of 4 per cent , and 0-0625 per cent , ( the chloride spectrum changes less with dilution , according to Liveing and others , and according to my own observations ; I have found also that the conductivity alters more with dilution in the case of the nitrate than with the chloride ) .
If the spectrum of the crystal is that of Di(N03)3 , modified very little by the water with which it is combined , and if that of a very dilute aqueous solution is that of the didymium ion , it may be a possible explanation of these observations that the nitrate is very * I was able to make up a solution of the anhydrous nitrate in anhydrous ethyl alcohol containing 21 per cent , of Di .
A layer of this , 0T65 cm .
thick , was photographed together with a 61-3 cm .
layer of a solution containing 0'057 per cent. , the quantities of absorbing didymium being the same , but the concentrations in the ratio 1 : 370 .
There was much less difference between the two spectra than in the corresponding case for aqueous solutions , the lines being shifted little , if at all , relatively to one another in the two spectra .
1912 .
] Absorption Spectra of " " Salts .
considerably ionised , even in a fairly strong solution , and that the subsequent changes on further dilution , which seem to be much greater in the case of the electric conductivity than in the absorption spectrum , may be due to an increase in mobility of the didymium ion , and not in its relative numbers .
The spectra of some of these solutions are almost certainly the combined spectra of two substances .
That it is so may be seen on reference to photographs 3 and 4 , which show the effect of adding to a very dilute ( 007 per cent. Di ) aqueous solution of didymium nitrate the exact amount of sodium acetate required by the equation !
Di(N08)3 + 3CH3C00Na = Di(CH3COO)3 + 3NaN03 , and also twice this amount .
In photograph 3 , with the smaller amount of acetate , line 8 is seen to be doubled , the centres of its components being 4274 and 4281 .
The component at 4274 is therefore identical in position with line 8 of the spectrum of aqueous didymium nitrate , whilst that at 4281 is probably due to non-ionised didymium acetate ( line 8 in an aqueous solution of didymium acetate , containing 4 per cent. Di , having its centre at 4282 ( see Table I ) ) .
In photograph 4 , addition of another equivalent of sodium acetate has caused the latter component to increase in intensity , and that at 4274 almost to disappear , effects which would be expected if more didymium acetate has been formed by the excess of sodium acetate present ; again , line 8 in a solution of didymium nitrate containing 4 per cent. Di appears composite , as though it consisted of the sharp line of the very dilute solution superposed on the wider , less intense line of the very concentrated solution .
Similarly , line 8 in the spectrum of a very dilute solution of the anhydrous nitrate in carefully dried ethyl alcohol is possibly double .
On the other hand , the spectrum of a dilute solution in water would seem to be that of a single substance , for the lines become increasingly narrow and definite as the dilution is increased .
I expected to obtain a distinctly composite spectrum on mixing quantities of the acetate and trichloracetate containing equal amounts of didymium , but obtained a spectrum having rather hazy lines and bands and resembling that of the acetate rather than that of the trichloracetate .
Mr. W. C. Ball .
On Changes in the [ Apr. 17 , Table II .
The following table gives the positions of certain of the lines , of their edges , and the extent of their shifts , for didymium nitrate in various solvents , and , for comparison , the corresponding data for the crystalline and fused salt , and for an alkaline solution .
The most dilute solution in water ( 00625 per cent. Di ) is taken as the standard , and the shift of any line is the number of o Angstrom units through which its centre is shifted from the position it occupies in this 0 0625-per-cent , solution .
C denotes the position in a line or band where the absorption is most intense E the position of the edges , and W the width of a line or band .
All shifts towards the red are marked + , those towards the violet \#151 ; .
The edge of a band or line towards the red is called the + edge , that nearer the violet the \#151 ; edge .
Solution of didymium nitrate in\#151 ; Line 8 .
Shift of 8 .
Lines 5 and 6 .
Shift of 6* Shift of 6 .
1 Water\#151 ; 0*0625 p.c. Di ... 0 .
4273-6 0 4751 : 4688 o 0 E. 4276 : 4272 W. 4-1 4*0 " ... C. 4274-0 + 0-5 4757 : 4694 + 6 + 6 E. 4280 : 4269 W. 11 25 " ... 0 .
4276-4 + 3 4753 : 4692 + 2 + 4 E. 4285 : 4271 Lines very faint .
W. 14 Ethyl alcohol\#151 ; Containing 2 p.c. C. 4282 + 9 4739 : 4704 -12 + 16 Di as anhy- E. 4291 : 4275 Lines 5 and 6 have drous salt W. 16 coalesced into wide band with above maxima of absorption .
Glycerol\#151 ; Containing 4 p.c. C. 4284 + 10 lines 5 and 6 have Di as hydrated E. 4289 : 4270 coalesced to a salt W. 19 broad band with In this case , unlike maxima at the others , the 4749 : 4701 -2 + 13 absorption is much greater near the + edge .
Acetone\#151 ; 4 p.c. Di as an- 0 .
4286 + 12 Lines 5 and 6 have hydrous salt E. 4289 : 4276 coalesced to a ' W. 13 broad band with maxima at 4746 : 4704 -5 + 16 Pyridine 0 .
4284 + 10 Lines 5 and 6 have Additional faint , coalesced to a rather narrow , line broad band with appears at 4308 .
maxima at 4783 , 4744 : 4708 -7 + 20 Absorption Spectra of " " Salts .
Solution of didymium nitrate in\#151 ; Line 8 .
Shift of 8 .
Lines 5 and 6 .
Shift of 5 .
Shift of 6 .
Di(N03)3,6H20 C. 4278 + 4 Lines 5 and 6 have fused E. 4285 : 4268 coalesced to a .
W. 17 broad band with maxima at 4737 : 4698 -14 + 10 Solid salt\#151 ; Di(N03)3,6H20 ... C. 4283 + 9 Lines 5 and 6 have coalesced to a broad band with maxima at Solution of didy- 4737 : 4700 -14 + 12 mium nitrate\#151 ; 2 p.c. Di , con- Yery sharp maxitaining cane- mum with diffuse sugar and part surrounding NaOH it .
0 .
4317 + 43 Lines 5 and 6 are Additional faint replaced by a line at 4330 .
broad band with maxima at j 1 4792 : 4739 + 41 + 51 # The maxima in the broad band which replaces lines 5 and 6 are rather indistinct and difficult to measure .
In consequence , the shifts of lines 5 and 6 are less accurately measured than those of line 8 ; this applies especially to the case of line 5 .
Table III.\#151 ; Positions of Lines and Bands in various Didymium Absorption Spectra .
C. S3 The centre of a line or band ( or , if the band be multiple , of the maxima of The + edge of a line or band is that edge nearer the red .
absorption in the band ) .
The\#151 ; , , .\#187 ; \#187 ; \#169 ; . .
\#187 ; * \#187 ; \gt ; vlo , \lt ; E. = The positions of the edges .
All measurements are in Angstrom units .
W. = The width .
Kegion of spec- trum .
Num- ber of line or band .
Aqueous solution of didymium nitrate , 0*0625 per cent. Di , 40 cm .
layer .
Aqueous solution of didymium nitrate , 25 per cent. Di , 0*1 cm .
layer .
Aqueous solution of didymium nitrate , 4 per cent Di , 3 cm .
layer .
Crystal of Di(N03)3,6H20 , 0*1 cm .
to 0*2 cm .
thick .
Didymium glass .
Aqueous solution of didymium nitrate , 4 per cent. Di + Na2S204 .
Aqueous solution of didymium | nitrate , 2 per !
cent. Di , with sucrose and caustic soda .
Orange 1 Sharply defined , contained four maxima E. 5790\#151 ; 5707 Centres of maxima\#151 ; 5783 5751 5735 5715 W. 83 Compared with 0'0625-per-cent .
solution , is wider in each direction , edges are less sharp and maxima less intense E. 5841\#151 ; 5695 Centres of maxima\#151 ; 5795 5762 5736 W. 146 In 3 cm .
layer no maxima could be seen .
They were visible in thinner layers C. 5774 E. 5855\#151 ; 5694 W. 161 This band appears to be divided into two portions .
One , an intense part with sharp edges at 5846\#151 ; 5708 , W. 138 .
The other a fainter part extending to 5987 and having two rather faint maxima with centres at about 5973 and 5944 Band very wide , and most intense portion at + side E. 5942\#151 ; 5684 W. 258 Maxima having centres at\#151 ; 5860 5827 5741 Very wide and intense E. 5987-5697 C. 5842 W. 290 Very wide , both edges shifted towards red .
E. 6028\#151 ; 5706 .
W. 322 .
Green 2 Two very sharp , narrow , lines , close together C. of 1st line , 5215 E. " " 5224\#151 ; 5211 W. " " 13 C. of 2nd line , 5201 E. " " 5207\#151 ; 5196 W. " " 11 Two lines as in 0*0625-per-cent .
solution , but the first of these has doubled in width , and the second has decreased in intensity C. of 1st line , 5224 E. " " 5235\#151 ; 5210 W. " " 25 C. of 2nd line , 5204 E. " " 5207\#151 ; 5197 W. " " 10 Multiple band E. 5335\#151 ; 5198 W. 138 Centres of maxima\#151 ; 5253 5231 5216 5203 The separation between the maxima at 5231 and 5216 is very slight and they generally appear as single maximum with C. at 5224 Band with four maxima , the two middle maxima being only faintly separated .
Band is intense Centres of maxima\#151 ; 5250 5229 5220 5197 .
Single band , very faint , wide and diffuse C. 5268 Band with two maxima E. 5344-5204 W. 140 Centres of maxima\#151 ; 5270 5232 Band with three ill - defined maxima having centres at\#151 ; 5295 .
5277 .
5267 .
Green 3 Double , fainter than band 2 C. of 1st line , 5117 E. " , , 5136-5104 W. " " 32 C. of 2nd line , 5087 E. " " 5093\#151 ; 5081 W. " " 13 Very faint band with two maxima Centres of maxima\#151 ; 5113 5086 E. of band , 5125\#151 ; 5082 Total W. of band 43 Double , fainter than band 2 ; diffuse edges E. 5149\#151 ; 5082 W. 67 Centres of maxima\#151 ; 5120 5091 Band with two maxima .
Weaker than band 2 Centres of maxima\#151 ; 5113 5087 Single band , very faint , wide and diffuse C. 5130 Single band E. 5154\#151 ; 5098 C. 5127 W. 56 i Very diffuse single band .
C. 5142 .
134 Mr. W. C. Ball .
On Changes in the [ Apr. 17 , Blue ... 4 Fairly sharp line C. 4816 C. 4820 C. 4821 W. 19 Blue ... 5 C. 4751 Very faint indeed C. 4753 C. 4758 W. 21 Blue ... 6 C. 4688 C. 4692 C. 4694 W. 14 Blue ... 7 Wide , rather diffuse C. 4436 Wider and more diffuse than in 0'0625-per-cent .
solution C. 4439 Wide , diffuse edges C. 4437 W. 38 Violet 8 Extremely sharp and narrow C. 4273-6 E. 4276\#151 ; 4272 W. 41 Wider and less sharp than in 0*0625-per-cent .
solution C. 4276-4 E. 4285\#151 ; 4271 W. 14 Narrow ; maximum intensity near\#151 ; edge C. 4274-0 W. 10 Violet 9 \#151 ; \#151 ; Wide , diffuse C. 4023 W. 28 .
Strong ; a Tly| narrow C. 4831 i Lines 5 and 6 are re- !
placed by band with j two maxima having their centres at 4737 | and 4700 Wide .
Edges indistinct C. about 4440 Sharply defined and narrow C. 4283 Possible faint trace of this band detected 1 Absent Absent Very faint trace , with centre about 4470 Very faint , wide , diffuse .
C.4301 .
Is possibly the maximum in a wide , very faint band C. 4830 W. 31 Faint C. 4761 W. 25 C. 4706 W. 28 C. 4456 W. 47 Wide C. 4289 W. 21 .
Wide , ill-defined .
C. 4853 .
' Lines 5 and 6 have merged into a band having two 1 maxima with centres at 4792 ^ and 4739 .
Very faint trace .
Centre about 4470 .
Very sharp max .
C. at 4317 .
Much weaker one .
C. at 4330 .
Diffused part at each side .
Absorption Spectra of " Didymium " Salts .
135 Mr. W. C. Ball .
On Changes in the [ Apr. 17 , Conclusions .
( A ) That the chief changes produced by dilution of an aqueous solution of didymium nitrate occur when a very concentrated solution is diluted slightly and that further dilution , although the didymium salt still alters in electric conductivity , produces comparatively small effects .
( B ) That conditions which would be expected to reduce the ionisation of didymium salts , such as combination of the didymium with a weaker acid , addition of the sodium or potassium salt of a weak acid , solution in a solvent of less general ionising power than that of water , or increase of concentration of the salt in solution , all produce fairly similar changes in the absorption spectra .
There are some curious points which I hope to investigate further , particularly as to why the spectrum of the nitrate alters so slightly between concentrations of say 10 per cent. Di to 0-05 per cent. Di , whereas the conductivity alters considerably .
Further investigations , with very dilute solutions , might also throw some light on the effects produced by the gradual addition of sodium acetate and other salts , particularly on the changes produced in band 1 .
These consist in the production of transient maxima of absorption within the band , and also of a minimum of intensity of the whole band , followed by a large increase .
I wish to express my cordial thanks to Mr. Abram , of the Physics Department , Guy 's Hospital Medical School , for his very kind and valuable help , especially in the taking and measuring of the photographs , and to Dr. Yeley for much valuable advice .
DESCRIPTION OF PLATE .
All spectra are reproduced half scale of originals .
Some of the finer details , in particular the maxima in bands 1 and 2 , and the doubling of line 8 in photographs 3 , A , and 4 , A , though very obvious in the originals , are much less clearly seen in the reproductions .
Photograph 1 .
Effect of adding excess of potassium acetate .
A. Aqueous solution of didymium nitrate , 4 per cent. Di , with excess of potassium acetate .
B. The same , without the potassium acetate .
In each case , 20 secs , exposure ; 3 cm .
layer ; width of slit , 0-01 cm .
Helium exposure , 120 secs .
Photograph 2 .
Comparison of effect of potassium acetate with that of sodium hyposulphite .
A. Aqueous didymium nitrate , 4 per cent. Di , with excess of potassium acetate , as 1 , A. B. The same , with sodium hyposulphite instead of potassium acetate .
Exposures , 30 secs .
Other conditions as in 1 .
,4^ Helium line D Green Helium Line Blue Helium Line Violet Helium Line A 5875-6 3 A 50157 A 4471-5 A 3889 1912 .
] Absorption Spectra of Salts .
Photograph 3 .
Effect of sodium acetate in dilute solution .
A. 61 '3 cm .
layer of aqueous didymium nitrate , 0*07 per cent. Di , containing one equivalent of sodium acetate .
B. The same , but without the acetate .
Exposures , 250 secs .
; width of slit , 0*005 cm .
Helium exposure , 240 secs .
Photograph 4\#151 ; A. As 3 , A , but with two equivalents of acetate .
B. As 3 , B. Other conditions exactly as in 3 .
Photograph 5 .
Solution of anhydrous didymium nitrate in ethyl alcohol .
A. Anhydrous nitrate in well-dried ethyl alcohol , 2 per cent. I)i .
Exposure , 60 secs .
B. Aqueous solution of the same strength .
Exposure , 50 secs .
3 cm .
layers ; width of slit , 0*01 cm .
Helium exposure , 180 secs .
Photograph 6\#151 ; A. Aqueous solution of didymium nitrate , 4 per cent. Di .
B. Solution of the anhydrous salt in acetone , 4 per cent. Di .
.1 cm .
layers ; width of slit , 0*005 cm .
Exposures , 40 secs .
; of helium , 180 secs .
Photograph 7 .
Spectra of dilute and of concentrated aqueous solutions .
A. 61'3 cm .
layer of aqueous didymium nitrate , 0T413 per cent. Di .
Exposure , 100 secs .
B. 0*205 cm .
layer of aqueous didymmm nitrate , 42*25 per cent. Di .
Exposure , 85 secs .
Width of slit , 0*005 cm .
Helium exposure , 240 secs .
These contained the same amount of didymium in the absorbing layers , but in concentration ratio 1 : 300 .
Photograph 8 .
As 7 , but concentration ratio 1 : 400 .
A. 0*1 cm .
layer of aqueous didymium nitrate , 25 per cent. Di .
Exposure , 50 secs .
B. 40 cm .
layer of aqueous didymium nitrate , 0*0625 per cent. Di .
Exposure , 210 secs .
Width of slit , 0*005 cm .
Helium exposure , 210 secs .
Photograph 9 .
Effect of variation in strength of acid combined with the didymium .
A. Aqueous didymium trichloracetate , 4 per cent. Di .
B. " dichloracetate , " C. " monochloracetate , " D. " acetate , " Exposures , 20 secs .
; 3 cm .
layers ; width of slit , 0*01 cm .
Helium exposure , 120 secs .
Photograph 10 .
Alkaline solution of didymium .
A. Aqueous solution of didymium ( as nitrate ) with sucrose and caustic soda , 2 per cent. Di .
Exposure , 90 secs .
B. Aqueous didymium nitrate , 2 per cent. Di .
Exposure 45 secs .
3 ; cm .
layers ; width of slit , 0*005 cm .
Helium exposure , 180 secs .
Photograph 11 .
Crystal of Di(N03)3,6H20 .
Thickness , 0*1\#151 ; 0*2 cm .
Exposure , 300 secs .
; width of slit , 0*01 cm .
Helium exposure , 180 secs .
|
rspa_1912_0065 | 0950-1207 | The changes in certain absorption spectra in different solvents. | 138 | 147 | 1,912 | 87 | Proceedings of the Royal Society of London. Series A, Containing Papers of a Mathematical and Physical Character | Thomas Ralph Merton, B. Sc. (Oxon)|Prof. J. M. Thomson, F. R. S. | article | 6.0.4 | http://dx.doi.org/10.1098/rspa.1912.0065 | en | rspa | 1,910 | 1,900 | 1,900 | 8 | 152 | 3,423 | http://corpora.clarin-d.uni-saarland.de/surprisal/6.0.3/?id=rspa_1912_0065 | 10.1098/rspa.1912.0065 | null | null | null | Atomic Physics | 26.228534 | Chemistry 2 | 22.818961 | Atomic Physics | [
-20.56133460998535,
-57.116336822509766
] | ]\gt ; The in Absorption in Different Solvents .
By BALPH MEItTON , B.Sc. ( Oxorl ) .
( Communicated by Prof. J. .
Thomson , F.R.S. Received April 17 , \mdash ; Read , 1912 .
In recent years a considerable amount of attention has been given to the absorption spectra of anic salts , and some conclusions of somewhat startling significance have been drawn from the results .
With the exception of a few cases , however , notably the recent work of Houstoun and his colleagues , * this work has been qualitatiye , and in most cases has been carried out by raphic methods .
The great disadvantages of these methods are now recognised , and it therefore becomes a matter of ance to discover whether accurate quantitative measurements will throw any further light on the subject .
The object of the present investigation has been to select some charactelistic substance and to make an accurate quantitative investigation of its absorption spectrum in different solvents .
In the course of the work the question of the radual replacement of one acid radicle by another has also been investigated , and an attempt had been made to investigate the possible effect of pressure on the absorption spectra of solutions .
The choice of material is somewhat restricted , the absorption of most inorganic salts being somewhat ill-defined , except in a few isolated cases .
After a number of preliminary inyestigations uranous chloride was chosen .
It can be obtained pure , it is soluble in a large number of solvents , and the absorption bands , which are comparatively well defined , are chiefly situated in the orange-red and green parts of the spectrum , and are , therefore , particularly well suited for photo- metric measurements .
The chemical properties of this substance have been fully investigated by Colani .
Up to the present , with the exception of the work of Jones and Strong , S only a few isolated measurements have been made on the absorption of this substance , the uranous salt having been in most cases prepared in solution by the reduction of the corresponding uranyl salt with zinc , a method obviously unsuitable for quantitative measurements .
The uranous chloride and all other chemicals used in this investigation were obtained from Kahlbaum .
The spectroscope used was a large model constant deviation type 'Roy .
Soc. Edin .
Proc 1911 , vol. 31 , p. 521 .
Cf .
' Ann. Rep. Chem. Soc , p. 16 .
'Ann .
Chem. Phys 1907 , ser. 8 , vol. 12 , p. 72 .
S 'Am .
Chem. Journ Feb. , 1911 , vol. 45 , No. 2 .
in Absorption in Solvents .
139 instrument by Hilger , the wave-lengths read directly on a helical drum with an accuracy of about 1 .
The photometric apparatus was of the type described by Houstoun , * the polarising rhomb contained in a brass cell which could be screwed on to the spectroscope in front of the slit .
The rotation of the analysing nicol in the eyepiece , which was proyided with a zero adjustment and a slow motion by rack and pinion , could be read on a divided circle with a vernier to one minute .
At the focus of the telescope objective was a slit the jaws of which were provided with a micrometer screw ad , ustment to shut off all but the narrow strip of the spectrum under observation .
In this instrument the upper and lower halves of the slit are illuminated by beams of light polarised at crht to one another , and the relation of the intensities is consequently given by the equation solutions examined were contained in a Schultz cell placed in front of the rhomb having a vlass block exactly 1 cm .
in thickness , and a small carbon arc lamp was used as a source of light .
As it was found that the accuracy of the setting varied with the absolute intensity of the light , number of neutral-tinted screens were used to cut down the light from the arc to whatever was found to be the most comfortable intensity for the eye .
Before determining the absorption of a solution it is necessary to determine the zero reading for each solvent used , owing to the loss of by internal reflection from the glass block in the Schultz cell , resulting in a different intensity in the two beams .
The real absorption of the solution is thus pressed by the equation ( solution ) : solvent ) The mean of five observations was taken in each case for determining the for each solvent .
The measurements were made at room temperature , which varied between and C. The specific extinction coefficients were determined according to the formula whel is the specific extinction coefficient , I and the intensities of the light after and before passing through the solution , the thickness of solution traversed , and the concentration expressed in grammes of salt per litre of solution .
The measurements were carried out as follows : solution of suitable concentration was prepared by dissolving a weighed quantity of salt in the solvent and making it up to 25 .
in a standard flask .
This solution was now introduced into the Schultz cell and first , examined qualitatively , 'Phil .
Mag 1908 , , vol. 15 , p. 282 . .
T. R. Merton .
Changes in [ Apr. 17 , the wave-lengths of the apparent maxima being noted .
A series of measurements of the ption was then made the entire range of the visible spectrum , care being taken to make a sufficient number of measurements in the neighbourhood of the maxima .
This method was thought to be preferable to that of taking the mean of a number of obseryations at a smaller number of points , since it was found that the single observations represented a considerable of accuracy , and the large number of points taken at short distances from one another were practically equivalent to taking the mean of a number of observations .
The following series of observations of the absorption of asso plate shows the accuracy of the results:\mdash ; .
Mean From these ures the probable error of observations , as repressnoed by the formula is approximately 15 ' .
In the solutions used this is equivalent to an error in of about .
In plotting the curves given , the values found are represented by circles the diameters of which correspond to an error of .
The refractive indices of the solvents were determined for sodium at C. by means of a Zeiss Pulfrich refractometer provided with an arrangement for controlling the temperature of the liquid examined .
This apparatus is now so well known that a description would be superfluous .
The values iven are correct to one unit in the fourth place of decimals .
esults ?
Water , Acetate , Forma lcolwl , and Ethyl Alcohol .
The refractive indices found for the solvents are as follows:\mdash ; at C. Water Methyl acetate Formamide Methyl alcohol Ethyl alcohol Beer 's law has been assumed to hold for the concentrations used , which varied up to 3 .
of salt per 100 .
of solution .
The results are shown in the curves given .
It will be at once seen from these curves that in the various solvents the differences do not merely consist in a shift of the maxima , but also in an entire change in the shape of the curve , and , in addition , there is a marked change in the intensity of absorption .
The differences in the shape of the absorption curves are too great for any attempt to be made to judge the applicability of Kundt 's law to these solutions .
912 .
] Ab.so , ption in Solvents .
FIG. 1 .
There owever , one point which at once suggests .
If two of these curves were superposed upon one another a number of apparently remarkable might be seen in the absorption spectra .
The resultants of two absorption curves superposed in three imaginary cases are given in fig. In case , the two curves do not intersect at any point , and therefore no change takes place in the apparent position of the maxima .
In case however , the resultant ( the algebraic sum of the two extinction coefficients ) , which is represented by the dotted line , shows that the apparent maximum will lie between the two maxima of the original curves , whilst in case anew band will have appeared .
This shows that , in mixtures of absorbing substances , the maxima will only appear to remain unchanged when they are situated at a certain *Cf .
Schuster , ' Rep. Brit. Assoc 1882 , p. 138 .
Mr. T. R. Merton .
in Certain [ Apr. 17 , distance from one another , depending on the form of the absorption curve .
Now the general rule given by Jones and Strong*is that , in mixed solvents , the bands due to each solvent retain their identity , whilst , when one acid radicle is replaced by another , there is a gradual shift of bands from one position to the other , which they interpret as being due to intermediate compounds .
Since the differences in the spectra in differen solvents are much greater than the differences due to the acid radicle , it becomes a matter of interest to discover whether in the latter case the gradual shift is not due to the superposition of the two curves .
The changes have been investigated in the case of aqueous solutions of nous chloride and sulphate and uranyl nitrate and chloride by the method ested by Burger .
The wave-length of an absorption maximum in an aqueous solution of uranous chloride was measured by placing the solution in two glass cells in front of the slit of the spectroscope , and taking the mean of a number of observations .
The experiment was now repeated for the corresponding band of uranous sulphate .
A third series of measurements was then made , one cell containing the chloride and the other the sulphate in series , and lastly , the two solutions were mixed and the measurements made .
The following results were obtained:\mdash ; chloride .
Uranous sulphate .
sulphate ieriesChloride asulphate mixed .
Chloride and ( The solutions were prepared from the corresponding uranyl salt by reduction .
) and for uranyl chloride and nitrate:\mdash ; .
cit. 'Ber .
Chem. Ges 1878 , vol. 2 , p. 1876 .
1912 .
] Absorption Spectra in Diffcrent Solvents .
Mean 47(K ) 4736 4708 It will thus be seen that the results are identical , whether the solutions are placed in separate cells or mixed .
The gradual shift of the maximum is therefore confirmed , but it is maintained that this is no evidence for the existence of intermediate compounds , since the results can be simply explained by the superposition of the two absorption curves .
It is therefore evident that the greatest caution must be exercised in interpreting changes in absorption spectra of this kind .
Results in Solva Ketone the of Free Acid .
Whilst the spectra in the solvents dealt with above consist of more or less diffuse bands without sharply defined maxima , the absorption spectra in ketones show , in addition to the hands , sharply defined absorption lines .
It was first observed by Jones and Strong*that when hydrochloric acid was added to a solution of uranous chloride in acetone the bands became split up into fine absorption lines .
It has been found that the strongest of these lines are visible in an acetone solution without the addition of hydrochloric acid , and that the effect of the acid is to diminish the general absorption , at the same time increasing the absorption of the lines .
It has also been found that the same effect can be produced by any soluble chloride , e.g. , potassium chloride , sodium chloride , calcium chloride , though the effect is not so marked in ths case of hydrochloric acid .
This effect of the addition of hydrochloric acid has been found to occur in all the solvents .
In water and formanlide the changes are very slight , in methyl alcohol the spectrum breaks up into two bands at 6762 and 6495 of about 60 and 40 A.U. in breadth respectively , whilst prolonged saturation of an ethyl alcohol solution with the dry gas gives rise to a spectrum which has been measured qualitatively with the following results .
In the second column the estimated intensities are given on an arbitrary scale , and in the third the apparent breadths in VOL. LXXXyII .
Mr. T. R. Merton .
in Certain [ Apr. 17 , Breadth .
The changes are , however , much more strongly marked in solvents containing a ketone group .
The following qualitative results were obtained for solution of uranous chloride in acetone saturated with dry hydrochloric acid gas .
The lines at 6686 and 6540 can be seen in an acetone solution without the addition of hydrochloric acid , but are rendered less distinct by a broad absorption band extending from about 6700 to 6520 .
Other ketone solvents investigated were\mdash ; Acetone at C. Propione , , Ethyl acetoacetate , , Acetophenone .
Measurements were also made in acetone , substituting the hydrochloric acid gas by potassium , sodium , and calcium chlorides , the results showing 1912 .
] Absorption Spectra in Different Sotvents .
that , though the broad band ( 6700-6520 ) did not completely disappear , the wave-lengths of the lines remained unchanged .
It was also found that dilution with another solvent such as water or alcohol caused a gradual disappearance of the lines , without shift , in accordance with the results of Jones and Strong .
* It was not found possible to prepare a concentrated solution of uranous chloride in propione , owing to its limited solubility in the latter , and also to the fact that some decomposition occurs .
The two lines were , however , identified at 6686 and 6540 , showing that there is no shift in from acetono to propione .
In acetoacetic ester and acetonitrile both the lines 6686 and 6540 are visible , 6540 being the stronger in acetoacetic ester .
and 6686 in acetonitrile .
On tl.eating the acetonitrile with dry hydrochloric acid gas both these lines disappeared , and a new set of very lines appeared .
These again disappear when the solution is heated to about C. , 6686 and 6540 appearing again .
The most remarkable spectrum observed was that in acetophenone with hydrochloric acid , the spectrum consisting of one very strong absorption line at 6561 with faint traces of other lines and bands .
The phenomena are altogether so complicated that it seems impossible to 146 Changes in Absorption in Different Solvents .
explain them satisfactorily in the present state of our knowledge .
It is , however , significant that no differences could be found in the lines measured in acetone and propione , although in this case there is a considerable change in refractive index .
The completely different spectra which have been found in different solvents also point to the fact that we must look to an explanation of the phenomena rather on the basis of chemical compounds than to a change in the optical properties of the solvent .
In the raph , which was taken with a small concave grating replica , are shown the absorption spectra of uranous chloride\mdash ; 1 .
In acetone with hydrochJoric acid gas ; 2 .
In acetophenone with hydrochloric acid gas ; 3 .
In acetonitrile with hydrochloric acid gas ; 4 .
In ethyl alcohol ; 5 .
In acetone .
In view of the hypothesis recently put forward by Prof. Richards on the compressibility of the atom , a number of experiments were performed with a view to discovering whether a change in the absorption spectra could be brought about by pressure .
The apparatus used consisted of a steel vessel provided with thick conical glass windows through which the spectra were observed , and was connected to a Bourdon pressure gauge , on which the pressures could be read to an accuracy of about 1 per cent. The pressure was by means of a plunger with cup washer which was operated by a screw .
The solutions to be examined were contained in a glass tube , the rest of the apparatus being filled with heavy paraffin oil .
Aqueous solutions of uranous chloride , uranyl chloride , uranyl nitrate , didymium nitrate , potassium permanganate and potassium chromoxalate were examined under pressures varying from atmospheric pressure to 750 atmospheres square inch ) .
No changes in the wavelengths of the maxima or in the clJaracter of the spectra were observed .
In the sharpest absorption spectrum observed , that of didymium nitrate , it may be stated that no change of wave-length as great as 2 .
occurs with a change of pressure of 750 atmospheres .
No conclusions have been arrived at with regard to a change of extinction coefficient with pressure , it being impossible to make spectrophotomotric observations with the apparatus used .
Summary .
1 .
The absorption spectra of uranous chloride in a number of organic solvents have been measured quantitatively , the results indicating that the On the Extinction of Light by an llluminated Retina .
147 differences cannot be considered as a shift of the bands , since the entire character and intensity of the absorption varies in different 2 .
The apparent gradual shifts observed when one acid radicle is replaced by another can be simply explained by the superposition of absorption curves , and evidence has been found in support of this explanation .
3 .
A marked change in the character of the absorption has been found in the presence of free acid , more especially in solvents containing a ketone group .
The addition of another solvent to these solutions causes a slow disappearance of the lines without shift , in accordance with the results of Jones and Strong .
4 .
The influence of pressures up to 750 atmospheres on the absorption spectra of solutions has been investigated , with negative results .
In conclusion , I should like to thank Prof. Herbert Jackson , of King 's College , London , for his kind advice and gestions in regard to the work , and to acknowledge the help given me by Dr. Jacques Biss in this ation .
On the Extinction of Light by By Sir WILLIAM , K.C.B. , F.B.S. ( Received May 4 , \mdash ; Read May 23 , 1912 .
) In " " Colour Photometry , Part III 'Phil .
Trans 1892 , and ' On the Sensitiveness of the Retina to Light and Colour 'Phil .
Trans 1897 , discussion on the extinction of light by a ' dark-adapted\ldquo ; eye is given .
Since the latter date , a large number of experiments have been made by myself and others on the extinction of light when the retina as a whole has been stimulated by illumination of white or coloured light .
In this communication the results obtained when the stimulation is by white light are described .
In the two papers above referred to the apparatus used when the eye was dark-adapted is described , but for the observations made an illuminated retina a modification had to be made .
A description of one form , which vered as well as any other form , is given .
BB is a box as in fig. 1 .
At the end of the box is cut a hole 34 inch in diameter and against it , but inside , is placed a 4-inch disc of white matt paper , in the centre of which is cut a -inch circular hole .
Behind the box is
|
rspa_1912_0066 | 0950-1207 | On the extinction of light by an illuminated retina. | 147 | 151 | 1,912 | 87 | Proceedings of the Royal Society of London. Series A, Containing Papers of a Mathematical and Physical Character | Sir William Abney, K. C. B., F. R. S. | article | 6.0.4 | http://dx.doi.org/10.1098/rspa.1912.0066 | en | rspa | 1,910 | 1,900 | 1,900 | 5 | 79 | 1,799 | http://corpora.clarin-d.uni-saarland.de/surprisal/6.0.3/?id=rspa_1912_0066 | 10.1098/rspa.1912.0066 | null | null | null | Optics | 76.788214 | Atomic Physics | 9.396263 | Optics | [
12.884787559509277,
-14.85895824432373
] | On the Extinction of Light hy an Illuminated .
147 differences cannot be considered as a shift of the bands , since the entire character and intensity of the absorption varies in different solvents .
2 .
The apparent gradual shifts observed when one acid radicle is replaced by another can be simply explained by the superposition of absorption curves , and evidence has been found in support of this explanation .
3 .
A marked change in the character of the absorption has been found in the presence of free acid , more especially in solvents containing a ketone group .
The addition of another solvent to these solutions causes a slow disappearance of the lines without shift , in accordance with the results of Jones and Strong .
4 .
The influence of pressures up to 750 atmospheres on the absorption spectra of solutions has been investigated , with negative results .
In conclusion , I should like to thank Prof. Herbert Jackson , of King 's College , London , for his kind advice and suggestions in regard to the work , and to acknowledge the help given me by Dr. Jacques Biss in this investigation .
On the Extinction of Light hy an Illuminated Retina .
By Sir William Abney , K.C.B. , F.R.S. ( Received May 4 , \#151 ; Read May 23 , 1912 .
) In " Colour Photometry , Part III , " 'Phil .
Trans./ 1892 , and " On the Sensitiveness of the Retina to Light and Colour , " ' Phil. Trans. , ' 1897 , a discussion on the extinction of light by a " dark-adapted " eye is given .
Since the latter date , a large number of experiments have been made by myself and others on the extinction of light when the retina as a whole has been stimulated by illumination of white or coloured light .
In this communication the results obtained when the stimulation is by white light are described .
In the two papers above referred to the apparatus used when the eye was dark-adapted is described , but for the observations made with an illuminated retina a modification had to be made .
A description of one form , which answered as well as any other form , is given .
BB is a box as in fig. 1 .
At the end of the box is cut a hole f inch in diameter and against it , but inside , is placed a 4-inch disc of white matt paper , in the centre of which is cut a ^-inch circular hole .
Behind the box is Sir W. Abney .
On the [ May 4 , a second end AA separated from the first by a couple of inches .
Opposite the aperture at the first end of the box is cut a circular aperture 1 inch in diameter , against which is placed a piece of doubly-ground white glass , and if necessary a second piece can be placed behind it .
The ray of the spectrum from the colour-patch apparatus can be reflected from a mirror M on to the ground glasses at d. The 4-inch white disc is illuminated by the white reflected beam of the same apparatus ( or by any other light ) through an Fig. 2 .
aperture CC cut in the side of the box .
This beam partly goes through the aperture at the end of the box and falls on G , a blackened surface , and is completely hidden from the eye end E. At the side of CC a small metal disc can be placed , which casts a sharp black image on the white disc , as shown in fig. 2 .
This may be taken as a measure of the blackness to be matched when extinguishing the light from the colour .
Annuluses ( as described in the second paper ) are employed , one to diminish the white light to any required extent , and another to extinguish the light from the colour .
This last is placed against the slit which is in the spectrum.* The box is furnished with a dark hood so that the only light which reaches the eye is from the end of the box .
The shadow cast by the disc is always the same blackness , though the illumination of the retina causes it to appear to vary .
It is not intended to give descriptions of any observations , except those which were made of the disappearance of the light coming through d , and its match with the black shadow , which is the extreme blackness which could be seen .
In one case , the luminosity of the white disc was 0*2 candle after Colour Fig. 1 .
* It will be noticed that by covering up CC the value of the extinction of a dark-adapted eye can be carried out .
1912 .
] Extinction of Light by an Illuminated Retina .
passing through the annulus at 20 ' of its scale .
Each succeeding 25 ' gave exactly half the illumination .
Measures were taken with the white light passing through the annulus at 20 ' , 70 ' , 120 ' , 170 ' , and 220 ' .
The extinction of the light was made by another annulus in which each degree corresponded to 0-0086 diminution in logs .
The illuminations of the disc are for\#151 ; 20 ' ... ... . .
0"2 candle .
70 ... ... . .
005 " 120 ... ... . .
0-0125 " 170 ... ... . .
0-00312 " 220 ... ... ... 0-00078 " The following table and diagram show the results of the observations:\#151 ; Table I.\#151 ; Showing Comparative Extinction of the Sensation of Light when the Retina is stimulated with different Degrees of White Light .
S.S.N. X. 220 ' .
170 ' .
120 ' .
70 ' .
20 ' .
Log. Inten- sity .
Log. Inten- sity .
Log. Inten- sity .
Log. Inten- sity .
Log. Inten- sity .
1 60 j 6728 2-79 624 2-90 800 3 1000 3-05 1120 3-18 1,620 58 6520 2-25 178 2-36 230 2-49 310 2-71 513 2*88 760 56 6333 ' 1-98 93 2-02 105 2-26 182 2-45 282 2-67 468 54 6152 1-68 48 1'85 71 2-11 129 2-36 230 2-54 347 52 5996 1 -46 29 1 -72 53 2 100 2-32 209 2-49 309 50 5850 1 -26 18 1-63 43 1 -94 87 2-28 190 2-49 309 48 5720 1-16 14 -5 1-55 35 5 1-89 78 2-24 174 2-54 347 46 5596 1 -07 35 -5 1-46 28 '8 1 -85 71 2-28 190 2-67 468 44 5481 1 -03 10 -7 1 -44 27-6 1 -85 71 2-32 209 2-82 660 42 5373 0-99 9 -8 1-46 28 -8 1 -94 87 2-42 263 2 -92 835 40 6270 0-99 9-8 1-51 32 *5 2 02 105 2-58 380 3-08 1,200 38 5172 1 -03 10 -7 1-59 39 2 11 129 2-71 513 3-18 1,520 36 5085 1-12 13 -2 1-68 48 2-21 162 2 81 640 3 -31 2,040 34 5002 1 -23 17 1 -80 63 2-36 230 2-92 835 3-44 2,750 32 4924 1 -38 24 1 -89 78 2-47 295 3-06 1150 3*59 3,900 30 4848 1 -46 29 2-02 105 2*58 380 3-18 1520 3-74 5,500 28 4776 1 -55 35 -5 2-11 129 2-69 460 3-30 2000 3-89 7,800 I 26 4707 1 -63 43 2-21 162 2-79 620 3-35 2460 4 10,000 !
24 4639 1-72 53 2-31 304 2 -88 760 3-48 3020 4-08 12,000 The intensities of the light in this table have to be multiplied by 7*7 to compare it with the extinction shown in Table III , " Colour Photometry , Part 111 .
" Sir W. Abney .
On [ May 4 , Fig. 3 .
It will be noticed that at S.S.N. 60 the red ray , when the illumination of the retina is 0*2 candle , is extinguished with an intensity 2*6 times greater than when the illumination is 0*00078 candle , and that the ratio of the maximum extinctions is for this illumination as 9*8 to 309 or as 1 to 32 .
The observation recorded in the same paper as to the recurrence of red in the determination of the extinction of colour is explained by these observations .
The white illuminates the retina more or less strongly and the red colour becomes visible .
The aperture of the pupil of the eye has not been taken into account .
An interesting and important fact is brought out by these experiments .
They show that , as the white illumination which stimulates the retina is increased , the point of maximum extinction travels between S.S.N. 's 40 and 52 .
With a very strongly stimulated retina and redder light , the point of maximum extinction may be even nearer the red than the latter number .
To illustrate this , the persistency curves ( reciprocals of the extinction curves ) have been calculated , the maximum in each case being made 100 .
The positions of these maxima give the positions of the maximum extinction .
The following table and diagram ( fig. 4 ) show the curves in which the illumination is 0 00078 , 0*0125 , and 0*2 candle , and also the persistency curve for a dark-adapted eye :\#151 ; 1912 .
] Extinction of Light by an Illuminated Retina .
Table II.__Persistency Curves of Extinction of Light on a Eetina differently stimulated by White Light .
S.S.N. Candles .
Dark-adapted .
0 -00078 .
0-0125 .
0-2 .
60 1 -6 6 -9 24 0-18 58 5 -3 13 -6 40 0-58 56 10 33 64 -6 1 -51 54 20 50 87 -1 4-17 52 33 1 66 98 9 -33 50 52 -5 80 9S 20 -4 48 66 -1 89 S7 39 -5 46 813 98 64 65 44 89-1 98 45 -7 92 42 100 83 -2 36 -3 99 40 100 66 25 -1 100 38 89-1 54 20 97 36 72 -6 41 -7 13 -1 87 34 56 2 30 -2 11 -1 74 32 40 23 -5 7-8 55 30 33 18 -2 5-5 39 -8 28 27 14 -2 3-9 26 26 22 -4 11 -2 3 17 24 1 18-2 9-1 2-5 11 -8 Fig. 4 .
The effect of stimulating the retina with lights of different colours will be treated of in another communication .
VOL. lxxxvii.\#151 ; a. M
|
rspa_1912_0067 | 0950-1207 | Physico-chemical determinations at high pressures by optical methods. | 152 | 153 | 1,912 | 87 | Proceedings of the Royal Society of London. Series A, Containing Papers of a Mathematical and Physical Character | Walter Wahl, Ph. D.|Sir James Dewar, F. R. S. | abstract | 6.0.4 | http://dx.doi.org/10.1098/rspa.1912.0067 | en | rspa | 1,910 | 1,900 | 1,900 | 1 | 34 | 874 | http://corpora.clarin-d.uni-saarland.de/surprisal/6.0.3/?id=rspa_1912_0067 | 10.1098/rspa.1912.0067 | null | null | null | Thermodynamics | 71.893429 | Optics | 9.561241 | Thermodynamics | [
-9.249534606933594,
-37.06420135498047
] | 152 Physico-Chemical Determinations at High Pressures by Optical Methods .
By Walter Wahl , Ph. D. ( Communicated by Sir James Dewar , F.R.S. Received April 20 , \#151 ; Read May 23 , 1912 .
) ( Abstract .
) Apparatus for Optical Measurements at High Pressures .
The apparatus consists of three chief units:\#151 ; ( 1 ) Plant for the production and measurement of pressures up to 4000 kgrm./ cm ? .
( 2 ) A " pressure-bomb " to hold the substances under investigation .
( 3 ) An optical bench for observations in polarised light , and for measurements of the change of refractive index , dispersion , rotatory power , absorption , double-refraction and optical-axial-angle , by pressure .
The " pressure-bomb " is fitted with two " windows " of boro-silicate glass ( Jena ) ; these have the shape of truncated cones , are 20 mm. thick , rest with the base upon a flat ring-shaped washer of vulcanised fibre , and are surrounded by a conical mantle of ebonite , the washers and ebonite mantles thus preventing an immediate contact of the glass and steel surfaces .
The chief object of using these washers and conical packings may be described as being that of keeping the glass constantly surrounded by a half-plastic mass , which flows slightly , and thus transmits the pressure to the glass body as evenly as possible .
The pressure-bomb has been tested under high pressures , both at liquid air temperatures and at temperatures up to 150 ' .
At ordinary temperatures the glass windows have , under favourable circumstances , withstood pressures of over 4000 kgrm./ cm.2 without being injured in any way. .
Optical Determinations of Diagrams of State .
Melting-points and transition-points between different crystalline modifications may be determined either at constant pressure by altering the temperature , or at constant temperature by altering the pressure .
Crystallisation and melting at constant temperature , " isothermal crystallisation " and " isothermal melting , " are of special interest , as it is possible not only to study the crystallisation , melting , and supercooling phenomena more in detail than under ordinary conditions when the transition is effected by temperature change , but it is also possible to study the phenomena connected with superheating of the crystalline phase .
Physico-Chemical Determinations by Optical Methods .
153 The Diagram of State of Carbon Tetrabromicle , CBr4 .
The melting-point of CBr4 is raised 1 ' by a pressure of only 16 kgrm./ cm.2 The transition-point from monoclinic to regular crystal-form is raised 1 ' by 32 kgrm./ cm.2 .
The melting-point curve and the transformation-point curve do not , therefore , intersect at high pressures to form a triple-point .
In consequence , the anisotropic monoclinic form of carbon tetrabromide cannot be caused to melt at any temperature or pressure whatever .
The Diagram of State of , u-fi-Dibrompropionic Acid , CH2Br .
CHBr .
COOH .
Beside the stable modification of the acid , melting at 64 ' , an unstable modification exists , melting at 51 ' .
Both forms crystallise in the monoclinic system .
As the unstable modification is not spontaneously transformed into the stable one so readily as in most other cases of " monotropy , " and only very small quantities are employed for an optical investigation , it has for the first time been possible in this case to determine the melting-point-curve of an unstable modification also .
The velocity of crystallisation , and also of melting , of both modifications is small , and it has therefore been possible to determine the limits within which not only supercooling , but also superheating , can be effected at different pressures .
During isothermal melting of the unstable modification , the pressure may be reduced as much as about 150 kgrm./ cm.2 below the true melting-point pressure before melting takes place with almost instantaneous velocity .
This pressure , 150 kgrm./ cm.2 below the melting-point pressure , corresponds to a superheating of nearly 3 ' .
The melting-point of the stable modification is raised 1 ' by a pressure of 51-28 kgrm./ cm.2 , and that of the unstable modification 1 ' by a pressure of 53-48 kgrm./ cm.2 .
The melting-point curves run further apart as the pressure increases , and the modification unstable at ordinary pressures thus remains unstable at all pressures .
The two melting-point curves , of which the upper one has been traced over a pressure range of 1060 kgrm./ cm.2 , and the lower one over a pressure range of 1330 kgrm./ cm.2 , are perfectly straight lines .
If we continue these melting-point lines towards negative pressure , we find that they intersect at a point corresponding to a temperature of between \#151 ; 270 ' and \#151 ; 280 ' , that is , at the absolute zero .
At any pressure , the difference between the absolute melting-points of the two modifications is therefore similar to the difference of the absolute melting-points at ordinary pressure .
This work has been executed at the Davy-Faraday Laboratory of the Royal Institution during the past year .
|
rspa_1912_0068 | 0950-1207 | Portland experiments on the flow of oil in tubes. | 154 | 163 | 1,912 | 87 | Proceedings of the Royal Society of London. Series A, Containing Papers of a Mathematical and Physical Character | S. D. Carothers, A. R. C. Sc. I.|Prof. W. McF. Orr, F. R. S. | experiment | 6.0.4 | http://dx.doi.org/10.1098/rspa.1912.0068 | en | rspa | 1,910 | 1,900 | 1,900 | 12 | 130 | 3,463 | http://corpora.clarin-d.uni-saarland.de/surprisal/6.0.3/?id=rspa_1912_0068 | 10.1098/rspa.1912.0068 | null | null | null | Tables | 29.334412 | Measurement | 25.08273 | Tables | [
41.36495590209961,
-28.975933074951172
] | ]\gt ; Portland Experiments on the Flow of Oil in Tubes .
By S. D. CAROTHERS , A.B.C.Sc .
I. ( Communicated by Prof. W. .
Orr , F.R.S. Received May 9 , \mdash ; In revised form June 7 , \mdash ; Read June 13 , 1912 .
) Experiments on Water .
It is a well-known experimental fact that , in the case of water flowing in a straight circular pipe of uniform bore , the resistance per unit length is exactly to the mean velocity if this is below a certain limit , which depends on the radius .
It is also well known experimentally that if the mean velocity exceeds a certain limit , the resistance is approximately proportional to a higher power of the velocity .
The index of this power in the case of water has been found to lie between and 2 .
This is usually expressed by stating that the resistance is nearly proportional to the square of the velocity .
It will be convenient to refer to these cases as flow according to the first and according to the second law respectively .
When the first law obtains , the motion is in straight lines ; but when the llow is subject to the second law , the motion is turbulent .
Experiment in the case of water also shows that , between the upper limit of velocity for the first law ] the lower limit for the second law , there is a " " gap\ldquo ; where neither law obtains .
When the velocity corresponds to that in any part of the gap , the motion may be at one time steady and at another time turbulent .
The mean velocity corresponding to that of the lower limit of the gap is called the lower critical velocity .
In the case of water flowing in straight circular pipes of uniform bore , the relation between the velocity and resistance at a particular place can be represented as follows:\mdash ; For the first law , ( 1 ) For the second law ( 2 ) ' where and are constants and is proportional to With regard to fluids flowing in pipes , a matter of vital importance has been the determination of a criterion as to whether the first or second law should hold in a particular case .
The principal experimenters in this connection have been Prof. Osborne Beynolds , M. Covett , and .
Mallock .
Portland Experiments on the Flow of Oil in Tubes .
The general result obtained by Prof. Beynolds was that the critical velocity varies directly as the kinematic viscosity and inversely as the radius of the pipe .
The chief theoretical workers in the same field have been Lord Rayleigh , Lord Kelvin , Prof. Osborne Reynolds , and Prof. Orr .
* The analysis , even for the simplest case , is extremely difficult , but the general result above mentioned , as found by experiment , is confirmed .
The last-named writer has treated the whole question of the stability of flow of both viscous and non-viscous fluids in great detail , and has taken into account much that was formerly overlooked by other writers .
He has obtained " " criteria of stability\ldquo ; for various cases of flow ; for a circular pipe his result is .
( 3 ) The sense in which his " " criterion of stability\ldquo ; is to be interpreted will perhaps be best understood from the following quotation : " " It is claimed that in each case the numbers I have found are true least values ( but with some reservation as to the effect of conditions ) ; that below them every disturbance must automatically decrease , and that above them it is possible to prescribe a disturbance which will increase for a time .
numbers obtained .
give velocities very much below those at which observers have found motions actually to become unstable ; this is to be expected In connection with the latter clause it is interesting to compare the various results obtained to date ; these are as follows:\mdash ; Beynolds obtained experimentally the value . .
1900 Covett , , , , , , 2150 Sharp , , theoretically , , 470 Sharp 's value , 470 , if corrected for an alleged numerical error , as is done by Prof. Orr , is reduced to 363 Orr obtained theoretically 180 These experimental results were obtained with water , which , as is well known , has a very low viscosity .
No experiments on any fluid of high viscosity flowing in pipes have so far been published , and the experiments about to be described , carried out with Texas oil , would seem to some extent to supply this omission .
It should at once be stated that these experiments , while going far , in the writer 's view , 'Roy .
Irish Acad. Proc 1907 , vol. 27 , sect. , Nos. 2 and 3 .
No references are given to other.writers , these are very fully dealt with in Prof. Orr 's papers here quoted .
Mr. S. D. Carothers .
[ June 7 , towards the existence of a criterion in the neighbourhood of that found by Prof. Orr , were undertaken for a different purpose .
They were carried out at tland , under the entire charge of Mr. G. P. Hayes , B.A. , B.E. , M.Inst .
C.E. , and Engineer J. B. Huddy , .
( now deceased ) .
Five different sizes of pipes were used , respectively , 2 , , 6 , and 10 inches in diameter .
The 2-inch and -inch pipes were of iron , alvanised internally .
The -inch and 6-inch pipes were of cast iron .
The 10-inch pipes were formed of lap-welded steel tubes , jointed ether with American taper threads and collars .
The ends of the 10-inch tubes did not in this instance come close together , but were separated by an average space of 6 inches , the collar itself forming the tube for this space .
The internal diameter of the collar was inches , and the average distance from collar to collar was about 15 feet .
The joints in the case of the cast-iron pipes were formed of lead and the ends of the tubes touched in the ordinary manner .
The joints in the case of the galvanised pipes were formed with screwed ends and sockets , but were not specially prepared with a view to give perfectly flush joints internally .
The actual diameters of the pipes used were measured near the ends in a number of places with ordinary callipers and the mean result taken .
no case could the error in measuring the meters be greater than 1 per cent. in the case of the smaller pipes , or more of 1 per cent. in the case of the 10-inch pipes .
Except in the experiments with the 10-inch pipes , three tanks were used ; these were : A storage tank of about 2000 llons capacity , containing a coil of pipes for passing steam , connected to a crane boiler close at hand .
This tank was provided with an outlet having a regulating valve attached .
The second tank was comparatively shallow and in the form of a tray , and was placed under the outlet from the storage tank .
The third tank of 600 gallons capacity was carefully calibrated at intervals , each of which corresponded to 50 capacity .
The inlet end of the pipe experimented on , projected into the side of the second tank and its outlet end was placed directly over the third tank .
The outlet of this pipe was supplied with a short bend turned in the upward direction , and in no case this end of the pipe submerged .
The oil experimented on was placed in the storage tank and raised to the requisite temperature by means of steam passed through the coil placed within the tank .
The temperature of the oil in the tank was kept constant and uniform by regulating the supply of steam , and also by continuous stirring of the oil .
An attendant who had charge of the valve attached to the storage tank regulated the supply so as to keep the oil at all times up to a 1912 .
] Porttand Experimaents on the Flow of Oil in Tubes .
mark on the sides of the tray and thus insure a constant head over the intake end of the pipe .
The temperature of the oil was measured both at the intake and at the outlet of the piPe by means of ordinary service thermometers and in each case the readings were compared with those of a standard instrument in which the errors were known .
In the case of the experiments with the 10-inch pipe the oil was merely allowed to flow by gravitation from the large storage tanks on the hillside to tank steamers in the harbour .
The oil was not heated , but the temperature of the oil was taken in the storage tanks and also in the tank steamers .
In all cases the head was measured by the difference of level between the surface of the oil in the tray and the centre of the pipe at the outlet .
This was done with a 14-inch dumpy level and the maximum error in any case except that of the 10-inch pipes probably did not exceed foot .
In the case of the 10-inch the error in the measurement of the head after making ample allowances was almost certainly less than 1 foot .
The tanks and pipes were arranged as shown on the accompanying .
FIG. 1 .
The oil experimented on was from Texas ; its specific gravity was at F. The variation of density with temperature was not noted in this instance as it had been found to be slight , but for purposes of calculation the density has been taken as given by the mean formula:\mdash ; .
( 4 ) The viscosity of the oil was measured with a Bedwood 's viscometer at intervals of F. , for all temperatures between and In the case of the oil on which the Portland experiments were performed the times for the flow of a given volume were plotted as ordinates and the temperatures as abscissae and a mean curve was drawn .
The observations were then trimmed so as to make them conform as nearly as possible with the mean curve .
The logarithms of the trimmed values were then plotted in the same way , and it was found that these almost fell on a straight line .
Mr. S. D. Carothers .
[ June 7 , Redwood 's viscosity at any temperature was found to be given by the formula .
( 5 ) It appears from Poiseuille 's experiments that in the case of water varies as ( 6 ) Also from the experiments of Helmholtz and Piotrowski , at .
( 7 ) Criterion of If we wish to obtain a criterion as to whether the first or second law should hold in a particular case and be applicable to a fluid for which Redwood 's viscosity is known , we have the equations ( 1 ) .
From these , if it is remembered that has been calculated on the assumption that is expressed in inches , there is easily obtained the relation ( 8 ) The mean value of , as found from Experiments 7 to 19 inclusive ( omitting Experiment 16 , which applies to a solitary length of pipe and gives a somewhat discrepant result ) , is There is thus obtained .
( 9 ) Taking now Prof. 's criterion of stability , 180 where is expressed in feet , , , , , inches , there is obtained from equation ( 9 ) the criterion ( say ) .
( 10 ) In order to see how far this is confirmed by the present experiments , each set of tests has been arranged according to and diameters of pipes and plotted in a separate diagram , the values of being plotted as ordinates and those of as abscissa .
The plottings are shown in figs. 3 , 4 , and 5 .
Consideration of equations ( 1 ) shows that so long as they hold and are applied to a single diameter of pipe the results should plot in a straight line inclined at to the axes , any decided declension of the line from indicating a failure of the capillary law .
Again .
consideration of equation ( 2 ) shows that unless is unity the 'Phil .
Trans 1883 , p. 943 . ?
12 .
] Experiments on the Flow of Oil Tubes .
points as plotted in the above scheme need not necessarily fall on a tJht line beyond the point where equations ( 1 ) break down .
When , however , is unity the points should .
still fall on a straight line inclined at the angle to the axis .
The point of intersection of the two branches , where such exist , has been taken as corresponding to a practical critical value .
FIG. 2 .
It will be noticed that there are eight diagrams and in the first of these ( fig. 2 ) the results of the whole of the experiments for all the pipes are plotted to the co-ordinates and ; this diagram has been constructed entirely at the suggestion of Prof. Orr .
On referring to the other diagrams ( figs. 3 , 4 , and 5 ) it will be seen at once that the only cases throughout the whole of the experiments in which Mr. S. D. Carothers .
[ June 7 , two distinct branches occur are in two sets of experiments on the 6-inch pipe , plotted on fig. 5 , viz. , Experiments 52 to 61 and Experiments 65 to 71 .
FIG. inch galvanised pipe .
-inch pipe .
-inch pipe .
FIG. 4 .
10-inch pipe .
1912 .
] Portland Experiments on the Flow of Oil in Tubes .
FIG. 5.\mdash ; 6-inch pipe .
two sets of experiments have been separately plotted for the reason that any errors in the measurement of the head .
flow , or errors in the diameters of the pipes caused in manufacture , or due to imperfect jointing , or errors due to bends , etc. , must of necessity be constant throughout each set , while these errors may differ to an appreciable extent as compal.ed between one set and the other .
The value of at the point of intersection of the two branches can be calculated from the identity DL ' ( 11 ) ' that and are known constants and is very nearly constant and can be obtained with considerable accuracy at the point of intersection from the value of as scaled at that point .
In the case of the two sets of expe ) .iments referred to the values corresponding to critical velocity are as follows:\mdash ; Experiments .
Value of H. Value of 52 to 61 65 to ?
1 Mean .
( 12 ) The values as found by experiment are thus almost identical with that obtained by Prof. Orr on theoretical rounds ; the diff'erence in the case of the higher experimental result is well within the limits of experimental errors or indeed errors in All the experiments in which is equal to or greater than have been selected , and an attempt has been made to obtain values for , and in equation to fit these experiments .
This has been attended with only partial success .
The values which best conform to the whole of those experiments appear to , and Experiments on the Flow of Oil in Tubes .
How far these values succeed may to a slight extent be gauged by the uniformity of the values of obtained .
These were as follows:\mdash ; 2-inch galvanised pipe . .
cast-iron pipe , , -inch galvanised pipe , , 6-inch cast-iron pipe , , 10-inch steel tubes , , It should , however , be remarked that the values of differ from one another in any one set of experiments to a much greater extent than is here shown , and thus the derived formula ' applicable to velocities within the range of the experiments above the critical point , would not appear to be at all well established .
It can only be iooked on as perhaps the best mean result .
Indeed other relations can be found which fit the greater portion of the experiments very fairly .
With regard to equations ( 2 ) and ( 13 ) , the reader may recollect that Prof. Osborne eynolds put forward on theoretical grounds an equation of the type , ( 14 ) which includes the particular case of ( 2 ) , in which , and considered that his experimental results for velocities higher than the critical are satisfactorily represented by this particular case if has the value Prof. Orr has indicated to the writer , however , that the theory on which ( 14 ) is based supposes that the motions in pipes of different diameters are dynamically similar ; this implies that the eddy-systems are similar and on linear scales proportional to the diameters ; it seems at least open to question whether this assumption is correct .
Prof. Orr has also indicated to the writer tha he inclines to the view that his so-called " " criterion of stability\ldquo ; obtained by the method which Reynolds was the first to employ does not by any means indicate a sharp dividing line between stability and instability , and that when the velocity exceeds or even approaches that given by the criterion , it is not unlikely that it depends on circumstances which may be described as accidental whether the motion is stable or unstable , as also what the value of the resistance may be .
He has also pointed out that the critical velocity below which every small disturbance automatically decays ( which is the velocity given by his criterion ) and the critical velocity ( if there be one ) beyond which the first law of resistance fails have not the same meaning and may well have different values in actual fact .
In conclusion , it should be stated that the results of these experiments are published by the courtesy of Colonel Edward Raban , K.C.B. , R.E. , Director of of the Navy .
Borohydrates.\mdash ; Part I. By MORRIS W. TRAVERS , D.Sc .
, F.R.S. , Director , Indian Institute of Science , Bangalore , and RAMES CHANDRA , M.Sc .
( Received May 20 , \mdash ; Read June 27 , 1912 .
) Introduction .
In 1881 Jones and Taylor*demonstrated the existence of a compound of boron and hydrogen , and 20 years later Ramsay and published a preliminary account of a research on the hydrides of boron , describing experiments which , even if they cannot be regarded as conclusive , opened up a field of investigation well worthy of attention .
They found that on passing the gas evolved by the action of dilute acids on magnesium boride through a bulb cooled in liquid air , a solid substance was iited which , on the bulb , volatilised and could be collected as a gas .
From the results of the analysis of the gas , and its density , its formula appeared to be ; but it appeared to consist of two isomeric substances , one stable , and the other unstable and readily decomposed by reagents .
The gas which was not condensed by liquid air appeared to consist mainly of , but to contain a hydride or hydrides of boron .
Assuming the trivalency of boron , it is possible , as Ramsay and Hatfield point out , that a very large number of ' hydroborons\ldquo ; may exist .
The simpler of these may be represented by the formulae:\mdash ; , ( ) ( b ) ( f ) BH ( ) BH\mdash ; BH .
( ) 'Chem .
Soc. Trans , p. 213 .
' Chem. Soc. Proc vol. 17 , p. 152 .
|
rspa_1912_0069 | 0950-1207 | Borohydrates.\#x2014;Part I. | 163 | 179 | 1,912 | 87 | Proceedings of the Royal Society of London. Series A, Containing Papers of a Mathematical and Physical Character | Morris W. Travers, D. Sc., F. R. S.|Rames Chandra Ray, M. Sc. | article | 6.0.4 | http://dx.doi.org/10.1098/rspa.1912.0069 | en | rspa | 1,910 | 1,900 | 1,900 | 14 | 311 | 8,024 | http://corpora.clarin-d.uni-saarland.de/surprisal/6.0.3/?id=rspa_1912_0069 | 10.1098/rspa.1912.0069 | null | null | null | Chemistry 2 | 64.120396 | Thermodynamics | 23.416489 | Chemistry | [
-7.936933994293213,
-45.957427978515625
] | Borohydrates .
criterion ) and the critical velocity ( if there be one ) beyond which the first law of resistance fails have not the same meaning and may well have different values in actual fact .
In conclusion , it should be stated that the results of these experiments are published by the courtesy of Colonel Sir Edward Eaban , K.C.B. , E.E. , Director of Works of the Navy .
By Morris W. Travers , D.Sc .
, F.E.S. , Director , Indian Institute of Science , In 1881 Jones and Taylor* demonstrated the existence of a compound of boron and hydrogen , and 20 years later Eamsay and Hatfieldf published a preliminary account of a research on the hydrides of boron , describing experiments which , even if they cannot be regarded as conclusive , opened up a field of investigation well worthy of attention .
They found that on passing the gas evolved by the action of dilute acids on magnesium boride through a bulb cooled in liquid air , a solid substance was deposited which , on warming the bulb , volatilised and could be collected as a gas .
From the results of the analysis of the gas , and its density , its formula appeared to be B3H3 ; but it appeared to consist of two isomeric substances , one stable , and the other unstable and readily decomposed by reagents .
The gas which was not condensed by liquid air appeared to consist mainly of hydrogen , but to contain a hydride or hydrides of boron .
Assuming the trivalency of boron , it is possible , as Eamsay and Hatfield point out , that a very large number of " hydroborons " may exist .
The simpler of these may be represented by the formulae:\#151 ; Borohydrates.\#151 ; Part I. Bangalore , and Eames Chandra Eay , M.Sc .
( Received May 20 , \#151 ; Eead June 27 , 1912 .
) Introduction .
( a ) BH3 , ( b ) BHa\#151 ; BH2 ( c ) BH=BH , ( d ) BHa\#151 ; BH\#151 ; BH2 BH\#151 ; BH .
* ' Chem. Soc. Trans. , ' vol. 39 , p. 213 .
+ ' Chem. Soc. Proc. , ' vol. 17 , p. 152 .
Dr. M. W. Travers and Mr. R C. Ray .
[ May 20 , They suggest that formulae e and / represent the " hydroborons " which are non-volatile at the temperature of liquid air , and that the volatile hydroboron is probably represented by formula a. The results of certain other experiments have been taken as evidence of the existence of solid hydroborons , but from the result of our own experiments it appears that the substances taking part in the reactions referred to may be more properly classed as " borohydrates , " as from our own investigation they appear to contain boron , hydrogen , and oxygen .
The experiments are of a purely qualitative character .
Reinitzer* investigated the yellow solution obtained by washing the product of the action of heat upon mixtures of potassium and boric acid with water .
The solution was concentrated and a solution of calcium chloride was added , when a greenish brown , slimy precipitate separated .
This , when dried in a desiccator over sulphuric acid , was found to contain 2-67 per cent , of hydrogen , and when heated in a tube it glowed , giving off a gas which burned with a green flame .
Ramsay and Hatfieldf observed that the residue obtained by treating magnesium boride with acid , when washed and dried , gave off torrents of hydrogen on heating .
It would serve no useful purpose to write the formulae for the various hydroxy derivatives , the borohydrates , which might be produced by replacing hydrogen by hydroxyl or oxygen in the hypothetical compounds of which the formulae are set down above .
Suffice it to point out that the types of groupings of atoms which can exist are not so numerous as in the case of carbon compounds , being limited to\#151 ; \#151 ; BHOH , \#151 ; B(OH)2 , \#151 ; BO , and =BOH .
If , however , hydroborons and borohydrates exist in which the boron is pentavalent , and from our experiments this appears to be possible , the problem becomes a much more complicated one , and one upon which it is unprofitable to speculate without first considering the facts .
Experimental Part .
( a ) Qualitative Experiments.\#151 ; When a mixture of two parts by weight of magnesium powder and one part by weight of anhydrous boric acid is heated to a bright red heat in an atmosphere of hydrogen , a grey mass is obtained which has .
generally been assumed to consist of a mixture of magnesium oxide with magnesium boride , BsMg3 , and free amorphous boron .
If the mass is reduced to powder and mixed with water the mixture becomes warm , gas is slowly evolved , and a solution is formed which is usually yellow in colour , and possesses certain properties which will be dealt with in this paper .
* ' Wien .
Akad .
Sitz .
, ' vol. 82 , p. 736 .
t Loc .
cit. Borohydrates .
1912 .
] Reference has already been made to the action of acid on the boride .
The acid liquid appears to behave towards many reagents in a manner similar to the solution obtained by the action of water alone , but its properties have not been fully studied .
The solution is slightly alkaline towards litmus .
On warming it deposits a slight gelatinous precipitate , and if boiled it gives off hydrogen gas .
It invariably possesses a peculiar odour , which is probably due to the presence of hydrides of boron .
On addition of dilute acids to the solution a considerable volume of gas is immediately evolved .
Though this gas possesses the characteristic odour of the liquid , and on explosion with oxygen burns with a green flame , repeated analyses have shown that it consists of hydrogen with not more than a trace of some boron compound .
Both the original solution and the solution to which acid has been added are powerful reducing agents .
The solutions absorb iodine , and precipitate the heavy metals from solutions of their salts .
A solution of silver nitrate gives an immediate black precipitate .
From a solution of mercuric chloride , mercurous chloride is first of all precipitated , and this turns grey in presence of excess of the reducing solution .
On addition of a small quantity of copper sulphate solution to the reducing solution , the latter first turns yellow , and on warming or standing precipitates what appears to be either a boride or amorphous boron as a dark browrn precipitate .
If a larger quantity of copper sulphate is used , and the solution is warmed , a red precipitate , which dissolves in a solution of potassium cyanide with evolution of gas , is thrown down .
This precipitate appears to be cuprous hydride , which can also be obtained by the action of a solution of a hypophosphite on a copper salt .
It appears to be most readily produced by the action of the copper sulphate on the acid solution of the boron derivative , the alkaline solution tending to precipitate amorphous boron .
The significance of this fact will be pointed out later .
A solution of a lead salt gives a yellowish white precipitate with the boron derivative , and this on standing or on warming turns black , forming metallic lead .
Other reactions , such as the reduction of ferrous to ferric salts , have also been studied .
Before passing on to describe the quantitative experiments which we have carried out , it will be well to point out that the yellow colour does not appear to be an intrinsic property of any compound present in the solutions , but to be due to colloidal boron .
The intensity of the colour does not appear to be in any way connected with the concentration or other property of any particular solution , and can be produced in any solution by the addition of a small quantity of a reducing agent .
If the solution is Dr. M. W. Travers and Mr. R. C. Ray .
[ May 20 , allowed to stand exposed to air the colour disappears , the solution remaining clear ; but if it is allowed to stand in vacuo it becomes colourless , and a slight brown precipitate is produced .
( b ) Preparation of Magnesium Boride.\#151 ; A mixture of one part by weight of anhydrous boric acid and two and a quarter parts by weight of magnesium powder was placed in a small graphite crucible , fitted with a lid through which passed an iron pipe connected with a hydrogen generator .
The crucible was heated in a gas injector furnace for about three quarters of an hour to a bright red heat , and was then allowed to cool down , hydrogen gas being passed into the crucible throughout the whole experiment .
When the crucible was cold it was found to contain a dark grey friable mass , which could be removed without difficulty and powdered in a porcelain mortar .
To remove excess of boric acid and to decompose traces of magnesium nitride the powdered boride was placed in a round-bottomed flask , fitted with a reflux condenser , and treated with methyl alcohol .
In the case of some samples of the boride a fairly violent reaction took place , and it was then necessary to cool the flask with water .
When , however , the reaction had subsided , the flask was heated on a water bath for some time , and then allowed to cool , and the methyl alcohol poured off and replaced by fresh methyl alcohol .
This operation was repeated several times .
It may be remarked that the methyl alcohol with which the boride had been treated possessed none of the properties of the solution obtained by treating the boride with water .
The boride was finally washed with methyl alcohol , and dried either in a desiccator or in an air bath .
( c ) Preparation of the Solution.\#151 ; When the powdered boride , prepared in the manner described in the last section , was mixed with water the mixture became warm , and the powder appeared to increase in bulk .
Gas was evolved , slowly at first , and more rapidly after the lapse of an hour or two .
In some experiments , which will be described later , the quantity of gas given off when the boride reacted with water , and the amount of the soluble boron compound produced at the same time were measured .
Altogether a large number of experiments were carried out , and , as the methods of preparation of the solutions differed considerably in points of detail , we have thought it advisable to catalogue them for future reference .
Solutions employed in the following experiment:\#151 ; iVo .
1.\#151 ; The boride was passed through a 120-mesh sieve .
The coarser portion was ground in an agate mortar , and 10 grm. of it was treated with 25 c.c. of water for 2| hours at 45 ' .
The solution was bright yellow .
It was used only for qualitative experiments .
Borohydrcttes .
1912 .
] No. 2.\#151 ; The residue from solution No. 1 was allowed to stand for 20 hours with 25 c.c. of water at about 25 ' .
The liquid was filtered off and made up to 100 c.c. It was yellow .
No. 3.\#151 ; A second preparation of the boride was ground in an agate mortar till the whole of it would pass through a 120-mesh sieve .
About 20 grm. of the powder was treated with 25 c.c. of water in vacuo for 2 hours at 25 ' .
The solution , which was yellow , was filtered off and made up to 100 c.c. No. 4.\#151 ; The residue from solution No. 3 was allowed to stand with 25 c.c. of water for 48 hours at about 25 ' .
The solution , which was deep yellow , was filtered off and made up to 100 c.c. No. 5.\#151 ; The residue from solution No. 4 was allowed to stand with about 25 c.c. of water for a further period of 70 hours at about 25 ' .
The solution was very pale yellow .
No. 6.\#151 ; The residue from solution No. 5 was treated with water for a further period of 24 hours .
The solution was colourless .
No. 7.\#151 ; That portion of the boride used in making solution No. 1 which passed through a 120-mesh sieve was treated with about 50 c.c. of water for 24 hours .
The solution was deep yellow .
No. 8.\#151 ; The residue from solution No. 7 was treated with about 10 c.c. of water for 48 .
hours at 25 ' , when the whole mass had become pasty .
Water wTas added and the solution was filtered off .
No. 9.\#151 ; A fresh quantity of boride , after treating with methyl alcohol , was washed with water and dried in a desiccator .
The product was ground in an agate mortar , and about 20 grm. of it was treated with 25 c.c. of water for 3j hours at 25 ' vacuo .
The solution was practically colourless .
No. 10.\#151 ; The solution was prepared in the same manner as solution No. 9 , except in that after washing with water the boride was dried in an air bath at 100 ' .
No. 11 , \#151 ; The residue from solution No. 10 was allowed to stand with about 25 c.c. of water for 20 hours at 25 ' .
No. 12.\#151 ; Boride prepared as for solution No. 9 was treated with water for 2 hours at 25 ' .
No. 13.\#151 ; The residue from solution No. 12 was allowed to stand with 20 c.c. of water for 42 hours at 25 ' .
Ao .
14 .
The residue from solution No. 13 was allowed to stand with water for a further period of 48 hours at 25 ' .
In this experiment and the following experiment the flask in which the preparation was carried ojut was closed by a rubber stopper , through which passed a bent glass tube , the end of which was immersed in water .
The gas generated by the action of the boride on the water expelled the air from the flask which , remained full of hydrogen .
The solution was slightly yellow .
No. 15 .
The residue from solution No. 14 was allowed to stand for a further period of 40 hours with water at 25 ' .
The solution was slightly yellow .
A'o .
16 .
About 10 grm. of the boride prepared as for solution No. 1 was treated with about 25 c.c. of water for 2\#163 ; hours at 25 ' in vacuo .
No. 17 .
That portion of a fresh preparation of the boride which passed through a 120-mesh sieve was treated with water , 30 grm. of boride to 50 c.c. of water , for 24 hours ; at 25 .
I he product , which was pasty , was mixed with water and the solution was filtered off .
The solution was pale yellow .
Ao .
18 .
The residue from the last experiment was allowed to stand with about 50 c.c. of water for a further period of 24 hours at 25 ' .
No. 19 .
The coarser portion of the boride used in making solutions Nos. 17 and 18 was ground in an agate mortar and treated with water\#151 ; 15 grm. of boride to 50 c.c. of water for 48 hours at 25 .
The solution was colourless .
VOL. LXXXVII.\#151 ; A. N Dr. M. W. Travers and Mr. R. C. Ray .
[ May 20 , ( d ) Analysis of the Solution.\#151 ; Qualitative examination of the solution obtained by treating the boride with water showed that it evolved hydrogen when treated with acids , and that both the original solution and the solution to which acid had been added absorbed iodine .
Beyond the elements of water the solution appeared to contain only boron and magnesium .
As the solution was most unstable it was necessary to carry out the various operations involved in the determination of the composition and properties of any particular sample simultaneously and as rapidly as possible .
It may here be pointed out that on account of the instability of the substances present in the solution , and of the complicated character of the changes which they appeared to undergo , no high degree of experimental accuracy was expected or looked for .
The reactions which have been studied are , however , of so marked a character as to make it difficult to misinterpret them , even when the experimental errors are obviously very large .
The following is a brief description of the experimental methods employed .
The solutions obtained by the methods described in the preceding section of the paper were diluted so that 5 or 10 c.c. of the liquid was available for each of the experiments which it was proposed to carry out .
The results are expressed in terms of the number of gramme-atoms of gas evolved , iodine absorbed , etc. , per 100 c.c. of the solution .
For the determination of the quantity of gas given off from the solution on the addition of dilute acid , a quantity of the solution was introduced by means of a pipette into a small distilling flask , which was fitted with a rubber stopper and tap-funnel , and connected with a Topler pump .
When the flask was exhausted dilute sulphuric acid was run into it through the tap-funnel , and the gas which was given off was collected through the pump and measured over mercury in a gas burette .
In many cases the gas was analysed by explosion with a measured quantity of oxygen , the excess of oxygen being afterwards absorbed by means of hot phosphorus .
In every case it was found that , though the gas burned with a green flame , the quantity of boron in it was extremely small .
The quantity of hydrogen evolved on the addition of acid to the solution , expressed in gramme-atoms per 100 c.c. of the solution , will hereafter be referred to as the " hydrogen equivalent " of the solution .
A decinormal solution of iodine in potassium iodide was used to determine the quantity of iodine absorbed by the solution .
As in the case of strong solutions of the boron compound hydrogen was evolved in small quantity on addition of the iodine , the experiment was always performed in the manner described in the last paragraph , the iodine solution being introduced from a pipette into the tap-funnel and allowed to flow thence into the flask .
Any Borohydrates .
1912 .
] gas evolved was collected and measured .
As the reaction between the iodine and either the original solution or the solution to which acid had been added did not become complete till after some hours , the liquid was washed out of the flask and tap-funnel into a stoppered bottle which was placed in a dark cupboard .
After 24 hours the excess of iodine was determined by titration with a solution of sodium thiosulphate .
The quantity of iodine absorbed by the acid solution , expressed in gramme-atoms of iodine per 100 c.c. of solution , will hereafter be referred to as the " iodine equivalent " of the solution .
For the determination of the boron 5 or 10 c.c. of the solution was placed in a tube about 15 mm. in diameter and 300 mm. in length , sealed at one end .
A small test-tube , with a thin glass rod sealed to the closed end , and containing 2 to 3 c.c. of strong nitric acid , was also placed in the tube , which was afterwards sealed and heated for a day in a water-bath , or for a shorter period to 150 ' .
In the meantime a quantity of lime , about three times as much as would be required to absorb the whole of the nitric acid and the boric acid present in the solution in the tube , was ignited to constant weight in a platinum crucible .
Water was first added to the lime in the crucible , and afterwards the contents of the tube .
The liquid was evaporated by placing the crucible in an air bath and raising the temperature slowly to 170 ' .
The crucible was then again ignited to constant weight , the increase in weight giving the weight of the boric acid and magnesium oxide derived from the solution .
In some cases it was necessary to concentrate the solution obtained by washing out the tube , and it was found that this could be effected without loss of boric acid by allowing the liquid to stand overnight in a basin in an exhausted desiccator containing solid caustic potash .
For the determination of the magnesium a measured quantity of the solution was evaporated to dryness with hydrochloric acid and a few drops of nitric acid or bromine .
The residue was then transferred to a flask , methyl alcohol and a little strong hydrochloric acid were added , and the liquid distilled off .
This operation was repeated several times ; the residue was then transferred to a beaker , and the magnesium was precipitated in the usual manner and finally weighed as magnesium pyrophosphate .
The following are the results of the experiments:\#151 ; o Table I.\#151 ; Results in gramme-atoms per 100 c.c. of solution .
No. of solution No. 3 .
No. 4 .
No. 5 .
No. 6 .
No. 7 .
No. 8 .
No. 9 .
No. 10 .
A. Hydrogen equivalent 0 -0067 0 -0270 ( 0 -0107)* 0-0061 ( 0 -0056)* 0 -0639 0 -0196 0 *00187 0 -00502 B. Iodine equivalent " ) " 0 -0058 0 -0272 0 0025 0 -0680 0 -0087 0 -00140 A + B 0 -0125 0 -0542 \#151 ; \#151 ; 0 -1319 0 -0283 0 -00327 C. Iodine absorbed by original solutionf T ) .
Boron 0 -0126 0 -0564 0 -0168 0 -0081 0 -00184 E. Magnesium 0 -0049 0 -0015 0 -ooio 0 -0096 \#151 ; 0 -00027 0-00056 No. of solution . .
No. 11 .
No. 13 .
No. 14 .
No. 15 .
No. 16 .
No. 17 .
No. 18 .
No. 19 .
A. Hydrogen equivalent 0 -0148 0 -0092 0-0052 0 -0196 0 -0056 0 -0270 0 -0140 0 -0143 B. Iodine equivalent 0 -0122 0-0056 0-0023 0 -0093 0-0030 0 -0261 0 -0123 0-0082 A + B 0 -0270 0 -0148 0-0075 0 -0289 0 -0086 0 -0531 0 -0263 0 -0225 C. Iodine absorbed by original solution I ) .
Boron 0 '0246 0 -0128 0 -0104 0-0067 0"0222J 0-0025 0-0140 E. Magnesium 0 -0016 0 -ooio 0 -00097 0-0012 0-0013 * 0\#151 ; B. f Including the equivalent of hydrogen evolved in addition of iodine to the solution .
J The mixture of boride and water had become pasty and may have lost boron .
Dr. M. W. Travers and Mr. R. C. Ray .
[ May 20 , Borohydrates .
1912 .
] ( e ) Discussion of the Results of the foregoing Experiments.\#151 ; From the foregoing experiments it is obvious that the hydrogen and iodine equivalents lie between very sharply defined limits , being either as 1 is to 1 or as 2 is to 1 , and generally approach to one value or to the other .
It also appears that the solutions contain one atom of boron for every atom of hydrogen given off on the addition of acid .
Supposing , therefore , that by the action of the iodine the boron in the solution is completely oxidised to boric acid , it would be possible to represent the changes taking place in the solution by means of the equations:\#151 ; Action of acid Action of iodine . .
B402 + 2H20 = B404 + 2H2 , B4O3 + 2H20 = B405 + 2H2 .
B4O4 + 2I2 4- 2H20 B4O6 -f- 4:111 , .B4O5+ I2+ H20 = B4O6 + 2HI .
'It appeared , at first sight , that these equations would fully explain the behaviour of the solutions .
Further experiments , which will now be described , prove , however , that such explanation is altogether inadequate .
( f ) Further Experiments with the Solution.\#151 ; The following experiments were undertaken with a view to determining whether it would be possible to obtain the boron derivative , or derivatives , free from water .
A measured quantity of the solution was introduced into a density bulb A ( fig. 1 ) , Fig. 1 .
which had previously been exhausted and weighed against a counterpoise in the usual manner .
The bulb was connected with the vessel B , which in the earlier experiments contained calcium chloride , and was cooled with water , but in the later experiments was empty , and was immersed in liquid air .
The apparatus was connected with a Topler pump through the stopcock b , and during the process of exhaustion the stopcocks a and b were opened alternately , so that any liquid evaporating from A was condensed in B. Dr. M. W. Travers and Mr. R. C. Ray .
[ May 20 , When liquid air was used to cool the vessel B the evaporation of the liquid in A proceeded very rapidly , and it was necessary to place the bulb in a basin of water at about 25 ' to prevent the liquid in it from freezing .
It was possible to evaporate about 15 c.c. of liquid in less than three quarters of an hour .
During the evaporation little or no gas was evolved , nor did any solid separate out from the solution , but as the liquid disappeared a viscous substance formed in the bottom of the bulb .
The latter observation points to the conclusion that the solutions contained little or no free boric acid .
At the moment at which the last trace of liquid disappeared the viscous residue began to evolve gas rapidly , the evolution of gas continuing till the viscous material had set to a semi-crystalline or glassy solid .
At this point the rate of the evolution of gas became very slow , and when the gas was removed from the apparatus and measured it was found that volume was equal to one-half the volume of the gas given off on addition of acid to the original solution .
Though when the evaporation of the liquid was carried out rapidly in the manner described above practically no gas was evolved till the residue became viscous , if the liquid was allowed to remain in an exhausted vessel for some time it gave off hydrogen .
No. of Solution , 16 .
Hydrogen evolved on addition of dilute acid to solution .
0*0056 Hydrogen evolved on standing vacuo for 16 hours ... ... . .
0'0022 Hydrogen evolved on evaporation ... ... ... ... ... ... ... ... .
0*0004 If the bulb containing the solid residue was allowed to remain in connection with the pump , gas continued to be evolved slowly , but after a time the evolution of gas ceased altogether .
If this gas was collected and measured it was found that its volume was equal to the volume of gas evolved at the moment that the liquid disappeared .
The rate at which the second quantity of hydrogen was evolved depended upon the degree of dryness of the residue in the bulb , and was much more rapid if calcium chloride was used as a dehydrating agent than if the bulb was connected to the pump through a tube containing pentoxide of phosphorus , or through one immersed in liquid air .
The addition of water to the contents of the bulb and re-evaporation of the liquid resulted in the immediate evolution of a considerable volume of gas , thus:\#151 ; No. of Solution , 16 .
Gas evolved on addition of dilute acid ... ... ... ... .
0*0056 Gas evolved on evaporation to dryness ... ... ... ... . .
0*0026 Gas evolved on re-evaporation to dryness ... ... ... ... .
0*00145 Gas evolved on addition of dilute acid to residue ... 0*00145 Borohydrates .
1912 .
] The addition of dilute acid to the contents of the bulb after evaporation of the liquid produced the same result , the quantity of gas given off , together with the gas evolved on evaporation of the liquid , being equal to the quantity of gas evolved on addition of acid to the original solution .
If when the bulb had been allowed to remain in connection with the pump till the evolution of gas had ceased it was gently heated with a Bunsen burner , a further quantity of gas sensibly equal to the quantity evolved on , or subsequently on standing , was given off .
If the ratio of the hydrogen and iodine equivalents of the original solution was as 1 is to 1 the contents of the bulb after heating absorbed a quantity of iodine approximately equivalent to the quantity of hydrogen evolved at either of the three stages already described .
If , on the other hand , the ratio of the equivalents was as 2 is to 1 the residue did not absorb iodine .
The results of these experiments may be expressed thus :\#151 ; Ratio of hydrogen to iodine equivalents in original solution ... ... . .
1/ 1 2/ 1 Hydrogen evolved on addition of acid to the original solution ... ... . .
2 2 Iodine absorbed by acid solution ... ... ... ... ... ... ... ... ... . .
2 1 Hydrogen evolved on evaporation ... ... ... ... ... ... ... ... ... ... ... ... ... 1 1 Hydrogen evolved on standing or on addition of acid to the residue ... 1 1 Hydrogen evolved on heating ... ... ... ... ... ... ... ... ... ... ... ... ... ... 1 1 Iodine absorbed by r esidue ... ... ... ... ... ... ... ... ... ... ... ... ... ... .
1 0 If , when the residue in it had become solid , the bulb was weighed , and if it was again weighed after standing for some time or even after being heated , it was found that the loss of weight was equal to the weight of the hydrogen evolved .
It appears , therefore , that the loss of hydrogen is not accompanied by the loss of water or of any boron compound in appreciable quantity .
From the original weight of the exhausted bulb , and the weight of the exhausted bulb containing the residue , the weight of the latter could be directly determined .
From the quantity of iodine absorbed by the residue it was possible to calculate the quantity of oxygen required to oxidise it to B2O3 , and knowing the quantity of magnesium oxide present in the solution , the quantity of boron in the residue could be obtained by difference .
In every experiment it was found that while Ratio of number of atoms of H evolved on addition of acid to original solution to number of atoms of B in solution =1/ 1 , Ratio of number of atoms of H evolved on addition of acid to original solution to number of atoms of B in residue = 2/ 1 .
It appears , therefore , that during the process of evaporation one-half the boron evaporates with the liquid .
It has been proved conclusively that it Dr. M. W. Travers and Mr. R. C. Ray .
[ May 20 , is not given off as a gas and collected with the hydrogen , and further , that it passes into the distillate before even the whole of the first fraction of hydrogen has been evolved .
It must , therefore , remain in the distillate , which , it may be remarked , gives off no gas when warmed to the air temperature in vacuo , but in what form has not been fully determined .
It has been observed that , except in one experiment in which the solution was very dilute , the distillate absorbed only a very small quantity of iodine , indeed , not more than could be fully accounted for by the fact that in the second formula set down above the ratio is always somewhat greater than 2 to 1 , indicating that some slight secondary reaction takes place , or that a small quantity of the non-volatile boron derivative , which is a powerful reducing agent , is invariably carried over with the distillate .
If this is the case the boron compound which distils over must be fully oxidised , and must have the formula ( B203)n .
That it is not boric acid is proved by the following experiments .
In the first place , supposing that it might be boric acid , an attempt was made to estimate it by the lime method already described .
It was found that the lime did not increase in weight .
It may be added that the sample of the distillate had stood for some days in a closed tube containing air , a condition under which a lower boron derivative would probably have been at least partially oxidised to boric acid .
Further , it was proved that under similar conditions boric acid is practically non-volatile with water vapour , so that any boric acid present in the original solution must ultimately be found in the residue in the bulb and not in the distillate .
It appears to us that it is necessary to assume that there exists a substance of the formula '(B203)n which is not an acid .
In the case of a carbon compound such an assumption would require but little justification ; and it finds support in the work of Bamsay and Hatfield , which points to the existence of isomeric compounds amongst the hydrides of boron .
The following are the results of our experiments :\#151 ; KWh W p Jsiteitt A. B. C. Table II.\#151 ; Results expressed in gramme-atoms per 100 c.c. of solution .
No. of solution No. 11 .
No. 13 .
No. 14 .
No. 15 .
No. 16 .
No. 17 .
| No. 18 .
No. 19 .
Hydrogen evolved with 0 -0148 0-0092 0 -0052 0 -0195 0 -0056 0 -0270 0-0140 0 -0142 acid Iodine absorbed by acid 0 -0122 0-0056 0-0024 0-0093 0-0030 0 -0161 0 -0123 0 -0082 solution Iodine absorbed by original 0 -0246 solution Boron in original solution ... 0 -0128 0-0104 0-0068 0 -0202 \#151 ; 0 -0222 0 -0140 Boron in residue \#151 ; 0-0058 0-0040 \#151 ; 0-0029 0 -0148 0-0064 0 -0064 Hydrogen evolved on eva- 0-0065 1 1 0 -0091 ** j 1 1 1 1 poration of solution V 0 -0055* and 0-0274* Hydrogen evolved by residue in the cold ] }\#166 ; 0-0131 \#187 ; 0-0074 0 -0078 }\#166 ; 0-0205 1 \gt ; 0-0188 0-0147 Hydrogen evolved by resi- 0 -0103 \#151 ; \#151 ; ~ due on heating J J J Total hydrogen 0 -0212 0 -0131 0-0074 0 -0272 \#151 ; \#151 ; 0 -0250 0 -0188 Iodine absorbed by residue 0-0047 0-0022 trace trace 0-0017 \#151 ; 0-0037 0-0036 Iodine absorbed by dis- \#151 ; \#151 ; \#151 ; \#151 ; 0 -0018 0-0014 0 -0011 0-0022 tillate A + B 0 -0246 ( c ) 0 -0148 0 -0076 0 -0288 0-0086 0 -0431 0 -0263 0 -0224 I + K + M 0 0259 0 -0153 0*0074 0 -0272 0-0090 \#151 ; 0 -0288 0 -0246 # In these experiments acid was added to the residue in the bulb after evaporation .
Borohydrates .
175 Dr. M. W. Travers and Mr. R. C. Ray .
[ May 20 , ( g ) Further Discussion of the Experimental Results.\#151 ; Assuming that the distillate contains a compound isomeric with boric acid it is now possible to explain the whole of the reactions which we have studied .
If , as was suggested before , the substances first formed in the original solution are hydrated derivatives of the oxides B4O2 and B403 these compounds must spontaneously undergo changes such as are represented by the equations:\#151 ; B4O2 + 3H2O = ( B2O3 ) + B202H6 , and B403 + 3H20 = ( B203 ) + B203H6 , the symbol ( B203 ) representing the non-acid and volatile isomer of boric acid .
The changes which take place on addition of acid to the original solution are represented by\#151 ; B2O2H6 = B2O2H2+ 2H2 , and B203H6 \#151 ; B303H2 4* 2H2 .
On evaporation of the original solution\#151 ; B2O2H6 \#151 ; B2O2H4 4 " H2 , B203He \#151 ; B203H4 4HaOn standing\#151 ; B2O2H4 = B2O2H2 + H2 , B203H4 = B203H2 + H2 .
On heating the residue\#151 ; B2O2H2 \#151 ; B202+H^ B203H2 = B203 -f- H2 .
Finally , if the ratio of the hydrogen to the iodine equivalent in the original solution had been as 2 :1 , the residue , after heating , would absorb no iodine , otherwise it would absorb iodine in accordance with the equation B202 4- H20 4- 21 = Ba03+2HL Until more concentrated solutions have been obtained and the molecular weights of the substances in solution have been determined , it is impossible to express a very definite opinion as to their constitution .
The compound of which the formula has been written B202H6 might , indeed , have been assigned the simpler formula BOH3 , or BH2OH , but if this formula is accepted it is not easy to explain the changes which the compound undergoes when treated with acid or when its solution is evaporated .
It is much more likely that the compound is a polymer of BOH3 containing pentavalent boron .
Before leaving the subject we wish to call attention to the close analogy which exists between the properties of the solutions of the borohydrates and solutions of hypophosphites on the one hand and of hydroxylamine salts on Borohydrates .
1912 .
] the other .
The fact that the solution of the borohydrates gives with copper sulphate solution a precipitate which closely resembles " copper hydride " may be taken as evidence that hypoborous acid is one of the decomposition products , a view which is supported by the fact that one of these products , viz. , B202H2 , may be looked upon as a derivative of B20 and H20 , just as hypophosphorous acid may be regarded as a product of P20 and 3H20 .
However , it is much more likely that the similarity is due to the presence of the group ^XHOH .
Generally speaking , the solution of the boron compounds exhibits marked similarity in its properties to a solution of hydroxyl-amine , as will be apparent if the properties of the latter are compared with those described on p. 165 .
( h ) The Reaction between the Boride and Water.\#151 ; In describing the method of preparation of the solutions used in these experiments it has been noted that in some cases the boride was allowed to react with water vacuo .
In these cases the gas which was evolved was collected through the pump and its volume was measured .
At the end of the experiment the flask containing the mixture was detached from the pump , the contents were rapidly filtered by means of a water pump , and the filtrate was made up to 100 c.c. for analysis .
The following results were obtained:\#151 ; Table III .
No. of solution Ho. 3 .
Ho. 9 .
Ho. 10 .
Ho. 16 .
Quantity of boride 20 grin .
25 c.c. 1 0 crrm Quantity of water XV/ gl JJu\#171 ; 25 c.c. 24 Period , in hours 3 3 Hydrogen evolved by boride ... Hydrogen equivalent of solution Iodine equivalent of solution ... 0-0113 0 -0067 0 -0058 0 -00461 0-00187 0-00140 0 -0104 0 -0050 0 -0112 0 *0056 0-0030 If the boron derivative , or derivatives , in solution were formed by the reaction of a boride of the formula B2Mg3 with water , the reaction would take place in accordance with the equation 2B2Mg3+14H20 = B402 + 6Mg(0H)2 + 8H2 .
For every atom of boron passing into solution four atoms of hydrogen would be evolved , and the solution when treated with dilute acid would evolve one atom of hydrogen .
According to the experiments which we have carried out the quantity of hydrogen evolved is almost exactly one-half of that required by the equation .
These experimental results , and the fact that a large quantity of boride gives but a very small yield of soluble boron derivative , led us to the Borohydrates .
conclusion that there must exist compounds of boron and magnesium other than the compound B2Mg3 .
The existence of a compound B4Mg2 would fully account for the formation of the soluble boron derivatives thus:\#151 ; B4Mg2 -|- 6H20 = 2Mg(OH)2 -f- B402 -t- 4H2 .
It is also possible that the solution may result from the interaction of water with an oxy-derivative of boron and magnesium present in the mixture , obtained by heating boric acid and magnesium powder .
This matter requires further investigation , but we think it worth while to record the results of two other experiments which we have carried out .
In the first experiment a small quantity of boric acid was heated with three times its weight of magnesium powder in a silica tube , and allowed to cool down in a current of hydrogen .
The contents of the tube were then transferred to a clean silica tube , and heated in vacuo for half an hour , when the whole of the free magnesium volatilised and condensed in the cool part of the tube .
On cooling , it was found that the lower end of the tube contained a grey friable mass , which dissolved readily in 20-per-cent , nitric acid on warming on a water-bath , leaving only 4'5 per cent , of insoluble residue .
On analysis it was found that the substance contained only 36 per cent , of magnesium instead of 67 per cent. , which should have been present if the product of the reaction were B2Mg3 and MgO .
In a second experiment a mixture of 8 grm. of boric acid and 24 grm. of magnesium powder was heated in a silica flask for half an hour , and allowed to cool down in an atmosphere of hydrogen .
The product of the reaction , which contained a large excess of magnesium , was crushed in a mortar and placed in a flask , and about 60 c.c. of water was added , the flask being cooled with water .
After four hours , about 50 c.c. of liquid , which was of a deep yellow colour , was filtered off by means of a water pump .
The following is the result of the analysis of the liquid :\#151 ; Hydrogen equivalent ... ... 0'00654 Iodine equivalent ... ... ... 0-01184 Magnesium ... ... ... ... ... .
0D154 Boron ... ... ... ... ... ... . .
0T220 It will be noticed that the iodine equivalent is twice the value of the hydrogen equivalent , and that the quantities of boron and magnesium in the solution are very much greater than in any of the solutions previously investigated .
The solution coagulated on warming , forming a translucent jelly .
This experiment was repeated , and the results , so far as the determination of the hydrogen and iodine equivalents and the behaviour of the solution on heating are concerned , were confirmed .
The residue , on further A Chemically Active Modification 179 treatment with water for successive periods , gave decreasing values'for the ratio of the iodine to the hydrogen equivalent .
The results of these experiments , though in themselves somewhat inconclusive , are worth recording , since they indicate that the reactions between boric acid and magnesium are by no means simple ones , and that further study of them may lead to the discovery of new compounds of magnesium and boron , of magnesium , boron , and oxygen , and also of new compounds of boron , oxygen , and hydrogen .
This is a field of research which has not yet been explored , and we propose to continue our investigations upon the earliest opportunity .
A Chemically Active Modification of , Produced by the Electric Discharge.\#151 ; IV* .
By the Hon. R J. Strutt , F.R.S. , Professor of Physics , Imperial College of Science , South Kensington .
( Received May 23 , \#151 ; Read June 13 , 1912 .
) S 1 .
General .
The properties of active nitrogen have been described throughout on the assumption that it is to be classed with other chemical substances , and that its reversion to ordinary nitrogen is to be regarded simply as a chemical reaction , as one would regard the change of ozone to oxygen , or of red to ordinary phosphorus .
I see no reason to abandon this position .
There are , however , some circumstances not at first sight falling in very naturally with it .
One of these is the acceleration of the change by cooling , f a phenomenon without parallel in any recognised reaction .
Another is the development of many of the bands of the nitrogen spectrum . !
This spectrum has never been produced by any other purely chemical process , but ( apart from active nitrogen ) is only observed when an electric current is actually passing through the gas at the moment of observation .
Lastly , the ionisation associated with a stream of glowing nitrogen has suggested serious doubts whether its chemical peculiarities are really due to the presence of a definite chemical substance in the ordinary sense , or to some unexplained survival of * I , 'ltoy .
Soc. Proc. , ' 1911 , A , vol. 85 .
p. 219 ; II , ibid. , 1911 , vol. 86 , p. 56 ; III , ibid. , 1912 , vol. 86 , p. 262 .
+ HI , p. 263 .
+ 'Roy .
Soc. Proc. , ' 1911 , A , vol. 85 , p. 377 .
|
rspa_1912_0070 | 0950-1207 | A chemically active modification of nitrogen, produced by the electric discharge.\#x2014; IV. | 179 | 188 | 1,912 | 87 | Proceedings of the Royal Society of London. Series A, Containing Papers of a Mathematical and Physical Character | the Hon. R. J. Strutt, F. R. S. | article | 6.0.4 | http://dx.doi.org/10.1098/rspa.1912.0070 | en | rspa | 1,910 | 1,900 | 1,900 | 4 | 214 | 4,662 | http://corpora.clarin-d.uni-saarland.de/surprisal/6.0.3/?id=rspa_1912_0070 | 10.1098/rspa.1912.0070 | null | null | null | Thermodynamics | 35.678321 | Atomic Physics | 20.186247 | Thermodynamics | [
-0.5555797815322876,
-46.97915267944336
] | A Chemically Active Modification 179 treatment with water for successive periods , gave decreasing values'for the ratio of the iodine to the hydrogen equivalent .
The results of these experiments , though in themselves somewhat inconclusive , are worth recording , since they indicate that the reactions between boric acid and magnesium are by no means simple ones , and that further study of them may lead to the discovery of new compounds of magnesium and boron , of magnesium , boron , and oxygen , and also of new compounds of boron , oxygen , and hydrogen .
This is a field of research which has not yet been explored , and we propose to continue our investigations upon the earliest opportunity .
A Chemically Active Modification of , Produced by the Electric Discharge.\#151 ; IV* .
By the Hon. R J. Strutt , F.R.S. , Professor of Physics , Imperial College of Science , South Kensington .
( Received May 23 , \#151 ; Read June 13 , 1912 .
) S 1 .
General .
The properties of active nitrogen have been described throughout on the assumption that it is to be classed with other chemical substances , and that its reversion to ordinary nitrogen is to be regarded simply as a chemical reaction , as one would regard the change of ozone to oxygen , or of red to ordinary phosphorus .
I see no reason to abandon this position .
There are , however , some circumstances not at first sight falling in very naturally with it .
One of these is the acceleration of the change by cooling , f a phenomenon without parallel in any recognised reaction .
Another is the development of many of the bands of the nitrogen spectrum . !
This spectrum has never been produced by any other purely chemical process , but ( apart from active nitrogen ) is only observed when an electric current is actually passing through the gas at the moment of observation .
Lastly , the ionisation associated with a stream of glowing nitrogen has suggested serious doubts whether its chemical peculiarities are really due to the presence of a definite chemical substance in the ordinary sense , or to some unexplained survival of * I , 'ltoy .
Soc. Proc. , ' 1911 , A , vol. 85 .
p. 219 ; II , ibid. , 1911 , vol. 86 , p. 56 ; III , ibid. , 1912 , vol. 86 , p. 262 .
+ HI , p. 263 .
+ 'Roy .
Soc. Proc. , ' 1911 , A , vol. 85 , p. 377 .
180 Hon. R. J. Strutt .
A Chemically [ May 23 , the conditions of the disruptive discharge .
Evidence will he brought forward in this paper which is considered to be entirely in favour of the former alternative .
S 2 .
Energy of Active Nitrogen .
These considerations have made it important to determine whether the energy emitted by active nitrogen in reverting to ordinary nitrogen is comparable with that liberated in other chemical changes .
The experiments to be described answer this question in the affirmative .
The general plan of experiment is to compare the energy given out by a definite stream of active nitrogen when allowed to revert to the ordinary kind , with the energy given out when the same stream reacts completely with nitric oxide .
It is plain that this enables us to compare the energy of active nitrogen with that given out by an equivalent quantity of nitric oxide in the reaction .
The latter is known from established calorimetric data .
I have only carried out this experiment in a semi-quantitative manner .
The time is scarcely ripe for attempting more .
A stream of nitrogen passes , first through a capillary tube of suitable dimensions , to regulate the flow , * then through a low-pressure discharge tube , to change it to the active condition ; next through a thin-walled tube , in which it loses the heat acquired in the discharge , !
and is approximately cooled to room temperature .
The active gas is then delivered into the tube a ( fig. 1 ) , vacuum-jacketed NITRIC OXYGEN Fig. l. and silvered for heat insulation , by the jet c. In the course of its passage along a towards the air pump it partly goes back to ordinary nitrogen , with * This was preferred to the use of a lubricated stopcock , as securing definiteness and constancy in the conditions .
t There is a certain want of definiteness about the initial temperature of the gas stream , for its internal energy is constantly being liberated all along its path .
An experiment was made in which thermo-couples were introduced into the gas , up-stream and downstream of an oxidised copper gauze plug , in which the internal energy was liberated .
The initial temperature was 25 ' C. ; the final temperature 60 ' .
1912 .
] Active Modification of .
181 rise of temperature .
At b it comes in contact with a roll of oxidised copper gauze , where the decomposition is completed by a surface action.* The oauze accordingly becomes heated , and the rise of temperature is measured by a thermocouple enclosed in it , with leads , f f , to a galvanometer outside .
When nitric oxide is led into the nitrogen stream by d , combination occurs , the characteristic flame being developed at the mouth of the jet c. If the two currents of gas are suitably adjusted the flame can be made to end short of the gauze plug .
This adjustment is best done in preliminary experiments , without a silvered vacuum jacket .
Under these conditions it is observed that a notable rise of temperature occurs at the plug when nitric acid is admitted .
This shows that the energy of active nitrogen is comparable with that of nitric oxide , for , when equivalent quantities of these substances react , the rise of temperature of the gas stream is notably greater than when the active nitrogen decomposes by itself .
To make the experiment definite , a precaution is necessary .
The air-pump used to draw the gases along has a limited intake , and when the nitric oxide stream is admitted , an increase in the pressure of the discharge tube necessarily results .
This alters the character of the discharge , and hence the percentage of active gas in the nitrogen stream and the rise of temperature resulting from its destruction .
This source of uncertainty is eliminated by always allowing a tributary stream of gas to flow in , either nitric oxide or , alternatively , an equal stream of oxygen .
The latter does not act chemically on active nitrogen , though hastening its decay , apparently by a catalytic action analogous to that of copper oxide.f Thus it assists the action of the oxidised gauze , and helps to secure destruction of all active nitrogen .
The oxygen stream has the further advantage of bringing the total gas stream up to nearly the same thermal capacity as it has when the nitric oxide is flowing , for oxygen and nitric oxide have about the same specific heat .
Thus a given rise of temperature of the stream indicates the same energy given to it in each case .
The oxygen and nitric oxide streams are made equal by using the same capillary tube g to regulate the admission of each .
Their viscosities are appreciably the same .
A two-way stopcock A serves to change over from one to the other .
A large number of experiments were made , and it was always found that admission of nitric oxide caused the temperature of the thermocouple to rise , and that it fell again when oxygen was substituted .
The ratio of temperatures depended very much on the precise arrangement of apparatus .
When nitric oxide is admitted , most of the heat is liberated near where * I , p. 226 .
t II , p. 56 .
182 Hon. K. J. Strutt .
A Chemically [ May 23 , the gases mix .
The hot stream has therefore more chance of losing heat before it gets to the gauze plug in which the thermocouple is embedded .
When no nitric oxide is passing , the chief liberation of energy is by contact action at the surface of the plug , thus the heat loss is less than in the former case .
This source of uncertainty tends to exaggerate the energy of active nitrogen compared with that of nitric oxide .
Under different experimental conditions the rise of temperature when nitric oxide was admitted varied between L2 and 1'8 times that obtained with nitrogen only .
The conditions could not be kept very constant , and , owing to the considerable thermal capacity of the plug , each experiment took time .
There was , however , invariably a definite rise of temperature when nitric oxide was admitted .
Thus the main point is established that the energy of active nitrogen is of the same order of magnitude as that of an equivalent of other substances .
Nitric oxide is highly endothermic , and the experiments make it probable that active nitrogen considerably exceeds it in this respect .
Experiments made with acetylene instead of nitric oxide gave similar results .
Since , however , tarry substances of unknown calorimetric value are produced in this reaction* it would be less suited for an exact quantitative determination .
S 3 .
Ionisation attendant on the Decay of Active Nitrogen .
The general features of this have already been described . !
I now pass to a quantitative investigation of it .
Some precautions necessary in experiments of this kind will first be described .
Great trouble is experienced from the tendency to stray electric discharges from the induction coil used to generate active nitrogen .
These discharges pass from the electrodes of the vacuum tube to those of the testing vessel , and disturb the electrical conditions there , so that the galvanometer behaves quite erratically .
To avoid them , the coil , Leyden jar , and discharge tube must be enclosed in a box { a , fig. 2 ) lined with tinfoil , which is earthed via the gaspipes .
Erom the discharge tube , 5 , the gas is led out by a tube which passes through a hole in the side of the box .
This tube should be locally constricted to 2 or 3 mm. internal diameter where it passes through the hole .
This precaution is important .
The electrode c nearest the exit should be in connection with the box , and a supplementary electrode e should be provided in metallic contact with both , as shown .
A small fraction of the current from the electrode d fails to flow away by c , but escapes past it , and gets to earth by any channel * I , p. 228 .
\#165 ; II , p. 60 .
Active Modification of Nitrogen .
1912 .
] available .
The supplementary electrode e provides the channel required , and prevents this residual discharge passing to earth the electrodes of the ionisation chamber .
The constriction of the tube assists towards the same object .
After leaving the discharge tube the gas passes to the ionisation chamber / , and flows between the parallel plate electrodes A , 10 mm. apart .
a -\#171 ; f\#151 ; N/ TROCEN TO VIR PUMP These are in circuit with a galvanometer and a battery of small storage cells .
The glow decays completely in its course along this vessel .
The first point was to examine the relation between current and E.M.F. It was found that with a bright active nitrogen glow between the plates at low pressure saturation could not be obtained , the current continually increasing with the E.M.F. until discharge occurred between the testing electrodes .
Probably ionisation by collision occurred under these conditions .
When , however , the pressure of gas in the ionisation vessel was higher , and the original generating discharge not too strong , saturation was obtained .
The following set of measurements , between plane electrodes 1 cm .
apart , maygbe given as an example :\#151 ; E.M.F. Current .
E.M.F. Current .
volts .
microamperes .
volts .
microamperes .
80 14 320 18 160 18 400 19 240 18 480 19 VOL. LXXXVII.- \#151 ; A. O 184 Hon. B. J. Strutt .
A Chemically [ May 23 , No effect whatever on the intensity of the luminous glow was observed when this saturating field was applied .
This is in accordance with previous experiments , * and affords conclusive evidence that the glow is not due to the presence of ions\#151 ; for it is unaffected by removing them .
The next point was to obtain a quantitative relation between the amount of active nitrogen entering the ionisation vessel per second and the current carried .
For this purpose the nitric oxide method of estimation was used/ j the reaction being allowed to take place in the same vessel as was used for ionisation tests .
A suitably regulated current of nitric oxide was admitted through a capillary tube to the ionisation chamber .
The tube by which it enters is seen in section at i. As in the heat experiments , previously described , the current of nitric oxide could be replaced by an equal current of nitrogen^ so as to avoid disturbing the pressure conditions .
When the nitrogen glow was developed between the electrodes , the ionisation current was about 20 microamperes .
On admitting nitric oxide the nitrogen glow was replaced by the nitrogen peroxide flameS with continuous spectrum , and the current fell to about 1 microampere .
It appears at once , therefore , that the amount of ionisation developed by a given stream of active nitrogen depends entirely on the particular fate which it meets with , and is not a fixed property of the stream .
Many more ions are produced if it goes back to ordinary nitrogen than if it reacts with nitric oxide .
Confining our attention to the case of nitrogen alone , it was found that the current carried was infinitesimal in comparison with that which would be conveyed by the same mass of nitrogen according to the electrochemical equivalent .
Thus , in one experiment , the stream of active nitrogen passing was such as to yield in 15 minutes 26*4 mgrm .
of the blue liquid N2O3 .
This indicates 26'4x 14/ 76 = 4'87 mgrm .
of active nitrogen in 15 minutes , or 19'5 mgrm .
per hour .
Now , if every atom of nitrogen in this contributed one positive and one negative ion , the saturation current would be 37T x 103 microamperes .
This is about 1,500 times greater than the saturation current actually observed , which was 24-9 microamperes .
Thus , only one nitrogen atom in 1,500 of those concerned gets ionised .
In the above experiment every precaution was taken to guard against error in the chemical determination .
Blank tests of 15 minutes ' duration , without a discharge to make the nitrogen stream active , were made before and after the actual experiment , but no nitrogen trioxide could be collected .
* II , p. 61 .
t II , p. 57 .
t Taken off by a branch tube from the supply of nitrogen to the original discharge tube .
S II , p. 57 .
Active Modification of Nitrogen .
1912 .
] As already mentioned , the ionisation associated with a stream of glowing nitrogen has suggested doubts whether its chemical peculiarities are really due to the presence of a definite chemical substance in the ordinary sense , or to some unexplained survival of the conditions of the disruptive discharge .
I think the latter possibility must now be dismissed ; for it is clear that the ions are so few , compared with the number of atoms concerned in the chemical action , that we can only regard them as a by-product of the processes which are going on .
The ions formed in the reversion of active nitrogen may be compared with those formed in the glow oxidation of phosphorus , which are also very few compared with the number of reacting atoms .
It is significant that each of these actions is accompanied by luminosity .
Is it not possible that the ionisation is the direct consequence of the luminosity ?
It is known that ionisation is produced by light in the far ultra-violet region of the spectrum\#151 ; the Schumann region.* Whether the active nitrogen glow extends to this region , and , if so , with what intensity , is not known , though the determination would not be difficult to an experimenter who possessed the very special appliances necessary .
It may be objected that the ionisation observed in the reversion of active nitrogen , though small compared with the number of atoms concerned , is still enormous compared with any observed to be produced by ultra-violet light .
But nitrogen luminosity , acting on nitrogen atoms , may produce special effects of resonance .
The subject is too speculative to pursue further , beyond the remark that this hypothesis is consistent with the change of ionisation which generally results when other chemical substances are added , modifying the nature of the glow.t S 4 .
Effect of Temperature .
In former experiments it was shown that the nitrogen glow could be brilliant at \#151 ; 180 ' C. , and that it was of shorter duration than would otherwise have been the case .
I find that these observations have been in part anticipated by C. C. Trowbridge.j His experiments were not , however , designed or interpreted with definite reference to the chemical nature either of the original gas present or of the change occurring .
As before mentioned , S local cooling causes concentration of the gas in the part of the vessel cooled , and proof is required that this is not the effective cause of the brightening .
Such proof was found in the shortened duration of the glow when the whole vessel wras suddenly plunged in liquid air .
It * Hughes , ' Camb .
Phil. Soc. , ' 1910 , vol. 15 , p , 483 .
t II , p. 60 . .
t ' Phys. Rev. , ' 1906 , vol. 23 , p. 296 .
S III , p. 262 .
186 Hon. R. J. Strutt .
A Chemically [ May 23 , would , however , be satisfactory to obtain in addition definite evidence that the luminosity is increased in intensity as well as shortened in duration .
There is difficulty\#151 ; not perhaps insurmountable\#151 ; in getting this when the vessel is cooled all over , for we have no convenient standard of comparison for the luminosity .
I returned , therefore , to the method of local cooling , compensating for the concentration thus caused by looking through a smaller thickness of luminous gas .
The evidence already given* justifies the supposition that the change is a bimolecular one , occurring at a rate proportional , ceteris paribus , to the number of collisions per second between molecules of active nitrogen .
If the gas is locally cooled in a closed vessel , with equality of pressure throughout , the number of collisions at any part of it is , according to the kinetic theory , proportional jointly to the square of the concentration and to the molecular velocity .
The former factor varies as t~2 , the latter as where t is the absolute temperature .
Upon the whole , therefore , the number of collisions per second in various parts of the vessel varies as If one part of the vessel is at room temperature ( 20 ' C. ) , and another in liquid air , the molecular collisions in the latter will be more numerous in the ratio 5-6:1 .
A bulb of 300 c.c. capacity { a , fig. 3 ) had a neck b 19 mm. in internal diameter .
A narrow tube c , 3'4 mm. diameter , was sealed on to it .
These diameters are in the above ratio 5-6:1 .
The bulb was exhausted and charged with nitrogen to a suitable pressure , so as to glow brightly after excitation by the electrodeless discharge .
The narrow neck was immersed in liquid air up to d , and , when the temperature had settled down , the bulb was excited .
The afterglow was seen to be intrinsically much brighter\#151 ; four or five times perhaps\#151 ; in c than in the broad neck b. It was found convenient to make b opaque with black varnish outside , except for a narrow strip of the same width as c. This made comparison easier .
Maximum brilliancy was observed at a point s somewhat above the level * III , p. 267 .
MAXIMUM \j LUMINOSITY 6--------------LIQUID AIR LEVEL Fig. 3 .
Active Modification of Nitrogen .
1912 .
] of the liquid air , though still in the narrow tube .
This may have been due to the restricted access of fresh supplies of active nitrogen to the narrow tube , where it was being used up so fast .
Thus an inadequate supply would reach the fully cooled part of the tube .
So far as this cause may have acted , it makes the experiment not less but more significant .
At least as many molecular collisions were occurring in the deep stratum of luminosity in b as in the shallow stratum at e. But e was much the brightest .
I wish now to enter more speculative ground .
There is considerable reason for thinking that active nitrogen is simply monatomic nitrogen .
Indeed the choice seems to lie between that and triatomic , * unless indeed we are prepared to consider the possibility of a very complex molecule .
Let us assume the monatomic view as a working hypothesis .
It may then be assumed that the ratio of specific heats ( the direct determination of which presents insuperable difficulties ) has the value 1*67 found in other monatomic gases.f If this is so , then , as Clausius first pointed out , the whole energy put into the gas by raising its temperature goes into increasing the translational energy of the molecules .
There is none left to increase their internal energy , whether rotational or otherwise . !
No other chemical action has been studied in which the reacting systems are monatomic .
The ' reversion of active nitrogen is the only chemical change we know of which is not accelerated by heating , and the only one in which the internal energy of the reacting systems is not increased by the same cause .
Is this an accident ?
When a non-explosive chemical change occurs throughout the volume of a gas or a gaseous mixture , it is certain that the collisions which result in chemical combination are a very small fraction of the total number .
The great change in the velocity of reaction which usually accompanies a rise of temperature affords proof of this .
What is the peculiarity of the molecules which make successful collisions ?
It is usually supposed , so far as I know , that they are molecules of exceptional translational velocity .
This would explain the great effect which a moderate rise of temperature produces on the velocity of reaction , for rise of temperature increases very greatly the number of molecules having velocities in excess of * III , p. 267 .
t As regards mercury vapour , no objection will be taken to this ; but as regards the helium group of gases , it may be objected that we rely on the ratio of specific heats to determine monatomicity , and that the argument cannot be used conversely .
Originally this objection would have been valid .
Now , however , many facts in radioactivity , intelligible on the hypothesis that helium is monatomic , would no longer be so if we abandoned that hypothesis .
There is also evidence from the periodic law .
t See , for instance , O. E. Meyer 's ' Kinetic Theory of Gases , ' p. 118 .
188 A Chemically Active Modification ofi .
some assigned value large enough to make the molecules in question exceptional .
But when we consider the reversion of active nitrogen this theory fails entirely .
For increase in the translational velocity of the molecules , so far from increasing the number of successful collisions , positively diminishes it .
I infer , therefore , that in this case , and probably in others also , it is not the exceptional violence of the collision which makes it result in combination .
Indeed , it is difficult to see , from a mechanical point of view , why it should do so .
If we permit ourselves the analogy of indiarubber balls coated with some adhesive substance , the more violent the collision , the less likely it is that the balls will permanently adhere .
We are reduced , then , to assume that a successful collision one that results in chemical union ) is mainly conditioned by something internal to the molecule .
As the upshot of these considerations the following theory is suggested .
High translational velocity of the molecules is in itself unfavourable to chemical union .
And if , as in the case of monatomic nitrogen , the whole energy of a higher temperature goes to increasing this velocity , the rate of chemical transformation will be diminished by heat .
In ordinary cases , however , when the reacting molecules are more than monatomic , the increase of internal energy more than outweighs the unfavourable influence of an increase in translational energy , and , upon the whole , a rapid increase in the rate of combination results .
It is not within the scope of this theory to explain how an increase of internal energy , probably rotational , can facilitate chemical union of diatomic or polyatomic systems .
A crude suggestion , indicating how this might be possible , would be that a rapidly rotating system , internally strained by centrifugal force , is readier to break up , preparatory to entering on a new configuration .
S 5 .
Summary .
( 1 ) Active nitrogen is a highly endothermic body , but its energy is of the same order of magnitude as that of other chemical substances .
( 2 ) In the reversion of active to ordinary nitrogen , the number of atoms ionised is a very small fraction of the whole number concerned in the change .
The ionisation is a subordinate effect , and may be due to light of very short wave-length emitted in the reaction .
( 3 ) Additional experiments are described to prove that the change of active nitrogen is more rapid at low temperatures .
This is thought to be connected with the monatomic character of the molecule , and to throw light on the connection between temperature and velocity of reaction in other cases .
|
rspa_1912_0071 | 0950-1207 | The existing limits of uniformity in producing optical glass. | 189 | 193 | 1,912 | 87 | Proceedings of the Royal Society of London. Series A, Containing Papers of a Mathematical and Physical Character | J. William Gifford|Sir David Gill, F. R. S. | article | 6.0.4 | http://dx.doi.org/10.1098/rspa.1912.0071 | en | rspa | 1,910 | 1,900 | 1,900 | 4 | 48 | 1,100 | http://corpora.clarin-d.uni-saarland.de/surprisal/6.0.3/?id=rspa_1912_0071 | 10.1098/rspa.1912.0071 | null | null | null | Tables | 41.577689 | Optics | 16.586073 | Tables | [
1.6802942752838135,
-34.07752990722656
] | ]\gt ; The Existing Limits of Uniformity in Producing Optical Glass .
By J. WILLIAM GIFFORD .
( Communicated by Sir David Gill , F.B.S. Received 23 , \mdash ; Read June 27 , 1912 .
) Since Dr. Hopkinson 's paper*little appears to have been published on the refractive indices of the different kinds of optical glass , except in regard to those varieties actually employed in the manufacture of optical combinations , and for these chiefly in the catalogues circulated by the makers themselves .
The work described in this paper has extended over the last 10 years , and includes 27 glass by Messrs. Schott of Jena , Messrs. Parra-Mantois of Paris , and Messrs. Chance of Birmingham .
In each case a portion or the whole of the was purchased\mdash ; in amounts varying from to some hundred kilogrammes in .
The method of measurement employed is described in previous papers .
As described in the last paper , three blocks were chosen at hazard from each elting and cut into approximate equilateral prisms , the surfaces of which were optically polished on all three sides .
The mean refractive index for wave-length 5270 ( E ) was then determined for each of the three prisms of each melting by the accurate methods described , S the results being reduced to , the temperature-coefficient for each melting being determined in the manner described in the paper in question .
The probable differences of these indices were independently computed by two methods:\mdash ; ( 1 ) As described , loc. cit. , p. 332 .
( 2 ) By the usual expression , in this case .
The two methods naturally give different results in the separate cases , but in the mean they as follows:\mdash ; Average probable error of by method ( 1 ) \ldquo ; ( 2 ) The index of refraction at C. for rays of wave-length 5270 having 'Roy .
Soc. Proc 1877 , vol. 26 .
especially ' Roy .
Soc. Proc February 13 , 1902 ; and ' Monthly Notices , R.A. December , 1908 .
king trisms tndeavour hways b surfaces as S 'Roy .
Soc. Proc vol. 70 , pp. 329\mdash ; 331 .
This probable error , of course , includes the actual difference in the refractive indices of different specimens of glass from the same melting , and the accidental error of the determination of the index of each .
As the refractive index of each of the three prisms of each melting was completely determined three times , the accidental probable error was readily determined and found to be \mdash ; in other words , so small as not sensibly to affect the above figures .
Mr. J. W. Gifford .
* 192 Existing Limits of Uniformity in Producing Optical been thus accurately determined for the mean of three specimens of each melting , the next step was to determine the indices for rays of other wavelengths .
These were determined , by the same process , from observations through one prism only of each melting , and , after correction to C. , were then reduced by simple proportion to the indices corresponding to the mean index of the melting .
The table gives for 13 values of the mean refractive index for each melting .
At the head of each column will be found the description of the glass , the letter and figure denoting the maker and his number of the melting Schott , Mantois , Chance ) , the value of , and the probable error of the index , computed by each of the two methods above described .
Interpolation .
\mdash ; It has already been shown*that if lists of refractive indices are placed in columns in ascending series of their dispersions , then , by interpolating between corresponding elements in contiguous columns , it is easy to find the index for any glass whose optical position lies between those of the glasses to which the columns correspond .
With this end in view a complete list of the refractive indices of all the glasses measured follows .
* Monthly Notices , .S .
, ' December , 1908 .
Electrical on Thin Anchor-Ring .
It will be seen above that the heavy barium crown glasses are those which show the greatest variation in homogeneity in the same melting .
My thanks are due to Sir David Gill for his great kindness and help in arranging the paper .
Etectrical brations on Thin Anchor-Ring .
By Lord RAYLEIGH , O.M. , F.B.S. Received Read June Although much attention has been bestowed upon the , subjec of electric oscillations , there are comparatively few examples in which definite mathematical solutions have been gained .
These problems are much simplified when conductors are supposed to be perfect , but even then the difficulties usually remain formidable .
Apart from cases where the propagation may be regarded as being in one dimension , * we have Sir J. Thomson 's solutions for electrical vibrations upon a conducting sphere or cylinder .
But these vibrations have so little persistence as hardly to deserve their name .
A more instructive example is afforded by a conductor in the form a circular ring , whose circular section is supposed small .
There is then in the neighbourhood of the conductor a considerable store of energy which is more or less entrapped , and so allows of vibrations of reasonable persistence .
This problem was very ably treated in 1897 , but with deficient explanations .
S Moreover , Pocklington limits his detailed conclusions to one particular mode of free vibration .
I think I shall be doing a service in calling attention to this investigation , and in exhibiting the result for the radiation of vibrations in the higher But I do not attempt a complete re-statement of the argument .
Pocklington starts from Hertz 's formulae for an elementary vibrator at the origin of co-ordinates , ( 1 ) where , ( 2 ) in denote the components of electromotive intensity , is ' Phil. Mag 1897 , vol. 43 , p. 125 ; 1897 , vol , 44 , ; ' Scientific Papers , ' vol. 4 , pp. 276 , 327 .
'Recent Researches , ' 1893 , SS301 , 312 .
'Camb .
Proceedings , ' 1897 , vol. 9 , p. 324 .
S Compare W. .
Orr , ' Phil. Mag 1903 , vol. 6 , p. 667 .
|
rspa_1912_0072 | 0950-1207 | Electrical vibrations on a thin anchor-ring. | 193 | 202 | 1,912 | 87 | Proceedings of the Royal Society of London. Series A, Containing Papers of a Mathematical and Physical Character | Lord Rayleigh, O. M., F. R. S. | article | 6.0.4 | http://dx.doi.org/10.1098/rspa.1912.0072 | en | rspa | 1,910 | 1,900 | 1,900 | 11 | 133 | 2,722 | http://corpora.clarin-d.uni-saarland.de/surprisal/6.0.3/?id=rspa_1912_0072 | 10.1098/rspa.1912.0072 | null | null | null | Fluid Dynamics | 40.246501 | Tables | 26.838091 | Fluid Dynamics | [
42.6630859375,
-45.782318115234375
] | ]\gt ; Electrical on Thin Anchor-Ring .
It will be seen above that the heavy barium crown glasses are those which show the greatest variation in homogeneity in the same melting .
My thanks are due to Sir David Gill for his great kindness and help in arranging the paper .
Etectrical brations on Thin Anchor-Ring .
By Lord RAYLEIGH , O.M. , F.B.S. Received Read June Although much attention has been bestowed upon the , subjec of electric oscillations , there are comparatively few examples in which definite mathematical solutions have been gained .
These problems are much simplified when conductors are supposed to be perfect , but even then the difficulties usually remain formidable .
Apart from cases where the propagation may be regarded as being in one dimension , * we have Sir J. Thomson 's solutions for electrical vibrations upon a conducting sphere or cylinder .
But these vibrations have so little persistence as hardly to deserve their name .
A more instructive example is afforded by a conductor in the form a circular ring , whose circular section is supposed small .
There is then in the neighbourhood of the conductor a considerable store of energy which is more or less entrapped , and so allows of vibrations of reasonable persistence .
This problem was very ably treated in 1897 , but with deficient explanations .
S Moreover , Pocklington limits his detailed conclusions to one particular mode of free vibration .
I think I shall be doing a service in calling attention to this investigation , and in exhibiting the result for the radiation of vibrations in the higher But I do not attempt a complete re-statement of the argument .
Pocklington starts from Hertz 's formulae for an elementary vibrator at the origin of co-ordinates , ( 1 ) where , ( 2 ) in denote the components of electromotive intensity , is ' Phil. Mag 1897 , vol. 43 , p. 125 ; 1897 , vol , 44 , ; ' Scientific Papers , ' vol. 4 , pp. 276 , 327 .
'Recent Researches , ' 1893 , SS301 , 312 .
'Camb .
Proceedings , ' 1897 , vol. 9 , p. 324 .
S Compare W. .
Orr , ' Phil. Mag 1903 , vol. 6 , p. 667 .
Lord Rayleigh .
[ May 24 , the period of the disturbance , and the wave-length corresponding in free aether to this period .
At a great distance from the source , we have from ( 1 ) .
( 3 ) The resultant is perpendicular to , and in the plane contaimng and Its magnitude is , ( 4 ) where is the angle between and The required solution is obtained by a distribution of elementary vibrators of this kind along the circular axis of the , the axis of the vibrator being everywhere tangential to the axis of the ring and the coef of intensity proportional to where is an integer and defines a point upon the .
The calculation proceeds in terms of semi-polar co-ordinates , the axis of symmetry being that of , and the origin being at the centre of the circular axis .
The radius of the circular axis is and the radius of the circular section is .
very small relatively to The condition to be satisfied is that at every.point of the surface of the ring , where , the tangential component of , shall vanish .
It is not satisfied absolutely by the above specification ; but Pocklington shows that to the order of approximation required the specification suffices , provided be suitably chosen .
The equation determining expresses the evanescence of that tangential component which is parallel to the circular axis , and it takes the form , ( 5 ) where .
( 6 ) In ( 5 ) we are to retain the large term , arising in the integral when is small , and the finite term , but we may reject small quantities .
Thus Pocklington finds , ( 7 ) the condition being to this order of approximation the same at all points of a cross-section .
1912 .
] Electri , Vibrcations on a Anchor-Ring .
The first integral in ( 7 ) may be evaluated for any ( integral ) value of Writing , we have .
( 8 ) The large part of the integral arises from small values of .
We divide the range of integration into two parts , the first from to where though small , is compared with , and the second from to For the first part we may eplace by unity , and by .
We thus obtain .
( 9 ) Thus to a first approximation .
In the second part of the range of integration we may neglect in comparison with , thus obtaining .
( 10 ) The numerator may be expressed as a sum of terms such as , and for each of these the integral may be evaluated by taking , in virtue of Accordingly , ( 11 ) when small quantities are neglected .
For example , The sum of the coefficients in the series of terms ( analogous to ) which represents the numerator of ( 10 ) is necessarily , since this is the value of the numerator itself when .
The particular value of chosen for the division of the range of integration thus disappears from the sum of ( 9 ) and ( 10 ) , as of course it ought to do .
When , corresponding to the gravest mode of vibration specially considered by Pocklington , the numerator in 10 ) is Lord Rayleigh .
[ May 24 , and the value of the integral is accordingly To this is to be added from ( 9 ) making altogether for the value of ( 8 ) .
( 12 ) The second integral in ( 7 ) contributes only finite terms , but it is important as determining the ginary part of and thus the rate of dissipation .
We may write it , ( 13 ) where approximately .
Pocklington shows that the imaginary part of ( 13 ) can be expressed by means of Bessel 's functions .
We may take , ( 14 ) whence } .
( 15 ) ( 13 ) may be replaced by .
( 16 ) Now so that .
( 17 ) The imaginary part of ( 13 ) is thus simply .
( 18 ) A corresponding theory for the functions does not appear to have been developed When , our equation becomes 1\mdash ; 2 cos2 , ( 19 ) *Compare ' Theory of Sound , ' S302 .
Gray and Mathews , ' Bessel 's Functions , ' p. 13 .
1912 .
] Etectrical Vibrations on Thin and on the right we may replace by its first approximate value .
Referring to ( 2 ) we see that the negative must be chosen for and , so that .
The imaginary term on the is thus For the real term Pocklington calculates , so that , being written for , .
( 20 ) " " Hence the period of the oscillation is equal to the time required for a free wave to traverse a distance equal to the circumference of the circle multiplied by , and the ratio of the amplitudes of consecutive vibrations is 1 : or \ldquo ; For the general value of is eplaced by , ( 21 ) where is a real finite number , and finally .
( 22 ) The ratio of the mplitudes of successive vibrations is thus in which the values of can be taken from the tables ( see and Mathews ) .
We have as far as equal to 12:\mdash ; . .
It appears that the damping during a single vibraf , ion diminishes as ?
increases , vi the greater the number of subdivisions of the circumference .
An proximate expression for the tabulated quantity when is large may be at once derived from a formula due to Nicholson , * who shows that when and are large and nearly equal , is related to Airy 's integral .
In fact , , ( 24 ) 'Phil .
Mag 1908 , vol. 16 , pp. 276 , 277 .
Lord Rayleigh .
[ May 24 , so that .
( 25 ) If we apply this formula to .
we get as compared with the tabular It follows from ( 25 ) that the damping in each vibration diminishes without limit as increases .
On the other hand , the damping in a given time varies as increases indefinitely , if slowly , with We proceed to examine mole in detail the character at a great distance of the vibration radiated from the ring .
For this purpose we choose axes of and in the plane of the ring , and the coordinates of any point may also be expressed as .
The contribution of an element at is given by ( 4 ) .
The direction cosines of this element are ; and those of the due to it are taken to be .
The direction of this disturbance is perpendicular to and in the plane containing and the element of arc .
The first condition gives , and the second gives ; so that The sum of the squares of the denominators in ( 26 ) is Also in ( 4 ) ; and thus .nsin To these quantities the components due to the element are proportional .
Before we can proceed to an integration there are two other factors to be rarded .
The first relates to the intensity of the source situated at To represent this we must introduce .
Again , there is the question of phase .
In we have ; and in the denominator of ( 4 ) we may the difference between and S 0.13166 .
1912 .
] on a Thin Anchor-Ring .
Thus , as the components due to , we have , ( 29 ) with similar expressions for and corresponding to the right-hand members of ( 28 ) .
The integrals to be considered may be temporarily denoted by , where , ( 30 ) being written for .
Here .
and in this , if we write for We thus find , ( 31 ) where .
( 32 ) In like manner , .
( 33 ) Now When is even , the imaginary part vanishes , and ( 34 ) On the other hand , when is odd , the real part vanishes , and .
( 35 ) Thus , when even , and are both odd and and are both pure imaginaries .
But wheu is odd , and are both real .
As functions of direction we may take to be proportional to Whether be odd or even , the three components are in the same phase .
On the same scale the intensity of disturbance , represented by is in terms of , ( 36 ) V0L .
LXXXVII .
Lord Rayleigh .
[ May 24 , an expression whose sign should be changed when is even .
Introducing the values of and in terms of from ( 31 ) , ( 33 ) , we find that ' is proportional to From this it appears that for directions lying in the plane of the ring the radiation vanishes with .
The expression ( 37 ) may also be written or , in terms of , by ( 34 ) , ( 35 ) , ( 39 ) and this whether be odd or even .
The argument of the 's is Along the axis of symmetry the expression ( 39 ) should be independent of .
That this is so is verified when we remember that vanishes except .
The expression ( 39 ) thus vanishes altogether with unless , when it reduces to simply .
* In the neighbourhood of the axis the intensity is of the order In the plane of the ring the general expression reduces to , or It is of interest to consider also the mean value of ( 39 ) reckoned over angular space .
The mean with respect to is evidently By a known formula in Bessel 's functions .
For the present purpose ; and ( 41 ) becomes .
( 43 ) To obtain the mean over angular space we have to multiply this by , and integrate from to .
For this purpose we require an integral which does not seem to have been evaluated .
[ June 20.\mdash ; Reciprocally , plane waves , travelling parallel to the axis of symmetry and incident upon the ring , excite none of the higher modes of vibration .
] 1912 .
] Electrical on a Thin Anchor-Ring .
By a known expansion*we have , .
, whence .
( 45 ) for the integral on the left and thus , ( 46 ) as in ( 15 ) .
Thus the mean value of is , ( 47 ) as before .
In order to express fully the mean value of at distance we have to introduce additional factors from ( 29 ) .
If , and these factors may be taken to be .
The occurrence of the factor , where is , has a strange appearance ; but , as Lamb has shown , is to be expected in such cases as the present , where the vibrations to be found at any time at a greater distance correspond to an earlier vibration at the nucleus .
The calculations just effected afford an independent estimate of the dissipation .
The rate at which energy is propagated outwards away from the sphere of great radius , is , ( 48 ) Gray and Mathews , p. 28 .
' Enc .
Brit " " Wave Theory of Light Equation ( 43 ) , 1888 ; 'Scientific Papers , ' vol. 3 , p. 98 .
' Proc. Math. Soc 1900 , vol. 32 , p. 208 .
Mr. J. J. Manley .
Apparent Change in [ May 29 , , since ( the period ) , the loss of energy in one comoAlete vibration is given by .
( 49 ) With this we have to compare the total energy to be found within the sphere .
The occurrence of the factor is a complication from which we may emancipate ourselves by choosing great in comparison with , but still small enough to justify the omission of , conditions which are Teconcilable when is sufficiently small .
The mean value of at a small distance from the circular axis is .
This is to be multiplied by , and integrated from to a value of comparable with which need not be further specified .
Thus ( 50 ) and , ( o1 ) in agreement with ( 23 ) .
On the Weight during By J. J. , Hon. M.A. Oxon .
, Daubeny Curator , Magdalen College , Oxford .
( Communicated by Prof. J. H. Pointing , F.R.S. Received hIay 29 , \mdash ; Read June 27 , 1912 .
) ( AbstracG .
) In this communication are considered some of the causes which to apparent chances in the total mass of chemically reacting substances .
A short review of the work of and the conclusions drawn by the late Prof. Landolt is first given , and then we deal with the conditions under which one of Landolt 's final experiments was repeated by us .
Next our balance and reaction vessels are briefly described , together with the preliminary treatment to which the latter were subjected prior to their being weighed .
Following this , our first plan for weighing is outlined and then illustrated with the aid of data given in the form of tables and otherwise ; then , by means of an actual : example , the method adopted for calculating final results from our two of preliminary experiments is explained .
|
rspa_1912_0073 | 0950-1207 | On the apparent change in weight during chemical reaction. | 202 | 204 | 1,912 | 87 | Proceedings of the Royal Society of London. Series A, Containing Papers of a Mathematical and Physical Character | J. J. Manley, Hon. M. A. Oxon|Prof. J. H. Poynting, F. R. S. | abstract | 6.0.4 | http://dx.doi.org/10.1098/rspa.1912.0073 | en | rspa | 1,910 | 1,900 | 1,900 | 2 | 47 | 1,320 | http://corpora.clarin-d.uni-saarland.de/surprisal/6.0.3/?id=rspa_1912_0073 | 10.1098/rspa.1912.0073 | null | null | null | Biography | 24.096335 | Biochemistry | 21.497387 | Biography | [
-13.001155853271484,
-44.070194244384766
] | 202 Mr. J. J. Manley .
Apparent Change in [ May 29 , or , since t ( the period ) = Sira/ mY , the loss of energy in one complete vibration is given by e\#163 ; E. r dt 8 7T4a4\amp ; 3g2a2r m2 ( 49 ) With this we have to compare the total energy to be found within the sphere .
The occurrence of the factor e2a*r is a complication from which we may emancipate ourselves by choosing r great in comparison with a , but still small enough to justify the omission of e2a*r , conditions which are reconcilable when e is sufficiently small .
The mean value of P2 + Q2 + R2 at a small distance p from the circular axis is 2 m2/ a2p2.This is to be multiplied by ^nra .Zirpdp , and integrated from e to a value of p comparable with a , which need not be further specified .
Thus E 8 m2rn2 f dp a J P 8m27r2 a loge ; ( 50 ) and dFi .
r E dt in agreement with ( 23 ) .
7r2-{J2m\#151 ; 1 ( 2 m)\#151 ; J2ot+i ( 2m ) } ~'log 6 ( 51 ) On the Apparent Change in Weight during Chemical Reaction .
By J. J. Manley , Hon. M.A. Oxon .
, Daubeny Curator , Magdalen College , Oxford .
( Communicated by Prof. J. H. Poynting , F.R.S. Received May 29 , \#151 ; Read June 27 , 1912 .
) ( Abstract .
) In this communication are considered some of the causes which give rise to apparent changes in the total mass of chemically reacting substances .
A short review of the work of and the conclusions drawn by the late Prof. Landolt is first given , and then we deal with the conditions under which one of Landolt 's final experiments was repeated by us .
Next our balance and reaction vessels are briefly described , together with the preliminary treatment to which the latter were subjected prior to their being weighed .
Following this , our first plan for weighing is outlined and then illustrated with the aid of data given in the form of tables and otherwise ; then , by means of an actual example , the method adopted for calculating final results from our two series of preliminary experiments is explained .
Weight during Chemical Reaction .
1912 .
] 20 ?
After a brief discussion of our first results , we indicate four chief sources of error , and then , for given cases , consider their possible quantitative effects upon the apparent weight of a charged glass vessel .
So far as we are aware , Landolt omitted the consideration of minor errors arising from the possible existence of ( 1 ) air streams within his balance case , and ( 2 ) differences in the superficial areas of his reaction vessels and the consequent possibility of a variation in the relative weights of any water skins upon the same .
Further , from his memoir , it does not appear that any very close attention was paid to effects producible by very slight and varying differences in the temperature of the contents of any pair of his reaction vessels .
For our present purpose these several points are of extreme importance , and accordingly devices were introduced for eliminating and neutralising the errors indicated ; they are here fully described and discussed .
Having directed attention to the probable existence and nature of certain minute but effective errors in Landolt 's experimental work , there are then given some results obtained under the new and improved conditions which are , it is believed , necessary for securing trustworthy values during the most refined weighings .
One of the concluding sections of the paper is devoted to a preliminary consideration of a new and hitherto unsuspected secondary chemical reaction occurring within our reaction vessels .
It is shown that this reaction may be somewhat accelerated by heat and greatly so by light from a " tantalum " lamp ; and it is further shown that as a result of the secondary reaction , which is , under ordinary circumstances , long continued , it was impossible with silver nitrate and ferrous sulphate solutions to reach any definite conclusion in our enquiry .
We then prove that by making use of a quickly terminating and practically perfectly complete chemical reaction , such as that which follows the mixing of solutions of barium chloride and sodium sulphate , decisive results may be secured .
Next we show that by availing ourselves of the now numerous devices and precautions which we have on more than one occasion introduced and advocated , the degree of accuracy in weighing to which Landolt attained and which he affirmed as the limit attainable under his own conditions of weighing , has been increased just fivefold .
Landolt 's estimated limit was + O'Ob mgrm .
; we find ours to be in the case of charged Jena glass vessels equal to + O006 mgrm .
Of the precautions and devices introduced and advocated for use in connection with refined weighings , special attention may be directed to the following :\#151 ; Prof. H. E. Armstrong and Mr. E. H. Podd .
[ June 6 , ( 1 ) The necessity for duly fatiguing the balance beam prior to effecting any final weighing .
( 2 ) The ensuring , by means of an inner and auxiliary case , of a practically perfect uniform temperature throughout the beam of the balance .
( 3 ) The extinction of air streams in the immediate vicinity of the balance pans .
( 4 ) The plan for continuously supplying very dry and carbon-dioxide-free air to the interior of the balance case , with the consequent removal of water skins from any objects that are to be weighed .
( 5 ) The employment of a tilt indicator whereby the horizontality of the balance shelf can , at any time , be almost instantly tested .
Finally , we may state that Landolt found the mean apparent change in mass during chemical reaction to be not greater than 1 in 1 x 107 .
With the aid of our additional devices and precautions we show that in one very fully investigated case in which barium chloride and sodium sulphate were the reacting bodies , the apparent change in mass was not greater than 1 in 1 x 108 .
Morphological Studies of Benzene Derivatives.\#151 ; III .
Para-dibromobenzenesulphonates ( .
) of the " Rare Earth " Elements\#151 ; a means of determining the Directions of Valency in Tervalent Elements .
By Henry E. Armstrong , F.R.S. , and E. H. Rod , B.Sc. ( Received June 6 , \#151 ; Read June 27 , 1912 .
) In a communication on the " Classification of the Elements " brought under the notice of the Society by one of us in 1902 , * a method of ordering the elements was advocated which was different , in essential respects , from that we owe to Mendeleeff , more especially in that it involved the systematic application of a principle dominant in organic chemistry\#151 ; the principle of homology\#151 ; in a manner and to an extent not generally recognised as necessary at that time .
The subject has been further discussed in a recent lecture to the Royal Philosophical Society of Glasgow , f various issues being considered which have been brought into prominence in the meantime\#151 ; e.g. the atomic * 'Roy .
Soc. Proc. , ' 1902 , vol. 70 , p. 86 .
t 'Glasgow Roy .
Phil. Soc. Proc. , ' 1912 ; 'Science Progress , ' 1912 , No. 24 .
I
|
rspa_1912_0074 | 0950-1207 | Morphological studies of Benzene derivatives.\#x2014;III. Paradibromobenzenesulphonates (Isomorphous) of the \#x201C;Rare Earth\#x201D; elements\#x2014;a means of determining the directions of valency in tervalent elements. | 204 | 217 | 1,912 | 87 | Proceedings of the Royal Society of London. Series A, Containing Papers of a Mathematical and Physical Character | Henry E. Armstrong, F. R. S.|E. H. Rodd, B. Sc. | article | 6.0.4 | http://dx.doi.org/10.1098/rspa.1912.0074 | en | rspa | 1,910 | 1,900 | 1,900 | 10 | 207 | 6,180 | http://corpora.clarin-d.uni-saarland.de/surprisal/6.0.3/?id=rspa_1912_0074 | 10.1098/rspa.1912.0074 | null | null | null | Atomic Physics | 38.78002 | Chemistry 2 | 29.724047 | Atomic Physics | [
-5.668052673339844,
-40.76580047607422
] | 204 Prof. H. E. Armstrong and Mr. E. H. Podd .
[ June 6 , ( 1 ) The necessity for duly fatiguing the balance beam prior to effecting any final weighing .
( 2 ) The ensuring , by means of an inner and auxiliary case , of a practically perfect uniform temperature throughout the beam of the balance .
( 3 ) The extinction of air streams in the immediate vicinity of the balance pans .
( 4 ) The plan for continuously supplying very dry and carbon-dioxide-free air to the interior of the balance case , with the consequent removal of water skins from any objects that are to be weighed .
( 5 ) The employment of a tilt indicator whereby the horizontality of the balance shelf can , at any time , be almost instantly tested .
Finally , we may state that Landolt found the mean apparent change in mass during chemical reaction to be not greater than 1 in 1 x 107 .
With the aid of our additional devices and precautions we show that in one very fully investigated case in which barium chloride and sodium sulphate were the reacting bodies , the apparent change in mass was not greater than 1 in 1 x 108 .
Morphological Studies of Benzene Derivatives.\#151 ; III .
Para-dibromobenzenesulphonates ( .
) of the " Rare Earth " Elements\#151 ; a means of determining the Directions of Valency in Tervalent Elements .
By Henry E. Armstrong , F.R.S. , and E. H. Rodd , B.Sc. ( Received June 6 , \#151 ; Read June 27 , 1912 .
) In a communication on the " Classification of the Elements " brought under the notice of the Society by one of us in 1902 , * a method of ordering the elements was advocated which was different , in essential respects , from that we owe to Mendeleeff , more especially in that it involved the systematic application of a principle dominant in organic chemistry\#151 ; the principle of homology\#151 ; in a manner and to an extent not generally recognised as necessary at that time .
The subject has been further discussed in a recent lecture to the Royal Philosophical Society of Glasgow , f various issues being considered which have been brought into prominence in the meantime\#151 ; e.g. the atomic * 'Roy .
Soc. Proc. , ' 1902 , vol. 70 , p. 86 .
t 'Glasgow Roy .
Phil. Soc. Proc. , ' 1912 ; 'Science Progress , ' 1912 , No. 24 .
I Morphological Studies of Benzene Derivatives .
205 .
1H 2 3 4 5 6 7L ; 8 9Be 10 It B 1* C 13 14 N 15 16 o'* !
17 18 19 F 20 *1 *2 *3 Na 24M\#171 ; 25 *6 27 Au *8 Si 29 30 31 P 32 S 33 34 35 Ol 36 37 38 39 K 40 Ca 41 4* 43 Sc 44 48 Ti 49 50 51 V 52 Cn 53 54 55 Mn 56 Ft 60 Cl 62 63 C\#187 ; 65 Zn 66 67 68 69 Ca 70 72 Ge 73 74 75 As 76 77 78 79 80 Bn 8 !
78 8* 83 84 85 Ra 86 79 Sc 87Sn 88 89 90 Yr 91 Zn 02 93 94 96 Na 96 Mo 97 98 99 100 10* Rw 103 Rh 105 106 107 108 Ac 109 ( 107 Po ifaco 113 114 115 In 116 119 Sn 120 1*1 Sb 122 123 124 1*5 1*6 1*7 I 1*8 = 130 131 13* 133 Cs 134 ) 128 Tc 137 8a j i 139 La 140 Cc 141 Pn 144 No 5 llll 150 Sm 15* Eu 157 Go 159 Tb I6*DY = 186 188 168 Er 169 Tu 170 171 17* 173 Ya 174 180 i 181 182 183 Ta 184 W 185 187 19 ] Os 1 193 1a 194 Pt 195 196 197Au 198 *00 Ha *01 *0* *03 204Tl *05 *1* *13 *14 215 207 Pb 208 Bi 209 *10 211 E 220 a*i a** **3 *24 2X6 Ra *28 229 *30 *31 232"Th *34 *35 *36 *37 *38 U 206 Prof. H. E. Armstrong and Mr. E. H. Rod .
[ June 6 , weights of argon and the allied inert elements , the nature of the radioactive , elements and the position of tellurium in the scheme of elements .
An amended table of the elements put forward in the lecture referred to is reproduced on p. 205 .
In this table , most of the elements derived from the so-called rare earths are arranged in a vertical series , as members of a single family , in a manner corresponding with that adopted in the case of homologous organic compounds .
Thus arranged they form the most conspicuous group in the table .
If the plan put forward be in any way permissible , it is obvious that the record of the elements must be far from complete , especially in the family of the rare earths : it is noteworthy that in the case of this family , since 1902 , doubt has been cast upon the existence of several reputed members of the group whilst others have been definitely foreshadowed in their place .
In any case , the group is one in which , more than in almost any other , it is likely that opportunities will occur of " proving " the nature of the relationship between closely allied elements .
It is therefore desirable that the methods of separating the rare earths should be perfected , also that the exact manner in which properties alter throughout the series should be ascertained .
At present our knowledge of the group is remarkably defective in many particulars .
When work was commenced , soon after 1902 , few salts had been examined other than those derived from the inorganic acids and a few simple organic acids ; it was therefore to be expected that many new salts characterised by desirable properties might be found .
As sulphonic acids have the advantage of being strong acids and it is possible to find among them acids giving salts of every degree of solubility , it was decided to make systematic use of such acids .
It was also decided to study the behaviour of the salts at various temperatures .
It is customary in separating substances by fractional crystallisation to allow more or less concentrated solutions to cool to the atmospheric temperature , so that crystallisation takes place finally at this temperature .
Bearing in mind the fact that hydrated salts often undergo changes in the degree of hydration on heating , it is to be expected that , by effecting crystallisation at definite temperatures above the transition temperature , it may be possible , in some cases , to establish differences greater than those the salts present at ordinary temperatures and , in this way , to effect separations otherwise difficult to secure .
For various reasons one of the acids first used was paradibromobenzene-sulphonic acid .
The didymium salt prepared from this acid separated from a hot concentrated solution , when this was allowed to cool to atmospheric 1912 .
] Morphological Studies of Benzene Derivatives .
temperature , in ill defined , faintly coloured , striated prisms containing a high proportion of water ; when , however , the magma was maintained at about 37 ' during a day or so , the pale striated crystals were converted into more deeply coloured , massive , beautifully defined prisms of a less hydrated salt .
The inquiry was laid aside until recently on account of the pressure of other work and especially because of the difficulty of obtaining the various earths in a purified state .
Meanwhile Holmberg* has published an account of a number of sulphonates of rare earth elements from which it is clear that sulphonic acids are likely to be of special value in separating these elements .
It is pointed out in the first of these studiesf that an inquiry , commenced about 20 years ago by one of us , carried on in the hope that it would be possible to correlate crystalline form eventually with internal molecular structure had been successful in that it was possible to discuss the data from the point of view of the remarkable and comprehensive theory introduced by Barlow and Pope .
It was shown in the second communication of the series* that the measurements recorded of a large number of derivatives of benzenesulphonie acid could all be interpreted with the aid of the theory , clear proof being given that it was possible to demonstrate the existence of a benzene framework in the molecules of the compounds examined .
In view of this result , it was desirable that metallic salts of the acids studied should be examined crystallographically : the crystallographic character of the framework of the acid being known , it was not improbable that it would be possible to draw useful conclusions from the crystalline form as to the disposition of the metal and also of water of crystallisation in the salt .
We have therefore resumed the study of sulphonates of the rare earth metals for the reasons given above and also because of the special opportunity these elements afford of investigating the relationship between a series of closely allied metals which , on various grounds , are of particular interest .
he results we have obtained are noteworthy in several respects .
Lanthanum , neodymium , praseodymium and cerium form paradibromo-benzenesulphonates of the formula ( C6H3Br3-S03)a(La , Nd , Pr , Ce),18Ha0 when crystallised from water at ordinary room temperatures .
The crystals are monosymmetric but unfortunately they are not measure-able : apparently , the four salts are isomorphous .
At 35'\#151 ; 37 ' they pass * 'Chem .
Soc. Journ. , ' 1907 , Abs .
II , p. 90 .
t 'Chem .
Soc. Trans./ 1910 , vol. 97 , pp. 1580\#151 ; 1584 .
X 'Chem .
Soc. Trans./ 1910 , vol. 97 , pp. 1585\#151 ; 1605 .
Prof. H. E. Armstrong and Mr. E. H. Rod .
[ June 6 , over into less hydrated salts containing nine molecular proportions of water , which crystallise in very beautiful orthorhombic prisms ; these four salts are closely isomorphous , the cerium salt , as might be expected , differing more from the others than these do among themselves:\#151 ; a. b. c. La ... ... ... ... 1-3965 : 1 : 0-8753 m ... ... ... ... .
1-3990 : 1 : 0-8789 Pr ... ... ... ... 1-3964 : 1 : 0*8798 Ce ... ... ... ... 1-4106 : 1 : 0-8873 In the case of samarium , only the hydrate containing 18H20 has been obtained as yet ; this apparently is isomorphous with the corresponding salts of the other four metals .
Judging from the few not very satisfactory measurements that have been made , the crystals are monosymmetric , the dimensions indicating a close approximation to orthorhombic symmetry .
Two hydrates of the gadolinium salt have been obtained : the higher of these contains only 12H20 , the lower the abnormal proportion 7H20.* Both hydrates crystallise out from the solution together at 37 ' ; at 50 ' only the lower hydrate is obtained .
It is therefore obvious that as the atomic weight of the metal increases peculiarities become manifest which are not noticeable in the case of the lower terms of the series .
We have not had sufficient material at our disposal to complete the determination of the solubility relationships of the various salts but have ascertained , in the case of neo- and praseo-dymium , that it is possible to extend the solubility curve of each hydrate many degrees beyond the transition temperature ; on this account the conversion of the higher into the well defined lower hydrate can be effected within a reasonable time only by raising the temperature considerably above the transition point .
This subject will be discussed fully in a later communication .
We are now studying salts formed from a considerable number of sulphonic acids in order to ascertain the manner in which degree of hydration at various temperatures and crystalline form are influenced by variations of the structure of the acid .
We may mention here that the paradiiodobenzene-sulphonates are very sparingly soluble salts .
Crystallographic Data .
The salts examined were prepared usually by neutralising the acid with the sesquioxide ; when praseodymia containing peroxide is dissolved , * Holmberg has obtained samarium and gadolinium metanitrobenzenesulphonates containing 7HsO ; the majority of the benzenesulphonates he prepared contained either 9H20 or 6H20 .
1912 .
] Morphological Studies of Benzene Derivatives .
209 oxygen is evolved .
The only case in which we experienced any difficulty was in preparing the cerium salt from the dioxide ; this is slowly dissolved and reduced when digested with the sulphonic acid and hydrogen peroxide but the method is unsatisfactory and the cerous salt is perhaps contaminated with ceric salt .
Neodymium Paradibromobenzenesulphonate , Nd(C6H3Br2S03)3,18H20.\#151 ; This hydrate is formed when a hot saturated solution of the salt is cooled or when a solution is allowed to evaporate spontaneously .
It separates in bunches of pale pink prisms which have not yet been obtained in form suitable for goniometric examination .
When viewed under ' the polarising microscope , the prisms show extinctions parallel with their length and they appear to be monosymmetrie .
Water : Found 22*41 ; calculated 22*93 per cent. Nd(C\#171 ; H3Br2S03)3,9H20.\#151 ; When a mass of crystals of the above hydrate is maintained in contact with the saturated solution at about 37 ' C. , the ill-defined forms change into massive amethystine prisms such as are depicted in fig. 1 .
The water of crystallisation is lost below 180 ' 0 .
Water : Found 12*58 ; calculated 12*95 per cent. The prisms belong to the orthorhombic system .
The forms observed were { 100 } , { 301 } , { 102 } , { 110 } , { 120 } and { 010 } .
The faces in the zone [ 100\#151 ; 010 ] are badly developed usually and excepting those of { 100 } are much striated in the direction of the c axis .
The form { 120 } has sometimes given very good reflections , but { 010 } is always bad .
The crystals generally grow on the form { 010 } , sometimes on { 100 } .
The cleavage is perfect parallel to { 100 } but indifferent in the direction perpendicular to the c axis .
Axial ratios : a:b:c \#151 ; 1*3990:1 : 0*8789 .
Prof. H. E. Armstrong and Mr. E. H. Rod .
[ June 6 , The following angular measurements were made:\#151 ; Angle .
No. of observations .
Limits .
Mean observed .
Calculated .
100 : 301 25 46 ' 11'\#151 ; 47 ' 0 ' % 42 ' 301 : : 102 25 25 10\#151 ; 26 1 25 41 25 ' 52 ' 102 : : 102 10 34 51 \#151 ; 35 18 35 7 34 52 100 : : 110 15 53 55\#151 ; 54 58 54 24 54 27 110 : : 120 15 15 44\#151 ; 16 3 15 55 15 53 100 : : 120 17 70 13 \#151 ; 70 30 70 20 \#151 ; 120 : : 120 9 39 17\#151 ; 39 24 39 21 39 20 120 : : 301 12 76 24\#151 ; 76 57 76 39 76 39 301 : : 120 12 102 55 \#151 ; 103 35 103 20 103 21 010 : : 301 2 89 57\#151 ; 90 0 89 58* 90 0 301 : : 010 2 90 1\#151 ; 90 3 90 2 90 * 0 Praseodymium Paradibromobenzenesxdphonate , Pr(C6H3Br2S03)3,18H20.\#151 ; This salt corresponds in all respects with that of neodymium , excepting that it has a pale green colour .
Water : Found 22*68 ; calculated 22*93 per cent. Pr(C6H3Br2S03)3,9H20.\#151 ; Except that it has a pronounced green colour , this hydrate is exactly similar to the corresponding hydrate of the neodymium salt .
System : orthorhombic .
Forms observed:\#151 ; { 100 } , { 301 } , { 102 } , { 110 } , { 120 } and { 010 } .
Water : Found 12*65 ; calculated 12*98 per cent. Axial ratios : a:b:c ==1*3964:1 : 0*8798 .
The following angular measurements were made :\#151 ; Angle .
No. of observations .
Limits .
Mean observed .
1 Calculated .
100 : 301 32 46\#174 ; 10'\#151 ; 47 ' 5 ' 46 ' 37 ' r 301:102 15 25 31 \#151 ; 26 26 25 48 25 ' 54 ' 102 :102 6 34 35\#151 ; 35 23 34 56 34 58 100:120 15 70 9\#151 ; 70 29 70 18 \#151 ; 120:120 3 39 14\#151 ; 39 33 39 23 39 24 100:110 3 54 24\#151 ; 54 29 54 26 54 24 110:120 3 15 49 - 15 56 15 51 15 54 120:010 2 19 34\#151 ; 19 40 19 37 19 42 120 : 301 11 76 24\#151 ; 76 49 76 39 !
76 40 301:120 10 103 6 \#151 ; 103 36 103 21 103 20 Lanthanum Paradibromobenzenesulphonate , La(C6H3Br2S03)3 , l8H20.\#151 ; This hydrate appears to be isomorphous with the corresponding salts of neo-and praseo-dymium ; like these salts , it effloresces when exposed to the air .
Water : Found 22*73 ; calculated 23*03 per cent. La(C6H3Br2S03)3,9H20.\#151 ; The crystals of this hydrate are very closely Morphological Studies of Benzene Derivatives .
isomorphous with those of the corresponding neo- and praseo-dymium salt , though the habit of development is generally slightly different from that of the other two ( fig. 2 ) .
The forms are the same , excepting that { 010 } rarely appears .
1IO * I O O Fig. 2 .
Fig. 3 .
Water : Found 12*95 ; calculated 13*0 per cent. System : orthorhombic .
Axial ratios : a : b : c \#151 ; 1*3965 :1 : 0*8753 .
The following angular measurements were made:\#151 ; Angle .
| No. of observations .
Limits .
Mean obsorved .
Calculated .
100 : 301 43 46 ' 32'\#151 ; 47 ' 3 ' 46 ' 46 ' 301 ; 102 23 25 32\#151 ; 26 5 25 48 25 ' 50 ' 102 :102 8 34 35\#151 ; 35 5 34 52 34 48 100 : 110 15 54 5\#151 ; 54 36 54 21 54 24 110 :120 9 15 41\#151 ; 16 7 15 55 15 54 100 :120 27 69 55\#151 ; 70 35 70 18 \#151 ; 120 :120 6 39 14\#151 ; 39 28 39 22 39 24 120 : 301 8 76 31\#151 ; 76 53 76 40\#163 ; 76 39 301 : 120 7 103 5\#151 ; 103 26 103 19 103 21 Cerium Paradibromobenzenesulphonate.\#151 ; Two hydrates of the cerium salt have been obtained containing respectively 18 and 9 molecules of water of Prof. H. E. Armstrong and Mr. E. H. Rod .
[ June 6 , v * crystallisation ; the latter was found to be closely isomorphous with the corresponding Nd , Pr , and La salts but as the purity of the salt is doubtful , the measurements are not quoted .
Gadolinium Paradibromobenzenesulphonate.\#151 ; By crystallising this salt at different temperatures , two different hydrates have been obtained , one separating at 25 ' with 12 molecular proportions of water , the other at 50 ' with seven ; at 37 ' both hydrates crystallised out together .
Gd(C6H3Br2S03)3,12H20.\#151 ; This hydrate crystallises in the form of fairly large , well-developed rhombs belonging to the monosymmetric system ( fig. 3 ) .
The salt effloresces very slowly in air at ordinary temperatures .
Water : Found 1644 ; calculated 16*39 per cent. The crystals are rhombic plates , the most prominent form being { 010 } ; other forms present are { 110 } , { Oil } , { 101 } and occasionally { 130 } .
No definite cleavage was detected .
System : Monosymmetric .
Axial ratios : 0*5952:1 : 0*3817 .
/ 3 = 76 ' 48 ' .
The following angular measurements were made:\#151 ; Angle .
No. of observations .
Limits .
Mean observed .
Calculated .
010 :011 15 69 ' 29'\#151 ; 70 ' 1 ' 69 ' 37 ' Oil : Oil 6 40 32\#151 ; 40 42 40 39 40 ' 46 ' 010:110 15 59 11\#151 ; 60 18 59 50 59 55 110:110 7 60 2\#151 ; 60 50 60 26 60 10 110:011 11 68 45 \#151 ; 69 7 68 56 \#151 ; Oil : 101 6 40 44 \#151 ; 40 57 40 48 : 40 51 101 :110 7 70 8\#151 ; 70 19 70 13 \#151 ; 010 : 101 4 89 55 \#151 ; 90 5 90 0 90 0 110 : Oil 6 89 22\#151 ; 89 29 89 25 89 28 Oil : 110 6 90 28 \#151 ; 90 40 90 35 90 32 Gd(C6H3Br2SO3)3,7H20.\#151 ; Three estimations of water in this salt gave 9*88 , 9*95 , 9*97 per cent , of water , the mean of these corresponding to 6*75 molecular proportions ; therefore the salt is probably the heptahydrate .
It forms very massive crystals ; when seen beside the colourless duodeca-hydrate , these appear to have a yellow tinge .
The crystals belong to the monosymmetric system but the forms developed do not allow of a complete determination being made of the axial ratios .
Samarium Paradibromobenzenesulphonate.\#151 ; The only hydrate of this salt prepared contains 18 molecules of water .
Water : Found 22*85 ; calculated 22*83 per cent. .
This salt is probably isomorphous with the corresponding hydrates of the Pr , Nd , La and Ce salts but has not been obtained in crystals good enough 1912 .
] Morphological Studies of Benzene Derivatives .
for goniometric measurement .
It separates in pale straw-coloured prisms , which effloresce rapidly in air .
Discussion of Results , On inspecting the series of axial ratios several facts of interest appear .
System .
a : b : Nd(C\#171 ; H3BiyS03)3 , 9H20 ... Orthorhombic ... 1-3990 : 1 : 0-8789 Pr \#187 ; . . .
\#187 ; . . .
1-3964 : 1 : 0-8798 La " .
) ) . . .
1-3965 : 1 : 0-8753 Ce . . . . . .
1-4106 : 1 : 0*8873 Gd 12H20 ... , Monosymmetric 0-5952 : 1 : 0-3817 , \amp ; = 76 ' The relationship between the three salts of Nd , Pr and La , as indicated by the approximate equality of the axial ratios of the crystalline substances , is much closer than is ordinarily observed between members of an orthorhombic isomorphous series ; a further indication is thus afforded of the correctness of the view that the metallic elements concerned form a very closely related group of the kind contemplated in the modified periodic table now given .
The axial ratios of the cerium salt diverge somewhat from those of the other salts , probably owing to the material being impure ; the axial ratios of the Nd , Pr and La salts are , however , identical within the limits of error of measurement .
It is next to be observed that the number 3 is frequently involved in connexion with the compositions of the orthorhombic salts ; these contain in the molecule 3 phenyl groups ( 3x3x2 atoms of carbon ) , 3 sul-phonic groups , each containing 3 atoms of sulphur and 3x3 atoms of sulphonic oxygen , 3x3 molecules of water , etc. , whilst the metallic atom has a valency of 3 .
The gadolinium salt is of lower crystalline symmetry and , at the same time , the frequency of repetition of the factor 3 in the composition is less marked in that the salt contains 3x4 molecules of water in place of 3 x 3 molecules ; the sums of the valency units in the molecular units , 150 and 162 , are also multiples of 3 .
The present is thus a suitable case to which to apply the conclusion drawn from the work of Barlow and Pope that the frequent repetition of the factor 3 in the manner indicated should lead to the presence in the crystal structure of a trigonal or pseudo-trigonal axis of symmetry.* The presence of a trigonal axis of symmetry involves the presence of a value 1 : v/ 3/ 2 = 1 : 0*8660 , amongst the axial ratios , if the crystal structure under discussion be referred to a rectangular system of co-ordinates ; the * Compare Jerusalem , 'Chem .
Soc. Trans. , ' 1910 , vol. 97 , p. 2190 .
Prof. H. E. Armstrong and Mr. E. H. Rod .
[ June 6 , presence of a pseudo-trigonal axis is revealed by the presence of a ratio approximating to the above value amongst axial ratios obtained by reference to approximately rectangular co-ordinates .
Since , in the orthorhombic series now described , the axial ratio , c:b , in each case approximates to the value quoted , it is clear that the axial direction a is that of a pseudo-trigonal axis .
Similarly , in the monosymmetric gadolinium salt , the axial direction c is that of a pseudo-trigonal axis , because the axial ratio b:a = 1-6801 : 1 = 2x0-8400:1 again involves a quantity approximating to ^/ 3/ 2 .
If , in the latter case , the axis c were truly trigonal , the angles in the zone [ 010:110 ] should all be 60 ' ; actually they have the values 60 ' 10 ' and 59 ' 55 ' , so that no doubt can exist concerning the pseudo-trigonal nature of the axis in question .
In discussing the crystalline structure of benzene derivatives , Barlow and Pope showed that one particular class of such substances could be represented as derived from a cubic closest packed homogeneous assemblage and that the derived assemblages should possess , in the ideal condition , a trigonal axis of symmetry .
On referring the assemblages in question to a rectangular axial system in which the axis c is the trigonal axis , the ratio of the other two , say a and b , should be , a:b = 1 : ^3/ 2 = 1 : 0*8660 ; further , on calculating the equivalence parameters , and of a substance of this class , it should be found that whilst : = 1:0-8660 = the third parameter , z , should have a somewhat lower value than z = 2-780 , the value calculated for crystalline benzene itself .
In order to exemplify these somewhat complex numerical relationships the case of y\gt ; -diiodobenzene may be quoted ; this substance is orthorhombic and the axial ratios of the crystals are 0*4342 : 1 : 0*3653 .
On dividing unit length along the axis b by two , the axis c is revealed as a pseudo-trigonal axis , because the axial ratios become a : b : c =\#166 ; 0*8684 : 1 : 0*7306 and the ratio a/ b is nearly .y/ 3/ 2 = 0*8660 .
Since c is the pseudo-trigonal axis , the equivalence parameter , z , corresponding to this direction , should be rather less than 2*780 , the value for benzene .
The sum of the valencies in the molecule is W = 30 and the equivalence parameters are x :y:z \#151 ; 3*1402 : 3*6161 : 2*6419 , The specified conditions are thus all fulfilled.* The markedly pseudo-trigonal character of the neodymium , praseodymium , lanthanum and cerium salts now described , the axis a being the pseudo* Barlow and Pope , 'Trans .
Cbem .
Soc. , ' 1906 , vol. 89 , p. 1702 .
1912 .
] Morphological Studies of Benzene Derivatives .
trigonal axis , indicates that the crystal structure is derived from the benzene structure of cubic origin typified by p-diiodobenzene ; the manner in which the salts are derived from this compound consisting in the opening out of the zigzag columns of atomic domains representing carbon atoms in the assemblage depicted by Barlow and Pope* to a sufficient extent to allow of the insertion , in homogeneous close-packing , of the domains representing the substituting groups in the salts .
Inasmuch as the structure must necessarily remain pseudo-trigonal in symmetry , the opening-out process must occur to an approximately equal extent in all directions perpendicular to the pseudo-trigonal axis .
The conditions which have been specified above enable a connexion of a far-reaching and quantitative character to be established between the crystalline forms of p-diiodobenzene and of the complex salts now described in the light of the Barlow-Pope theory ; this may be stated as follows :\#151 ; The axial ratios , the equivalence parameters and the valency volume of p-diiodobenzene are taken as , a !
\ V \ c , x ' : y ' : z ' and W ' and the corresponding values for the metallic salts as a " : V ' : c " , a " : y " : z'\ and W " .
W ' = 30 and W " = 150 .
The directions a ' and c " being pseudo-trigonal axes , the following conditions hold in the manner essential to the theory :\#151 ; a ' : V = 0 8684 : 1 , c " : 5 " = 0-8789 : 1 , : 1 = 0-8660 approx. Further , c ' : 6 ' = 0*7306 : 1 = 1 : 1-3687 , 5 " : = 1 : 1-3990 approx. The close correspondence between the theoretical equalities just stated affords convincing proof of the existence of the quantitative relationship which the theory indicates between p-diiodobenzene and the salts now described .
It remains to find simple multiples of the axial ratios of the orthorhombic salts which lead to the calculation of equivalence parameters such that the value of x " for the salts is approximately equal to the value z ' \#151 ; 2*6419 for p-diiodobenzene ; this last condition is fulfilled by taking a"/ 3 and 2c " .
The equivalence parameters then assume the following values :\#151 ; W. x " .
z " .
Nd(C6H3Br2S03)3,9H20 150 2-6475 : 5-6773 9-9796 Pr A A \#187 ; \#187 ; .
150 2-6434 : 5-6788 9-9925 \gt ; \gt ; )y . .
150 2-6480 : 5'6885 9-9582 Ce " " 150 2-6537 : 5-6438 10-0154 * Figs. 7 to 9 , loc. cit. VOL. LXXXVII.\#151 ; A. Q Morphological Studies of Benzene Derivatives .
The requisite correspondence between the value for diiodobenzene , z \#151 ; 2*6419 , and the mean value of x"for the first three salts which have been accurately measured , namely x " = 2*646 , is quantitatively complete to within about one part in one thousand .
It is now necessary to find simple fractions of the axial ratios for the gadolinium salt , a : b:c = 0*5952 :1 : 0*3817 , / 3 = 76 ' 48 ' , such that the equivalence parameter measured in the direction of the pseudo-trigonal axis c has the same value as the parameter z ' \#151 ; 2*6419 for diiodobenzene and x ' = 2*646 for the three orthorhombic salts ; all the other conditions specified in connexion with these latter salts are fulfilled .
On calculating the equivalence parameters of the gadolinium salt , taking 2c/ 3 , the following values are obtained : / 3 = 76 ' 48 ' , W. x. y. z. Gd(C6H3Br2.S03)3,12H20 . .
162 6*1415 : 10*3185 : 2*6257 .
In this case also the parameter z is identical within very narrow limits with the z value for diiodobenzene .
The mass of quantitative correspondence which has now been adduced between the crystal structure assigned to ^\gt ; -diiodobenzene and that possessed by the pseudo-trigonal salts now described , is a conclusive demonstration that we are in possession of a very powerful method of correlating crystalline form with chemical composition and constitution .
The crystal structure of the metallic salts under discussion must be regarded as one in which the zigzag columns of carbon domains depicted in the diagrams referred to remain intact but are merely pushed apart so as to allow of the introduction of the substituting groups by means of which the salts are derived from benzene.* Under these conditions the plane ( 100 ) perpendicular to the pseudo-trigonal axis a in the orthorhombic salts should exhibit differentiating physical properties because it is the plane which separates layers of aggregated molecules of the salt ; in accordance with this it is observed that ( 100 ) is a plane of perfect cleavage in the crystals .
One other conclusion of importance remains to be mentioned .
Hitherto it has been possible to determine the directions in which valency acts only in the case of carbon and the allied quadrivalent elements , the method used being one which involves the application of geometrical and optical but not of crystallographic considerations .
The proof arrived at in this communication , by a crystallographic method , that the three directions of valency in the tervalent elements La , Nd , Ce , Pr , Sm , Gd are symmetrically disposed , the metal occupying the central position in a plane containing three benzene groups , is therefore of special interest , as the first example of a novel method * Loc .
citp .
1700 .
Series Involving the Fourier Constants of a Function .
217 of determining the directions in which valency acts .
It is well known that this is a problem which has attracted much attention of late years in the case of nitrogen .
We are now studying the salts of tervalent metals generally , in order to ascertain if the method be applicable to all such elements : it is proposed also to apply the method to the elements of the nitrogen group .
In conclusion , we cannot refrain from calling attention explicitly to the proof that is again given of the service crystallography can render to chemistry and of the value of the Barlow-Pope theory as a means of correlating external form with internal molecular structure .
O71 the Convergence of Certain Series Involving the Fourier Constants of a Function .
By Prof. W. H. Young , Sc. D. , F.RS .
( Received May 16 , \#151 ; Read June 13 , 1912 .
) S1 .
In a paper " On the Fourier Constants of a Function , " published in the ' Proceedings ' of this Society , * I showed how certain theorems , previously given by myself , might be employed to obtain formulae for the sums of certain series involving the Fourier constants of a function .
In the case in which the function is bounded , it was only proved that the formulaef hold whenever the series converge , or , more generally , when the summation is performed in the Cesaro manner ( index unity ) .
In a more recent paper , also published in the ' Proceedings ' of this Society , !
" On a Mode of Generating Fourier Series , " I showed incidentally that the formulae are still applicable when the function has every power of index less than 1 +p summable , provided only the index q , which occurs in the formulae in question , is greater than 1/ ( 1 +p)\gt ; Here again the theorem , as stated , contained the restriction that the summation was to be made in the Cesaro way .
The main object of the papers in question was , in fact , to explain how certain methods might be employed , and these methods were in themselves inadequate for the purpose of removing the restriction .
The theorems used involve the general theory of the integration of the Fourier series of * 1911 , A , vol. 85 , pp. 14\#151 ; 24 .
t Loc .
cit. , S 4 .
t 19H , A , vol. 85 , p. 422 .
|
rspa_1912_0075 | 0950-1207 | On the convergence of certain series involving the fourier constants of a function. | 217 | 224 | 1,912 | 87 | Proceedings of the Royal Society of London. Series A, Containing Papers of a Mathematical and Physical Character | Prof. W. H. Young, Sc. D., F. R. S. | article | 6.0.4 | http://dx.doi.org/10.1098/rspa.1912.0075 | en | rspa | 1,910 | 1,900 | 1,900 | 4 | 106 | 2,714 | http://corpora.clarin-d.uni-saarland.de/surprisal/6.0.3/?id=rspa_1912_0075 | 10.1098/rspa.1912.0075 | null | null | null | Formulae | 79.398673 | Tables | 14.690214 | Mathematics | [
71.10370635986328,
-47.56830596923828
] | ]\gt ; Series the ojFunctio .
217 of the directions in which valency acts .
It is well known that this is a problem which has attracted much at , tention of late in the case of nitrogen .
We are studying the salts of tervalent metals generally , in order to ascertain if the method be applicable to all such elements : it is proposed also to apply the method to the elements of the nitrogen group .
In conclusion , we cannot refrain from calling attention explicitly to the proof that is again given of the service raphy can render to chemistry and of the value of the Barlow-Pope theory as a means of correlating external form with internal molecular structure .
On the Convergence of Certain Series the of a Function .
By Prof. W. H. YOUNG , Sc. D. , F.E.S. ( Received May 16 , \mdash ; Read June 13 , 1912 .
) S1 .
In a paper " " On the Fourier Constants of a Function published in the 'Proceedings ' of this Society , * I showed how certain theorems , previously given by myself , might be employed to obtain formulae the sums of certain series involving the Fourier constants of a function .
In the case in which the function is bounded , it was only proved that the formulae hold wheuever the series converge , or , more generally , when the summation is performed in the Cesaro nlanner ( index unity ) .
In a more recent paper , also published in the 'Proceedings ' of this Society , " " On a Mode of Generating Fourier Series I showed incidentally that the formulae are still applicable when the function has every power of index less than su1llmable , provided only the index , which occurs in the formulae in question , is greater than .
Here again the theorem , as stated , contained the restriction that the summation was to be made in the way .
The main object of the papers in question was , in fact , to explain how certain methods might be employed , and these methods in themselves inadequate for the purpo removing the restriction .
The theorems used involve the ) eneral theory of the integration of the Fourier series of vol. , S4 .
1911 , , vol. 85 , p. 422 .
218 Prof. W. H. Young .
The Convergence of Certain [ May16 , function term-by-term , when multiplied by another function .
The coefficient in the series and considered , is , however , itself the typical Fourier constant both of an odd and an even function , which may be expected to possess special properties bearing on the matter in hand .
A careful scrutiny of these properties has accordingly enabled me to take the step of removing the restriction above explained .
The former of the main results , above stated , may be otherwise expressed by saying that , though the Fourier series of a mded function need not converge , even if the function be continuous , it , and its allied series , will be made to converge , by dividing its coefficients by any power , however small , of the index denoting their respective places in the series .
This affords a convenient necessary test that a given series is the Fourier series of a bounded function .
In the same have a corresponding necessary condition that a Fourier series should have a function whose power is sulnmable for associated function .
It is worth hat in all these statements the function whose Fourier series is considered need not be homogeneous in character .
They still hold if the function be only summable , except in a fixed interval con the origin .
The paper terminates with a comparison of the result of the present paper a function whose power is summable , and one deducible from a theorem given in my paper , " " On the Mode of Generating Fourier Series From the theorem in question it , in fact , may be shown that the series whose general terms are and converge absolutely , when It should finally be remarked that the interesting question arises as to how the coefficient may be replaced in the theorems of the present paper and its predecessors by a coefficient of a more general nature .
This question is too large a one to be dealt with in the present communication .
S 2 .
We with the following general theorem:\mdash ; 1.heorem.\mdash ; The succession of the partial summations of the series nx , , 'is bounded below , whatever fixed positive value be ascribed to .
The is true of the , where , is any monotone descending with zero as limit .
Let denote the partial summation of the latter series , which includes the former as a special case .
Then 1912 .
] Series Involving the Fourier of Function .
219 where Hence Here every term except the first is positive , since , and the q 's form a positive monotone decreasing sequence .
Thus and , therefore , in the interval . .
( 1 ) Again where Thus 2 .
( 2 ) Since each term on the after the first is positive and therefore , in the interval , .
( 3 ) From ( 1 ) and ( 3 ) it follows that , in the interval , since , which proves the theorem .
Cor.\mdash ; The partial summations of the series all positive , provided form a monotone sequence with zero as limit .
The proof then stops at ( 1 ) , which holds for It is easily seen from ( 2 ) that the partial summations are also bounded above in the right-hand half of the interval .
This is , however , obvious from the well-known fact that series of the form as well as those of the form , when the 's form a monotone descending sequence with zero as limit , converge.uniformly in every closed interval not containing the origin .
This follows immediately by the use of Abel 's Lemma .
Since the series is a sine series , it immediately follows that , in the interval , the partial summations of the series are bounded above , and are negative if , , are S3 .
The preceding result permits us to prove the following theorem:\mdash ; Theorem.\mdash ; If is any bounded function , whose Fourier sine constants are then the series 220 Prof W. H. Young .
Convergence of [ May 16 , to rrhpre the of the Moreover , the , afler ?
liach ternb by be integrated ter/ 7b-by-ter7/ b any interval or of points .
It is evidently only necessary to prove the latter statement , from which the former statement imnlediately follows , choosing for the interval of ration the whole interval .
Since the series is an ordinary Fourier series , the integrated series to a Lebesgue integral , *whose integrand is the metion to the Fourier series , that is , since the Fourier series everywhere .
In other words , the Fourier series in question is capable of term-by-term integration .
Again , by the preceding theorem , the partial summations of this Fourier series are bounded below in the closed interval , and bounded above in the closed inlerval Now has proved that , if the partial summations of a series of functions are mded either below or above in any interval , the necessary and sufficient conditions that the series should be capable of term-by-term ation are ( a ) that the series should converge , that the double limit Therefore , denoting the partial summation of the Fourier series , the preceding double limit is zero , and therefore , being a bounded function , The series is therefore , by theorem of Vitali already quoted , integrable term by term , since converges to .
Moleover , by a further theorem of Vitali 's , S this series is absolutely See W. H. Young , " " On the Conditions that a Trigonometrical Series should have the Fourier Form ' Lond. Math. Soc. Proc 1910 , Series 2 , vol. 9 , p. 423 .
G. Vitali , " " Sull ' Iutegrazione per Serie ' Rend .
di Palermo , ' 190 vol. 23 , pp. 137\mdash ; 155 ; see , in particular , S 9 .
The of the theorem used above is that given to it in my paper " " On Semi-integrals and Oscillating Successions of Functions 'Lond .
Math. Soc. Proc 1910 , Series 2 , vol. 9 , pp. 286\mdash ; 324 ; see SS 23 , 24 , and 26 .
An exceptional set of content zero of course makes no difference .
S .
cit. , SS1 , 6 , and 7 .
This theorem , as well as the otl1er , is included in the articles quoted from " " Semi-integrals.\ldquo ; 1912 .
] Series Invohing the Fourier Constants of Functvon .
221 integrable , that is to say , the statement made in the enunciation of the present theorem is true .
This proves the theorem .
S4 .
To prove the statement for the coefficients of the cosine terms , we have to show that vanishes , denoting the n-th partial summation .
For this purpose we shall require the lemma : Lemma.\mdash ; The function sin , as well as , satisfies inequalities of the form , where and depend on.on is an consequence of the fact that , since is periodic and is monotone , the function , that is , is a bounded continuous function , whose greatest and least values are situated in the interval .
S5 .
In with the sine series we proved that the partial summations are all greater than a certain } ative quantity on the right of the origin , and less than a certain positive quantity on the left .
It was unnecessary to examine whether the partial summations were as a mattel of fact positive , as is known*to be the case when is unity .
In dealing with the cosine series I shall again prove a result hoc , and shall not examine whether , as is the case when is unity , the partial summations are all reater than a certain negative finite quantity .
It is sufficient in fact for our purpose to show that they are all greater than a certain negative summable function .
Theorem.\mdash ; The partial nnmaiions of the sljries all greater tharb , where A is a negative constant only Writing for the n-th partial summation of this series , we have 2 siu S where the partial summation has been shown in S2 to be positive , .
Therefore , using the preceding lemma , * Dunham Jackson , " " Ueber eine trigonometrische Sum 'Rend .
di Palermo , ' 1912 , vol. 32 , pp. 257\mdash ; 263 .
See a forthcoming paper by myself , ' On a Certain Series of Fourier presented to the London Mathematical Society .
222 Prof W. H. Young .
The vergence of [ May 16 , which proves the theorem , since S6 .
We now proceed to apply the preceding result to the series whose general term is , where is the typical Fourier cosine constant of a bounded function .
Theorem.\mdash ; If is bounded nction , whose ourier cosine constants , then the series , converges to where is the sum of the Fourier series Moreover the latter series , after multiplying each term by , may integrated -by-term over any interval or set of points .
For , by the preceding theorem , and the integral of this function converges to .
Therefore , as in S3 , and therefore , since is summable , Hence , as in S3 , the required results follow .
S7 .
We now pass to the case in which has its power summable .
We may , if we please , use the lemma of S4 once more , and write S where is and depends only on .
This partial summation is less than a finite quantity independent of , provided , since is of the order .
Hence for such values of and , therefore , for all values of , that is for all values of Sx has its power summable ; moreover , 1912 .
] Series Involving the Fourier of Function .
223 , But sinpe , by So , whence , since* we have Writing , we have Hence , finally , if denote the partial summation of the series , then for all positive values of such that , we have S8 .
From last result it at once follows that , if any whose power is summable , and has the meaning of the preceding statement , provided that Henc these cireurnstances , th converges , being the of in the Fourier series of By a method similar to that of the preceding article we may establish a corresponding result for the cosine coefficients of the Fourier series of function whose power is summable , but I shall not give the proof Indeed , my chief object in writing out the proof just given is to further illustrate the usefulness of the lemma of S4 .
If we make use of a result * F. Riesz , " " Untersuchungen uber Systeme integrierbarer Funktionen S 2 , 'Math .
Ann 1910 , vol. 69 , p. 456 .
W. H. Young , " " On Successions of Integrals and Fourier Series S6 Cor. and S 4 Cor. , 'Lond .
Math. Soc. Proc 1912 , Series 2 , vol. 11 , pp. 57 and 52 .
We only have to use the Schwarz-Riesz inequality .
224 Series Involving the Fourier Constants of Function .
already obtained in a previous paper , *namely that the Fourier series obtained by the process in question , and its allied series , have continuous functions for their associated functions , we may dispense with further proof .
If , in fact , be any quantity greater than , we may perform the process of dividing by in two .
We may firstdivide by , where ; we thus get Fourier series of continuous , and therefore bounded , functions .
Then , dividing by , it follows by SS 3 and 6 that the series and converge , when and are Fourier constants of a function whose power is sumnbable , provided S9 .
It will be noticed that , in the case of a function whose power mable , what we have proved is that , if , the series whose genero)terms are and necessarily converge , we have not proved that the convergence is absolute .
In this connection it may be well to point out that one of the simple consequences of the last result obtained in my paper " " On a Mode of Generating Fourier Series\ldquo ; is that the series whose general are converge absolutely the sam circumstances .
This follows , utilising simultaneously the convergence of the series and S10 .
Another consequence of the same theorem may also be mentioned .
If and now denote the Fourier constants of the integral of a function whose power is , we can assert that the series whose general terms and converge , if any value .
In particular , however small may be , the corresponding Fourier series and allied series both converge uniformly and absolutely .
To prove this we have merely to employ the inequality making use of the converging series and , where and writing and for the general terms of these series , being so chosen that .
* W. H. Young , " " On a Mode of Generating Fourier Series 'Roy .
Soc. Proc 1911 , , vol. 85 , p. 421 .
|
rspa_1912_0076 | 0950-1207 | On classes of summable functions and their Fourier Series. | 225 | 229 | 1,912 | 87 | Proceedings of the Royal Society of London. Series A, Containing Papers of a Mathematical and Physical Character | Prof. W. H. Young, Sc. D., F. R. S. | article | 6.0.4 | http://dx.doi.org/10.1098/rspa.1912.0076 | en | rspa | 1,910 | 1,900 | 1,900 | 6 | 65 | 1,854 | http://corpora.clarin-d.uni-saarland.de/surprisal/6.0.3/?id=rspa_1912_0076 | 10.1098/rspa.1912.0076 | null | null | null | Formulae | 77.027009 | Tables | 17.617182 | Mathematics | [
70.91893005371094,
-47.96356201171875
] | ]\gt ; On Classes of Functions and their Four Series .
By Prof. W. H. YOUNG , ( Received May 30 , \mdash ; Read June 27 , 1912 .
) S1 .
Functions which are summable may be such that certain functions of them are themselves summable .
When this is the case they will possess certain special properties additional to those which the mere mability involves .
A remarkable instance where this has been nised is in the case of summable functions whose squares also are .
The\mdash ; in its formal statement almost self-evident\mdash ; Theorem of Parseval which asserts tha6 the sum of the squares of the coefficients of a Fourier series of a function is equal to the of the square of , taken between suitable limits and ultiplied by a suitable constant , has been recognised as true for all functions whose squares are summable .
Moreover , not only has the converse of this been shown to be true , but writers have ) led to develop a whole theory of this class of functions , in connection more especially with what are known as integral equations .
That functions whose power is summable , where , but is not necessarily unity , should next be considered , was , of course , As was to be expected , it was rather the of such functions the functions themselves properties were required .
Lebesgue had already given the necessary and sufficient condition that a function should be an integral of a summable function .
F. Biesz*then showed that the necessary and sufficient condicion that a function should be the integral of a function power is summable had a form which constituted rather the genelalisation of the expression of the fact that such a nnction has bounded variation , than one which included the condition of as a icular case .
S2 .
I myself was led to consider functions in connection with the problem of the integration of Fourier series , and , in a paper published in the ' Proceedings ' of the Society , I have proved that term-by-term integration of the Fourier series of such a function is allowable after it has been multi- plied by a function belonging to the complelllentaty provided only the summation is carried out in the Cesaro manner .
The method I employed in the paper in question has the great ' ' Systeme Integrierbarer Funktionen ' Math. Ann 1910 , vol. 69 , pp. 449\mdash ; 497 .
in the Theory of Fourier Prof. W. H. Young .
On of Summable [ May as regards the details of the work that it is based on an extremely simple inequality .
From this point of view it is far superior to the other methods of proof , almost intuitive as they are , when the necessary preliminary theorems have been proved , that I have indicated elsewhere .
* Instead of requiring the generalisation of Schwarz 's well-known inequality , it suffices to be acquainted with the generalisation of the relation 2 , namely , that In the prosecution of research one is often hampered by the difficulty of generalising a known formula , owing to the very simplicity and obviousness of its statement .
The inequality just written down possesses , however , the great advantage over Schwarz 's inequality that its generalisation is almost immediate .
It is as follows:\mdash ; If a positive monotone increasing function of a positive real variable possessing a differential coefficient is positive , and the inverse function such that , then , ( 1 ) where .
In fact the function of represented by has a negative second differential coefficient , its first differential coefficient vanishes when , that is when .
It has accordingly a maximum whose value is , that is ; or , what is the same thing , .
Hence the inequality in question follows .
S3 .
With this inequality in our minds we may conceive of summable functions grouped in pairs of classes in such a manner that the product of twc functions , one from each dass of such a pair , is summable .
If , for example , we put we see that if and are summable functions of , where and are themselves functions of , then is also a summable function of " " Successions of Integrals and Fourier Series S26 seq. , 'Proc .
L.M.S. , ' 1911 , Series 2 , vol. 11 , pp. 43\mdash ; 95 .
1912 .
] Functions and their Fourier Series .
Moreover we have to retrace the reasoning of SS7 seq. of the paper cited on ' A Class of Parametric Integrals\ldquo ; to see that is a continuous function of , provided and to such a pair of classes of summable functions , and that accordingly we may assert that if we multiply the Fourier series of one of them by the other and intra term by term , the result obtained the integral of the product of the two functio between the limits of integration , provided only we the summation in the Cesdro manner .
In particula , and , denote the typical Fourier constants of two such functions we the summation being formed in the manner .
S4 .
But further we are naturally led , in virtue of the great generality of the theorem just enunciated , to attempt to extend to such new classes of functions the general theory of the functions whose powers are summable .
In particular we require the necessary and sufficient condition that a function should be the function belonging to such a class .
For this purpose it will be found that the inequality is sufficient , ( 2 ) where is the indefinite integral of a positive function whose differential coefficient is positive .
This inequality follows in fact by the theory of integration from the simpler inequality which is obtainable at once by making the right hand side a subject to the condition that should be constant .
We thus obtain the necessary and sufficient condition that a function should be such that , where possesses a positive differential coefficient , is a summable function of that where the integral of , is constant , ) endent of , and of the set of non-overlapping over which the summation is extended .
Prof W. H. Young .
On Classes of Sum [ May 30 , The necessity of the condition is , in fact , an immediate consequence of the inequality ( 2 ) , while its sufficiency follows from reasoning similar to that employed by ] .
Riesz in the special case in which S5 .
The theory of sumnlable functions is interesting from the abstract side from two points of view .
As compared with the theory of the con .
vergence of series we have the great that necessary and sufficient conditions exist , and can be easily formulated .
Just as , however , given a convergent series , we can always find a series which is less , and one which is more convergent , so , iven any summable , we can find whole classes of functions which are less summable , as well as classes of functions which are more summable .
It would appear , indeed , that , given any summable function , a function exists , of the type considered , such that is also summable .
If this be so , the fact that , if we put , for example , in the condition of F. Biesz , above referred to , and make the substitutions in the various conditions of which the general type has been written down , we get the condition for bounded variation , finds its explanation .
The theory of summable functions is also of intel.est when we are concerned with potency and correspondence , and compare the ensemble of all summable functions with , for example , that of the continuum .
If we were to confine our attention to functions some power of which is summable , 01 rather to the grouping into classes determined such considerations , we should , of course , have -correspondence between the classes and the continuum .
In point of fact , however , we have functions which , for example , have their squares summable , and no higher power ; while we also have functions whose squares are not summable , but which , in a more than continuously infinite manner , have all powers less than the second summable .
S6 .
I do not propose on the present occasion to enter into other generalisations for the wider classes here considered , of the properties of known classes of summable functions .
I may say , however , that the results , for example , iven in the paper by F. iesz , already cited , are readily generalisable , as well as the cognate results of Weyl and others .
To obtain the complete generalisation in the case of certain theorems , if not of the results at least of the methods , employed by these authors , it will be necessary to obtain the most general form for the purpose in hand of the inequality of Schwarz .
The nature of this generalisation may perhaps be inferred from the following special case , which is deducible bylimiting processes from Riesz 's form , or may be proved independently by considerations of maxima and minima:\mdash ; and being positive functions .
1912 .
] Functions and their Series .
In the same connection the following formula will be found of Such inequalities will be found useful for example , in extending the results on Fourier series contained in my paper on " " Successions of and Fourier series S7 .
We thus obtain , for example , theorems of the following type : If denote the -th Cesaro partial sumrnation of the Fouri series of positive function , which ?
such that is denote th -th partial surnmation of the Fourier series of the function , then .
From this also we deduce that , if denote the n-th partial mation of the Fourier series of a function [ which is such that is , then has the double limit ; and that Finally we may remark that from analogous considerations we may establish the truth of the theorem on double successions:\mdash ; If the summations of the first }of the series of two funwtions , belonging to a paiir of classes of summfunctions , such as here sidered , Negative After-Images Successive with Pure Spectral Colours .
By A. W. PORTER , B.Sc. , F.RS .
, and F. W. EORIDGE-GBEEN , , F.R.C.S. ( Received May 28 , \mdash ; Read June 27 , 1912 .
) [ This paper is published in ' Proceedings , ' Series , No. 581 .
] VOL. LXXXVII .
It
|
rspa_1912_0077 | 0950-1207 | Negative after-images and successive contrast with pure spectral colours. | 229 | 229 | 1,912 | 87 | Proceedings of the Royal Society of London. Series A, Containing Papers of a Mathematical and Physical Character | A. W. Porter, B. Sc., F. R. S.|F. W. Edridge-Green, M. D., F. R. C. S. | article | 6.0.4 | http://dx.doi.org/10.1098/rspa.1912.0077 | en | rspa | 1,910 | 1,900 | 1,900 | 2 | 11 | 396 | http://corpora.clarin-d.uni-saarland.de/surprisal/6.0.3/?id=rspa_1912_0077 | 10.1098/rspa.1912.0077 | null | null | null | Formulae | 87.197245 | Optics | 5.917471 | Mathematics | [
71.50076293945312,
-48.532649993896484
] | 1912 .
] Functions and their Fourier Series .
In the same connection the following formula will be found of use :\#151 ; ( uv dx log\uvdx^\uv log J uv log f ua dx .
Such inequalities will be found useful , for example , in extending the results on Fourier series contained in my paper on " Successions of Integral and Fourier series .
" S 7 .
We thus obtain , for example , theorems of the following type:\#151 ; If Sn denote the n-th Cesdro partial summation of the Fourier series of a positive function f(x ) , which is such that f ( x ) log/ pc ) is summable , and Tn denote the n-th Cesdro partial summation of the Fourier series of the function f ( x ) log / ( x ) , then ( p ) log ( ) \#151 ; 1 From this also we deduce that , if fn ( ) denote the n-th Cesdro partial summation of the Fourier series of a function f(x ) which is such that | log | f(x ) | is summable , then I \fn ( x ) j log \fn ( p ) | dx has the unique double limit zero , when Je E \#151 ; 0 and n-*oz ; and that fn{F ) log fn 0 ) dx \f(P ) log fip ) dx .
Finally we may remark that from analogous considerations we may establish the truth of the following general theorem on double successions:\#151 ; If fnip ) and gm(x ) denote the Cesdro summations of the first ( 2^+1 ) terms of the Fourier series of two functions f(x ) and g ( x ) , belonging to a pair of complementary classes of summable functions , such as those here considered , then Lt j/ " ( x ) gm ( x ) dx \#151 ; J/ g ( x ) dx .
m -* oc , n -* oo w Negative After-Images and Successive Contrast with Pure Spectral Colours .
By A. W. Porter , B.Sc. , F.R.S. , and F. W. Edridge-Green , M.D. , F.R.C.S. ( Received May 28 , \#151 ; Read June 27 , 1912 .
) [ This paper is published in ' Proceedings/ Series B , No. 581 .
] VOL. LXXXVII.\#151 ; A. R
|
rspa_1912_0078 | 0950-1207 | The number of \#x3B2;-particles emitted in the transformation of radium. | 230 | 255 | 1,912 | 87 | Proceedings of the Royal Society of London. Series A, Containing Papers of a Mathematical and Physical Character | H. G. J. Moseley, B. A.|Prof. E. Rutherford, F. R. S. | article | 6.0.4 | http://dx.doi.org/10.1098/rspa.1912.0078 | en | rspa | 1,910 | 1,900 | 1,900 | 7 | 461 | 11,593 | http://corpora.clarin-d.uni-saarland.de/surprisal/6.0.3/?id=rspa_1912_0078 | 10.1098/rspa.1912.0078 | null | null | null | Atomic Physics | 48.347825 | Tables | 16.989969 | Atomic Physics | [
-21.228321075439453,
-15.285244941711426
] | 230 The Number of fi-Particles Emitted in the Transformation of Radium .
By H. G. J. Moseley , B.A. , Assistant Lecturer and Demonstrator , University of Manchester .
( Communicated by Prof. E. Rutherford , F.R.S. Received May 8 , \#151 ; Read June 13 , 1912 .
) CONTENTS .
PAGE 1 .
Introduction ... ... ... ... ... ... ... ... ... ... ... ... ... ... ... ... ... ... . .
230 2 .
Methods of Measurement ... ... ... ... ... ... ... ... ... ... ... ... ... ... ... .
232 3 .
Comparison of the Two Methods ... ... ... ... ... ... ... ... ... ... ... ... . .
235 4 .
Absorption of the / 3-Radiation from Active Deposit of Radium ... ... ... 235 5 .
Comparison of the Radiation from Radium B and Radium C ... ... ... ... 239 6 .
Number of j3-Particles Emitted by Radium B and by Radium C ... ... . .
241 7 .
Number of / 3-Particles from Radium E ... ... ... ... ... ... ... ... ... ... . .
243 8 .
Ionising Power of a / 3-Particle ... ... ... ... ... ... ... ... ... ... ... ... .
245 9 .
Secondary / 3-Radiation from y-Rays ... ... ... ... ... ... ... ... ... ... ... . .
249 10 .
Secondary and d-Rays ... ... ... ... ... ... ... ... ... ... ... ... ... ... ... ... . .
250 11 .
Summary of Results ... ... ... ... ... ... ... ... ... ... ... ... ... ... ... ... . .
254 1 .
Introduction .
The recent researches of Baeyer , Hahn , and Meitner* have shown that the / 3-radiation from a substance can usually be resolved by a magnetic field into a number of distinct groups of approximately homogeneous rays .
It has been shown by Danyszf that more than 23 such groups are present in the radiation from radium B and radium C. From our knowledge of the approximate value of the charge carried by the / 3-partides from radium it is clear that each atom in disintegrating cannot emit one / 3-particle of each kind , and it is therefore safe to conclude either that different atoms of the same substance give rise to different radiations , the process of disintegrating being different in each case , or J that the radiation which results from the disintegration is originally uniform but becomes modified by its passage through the atom .
It is in this connection of importance to know the average number of particles emitted by an atom .
If this proves to be an integer , the process of disintegration is probably simpler than it appears at first sight .
At the suggestion of Prof. Rutherford , a careful investigation was * Baeyer , Hahn , and Meitner , 'Phys .
Zeit./ 1911 , vol. 12 , pp. 273 and 1099 .
t Danysz , 'Le Radium , ' 1912 , vol. 9 , p. 1 .
% Rutherford , 'Proc .
Manchester Lit. Phil. Soc./ Feb. 6 , 1912 ; 'Nature/ vol. 88 , p. 605 Feb. 29 , 1912 .
ft-Particles Emitted in Transformation of Radium .
231 undertaken to determine the number of / 3-particles emitted by radium C. This work has included a study of the best methods of measuring accurately the number of / 3-particles from an atom , with the intention of subsequently applying these methods to as many cases as possible .
It has been found that , on an average , an atom of radium B or radium C emits slightly more than one / 3-particle , while radium E appears to emit on an average little more than one-half a / 3-particle .
The only substance for which this number had hitherto been determined is radium C. The first determination , by Wien* * * S gave only approximate results ; the second , by Rutherford , f needed correction by a somewhat uncertain factor , owing to the reflection of some of the rays from the metal cylinder on which the active material was deposited ; the third , by Makower , J eliminated the error due to reflection , and gave one , or possibly two , as the number of / 3-particles emitted .
The chief sources of uncertainty in this case were , firstly , the correction made for the radiation from radium B ; and , secondly , the correction for the absorption of the rays by the tube in which the active material was contained .
In the present work a direct comparison of the radiations from radium B and radium C avoided the first source of uncertainty .
The second was minimised by using as an active source radium emanation contained in a glass tube sufficiently thin to allow the passage of the a-particles , and then covering with just enough material to stop these particles ; for the a-particles in their passage through matter produce 8-particles in numbers sufficient to render measurements of the charge carried by the / 3-rays impossible .
A careful study has been made of the absorption of the / 3-radiation , and it is believed that in the case of radium C no serious error is introduced by the inevitable extrapolation .
These measurements were complicated by the fact that a secondary radiation is emitted by surfaces traversed by / 3-rays .
This radiation , which has not been observed by previous investigators , was studied in some detail , and a comparison of its properties with those of the 8-rays is given at the end of this paper .
From the results of Geiger and KovarikS on the ionisation produced by the / 3-radiation from various atoms , it would be possible to determine the number of particles emitted by each atom but for our lack of precise knowledge of the ionising power of a / 3-particle .
For this reason , a determination has been made of the number of ions produced per centimetre of air by / 3-particles of different penetrating powers .
With the help of these * Wien , 'Phys .
Zeit .
, ' 1903 , vol. 4 , p. 624 .
t Rutherford , ' Phil. Mag. , ' 1905 , vol. 10 , p. 193 .
J Makower , 'Phil .
Mag. , ' 1909 , vol. 17 , p. 171 .
S Geiger and Kovarik , 'Phil .
Mag. , ' 1911 , vol. 22 , p. 604 .
R 2 Mr. H. G. J. Moseley .
Number of fi-Particles [ May 8 , data an estimate has been formed of the number of / 3-particles emitted by each atom of the substances examined by these authors .
A quantitative examination of the secondary / 3-radiation emerging from a sheet of material traversed by 7-rays has led to an estimate of the energy contained in the 7-radiation from radium C. 2 .
Methods of Measurement .
The number of / 3-particles emitted by radium B and radium C was determined by two methods .
In the first method the particles were collected in a brass box thick enough to stop them all , and their number was deduced from the negative charge gained by the box .
In the second method measurement was made of the positive charge gained by the active material as the result of the loss of / 3-partieles .
If I is the charge gained per second by the collecting box or active material , when radium active deposit corresponding to M grm. of radium is used as the source of radiation , n , the number of / 3-particles emitted at the disintegration of one atom of radium B and one atom of radium C , is given by U N0M ; ( 1 ) where N is the number of atoms disintegrating per second in 1 grm. of radium , and e the charge carried by a / 3-particle .
In all calculations of n , the value of has been taken to be 15*8 E.S. units per gramme of radium per second .
The reason for assuming this value is discussed in Section 6 .
The form of apparatus finally adopted for use by the first method , apparatus A , is shown in fig. 1 .
The apparatus is contained in a glass tube fitted at one end with a large ground joint , and at the other end closed by a plug of ebonite , into which fits a brass tube G , acting as guard ring , and a ho electrometer \\\V Apparatus A. 1912 .
] Emitted in the Transformation of Radium .
233 smaller plug , through which passes a brass rod , connected to the electrometer .
Joints are sealed airtight with white wax .
The brass tube T , of length 12 feet , which surrounds the wire leading to the electrometer , is sealed with soft wax to G , and can be exhausted .
The brass cylindrical collecting box B , of internal length 5'3 cm .
, diameter 2'2 cm .
, and thickness 2-7 mm. , a thickness probably sufficient to stop all / 3-rays , is supported by the brass rod .
The box can be unscrewed from the rod , and withdrawn from the apparatus , and one end can then be removed for the purpose of altering the lining of the box .
The glass is lined with a brass tube L , fitted at one end with a collar , into which slides the brass handle H , from which projects a short thin brass tube .
On to this tube fits the thin brass collar of the paper tube P , of which the other end is closed .
The aluminium leaf , with which the surface of P is covered , is in metallic connection through the collar , the thin tube and the handle with the lining L. L is connected to a battery of storage cells , G and T being earthed .
The active material is placed inside P. The form of apparatus used in the second method , apparatus B , is shown in fig. 2 , and consists of a round litre glass flask , of which the inner surface Apparatus A To pumpehc .
electro- meter to earth V potentiometer v---------ihl'l------^ Diagram of Connections .
Apparatus B. is silvered .
The mouth of the flask is connected by a large ground joint to a glass tube , of which the end is closed by an ebonite plug , fitted with a guard ring .
Through the plug passes a long brass rod , connected with the electrometer , and carrying the paper tube P , which contains the active material .
In order to avoid disturbance by ionisation , the apparatus was evacuated either by a Gaede pump or by the charcoal method .
Accurate results were not obtained when the pressure registered by a McLeod gauge was much greater than 0*001 mm. of mercury .
In every series of measurements the 234 Mr. H. G. J. Moseley .
Number oj ft-Particles [ May 8 , current through the apparatus in the absence of the active material was tested , but was usually found to be negligible .
The measurements of current were made by a balance method , the charge communicated in one minute , for example , to the insulated system being taken up by a condenser , of which the potential of the other surface was gradually raised during the course of a measurement by means of a potentiometer .
The electrical connections are shown diagrammatically in fig. 3 .
A Dolezalek quadrant electrometer of which the sensitiveness was varied from 250 to 2500 mm. per volt was used to test the accuracy of the compensation .
The fact that when using this induction balance* the insulated system is always approximately at the potential of the earth , minimises disturbance by ionisation by 7-rays which escape from the testing vessel .
To avoid such ionisation in the electrometer itself , it was placed at a distance of 12 feet from the active material , and a large mass of lead was interposed .
As a further precaution the earthed brass tube , which enclosed the connecting wire , was usually kept exhausted . .
It has been mentioned that the / 3-particles in their passage through metals produced slow-speed electrons , the number of which is , however , very small compared with that given by the same number of a-particles .
A special investigation , of which an account will be given in a later section , was made with the purpose of finding out the most suitable method of correcting for this secondary radiation .
In order to do so it is necessary to observe , firstly , the maximum current Ii , got by increasing the negative potential of the central electrode of apparatus A until the current becomes independent of the potential , and , secondly , the minimum current I2 , got in the same way by the use of a positive potential .
It has been found that the true current I is given by the equation , j* I = Ia + KIi-Ia ) = fli +(2 ) An account will also be found in a later section of a simpler method of measuring I. This method , which depends on the use of a magnetic field , was worked out after most of the measurements had been made .
Difficulty was for some time experienced in getting concordant estimates of the current carried by the / 3-particles , owing to the large differences often found between the currents Ii and I2 .
It was eventually found that uniformly small values of the secondary radiation , which was the cause of this disturbance , were obtained by the use of dry aluminium surfaces to the central electrode and collecting box .
* Townsend , 4 Phil. Mag. , J 1903 , vol. 6 , p. 603 .
t Cf .
p. 254 .
1912 .
] Emitted in the Transformation of Radium .
235 3 .
Comparison of the Two Methods .
Good agreement was obtained between the results given by the two methods .
This was tested by a special set of measurements made by both methods with the same active material and absorbing screens .
After the currents obtained by the first method had been corrected for the radiation which escaped from the collecting box , the corresponding values of I were found to differ by only 1 per cent , in each case .
I had in the second method been deduced from Ii and I2 by means of equation ( 2 ) , which has only been proved in the case of the first method .
There is , however , little doubt that this relation will still approximately hold good , and the agreement between the results of the two methods can be taken as justifying the assumption that the further corrections to be applied in - the first method are small .
The first method used apparatus which could rapidly be exhausted ; while the ease with which the collecting box could be removed afforded convenient means of studying the influence of the nature of the surface on the secondary radiation .
This radiation was , moreover , somewhat smaller and more constant from the collecting box than from the silvered surface used in apparatus B. Also the field required to obtain the minimum current I2 was 50-100 volts in apparatus A , but quite 600 volts in apparatus B. For these reasons the second method was not much used , although the considerable space which it provides for active material and absorbing screens is required for many measurements .
4 4 .
Absorption of the / 3-Radiation from Active Deposit of Radium .
The chief object in measuring the relative numbers of / 3-particles which penetrate various thicknesses of material was to provide data for an estimate of the total number of / 3-particles emitted .
This number cannot be directly measured , and it is therefore necessary to make a series of measurements , starting with only just sufficient material to stop the a-particles .
The source of activity was radium emanation in equilibrium with its disintegration products .
Since of these only radium B and radium C are known to emit / 3-particles , this source will usually , for the future , be called active deposit of radium .
The radium emanation , after purification by the condensation method , was placed in a small glass tube , of which the walls were thin , being equivalent in their power of stopping a-particles to about 2 cm .
of air .
The tube , surrounded by a small cylinder of absorbing material , was placed inside the paper cylinder which acted as central electrode in the measuring apparatus .
This plan of always keeping the same central electrode did much to ensure the constancy of the secondary radiation , and had other obvious advantages .
The material of which the Mr. H. G. J. Moseley .
Number [ May 8 , absorbing cylinders are made must be of low atomic weight , since it is desired to stop the a- but not the / 3-particles .
It must also , when in thin sheets , be uniform in thickness , and must be tough and flexible to allow of its being rolled accurately into cylinders composed of an exact number of layers .
Oxford India paper , for the gift of which I am indebted to the Oxford University Press , satisfied these requirements .
It is , however , hygroscopic , and when intended for use in a vacuum , must be previously kept in a desiccator .
It was found to weigh 2'93 mgrm .
per square centimetre , and to be equivalent in power of stopping / 3-radiation to exactly 0 01 mm. aluminium .
The thickness of wall of each glass tube was found by a radioactive method .
The range in air of a-particles , either from the radium emanation contained in the tube , or from the polonium , which after some months took its place , was determined by the method of scintillations , and the thickness of the tube calculated from its stopping power , using the values given by Rutherford* for the range of a-particles in glass .
The result of a set of measurements of absorption by paper is given in Table I , the currents n\ and \#171 ; 2 being calculated by means of equation ( 1 ) in terms of the number of electrons carrying the current per atom of radium C disintegrating ; n is calculated from ri\ and \#187 ; 2 by means of equation ( 2 ) .
In the first column is given the thickness of aluminium equivalent to the absorbing material ( paper , glass , aluminium leaf and gum ) .
Table I.\#151 ; Absorption by India Paper of / 3-Radiation from Active Deposit of Radium .
Total absorption equivalent of paper , glass , etc. nv Sum of currents carried by / 3 and emergent secondary radiations .
w2 .
Difference between currents carried by / 8 and incident secondary radiations .
n. Number of / 8-particles from active deposit per atom of radium C disintegrating .
0 -037 mm. aluminium ... 1 *865 1*555 1 *74 0-047 " " ... 1*735 1*495 1 *64 0*057 " , , ... 1 *625 1 *39 1 *53 0-067 " " ... 1 *57 1*315 1 *47 0-077 " " ... 1 *46 1 *24 1*37 0-097 " " ... 1 *355 1*145 1*27 0-117 " " ... 1 *24 1 *04 1 *16 Each sheet of paper was found to be equivalent in stopping power to 0'010 mm. aluminium , the thickness being calculated from the weight on the assumption that the density of aluminium is 2'7 .
The values of n obtained through different thicknesses of paper are plotted * Rutherford , ' Phil. Mag. , ' 1910 , vol. 19 , p. 192 .
1912 .
] Emitted in the Transformation of Radium .
237 in fig. 4 .
The curve shown in this figure is theoretical , and its meaning will be discussed later.* From an inspection of the experimental points it is evident that slightly more than two / 3-particles are emitted by radium B and radium C together , when one atom of each disintegrates .
Fig. 4 .
Hundredths of a millimetre of aluminium .
Absorption by Paper of / 3-radiation from Active Deposit of Radium .
These measurements were made in apparatus A , and since there was no room for bulky absorbing cylinders , other absorbing materials were used in many cases .
The results obtained with lead , which was unfortunately later found to contain 8 per cent , of tin , are given in Table II .
The currents observed through the greatest thickness of lead , which have , of course , been corrected for the natural leak through the apparatus , are not due to the primary / 3-radiation , which has presumably been entirely absorbed , but to the secondary / 3-rays excited by the 7-rays .
Since the stream of 3-rays produced by them in the lead will be nearly balanced by the stream of rays leaving the collecting box , the observed currents are a measure of the secondary 3-radiation produced in the brass lining of the glass tube which contains the apparatus .
The radiation from the brass lining which reaches * Cf .
p. 241 .
238 Mr. H. G. J. Moseley .
Number [ May 8 , Table II .
Absorbing material equivalent to lead weighing Observed values .
After correction for secondary / 3-radiation .
n2 .
nx .
n2 .
n. 0 *074 grm. per sq .
cm .
0-515 0*441 0*506 0 *438 0-479 0 *108 " 0-319 0-265 0*310 0*262 0*291 0 *148 " 0-221 0-185 0*212 0-182 0-200 0 *183 " 0-160 0-134 0 -151 0*131 0*143 0 *219 " 0 -1225 0-102 0-113 0-099 0-108 0 *262 " 0 -0929 0 -0758 0 -0838 0 -0725 0 *0793 0 -313 " 0-0671 0 *0558 0 -0580 0 -0525 0 *0558 0 *415 " 0 -0376 0 -0282 0 *0285 0 -0249 0 -0271 0 *501 " 0 -0250 0 *0156 0 -0159 0 -0123 0 -0145 0 *739 " 0 -0L60 0 *0084 0 *0069 0 *0051 0 *0062 .1 *25 " } } 0 -0091 0*0031 the collecting box is opposed in direction to the 7-rays and is therefore* smaller in amount than the secondary / 3-radiation from the lead , measurements of which are given in a later section .
The relatively large differences between ni and n2 which are noticeable in all measurements through the greater thicknesses of lead are due to the secondary slow-speed radiation excited by the secondary / 3-rays , and are of the magnitude expected , when all the radiating surfaces are taken into account .
The values of % and n2 given in Fig. 5 .
Grammes per sq .
cm .
lead .
Absorption by Lead of / 3-radiation from Active Deposit of Radium .
* Bragg and Madsen , ' Phil. Mag. , ' 1908 , vol. 16 , p. 918 .
1912 .
] Emitted in the Transformation of Radium .
239 columns 4 and 5 were obtained by subtracting in each case the values obtained through lead weighing T25 grm. per square centimetre .
That this correction has been successful in eliminating the secondary / 3-radiation is indicated by the fact that the relative differences between and n2 have now been reduced to their usual value .
The logarithms of the corresponding values of n are in fig. 5 plotted against the thicknesses of the lead absorbing cylinders .
The absorption is over the greater part of the range exponential , the absorption coefficient of the radiation being 7'1 ( gramme per square centimetre)-1 .
5 .
Comparison of the Number of / 3-Pa Emitted by Radium B and Radium C. Experiments will now be described which determine how many of the / 3-particles emitted by active deposit of radium in equilibrium with emanation come from radium B , and how many come from radium C. Radium B was deposited by recoil from radium A on the inside of a paper tube , and measurements were made of the change with time of the number of / 3-particles emitted through the walls of the tube .
It has been shown by Makower and the author* that by this method radium B can be obtained \#166 ; entirely free from radium C. It is , therefore , possible to calculate from these measurements the relative number of particles ejected through the paper tube by each atom of radium B and radium C wThich disintegrates .
The paper tube , after three minutes spent in collecting radium B , was fitted to the handle H in apparatus A. The apparatus was exhausted to a low pressure and readings were taken for an hour of the charge gained by the collecting box .
The currents observed being small , each measurement extended over three minutes .
The ratio of the secondary radiation to the / 3-radiation was found to be approximately constant , provided measurements were not taken until the apparatus had been exhausted to a pressure of a thousandth of a millimetre for some few minutes .
To avoid the error which would have been introduced by any variation in this ratio , a field of alternately + 80 volts was maintained between P and the collecting box , and the mean of each two consecutive readings was taken as a measure of the number of / 3-particles emitted .
The observed variation with .time in the number of particles emitted is shown in fig. 6 , the experimental points on the curve being obtained when the stopping power of P was equivalent to that of 0049 mm. of aluminium .
The curve drawn is a theoretical curve 'Calculated on the assumption that , if the number of / 3-particles transmitted by the paper at the disintegration of an atom of radium C is arbitrarily taken as 1 , the number transmitted per atom of radium B is 0715 , this * Moseley and Makower , ' Phil. Mag. , ' 1912 , vol. 23 , p. 302 .
240 Mr. H. G. J. Moseley .
Number of [ May 8 , ratio being so chosen as to make the curve agree with experiment .
The time is reckoned from the end of the three minutes during which the radium B was being deposited , allowance being made for the small quantity Fig. 6 .
\#187 ; 60 10 20 30 40 50 60 Time in minutes .
of radium G which grew on the paper during that time .
The half-value periods of radium B and radium C have been taken as 26'7 minutes and 19'5 minutes .
Similar experiments were made using paper of two other thicknesses .
Taking , therefore , the values given by fig. 4 , for the total number of ,0-particles ejected through the paper by the active deposit in equilibrium with emanation , we obtain the following table:\#151 ; Table III.\#151 ; Comparison of / 3-Itadiation from Radium B and Radium C. Total thickness of absorbing material equivalent to Number of ( 3-particles from active deposit per atom of radium C disintegrating .
Relative number of / 8-particles from radium B and radium C penetrating the absorbing material .
Number of / 8-particles penetrating the absorbing material from each atom of Radium B. Radium C. 0 *049 mm. aluminium 1-62 71-5 : 100 0-675 0*945 0*065 " " 1*48 64 -0 : 100 0-577 0-903 0*092 " * " 1 -29 50 -0 : 100 0-43 0*86 The ratios B : C found in the table may , owing to the insensitiveness of the method employed and the smallness of the observed currents , be in error by perhaps 2 per cent. The logarithms of the numbers of / 3-particles from radium B and radium C are , in fig. 7 , plotted against the thickness of absorbing material through which they have passed .
The absorption is 1912 .
] Emitted in the Transformation of Radium .
241 assumed in the case of radium B to follow an exponential law .
In the case of radium C it is known that the absorption is not exponential .
The absorption curve given in fig. 7 was obtained by assuming that radium C Hundredths of a millimetre of aluminium .
Absorption by Paper of / 3-radiation from Radium B and Radium C. gives equal quantities of soft radiation of absorption coefficient 50 cm."1 aluminium and hard radiation of about 13 cm"1 .
This assumption is taken from the result obtained by Geiger and Kovarik.* Their data , which are based on measurements of ionisation , have been corrected for the variation of ionisation with the hardness of the radiation .
Extrapolation then gives as the total number of / 3-particles emitted by each atom , 1T0 for radium B and the same number for radium C. The curve given in fig. 4 has been obtained by adding together the numbers of ^-particles from radium B and radium C taken from the curves in fig. 7 .
It satisfactorily fits the observations through the smaller thicknesses of paper , but afterwards gives values which are somewhat too low ; probably the absorption coefficient of radium B there becomes smaller .
6 .
The Number of / 3-Particles Emitted by an Atom of Radium B or Radium C. The determination of the number of / 3-particles emitted by an atom of radium B or radium 0 depends on four factors , on the three quantities M , He , and I given in equation ( 1 ) , p. 232 , and on the absorption of the yS-particles by the paper used to stop the a-radiation .
We have seen that both radium B and radium C appear to emit slightly more than one / 3-particle for each atom disintegrating , and since this conclusion is of some theoretical importance , it will be supported by a short discussion of the errors involved in the determination .
* Geiger and Kovarik , 'Phil .
Mag. , ' 1911 , vol. 22 , p. 604 .
242 Mr. H. G. J. Moseley .
Number of / 3-Particles [ May 8 , The quantities of radium B and radium C used in the present work have been measured , by comparison of the 7-radiation , with that of the radium standard of this laboratory .
The results obtained will therefore not be affected by error in the standard , provided the value assumed for has been referred to the same standard .
Two such values for Ne have been obtained , the one by Rutherford and Geiger , * by measuring the charge carried by the a-particles emitted by a measured quantity of radium C , the other by Boltwood and Rutherford , f by measuring the volume of helium produced from radium in a definite time .
Reckoned in E.S. units per gramme of radium per second , these values are 15*8 and 15*6 .
It seems therefore probable that the value ISte = 15*8 assumed in the present work is sensibly correct .
The measurements of current made by the author depend on the capacity of the condenser employed , and on the potential to which it is charged .
The latter was compared with that of a standard cell .
The condenser used in most of the measurements had been carefully standardised by an electromagnetic method some years ago .
Later measurements of current were made , using a condenser standardised to within 1 per cent , by direct comparison , both with a half micro-farad standard and with a concentric cylinder condenser , fitted with guard rings , of which the capacity was calculated from the dimensions .
The different sets of measurements were made with radium emanation contained in glass tubes of varying thicknesses , so that direct comparison of the results is impossible .
Each measurement has therefore been compared with the value taken for the appropriate thickness of absorbing material from the curve given on fig. 4 , and the mean percentage difference between the results of each set of measurements and the curve has been tabulated in Table IV .
Table IV.\#151 ; Summary of Results .
Series of experiments .
Method of measurement .
Mean result compared with smoothed curve , fig. 4 .
I to IV First method Secondary radiation large , results therefore doubtful .
2| per cent. low .
Used to obtain the curve , therefore 1 per cent , high after correcting .
1 per cent. low .
0 per cent. low .
2\ per cent. low .
1 per cent. low .
v First method YX First method VI ( about a week later ) ... VII J First method \ Second method . .
Second method ... YXII First method * Rutherford and Geiger , 4 Roy .
Soc. Proc. , J 1908 , A , vol. 81 , p. 162 .
t Boltwood and Rutherford , 4 Phil. Mag. , ' 1911 , vol. 22 , p. 586 .
1912 .
] Emitted in the Transformation of Radium .
243 The values obtained by the first method have all been increased by 1 per cent , to allow for those ^-particles which escape through the hole in the collecting box .
The agreement between the later sets of values is seen to be close , and the error involved in taking the curve to be correct is probably not more than about 2 per cent. The error introduced by the reflection of the / 9-particles will now be considered .
Although some / 9-particles reflected from the walls of the collecting box will return to the central electrode , they will , when the electrode consists only of a small thickness of paper , pass through it for the most part unabsorbed .
The slower particles which might be stopped by the paper are not so often reflected as the faster , but , as a precaution , the walls of the collecting box were lined with paper or aluminium foil so as further to diminish the reflection .
Reflection then introduces no appreciable error .
When the central electrode contained cylinders of lead the reflected rays which hit it were for the most part again reflected , and it can be calculated from data given by Kovarik* that the lead cylinders absorbed little more than 1 per cent , of the radiation which originally escaped from them .
It is obvious from an inspection of fig. 4 that somewhat more than two / 9-particles are emitted during the transformation of radium active deposit\#151 ; that is during the disintegration of one atom of radium B and one atom of radium C\#151 ; provided , of course , that the value assumed for Ke is correct .
It is by no means so obvious from an inspection of fig. 7 , either that an atom of radium B or that an atom of radium C emits more than one / 9-particle .
In the case of radium B , indeed , the extrapolation is so large that it is impossible to give a definite opinion on this point .
The case of radium C is clearer , for here the extrapolation is small and fairly definite , but it will perhaps be best to accept provisionally the value 1T0 / 9-particles given by fig. 7 both for an atom of radium B and of radium C , deferring , however , any explanation of the departure from a whole number until more is known about the initial absorption of heterogeneous / 9-radiation .
This estimate does not include / 3-radiations with velocities only 036 and 041 of that light , stated by Hahnf to be emitted by radium B , as these would be entirely absorbed by the material used to stop the a-rays .
7 .
The Number of ft-Particl from Radium E. A preliminary investigation of the number of / 9-particles emitted by radium E will now be described .
Three sources of radium D and radium E in radioactive equilibrium were employed , the first two being thin-walled * Kovarik , ' Phil. Mag. , ' 1910 , vol. 20 , p. 849 .
+ Baeyer , Hahn , and Meitner , 'Phys .
Zeit .
, ' 1911 , vol. 12 , p. 1099 .
Mr. H. G. J. Moseley .
Number of ( 3-Particles [ May 8 , glass tubes , which had some months previously been filled with a measured quantity of radium emanation for use in the work on radium B and radium C. The third source was some aluminium leaf which was exposed for a definite time to radium emanation .
From subsequent measurements of the 7-ray activity of the leaf , the activity at the moment of removal was calculated , and hence also the total quantity of active material deposited during the exposure .
The quantity of radium D and radium E present in one of the sources can easily be deduced , assuming 16*5 years* to be the half value period of radium D , but such calculations are subject to several possibilities of error .
The activities of the three sources were therefore compared by ionisation methods , and were proved to be proportional to the quantities of radium emanation from which they arose .
The third source , originating from the decay of about 13 millicuries of radium emanation , was surrounded by four sheets of India paper and used for measurement of the current carried by the / 3-particles .
The observed current was small , the system when insulated charging at the rate of about 0*005 volt per minute .
The chief difficulties experienced in getting reliable readings were traced to three causes , namely , leakage of charge from the surfaces of insulators , changes in the potential of the field used for controlling the secondary radiation , and leakage from the needle to the quadrants of the electrometer .
The first difficulty was overcome by screening the insulating surfaces , the second by the use of batteries of small cadmium cells , the third by balancing the leak from the electrometer needle against the leak through a condenser , which was included in the insulated system , and was used for standardising the observed current .
The current through the exhausted apparatus in the absence of active material was also observed .
Successful measurements of the current carried by the ,8-particles were finally made in apparatus B , the result found being that the number of / 3-particles penetrating four sheets of India paper , equivalent in all to 0*04 mm. aluminium , is 0*525 particle per atom of radium E disintegrating .
No great accuracy is claimed for this measurement , but it is not likely to be more than 10 per cent , in error , provided the value assumed for the period of radium D is correct .
Accurate values and a knowledge of the manner in which the radiation is absorbed are no doubt attainable by the use of more active material , but if the explanation which will be offered for this curious result is correct , little would thereby be gained .
The absorption curve of the radiation from radium ]D and radium E at first falls more quickly with increasing thickness of absorbing material than subsequently , when the absorption obeys an exponential law .
The part of * Antonoff , 'Phil .
Mag.,5 1910 , vol. 19 , p. 825 .
1912 .
] Emitted in the Transformation of Radium .
245 ' the radiation included when the exponential curve is extrapolated back to the origin will be termed " hard " radiation , and the rest " soft " radiation .
From the observations of Geiger and Kovarik , * which do not depend on a knowledge of the period of radium D , it may be deduced , by the method given later in Section 8 of this paper , that of the " hard " ' radiation O'ol / 3-particle and of the soft radiation about 0035 / 8-particle will penetrate 0'04 mm. aluminium for every atom of radium E which disintegrates .
The total value 0'545 is in reasonable agreement with the 0-525 / 3-particle per atom disintegrating given above .
A preliminary observation on the growth of radium E from pure radium D has convinced the present writer that , contrary to the opinion expressed by Kovarik , f a part at least of the " soft " radiation is emitted by radium E itself .
In view of the resulting uncertainty in the amount of / 3-radiation absorbed by 0'04 mm. of aluminium , it is not possible to state definitely that each atom of radium E does not emit a / 3- particle , although we have no reason to suspect such a large proportion of easily absorbed radiation .
In such a case it is obviously unsatisfactory to measure the radiation after passage through absorbing screens , and an attempt is being made to eliminate the effect of 8-rays , and so obtain direct measurements of the charge carried by a mixture of a- and / 3-particles .
8 .
The Ionising Power of a The number of ions produced in air by a / 3-particle per centimetre of path has been determined by Durack , J but owing to the reflection of the / 3-particles within his apparatus he did not obtain an accurate result .
In the measurements which will now be described the error due to reflection has been eliminated .
Separate measurements have been made ( 1 ) of the current carried in vacuo by / 3-particles and ( 2 ) of the saturation ionisation current which / 3-particles produce in air at atmospheric pressure .
The source of radiation was in either case a definite amount of active deposit of radium , the quantity used in the second measurement being smaller than in the first .
If the currents ( 1 ) and ( 2 ) are for active deposit per curie of emanation Oi and C2 , N , the number of pairs of ions produced per / 3-particle-per centimetre of path , is given by where L is the average path of a / 3-particle in the ionisation vessel .
By measuring Ci and C2 after the radiation has passed through various* Log. cit. t Kovarik , ' Phil. Mag. , ' 1910 , vol. 20 , p. 849 .
x Durack , 'Phil .
Mag. , ' 1903 , vol. 5 , p. 550 .
VOL. LXXXVII.\#151 ; A. S Mr. H. G. J. Moseley .
Number of fi-Particles [ May 8 , thicknesses t of absorbing material , the variation of N " with X , the absorption coefficient of the radiation , has been found .
X has been calculated from the slope of curves drawn to show the variation of C with t. The method of measuring C has already been described , and the greater part of the data used here in calculating C and X has been given in Section 4 of this paper .
*C2 was measured in an ionisation chamber , of which the walls were so thin as to reflect back no appreciable amount of / 3-radiation .
Across a large outer framework of steel knitting needles were stretched fine brass wires .
\#187 ; Where the wires crossed they formed two small squares , which when connected together formed the skeleton of a cube .
The sides of the cube were made of aluminium foil of thickness ( \gt ; 00024 cm .
The source of j3-radiation , a thin glass tube containing radium emanation , was placed inside an absorbing tube of paper or lead .
This in its turn was inside a thin aluminium-coated paper cylinder , which acted as a central electrode to the cube , the mean path of a / 3-particle between the electrode and the cube being 1b50 cm .
The saturated ionisation current was measured with an electrometer .
To allow for absorption of the radiation by the air the equivalent of | L = 1*75 cm .
of air was included in the thickness of the absorbing material .
A few of the values of N obtained from these data are given in the following table :\#151 ; Table Y. Absorbing material equivalent to X in cm.-1 aluminium .
0 , . .
Current carried by / 3-particles from active deposit per curie of emanation .
c2 .
Current carried by ions from active deposit per curie of emanation .
N. Number of ions per / 8-particle per cm .
of path in air at 760 mm. and 15 ' C. 0 *0053 cm .
aluminium 53 25*0 3080 123 0 -0173 " 36 14 *7 1560 106 0 *149 grm. per sq .
cm .
lead 15 3*16 259 82 The values both of Ci and C2 have been corrected for the effect of 7-radiation .
Before discussing these results an account will be given of experiments from which the value of N was determined for the radiation from pure radium B. The variation of ionisation with time was measured in the ionisation chamber described above , starting with pure radium B. From this the relative ionisations produced by the radiations from radium B and radium C were deduced in the same way as were the relative numbers of , / 3-particles in the experiments described in Section 5 .
With care the 1912 .
] Emitted in the Transformation of Radium .
inevitable contamination of the apparatus with radium emanation was reduced , until it became negligible compared with the radium B obtained by a recoil lasting three minutes .
The results obtained are given below , the relative number of / 3-particles given in column 3 being taken from curve 7:\#151 ; Table YI .
t. Thickness of absorbing material equivalent to Eatio of activities , after passing through t , of / 3-rays from radium B and radium C in equilibrium .
Eatio of ionisations B : C. Eatio of numbers of / 8-particles .
0 '057 mm. aluminium 0-100 " " : : 1 -15 : 1 0 -75 : 1 : : 0 *664 : 1 0*49 : 1 When t = 0'057 mm. aluminium we see that radium B contributes 1T5/ 2T5 or 53'5 per cent , to the ionisation produced by active deposit of radium , 0"664/ T664 or 39'8 per cent , to the number of / 3-particles emitted .
Hence N for radium B:N for active deposit : : 53"5 : 39'8 .
From this the following values of N for radium B are deduced:\#151 ; Table VII .
t. A for active deposit in cm.-1 aluminium .
N for active deposit .
N for radium B. A for radium B. 0 '057 mm. aluminium ... 52 122 164 About 100 0-100 " " ... 46 117 152 About 90 The method by which these values are calculated does not lead to very exact results .
The variation of N with X given in Tables V and VII is plotted in curve 8 .
These results , which are of practical rather than theoretical interest , are in general agreement with the conclusion of W. Wilson , * that for homogeneous / 3-radiation , N varies inversely as the square of the velocity .
Similar results would not have been found if an ionisation chamber with thick walls had been employed .
Makower , f using a small ionisation chamber , found that over a considerable range N was independent of This result , the approximate truth of which was confirmed when using apparatus A as ionisation chamber , is due to the * W. Wilson , 'Roy .
Soc. Proc. , ' 1911 , A , vol. 85 , p. 240 .
t Makower , ' Phil. Mag. , ' 1909 , vol. 17 , p. 171 .
S 2 248 Mr. H. G. J. Moseley .
Number of [ May 8 , increase of reflection with velocity* of a / 3-particle up to a certain speed , and does not hold good when larger ionisation chambers are used .
Fig. 8 .
Absorption coefficient in em.~l aluminium .
Ionising Power of a / 3-particle .
The main object of this study of ionisation was to throw light on the results obtained by Geiger and Kovarik .f These authors have measured W:\gt ; , the ionisation produced per centimetre by the / 3-radiation which accompanies the disintegration of an atom , b being the number of / 3-particles ejected by each atom .
Since they had no accurate knowledge of the value of N , and knew nothing of its variation with X , no reliance could be placed on the values they suggested for b. It is now , however , possible , with the help of the values of N given by the curve in fig. 8 , to estimate b with some accuracy .
These values of b , and the data from which they have been calculated , are collected in Table VIII .
Table VIII .
Source of radiation .
X in cm .
1 aluminium .
m. 1ST .
b. Radium B About 100 133 164 0*81 Radium C About 31 108 100 1 *08 Radium E 43 *3 60 ' 113 0 *61 Actinium D 28*5 136 98 1 *39 Thorium 0 + 13 16 *3 68 83 0 *82 Uranium X 14 *4 78 81 0 *965 * Kovarik , loc. cit. t Log. cit. 1912 .
] Emitted in the Transformation of Radium .
249 The values of X are for radium B and radium C the initial values assumed earlier in this paper , the other values are taken from their paper .
The result is for radium C and radium E in satisfactory agreement with the values found by a direct method.* The value found in this way for radium B is much lower than that found directly , the explanation probably being that , in assuming 75 cm."1 as the absorption coefficient of the radiation , they have allowed too little for the initial absorption .
Fajans and Makowerf have recently found the absorption coefficient to be 91 cm."1 .
The value of N6 given by Geiger and Kovarik for thorium D has been halved , since it was calculated by them on the assumption that thorium Ci and C2 were successive products , each atom emitting one a-particle , whereas it is now knownJ that this is not so .
From the three new values of b which have in this way been found , we gather that an atom of uranium X emits one / 3-particle , provided the soft / 3-radiation which appears also to come from this substance is disregarded .
The transformation of thorium C and thorium D is complicated , and a discussion of the meaning of the value of b found for these substances would be premature .
The result obtained in the case of actinium D calls for further enquiry . .
9 .
Secondary ( 3-Radiation from y-Rays .
An account will now be given of an experiment made to test the number of secondary / 3-particles emitted by material traversed by 7-radiation .
A glass tube , of thickness 1 mm. , surrounded by a lead cylinder , of thickness 2*5 mm. , was fixed to the central electrode of apparatus B , which was then exhausted .
The tube contained a few millicuries of radium emanation and its disintegration products .
Since the 7-rays are known to be uncharged and it is improbable that any / 3-rays could penetrate 2*5 mm. of lead , the small positive charge gained by the lead cylinder was attributed to the loss of secondary / 3-rays .
The charge gained by the cylinder was measured with alternately positive and negative fields between the cylinder and the enclosing vessel , the mean current from the cylinder being found to correspond to the emission of 1*89 xlO6 / 3-particles per second , while the 7-radiation which emerged from the cylinder was found to correspond to the total 7-radiation from 6*5 mgrm .
of radium , by measurement with an electroscope , of which the lead walls were of thickness 3 mm. It follows that 7-radiation equivalent to that from 1 grm. of radium causes the emission from the cylinder of 2*9 x 108 / 3-particles per second .
This number was approximately unaltered when the lead was covered with 0*9 mm. of paper .
* Cf .
pp. 241 and 245 .
+ Fajans and Makower , ' Phil. Mag./ 1912 vol. 23 , p. 292 .
X Marsden and Barrett , ' Proc. Phys. Soc. Lond. , ' 1911 , vol. 24 , p. 50 .
250 Mr. H. G. J. Moseley .
Number [ May 8 , If Bragg 's theory of the conversion of a 7-ray into a / 3-particle is accepted , it follows that 7-rays N in number passing through a thick sheet of lead cause the emission from the sheet of / 3-particles of which the number B is given by I* CO B = J N/ , ie~udt = N ^ , ( 4 ) where X and ji6 are the absorption coefficients for lead of the secondary / 3- and the 7-radiations .
It appears from measurements of made by Bragg , * and of X made by Soddy.f that / jl/ X is approximately 1/ 170 for the 7-rays which penetrate 1*5 cm .
of lead .
This value of fi/ X can without great error also be taken for the 7-rays which penetrate 2*5 mm. of lead , since X is known to increase with / / , , and the difference between the values of / u , found for these two types of 7-radiation is not very large .
Let Ni be the number of 7-rays emerging per second from the cylinder when this radiation is equivalent , as measured in the electroscope , to that from 1 grm. of radium .
Owing to the difference in penetrating power between the radiation from the cylinder and that from the radium , N2 , the whole number of rays emitted by 1 grm. of radium per second , is considerably greater than Ni .
It must on the other hand be remembered that part of N2 is due to the disintegration of radium B. Now Ni = 170 x 2*9 x 108 = 5 x 1010 , so that , correcting for these two factors , and taking the number of atoms disintegrating per second in 1 grm. of radium to be 3*4 x 1010 we conclude that the number of 7-rays emitted by an atom of radium C is to the nearest whole number two .
Quite apart from Bragg 's theory , we should have to conclude that the 7-radiation from radium C contained more energy than the / 3-radiation , were it not for our knowledge^ of the existence of an undetermined number of / 3-particles with velocities approaching that of light , each of which must contain a very large quantity of energy .
It may be recalled that EveS as the result of measurements of ionisation expresses the opinion that the 7-radiation from radium C contains twice as much energy as the / 3-radiation .
10 .
Secondary and S-Rays .
It has already been stated that surfaces penetrated by / 3-rays emit a secondary radiation consisting of slow-speed electrons .
Previous investigators have noticed that the current carried by the / 8-rays depends on the potential difference maintained between the source of radiation and the collecting box , * Bragg and Madsen , 'Phil .
Mag./ 1908 , vol. 16 , p. 918 .
t F. and W. M. Soddy and Russell , 'Phil .
Mag./ 1910 , vol. 19 , p. 725 .
X Danysz , ' Le Radium/ 1912 , vol. 9 , p. 1 .
S Eve , 'Phil .
Mag./ 1911 , vol. 22 , p. 551 .
1912 .
] Emitted in the Transformation of Radium .
251 and have assumed this effect to be caused by the ionisation of residual gas left in the apparatus after evacuation .
This effect was found to persist even when the pressure registered by a McLeod gauge was less than O'OOOo mm. of mercury .
This is , however , no proof that the effect is not due to ionisation , since a comparatively large quantity of vapour from tap grease would , if present , have escaped detection .
A number of determinations under different conditions have been made of the variation with the strength and direction of the electric field of the current carried by the / 3-rays .
The results all had one feature in common ; as the field was increased in either direction , the current approached a limiting value , the maximum value being obtained by the application of a few volts , the minimum requiring 50-100 volts in apparatus A , and about 500 volts in apparatus B. It is evident that a very small field would have sufficed to saturate ionisation of the usual kind , while if ionisation by collision were taking place , the current would have reached no limiting value .
It appeared , therefore , certain that the observed effect was not due to ionisation .
Since the fields employed were far too small to turn back any / 3-rays , it was concluded that the effect was due to the emission of charged particles from the surfaces struck by these rays .
The fact that a much larger electric field was needed to obtain the minimum than the maximum value of the current proved that these particles carried a negative charge .
The fact that the potential required to obtain the minimum current increased with the size of the collecting vessel admits of two alternative explanations .
Either the emission of the particles depends on the electric intensity at the surface from which they are emitted , or particles leave the surface of the collecting vessel with considerable velocity , and so require a powerful field to make them reach the small central electrode .
The variation of current with field in apparatus A is shown in fig. 9 , the source of radiation being radium B and radium C in equilibrium .
The central electrode was made of paper coated with aluminium leaf , the collecting box being lined with aluminium foil .
The potentials are those of the central electrode , the potential of the collecting box being always approximately zero : the currents are expressed in percentages of the maximum .
The points marked with crosses represent currents obtained when a magnetic field was applied in the direction of the axis of symmetry of the apparatus. .
The magnetic field was obtained by sending a current through a solenoid wound on the apparatus , and its strength was of the order of 250 gauss .
The marked effect on the current of a magnetic field shows that the secondary radiation consists of slow-speed electrons .
The fact that in the absence of an electric field the magnetic field has absolutely no effect on the current shows that 252 Mr. H. G. J. Moseley .
Number of [ May 8 , the secondary radiation exists only in the presence of an electric field , the electrons released from the atoms in the surface being of themselves unable to escape .
In this case , therefore , we see that the second of the two Potential of Central Electrode , in volts .
alternatives offered is the true explanation of the variation with the size of the apparatus of the potential required to obtain the minimum current .
Here there would appear at first sight to be a striking difference between the secondary and the 8-rays .
The latter are electrons emitted from a .surface penetrated by a-particles , and several authors have attributed to them a very considerable velocity .
Eecently , however , Campbell , * as the result of a complete discussion of this point , has concluded that all determinations of the velocity made by previous investigators are quite untrustworthy , and gives some evidence that the velocity is much smaller than is commonly supposed .
Now this same method by which the velocity of emission of the secondary rays has been investigated is equally applicable to the 8-rays .
The difference between the method adopted in this experiment and that employed by others consists in the absence of symmetry , whereby , if there is no electric field , the rays emitted by the central electrode will all reach the collecting box , while of those emitted by the collecting box only a negligible fraction will reach the central electrode .
If , in the absence of an electric field , the current is unaffected by a magnetic field , we are justified in assuming that there is then no radiation from the central electrode .
The experiment described above was therefore repeated , using as central electrode a fine glass tube coated with aluminium leaf .
* Campbell , 'Phil .
Mag. , ' 1912 , vol. 23 , p. 46 .
1912 .
] Emitted in the Transformation of Radium .
Through the walls of the tube passed a-rays from radium emanation and active deposit , which it contained .
The observed variation with the electric field of the current between the electrodes is shown in fig. 10 .
The points marked with crosses refer to the currents obtained under the influence of a magnetic field of about 500 gauss .
It will be seen by inspection of this curve that nearly half of the S-rays are only emitted from the central electrode under the action of an electric field , while the rest are emitted \#171 ; with a velocity such that a potential difference of about 2 volts is required to stop them .
No significance can be attached to this difference between the velocities of the secondary and S-rays .
Radiations such as these are greatly influenced by the condition of the surface , and this may well have differed in the two cases .
The maximum amounts of radiation ejected by one particle from the central electrode and from the collecting box when helped by an electric field will , for the future , be termed the emergence and the incidence radiation .
Taking 0*6 on the scale on which this curve is drawn to be the current carried by the charges on the a- and / 3-particles , we obtain 10*6 for the emergence radiation and 7*45 for the incidence radiation .
It will be seen by reference to fig. 9 that for the secondary rays the incidence radiation is the greater , the incidence radiation being 0*096 , while the emergence radiation is 0'064 .
This may be attributed to the effect of the reflection of the / 3-particles at the walls of the collecting box , each reflection adding two to the number of times the / 3-particle penetrates the surface .
If the S and secondary rays are really of the same character , and are due 254 Mr. H. G. J. Moseley .
Number of / 3-Particles [ May 8 , to a process analogous to ionisation in the surface , the relative amount of their emergence radiation should be approximately the same as the relative ionising power in air of the a- and / 3-rays .
The emergence radiation from aluminium due to a / 3-particle was , in the experiment described above , 0*064 , that from an a-particle approximately 14 ; the corresponding ionisations per centimetre in air being 110 and about 25,000 .
The close agreement between the ratio 0*064/ 14 and 110/ 25,000 is partly accidental , the amount neither of the secondary nor of the S-radiation being known with any accuracy , but even a rough agreement is a striking illustration of the similarity of the two radiations .
Both the secondary and the S-radiations proved to be somewhat variable in amount , and values similar to those given above can only be consistently obtained if certain precautions are observed .
The smallest values of the secondary radiation were obtained by using very dry aluminium surfaces , the secondary radiation from surfaces of brass and tin being always slightly larger and more erratic than that from aluminium .
In more than one case in the earlier measurements the amount of secondary radiation was more than doubled , consistently high values being obtained without any assignable reason through a whole series of experiments .
When the apparatus was freshly exhausted the secondary radiation was at first somewhat large , and continued slightly to diminish for some hours .
The original object of this investigation of the secondary rays was to find a method by which their effect on the current carried by the / 3-rays could be eliminated .
It has been seen that their effect can be eliminated by experiment merely by keeping the two surfaces at the same potential , and it can be eliminated by calculation by taking as the true current carried by the / 3-rays the minimum current plus three-fifths the difference between the maximum and the minimum , thus allowing for the fact that the incidence is 50 per cent , greater than the emergence radiation .
This calculation only applies strictly to measurements made in apparatus A. For accurate work it is unsafe to trust the experimental method without a magnetic field by which the absence of secondary radiation can be confirmed .
It is equally unsafe to employ the method of calculation if the secondary radiation is much greater than normal in amount .
The error made by taking the mean current as the current carried by the / 3-particles is usually small .
11 .
Summary of Results .
1 .
Each atom of radium B and of radium C emits on disintegrating probably one / 3-particle , although measurement gives in either case as the average number 1*10 / 3-particles .
Each atom of radium E appears to emit less than one / 3-particle .
1912 .
] Emitted in the Transformation of Radium .
255 2 .
The absorption of the / 9-radiation from radium active deposit has been studied , measurements being made both of the number of / 9-particles penetrating the absorbing material and of the ionisation they produce .
From these data the ionising power of a / 3-particle in air and its variation with the absorption coefficient of the radiation have been calculated , the number of ions produced per centimetre of path being found to vary from 82 when \ = 15 cm.-1 aluminium to about 160 when \ = 100 cm.-1 .
3 .
With the help of data obtained by Geiger and Kovarik the numbers of / 8-particles emitted on disintegration by atoms of uranium X , thorium D , and actinium D have been estimated to be 1 , 0'8 , and 1'4 respectively .
4 .
The number of secondary / 3-particles emitted by material traversed by y-rays has been measured .
It has been deduced on certain assumptions that each atom of radium C emits on disintegrating two y-rays .
5 .
Surfaces penetrated by / 3-rays emit a secondary radiation .
This radiation is very similar to the 3-rays .
It appears that the secondary radiation cannot leave the surface unless assisted by an electric field , and that of the 3-rays some are emitted with a small velocity corresponding to a difference of potential of the order of 2 volts .
In conclusion I wish to express my sincere gratitude to Prof. Rutherford , who has both suggested this research and taken a kind interest in its progress .
|
rspa_1912_0079 | 0950-1207 | On the series lines in the arc spectrum of Mercury. | 256 | 268 | 1,912 | 87 | Proceedings of the Royal Society of London. Series A, Containing Papers of a Mathematical and Physical Character | J. C. McLennan |Sir J. Larmor, Sec. R. S. | article | 6.0.4 | http://dx.doi.org/10.1098/rspa.1912.0079 | en | rspa | 1,910 | 1,900 | 1,900 | 18 | 146 | 3,774 | http://corpora.clarin-d.uni-saarland.de/surprisal/6.0.3/?id=rspa_1912_0079 | 10.1098/rspa.1912.0079 | null | null | null | Atomic Physics | 73.808989 | Tables | 22.536772 | Atomic Physics | [
15.540815353393555,
-48.71634292602539
] | ]\gt ; On the Series in the Arc Spectrum of By J. C. McLENNAN , Professor of Physics , University of Toronto .
( Communicated by Sir J. Larmor , Sec. R.S. Received May 14 , \mdash ; Read June 13 , 1912 .
) [ PLATES 2 AND 3 .
] I. Introduction.\mdash ; This communication is intended to constitute the first of a series of studies which have been made by the writer during the past two years .
as opportunity offered , on the distribution of series lines in the arc spectrum of mercury , as well as on the constitution of some of these lines , and on their resolution by magnetic fields .
In making these studies , one of several objects kept in view was the determination , in so far as was available , and the facilities of the laboratory permitted , of the experimental conditions which should be adopted in order to obtain photographic records which would exhibit the yreabest possible amount detail .
In the present paper a summary is iven of the results obtained so far , in an eHort to make as complete as possible the identification of the lines iJlg to the different series in the arc spectrum of mercury .
Of the series formulae in use , that proposed by is the one most generally adopted .
In his scheme of representation , ( the number of wavelengths in 1 cm .
in a vacuum , i.e. ) is iven by , ( 1 ) or , approximately , by where is a universal constant is an order number , A is the limit of the series , and and are constants which characterise the course of the series .
In referring to different series , it has become usual to adopt the abbreviation , for , and in what follows in the paper this practice will be adhered to .
As illustrating the use the Ritz equations , a system of a main and a first and second subordinate series of triplets would have the following representation:\mdash ; Ritz , ' .
Zeit 1908 , vol. 9 , p. 521 .
On the Series Line in the Arc Main Series .
ortest wave-length , , greatest where , 4 , etc. First Subordinate or Diffuse , greatest wave-length , shortest where , 4 , 5 , etc. Second Subordinate or Sharp Series .
reatest wave-length , , shortest where , etc. Preliminary to proceeding with the identification of series lines in the arc spectrum of mercury , a rlumber of photographs were taken of this spectrum with a quartz prism spectrograph .
The sources used in turn for the production of the light included ( 1 ) a fused quartz Geissler tube with mercury electrodes ; ( 2 ) a quartz glass Heraeus mercury arc-lamp ; ( 3 ) fused quartz arc-lamp of special design shown in fig. 1 , which permitted either end-on or lateral the electrodeless discharge in the FIe .
1 .
*This formula is also written in a more abbreviated form\mdash ; Prof J. C. McLennan .
On the Series [ NIay 14 , vapotlr of mercury heated in an exhausted fused quartz bulb ; and commercial Cooper lamp with a side tube attached , which was closed ) a thin plate of crystalline quartz .
Of all these sources , the last mentioned the best defined and the greatest number of spectral lines .
The eproduction shown in figs. 2 and 3 was made from a photograph of the spectrum taken with this lamp .
The lines , some of which have become weakened in the process of reproduction , extend from slightly over .
down to about .
This range is somewhat greater than that obtained by ] and Retschinsky*with a fused quarLz glass Heraeus lamp , and by with an amalgam -lamp of the same type .
In the spectrograms published by both of these investigators , the red end of the spectrunl does not extend beyond , and the violet does not go below The otographic plate used in obtaining the , spectrogram in figs. 2 and 3 was a Wratten and Wainwright panchromatic .
( See Plates 2 and 3 .
) In taking the photographs , the red lines were brought out by placing a glass plate covered with a film stained with the dye imperial scarlet before the slit of the raph during an of about an hour .
A cell containing a solution of ymium ammonium nitrate , and a plate covered with a film stained with the dye rhodamine pink , were then inserted for 20 minutes , to bring out the blue-greens .
Afterwards , an exposure of three minutes without a screen was made , to bring out the balance of the .
By adopting this procedure , the fogging effect due to the relatively strong intensities of the brighter lines was greatly reduced .
In figs. 4 and 5 are shown ) roductions of an enlargement of portions of this in the neighbourhood of and .
In each of these regions it will be seen there are a number of lines which evidentl constitute the ends of series .
These terminal lines , together with between 40 and 50 additional ones which appear in the shown in figs. 2 and 3 , seem not to have been observed by Stiles , they do not appear in a somewhat extensive list of aro lines given by him in a recent paper on the spectral lines of mercury .
As a majority of these new lines was absent in the rams taken by the writer with the other sources mentioned above , and as the lamp used by Stiles was somewhat different from the Cooper Hewitt lamp used in these experiments , it is clear that the character of the spectrum one obtains from the mercury arc is determined to a very considerable extent by the type of lamp used .
* Kuch and } , ' Ann. der Phys , No. 22 , p. 852 .
Arons , ' Ann. der Phys 1907 , No. 23 , p. 176 .
'Astrophys .
Journ 1909 , vo ] .
30 , p. 48 .
1912 .
] Lines in the Arc Spectrum of Mercury .
Previous to the appearance of a paper by Dr. S. R. Milncr*on the series spectrum of mercury , but little had been done in sorting out lines of this into series .
Kayser and Rung , their study of th ' spectrum , identified only four complete members of triplets which constitute the or diH'use series and the second subordinate or sharp series of this in his paper , indicates si-x of each of the gloups of the first subordinate series , and seven members in the first group , and six in each of the other two roups of til sharp series , while Kuch and Befschinsky , S in the sprogam iven by indicate seven complete embers for each of the subordinate series .
The principal series was not identified until recently , when Paschcn succeeded in locating the lines in series of greatest wave-length in infra-red region .
By far the first to do extensive work in the lines of the spectrum of mercury and sorting them into series was Milner .
In his paper he gave the wave-lengths of 16 lines , which , in his riew , to the strong group of the principal series of triplets .
He also the wave-lengths of 16 members of the first group of the first subordinate series of triplets and the wave-lengths of 14 members of the first group of the sharp series .
He showed , moreover , that a frequency formula of the Rydberg type gives a close representation of the lines the principal series , .
:\mdash ; , where For the diffuse series , he found the best representation was given a frequency formula of the suggested by Hicks , .
:\mdash ; where ] In a later paper Paschen , who has since made a more exhanstive study of the series lines of this spectrum , identified not only a great many lines constituting the main and the first and second subordinate series of triplets but also a number of the lines which constitute a main and a first as well as * Milner , ' Phil. Mag October , 1910 , p. 636 .
Kayser and Rung , ' Ann. der , vol. 43 , p. Arons , .
cit. S Kuch and Retschinsky , loc. .
cit. Paschen , ' Ann. der Phys 1909 , ( 4 ) , vol. 29 , p. Milner , ' Phil. October , 1910 , p. 636 .
Hicks , ' Phil. Trans 1910 , vol. 210 , p. 57 .
Paschen , ( Ann. der Phys 1911 , No. 10 , p. 869 .
Prof J. C. McLennan .
On the Series [ May 14 , a second subordinate series of single lines .
He has been able , too , to confirm the accuracy of his identification by showing that certain of lines in the spectrum correspond to new combination series formed from elements of the triplet system and of the system of single lines in accordance with a scheme proposed by Ritz .
* II .
Triplet System.\mdash ; According to Paschen the frequencies of the lines of main triplet series are given approximately by the Ritz frequency , where and wave-lengths of the lines of this series are given in Table I , and their distribution in the spectrum is shown in ( Plate2 ) .
Table I. As the diagram indicates it was possible to identify 18 members of the strong roup of the principal series of on the plate from which the figure bCJiven in this paper was made .
Lines of the medium group up to could also be picked out , but none of the lines of the weak group of the principal series of triplets except that to were of sufficient intensity to permit of their identification with certainty .
The lines in the first subordinate series of triplets which it has been Bitz , 'Phys .
Zeit 1908 , vol. 9 , p. 521 ; and ' trophys .
Journ 1908 , vol. 28 , p. 237 .
1912 .
] Lines in the Arc Spectrum ercury .
possible to identify are given in Table II , and are shown rammatically in fig. 2 .
They are , as Milner has pointed out , closely represented by the Hicks formula* where As can be seen from the diagram it has been possible to extend the first roup of lines of this series as ) yiven by Milner , and also to add a very considerable number of lnembers of each of the second and ) groups .
Table II.\mdash ; Mercury Arc Lines of the First Subordinate or Diffuse Series .
III contains lists of the lines belonging to the second subordinate or lsharp series of triplets which it been possible to pick out from the plates .
These are also shown in .
In the first group it will be seen that the lines have been traced to , of the second to , and of the third to The majority of these lines can be identified quite readily in the differer ) plates excepting the higher members of the first group .
These lie close to the members of the first group of the diffuse series , and while they were distinguishable on the negatives they have become somewhat obliterated in the reproductions .
This identification of a number of lines in excess of those * Hermann , 'Ann .
der Phys 1905 , vol. 16 , p. 705 .
For this series ives the formuJa VOL. LXXXyII.\mdash ; A. Prof. J. C. McLennan .
On the Series [ May 14 , noted by Milner was rendered possible , it would appear , through having obtained rather definition in the ultra-violet below , and to bringing out with exceptional clearness the group of lines indicated in fig. 5 in the region between and Table III.\mdash ; Mercury Arc Lines of Sharp Series .
he wave-lengths of the new lines of the erent series just considered were obtained by means of a calil ) ration scale supplied by the Adam Hilger Conlpany with the spectrograph .
All that is claimed for them , therefore , is only a fair approximation to their correct values .
It will be seen , however , that they fit in fairly well with a represelltative formula containing the constants given by Paschen for the principal selies .
III .
Single .\mdash ; In addition to the main and subordinate series of triplet lines the plates in the present paper also serve to indicate the distribution of a main and two subordinate series of single lines recently discovered by A main series whose frequencies Paschen has calculated from the Ritz nsists of the lines iven in Table schen , ' Ann. der Phys 1939 , vol. 30 , p. 746 ; and 1911 , vol. 35 , 1912 .
] Lines in the Arc of Table \mdash ; Main Series of Single Lines , , P. These lines have not as yet been detected , and since they all lie well into the ultra-violet are , of course , beyond the range covel.ed in the } ) lates accompanying this ( b ) A second main series however , consists of lines which fall in part within the limits of the } ) graphs .
Their wave-lengths given in Table able VMain Series of Lines , where and being and being : ; 13571.9 c ) 5803.77 With the exception of the first two members these lines are shown in fig. 3 down to .
As in the case of the main series of triplets the intcI)sitics of lines were comparatively weak , and it was not found possible to identify them beyond the above mentioned linlit .
In his ) Paschen*states that his collaboratol Wiedemann was able to trace the series in .
plates to the member , which would seem to indicate that the consumption of energy in the Arons tube run at 20 which they served to bring out with very exceptional clearness the lines in the red end of ) spectrum .
( c ) The wave-lengths of the different members of the first and second *Paschen , ' Ann. der 1911 , vol. 35 , p. 860 .
Prof J. C. McLennan .
the Series [ May 14 , subordinate series of single lines , which Paschen found to be fairly well represented by the frequency formulae , and iven i Tables and and their distribution is shown in fig. 3 .
Table \mdash ; First Subordinate Series of Single Lines , here 2 , and whele 3 , I ) , , 4 , , 5 , \amp ; c. Table .\mdash ; Second Subordirlate Series of Single Lines , where 2 , and \amp ; c 2.5 3.5 4916.19 4.5 4108.7 5.5 6.5 3.560 8.5 9.5 10.5 11.5 12.6 As the tables and the rams show , the lines of these two series have been identified down to ?
respectively , which are limits somewhat gher than those given by Paschen .
In the table of lines given by Paschen for these series is highest member he cites for the second subordinate series and is the highest 1llember of the first ordinate series he states that Wiedemann was able to identify in their 1912 .
] Lines in the Arc Spectrum of Jlercury .
IV .
Combination \mdash ; In support of the accuracy of his identification of the liflerent members of the triplet and single series of lines in the mercury arc spectrum , Paschen has calculated after the scheme proposed by number of " " combination series\ldquo ; from elements supplied by the triplet and single series formulae , and in all the examples of these combination series which he cites there is an close agreement between the calculated and the positions of these lines .
In his first " " combination series\ldquo ; formed from elements of the principal series of triplets and the first subordinate series of single lines the frequencies are given by where 2 , , 2 , The wave-lengths corresponding to this formula are given in Table VIII , Table VIII .
, D. 'D .
'D .
and by comparing them with those given in Table II it will be seen that they lie close to the lines of the diffuse series of triplets .
In a number of cases they be detected quite readily in the plates accompanying this paper .
This combination series was at first supposed by Pascben to constitute the lines of the third series of satellites of the diffuse series of triplets .
( b ) A second " " combination series\ldquo ; which has been cited by Paschen is given by , where 3 , The linlit of the series is approximately given by and the bers as a consequence all lie in the -red and , therefore , do not appeal in the ) lates in this paper .
Paschen 's .
in this region show a close reement between the observed and calcnlated wave-lengths for the members and ( c ) A third combination series given by him is represented by the frequency formulae where , 4 , 5 , etc. , and is formed from elements of the first subordinate series of single lines , and of the diffuse series of triplets .
The wave-lengths of the lines of this series are given in Table IX .
Prof. J. C. McLennan .
On the [ May 14 , Table IX .
They consist of sets of close triplets with the member of longest wavehaving the reatest intensity and the member of intermediate wavelength having the least .
By comparing these lines with those iven in Table , it will be seen that they lie close to the lines constituting the first subordinate series of single lmes .
A majority of the members of this selies of triplets as given in Table IX could be identified in the eratives , but , as the plates show , only two or three members can be distinguished in the reproductions .
( d ) A fourth " " combination series\ldquo ; given by Paschen is represented by the frequency formula , where 2 , and The first three members of this series are given in Table X. Table X.\mdash ; Combination Series 3.5 4.5 As the table shows the first member of the series lies in the infra-red .
The second member can be readily seen in the plates accompanying this paper , but the third member is not shown in the reproductions .
This line is not given by Stiles in his list of arc lines for mercury , but one very close to it appears in his list of park lines for this element .
In the plates of the writer it is detectable as a faint sharp line , and close to it can be seen another line of about the same intensity and sharpness .
This additional line does not appear in either of the lists of arc lines given by Wiedemann or Stiles .
The positions of the second and third members of this series are shown in one of the diagrams of fig. 3 .
( e ) As representing a fifth combination series Paschen gives the relation , where and , has the values given in Table XI .
1912 .
] Lines in the Arc Spectrum of Mercury .
Table XI.\mdash ; Combination Series , P. 5316.87 4822.5 They have , as the frequency formula shows , a constant frequency difference of with the lines of the main series of single lines .
Their distribution in the spectrum is shown in the reproduction of fig. 3 , from which it will be seen that the members have been identified up to .
Owing to lack of intensity , however , it was impossible to trace the series beyond this limit .
( f ) The last combination series cited by Paschen is represented by , where 2 , and , has the values given in Table XII .
The first seven members of this series are iven in Table XII .
Table XII.\mdash ; Combination Series , S. 3 .
9775.69 4 .
5776.06 5 .
3814.90 6 .
7 .
4078.05 2857.07 2564.14 2378.4 The lines of this series , as can be readily seen , have a constant frequency difference with the corresponding members of the second subordinate series of single lines which is given by .
The positions of the lines in the spectrum are shown in fig. 3 down to .
Beyond this limit the members of the series practically coincide with the higher members of the second group of the sharp series of triplets , and it is difficult to uish them in the plates .
On the Series Lines in the Arc Spectrurn .
Summary of Results .
I. By means of a modification of the Cooper Hewitt mercury arc lamp , raphs of the mercury spectrum were obtained showing well defined lines ranging from to beyond II .
In the triplet series of lines in the mercury arc spectrum the following members have been identified:\mdash ; Principal series\mdash ; First group to Second group to Third group First subordinate series\mdash ; First group to Second group to Third group to Second subordinate series\mdash ; First group to Second group to Third group to III .
In the series of single lines in the mercury arc spectrum the following members have been identified:\mdash ; Principal series .
to 9 First subordinate series to Second subordinate series to IV .
Illustrations are given of the " " combination series\ldquo ; lines , calculated according to the scheme proposed by Ritz from elements of the triplet series and single line series formulae .
In conclusion , I desire to acknowledge my indebtedness to Mr. S. A. Kennedy for kindly assisting me in some preliminary work with the spectrograph used in this investigation . . . .
Roy .
Soc. Proc. , vol. 87 , PI .
3
|
rspa_1912_0080 | 0950-1207 | On the constitution of the mercury green line \#x3BB; = 5461 \#xC5;. U., and on the magnetic resolution its satellites by an echelon grating. | 269 | 276 | 1,912 | 87 | Proceedings of the Royal Society of London. Series A, Containing Papers of a Mathematical and Physical Character | J. C. McLennan |Sir J. Larmor, Sec. R. S. | article | 6.0.4 | http://dx.doi.org/10.1098/rspa.1912.0080 | en | rspa | 1,910 | 1,900 | 1,900 | 6 | 136 | 3,993 | http://corpora.clarin-d.uni-saarland.de/surprisal/6.0.3/?id=rspa_1912_0080 | 10.1098/rspa.1912.0080 | null | null | null | Atomic Physics | 71.526908 | Optics | 8.979535 | Atomic Physics | [
21.250028610229492,
-31.618497848510742
] | 269 On the Constitution of the Mercury Green Line X = 5461 A.U. , and on the Magnetic Resolution its Satellites by an Echeloyi Grating .
By J. C. McLennan , Professor of Physics , University of Toronto .
( Communicated by Sir J. Larmor , Sec. R.S. Received May 14 , \#151 ; Read June 13 , 1912 .
) [ Plates 4 and 5 .
] In a previous communication on the series lines in the arc spectrum of mercury , attention was drawn by the writer to the excellence of the spectrograms obtained when a highly exhausted commercial Cooper Hewitt mercury arc-lamp was used as the source of the light .
With this lamp , provided with a side tube carrying a window of thin crystalline quartz , it was found that exceedingly good definition was obtained over the whole range of the spectrum from slightly beyond X \#151 ; 7000 down to X = 2150 .
When using the lamp at a later period in making some observations with an echelon grating of high resolving power on the structure of some of the finest lines in the visible portion of the spectrum , it was found that the components of a number of these lines also came out with exceedingly good definition .
A special study was made of the mercury green line X = 5461 and its satellites under a variety of conditions , and the present paper , which deals with some of the results obtained , contains a number of specimens of the photographs which were taken in following up points of interest which arose in the course of this work .
I. The Structure of the Mercury Green = 5461 .
The echelon grating used in the investigation was made by the Adam Hilger Company , and consisted of 30 plates P004 cm .
thick , with a width of step of 1 mm. The refractive indices of the glass of which the plates were made , taken from data supplied by the maker , were yac = 1*5712 , yap =1*5752 , yaP = 1*5852 , and yaG = 1*5935 .
With these a Hartmann dispersion formula ya = 1*553706 + 764860 X-2\#151 ; 4*8887 x 10I .
* * * * * 7 X-4 was established for the instrument .
Three reproductions of plates taken with the echelon of the green line X = 5461 and its satellites are shown in figs. 1 , 2 , and 3 ( Plate 4 ) .
Pig .
1 shows the resolution obtained with the light intensity thrown into a single order , 270 Prof. J. C. McLennan .
Constitution of the [ May 14 , and fig. 2 with the intensity concentrated in two successive orders .
In both these cases the source of the light was the Cooper Hewitt lamp mentioned above , and the green line in the spectrum in both cases was isolated by passing the light from the tube through a Hilger constant deviation spectroscope .
Fig. 3 shows the results obtained when the green line was isolated with an absorbing fluid .
The light , after leaving the tube , was passed through a glass cell containing a solution of neodymium ammonium nitrate , then through a second filled with a dilute solution of potassium bichromate , and finally sent into the echelon grating .
The various satellites in this case it will be seen are almost of the same intensity as those shown in figs. 1 and 2 .
A number of plates were made similar to those shown in figs. 1 , 2 , and 3 , and five of the best of them were accurately measured by Mr. J. K. Robertson , who kindly offered to do this for me .
The results are given in the following table , all measurements being made from the centre of the main line , which is given by some as a doublet , but which in my plates was not resolved:\#151 ; Table I.\#151 ; Resolution of Hg line \ \#151 ; 5460-95 .
Plate .
Sat. ] .
Sat. 2 .
Sat. 3 .
Sat. 4 .
Sat. 5 .
Sat. 6 .
A 0*210 0-137 0-090 -0 '070 -0 -105 -0-242 B \#151 ; 0-134 0-091 -0 -069 -0 *104 -0-243 C \#151 ; 0-137 0-091 -0 -070 -0-102 -0 -241 D 0*213 0-135 0-091 -0-071 -0 -104 -0 -243 E \#151 ; 0-134 0-089 -0-072 -0 -105 -0 -244 Average + 0-21 + 0 -135 + 0 -090 -0-070 -0 -104 -0 -243 As can be seen from figs. 1 , 2 , and 3 , all of the satellites given in Table II are clearly defined , excepting the one of greatest wave-length + 0'21 .
This satellite was too faint to be detected on most of the plates , but on two or three of them faint traces of it were seen .
For comparative purposes , the results obtained for the resolution of this line by a number of observers are taken from a paper by Luneland , and are given in Table II .
From this table it will be seen that the resolution obtained by the writer , both as to the number of satellites and as to their relative intensities , agrees best with that obtained by G-ale and Lemon with a Michelson grating , and with that of Stansfield obtained in his later work with an echelon .
The values obtained for the positions of the satellites + 0*090 and +0T35 are , however , somewhat greater than those obtained by other observers .
Table II.\#151 ; Resolution of Hg line X = 5461 by different Observers .
1912 .
] Mercury Green Line 5461 A.U. ft ^ \#163 ; r2 -*-'7 |1 Sh * *dg c3 ^ tdD \#169 ; * H fc'- ' rd d 13,2 cd ^ 0Q rP a \#169 ; QQ w g.S o III " ?
o 'S'i 1 " fi ?
* a js PQ rj g T5 fl f H cS \#169 ; \#169 ; / " -s JSflJ SM 5 * | hP ^ l ^ 0 k *d g^ .si-lg g \#169 ; rP -g 0 ^ .2 g 'SS W ) ^ 1 i | | r ?
1 ^ 1 e s 9 I I 9 o 05 1 9 1 to CO ^ 1 |S | | o 1 o 1 0 o 1 o o o tO | rl H H H 1w 1 on oo \#169 ; 1 \#174 ; 1 * 1 rH on | j 3 ?
* | to r\#151 ; 1 05 rH H 05 CO T* on r-t H rH \#169 ; 1 ^ 05 00 CO o to on o 19 9 9 9 CO 1 9 1 GO ^ | 00 to to O I I \#169 ; 1 o o o o ( III o 1 o o o o I 1 1 o o o o OH rH rH | rH rH HlOHbCOO on C5 on to on j tJ* CO 05 l\gt ; CO CO ( M H on on on Tf\lt ; tOCOiOrHCOa\gt ; X\gt ; 0 i\gt ; -^onrHOoOiOonQ I rHrHr-irH*\#151 ; HOOOO to oo on ^ co CO CO G5 rH CO O O O rH rH O CO H O on to | on on on \#169 ; \#169 ; \#169 ; 1 1 I oooooooooooooo 1 1 1 1 1 1 1 1 \#169 ; o o 1 to " Hh on | | 1 1 \#169 ; 1 ^ O CO o oo on o 19 199 ^ o 00 1 ^ 1 o | 9 | | o 1 o 1 o o o 1 1 o \#169 ; C5 on | I on 1 ?
So S 8 19 9 19 cq 1 ^ 2 i ?
1 Ml !
o 1 \#169 ; 1 o o o 1 1 \#169 ; o S-l 1 !
1 1 1/ 10 I\amp ; 111 IS- 1S-1 1 1 1 1 to ^ I on 1 1 1 1 1 on 1 0 05 loin to 1 1 9 iP i 1 1 1 1 \#166 ; o i o 1 o 1 o o on | 1 111 1 * j CO to rH | 1 1M 1 Mil CO on 1 | 1 1 1 1 ^ 00 05 TH O | ?
lSS CO 00 1 9 to on 1 ^ i Mil o 1 o 1 o o o o 1 1 1 \#169 ; o \#169 ; on 1 1 1 1 1 1 \#169 ; 1 * 1 II 1rH I w 1 1 II 1 on TfJ on 1 1 1 1 1 rH 1 ?
8 8 | 9 | | 9 JO 1 9 Sq 1 ^ 1 i c9 | , 1 w 1 o 1 o 1 \#169 ; \#169 ; 1 \#169 ; \#169 ; on i rH 1 1 1 1 1 j CO 1 M 1 1 1 | on 1 M 1 Mil CO r* on 1 1 1 1 1 |S \#169 ; 8 9 | | 9 o 1 9 1 ^ 1 S Mil o 1 o 1 \#169 ; \#169 ; 1 o o \#169 ; g P-I r\#151 ; i r-H* 0 r\#151 ; i *5 \#171 ; . !
-^ p , oo 00 o CP 05 JO A i jo m -2 Ph p , to~ r-H :i M -S n m A ~ ^ o " ^ " ... N or 11^ ill* S \#171 ; OQ ^ " S ^ 00 ^ ^ 05 ^ 51 b ?
\#174 ; ^ .
n .co \#163 ; ^ 2 g\lt ; S ^ ^ W . .
a ^ cT \#163 ; OQ \#169 ; o O .
EH JS fi S \#163 ; *3 ^ .
4^:-iiis j,4|S2fg9 g n " .
" * Mi ?
1\#187 ; 2^ rP 4i ^ I ^Ill 'll J 'd * 3 ^ ^ ^ S S \#163 ; M 3 \#169 ; T~^ 1* j\#187 ; g ^ is 3 S pq r* g *S 2-1 \#166 ; 3 -s S | I j 5 ?
S * H\#151 ; +.+ too = |jF * *4\#151 ; 272 Prof. J. C. McLennan .
Constitution of the [ May 14 ; IT .
Variations in the Structure of the H Line \#151 ; 5461 obtained by Varying the Source .
While investigating the structure of the green line with light from a number of other sources , an effect was noted which had been observed and described by Janicki , * Prince Galitzin and Wilip , f and by Stansfield.ij : The effect was observed with an Heraeus quartz glass arc-lamp , and with a lamp of special construction , described in a previous communication , both with end on and with side exposure .
With these lamps , immediately after the arc was struck , the structure of the green line was much the same as that given in figs. 1 , 2 , and 3 .
As the lamp became heated , however , the appearance changed to that shown in fig. 4 , which was that obtained with the Heraeus lamp , and to that shown in fig. 5 , which was obtained with an end-on exposure with the special lamp referred to above .
The change consisted in the central bright band splitting up into two , while the lines corresponding to the satellites widened and became more diffuse .
In the final appearance the two branches of the main line , and the bands corresponding to the satellites \#151 ; 0'070 , \#151 ; OT04 and +(H)90 , 4- 0T35 , were all about the same width and of the same intensity .
These six bands can be seen in both figs. 4 and 5 , where they appear between two successive orders of the satellite \#151 ; 0'243 .
This structure is somewhat different from what Janicki observed .
In the paper in which he described this effect he states that he observed in place of the original line and its satellites a peculiar system of five equidistant bands when the original Fig. 6 .
* Janicki , 4 Ann. der Phys. , ' 1906 , vol. 19 , p. 35 .
t Prince Galitzin , ' Bull , de l'Acad .
Science de St. Petersbourg , ' 1907 , p. 159 .
J Stansfield , ' Phil. Mag. , ' September , 1909 .
L912 .
] Mercury Green Line X = 5461 A.U. components of the lines were lost in a continuous spectrum .
The appearance which he obtained is shown in fig. 6 , which is taken from his paper .
Prince Galitzin and Wilip suggest that the effect is probably due to a reversal of the lines or to some property of the echelon , while Stansfield rather favours the view that the bands are due to secondary spectra produced by the echelon .
To the writer , the phenomenon had the appearance of a reversal of the main line due to absorption , together with a widening and an intensification of the satellites arising from an increase in the temperature and the pressure of the mercury vapour in the tube .
III .
On the Magnetic Resolution of the Satellites of the Green of Mercury X = 5461 .
In attempting to obtain photographs of the Zeeman effect with the satellites of the Hg line X = 5461 it was found necessary to use light of strong intensity and to give exposures of long duration .
To meet these experimental requirements the arrangement shown in fig. 7 was adopted .
The magnet was provided with pole pieces each of which was divided into two H " Fig. 7 .
parts that could be bolted together .
Along the break each of these parts had a groove in it , and into this groove the Cooper Hewitt lamp was fastened as shown in the figure with its axis parallel to the direction of the magnetic field .
This tube emitted light of strong intensity and when the field was on the discharge was concentrated along its axis .
This protected the glass from the discharge and therefore permitted exposures of long duration to be made .
It was found possible with this arrangement to obtain fields up to about 3500 gauss .
With the apparatus arranged in this way photographs were taken of the magnetically resolved satellites \#151 ; 0 243 and +0'090 .
Two reproductions are 274 Prof. J. C. McLennan .
Constitution of the [ May 14^ shown in figs. 8 and 9 , which illustrate the magnetic resolution of the satellite \#151 ; 0243 .
In taking the plates from which these reproductions were made a double image prism was inserted in the telescope of the echelon .
The eyepiece was removed from this telescope and a microscope objective provided with a camera bellows and plate holder was focussed on the two real images formed in the focal plane of the object glass of the echelon ( see Plate 5 ) .
The echelon itself was so disposed that the light was thrown into two successive orders ; and the satellite in question , it will be seen , appears in the centre of each of the figures .
The upper part of the figure gives vibrations perpendicular to the lines of force and the lower part those parallel to the field .
In the upper plate of fig. 8 the satellite appears as a wide doublet and in the lower plate as a narrower doublet .
Fig. 9 represents the same result , but in this reproduction while the outer pair of the quartet is rather faint the inner pair is quite clear and well defined .
This photograph also shows the main line resolved into three diffuse components , the outer ones in the upper part of the figure being perpendicular to the field and the inner one in the lower part being parallel to it .
This photograph permitted the separation of the outer pair of the satellite 's quartet to be compared with that of the outer pair of the components of the main line .
Since the main line is known to be resolvable into a nonet under a high magnetic field with its lines displaced 0 , + fa , +a , + f + 2 where a , represents the displacement of each of the outer components of a normal triplet , it follows that the mean displacement for the outer pair of the main line shown in the upper part of fig. 9 corresponds to 3a .
A number of settings on plates similar to that shown in fig. 9 showed the displacement of the outer pair of the quartet of the satellite to be double that of the inner pair and equal to the mean distance between the outer pair of the main triplet .
It follows then that the components of the quartet into which the satellite \#151 ; 0*243 was resolved by the field used are represented by the + f and +-| a. The reproduction shown in fig. 10 was made with the echelon adjusted so as to throw the light well into the \#151 ; 0*243 satellite of one order and into the +0*090 satellite of the neighbouring order .
In the upper part of the figure each of these satellites is shown divided into two bands , one of the outer bands of satellite + 0*090 being displaced so as to obscure the satellite + 0*135 .
In the lower part of the figure neither of the satellites is resolved , as the field used was not sufficiently intense .
In fig. 11 a stronger magnetic field was used , and it will be seen that the components of the satellite +0*090 parallel to the field were resolved into a doublet , as well as those of the satellite \#151 ; 0*243 .
In the upper part of the figure it will be seen the separation of the outer components of both 1912 .
] Mercury Green Line A. \#151 ; 5461 A.U. satellites was so great as to cause overlapping with the components of the neighbouring satellites .
Comparative measurements made on the relative displacements of the different members of the quartets into which each of these satellites was divided showed the distance between the outer pair of the satellite + 0*090 to be the same as that between the outer components of the satellite \#151 ; 0*243 , while the distance between the inner pair of the former satellite proved to be only about four-fifths of that of the inner pair of the latter satellite .
The lower part of fig. 8 brings this point out very clearly , for in that reproduction while the field used was sufficient to resolve the inner pair of the satellite \#151 ; 0*243 , the inner pair of the satellite +0*090 does not show any separation .
The displacements of the four members of the quartet into which the satellite 0*090 was resolved are represented therefore by + fa and + fa , where as before a represents the displacement of the outer component of a normal triplet .
Lohmann* in his paper on the Zeeman effect states that he observed that the satellites of the Hg line \ = 5461 underwent a complex resolution in a magnetic field , but he apparently made no measurements on the displacements of the components .
This , however , was done by G-ehrcke and von Baeyer by means of crossed Lummer plates .
In their experiments they only succeeded in resolving the satellites mentioned above into triplets , and from the displacements of the outer components they deduced the mean value ejm \#151 ; 2*63 x 10~7 for the satellite of shorter wave-length and e/ m = 2*77 xlO-7 for the satellite of longer wave-length . .
These results it will be seen correspond closely to the value f-a obtained for the separation of the outer component of both satellites on my plates .
Lunelandf in his recent paper gives a quartet for the resolution with moderate fields of each of these satellites , and states that with high fields the lines forming the quartets appeared to be capable of still higher resolution .
As regards resolution of the two satellites into quartets there is therefore an agreement between his results and those given in the present paper .
In one particular , however , they differ .
In his resolution the separation of the outer components of both satellites was the same ; and the separation of the components of both satellites vibrating parallel to the magnetic field was very closely one-half that of the components , vibrating perpendicularly to the field .
According to my measurements , on the other hand , while this * Lohmann , ' Inaug .
Biss .
, ' 1907 .
t Luneland , ' Ann. der Phys. , ' 1911 , vol. 34 , p. 505 .
276 Constitution of the Mercury Green Line \ \#151 ; 5461 A.U. latter characteristic was true of the separation of the components of the satellite \#151 ; 0243 , it was not true of the separation of the components of the satellite + 0*090 where the displacement of the inner pair was only four-fifths of that of the outer pair .
The reproduction shown in fig. 8 makes this point of difference quite clear .
The magnitude of the separation obtained by Luneland for the outer components of the two satellites is in practical agreement with that obtained by Gehrcke and von Baeyer and with that shown by my own plates .
1Y .
Summary of .
( 1 ) The line Hg X = 5461 from a Cooper Hewitt mercury arc lamp has been resolved by a 30-plate echelon into a main line which is probably a doublet , together with three satellites of greater wave-length and three of shorter wave-length .
( 2 ) When the mercury arc was formed in a fused-quartz lamp , with a large consumption of energy , the main component of the Hg line X = 5461 broke up into two members , probably the result of absorption , and all the satellites widened and became approximately of the same intensity .
( 3 ) The use of a Cooper Hewitt mercury arc lamp with its axis along the magnetic lines of force provided a source of light of strong intensity and permitted exposures of any desired length of time to- be made .
( 4 ) The satellite \#151 ; 0*243 of the Hg line X = 5461 has been resolved by a magnetic field into four components whose displacements are represented approximately by + f a and +fa , and the satellite +0*090 of the same line into a quartet for the components of which the displacements are approximately +f a and + -| a , where a represents the displacement of the outer component of a normal triplet .
For much preliminary work in adjusting the apparatus used in this investigation I am indebted , and my thanks are due , to my students Messrs. E. N. Macallum , S. Smith , and S. Kennedy .
MLennan .
Ro* ' So'- P , ,oc- A ' vo1 ' 87\gt ; plFig .
3 yicfennan .
Roy .
Soc. Proc. A , vol. 87 , PI .
5 .
|
rspa_1912_0081 | 0950-1207 | On an expansion apparatus for making visible the tracks of ionising particles in gases and some results obtained by its use. | 277 | 292 | 1,912 | 87 | Proceedings of the Royal Society of London. Series A, Containing Papers of a Mathematical and Physical Character | C. T. R. Wilson, M. A., F. R. S. | article | 6.0.4 | http://dx.doi.org/10.1098/rspa.1912.0081 | en | rspa | 1,910 | 1,900 | 1,900 | 3 | 343 | 7,817 | http://corpora.clarin-d.uni-saarland.de/surprisal/6.0.3/?id=rspa_1912_0081 | 10.1098/rspa.1912.0081 | null | null | null | Atomic Physics | 27.561742 | Thermodynamics | 22.118294 | Atomic Physics | [
2.9895055294036865,
-72.52582550048828
] | 2 77 On an Expansion Apparatus for making Visible the Tracks of Ionising Particles in Gases and some Results obtained by %ts Use .
By C. T. R. Wilson , M.A. , F.R.S. ( Received June 7 , \#151 ; Read June 13 , 1912 .
) [ Plates 6\#151 ; 9 .
] In a recent communication* I described a method of making visible the tracks of ionising particles through a moist gas by condensing water upon the ions immediately after their liberation .
At that time I had only succeeded in obtaining photographs of the clouds condensed on the ions produced along the tracks of a-particles and of the corpuscles set free by the passage of X-rays through the gas .
The interpretation of the photographs was complicated to a certain extent by distortion arising from the position which the camera occupied .
The expansion apparatus and the method of illuminating the clouds have both been improved in detail , and it has now been found possible to photograph the tracks of even the fastest / 9-particles , the individual ions being rendered visible .
In the photographs of the X-ray clouds the drops in many of the tracks are also individually visible ; the clouds found in the a-ray tracks are generally too dense to be resolved into drops .
The photographs are now free from distortion .
The cloud chamber has been greatly increased in size ; it is now wide enough to give ample room for the longest a-ray , and high enough to admit of a horizontal beam of X-rays being sent through it without any risk of complications due to the proximity of the roof and floor .
The .Expansion Apparatus .
The essential features of the expansion apparatus are shown in fig. 1 .
The cylindrical cloud chamber A is 16'5 cm .
in diameter and 3'4 cm .
high ; the roof , walls and floor are of glass , coated inside with gelatine , that on the floor being blackened by adding a little Indian ink .
The plate glass floor is fixed on the top of a thin-walled brass cylinder ( the " plunger " ) , 10 cm .
high , open below , and sliding freely within an outer brass cylinder ( the " expansion cylinder " ) of the same height and about 16 cm .
in internal diameter .
The expansion cylinder supports the walls of the cloud chamber and rests on a thin sheet of indiarubber lying on a thick brass disc , which forms the bottom of a shallow receptacle containing water to a depth of about 2 cm .
The * ' Roy .
Soc. Proc. , ' 1911 , A , vol. 85 , p. 285 .
VOL. LXXXVII.\#151 ; A. 0 Mr. C. T. R. Wilson .
Apparatus for making [ June 7 , water separates completely the air in the cloud chamber from that below the plunger .
The base plate rests on a wooden stand , not shown on the diagram .
The expansion is effected by opening the valve B and so putting the air space below the plunger in communication with the vacuum chamber C Fig. 1 .
through wide glass connecting tubes of about 2 cm .
in diameter .
The floor of the cloud chamber , in consequence , drops suddenly until brought to a sudde'n stop , when the plunger strikes the indiarubber-covered base plate , against which it remains firmly fixed by the pressure of the air in the cloud chamber .
To reduce the volume of air passing through the connecting tubes at each expansion the wooden cylinder D was inserted within the air space below the plunger .
The valve is opened by the fall of a weight W released by a trigger arrangement T ( fig. 3 ) .
On closing the valve and opening communication with the atmosphere through the pinch-cock F , the plunger rises and so reduces the volume of the air in the cloud chamber .
By means of the two-pinch-cocks F and G ( the latter on a tube communicating with the vacuum chamber ) , the plunger may be adjusted to give any desired initial volume V\ between the upper limit v2\#151 ; the maximum volume of the cloud chamber\#151 ; and the lower limit reached when the pressure below the plunger is that of the atmosphere .
The final volume v2 is always the same ( about 750 c.c. ) , the expansion ratio v2/ videpending only on the initial volume .
A scale attached to the side of the cloud chamber enables the position of the top of the plunger to be read , 1912 .
] Visible the Tracks of Ionising Particles Gases .
279 and hence the initial volume to be determined , the area of the cross-section of the plunger and the maximum volume v2 of the cloud chamber being known .
In setting up the apparatus , the plunger is placed on the rubber-covered base plate , and the expansion cylinder slipped over it , a hole in the side of the cloud chamber being open at this stage to allow of the imprisoned air escaping .
Then , by blowing in air through F , momentarily opened for the purpose , the plunger is driven up to a height sufficient to allow of the largest desired expansions being made .
The aperture in the wall of the cloud chamber is then closed , and the mass of imprisoned air remains unchanged during subsequent operations .
The gelatine layer under the roof of the cloud chamber is connected , through a ring of tinfoil cemented between the cylindrical wall and the roof , with one terminal of a battery of cells of which the other terminal is connected , through the brass expansion cylinder and plunger , with the layer of blackened gelatine on the floor of the cloud chamber .
An approximately uniform vertical electric field of any desired intensity may thus be maintained in the cloud chamber .
The gelatine lining of the roof and walls is formed by pouring into the cloud chamber , before attaching it to the expansion cylinder , a hot solution containing about 4 per cent , of gelatine and OT per cent , of boracic acid and allowing the surplus to drain away by inverting the vessel .
The thin coating of gelatine which remains is allowed to dry over calcium chloride .
The cloud chamber is cemented to the expansion cylinder by means of gelatine .
A comparatively thick layer ( about 1 mm. ) of a solution containing 15 per cent , of gelatine , 2 per cent , of boracic acid , and 3 per cent , of Indian ink is poured on to the glass plate which forms the floor of the cloud chamber , the brass walls of the plunger being prolonged for about 1 mm. above the upper surface of the plate , thus forming a shallow receptacle for the gelatine and making an efficient electric contact with it .
The blackened gelatine is not allowed to dry , but at once covered to prevent evaporation and to protect it from dust till ready for use .
The gelatine is in all cases previously sterilised by heat .
Method of Illuminating and the Clouds .
As in the experiments described in my last paper , a Leyden jar discharge through mercury vapour at atmospheric pressure is used for the instantaneous illumination pf the clouds resulting from the expansion .
A horizontal silica tube ( fig. 2 ) about 15 cm .
long , and having an internal diameter of about 1 mm. , is filled with mercury and enclosed , for the central 4 cm .
of its 280 Mr. C. T. R. Wilson .
Apparatus for making [ June 7 , length , by a close-fitting silver tube about 2 mm. thick , and having a slot about 1 mm. wide extending from end to end .
The silver tube when heated by a small flame serves to keep the enclosed portion of the silica tube at a nearly uniform temperature high enough to vaporise the mercury , and thus \#169 ; Fig. 2 .
form a mercury-vapour spark-gap .
Connection with the Leyden jars is made through platinum wires fused through the ends of glass tubes filled with mercury and inserted into the ends of the silica tube .
The silica tube is first filled with mercury , the end pieces inserted , and a small flame placed under the silver tube .
When the mercury occupying the portion of the silica tube which is surrounded by the silver jacket has all been vaporised ( the excess of mercury escaping from the ends of the tube ) no further change takes place and the spark-gap is ready for use .
The very considerable capillary forces set up when the mercury is forced into the narrow space between the glass end pieces and the surrounding silica tube effectually prevent the violent oscillatory motions which are apt to be the principal source of trouble in the use of a mercury spark-gap of this type .
For firing the spark the arrangement used is essentially that which has generally been employed in instantaneous photography by the Leyden jar discharge .
The outer coatings of two sets of 4 or 5 " gallon " Leyden jars , standing on the floor of the room , are connected to the terminals of the illuminating spark .
The inner coatings are connected to the terminals of a Wimshurst machine and to two brass balls separated by a space of about 5 cm .
which forms the primary spark-gap .
The jars having been charged almost to sparking potential , a metal ball is allowed to fall between the terminals of the primary spark-gap , causing a spark to pass at both gaps .
The ball whose fall causes the spark is hung by a fine thread , just strong enough to carry it , from the weight W which works the valve of the expansion apparatus .
The arrangements for firing the spark at a definite interval after the expansion are shown diagrammatically in fig. 3 .
The weight W is carried by a cord which passes through an iron ring in a firm support , and thence nearly horizontally to the trigger T , to which it is attached by a loop .
A second string , slack at this stage , connects a point on the first cord with the valve of 1912 .
] Visible the Tracks of Ionising Particles in Gases .
281 the expansion apparatus .
On pulling the trigger the cord attached to it is released and the weight falls until the second string is stretched tight , when it is brought to a sudden stop , the valve being simultaneously opened and the expansion thereby effected .
The thread breaks at this moment and the steel OPO sphere continues to fall , finally passing through the primary spark-gap , P , and causing the illuminating spark to pass at S. The upper spark-gap , Q , shown in the figure , was only employed in the experiments with X-rays .
In the experiments described in this paper , the camera lens has always occupied one of the two positions indicated diagrammatically in fig. 4 , ( a ) and ( b ) .
In ( a ) the small circle represents a transverse section of a narrow Fig. 4 .
horizontal beam of ionising rays crossing a diameter of the cloud chamber .
The camera looks in a horizontal direction normal to the ionising beam .
The mercury spark-gap is at S , at the principal focus of a cylindrical lens about 282 Mr. C. T. R. Wilson .
Apparatus for making [ June 7 , 20 cm .
long and 2 cm .
wide , and having a focal length of about 3 cm .
With this arrangement the whole of the cloud produced by a considerable length of the ionising beam is illuminated , while the direction of the incident light makes a comparatively small angle ( about 25 ' ) with the axis of the camera .
Arrangement ( b ) has been used chiefly with the a-rays , which give clouds of sufficient density to scatter a large amount " of light at right angles to the illuminating beam .
The camera lens is vertically over the centre of the cloud chamber ; and by means of two similar mercury spark-gaps ( arranged in series ) , each at the principal focus of a cylindrical lens like that used in ( a ) , a horizontal stratum of about 2 cm .
in vertical thickness and extending across the whole area of the vessel , is illuminated .
The lens which I have used is a Beck " isostigmar , " the full aperture , marked F 5*8 , being utilised ; Ilford " Monarch " plates were employed .
Ionisation by u-Bays .
( Plate 6 , and fig. 1 of Plate 7 .
) Fig. 1 ( Plate 6 ) is a typical photograph of the cloud obtained on expansion when a minute quantity of radium is placed on the tip of a wire projecting into the cloud chamber .
A potential difference of 40 volts was maintained between the roof and floor , the roof being at the higher potential .
The camera was placed with its axis vertical , and a horizontal section of the cloud chamber , about 2 cm .
in depth , was illuminated ( arrangement ( b ) of fig. 4 ) .
The / 3-rays are not visible in the photographs obtained with this mode of illumination .
The narrow , sharply defined rays of these photographs are clouds condensed along the tracks of a-particles which have traversed the supersaturated air after the expansion , so that there has been very little time for the ions to diffuse before losing their mobility through condensation of water upon them .
The diffuse rays are clouds condensed upon ions set free by a-particles which have traversed the air before its expansion , so that there has been time for diffusion of the ions before the formation of the cloud .
The weaker the electric field the greater is the maximum possible age , and consequent diffuseness , of the tracks which may be present ; with a potential difference of only two or three volts , wide finger-like clouds are formed on expansion .
a-rays which pass after the expansion can only leave visible trails if the degree of supersaturation still remains sufficient to cause water to condense on the ions .
In the immediate neighbourhood of the cloud already condensed on an older track , the supersaturation remaining may be insufficient to cause condensation , although elsewhere the a-particle may leave a visible trail .
This is doubtless the explanation of the fact that 1912 .
] Visible the Tracks of Ionising Particles in Gases .
283 most of the sharply defined trails only seem to begin at some considerable distance from the radium , the diffuse cloud trails formed at the moment of expansion being so closely packed near the source of the rays that there is little chance of an a-particle , ejected after the expansion , finding the supersaturation necessary for rendering its trail visible , until it has travelled for some distance .
Except in the case of photographs taken very soon after the insertion of the radium , the trails of a-particles from the emanation and later radioactive products also appear .
Fig. 4 is a photograph of the cloud formed by expansion after the radium-tipped wire had been for some days in the cloud chamber and had then been removed ; a-rays are seen running in all directions .
A sharply defined trail may sometimes be observed crossing one or more diffuse ones , and is then frequently invisible for some little distance on either side of the diffuse ray , the necessary supersaturation not being attained owing to previous condensation on the ions of the older trail .
For some purposes ( if , for example , the ranges of the a-particles were under investigation ) it would be necessary to know definitely whether the a-particle giving rise to any given trail had passed before or after the expansion , the density of the air traversed being different in the two cases .
The trails of a-par tides passing previously to the expansion have their dimensions altered between the liberation of the ions and the deposition of water upon them ; but , the displacement of the air being everywhere nearly in a vertical direction , the horizontal dimensions are almost unaffected .
In the photographs it will be observed that the diffuse rays are shorter than the sharply defined rays in accordance with the greater density of the air at the moment of passage of the a-particle .
There is .
no difficulty in securing that the particles whose tracks are being photographed shall have passed either all before or all after the expansion .
It is only necessary to attach to the plunger a vertical plate ( glass 2 mm. thick was used ) immediately in front of the source of the rays , and with a horizontal slot so placed that it shall be at the level of the radiant point either before or after the expansion .
Fig. 2 is a photograph taken under the latter condition ; the diffuse tracks are now absent .
This method is , of course , inapplicable to the study of the rays from the .
emanation within the cloud chamber .
As will be seen from the photographs , the a-rays are generally straight over the greater part of their length , but they nearly all are bent , often abruptly , in the last 2 mm. of their course .
Abrupt bends through considerable angles are seen much earlier in the course of some of the rays .
In fig. 3 of Plate 6 is shown an enlargement of a particularly interesting 284 Mr. C. T. R. Wilson .
Apparatus for making [ June 7 , trail .
Here there are two absolutely abrupt bends\#151 ; the first through about 10| ' , the second through about 43 ' .
There is a very well-marked spur at the second bend , which it is difficult to interpret otherwise than as being due to ionisation by the recoil of the atom , by collision with which the course of the a-particle has been abruptly changed .
( But for the spur this a-ray shows an astonishingly close resemblance to one in a diagram constructed by Prof. Bragg* to illustrate what he considered to be likely forms of a-ray paths .
) Apart from these sudden bends a certain amount of curvature is apparent in some of the tracks .
In some cases , where the curvature occurs close to the walls of the cloud chamber , it is certainly a spurious effect , due to displacement of the tracks by air motions or to optical distortion arising from a thickening of the gelatine round the circumference of the roof .
Where , however , it appears at no great distance from the centre of the cloud chamber it is probably genuine , indicating deviation of the a-particle by repeated small deflections .
There is generally unmistakably genuine curvature in the last millimetre of the track .
The photographs thus furnish evidence of two distinct ways in which a-particles are " scattered " in passing through air , what Eutherfordf has called " single " and " compound " scattering respectively .
And , as Eutherford has contended , the scattering of large amount is in the case of a-particles mainly due to the former process , that is to say , it is the result of single deflections through considerable angles and not a cumulative effect due to a very large number of minute deviations .
When the a-rays arise from the emanation it is possible to photograph the complete track of an a-particle , including the beginning and end .
The latter is at once recognisable by its characteristic bend or hook .
In figs. 4 and 5 ( Plate 6 ) are shown the tracks of two a-particles , each of which has completed its course in the illuminated layer ; in both cases the beginning of the trail is seen to be marked by an enlarged head in which the cloud is of greater density than elsewhere .
This may represent ionisation by the recoil of the atom from which the a-particle has escaped .
The same characteristic head appears at what is presumably the beginning of other , obviously foreshortened , tracks whose ends lie outside the illuminated layer .
Of the two complete a-ray tracks from the emanation one has a length ( when reduced to 760 mm. and 15 ' C. ) of 4'3 cm. .
, in good agreement with the usually accepted value of the range .
The other is apparently somewhat shorter , about 3'8 cm .
, the low value being probably due to foreshortening .
* 'Archives of the Rontgen Ray , ' April , 1911 .
t 'Phil .
Mag. , ' 1911 , vol. 21 , p. 669 .
1912 .
] Visible the Tracks of Ionising Particles Gases .
285 Some photographs of a-ray trails were obtained with the camera in the lateral position and with oblique illumination\#151 ; arrangement ( a ) of fig. 4 ( p. 281 ) .
The radium tipped wire was surrounded by a glass tube about 1 mm. wide open at the end and projecting for about 1 cm .
beyond the radium , the object being to confine the rays to a moderately narrow pencil with its axis in the plane for which the camera was focussed .
An example of one of the photographs obtained in this way is shown in Plate 7 , fig. 1 , which is an enlargement of the original negative .
The track of an a-particle is seen near the bottom of the picture .
Some of the ions appear to have retained their mobility in the supersaturated atmosphere long enough to enable them to travel some distance under the action of the electric field before growing into drops , thus giving rise to a vertical sheet or curtain of drops .
The effect is most marked above the main track , i.e. on the side to which the negative ions would travel .
I have not yet succeeded in obtaining photographs in which all the drops in a known length of the cloud trail left by an a-particle could be counted .
It would obviously be of interest to determine by a direct method of this kind the number of ions produced by an a-particle .
Ionisation by ( 3-Rays .
( Plate 7 .
) When the camera is in the lateral position and oblique illumination is used the individual cloud particles , so long as they are not too close together for resolution , leave distinct images on the photographic plate .
It is possible , therefore , to photograph the track of any ionising particle , however small the number of ions produced per centimetre of its path may be .
Some photographs of / 3-ray trails were obtained along with those of the a-rays in the course of the experiments last described .
Figs. 1 , 3 , and 4 of Plate 7 were obtained in this way ; fig. 2 shows the result of passing a narrow beam of 7-rays through the cloud chamber ; the tracks in this case are doubtless those of / 3-particles starting in the walls of the vessel .
The almost straight trail of figs. 3 and 4 ( the actual length of trail photographed amounts to about 4 cm .
) is evidently that of a / 3-particle in the earlier stage of its free existence while its velocity is still very high .
This is indicated not only by the straightness of its path but also by the very small ionisation along it .
The distribution of the ionisation along the path is interesting .
Over considerable distances the ions occur mainly in pairs , but here and there 20 or 30 appear to have been liberated in a closely packed group .
( A similar distribution appears in a second approximately straight ray which crosses the first .
) The groups show a peculiarity which is also met with in the clouds condensed on the cathode rays produced by X-rays when a 286 Mr. C. T. R. Wilson .
Apparatus for making [ June 7 suitable expansion ratio is used : while the negative ions have given rise to a densely packed cluster of drops the positive ions have been drawn out by the electric field before losing their mobility , giving the appearance of a shower of drops falling from the negative cloud .
If we omit the clusters , the number of ions in the trail amounts to about 32 , i.e. 16 pairs , per centimetre at atmospheric pressure .
If we take into account the groups the number of ions per centimetre is roughly doubled , giving a number not very much lower than the estimate of 48 pairs per centimetre obtained by Eve* by indirect methods .
The occurrence of the groups or clusters of ions may be interpreted as indicating that in certain cases the corpuscle liberated from an atom by a / 3-particle of high velocity may itself have energy enough to ionise for a very short distance .
The / 3-rays of fig. 2 are obviously of smaller velocity , producing much more ionisation per centimetre and being much more readily deviated .
A still later stage of slower velocity has been reached by the particles giving the abruptly ending coiled up trails which appear in figs. 1 and 3. .
These / 3-ray endings are indistinguishable from the cathode rays , produced in air by Bontgen rays , such as are shown in the succeeding plates .
It will be noticed that the / 3-rays photographed do not show abrupt deflections like the a-rays , but , except while the velocity remains very high , they show gradual bending resulting in large deviations .
The scattering of the / 3-rays is thus mainly or entirely of the cumulative or " compound " type , , being due to a large number of successive deflections , each in itself inappreciable .
Ionisation by Rontgen Rays .
( Plates 8 and 9 .
) The X-ray bulb was excited by a Leyden jar discharge , in most cases so timed that the rays traversed the cloud chamber immediately after the expansion , while the gas was in the supersaturated condition .
The ions had thus extremely little time in which to diffuse before being fixed by the condensation of water upon them .
The terminals of the upper spark gap Q of fig. 3 ( p. 281 ) were connected with the inner coatings of two Leyden jars , the outer coatings of which were connected to the Crookes tube .
The inner coatings were also connected through glass tubes filled with water to the terminals of the Wimshurst machine .
The steel ball in its fall first caused the X-ray discharge and afterwards the illuminating spark , the water tubes having a sufficiently high resistance to prevent the jars supplying the illuminating spark from discharging , while the ball traversed the upper spark gap , but conducting sufficiently well * ' Phil. Mag. , ' 1911 , vol. 22 , p. 551 .
1912 .
] Visible the Tracks of Ionising Gases .
28 to allow of both sets of jars being simultaneously charged by means of the Wimshurst machine .
The moment of occurrence of the X-ray flash relative to the expansion was adjusted by varying the length of the thread suspending the steel ball .
Tests were made of the length of thread required to make the X-ray discharge simultaneous with the completion of the expansion ; it was then known that with a thread shorter than this the X-rays would pass after the expansion .
For the purpose of making this test the X-ray tube was removed , and the wires supplying it were connected instead to the mercury spark-gap ; two illuminating sparks thus traversed the mercury vapour during the fall of the ball , the interval between them being the same as that between the X-ray flash and the illuminating spark , for the same length of thread , in the ordinary use of the apparatus .
A series of photographs was taken with different lengths of thread , the camera , placed horizontally , being focussed on a pointer attached to the plunger ; a single image of the pointer on the photographic plate indicated that the expansion had been completed before the passage of the first spark , a double image resulting if the first spark passed before the expansion was completed .
These photographs also furnished information regarding the rapidity of the expansion ; it was found to be completed within about l/ 50th of a second .
The Crookes tube was fixed at a distance varying from 30 to 70 cm .
from an aperture in the wall of the cloud chamber about 1*2 cm .
in diameter ; this was closed by a quartz plate 0*38 mm. thick .
The quartz window was used as it happened to be convenient for another purpose .
The rays passed through a narrow cylindrical channel , in most cases of 2 mm. bore , in a lead block about 5 cm .
thick placed close to the quartz window , lead screens being also inserted to shield the rest of the cloud chamber from the rays .
I he camera occupied position ( a ) of fig. 4 .
A horizontal cylindrical beam of X-rays was in this way made to traverse the cloud chamber across its centre , and was at such a distance from the camera that the magnification was about 2'4o diameters .
To avoid distortion by the cylindrical walls of the cloud chamber a portion of the cylinder 5 cm .
in length was removed and replaced by a plane parallel glass plate .
1 hotographs of some typical X-ray clouds are shown in Plate 8 .
In all cases ( with one exception , fig. 5 ) the rays traversed the supersaturated gas , the order of events being : ( 1 ) Production of the supersaturated condition by sudden expansion ; ( 2 ) Leyden jar discharge through the Crookes tube , causing ionisation within the cloud chamber ; ( 3 ) condensation of water upon the ions , ( 4 ) passage of the illuminating spark , giving a photograph of the cloud condensed on the ions .
Mr. C. T. R. Wilson .
Apparatus jor making [ June 7 , The potential difference between the top and bottom of the cloud chamber was in some cases 40 yolts , in others only 4 volts , the top being always positive .
In most cases the expansion ratio was between T33 and T36 ; i.e , it considerably exceeded the minimum ( approximately 1*31 ) required to cause condensation on the positive as well as the negative ions ( the minimum for the latter is 1*25 ) , but less than is required to give dense clouds in the absence of ions ( v2/ vi = T38 ) .
Under these conditions , as the photographs show , the tracks of the cathode- or / 3-particles produced in the gas by the X-rays are very sharply defined , the ions being fixed by condensation of water upon them before they have had time to diffuse , or travel under the action of the electric force , for any appreciable distance .
The following are among the* more striking features of the photographs , of which figs. 1 to 4 of Plate 8 are a few examples out of a considerable number obtained under these conditions .
1 .
Cathode or / 3-rays are seen to start from within the track of the primary X-ray beam , many of them extending to some distance outside it .
2 .
There is no indication of any effect of the X-rays on the gas other than the production of the corpuscular radiation ; the track of the primary X-ray beam is not distinguishable otherwise than as being the region in which the / 3-rays have their origin .
In some photographs , it is true , there appear scattered throughout the region illuminated by the spark drops which might be taken to represent ions set free by the X-rays , but these show no concentration along the path of the primary beam , and , moreover , they appear in equal numbers in comparison photographs taken under conditions otherwise identical but without any X-ray discharge .
There is no doubt , I think , that these scattered drops are condensed upon uncharged nuclei similar in nature to those produced by weak ultra-violet light and certain metals , which require a similar expansion to catch them .
They appear to be due to a chemical action in which some trace of impurity plays an essential part , as they are much more numerous when the air in the apparatus has recently been renewed .
Ionisation by X-rays appears therefore to be , as Bragg has suggested , entirely a secondary process , except in so far as , each cathode ray produced in the gas may be said to indicate the formation of one pair of ions by the X-radiation .
3 .
The number of cathode rays produced in air in a known length of a limited beam of X-rays can readily be counted by this method .
4 .
The X-radiation thus far used has been heterogeneous .
It is to be expected therefore that the cathode rays should be of varying length .
Reduced to atmospheric pressure , a frequent length , measured along the 1912 .
] Visible the Tracks of Ionising Particles in Gases .
289 path , was from f to 1 cm .
, or measured in a straight line from beginning to end of the path , about half these amounts .
Tracks as long as 2 cm .
were , however , met with .
5 .
The rays show two distinct kinds of deflection as a result of their encounters with the atoms of the gas\#151 ; Rutherford's"single " and " compound " scattering .
The gradual or cumulative deviation due to successive deflections of very small amount is evidently , however , in this case much the more important factor in causing scattering , all the rays showing a large amount of curvature , while quite a small proportion show abrupt bends .
When abrupt deflections occur they are frequently through large angles , 90 ' or more .
6 .
The rays tend to become more and more bent as the end is approached , the actual end of each cloud trail being also enlarged into a kind of head , possibly owing to the path of the corpuscle finally becoming extremely irregular in form .
7 .
In many of the photographs there are cloud trails sufficiently sharply in focus over at least a portion of their length to show the individual drops and , therefore , allow of the ions on which they have condensed being counted .
An enlargement of one such track is shown in fig. 6 of Plate 8 ; the number per cm .
of this trail amounts to about 278 , the equivalent of 376 ions or 188 pairs of ions at atmospheric pressure .
This number appears to be fairly typical for the middle portions of the tracks , i.e. about 5 mm. from the end .
Out of 12 counts of this kind , the smallest number obtained is 150 pairs per era .
( at atmospheric pressure)\#151 ; this is at the beginning of a ray\#151 ; the largest 2160 pairs per cm .
in the last ^ mm. of a ray .
8 .
The cathode rays appear to start in all directions .
I have not yet attempted any systematic statistical study such as would be required to determine the relative frequency of different initial directions of the rays with respect to the direction of propagation of the Rontgen radiation .
When the expansion ratio is less than about 1'33 , the cathode-ray cloud-trails begin to lose their sharpness , as is illustrated by the photographs in Plate 9 .
With expansion ratios between 1*31 and P33 , the positive ions are spread out by the electric field before becoming fixed , giving rise to what looks like a shower of drops falling from each trail , which is still marked by the negative ions .
When the expansion falls below that required to catch the positive ions , the negative ions begin to show a similar spreading out under the action of the field , and finally , while the expansion still considerably exceeds that required to catch negative ions , the clouds cease to give any picture of the original path of the corpuscle .
To get the form of the path of an ionising particle as accurately as possible , the expansion ratio ought to 290 Mr. C. T. R. Wilson .
Apparatus for making [ June 7 , exceed 1*33 ; but , on the other hand , for counting the ions , a smaller expansion has advantages .
An expansion just too small to catch positive ions is perhaps the best for counting the ions ; it was only in photographs obtained under such conditions that the ionisation at the ends of the trails could be determined .
When the Rontgen rays are flashed through the cloud chamber before the .expansion of the air , diffuse double tracks are obtained , the positive and negative ions being separated by the electric field , and a certain amount of diffusion of the ions occurring in both positive and negative trails ( Plate 8 , fig. 5 ) .
It would have been interesting to obtain by this very direct method a test as to whether the number of positive and negative ions set free is the same , or , in other words , whether the positive and negative ion carry equal charges\#151 ; a question which has been raised by certain experiments by Townsend .
Unfortunately .
I have thus far only succeeded in obtaining on the negatives a few very short portions of such double tracks , which are at the same time sharply in focus and free from complications due to overlapping with other tracks .
These short portions do , however , show equality in the numbers of positive and negative ions ; the positive and negative clouds , to take one example , containing each 30 to 31 drops , there being .some uncertainty in one or two cases as to whether an image on the plate represents one drop or two .
These experiments have been carried out in the Cavendish Laboratory .
I have to thank Mr. F. Lincoln and his assistants in the workshop for most efficient aid in the construction of the apparatus .
1912 .
] Visible the Tracks of Ionising Particles Gases .
291 DESCRIPTION OF THE PLATES .
The pictures are photographs of clouds condensed on the ions set free in moist air by rays of different kinds .
In what follows , px is the density of the air before expansion ( relative to saturated air at 15 ' C. and 760 mm. ) , p2 the density after expansion , v2/ v1 the expansion ratio , V the potential difference between the roof and floor of the cloud chamber , and M the magnification .
In all cases the roof of the cloud chamber was positive , so that positive ions travelled downwards , negative upwards .
Plate 6 .
Ionisation by a-rays .
A-ris of camera vertical ; horizontal layer of 2 cm .
in depth illuminated by mercury spark .
Fig. 1 .
a-Rays from radium .
Some of the a-particles have traversed the air before the expansion , others after the expansion .
px = 0'98 , v2jvx \#151 ; 136 , p2 = 0'72 , V = 40 volts , M = 1/ 2*18 .
Fig. 2 .
a-Rays from radium .
The a-particles have all traversed the air after the expansion .
Pi = 0-97 , v2/ vx = 1-33 , p2 = 0*73 , V = 40 volts , M = 1*05 .
Fig. 3 .
a-Rays from radium .
Enlargement of a portion of fig. 2 .
Pi = 0*97 , vihi = 1*33 , p2 \#151 ; 0*73 , V = 40 volts , M = 2*57 .
Fig. 4 .
a-Rays from radium emanation and active deposit .
Pi = 1*00 , v2/ vi = 1*36 , p2 = 0*74 , V = 40 volts , M = 1/ 1*24 .
Fig. 5 .
A complete a-ray from radium emanation .
Pi = 0*97 , v2\vx = 1*36 , p2 = 0*71 , Y = 40 volts , M = 1*16 .
Plate 7 .
Ionisation by a- and / 3-rays .
The source of the rays is on the right of the picture .
Axis of camera horizontal ( arrangement ( a ) of p. 281 ) .
Fig. 1 .
a- and / 3-Rays from radium .
Fig. 2 .
Pi \#171 ; 0*98 , vjvi = 1-33 , p2 = 0*74 , 0-Rays produced by ^-radiation .
Y = 30 volts , M = 6*0 .
Fig. 3 .
Pi = 1*00 , =1-34 , 0-Rays from radium .
p2 = 0*75 , V = 40 volts , M = 6*0 .
Pi = 0-99 , vjvi = 1-31 , P2 = Y = 40 volts , M = 2*45 .
Fig. 4 .
0-Rays .
Enlargement of a portion of fig. 3 .
Pi = 0*99 , v2/ Vi = 1*31 , p2 = 0*76 , Y = 40 volts , M = 6*0 .
292 Tracks of Ionising Particles Gases .
Plate 8 .
Ionisation by Kontgen rays .
Axis of camera horizontal , X-rays passing from right to left .
In all cases except fig. 5 the X-rays traversed the air after the expansion .
Fig. 1 .
Ionisation by cylindrical X-ray beam about 2 mm. in diameter .
p1 = TOO , v2/ v1 \#151 ; 1*35 , p2 \#151 ; 0'74 , V = 4 volts , M = 2'45 .
Fig. 2.* Ionisation by X-ray beam about 2 mm. in diameter .
p{ = POO , v2/ v1 = 1*34 , p2 = 0*75 , V = 4 volts , M = 2*45 .
Fig. 3 .
Ionisation by X-ray beam about 2 mm. in diameter .
px \#151 ; 0-93 , v2jvx = 1*33 , p2 = 0'70 , Y = 40 volts , M = 2'45 .
Fig. 4 .
Ionisation by X-ray beam about 5 mm. in diameter .
p1 = POO , / o2fvl = P36 , p2 = 0'74 , Y = 40 volts , M = 2'45 .
Fig. 5 .
Ionisation by X-ray beam about 5 mm. in diameter .
The X-rays traversed the air before its expansion ; the positive and negative ions have been separated by the electric field before losing their mobility by the condensation of water upon them .
Pj = POO , v2/ v1 = 1*36 , p2 = 0*74 , Y = 40 volts , M = 2'45 .
Fig. 6 .
Portion of fig. 4 enlarged , showing the individual ions produced along a portion of one of the cathode-ray tracks .
( The fig. has been turned through 90 ' .
) px = 1-00 , v2/ v1 = 1-36 , p2 = 0-74 , Y = 40 volts , M = 14*7 .
Plate 9 .
Ionisation by Kontgen rays .
Conditions as in Plate 8 ; X-ray beam about 2 mm. in diameter .
Figs. 2 , 3 , and 4 belong to a series in which the expansion ratio was varied while all other conditions were kept constant .
Fig. 1 .
Enlargement of a portion of fig. 1 , Plate 8 .
px = POO , vJvi \#151 ; P35 , p2 = 0'74 , Y = 4 volts , M = 6'0 .
Fig. 2 .
Enlargement of portion of fig. 3 , Plate 8 .
In this , as in all the preceding X-ray pictures , the maximum supersaturation attained has been sufficient to cause the ions to lose their mobility immediately after being set free so that the cathode-ray particles leave sharply defined trails .
Pl = 0-93 , vjvx = 1*33 , p2 = 0-70 , Y = 40 volts , M = 6'0 .
Fig. 3 .
The maximum supersaturation has only slightly exceeded that required to cause condensation on the positive ions , which have therefore travelled varying distances under the action of the electric field before becoming fixedjby condensation of water .
px = 0*92 , v2/ vt \#151 ; 1*31 , p2 = 0'70 , Y = 40 volts , M = 6 ; 0 .
Fig. 4 .
Negative ions , which alone are caught with the maximum degree of supersaturation attained , have retained their mobility for varying lengths of time , the cathode-ray trails being therefore drawn out into diffuse sheets under the action of the electric field .
px = 0'90 , v2/ vl = P28 , p2 = 0*70 , Y = 40 volts , M = 6-0 .
* Fig. 2 of Plate 8 has by accident been placed upside down .
Wilson .
Roy .
Soc. Proc. , A , Roy .
Soc. Proc.y A , vol. 87 , PL 8 .
Wilson .
|
rspa_1912_0082 | 0950-1207 | Report on the total solar eclipse of 1911, April 28. (Observed the expedition of the joint permanent eclipse committee to Vavau, Tonga Islands, South Pacific.) | 293 | 301 | 1,912 | 87 | Proceedings of the Royal Society of London. Series A, Containing Papers of a Mathematical and Physical Character | Rev. A. L. Cortie, S. J., F. R. A. S. | astronomical-observation | 6.0.4 | http://dx.doi.org/10.1098/rspa.1912.0082 | en | rspa | 1,910 | 1,900 | 1,900 | 3 | 197 | 4,372 | http://corpora.clarin-d.uni-saarland.de/surprisal/6.0.3/?id=rspa_1912_0082 | 10.1098/rspa.1912.0082 | null | null | null | Astronomy | 28.343707 | Optics | 15.869777 | Astronomy | [
84.01058959960938,
1.4409180879592896
] | 293 Report on the Total Solar Eclipse of 1911 , April 28 .
( Observed by the Expedition of the Joint Permanent Eclipse Committee to Vavau , Tonga Islands , South Pacific .
) By the Key .
A. L. Cortie , S.J. , F.R.A.S. ( Communicated by the Joint Permanent Eclipse Committee .
Received June 7 , \#151 ; Read June 27 , 1912 .
) [ Plate 10 .
] 1 .
General Arrangements .
The expedition to observe the total solar eclipse of 1911 , April 28 , was organised by the Joint Permanent Eclipse Committee , the expenses being defrayed by the Government Grant Fund .
Of the few islands in the South Pacific crossed by the track of the moon 's shadow during totality , Vavau , one of the northernmost group of the Tonga or Friendly Islands , was the most suitable for observing the eclipse , the duration of totality being computed at 217 seconds , and there being a reasonable prospect of good weather .
The programme of observations consisted of photographs of the corona on a large and relatively small scale for coronal detail and extension of the streamers , and photographs of the spectrum of the corona and of the lower chromosphere .
For these purposes the expedition was furnished with a 4-inch photographic lens of 20 feet focal length , kindly lent by the Council of the Royal Irish Academy , and the 4-inch Dallmeyer " Abney " lens of 34 inches focal length .
For the spectrum of the corona Prof. Newall kindly lent the quartz spectroscope of four prisms , presented to the Cambridge Observatory by Major Hills , in order further to investigate the ultra-violet spectrum .
The fourth instrument was made up of a large 7-inch prism of 40 in combination with a 6-inch Dallmeyer portrait lens of 30 inches focal length .
This objective prismatic camera gave a short but very bright spectrum , 4*5 cm .
from Ha to H^ .
The intention was to investigate the red end of the coronal spectrum on dyed plates , and incidentally to photograph the flash spectrum .
Hie members of the expedition were Father Cor the and Mr. W. McKeon , from the Stonyhurst College Observatory , and Father E. Pigot , Director of the Observatory of St. Ignatius ' College , Riverview , Sydney , N.S.W. , who also acted as agent for the expedition in Sydney , in the preparation of huts to cover the instruments , and in the gathering of materials for building the piers for the foundations .
The Admiralty gave instructions that VOL. lxxxvii.\#151 ; a. x 294 Rev. A. L. Cor the .
Report on the [ June 7 , H.M.S. " Encounter " should convey the observers and the instruments from Sydney to Vavau and back , and that every assistance should be rendered to the expedition in the erection of the instruments and in the observations .
The expedition is greatly indebted to Captain Colomb , and to the officers and men of the " Encounter , " for their enthusiastic co-operation in the work of the expedition .
The Stonyhurst observers left Tilbury , with the instruments , on board the Orient Line R.M.S. " Otway , " on February 3 , and arrived at Sydney on March 16 .
The " Encounter " sailed from Sydney on March 25 and arrived at Vavau on April 2 .
2 .
Erection of Instruments .
All the cases containing the instruments were landed ashore by April 5 , and a clearing was made of dense undergrowth and of some coconut palm trees on the space reserved as a coaling ground by the Admiralty .
The co-ordinates of the observing station are approximately longitude 173 ' 59*4 ' W. , latitude 18 ' 40'5 ' S. Two expeditions , namely , that organised by the Joint Permanent Committee , and that from the Solar Physics Observatory under the leadership of Dr. Lockyer , occupied adjoining stations , and we are considerably indebted to Mi1 .
Brooks , of Dr. Lockyer 's party , for determining the meridian of all our instruments .
Fortunately the weather remained fine until the evening of April 10 , by which date the sailors had cleared the ground , had made concrete bases for the mounting of the ccelostats , and had assisted in the considerable progress which had been made in the erection of the instruments .
After that date , until and including the day of the eclipse , the weather was broken , with at times torrential showers of tropical rain .
The Coronagraphs.\#151 ; -These two instruments of long and short focal length were mounted side by side , horizontally , so that the prolongations of their axes were in the azimuth of sunset , 14 ' 47 ' N. of W. , the azimuth of the sun at totality being *49 ' E. of N.,.and its altitude 43 ' .
Exact focussing was secured by a series of photographs of sunspots taken during the days preceding the eclipse .
The best images in the 20-foot coronagraph were secured with a diameter of the sun 's image of 2-J^ inches .
The camera body was made in sections of zinc , gradually increasing in cross section so as to fit a camera bellows with rack-and-pinion adjustment , carrying plate-holders 10 x 8 inches .
For stability the camera was mounted on a long trestle table , secured by battens , the ends of the trestles being sunk several inches in the ground .
Deformation of the images on the ground-glass screen was caused by convection currents , due to unequal heating of the sections'of the long zinc 1912 .
] Total Solar Eclipse 1911 , April 28 .
295 tube .
This was altogether remedied by protecting the whole instrument from the direct rays of the sun by a roofing of palm-leaf thatch , and by hanging matting from the flat roof on the sunward side .
In addition the lens end of the camera had a double awning over it .
Fortunately , the soil was a rich loam without any dust , and as the centres of the lenses were raised 4 feet 3 inches above the level of the ground , and the ground was covered with loose palm leaves , the effect of radiation from the ground was practically eliminated .
The two coronagraphs were supplied with light from the mirror of a 16-inch ccelostat , mounted solidly on a box filled with coral and earth , which was itself mounted on a concrete pier .
The driving clock stood on a separate pillar .
One weight of 24|- lb. sufficed to drive it , the position of fall on a tall upright , which corresponded to the best rate , being found by repeated experiments .
The ccelostat was placed in position and its polar axis adjusted for latitude by the ordinary methods , frequently described in former eclipse reports .
An Abney level is a most useful adjunct to the instrument , especially so in cases when there is no attached theodolite .
The 20-foot coronagraph was under the charge of Mr. W. McKeon , S.J. , assisted by Mr. Baker , gunner , who made the exposures , and three stokers to hand and take plate-holders , and to record exposure times .
Lieutenant Elmsley operated the 34-inch coronagraph , and he was assisted by four stokers .
The 16-inch ccelostat was under the charge of Chief Engine-room Artificer Langhorn , who spent much time in remedying defects in the instrument , in contriving mechanical devices for its stability , and in regulating the clock .
The following programmes for exposures during totality were carried out .
The 20-foot Coronagraph .
Number of slide .
Plate .
Speed number ( H. and D. ) .
Time by eclipse clock .
Exposure .
Result .
1 f.g.o. 50 217\#151 ; 215 secs .
2 Blank .
2 f.g.o. 50 200\#151 ; 195 5 yy 3 n.f. 200 185\#151 ; 170 15 4 n.f. 200 160\#151 ; 140 20 5 n.f. 200 130\#151 ; 80 50 6 At n.f. 200 65\#151 ; 40 25 Weak impression .
/ 8 f.g.o. f.g.o. 50 50 30\#151 ; 25 15\#151 ; 13 5 2 n a a a 296 Rev. A. L. Cortie .
Report on the [ June 7 The 34-inch Coronagraph .
Number of slide .
Plate .
Speed number ( H. and D. ) .
Time by Eclipse clock .
Exposure .
Result .
1 f.g.o. 50 217\#151 ; 215 secs .
2 Faintest impression .
2 f.g.o. 50 200\#151 ; 196 4 3 n.f. 200 180\#151 ; 165 15 Blank .
4 n.f. 200 150\#151 ; 130 20 5 n.f. 200 115\#151 ; 75 40 Faint impression .
6 n.f. 200 65\#151 ; 40 25 Strong impression .
7 f.g.o. 50 30\#151 ; 24 6 Faintest impression .
8 f.g.o. 50 10-7 3 Faint impression after totality .
The letters f.g.o. stand for Imperial fine grain ordinary plate , and n.f. for Imperial ortho-chromatic non-filter plate .
For the purpose of orientation a double exposure of the partial eclipse was made on a single plate shortly after totality .
The Prismatic Camera and Associated Instruments.\#151 ; These instruments were under the charge of Father Pigot , who was assisted by Engineer-Lieutenant McEwan , who operated the exposures for the prismatic camera , Chief Petty Officer Eeid , three stokers and one seaman .
Father Pigot determined the deviation by the prism at when placed horizontally to be approximately 28*5 ' .
Dr. Crommelin had kindly worked out that the point of second contact on the sun 's image seen in the coelostat mirror was 34 ' 45 ' to the left of the vertex , when viewed from the side away from the coelostat , and the corresponding position of third contact 171 ' to the right of the vertex .
These positions would have been extremely awkward for obtaining symmetrical and concentric arcs in the flash spectrum .
The instrument was therefore rigidly fixed to the top of a table , the legs of which were sunk in the ground , and tilted through an angle of 55 ' .
This was effected by hinging the lid of the table and lifting the further edge by means of two iron rods with rough screw adjustment .
This diminished the deviation at by the cosine of the angle of tilt , so that it was reduced to 16 ' 287 .
The azimuth of the axis of the telescope , owing to the deviation of the prism , was 13 ' 6 ' N. of W. Two subsidiary instruments were placed on the tilted lid of the table , a grating camera made up of a Thorp replica 2 x 1*5 inches ruled surface , 14,438 lines to the inch , placed in front of the front combination of a portrait lens 2*3 inches clear aperture and 30 inches focal length ; and a Hilger one-prism spectroscope , the prism being replaced by a similar Thorp transmission grating .
The image of the sun was focussed on the slit of this latter instrument by means of a long-focus telescope lens lent by the captain of The " Encounter .
" Its function was intended to be to give independent 1912 .
] Total Solar Eclipse of 1911 , April 28 .
signals for the flash spectrum at the beginning and end of totality .
Besides exposures on the flash spectra , three exposures for the spectrum of the corona were planned on Wratten and Wain wright 's panchromatic plates , the first for 30 seconds from count 205 to 175 seconds , the second of 90 seconds at mideclipse from 170 to 80 , and the third of 55 seconds from 75 to 20 .
A 12-inch coelostat , under the charge of Chief Engine-room Artificer Firth , supplied a beam of light to the three instruments .
The whole installation was conveniently covered by a tent , 12 x 6 feet , rising 8 feet 2 inches to the top of the gable .
Waterproof material hung in sections over it , and the flaps could be raised when observations had to be made .
The Quartz Spectroscope.\#151 ; This instrument has been freely described in the eclipse reports of former observers .
The adjustments finally adopted , after considerable preliminary experimental work at Stonyhurst , were substantially the same as those made by Dr. Dyson in Sumatra in the eclipse of 1901 , * except that the prisms were at minimum deviation at \3570 .
The object glass was focussed for X 3400 approximately , and the image on the slit , visually out of focus , was viewed by an opal glass kindly lent by Dr. Dyson .
The spectrum was in good focus for about three inches from \ 4000 to X 3300 .
The light was supplied by a 12-inch silver-on-glass mirror mounted in the meridian as a heliostat .
As silver absorbs violet light a speculum-metal mirror would have been preferable .
The spectroscope was placed horizontally on a table , and the quartz 5-inch object glass on a tripod stand .
The whole instrument was covered by a tent similar in construction to that described * above .
Father Cortie took charge of the instrument , assisted by Mr. Bright , torpedo gunner , to whom was entrusted the delicate operation of placing the sun 's image in the proper positions on the slit for the first and second flash , and for the coronal spectrum , on which one long exposure was to be made .
Three stokers also assisted , and the heliostat was under the charge of Stoker Petty Officer Ash .
Unfortunately , clouds spoiled all the exposures on the day of the eclipse .
There is nothing on the plates , except an impression of continuous spectrum at second contact .
Even had the wmather been fine , the atmosphere was so humid that it is doubtful whether there would have been many ultra-violet lines recorded .
Frequent drills for all the observers were held on the five days preceding the eclipse , under the general command of Captain Colomb .
3 .
Day of the Eclipse and After .
The fine weather of our first week at Vavau gave place on April 10 to bioken weather with heavy showers nearly every day .
The mornings were * ' Roy .
Soc. Proc. , ' vol. 69 , p. 245 .
Rev. A. L. Cortie .
Report on the [ June 7 , generally fine at about the time of eclipse .
On April 26 a fresh S.E. breeze brought up a new development , in the formation of thick and extensive cirrus clouds .
On April 28 ( we reckoned the civil day by Sydney time ) there was much cloudiness , which persisted during the night , and into the early morning of the 29th .
The sky cleared just before first contact , and remained beautifully clear , with , however , passing cumuli , during the earlier phases of the partial eclipse .
As totality approached dense cirro-stratus formed over the partially eclipsed sun .
These clouds were purely local , as going north the weather conditions improved , being good for M. Stefanik at the Catholic Mission compound ; better for the Australians in their camp near Neiafu , and best for Mr. Worthington , removed some 500 yards from the Australians .
From the deck of the s.s. " Boveric , " anchored off the wharf at Neiafu , some two miles distant , a perfect view of the eclipse was obtained .
The local clouds at the British station were due to the fall in temperature , and the consequent condensation of the aqueous vapour , conditioned by the proximity of an eminence which deflected the wind and prevented it blowing the clouds away .
The total phase commenced about 20 seconds before the predicted time , an experience which was corroborated at the Australian station .
The clouds cleared somewhat towards the end of totality , some 90 seconds approximately .
Through a veil of thin cirrus a typically minimum corona appeared , the extension being greatest in the N.E. quadrant , and of about one lunar diameter .
Around the moon 's limb was a bright ring , which would have been very bright in a clear sky .
Just before the sun 's limb appeared , a beautiful red prominence was seen , almost at the exact angle of third contact from the N. point , which shone out like a vivid glow lamp .
During totality the light scattered by the clouds rendered the use of lamps unnecessary .
A loud chorus of chirping crickets , as at the approach of nightfall , was raised and continued during totality .
A Kanaka gave a howl and ran away frightened into the bush .
But there was no noise from the Tongans , the native governor having considerately given orders that silence was to be maintained , and that no fires were to be lighted so that there should be no smoke .
Mr. McKeon commenced developing the plates the same night , when it was comparatively cool , at the Catholic Mission School .
But as the conditions for working were not very satisfactory , the plates still undeveloped were kindly finished on the following night by Mr. Baker , the official photographer of the Australian expedition .
The instruments were all dismounted and packed on board the " Encounter " by May 2 , and we sailed for Suva , Fiji , on the 4th , arriving May 6 .
We sailed for Sydney on May 11 , which was reached on the 17th .
Commander Mellor , who had been indefatigable in all arrangements with regard to the 1912 .
] Total Solar Eclipse 1911 , April 28 .
299 expedition , superintended the landing of the instruments .
They were transhipped to the Orient liner " Orontes , " which sailed from Sydney on June 10 and arrived at Tilbury , July 23 .
4 .
Results .
Under the untoward circumstances narrated above the results obtained are very meagre .
With the 20-foot coronagraph two plates show the lower corona in the immediate neighbourhood of the moon 's periphery .
The first was exposed from 45 to 20 seconds , approximately , before the end of totality , the allowance being 20 seconds difference from the recorded time , and the second from 10 to 5 seconds .
There is a very fine bank of prominences from position angle 240 ' to 258 ' on the latter photograph , covering the position of third contact .
Several other small prominences appear on the two plates .
The following are the angles:\#151 ; N umber .
Plate 6 .
Plate 7 .
1 189 ' 187\#151 ; 192c 2 210 210 3 213 4 247 240 I 5 254 [ 6 256 258 J 7 261 8 287 288 9 299 300 In addition , both plates show a distinct brightening in the lower corona at position angle 50 ' on the E. limb , evidently the base of a bright streamer .
With the 34-inch coronagraph one fairly good impression of the corona was obtained , on a plate exposed between 45\#151 ; 20 seconds before third contact .
On this photograph the corona extends about one-half a lunar diameter on the E. limb , and barely that extent on the W. limb .
The lower corona is very bright , and several polar rays are discernible .
A reproduction of the photograph appears with this report ( Plate 10 ) .
Only one of the exposures for the spectrum is of any value , and that was secured just before , and at the time of , the second flash , with the prismatic camera .
The plate was to have been exposed from 75 to 20 seconds for the coronal spectrum ; it was really exposed , owing to the eclipse beginning before the predicted time , from 55 to the end of totality , and so caught the second flash .
The hydrogen series from Ha to 110 is impressed on the plate , on a strong continuous background which extends between the approximate limits A. 7065 and X 3700 , the portion from the red end to the K line being 300 Rev. A. L. Cortie .
Report on the [ June 7 in good focus .
It is a very dense negative and it is difficult to make measures on it .
There are seven lines beyond IIa in the red , including the two helium lines X 7065'5 and X 6673 3 , and about twenty other lines between Ha and Hp .
Under the conditions of exposure these may be taken to be the strongest lines in the chromospheric spectrum .
There is a suspicion also of the presence of some purely coronal lines .
This plate will receive a more careful examination later on .
5 .
Conclusions .
The corona of 1911 was of a markedly minimum type , flattened at the poles , and with the wings confined to middle solar latitudes .
It occurred at a period of very low spot activity , the mean daily disc area of sunspots , in terms of the 1/ 5000 of the visible surface , being for the year , from the Stonyhurst drawings , 0-3 ; a drop of over 83 per cent , on the number for the preceding year .
The month of April was by far the most active of the year , the mean daily number rising to 1'3 .
The actual maximum area of spotted surface for the year occurred on the day , and the day preceding the eclipse .
The spots furnishing this ai'ea were on or near the central meridian on the day of eclipse .
Had they been near the limbs , it is not unlikely that arches would have been seen in the lower corona as in 1901 .
But , in fact , it was absolutely uniform , without any structure whatsoever .
Although the eclipse took place in a year of very few sunspots , yet the actual minimum was probably about a year later .
A considerable and sympathetic reduction in prominence activity had also occurred , and prominences in high latitudes were practically non-existent .
Mr. Newbegin 's results* for prominence observations indicate " that the points in latitude mainly affected were between 50 ' 7ST .
and 50 ' S. , and more particularly between 30 ' and 50 ' S. " These regions are precisely those marked by the two main wings constituting the " leather " of the " wind-vane " on the E. side of the solar corona .
The brightening at about 50 ' N. on one of the plates has already been noticed .
A. close connection between the streamers of the solar corona and the regions of prominence activity has often been suggested by eclipse photographs .
The position angle of the N. end of the sun 's axis on the day of the eclipse was 24 ' 50 ' W. of the N. point .
The solar corona is symmetrical about the axis .
'here is , too , a great similarity between the photographs of the corona : 18 ) 3 , July 29 ; 1889 , January 1 ; 1889 , December 21 ; 1900 , May 28 ; and 1911 , April 28 .
All are of the " wind-vane " type , associated with minimum periods of solar spot and prominence activity , but , if the * 'Journal B.A.A. , ' vol. 22 , p. 5 .
Cortie .
Roy .
Soc. Proc. , A , 87 , 10 .
Sun'sAxis .
N n. s Sun 's Axis , s. Photograph of Corona , obtained with Dallmeyer Rapid Rectilinear Lens of 4 inches aperture .
Exposure 25 seconds through clouds .
Twofold enlargement .
1912 .
] Total Solar Eclipse of 1911 , April 28 .
301 photographs be compared among themselves , it will be noted that the arrow of the vane points E. and the feather W. in those of 1878 , 1889 , and 1900 , whereas the direction is reversed in the eclipse of 1911 .
We cannot conclude without recording with thanks the kind offices of the Astronomer Royal , Dr. Crommelin , Vice-Admiral Mostyn Field , and Prof. Newall , on behalf of the expedition .
Thanks are also due to Prof. He wall and the Council of the Royal Irish Academy for the loan of instruments , and to Dr. Lockyer , Mr. F. McClean , and Mr. Brooks , for much kind assistance .
In Australia , Father Pigot , Mr. J. Nangle , and Mr. Baracchi were most active in furthering the ends of the expedition , and much kind hospitality and assistance was rendered at Yavau by Fathers Mace and Deguerry .
We are greatly indebted to Captain Colomb , Commander Mellor , and the officers and crew of H.M.S. " Encounter , " for their valuable assistance , and , in particular , to Lieutenant Elmsley , Engineer-Lieutenant McEwan , and to Mr. Bright , Mr. Baker , and Mr. Head , our own particular assistants .
We cannot fail to recognise the kind courtesy of the Orient Steamship Company in carrying our instrumental outfit free of charge , and the ready assistance of the captains and officers of the " Otway " and " Orontes " in the careful landing of the instruments .
VOL. lxxxvii.\#151 ; A. v
|
rspa_1912_0083 | 0950-1207 | The molecular statistics of some chemical actions. | 302 | 309 | 1,912 | 87 | Proceedings of the Royal Society of London. Series A, Containing Papers of a Mathematical and Physical Character | the Hon. R. J. Strutt, F. R. S. | article | 6.0.4 | http://dx.doi.org/10.1098/rspa.1912.0083 | en | rspa | 1,910 | 1,900 | 1,900 | 7 | 168 | 3,425 | http://corpora.clarin-d.uni-saarland.de/surprisal/6.0.3/?id=rspa_1912_0083 | 10.1098/rspa.1912.0083 | null | null | null | Thermodynamics | 34.956872 | Fluid Dynamics | 18.481347 | Thermodynamics | [
-12.783013343811035,
-50.004371643066406
] | ]\gt ; The Molecular tistics of some Chemical Actions .
By the Hon. R. J. STRUTT , F.E.S. , of Physics , Imperial of Science , South Kensington .
( Received June 13 , \mdash ; Read June 13 , 1912 .
) S1 .
Introduction .
Very little has been written on the kinetic theory of gases in its chemical aspect .
There can be no doubt that when a gas is absorbed or chemically acted on by a solid surface , the rate at which the change proceeds must depend the number of collisions made by gas molecules with the surface .
But how many such collisions are required before a result is achieved ?
The usual methods of investigating the velocity of chemical action in gases are not capable of giving much information on this subject .
For under the usual conditions the action at the surface takes place so quickly as to be virtually instantaneous , and the observed effects are mainly governed by the rate at which new unaltered material can make its way to the scene of action .
Again the solid will , in most cases , be altered in the course of the action , becoming less efficient .
This introduces another difficulty .
I have been able , by the selection of certain rather special cases , to evade or overcome these difficulties , and wish now to present the results .
I shall also discuss from the kinetic standpoint a case of chemical change occurring entirely aseous molecules .
S2 .
Action The first case to be discussed is the well known action of silver , or rather of silver oxide , in a silver surface is presented to this , it rapidly becomes oxidised and is then capable of destroying any quantity of ozone , without itself under , further permanent change .
* The exact nature of this action is not definitely known .
It has been suggested that it may consist of alternate oxidation and reduction However this may be , it is certain that some of the ozone moIecules which strike ainst the solid surface are destroyed , and do not return to the gas as ozone .
The question here proposed for experimental investigation is this\mdash ; what fraction of the total number of such collisions produce this result ?
Or , * Andrews and Tait , ' Roy .
Soc. Proc 1859 , vol. 9 , p. 607 .
The Motecular tistics of some Chemical Actions .
in other words , how many times must an ozone molecule strike a silver surface before it is destroyed ?
If a current of air at low pressure is passed through an electric discharge tube , the issuing gas is luminous with a greenish-yellow .
The glow is due to the presence of ozone and nitric oxide , after the electric rJischarge has passed .
These substances react to the glow .
For the proof of these statements I refer to a former paper .
* If now the gas is allowed to pass a silver ze partition , the luminosity is completely extinguished .
This is undoubtedly due to the above action of silver in destroying ozone ; for if we put in more ozone into the stream after it has passed the silver gauze , the glow is restored .
Let A be the area of the total silver the velocity of mean square of the ozone molecules , the density of ozone in the stream as it arrives at the silver gauze .
Then the mass moving up to the surface per second , in virtue of the molecular velocity of itation neariy .
S Now let be the volume of the rarefied actually the gauze per second .
Then the mass of ozone passing per , and mass on silver per second , divided by total per second , is ) .
If now we measure the mass by the number of molecules , the above algebraical expression ives us the ratio of number of collisions to number of molecules passing , or , in other words , the number of times each molecule must ( the average ) strike the silver surface as it passes .
Every quantity entering into the formula is assignable , and we can , accordingly , determine the above number .
If the gauze is of just sufficient area to quench the completely , we may infer that molecule of ozone is destroyed , and consequently we a superior limit to the number of collisions ( on the average ) necessary to effect this .
The interest and nificance of the result will on how close the limit thus deduced is to the true value .
This will depend in turn on how far we can give all the ozone cules an equal chance of striking the surface .
If some of the molecules have to diffuse through a considerable layer of gas before they can get near to it , then those initially in a more favourable position will have collided many times the former have * Phys. Soc. Proc December , 1910 , vol. 23 , p. 1 .
, p. 34 .
Not the area of the gauze , but the aggregate area of the wires which constitute it , which is usually about twice as great for fine gauzes .
S O. E. Meyer , ' Kinetic Theory of Gases , ' p. 83 .
Hon. R. J. Strutt .
[ June 13 , done so at all , and the experiment will measure , not the number of necessary to destroy the ozone molecule when it has got to the surface , but rather the amount of obstruction it has to overcome in getting there .
To render these conceptions precise would lead us into very difficult problems .
It is evident , however , that the finer the gauze , and the lower the pressure of the gas stream , the more nearly we shall approach the ideal of oiving every ozone molecule in turn its fair and equal chance of reaching the silver surface .
We shall see from the actual experimental result that the ideal can be closely approached in practice .
It is not necessary , therefore , to attempt the difficult task of foreseeing the necessary conditions The apparatus used is shown in fig. 1 .
A stream of air enters stopcock where its pressure reatly reduced .
Thence it passes through the discharge FIG. 1 .
tube , where it is charged with ozone and with nitric oxide , which , as already indicated , shows the presence of ozone by the luminosity of their interaction in ; thence to the silver gauze partition , where the ozone is destroyed , and the glow ceases .
It was desired to find the minimum area of silver which would produce this result , and experience proved that the area in question was very small .
The silver gauze available had 22 wires per centimetre in each direction , and the diameter of each wire was mm. Each square centimetre of the gauze accordingly presented sq .
cm .
of silver surface per square centimetre .
The diameter of the gauze-filled diaphragm could not well be reduced below 2 mm. , since a smaller aperture would have unduly restricted the flow of rarefied gas , and 2 mm. still seemed more than enough to all the ozone , with the stream of gas as rapid and as highly rarefied as the 1912 .
] The Molecular Statistics of some Chemical Actions .
305 air pump available could make it .
, the part of the gauze filling the aperture was unravelled , leaving only the wires parallel to one direction , and thus reducing the silver area by half .
The gauze was mounted between two discs of mica , in each of which there was a hole 2 mm. diameter .
The unravelled gauze between the holes exposed to the gas stream was mechanically supported by the part behind the mica .
The latter part of the gauze was not unravelled .
The sealed-in glass funnel was to support the mica as shown .
On either side of the diaphragm were tubes either of which could be put into communication with a McLeod gauge .
The rate of air intake was easily measured in cubic centimetres per second by drawing in the air from a graduated vessel standing over ater , and from this , combined with the pressure , the volume of the -pressure stream passing the gauze per second could be deduced .
The following are examples of experiments made with the apparatus thus arranged:\mdash ; Area of Silver Surface exposed to the as Stream , sq .
We may take as a round figure that sq .
cm .
of silver is capable of completely removing the glow from a stream of gas amounting to 200 per second , measured at the low pressure .
Taking the value of , the velocity of mean square for ozone as cm .
per second , we get for the ratio of number of impacts with silver to number of molecules passing , the value , or nearly .
It follows , therefore , that collisions with the silver surface certainly suffice on the average to destroy a molecule of ozone .
It must be remembered that this number is a superior limit which can hardly , in the nature of the case , be within a small percentage of the exact value .
For if all the ozone molecules are without fail to strike the surface once ( and the extinction of the glow implies this ) then some will inevitably strike it more than once .
Bearing this in mind the results point strongly to the conclusion Hon. R. J. Strutt .
[ June 1S , that one collision with a silver surface , one onty , enough to destroy an ozone lolecule .
Indeed , even postulating this , it is somewhat surprising that so low a value as for the ratio of number of collisions to number of molecules should be consistent with complete extinction of the glow .
S3 .
Action of Copper Oxide on Active Nitrogen .
The next case to be considered has many points in common with the preceding .
I have described in several publications*an active modification of nitrogen produced by electric dischalge .
This active modification probably consists of monatomic , and , for the sake of clearness , I shall assume definitely that such is the case .
The monatonlic nitrogen usually reverts to the ordinary kind with luminosity in the course of a few minutes , the change a volume one .
But , by the action of a copper oxide surface the action becomes almost instantaneous .
The surface must be supposed in some way to hold the impinging molecules so as to them a better chance of uniting , as in the union of oxygen and hydrogen in contact with platinum .
This is well illustrated by the following experiment , which was shown to a large audience at the Royal Society Soiree on May 11 , 1912 , but has not been otherwise published .
A bulb ( fig. 2 ) of 300 .
capacity is provided with a side tube as shown .
In this lies an oxidised copper wire , which fits it as closely as is consistent with easy sliding .
The bulb contains rarefied nitrogen at a suitable pressure , about After passing the electrodeless disobarge it glows brilliantly for a minute or more , during which time the reversion of active nitrogen is in progress .
On turning the bulb so as to drop the wire into it , the luminosity is extinguished in less than one second .
The same method and apparatus as were used for ozone and silver were available in the present instance , with little modification .
A current of pure nitrogen was used , and a jar discharge passed to produce the active modification .
Oxidised copper gauze was used of silver , and a very much larger surface was found necessary to destroy the glow .
The copper auze used had wires per centimetre , the diameter of each wire being mm. This gives sq .
cm .
( oxidised ) copper surface per square centimetre of 'Roy .
Soc. Proc 1911 , , vol. 85 , p. 219 ; 1911 , , vol. 86 , p. 56 ; 1912 , , vol. 86 , p. 262 .
1912 .
] The Molecular Statistics of some Actions .
307 gauze .
The discs used filled the entire cross-section of the tube in which they were mounted , tead of being fixed in a , and their diameter was 14 mm. One such disc was not found nearly capable of extinguishing the glow , and two or more were accordingly used in succession .
There was no reason for unravelling the gauze as in the silver-ozone experiments .
It was used intact .
The velocity of meftn of the active nitrogen molecule at ordinary temperatures is taken as .
This is on the supposition of a monatomic ] ecule .
If some othel ' hypothesis is preferred , the appropriate correction can be introduced , but it will not much affect the broad conclusion .
I quote two experiments\mdash ; ( 1 ) Two discs of oxidised gauze .
gregaCe surface sq .
cm .
intake .
per second at 760 mm. Pressure at gauze mm. Hence , vohune of gas stream 190 .
per second .
Number of collisions divided by number of lnolectlles is 520- .
The bolow was distinctly perceptible , though feeble , after passing the discs .
( 2 ) Three discs of oxidised gauze .
nface 9 sq .
cm .
Nitrogen intake c.c. per second at 760 mm. Pressure at gauze mm. Hence volume of gas stream 145 .
per second .
Number .
collisions divided by number of molecules is 1030 .
The glow was completely uished after passing the third disc .
We may take the mean value 780 for the above ratio as the minimum for complete extinction under the experimental conditions .
These were nearly the same as in the silver-ozone experiments of S2 .
In those experiments it was concluded as probable that the actual number of collisions necessary to destroy a molecule was less than the superior limit indicated by obseryation in the ratio ] .
If we assume that the holds in the present case , we find that an active nitrogen molecule must on the collide 500 times with an oxidised copper surface before it is destroyed .
I have noticed , however , that the efficiency of an oxidised copper surface in this respect is by no means constant , but varies according to the treatment it has received .
Thus its efficiency is greater after heating in a vacuum .
The improvement persists for some time after cooling , but eventually disappearH .
The above number is only illustrative , and is not to be regarded as a definite constant .
S4 .
Volume Chcmge of Ozone to There is not the same difficulty in treating chemical change occurring throughout the volume of a gas from the kinetic standpoint , as is encountered Hon. R. J. Strutt .
[ June 13 , when the action occurs at a solid surface ; the complication introduced by what may be called imperfect , alluded to above , is absent .
On the other hand , very few chemical changes are known in gaseous systems which proceed at a conveniently measurable rate , and are independent of anything happening at the walls of the vessel , or of stimulation by light from The only data I have been able to find are some given by Chapman and Jones*on the change of ozone into oxygen .
They show that this change proceeds at a rate independent of the area of walls of the glass vessel , and approximately proportional to the square of the ozone concentration .
This justifies the assumption that the change results from collisions between ozone molecules throughout the volume of the gas thus : Their experiments were made at 10 C. In one series the change of pressure due to conversion of ozone into oxygen proceeded initially at a rate of cm .
of sulphuric acid per minute .
Remembering that two volumes of ozone decompose into three volumes of oxygen , this gives for the partial pressure of the ozone decomposed cm .
of sulphuric acid per minute , or atmospheres per second .
The number of molecules per cubic centimetre of a gas under standard conditions may be taken as , or per atmosphere at Thus the number of ozone molecules decomposed per second was , or I shall call those collisions between ozone molecules which result in chemical decomposition , successfut collisions .
The number of these is half the number of ozone molecules decomposed .
There were , therefore , successful collisions per cubic centimetre per second .
We require next the total number of collisions between ozone molecules per cubic centimetre per second .
The collision frequency of a molecule is , where is the pressure and the coefficient of viscosity .
If molecules are present , the number of collisions made altogether per second is .
Each collision , it is to be remembered , affects two molecules .
To evaluate this expression in the actual case we require a value for the viscosity of ozone at 10 C. No experimental values for this quantity are available , indeed the difficulty of working experimentally with highly concentrated ozone at this temperature would probably be insuperable .
As , however , only a rough idea is necessary , and since the viscosities of all 'Trans .
Chem. Soc 1910 , vol. 97 , p. 2476 .
1912 .
] The Motecular tistics of some Chemical Action. .
309 gases are of the same order of magnitude , it will suffice to guess a value .
I take In the experiment of Chapman and Jones , already referred to , the ultimate change of pressure when all ozone was destroyed amounted to cm .
of sulphuric acid .
The initial ozone pressure must therefore have been twice this , i.e. of sulphuric acid , or dynes per square centimetre .
This makes the number of ozone molecules per cubic centimetre initially present , Substituting these values , we get for the number of collisions per cubic centimetre per second , We get then ratio of total number of collisions to number of successful collisions It is to be observed that this result is independent of the constant , the number of molecules per cubic centimetre of a gas under standard conditions .
constant has only been introduced because it seemed to help exposition .
The broad result is that molecules of ozone at 10 C. must , on the averag coltide times before the right sort of coltision occrn.s for chemical union .
S5 .
ondusio and Sum The methods here applied in special cases may , perhaps , admit of more extended application .
It may , for instance , be possible to study from a kinetic-molecular point of view the oxidation of copper , or the reduction of copper oxide by .
If a small quantity of hydrogen were carried by a stream of rarefied nitrogen past a heated copper oxide gauze , the area necessary to completely take out hydrogen might be determined , and an estimate of what fraction of all the collisions is chemically effective might be made .
I hope experimenters may be induced to take up this and similar problems .
Summary .
When ozone acts on a silver oxide surface , every collision results in the destruction of the ozone molecule concerned .
( 2 ) An active nitrogen molecule must , on the average , collide 500 times with an oxidised copper surface before it is destroyed .
( 3 ) Two molecules of ozone at 10 C. must , on the average , collide times before the sort of collision occurs for chemical union .
|
rspa_1912_0084 | 0950-1207 | On the absorption and reflection of homogeneous \lt;italic\gt;\#x3B2;\lt;/italic\gt;-Particles. | 310 | 325 | 1,912 | 87 | Proceedings of the Royal Society of London. Series A, Containing Papers of a Mathematical and Physical Character | W. Wilson, B. A., M. Sc.|J. J. Thomson, O. M., F. R. S. | article | 6.0.4 | http://dx.doi.org/10.1098/rspa.1912.0084 | en | rspa | 1,910 | 1,900 | 1,900 | 11 | 245 | 6,394 | http://corpora.clarin-d.uni-saarland.de/surprisal/6.0.3/?id=rspa_1912_0084 | 10.1098/rspa.1912.0084 | null | null | null | Atomic Physics | 36.852232 | Electricity | 18.274458 | Atomic Physics | [
9.142193794250488,
-78.68436431884766
] | 310 On the Absorption and Reflection of Homogeneous By W. Wilson , B.A. , M.Sc .
, Wollaston Research Student , Gonville and Caius College , Cambridge ; 1851 Exhibition Scholar of the University of Manchester . .
( Communicated by Sir J. J. Thomson , O.M. , F.R.S. Received June 19 , \#151 ; Read June 27 , 1912 .
) The following paper is divided into two parts .
The first deals with the absorption , and the second with scattering or reflection of beams of homogeneous / 3-particles:\#151 ; I. The Absorption of Homogeneous / 3-Particles by Matter .
Introduction.\#151 ; Three years ago it was shown by the author* that homogeneous / 3-particles are not absorbed by matter according to an exponential law , but according to a law in which the rate of absorption increases with the thickness of matter traversed .
The experiments were repeated by Crowther , *J* who used more homogeneous rays , and found a still greater deviation from the exponential law .
How the absorption coefficient of / 3-particles increases with decreasing velocities of the rays , which suggests that there is a diminution in the velocity of the / 3-particles as they penetrate matter .
Experiments proving this point were made by the author } and Crowther , S and later by v. Bayer , Hahn , and Miss Meitner .
|| It was further shown that the exponential law of absorption found for a beam of rays emitted by a single radioactive substance can be explained by assuming that the numbers of particles composing the beam are distributed according to some special law with respect to their velocity .
CrowtherlT found that homogeneous rays are absorbed by platinum according to an exponential law , and , further , that rays initially homogeneous which have passed through a small thickness of platinum are absorbed according to this law by aluminium .
He attributed the departure from the exponential law in the case of the direct absorption by aluminium to the fact that the rays striking the absorbing screens were not " completely scattered .
" On this view , the rays strike the first sheet of aluminium * W. Wilson , ' Roy .
Soc. Proc. , ' 1909 , A , vol. 82 .
t Crowther , ' Camb .
Phil. Soc. Proc. , ' vol. 15 , p. 5 , and ' Roy .
Soc. Proc. , ' 1910 , A , vol. 84 .
+ Loc .
cit. , and ' Roy .
Soc. Proc. , ' 1910 , A , vol. 84 .
S Crowther , loc. cit. || v. Bayer , Hahn , and Meitner , 'Pliys .
Zeit .
' January , 1911 .
IT Crowther , 'Camb .
Phil. Soc. Proc. , ' vol. 15 , p. 5 , and 'Roy .
Soc. Proc. , ' 1910 , A , vol. 84 .
Absorption and Reflection of Homogeneous ft-Particles .
311 approximately at right angles , but on penetrating it are scattered , and become , on the average , inclined at an angle to the normal .
On this account the second layer produces relatively more absorption than the first , and this continues for successive layers until a state of complete scattering is reached , when the absorption takes place according to an exponential law .
This final steady state is reached with light substances such as aluminium only after the rays have penetrated to a considerable distance , while with heavy substances like platinum it is reached after the rays have passed through a very thin layer .
This explanation , however , is unsatisfactory , and does not hold for rays such as those from radium E , which , under normal conditions , are absorbed according to an exponential law , for Gray and Wilson* have shown that when these rays are allowed to impinge normally on aluminium the exponential law of absorption still holds after the rays have passed through the first thin layer , and that the deviation from this law observed in the first sheet is in the opposite direction to that observed in the experiments made with homogeneous rays .
Further , it is difficult to see how the observed decrease in velocity as the rays penetrate matter can occur if they are absorbed according to an exponential lawT , for the essential feature of this law is that the absorption coefficient remains constant no matter how much of the absorbing medium the rays have passed through , and , as pointed out above , the decrease in velocity must be accompanied by an increase in the absorption coefficient .
The alternative explanation offered is that in their passage through matter some of the particles undergo more violent encounters with the atoms they traverse than others , and there is therefore a tendency for the beam to become heterogeneous .
This proceeds until a definite state of equilibrium is reached , when the further passage of the beam through matter produces no alteration in its properties , and the beam is then absorbed according to an exponential law .
It is interesting to note that in such abeam the distribution of numbers of the rays composing it with respect to velocity would not alter as it penetrated matter , the greater absorption of the rays of lower velocity being compensated by the decrease in velocity of the more rapid rays , and we should expect experiments to show little or no decrease in average velocity of the rays comprising the whole beam .
Experiments showing such results have been made by Schmidtf and v. Bayer , Hahn and Meitner4 * Gray and Wilson , ' Phil. Mag. , ' November , 1910 .
t Schmidt , 'Phys .
Zeit .
, ' 1907 , vol. 8 .
f v. Bayer , Hahn , and Meitner , loc. cit. 312 Mr. W. Wilson .
Absorption and [ June 19 , The observed facts can also be explained by the production of secondary / 3-radiation as the rays penetrate matter , and this point will be referred to later .
The points outlined above are dealt with in the following experiments:\#151 ; Apparatus and Method of Experiment.\#151 ; The method used was similar in principle to that of the earlier experiments , homogeneous / 3-rays being used , which were separated out by means of a magnetic field from the heterogeneous beam given out by radium B and C. The source of radiation was 30 mgrm .
of radium bromide in equilibrium with its disintegration products .
The specimen was rather impure , and steps had to be taken to eliminate the effects due to the y-rays , which were very strong .
The final form of apparatus used is shown in fig. 1 .
Fig. 1 .
The radium , A , which was contained in a glass tube , was surrounded by lead screens B and C. The / 3-rays from it entered a magnetic field , which was at right angles to the plane of the diagram , and described circular paths , some passing through a circular hole D in a lead screen , and into the opening E of a channel F in an iron block G. The diameters of the hole D , and of the ends of the channel , were 0*8 cm .
The length of the iron block was 6'5 cm .
, and a comparatively pure beam of rays was obtained , which impinged normally on screens of various metals , which were placed in its path by means of the slide H. The radius of curvature of the path of the rays which came under observation was 3'5 cm .
The iron block was secured to the pole-pieces of the electromagnet by means of the brass angle-pieces J. 1912 .
] Reflection of Homogeneous After traversing the channel , the / 9-particles entered the hemispherical copper ionisation vessel K ( 8 cm .
diameter ) , whose base wras closed by a thin sheet of aluminium leaf .
A central electrode passed from this vessel through an ebonite plug L , which was surrounded by an earthed conductor , and through a second cylindrical ionisation vessel M to a tilted electroscope Q , whose sensibility was of the order 40 scale divisions per volt .
The electrode could be connected to earth or insulated by means of the key N. The vessel K was maintained at a positive potential of about 200 volts by means of a battery of 100 small accumulators .
This voltage was much more than sufficient to produce saturation with the strengths of ionisation employed .
The vessel M and the plate of the gold leaf electroscope were connected to the negative pole of a similar battery , the other pole of which was earthed .
In order that the sensibility of the instrument should not vary during the course of an experiment , the potential on the plate of the gold leaf electrometer was kept constant by means of a potential divider .
The size of the vessel M was so arranged that the ionisation in it due to the 7-rays from the radium was approximately the same as that due to the 7-radiation in K. The walls of the vessels being maintained at high potentials of opposite sign , the ionisation currents in them were approximately equal and opposite , so that when no / 9-radiation was allowed to enter the vessel K , the rate of motion of the gold leaf in the electroscope was very slow .
In this way the 7-ray effect was to some extent eliminated .
The arrangement worked very well when the cells were constant , but slight variations in the voltage produced errors of considerable magnitude .
Experiments were made to test for errors due to an ionisation leak in the small chamber containing the key 1ST , but it was found that in general this was small and only needed to be taken into consideration when the ionisations in the two chambers were nearly balanced .
The method of making an experiment was as follows:\#151 ; By means of the slide H a small sheet of aluminium of sufficient thickness ( 3 mm. ) to absorb all the / 9-radiation was inserted in the path of the rays and the rate of motion of the gold leaf determined when the central electrode was insulated .
The aluminium screen was then removed and the / 3-radiation allowed to enter the ionisation vessel .
The rate of motion of the gold leaf was again determined , and the difference between this reading and that obtained with the thick sheet of aluminium in position is a measure of the intensity of the / 9-rays , since the aluminium screen is so small that it does not absorb the 7-rays to any appreciable extent .
Sheets of aluminium of different thicknesses were placed in the path of 314 Mr. W. Wilson .
Absorption and [ June 19 , the rays by means of the slide , and by measuring the intensity of the transmitted / 3-radiation in each case the absorption curve for the / 3-particles could be determined .
By altering the current passing through the coils of the electromagnet / 3-particles of different speeds could be brought under consideration .
The magnetic fields were measured by means of a Grassot fluxmeter , and the velocity of the particles deduced from the product of the magnetic field and radius of curvature by means of the equations the latter being required to correct for the increase in mass of a corpuscle as its velocity approaches that of light .
H is the field strength , p the radius of curvature of the path of the rays , v the velocity of the rays , and c that of light .
The value of e/ m0 was taken as l'74x 107 E.M.U.* Results.\#151 ; The results obtained showed the same disagreement with the exponential law as those previously obtained by the writer and by Crowther .
The absorption curves for aluminium which are shown in fig. 2 approximate Thickness of Aluminium .
Fig. 2 .
a. Yel .
= 2-88 x 1010 cm .
per sec. [ b. Yel .
= 2'84 x 1010 cm .
per sec. c. Yel .
= 2'63 x 1010 cm .
per sec. more closely to those obtained by the latter .
They show that , measured by the ionisation method , the absorption at first is very slow .
In fact for the quickest rays examined the ionisation not only shows no sign of diminution until a considerable amount of aluminium has been placed in its path , * Bucherer , ' Phys. Zeit .
, ' 1908 , p. 755 .
Reflection of Homogeneous ft-Particles .
1912 .
] but also a slight but perceptible increase when the rays have passed through thin sheets .
For these rays the ionisation only falls by 5 per cent , when the rays have passed through 0*5 mm. of aluminium .
It is interesting to compare this with the absorption by the same amount of matter of some of the rapid rays given out by radioactive bodies .
Thus for the quickest group of rays given out by radium C the intensity would have been diminished by 48 per cent. , while for the quick group given out by uranium X it would have fallen to less than half value .
Curves were also obtained for the absorption of homogeneous rays by tin and copper , and examples are given in fig. 3 , the velocity of the rays being Amount of absorbing matter in 1/ 10 grm. per cm .
Fig. 3 .
Velocity of rays = 2'63xl010 cm .
per sec. a. Aluminium , b. \#169 ; Copper , c. + Tin .
the same in each case .
The amount of absorbing matter is given in grammes per square centimetre , and it will be seen that although the curves are similar to those obtained for aluminium the absorption takes place at a more rapid rate for these elements , the initial period of slow absorption being less marked .
The absorption curves thus obtained can be explained in two ways .
( 1 ) The rays pass through the first sheets of matter without being much affected by the atoms they encounter in their path , the encounters are not sufficiently violent to produce a complete stoppage of the particles .
They are , however , slowed down , and the rays striking subsequent layers are still further reduced in speed until a velocity is reached when an appreciable number of the rays are absorbed on traversing the atoms .
Actual stoppage of the numbers of particles then takes place , the rate of absorption increasing as the average velocity decreases .
The average velocity does not appear to Mr. W. Wilson .
Absorption and [ June 19 , decrease indefinitely , the whole beam becoming heterogeneous and a final steady state being reached when the distribution of the rays with respect to velocity in the beam does not alter with the amount of matter penetrated .
The initial rise of the curves obtained with the very fast rays is due to the increased ionising power per centimetre path of the rays as they decrease in velocity .
( 2 ) The homogeneous / 3-rays themselves are absorbed according to an exponential law , but on absorption produce a quantity of secondary radiation of slightly slower type than the primary .
This in turn produces a still slower type of tertiary radiation , and we finally obtain a state of equilibrium in which the proportion of the number of particles of any definite velocity to the number of particles in the whole beam remains constant .
The absorption would then take place according to an exponential law .
The second case is practically included in the first , for we have , at present , no experiments which help us to decide between real secondary and scattered primary rays .
The first case necessarily would involve a continuous distribution of the particles with regard to speed when the equilibrium value has been obtained , while in the second we have nothing to tell us whether the distribution of the rays would be continuous or discontinuous .
The recent remarkable photographs of the paths of / 3-particles through gases , made by C. T. E. Wilson , * show that the / 3-particle ionises continuously along its path and apparently not by sudden jumps .
This suggests that there is a continuous loss of energy along the path of the / 3-particle , and affords strong confirmation of the first view given above .
Further , no mention was made of any branch lines in these photographs , which would occur if the / 3-particles had the power of producing secondary rays with velocities at all comparable with their own .
It is important to note that in both cases it follows that in order to obtain an exponential law of absorption we must have a heterogeneous beam .
Experiments were next made on particles , originally homogeneous , which had passed through 0003 cm .
of platinum to test the correctness of the hypothesis advanced above to account for their exponential law of absorption .
Particles of velocity 2-63 x 1010 cm./ sec. , corresponding to a value of Hp3090 gauss cm .
, were used .
The rays were allowed to pass through the sheet of platinum immediately before falling on the absorbing screens of aluminium , and the curve obtained is shown in fig. 4 ( b ) , the curve for the rays passing directly through aluminium being given for comparison , fig. 4 ( a ) .
The two curves are very different , and * C. T. R. Wilson , 'Roy .
Soc. Proc. , ' 1911 , A , vol. 85 .
Reflection of Homogeneous .
1912 .
] as will be seen from fig. 5 ( b ) , where the logarithm of the ionisation is plotted against the thickness of matter traversed , the absorption of the rays which have passed through the platinum takes place according to an exponential law .
.2 6o c *03 04 -05 Thickness of Aluminium .
Fig. 4 .
2-00 1-20 1-00 12 -03 -04 *05 Thickness of Aluminium .
Fig. 5 .
The platinum sheet was then placed in a slit P in the iron block G- ( fig. 1 ) , so arranged that the / 3-rays were intercepted after they had traversed only 2 cm .
of the tube .
Many of the particles were scattered into the side of the tube and the effect of the ionisation in K was considerably reduced .
The absorption curve for the transmitted rays was determined as before by interposing sheets of aluminium in the path in the slide H. VOL. LXXXVII.\#151 ; a. z 318 Mr. W. Wilson .
Absorption and [ June 19 , " Now , owing to the large distance in the channel the rays had to travel after emerging from the platinum , those which strike the absorbing screens do so approximately at right angles , and it is easily seen that if the difference between the curves a and b , figs. 4 and 5 , is due to mere scattering of the ^-particles by the platinum , the absorption curve obtained in the present case should approximate to the former , while if the difference in the curves is due to the fact that as the / 3-particles traverse the platinum the beam is rendered heterogeneous the curve obtained should approximate to the latter .
The means of a large number of curves thus obtained are shown in figs. 4 and 5 , curves c , which are obviously in much better agreement with the curves b than with the curves a. In fact b and are identical , as will be seen from fig. 5 , except for the absorption in the first sheet of aluminium .
This difference is to be expected since in the curve b the pencil of rays striking the aluminium is diffuse , while in the curve c it is parallel .
Thus / 3-particles initially homogeneous after passing through platinum are absorbed in a different manner to the original beam , and we have shown that this difference is not due to mere scattering of the rays .
The only other way in which the beam can have altered is in respect to its homogeneity , and we therefore conclude that after passing through the platinum the numbers of the particles are distributed in such a manner with respect to their velocity that the whole beam is absorbed according to an exponential law .
II .
The Reflection of Homogeneous / 3- .
We have seen that the method of absorption of homogeneous / 3-particles may be explained in two ways , either by assuming a gradual decrease in the average velocity of the whole beam , during which process the beam is rendered heterogeneous , a steady state being finally reached when the absorption takes place according to an exponential law , or by assuming that homogeneous / 3-partieles are absorbed according to an exponential law , but produce on their disappearance a number of secondary particles whose number must be comparable to the number of particles absorbed and whose velocity is not very different from that of the primary beam .
In the course of some experiments on the scattering of the / 3-particles emitted by uranium X* it was found that the scattered radiation could be split up into two parts , one very easily absorbed , and the other with absorption coefficient not very different from that of the primary beam .
McClellandf had earlier concluded from some experiments on the reflection of / 3-rays that in addition to a reflected radiation there is a * W. Wilson , ' Roy .
Soc. Proc. ' Read May 9 , 1912 .
t McClelland , * Roy .
Soc. Proc. , ' 1908 , A , vol. 80 .
Reflection of Homogeneous 1912 .
] production of real secondary radiation , and these experiments appear to uphold this view .
It must be remembered , however , that the primary rays used were heterogeneous , and the two types of rays observed may correspond roughly to the reflected particles from the slower and quicker portions of the primary beam .
Similar experiments with homogeneous beams would throw much light on this problem , but could not be performed with the radium available .
Experiments were therefore made using homogeneous rays to determine the variation of the amount of reflected radiation with thickness of the reflector .
If there is any large amount of slow radiation produced it should be made evident by a rapid rise in the reflected radiation for the first sheet of aluminium of such thickness as that used in the present experiments .
If there is no such formation of a slow secondary radiation but merely a gradual scattering of the primary beam the initial rise should be much less abrupt .
Apparatus.\#151 ; The apparatus used was similar to that described in the first part of the paper and is shown diagrammatically in fig. 6 .
\#163 ; \lt ; 3 , rCh Fig. 6 .
Fig. 6a .
Homogeneous rays which had been sorted out by a magnetic field traversed the hole F in the iron block G. They then passed through the ionisation vessel C , which was a circular brass box 8 cm .
diameter , 3 cm .
deep , with flat ends .
In one of the ends there was a hole 2 cm .
in diameter closed by a thin sheet of aluminium leaf , while the other had a large square hole 5'3 cm .
side , which was also closed by a thin sheet of the same leaf .
This vessel is shown separately in fig. 6a .
A central electrode passed from this vessel through an ebonite plug , through a second ionisation chamber M , and thence to a gold leaf electroscope .
The method of balancing the 7-ray action as used in the absorption experiments was first tried .
With this arrangement of apparatus , however , Mr. W. Wilson .
Absorption and [ June 19 , the chamber E containing the earthing key was brought much nearer to the source of radiation , and the leak in it due to the 7-ray effect necessitated the application of a considerable correction when the ionisations in C and M were nearly equal .
To overcome this a steady deflection method was used .
The vessels M and E were connected to earth and the vessel C charged to a potential of 200 volts .
When the central electrode was insulated the ionisation current in C caused its potential to rise .
Owing to the rise of potential of the electrode an ionisation current of the reverse sign to that in C passed in the vessels M and E , which increased till the voltage on the electrode was such that this current was the same as that in C. When this stage was reached the gold leaf of the electrometer took up a steady position .
The electroscope was so arranged that it was very sensitive , of the order 200 divisions per volt in the steady position .
The earthing key was connected to a potential divider whereby its potential , and through it that of the central electrode , could be brought to any desired value and the potential corresponding to that of the steady position measured directly .
To calibrate the apparatus the central electrode was cut off at the ebonite stopper between C and M and the ionisation current determined for various voltages applied to the vessels M and E. From the results thus obtained we can determine the ionisation current for any voltage on the central electrode , and hence the ionisation corresponding to the steady state .
This method gives much more accurate results for small ionisations such as we are measuring than the method used in the first part of the paper .
We get rid of all errors due to changes induced by slight alterations in the potential of the cells , which are always present when slow readings are being taken .
All errors due to changes of sensibility of the electroscope are avoided , since the potential is measured directly each time a reading is made , and further no corrections have to be applied for ionisation leaks such as that in the vessel E. The method of making an experiment was as follows:\#151 ; The / 3-rays were allowed to pass through the ionisation vessel C and the intensity of the ionisation determined as above .
This ionisation is due to the / 3- and 7-rays .
A sheet of aluminium of sufficient thickness to absorb the / 3-rays was then placed in their path by means of the slide J and a second reading of the ionisation current taken .
The difference of these two readings gives the ionisation due to the / 3-particles alone .
By means of the clamps A , A , fig. 6a , a sheet of aluminium of any desired thickness was next screwed tightly to the back of the vessel C. The difference of two readings similar to the above gives us the effect due both to the primary / 3-rays and to the rays reflected by the sheet of aluminium , and 1912 .
] Reflection of Homogeneous / 9- .
knowing the intensity of the / 9-radiation alone we can determine the intensity of the reflected radiation .
By making experiments with screens of different thicknesses the connection between the amount of reflected radiation and the thickness of the reflector was determined .
From the number of readings in these experiments in which differences occur it will be seen that very accurate measurements were necessary .
The final results were arrived at by taking the means of a large number of reflection curves .
For the two which have been done most exactly ( Hp = 3090 and H p \#151 ; 4270 respectively ) , about twenty experiments were taken to obtain each curve .
Since the initial portions of the curves are of great importance several experiments were performed on this point alone .
Results.\#151 ; The results obtained using rays of widely different velocities are shown in fig. 7 , in which curves a , b , c and d correspond to rays having velocities 2*14 , 2*63 , 2*78 and 2'88 x 1010 cm./ sec. respectively .
.02 *03 -04 '05 -06 Thickness of Aluminium Reflector .
Fig. 7 .
It is more convenient to discuss these results with reference to some further experiments which were made with rays which had first passed through a sheet of platinum .
As in the absorption experiments there is a great difference between the curves obtained for these rays and those for homogeneous rays .
Fig. 8 shows the reflection curves for the two types of rays , the original velocity being 2*63 x 1010 cm .
per sec. We have seen that rays originally of this speed are absorbed according to an exponential law after passing through a small thickness of platinum with absorption coefficient 42'5 cm.-1 , which is approximately that of the radium E rays .
It was therefore thought to be of interest to compare the reflection curve obtained with that of the reflection of the rays given out by radium E. Mr. W. Wilson .
Absorption and [ June 19 , A reflection curve was therefore determined for the rays from a sample of radium E kindly lent to me by Prof. Eutherford .
This curve is shown in fig. 8 and will be seen to agree very well with that for rays which have passed through a sheet of platinum , and we may therefore conclude that rays originally of velocity about 2'63 x 10A0 cm .
per sec. can be transformed into rays similar to those given out by radium E. It is interesting to note that the velocity of the original homogeneous rays was that corresponding to H p = 3090 gauss cm .
, while the mean velocity of the rays from radium E is that corresponding to H p = 2200.* O -OX -02*03 .O'J '05 COT .
Thickness of Aluminium Reflector .
Fig. 8 .
a. Homogeneous rays .
b. Rays from radium E. c. Rays which have passed through 0'003 cm .
platinum .
Now it will be noticed that the amount of radiation reflected by thin sheets of aluminium is much greater for the rays which have passed through platinum than for those which have not , and it has been shown in a previous paper that the radiation reflected when the rays from uranium X , which are absorbed according to an exponential law , are allowed to fall on thin sheets of aluminium consists largely of rays of a very absorbable type .
These rays correspond to the radiation reflected when thin sheets of aluminium are bombarded by rays which have passed through platinum , and , since the amount reflected is great compared with that reflected by the same sheets when homogeneous rays are used , the increased amount of reflection must be due to the reflection of the slower parts of the primary beam .
We are thus brought to the conclusion that the experiments recorded in the previous paper do not uphold the view that any real secondary radiation is produced * Schmidt , loc. cit\gt ; ; Gray and Wilson , loc. cit. Reflection of Homogeneous 1912 .
] when / 3-particles strike a screen , the two types of rays given off being due to the heterogeneity of the primary beam .
General Discussion .
We can use the experiments on absorption and reflection given above to enquire more deeply into the probability of the production of secondary rays .
If we add the ionisation produced by the reflected rays from a thin sheet of aluminium to that of the transmitted radiation we obtain the ionisation produced by the rays which have not been absorbed by the material .
Now knowing the initial velocity of the rays , we can determine their mean velocity after they have passed through a given thickness of matter.* The variation of the ionising power with the velocity is also known , f and by applying these two factors we can calculate the numbers of particles emerging from both sides of a thin plate which is bombarded by the / 9-rays .
A separate experiment was attempted in which the amount of / 3-radiation reflected by a thin plate was determined after the primary rays had passed through various thicknesses of aluminium , but owing to the scattering of the rays by the absorbing screen and the small amount of / 3-radiation available no consistent results could be obtained .
The numbers of particles actually absorbed by sheets of aluminium of various thicknesses were therefore determined from the curves already obtained for absorption and reflection of the rays .
Eesults obtained are given in Table I. Table I. Thickness of screen .
V elocity of emergent rays .
Sum of reflected and transmitted radiations .
Sum of reflected and transmitted rays corrected for velocity .
cm .
i 1010 cm .
per sec. .
o-oo 2-63 100 100 o-oi 2-59 104 100-5 0-02 2 '55 100 94 0-03 2-50 88 79 0*00 2*84 100 100 o-oi 2-83 104 102 0-02 2-82 106 102 0-03 2 -80 106 101 0-04 2 79 104 98 0-05 2 77 98 90 o-oo 2-88 100 100 o-oi 2-87 103 101 0-02 2 -86 105 -5 102 0 *03 2*85 106 100 0-04 2 -84 106 100 0-05 2 -82 105 1 98 * W. Wilson , loc. cit. t W. Wilson , 'Roy .
Soc. Proc. , ' 1911 , A , vol. 85 .
324 Mr. W. Wilson .
Absorption and [ June 19 , It will be seen that for the rays of high velocity the number emerging from a thin sheet of aluminium is approximately equal to the number impinging on it .
From this it follows that the amount of secondary radiation , if it exists at all , must for these velocities be equal to the amount of primary radiation absorbed , and there is apparently no means of distinguishing it from the scattered radiation .
It is then simplest to assume that all the radiation given out by a body exposed to / 3-particles is due to rays which have been scattered by the atoms they have encountered .
A further point of interest is that yS-rays of high velocity can penetrate a comparatively large amount of matter without any appreciable number of them being absorbed .
The mechanism of the absorption therefore can be taken as consisting of an initial slowing down of some of the rays by the matter they encounter in their path , which process continues till some of the rays are moving sufficiently slowly to be capable of absorption by collision with an atom of the absorbing medium .
It was thought to be of interest to determine as above the numbers of particles transmitted by the absorbing screens by correcting the ionisation curves for decrease in velocity and variation of the ionising power with velocity .
Curves obtained in this way are shown in fig. 9 .
ioo .06 -o8 *io Thickness of Aluminium .
Fig. 9 .
a. Yel .
= 2'88 x 1010 cm .
per sec. b. Vel .
= 2*84 x 1010 cm .
per sec. c. Vel .
= 2'63 x 1010 cm .
per sec. 1912 .
] Reflection of Homogeneous Conclusion .
Curves representing the absorption of homogeneous / 3-rays by aluminium , tin , and copper have been obtained .
It has been shown that / 3-ray beams of high velocity can penetrate considerable quantities of matter without appreciable reduction in intensity as measured by the ionisation method .
The fact that / 3-rays , initially homogeneous , are absorbed by aluminium according to an exponential law after passing through a small thickness of platinum has been confirmed , and it has been shown that this is not due to mere scattering of the rays but to the fact that the beam is rendered heterogeneous in its passage through the platinum .
The reflection of homogeneous rays by aluminium has been studied and it has been shown that the slow rays reflected when the rays from uranium X strike matter are due to reflection of the slower portion of the primary beam .
By a combination of the results obtained for reflection and absorption of homogeneous rays , it has been shown that there is no necessity to assume any production of real secondary radiation when / 3-rays strike matter , the reflected beam consisting merely of particles which have been scattered by the atoms they have encountered in their path .
There is apparently no abrupt stoppage of / 3-particles of high speed , or if there is it is accompanied by the ejection of an equal number of secondary rays which are indistinguishable from the particles which are merely scattered .
The absorption curves for homogeneous rays have been corrected for decrease in velocity as they pass through matter , and curves are given in which the number of / 3-particles transmitted is plotted against the thickness of matter traversed .
I wish to thank Prof. Sir J. J. Thomson for the kind interest he has taken in these experiments .
|
rspa_1912_0085 | 0950-1207 | Colour-blindness and the trichromatic theory of colour vision. Part IV. -Incomplete colour-blindness. | 326 | 330 | 1,912 | 87 | Proceedings of the Royal Society of London. Series A, Containing Papers of a Mathematical and Physical Character | Sir William Abney, K. C. B., D. Sc., D. C. L., F. R. S. | article | 6.0.4 | http://dx.doi.org/10.1098/rspa.1912.0085 | en | rspa | 1,910 | 1,900 | 1,900 | 2 | 74 | 2,077 | http://corpora.clarin-d.uni-saarland.de/surprisal/6.0.3/?id=rspa_1912_0085 | 10.1098/rspa.1912.0085 | null | null | null | Optics | 69.099163 | Tables | 28.189321 | Optics | [
10.020501136779785,
-12.690343856811523
] | 326 Colour-Blindness and the Trichromatic Theory of Colour Vision .
Part IV.\#151 ; Incomplete Colour-Blindness .
By Sir William Abney , K.C.B. , D.Sc .
, D.C.L. , F.R.S. ( Received June 24 , \#151 ; Read June 27 , 1912 .
) A Simple Test.\#151 ; In Parts II and III of this series of papers I have indicated several methods of giving a quantitative value to the amount of green or red sensation which exists in the incomplete green- or red-blind eye as compared with the normal eye .
I need not summarise what has already appeared at recent dates in the ' Proceedings ' of the Royal Society , but I will at once explain a very simple test which gives quantitative measures of the sensations in incomplete colour-blindness .
In my last paper* of the series a table is given of the luminosity of the arc spectrum and the percentage composition of the tabulated rays of the spectrum , and from the same table the amount of white which exists in these several rays can readily be calculated .
Owing to change in hue which white causes in a mixture of a pure red with a green ray I pointed out that the match of the I ) line by two such rays is open to error , not considerable perhaps , but still appreciable .
In my communication " On the Change of Hue of Spectrum Colours by Dilution with White Light , it was showTn that the change in hue at the point where the two curves of red and green sensations cut when their areas are made equal is nil .
For reasons given later it may also be mentioned that a ray at this point when mixed with a blue where the same red and green sensation curves cut , will , with proper adjustment of the widths of the slits , match the white of the reflected beam of the arc light .
The same happens for any other source of light if the curves of equal areas are calculated for such a light .
The position of the point of intersection in the yellow part of the spectrum varies with the kind of light forming the spectrum .
Looking at the table it will be seen that from S.S.N. 50 to the extreme red there is no blue sensation present in measurable quantities .
Suppose that in a beam of the arc spectrum a cell containing a saturated solution of potassium chromate of ( say ) f inch in thickness is placed ; the beam becomes yellow with very little blue present .
If a slit is caused to traverse the spectrum in the colour patch apparatus a position will be found for it which exactly matches the hue of the white light which passes through * ' Roy .
Soc. Proc. , ' A , voi .
86 , p. 44 .
t ' Roy .
Soc. Proc. , ' 1909 , A , vol. 83 , p. 120 .
Colour-Blindness and Trichromatic Theory of Colour Vision .
327 the chromate solution , and will be at S.S.N. 49'6 or \ 5828 to the normal eye .
This , like other rays , contains a fixed ratio of green to red sensations , but no blue which is measurable .
Making the red sensation unity it will be found that the green sensation present is 0*385 .
A table of the ratio of red to green sensation ( making red unity ) for the standard spectrum scale is annexed , as is also a table of wave-lengths with the like ratios:\#151 ; S.S.N. G.S. X. G.S. ' Gr .
S. corrected from diagram .
56 0 047 6300 0 -050 0-050 54 0-105 6200 0*080 0-080 52 0 -187 1 6100 0 *127 0-127 50 0*338 6000 0 -185 0-185 48 0-475 5900 0 -280 0*280 46 0 -603 5800 0-390 0-385 44 0-717 5700 0-500 0-490 42 0-830 5600 0-600 0-595 40 0-934 5500 0-700 0 -700 38 1 -15 5400 0 *805 0-805 36 1 *16 1 5300 0-910 0-910 34 1 -26 5200 1 -015 1 -015 32 1 -33 5100 1 *135 1 *120 30 1 -29 5000 1 -260 1 -225 28 26 1 -14 0-82 ; 4900 1 -340 1 *330 From these tables , a full sized diagram ( fig. 1 ) can be drawn , from which the ratios of red to green can be read off for any scale number or wavelength.* If , instead of a normal eye making a match , an incompletely green blind has to make one , the slit would have to be moved from S.S.N. 49*5 towards the red .
When he considers the match to be correct , the scale number of the ray is read off and referred to the diagram .
Supposing that the mean of several readings was 52 , the amount of green in that ray ( to the normal eye ) would be 0*187 .
By dividing this number by 0*385 ( the match for the normal eye ) , we get very closely 0*5 , and this would be the amount of green sensation ( compared with the normal ) that this incomplete green-blind possesses .
Again , if we have the reading of another incompletely colourblind at ( say ) S.S.HST .
46 , we know at once he is incompletely red-blind ; as that S.S.N. contains 0*603 green sensation , the amount of red sensation he possesses is obtained by dividing 0*385 by 0*603 , which makes him to have 0'64 R.S. as compared with unity R.S. in the normal eye .
It will be seen from an inspection of the Diagram I that the maximum * The table in ' Roy .
Soc. Proc. , ' vol. 64 , p. 44 , gives the wave-lengths of the different standard scale numbers ( S.S.N. 's ) .
328 Sir W. de W. Abney .
Colour-Blindness and the [ June 24 , green sensation is near S.S.N. 30 , where it is about 1*32 , when the red sensation is unity .
At S.S.N. 49'6 , which matches the chromate solution , the amount of green sensation is 0-385 .
It is evident that the maximum red sensation of a red-blind that can be diagnosed quantitatively by the chromate is 0-385/ 1-32 , or an R.S. of 0*29 .
In order to ascertain quantitatively a Fig. 1.\#151 ; Showing ratio of Green Sensation to Red Sensation .
lower R.S. ( say 0"2 R.S. ) , the place of matching must be nearer the red .
The passage of the white light through a cell of bichromate of potash solution , which is at S.S.N. 51*1 , will enable such a small R.S. factor to be determined .
By matching the colour of a scarlet glass , there will be a still longer range .
On the other hand , for green-blindness of an extreme type , the chromate cell will answer , but a more open scale will be given by passing the white light through the chromate cell and a very pale solution of copper sulphate in a second cell .
The test described is so delicate that the slightest deviation from normal colour-sensation can be determined quantitatively with great accuracy to almost the second place of decimals , and it has the advantage of great simplicity .
Trichromatic Theory of Colour 1912 .
] I will give one example of the accuracy and delicacy of the test .
A partially green blind was tested by matching the chromate colour .
The normal eye made a match at S.S.N " .
49*6 , and the green-blind made it at S.S.N. 41*5 .
From the diagram the first named made a match which had 0*385 green , whilst the second match contained to the normal eye 0*855 green ( red sensation unity in both cases ) .
This gave the factor 0*45 for the green sensation in the green-blind .
The same person was tested by the luminosity method described in my previous paper , and from his observations the factor was 0*45 .
From his colour equation to match white his factor was 0*37 .
The factor from the mean of the three was thus 0*42 .
But I have no doubt that the factor obtained by the new test was nearer the truth .
In this method only one slit has to be used and is independent of the luminosity .
( I should say that before making the test the position of the maxima of the colour sensations had been determined as being the same as those in the normal curves which I have published in the ' Phil. Trans. ' ) In the match with the D light two slits are employed to match a pure colour .
In the new test only one slit is used to match a mixed colour .
When using this test it is well that the luminosities of chromate " white " should be the same as that of ray coming through the slit .
My own practice is to reduce the " white " luminosity by means of an annulus or sectors , and get a final equality by opening or closing the slit .
Four determinations are usually sufficient , two by reaching the match from the red side and another two from the blue side of a first approximate match .
A mean of the four readings is taken as the position of the correct match , though not unfrequently all four will be exactly the same .
It will be advisable now to show how the amount of any shift or displacement in the position of the maxima of sensation curves can be determined .
At the beginning of this communication it was pointed out that when a slit was placed at the ray where the two curves of equal area or stimulation cut , the addition of pure blue enabled a match to be made with the white of the light which formed the spectrum .
Let a a , bb ( fig. 2 ) , be two portions of the curves of green and red sensations respectively , cutting at O , and with an ordinate OC ; then a slit placed at C in the spectrum will allow a ray to pass which , with blue , will make white.* If the green curve were ( say ) moved bodily to the left the curves would no longer cut at O but at O ' , so that the slit would have to be moved * The same holds for the colour-blind , since the curves under consideration are " equal area " curves .
The white matched is the " colour-blind white .
" 330 Colour-Blindness and Trichromatic Theory of Colour Vision from C to C ' before a white would be produced .
Similarly , if the red curve were moved bodily the intersection of the curves would not be at O , and C would have to change position .
By obtaining observations it is Fig. 2.\#151 ; Scale of Prismatic Spectrum ( S.S.N. ) .
easy to find , if the curves remain in the position of the normal curves , whether there is any colour-blindness or not .
Should such an alteration in the place of intersection of the curves be found when making the new test described above , the difference in position of the normal intersection and that of the shift should be noted and added to or subtracted from the normal position of the match with the chromate .
If there be colourblindness the amount should be determined from this corrected position of the normal match .
The amount of any shift in either of the curves would also be found , when testing by the luminosity method , by taking the mean of factors obtained on the red side of the maximum of the normal curve and of those on the blue side of the maximum .
The mean of the two sets will give the real factor for the sensation which is in defect .
The method described for ascertaining the amount of shift , if there ever is any , is a reliable one .
|
rspa_1912_0086 | 0950-1207 | On the multiplication of successions of Fourier constants. | 331 | 339 | 1,912 | 87 | Proceedings of the Royal Society of London. Series A, Containing Papers of a Mathematical and Physical Character | Prof. W. H. Young, Sc. D., F. R. S. | article | 6.0.4 | http://dx.doi.org/10.1098/rspa.1912.0086 | en | rspa | 1,910 | 1,900 | 1,900 | 7 | 100 | 2,880 | http://corpora.clarin-d.uni-saarland.de/surprisal/6.0.3/?id=rspa_1912_0086 | 10.1098/rspa.1912.0086 | null | null | null | Formulae | 83.418507 | Tables | 14.370693 | Mathematics | [
71.3353271484375,
-48.715248107910156
] | ]\gt ; On the ofSuccessions of Fourier Constants .
By Prof. W. H. YOUNG , Sc. D. , F.R.S. ( Received June 25 , \mdash ; Read June 27 , 1912 .
) S1 .
In a short note to appeal in the ' Comptes Rendus ' I have shown , by means of reasoning of a somewhat delicate nature , that , if we multiply together corresponding constants of two successions of Fourier constants , the succession of constants so obtained is the succession of the Fourier constants of a function whose summability depends on those of the two functions to which the two given successions belong in a certain definite way .
If and represent the indices of the summability of the given functions , that of the new function so obtained is denoted by .
I have there shown how this theorem may be applied to obtain a notable extension of Parseval 's theorem , and I have briefly indicated that we are thus able to give to that generalisation a still more complete form , namely , that the series , where .
is any positive integer , converges if the power of the function of which and are the Fourier constants is summable .
In the present communication I propose to give the necessary additional reasoning by which this result is obtained , and to deduce other important consequences .
For this purpose we quire the following generalisation of the first result noted above : the denominator of the expression where denotes the sum of the products of the positive quantities , taken at a time , is positive , then the succession of constants obtained by multiplying successions of Fourier constants together is associated with a function whose index of summability is , when those of the separate functions are , for all values of .
from 1 to ?
In this statement the sine and cosine constants of the original functions may be interchanged an even number of times without affecting the truth of the statement .
When the 's are all equal , our formula takes the simple form Prof. W. H. Young .
[ Jime 25 , The lilnitation that the denominator has to be positive imposes a certain restriction in the enunciation of the theorems obtained .
Thus it appears that , if , and and denote the typical Fourier constants of a function whose power is summable , the series and converge this is an extension for the case in which of a result I had already obtained by a different method in a communication already made to the Society , namely , that these series converge , whatever positive value be imputed to .
The absolute convergence in the case when follows from the convergence , proved below , of the series As has been stated , our results have only been obtained on the supposition that is less than unity .
That the convergence of this latter series does not continue to subsist when is greater than unity , follows from the examination of the Fourier series which defines Weierstrass 's non-differentiable function .
It appears , in fact , that continuous functions can be constructed whose Fourier constants , when raised to any positive power , however , give a divergent series when multiplied by any power of , however small .
Thus we have no new theorems about the squares of the coefficients , if the function has more than its square summable ; none about the fourth powers of the coefficients , if it has a power higher than 4/ 3 summable , and so on .
Moreover , the remaining theorems of the type considered are certainly the most that can be obtained by the method here explained .
In particular , we can only assert that the series whose general term is , converges , if , and can only assert that , when is odd , the convergence is absolute , if .
It shouJd also be remarked that we are only able to prove the former of these statements by applying the result of a paper presented some weeks ago to the Society .
When the denominator of the expression vanishes , it appears that the new function is a continuous function , so that its Fourier series converges when summed in the Cesaro manner .
This is a remarkable extension of a result which I have already given for a pair of series .
This extension leads to the conclusion that the series converges when the 's are positive , and , more generally , converges , whatever be the signs of the , when summed in the Cesaro manner , provided the power of the associated function is summable ; and if , as appears probable , the power of the function associated ith the allied 1912 : ] Multiplication of Successions of Fourier .
333 series of a Fourier series is summable when a greater , or perhaps even an equal , power of the function associated with the Fourier series is summable , it leads to the result that the series converges in the same manner , if the summability of the function is more than , or perhaps even equal to , .
It appears improbable that more than this can be stated .
Indeed , when is zero , it is not true that eVen in the ordinary manner , in the case in which the function has every power summable , or is even bounded .
Still less is it true that converges .
There is an obvious direction in which those of our results which contain power of may be generalised .
A modification may be shown to be allowable .
We may , for example , for such an expression as , where , write , where is a suitable monotone function whose limit is zero .
It would be foreign , however , to the purpose of the present paper to extend its results in this direction .
S2 .
In the note cited from the ' Comptes Rendus , ' I show first that if and summable , exists as convergent , jxcept for values of forming set of content zero , summable function of .
I then prove that the series , ( C ) where and are the constants of the ) functions and , is the Fourier series of I then obtain the following inequality , where Putting , and the power of the former and the power of the latter to be summable , it follows from the first result quoted that the first integral on the right of the preceding inequality exists as an absolutely convergent integral , except for a set of values of of content zero , and represents a summable metion of Since the second and third integrals exist , the second being a bounded function of , and the third independent of , it follows that the left-hand side represents a summable function of .
In other words the series ( C ) is ' Fourier series of a function whose power is provided has its its and VOL. LXXXVII.\mdash ; A. 2 Prof. W. H. Young .
June 2 S3 .
Hence by Parseval 's theorem in its completed form , converges if and are summable , provided Choosing , we may take , ( 2 ) since the function corresponding to the Fourier series differs only by a continuous function from a constant multiple of Fronl ( 1 ) and ( 2 ) and therefore Thus we have the heoreln : \mdash ; If is the typical constant of a function , power is converges .
th converges , being typical of , since the reasoning of the article holds when we into This is an extension of the result given in S 15 of my paper " " On a Mode of Generating Fourier Series where the lower bound given for was .
S4 .
Hence we have also the following theorem:\mdash ; Theorem.\mdash ; If constants of a function whose poeoer le where , the series converge absoh , provided .
For by the theorem , provided .
Hence , for such values of , which proves the first statement .
Similarly , the second statement follows , changing into I have ah.eady proved that these series are convergent , though not that they are absolutely convergent , also for values of , in a paper presented to the Society on May 11 of the present year , entitled " " On the ence of Certain Series the Fourier Constants of a Function 1912 .
] of Successions of S .
From what precedes , it follows that if has its power summable and its power summable , where , the series is the Fourier series of a function whose ( power is summable .
Hence we immediately get the result that , if in addition has its power summable , the series where is the typical Fourier cosine constant of , is the Fourier series of a function whose summable , where denoting the sum of the products of the indices , ( 1 , taken at a time , and the denominator is supposed positive .
We have ingly ving theorenl , which ' oved by induction:\mdash ; Theorem.\mdash ; lf has , for , 2 , , its typical , cosine the scri . .
is the Fourier of afuiction whose } , where denoting the of the products of the tities p , , provided the of is positive .
In fact , since the numerator of the above fraction may be written we have , assuming the theorem proved up to and adding another metion , for the index of the required power a fraction whose numerator evidently has the required form , and the denominator is which , when the products involving are combined with the remaining products according to dimensions , takes the required form .
Since the statement has been proved for three this proves the theorem .
{ 336 Prof W. H. Young .
Cor.\mdash ; If a is , lvhere , is Fourier of a function power is lJnable .
In fact , denoting the denominator of the fraction iven in the enunciation of the theorem , when all the are equal , by , we have whence that Since the numerator is } ) , this giyes the required result .
S6 .
We can now proye the theorem : Theorem.\mdash ; If is a function ?
power is , 'cos'w ; is the series of For , writing .
Hence , by the preceding theorem , the series ( i ) is the Fourier series of a function whose power is summable , where But Thus , by the same argument , the series ( ii ) , got from ( 1 ) by changing into , is the Fourier series of a function whose power is summable .
Hence , by a known theorem , cosine series from ( i ) and ( ii ) by ultiplying together coefficients to form the coefficient of the corresponding term of the new series is the Fourier series of a continuous function .
This proves the theolenl .
As an immediate corollary we have the following theorem:\mdash ; Theorem.\mdash ; If has its power when in ro .
Hcnc , if positive for all of , or the integcis in th *W .
H. Young , " " On a Class of Parametric Integrals and the Theory of Fourier Series ' Bo Soc. Proc 1911 , , vol. 85 , and 1912 .
] Multiplicalion of ofConstants .
337 S7 .
We have seen in S5 that , if there are functions , the fraction giving the summability of the fimction corresponding to the Fourier series of cosines whose coefficients are the products of those in the Fourier series of the functions may be written proyided the denominator of this expression is positive .
If , on the other hand , the denominator is zero , we have , with the notation of S5 , Hence , by the same reasoning as in the preceding article , we have the following theorem , of which the first theorem of the article is a particular case : Theorem.\mdash ; If has its rnmablj , , 2 , its cosine constant the is the of a continuous function , ovided the of the which , if give the of the function corresponding to the series , zero , provided where denotes the of the of th positive uantities p , taken at time .
S8 .
If , as in S3 , we take and , applying the work of the preceding article , put we shall have Hence we have the first result of the following theorem , using the result of S7 .
The final statement follows from a theorem lately proved by 1nyself in the paper already cited in S4:\mdash ; Theorem.\mdash ; If for , 2 , .
, the function has its power summable , and has for its pical .
cosine constant , the oos is the Fourier scries of continuous function , provided , where has signific ) of S5 .
Moreover , the series then Prof. W. H. Young .
[ June 25 , A special case is embodied in the following theorem:\mdash ; Theorem.\mdash ; If has ?
power summable , is its ' cosine constant , is the serics of , provided and is then S9 .
We cnn strife ?
than the convergence of the if ?
fttrther strict p so as to ) , , of course , now an odd integer .
the lestion ?
th absolutely convergent .
When , this from S6 , since the series is convergent , and absolutely for When , the result follows from the final theorem of the preceding article , since the series then convel.ges absolutely , proyided This proves the statement ) at the of the present article .
Putting , we have the special case : If , the is convergent , and it is certainly alt positive of all cases quan tity greatethan Again , have the following:\mdash ; If ' convergent , and it is if in all .
S 10 .
Since has the same degree of summability as , .
the , and has its power summable , the series is the Fouriel selies of a function whose power is summable .
Hence it at once follows from the arguments used that in our 1912 .
] Successions of theorwe replace even number of the successions of cosine constants by sine constants .
S 11 .
If however in the series ( C ) we replace the 's by zeros and the 's by zeros , which , as we saw , is legitimate , we get a sine series , and not , as in the preceding article , a cosine series .
Thus the subsequent arguments used would not apply ; they would of course apply if the 's and 's could be interchanged in the series , that is if it is true that the allied selies of the Fourier series of a function whose power is summable is also the Fourier series of a function whose power is summable .
This proposition has not been proved , although , for various reasons of a more or less convincing character , I am inclined to believe that it is true , or at least that the allied series is the Fourier series of a function whose power is summable , where is any quantity less than S12 .
In the various theorems here obtained there has always been a limitation on the value of .
Thus in the theorem concerning the convergence of had to be less than unity ; if we have the theorem of Parseval ; in the theorem concerning the ence of had to be less than 1/ 3 , while , if , the series is and so on .
It should be noticed that , when has a value greater than the limit imposed in the present paper , the index of the power to which raised changes sign .
Our reasoning evidently fails in these The quest , ion fore remains over as to whether the formulae are none the less true without ths limitation imposed on .
That the answer to this question must be negative appears from a consideration of the series Weierstrass 's non-differentiable function .
This shows that cannot even assert in the case of a continuous function that any positive power of however small , multiplied by any power of , however , need be the general term of a convergent series .
Indeed Weierstrass 's series is where is an odd integer , and .
This is a Fourier series with groups of terms absent owing to the corresponding Fourier constants being zero .
The series under consideration is therefore This will therefore certainly diverge if
|
rspa_1912_0087 | 0950-1207 | Experiments with rotating liquid films. | 340 | 350 | 1,912 | 87 | Proceedings of the Royal Society of London. Series A, Containing Papers of a Mathematical and Physical Character | C. V. Boys, F. R. S. | article | 6.0.4 | http://dx.doi.org/10.1098/rspa.1912.0087 | en | rspa | 1,910 | 1,900 | 1,900 | 8 | 224 | 5,961 | http://corpora.clarin-d.uni-saarland.de/surprisal/6.0.3/?id=rspa_1912_0087 | 10.1098/rspa.1912.0087 | null | null | null | Optics | 39.13966 | Measurement | 22.493839 | Optics | [
10.589780807495117,
-59.39427185058594
] | 340 Experiments with Rotating Liquid Films .
By C. Y. Boys , F.R.S. ( Received June 26 , \#151 ; Read June 27 , 1912 .
) Plateau , in his great work ' Statique des Liquides , ' has given a very short description of an experiment by Eisenlohr , who enclosed in a vacuous globe of glass some soap solution .
On manipulating the globe he obtained films crossing the globe , and on rotating the globe he obtained coloured rings in the film .
So far as I can understand the very short description , the position of the film must have been a matter of chance , and consequently the curvature , so that to obtain a plane film by this method would have been a matter of chance , and obviously it would have been impossible to manipulate with the film itself .
Not knowing of this experiment , I desired last year to make some experiments with rotating films , and designed and constructed for the purpose the apparatus I am about to describe , and the phenomena obtained are so interesting and beautiful that I wish to present to the Royal Society a short but sufficient account of them .
I intend to make a more detailed explanation in the form of an additional chapter to my book on ' Soap Bubbles ' ( published by the Society for Promoting Christian Knowledge ) .
I have made up the apparatus in many forms and sizes , but for observing the phenomena I have found that to be described the most suitable .
A cheaper form is being made and will shortly be available for general use .
Referring to the figure , which is a vertical section , a box of circular cross-section is mounted upon a tubular support into which a steel ball has been forced .
The whole runs on a steel upright fixed in a heavy tripod with three levelling screws .
A number of pulley grooves make it possible to turn the box at very different speeds by means of a string driven by a small motor , but the most convenient method of driving for ordinary observation is by rolling the hand or fingers over the tubular support , which is roughened to increase the friction .
A transparent conical cover of thin celluloid fits easily over the box .
A central binding screw made of brass is secured to the celluloid , and through the centre of this there is a small hole fitted with a conical stopper which can be removed or replaced while the box is spinning .
The in turned rim is drilled with a number of holes , so that when a film is stretched on the feather edge of the rim there is free air communication between the air in the two spaces above and below the film ; this is essential where it is desired to maintain the plane form of the film .
When the film is curved the Experiments with Rotating Liquid Films .
brilliance and beauty of the phenomena are not so marked .
The interior of the box is dead black .
The diameter of the film in the apparatus now described is 4 inches ( 10 cm .
) , but I have made them both much larger and much smaller .
The best liquid to use is a solution of pure oleate of soda in 40 times its weight of distilled water , with the addition after solution of 10 per cent , by volume of pure glycerine , but for special purposes either more or less glycerine , or even none at all , should be used .
I have used also melted resin , which works quite well if all is hot and the box is much smaller , but this is tiresome .
A solution of saponine in water is possible , but this , owing to the surface rigidity , is not desirable , though that property may be demonstrated with the apparatus if *a very small ring be used .
The easiest way to stretch a film is to dip a wiper of thin celluloid in the liquid and then to wipe this across the rim .
If the holes in the edge are wanted to be closed they will all be closed at the same time , each with its own film .
These can be broken instantly if they are wanted open .
In order to Mr. C. Y. Boys .
[ June 26 , see the phenomena best it is well to place the instrument in a window with an extensive sky area opposite and it is best not to be facing the sun .
The following experiments may be made with this apparatus , which are instructive or beautiful , and all are attractive :\#151 ; 1 .
Having a film stretched on the rim and the small holes open , turn the box without its cover .
The centrifugal force of the air causes the film to be drawn in and the relation between this force and the tension and curvature of the film may be determined .
2 .
If the holes are covered and the film is plane when starting , the mean pressure within remains the same as that of the atmosphere , but it is less near the centre and more near the edge , so that the film is concave near the centre and convex near the edge .
3 .
If a film is on the rim and the cover is in place and one or more of the small holes are open , then on starting the rotation the film rises until the pressure of the air below the film has fallen to that determined by the centrifugal force of the air at the edge of the cover .
Conversely , when the rotation is stopped or reduced , it falls .
The object of having so many holes is to make this process more rapid and to ensure working with a plane film .
4 .
If a film is on the rim and the cover is in place and the box is slowly turned , the film gradually takes up the rotation and under centrifugal force is both stretched and drained .
Soon a ring pattern is seen which develops gradually , and the lower order colours appear successively at the centre .
The elastic character of the film may be seen now , for if the rate of rotation is reduced , the rings become smaller .
If increased , they expand again .
With sufficient speed , the integrated centrifugal force may stretch the film with a force as much as about 20 per cent , more than its normal tension .
The surface tension then has a range over the proportion 5 to 6 .
About and within this range the film may be said to be elastic and not merely to exert a constant surface tension .
I have found about the same range by a statical experiment described on p. 108 of my book on ' Soap Bubbles , ' 1912 edition .
When this high tension is reached , the film rapidly thins in both experiments so as to prevent the force which the increased surface tension has to withstand from rising more .
The brilliance and beauty of the ring patterns exceed those of any phenomena with bubbles that I know .
When the colours of the first order are reached and the centre is straw colour or white , a central black spot will soon appear .
This grows very slowly under constant rotation , but if , when the black is seen , the rotation is stopped and the base is so placed that the film is not quite level , the black spot will trend upwards while the thicker parts will trend downwards , and if left long enough the well-known 1912 .
] Experiments with Rotating Liquid Films .
343 horizontal band pattern will appear .
If at any time during this process the box is set into rotation again , the black spot , wherever it is , will be drawn out into a long thread and the extent of the black surface will then rapidly grow , for the edge of the black is unstable .
The two layers which meet where the film is black tend to extend the area where they meet , but they cannot drive away the liquid between the layers , owing to its viscosity .
They can , however , drive the liquid into little blisters all round the periphery of the black area , which the colour shows to be thicker than the adjacent portions of the film .
Then these blisters , being thicker and heavier , move away from the black downwards or outwards , as the case may be , while the black travels in the other direction through the film .
Thus it is that when the black is all collected at the centre again it is larger .
This process may be repeated and a black centre spot 5 cm .
or more in diameter may soon be attained .
5 .
When the black spot is large enough to be conspicuous , like the pupil of the eye of a great beast wdth a brightly coloured iris , and the rotation is stopped and then started again slowly when the spot has moved say half-way towards the edge , the formation , first of a comma , then of a spiral of several turns , becomes very striking .
If the rotation is slow , the way the black spiral breaks up so that its parts may move inwards may be seen .
It is curious .
If when the film is at rest and inclined , and a well-developed parallel band pattern has been established , the box is made to turn , the conversion of these into double-threaded spiral patterns is beautiful beyond all expectation ; if when the spiral pattern is well formed the rotation is reversed the spiral will unwind .
The appearance of black among the brilliant colours enhances their brilliance .
Sometimes the instability due to the edge of the black is unduly marked , and then when the black begins to form and is drawn in a spiral through the film the increase of the black is so rapid that it would all become black in a few seconds .
The film never remains long when this is the case .
When however , the process is normal , the film may last for two hours before half of it has become black .
This is more especially the case when the glycerine is increased up to one-third of the original oleate solution .
The black spiral lines intersecting the film infect it with the unstable quality and the black and blue spots soon pervade it all and can then be sorted out by centrifugal force by rotating the box .
6 .
While anything from 1/ 10 to 1/ 3 of glycerine is a suitable addition when making the experiments previously described , a solution without glycerine is better when the black film is the object of examination .
With this solution I have with a smaller box soon obtained the whole film black , the last luminous specks round the periphery gradually disappearing .
With Mr. C. V. Boys .
[ June 26 , such a film the phenomenon of the double black , that is of a film of half the normal black thickness , or about 6 instead of about 12 micromillimetres , may be well seen .
Further , as the double black only weighs half as much per unit area as the common black it may be collected so as to form a central extra black spot in the black .
Here , however , the separating forces are much smaller than they are in a coloured film and the process is slow .
Whatever view may be held as to the existence of an unstable thickness between about 12 and 100 micromillimetres , it is not easy to imagine valid cause for a second between about 6 and 12 micromillimetres .
It would appear then that there should be some independent cause for the sharp division between the two blacks , one double the thickness of the other .
Great familiarity with the appearances suggests that the surface layers which meet in the ordinary black may act almost like actual skins and where the double black is seen one is broken and the remaining portions are adherent to the unbroken film , a kind of viscosity preventing the sliding which the surface tension of the broken skin should induce .
The unbroken one would then be under double its normal tension in the double black parts , and if the layer acquires its normal tension from being in contact with the air on one side , then this gets its double tension from having the air on both sides .
I fear this is a gross way of regarding these molecular structures .
It at least is consistent with appearances .
With regard , however , to the existence of any unstable thickness which would make the thinner whites impossible , I do not find any experimental evidence of this in particular .
If the film is very nearly level the combined suction of the edge and the draining give rise to small areas which show every gradation from black , through grey and white , to the colours of the first order .
I do , however , find a marked instability at the edge of the black when it is drawn out and broken up in a coloured layer .
The steep edge then breaks into blisters as already described , the result possibly of the longitudinal instability of a thickened edge , and this continues with thicker films .
It is only when these show colours of higher order than the first that any evidence of the slope of the edge is visible , for then with a pocket lens a luminous edge can just be detected .
7 .
Using the ordinary liquid , again spin the film until a ring pattern is well developed and then remove the central stopper of the shade .
There will be an axial indraught of air , the air escaping round the edge of the cover .
Where the indraught strikes the film it will cause it to become thinner , and a central thin spot may be recognised by its colour .
8 .
Then hold the stopper of an ammonia bottle containing dilute ammonia for a moment near the hole in the shade .
Immediately the indraught of 1912 .
] Experiments with Rotating Liquid Films .
vapour acts on the film , increasing the surface tension of a central spot , which immediately thickens , and then very soon , being in an unstable position in the centre , undergoes a convulsion and makes a hurried dash for the edge .
9 .
After ammonia treatment the thinning effect of an indraught of clean air is more marked .
10 .
Other vapours may be used .
Many , such as acetate of amyl , aniline , orthotoluidine , formaldehyde , make a thick spot ; others such as ether make a thin spot .
11 .
Instead of turning the box leave it in a slightly inclined position until horizontal bands of colour have become established , and then , holding the ammonia near the edge of the shade , gently raise this on the side where the ammonia is held .
Immediately the part of the film near the inrush is thickened at the expense of the rest of the film , and if this is already thin enough to show the brighter colours of the first and second order it may all flash into a straw colour or white of the first order with a thick blue or green streak due to the ammonia .
12 .
Using a spirit level or the film as a guide , adjust the position by the aid of the levelling screws until the film is level .
Then if the three screws are in a circle 6 inches ( 15 cm .
) in diameter the film may be tilted roughly to any desired angle by inserting pennies under one foot .
Each penny increases the angle by half a degree .
Set the film at a small inclination not exceeding 3 ' , and to save time get rid of much superfluous fluid by spinning it a short time or until a good black spot has been formed .
Then leave the film at rest .
After several minutes probably an action will have started which keeps the coloured portion of the film in constant movement and gives rise to an amazing network of black lines with coloured margins .
Whether it is the formation of a thin spot near the lowest side due to suction of the edge rising through the film , or the falling through the black of a coloured spot which has gathered together at the upper edge , the result is the passage up or down , as the case may be , of a black line which is persistent .
With angles much steeper than 3 ' a rising black spot is in such a hurry that the long black tail which it leaves cannot follow , and gets drawn off , but this is not the case at small inclinations .
A heavier spot falling through the black carries down a black line .
The margins of these black rivers cannot meet , for the black is constantly growing and encroaching on its banks , piling them up as coloured spots on either side , which descend as already described .
These thicker parts falling and thin spots caused by the suction of the ring rising occasionally hit a black river and bend it with its banks out of its course , and the process continues in a stealthy and persistent way for some 346 Mr. C. V. Boys .
[ June 26 , hours , and the number of black lines continually increases .
Examined with a lens the phenomenon is one of marvellous beauty .
13 .
The rivers are constantly flowing upwards to feed the black area which is formed in this way , not by ordinary draining .
Curious blobs of black are formed in the rivers and break away through the mass of coloured islands , and where they enter the black sea they often draw out from the islands an extended isthmus , which becomes longer and narrower , and then breaks at one or more points .
The liberated promontories or islands instantly contract under the action of a well-marked " line tension , " and either retreat into the main coloured area or form absolutely circular coloured islands , which gently settle down and rest against a host of other islands formed in the same way .
14 .
While the banks on the opposite sides of a black river cannot squeeze out the black river and coalesce , these circular islands , with their sharply curved edges , are able to do so , and they are constantly joining to form larger islands .
The smaller the inclination the less this should recur .
15 .
The existence of this line tension on the margin of the black is certain , and its effect is conspicuous .
I have seen the same phenomenon with the thinnest colours in thicker colours , but here it is less marked , and it is also to be seen , but not in so marked a degree , on the edge of the double black .
While there can be no doubt as to the fact , I think the following a probable reason , and the figures here given would indicate that it is not impossible .
The black areas abut into the coloured areas often without any visible gradation of colour , or where the adjacent colour is of a higher order than the first it may be that there will be a luminous margin just discernible with a pocket lens .
The greys , which would be seen if the black thickened gradually , are not often seen except as described above under the number 6 .
The banks of the black rivers and spots may therefore be very steep , and if these intermediate thicknesses really are unstable , this probably is the case .
If the banks should be actually vertical then , where they occur , there is an increased surface equal in amount to the heights of the banks on the two sides of the films .
Taking a black river , with banks showing the brown colour of the first order , this amounts to 200 \#151 ; 12 or 188 micromillimetres .
If the ordinary surface tension of 2'8 dynes to the millimetre acts on this bank there would be an additional tension appearing as a line tension equal to 2*8 x 188 microdynes .
This is 5-25 x 10-4 dynes .
This quantity is a maximum quantity , calculated on the assumption that the banks are vertical .
If not vertical , but inclined , the extra surface , and consequently the line tension , will be less .
The two 1912 .
] Experiments with Rotating Liquid Films .
edges of a brown promontory may then pull it in with a force which cannot much exceed 10-3 dynes , and which may be very much less .
It is not possible to calculate the rate of movement from the viscosity , partly because there is no means of telling over what area of the black the shear extends , and partly because viscosity may well be anomalous in such films .
This , however , is of no consequence , because the same experiment provides the means of ascertaining what velocity is given to a coloured island under an exactly ascertainable force .
For instance , taking an island of 10 sq .
mm. area , brown of the first order in colour , in a black film sloping at an angle of 1 in 20 , the weight of such an island will be 2 x 10-6 grm. , and the excess of its weight over an equal area of the black will be T88 x 10-6 grm. The force causing this to descend will then be 1-88 x lO"6 x 981-4-20 = 0'92 x 10~4 dine .
This is of the same order of magnitude as the line tension due to moderately sloping banks , and experiment shows that such an island descends through the black at a speed of the same order of magnitude as that of a contracting promontory .
I should say that at the first rupture of the very slender neck the first part of the retreat is much more rapid than that which follows .
16 .
Having the film with a large amount of black , whether the black network intersects the coloured portion or not , turn the box slowly so as to draw it out into a wide spiral pattern of black and colour .
Reverse the directions a few times and gradually the whole area may be converted into one of coloured islands on a continuous black sea with a long isthmus several centimetres long here and there ; or if the black is less developed then there may be innumerable black circular spots on a continuous coloured ground .
On leaving this to settle when the film is inclined not more than 1 ' the actions described above will be seen in great variety .
17 .
If a little ammonia is allowed to enter the gently revolving box when the film is composed of coloured islands floating in a black sea , the islands where the vapour impinges will suddenly change in colour and contract , but the black will not appear to change at all .
I have , however , seen a large central black spot become suffused with a blush of greyish white on the entrance of ammonia , but it almost immediately broke .
When black abounds ammonia must be used with discretion .
18 .
If an air bubble be blown in the film it will take the form of two spherical segments meeting each other and the film at angles of 120 ' .
Each segment has therefore an area equal to that of a great circle of the sphere of which it forms a part .
The bubble will therefore weigh more than double as much as the plane film which it replaces , for the surface is 2S times as great .
On turning the box therefore the bubble goes to the edge and sticks there .
348 Mr. C. V. Boys .
[ June 26 , If , however , the bubble be blown with coal gas or hydrogen the gas and film will , if the bubble is large enough , be lighter than the air and film which it replaces and so on turning the box it will go to the centre and remain there absolutely true in position .
As , however , the surrounding film becomes thinner , which it does more quickly than the bubble , rings of colour of a lower order appear round it looking like the planet Saturn , the position gradually becomes unstable and the bubble fidgets round to a gradually increasing extent .
I have seen such a bubble in a black area and it is curious that the liquid of the bubble does not seem able to pass readily through the junction line and the black .
19 .
If a piece of spun glass from 10 to 15 cm .
long , or a piece of human hair about 15 cm .
long , have its ends joined so as to form a ring and this be laid on the rim of the box so as to overlap the film , then on breaking the film in the space between the fibre and the rim the fibre will shoot into the film , where it will appear perfectly circular in form .
If now the box is gently inclined the ring will float up or down until it has found a place where the weight of fibre is equal to that of the coloured bands which it replaces .
If the inclination is only a few degrees these bands tend to become broad , and the weight of the film can readily be compared with that of the ring by reference to the colour plate in my book on e Soap Bubbles .
' If this is not available the weight of any part of the film can be ascertained by inspection ; for the quarter wave-length of green light in the solution is yowo mm-\gt ; and green light will be reflected vertically when the film is 1 , 3 , 5 , 7 , etc. , ten-thousandths of a millimetre thick , or when it weighs 1 , 3 , 5 , 7 , etc. , hundredths of a milligramme per square centimetre .
The first of these odd numbers is in the white of the first order , the second is in the nondescript white of the second order between the blue and the yellow , the third is in the conspicuous apple green and this is T-S-\#165 ; milligram to the square centimetre .
The following greens , first dull , then bluish , then pale , and then paler , are 7 , 9 , 11 and 13 hundredths of a milligram per square centimetre .
All therefore that is necessary is to look for the apple green , which cannot be mistaken .
That is 5 , and the thicker greens may be counted from this , using odd numbers only .
As a variation the ring may be set loose in the film , but not have the inner film broken .
This is best done with spun glass , which should be laid on to the film at its upper part where it is already coloured .
The ring then settles down into the lower regions and the difference of the weights of the films within and without are equal to the weight of the ring .
Then when the inner film breaks , which it often does first , the ring immediately darts upwards to its new position of rest .
I have made this experiment with rings of various sizes , but those mentioned 1912 .
] Experiments with Rotating Liquid Films .
are suitable as the equilibrium position is then in a conveniently coloured region .
20 .
If the box is rotated slowly with a ring such as I have described under 19 in the film , the ring will go to the centre and stay there until the rings of colour round it reach that colour in which it is in equilibrium .
When this is the case the ring behaves as the bubble did and gradually gets further away from the central position .
All the time the ring pattern can be seen and the positions where the ring is nearest and furthest are easily seen , but this is not convenient for weighing the film , whereas the method under 19 is , and I do not know of any other simple way by which this may be done .
21 .
Plateau has described ( vol. 1 , p. 277 ) an experiment by Van der Mensbrugghe , who placed a light spherical bulb of glass in a soap film stretched on a vertical ring .
He found , on turning the ring , that the sphere resting on the edge rolled and maintained its position .
I have made a convenient variation of this experiment , and shown it as a lantern slide , using the blown egg of a bird , not exceeding in size that of a house sparrow .
The hole in the egg-shell should be mended with a small disc of tissue paper and celluloid dissolved in acetate of amyl .
The egg immediately turns round , so that its maximum and oval cross-section lies in the plane of the film , and , when the ring is turned , the egg-shell slides or rolls , and , when the speed is increased , it rolls and jumps all over the area occupied by the film .
The smaller birds ' eggs will actually remain supported by the film when this is horizontal .
Small rings of celluloid , of elliptical or other shape , and convex in the * transverse direction , should do just as well .
They should be more easy to handle , and they would remove the only good excuse for robbing the nests of our precious birds .
I have , in the description of the experiments , expressed myself as shortly as possible , but I hope sufficiently to show that the instrument may provide not only a useful method of investigation and much philosophical entertainment , but may be a valuable addition to the appliances of a physical laboratory , and one with which students may make many useful and instructive experiments .
I have not thought it worth while to add what might be called laboratory notes on some of the experiments , notably , on that of weighing the film .
I have made a machine for viewing the rotating film , so that it may appear stationary .
A reflecting prism is mounted with its large face and long edges parallel to the axis within a tube which can run in ball bearings .
This device , which was used by the late Mr. Jervis-Smith in a dynamometer , causes fixed things to appear to turn twice as fast as the prism is turning and in the same direction .
If the prism does not rotate and the object does , it VOL. LXXXVII.\#151 ; A. 2 B Mr. C. E. Haselfoot .
[ June 26 , appears to rotate at its own proper speed , but in the reverse direction .
If both rotate in the same direction , but the object twice as fast as the prism , it does not appear to rotate at all .
I have examined the rotating soap film with this but have not obtained any striking results .
I have , however , observed the curious effect of angular error in position of the prism .
This causes a point in the axis of the motion to appear to describe a circle once for every turn and in the same direction .
If the prism were truly in position a point not in the axis would appear to turn twice for every turn and in the same direction .
If the prism is not truly placed a point not on the axis will appear to move with a combination of these movements , it will describe a trochoidal curve .
The Diffusion of Ions into Gases at Loiv Pressure .
By C. E. Haselfoot , Fellow of Hertford College , Oxford .
( Communicated by Prof. J. S. Townsend , F.R.S. Received June 26 , \#151 ; Read June 27 , 1912 .
) 1 .
In papers published in the ' Proceedings ' of the Royal Society , * ' the charges on ions produced by the action of Rontgen rays and radium on air * were determined by a method depending on the diffusion of the ions , and in the course of the investigations it was observed that the removal of water-vapour from the gas produced a large change in the motion of negative ions .
In this paper the results are given of some accurate experiments on the ions produced by radium , and experiments at low pressures on the motion of the ions produced by ultra-violet light are described .
In the latter case , effects similar to those observed by Prof. Townsend when the gas was ionised by Rontgen rays have been found , and some interesting results at pressures lower than those previously employed have been obtained .
2 .
The arrangement of the apparatus is here reproduced ( fig. 1 ) .
The ions are generated in the field A by radium placed in shallow horizontal grooves/ , covered with aluminium foil , in brass blocks F. They pass under the action of the electric force through the grating g and the aperture h into the field B , which was kept constant by means of the brass rings G maintained at definite potentials .
Here they diffuse and the ratio R of the charge received by the disc D to the charge received by the disc and the ring S together is measured .
This ratio is a known function of E7 ?
Z/ P , * Yol .
80 , p. 207 ; vol. 81 , p. 464 ; vol. 82 , p. 18 .
|
rspa_1912_0088 | 0950-1207 | The diffusion of ions into gases at low pressure. | 350 | 357 | 1,912 | 87 | Proceedings of the Royal Society of London. Series A, Containing Papers of a Mathematical and Physical Character | C. E. Haselfoot|J. S. Townsend, F. R. S. | article | 6.0.4 | http://dx.doi.org/10.1098/rspa.1912.0088 | en | rspa | 1,910 | 1,900 | 1,900 | 2 | 112 | 3,155 | http://corpora.clarin-d.uni-saarland.de/surprisal/6.0.3/?id=rspa_1912_0088 | 10.1098/rspa.1912.0088 | null | null | null | Electricity | 32.600607 | Thermodynamics | 24.506154 | Electricity | [
3.3773033618927,
-69.79336547851562
] | 350 Mr. C. E. Haselfoot .
[ June 26 , appears to rotate at its own proper speed , but in the reverse direction .
If both rotate in the same direction , but the object twice as fast as the prism , it does not appear to rotate at all .
I have examined the rotating soap film with this but have not obtained any striking results .
I have , however , observed the curious effect of angular error in position of the prism .
This causes a point in the axis of the motion to appear to describe a circle once for every turn and in the same direction .
If the prism were truly in position a point not in the axis would appear to turn twice for every turn and in the same direction .
If the prism is not truly placed a point not on the axis will appear to move with a combination of these movements , it will describe a trochoidal curve .
The Diffusion of Ions into Gases at Loiv Pressure .
By C. E. Haselfoot , Fellow of Hertford College , Oxford .
( Communicated by Prof. J. S. Townsend , F.R.S. Received June 26 , \#151 ; Read June 27 , 1912 .
) 1 .
In papers published in the ' Proceedings ' of the Royal Society , * ' the charges on ions produced by the action of Rontgen rays and radium on air * were determined by a method depending on the diffusion of the ions , and in the course of the investigations it was observed that the removal of water-vapour from the gas produced a large change in the motion of negative ions .
In this paper the results are given of some accurate experiments on the ions produced by radium , and experiments at low pressures on the motion of the ions produced by ultra-violet light are described .
In the latter case , effects similar to those observed by Prof. Townsend when the gas was ionised by Rontgen rays have been found , and some interesting results at pressures lower than those previously employed have been obtained .
2 .
The arrangement of the apparatus is here reproduced ( fig. 1 ) .
The ions are generated in the field A by radium placed in shallow horizontal grooves/ , covered with aluminium foil , in brass blocks F. They pass under the action of the electric force through the grating g and the aperture h into the field B , which was kept constant by means of the brass rings G maintained at definite potentials .
Here they diffuse and the ratio R of the charge received by the disc D to the charge received by the disc and the ring S together is measured .
This ratio is a known function of E7 ?
Z/ P , * Yol .
80 , p. 207 ; vol. 81 , p. 464 ; vol. 82 , p. 18 .
1912 .
] The Diffusion of Ions into Gases at Low Pressure .
351 where e is the charge on an ion , N the number of molecules in a cubic centimetre of air at pressure P at the temperature of the laboratory , and Z the electric force in the field B. -------G ' Field A Field B D 5 Fig. 1 .
The relation between R and c is shown graphically in fig. 2 , for the case where the aperture h is 7 cm .
from the disc D , the diameter of the aperture being 1*5 cm .
, and the diameters of the disc D and the ring S being 1*5 cm .
and 5 cm .
respectively .
From the value of R determined experimentally when an electric force Z is acting , the value of c is found by means of the curve , and No is deduced , being 3*042 x 108 x e/ Z , when N corresponds to a pressure of 760 mm. of mercury and Z is expressed in volts per centimetre .
Thus if No = 1*225 x 1010 the value of c corresponding to 1 volt per centimetre is approximately 40 .
The lower values of the ratio R in terms of c as calculated by the theory are given in the following table .
It will be noticed that as the effect of diffusion increases and c diminishes the ratio R falls but little below the value 0*2 , although the ratio of the area of the disc D to the area of the two electrodes D and S is 0*09 .
This is due to the effect of the rings G , which 2 b 2 352 Mr. C. E. Haselfoot . .
[ June 26 , are assumed , in the " theory , to discharge all ions that reach a distance of 2*5 cm .
from the central line of the field B. The density of ionisation near the edge of the ring S is therefore small and equal to zero at the ring G even when the lateral diffusion of the stream is very great .
c ... 2 4 8 12 16 20 24 28 32 R ... ... 0195 0-197 0-210 0-235 0-266 0-298 0-329 0-357 0-384 X ... ... o-i 0-323 0-661 0-831 0-915 0-953 0-975 0-986 0-992 Thus , as the stream spreads out , some of the ions reach the rings , and the 1912 .
] The Diffusion of Ions into Gases at Low Pressure .
353 proportion X of those that arrive at the electrodes to those that come through the aperture li may be calculated in terms of c , so that X is known when R has been determined experimentally .
3 .
The experiments on radium were made under the conditions stated in the previous paper as most favourable , viz. at pressures of 4 mm. and 7 mm. and with forces of 1 , 1*5 , and 2 volts per centimetre .
With these forces the ions do not diffuse beyond the ring , and the correction for self-repulsion , which depends on the force , the pressure , and the amount of ionisation , never exceeded 4 per cent. It is necessary to allow also for the effect due to ions generated by the emanation in the field B. In the case of negative ions it was found possible almost to eliminate this effect , but with positive ions it was seldom less than one-third of that due to the field A. When there was a very large amount of emanation present the values deduced for IsTe were generally larger than those obtained when the correction for the ionisation in B was small .
Of the experiments made , the seven which gave results closest to the mean were chosen , both with positive and negative ions .
The mean value of He deduced from these was in each case l-22 x 1010 , the value given by each experiment not differing from this result by more than 5 per cent. 4 .
The apparatus used for the ultra-violet light experiments was identical with that employed for radium , except that the blocks F were removed and a tube L closed by a quartz plate was inserted in the cover of the apparatus and so placed that the ultra-violet light after passing through it was incident on the zinc plate C ( fig. 1 ) , which forms the upper boundary of the field A. The rings G , G ' , were cut away in the path of the stream to avoid interference with the ultra-violet light and fine wires inserted to keep the potentials unchanged .
The ionisation was made uniform and of sufficient intensity by placing the spark-gap at the focus of a quartz lens which was mounted on a special frame , arranged so that the axis of the beam coincided with that of the tube .
The experiments have two advantages over those with Rontgen rays and radium .
In the first place , the ionisation due to the field B is always small ; and , secondly , the ionisation from the field A does not fall off as the pressure is reduced , so that observations may be made at low pressures ( and thus the correction for self-repulsion is reduced ) .
This method was therefore used especially to investigate the motion at very low pressures , when the abnormal increase of the rate of diffusion observed by Prof. Townsend in gases which have been thoroughly dried becomes very marked .
Large drying tubes were connected by wide tubing with the apparatus , and the value of R was determined at intervals .
It diminished gradually for about a month , after which Mr. C. E. Haselfoot .
[ June 26 , no further change was observed , and experiments were then made at pressures of 7 , 3*3 , 1*6 , and 08 mm. No correction was made for self-repulsion , as it is known that in dry gases the velocity of the ions is very large .
Preliminary experiments had shown that the ratio E given by the apparatus under ordinary conditions , when the gas had not been dried , was higher than that corresponding to the value l-23 x 1010 of Ne , the mean difference being about 5 per cent. This was probably due to an effect of contact potential , as it was observed when the apparatus was taken down that the ring and disc were unequally oxidised .
Allowance was made for this , and the results so corrected are shown in fig. 2 .
The dotted curves show the values of E for the different pressures .
The continuous curve represents the value of E when the gas is slightly moist and there is no abnormal diffusion .
It will be seen that there is a very large increase in the lateral diffusion ( E is diminished ) , becoming more marked as the pressure is diminished and the force increased .
The results may be compared with those found by Prof. Townsend , * who attributes the effect to an increase in the energy of the ions due to the electric force .
He points out that the large increase in the lateral diffusion shows that the mean kinetic energy of translation of the ions must exceed that of an equal number of molecules of the gas .
This effect occurs to a marked degree in gases which have been thoroughly dried , and increases as the electric force is increased and the pressure diminished .
The phenomenon is connected with the tendency of the ions to assume the electronic state , as it has been found that the prevalence of this state depends on exactly the same conditions as those under which the abnormal increase in the rate of diffusion occurs .
It is possible to deduce from the experiments an estimate of this increase of energy or , in other words , of the increase of the partial pressure of the ions .
It may be shown that if the partial pressure is increased in the ratio k : 1 , the effect on the ratio E is the same as if there had been no increase , but the electric force Z had been diminished in the ratio 1 : In the following table p is the pressure , Z the force in volts per centimetre , Zi the force , as deduced from the theoretical curve , which would give the same value of E when k \#151 ; 1 and Ne = P23 x 1010 , so that k is the ratio of Z to Zi .
In the apparatus used the radius of the ring E was 4'8 cm .
, it being necessary to have a space between it and the ring G , of inner radius 5 cm .
, which determined the field .
The values of found should probably therefore be slightly diminished , but this correction was not made as the other sources of error are considerable .
* ' Eoy .
Soc. Proc. , ' voh 81 , p. 468 .
1912 .
] The Diffusion of Ions into Gases at Low Pressure .
355 Dry Air .
p. Z. R. Zi .
Jc .
zip .
7 1 -03 0-296 0-488 2 -1 0-15 7 2-Q5 0-307 0-520 3 -9 0-29 7 4-13 0-342 0-646 6-4 0-59 7 6-07 0-357 0-695 8-7 0-87 3-3 1 -03 0-232 0-297 3-5 0-31 3-3 2-04 0-250 0-351 5-8 0-62 3-3 4-10 0-254 0-356 11 -5 1 -24 1 -6 1 *03 0-205 0-168 6-1 0-64 1-6 2-04 0-222 0-254 8-0 1 -3 1-6 4-10 0*206 0 171 24 2-6 0-8 1-03 0-205 0-168 6-1 \#187 ; 1 25 Partially Dried Air .
P- Z. R. Zi .
Jc .
Zip .
1 -03 1 -02 0-402 0-872 1 -2 1 1 -03 2 -04 0 -441 1 -08 1 -9 2 1 -03 4-04 0-266 0-406 10 39 0-48 1 -03 0*400 0-828 1 -2 2-15 0-48 2-04 0-357 0-693 2-9 4 -25 0-48 4-05 0-214 0-200 20 8-4 0-35 1 -03 0-374 0-752 1 -4 2-94 0-35 2-04 0-249 0-351 5-8 5 -83 0-26 1 -03 0-357 0-695 1 -5 4 0-26 2-04 0-219 0-235 8-7 7-8 0-26 4-09 0-211 0-196 21 15-7 Prof. Townsend points out that on his theory should be a function of Z/ p , and verified this in his experiments with Rontgen rays .
In the present experiments this is only approximately the case .
From the graphical representation ( fig. 3 ) , however , in which the values of k and are the co-ordinates , it appears that many of the points lie approximately on a straight line , meeting the axis of kat a distance 1 from the origin .
This would indicate that the factor k\#151 ; 1 by which the energy of translation of the ions is increased is proportional to the energy acquired by the ions as they move along their free paths under the electric force , since the latter quantity is proportional to Z]p .
Prof. Townsend 's experiments are indicated by the mark x. It should be noticed that the possibilities of error are very great when R is small .
In this case the charge received by the disc is small , and a considerable experimental error is possible , leading to a much greater error in k.For example , a 5-per-cent , error in R , when R is about 0-228 , might lead to a 20-per-cent , error in k. This cause of error is enormously increased when R approaches the value 0*2 , and little reliance 356 The Diffusion of Ions into Gases at Low Pressure .
can be placed on values of E smaller than 0:22 .
For this reason no experiments were made with perfectly dry air at a lower pressure than 08 mm. With air that has not been thoroughly dried , the pressure must be much reduced before these abnormally low values of E are reached .
Several experiments were made , and it was often found that E diminished as the force increased , that is , the lateral diffusion was actually greater with higher forces than with lower .
This is seen in fig. 3 , where a curve for k at a pressure of 1*03 mm. is shown with a dotted line .
It will be observed that the rate of increase of k with the force becomes very large as the force Effect of Magnetic Force on Motion of Negative Ions .
357 increases .
The values obtained , of course , depend on the degree of drying , so that observations for any one curve must be made on the same day .
A possible explanation of the diminution of R with X is that , in a gas which has been imperfectly dried , the number of ions which attain and continue in the electronic state increases more rapidly with the force than when the gas is perfectly dry .
Thus , with the larger values of X/ y\gt ; , the negative ions move as electrons in the gas even when some water vapour is present .
I wish , in conclusion , to express my thanks to Prof. Townsend , to whom I am greatly indebted for advice and assistance throughout .
Effect of a Magnetic Force on the Motion of Negative Ions in a Gas .
By J. S. Townsend , F.R.S. , M.A. , Wykeham Professor of Physics , Oxford , and H. T. Tizard , M.A. , Fellow of Oriel College , Oxford .
( Received June 26 , \#151 ; Read June 27 , 1912 .
) 1 .
When the velocity of a charged particle in a gas is proportional to the electric force and inversely proportional to the pressure , the size of the particle is unaltered either by changes in the pressure or in the force .
For a large range of pressures and forces the mass of an ion is thus shown to be constant , since the velocity is proportional to the ratio X/ P. At low pressures when the ratio X/ P exceeds a certain value the velocity of the negative ions undergoes large changes when small variations are made in the force or in the pressure .
The increase in the mobility may be explained on the hypothesis that the mass associated with the negative ion diminishes .
Thus in dry air at a pressure of 29 mm. the velocity of the negative ions is 926 cm .
per second , under a force of 2'3 volts per centimetre , * whereas if the ion travelled with the same mass that it has at atmospheric pressure the velocity would be about 114 cm .
per second .
Also under these conditions it may be shown that the velocity of a molecule of air with an atomic charge would be of the order 370 cm .
per second .
It thus appears that at low pressures the mass associated with the negative ions has an average value less than that of a molecule , so that along some of its free paths between collisions with molecules the ion moves as an electron .
It is of interest to make further investigations at lower pressures and to find to what extent the electronic state prevails as the pressure is reduced .
* R. T. Lattey , 'Roy .
Soc. Proc. , ' 1910 , A , vol. 84 , p. 173 .
|
rspa_1912_0089 | 0950-1207 | Effect of a magnetic force on the motion of negative ions in a gas. | 357 | 365 | 1,912 | 87 | Proceedings of the Royal Society of London. Series A, Containing Papers of a Mathematical and Physical Character | J. S. Townsend, F. R. S., M. A.|H. T. Tizard, M. A. | article | 6.0.4 | http://dx.doi.org/10.1098/rspa.1912.0089 | en | rspa | 1,910 | 1,900 | 1,900 | 9 | 116 | 3,454 | http://corpora.clarin-d.uni-saarland.de/surprisal/6.0.3/?id=rspa_1912_0089 | 10.1098/rspa.1912.0089 | null | null | null | Fluid Dynamics | 37.705307 | Electricity | 28.926052 | Fluid Dynamics | [
6.437075138092041,
-69.21783447265625
] | ]\gt ; Eflect of gnetic Force on Motion of ) Ions .
357 increases .
The values obtained , of course , depend on the degree of so that observations for any one curve must be made on the same day .
possible explanation of the diminution of with X is that , in a which has been imperfectly dried , the number of ions which attain and continue in the electronic state increases more rapidly with the force than when the gas is perfectly dry .
Thus , with the larger values of , the ative ions move as electrons in the gas even when some water vapour is present .
I wish , in conclusion , to express my thanks to Prof. Townsend , to whom I am greatly indebted for advice and assistance houb .
Effect of a Magnetic Force on the Motion of ) Ions in Gas .
By J. S. TOWNSEND , F.B.S. , M.A. , Wykeham Professor of Physics , Oxford , and H. T. TIZARD , M.A. , Fellow of Oriel , Oxford .
( Received June 26 , \mdash ; Read June 27 , 1912 .
) 1 .
When the velocity of a charged particle in a is proportional to the electric force and inversely proportional to the pressure , the size of the particle is unaltered either by chances in the pressure or in the force .
For a large range of pressures and forces the mass of an ion is thus shown to be constant , since the velocity is proportional to the ratio At low pressures when the ratio exceeds a certain value the velocity of the negative ions undergoes large changes when small variations are made in the force or in the pressure .
The increase in the mobility may be explained on the hypothesis that the mass associated with the negative ion diminishes .
Thus in dry air at a pressure of 29 mm. the velocity of the negative ions is 926 cm .
per second , under a force of volts per centimetre , *whereas if the ion travelled with the same mass that it has at atmospheric pressure the velocity would be about 114 cm .
per second .
Also under these conditions it may be shown that the velocity of a molecule of air with an atomic would be of the order 370 cm . .
second .
It thus appears that at low pressures the mass associated with the rative ions has an average value less than that of a molecule , so that some of its free paths between collisions with molecules the ion moves as an electron .
It is of interest to make further gations at lower pressures and to find to what extent the electronic state prevails as the pressure is reduced .
* R. T. Lattey , 'Roy .
Soc. Proc 1910 , , vol. 84 , p. 173 .
Prof. Townsend and Mr. Tizard .
Effect of [ June 26 , As it seemed impracticable to measure velocities greater than about 3000 cm .
per second ) the method used by Lattey , experiments were made to measure the netic deflection of a stream of ions moving with a constant velocity under a small electric force in air at FIG. 2 .
each half a millimetre wide , and were parallel to the slit in the plate B. The stream of ions , after coming through the slit in the metal plate , opens out considerably , so that all the ions are not received by the central electrode .
This lateral diffusion increases as the pressure is diminished when the electric force is constant , as is indicated by the following ratios of the charges , received by the three electrodes when the electric force is volts per centimetre .
The ratios of the charges were 1 : 4 : 1 for a pressure of 10 mm. , and were 1 : for the pressure mm. This abnormal increase in the rate of lsion of the negative ions was previously investigated for pressures between and 16 mm. of air when the negative ions were enerated by Rontgen rays .
* J. S. Townsend , ' Roy .
Soc. Proc 1908 , , vol. 81 , p. 464 .
1912 .
] gnetic Force on the )of Negative Ions .
Recently , a further investigation has been made with lower by Mr. Haselfoot , being produced by the action of ultra-violet light on a metal plate .
The lateral diffusion continued to increase as the pressure was diminished , so that at mm. pressure it was estimated that in these expeliments 15 to 20 per cent. of the ions received by the electrodes may come within a centinletre of the circular edge of the electrodes when a force of volts per centimetre is used .
The pressure to which the air may be reduced is limited by this effect , and , with the forces that were used , it was considered that the experiments would not be accurate if the pressure were reduced below 3 mm. , as some ions might be deflected off the electrodes when the magnetic field is } ) plied .
At first sight , it might appear that this effect would almost certainly produce inaccuracies at 3 mm. , but a point to be noticed is that the netic field diminishes the lateral diffusion , so that , as the deflection increases , the ions do not spread out so much from the centre of the stream , the chance of being deflected off the electrodes is diminished .
The effect of a magnetic field on the rate of diffusion of the ions is at present being ated experimentally , and it is not yet possible to say the exact extent to which it would diminish the lateral diffusion , but theory shows that the effect is probably quite large .
The netic field was produced by a current in two circular coils 33 cm .
diameter , the direction of the force parallel to the slits between the electrodes .
The whole stream of ions was deflected , and , for a particular value of , the centre of the stream fell on the slit between and .
In a series of experiments at arious pressures , the electrodes and were joined , and the charge they received , , was compared with the charge received by , by means of a sensitive electrostatic induction balance .
Variations were made in the intensity of the magnetic field , and the corresponding ratios were observed .
3 .
The results of the experiments shown by the curves for the different pressures when a constant electric was used .
The defiection was practically the same when electric forces from 1 to 3 yolts per centimetre were used .
When the netic force is zero the centre of the stream of ions falls on the centre of lihe electrode , which is 9 mm. wide and is 7 cm .
from the aperture in B. For a particular value of the magnetic force the charge is equal to and the centre of the stream is then deflected to the centre of the air space between the electrodes and and the tangent of the angle of deflection is If the ratio of the charge to the mass of an ion is the same all its * See preceding paper .
Prof Townsend and Mr. Tizard .
Effect of [ June 26 , free paths , then , according to the theory , the deflection is proportional to the netic force when the deflection is small .
In all these experiments small deflections were used but it was only at the lower pressures that the deflection was found to increase continuously with the force .
At the higher pressures , 8 to 10 mm. , the ratio diminished at first as the magnetic force was increased , and for a certain of the charge became equal , indicating that a deflection of had been attained .
When further increases were made in the magnetic force the ratio attained a minimum value and then increased , as is shown by the curve ( FIG. 3 .
corresponding to the pressure of 10 mm. When air at pressures was used , it was found impossible to deflect the stream through the angle with magnetic forces of the order of 100 electromagnetic units .
The curves represent the effects obtained in air that had been thoroughly dried ; when traces of moisture are present the deflections are very much smaller .
4 .
It will be seen from the following investigations that the deflections observed even at the higher pressures are so that the electrons cannot be associated with molecules continuously while they pass from the aperture in to the electrodes .
1912 .
] Magnetic Force on the Motion egatvve Ions .
It has been shown that when an ion moves through a gas under an electric force X in a netic field in which the direction of the magnetic force is perpendicular to the electric force , the direction of motion of the particle will make angle with the direction of the electric force , where He being the charge of the particle in electrostatic units , its mass , the mean interval between collisions with molecules .
In the same notation the velocity in the direction of the electric force is , so that when is small the velocity due to the electric force is approximately X The deflections that would be produced in air at a pressure of one hundredth of an atmosphere by a magnetic force of 100 neCic units , when the mass associated with the moving atomic charge is equal to the mass of a molecule of air , may be found from the above formula .
In this case the mean interval between collisions is obtained from the mean free path and the velocity of agitation of a molecule of air .
The ordinary formula for the viscosity of a in terms of the mean free path of a molecule , is , but it is subject to small corrections .
It has been shown by Jeans that the principal error arises from neglecting the persistence of the velocities of the molecules after collisions , and when corrected for this effect the formula becomes .
The mean free path of a molecule in air at 760 mm. pressure and C. obtained from this formula is cm .
The velocity of agitation being cm .
per sec. , the interval between collisions in air at mm. pressure is sec. When is the mass of a molecule of air and is 100 electromagnetic units the value of is , so that .
Thislt deflection is very small compared with the deflections that have been observed , so that it would be impossible to explain any of the experiments on the hypothesis that the negative ions are pelmanently connected with molecules of the gas while they move from the plate to the electrodes C. It appears , therefore , that the ative ion must still be in the electronic state when traversing some of the free paths between collisions , after passing through the 6 cm .
of air between the plates A and , even when the pressure is as high mm. 5 .
At the lower pressures where the deflections increase continuously with the magnetic force , the formula given above for the deflection of a stream of ions may be applied to the results of the experiments in order to find the average mass of the ion .
It is necessary to assume that the average size of Jeans , Dynamical Theory oases , Proc. Prof Townsend and Mr. Tizard .
Effect of [ June 26 , the ion is small compared with a molecule , and the mean free path of the ion may be deduced from the mean free path of a molecule of air .
The mean free path of the ion is , the multiplier 4 accounting for the fact that the dimensions of the ion are small as compared with those of a molecule of the gas , and the additional factor represents the increase of the free paths of the ion from its high velocity of itation , in comparison with the molecules may be supposed to be at rest .
The mean value of in terms of quantities that have been determined is then given by the formula for the deflection in which is substituted for , the interval between collisions .
Thus ' being the number of molecules of a gas at atmosphelic pressure , and the velocity of agitation of the ions .
Undel ordinary conditions when the ions are in thermal equilibrium with the quantity is three times the pressure of an atmosphere , but when the ions move electrons the kinetic energy of translation is greater than that of the surrounding molecules by factol depends on the pressure and electric force .
In dry air at mm. pressure under a force of volts per centimetre the factor is , and rises to 8 when the force is 3 volts per .
Thus for being the value of atmospheric pressure in dynes per square centimetre .
When the pressure is mm. , for a tYnetic force of 14 netic units , as ieen froul the ) eriments , and the expression for then gives This shows that the ion must be in the electroqic state while many of the free patbs between collisions with molecules since the value of for an electron is ap , and the value of when is a molecule of air is The electronic state prevails to a greater extent the electric force increases since the same deflection is obtained with the magnetic force of 14 electrolnagnetic units when the electric force is increased from to 3 volts per centimetre .
The value of .
increases from to 8 , so that at a pressure of mm. and a force of 2 volts per centimetre the mean value of becomes Further investigations are made with an apparatus suitable for measuring the effects at lower pressures and higher electric forces as it is of interest to see how the ratio as obtained by this method compares with the value , that has been obtained for cathode rays when the 1912 .
] Magnetic Force on the Motion of Negative Ions .
motion of the particle is not controlled by collisions with molecules of the gas .
When is small the velocity in the direction of the electric force is not affected by the magnetic field , and The above experiments thus a value of the velocity due to an electric force which for 1 volt per centimetre is cm .
per second in air at mm. pressure .
These investigationls at low pressures , therefore , lead to the conclusion that with small electric forces of the order of two volts per centimetre the mass associated with the ative ion varies the motion .
Its ayerage value in air diminishes as the pressure is reduced from 30 mm. to 3 mm. and approaches the mass of an electron at the lower pressures .
6 .
It is possible on this hypothesis to explain the effects observed at the pressures above 8 mm. when the nlagnetic deflection attained a maximum value and then diminished as the force was increased .
If the electrons move freely along some of their paths between collisions and if the other paths they are associated with a molecule or a roup of molecules of the , it is necessary to find correct expressions for the velocity due to an electric force and for the magnetic deflection of a stream , as the ordinary formulae do not apply accurately when the mass associated with the atomic charge variations .
Let be the velocity of a free electron in the electric field when the magnetic force is zero , and the velocity when the electron is associated with a molecule or boroup of molecules of the gas .
Let , where is the netic force , the charge and the of an electron , and the mean interval between two consecutive collisions of an electron with molecules of the gas .
Also let the sum of the intervals which the electron moves freely be , and the sum of the intervals when the electron is associated a comparatively large mass .
When the magnetic force is acting the velocity in the direction of the electric force is during the time , and time the velocity is , since magnetic force has practically no effect on the motion of the mass .
The distance traversed in the direction of the electric force in the time is therefore The velocity in a direction perpendicular to the electric force is for the time , and } the time the magnetic deflection is inappreciable .
Hence the distance that the charge travels in this direction in the time is .
Prof. Townsend and Mr. Tizard .
Effect of [ June 26 , The angle of deflection of the stream is therefore given by the equation If it be assumed for simplicity that the ratio is not affected by the netic f , then is the only quantity in the expression for that involves , and the angle has a maximum value when vanishes .
Thus the equation or gives the value of for which is a maximum , and , the maximum value of , is given by the equation As the pressure is increased groups of molecules are formed more fiequenGly round the ions so that increases and the maximum deflection diminishes , which rees with the observations .
The maximum value of may also be expressed in terms of as follows:\mdash ; , or so that when the maximum value of is small the netic force required to produce the maximum deflection is given approximately by the equation or , At 10 mm. pressure the mean free path of an electron is of the order cm .
, and the velocity of agitation is cm .
per second .
The quantity represents the abnormal inclease of the partial pressure , and depends on the electric force .
In this case , X one volt per centimetre , so that the velocity of agitation i cm .
per second .
The value of may thus be estimated and , if the value of for the electron be taken as , the value of that Qives the maximum deflection is 270 netic units .
The value obtained experimentally was about 100 netic units .
A closer agreement between the theory and the observations callnot be expected owing to the uncertainty of the effect of the magnetic field on the ratio , and also , perhaps , on the value of 7 .
It should be pointed out in connection with this theory that the velocity of an ion due to an electric force as obtained by a direct method is not in general ths same as the velocity deduced from the netic deflection .
They represent average velocities taken in different ways , and are accurately the same only when the mass of the ion does not undergo ' Roy .
Soc. Proc 1908 , , vol. 81 , p. 464 .
1912 .
] lllagnetic Force on Motion of Negative Ions .
variations during its motion from one point to another in the gas .
If the variations in the mass were small , the two velocities would be approximately equal , but , when the mass may change from that of an electron to that of a molecule of the gas , they may be widely different .
The distance traversed by the charge when is zero is , in the time , and the velocity of the ions , as determined by a direct method , is The velocity as deduced from the magnetic deflection is , where , and Hence , If the value of be very small , so that the ratio will be the same in the two cases , then , neglecting , the value of becomes When and are of the sanoe order , is much greater than , but they become equal when , that is , when the ions are in the electronic state throughout the motion .
VOL. LXXXVIL\mdash ; A.
|
rspa_1912_0090 | 0950-1207 | Optical properties of substances at the critical point. | 366 | 371 | 1,912 | 87 | Proceedings of the Royal Society of London. Series A, Containing Papers of a Mathematical and Physical Character | Clarence Smith.|Prof. J. T. Hewitt, F. R. S. | article | 6.0.4 | http://dx.doi.org/10.1098/rspa.1912.0090 | en | rspa | 1,910 | 1,900 | 1,900 | 6 | 78 | 1,929 | http://corpora.clarin-d.uni-saarland.de/surprisal/6.0.3/?id=rspa_1912_0090 | 10.1098/rspa.1912.0090 | null | null | null | Tables | 53.379832 | Chemistry 2 | 16.321278 | Tables | [
-2.962470293045044,
-33.73788070678711
] | ]\gt ; Optical Properties of at the Critical Point .
By CLARENCE ( Communicated by Prof. J. T. Hewitt , F.R.S. Received July 11 , 1912 .
) Clausius has shown*that , assuming the molecules of a substance are spherical perfect conductors , Maxwell 's electromagnetic theory leads to the relation ' where is the dielectric constant as defined by Maxwell , and is the ratio of the volume actually occupied by the molecules to that apparently occupied by the molecules .
Therefore since the electromagnetic theory of light requires that the dielectric constant , should be very approximately equal to the square of the refractive index for light of infinite wave-length .
Dealing with unit volume of a substance of density volume of the molecules in unit volume , and , therefore , true density of the molecules ; that is , the mass of unit volume of molecules without intermolecular spaces .
The reciprocal is the true volume of mass of the molecules .
Were the absolute weight , , of a molecule of the substance known would be the true volume of a molecule .
Since the ordinary molecular weights of chemistry are relative numbers , the molecular refraction is proportional to the true volume of the molecules in a grammolecular quantity of the substance .
Since the magnitude of van der Waals ' equation is also proportional to the volume actually occupied by the molecules , it follows that constant .
'Warmetheorie , ' 1879 , vol. 2 , p. 94 ; .
also Maxwell , ' Electricity and Magnetism , 1872 , on conduction in compound media .
Optical Properties of Substances at the Critical Point .
367 This relation , which was first established by Guye , * has been tested thol.oughly by Traube .
In the case of a large number of organic liquids hydrocarbons , alcohols , ethers , esters , acids , aromatic and hydro-aromatic substances ) , the mean value of the constant is .
True it is that the values in individual cases differ considerably from the mean , those of carbon tetrachloride , benzene , chloro- , bromo- , and iodobenzene being particularly low , and those of methyl alcohol , ethyl alcohol , and acetic acid being somewhat high , but that the average experimental value , , of the constant must be near the true value is rendered probable by the following considerations .
Guye has examined inorganic and organic substances , and finds that , although their critical temperatures lie between the extreme values and absolute , their critical pressures between 30 and 115 atmospheres , and their molecular refractions between and , yet the mean value of the ratio of the molecular refraction to the critical coefficient , is , 75 per cent. of the values between and If molecular refraction , and 403molecular refraction , therefore ; or , since , where is the critical volume of a -molecular quantity , therefore The value is alnlost exactly the mean of the values of namely , obtained by for ethyl ether , ethyl acetate , [ $nd benzene , and deduced by in another mamler .
S Considerable reliance , therefore , may be placed on the value for the ratio of to the molecular refraction .
Theoretically , the specific refraction , ' of a substance should be independent of the temperature , pressure , and state of .
This has been shown to be very approximately the case by the experiments of Lorenz Prytz , Bleckrod Chappuis and Biviere .
Assuming , therefore , that the specific refraction is constant for all temperatures up to the critical point , Traube 's equation , after dividing both sides by the value of the molecular weight , can be written ' Ann. Chim .
Phys 1890 , [ 6 ] , vol. 21 , p. 206 .
' Ann. der Phys 1901 , vol. 5 , p. 552 .
' Ann. Chim .
Phys 1890 , [ 6 ] , vol. 21 , p. 211 .
S ' Zeit .
Phys. Chem 1895 , vol. 16 , p. 1 ; 1900 , vol. 32 , p. 125 .
'Wied .
Ann 1880 , vol. 9 , p. 70 .
, 1880 , vol. 11 , p. 104 .
' Journ. de Phys 1884 , [ 2 ] , vol. 4 , p. 109 ; 'Roy .
Soc. Proc 1884 , vol. 37 , p. 339 .
'Ann .
Chim .
Phys 1888 , [ 6 ] , vol. 14 , p. 5 .
Mr. C. Smith .
Optical Properties of [ July 11 , where now refers to unit mass of the substance and is the refractive in dex at the critical temperature .
Since therefore , whence ; that is , all substances at the critical point the refractive The validity of the assumption on which this deduction rests , namely , that the specific refraction is constant for all tures , must be verified experimentally , but , accepting it as true , data are available for alculating the value of for different substances .
When the critical density , , of a substance is known , cau be calculated from the equation ( 1 ) If is unknown , can be calculated approximately by using Mathias 's relation here d is the density of the liquid at a nperature , well below the normal boiling point , and Equation ( 1 ) then becomes .
( 2 ) The data used in the accompanying tables have been taken mainly from ' Landolt-Bornstein Physikalisch-Chemische Tabellen ' ( 1905 ) .
Some of the critical densities are the experimental values , others have been calculated by the Law of the Rectilinear Diameter .
The experimental determination of the critical density is a matter of extreme difficulty .
Moreover Young has shown*that Cailletet and Mathias 's law holds accurately only for pentane ; for other substances the diameter is curved , and therefore the critical density cannot be determined graphically with any great degree of accuracy .
Now , the values of should be , theoretically , those of the absolute refractive indices calculated for light of infinite wave-length .
However , the data for such calculations are not very abundant .
As a first approximation in this introductory paper , then , the refractive indices at the critical point are those , lelative to air , calculated for the lin .
The value , , of Traube 's constant is calculated from the molecular refractions of substances at for the line .
For the line , therefore , the constant will have a slightly different value , but since the last step in the calculation of the critical refractive index is the solution of a square root , the error introduced by calculating for the line ( instead of the line , with which the theoretical 'Phil .
Mag 1900 , vol. 50 , p. 291 .
1912 .
] Substances at the Critical Point .
value , , of corresponds ) will be small in comparison with the probable errors in the values of the critical densities .
The results collected in the accompanying tables show that the refractive indices of the most diverse substances at the critical temperature approximate very closely to the theoretical value .
In the tables , Columns I and the temperature and the critical temperature respectively , in degrees centigrade .
Columns II and V give the densities of the substances at the temperature and the critical temperature respectively , refelred to water at .
Column III shows the refractive index for the line at the temperature ( and at the normal pressure in the case of gaseous substances ) .
The calculated values of are given in Column Column shows the difference of from the theoretical value , Table I.\mdash ; Gases and Vapours .
The densities in Column II are those of the fases at and 760 mm. Table II .
\mdash ; Inorganic Liquids and Condensed Gases .
370 Optical Properties of at the Critical Point .
Table III.\mdash ; Organic Liquids .
A study of the preceding tables shows the remarkable constancy of the critical refractive index .
In the majority of cases the difference from theoretical value is well within 1 per cent. , whilst the greatest erence is only .
No matter whether the substance under consideration is a difficultly liquefiable gas like oxygen , having a refractive index and a density at , or an easily condensible like sulphur dioxide , or a heavy organic liquid like methyl acetate , a density and refractive index , no matter whether the critical refracbive index is calculated for a substance in the liquid or in the gaseous state , the value of approac'nes very nearly to the theoretical value , There can be little doubt , therefore , as to the truth of the statement that all substances have the same refractive index at the critical point .
The preceding examples have not been selected ; substances have been taken at random , as the data for the calculation of have been available .
Some apparent exceptions have been discovered , which are given in Table At the present stage of the investigation it is impossible to give any satisfactory reason for these discrepancies .
It is noteworthy , however , that the substances in Table are either aromatio substances or contain a halogen .
Evidently the whole subject of the variation of the refractive index over a range of temperature extending up to and beyond the critical temperature requires experimental treatment .
This field of investigation the author wishes to reserve .
If the equality of the critical refractive indices of substances is verified by experiment , consequences of importance can be deduced .
Some of these are the evaluation of and of the critical density , and the temperatures of comparison of molecular volumes ; moreover , doubtless the fact that the velocity of light is the same through all substances at the critical point will lead to important conclusions in connection with the netic theory Optical Investigation of llised Nitrogen , etc. Table VII .
Percentage difference .
( liquid ) Chloroform ( liquid ) Chlorobenzene Bromobenzene Iodobenzene of light and the electronic theory of the constitution of matter .
These developments , however , are reserved for later treatment , after the fundamental assumption has been tested by experiment .
Optical Investigation of llised Nit'rogen , Argon , and some of the simpler Organic Compounds , of Low Melting Points .
By WALTER WAHL , Ph. D. ( Communicated by Sir James Dewar , F.R.S. Received June 21 , \mdash ; Read June 27 , 1912 .
) Nothing is known about the crystallographic properties of the elements gaseous at ordinary temperatures and of many of the most simply constituted organic bodies .
As it is not probable that the preparation of well-developed single crystals , nor the measurement of such crystals by the methods now used for crystal measurements , would be successful , some observations on the solid forms of these bodies by crystallo-optical methods have been undertaken and will be described in this paper .
The experimental difficulties are too great to permit of an investigation as complete as that which may be undertaken with substances crystallising at ordinary temperatures , but in spite of the character of the results obtained , they throw
|
rspa_1912_0091 | 0950-1207 | Optical investigation of crystallised nitrogen, argon, methane, and some of the simpler organic compounds, of low melting points. | 371 | 380 | 1,912 | 87 | Proceedings of the Royal Society of London. Series A, Containing Papers of a Mathematical and Physical Character | Walter Wahl, Ph. D.|Sir James Dewar, F. R. S. | article | 6.0.4 | http://dx.doi.org/10.1098/rspa.1912.0091 | en | rspa | 1,910 | 1,900 | 1,900 | 5 | 161 | 4,293 | http://corpora.clarin-d.uni-saarland.de/surprisal/6.0.3/?id=rspa_1912_0091 | 10.1098/rspa.1912.0091 | null | null | null | Thermodynamics | 53.226708 | Chemistry 2 | 20.616723 | Thermodynamics | [
-9.095254898071289,
-45.47829055786133
] | Optical Investigation of Crystallised Nitrogen , etc. Table IV .
I. t. II .
III .
IY .
tc\#187 ; V. dc .
YI .
nc .
VII .
Percentage difference .
Hydrogen iodide 12 2-270 1*466 150 *7 1*162 + 3*2 ( liquid ) 1*000447 Hydrogen chloride 0 0 *0016282 52 *3 0*61 1 *173 + 4*2 ( gas ) Bromine ( vapour ) 0 0 *0071412 1 *001132 302 *2 1*18 1 *194 + 6*0 Chloroform 20 1 *4896 1 *44621 260 \#151 ; 1 *142 + 1 *4 ( liquid ) Ethylidene dichloride ( liquid ) Carbon tetrachlo- 0 1 *2069 1 *42881 250 0*419 1 *138 + 1 *0 12 *3 1 *6095 1 *4656 283 *15 0 *5576 1T48 + 1*9 ride Tin tetrachloride 20 2*231 1 *5124 318 *7 \#151 ; 1 *154 + 2*5 Benzene 20 *2 0 *8788 1*50054 288 *5 0 *3045 1T57 4 2*7 Chlorobenzene ... 15 1 *1019 1 *5268 360 0 *3654 1 *157 4-2*7 Bromobenzene ... 13 *2 1 *5084 1 *5635 397 0 *4853 1 *162 + 3*2 Iodobenzene 8 1 *8482 1 *62707 448 0 *5814 1 *173 + 4 *2 of light and the electronic theory of the constitution of matter .
These developments , however , are reserved for later treatment , after the fundamental assumption has been tested by experiment .
Optical Investigation of Crystallised Nitrogen , Argon , Methane , and some of the simpler Organic Compounds , of Low Melting Points .
By Walter Wahl , Ph. D. ( Communicated by Sir James Dewar , F.R.S. Received June 21 , \#151 ; Read June 27 , 1912 .
) Nothing is known about the crystallographic properties of the elements gaseous at ordinary temperatures and of many of the most simply constituted organic bodies .
As it is not probable that the preparation of well-developed single crystals , nor the measurement of such crystals by the methods now used for crystal measurements , would be successful , some observations on the solid forms of these bodies by crystallo-optical methods have been undertaken and will be described in this paper .
The experimental difficulties are too great to permit of an investigation as complete as that which may be undertaken with substances crystallising at ordinary temperatures , but in spite of the fragmental character of the results obtained , they throw 372 Dr. W. Wahl .
[ June 21 , light upon the general crystallographic properties of these substances , and may for certain general purposes be sufficient .
Methods of Investigation and Apparatus .
Of the two methods employed at ordinary temperatures for crystallo-optical investigations , namely that of cutting thin sections of the crystal in certain directions , and that of allowing the substance to crystallise in a thin layer between a slide and a covering glass under the polarisation microscope , only the latter method can be adopted for work at low temperatures .
As the gas has first to be condensed to a liquid between the glass plates , and has then to be crystallised , I first tried to obtain a suitable crystallisation vessel by blowing a small bulb on to a glass tube and squeezing the bulb flat while the glass was still soft .
A few experiments with nitrogen were made in crystallisation vessels of this kind , but as it is not possible to obtain vessels with perfectly flat surfaces the crystal growth cannot be seen sufficiently clearly under the microscope .
Besides , these glass vessels usually crack if they are made so narrow that the walls nearly touch each other .
I therefore started to make the crystallisation vessels out of quartz-glass bulbs .
As , however , polished quartz-glass plates\#151 ; unlike glass plates for optical work\#151 ; may be sealed to any piece of quartz glass without cracking , I managed to make a small extremely narrow vessel with polished surfaces by placing a ring-shaped piece of iridium foil , 0*02 mm. thick , between two round quartz-glass plates , 15 mm. in diameter and 0*8 mm. thick , and melting the edges of the two plates together before the oxygen blowpipe , except at one point , where they were widened out to form a funnel-shaped opening to the flat interior space between the plates .
A small quartz-glass tube was then sealed to the plates at this point , the tube thus forming a kind of neck to the bottle-shaped vessel .
A difficulty arose on account of the iridium evaporating to some extent and condensing on parts of the inner surfaces of the quartz-glass plates during the process of melting together the edges of these plates .
Subsequently Mr. Lascelles ( of the Silica Syndicate , Hatton Garden , E.C. ) kindly undertook to prepare more of these vessels for me .
After some tests it was found preferable to fit the two quartz glass plates to each other by adding molten quartz glass to the edges instead of melting them together .
The quartz glass plates then get less hot and a thin platinum wire can be used to keep the discs apart during the process of fixing the plates to each other , instead of the iridium foil .
When the plates have been sealed together in this way , the platinum wire is drawn out of the vessel .
and a piece of quartz-glass tube* forming the neck of the flat bottle , attached to it .
1912 .
] Optical Investigation of Crystallised Nitrogen , etc. 373 In this way it is possible to manufacture vessels with a nearly " plane-parallel " space between the polished surfaces , these being from 0*05 mm. upwards apart , according to the size of the platinum wire employed .
The thickness of the layer of the substance crystallising inside such a crystallisation vessel is thus equal to that of the thicker " thin sections " of rocks used in petrographical investigations , and many of the same crystallo-optical methods may therefore be employed with advantage in studying crystallisations in these quartz-glass vessels .
Fig. 1 shows one of these vessels in front and in side view.* In the investigation of substances liquid at ordinary temperatures , a few drops of the liquid are brought into the stem of the vessel , the air from the flat space between the plates is expelled , and the liquid sucked into this by alternately gently heating and cooling the plates a few times .
The most effective way to clean the vessel has been found to be by sucking in a few drops of concentrated sulphuric acid , heating and evaporating this , and finally slightly igniting the whole piece of apparatus .
If the apparatus is strongly heated directly after having contained some organic liquid , carbon is deposited , which can only be removed by repeated treatment with hot concentrated sulphuric acid .
In the case of gases , a T-piece is attached to the neck of the vessel by means of a piece of rubber pressure tubing , and the other ends of the T-piece connected with the gasholder , and with an air-pump .
After the apparatus has been exhausted , it is sealed-off from the pump , and the gas from the gasholder is permitted to enter .
The vessel is cooled until the gas liquefies between the plates , and the liquid is further cooling .
In the case of methane and argon , it was sufficient to cool the crystallisation vessel by keeping it inside a small vacuum vessel containing a few cubic centimetres of liquid air at the bottom , and evaporating this under exhaust .
Through a syphon fresh quantities of liquid air could be admitted to the vacuum vessel .
The crystals were observed through slits * The vessels were originally constructed in order to be used inside a high-pressure bomb to hold liquids which attack rubber , although they have first been employed for the purposes of this investigation .
The author intends to measure the absorption spectra of sulphur at high temperatures , and of bromine at low temperatures , with the aid of these same vessels .
then crystallised by Dr. W. Wahl .
[ June 21 , in the silvering of the vacuum vessel by means of an ordinary polarisation microscope clamped in horizontal position .
In the case of nitrogen , it was necessary to employ a slightly more complicated apparatus in order to be able to exhaust also the liquid nitrogen contained in the crystallisation vessel .
This arrangement is described below in connection with the data concerning nitrogen .
The organic liquids crystallising below \#151 ; 100 ' were cooled in the same way as methane .
In the case of those crystallising at higher temperatures , the lower half of the silvered vacuum vessel was filled with dry petrol-ether , and this was cooled gradually by adding liquid air drop by drop .
Substances liquid at ordinary temperatures can easily be melted by bringing a metal wire into the neck of the crystallisation vessel .
By withdrawing it more or less high up in the neck of the bottle , crystallisation is again brought about at varying speeds .
Crystallisation of the liquid can in this way easily be brought about a great number of times in a short period , and growth-structures and the faces of the growing crystals observed under varied conditions .
By observing between crossed nicols and determining extinction angles , double refraction , and the optical character of the crystal zones developed , it is , of course , not always possible to tell exactly to what crystal system the substance belongs , as the crystals of some substances are developed only in one certain crystallographieal direction , but in most cases it is possible to bring about crystallisation in different directions by varying the rate and conditions of cooling .
In most cases it is therefore possible to make out with certainty whether the substance belongs to either of the following general groups of crystal symmetry : ( 1 ) regular ( isotropic ) ; ( 2 ) tetragonal or hexagonal ; ( 3 ) rhombic ; ( 4 ) monoclinic or triclinic .
Nitrogen .
The apparatus for crystallising nitrogen , as finally adopted , is shown in fig. 2 .
The crystallisation vessel ( c.v. ) of quartz glass which has been described above is contained in a small silvered vacuum vessel A , with two slits in the silvering through which the crystallisation vessel is observed by means of a polarisation microscope clamped in horizontal position , an incandescent gas-burner being used for illuminating purposes .
The polarising nicol and the analyser of the microscope are connected by a bar , by means of which they can be revolved simultaneously .
The interior of the vacuum vessel A , the syphon S and the exterior of the crystallisation vessel are first carefully dried by keeping them connected with the charcoal bulb E 1912 .
] Optical Investigation of Crystallised Nitrogen , etc. 375 immersed in liquid air .
The interior of the crystallisation vessel , and the T- and U-pieces connecting the crystallisation vessel with the gasholder , are likewise exhausted , then filled with pure nitrogen from the gasholder F , again exhausted by means of the mechanical pump , and then kept in connection with the charcoal bulb C , immersed in liquid air .
After all moisture has been expelled from the apparatus in this way , the interior of the vacuum vessel A is connected with the mechanical pump through the three-way stopcock a , and liquid air previously filtered and quite clear is admitted from the vacuum vessel B , by opening the screw of the syphon S. This syphon is of the kind described by Sir James Dewar* and used throughout his experiments at low temperatures .
The valve of the syphon is then closed by means of the screw and the liquid Fig. 2 .
air in A exhausted by the mechanical pump .
The U-tube D is immersed in liquid air and nitrogen is admitted through it to the crystallisation vessel , where it begins to liquefy as soon as the temperature of the surrounding liquid air has been lowered sufficiently by the exhaust .
When a sufficient quantity of liquid air has been collected in the crystallisation vessel , the gas-holder is closed and the three-way stopcock turned so that the liquid nitrogen is connected with the mechanical pump , or else with the charcoal bulb C. The liquid nitrogen is thereby cooled so much that it either crystallises or becomes a jelly .
When crystallised by sudden exhaust a kind of shower of small nitrogen crystals is instantaneously formed , and it is not possible to make out the crystallographic properties of these , as they , even in so thin a layer , form an opaque mass .
* Dewar , 'Boy .
Inst. Proc. , ' January , 1901 , p. 7 , fig. 1 .
Dr. W. Wahl .
[ June 21 , By closing off the charcoal exhaust and opening the stopcock b , the crystal mass is caused to begin to melt , and may then again be crystallised by connecting the mechanical pump with the vessel containing the half-molten mass .
By manipulating the three-way stopcock regulating the exhaust on the nitrogen , it is possible to melt and crystallise the nitrogen , and in this way one sometimes succeeds in producing a homogeneous transparent crystal growth , and may observe the fringe of the growing crystals .
In the preliminary experiments nitrogen prepared from air was used , and later , when the method was found to work , a quantity of nitrogen was prepared in the way described by Lord Bayleigh , by treating a solution of potassium nitrite and ammonium chloride on the water-bath and passing the gas over red-hot , previously reduced copper , and subsequently through potash , concentrated sulphuric acid , and over phosphorus pentoxide.* After the influence of the state of purity of the gas upon the readiness with which good crystals may be obtained had been noticed in the course of the investigation of methane , the nitrogen prepared in the above way was liquefied and fractionated , a middle fraction being collected over mercury and used for these crystallisation experiments .
In those instances where crystallisation took place at a slow rate and large transparent crystal fields were formed , it was easy to study the behaviour of the crystal-film towards polarised light .
It was found to be entirely dark between crossed nicols in all positions of the nicols , that is isotropic .
Nitrogen thus crystallises in the regular crystal system .
This result is also confirmed by the observation , in a few instances , of the formation of crystal growth-structures in which the branches grew at right angles to each other .
In the periodic system of elements nitrogen is the first member of a vertical row in which the other members are known to occur in several polymorphic modifications .
The modifications existing at the lowest temperature , of both phosphorus and arsenic , white phosphorus and yellow arsenic , are regular , and so is probably also yellow antimony .
Thus the crystal symmetry of nitrogen is in harmony with that of the other members of the same vertical group at low temperatures . .
Argon .
In the case of the crystallisation of argon only the parts A and B of the apparatus shown in fig. 2 were necessary .
The crystallisation vessel was connected to the gasholder containing the argon by an intermediary T-piece through which the apparatus was exhausted before the argon was admitted to the crystallisation vessel .
* Rayleigh and Ramsay , 'Phil .
Trans. , ' 1895 , A , vjA .
186 , p. 187 .
1912 .
] Optical Investigation of Crystallised Nitrogen , etc. 377 It is sufficient to have a small quantity of liquid air at the bottom of the vacuum vessel , A , and thus cool the crystallisation vessel in the vapour of the air evaporating under reduced pressure .
When this small quantity of liquid air evaporates under diminished pressure , it rapidly gets richer in oxygen and the temperature gradually rises correspondingly .
By admitting fresh air , richer in nitrogen , through the syphon the temperature is again lowered , and by continuously allowing a small quantity of fresh liquid air to enter the vacuum vessel A , through the syphon , the temperature can be kept close to that of the melting point of argon \#151 ; 187'9'* The melting point and boiling point of argon are only T8 ' apart , and the liquefaction , crystallisation , and melting of the argon can therefore be effected simply by regulating the screw valve of the syphon as explained above .
It is , therefore , easier to make observations on the crystallisation of argon than on that of nitrogen .
The only difficulty arises from the circumstance that the boiling point and melting point of argon are so close to each other at ordinary pressures .
A crystallisation vessel of 10 mm. diameter of disc , and about 3 mm. diameter of neck-tube was used , and less than 10 c.c. of argon was required for the investigation .
Crystallised argon is isotropic .
Argon thus crystallises in the regular crystal system .
The crystals grow very rapidly and usually in the form of very fine growth-structures with a great number of branches .
Methane .
The apparatus for investigating the crystallisation of methane was the same as used for argon .
Methane condenses to the liquid state at \#151 ; 164 ' , and its melting point , \#151 ; IBS'S0 , is very close to that of argon.f The crystallisation and melting could therefore be effected as described in the case of argon , simply by regulating the amount of nitrogen-rich liquid air admitted to the vacuum vessel by means of the screw valve of the syphon .
As methane condenses to liquid at a much higher temperature than argon , the crystallisation phenomena could be much more easily studied in the case of methane .
The methane used for the investigation was prepared by heating a mixture of sodium acetate and barium oxide and passing the gas twice through caustic potash and concentrated sulphuric acid .
The liquefied gas , however , did not crystallise well , and as part of the gas remained uncondensed when cooled in liquid air , and a small amount of crystals were formed even at a temperature near the boiling point of oxygen , it was thought that the gas * Ramsay and Travers , ' Zeitschr .
f. Phys. Chemie , ' 1901 , vol. 38 , p. 641 .
t Olszewski , ' Count .
Rend .
, ' vol. 100 , p. 970 .
Dr. W. Wahl .
[ June 21 , contained a not negligible amount of hydrogen and higher hydrocarbons of the methane series .
The gas was therefore purified by liquefying it and fractionating the liquefied part , the middle fraction being collected in a gasholder over mercury , and employed during the further experiments .
This pure methane crystallised very readily when cooled with liquid air under exhaust .
Crystallisation usually sets in simultaneously from a great many centres and beautiful spherulites are rapidly developed .
By partly melting the crystallised layer between the discs of the crystallisation vessel , and causing it to crystallise again , a linear crystallisation front is obtained which grows and moves uniformly over the field of the microscope .
The more slowly the cooling is done , the more slowly the crystals grow , and the coarser are the branches of the growth-structures ; the more rapid the crystallisation , the finer the growth-structures produced .
The growth-structures of methane are always developed according to the hexahedron and greatly resemble those of ammonium chloride .
The crystals are isotropic .
Methane therefore also belongs to the regular system .
Ethyl Ether .
Ether was brought into the same crystallisation vessel which previously had been used for the crystallisation of argon and methane .
The liquid was sucked into the narrow space between the quartz-glass discs , and the crystallisation vessel cooled in the manner already described .
Ether crystallises readily , in long well-developed prismatic needles which exhibit vivid interference colours between crossed nicols .
The extinction is always parallel to the crystal axis .
The double refraction of the prismatic zone is about 0-030 .
Judging from these data , the absence of isotropic sections , and the way the growing prisms are terminated by two flat dome faces , ethyl ether belongs to the rhombic system .
Ethyl Alcohol .
When ethyl alcohol is cooled in the crystallisation vessel it gradually becomes thick and sticky , and finally , at the temperature of liquid air , glassy .
If the crystallisation vessel , however , is slowly warmed and the inner side of the vessel scratched with a metal wire when the alcohol glass begins to get soft , crystallisation occasionally takes place .
The crystals grow as numerous small spherulites in the sticky alcohol , and the rate of growth is extremely slow .
With regard to the power of crystallisation , ethyl alcohol thus belongs to the same group of substances as certain silicates and borates , which on cooling are more easily obtained glassy than crystallised .
The individual crystals of the spherulites which are obtained show vivid inter1912 .
] Optical Investigation of Crystallised Nitrogen , etc. 379\gt ; ference colours between crossed nicols , but on account of their smallness it is not possible to determine if alcohol belongs to the rhombic , monoclinic , or triclinic system .
Acetone .
Acetone crystallises in long prismatic crystals which belong either to the monoclinic or triclinic crystal system .
The double refraction in the prismatic zone is strong , about 0*030\#151 ; 0*035 .
When the liquid is cooled it is generally at first super-cooled , and when crystallisation sets in , the prismatic crystals growing from a common germ , , grow with almost instantaneous velocity across the whole crystallisation vessel .
If part of the crystals are melted by inserting a metal wire in the crystallisation vessel as described , and the wire is then withdrawn , crystallisation takes place at a temperature only slightly lower than that of the melting point .
As in the case with a liquid crystallising in a narrow tube , the rate of growth is constant for a certain distance , and the velocity of crystallisation can be determined with the aid of a micrometer eyepiece and stop-watch .
The values obtained are remarkably constant .
They are of course not absolute values , but may in any case be regarded as indicating the degree of rapidity with which a substance crystallises at these low temperatures .
The value obtained for acetone is 5*3 mm. per minute .
Methyl Alcohol .
Methyl alcohol crystallises well , forming prismatic needles belonging to the monoclinic or triclinic crystal systems .
The double refraction is about 0*020\#151 ; 0*025 .
The velocity of crystallisation in the thin film at temperatures close to the melting point is 2*1 mm. per minute .
When the temperature is lowered by cooling with liquid air , these long prismatic crystals of high double refraction change into another crystal modification , which is developed in the form of small needles showing low interference colours .
On raising the temperature , the strongly double refracting modification again appears before melting .
Methyl alcohol thus occurs in two polymorphic modifications which change enantiotropically into each other .
Carbon Disulphide .
Carbon disulphide crystallises in the form of spherulites , and on melting and recrystallisation , when crystals are already present , in the form of long needles .
The crystals belong to the monoclinic or triclinic system , more probably to the triclinic .
The velocity of crystallisation in the thin film is 3 mm. per minute at temperatures not much below the melting point , 380 Optical Investigation of Crystallised Nitrogen , etc. but rises rapidly with decrease of the temperature , and takes place with almost instantaneous velocity when the crystallisation sets in after the liquid has been to some extent super-cooled .
Summary of Results .
A quartz glass vessel , holding a very thin layer ( 0*05 mm. ) of substance between polished quartz-glass plates , has been constructed .
In this vessel N , A , CH4 , etc. , have been crystallised and investigated crystallo-optically:\#151 ; ( 1 ) Nitrogen crystallises in the regular system .
( 2 ) Argon is regular .
( 3 ) Methane is regular .
( 4 ) Ethyl ether is rhombic .
Ethyl alcohol , acetone , methyl alcohol , and carbon disulphide are monoclinic or triclinic .
Methyl alcohol occurs in two polymorphic forms , changing reversibly into each other .
The experiments described have been made in the Davy-Faraday Research Laboratory of the Royal Institution .
My thanks are due to Prof. Sir James Dewar for kindly lending me the vacuum vessels and charcoal condensers , and placing the necessary quantities of liquid air at my disposal .
|
rspa_1912_0092 | 0950-1207 | Absorption of helium and other gases under the electric discharge. | 381 | 384 | 1,912 | 87 | Proceedings of the Royal Society of London. Series A, Containing Papers of a Mathematical and Physical Character | The Hon. R. J. Strutt, M. A., F. R. S. | article | 6.0.4 | http://dx.doi.org/10.1098/rspa.1912.0092 | en | rspa | 1,910 | 1,900 | 1,900 | 3 | 76 | 1,698 | http://corpora.clarin-d.uni-saarland.de/surprisal/6.0.3/?id=rspa_1912_0092 | 10.1098/rspa.1912.0092 | null | null | null | Thermodynamics | 66.799267 | Chemistry 2 | 10.65138 | Thermodynamics | [
-3.606520175933838,
-46.34918212890625
] | 381 Absorption of Helium and other Gases under the Electric Discharge .
By the Hon. R. J. Strutt , M.A. , F.R.S. , Professor of Physics , Imperial College of Science , South Kensington .
( Received July 10 , 1912 .
) Berthelot announced in 1896 that he had succeeded in observing an absorption of argon , and later of helium , when these gases were submitted to the silent electric discharge , in the presence of either benzene or bisulphide of carbon : further , that the gases could be extracted by heat from the solid substances deposited on the walls of the vessel .
The experiments were regarded as proving that argon and helium were after all capable of entering into chemical combination .
I shall confine discussion to the supposed interaction of helium and carbon bisulphide .
Berthelot obtained more definite results with this reagent than with benzene.* ' At the time they were published , these accepted , and , so far as I have been able to learn , they have not been more favourably regarded since .
Berthelot , however , adhered to them in his ' Traite Pratique de l'Analyse des Gaz , ' published in 1906 , about the time of his death , and other experimenters have not produced definite evidence against them .
The subject cannot be considered unimportant , and I have long felt that the experiments ought to be repeated .
This has now been done , with results altogether negative .
The helium used was freed from hydrogen by explosion with excess of oxygen , and then purified by cooled charcoal .
The gas stood over mercury in a Siemens tube as shown in the figure .
This tube was graduated , and on the mercury floated a layer of bisulphide of carbon .
The induction coil used was worked by a mercury turbine interrupter , and resistances were interposed in the primary circuit to reduce the spark it was capable of giving to about \#163 ; inch .
This was to avoid danger of piercing the * ' Annals de Chimie et de Physique , ' 1897 , Series 7 , vol. 11 , p. 15 .
VOL. LXXXVII.\#151 ; A. 2 D results were not generally 382 Hon. R. J. Strutt .
Absorption of Helium and [ July 10 , glass .
When the discharge is passed , solid decomposition products of disulphide of carbon are deposited on the walls of the glass tube , and the quantity of liquid bisulphide diminishes .
In the final and most prolonged experiment , on which reliance is chiefly placed , about 2'5 c.c. of pure helium was placed in a small Siemens tube with bisulphide of carbon , which brought up the volume ( at room temperature ) to 4 c.c. The coil was kept in continuous action for 120 hours ; during this period the volume reading oscillated a little around its initial value owing to inevitable variations of temperature , to which of course the vapour-tension of the bisulphide is very sensitive .
These variations , however , did not show any tendency to one direction rather than the other , and at the end of the 120 hours ' sparking the volume actually read was 4*2 c.c. There was no tendency whatever to contraction .
In the course of this experiment about 0-75 c.c. of liquid bisulphide of carbon was converted into solid products .
Since no contraction had occurred , there did not seem much prospect of extracting helium from this solid material .
It was thought desirable , however , to test the point independently .
The Siemens tube was well washed out with air , and attached to a small vacuum tube and charcoal reservoir and exhausted .
The deposit was heated to the softening point of the glass containing it , but when the charcoal was cooled all gas was absorbed , so that the spectrum tube could not be excited .
The charcoal was allowed to warm up , and the spectrum watched as it was cooled again .
Nothing could be seen of the helium line at any stage .
It was not thought necessary to estimate precisely the sensitiveness of this test as carried out , for it was certainly more than enough .
Nothing like 1/ 10 e.c. of helium can have been extracted , for any such quantity would have been glaringly conspicuous .
Asa test of the methods of manipulation employed , I tried the absorption of nitrogen by bisulphide of carbon under the same conditions .
The initial volume ( nitrogen-f carbon disulphide vapour ) was 4 c.c. On passing the discharge , a slow but steady contraction occurred , the volume diminishing in 29 hours to 2'4 c.c. The mercury had then risen to a level in the tube which was obscured by the black deposit of decomposition-products , and the experiment was discontinued .
The rate of contraction with helium ( if any ) was certainly not more than one-seventieth part of this .
My results are , then , quite definitely negative , and the conditions apparently not materially different from those of Berthelot 's experiments .
Yet the latter are so minutely described , and so apparently conclusive , that even with this experience it is difficult not to feel some hesitation in 1912 .
] other Gases under Electric Discharge .
rejecting them .
If any future experimenter should succeed in getting the absorption , I should be disposed to regard it as mechanical rather than chemical , like the undoubted absorption of helium by aluminium scattered from the cathode of a vacuum discharge tube.* The solid decomposition-products of carbon bisulphide are deposited on the glass in a compact film , and gas may be absorbed mechanically as in the case mentioned .
It is known that phosphorus under the influence of electric discharge is capable of absorbing gases .
The method has been used by Sir Oliver Lodge for exhausting his vacuum valves.]* The considerations just mentioned raise the question whether this action is chemical or mechanical .
For the discharge passing through phosphorus vapour converts it into the red modification , which is deposited as a coherent film on the glass , and mechanical retention of gas under these circumstances is quite conceivable .
I pass to some experiments designed to test the question .
The discharge vessels used were oval bulbs of about 50 c.c. capacity .
These were provided with aluminium wire electrodes , and were connected to an apparatus for admitting any desired gas in small successive doses , and to a siphon vacuum gauge reading to 1 mm. The first experiments were made with nitrogen ; 50 mgrm .
of phosphorus were placed in the discharge vessel , which was highly exhausted , and a dose of nitrogen ( L43 c.c. ) admitted .
The discharge was passed , and in about five minutes the manometer indicated that all gas had been absorbed .
This was repeated till four doses had been absorbed .
The action had then become slower , and the bulb was strongly heated with a Bunsen flame .
This did not liberate any of the absorbed gas , but it reconverted the red phosphorus deposited on the walls to yellow phosphorus .
Two more doses of nitrogen were admitted and absorbed .
Heating was repeated .
Finally , one more dose was admitted , and could only partially be absorbed .
The total absorption amounted to 10 c.c. , or 200 c.c. per gramme of phosphorus .
The tube was finally heated to incipient softening of the glass , but the manometer did not indicate any liberation of gas .
Similar experiments were made with hydrogen .
The amount of absorption effected was at the rate of 84 c.c. of hydrogen per gramme .
Here , again , the gas could not be extracted by heat .
This circumstance , considered in connection with the comparatively large quantity of gas absorbed , justifies the conclusion that nitrogen and hydrogen both enter into chemical union with phosphorus under these conditions .
There is scope for an interesting chemical research in examining the solid products .
* Soddy and Mackenzie , ' Roy .
Soc. Proc. , ' 1907 , A , vol. 80 , p. 92 .
t British Patent No. 25047 , 1905 .
Absorption of Helium and other Gases .
Experiments of a similar kind were made with pure helium in place of hydrogen or nitrogen .
In this case , too , a distinct absorption of gas was observed , but it was very slight , and of a smaller order of magnitude than in the previous case .
Four grammes of phosphorus were placed in a 50 c.c. discharge vessel , which was provided with a manometer .
Helium was admitted to 13 mm. pressure , and the tube sealed off .
After 70 hours ' run the pressure had fallen to 3 mm. , and could not be made to fall further .
This represents an absorption of 0T6 c.c. per gramme , as compared with 84 c.c. for hydrogen , and 200 c.c. for nitrogen .
On heating the helium was nearly all liberated again , as indicated by the manometer .
The behaviour of helium is , then , sharply distinguished from that of hydrogen or nitrogen .
The absorption is only 1/ 500 part , or less , and the gas can be liberated by heat , whereas nitrogen or hydrogen are firmly retained .
I conclude , then , that helium is mechanically , and hydrogen or nitrogen chemically , retained by phosphorus .
Summary .
Attempts to repeat Berthelot 's absorption of helium by carbon bisulphide under the influence of the silent discharge have given absolutely negative results .
Helium is slightly absorbed by phosphorus under electric discharge , though in much less quantity than nitrogen or hydrogen .
The absorption in the former case is regarded as mechanical , in the latter as chemical .
|
rspa_1912_0093 | 0950-1207 | A standard measuring machine. | 385 | 390 | 1,912 | 87 | Proceedings of the Royal Society of London. Series A, Containing Papers of a Mathematical and Physical Character | P. E. Shaw, B. A., D. Sc.|Prof. J. H. Poynting, F. R. S. | article | 6.0.4 | http://dx.doi.org/10.1098/rspa.1912.0093 | en | rspa | 1,910 | 1,900 | 1,900 | 7 | 113 | 2,991 | http://corpora.clarin-d.uni-saarland.de/surprisal/6.0.3/?id=rspa_1912_0093 | 10.1098/rspa.1912.0093 | null | null | null | Measurement | 69.643895 | Tables | 18.690743 | Measurement | [
34.941200256347656,
-11.820862770080566
] | 385 A Standard Measuring Machine .
By P. E. Shaav , B.A. , D.Sc .
( Communicated by Prof. J. H. Pointing , F.R.S. Received June 4 , 1912 .
) [ Plate 11 .
] In some physical researches it is required to measure the dimensions of a regular solid , whether parallel-sided , cylindrical , or spherical-ended , with the greatest possible accuracy .
Again , in the regular work of a metrology bureau , accurate comparison of the size of an end-standard of length with reference to a line-standard is required .
Until 1906 the only apparatus available for these purposes was the measuring machine made for comparing engineering gauges .
In that year the writer described a machine* based on the principle of electric touch , which was much more delicate than the older mechanical machines .
It also had facilities for exploring the solid under test , to prove its accuracy of figure .
This machine has been installed and used in the National Physical Laboratory since 1909 .
Improvements in it were described later.f The present paper gives an outline of an improved machine of the same type embodying the experience gained in using the 1906 machine .
The chief novelties are : ( 1 ) greater strength in the supporting parts , and consequent rigidity of the whole apparatus ; ( 2 ) larger and much improved table to carry the solid under test ; ( 3 ) improved measuring-ends ; ( 4 ) an innovation for making absolute measurements , whereby the line-standard moves but the reading microscope remains fixed ; ( 5 ) side girders to relieve the bed of load and so reduce friction , abrasion , and strain .
The engineering machine serves well where quickness rather than extreme accuracy is required .
The present machine is constructed so as to avoid the following defects in the engineering machine : ( 1 ) lack of adjustments , the observer not having the means of testing and " trueing " the mechanism ; ( 2 ) assumption of the truth of the measuring-ends and of certain other flat surfaces employed ; ( 3 ) no provision for setting the solids to be measured accurately along the line of measurement ; ( 4 ) application of considerable forces during measurement .
The accompanying plate shows the new machine ( fig. 1 ) as set up in the works .
In use in the laboratory the machine rests on a concrete table , built from the foundation , and there are certain fittings not shown in the VOL. lxxxvii.\#151 ; A. * ' Boy .
Soc. Proc. , ' 1906 , A , vol. 77 .
t ' Boy .
Soc. Proc. , ' 1910 , A , vol. 84 .
Dr. P. E. Shaw .
[ June 4 , plate : { a ) The electrical circuit and telephone ; ( b ) the fixed microscope used for reading the scale D , and rigidly attached to the concrete table .
The complete length over all is 8 feet , and total weight about 800 lbs. At the extreme front and back are seen parallel girders mounted on pillars .
These carry the chief weight of the movable parts AD , B , C , the load being conveyed through vertical spring boxes to the ball-bearing castors running on the girders .
The girders serve several purposes : ( 1 ) to relieve the bed of most of the load ( about 200 lbs. ) of the movables , and so reduce flexure of the bed ; ( 2 ) to render the movement of the movables on the bed easy ; ( 3 ) to reduce the wear on the bed by lessening the pressure on the bed of the five feet of each movable .
Inside , but not touching the girders , is the bed of the machine , resting on the concrete bed by three feet .
There are two bow-shaped vertical webs forming the sides , 15 inches deep at the centre , tapering to 6 inches at the ends .
These are 1 inch thick , increased to 2 inches at the edge flanges .
The webs are joined by nine vertical cross webs , also 1 inch thick .
One main web is surmounted by a horizontal plane surface , and the other web by two plane surfaces inclined at 90 ' to one another , and each at 45 ' to the horizontal .
Each web is pierced by six holes to reduce dead weight .
It will be seen that this bed is unusually strong .
The bed was cast and aged with great care , the process of repeated scaling , ageing and final scraping taking nine months .
Four months after the final scraping the writer applied his tester for plane surfaces* and found the cumulative error from truth of the bed surfaces from end to end was not more than 0*01 mm. , which is negligible .
The central movable part , or table ( B in the plate ) , carries the solid under test and provides it with the rotations and translations necessary .
As explained in the former paper , f two rotations are required to set a parallelfaced solid true in the line of measurement , and two translations are necessary for exploration of the faces .
The way in which these are obtained ( similar in general principle to that shown in the two former papers ) cannot be shown without detailed drawings .
The greatest care was taken in every detail of design and manufacture , as practice has shown that the table is more liable to error than any other part of the mechanism .
The proof of efficiency lies in the accurate repetition of readings ( see tables ) . .
The headstocks A and C carry micrometer screws .
A is attached to a long bracket carrying the line-standard D , whereas C is plain .
These * 'Boy .
Soc. Proc. , ' 1912 , A , vol. 86 .
t Log , cit. A Standard Measuring Machine .
1912 .
] micrometers read to OT micron ( = 1/ 10,000 mm. ) , and will be understood from the former paper ; but fig. 2 shows two additional details : a , the reading-microscope for the divided circle of the micrometer ; 6 , the measuring end .
The line-standard has its ruled surface carefully set level with the measuring-ends .
It is obvious that it is sounder to have a fixed microscope and moving scale , as here arranged , than a fixed scale with microscope movable , as is usual .
In the latter case , any error in that part of the bed traversed by the headstock produces direct error in the reading , whereas , on the present plan , no error of the first order can arise , if the bed surfaces be even moderately true .
The present complex form of the measuring-end , the details of which cannot be given in the present outline , is designed so that : ( 1 ) The electrical contact shall be made , not on the solid under test , but between two smooth , clean , surfaces of iridio-platinum .
( 2 ) A flat end-surface which can be accurately adjusted true .
The measuring end has many advantages over the old form , viz. : ( 1 ) Non-metallic solids can be measured .
( 2 ) The adjustable flat ends are convenient for many measurements , but for exploring the ends points are generally used .
( 3 ) Contact sounds made between two surfaces of iridio-platinum are clearer than between one of platinum and one of iron , brass , etc. ( 4 ) The cleaning of the contact surfaces is easy and causes little thermal expansion , invar being used through most of the projecting end .
Before commencing measurement the writer adjusted the upright reference plane of the table true , and set the run of both micrometer screws parallel to that of the bed .
The following are the possible errors arising from the use of the machine :\#151 ; ( 1 ) Bed irregularities\#151 ; Flexure and pit-marks together produce negligible error as shown by the surface-tester ( see above ) .
( 2 ) Irregularity in the upright plane of the table\#151 ; The greatest error observed in a set of observations on this point was 0*0015 mm. ; the resulting error , being a cosine one , is negligible .
( 3 ) Temperature change\#151 ; The bodies , if long , are swTaddled in flannel to minimise temperature change , which is slight in a thermostatic room , and a thermometer bulb is placed between the flannel and the solid .
A change of 0*1 ' C. in a 4-inch iron bar is equivalent to one unit in the micrometer .
( 4 ) Calibration errors of the screws\#151 ; This was worked out in the former paper .
( 5 ) Microscope readings\#151 ; Uncertainty in reading the line standard is about 0*3 micron for a single reading with the invar standard , H pattern , used .
( 6 ) The irregularity of the flat end-surface\#151 ; These are circular , \ inch in diameter , and the departure from true fiat as seen by interference rings is 0*2 micron , and as the end-surfaces are both slightly convex , the resulting error on measurements is negligible .
Dr. P. E. Shaw .
[ June 4 , An electric circuit containing a cell , resistance of 5000 ohms , telephone and switch , is connected to the movables , A , B , C. The switch enables circuit to be completed in three ways , A to B , B to C , A to C , when the contact surfaces in the measuring-ends are touching .
A and C are insulated from the bed .
As an example of the working of the machine , suppose it is desired to compare a simple 1 inch Johansson gauge ( A ) with a composite 1 inch Johansson gauge B ( 0*40 + 0*35 + 0*25 ) .
Insert these side by side in the table , clamp their centres and wrap in flannel and leave to settle .
Use the point end-surface .
First set the left side of A by making electric contact and working the adjusting screws till contact readings all over the gauge surface agree ( see former paper for details ) .
Let the rectangular figure represent the left face of the gauge .
Mark off 11 places regularly spaced as shown ; enter them in column 1 , Table I , translate the gauge till the contact end is at place 1 .
Take the left micrometer reading ( 157*3 ) and enter it in column 2 .
Change the switch and bring up the right contact point to the right face of the gauge .
Take the micrometer reading ( 352*4 ) and enter it at top of column 3 .
Add the two readings and enter the result ( 509*7 ) at top of column 4 .
Proceed thus for all 11 places on the gauge and obtain the resultant column 4 .
The numbers in column 4 do not signify actual length of the gauge , but the difference between the numbers shows how the gauge differs in length according to the line used for measuring .
Thus the greatest difference in length given by column 4 is 0*4 micron .
Repeat the whole process four times , obtaining resultant columns 7 , 10 , 13 .
The arithmetic means are in column 14 .
The whole process of filling this table will occupy , perhaps , one and a half hours , and , if there is no progressive change to indicate alteration in temperature , the results in column 14 may be accepted as showing accurately differences all over the gauge .
Remembering that high reading shows smaller gauge length than low reading , it is seen that this gauge is slightly wedge-shaped , the left side being about 0*2 micron larger than the right .
Having completed the test of gauge A , proceed to set the composite gauge B. Take measurements as before and so obtain Table II .
The resultant column 11 shows that the bottom end of the gauge is smaller than the top , whereas right and left are nearly identical .
From the Tables I and II , it is evident that errors due to the machine average about 0*13 micron , whereas the gauge errors are distinctly greater than this amount .
It is easy , provided the gauge remains fixed , to repeat 4 11 7 3 10 6 2 9 5 1 8 Table I.\#151 ; 1-inch Johanss 1912 .
] A Standard Measuring Machine .
14 .
Means .
H CO^O T ?
rf\lt ; H. Q G5 cj 99999999999 05C505C505050C5000 O O O O O O rH O pH rH rH VOVOVOVOVQVOVOVOOVOVO , f4 CO + 509 *9 509 *85 509 *7 509 *95 509 -95 510 0 510 *0 510 *05 510 *0 510 *05 510 *1 9\#171 ; VO vO VO VO 9COHHM999HO9 COCO\lt ; MCOVOCO\lt ; MH^HVO VOVOVOVOVOVOVOVOVOVOVO COCOCOCOCOCOCOCOCOCOCO VO VO VO pvpcpfN^ocoqcqoiw^ COCOi^CD^COlHVOVOvOrJi VOVOVOVOVOVOVOVOVOVOVO HHrtrlHHrlHrtHH .ri s + Hi i\#187 ; 999999 ?
997i 0505050505C50J5000 OOOOOOHOHr-lrH VOVOVOVOVOVOVOVOVOVOVO pvppp^i\gt ; T ?
xvpoqvp ( Moqcqcq^fMoqcococovo VO VO VO VO VO VO VO l O VO VO VO cococococococococococo 0014 9 tp 9 9 9 9 9 h 0 9 9 CO t\gt ; t\gt ; X\gt ; VO t\gt ; CO CO CD ^ VOVOVOVOVOVOVOVOVOVOVO H rH rH H rH rH rH rH r\#151 ; i rH rH .\#171 ; *\gt ; + Hi 99999999O9O 0505050505 OOOOOO OOOOOrHrHrHrHi\#151 ; 1 H vovovovovovovovovovovo VO VO VO 9^^99999^9^ ( ?
q\lt ; M\lt ; M(Mvoco\lt ; MvoTjicqvo vovovovovovovovovovovo cococococococococococo VO VO VO VO p^rHTffpvHMpvpOCp G5i\gt ; .t\gt ; ^^CO^VOVOQ0^ lOVOvOiOVOvOVOvOvOVOVO HHHHHHHHHHH .rf + h !
^*999999971719 050505000000005 O O rH r-H rH rH rH rH *-H O lOiOlOlOlOiQiOiOlOiOlO copj ^999991-99^9 NCOCO-HOH(COvOHt'HVO vovovovovovovovovovovo cococococococococococo 9999999^h99 ncocdvo-^cded^cocoh* vovovovovovovovovovovo rH rH rH rH H pH rH iH rH rH rH 1 .
Place .
HIMCO^VOCO^OODOH rH rH | id a a .
rH .
r\#151 ; I .pH o o o OlOlO rti co cq o o o \/ a o CQ m cs rG O o .
rH hH I\#151 ; I c3 H 03 rH OHQOOOQQOpaS .^TfCOCO^COCO^^COCC cococococococococococo ooooooooaoaoooooooocuo iNOQOoSftHOOJN VO \lt ; bt\gt ; vovococ5cocoi\gt ; vovo VO VO VO \#169 ; TfOWippQOHOOON I\gt ; COC500t^TFi\gt ; 00.t\gt ; 0000 VO^OVOIOIOVOVOVOVOVOVO cococococococococococo \#171 ; J\gt ; + H VO VO VO 995999900999^ HC0C0HlH\lt ; C0C0H\lt ; '^ , C0C0 cococococococococococo ooooaoaoaoooooooaoooao \lt ; 6# VO VO p^vpvp^rort\lt ; aoa)i\gt ; ^ H 00 05 H CO CO N l\gt ; QO CO CO ^vp^^oocp^oqoqoico ( MO^\lt ; MOOHCOi0 1\gt ; N COCOCO^OCOCOCOVOVOVOVO COCOCOCOCOCOCOCOCOCOCO ^ + Hi VO VO VO VO VO H9999999999 TjH^TflCOTfi^CO^TftCOCO cococococococococococo 00 00 00 00 00 00 00 00 00 00 00 cop^ ' pvopH^iHJHcq^oop VO VO VO VO ONf NOOMN9999 O5NOO5OO0HOOOHH JOVOCDICVCVCCD0VOCO\#169 ; cococococococococococo \lt ; 35 H S s + Readings are expressed in microns ( 1/ 1000 mm. ) , A Standard Measuring Machine .
readings to 0 05 micron ; this shows that right and left micrometer are free of backlash and like errors , but in this exploration work the gauge has to be moved parallel to itself through a cycle , and it has been a difficult mechanical problem to provide such true parallel movement that readings at any one place on the gauge will agree to the accuracy of Tables I and II .
Probably the table could yet be improved so that the mean errors would be less than OT micron after a cycle .
A great variety of gauges and other solids , parallel-faced , cylindrical , and spherical-ended , of English and foreign make , have been examined by this machine .
The Johansson bars are the best worth testing , other makes being in general of a lower order as regards accuracy of figure .
No previous machine of this or other type has been accurate enough to prove errors in the Johansson gauges , but with this machine , if care be taken , it is possible to detect errors of the order shown in the tables . .
As to absolute measurements of length , these are best made with the flat surface-ends shown in fig. 2 ( Plate 11 ) .
But these ends must be " trued " as follows : A contact point is clamped in the table and so can be provided with two translatory movements .
If the surface-end is true the micrometer readings when contacts are made at various places on it will agree .
If not , agreement is obtained by three adjusting screws .
Procedure for absolute measurement is then straightforward and will be understood from the description given above .
The above paper gives , in outline , the scope of the machine .
Full details and tables of results will be published later .
The machine took 18 months to construct , and when completed was set up in the metrology department , National Physical Laboratory .
The writer 's thanks are due to Dr. E. T. G-lazebrook for encouragement and for facilities afforded in the long work of installation , and to Dr. T. E. Stanton for much help in obtaining skilled mechanical assistance for alterations during the testing of the machine .
|
rspa_1912_0094 | 0950-1207 | On the determination of the absolute unit of resistance by alternating current methods. | 391 | 414 | 1,912 | 87 | Proceedings of the Royal Society of London. Series A, Containing Papers of a Mathematical and Physical Character | Albert Campbell, B. A.|R. T. Glazebrook, F. R. S. | article | 6.0.4 | http://dx.doi.org/10.1098/rspa.1912.0094 | en | rspa | 1,910 | 1,900 | 1,900 | 23 | 347 | 7,906 | http://corpora.clarin-d.uni-saarland.de/surprisal/6.0.3/?id=rspa_1912_0094 | 10.1098/rspa.1912.0094 | null | null | null | Electricity | 50.251782 | Tables | 42.143266 | Electricity | [
22.99380111694336,
-64.92369079589844
] | ]\gt ; On the Determination of thoe Absolute Unit of Resistance by Current Jlethods .
By ALBERT CAMPBELL , B.A. ( Communicated by R. T. Glazebrook , F.R.S. Received July 2 , 1912 .
) ( From the Natioual Physical Laboratory .
) CONTENTS .
PAGE 1 .
Introductory 391 2 .
Standard Mutual Inductance .391 3 .
Secondary Standard : Mutual Inductometer 396 4 .
Comparison of Resistance and Mutual Inductance by Two-phase Method 398 5 .
Method of Intermediary Condenser 402 1 .
Introductory.\mdash ; Recently at the Physical Laboratory we have constructed a standard of mutual inductance of novel type , whose value has been accurately calculated from the dimensions .
This inductance has formed the basis for the determination of the unit of resistance in absolute measure by two different methods , in both of which alternating current is employed .
Although there is no doubt that the accuracy attainable by these methods could be increased by greater elaboration of the apparatus used , the results already obtained seem to be of sufficient interest to warrant publication .
It should be mentioned that the accuracy here aimed at was of a considerably lower order than that contemplated in the determination of the ohm by the Lorenz apparatus which is at present out in the laboratory .
For the experiments here described , no apparatus was specially constructed , but use was made of instruments which had already been and set up for the measurement of inductance and capacity .
I shall first a brief description of the standard inductance and then pass on to the methods and results .
2 .
Standard Mutual Inductance.\mdash ; The design of the mutual inductance has already been described .
* The electrical circuits have the form and arrangement shown in section in fig. 1 .
The primary circuit consists of two single-layer coils connected in series , while the secondary is a coil of many layers wound in a com- paratively narrow channel .
The dimensions and positions of the coils are such that the magnetic field due to current in and is practically zero over the space occupied by the 'Roy .
Soc. Proc May , 1907 , , vol. 79 , p. 428 .
Mr. A. Campbell .
Absolute Unit of [ July 2 , windings of H. Thus ( a ) the calculation of the mutual inductance can be made with accuracy without an accurate of the dimensions of the many-layered coil , provided the dimensions of and can be accurately FIG. 1 .
measured ; ( b ) slight eccentric or axial displacements of the coil from the symmetrical position have very mall effect on the value of , and hence the of into its proper position can be done without difficulty .
The actual construction is shown in fig. 2 .
The coils and consisted of bare hard copper wire ( diameter mm. ) wound in right and left handed screw threads cut on a single white marble cylinder , the pitch of the screw being 1 mm. The treatment of the marble and the process of winding of these coils were very similar to those used by Mr. F. E. Smith in the construction of the standard ampere balance , need not be further described here .
The same remark applies to the measurement of the dimensions of the ooils and , which was carried out by Mr. L. F. Richardson , of the Department .
As the distance from wire to wire of the was about mm. it was not considered necessary to employ bifilar winding .
After winding , the coils were dipped in melted paraffin wax .
The leads were led out parallel to the axis and almost touching the outer surface of the winding .
The coil was of nearly square section and was wound of double silk covered copper wire ( diameter mm. ) in a channel accurately turned in a large white marble ring , supported by a ring of built mahogany having three solid ebonite feet and provided with screws by which the level and centrality could be independently adjusted .
The main part of coil was in four nearly equal sections brought 'Phil .
Trans , vol. 207 .
1912 .
] by Alternating Current Methods .
393 out to separate leads and having 97 , 145 , 145 , and 98 turns respectively .
thin strip of paper was interposed between each layer and the whole was well soaked in melted paraffin after winding .
An auxiliary coil ( for 1 millihenry ) was wound over the main coil ; it was not , however , used in the present iments .
Outside of this was wound a single turn which was connected in series with the main coil so as to make the total value of the mutual inductance almost exactly millihenries .
During winding , the number of turns was recorded by a counter , and when the coil was complete , the of the counting and the sufficiency of the insulation were checked by separately the mutual inductance of each section , using and as primary .
Duling the winding the irth of each layer was tested by a carefully calibrated steel tape .
The dimensions at C. were as follows:\mdash ; Coils and D.\mdash ; 75 turns each .
Mean diameter , cm .
1)istance between inner ends of coils , cm .
; between outer ends , Main Coil H.\mdash ; 485 turns .
Mean diameter , cm .
Axial depth , cm .
Radial depth , cm .
Mr. A. Campbell .
Absolute Unit of [ July 2 , The calculation of the mutual inductance was made in the following manner .
To with , an arrangement of coils was chosen , having the dimensions of and round numbers ; for convenience I shall refer to as " " the model it was not actually constructed .
The dimensions as shown in fig. 1 were , and cm .
respectively .
The mean radius of the main coil was chosen so as to give maximum mutual inductance between its central filament and the coils and .
This was done as already described* by calculating the mutual inductances between and connected in series and a series of circles midway between them of radii and cm .
respectively .
The results of the more accurate recalculation are give1l in able I the product of primary and secondary turns , being taken as 100,000 .
In the last column are given the corresponding values of Table I. cm .
, to 10 cm .
, If , then from the numbers in the table we find Hence is a maximum for variation of when ; also , when , we have For , the maximum value Integration over Cross-section of Main Coil.\mdash ; The mean radius of the actual main coil is cm .
When this is reduced by dividing by to corre- spond with the model ws have .
As the variation of with is very small , this value may be taken as a close enough approximation to , the value giving maximum M. This maximum refers to a single circle , the central filament of the rectangular cross-section of the 1912 .
] Resistance by Alternating Current Methods .
main coil .
In order to derive from ) due to the whole coil I make use of a theorem kindly communicated to me by Mr. G. F. C. Searle ; it gives in the present case , ( 1 ) where radial depth , axial depth of cross-section , and The second term in ( 1 ) vanishes , since , and the terms beyond that in will be found to be quite negligible .
For the model , 2 and 2 cm .
Thus we obtain millihenries .
to Dimensions.\mdash ; The actual dimensions of the coils are\mdash ; cm .
, cm .
, cm .
Dividing by , we have cm .
cm .
cm .
The differences of the last numbers from 5 and 10 give respectively and Thus is equivalent to a model with primary turns , and the annuluses ( equivalent to circles ) at distances 5 and 10 cm .
from the secondary coil , their turns being and respectively .
The fraction 5 The mutual inductances for the circles were calculated by the formula where and and are complete elliptic integrals ; for the inductances were and millihenry ( in a total of ) , a factor of Hence for the actual coils , in which millihenries .
Mr. A. Campbell .
Absolute Unit of [ July 2 , Prof. B. Ll .
Jones , of the Presidency College , Madras , very kindly carlied out the calculation by an entirely different method , using the series formula developed by Rosa*extended to nine terms to ensure accuracy of 1 in 100,000 , and applying the Purkiss formula to integrate over the section of the secondary coil .
He obtained as result millihenries .
The agreement between the two methods is very sa , tisfactory .
It thus appears that the calculation is accurate to within 1 in 100,000 .
The probable error in due to the uncertainties in measuring the dimensions may be taken as follows:\mdash ; Parts in 100,000 .
Diameter of single-layer coils channel coil Axial lengths Accordingly the total probable error in may be taken as in 100,000 .
3 .
: Mutual Inductorneter .
\mdash ; The primary standard already described is not of the most suitable form for direct comparison with resistance coils or other inductances ; the resistance of the secondary coil is rather high , being 140 ohms , and , besides , it possesses quite appreciable distributed capacity .
For this reason and for other purposes a secondary standard was constructed in the form of a mutual inductometer ( variable mutual inductance ) of very wide range .
It was of the type already described by me in which the larger subdivisions are obtained by multiple-stranded fixed secondary coils , while the smaller ones are given by a movable secondary coil which can be turned in a plane parallel to two primary coils and midway between them .
Its higher is from 11,000 microhenries down to microhenry , and the scale can be read to an accuracy of at least microhenry at any point .
For permanence the main working parts , including the bobbins the coils , were made of white marble .
To avoid eddy currents the coils were wound of highly stranded wire ( to mm. diameter ) and all metal was avoided as far as possible near the coils .
The proportionality of the ions throughout the whole range was checked both by Maxwell 's method of comparing mutual inductances and by other methods similar to those used in accurate resistance measurement where a building-up system is employed .
The errors from exact proportionality were very small , and were taken account of in all the experiments .
The inductometer was tested against the primary standard close to the value 10,000 microhenries by the method shown in fig. 3 , but before this test 'Bulletin of Bureau of Standards , ' No. 3 .
Phys. Soc. Proc vol. 21 , p. 69 ; and ' Phil. Mag January , 1908 , p. 155 .
1912 .
] Resistance by Alternating Current Methods .
the secondary coil of the primary standard ( I ) was adjusted to be ( a ) exactly midway between the two primary coils , and ( b ) coaxial with them .
Adjustment was effected by connecting the two primary coils of ( I ) in series but opposing one another magnetically , while the secondary was connected to a telephone .
Alternating current at ) second was passed through the primary circuit and the position of the secondary coil was adjusted until silence was reached in the telephone .
Adjustment ( b ) was made the comparison with the inductometer , the relative positions of the coil-axes being altered until the minimum reading on the inductometer was obtained .
FIG. ,3 .
In fig. 3 the inductometer ( m ) and the standard ( I ) have their primary coils connected in series to , a source of alternating current of frequency their secondary coils being connected in series ( and opposition ) to a tuned vibration galvanometer G. By varying the value of an approximate balance can be obtained ; the want of exact balance is due to the difference in distributed capacity of the two secondaries ( and of the primaries also ) .
The balance can be made exact by adjusting a variable condenser connected across the seQondary of ( in our case ) .
If the resultant distributed capacity effects be represented by a capacity across , and if , and be the self-inductances and resistances as in the figure , and , it is easy to show that .
( 2 ) When is nearly equal to ?
, we have as a sufficient approximation .
( 3 ) The actual values were heury , ohms , Hence millihenries .
heury .
oh1ns .
Mr. A. Campbell .
A bsolute Unit of [ July 2 , The comparisons were made at three frequencies .
For the alternating current was replaced by direct current with a single reversal , and the vibration galvanometer by a ballistic one .
In Table II are given the results .
Table II .
ApparentError ofPar .
The corrected values show satisfactory yreement , and thus when the inductometer reads 10000 , the true value is microhenries .
It was found that when a current of 1 ampere was passed through the primary circuit of the inductometer for several minutes , the slight of the coils caused a gradual change ( of the order of 1 to 2 parts in 100,000 ) in the error .
A small correction for this was applied when necessary in the experiments described below .
4 .
of esistance and Mutual by Two-Phase JIethod .
The most direct comparison of resistance with mutual inductance was made by the method already briefly described by m which two-phase alternating currents are used .
In fig. 4 , is the inductometer , a standatd oil-cooled resistance , and FIG. 4.\mdash ; Two-phase Method .
'Roy .
Soc. Proc 1908 , vol. 81 , p. 450 .
1912 .
] Resistance b.y Alternating Current Methods .
a vibration galvanometer tuned to the frequency of the alternator .
Let A and be the instantaneous values of currents in quadrature ( as shown ) ; then if alvanometer shows no deflection .
( 4 ) In practice A is very nearly equal to , but is not perfectly non-inductive .
Let its self-inductance be , causing circuit A to be slightly out of quadrature with by a small .
Then for a balance ( when ) we have ; or , since is small compared with Thus , as before , and If is even as as 1/ 1000 , will not differ from by more than 1 in 2,000,000 .
The small phase displace1oent is balanced in the adjustment of .
The actual value of for the coil used was microhenry , while was microhenries ; thus the correction is quite negligible .
Determination of \mdash ; The ratio of A to ( which is taken very nearly equal to unity ) is found by observing the effective values of the two currents by the respective potential differencesproduced in the ( very nearly ) equal resistances and , tb es voltages being read alternately on a very sensitive electrostatic voltmeter .
If the wave forms are not exact sine curves , the instantaneous values of the currents may be written and respectively , where , 3 , In this case the ratio of the effective values will be .
( 5 Now in the alternator used , the wave forms had been carefully traced and it was known that and were neither of them of an order greater than 1/ 100 ; hence expression ( 5 ) will not differ from by more than 1 part in 20,000 .
The error , if any , can , howeyer , be ehminated by repeating the experiment with the coils of the alternator interchanged .
of Distributed Capacity Inductometer.\mdash ; The coils of the inductometer have small distributed capacities , the total effect of which may represented by a small capacity across the ends of the secondal'y coil of self inductance L. It is easy to show that for equation ( 4 ) we must write .
( C ) Mr. A. Campbell .
Absolute Unit of [ July 2 , The correction is proportional to the square of the frequency .
As will be shown later , it was evaltlaCed by testing an air condenser against the inductometer at various up to second .
At second , the used , the correction was approximately 6 in 1,000,000 .
of \mdash ; By a worm and wheel connected to the nator spindle , at every revolutions an electr.ic contact was made and this caused a record to be made by the pen of a raph to which at the same time the standard clock was sending signals each second .
A comparison of their respective marks over a sufficiently long interval gave the avel a frequency .
of \mdash ; The alternator was run at as steady a speed as possible , the vibration galvanometer was tuned to resonance with the frequency , and at every half minute a balance was obtained by slight alteration of the , and also of the phase of the circuit , the latter adjustment being made by a small variable self-inductance ( fig. 4 ) .
At the a second observer switched the voltmeter allernately from to , obtaining a at each half minute .
The ratio was usually about and thus the readings were all taken at very nearly the same part of the scale of the eCer .
The scale was very open , giving about 2 mm. for a difference of 1 part in 10,000 .
The measured part of each run lasted 15 minutes , and the mean frequency was alwnys detel.mined over the whole interval ; the maximum variation from the mean to 3 parts in 1000 .
The vibration ) alvanometel .
was of t , he -coil type such as I have already described As it gave a deflection of 10 mm. at 1 metre for a current of 1 microampere at 100 ] ) second , it was ) sensitive for the purpose and usually had a resistance placed in series with it .
The resistances and consisted of two large frames of wire ( wound non-inductively ) ; they were nominally 100 ohms each , the ratio being .
The resistance was a )-ohm coil of silk- covered manganin wire wound on a mica frame and immersed in oil .
Its value at C. was found , by comparison with the laboratory standards , to be international ohms , with a temperature coefficient of per degree C. In each experiment the mean temperature of the oil was observed and the result reduced to C. by the above coefficient .
Corrections.\mdash ; In addition to the resistance temperature corrections , the following corrections were applied to the value of deduced from each experiment by formula ( 4 ) 'Phil .
October , 1907 , p. 498 .
1912 .
] by Alternating Iethods .
Correction .
Parts in 100,000 .
For clock rate For heating of inductometer For capacity of , , Results.\mdash ; In Table are shown the final results of expe1ineuCs , the second column the values of deduced from , while the third column gives the ratio of this absolute value of to the value measured in international ohms .
The experiments are arranged in pairs , as systenlatic interchanges were made ( for each ) in the connections of the two pairs of leads to the voltmeters and those to , in order to eliminate as far as possible the slight inequality in capacity and leakage of the leads and any effect of stray field from the coil .
In experiments and the connections to the alternator coils were altered from the arrangement in the other experiments so as to interchange the positions of coils relative to and M. The mean of D6 and D8 is so near the eneral meam that the whole set have been together .
Table It will be noticed in the third column , the reatest variation from the mean is 8 in 100,000 .
This is probably only partly due to errors of experiments , as the of the leads , etc. , was expected to cause small variations in the conditions .
The general mean gives the value of the ratio of the international ohm to the true ohm as The probable error is discussed at the end of the next ) ( S5 ) .
With regard to the above method it may be remarked that the resistance evaluated is much higher than that given by methods like that of Lorenz ; also that the method affords a means of inductances in terms of known resistances .
VOL. LXXXVII.\mdash ; A. Mr. A. Campbell .
Absolute Unit of [ July 2 , 5 .
of \mdash ; In the second method the capacity of a condenser is evaluated in terms of a resistance ( B ) and a frequency by Maxwell 's comlnutator method , and in terms of two resistances and P ) and a calculated mutual inductance by Carey Foster 's method .
From a comparison of the two values we obtain in absolute measure the value of the unit in which the resistance been measured .
Thus in fig. 5 , if the frequency of ( and discharge ) by the commutator is per second , then where is the small correction depending on the resistances of the galvanometer , battery , etc. As will be shown below , in the Carey Foster method , corrections , PKR M. Hence , ( 8 ) which gives in terms of a mutund inductance and a frequency .
JTethod.\mdash ; Maxwell 's method is now so familiar that it is unnecessary to do more than mention some of the details of the setting ) .
The rotating commutator was very similar in design to that used by Thomson and Searle in 1889 , but special care was taken with the insulation .
The frequency was held extremely steady , and was determined by a chronograph just as in the two-phase method .
The galvanometer had a resistance of about 700 ohms , and the arms and were usually nominally 10 and 2,000 ohms respectively , their exact ratio being very carefully checked from time to time .
The SenSitiyity was of the order of 4 to 8 mm. deflection at 2 meters ' scale-distance for a of 1 in 100,000 .
The battery was reversed in the middle of each run . ?
Foster Method.\mdash ; The Carey Foster method of capacity is not so familiar , although in our experience it is one of the most direct and convenient .
When current is used , it is essential to employ Heydweiller ' modification in which an adjustable resistance is placed in series with the condenser .
For the accuracy here required we must consider the general case where none of the resistance coils employed can be assumed to be quite noninductive .
In fig. 6 let be the alternator , the vibration galvanometer or telephone , and the condenser ; and let A be the adjustable coils of the mutual inductometer , the fixed coils being in the arm BC with a 'Ann .
der Phys 1894 , vol. 53 , p. 499 .
312 .
] Resistance Current Methods .
suitable added resistance .
Let , and be the resistauces and self-inductances respectively of the three bran ches as shown including a part the absorption in the condenser ) .
When , by adjustment of the inductometel and , the current in the is reduced to FIG. 6 .
FIG. 6 .
zero , let be the of the inductometer , and let the instantaneous values of the currents be , and as .
Then the current in CD will also be .
Let ( being the frequency ) , and let Then , since at every moment the potentials of and are equal , or .
( 9 ) Also .
( 10 ) Hence .
Separating the real and inary parts , we have ( 11 ) and MS .
( 12 ) When the residual inductances and are yibly small , these equations reduce to the ordinary case and .
( 13 ) , ( 14 ) If be read in microhenries , while and are in ohms , will come out in microfarads .
By a suitable series of coils for and , capacities from a few microfarads vards can be directly measured .
If be obtained Mr. A. Campbell .
Absolute Unit of [ July 2 , by equation ( 12 ) while is the actual resistance added to the condenser branch , then enables the energy loss in to be evaluated .
If the condenser carries a current of effective value I of pure sine wave form at frequency then the power loss in the condenser is When the power factor is very small , as in good mica condensers , both and the residual inductance must be accurately determined .
In most of the present experiments the values of the quantities in equation ( 11 ) were approximately as follows:\mdash ; microhenries , .
It will be seen , therefore , that the correction involving in equation is less than one part in 1,000,000 and is igible for our purpose .
Effect of .\mdash ; The primary and secondary circuits of the mutual inductometer have distributed capacity , and this introduces a small error which may become quite appreciable at frequencies of 1000 or second .
With inductometers in which the subdivision is done by stranding the wires , the capacity effects are somewhat increased .
The following investigation deals the fairly ooeneral case in which both the primary and secondary circuits have each distributed capacity .
In fig. the distributed capacities be represented by capacities and in parallel with the coils of the inductometer , and being respectively FIG. 7 .
1912 .
] Resistance by Current Methods .
the resistances and self inductances of these coils and their mutual inductance .
Let the current in the galvanometer be zero , the instantaneous values of currents in the other branches being , , , as shown , and let instantaneous value of the potential difference between and F. Then we have and Also ; therefore .
( 15 ) Also But , and therefore Thus whence .
( 16 ) This expression for is applicable to other methods in which a mutual inductometer is used .
Since the galvanometer terminals are at the same potential we have or , ( 17 ) .
( 18 ) From these two equations and ( 16 ) , by eliminating , and only the real part , we obtain ( 19 ) In the actual inductometer used henry , henry , while and are each less than being about 18 ohms , and not greater than 6 ohms .
Thus up to second we may neglect and in equation ( 19 ) and we then have M KB .
( 20 ) Accordingly , the correction for distributed capacity is here practically proportional to the square of the frequency .
This was found experimentally to be true by testing air condensers ( presumably constant with frequency ) against the inductometer at various frequencies from 50 up to Mr. A. Campbell .
A bsolute Unit of [ July 2 , second .
From these and other experiments in which self-inductances with negligible self-capacities were tested , the error of the inductometer as used was found to be about parts in 1000 at 2000 per second , and hence about 1 in 100,000 at 100 per second , which was the order of the fi'equency used in the experiments .
This value of the correction was also corroborated by tests against another inductometer of later design in which the error was scarcely appreciable .
* Coefficicnt of Inductometer.\mdash ; Since the exlJeriments on the two-phase method were completed , the inductometer has been compared with the primary standard on several occasions and at ious temperatures .
In the results to standard temperature it has been assumed that the primary standard has a temperature coefficient equal to that of the white marble on which the coils are wound , for the value of the is almost entirely governed by the dimensions of the bare wire coils which are wound under iderable tension into screw threads on the marble cylinder .
A meall value of in 1,000,000 per degree C. was taken for this coefficient .
The resulting calibration values obtained for the inductometer when plotted yainst actual temperatures indicate that the inductometer has temperature coefficient of approximately in 1,000,000 per degree C. As might be expected this lies between the coefficients of marble and copper respectively ) since the coils are of stranded copper wire wound not too tightly on marble bobbins .
In Table are the results of the comparisons on the Table Calibration of Inductometer DecJune .
* In a mutual inductometer with a range from up to 10 millihenries , when care is taken to arrange the coils so as to minimise the capacity effects , good accuracy can be obtained even at frequencies of per sec. 1912 .
] Resistamce by Alternating Current Methods .
different dates , all reduced to a temperature of C. , the last column , differences from a slightly weighted mean value , 1lamely , 10 , which was that used finally .
In experiments , 8 , 9 , and 10 the temperatures were not so accurately known as in the others , by reason of quicker variation of room temperature and other causes .
When we take into account the fact that the were made over a period of two and a half years , at various temperatures , both by ballistic and alternating current methods , and with fresh adjustments of the primary standard on each occasion , the constancy of the inducton ) eter as shown by Table is satisfactory .
of \mdash ; The resistances used were of oil-cooled type and consisted of silk-covered manganin wire wound ( so as to very small in ductance ) on mica frames and shellacked .
Their values were determined in international ohms by Mr. : E. Smith by comparison with the laboratory standards .
Their temperature coefficients were determined , and hout the course of each experiment the temperatures were observed and the appropriate corrections made .
The olute value of the resistance was not required , as it is eliminated by the combination of the two sets of measurements .
In a few cases the two halves of the used in the Foster test were } ) in parallel to form the -arm in the commutator test , but this procedure still allowed the absolute value to be eliminated .
The resistance was made up of two parts\mdash ; an accurately known manganin coil , and the copper wire primary coil of the inductometer .
The coil being 18 ohms , formed a considerable fraction of the total , which was 200 ohms , and hence , before and after each reading of the illductometer , careful had to be taken of the resistance .
The current used was of the order of ampere through the primary coil , the source being a wire interrupter through a transformer with an earthed screen between the primary and secondaly coils .
To eliminate the effects of unbalanced capacities ( of bridge coils , etc. ) to earth , the point where the current entered the coil was put to earth , and , in addition , every reading was repeated with the leads from the source reversed , the mean of the two directions being taken .
The difference on reversal was very small , being only about or 4 parts in 100,000 .
In { cases ( as also in the comnrutator method ) the condenser was disconnected and measurements of the capacity of the leads , which was of the order of .
This was done without difficulty , for the scale of the inductometer is very open near the zero point .
In each test the current was on for only one or two minutes ; the temperature of the inductometer was usually deduced from the observed resistance of the primary coil .
Mr. A. Campbell .
Absolute Unit of [ July 2 , In a single set of tests the observations were generally made in the order:\mdash ; Temperatures ( of all coils ) .
Temperatures .
Resistance of primary coil .
Second Carey Foster tests .
First Carey Foster tests .
Resistance of coil Temperatures .
Temperatures .
Commutatol run ( 15 to 20 mins This procedure was necessitated by the fact that all the condensers tested had temperature the order of to parts in 10,000 per degree C. During the tests the condenser was kept in a well box , and the effect of change of temperature was largely elim inated by taking the mean of the first and second Carey Foster tests .
Variation of pacity due to Chamge of the purpose of comparisons such as are described above , air condensers would appear the most suitable , but when put to the test of experiment those available did not prove quite satisfactory , probably mainly for two reasons ; the total capacity .
was rather too small to give the required accuracy , and the whole volume of the condensers was so as to make the capacity of the outside to earth too prominent .
, all the comparisons were made with mica condensers .
The fact that all such condensers , in greater or less degree , show absorption , formed the crucial difficulty of the whole ation .
To elucidate the matter a variety of experiments were made , but I shall confine myself to describing only those that are important for the present purpose .
In both the Carey Foster and the commutator methods the effective capacity diminished in all cases as the frequency was raised .
For example in fig. 8 is shown the behaviour of one of the condensers ( A1 ) with Carey Foster 's method over a wide range of frequency .
Before examining and comparing actual curves of change with frequency , I would first draw attention to one of the fundamental differences between the two methods .
In the Carey Foster method the behaviour of the given condenser with frequency is entirely specified by an effecDive capacity in series with a resistance .
If this be equivalent to a capacity with a parallel resistance , then it is well known*that ( 21 ) and .
( 22 ) In most of the experiments for a frequency of second the term was of the order of to , and hence to the * M. Wien , ' Wied .
Ann , p. 681 .
Resistance by Alternating Current Methods .
aimed at ; thus the method here gives the effective capacity independent of the actual leakage resistance ( absorptive and ohmic ) .
In the commutator method , on the other hand , while a series resistance of a few ohms will have no appreciable effect on the observed capacity , an ohmic leakage resistance makes the observed capacity , where ratio of period of charge to whole period of cycle .
Accordingly the commutator method does not separate the ohmic effect from that of pure capacity .
Hence a condenser in 1 , ooo 1,500 2,000 encg se .
8\mdash ; Change in Effective Capacity .
which the ohmic is appreciable will show different apparent capacities by the two methods .
Now if it is attempted to determine the ohm by ring the values of capacity given at the sanne frequenc , ( say 100 per second ) by the two methods , it is found that various mica condensers quality give results disagreeing with one another by as much as two or three in 10,000 .
The differences cannot be accounted for by the effect of the ohmic resistance in the commutator method , for such condensers have a direct current insulation of the order of 10,000 megohms ( for 1 mfd and would be less than one two-millionth part of .
The discrepancies are really due to the other fundamental difference between the two methods , namely , that the .
A. Campbell .
A bsolute Unit of [ July 2 , wave form of the applied voltage is entirely different in the two cases .
In the Carey Foster method it is a pure sine wave , while in the ordinary form of the commutator method it is very appl'oximately a pulsating wave of rectangular form never passing below the zero line .
Tbis wave is equivalent to a similar alternating wave of voltage superposed on a continuous voltage of half its maximum value .
With good condensers , o.t least , this continuous component has no appreciable effect , for practically the same results were obtained with a reyersing commutator ( as in Maxwell 's original description ) as with the charging and short-circuiting cornmutatol commonly employed .
* Witl ] an air condenser the sine wave and square topped wave will give same capacity , but when absorption is present the square topped wave is found to give , for the same frequency , higher value of the effective capacity than that iven by the sine wave ; and the difference is greater the more the condenser .
Also for an absorptive condenser the curve of change of capacity with frequency for the sine wave form is different from that for the square topped wave .
FIG. 10 .
per sec. FIG. 9 .
Fig. 9 illustrates the nature of the difference , the curve ABC showing the change of capacity with sine wave folYn , and AD the change with square topped form , taking100 per second as the standard frequency in each case .
The question now arises : For square topped form of frequency , is it possible to specify an equivalent frequency , which with a sine wave form will give the same capacity as does with the square form ?
In order to answer this question * See also .
Mattenklodt , ' Ann. der Phys 1908 ( 28 ) , p. 359 .
1912 .
] Resistance by Alternating several condensers of various absorptive powers were tested for variation of capacity with frequency both for square topped and sine wave forms , curves like those in fig. 9 being obtained .
It was found in each case that the curve practically fitted a part BC of the curve , when was plotted to equivalent frequencies , where ) Thus in fig. 10 the forms ( of same maximum ) five the same variation with frequency when area area Odo or The equivalence assumption here adopted may be put into the following form : The two methods will the same value of the capacity of a well insulated condenser , provided that in the commutator method the eriod of charge ( and of equal short circuit ) is equal to times the half period of the sine wave in the Carey Foster method .
In estimating the periods of charge and short circuit , account is here taken of the air on the mutator , which in most of the experiments formed about 10 .
cent. of the whole circumference .
The above assunlption is probably only an approximation to the truth .
It is quite arbitrary and only justiIiable by tlJe way it Frequenc9 sec. brings the various divergent results into reement .
For example , in fig. 11 are given the curves of change of capacity with frequency for two different condensers ( Al and E ) .
The points marked by circles were obtained with sine wave form ; Mr. A. Campbell .
Absolute Unit of [ July 2 , those marked by crosses with square topped form , the actual fiequency reduced to the equivalent sine wave frequency by the assumption stated above .
It will be seen that the two methods are thus into reement as far as the frequency variation curves are concerned .
We can now proceed to the comparison of the absolute values given by the two methods Sor a number of different condensers .
In Table are given the nominal of these condensers , their power factors at second , and wave form corrections obtained from observed change of capacity with frequency for sine wave form in each case .
The values iven in the table indicate considerable variety in absorption effects .
The fact that the capacity temperature coefficients of these condensers were of the order of per degree C. necessitated great care in the experiments by which the changes of capacity with frequency were determined .
The values in Table refer to temperatures near C. The condenser marked A2 was the microfarad section of Al , which was subdivided into live sections .
Condenser has been cluded in the table as it has already been referred to ( fig. 11 ) .
Condensers and have power factors much higher than the others ; they will be discussed separately below .
tesults .
Table are yiven the final results obtained with the first five condensers of Table , the dates of the various experiments being also shown .
The numbers in the third column give the values of the ratio , where is the resistance in absolute ohms , while .
is its value in international ohms .
The last column gives the mean for each condenser .
For condenser the mean is a weighted one , as the raph record on January 23 was not so good as the others .
In the earlier experiments ( June and July , 1911 ) , the comparisons were not quite so direct as the equations and ( 7 ) indicate ; the 's were not in the two methods , but were each tested against a standard box .
able V 1912 .
] Resistance by Current Iethods .
Table The results in the last column of Table show that the wave-form corrections of Table have the various condensers into good agreement ; without these corrections the extreme would have been in 10,000 .
To illustrate the behaviour of inferior condensers , Table VfII boives the results obtained from the condensers and G. Table VIII .
Paraffined a It was found that the insulation of was not ) ; with direct and 10 seconds electrification it only gave 1250 megohms per microfarad , while condenser Al gave 11,000 megohms .
Thus the direct leakage was sufficient to invalidate to some extent the comparison between the commutator and the Carey Foster methods .
The value given by the pal.aHined paper condenser ( G ) shows that even a poor condenser ives a fair approximation to the true result .
Reverbing to the normal results ( Table ) , we may remark that and should not carry so much weight as the others , and hence the meaIl of may be taken as .
This number is alnlost identical with that already obtained by the two-phase method .
The closeness of the agreement is probably accidental ; it must be remembered that ) results are derived from the same mutual inductance standard and by the help of the same inducto1neter ; and any errors in either of these standards 414 Absolute Unit ofResistance by Alternating Current .
may affect both equally .
It is not easy to estimate the probable error in the final results .
For the primary inductftllce standard it has already been estimated in 100,000 ( see S2 ) .
] with this the uncertainties in the experimental part of the work , the probable error of the final would be about .
in 100,000 .
International ohm/ true ohm The results indicate that , in measurements of resistance , inductance , and capacity with alternating current , it is possible to obtain consistency to abouC 1 part in 10 , conchnsion which will , I am sure , be satisfactory to oGhel .
experimenters .
\mdash ; The wave-form difficulty inherent in the commutator method is avoided in 's metho this was not foumd to be capable of giving sufficient accuracy .
Another method already partly described by the was tried ; the results obtained showed it to be worth further ration .
In conclusion , my best thanks are due to a number of persons who helped in the research : in the first place to Mr. D. W. Dye , who assisted in most of the experiments ; to his reat skill in and his in the discussion of difficulties a large part of the accuracy is due . .
F. E. Smith gave most important help , not only in regard to the construction and winding of the nlarble cylinder , but also by the resistance coils .
The late Mr. and Mr. NIurfitt carried out the construction of the inductance standards with admirable accuracy , and all the easurements of the dinlensions made by Mr. L. F. Richardson .
For the two-phase method Mr. C. C. Paterson pnt at my the Siemens alternator of the Electrotechnical Department and one of the long- scale ostatic voltmeters with which he has succeeded in such extremely accuracy of reading .
Dr. G. F. .
Searle very kindly supplied the formula by which the integration over the of winding in the primary standard was eifected , and Prof. E. Ll .
Jones carried out an independent calculation for that standard to a very high of accuracy \mdash ; a piece of work involving skill and toil .
Condenser Al was presented to the laboratory by Dr. Alexander Muirhead , and several of the other condensers used were kindly lent by him and by .
H. Tiusley .
Lastly , I would express my thanks to our director , Dr. Glazebrook , for his kind interest valued help in the ] opment of the methods and by which the research has been carried out .
See Rayleigh , ' Phil. Mag 1886 .
Phys. Soc. Proc February , 1912 , p. 110 .
|
rspa_1912_0095 | 0950-1207 | Trichromatic theory of colour vision.\#x2014;The measurement of retinal fatigue. | 415 | 427 | 1,912 | 87 | Proceedings of the Royal Society of London. Series A, Containing Papers of a Mathematical and Physical Character | Sir W. de W. Abney, K. C. B., F. R. S. | article | 6.0.4 | http://dx.doi.org/10.1098/rspa.1912.0095 | en | rspa | 1,910 | 1,900 | 1,900 | 10 | 169 | 3,879 | http://corpora.clarin-d.uni-saarland.de/surprisal/6.0.3/?id=rspa_1912_0095 | 10.1098/rspa.1912.0095 | null | null | null | Optics | 72.213355 | Tables | 24.362205 | Optics | [
11.862791061401367,
-15.346137046813965
] | ]\gt ; Theory of Colour Vision.surement of By Sir W. DE W. ABNEY , K.C.B. , F.B.S. ( Received August 17 , 1912 .
) That of the retina by a colour will the hue of the spectrum is well known .
In this paper a method of measuring the amount of fatigue is described , showing that by fatiguing the retina colour-blindness is produced which is the same as that found when one of the three sensations is deficient in sensitiveness .
In the first part of this communication the fatigue is produced in one eye , and change in hue is registered by the unfatigued eye , and from these observations what we may call the factor of the fatigue is calculated , which is the ratio in sensitiyeness of the unfatigued sensation to that of the fatigued .
In the second part of the communication a method is described of measur .
the luminosity of what , for sho1t , we will call the fatigue spectrum , which is , of course , the luminosity of the spectrum as seen by the eye .
In previoos papers the value of the three sensations in luminosity to the normal eye has been given , and the red , green , and blue sensations have been indicated in equations as , and B.S. In this paper the luminosities of the three sensations of the spectrum have to be shown as curves of equal stimulation , and the percentage values of the different colours have been derived from these curves .
The curves of equal stimulation of the spectrum are the rdinary sensation curves , two of which ( the blue and the green ) have to be multiplied by factors to make them of equal area .
Equal ordinates in these curves will then give the amount of white light existing in the different colours .
The sensations of equal stimulus are indicated for the sake of brevity as , and For the purpose of deriving the amount of fatigue existing in the retina after an exposure to some ray of spectrum , the percentage value of the different colours of the spectrum in terms of , and .
will be employed , and the following table is given to show the amounts of each in the different rays .
A column is added to give the proportion of .
to found in the colours tabulated .
Column I gives the spectrum standard scale numbers , II the wave-lengths , III , and the , and , and Column the ratio of .
to unity .
Fig. 1 shows diagrammatically the figures in the table .
Trichromatic Theory of Colour Vision .
shows the arrangement of the viewing stand .
A and are slits in spectrum apparatus , with the collecting lenses and in situ , patches of the same or different colours can be thrown on two white screens and D. ( If a is required on the screen , the is removed , and the whole is collected by , and its can be reduced by sectors or means .
) is a thin screen standon the table , which bears the two screens and , and is so pointed its prolongation would divide the between and equally .
This screen is of such a length that ray from the slit A will not be interrupted by it .
and show the of the eyes , the forehead resting on a pad fixed to for the sake of With this arrangement the right eye sees only , and left eye only C. In the position shown in the figure , the retina of the right eye is that which is to be fatigued .
To bring a fatiguing ray to the eye , a third spectrum , formed by the reflected white beam*of the apparatus coming from is employed , with a lens L The ray from the slit in this spectrum is projected to mirror ( the addition of which was suggested to me by Dr. Watson , who worked me in these observations ) .
The mirror reflects the beam the eye E To fatigue the whole pupil , a lens is inserted in the of the ray , which is there seen as a more or less bright patch of light works on a pivot , and can be rapidly turned against the side when fatiguing gives place to observation of D. When the eyes are in position , the distance apart of and is altered till the two patches to touch when observed , one by one eye and the other by the other .
When it is desired that the same colour shall be in each patch , the scale of A and spectra being known , this is readily effected , and a confirmation the correctness of the match can be obtained by throwing one patch over other , and obtaining two illuminated shadows side by side by the method .
The slits in each spectrum can be adjusted so that appear equally bright .
describing a set of observations made with a fatigued retina it is as a comparison light .
light can be much reduced by substituting a white surface for the , and this has been frequently used .
Sir W. de W. Abney .
well that the following should be borne in mind .
If the retina is white there is no change in its hue ; it merely becomes darker , at the light is well nigh extinguished .
In white light fatigue , it follows the sensations are equally fatigued .
Again , as the curves of equal to every kind of vision , normal and colour-blind ( the only difference the white they make ) , it follows that , supposing a match of some spectrum as seen by a colour-blind eye can be made ( by some means or with another colour by the normal eye , the ratio of the colour-blind stimulus sensations at the place in the spectrum which the erved must be the same as those of the normal eye , in that in the spectrum where the match was made .
The observation of the colour by both eyes independently , one being fatigued , is amode of registering such matches .
When a set of observations is to be made the eyes are placed in position as shown in the figure .
The fatiguing ray is thrown on the mirror and the right eye*is fatigued .
There is a time after which the fatiguing action and the action of ecovery from the fatigue practically balance one another .
When this staoe is reached the mirror is rapidly turned against and the two patches having the same colour inally are viewed together .
The slit of is quickly moved till the colour viewed by the left eye appears to approximate to that seen by the fatigued eye .
Four or five " " fatigues\ldquo ; are given by the mirror , and after each the match is made more closely correct .
When no alteration is found necessary , the observation is at an end and the position of the matching colour is read off on the scale .
If a match goes no further than the full green of the spectrum when a colour in the red or yellow of the spectrum is viewed by the fatigued eye a good match in hue can be made .
When a match , however , falls in the blue-green , or blue , or purple only the general hue of the fatigue colour can be matched , as the sensation colours in these parts of the spectrum are contaminated with the white .
A glance at fig. 1 will at once show how this arises .
When red is the fatiguing colour and is fairly bright and a green ray in the spectrum is observed it is sometimes difficult to form an exact match , as the fatigue colour is more saturated in hue than any colour seen by the unfatigued eye .
This question of the saturation of colour , it is hoped , will be treated of shortly .
For the present I must confine myself Go the method of measuring the fatigue .
A good illustration will be found in the following record of matches by eye of fatigue colours .
When we use the expression " " fatiguing an eye\ldquo ; it is intended always to fatiguing the retina .
The first point to call attention to in the above is that from S.S.N. 56 ( in which there is a small quantity of ) to S.S.N. , where there is no change in hue capable of being measured accurately , the matches are throughout lower in S.S.N. than the fatigue colour .
In Column VI , in Table I , it is seen that at that S.S.N. the ratio of red to green is at its minimum .
From this number to S.S.N. 60 the readings of the matches are always higher .
In both divisions of the spectrum , less red in the fatigue oolour is shown in its match .
This is a direct general confirmation of the truth of the percentage curves of the three sensations , and therefore of the luminosity curves from which they were derived .
Studying the observations in detail so far as is necessary , it will be found that the amount ( or factor ) of fatigue on the retina is a fixed one when the observations are made as described .
One will now be taken in which there is a large proportion of .
to , say S.S.N. .
The match to this colour is at S.S.N. and have for their sensation compositions 7822 ( 49.64 ) 5644 The only alteration made in S.S.N. when the fatigued eye observes it is a diminution of the .
; the .
remains tered .
In the match there is , of course , the normal proportion of .
to .
If , then , we make the .
of the fatigue and the match composition the same , we can directly compare the .
in the colour with its .
when the eye is not In the case in point , it happens that the .
in the match colour is Sir W. de W. Abney .
exactly half of that in the fatigue colour .
Its composition is equally expressed as 2822 .
The fatigue .
is therefore 28/ 78 of the normal in S.S.N. , and the factor is .
Taking S.S.N. , its match at S.S.N. 39 .
The compositions of these two are and or From this we see that the factor is of Tn the same way , taking S.S.N. 's and , having composition 49492 and , we obtain a factol of At we have a match with , with composition of and .
The factor for this , after deducting the white present in the fatigue colour , is At S.S.N. 56 , where the match is at S.S.N. , the compositions are and these we get a factor for .
of If we examine the match to S.S.N. , which is at S.S.N. , we have the following compositions and 164440 .
After the white in the fatigue colour from both , we have .
White . .
White .
and Treating these compositions in the same way .
we get as a factor This increase equires an explanation .
The .
to .
in the match colour is 1 to , and turning to Table I it will be seen that there is no colour which has so low a ratio , hence the eye has to do the best it can in finding a match .
The same is the case with the next two numbers .
In my paper on the " " Change in Hue of Spectrum Colours by the Addition of White Light , will be seen that from S.S.N. 36 to about 56 the blue which is added by the white light is ignored by the eye and the hue of a colour is judged by .
and .
only .
After S.S.N. 34 is passed towards the blue ) this no longer holds good .
It is the same also in the matching of the fatigue colours .
For instance , let us consider S.S.N. 32 , which matches itself .
composition is .
The average factor for the .
is 'Roy .
Soc. Proc 1909 , , vol. 83 .
Trichromatic Theory of Colour Vision .
multiply the 12 .
by this number we have .
in the fatigue There is therefore no change in it except a greater degree of in these two equations into sensation and white , we get The mixture of white and the green and blue sensations is paler in the first than in the econd equation , but the general hue would be the same .
This is the in all degrees of fatigue tried ; the match at S.S.N. is invariably that S.S.N. itself , the only difference being paleness , the differing but little in each equation .
One more match must be considered , that at S.S.N. , which , when it was a fatigue colour was matched at S.S.N. The composition of is , the in excess of the Taking as the factor we get ( nearly ) .
It is all used up in making the white S.S.N. has a composition of .
White .
or the .
being greater than the Reducing the last composition to make the .
the same as that of the fatigue colour we get The ratio of white to .
is not very different in the two , and the eye ignores the excess of .
in the first .
( It must be recollected that the luminosity of the .
is 190 times smaller than that shown as ) In this case the fatigue alters ths ratio of .
to .
to such a degree that the match lies on the other side of the second point of intersection of the red and green sensation curves , viz. , at S.S. When the factor of is much smaller , the fatigue colour has to be closer to S.S.N. before the match lies on the other side .
) I give a record of observations made with the fatiguing red reduced to of that used in the other record , and factor of red fatig ue in the same way as above is shown .
Sir W. de W. Abney .
Alongside of this record is one when fatigue was induced by a red lithium light eflected from a card which had a luminosity for the of two candles at 1 foot distance from the screen .
The factors derived this record are also given .
I have only taken , as an example , red fatigue .
I might have given examples reen and violet fatigues , but I believe it is more satisfactory to deal with a single kind of fatigue that other fatigues can be dealt with in exactly the same manner and the same kind of results will be obtained .
place in the spectrum for fatiguing the retina which is of reat theoretical interest is that of S.S.N. , where the .
and .
curves cut .
The only effect this fatigue hss is to heighten the blue curve , the proportion of red and green sensations remains the same .
In fatiguing the retina by any colour the general sensitiveness ( regardless of any particular sensation or sensations with which the fatigue is induced ) appears to be lowered .
Feeble luminosities are extinguished by the condition of the retina .
It is somewhat curious to note the advent of a colour which is quite ) arent and measurable by an unfatigued retina , but which has vanished when one which is fatigued looks for it .
As the fatigue lessens the colours gradually come into view .
It has been stated to myself that the retina has some sort sympathetic action with the fatigued one .
Personally , I can find no trace of such synlpathy .
It is satisfactory to know that after observations have been Trichromatic Theory of Colour Vision .
to match a fatigued colour , the addition of the fatiguing colour will give hue of the original colour to the unfatigued eye .
I now turn to another class of observation in which only the fatigued eye be employed .
If the fatigue can be reduced to a factor , as has been in the foregoing pages , it follows that the luminosity curve of the observed with a fatigued retina should be the same as that of a colour-blind person .
This is a direct method of getting the factor of fatigue Dr. Watson suggested .
His suggestion I have carried out , modifying the arrangement shown in fig. 2 to a certain extent .
Most of the description of fig. 2 may be read as applicable to this , Only one screen , , is employed , and the fatiguing colour is obtained from the second spectrum , B. On leaving the lens a mirror is inserted in the path of the rays issuing from the slit .
This is again reflected by another mirror on to the mirror on the screen .
The white beam ( which in the last set of observations was utilised to form a third spectrum ) now proceeds direct , and by placing a rod in the paths of rays coming from A and of the white beam , a patch of the colour is placed alongside a patch of white as in the ordinary measures of luminosity .
The eye is placed at and the retina can be fatigued as before , when the mirror ( or card ) is in the position shown .
When the fatigue induced is steady is turned back and the colour and the white are made of apparently the same luminosity , by means of an annulus*which I have described in other being placed in the white beam .
Before commencing fatiguing the eye , the luminosity of the spectrum may be taken in the usual way , or if more convenient the luminosity of the coloured ray on the screen may be measured by the unfatigued eye .
When the whole spectrum at close intervals has been measured by the fatigued eye and also by the unfatigued , the annulus readings are converted into luminosities , and from this two luminosity curves can be plotted and compared with each other .
The example I give will again be one dependent on red fatigue , the fatiguing colour being at the place of the red lithium line .
The hues of the fatigued colour and white are noted .
This is reaUy a screen , graduated from light to dark , through which the white has to ' Phil. Trans 1900 .
From these observations two curves were drawn .
The curve from the unfatigued eye is identical with that obtained previously when the source of light for forming the spectrum was the arc light , with the positive pole in a horizontal position , the current being 100 volts and 22 amperes .
In fig. 4 this curve with that of the adopted curve for the " " fatigue\ldquo ; luminosity is shown together with the readings in the preceding tabla ( Table ) .
We can from these curves ascertain the factor of red sensation fatigue as was done in my communication*to the Royal Society .
The first method of using the two curves is employed .
*Blind and the Trichromatic Theory of Colour Vision .
Part mplete Red or Green Blindness ' Prpc .
Roy .
Soc , vol. 84 , 1910 .
Sir W. de W. Abney .
When a colour-blind has to give a luminosity curve of the spectrum , is always a doubt as to amount of pigmentation of the yellow spot which possesses , and it is not sa fe to assume that any factor derived from an below 42 will agree with one obtained from higher S.S.N. 's .
In the case of fatigued eye by which the normal luminosity curve has been measured difficulty doss not arise , since the pigmentation is the same .
Commencing with two S.S.N. far apart , we may find a factor should hold good throughout .
Taking S.S. and 38 for the bwo points required by Method I in paper referred to , we get two equations , where is the factor which the curve has to be multiplied by to reduce it to the proper scale for the colour-blind ctlrve , and is the factor by which the sensation ( in this case the red sensation ) has to be multiplied .
The equation for S.S.N. is as follows:\mdash ; 21 .
The numbers of the left-hand member of the equation are the luminosities of the normal and fatigue blind shown on the curve and tables .
The right- hand member is the value of the red sensation at S.S.N. In a similar way the equations below are arrived at .
The two equations are For S.S.N. 58 S.S.N. 38 Solving the equation , we get By the method employed , is the deficiency of the sensation .
The factor of the sensation ( which we will call x ) is Taking S.S.N. and 36 , which are again far apart , we get the following equations:\mdash ; S.S.N. 56 . .
S.S.N. 36 This gives , and S.S.N. and 46 give and S.S.N. and 40 give , and of Colour Vision .
S.S.N. and 44 give and As a final pair of equations , we will take S.S.N. 's 52 and 42 , The mean of the sensation factors ( x ) is .
and the curve must be multiplied by to compare it with the normal curve .
The luminosity curve of the spectrum , as measured by an eye fatigued with pure red sensation , is the same as that of a red-blind eye , which has a factor 0 .
Other curves with larger or less factors of fatigue could be giyen , all of which would stand the same test as that just given .
The same applies to the retina fatigued with green and other colours .
But it may be stated that the luminosity curves obtained with eyes fatigued by any colour as far as the blue-green give indications that they can be sorted into two classes , red- and green-blind , as the sensation curves indicate , except in the case of the greenish-yellow ray at , where the curve retains the characteristics of the normal , modified slightly in the extreme red ( where only the red constituent is active ) , and in the blue end of the spectrum .
|
rspa_1912_0096 | 0950-1207 | On the discharge between concentric cylinders in gases at low pressures. | 428 | 436 | 1,912 | 87 | Proceedings of the Royal Society of London. Series A, Containing Papers of a Mathematical and Physical Character | F. W. Aston, B. A., B. Sc., A. I. C.|Sir J. J. Thomson, O. M., F. R. S. | article | 6.0.4 | http://dx.doi.org/10.1098/rspa.1912.0096 | en | rspa | 1,910 | 1,900 | 1,900 | 9 | 99 | 2,578 | http://corpora.clarin-d.uni-saarland.de/surprisal/6.0.3/?id=rspa_1912_0096 | 10.1098/rspa.1912.0096 | null | null | null | Electricity | 36.890926 | Tables | 23.425862 | Electricity | [
1.6605188846588135,
-51.62135314941406
] | ]\gt ; the Discharge Concentric in Gases at Low Pressures .
By F. W. ASTON , B.A. , B.Sc. , A.I.C. , Trinity College , Cambridge .
( Communicated by Sir J. J. Thomson , O.M. , F.R.S. Received August 23 , 1912 .
) In some previous communications*the author has described inyestigations upon the length of the Crookes dark space and the relation between current and potential in the discharge between large plane aluminium electrodes in different gases at various pressures .
For all the chemically active gases , and also for the gases of the helium when these are not in a state of great purity , the two ollowing equations were found to hold over a considerable range of the four variables:\mdash ; , ( I ) , ( II ) where is the length of the dark space , the pressure , the potential difference between the electrodes , and the current density .
On examining the values of the four constants , and , it will be seen that ] , and have widely different values for different ases the variations in the values of ( taking the cases of gases in which it was fairly constant } are very small and may be regarded as insignificant considering the difficulty of its accurate determination .
In such cases of cylindrical discharge tubes with plane electrodes filling the tubes it is clear that so long as we only consider the part of the not affected by the glass wall the current density will be the same at every point along the , and therefore no information can be obtained as to the particular part of the discharge upon which the value of the current factor of the dark space depends .
If now the parallel plane electrodes are replaced by two in the form of concentric cylinders the current density will vary from point to point throughout the discharge , so that valuable information upon and the nature of the discharge in general might be expected from accurate measurements of the values of , and for electrodes of this The present paper contains the results obtained with the discharge between such cylinders in the ases oxygen and * F. W. Aston , 'Roy .
Soc. Proc 1907 , , vol. 79 .
p. 80 ; F. W. Aston and H. E. Watson , ibid. , 1912 , , vol. 86 , p. 168 .
Discharge between Concent , The discharge tube is shown in section in .
The vessel was a glass shade , into this was pushed a cylinder of thin aluminium sheet A which just fitted it , the inside surface of this formed the outer electrode .
The inner electrode was an aluminium tube , of exactly the same ) as whose outer surface formed the inner electrode .
It was supported in an exactly concentric position with regard to A upon a lass tube passing the neck of the shade .
This system of cylinders was closed at one end by the mica sheet , and at the other by the disc , which was cemented on to the ground end of the shade with sealing FIG. 1 .
wax .
By means of a side tube ( not shown ) the apparatus was connected to an arrangement by which gas could be admitted , and also to pumps and a liquid air charcoal tube by which the correct of exhaustion could be obtained .
The pressure was read on a special McLeod gauge designed by the author and capable of reading to a high degree of accuracy over the ranges employed .
The current , as in the previous experiments , was derived from a ' battery of small accumulators and controlled by two water resistances in parallel .
An exceedingly delicate and accurate Hartmanm and Braun mllliamp meter available , this was used to measure both the current and the potential by an ement of connections shown in the diagram ( fig. 2 ) , in hich A is the ammeter , the discharge tube , a resistance equal to that of the ammeter , and a heavy standard By rocking the connecting link of the ordinary six-pole see-saw reversing switch , the ammeter can be made to read the current flowing through the discharge tube , or that flowing through the , at will .
As the whole scale of 100 divisions read 1 milliampere , the latter arrangement formed a dead-beat voltmeter reading up to a thousand volts with an accuracy volt .
4.30 .
F. W. Aston .
Discharge between [ Aug. 23 , By a low esistance shunt in the position indicated in the dia , , the of the ammeter could be multiplied to any degree to suit the current values used without interfering with its function as a voltmeter .
The cylinders had diameters and cm .
respectively , with a common length of cm .
Hence the effective cathode areas , i.e. , the inner surface area of the outer cylinder and the outer surface area of the inner cylinder were ( neglecting the edge effect at the ends ) 463 and 72 sq .
cm .
respectively , and a shunt giving divisions per milliampere was enerally used .
As there were no guard-ring arrangements on the electrodes the edge effect , which in this case was an end effect , was not eliminated , so that the values of the current stated are only approximate measures of the current densities .
The length of the Crookes dark space was measured by a simple sighting arrangement similar to that already described , which was mounted on a micrometer carriage giving readings to mm. The hydrogen and oxygen used were prepared by the electrolysis of a solution of barium hydrate and were admitted into the tube in a perfectly dry state .
The order of experiment was the same as had been found most convenient in previous work of this kind ; that is to say , a series of readings of dark space and voltage for four or five definite current values ( chosen to be suitable for curve ) were taken at constant pressure ; the pressure was then altered , either by letting in fresh gas or pumping out , and another series taken .
The range of current , which ] is limited on the one side by the fact that it 1912 .
] Concentr.ic Cylinders in at Pressures .
must be considerably than that necessary to cover the cathode with glow , and on the other by the heat giveu out and the voltage at disposal , was much the same whether the inner or the outer cylindel was cathode .
Owing to the disparity between their respective areas the of current density at the cathode surface was over values for the inner than the outer , the two ranges barely oyerlapping .
The discharge , as was to be expected , resembled that between plane electrodes in its ooeneral appearance .
With oxygen the of the space was absolutely sharp at all the ative glow became faint at low when the inn er cylinder was used as cathode .
The surface of the negative appeared almost perfectly cylindrical over a considerable range of space whichever way the current passing .
Beyond a certain limit , however , the dark space was shorter in the middle of the tube than at the ends and the current density evidently not uniform .
There is , therefore , little value in the leadings of the dark space which exceed 2 to When the length of the dark space approached the distance between the electrodes this uneven distl.ibtltion of the discharge became very mark and in the case of the outer cathode the negative glow finally appeared in the form of a bright cloud of a shuttle shape surrounding the middle of the inner cylinder .
The appearance with hydrogen was much the same as that with oxygen , except that the of the dark space was not nearly so well defined and almost impossible to measure at low currents .
The quite visible at low current densities and very much clearer at the outer cathode than the inner .
The conditions of the experiments were not suitable for its accurate measurement .
In the four tables are given the actual readings obtained .
is expressed in centimetres , in hundreths of a millimetre of mercu1y , and in volts .
The values of are those of the total current flowing the tube in fifths of a milliampere ; for the calculation of the constants they are reduced to current densities , employing the convenient unit , previously used , of one-tenth of a milliampere per square centimetre .
* F. W. Aston , ' Roy .
Soc. Proc. , 1907 , , vol. 80 , p. 45 .
F. W. Aston , 'Roy .
Soc. Proc 1907 , , vol. 79 , p. 80 ; F. W. Aston and H. E. Watson , ibid. , 1912 , A. vol. 86 , p. 168 .
Mr. F. W. Aston .
Discharge between [ Aug. 23 , Table I.\mdash ; Oxygen .
Outer Cylinder used as Cathode .
Table II.\mdash ; Oxygen .
Inner Cylinder used as Cathode .
1912 .
] Concentric Cylinders in Gases at Low Table III.\mdash ; Hydrogen .
Outer Cylinder used as Cathode .
Table .
Inner Cylinder used as Cathode .
On plotting these values it was foumd that in seven out of the eight relations examined , the curves so obtained satisfied the same form of fUmdamental equations as those quoted on p. 428 for plane electrodes\mdash ; a result which is particularly when one takes into account the fact that the radius of curvature was of same order as the length of the dark space , so .
that the current density at the of the negative glow must have been widely different from that at the surface of the cathode , and its distribution continually altering with the alteration in the length of the dark space .
The relation which forms the exception is the result in oxygen when the outer cylinder was used as cathode and is an interesting one on account of the surprisingly small change in the potential over large ranges of current and pressure .
It will be seen also that the general rule of increase of voltage with decrease of pressure appears actually reversed in one case ; this series , however , was nob made at ) same date as those at .
pressures immediately above and below .
At the very outset of the experiments it was seen that the alteration of what for want of a better term may be called the " " resistance\ldquo ; of the tnbe VOL. LXXXVII.\mdash ; A. 2 Mr. F. W. Aston .
between [ Aug. 28 , when the current was reversed was far greater than might be expected from considerations of cathode area only .
Such a tube is , in effect , an electric valve and , properly designed , form an efficient rectifier , since the restriction of the volume of the negative glow caused by the use of the outer cylinder as cathode seemed to help rather than hinder the passage of the current .
The most important relation , to determine which these experiments were rily undertaken , is that connecting dark space with pressUl.e and current .
On the accompanying yram ( are plotted some of the results for oxygen .
It was soon evident that the slopes of the lines , , the Length of Dark Space , in centimetres .
1912 .
] Concentr.ic Cylinders in Gases at Pressures .
values of , were practically identical with each other whichever cylinder used as cathode , and also equal to already determined for plane cathodes provided that current .
each exprcssed current density ' at tl , of the cathode .
This very important result ] to indicate that whatever may be the explanation of the of the dark space with increase of current density , the mechanism which causes it is probably ' very near the surface of the cath.ode .
The pressure factor A is , in oxygen , practically constant for the convex cathode , and also for the concave one at low pressure .
It is much larger in the first case than in the second , the value for plane electrodes between the two .
As is the same for all , it follows that the effect of curvature of cathode on the of the dark space is exactly like a in the pressure , an increase if it is concave , and a decrease if it is convex .
Hydrogen yields results of a similar natul.e , only , as this gas does not give so sharp a dark space edge , they are not so accurate .
In this gas the difference veen the values of A for the two inders is not so Root of nt Den sitq .
between lcentric Cylinders .
neither\mdash ; in the case of the outer cylinder\mdash ; is A so constant , but shows a tendency to decrease with decrease of sure .
Fig. 4 shows the relations between current density and for hydrogen , in which it will be seen that both concave and convex cathodes obey equation ( II ) with fair exactness , being the same for both .
is higher for the inner than the outer cylinder , and in both cases tends to decrease with decrease of pressure .
Similar sCl.aight lines are give by the in ner cathode in oxygen .
The following are the mean values of the constants for the three forms of aluminium hodes : aneConvex .
Our present knowledge of the mechanism of the dark space is inadequate to give any explanation of these figures .
As its length seems to depend on the density of the ionisation within it , one might expect it to be greater for convex than for concave surfaces , since the cathode rays are diyergent in the former case and convergent in the latter .
Further information on this point be gained by the use of cylinders of various diameters .
view , however , of the apparent dependence of the constant upon the current density at the surface of the cathode only , it seemed to the author more important that observstions should be commenced upon the influence of the of the cathode upon this and other phenomena of the discharge .
of Results .
1 .
The relations between pressure , , itlld the length of the Crookes dark space in the discharge between concentric cylinders take much the same form as those in the discharge between parallel planes .
2 .
Curyature of the surface of the cathode appears to have no influence upon the rate of alteration of the length of the dark space with change of current density , so long as the latter asured at the surface of the cathode .
3 .
eteris p , the length of the dark space is greater for a convex cylindrical surface than a plane , and for a plane than a concave one .
|
rspa_1912_0097 | 0950-1207 | On the influence of the nature of the cathode on the length of the crookes dark space. | 437 | 451 | 1,912 | 87 | Proceedings of the Royal Society of London. Series A, Containing Papers of a Mathematical and Physical Character | F. W. Aston, B. A., B. Sc., A. I. C.|Sir J. J. Thomson, O. M., F. R. S. | article | 6.0.4 | http://dx.doi.org/10.1098/rspa.1912.0097 | en | rspa | 1,910 | 1,900 | 1,900 | 10 | 234 | 6,288 | http://corpora.clarin-d.uni-saarland.de/surprisal/6.0.3/?id=rspa_1912_0097 | 10.1098/rspa.1912.0097 | null | null | null | Electricity | 34.798408 | Thermodynamics | 20.026343 | Electricity | [
1.8502355813980103,
-52.1606559753418
] | 437 On the Influence of the Nature of the Cathode on the Length of the Crookes Dark Space .
By F. W. Aston , B.A. , B.Sc. , A.I.C. , Trinity College , Cambridge .
( Communicated by Sir J. J. Thomson , O.M. , F.R.S. Received August 23 , 1912 .
) In the work previously communicated by the author upon the subject of the cathode dark space only one metal , aluminium , was employed in the construction of the cathodes used .
It therefore seemed desirable that cathodes of various metals , etc. , should be experimented with in order to find out to what extent the relative values of length of dark space , pressure , current density , and voltage were affected by the material of the cathode .
The cathode fall which is intimately connected with the ratio between current and voltage is certainly widely different for different metals* so that it was thought very probable that the length of the dark space might also be affected .
Preliminary experiments fully justified this expectation , and an apparatus was therefore designed for a systematic enquiry using cathodes of many different materials .
At the outset one was faced with the difficulty that , for reasons given in a previous communication , in order to get absolute values of the quantities measured the cathode should be large and of the " guard-ring " type .
As this would put several interesting substances out of court and involve much labour and complication it was decided to use moderate-sized cathodes of the simplest form and treat the values obtained as relative only .
The method adopted of constructing the apparatus so that cathodes could be changed with the least difficulty and risk of accident is indicated in fig. 1 .
B Fig. 1 .
The discharge tube itself was a thin glass shade , of the kind used to protect statuettes , with a hole blown in the end to admit the rod carrying the anode A. Instead of closing the other end with a thick glass plate , which , even with the most careful heating , would be very liable to crack , a thin glass * J. J. Thomson , ' Conduction of Electricity through Gases , ' ed. 2 , pp. 538 and 560 .
Mr. F. W. Aston .
Influence of Nature of [ Aug. 23 , bulb B was used which could be heated up in a naked Bunsen flame with impunity .
The joint was made with sealing-wax and though it was taken apart and remade over 20 times during the research it never showed any tendency to leak .
Through the flask passed the rod R , at the end of this could be screwed the cathode 0 , the face of which consisted of the material under observation .
Both electrodes were circular discs 10 cm .
in diameter , their distance apart about 11 cm .
For simplicity in calculating the current density the whole surface area of 78'5 sq .
cm .
was used .
This involves an edge error , which , however , is probably much the same for each metal used .
The anode was of aluminium and was not changed .
The gases used were oxygen and hydrogen , chosen , the former on account of the abnormal sharpness of the edge of its dark space , the latter for contrast and because it was one which exhibited the primary cathode dark space.* The measuring instruments employed and the procedure of the experiment were the same as described in the foregoing paper on cylindrical cathodes .
As in all work of this kind it was necessary to wash the cathode and the * tube thoroughly with oxygen , while the current was kept running until the effect of a heavy current upon the colour of the discharge was insignificant .
This is a very delicate test , as the characteristic colour of the discharge in pure oxygen is extremely sensitive to impurities .
The duration of such washing varied enormously with the different cathodes used .
Experimental Results .
The behaviour of the cathodes of the different materials used will now be considered in detail , beginning with the metals in the order of their atomic weights .
As before , the length of the dark space D is expressed in centimetres , P the pressure in hundredths of a millimetre of mercury , V the potential difference between the electrodes in volts , and C the current in fifths of a milliampere .
Measurements were only made under restrictions , viz. : that the current must be considerably greater than that necessary to cover the whole cathode with glow , and no positive column should be present .
Under these conditions all the metals satisfied very nearly the two empirical equations obtained with aluminium cathodes , f so that by plotting I ) against 1/ ^/ 0 and V against fC straight lines were obtained from which approximate values of the constants could be calculated , the equations being D A P Vc .
' v = E+^y^ .
* F. W. Aston , 'Roy .
Soc. Proc. , ' 1907 , A , vol. 80 , p. 45 .
t F. W. Aston , ' Roy .
Soc. Proc. , ' 1907 , A , vol. 79 , p. 80 .
1912 .
] Cathode on Length of Crookes Dark Space .
439 C is here the current density , the unit adopted , as before , being one-tenth of a milliampere per square centimetre of cathode surface .
Magnesium.\#151 ; Cathode a plate of the metal about 1*5 mm. thick made by Messrs. Johnson and Matthey .
The surface was not quite flat , so that the measurements of the length of the dark space are not so accurate as desirable .
When first used it disengaged very large quantities of gas , which appeared from spectroscopic observation to be fairly pure hydrogen , for .
which reason it had to be run for a long time before measurements could be made .
No sputtering was observed with this metal .
The surface sustaining the discharge glowed green apparently by impact of the positive rays , this glow became quite brilliant at high voltages and showed the green magnesium line .
This very interesting effect showed a tendency to weaken after prolonged running with hydrogen , so may be due to a surface layer of oxide .
In connection with this phenomenon the author has often observed that cathodes of aluminium , iron , or platinum which have not been specially cleaned give a brilliant yellow fluorescence when first used .
This fluorescence gives the sodium line and disappears rapidly with continued running ; it is doubtless due to the casual presence of salts of that metal on the cathode surface .
It will be seen from the following figures that magnesium at a given pressure and current density exhibits the smallest dark space and requires the lowest potential of all the metals as yet experimented upon .
Magnesium\#151 ; Oxygen .
p 13 3 10 -o 8-1 6-9 6-0 c. V. D. y. D. V- D. y. D. !
y. D. 10 358 1 -155 373 1 -285 392 1 -420 413 1 -555 437 1 -690 16 363 1 -ooo 390 1 -135 415 1 -260 440 1 -390 470 1 -540 25 377 0-870 408 1 -ooo 440 1 -125 471 1 -250 508 1 -400 44,1 .
398 0-730 442 0-860 487 1 -ooo 527 1 130 575 1 -265 Magnesium\#151 ; Hydrogen .
| P ' ' | 27 -6 25 2 19 -8 17 -0 14-5 C. V. D. !
V. I ) .
y. D. V. D. V. D. 16 I 302 1 *460 310 1 -560 j 353 1-815 383 1-955 432 2-190 25 325 1 *380 341 l -440 i 392 1-660 430 1 -840 490 2-075 44i 370 1 *235 397 1 -325 460 1 -545 510 1 -730 583 1 945 64 410 1 *155 442 1 -255 | 515 1 -485 570 1 -670 658 1 -880 440 Mr. F. W. Aston .
Influence of Nature of [ Aug. 23 , Aluminium.\#151 ; Cathode a plate 3 mm. thick , turned flat in the lathe .
As it is light , easy to work , and carries more current with less sputtering than any of the other metals easily available , its technical use as material for cathodes is almost universal .
For purposes of research in which pure gases are required these advantages are considerably discounted by its unfortunate property of giving off very large quantities of gas when in use .
On this occasion the evolution of this gas , which appears to consist of .carbon compounds , did not wholly cease even after many days ' running .
During such long running its surface appears to become fatigued , but when once thoroughly run with oxygen it gives very consistent results so long as the vapour of mercury is carefully excluded from the apparatus .
Aluminium\#151 ; Oxygen .
p 16 -5 11 *2 9-9 7-8 7 -2 0 .
y. D. y. D. y. D. y. D. y. ] ) .
10 362 1 -200 388 1 -370 400 1 -465 430 1 -625 448 1 -760 16 372 1 -030 405 1 -185 42 L 1 -310 460 1 -450 485 1 -550 25 385 0-910 428 1 -050 456 1-150 496 1 -300 529 1 -430 44| 1 411 0-750 467 0-910 505 1 -020 555 1 -135 600 1 -255 Aluminium\#151 ; Hydrogen .
P 33 -3 26 -0 22 -0 19-3 15 -7 C. j y. D. y. P. y. D. V. D. y. D. 10 367 2-080 430 2-450 16 313 1-375 340 1 -605 360 1 -780 417 1 -940 495 2 -300 25 333 1 -240 380 1-465 411 1 -640 480 1-830 574 2-150 44 ^ 380 1 -105 450 1 -340 490 1 -540 578 1 -730 700 2-090 64 421 1 -045 508 1 -275 560 1 -500 \#151 ; \#151 ; \#151 ; Iron.\#151 ; Cathode a plate of soft iron of the quality used for magnet laminations .
The surface was well cleaned with emery paper ; it gave off very little gas , but sputtered rather badly in hydrogen .
1912 .
] Cathode on Length of Crookes Dark Space .
Iron\#151 ; Oxygen .
p 15 -9 13 .o 11 -o 9-6 0 .
y. D. y. I\gt ; .
V. D. y. I ) .
10 432 1 -270 440 1 -380 456 1 -500 480 1 640 1G 450 1 -115 462 1-230 487 1 -350 517 1 -470 25 46G 1 -ooo 492 1 115 522 1 -230 563 1 -355 44# 500 0-8S0 542 1 000 589 1 -no 640 1 -240 Iron \#151 ; Hydrogen .
P 40-3 32 -6 28 -7 23 -8 C. y. D. y. D. 1 y. D. Y. 1 D. 16 427 1 -625 438 1 -780 468 1 -880 507 2-055 25 451 ; 1 -475 483 1 -635 520 1-750 569 1 -915 44# 490 1 -320 560 1 -485 608 1 -610 676 1 -765 64 j 530 1 -250 620 1 -420 680 1 -540 760 1 -710 Copper.\#151 ; Cathode a plate of the commercial metal about 8 mm. thick , the surface being cleaned with emery paper just before it was put in the tube .
It gave off very little gas , and except for sputtering behaved very well .
Contrary to expectations the surface did not become discoloured by the discharge in oxygen .
Copper\#151 ; Oxygen .
P 13-4 10 -5 9-2 : !
7 -8 C. v ' i D. y. D. y. D. y. D. 10 440 1 -435 477 1 -610 505 1 -740 542 1 -945 16 470 1 -285 514 1 -460 548 1 -580 595 1 -760 25 503 1 -165 559 l -340 598 1 -470 657 1 -625 44# 561 1 -045 632 1 -210 683 1 -330 753 1 -490 Copper\#151 ; Hydrogen .
P 44 -9 i 37 -0 30-8 26 *7 C. !
T. !
1 1 D. V. D. y. D. y. D. !
16 477 1 -835 527 2 -020 596 2 -230 660 2 -435 !
25 517 1 -670 590 1 -860 672 2-105 745 2 -325 1 44# 590 1 -500 690 1-730 800 1 -940 894 2 -175 64 645 1 -420 763 1 -640 897 1 -860 980 2 -100 Mr. F. W. Aston .
Influence of Nature of [ Aug. 23 , Zinc.\#151 ; Cathode a plate of the commercial metal about 1 mm. thick .
This metal behaved remarkably well as a cathode , giving off very little gas , so that the time of running was comparatively short before constant results were obtained .
At the close of the set of readings when taken out it had a faint greyish bloom on the part carrying the current , but no sputtering effect was noticeable on the glass walls of the tube .
Zinc\#151 ; Oxygen .
p 13-1 11 -1 96 7-8 6-3 1 0 .
V. D. Y. D. y. D. V. D. V. D. 10 417 1 -380 440 1 -550 459 1 -630 495 1 -820 550 2-130 16 438 1 -245 470 1 *350 490 l -440 538 1 -640 605 1 -930 25 470 1 -085 504 1 -210 530 1 -315 590 1 -505 670 1 -765 44* 517 0-965 562 1 -070 595 1 -170 668 1 -380 773 1 -620 Zinc\#151 ; Hydrogen .
P 42 -4 39 *2 31 -5 27 -6 C. y. D. V. D. V. D. y. D. 16 378 1-645 408 1 -740 465 2 -010 503 2 -200 25 411 1 -485 450 1 -630 528 1 -890 580 2 -080 44* 478 1 -375 528 1 -500 627 1 -765 697 1 -970 64 528 1 -300 590 1 -430 700 1 -700 783 1 -880 Silver.\#151 ; Cathode thick bright foil stretched upon the copper cathode already described .
When used with oxygen the surface very soon took a brownish tinge , which it lost almost completely in hydrogen .
Silver gave in oxygen larger values of D than any other metal , but sputtered very badly , in hydrogen so badly that very few reliable readings could be obtained .
Silver\#151 ; Oxygen .
P 19 -5 15 -0 12-8 11 -o 9-6 1 C. y. D. y. i d. !
V. D. y. D. y. D. 10 452 1 -330 471 1 -400 480 1 -600 508 1-730 535 1 -870 16 417 1 -185 493 1 -315 512 1-435 548 1 -575 583 1 -715 25 487 1-075 517 1 -200 550 1 -305 596 1 -450 640 1-575 44* 522 0-965 572 1 -090 622 1 -200 685 1 -340 740 1 -470 1912 .
] Cathode on Length of Crookes Dark Space .
Silver\#151 ; Hydrogen .
p 58 -5 48-1 40-0 c. V. D. V. D. V. D. 16 460 1 -600 510 1 -800 560 1 -940 25 490 1-460 552 1 645 620 1 -815 44 !
530 1 -315 630 1 -500 722 1 -670 64 597 1 -220 690 1 -415 \#151 ; \#151 ; Tin.\#151 ; Cathode thick bright foil , used in the same way as the silver .
Sputtered very much less than that metal and did not become discoloured .
It gave off very little gas , and on the whole was the most satisfactory of the heavy metals .
Tin\#151 ; Oxygen .
P 19-0 13 -4 9-8 8-2 C. Y. D. y. D. Y. D. Y. 1 D. 10 436 1 " 220 450 1 -395 483 1 -600 515 1 -755 16 448 1 -070 472 1 -220 520 1 -430 557 1 -610 25 462 0-945 500 1 -100 560 1 -300 605 1 *465 44 !
489 0-810 548 0-970 627 1 -180 687 1 -330 Tin\#151 ; Hydrogen .
P 47-5 39-4 34-4 30-6 C. V. D. V. D. Y. D. Y. !
D- 16 ( 432 ) 1 -520 450 1 -745 487 1 -905 520 2-045 25 ( 465 ) 1-395 487 1 -765 548 1 -765 590 1 -920 44 !
( 502 ) 1 -240 565 1 -450 650 1 -620 705 1 -780 64 540 1 -190 625 1 -355 725 1-545 Note.\#151 ; Readings in brackets are unreliable owing to the presence of a positive column .
Platinum.\#151 ; Cathode thick foil cemented upon the zinc plate already used .
The metal gave off a considerable amount of gas , and sputtered very badly .
Mr. F. W. Aston .
Influence of Nature of [ Aug. 23 , Platinum\#151 ; Oxygen .
p 16-9 12 1 10 -o 9 -4 7 -9 c. Y. D. Y. D. Y. D. Y. D. Y. D. 10 435 1-315 462 1 -480 481 1 -620 508 1 -765 547 1-950 16 449 1 -170 490 1 -335 520 1 -455 552 1 -600 600 1-770 25 471 1 -055 522 1 -205 568 1 -340 608 1-470 665 1 -650 44 j 510 0-915 582 1 -090 648 1 -220 698 1 -350 773 1-515 : .
Platinum\#151 ; Hydrogen .
P 45 -4 37 -9 31 -8 27 -5 c. Y. D. | Y. D. Y. D. V. D. 16 422 1 -715 434 1-855 514 2-130 588 2-315 25 456 1 -565 495 1 -735 583 1 -990 683 2-200 44i 510 1-430 580 1 -595 697 1 -840 808 2 -045 64 562 1 -355 640 1-535 780 1 -750 910 1 -970 Lead.\#151 ; Cathode a thick plate well scoured with emery paper just before use .
The oxygen discharge turned the surface a rich brown , which was reduced to a greyish appearance in hydrogen .
This metal was the worst of all for sputtering , measurements in hydrogen being almost unattainable , and not to be relied on .
Lead\#151 ; Oxygen .
P 15 -3 11 -9 9-3 7-8 0 .
Y. D. V. D. Y. D. Y. D. 10 452 1 -380 467 1 -550 516 1 -730 566 1 -940 16 474 1 -230 505 1 -365 562 1 -570 620 1 -800 25 500 1 -100 548 1 -235 618 1 -440 684 1 -630 44\#163 ; 555 0-955 619 1 -120 708 1 -300 785 1 -480 | Lead\#151 ; Hydrogen .
P 49 -1 39 -7 35 -9 C. Y. D. Y. D. Y. D ' 16 ( 500 ) 1 -880 564 2 -130 628 2 -320 !
25 ( 570 ) 1 -700 656 2-000 708 2-125 44A ( 648 ) 1 " 525 770 1-830 835 1 -985 '64 710 1 -420 850 1 -740 \#151 ; 1 1912 .
] Cathode on Length of Crookes Dark Space .
Experiments on Carbon .
It was thought on account of its extreme position in the Volta series that this element might yield remarkable results .
A carbon surface was first prepared by coating a lead cathode with ordinary graphite stove-polish .
This did not give satisfactory results , so a cathode was cut out of an old gas-carbon battery plate about 5 mm. thick .
This was well washed , dried , and ignited in a muffle , and finally the surface was ground flat with emery .
After long continued running and pumping the gas which it gave off was apparently exhausted , but it proved quite impossible to get reliable readings in oxygen , owing no doubt to the formation of oxides of carbon .
A few single readings , however , show definitely that its dark space length is not greater than that of silver .
In hydrogen some successful observations were made with results given below .
Carbon\#151 ; H y d rogen .
p 52 1 45 -0 34 -2 28-5 c. Y. D. Y. D. Y. D. V. D. 16 ( 422 ) 1 -420 443 1 -520 480 1 -780 537 2-030 25 ( 430 ) 1 *260 458 1 -400 539 1 -640 615 1 -900 44J ( 480 ) 1 -120 510 1 -265 644 1 *550 747 1 -790 64 ( 515 ) 1 *050 555 1 -170 725 1 -500 840 1 -745 Experiments with Liquids .
By means of another and smaller discharge tube some rough measurements were made with liquid electrodes .
The tube was in this case vertical ; the surface of the liquid itself formed the cathode , the anode being an aluminium plate .
Mercury.\#151 ; This metal acted quite well as a cathode when perfectly pure and superficially clean .
It showed no outstanding peculiarities which would warrant the trouble of making a special apparatus for the determination of its constants .
These appear much the same as those of zinc .
Sulphuric Acid.\#151 ; When the mercury was replaced by concentrated sulphuric acid it gave off such volumes of vapour , when used as a cathode , that it was impossible to make measurements at constant pressure .
When the surface was used as an anode , although the volume of gas liberated by electrolysis would be the same , this did not occur ( a very interesting point , since mercury did not behave in this way ) , so that it was possible , by the use of the aluminium disc as cathode , to get the aluminium value Mr. F. W. Aston .
Influence of Nature [ Aug. 23 , for the dark space at the prevailing conditions , and then by instantaneously reversing the current obtain a rough comparative value for the sulphuric acid .
This was found to be about the same as the aluminium one .
Experiments on the Surface Configuration .
In order to ascertain how far roughness , as apart from cleanness , of the cathode surface affected the results , a plate of zinc was taken and the entire surface cut in parallel grooves in a shaping machine .
The grooves were contiguous and about 0'5 mm. deep , so that the actual surface area of the cathode was increased some 50 per cent. A series of readings were taken , when it was found that , so long as D was measured from a point about half way down the grooves , the values of all the constants were practically identical with those for the flat plate .
This definitely shows , first , that mere roughness , even of an exaggerated kind , does not affect the discharge , and secondly , that the current factor B depends on the mean normal current density so long as the irregularities of surface are small compared to D. { Compare with results in previous paper on curved cathodes .
) Experiments with Perforated Cathodes .
The subject of cathodes with discontinuous surface is a very complex one , and one of peculiar interest , inasmuch as the whole of the work on positive rays has been done with their aid .
On this occasion two cases only were considered , which are rather to be regarded as tentative experiments in a new field than properly part of the work now described .
Commercial perforated zinc was used in these experiments .
The perforations were about 1*2 mm. in diameter , and so numerous that they took up approximately half the surface .
In the first case , 3 mm. in front of the zinc cathode already used , a disc of the same size was mounted on thin metallic supports ; if it was put further away , the* discharge struck back through the perforations .
With this arrangement it was found that , notwithstanding the enormous reduction in the surface of metal immediately exposed , the current actually passed more easily than with the plane zinc cathode , streamers of light , doubtless due to positive rays pouring past the perforated plate upon the other , could be seen behind the holes , and the light in front of the cathode was certainly more intense in front of the perforations than elsewhere .
As soon as a series of readings had been taken , a plate of mica was introduced at the back of the perforated plate to prevent the streams of positive rays reaching the plate behind .
The cathode now carried considerably 1912 .
] Cathode on Length of Crookes Dark Space .
447 less current than the plane one , the dark space being correspondingly larger .
These perforated cathodes were the only ones that showed any marked tendency to diverge from the normal behaviour expressed by the two empirical equations already quoted .
The values given to their constants in the tables are only approximate .
Primary Dark Space*\#151 ; All the cathodes used in hydrogen exhibited a primary dark space of approximately the same dimensions with that gas .
Behaviour of the Anode.\#151 ; Towards the end of this research , the anode , which had been used continuously the whole time , gave evidence of a new and interesting phenomenon .
This was the anode dark space described in a letter to ' Nature .
' !
It was thought that the presence of this surface-fatigue effect might interfere with the accuracy of the voltage readings , so the cathode under observation at the time was removed , and the original aluminium one replaced .
Although this did not affect the appearance of the anode dark space , the original values of the voltage , etc. , were given again within the limits of experimental error , a very satisfactory check on any changes in the apparatus which might have occurred during the time over which the experiments extended .
Table of Constants .
Oxygen .
1 A. 1 B. E. F. F/ A. Di- V|* Vi/ D l Mg 4-8 0-41 310 13 -5 283 0-890 434 486 A1 5-7 0-43 310 17 -5 302 1 -035 492 483 Fe 8-5 0-38 337 26 -0 306 1 -230 597 484 \lt ; Ju 8 *9 0-40 340 28 -5 318 1 -290 630 487 Zn 7-3 0-43 335 23 -5 322 1 -170 570 487 Ag 10 -9 0-36 350 33 -0 303 1 -470 697 475 Sn 7-9 0*40 363 24 -0 304 1 -190 603 508 Pt 8-8 0-40 335 30*0 340 1 -240 627 505 Pb 8-7 0-41 340 31 -5 362 1 -280 650 507 Z ' 6-6 0-43 350 ?
24 -0 \#151 ; 1 -128 566 \#151 ; Z " 8-3 0-43 350 33 -0 \#151 ; 1 -290 | 678 \#151 ; ( Z ' , perforated zinc .
Z " , perforated zinc backed with mica .
) * F. W. Aston , ' Roy .
So Proc. , ' 1907 , A , vol. 80 , p. 45 .
t ' Nature , ' May 2 , 1912 .
448 Mr. F. W. Aston .
Influence of Nature of [ Aug. 23 , Hydrogen .
" A. B. E. F. F/ A. Mg 23 0 39 190 50 217 A1 23 0-41 170 66 287 Fe 34 0 *44 260 91 267 Cu 47 0*45 300 130 277 Zn 43 0*41 220 118 275 Ag 51 0*47 325 140 275 Sn 41 0*45 250 ' 120 294 pt 45 0 *42 270 120 268 Pb 51 0*50 320 166 310 C !
39 0*43 230 137 284 The above table gives the mean values of the constants of the two empirical equations worked out where possible for all the cathodes used .
In addition , in the case of oxygen , are given Di , the length of the dark space at unit current density and a pressure of one-tenth of a millimetre , and the potential under those conditions .
These are obtained by interpolation and so may be regarded as the most accurate of the numbers given .
It will be seen that the values of A , E , F , Di , Yh follow very approximately the same order as the cathode falls given by Skinner* and Mey.f F/ A is practically constant and very nearly the same for both oxygen and hydrogen .
The values of Vi and Th are exceedingly interesting and are plotted against each other on the accompanying diagram ( fig. 2 ) .
All the metals lie on a straight line through the origin except Sn , Pt , and Pb , which are about equal distances above it .
The value of B cannot be determined with much accuracy but shows no striking variation at all .
The edge error tends to make these values of B too low .
This remarkable constant , which represents the contraction of the dark space with increase of current density at the surface of the cathode , has already been shown to be almost unaffected by the pressure and the nature of the gas , } and is now proved by the results of this and the previous paper to be also practically independent of the nature and curvature of the cathode surface .
Turning to the influence of the nature of the cathode upon the dark space at constant C and P , its change of length may to a certain extent be accounted for by some such hypothesis as this:\#151 ; Let us suppose that under such unit conditions the density of the ionisation * ' Phil. Mag. , ' [ 6 ] , vol. 8 , p. 387 .
t ' Yer .
Deut .
Phys. Ges .
, ' 1903 , vol. 5 , p. 72 .
+ F. W. Aston and H. E. Watson , 'Boy .
Soc. Proc. , ' 1912 , A , vol. 86 , p. 168 .
Cathode on Length of Crookes Dark Space .
at the edge of the negative glow is the same for all cathodes .
It is quite probable that this density of ionisation is a function of ( 1 ) the number of cathode particles emitted from the cathode surface , ( 2 ) the distance through which they travel , Di , and ( 3 ) the total energy available from each , Vi .
How if any one of these variables becomes less , one or both of the others will probably become greater , so that as we pass along the series from metals which easily give off electrons to those which do so with more and more difficulty , we Sn 0 X '6 -8 1-0 1*2 1-4 1-6 Length of Dark Spa.ce in cms .
should expect an increase in the length of the dark space , and the fall of potential across it , as is actually the case .
This rough hypothesis will account for the supply of positive ions at the edge of the negative glow , but when we come to consider more closely their transport across the dark space to the cathode the most formidable difficulties are met with .
Thus the author has shown , * by a method which seems very free from objection , that for an aluminium cathode the density of positive electrification p is practically constant throughout the dark space .
It is equal to V/ 27tD2 , and the electric force at the surface of the cathode 2Y/ D. * F. W. Aston , ' Roy .
Soc. Proc. , ' 1911 , A , vol. 84 , p. 526 .
VOL. LXXXVII.\#151 ; A. 2 I 450 Influence of Cathode on Length of Crookes Dark Space .
Taking the actual case of aluminium at P = 0T mm. , D = 1-035 cm .
, V = 492 volts , and C = 01 milliampere or 3 x 105 E.S.U. , works out to be 0-244 E.S.U. per c.c. , so that even if we give the positive ions the velocity-necessary for the carriage of the -whole of the current passing through the tube this will only amount to 1*23 x 106 cm./ sec. , a speed nearly ten times too small for the mobility worked out for the pressure and electric force given above .
It is very unlikely that such a large discrepancy can be met by supposing that the ionic mobilities at such low pressures do not follow the ordinary laws , for Mr. Todd 's most recent measurements of mobilities at pressure of this order show an increase rather than a* decrease in the expression velocity x pressure/ electric force for positive ions .
A more reasonable explanation is supplied by the hypothesis suggested by Skinner* that many of the positive ions rebound from the cathode without giving up their charges , but in this case the electric force should increase much more rapidly than it does close to the cathode .
A moment 's consideration will show that surface layers of positive electrification advocated by Skinner and lately by Westphal , t even if they exist , are of no assistance , as in this case the actual electric force and its rate of change ( 47 were directly measured within a millimetre of the cathode .
Again if the distribution of electric force is the same for other metals as for aluminium the values of Vi , Di , given above show a constant field at the cathode surface with a value of p continually diminishing as we go from Mg to Ag , so that in order to supply the deficiency of current we should be forced to suppose the percentage of this carried by the negative ions greater in the case of silver than in that of magnesium .
This seems unlikely , and at first sight to be in direct contradiction to our original hypothesis ; but the possibility must not be ignored that the electrons emitted by such a metal as silver may start off with too high a velocity to be efficient ionisers .
The attack on these and other difficulties would be greatly assisted by even rough direct comparisons between the current carried up to the cathode by positive ions and that carried away from it by negative ones .
Experiments have now been commenced with perforated cathodes in an attempt to solve this problem .
Summary of Results .
( 1 ) The relations between the values of pressure , voltage , current , and the length of the dark space are determined for plane cathodes of many different * 1 Phil. Mag.,5 1902 , [ 6 ] , vol. 4 , p. 490 .
t ' Yerhand .
d. Deut .
Phys. Ges.,5 1210 , vol. 12 .
Emissivity of Solid and Liquid Gold at High Temperatures .
451 materials , and found to satisfy the same form of equations as those previously given for aluminium , the constants varying considerably .
( 2 ) Roughness of the cathode surface does not appear to affect the discharge , if the dimensions of the irregularities are small compared with the length of the dark space .
( 3 ) The length of the dark space is shown , in the cases examined , to be greatest for silver and least for magnesium , the metals following the same order as in the case of the cathode fall .
( 4 ) The rate of change of length of the dark space with change of current density at the surface of the cathode seems much the same for all cathodes .
( 5 ) Difficulties in the way of arriving at a satisfactory explanation of these and other data connected with the dark space are indicated and shortly discussed .
/ In conclusion the author wishes to express his best thanks to Prof. Sir J. J. Thomson for his kind interest and advice during the investigations described in this and in the previous paper .
A Speetro-photometric Comparison of the Emissivity of Solid and Liquid Gold at High Temperatures that of a Full Radiator .
By C. M. Stubs , M.A. , 1851 Exhibition Scholar , University of New Zealand , and E. B. R. Prideaux , M.A. , D.Sc .
( Communicated by Prof. F. G. Donnan , F.R.S. Received June 21 , 1912 .
) ( From the Muspratt Laboratory , University of Liverpool .
) Introductory .
It is well known that copper and gold emit greenish or bluish light at high temperatures .
KirchhofFs radiation law obviously suggests a connection between this selective emissivity and the selective reflectivity of these metals at ordinary temperatures , which gives rise to their colour .
According to that law the emissivity E ' of a surface at a temperature T is connected with its absorptivity A , by the relation * E'/ E = A , where E is the emissivity of a full radiator or " black body " at the same temperature T. This relation holds for each particular wave-length .
The ratio E'/ E may be conveniently called , and will be referred to hereafter in
|
rspa_1912_0098 | 0950-1207 | A spectro-photometric comparison of the emissivity of solid and liquid gold at high temperatures with that of a full radiator. | 451 | 465 | 1,912 | 87 | Proceedings of the Royal Society of London. Series A, Containing Papers of a Mathematical and Physical Character | C. M. Stubbs, M. A.|E. B. R. Prideaux, M. A., D. Sc.|Prof. F. G. Donnan, F. R. S. | article | 6.0.4 | http://dx.doi.org/10.1098/rspa.1912.0098 | en | rspa | 1,910 | 1,900 | 1,900 | 13 | 242 | 6,103 | http://corpora.clarin-d.uni-saarland.de/surprisal/6.0.3/?id=rspa_1912_0098 | 10.1098/rspa.1912.0098 | null | null | null | Thermodynamics | 34.804142 | Tables | 28.381384 | Thermodynamics | [
0.5149043798446655,
-25.28730583190918
] | ]\gt ; Emissivity of Solid and Liquid at High Temperatures .
451 materials , and found to satisfy the same form of equations as those previously given for aluminium , the constants considerably .
( 2 ) hness of the cathode surface does not appear to affect the discharge , if the dimensions of the irregularities are small compared with the length of the space .
( 3 ) The of the dark space is shown , in the cases examined , to be greatest for silver and least for nesium , the metals the same order as in the case of the cathode fall .
( 4 ) The rate of of length of the dark spnce with of current density at the surface of the cathode seems much the same for all cathodes .
( 5 ) Difficulties in the way of , at a explanation of these and other data connected with ) dark space are indicated and shortly discussed .
In conclusion the author wishes to express his best thallks t Prof. Sir J. J. Thomson for his kind interest and advice during the ions described in this and in the previons paper .
A Spectro-photometric Comparison of the Emissivity of Solid Liquid Gold at High Temperatures ) of a Full By C. M. STUBS , M.A. , Exhibition Scholar , University of New Zealand , and E. B. R. PRIDEAUX , M.A. , D.Sc .
( Communicated by Prof. F. G. Donnan , F.R.S. Received June 21 , 1912 .
) ( From the Muspratt Laboratory , University of Liverpool .
) Intro It is well known that copper and gold emit reenish or bluish light at high temperatures .
Kirchhoff 's radiation law obviously ests a connection between this selective emissivity and the selective reflectivity of these metals at ordinary temperatures , which gives rise to their colour .
According to that law the emissivity of a surface at a temperature is connected with its absorptivity , by relation where is the emissivity of a full radiator or black body\ldquo ; at the same temperature T. This relation holds for each particular wave-length .
The ratio may be conveniently called , and will be referred to hereafter in Mr. Stubs and Dr. Prideaux .
Emissivity of this paper as , the " " relative emissivity\ldquo ; of the surface .
The above law then states that the relative emissivity of a body is equal to its absorptivity for the same wave-length and temperature .
For opaque bodies , such as metals , the reflectivity is equal to : and hence the relative emissivity This relation holds strictly only if emission and reflection take place at the same temperal , ; but if , as stated by several investigators , the reflectivity of metals for visible rays does not vary with the temperature , a heated metallic surface should emit well those rays for which it is when cold a poor reflector , and vice .
This has actually been observed qualitatively for gold and copper by Schaum and Wustenfell* in a recent comparison of the emission spectra of these metals with that of an approximate " " black body They also draw attention to the " " green-glow\ldquo ; which first makes its appearance when these metals are heated , instead of the usual \ldquo ; In the present research is attempted for the first time a more accurate investigation of these phenomena for a " " coloured\ldquo ; metal , by a systematic spectro-photolnetric examination of the emissivity of gold , in both the solid and liquid state .
The nearest approach to such an investigation has been made by Burgess , the main object to fix for pyrometrical purposes the true temperature corresponding to the\ldquo ; black body\ldquo ; temperature of molten copper .
The " " black body\ldquo ; teluperature was observed by means of a Holborn-Kurlbaum optical pyrometer fitted with red and green glasses as light filters .
Two measurements of the radiation from gold have been made by Holborn and Henning .
In this case also coloured glasses were employed .
These researches will be referred to later ; suffice it to say here that the smallness of portion of the spectrum ated , as well as the lack of monochromatism of the coloured glasses , render the results of somewhat uncertain value .
Assuming that the reflectivity does not vary with the temperature , the present investigation would be expected to yield an interesting confirmation of Kirchhoff 's law ; if , however , such a variation take place , ibs nature would be determined .
Of particular interest was the question whether to the change of physical state at the melting point of the metal there corresponded a sudden change in emissivity , to the sudden change in electrical conductivity and certain optical constants observed in the case of tin and other metals at their melting points .
S In their choice of gold as the first 'Zeits .
wiss .
Phot 1911 , vol. 10 , p. 213 .
'Bull .
Bur .
Standards , ' 1909 , vol. 6 , p. 111 .
Sitz .
Ber .
Berlin Akad 1905 , vol. 12 , p. 311 .
S Nicholson , ' Phil. Mag Aug. , 1911 , p. 266 .
1912 .
] Solid Liquid at High Temperatures .
metal to be ated the authors have been gnided by several considerations , prominent among which stood the absence of difficulties connected with surface oxidation .
Copper is now under inyestigation by one of us , and it is hoped that the results for this metal also will shortly be ready for publication .
Appartus and Method .
The principle of the method used to measure the relative emissiviCy of the gold was as follows : The metal was heated in a vertical electrical resistance furnace , the te1nperature being determined by means of a thermocouple dipped in the metal .
The emissivity , for different wave-lengGhs , of the plane horizontal liquid or solid surface was then compared , by means of a spectro-photometer looking vertically down on the surface , with the from the standard electric lamp of the instrument .
In a second experiment , \ldquo ; black body\ldquo ; replaced the gold , the temperature was read as before , and the " " black body\ldquo ; emissivity compared with the standard lamp .
By interpolation , using the " " black body\ldquo ; radiation for the exact temperatures at which the radiation had been measured could then be calculated in terms of the comparison lamp , and through the medium of the latter compared with the gold radiation , thus giving the relative emissivity of the gold , for the various .
The apparatus used will now be described in detail .
The was Messrs. Johnson and Matthey 's " " fine gold of ohest purity , from to fine About 125 .
were heated in a silica capsule of about 4 cm .
internal diameber , the depth of metal being thus about 6 mm. * When the radiation from the solid metal was to be obseryed , the gold was turned to a flat surface and polished , as described later .
The experimental " " black body\ldquo ; consisted of a graphite block 11 cm .
long and 5 cm .
in diameter , in the centre of which was bored a hole 12 mm. wide and 9 cm .
deep .
It was placed so that the lower half was in the hottest part of the furnace , and the graphite wall being thick and a good conductor ensured several centimetres of nearly uniform temperature .
Practical evidence of the fact that the bottom of the hole radiated very approximately as a " " black body\ldquo ; was that the white thermo-couple tube .
which protruded into it , was indistinguishable from its surroundings .
The heating tube of the platinum-wound resistance furnace was 5 cm .
in internal diameter , and cm .
long ; its lower half was blocked with asbestos and sand .
By the external resistance , the temperature could be * It may be noted in passing that , on cooling , the gold in each case adhered to and shattered the crucible , some of the fragments being so firmly attached that it was necessary to dissolve them in hydrofluoric acid .
454 Mr. Stubs and Dr. Prideaux .
Emissivity of [ June 21 , kept constant to within , at any point up to the safe temperature-limit , viz. , 120 C. In order to minimise heat-losses , several diaphragms of sheet nickel and asbestos were suitably placed at the top of the furnace .
When the gold was being observed the central apertures of these diaphragms were of such a calculated size that no radiated or reflected light from any of the could , by reflection at surface , become visible in the spectro-photometer .
The latter instrument , which looked vertically down at the field to be observed , was supported on a board above the furnace , and to protect it from the heat of the furnace , a water-cooled copper plate provided with a small hole through which observations were made was interposed immediately below it .
The bottom of this plate was lampblacked , and with these precautions no ap direct or reflected light , save that emitted by the surface examined , could possibly be visible in the field of view .
The spectro-photometer was of the Konig-Wanner type , as modified by Nernst , and manufactured by Schmidt and Haensch .
* Attention may be drawn to the fact that , as light emitted obliquely from metallic surfaces is known to be partially polarised , this type of spectro-photometer can only be used\mdash ; as was the case in these experiments\mdash ; to measure the normally emitted mpolarised 1 .
The standard source of light used in connection with the instrument was a special 2-volt Osram glow-lamp , illuminating a matt lass screen .
The method of ensuring the constancy of this lamp will be described below .
The scale and ometer circle indicating the portion of the spectrum examined were calibrated in terms of the wave-lengths:\mdash ; Li , Na , ; Ne , ; Tl , ; ; He , ; He , ; and .
The light visible in the field of view was found to have a spectral breadth of about 8 ; the " " wave-lengths\ldquo ; tabulated below are the optical centres of gravity of such spectral regions .
The temperatures were measured by means of two thermocouples enclosed in thin-walled tubes .
The , taken alternately , served to check one another , and permitted a greater accuracy .
The thermocouples were thrice calibrated during the course of the experiments , and showed little variation .
The fixed points chosen for the calibration were the freezing points , in a reducing atmosphere , of silver and copper on the thermodynamic scale .
The constants in the formula , , connecting temperature and , were thus determined ; and since the temperature was never far removed from * Konig , ' Wied .
Ann 1894 , vol. 53 , p. 783 ; Hildebraud , ' Zeits .
Elektrochemie , ' 1908 , vol. 14 , p. 349 .
Day and Sosman , ' Amer .
Journ. Sci 1910 , vol. 29 , p. 93 .
1912 .
] Solid and Liquid Gold at Higf , , the above fixed points , the formula would give relial ) results .
The E.M.F. of the couples was measured on a Clark-Fisher -unit pyro-potentiometer , which read directly to 1 microvolt , corresponding to C. Sources of Er ror and their ) In the present research the chief experimental arose in connection with the surface condition of the gold , the measurement of temperature , and the of the spectro-photometer .
These three sources of error , the methods used to avoid them , and their on the final result , will now be discussed .
1 .
Impurities or inequalities on the surface of the gold were the source of considerable trouble .
The htest surface film influences the enlissivity to a marked extent , increasing the red radiation in which the gold is so weak .
These surface impurities were easily and finally remoyed from the molten metal by fusion with bolax ; the surface was obtained absolutely free from scum , and bright objects held above it vere mirrored perfectly .
The dark centre ring ( inage of the in the ) was clearly defined , and reflected no from the diaphragms or furnace walls .
In the case of the ] ished solid ever , considerable difficulties were encountered .
The surface was turned flat in a lathe , then treated successively with four rades of fine emery paper ; and finally polished with jeweller 's .
An apparently perfect mirror was thus obtained ; but , though variations in the method of polishing were , there invariably appeared , on to incandescence , a conspicuous red film , which quite changed the character of the radiation .
Recrystallisation ( distinct from the above filming ) also took place on heating .
It was finally found that the film , due presumably to particles of polishing material , could be permanently removed by ) eated treatment of the surface with borax at a temperature near the melting point of gold .
Another method of obtaining a clear solid gold surface Yould be to allow the liquid with a clear surface to solidify .
Usually when this is done , however , the qurface , though possessing a brilliant lustre , is uneven , to contraction on solidification , crystallisation , etc. ; and hence reflects from the furnace walls .
By slow cooling , however , an area of the surface can sometimes be got free from this unevenness , and so lowing only with its own blue elnitted light .
One series of measurements , described below , was made on such a surface a few degrees below the melting 2 .
The inlportance of accuracy in temperature is by the following consideration .
For a full radiator , to Wien 's law of spectral energy distribution , Mr. Stubs and Dr. Prideaux .
Emissivity of [ June 21 , where is the emissivity , and are natural constants , is the wavein is the absolute temperature .
Hence , by logarithmic differentiation , Thus , since abont 14,450 , we have for orange , where and for absolute temperature 1337o ( melting point of gold ) , Thus , to an increase of temperature of 1o C. colresponds a -per-cent .
increase in radiation , a difference which can be detected by careful measure- ment .
Special care is therefore necessary in measuring temperature .
In measuring the temperature of the " " black body one of the thermocouples protruded slantwise into the bottom of the radiating hole , and the other was completely enclosed in the graphite , to the same depth as , and adjacent to , the hole .
The former always indicated about C. lower than the latter , and was taken ( probably with very little error ) as giving the true of the radiating surface .
The temperature of the gold was measured by means of the same two thermocouples , which dipped into the liquid gold on either side of the field of observation , and in the case of the solid were similarly fitted into holes previously bored to receive them .
Owing to the shallowness of the gold ( 6 mm. ) and consequent loss of heat by conduction along the thermocouple wires and tube , the temperature indicated was always too low .
In order to determine the true temperature , a careful reading of the apparent temperature when the gold was ( visibly ) at its ting point was taken .
Thus in one case the thermocouples indicated and respectively when the gold was melting ; in other cases the difference between true and observed temperatures was greater .
It was then assumed that within the of investigation the difference between true and observed temperatures remained constant ; and a correction was accordingly added to the latter to obtain the former .
This method in all probability gave when near the melting point a result correct at least to one or two degrees ; and it is significant that even at temperatures over 10 above the melting point , the two thermocouples , whose readings were corrected independently , gave ' true temperatures by only , though " " apparent temperatures\ldquo ; were apart .
The authors consider that the uncertainty in the temperature of the gold due to the above circumstances would never exceed two or three degrees , and is probably less in most cases .
1912 .
] Solid and Liquid Gold at High Temperatures .
To ensure the highest accuracy in measuring the E.M.F. of the couples , the potentiometer was calibrated ; and the working standard cell was repeatedly compared with a certified standard .
There were , however , two sources of error which gave considerable trouble .
The first was a leak from the circuit to the potentiometer , and thence to earth , causing irregular fluctuations in the E.M.F. This was only overcome by thorough insulation of every part of the measuring apparatus , including the accumulators used with the potentiometer .
The second was a variable thermal E.M.F. originating in the poterltiometer , and usually ranging from to 40 microvolts .
It was attempted to correct for this by its magnitude from time to time , and applying a correction to the apparent E.M.F. of the thermocouples .
3 .
The constancy of the spectro-photometer and its comparison lamp is highly important , and the authors took care to ensure it .
Experiment showed that , in the red , e.g. , a l-per-cent .
variation in the produced 9-per-cent .
variation in the light emitted by the comparison lamp .
It was therefore desirable to regulate the current with extreme accuracy .
A precision voltmeter , to regulate the voltage on the lamp terminals , was not a success , as the pressure contact of the lamp in its socket was variable , causing a variation in the resistance of the circuit .
A Weston ammeter in series was then tried , and actually used in some of the earlier measurements .
It was not , however , sufficiently delicate , as it was found to vary in its indications with time of use , temperature of , etc. Finally , the precision voltmeter was crain used , this time however as an ammeter , by the fall of potential between the ends of a fixed low resistance in the lamp circuit .
This method gave perfectly satisfactory results ; the indications of the voltmeter were compared with a standard cell by means of the potentiometer , and found on different days and with different room temperatures not to vary appreciably .
The current the lamp could be kept constant to within per cent. The -volt lamp was run on about volts latter part of the time on still less ) , so that would be very slow .
In order , however , to detect a possible ageing , or other of the optical parts of the spectrophotometer , the instrument was checked against a standard Harcourb 10 .
pentane lamp several times dnring the experiments , and its indications found to show a satisfactory constancy .
In the brighter parts of the spectrum , the mean of 10 readings ( that being the number usually taken at each ) was reproducible to a tenth of a degree .
But if be the the of setting of the analysing nicol of the Mr. Stubs and Dr. Prideaux .
ssivity of [ June 21 , spectro-photometer , the intensity of the field under observation is proportional to ; thus since a change of in the reading corresponds to a per cent. change in radiation .
Taking as , say , , the above has the value per cent. , ) owing that this small change in radiation could be detected .
To sum up , the authors consider that the reatest sources of error lie in the temperature measurement , and ( for the solid Doold ) in the difficulty of obtaining pure surface .
From the considerations set forth above , the values given in Tables I and II below for the ratio would be estimated to be correct to within about 3 per cent. of themselves .
As a matter of fact , an examination of the tables shows that for all except the extreme wave-lengths observed , the average deviation of the individual experimental values from the weighted means given in the last column is about per cent. for the liquid , and per cent. for the solid closer reement than expecced .
esults Since considerations of space make it impossible give the full experimental data from which the results in the following tables are derived , the method adopted in calculating the relative emissivities may be briefly mentioned .
To each series of measurements made on the gold corresponded a series , under as far as possible the same conditions , on the " " black body This served as an additional precaution errors due to change in the comparison lamp , etc. , and gave each of measurements an independent value .
In the tables below to one set , and to a second , , and , to a third , and , and , to a fourth .
The task of measuring the radiation of the gold and " " black body\ldquo ; at precisely the same temperatures was not attempted ; but the ratio of their emissiyities was determined as follows :According to Wien 's equation , which holds for full radiation so long as ( as here ) is less than 3000 , But if be the spectro-photometer where is a constant depending on the comparison lamp and optical parts of the instrument .
Hence or 1912 .
] Solid and Liquid Gold at High ) Measurements of black body\ldquo ; radiation were each time made at two or more diflerent temperatures , and for each wave-length it was found that , determined by the above equation , had a satisfactory constaIJcy , varying by only about two or three per cent. , while the radiation varied several hundred per cent. A weighted mean was taken for the true value of .
If now were the spectro-photometer reading for the radiation of wave-length , and at temperature , the and the relative emissiyity ; and therefore 5 ; and , all the quantities on the right being knowl ] , was determined .
The ving are the summarised results .
To the various series have been assigned as follows in mean value of , in accordance with the considerations of accuracy of temperature measurement , surface condition , and lamp current constancy described above : For liquid gold , ; for solid , .
The bracketed values in Table II are not weighted , as they were vitiated by the presence of film which was more completely removed in the other cases .
The mean temperature at which each series was made is ) at tlJe head of the column .
The results are shown graphically in the curves marked " " relative emissivity , liquid\ldquo ; and " " relative emissivity , solid\ldquo ; in the ralu .
In Table II , the values in column are those obtained for a clear surface naturally crystallised from the liquid , as previously mentioned ; the other values are for an artificial } polished mirror .
The agreement is Mr. Stubs and Dr. Prideaux .
Emissivity of June 21- , Table II.\mdash ; Relative Emi The results show that on passing from the solid to the liquid phase a sharp discontinuity occurs , the relative emissivity increasing in the red and decreasing in the violet .
This result is not in agreement with that of 1912 .
] Liquid Gold at High Ternperatures .
Holborn and who state that no change in emissivity was discernible at the melting point , and that when both phases vere present the emitted light was so uniform that they could only be perceived by shaking the crucible .
The authors , on the contrary , found that solid and liquid differed strikingly in appearance , the solid of a much deeper blue .
This was also shown by a rough spectro-photometric measurement made when both phases were in the field of view ; in the red , the emissivity of the solid was only three-fifths that of the liquid .
Holborn and Henning 's obseryation is difficult to explain ; it may be that there was still a thin layer of liquid on top ( the solid being denser ) ; or that the crystal faces were from the furnace walls ; or that a film of impnrity , which causes errors even when in very small quantity , and which they do not mention any attempt to avoid , was obscuring the true emissivities .
The authors ' result agrees with the observation of Mendenhall and Ingersoll that gold and other metals a marked increase of radiation on .
A difference in optical properties would be expected to accompany the change of state on melting , parallel with a in electrical properties which is known to take place in other metals , and presumably does so in the case of gold .
A study of the change of optical properties and of electrical conductivity at the melting point should , as shown recently by Nieholson , lead to conclusions as to the of number of free electrons in the molecule .
Assuming the truth of Kirchhoff 's law , the results might be expected to show whether the absorptivity of the solid metal had changed in the 1050o range between the melting point and ordinary temperatures .
According to numerous observel .
S , the refiectivity and other optical constants of metals have in the visible spectrum no appreciable temperature coeflicient .
In particular , Koiober , S and have shown this to be so for gold .
Their results were , however , obtained at comparatively low temperatures , up to C. For platinum , the optical properties been shown to remain constant up to or 1500o C. Two measurements of the emissivity of gold in the green and red by Holborn and .
cit. .
Rev 1907 , vol. 25 , 1 ; quoted ' Sci. Abstracts , ' 1907 , No. 1640 . .
cit. S 'Verh .
Deut .
Phys. Ges 1899 , vol. 1 , p. 247 .
'Wied .
Ann 1890 , vol. 39 , p. 481 .
$ 'Wied .
Ann 1896 , vol. 68 , p. 493 .
Rubens , ' Phys. eits 1910 , vol. 11 , p. 139 ; Laue and Martens , ' Phys. Zeits 1907 , vol. 8 , p. 853 .
Mr. Stubs and Dr. Prideaux .
Ernissivity of [ June 21 , Henning*appear to point to a sinlilar conclusion for that metal .
The accuracy of their results has , however , already been shown to be open to question ; and , moreover , Holborn and used coloured glasses instead of monochromatic light in their optical pyrometer .
It may easily be shown that the lack of monochromatism of coloured glasses ( the limits of transpareJlcy of those used in the above research being from and from to respectively ) may give rise to very considerable errors , especially when , as in the case of gold , the ' relative emissivity\ldquo ; varies rapidly with the wave-length see .
Holborn and Henning 's data nJust therefore be regarded as inadequate , and it remains an open question whether at temperatures the optical properties of solid gold undergo change .
The reflectivity of gold has been measured directly by Hagen and Bubens , calculated indirectly from other optical constants by and Tool .
S The various results ether only fairly .
Taking Hagen and directly obtained figures , the absorptivity A is given in terms of the wavelength as follows:\mdash ; 0.500 0.530 0.550 0.156 0.650 0.111 0 .
0.077 These values are shown graphically by the curve marked " " absorptivity , solid in the diagram .
The authors ' curve for the relative emissivity of the solid is seen to be of the same general shape as , but to lie above , Hagen and ' absorptivity curve .
The difference is undoubtedly greater than could be due to experimental errors .
Surface impurity of the solid would hardly account for it , since , apart from the fact that near the melting point the reflecting surface of solid gold was repeatedly treated with borax till no further film could be removed or detected , there is a satisfactory agreement between the values in column for the clear surface of the solid crystallised from the liquid , and those in columns and for the mechanically prepared mirror .
At first sight it would seem , then , that in the wide temperaturerange the absorptivity curve had , as usually the case with coloured nondlic bodies , shifted toward the lon wave-lengths .
But another cit. 'Ann . .
Phys 1902 , vo ] .
8 , p. 1 'Ann . .
Phys 1910 , vol. 31 , p. 1017 .
S 'Phys .
Rev 1910 , vol. 31 , p. 1 .
1912 .
] Solid Liquid Gold at explanation is that the character of the surf changed on heating .
In a polished metal the surface layer must be largely amorphous , and the metal particles almost inevitably mixed with some from the material ; * recrystallisation begins at about , and actually erved to have occurred in the heated solid gold .
It is at least cel.tain that the structure and method of preparation of the surface has a effect on its optical properties , and Drude nlentions that a silver mirror loses its polish when heated , even in a atmosphere .
it still remains an open question whether the absorptivity A has a true temperature coefficient , independent of a change in physical structure of the surface .
Evidently a standard surface condition must be chosen ; that of a natural crystal surface , obtained on solidification of a liquid , ecolnlnends itself .
If large enough flat crystalline surfaces could be obtained , and their at low and emissivity at high telnperatures measured , the question would admit of a solution .
As far as the limits of tempel'ature allowed , no of the relative emissivity of either liquid or solid gold with temperatnre could be discerned .
The high values in the red and yellow in series were due , as already mentioned , to a film which could not be completely removed at the comparatively low temperature of that series .
For the molten metal , the values in series , and , over a temperature of , remain constant within experimental error .
The authors may be permitted to add a note as to the " " spectral energy equation\ldquo ; of gold and similar lnetals .
Some have assumed an equation , similar to the Wien equation , to hold for lletalli radiation , the constants , and being different from those for a and woulddetermine the selectivity of the radiation from the metal .
For platinum Paschen gave , Lummer and rsheim was given as somewhat reater than .
This aspect of selective radiation is , however , neither simple nor satisfactory .
Evidently the quantity concerned is not absolute emissivity , but what has been called the relative emissivity , equal according to Kirchhofl to the absorptivity .
Thus , if denote the absorptivity as a function of wave-length and tempernture , emissivity is given by Tool , , p. 13 .
Tool , .
cit. , p. 14 ; Hagen and Rubens , 'Phil .
Mag 1904 , vol. 1 , p. ; Drude , ' Ann. .
Phys 1890 , vol. 39 , p. 481 .
Burgess , 'Bull .
Bur .
Standards , ' 1905 , vol. 1 , p. 443 ; Coblentz , ibid. , 1909 , vol. 5 , p. 339 , etc. Mr. Stubs and Dr. Prideaux .
Emissivity of [ June 21 , If , as for metals , absorptivity of visible rays does not vary with the temperature , this reduces to In the case of platinum , as it happens , for a considerable portion of the visible spectrum roughly approximates to the form \mdash ; hence Lummer and Pringsheim 's result .
But such a result would not hold for gold and other metals , is obviously of a more complex form .
Even according to the formula for metallic radiation , the supposed valiation of may be shown to be incorrect : for by logarithmic differentiation of the ratio ; which , if is appreciably different from , involves , in conflict with fact , considerable temperature coefficient of absorptivity .
Finally , from a pyrometric point of view it may be of interest to the " " black body\ldquo ; temperatures of solid and liquid gold in terms of their true temperatures , the " " black body\ldquo ; temperature at a given wave-length being that of a full radiator emitting of the same intensity as the gold .
If be the ' black body\ldquo ; temperature , and the true temperature ( on absolute scale ) , the absorptivity or relative emissivity , it may be easily shown that The " " black body\ldquo ; temperatures of solid and liquid gold at the melting point will accordingly be as fiven in the following table:\mdash ; Table III.\mdash ; " " Black body\ldquo ; Teml ) erature of Gold at the Melting oint .
1912 .
] Solid Gold at Temperatnres .
1 .
The emissivity of solid and liquid gold at high teml ) eratures , relative to the emissivity of a full .
at same temperatures , has been measured throughout the visible spectrum .
2 .
A sharp discontinuity in the emissiviuy takes place at the point , the liquid yold emitting more strorrly than the solid in the red and yellow , and less in the extreme blue .
The shape of the relative enlissivity\ldquo ; is quite diffel.ent in the two cases .
3 .
The curve of " " relative emissivity\ldquo ; of solid gold at high temperatures is similar to that of absorptiyity at low tempelatures as determined from reflectivity measurements ; whether it is identical , in which case the temperature coefficient of the absorptivity vould be , could not be absolutely determined , owing to the of stl.ucture which polished surface ooes on 4 .
No temperature coefficient of " " relative emissivity\ldquo ; could be detected for the liquid metal , through a range of over 5 .
" " Black \ldquo ; temperatures of solid and liquid gold at the melting point have been calculated .
6 .
It been shown that the general equation the radiation of a selective radiator is of the form which in the case of and other metals cannot be reduced to the form of Wien 's equation for a full radiator with values of the constants .
The authors desire to acknowledge their reat indebtedness to Prof. .
G. Donnan , for his invaluable assistance and advice givell throughout the course of the research ; to Dr , E. K. Muspratt for a loan which permitted the of platinum wire and gold for the experiments ; and to the Government Grant Research Committee of the Society for a grant which defrayed a portion of the expenses of the research .
VOL. LXXXVII.\mdash ; A.
|
rspa_1912_0099 | 0950-1207 | Some unclassified mechanical properties of solids and liquids. | 466 | 478 | 1,912 | 87 | Proceedings of the Royal Society of London. Series A, Containing Papers of a Mathematical and Physical Character | A. Mallock, F. R. S. | article | 6.0.4 | http://dx.doi.org/10.1098/rspa.1912.0099 | en | rspa | 1,910 | 1,900 | 1,900 | 12 | 198 | 5,606 | http://corpora.clarin-d.uni-saarland.de/surprisal/6.0.3/?id=rspa_1912_0099 | 10.1098/rspa.1912.0099 | null | null | null | Fluid Dynamics | 44.172607 | Measurement | 27.402929 | Fluid Dynamics | [
49.99642562866211,
-60.655941009521484
] | ]\gt ; Some Unclassfied Properties of Solids By A. MALLOCK , F.R.S. ( Received July 23 , \mdash ; Read November 7 , 1912 .
) In ordinary physical investigations solids and liquids are treated as having density and two species of elasticity .
The limits of elasticity are also recognised as ards direct pull or thrust and shear ; and since fracture or yielding of solids under these stresses give a convenient measure of their strength for constructional purposes this subject has received much attention .
In liquids and semi-liquids the resistance to shear is as viscosity , and is taken to be directly proportional to the rate of shearing .
If the forces of surface attraction are included , the above-mentioned list contains all the qualities ( not chemical or electrical ) from which the behaviour of the materials in various circumstances is generally deduced .
In conversation and ordinary language , however , many other qualities are definitely recognised and have been distinguished by special adjectives , but their relations to the fundamental properties of the substances which exhibit them are unclassified .
A list of some of these adjectives is subjoined , and it is the purpose of the present note to suggest the relations between the qualities so denoted and the various measurable constants of the substances to which they are applicable .
List of adjectives relative to\mdash ; Solids .
Surfaces .
Liquids .
Hard . .
Hard .
Smooth .
Mobile .
Soft .
Ductile .
Soft .
Oily .
Brittle .
Malleable .
Fibrous .
Viscid .
Friable .
Plastic .
Granular .
Frothy .
In a paper on " " The Extension of Cracks in an Isotropic Substance\ldquo ; * I said that it seemed more correct to consider the limit of shear and the limit of volume extension as the fundamental limits of a material rather than the limits of shear and of tensile or crushing stress , the latter being compound stresses involving in themselves ) shear and variation of volume ; and since reference to the first-named pair of limits will be frequently made in the present note , the following amplification of the sense in which the words shear limit and volume limit are read is here inserted .
' Roy .
Soc. Proc , vol. 82 , pp. 26\mdash ; 29 .
Undassified operties of Solids and Liqu ids .
467 Suppose a material to be ma uP of a quantity of symmetrically arranged particles which react on one another by two different sets of forces , one in the direction of the normal to the lines joining them , the other in the pla1les at right angles to the nornlals and that when the material is not subject to nny external stress both forces are zero .
* Suppose also that for very small strains the displacements and forces are directly proportioned to one another , but that for greater displacements the relation in each case is some unknown function which ultimately makes the variation of stress zero for shear and also for volume dilatation , but that if the strain presses the adjacent parts into closer contact , the force between required for the purpose has no superior limit .
A mateJ'ial so constructed would have many of the properties which racterise real bodies , and without for a moment suggesting that this is the actual form which molecular , takes , the conception may be used to define the terms used in this note .
Thus by shear limit is understood the alteration of the between .
the lines joining neighbouring particles , at which the increase of sponding resistance to the displacement rapidly falls , or at which the stress becomes zero .
By volume limit , in the same way , is understood the increase of distance between adjacent particles at which the attraction either ) ains constant or vanishes .
There are really two limits to be considered both for shear and volume expansion , na1nely , the linlit at which the stress ceases to increase with the strain and the limit of lpture at which the stress ceases there .
These will be referred to as the first and second limits .
It will be seen that explanations of all the properties indicated by the list of adjectives given above can be explained by relations between ( 1 ) The absolute values of resistance to change of olume ftnd change of shape .
( 2 ) The volume limits and shear limits .
( 3 ) Forces belonging to the surfaces ( surface tension in liquids and forces of the same nature in solids ) .
Consider , for instance , the fracture of a material by tensile stress .
In fig. 1 ( which is nearly the same as that given in Thomson and Tait , ' Not .
Phil vol. 1 , Part 2 , p. 220 ) let a cube of material be subject to a tension , F. The eHect of this tension can be represented by a volume expansion such as would be caused by an outward force acting on all ertain torces aiffereIlt , of these matters offers a wide field for useful experiment .
Mr. A. Mallock .
Some [ July 23 , the the ) , together with two shears such as would be caused all inward force the faces parallel to and , and an force 2 acting on the two faces parallel to XOZ .
The volume expansion caused by is , and the linear dilatation , two Hhears together cause an extension parallel to of or , and a linear contraction of parallel to X and and the coefficients of volume expansion and shear .
If and are considered not as constants but as functions of the refcr to , the total extension will be , but the relation of the total force to the and dilating stress is always 3 : 2 itnd 3 : whatever relations and bear to the extension .
Since is very little infor } ation available on the actual values of outside the elastic limits , will assume for the present that both FI G. 1 .
constant up to the limitsc above defined , and an examination of the different effects produced according as the shear limit or volume limit is first reached will go far to explain the great variety observed in the character of the fractures of different otropic substances .
Of course , with substances which not isotropic , the variety may be even greater .
In fig. 2 let OK , ON , be the straight lines defined by and ectively , where and ?
are the forces due to the volume extension and the shear extension If the total tensional stress is / ?
and , and the extension of the material by the force is represented by the line OA , whose equation is , or , since , we have .
The construction for OA is obvious from the figure .
In the same way OB gives the lateral contraction for same tension .
1912 .
] Mechanical Properties of Solids and Liquids .
Now suppose that for volume extensions greater than , and extensions greater than , the applied force can never exceed , and can only reach this value when .
In any other case rupture will 0CCU1 either by the volume limit or shear limit being exceeded , according as is smaller or greater than If , the first } ) ture may occur in any direction with reference to the direction of the tension , but in most real cases the strain will be concentrated at some section at right angles to the direction of the pull , and will be .
intensified by the rupture of any part at that section .
The general direction of the fracture will therefore be more or less directly across the direction of pull , but will present a rough or granular appearance from the running together of the differently oriented individual ruptures .
If , on the other hand , , the rupture is due to shear , and the character of the surface of the fracture will depend on the shear extension which can occur in excess of before actual rupture takes place .
When this is very small the fracture proceeds as a spreading crack , when large it presents fibrous surface , on account of the drawing out of the parts veen many individual ruptures .
The fact that few homogeneous solids are much altered in density by any mechanical treatment shows that such volume extension as may be produced by stress is chiefly elastic , and hence in eneral complete rupture will occur when the first volume limit is reached , but , as regards the shear limits , there is often , as everyday experience shows , a very large interval between the strain at which stress and strain cease to be directly proportional and tlJe strain at which rupture takes place .
When the stress is removed from a substance which has passed the shear limit for the first time , it is generally found that , not only is some of the extension permanent , so that the diagram of stress and strain is of the character shown in fig. 3 , but that , when the stress is reapplied , the value of , measured from the new zero , is increased , thus showing that some rearrangement of has taken place which favours elastic .
The stress limit of rupture is much less affected .
When the stress is a pressure instead of a , rupture must depend entirely on the shear limit , since there is no known limit to the volume compression which a substance , whether isotropic or not , can withstall( without rupture ; nor in the case of isotropic substances does there seem Mr. A. Mallock .
Some Unclassijied [ July 23 , any reason to expect that sucl ] a linut exists .
Thus it may very well happen that a material which cannot be stretched to any great extent without rupture will yield under end pressure without loss of continuity .
In liquids and semi-liquids not only the absolute strains have to be considered , but the rate at which they are increased .
There is no experi- mental reason to believe that the volume stress and strain relation involves time , or differs , except in , from that which holds solids , but as regards shear , and in the cnse of mobile fluids , the shearing stress appears to be exactly proportioned to the rate at which the strain is applied , and the limits to large or infinite .
With thick fluids , such as oils or pitch , there are finite limits to the rate at which shear can be applied without rupture , and for viscous solids ( e.g. cold pitch ) these limits are often small .
Many actual solids also ( lead , zinc , marble , slate , etc yield in time to forces which if applied rapidly cause no permanent distortion .
After these preliminary remarks the relation suggested between the constant of the various materials and the qualities denoted by the adjectives , suggested in the orams and explanations , will be readily followed .
Hard ; Soft .
These words have different meanings when applied to the substance and to the surface of a material .
Body hardness may be measured absolutely by the ratio of the stress at the shear limit to the corresponding strain , but in practice the hardness tests only give comparative results .
One of the tests most commonly used is the size of depression made by a hard steel ball when pressed into the material by a known force .
This has the merit of simplicity , but is open to various objections , among which may be mentioned the change of curvature in the surface of the ball over the area of contact when the hardness of the latter and of the material are comparable , and also the change in the character of the deformation as the ' increases .
A better forll of test is the measurement of the depth to which a givelI force will drive a edge or conical point .
With a wedge the character of the strain is nearly , and with a cone quite , independent of the depth of penetration , and without much trouble either of these tests can be made to furnish a hardness value in absolute measure .
Penetration methods , however , are only to materials which yield without breaking , but for those which rupture before taking a permanent set there is at present no recognised hardness test .
If the materials can be worked with steel tools their hardness be deduced 1912 .
] Properties of Solids Liquids .
from the force required to take a cut of known cross section with a tool of standard form .
The rate at which , under defined conditions , removes the material also be used as a measure of hardness , but from the nature of the operation the results would only be comparative .
Resistance to volume compression , to which there is no known limit , may occasionally be confounded with hardness , as for instance when ( as I have seen happen ) a turned-up corner of a sheet of paper has left au impression on the surface of the steel rollers through which it has passed . .
Tough .
These words express qualities which are to some extent opposites , and imply that the limits to which the material can be strained are either very small or very large .
But toughness also means that the resistance to shear continues to increase , or at any rate does not diminish , after the elastic has been passed .
A substance may be brittle either because of the smallness of the volume , or of the shear limits , but there is no known instance of the volume limit being enough to confer the property of hness .
As was noticed in the paper on " " The Extension of Cracks\ldquo ; referred to ) , the behaviour of a substance during rupture differs according as the volume limit or shear limit is first reached .
A good example is furnished by a gelatine mass , which if containing much water ( a jelly , in fact ) has large shear limits , but becomes more and more rigid ( with strain and increasing stress limits ) as it dries , and , when in the condition of ordinary glue as sold in sheets , is actually brittle .
If the end of a crack in a soft jelly containing much water is examined it will be seen that it forms an angle of perhaps to , or more , but with a fairly sharp edge .
A stiffer jelly exhibits , in place of a sharp edge , a rounded end with a tendency , sometimes rather pronounced , for the opposite walls to form stringy buttresses , and as the amount of water diminishes the radius of curvature of the end of the crack diminishes .
When dryness is approacbed the character of the rupture changes rather suddenly from fig. 4 ( c ) to .
These facts may be explained by supposing that the first and second limits for shear differ independently for jellies of different water-content .
In let AB be the curve on which the first shear limits lie , from 4 ' dry\ldquo ; at A to the maximum water-content at B. A straight line through to any point on AB will represent the stress- strain relation up to the first shear limit for a jelly whose water-content is indicated by the position P. Let CD be the curve for the second shear limit ( where rupture takes place ) .
Mr. A. Mallock .
Some ssified [ July 23 , It may be assumed that the stress between the first and second limits is nearly constant , and also that , although the volume limits differ with the change of position of , the stress-strain relation for volume dilatation remains unaltered .
The character of the rupture of three jellies colresponding to FIG. 4 .
FIe .
5 .
will differ as follows : , where the jelly is nearly dry and the volumelimit stress is greater than half the ordinate of , the rupture takes place by shear , but as at the first and second shear limits are coincident there is no permanent extension and the fracture is a crack .
At , where the distance between the ) is a maximum , the rupture still takes place by shear but with considerable permanent deformation , and volume limit is probably but little greater than half the ordinate of For the appearance of the ruptured surface suggests that stress at may be less than half the ordinate of and that the rupture may be due to insufficient cohesion . .
Ductile .
A alleable material is one t$ hich will yield without lupture under blows , and ductility implies that the llaterial will , in the same way , yield to pull .
The stresses are the same in both cases except as regards the sign of the olume alteration .
Under the hammer the material undergoes shear and volume compression , and when drawn , shear and volume dilatation .
Any material , therefore , capable of taking large permanent set will be malleable , but only those materials capable of taking large permanent set at stresses less than the volume limits for dilatation will be ductile .
Plastic .
A material is plastic when , if constrained to take any shape , it retains that shape when the constraint is removed .
Thus plasticity implies the vanishing 1912 .
] Mechanical Properties of Solids crnd Liquids .
of elastic strain ether with a great or unlimited sheal-rupture .
The diagram of stress and strain for an ideal plastic material is nilar to that for a perfect fluid , except that the resistance to shear is finite instead of zero at zero velocity .
Moist clay is one of the typically plastic substa1lces , and the plastic state it appears that the resistance to deformation is not influenced by magnitude of a general volume compression .
so that it would take the work to produce the same deformation whether the vohnne compression were a pound or a ton per square inch .
SURFACE QUALITIES . .
Soft .
The hardness of a surface is the 's hardness , relatively by the facility with which the surface can be scratched .
Of any two materials the one which will produce a scratch on the surface of the other is said to be the harder , and in this a scale of hardness has been made , with diamond at one end ( hardness 10 ) and talc at the other ( hardness 1 ) .
This kind of hardness has no known relation to body hardness .
Quartz , for instance , will scratch hard steel but is easily crushed by it , thus showing that steel will bear internal stress without rnpture , and , as far as body and hardness are concerned , hard steel is the hardest substance known ( not excepting diamolld ) .
I believe , though I have not proved , surface hardness should be defined as the limiting which can be applied to a surface without causing rupture .
Every conception one can form of the molecular points to a thin layer of the surface being in a different condition from the interior , and the phenomena of surface tension prove that this is actually the case .
It is difficult to believe that the same class of forces which cause surface tension cease to operate when a fluid passes to the solid state ; it seelns more probable that they intensified by the change .
If this is the the surface limits , both for shear and volume , would differ from the same quantities in the interior , but in a way which could only be determined by a ] of the molecular structure .
Molecular relations may be easily which would either raise or lower the limits , but , in default of definite tion , the surface tension analogue affords a not improbable explanation of the differences between the 's hardness and hardn as mderstood by constructors .
The remaining qualities denoted by the adjectives in the list apply chiefly to surfaces caused by fracture .
Mr. A. Mallock .
Sonoe Unclassified [ July 23 , Fibrous ; These ma.y , of course , be due to actual fibres or grains e.g. wood or sandstone ) but in an isotropic substance the first may be caused , as before indicated , by toughness , which allows of considerable permanent extension by shear ) where rupture ultimately happens by volume extension , and the secolJd when the shear limits are very narrow and less than the volume limit .
The ranular texture thus produced may be so fine that the broken surface is smooth but with a slightly pearly look , such as is seen in some carbon steels and broken , or flint .
A brittle , non-crystalline luatelial , which raptures by shear , genelally presents facets in its fracture , not necessarily a smooth surface .
When a crack spreads with high velocity in a substance , as it does when started by a blow , for instance , the broken surface often shows what is called conchoidal fracture , may be explained by the velocity of extension of the crack ) arable with the speed of propagation of elastic waves in the matelial , for at the end of the crack there will be a periodic variation of the direction of the sheal.ing stress on the difference of the two velocities .
Where the fractured body is small enough for the waves reflected from the boundaries to again aiiect the region in the end of the crack is at the time , the conchoidal marking may be very complicated , but in large and massive blocks only a few successive aves appear .
FLUIDS AND SEIII-FLUIDS .
Substituting for the stress and strain diagram of a perfect fluid reduces itself to two straight lines coincident witil the axes of for all Yalues that is , there is infinite resistance to compression or extension and none to shear .
In evely real fluid , though , is always finite and has a definite limit , while ( the elastic resistance to shear ) is immeasurably small for such fluids as water , alcohol , ether , etc. In certain viscous liquids , however ( gelatine solutions , for instance ) , has a finite value when , so that there is some elastic reaction even at anishing velocities , and in the semi-fluids , such as pitch , this is still more marked .
for many other fluids , such as treacle and , although the viscosity is great there seems to be no indication of elasticity as regards 1912 .
] Mechanical Properties of Solids and Liquids .
The point of interest is to examine how these properties , when in conjunction with surface tension , affect the behaviour of the material which possesses them .
Mobile .
This term is applied to liquids whose kinematic viscosity is small .
The magnitude of and its limit does not affect this quality , but the ternl relates also to the appearance of the surface of the fluid where it meets a solid and would be applied only where in addition to small viscosity there was small surface tension .
Thus water and mercury would hardly be called 4 ' mobile while alcohol and ether , with their small viscosity and low surface tensiou , are typically so .
Oily .
The characteristic of oiliness\ldquo ; is considerable viscosity and low surface tension .
Viscid .
A fluid is said to be viscid if it shows a tendency to draw out into or fibres when subject to ) .
This property implies that the cohesion , which depends on the volume linlit , is ) the shear limit , and for viscid liquids the shear limit at the velocity of separation is collpared to the rees of surface tension .
In the case of semi-fluids where , with the requisite cohesion , the viscosity very great , the surface tension ceases to have much influence on the result , as is shown by the irregular cross-section of the fibres which may be from it .
Since the resistance to shear in viscous fluids increases continually the rate of shear , there is always a speed for the formation of a filament , the speed , nely , at which the force required to produce the necessary shear exceeds the shear If surface tension were absent a fibre or filament of a viscous fluid would , when the tension which produced it ceased to act , be in neutral equilibrium .
The action of surface tension , however , produces instability , because if the diameter of any portion is htly altered over a length greater than its circumference , surface is diminished , and the surface tenbion will ultirnately cause the fibre to assume that form exposes the minimum surface permitted by the tances .
In the fibres which are most familar ( e.g. , spider web , silk , glass , quartz , etc permanence of form depends on a in the constants of * Rayleigh , " " Instability of Jets 'Lond .
Math. Soc. Proc 1879 , vol. 10 , p. 413 ; or ' Collected Papers , ' vol. 1 , p. 361 .
Mr. A. Mallock .
Some Unclassifi , ed [ July 23 , the substance the process of drawing , quick enough to fix the form before the surface tension has had time to take its full effect .
In the case of silk the hardening must ) very rapid , for the cross-section of the fibres , is not even cylindrical .
Frothy .
property of forming bubbles or liquid films , possessed by many and to which the term frothy applies , depends on the relation between viscosity and surface tension , but on cohesion also , even to a greater thal } in the formation of filaments .
For if a cube be subject bo a tension normal to the four lateral faces , with the condition that no force acts on the end faces , it will be readily seen from fig. ( 6 ) that the stress can represented by two shears each , and a volume extension force of ( instead of volume extension force , and shear as in the case of tension in one Sion ) .
In the production of a film , therefore , volume limit will be reached at one-fourth of the velocity of extension which required to attain the same result in drawing a filament .
As with a filament , if surface tension is absent , a fluid lilm is in neutral equilibrium , but if present , it is a stabilising force tending to thicken any thin places and to the thicker parts , and were it possible to a portion of a fluid film and make the boundary conditions such that the fluid surfaces were nornffi to the solid at the lines of their junction , the film would be stable for any form of displacement ( short of rupture ) which could be imposed on it .
Such boundary conditions , however , cannot be fulfilled with real fluids , for unless the fluid wets the boundary the latter cannot supply the requisite tension , and when wetting takes place the curvature of the surface in the neighbourhood of the boundary causes the pressure in the fluid to be less. .
here than in the distant parts where the film is nearly flat or of nearly uniform thickness .
For this reason there is a constant drain of fluid from 1912 .
] Mechanical Prol of Solids and Liquids .
the film towards the boundaries .
Thus any real film is un stable , the time required to thin the film in way to ) point of rupture with some fluids be reckoned in hours or even in days .
It should be added that the stability .
a film ( apart from boundary conditions ) is limited by the assumption in no place is it thin that the SUl.face tension falls off In fig. OK represent the ) to cause the dilatation , and ON be the force equired to at rate .
In the production of ament / , and in the lnction of a film with linear extension surface extension ) the rate Thus by an obvious construction , when surface tension is not taken into account , OD and OC are the stress and strain for the production of a fibre and a filament respectively from the same liquid ; and if the point on OB at ) cohesion ) reaks down , and on ON the point at which the velocity makes the shear force greater than the liquid will stand ; then , according the view suggested in this paper , a viscid lluid is one for which the volume limit / ?
is at any rate not less than at the velocity of extension .
and for which also the surface tension is sltRll enough not to break up the iibl e before it has attained a considerable lengtb .
A frothy fluid on the other hand ) have ?
not less than / and to correct accidental variations of thickness while the film is extended .
In the absence therefore of surface tension it would always be possible to form either a film or a filanlent from any liquid if the velocity was sufFiciently reduced , but surface tension int account it llay happen that the production of a filament becomes impossible any velocity , from the fact that when the latter is slow enough to the tensional force Messrs. A. S. Russell and R. Rossi .
[ Sept. 26 , within the limits of the substance , the surface tension may have time to cause the filament to break from instability .
It would appear , therefore , that any liquid which can be drawn into threads can also produce films , but that the converse is not true , and this seems to agree with observed facts .
Since the explanations which I have put forward in note depend more on observation thau experiment , it is probable that an exact knowledge of the relations of and some modification necessary ; but that the separate limits of volume dilatation and shear are the groundwork of the characteristics which are denoted by the adjectives in the ] ( and many others ) is , I think , almost certain .
An Investigation of the of Ionium .
By A. S. , Carnegie Research Fellow of the Uniyersity of Glasgow , and R. ROSSI , M.Sc .
, Hon. Research Fellow of the University of fanchester .
( Communicated by Prof. E. Rutherford , F.R.S. Received September 26 , \mdash ; Read November 21 , 1912 .
) The preparation of described by Prof. Rutherford in the footnote consisted of a mixture of the oxides of ionium and thorium .
The percentage of ionium oxide in the preparation is not known .
It can be calculated , however , provided we know both the period of ionium and the number of -particles emitted by 1 .
of the substance per second .
The latter has been determined by Dr. H. Geiger , who found that 1 expelled -particles per second .
The period , however , is not known with certainty .
Soddy has found that , on certain assumptions , it is at least *The preparation of ioniun ] examined by Messrs. Russell and Rossi was separated from the actinium residues loaned to me by the Royal Society in 1907 .
A detailed statement of the methods employed in its separation has been given by Prof. B. B. Boltwood in a paper entitled " " Report on the Separation of and Actinium from certain Residues , on the Production of Helium by Ionium\ldquo ; ( ' Roy .
Soc. Proc 1911 , , vol. 85 , p. 77 ) .
The preparation consisted of pure thorium oxide , containing an unknown percentage of ionium oxide .
From measurements of the number of -particles emitted by the preparation it was concluded that it should contain at least 10 per cent. of ionium , if the period of the latter were not less than 100,000 years .
On these data itwas anticipated that the preparation should show clearly the strong spectroscopic lines of ionium as well as a complete spectrum of thorium.\mdash ; E. RUTHERFORD .
|
rspa_1912_0100 | 0950-1207 | An investigation of the spectrum of ionium. | 478 | 484 | 1,912 | 87 | Proceedings of the Royal Society of London. Series A, Containing Papers of a Mathematical and Physical Character | A. S. Russell, M. A.|R. Rossi, M. Sc.|Prof. E. Rutherford, F. R. S. | article | 6.0.4 | http://dx.doi.org/10.1098/rspa.1912.0100 | en | rspa | 1,910 | 1,900 | 1,900 | 7 | 139 | 3,100 | http://corpora.clarin-d.uni-saarland.de/surprisal/6.0.3/?id=rspa_1912_0100 | 10.1098/rspa.1912.0100 | null | null | null | Atomic Physics | 47.107751 | Chemistry 2 | 28.541979 | Atomic Physics | [
0.3945011496543884,
-78.80754852294922
] | ]\gt ; Messrs. A. S. Russell and R. Rossi .
[ Sept. 26 , within the limits of the substance , the surface tension may have time to cause the filament to break from instability .
It would appear , therefore , that any liquid which can be drawn into threads can also produce films , but that the converse is not true , and this seems to agree with observed facts .
Since the explanations which I have put forward in note depend more on observation thau experiment , it is probable that an exact knowledge of the relations of and some modification necessary ; but that the separate limits of volume dilatation and shear are the groundwork of the characteristics which are denoted by the adjectives in the ] ( and many others ) is , I think , almost certain .
An Investigation of the of Ionium .
By A. S. , Carnegie Research Fellow of the Uniyersity of Glasgow , and R. ROSSI , M.Sc .
, Hon. Research Fellow of the University of fanchester .
( Communicated by Prof. E. Rutherford , F.R.S. Received September 26 , \mdash ; Read November 21 , 1912 .
) The preparation of described by Prof. Rutherford in the footnote consisted of a mixture of the oxides of ionium and thorium .
The percentage of ionium oxide in the preparation is not known .
It can be calculated , however , provided we know both the period of ionium and the number of -particles emitted by 1 .
of the substance per second .
The latter has been determined by Dr. H. Geiger , who found that 1 expelled -particles per second .
The period , however , is not known with certainty .
Soddy has found that , on certain assumptions , it is at least *The preparation of ioniun ] examined by Messrs. Russell and Rossi was separated from the actinium residues loaned to me by the Royal Society in 1907 .
A detailed statement of the methods employed in its separation has been given by Prof. B. B. Boltwood in a paper entitled " " Report on the Separation of and Actinium from certain Residues , on the Production of Helium by Ionium\ldquo ; ( ' Roy .
Soc. Proc 1911 , , vol. 85 , p. 77 ) .
The preparation consisted of pure thorium oxide , containing an unknown percentage of ionium oxide .
From measurements of the number of -particles emitted by the preparation it was concluded that it should contain at least 10 per cent. of ionium , if the period of the latter were not less than 100,000 years .
On these data itwas anticipated that the preparation should show clearly the strong spectroscopic lines of ionium as well as a complete spectrum of thorium.\mdash ; E. RUTHERFORD .
1912 .
] An of the Spectrum of Ioniurn .
100,000 years , and this is the only experimental result that we have at present .
If be the percentage by weight of ionium present in the material , and the period of ionium in years , then and connected by the equation being the nunlber of -particles expelled by 1 .
of radium per second , and 1760 the period of radium in years .
Thus , if the period of ionium be 100,000 years , there is less than 16 per oent .
of ionium oxide in the preparation .
It is well known that ionium and thorium are chemically non-separable .
The most persistent efforts , first of Keetman , later of Aver .
Welsbach and others , have failed to separate these two elements from one another , or to alter the concentration of one of them in the least degree , the sensitiyeness of the methods of radioactivity for the slightest change of concentration .
For this reason , the conclusion is hardly to be avoided that these two elements are not merely chemically similar , chemically identical .
It is therefore highly interesting , apart altogether from the interest in the spectrum of a new body , to examine the influence of a slight difference in the atomic weights of two very sinlilar elements , on so characteristic a property of an element as its spectrum .
Before its spectrum was taken , the ioninm preparation was puriiied from any impurities it contain by the usual well-known methods of purification of thorium .
A quantity of ordinary thorium was pulified also .
The most likely } ) urities in thorium are cerium , lanthanum , and didymium .
The only probable rity in the ionium-thorium is scandium since all others should have been separated completely by the chemical methods employed by Boltwood .
The preparation was treated , however , as if every known element were present impurity .
The strongly ignited oxide was fused in a platinum crucible with potassium bisulphate , the resultant mass powdered , and dissolved in hot water .
The ionium and thorium were then precipitated as hydroxide by ) monia , and the precipitate , after being well washed , was dissolved in hydrochloric acid .
To this solution was added a strong solution of ammonium oxalate in excess , and the whole diluted to 800 , and , after standing over , filtered .
To the filtrate was added hydrochloric acid in excess , and the ionium-thorium 'Jahr .
Radioaktivitat , ' 1909 , vol. 6 , p. 269 .
'Wien Ber 1910 , vol. 119 ( iia ) , p. 1011 .
Messrs. A. S. Russell and R. Rossi .
[ Sept. 26 , oxalate fltered off .
The oxalate was converted into hydroxide , and the lattel dissolved in hydrochloric acid .
The -thorium was precipitated from ] this solution as hydr xide 1 lleans of sodium thiosulphate , this operation repeated .
The solution of the hydroxide , after the second precipitation with thiosulphate , was eated with ammonium oxalate solution , and the whole series ) , described above was gone through .
After the fourth treatment tbiosulpLate , the ionium reci i by moni and ignited .
By this sei.ies of sbes t ilihiu preparation was tained in a very ) Two amlue of thorium nitrate were purified by exactly the same ethods , used as arison body in the spectroscopic of ioninm purified was precipitated from a neutral solution hydrogen peroxide in excess .
The itate was filtered ofl in nitric acid , and the solution evaporated to yness .
The ioni -thi was then dissolved in water , and the precipitation with oxide 1epeated .
substance was brought solution us before , and the ionium-thorium precipitated from a neutral solution by ) -nitrobenzoic acid .
The flocculent precipitate was fltered off , dissolved in nitric acid , and the lepeabed .
The precipitate was then nited .
This second process of purification is simpler than the first , and ensures in the end quite as pure a preparation of ionium-thorium oxide .
The arc spectrum of pure oxide was compared with that of ionium-thorium oxide by the one above the other on the same phic plate .
The examined extended from 3800 to The arc was between poles of graphite .
A hole was bored in the lowel } ) was positive , and in it was placed from 40 to 60 mgrnl .
of the oxide .
At first , a small grating of 1 metre radius was used , but the first order of a vland concave grating , feet in radius of culvature , elnployed .
The latter gave a dispersion of gstrom units per millimetre on the raphic plate .
With the smaller ?
rating an exposule of 10 seconds was sufficient , and with the larger grating to 6 } inutes .
When the ionium preparation was burned in the arc , bulb surrounded the poles to pr.event loss of the yaluable material by spluttering .
Two comparison experiments were carried out with the smaller , and three with the rating .
In each of the five cases , however , the spectrum of the ionium and thorium was identical with thaG of pure thorium , except 1912 .
] An Investigation of thoe Spectrum of for the presence of about five of the strongest lines of scandium in the former preparation .
Careful examination with a lens reyealed no other difference .
The scandium lines were much weaker in the ionium preparation purified by the first method than in that purihed by the second , that some of the scandium had been removed by the chemical processes .
The scandium lines were quite marked in unpurified ionium oxide .
Scandium is an element detectable in very small amount , ; partially to its low atomic weight and partially to the great intensity of some of its lines .
The amount of it in the was estimated at less than three or four parts in a thousand .
Its presence in the ionium preparation absence in the pure thorium preparation can be explained easily .
Scandium , of all the rare earths , resembles thorium most strongly .
Like thorium it is precipitated by hydrofluosilicic acid in acid solution and by sodium thiosulphate .
It is readily soluble in alkali carbonates and alkali oxalates .
It is also precipitated quantitatively by meta-nitrobenzoic acid , and also to a cel.bain extent by hydrogen peroxide in neutral solution .
* In the pitchblende , from which the ionium was concentrated , some scandium must have been present , and this amount has been ] centrated with the ) and the ionium ; in monazite sand , from which the pure thorium is obtained , it is , however , absent .
As ionium was present in the mixture in amount less than could be detected spectroscopically , further experiments were carried out to determine how small a percentage of impurity could be detected with certainty in pure thorinm .
The bodies chosen for this purpose were and .
The former was selected because it is a rare earth very similar in chemical properties to thorium , and has the same type of spectrum .
As bodies of low atomic weight , in eneral , are detectable spectroscopically in smaller amount than bodies of high atomic weight , the oxide of uraninm , whose atomic weight is very similar to of ionium , was also used as an impurity .
It was found with the larger that 1 per cent. of was very easily detected , and both 2 and 1 per cent. of could be detected with certainty ; per cent. of could not be detected ; 1 per cent. of is just on the limit of detection .
It is natural to expect that the spectrum of is of the same type as the of thorium and cerium , since it is a rare earth , and also that it would be quite distinct and characteristic .
Again , a percentage of oc .
, ' 1908 , , vol. 84 , p. 82 ; R. J. Meyer , ' .
fiir VOL. LXXXVII.\mdash ; A. Messrs. A. S. Russell and R. Rossi .
[ Sept. 26 , ionium not greater than that of the used should be sufficient for its detection in the ionium-thorium preparation .
There is , however , not the slightest trace of any new lines due to ionium .
The obvious conclusion , therefore , is that ionium is present in the active preparation to the extent of not more than 1 or 2 per cent. The maximum value of the period of ionium , therefore , cannot exceed years , i.e. 12,000 years , provided radium is the only transformation product of ionium .
There is no experimental evidence which contradicls this maximum value of the period .
Soddy , * whose work on the rowth of radium from purified uranium extending over six years has contributed much to our of the period of ionium , gives 100,000 years as a minimum estimate , provided that ionium is the only member of the disintegration series between uranium X and radium .
From an entirely different set of experiments on the growth of ionium from active preparations of uranium X , the same author concludes that if uranium X is transformed directly into ionium , the period ' the latter must exceed 30,000 years . .
result is consistent with both results of Soddy , if ionium be not the only body between uranium X and radium in the disintegration series .
There must be ab least one new body preceding ionium .
This body has not yet been detected chemically .
It does not emit -rays , for all the -rays emitted by uranium and its products are already accounted for .
It is very probably rayless , or it emits soft -rays only .
Quite recently , and Nuttall have shown that there is a relation- ship between the ranges of the -ray products of the uranium-radium series , and the periods of these substances .
If the logarithms of the ranges of the -rays are plotted against those of the transformation constants , straight line joining the points is obtained .
From this line the authors , knowing the of the -ray , have deduced a period of 200,000 years for ionium .
This estimate is , of course , independent of any assumption as to whether or not ionium is the only product between uranium X and radium .
This value is nearly twenty times reater than the maximum value obtained by us .
The relation of Geiger and Nuttall is , however , merely empirical , and , as they themselves point out , it is not obeyed strictly by radium C. Ionium Summary of Results , given in lecture at Royal Institution on March 15 , 1912 , ' Nature , ' 1912 , vol. 89 , p. 203 ; also ' Phil. Mag 1910 , vol. pp. 340 and 342 .
'Phil .
Mag 1911 , vol. 22 , p. 613 ; 1912 , vol. 23 , p. 439 .
1912 .
] An Investigation of the Spectrwrn of Iomium .
also seems to be an exception .
It may , therefore , be said that , while the result of and Nuttall does not confirm our result , it does not necessarily disprove it .
There are , however , two othel possible ways of explaining our failure to obtain a distinct spectrum for ionium , besides the one discussed above .
It is possible that : ( 1 ) Ionium has no arc spectrum in the region investigated , or ( 2 ) Ionium and thorium have identical spectra in the region investigated .
The first possibility is highly improbable , for all solids of atomic weight have arc spectra , and , further , all rare earths have complicated spectra .
The second possibility , though somewhat speculative in nature , is suggested by some recent work on the chemical properties of the radio-elements .
There is no evidence at present to disprove its truth .
It is well known that there are no less than four sets of ] radio-elements , the members of each of which are chemically non-separable .
These elements do not all belong to the group of rare earths , many non-radioactive members of are to be chemically very similar .
Mesothorium , for instance , which is chemically non-separable from radium , belongs to the alkaline earth group .
Again , the two non-separable -ray products which are present in ordinary uranium , and which have been called by and Nuttall ( loc. cit. ) nranium 1 and uranium 2 , to the chrornium-molyb(Ieuum-tungsten roup ( elements .
The explanation of these striking chemical similarities is very p1obably that the two very similar bodies are really different members of the same group of eleInents , the difference in their chemical properties being less pronounced than the differences between other meml ) of the same , owing to the small difference in their atomic weights .
But the possibility that they are identical in all physical and chemical properties , and differ only in atomic weight and in radioactive properties , should not be lost of .
If this explanation should eventually prove to be justified , the spectrum of ionium would be identical with that of thorium .
The arc spectrum of a highly active preparation of ionium containing thorium has been ated .
No new lines due to ionium have been obtained .
From this result it has been deduced the period of ionitun cannot exceed 12,000 years .
This result , taken in conjunction with Soddy 's results on the period of ionium , points to the existence of at least one new comparatively long-lived body between uraniulu and ionium in the yration series .
484 of the Spectrum of Ionium .
We have to thank Prof. Rutherford very much , not only for his constant help and advice , but also for putting facilities for chemical work at our disposal , and for the loan of the very valuable preparation of ionium used in the expel.iments .
[ Note add 5 , 1912.\mdash ; After this research had been and the results communicated to the Royal Society , our attention was drawn to a paper read by Prof. F. Exner and Dr. E. Haschek before the Vienna on June 20 , and published in the ' Wiener Berichte , ' 1912 , vol. , pp. 1075-77 .
These authors have investigated the spectrum of an ionium preparation arated by .
Welsbach from pitchblende ; 1 .
of this preparation contains approximately two-thirds of the amount of ionium in our preparation .
The spectrum was investigated both in the visible and the ultra- violet region of the spectrum .
The spectrum obtained showed lines of ceritun , scandium , and yttrium , and also of five less common rare earths .
No lines , however , could be assigned to ionium .
They point out , as we have done , that the period of ionium has been very much over-estimated , and estimate that it may be even less than that of radium .
They do not discuss , however , how this result may be reconciled with the estimates of Soddy .
]
|
rspa_1912_0101 | 0950-1207 | Note on the electric capacity coefficients of spheres. | 485 | 487 | 1,912 | 87 | Proceedings of the Royal Society of London. Series A, Containing Papers of a Mathematical and Physical Character | Alexander Russell, M. A., D. Sc.|Dr. C. Chree, F. R. S. | article | 6.0.4 | http://dx.doi.org/10.1098/rspa.1912.0101 | en | rspa | 1,910 | 1,900 | 1,900 | 3 | 47 | 897 | http://corpora.clarin-d.uni-saarland.de/surprisal/6.0.3/?id=rspa_1912_0101 | 10.1098/rspa.1912.0101 | null | null | null | Tables | 47.459625 | Fluid Dynamics | 21.551193 | Tables | [
23.272018432617188,
-69.18073272705078
] | ]\gt ; Note on the Electric Capacity Coefficients of Spheres .
By ALEXANDER , D.Sc .
( Communicated by .
C. Chree , F.R.S. Received October 8 , \mdash ; Read November 21 , 1912 .
) In the ' of the Society , vol. 87 , p. 109 , Mr. Jeffery obtains a general solution of Laplace 's equation in a form suitable for physical problems in connection with two spheres .
As an illustration he applies his solution to the problem of finding the capacity coefficients of two equal spheres , a result which he shows to be equivalent to one of Maxwell 's series formulae .
He then computes a table of the numerical values of these coefficients .
Presumably , in order to lessen the labour of computation , he calculates the values corresponding to equal increments of a function ?
, which equals where is the distance the centl.es of the spheres and is the radius of either .
Even in these cases , when is small , the computation by Maxwell 's formula is laborious , and this possibly accounts for the errors in the tables given .
In practical laboratory work the values of these coefficients are sometimes required , and so I gave*a table and a number of formula to simplify their calculation .
For } , when the spheres are close ether , we can use the formula where is the self-capacity coefficient of either sphere .
If , for instance , we put , we get The value given by .
Jeffery is When From the tables given in my paper referred to above we find that when .
It will be seen that a small in the value of makes an appreciable in the alue of the capacity coefficient .
I have recomputed the first of Mr. Jeffery 's tables given on p. 119 of his paper .
The values of the ratio of the diameter of either sphere to the distance between them ( sech simply ) have not been accurately computed , 'Roy .
Soc. Proc , vol. 82 , p. 529 .
486 Note on the Electric Coefficients of Spheres .
but as these values have not been used in calculating the capacity coefficients , the errors in the latter are due to other reasons .
( p. 119 ) .
Table I.\mdash ; The Self-capacity Coefficient of either Sphere .
The remaining six values in the table are given correctly .
Mr. Jeffery also gives a table of the values of the capacity ( Maxwell 's definition ) of a sphere in the presence of an infinite conducting plane .
By utilising Kelvin 's method of images and the formula given in my paper , we find at once that when the distance between the sphere and the plane is not greater than the radius of the sphere , we have where is the capacity of the sphere , or , as it is perhaps better called , the capacity between the sphere and the pJane .
The nearer the sphere is to the plane the easier it is to find by this mula .
For example , when , we find that , the last three terms of the formula being negligible when this accuracy onIy is desired .
In the following table is the distance between the centre of the sphere and the plane .
A Note on the Absorption of -Rays .
The Capacity between a Sphere and an Infinite Plane .
2.6749 1.6679 The simple formulae used for the latter half of this table will be in the ' Journal of the Institute of Electrical Engineers , ' vol. p. 257 , and in the ' Proceedings of the Physical Society , ' vol. 23 , p. 352 .
In the ' Annalen der Physik , ' vol. 27 , p. 673 ( 1886 ) , Kirchhoff applies Clausen 's theorem to recompute some of the values given in Kelvin 's well known table ( Reprint ' On Electrostatics , ' p. 83 ) .
ote on the of -Rays .
By J. A. GRAY , M.Sc .
, 1851 Exhibition Scholar , University of Melbourne , Hon. Research Fellow , University of Manchester .
( Communicated by Prof. E. Rutherford , F.B.S. Received September 26 , \mdash ; Read November 21 , 1912 .
) It is clear , from the experiments of W. and that one of main factors in the absorption of -rays is the loss in velocity of -rays in passing through ulatter .
It follows from this that -rays of a definite speed must have what may be called a maxiulutl range , and also that an } ) onential law of absorption for -rays can only be approximate .
These facts are brought out in the experiment on the ) of radium E. Two preparations of radium were used , one relatively weak .
The weaker preparation was placed 2 cm .
below an electroscope 4 cm .
* W. Wilson , ' Roy .
Soc. Proc 1909 , , vol. 82 , p. 612 ; 1910 , , vol. 84 , Crowther , 'Proc .
Camb .
Phil. Soc 1910 , vol. 15 , p. 6 ; .
Baeyer , Hahn and Meitner , 'Phys .
Zeit Jan. , 1911 .
|
rspa_1912_0102 | 0950-1207 | A note on the absorption of \#x3B2;-rays. | 487 | 489 | 1,912 | 87 | Proceedings of the Royal Society of London. Series A, Containing Papers of a Mathematical and Physical Character | J. A. Gray, M. Sc.|Prof. E. Rutherford, F. R. S. | article | 6.0.4 | http://dx.doi.org/10.1098/rspa.1912.0102 | en | rspa | 1,910 | 1,900 | 1,900 | 3 | 55 | 1,224 | http://corpora.clarin-d.uni-saarland.de/surprisal/6.0.3/?id=rspa_1912_0102 | 10.1098/rspa.1912.0102 | null | null | null | Atomic Physics | 62.523663 | Tables | 12.317453 | Atomic Physics | [
9.429737091064453,
-78.87825012207031
] | A Note on the Absorption of / 3-Rays .
The Capacity between a Sphere and an Infinite Plane .
dp .
u. qn/ r ( p. 120 ) .
in/ r. 2 *0401 0*2 2 8994 2 -8996 2 1621 0*4 2 -2307 2 -2477 2 *3709 0*6 1 *8982 1 *8953 2 -6749 0-8 1 -6679 1 -6679 3 *0862 1 -o 1 -5093 1 *5095 3 *6213 1-2 1 -3942 1 *3942 4 *3018 1 *4 1 *3083 1 -3083 5 *1549 1 *6 L *2429 1 *2430 6*2150 1 -8 1 *1915 1 * 1927 7 *5224 2*0 1 *1434 1 -1537 12 -265 2*5 1 *0887 1 -0887 20 *135 3*0 1 -0525 1 -0523 The simple formulae used for calculating the latter half of this table will be found in the'Journal of the Institute of Electrical Engineers/ vol. 48 , p. 257 , and in the ' Proceedings of the Physical Society/ vol. 23 , p. 352 .
In the ' Annalen der Physik/ vol. 27 , p. 673 ( 1886 ) , Kirchhoff applies Clausen 's theorem to recompute some of the values given in Kelvin 's well known table ( Reprint ' On Electrostatics/ p. 83 ) .
A Note on the Absorption of / 3-Rays .
By J. A. Gray , M.Sc .
, 1851 Exhibition Scholar , University of Melbourne , Hon. Eesearch Fellow , University of Manchester .
( Communicated by Prof. E. Rutherford , F.R.S. Received September 26 , \#151 ; Read November 21 , 1912 .
) It is clear , from the experiments of W. Wilson* and others , f that one of the main factors in the absorption of / 3-rays is the loss in velocity of / 3-rays in passing through matter .
It follows from this that / 3-rays of a definite speed must have what may be called a maximum range , and also that an exponential law of absorption for / 3-rays can only be approximate .
These facts are brought out in the following experiment on the / 3-rays of radium E. Two preparations of radium ( D +E -f-F ) were used , one relatively weak .
The weaker preparation was placed 2 cm .
below an electroscope 4 cm .
* W. Wilson , ' Roy .
Soc. Proc./ 1909 , A , vol. 82 , p. 612 ; 1910 , A , vol. 84 , p 141 .
t Crowther , ' Proc. Camb .
Phil. Soc./ 1910 , vol. 15 , p. 5 ; v. Baeyer , Hahn and Meitner , 'Phys .
Zeit .
, J Jan. , 1911 .
A Note on the Absorption of / 3-Rays .
cube , and absorbing sheets of paper were placed directly below the electroscope , the mass per unit area of one sheet being 0*00877 grm. The readings obtained , corrected for 7-rays , are given in Table I:\#151 ; Table I. Absorber .
Divisions per minute .
Percentage of / 3-rays transmitted by 5 sheets .
33 1 sheet 27*4 \#151 ; 6 sheets 13 *67 50 11 " 7*07 51 16 " 3*68 52 21 " 1 *83 50 26 " 0*87 47 *5 31 " 0*36 42 The numbers are accurate enough to show that the exponential law for paper is at the best only approximate , and that after passing through 21 sheets the rays are becoming more and more absorbable .
Similar experiments were made with the stronger preparation .
This was placed 6 cm .
below the electroscope and 31 sheets of paper were placed directly above it .
The / 3-rays coming through this amount of paper were examined as before , and readings , corrected for 7-rays , are given in Table II .
Table II .
Absorber .
Divisions per minute .
Percentage of jS-rays transmitted by 5 sheets .
31 sheets 14 *2 36 " 5 5 38 41 " 1 *8 32 46 " 0*43 24 51 " 0-05 10 56 " \#151 ; \#151 ; It will be seen that the readings confirm and extend those of Table I. The / 3-rays become more and more absorbable , so that practically none of them pass through 56 sheets of paper .
These results have been confirmed by placing the stronger preparation of radium D 12 cm .
below an electroscope and deflecting the / 3-rays away by a magnetic field , thus allowing directly for the effect of 7-rays .
A rough explanation of the results obtained may be given as follows :\#151 ; A true exponential law of absorption would mean that the distribution of the / 3-rays with respect to velocity would be unaltered as the / 3-rays passed The Similarity in Nature of X- and Primary y-Rays .
489 through matter , always assuming that the / 3-rays had passed through enough matter to nullify the effects of scattering .
If we assume such a distribution and from it plot the number of / 3-rays against the velocity , there will be a certain velocity for which the number of / 3-rays is a maximum .
We will call this velocity the mean velocity , the / 3-rays with a smaller velocity the slower / 3-rays , and those with a greater velocity the faster / 3-rays .
The exponential law would probably mean that the very slowest / 3-rays were absorbed , while the faster / 3-rays simply lost energy , * the distribution keeping the same .
This hypothetical distribution , however , cannot be kept indefinitely , as the faster / 3-rays must ultimately have a smaller velocity than the mean velocity , and so , as we have seen above , the exponential law can only be approximate , and after a certain thickness the / 3-rays must become more and more absorbable .
Similar results to those obtained above can be deduced from a table given in a paper by H. W. Schmidt* on the absorption ( in aluminium ) of the / 3-rays of radium E. The Similarity in Nature of X- and Primary y-Rays A By J. A. Gray , M.Sc .
, 1851 Exhibition Scholar , University of Melbourne , Hon. Research Fellow , University of Manchester .
( Communicated by Prof. E. Rutherford , F.R.S. Received September 26 , \#151 ; Read November 21 , 1912 .
) Introduction .
It has generally been supposed that X- and primary 7-rays are of the same nature .
Both radiations are not deflected by electric and magnetic fields , and both excite cathode or / 3-rays in materials in which they are being absorbed , the velocities of these cathode or / 3-rays being independent of the material in * Schmidt , " Phys. Zeit .
, ' 1907 , vol. 8 , p. 362 .
t The term X-rays is arbitrarily limited to the X-rays excited by cathode rays in vacuum tubes or to the scattered and characteristic radiations formed from these X-rays in suitable radiators .
The most penetrating X-rays so far experimented on are a little more penetrating than the X-rays characteristic of cerium .
We keep the term y-rays for y-rays excited by / 3-rays .
Primary y-rays are y-rays emitted from radioactive atoms .
i
|
rspa_1912_0103 | 0950-1207 | The similarity in nature of X- and primary \#x3B3;-rays. | 489 | 501 | 1,912 | 87 | Proceedings of the Royal Society of London. Series A, Containing Papers of a Mathematical and Physical Character | J. A. Gray, M. Sc.|Prof. E. Rutherford, F. R. S. | article | 6.0.4 | http://dx.doi.org/10.1098/rspa.1912.0103 | en | rspa | 1,910 | 1,900 | 1,900 | 11 | 238 | 5,438 | http://corpora.clarin-d.uni-saarland.de/surprisal/6.0.3/?id=rspa_1912_0103 | 10.1098/rspa.1912.0103 | null | null | null | Atomic Physics | 78.655427 | Tables | 7.858759 | Atomic Physics | [
9.315572738647461,
-78.58505249023438
] | The Similarity in Nature of X- and Primary y-Rays .
489 through matter , always assuming that the / 3-rays had passed through enough matter to nullify the effects of scattering .
If we assume such a distribution and from it plot the number of / 3-rays against the velocity , there will be a certain velocity for which the number of / 3-rays is a maximum .
We will call this velocity the mean velocity , the / 3-rays with a smaller velocity the slower / 3-rays , and those with a greater velocity the faster / 9-rays .
The exponential law would probably mean that the very slowest / 3-rays were absorbed , while the faster / 3-rays simply lost energy , ' the distribution keeping the same .
This hypothetical distribution , however , cannot be kept indefinitely , as the faster / 3-rays must ultimately have a smaller velocity than the mean velocity , and so , as we have seen above , the exponential law can only be approximate , and after a certain thickness the / 3-rays must become more and more absorbable .
Similar results to those obtained above can be deduced from a table given in a paper by H. W. Schmidt* on the absorption ( in aluminium ) of the / 3-rays of radium E. The Similarity in Nature of X- and Primary .f By J. A. Gray , M.Sc .
, 1851 Exhibition Scholar , University of Melbourne , Hon. Research Fellow , University of Manchester .
( Communicated by Prof. E. Rutherford , F.R.S. Received September 26 , \#151 ; Read November 21 , 1912 .
) Introduction .
It has generally been supposed that X- and primary 7-rays are of the same nature .
Both radiations are not deflected by electric and magnetic fields , and both excite cathode or / 3-rays in materials in which they are being absorbed , the velocities of these cathode or / 3-rays being independent of the material in * Schmidt , 'Phys .
Zeit .
, ' 1907 , vol. 8 , p. 362 .
t The term X-rays is arbitrarily limited to the X-rays excited by cathode rays in vacuum tubes or to the scattered and characteristic radiations formed from these X-rays in suitable radiators .
The most penetrating X-rays so far experimented on are a little more penetrating than the X-rays characteristic of cerium .
We keep the term y-rays for y-rays excited by / 3-rays .
Primary y-rays are y-rays emitted from radioactive atoms .
[ Sept. 26 , 490 Mr. J. A. Gray .
The Similarity in which they are excited , and increasing with the penetrating power* of the X- and 7-rays.f These mutual properties , combined with the facts that / 3-rays can excite y-rays , !
and that primary 7-rays are emitted by / 3-ray products , leave little doubt of the identity in nature of X- and primary 7-rays , although penetrating 7-rays , like those of radium , possess many properties apparently different from those of X-rays .
Further and practically conclusive proof , however , of the similarity in nature of X and 7-rays has been found by the writer in the course of some experiments on two types of very " soft " 7-radiation , viz. , the primary 7-rays of radium E , and the 7-rays excited by the / 8-rays of radium E in lead .
The experiments show , for example , that the " softer " the 7-rays , the more nearly do their properties , with respect to absorption and scattering , approach those of X-rays .
Further , the primary 7-rays of radium E excite the characteristic X-radiations of silver , tin , and other metals .
A description of these experiments is given below , together with a comparison of some properties of X- and 7-rays .
It is convenient to divide the description into the following sections :\#151 ; S 1 .
Absorption of y-rays\#151 ; ( a ) Primary y-rays of radium E. ( b ) y-rays excited in lead by the ( 3-rays of radium E. ( c ) Comparison with X-rays .
S 2 .
Scattering of the primary y-rays of radium E and the excitation of characteristic radiations by them .
S 3 .
Comparison of the scattering of X- and y-rays .
S 1 .
Absorption of 7 ( a ) Primary y-Rays of Radium E.\#151 ; It has been shown in previous papersS that less radiation is excited in carbon by the / 3-rays of radium E than in radiators of higher atomic weight , and consequently it is convenient to cut off the / 3-rays of radium E by graphite when the properties of primary 7-rays are under examination .
In these circumstances , the 7-rays coming - through the graphite consist mainly of primary 7-rays , as the following ; experiment shows ( see fig. 1):\#151 ; The active material A was placed 5 cm .
below the electroscope E , and a * * * S * Unless otherwise stated , penetrating power refers to penetrating power in .
aluminium .
t Bragg and Madsen , 'Phil .
Mag. , ' 1908 , vol. 16 , p. 918 ; Sadler , 'Phil .
Mag. , ' 1910 , vol. 22 , p. 447 .
\ Gray , 'Boy .
Soc. Proc. , ' 1911 , A , vol. 85 , p. 131 ; 1912 , A , vol. 86 , p. 513 .
S Gray , toe .
cit. 1912 .
] Nature of X- and Primary graphite plate 3*2 mm. thick placed above it .
The electroscope was a cube of 18 cm .
length , and the bottom of it was formed by cardboard 2'5 mm. thick , covered with aluminium foil .
This thickness of cardboard is sufficient to cut off / 3-rays excited by 7-rays in the absorbing sheets , and , together with the graphite , is sufficient to cut off the / 3-rays of radium E. Readings were taken with and without a lead radiator under the active material .
Absorbing sheets could be placed above the graphite plate .
Readings in divisions per minute are given in Table I. From previous work , we know that the increase is mainly due to 7-rays excited in the lead radiator by / 3-rays .
Without the radiator , the reading is due to primary 7-rays and 7-rays excited by the The latter part is small in amount compared with the intensity of the y-rays from the lead .
The table therefore shows that , with no radiator under the active material , most of the 7-rays coming through the graphite are primary 7-rays .
Table I. Absorber .
* Divisions per minute .
i No radiator .
Lead radiator . !
Increase due to radiator .
Graphite 3 *2 mm. thick 38 -5 46 -5 8-00 Graphite + lead 0 '132 mm. thick ... ... 2 -75 6-05 3 -30 Graphite + lead 0 *264 mm. thick 1 -15 3-16 2*11 Fig. 1 .
/ 3-rays in the graphite .
To measure the absorption of these 7-rays , the active material was kept in the same place , and absorbing materials were placed directly above the graphite plate , the reading through the latter being taken as the initial reading .
Carbon , aluminium , iron , tin , and lead were used as absorbing materials .
In the curves ( figs 2a , 2b ) the intensity of the 7-radiation ( measured by ionisation ) is plotted against the mass per unit area of the absorbing sheet .
Mr. J. A. Gray .
The Similarity in [ Sept. 26 , MASS OF ABSORBER IN GRAMMES PER 0-30 0-20 0-10 MASS OF ABSORBER IN GRAMMES PER CM Aii analysis of the curves gives the following results:\#151 ; ( 1 ) There is a very soft type of 7-rays present .
Aluminium 0*5 mm. thick cuts the whole radiation down to 40 per cent. , whereas it takes a sheet of aluminium 6 mm. thick to cut the radiation passing through 0'5 mm. of aluminium down to 40 per cent. ( cf. Table I ) .
The average mass absorption 1912 .
] Nature ofX- and Primary coefficient in the first ^ mm. of aluminium is approximately 8*3 and as the radiation coming through this thickness of aluminium is so much more penetrating , a considerable portion ( about half ) of the total radiation must consist of rays which , in aluminium , have a mass absorption coefficient much less than 8*3 .
Barkla and Sadler* have found that the X-rays characteristic of molybdenum have a mass absorption coefficient 4*8 in aluminium .
The X-rays characteristic of cerium have a mass absorption coefficient in aluminium = 06 .
It is , therefore , apparent that in the 7-rays we are examining there are present some 7-rays much less penetrating than some types of X-radiations .
It is not improbable that these very soft rays come from radium D. ( 2 ) After passing through 2 cm .
of carbon , after the soft radiation referred to above has been cut out , the rays are absorbed very nearly exponentially by carbon , the mass absorption coefficient being = 0116 approximate .
( 3 ) Lead absorbs the more penetrating part of the radiation 28 times as much as aluminium and four times as much as iron .
Otherwise , these substances absorb and " harden " the rays similarly .
This has been shown by testing the radiation coming through different thicknesses of aluminium , iron or lead by an aluminium screen .
Between 0*0462 and 0*0924 mm. of lead , the absorption is approximately exponential , the mass absorption coefficient being 11*2 .
After traversing 0*132 mm. of lead , the mass absorption coefficient is approximately 8 , and after 0*264 mm. 5 .
( 4 ) Tin absorbs the radiation abnormally .
With only the cardboard above the absorbing sheets , tin lets through , apparently , more radiation than lead ( see fig. 2b ) , but the radiation coming through the tin is less penetrating , so that when 3*3 mm. of aluminium is placed above the absorbing sheets , there is a smaller reading with tin absorbers .
Normally tin absorbs less radiation than lead .
It will be seen later that the primary 7-rays of radium E excite the characteristic radiation of tin .
This explains the abnormal absorption of tin and the smaller penetrating power of the radiation coming through the tin .
( b ) Absorption of the 7 -Raysexcited by the / 3-Pays of Radium E in Lead.\#151 ; For these experiments the active material was placed between two lead sheets ( 0*1 mm. thick ) and then on the same position as before , the graphite plate , 3*2 mm. thick , being placed above the upper lead sheet .
The absorption experiments were carried out as before except that 2 mm. of graphite were placed above the absorbing sheets to be sure of cutting off all the / 8-rays from them .
* Barkla and Sadler , 'Phil .
Mag. , ' 1909 , vol. 17 , p. 739 .
Mr. J. A. Gray .
The Similarity in [ Sept. 26 , The initial reading was 15 divisions per minute and the previous results ( fig. 2b ) show that primary 7-rays can only form about 20 per cent , of this .
The same absorbing materials were used as before , and in fig. 3 the intensity of the radiation is plotted against the mass per unit area of absorbing material .
The rays are much more penetrating than the primary 7-rays .
MASS OF ABSORBER IN GRAMMES PER CM2 ^Compared with the results of the previous experiments , carbon absorbs more , relatively , than the other absorbing materials , aluminium more than iron , tin , and lead , but iron and tin less than lead .
Carbon absorbs the radiation very nearly exponentially , the mass absorption coefficient being 0- 074 approximately .
Other substances " harden " the radiation .
The initial mass absorption coefficient of the radiation in lead is 3*7 ; at 0*2012 mm. , 1- 88 ; and at 0*67 mm. , 1*1 .
Some of the rays are still more penetrating and about 1 per cent , of the radiation passes through 1 cm .
of lead .
The radiation coming through lead has been examined by an aluminium screen in order to compare the relative penetrating powers of the radiation in aluminium and lead .
Tin absorbs decidedly less than lead and the radiation coming through small thicknesses of tin is just as penetrating as that coming through lead .
For example , a sheet of tin of mass per unit , area 0*311 grm. reduces the reading to 6*95 , lead of mass per unit area 0*300 grm. to 6*39 .
12*15 mm. of aluminium reduce the respective readings to 5*21 and 4*59 .
( c ) Comparison ivith X-Rays.\#151 ; In the table below , values are given of the mass absorption coefficient of different types of X- and 7-radiation in Nature ofX- and Primary y-Rays .
1912 .
] different materials .
The values for the 7-rays from radium E are taken from the present work ; those for X-rays from a paper by Barkla and Sadler* and those for the 7-rays of actinium and radium from a paper by Kussell.f Table II .
Type of radiation .
Mass absorption coefficient .
Carbon .
Aluminium .
Iron .
Tin .
Gold .
Lead .
r | Fe X-rays t 10*1 88 -5 66 -1 472 -0 367 0 Se X-rays 2-.04 18 -9 116 *3 112 -0 100-0 \#151 ; Ag X-rays 0-41 2*5 17 -4 13 -3 61 -4 \#151 ; I Ce X-raysJ 0 '248 0-6 \#151 ; \#151 ; \#151 ; \#151 ; j Primary 7-rays of radium E 0-116 0-4 2 -8 11*2 \#151 ; 11 -2 7-rays excited in lead by 0 -074 0-135 0-64 3 T \#151 ; 3-7 \#163 ; -rays of radium E 0-115 1 -88 0-098 0-7 7-Bays of actinium \#151 ; 0-084 \#151 ; \#151 ; \#151 ; 0-37 to 0-16 7-Rays of radium \#151 ; 0-04 0-04 \#151 ; \#151 ; 0-044 ; 1 It is desirable here to draw attention to the fact that the writer has measured the absorption of 7-rays somewhat differently to Barkla and Sadler .
Barkla and Sadler measure absorption by the diminution in intensity of a parallel beam of X-rays , allowing for scattering and the production of characteristic radiations .
In these experiments we have not used a parallel beam and cannot allow for all scattered radiation .
The effect of not using a parallel beam is to obtain too large a value for the absorption coefficient .
Compared with Barkla and Sadler 's values , the effect of the scattered radiation is to decrease the absorption coefficient , but this matters little when the scattering is small compared with the absorption , as the following considerations show .
Suppose a parallel beam of X-rays passes normally through a plate in which its absorption coefficient is n , and that its intensity at a depth x of the plate is I. Then , if the intensity of the emergent scattered radiation from a layer of thickness is aldx , and we measure emergent scattered radiation as well as the initially parallel radiation in taking an absorption curve , the apparent absorption coefficient will be approximately / x \#151 ; a. * Barkla and Sadler , loc. cit. t Russell , ' Jahr .
der Rad. , ' vol. 9 , Part 3 , p. 440 .
J Barkla and Collier , 'Phil .
Mag. , ' 1912 , vol. 23 , p. 987 .
496 Mr. J. A. Gray .
The Similarity in [ Sept. 26 , In the case of the primary 7-rays of radium E , the scattering is small compared with the absorption except in the case of absorption in carbon ( see p. 500 ) .
In the case of absorption in other substances , the values given for the absorption coefficient are probably too high , owing to the fact that we have not used a parallel beam of rays .
It will be seen from the table that the 7-rays of radium E are absorbed somewhat similarly to Ag X-rays , iron absorbing the latter seven times as much as aluminium , and gold nearly twenty-five times as much .
On the other hand , tin absorbs the primary 7-rays of radium E 28 times as much as aluminium , but Ag X-rays only 5'32 times as much .
This again shows the abnormal absorption by tin in the former case .
The table also shows that the less penetrating 7-rays excited by the / 3-rays of radium E in lead are absorbed similarly to the primary 7-rays of radium E , while the more penetrating 7-rays are absorbed similarly to the 7-rays of actinium .
The absorption experiments show , therefore , that there is no discontinuity , with respect to absorption , between X and 7-rays .
The reason that the rays we have examined are absorbed exponentially by carbon , while hardened by other substances , is due to the fact that for large changes in penetrating power of the rays in these substances there are only small changes in penetrating power in carbon .
Comparing the 7-rays excited by the / 3-rays of radium E in lead with the 7-rays of actinium and radium , it will be seen that absorption increases with the atomic wreight , the less penetrating the radiation .
This gives the main explanation of the " hardening " of the 7-rays of radium by elements of high atomic weight .
S S 2 .
Scattering of the Primary y-Rays of Radium E and Excitation of Characteristic Radiations by them .
In a previous paper attention was drawn to an effect observed when the primary 7-rays of radium E fell on radiators of low7 atomic weight ( see fig. 4 ) .
It was found that radiators E of low atomic weight produced a marked increase in the reading when placed just below the active material A , which was surrounded by graphite thick enough to cut off the / 3-rays of radium E. For example , a " thick " carbon radiator increased the reading 25 per cent. , a " thick " sulphur 5 per cent. , whereas iron and lead radiators increased the reading less than 1 per cent. It was thought at the time that the radiation from the carbon was too large in amount to be due to scattering , but that it might be due to the excitation of a characteristic radiation .
This , however , is not the case , as further experiments showed that the effect was due to scattering .
On the Nature of X- and Primary 1912 .
] other hand , it has been found that the primary 7-rays excite the characteristic radiations of silver , tin , and other metals .
In these experiments the active material was placed in the same position as in the previous absorption experiments , and a measure of the absorption in aluminium of the radiations returned from the different radiators used was found by placing aluminium above the active material , and taking-readings with and without the radiators .
Readings in divisions per minute of the electroscope are given below in Table HI .
The mass per unit area of the absorbing materials is given in the table .
It will be seen from the table that the radiation returned by the carbon is at first more penetrating than the exciting radiation .
This is due to the presence in the latter of the soft 7-radiation referred to above .
After this soft 7-radiation has been cut out , the radiation returned by the carbon is somewhat less penetrating .
The radiation returned by an iron radiator is much smaller in amount .
This is due to the fact that iron absorbs the radiation more than carbon .
Fig. 4 .
Table III .
Reading .
Increase in reading due to radiator .
Absorber .
) ' No radiator .
0 .
S. Fe .
Ag .
Sn .
Ra .
Ce .
Di .
Er .
Pb .
aphite 0 *537 grm 43-0 4-5 aphite + wood 0 *88 grm 17 -2 3 -22 \#151 ; 0*1 0-62 1 -o 1 -25 1 -32 \#151 ; \#151 ; 0*05 aphite + wood + A10 *132 grm. 12 -6 2 -9 0*62 \#151 ; 0-4 0-81 1 -15 1 -25 1 2 0*05 \#151 ; aphite + wood + A10 *595 grm. 9-03 2-15 0*4 \#151 ; o-i 0-4 0-78 0-9 \#151 ; \#151 ; \#151 ; 1 *48 grm 6*54 1 *41 \#151 ; \#151 ; \#151 ; o-i 0-35 0-47 0-5 \#151 ; \#151 ; 3 *24 grm 3 5 0-7 \#151 ; \#151 ; \#151 ; \#151 ; o-i \#151 ; j Tor let us suppose that a beam of X- or 7-radiation enters a plate in which its absorption coefficient is jjl .
Let Io be its initial intensity , I the intensity at depth x of the plate , and let a fraction scattered back on its path , and assume the scattered radiation to have the same absorption coefficient / x. Then at depth x of the plate the intensity of the radiation will be loe-^ .
Of this the fraction scattered back by a layer of thickness dx is pI0e-M dx .
The total amount of radiation returned from a plate of infinite thickness will therefore be approximately f pi oe-^dx = ; Jo \#163 ; ft VOL. LXXXVII.\#151 ; A. 498 .
Mr. J. A. Gray .
Similarity in [ Sept. 26 , or , if P is the fraction returned or " reflected " by a " thick " plate , P == i ?
/2ya , so that if the scattering per unit mass is the same for all substances P should vary inversely as the mass absorption coefficient .
Taking P for carbon as 024 and using the relative values of given in Table II , we find the following values of P for other substances ; iron , 0 01 ; tin and lead , 0,0025 .
Except in the case of tin , these numbers agree as well as can be expected with the numbers found , and we can explain the results by assuming that the radiators scatter the same amount of radiation per unit mass .
The radiations returned from silver , tin , etc. , are so much greater in intensity that the obvious assumption to make is that these radiations are those characteristic of the radiator .
The radiations are less penetrating , the lower the atomic weight of the radiator , and less penetrating than the scattered radiation from the carbon .
The table gives a measure of the penetrating power of the radiations , but from the way they have been obtained the numbers cannot be regarded as accurate enough to give the true absorption coefficients of the respective characteristic radiations .
For comparison with the known absorption coefficients , numbers have been calculated ( Table IY ) by using these absorption coefficients and the initial values of the radiation returned from the different radiators ( .
1*32 for cerium ) and then calculating the intensity of the radiation which should come through the different aluminium screens .
Table IY .
Absorber .
Silver .
Tin .
Barium .
; Cerium .
0-62 1 -o 1 *25 1 -32 A1 0 -132 grm 0-45 0-8 1 -12 1 -22 0 -595 " 0-14 0-39 0*77 0-92 1 *480 " \#151 ; 0-1 0-38 0-54 3 -240 " \#151 ; \#151 ; \#151 ; 0*19 A comparison of the numbers in Tables III and IY shows that the radiations returned from the different radiators differ but little in penetrating power from the characteristic radiations of the different radiators , and from the large amount of radiation returned it is concluded that such radiation consists mainly of the radiation characteristic of the radiator .
We have previously seen that tin absorbs the primary 7-rays of radium E abnormally .
The didymium and erbium radiators were tried some Nature of X- and Primary y-Rays .
1912 .
] time after the other radiators .
The erbium radiator behaved very much like lead , but the result from didymium shows that the characteristic radiations of both praseodymium and neodymium are excited , for praseodymium forms about one-third of the mixture , and if only its characteristic radiation was excited , the intensity of the radiation returned from didymium would only be about one-third of that returned from cerium .
These experiments , by showing that the primary 7-rays of radium E excite the characteristic radiations of various elements , give perhaps the most definite proof possible that these 7-rays are of the same nature as X-rays .
We have also seen that there are no differences to be noted in the absorption of X- and 7-rays other than those due to differences in penetrating power .
It is therefore concluded that , whatever their origin , 7-rays are of the same nature as X-rays .
It is to be expected that the 7-rays excited in lead by the / 3-rays of radium E will excite the characteristic radiations of some elements of higher atomic weight than neodymium .
So far no experiments have been made to test this point , but it is worthy of notice that , compared with iron , lead absorbs the 7-rays excited in lead by the ,3-rays of radium E more than the primary 7-rays of radium E. Further the radiation ( 7-rays excited by / 3-rays ) coming through lead absorbers appears to be somewhat less penetrating than the radiation through tin absorbers .
There is some slight evidence that the characteristic radiation of lead is being excited .
S 3 .
Comparison of the Scattering of X- and ( a ) Experiments on X-rays show that it is probable that there are two or more ways in which X-rays can be scattered .
For ' example , Crowther* has examined the distribution of scattered X-radiation from a paper radiator , and divides the scattered radiation into\#151 ; ( 1 ) The true scattered radiation , the distribution of which is given by the pulse theory .
( This distribution is given by the expression Ifl=I"/ a ( 1 + cos2 6 ) , where 6 is the angle the direction of the scattered radiation makes with the direction of the primary radiation .
The most significant feature is that the intensity of the scattered radiation is less at an angle of 90 ' from the primary radiation than in any other direction .
) ( 2 ) The excess radiation , which appears only in directions close to that of the exciting beam .
In a later paper , Crowtherf considers that the excess radiation he is * Crowther , ' Roy .
Soc. Proc. , ' 1912 , A , vol. 86 , p. 478 .
t Crowther , ' Camb .
Phil. Soc. Proc. , ' 1912 , vol. 16 , Part 6 , p. 534 .
2 m 2 Mr. J. A. Gray .
Similarity in [ Sept. 26 , examining might be due to the excitation of X-rays by cathode rays , formed by the absorption of the primary X-rays .
Scattered X- or 7-rays must be partly formed in this way .
On the other hand the scattering of penetrating 7-rays like those of radium is similar to the scattering of a pencil of \#171 ; - or / 3-rays.* It is too large an amount to be due to the excitation of 7-rays by / 3-rays and is probably due to collisions with the atoms of the radiator .
We may therefore conveniently divide scattered X- or 7-radiation into three types : ( 1 ) A scattered radiation , the distribution of which is given by the ordinary pulse theory .
( 2 ) A scattered radiation , caused by a direct scattering of the X- or 7-rays , analogous to the scattering of a pencil of a- or / 3-rays .
( 3 ) X- or 7-rays formed by cathode or / 9-rays excited in the radiator during the absorption of X- and 7-rays .
With X-rays , the first and third types may be more prominent .
With the 7-rays of radium the second type is most prominent .
( b ) Prof. Barklaf has found that the lighter elements scatter X-rays differing widely in penetrating power to the same extent , mass for mass , the scattering referring to the first type noted above .
A parallel beam of X-rays , in passing through a layer dx of absorbing material , is assumed to lose a fraction S dx by scattering .
Barlda found that S/ p = 0200 ( p = density ) for all types of radiation examined .
If we introduce a coefficient , Si/ p , referring to the radiations scattered in directions between 90 ' and 270 ' from that of the primary beam , Si/ p cannot be greater than the absorption coefficient , however we measure it .
Por X-rays Si/ p = 0100 .
It is therefore obvious that Barkla 's law must break down .
In the case of the 7-rays of radium , Si/ p is very small .
For the primary 7-rays of radium E , Si/ p for carbon = 0-24 x 2 x 0116 = 056 approximately , for ? !
= ^ P ( see p. 497 ) .
P P This value is of the same order as that obtained for X-rays and shows that the scattering of the primary 7-rays of radium E is similar in magnitude and probably similar in character to the scattering of X-rays .
( c ) Iron and lead do not apparently scatter the primary 7-rays of radium E more per unit mass than carbon .
Scattering of X-rays increases * Madsen , ' Phil. Mag. , ' 1909 , vol. 17 , p. 423 ; Florance , ' Phil. Mag. , ' 1910 , vol. 20 , p. 921 .
t Barkla , ' Phil. Mag. , ' 1903 , vol. 5 , p. 685 ; 1904 , vol. 7 , p. 543 ; 1906 , vol. 11 , p. 812 1911 , vol. 21 , p. 648 .
Nature of X- and Primary y-Pays .
1912 .
] with the atomic weight , Crowther* finding that tin scatters a certain radiation five times as much as carbon .
On the other hand Floranee ( , loc. cit. ) has found that carbon scatters the 7-rays of radium just as efficiently as iron or lead .
Summary .
A description has been given above of some experiments on two types of soft 7-rays and the results of these experiments may be summarised as follows :\#151 ; 1.Absorption experiments show that there is no fundamental difference in the absorption of X- and 7-rays .
2 .
The primary 7-rays of radium E excite the characteristic radiations ( series K ) of silver , tin , barium , cerium , praseodymium , and neodymium , and this result with the first proves the similarity in nature of X- and 7-rays .
3 .
The scattering of the primary 7-rays of radium E is probably similar in character and magnitude to that of ordinary X-rays .
In conclusion the writer has much pleasure in expressing his best thanks to Prof. Rutherford for his very kind interest in this research and for the continued loan of a very active preparation of radium ( D + E -f E ) .
* Crowther , ' Camb .
Phil. Soc. Proc. , ' 1912 , vol. 16 , Part 4 , p. 365 .
|
rspa_1912_0104 | 0950-1207 | The elastic hysteresis of steel. | 502 | 511 | 1,912 | 87 | Proceedings of the Royal Society of London. Series A, Containing Papers of a Mathematical and Physical Character | Bertram Hopkinson, F. R. S.|G. Trevor Williams | article | 6.0.4 | http://dx.doi.org/10.1098/rspa.1912.0104 | en | rspa | 1,910 | 1,900 | 1,900 | 11 | 146 | 4,166 | http://corpora.clarin-d.uni-saarland.de/surprisal/6.0.3/?id=rspa_1912_0104 | 10.1098/rspa.1912.0104 | null | null | null | Measurement | 56.554612 | Electricity | 17.059938 | Measurement | [
47.2880973815918,
-61.68334197998047
] | 502 The Elastic Hysteresis of Steel .
By Bertram Hopkinson , F.R.S. , and G. Trevor Williams .
( Received October 16 , \#151 ; Read November 21 , 1912 .
) In a recent communication to the Society* one of us described a machine whereby a bar of steel 4 inches long by \ inch diameter can be submitted to direct alternating stress at the rate of 120 cycles per second or more .
The machine is worked by the pull of an electromagnet excited by alternating current , the pull being magnified from 20 to 60 times by resonance between its period and that of a weight attached to one end of the piece , which behaves as a spring .
The stress varies between equal limits of tension and compression , and may be of any desired range up to 30 tons per square inch or more .
The piece is fitted with an optical extensometer by which the extreme change of length of the piece in a cycle can be observed while the machine is in action and the range of stress calculated .
An independent measure of the stress can be obtained by observation with a microscope of the movement of the weight attached to the end of the piece , whose acceleration is the chief element determining the tension or compression .
Full details of these measurements are given in the paper referred to , and it will suffice to state here that similar precautions to secure accuracy in the measurements of stress were taken in the course of the work to be described , and that from the agreement between the different methods it may be taken as certain that these measurements are correct to about half a ton per square inch .
The present paper contains an account of experiments which we have made with the alternating stress machine with the object of measuring the energy dissipated by elastic hysteresis when steel undergoes cyclical variations of stress within the elastic limit .
The method used is to measure the fall of temperature between the centre and ends of the test piece when it is undergoing continuous alternating stress through a constant range .
The fall of temperature is proportional to the rate at which heat is being generated and conducted away , and the absolute rate of dissipation in ergs per cubic centimetre can readily be obtained by passing an electric current along the specimen when at rest , and finding the relation between the temperature and the energy dissipated by resistance .
The steel used was the same material as in the previous experiments on fatigue .
It contains about 048 per cent , carbon and 0'7 manganese , and it breaks under a load of about 29 5 tons per square inch ( 46'5 kgrm .
per * 'Boy .
Soc. Proc. , ' 1912 , A , vol. 86 , p. 131 .
The Elastic Hysteresis of Steel .
square millimetre ) with an elongation of 16 per cent , ( on 8 inches ) .
According to the fatigue test made by Dr. Stanton at the National Physical Laboratory , the limiting range of stress is about 25 tons per square inch ( say , 40 kgrm .
per square millimetre ) .
At the much higher speed of reversal reached in our machine the resistance to alternating stress is considerably greater , and more than one piece has remained unbroken after ten million cycles or more between the limits of 14|- tons tension and 14f tons compression , giving a total range of 29 tons .
The test-piece is shown in fig. 1 .
A detailed drawing of the extenso- X ' 8S r WATT-METER .
P THERMO - COUP WIRE I * | $ $ \gt ; S M i I LL FIG. I. THERMO - COUPLE h/ /RE THERMO-COUPLE h/ /RE hTATT-METER PRESSURE LEAD meter is given in fig. 3 of the previous paper .
For measuring the temperature three constantan wires are fixed to the reduced portion , one at the middle and one at each end ( points A , B , and C in the figure ) .
The middle wire and one of the end wires are connected to a galvanometer whose deflection is nearly proportional to the difference of the temperature between them .
By using three wires and taking the mean of the falls of temperature in the upper and lower halves of the piece any flow of heat from external causes , such as arises for example from the eddy currents induced by the attracting magnet in the weight and in its attachments , is eliminated .
Messrs. B. Hopkinson and G. T. Williams .
[ Oct. 16 , The arrangements were such that the temperature difference between the centre and the end could be measured correct to about 1/ 20 ' C. Under a stress of 28 tons range the fall of temperature is about 10 ' C. The determination of the dissipation of energy corresponding to a given fall of temperature is effected by passing alternating current along the piece , which is kept in position in the machine , only the extensometer being removed .
The current is taken through the fixed coils of an ordinary suspended coil watt-meter , the leads of whose shunt or pressure coil are attached near the ends of the reduced portion of the test-piece ( fig. 1 ) .
The watt-meter measures the energy dissipated between the points at which these leads are attached ; that dissipated in the reduced part between the points A and C is obtained by multiplying the measured watts #by 085.* Simultaneous readings of the watt-meter and of the thermo-couple galvanometer are taken and a direct calibration of the latter is thus obtained in ergs per cubic centimetre .
This is all that is required for the purpose of these experiments ; the readings of the thermo-couple galvanometer were , however , also calibrated in terms of temperature , and it was found that the dissipation of energy shown on the watt-meter was accurately proportional to the temperature difference .
The apparent thermal conductivity of the steel calculated from these observations , on the assumption that the whole of the heat is removed by conduction along the metal , was 0T7 .
The true conductivity of this material is probably about 0T4 , whence it may be inferred that about five-sixths of the heat is in fact removed by conduction , the remainder escaping to the air surrounding the rod .
In making an experiment on elastic hysteresis , the machine was set to work at a certain stress , which was kept constant .
The temperature rose for about five minutes and then remained steady .
The experiment was usually continued for from half an hour to one hour , continuous observation being kept of tne temperature and of the stress .
The results are collected in fig. 2 .
The actual observations are shown , and it will be seen that fairly consistent values have been obtained .
It has been found possible to repeat the measurement of hysteresis loss at the higher stresses within 2 or 3 per cent. , though the different measurements were separated by considerable intervals of time , during which the apparatus was taken to pieces or disturbed in various ways .
* This factor was obtained by a special measurement in which watt-meter leads were attached at A and C , and the reading compared with that shown ( for the same current ) when the leads were attached at the outer points .
It agrees with the result of calculation on the assumption that the alternating current is confined mainly to the skin of the metal , so that the effective resistances of different portions are inversely proportional to their diameters .
The Elastic Hysteresis of Steel .
1912 .
] The energy dissipated in hysteresis increases about as the fourth power of the stress range .
It is interesting to note that under a range of stress of , say , 25 tons per square inch ( 39 kgrm .
per square millimetre ) the energy dissipated per cycle by elastic hysteresis ( 25,000 ergs per cubic centimetre per cycle ) is of the same order of magnitude as that dissipated by the magnetic hysteresis of similar material in fairly strong magnetic fields .
There seems to be no reason to suppose that in either case is there any cumulative change in the properties of the material associated with the work which is being done upon it .
But if the stress range be increased , the point must come at which there is such a cumulative effect , resulting ultimately in the destruction of the material by fatigue .
The first sign of such a change would probably be an increase in the energy dissipated by hysteresis .
The biggest stress range in these experiments was 28-6 tons per square inch ( 45 kgrm .
per square millimetre ) and there was no sign of any increase in hysteresis after half an hour of the application of this range of stress , corresponding to about one quarter of a million reversals .
From Dr. Stanton 's results , however , it would appear most probable that under this range of stress , if applied 20 times per second , the material would break after less than 100,000 reversals , and that therefore there must be some permanent effect , though it is perhaps almost negligibly small at the higher speed of reversal .
The experiments are being continued with the object of finding evidence of this increased hysteresis and generally of discovering how the hysteresis loss is related to the elastic limit .
Messrs. B. Hopkinson and G. T. Williams .
[ Oct. 16 , Static Tests .
The effect of elastic hysteresis is that the stress-strain diagram corresponding to a cycle ranging between equal tension and compression is a closed loop as shown in fig. 3 , instead of a straight line.* It is the work represented by the area of this loop which is measured in the experiments which have been described .
It appeared important to get some approximation to the stress-strain curve obtained in a static test , in order to ascertain whether the speed of reversal had any effect on elastic hysteresis .
The only absolute measurements of elastic hysteresis of which we are aware are those described by Ewing , who loaded and unloaded a long wire by means of weights.f Traces of apparent hysteresis have been observed in ordinary measurements of elasticity with an extensometer and testing machine , but there is always a doubt in such cases whether a large part of the difference observed between loading and unloading is not due to friction in the testing machine or in the extensometer .
The difference of length to be measured is not more than one hundredth of the total variation of strain , and on apiece 4 inches long amounts to but 1/ 50000 inch , so that the measurement is a very delicate one , an error of one-millionth of an inch in absolute length being equivalent to 5 per cent , in the result .
FIG.3 .
HYSTERESIS STRESS DIFFERENCE STRAIN \#166 ; -B/ -OYA- In the present instance no attempt was made to determine a complete stress-strain curve , but the maximum difference of length AB ( 'fig .
3 ) was * The width of the loop is much exaggerated , t ' Brit. Assoc. Report , ' 1889 , p. 502 .
1912 .
] The Elastic Hysteresis of Steel .
measured .
The same piece of steel as that used in the alternating stress machine was first subjected in a testing machine to compressive stress of the amount desired , say , 10 tons per square inch .
It was then removed from the compression machine and loaded in tension with weights and a lever to 10 tons per square inch .
After this process of alternate compression and tension had been repeated several times in order to get the piece into a cyclical state , measurements of length were taken by means of an extenso-meter , first , after the piece had been put into the testing machine , having just previously been loaded to 10 tons per square inch compression , and , second , after a load of 10 tons per square inch tension had been applied and removed .
The piece was a little longer in the second case than in the first , and the difference in length is the quantity sought .
The advantage of this procedure is that there is no measurement of load ; when taking both readings the piece was hanging practically free , and there was no possibility of any stress in it .
The only errors are those due to strain and backlash in the extensometer , and it was found possible to eliminate these .
The resulting values of A'B ' ( the stress difference corresponding to the change of length AB ) are probably correct within 1/ 100 ton per square inch .
Details of the measurements and of the extensometer are given in an Appendix .
The following are the final results .
In each case the cycle of loading was between equal limits of tension and compression , and the " range of stress " given in the first column is twice either of these limits:\#151 ; | Kange of stress ( tons per sq .
in .
) .17 -0 20 -0 23 -0 Corresponding stress difference ( A'B ' ) 0-05 0-08 0-12 ( tons per sq .
in .
) Length difference ( AB ) ( millionths 15 24 36 of an inch ) These figures agree as regards order of magnitude with those given by Ewing .
The range of stress in one of his experiments was about 15 tons per square inch , the limits being roughly 5 tons and 20 tons per square inch respectively ( both in tension ) .
At the intermediate load of 12\#163 ; tons the strain in the wire was greater during the unloading part of the cycle than that corresponding to the same stress when loading , by about 1/ 150 part .
At 17 tons range in the above table the corresponding ratio is 0'0o/ 8'5 , or 1/ 170 .
The area of the hysteresis loop can , of course , only be roughly guessed .
Assuming , as is probable , that the loop is of the lenticular form shown , its area must lie between AB .
MK and half that amount .
If the two sides are arcs of circles the area is S AB .
MN .
On the assumption that this is , in Messrs. B. Hopkinson and G. T. Williams .
[ Oct. 16 , fact , the area , the value of AB has been calculated from the work done per cycle as measured in the high speed alternating stress machine .
The width of the loop on the stress line A'B ' is AB multiplied by E , and this has been plotted in fig. 4 .
On the same figure is shown the value of A'B ' as determined from the statical experiments .
HYSTERESIS STRESS PREFERENCE AND STRESS RANGE .
FULL UNE : HIGH SPEED TESTS .
( STRESS DIFFERENCE CALCULATED FROM ENERGY LOST ) DOTTED UNE : STATIC TESTS .
IO / 5 20 STRESS RANGE .
TONS PER SQ .
IN .
It will be observed that the stress difference calculated from the energy loss bears a substantially constant ratio of 0'8 to that measured statically .
This ratio , of course , depends entirely on the factor chosen for calculating the area of the loop from its dimensions .
On the extreme suppositions that this factor is 1 and ^ respectively ( instead of S ) , the ratios of high speed to static hysteresis would become 0'53 and T06 respectively .
It seems probable , therefore , that the hysteresis in cycles performed 120 times per second is ( if anything ) less than that found in static tests , but it is unlikely that the difference is more than 30 per cent. Lord Kelvin , as the result of his experiments on the torsional oscillations of wires , was led to no very definite conclusion as to the relation between the dissipation of energy , in a vibration of given amplitude , and the period , but apparently thought that the loss increased slightly with the speed.* Wire , and especially the outer skin of wire ( which is alone operative in torsional experiments ) , is , however , in an abnormal condition , and may give results which are both irregular ( as was found by Kelvin ) and different from those found in a bar of the same material .
* ' Math , and Phys. Papers , ' vol. 3 , p. 24 .
1912 .
] The Elastic Hysteresis of Steel .
Appendix .
The extensometer is shown diagrammatically in fig. 5 .
It is similar in principle to the well-known Ewing instrument , except that a tilting mirror observed from a distance through a telescope is substituted for the microscope .
Two rings , A and B , surround the thickened part of the test-piece , and each is fixed to it by a pair of pointed screws so that the rings pivot about the axes C and D respectively , which are fixed in the piece .
The rod E is rigidly fixed at its lower end to the ring B , and its rounded upper end engages with a conical recess in the end of a screw fixed in A , being held up by the spring K. The pillar F , which is fixed to the ring A , engages at its lower end with a steel ball at the end of an arm ( about 0'08 inch long ) attached to the mirror G. This mirror is pivoted in bearings attached to the pillar H ( fixed to ring B ) so that it can turn about a horizontal axis I. The reflection of a vertical scale in the mirror is observed in a telescope at a distance of about 6 feet .
It is possible to read the scale correct to 1/ 10 mm. , which corresponds to a change of length of about 1*2 millionths of an inch .
A fixed mirror carried on the piece serves to measure any tilt of the apparatus as a whole .
The instrument is calibrated with sufficient accuracy for the purpose by loading the piece with a known tension .
The Elastic Hysteresis of Steel .
Change of temperature in the piece , due either to conduction of heat to or from the testing machine attachments , or to slow change in the room temperature , causes a gradual change of length .
This was allowed for by observing the rate of change before and after an observation .
It was found that after putting the piece in the testing machine ( having previously compressed it in the compression machine ) the zero was at first not constant ; that is to say , after the application and removal of a load of , say , 2 tons per square inch , whose effects as regards elastic hysteresis must be quite negligible , the reading did not return to the same value .
After a few applications and removals of this small load , however , the instrument seemed to settle down and the full tension load was then put on and removed , the corresponding change of length being noted .
In order to make quite certain that the change of length observed as the result of application and removal of tension in a piece which had previously been compressed was really due to the elastic properties of the material , and not in any way to the extensometer , a control experiment was performed .
The piece was put in the tension machine , and a load equivalent to 10 tons per square inch was applied and removed a number of times .
The piece was then removed from the machine , and handled as nearly as possible in the same way as after its removal from the compression machine in the experiments which have been described .
It was then replaced in the tension machine and treated again in the same way , that is , a load of about 2 tons per square inch was applied and removed about a dozen times , so that the zero became perfectly constant .
The full tension load of 10 tons per square inch was then applied and removed , and the consequent change of length was noted .
It will be seen that in this control experiment every circumstance is exactly the same , except that , prior to its commencement , the piece was loaded in tension instead of in compression , and was brought into the cyclical state corresponding to the application and removal of 10 tons per square inch tension .
It was found that the apparent change of length in the control was usually unmeasureable and was never more than about 10 per cent , of the change occurring in the full cycle from compression to tension .
It may be inferred from this , and from the general agreement between the experiments , that the width of the hysteresis loop over a range of 20 tons per square inch has certainly been measured correct to within 10 per cent. , or , say , to within 1/ 100 of a ton per square inch .
It should be added that it was found necessary , for the prevention of buckling , to enclose the test-piece when undergoing compression in a closely fitting jacket .
This jacket was formed by casting type-metal round the piece , the casting being split so that it could be removed .
The jacket was , Production of Characteristic 511 of course , taken off when the piece was removed from the compression machine and put into the tension machine .
The amount of compressive stress applied was measured with sufficient accuracy for the purpose by means of the extensometer .
In this way the effect of friction between the jacket and the piece was eliminated from the measurement of stress .
The Direct Production of Characteristic Rontgen Radiations by Cathode P By R T. Beatty , M.A. , D.Sc .
, Emmanuel College , Clerk Maxwell Student of the University of Cambridge .
( Communicated by Sir J. J. Thomson , O.M. , F.RS .
Received October 29 , \#151 ; Read December 5 , 1912 .
) It is now well known that many elements can be stimulated to produce characteristic X-rays .
So far , the only successful method of obtaining the characteristic rays has been to place the element in the path of a beam of X-rays , whereupon it becomes a secondary radiator ; and , if the exciting X-rays have the necessary penetrating power , the characteristic rays will make their appearance .
Some years ago a remarkable paperf by Kaye appeared , in which he showed that if an element , say , copper , were made the anticathode in an X-ray bulb , it could become a source of intense radiation characteristic of copper .
An explanation of these results was at once suggested by Barkla and Sadler . !
Their view was that the cathode rays on striking the copper plate gave rise to X-rays , some of which penetrated into the copper and thus excited the radiation characteristic of copper .
In other words , the effect was indirectly produced by the cathode rays .
But with our present knowledge of the amount of energy transformed in such an operation , we can calculate the magnitude of the effect to be expected on this theory .
But the amount of characteristic radiation found by Kaye is about ten times greater than can be accounted for by such a calculation .
In the present paper an attempt has been made to find the method of * The expenses of this research have been partially covered by a Government Grant made through the Royal Society .
t Kaye , ' Phil. Trans. , ' A , vol. 209 , pp. 123\#151 ; 151 .
X Barkla and Sadler , ' Phil. Mag. , ' May , 1909 , pp. 739\#151 ; 760 .
|
rspa_1912_0105 | 0950-1207 | The direct production of characteristic R\#xF6;ntgen radiations by cathode particles. | 511 | 518 | 1,912 | 87 | Proceedings of the Royal Society of London. Series A, Containing Papers of a Mathematical and Physical Character | R. T. Beatty, M. A., D. Sc.|Sir J. J. Thomson, O. M., F. R. S. | article | 6.0.4 | http://dx.doi.org/10.1098/rspa.1912.0105 | en | rspa | 1,910 | 1,900 | 1,900 | 4 | 124 | 2,937 | http://corpora.clarin-d.uni-saarland.de/surprisal/6.0.3/?id=rspa_1912_0105 | 10.1098/rspa.1912.0105 | null | null | null | Atomic Physics | 43.317652 | Electricity | 29.694843 | Atomic Physics | [
11.983084678649902,
-77.65194702148438
] | Production of Characteristic 511 of course , taken off when the piece was removed from the compression machine and put into the tension machine .
The amount of compressive stress applied was measured with sufficient accuracy for the purpose by means of the extensometer .
In this way the effect of friction between the jacket and the piece was eliminated from the measurement of stress .
The Direct Production of Characteristic Rontgen Radiations by Cathode P By R T. Beatty , M.A. , D.Sc .
, Emmanuel College , Clerk Maxwell Student of the University of Cambridge .
( Communicated by Sir J. J. Thomson , O.M. , F.RS .
Received October 29 , \#151 ; Read December 5 , 1912 .
) It is now well known that many elements can be stimulated to produce characteristic X-rays .
So far , the only successful method of obtaining the characteristic rays has been to place the element in the path of a beam of X-rays , whereupon it becomes a secondary radiator ; and , if the exciting X-rays have the necessary penetrating power , the characteristic rays will make their appearance .
Some years ago a remarkable paperf by Kaye appeared , in which he showed that if an element , say , copper , were made the anticathode in an X-ray bulb , it could become a source of intense radiation characteristic of copper .
An explanation of these results was at once suggested by Barkla and Sadler . !
Their view was that the cathode rays on striking the copper plate gave rise to X-rays , some of which penetrated into the copper and thus excited the radiation characteristic of copper .
In other words , the effect was indirectly produced by the cathode rays .
But with our present knowledge of the amount of energy transformed in such an operation , we can calculate the magnitude of the effect to be expected on this theory .
But the amount of characteristic radiation found by Kaye is about ten times greater than can be accounted for by such a calculation .
In the present paper an attempt has been made to find the method of * The expenses of this research have been partially covered by a Government Grant made through the Royal Society .
t Kaye , ' Phil. Trans. , ' A , vol. 209 , pp. 123\#151 ; 151 .
X Barkla and Sadler , ' Phil. Mag. , ' May , 1909 , pp. 739\#151 ; 760 .
512 Dr. R. T. Beatty .
Production of Characteristic [ Oct. 29 , production of characteristic radiation under these conditions ; the conclusion arrived at is that the bulk of the effect is due to a direct transformation of the energy of the cathode rays into characteristic X-rays ; that the small remainder is due to the indirect action suggested by Barkla and Sadler , and that the direct and indirect effects happen simultaneously as soon as the speed of the cathode rays exceeds a definite value .
Apparatus .
A pencil of cathode rays from a discharge tube entered a brass cylindrical vessel which was wound with wire to form a solenoid.* Bays of given speed could thus be separated out by magnetic deflection , and allowed to pass into the glass tube A ( fig. 1 ) which contained the anticathodes ; the latter were arranged on a moving car which could be moved by an external magnet which Cedhode rays of known speed +200 volts attracted an iron armature on the car .
Thus different substances could be brought in turn into position to serve as a target for the pencil of cathode rays .
The X-rays thus produced emerged through an A1 window O'OOl cm .
thick and were received in the ionisation chamber B , which was closed at the ends by thin A1 leaf .
The ionisation thus produced in B was measured by the * For details of the method of isolating rays of given speed , see Whiddington , 'Boy .
Soc. Proc. , ' 1911 , A , vol. 85 .
See also Kaye ( .
cit. ) for the manipulation of a set of anticathodes .
1912 .
] Rontgen Radiations by Cathode Particles .
electroscope C , which was of the balanced quadrant pattern described by the author some years ago in the ' Philosophical Magazine .
' It will be understood that the apparatus was thoroughly shielded from the X-rays , so that only a narrow pencil was allowed to pass along the axis of the chamber B. It is necessary to know the number of cathode rays which strike the anticathode during an observation in order to correlate the ionisations observed with different anticathodes .
A method of doing this was devised which simplified the labour of reducing the observations and was accurate in practice .
The interior of the tube A was lined with A1 foil and placed in metallic connection with the system of anticathodes .
The current due to the cathode rays passed from A to earth through a variable resistance P. Part of the current also passed through a much higher resistance Q to the ionisation chamber .
By varying the resistance P the leak in the chamber due to the X-rays from A could be balanced by the fraction of current due to the cathode rays which entered the chamber through Q , and so the electrode could be kept at zero potential throughout an observation .
Let C be the current leaving A ; a fraction PC/ ( P + Q ) will enter the ionisation chamber : since P is small compared with Q we may write PC/ Q : hence when a balance is obtained the leak due to X-rays while unit quantity of electricity is transported by the cathode rays is proportional to P. Hence the only observations to be taken are those of the resistance P and of the deflecting current in the solenoid : the latter gives the speed of the cathode rays .
For the resistance P a uniform glass tube containing a mixture of glycerine and copper sulphate was used , with a sliding electrode to regulate the length of tube employed .
The tube was calibrated from time to time and the resistance was found to keep constant ; the electrodes were made of copper and no polarisation effect greater than 1/ 200 volt could be observed .
The currents used were of the order of 10-5 ampere , so that no polarisation effects due to unequal concentration of the electrolyte were to be expected .
The resistance Q was more difficult to devise .
The problem was to construct a resistance of about 1012 ohms and to avoid polarisation and creeping of electric charges .
A mixture of xylol and alcohol in a glass tube was tried , as described by Norman Campbell , but the electric absorption of the glass caused large and irregular deflections in the electroscope .
Thus if the end A of the glass tube were earthed while B was raised to a potential of 10 volts , then on earthing B and connecting A to an electroscope fluctuations of the leaf took place for several seconds .
VOL. LXXXVII.\#151 ; A. 514 Dr. R. T. Beatty .
Production of Characteristic [ Oct. 29 , Among other things a fine cotton thread was tried as a resistance ; it was kept in tension between two metal hooks .
Owing to the small volume of the thread the absorption effect was eliminated , also the thread obeyed Ohm 's law and showed no polarisation effect of more than 1/ 100 volt .
Unfortunately such threads are susceptible to temperature changes and will not maintain a constant resistance over many hours .
Finally a quartz tube was used .
Copper caps were soldered to its ends , and the tube was filled with a mixture of xylol and alcohol ; a movable plunger sliding at the upper end served to alter the effective length of the tube .
Such an arrangement behaves in every way like a metallic resistance and is recommended to workers who wish to use a resistance of the order mentioned .
Results .
It will simplify our conceptions if we create a phrase to describe that part of the radiation from any anticathode which only depends in quality on the speed of the cathode rays : in opposition to the " characteristic radiation " we shall refer to this as the " independent radiation .
" Thus we have emerging from any anticathode a beam consisting of two parts\#151 ; the independent radiation , which is always present , and the characteristic , which only appears when the cathode rays are sufficiently fast .
Let us now find the relative radiation from any anticathodes for different speeds of the cathode rays , and with absorbing screens of A1 placed in the path of the X-rays .
The results of such a series of experiments are shown in fig. 2 , where the ordinates represent the ionisation observed when Cu is used as anticathode divided by that observed when Cu is replaced by Al .
The relative radiation remains constant till the cathode rays attain a speed of 6'25 x 109 cm .
per sec. , at which speed the characteristic radiation of Cu appears .
By interposing continually thicker Al screens the characteristic radiation is screened off relatively to the independent radiation , which is more penetrating .
A glace at the curves will show that as this happens the curvea make a more and more rapid return to the line from which they had departed .
In other words the ratio of the independent radiations from any two anticathodes is unaffected by the appearance of the characteristic radiation in one or both of them .
The value of the ratio itself is not quite constant for any particular element relative to Al , when the velocity of the cathode rays is varied ; it tends to rise in some cases with higher speeds .
The ratio in the case of Cn and Al , however , keeps the constant value of 3 throughout .
The next step was to prepare two Cu anticathodes , one 0'2 cm .
thick , the 1912 .
] Rontgen Radiations by Cathode .
other 0 0005 cm .
thick .
Two similar anticathodes were also made and covered with a single sheet of A1 foil 0'0003 cm .
thick .
The radiation from these anticathodes was passed through Cu screens ; by 4p3cm ?
06cm ^04 cm ^OBcrrT Speed of cathode particles -s- 10 ' .
The numbers on the curves represent the thickness of absorbing sheet of A1 used .
this means a selective transmission of the Cu radiation is effected and the independent radiations are largely screened off .
Now consider the effects which may conceivably be produced when cathode rays fall on a Cu anticathode .
We may arrange the effects in a table of transformation of energy as follows:\#151 ; Cathode rays .
Independent radiations .
Characteristic radiations . !
Characteristic radiations.* * Produced by that half of the independent radiation which enters into the Cu ; hence an indirect product of the cathode rays , t Produced directly by the cathode rays .
Thus the emergent radiation is composed of three parts ; the independent radiations , and the direct and indirect characteristic radiations .
2 n 2 516 Dr. R. T. Beatty .
Production of Characteristic [ Oct. 29 , Using symbols for brevity , we may write the tables thus:\#151 ; Bare Cu anticathode .
Cathode rays .
3x y I 3z Cu anticathode covered with A1 foil .
Cathode rays .
x 6* z * Since the cathode rays cannot reach the Cu .
We have shown that Cu is three times as efficient an " independent " radiator as Al , so , where we write xand 2 in one case , we must write and 3z in the other .
The Al foil may be taken to be perfectly opaque to cathode rays , and to transmit 99 per cent , of the X-rays used .
Hence , when the radiations emerging from the bare Cu plate would give ionisation represented by 3 x + y+ 3z , those from the covered plate would give But , since the radiations pass through Cu screens , the independent radiations are cut down Speed of cathode particles -r- 109 .
Speed of cathode particles 4-109 .
Anticathodes\#151 ; ( 1 ) Thick Cu ; ( 2 ) Thick Cu ( 1 ) Direct characteristic ( y ) ; ( 2 ) Indirect ( Al covered ) ; ( 3 ) Thin Cu ( Al covered ) ; characteristic ( 3 ( 4 ) Al .
1912 .
] Rontgen Radiations by Cathode Particles .
517 relatively to the characteristic radiations , so that we may write and kx + s , where k is a small fraction .
Now , in fig. 3 , AB = kx ( independent radiation from an A1 anticathode ) .
AO = kx -I- z. AD = 3kx -f- y-j- 3z .
Hence we can find y and 3z for given speeds of cathode rays ; the corresponding numbers give the amounts of the characteristic radiations produced directly and indirectly respectively .
These radiations are plotted in fig. 4 ; evidently , the direct effect is much larger .
Both effects disappear below a speed of 6*25 x 109 cm .
per second , which is close to the value which was found by Whiddington to be the speed at which the characteristic radiation of Cu is just excited .
It is very remarkable that , whether energy be carried in the form of a cathode particle or of an X-ray caused by that cathode particle , it should be capable of exciting a characteristic X-ray ; one is strongly driven to the conclusion that the same amount of energy is present in each of these two exciting agencies .
Further , fig. 2 shows that there is no diminution in the intensity of the independent radiation when the characteristic appears , that is , the latter is not produced at the expense of the former .
It would seem that , when the characteristic radiation appears , a new mechanism is brought into action quite independent of the mechanism which accounts for the independent radiations .
Note.\#151 ; What is here called direct action may be considered by some readers to be really a transformation of energy of cathode rays into independent radiations , which , within a short distance , are again transformed into characteristic radiations .
That is , the independent radiations might be specially absorbed within a region of molecular size round the region of those radiations .
But , if this were so , there should be a diminution in the intensity of the independent radiation when the characteristic appears ; now , the curves in fig. 2 show that no such effect happens .
In addition , a direct experiment was made to attempt to detect such special absorption , if it existed .
A Cu anticathode , O'OOl cm .
thick , was mounted so as to make an angle of 45 ' with the cathode rays ( as in fig. 1 ) .
Then , by means of an external electromagnet , the frame which held this anticathode could be rotated about a horizontal axis through 90 ' .
That is , the line which represents the side view of the anticathode in fig. 1 would rotate about its centre and , keeping in the plane of the paper , would take up a final position at right angles to its original position .
After such a rotation the 518 Production of Characteristic Radiations .
cathode rays would evidently strike the same point on the anticathode as before , but in the second position the X-rays would be compelled to penetrate the thickness of the anticathode before emerging from the window .
Hence , by taking readings of the ionisation produced when the anticathode was in each of the two positions , the absorption of the X-rays due to passing through the anticathode could be measured .
A similar piece of Cu was then placed in the path of the X-rays after they had emerged from the window ; it was , of course , also placed at an angle of 45 ' to the emerging rays ; the absorption due to it was then measured , and it was found that this absorption was the same as the absorption due to the similar piece of Cu inside the tube , and which served as anticathode .
Hence a sheet of Cu foil cut down the radiation by the same amount whether it was interposed at the actual origin of the rays , or at any point along their path .
Hence no evidence of special absorption could be discovered .
Condusions .
1 .
Cathode rays are able to produce characteristic X-rays directly .
2 .
The atomic mechanisms which account for the independent radiations and for the characteristic radiations are not connected with each other .
I beg to thank Prof. Sir J. J. Thomson for his counsel and encouragement during the progress of this research .
|
rspa_1912_0106 | 0950-1207 | An electric furnace for experiments in vacuo at temperatures. | 519 | 524 | 1,912 | 87 | Proceedings of the Royal Society of London. Series A, Containing Papers of a Mathematical and Physical Character | R. E. Slade, M. Sc. (Vict.).|Prof. F. G. Donnan, F. R. S. | article | 6.0.4 | http://dx.doi.org/10.1098/rspa.1912.0106 | en | rspa | 1,910 | 1,900 | 1,900 | 4 | 107 | 2,477 | http://corpora.clarin-d.uni-saarland.de/surprisal/6.0.3/?id=rspa_1912_0106 | 10.1098/rspa.1912.0106 | null | null | null | Thermodynamics | 60.227845 | Measurement | 21.687142 | Thermodynamics | [
-6.871695041656494,
-50.97635269165039
] | 519 An Electric Furnace for Experiments in vacuo Temperatures up to 1500 ' C. By R. E. Slade , M.Sc .
( Viet .
) .
( Communicated by Prof. F. Gr .
Donnan , F.R.S. Received September 24 , \#151 ; Read November 21 , 1912 .
) ( From the Muspratt Laboratory of Physical and Electro-Chemistry , University of Liverpool .
) This furnace was designed with a view to investigating at temperatures up to 1500 ' C. certain cases of heterogeneous equilibrium in which the equilibrium is defined by the pressure of the system .
Instances are the dissociation of certain oxides , nitrides , and carbonates , and the reduction of oxides by carbon .
The furnace could not be constructed of carbon , as carbon would react with some of the gases of which the pressure had to be measured , and also because it is almost impossible to remove the adsorbed gases from large quantities of carbon .
' Tubes of Royal Berlin porcelain in a platinum-wound resistance furnace may be used for temperatures up to 1200 ' , but at about this temperature they become soft , while the glaze runs and combines with any boat or other substance in the furnace .
Tubes of silica are not suitable , because they are porous at high temperatures , and because they disintegrate owing to crystallisation taking place .
It was decided to make the furnace of a platinum tube and to heat it by passing a large current through it .
As some of the substances which it would be necessary to place in the furnace react with platinum , .
copper formed by the dissociation of cuprous oxide , it was necessary to make the furnace sufficiently large to take a boat or crucible of magnesia large enough to contain the reacting substance and thick enough to protect the tube .
On the other hand , the tube ought to be as small as possible , in order that in determining the dissociation pressures all the charge should not be decomposed before the equilibrium is attained .
No data are available as to the strength of platinum at high temperatures , so that it was impossible to calculate what thickness of tube was necessary to withstand the pressure of the atmosphere when the tube was evacuated .
The first furnace constructed consisted of a platinum tube 2 cm .
in diameter , 17 cm .
long , and with walls 1 mm. thick .
It was mounted in water-cooled terminals at the ends as in the final form ( see below ) .
When evacuated and heated to 1195 ' C. it collapsed under the atmospheric pressure .
520 Mr. R. E. Slade .
An Electric Furnace for [ Sept. 24 , Since it was not feasible to make the tube walls any thicker on account of the high price of platinum and on account of the already low resistance of the tube , the whole furnace after being re-made was placed in an enclosure in which the pressure could be regulated so as to be nearly the same as that inside the furnace .
In this way the platinum tube was freed from pressure , and the furnace has been found to work satisfactorily up to 1500 ' C. The furnace is shown in section in figs. 1 and 2 .
The platinum tube\#151 ; 2 cm .
diameter , 17'5 cm .
long , and with walls 1 mm. 77/ 777X 7777 , Scale of centimetres .
Fig. 1 .
thick\#151 ; is mounted at each end in a water-cooled brass terminal shown in section in fig. 2 .
This terminal consists of an upper and a lower part , which are screwed together ( screws a , a)to hold the tube .
Both parts are cooled by a stream of water flowing through the bored channels and d ( tigs .
1 and 2 ) .
The lower parts of the terminals are screwed to the wooden bases c , c , which have a large hole through which pass the brass tubes carrying water to the channels b , b. Of these two wooden bases , one is fixed to the wooden bridge e , whilst the other is free to slide , to take up the expansion of the tube on heating .
The terminals are connected to copper bus bars , the fixed one directly and the movable one by means of a loop of very flexible bare cable .
One end of the tube is closed by the silver plate f , 1912 .
] Experiments in vacno up to 1500 ' C. which is silver-soldered to it .
To a hole in the centre of the plate is soldered a silver capillary tube g. These fittings are prevented from becoming hot by the water chamber h. The other end of the silver capillary tube fits easily into the thick-walled glass tube i. This joint is then made quite gas-tight with a , little Golaz wax.* The other end of the platinum tube is closed by the water-cooled stopper which is ground to fit the end of the tube .
The end of this stopper , the part making the friction joint , and the tube passing down the centre of it are of silver .
The ground joint at the end of the platinum tube is made tight by means Vertical section across A.B.OWf.i .
) 6 cms .
I \#166 ; I Scale of centimetres .
Fig. 2 .
of a little soft waxf which is run round after the stopper is in place ; no lubricant is used on the ground surfaces .
The hard wax is not used here , because this joint must be opened to introduce the boat into the furnace .
Into the silver tube passing through the stopper fits the glass Y-piece , through which the thermo-couple is sealed at the points l and m. In each of the arms of the Y is a coil of the couple wire , so that in case of damage to * A low-melting hard wax , not quite so brittle as sealing wax .
It is obtained from L. Golaz , 23 , Avenue du Parc de Mont Souris , Paris .
+ A soft wax which does not become hard on cooling , and shows no tendency to contract , and leave a metal or glass surface .
It is obtained from J. Gautseh , Miinchen , Nympmenburger Str. 3 .
522 Mr. R. E. Slade .
An Electric Furnace for [ Sept. 24 , the couple the end may be cut off and more wire drawn out without having to interfere with the seals / and mand even without having to undo the glass-silver joint o which is made permanently tight with Golaz wax .
The boat is placed in the middle of the tube and is protected from radiation to the cool ends by means of two discs of thin platinum at each side .
The platinum tube is enclosed in an asbestos box which is filled with magnesia .
The furnace stands on the cast iron base which is supported by three feet .
This base is bored with ten holes , each of which is fitted with a rubber stopper through which passes the respective connection to the furnace .
Through two of the holes pass copper bus bars leading in the current , through two the water flows in and out for cooling the terminals , and through another two the water for cooling the end pieces .
The water connections inside the furnace enclosure are made by means of thick-walled rubber or lead tubing so that they will not burst when the enclosure is evacuated .
The rubber tube is of course used where it is necessary to avoid a short circuit , e.g. the tube p. The glass tube is brought out through a hole fitted with a rubber stopper .
This tube is sealed to a manometer and Topler pump .
The two ends of the thermo-couple dip into glass tubes fitted by rubber stoppers into holes in the base .
These glass tubes , one of which is shown in fig. 1 , contain mercury , and each has a platinum wire sealed through the bottom .
The bottoms of these two tubes , which project below the base and so are outside the furnace , dip into wider tubes containing mercury , into which dip the wires leading to the measuring instrument .
These outer tubes may be surrounded by ice to keep the cold junction of the thermo-element at 0 ' C. The other hole through the base is fitted with a tube leading to two Bunsen filter pumps and a pressure gauge .
By means of these two pumps the enclosure can be evacuated to the vapour-pressure of water ( 12 to 14 mm. ) in 15 to 20 minutes .
Between the pumps and the furnace is interposed a calcium chloride tube to keep the atmosphere within the enclosure dry .
For this purpose also a dish of calcium chloride is always placed under the cover before sealing it up .
It is important to keep the atmosphere dry or there will be a dissociation of water vapour on the outside surface of the platinum tube and hydrogen will diffuse through the platinum into the furnace .
The iron dome , which is fitted with a wide flange , is lifted on and off by means of two handles fitted to the top .
The contact between the flange and the plate is smeared with tap grease ( vaseline and burnt rubber ) .
Soft wax is run into the channel q. All the holes in the base plate are made quite air-tight by running w'ax into the holes on top of the stoppers .
This outside enclosure holds so well that when shut off from the pumps the pressure only rises 20 to 40 mm. in 14 hours .
The inside Experiments in vacuo up to 1500 ' C. 1912 .
] tube or furnace when pumped out with the Topler pump and then shut off from the latter shows a pressure of less than 01 mm. after 14 hours .
In another experiment the pressure only rose to 0*1 mm. in 2 hours at 1150 ' C. The thermo-couple is of platinum-platinum-rhodium .
The E.M.F. of the couple is measured by means of a potentiometer .
The couple has been calibrated at the melting point of copper , 1083 ' C. , and was found to agree with the maker 's calibration to within 1 ' at this point .
The extrapolation formula used was log e = T22 log t \#151 ; 2'65 wTiere e is the E.M.F. in millivolts .
The furnace requires about 350 amperes at 3 volts to heat it to 1400 ' 0 .
when the enclosure is evacuated .
With increase of pressure in the enclosure the thermal conductivity increases so that more power is needed to maintain the same temperature .
The current is obtained either from two dynamos in parallel capable of giving together 500 amperes , or from an accumulator battery of 12 cells arranged in six sets of two in series , the six sets being in parallel as shown diagrammatically in fig. 3 .
The normal discharge rate of the AA/ vWA^ Fig. 3 .
cells is 75 amperes each , whilst they may be discharged up to 125 amperes each .
It was found necessary to use the cells whenever a steady temperature had to be maintained , as the voltage of the power mains off which the motor working the dynamo was driven continually varied , thus changing the speed of the motor , the E.M.F. of the dynamo and the current through the furnace .
By using the accumulator battery the temperature can easily be kept within 1 ' for several hours at temperatures up to 1500 ' C. A fine adjustment of the current was obtained by shunting up to 15 amperes across Messrs. IT .
E. Slade and F. D. Farrow .
[ Sept. 24 ) the furnace through the ammeter and resistance shown at a in fig. 3 .
The coarse adjustment of the current is made by means of a water-cooled brass tube resistance .
The current flows in series through two brass tubes 5 feet long fixed in a frame side by side , whilst a stream of water flows through to cool them .
By means of two stout brass clips across the two barsfany fraction of them can be short-circuited .
The maximum resistance of these tubes is 1/ 300 ohm .
This furnace has been used in an investigation of the dissociation of cuprous oxide , and has been found to be in every way satisfactory .
Part of the expense of the construction of this furnace was defrayed by a grant from the Government Grant Committee of the Royal Society , to ' whom the author wishes to express his thanks .
An In vestigation of the Dissociation Pressures and Melting Points of the System Copper-Cuprous Oxide .
By R. E. Slade , M.Sc .
( Viet .
) , and E. D. Farrow , M.Sc .
( N.Z. ) .
( Communicated by Prof. F. G. Donnan , F.R.S. Received September 24 , \#151 ; Read November 21 , 1912 .
) ( From the Muspratt Laboratory of Physical and Electro-Chemistry , University of Liverpool .
) E. Heyn* determined the melting points of mixtures of copper and cuprous oxide of compositions varying between 100 per cent. Cu and 88*24 per cent. Cu , 11*76 per cent. CU2O .
The results of his experiments are shown by the points marked + in fig. 1 .
These points fall on two curves intersecting at the eutectic point 1065 ' C. , CU2O 3*5 per cent. , Cu 96 5 per cent. Heyn found that all his mixtures showed a halt in the cooling curve at this eutectic temperature , so that within the range of his experiments there is no evidence of the existence of solid solutions .
C. N. Otin*f* has lately published some experiments on the melting points of the system cuprous oxide-silica .
He attempted to determine the melting point of cuprous oxide , but as some oxidation always took place in his experiments , and as he did not analyse the solid obtained ( on account of * ; Zeit .
anorg .
Chem. , ' vol. 39 , p. 11 .
+ ' Metallurgie , ' vol. 9 , p. 92 .
|
rspa_1912_0107 | 0950-1207 | An investigation of the dissociation pressures and melting points of the system Copper-cuprous oxide. | 524 | 534 | 1,912 | 87 | Proceedings of the Royal Society of London. Series A, Containing Papers of a Mathematical and Physical Character | R. E. Slade, M. Sc. (Vict.).|F. D. Farrow, M. Sc. (N. Z.).|Prof. F. G. Donnan, F. R. S. | article | 6.0.4 | http://dx.doi.org/10.1098/rspa.1912.0107 | en | rspa | 1,910 | 1,900 | 1,900 | 7 | 231 | 4,085 | http://corpora.clarin-d.uni-saarland.de/surprisal/6.0.3/?id=rspa_1912_0107 | 10.1098/rspa.1912.0107 | null | null | null | Thermodynamics | 64.841561 | Tables | 13.691886 | Thermodynamics | [
-7.154740333557129,
-51.49964904785156
] | ]\gt ; Messrs. R. E. Slade and F. D. Farrow .
[ Sept. 24 , the furnace through the ammeter and resistance shown at in .
The ooarse adjustment of the current is made by means of a water-cooled brass tub resiqtance .
The current flows in series through two brass tubes 5 feet lon fixed in a frame side by side , whilst a stream of water flows through to cool .
By means of two stout brass clips across the two fraction of them can be -circuited .
The maximm resistance of these tubes is 1/ 300 ohm .
This furnace has been used in an investigation of the dissociation of cuprous oxide , and has been found to be in every way satisfactory .
Part of the expense of the construction of this furnace was defrayed by a grant from the Government Grant Committee of the Royal Society , whom the author wishes to express his thanks .
An of the Dissociation Pressures Points of the Systern Copper-Cuprous Oxide .
By B. E. SLADIi , M.Sc .
( Vict .
) , and F. D. FARROW , M.Sc . .
( Communicated by Prof. F. G. Donnan , F.R.S. Received September 24 , \mdash ; Read November 21 , 1912 .
) ( From the Muspratt Laboratory of Physioal and Electro-Chemistry , University of Liverpool .
) E. Heyn* determined the points of mixtures of copper and cuprous oxide of compositions varying between 100 per cent. Cu and per cent. Cu , per cent. .
The results of his experiments are shown by the points marked fig. 1 .
These points fall on two curves intersecting at the eutectic point 1065o per cent. , Cu per centHeyn found that all his mixtures showed a halt in the cooling curve at this eutectic temperature , so that within the of his experiments there is no evidence of the existence of solid solutions .
C. N. has lately published some experiments on the melting points of the system cuprous oxide-silica .
He attempted to determine the melting point of cuprous oxide , but as some oxidation lwavs took place in his , and as he did not analyse the solid obtained ( on account of : Zeit .
anorg .
vol. 39 , p. 11 .
Metallurgie , ' vol. f ) , p. 92 .
1912 .
] of the System Copper-Cuprou , $/ Oxidc .
525 to remelt it to get it out of the platinum ) , there is some doubt as to the actual composition of the substance of which he determined the melting point .
The highest temperature at which he found a halt in the cooling curve was 1205o C. Foot and Smith* found that the dissociation pressure of cuprous oxide does not exceed 1 mm. at 1020o C. It was the original intention of the authors to place a weighed amount of cuprous oxide in the furnace described in the previous paper , evacuate , heat to a certain temperature , determine the steady pressure obtained , and then to pump off the oxygen a little at a time , measure it , and determine again the steady pressure obtained .
From the amount of pumped off the composition of the mixture of copper cuprous oxide in the furnace at any time could have been determined after allowing for the known volume of the apparatus .
In this way a sel.ies of pressure-composition isothernls would have been obtained , from which the pressure , temperature , and temperature-composition rams could have been constructed .
Ths method was found to impossible , ving to the rapid volatilisation of the mixture from the boat into the cool ends of the tube , and it became necessary to investigate that portion of the melting diagram which was untouched by Heyn , in order to explain the results of our dissociation pressure measurenlents .
The Meltiny Point \mdash ; Two samples of cuprous oxide obtained from Kahlbaum were analysed by reduction in hydrogen and were found to contain and 8 per cent. respectively .
The former was a sample which had been in the laboratory stock for three years .
The cuprous oxide used in the following experiments was made by reducing an alkaline solution of copper sulphate with rape sugar at C. in presence of tartaric acid .
The product usually contained a small quantity of metallic copper .
The copper used in making up the mixtures for melting point determinations was either powder reduced from the oxide by heating in hydrogen , or electrolytic copper in form of short pieces of thin wire .
The oxide or mixture of oxide and metal was placed in ] azed crucible of Royal Berlin porcelain of the form generally sold as a Rose crucible .
These crucibles were found to be quite inappreciably attacked by or , even when exposed to their action for all hour at 1350o C. Each crucible held about 25 .
of the mixture .
The thermo-couple was protected by tubes of the same material as the crucibles .
The thermo- couple was threaded through one of the tubes intended for introducing the 'Amer .
Chem. Soc. Journ vol. 30 , p. 1344 .
Messrs. R. E. Slade and F. D. Farrow .
[ Sept. 24 , gas into a Rose crucible , so that the junction was about the middle of tube .
By heating at this point in an oxy-gas flame the tube softened and then be benC double at the point which contained the junction .
The crucibles were heated in a platinum-wound resistance furnace , through which was passed a stream of to avoid oxidation of the charge .
After the substance had become completely melted , the heating current was cut off and the cooling curve obtained .
temperatures were read on a miilivolt meter which was checked from time to time by means of potentiometer .
The couple was of platinum-platinum-rhodium ; it had been calibrated at the point of copper .
After the cooling curve been obtained the mass was broken up , from the adhering pieces of crucible , and analysed by reduction in hydrogen .
Over a certain of nposition it was found that two layers vere formed .
The lower one rich in copper and the upper one rich in cuprous oxide , the following results ) tained : Table I. ition .
point .
( bottom layer ) experiments were then made in which the melt was heated a known steady temperature for 30 to 60 minutes and then the crucible rapidly removed from the furnace and quenched in water .
In one Jeriment the crucible was allowed to cool very slowly in the furnace so that equilibrium might be attained at the lowest temperature at which the two phases could exist , that is at 1195o .
Table II .
1912 .
] Investigation of the System Oxide .
527 In the two following experiments mixtures of copper and cuprous oxide were melted in a carbon tube resistance furnace and quenched from temperatures in the hbourhood of 1400o C. Two layers were formed in each case , having the following compositions:\mdash ; Table Experiment .
layer . .
Experiment .
Botton ) layer . .
Experiment .
Botton ) layer . .
Experiment .
Botton ) layer . .
Experiment .
Botton ) layer . .
Experiment .
Botton ) layer . .
Experiment .
Botton ) layer . .
Experiment .
Botton ) layer . .
Experiment .
Botton ) layer . .
Experiment .
Botton ) layer . .
Experiment .
Botton ) layer . .
Experiment .
Botton ) layer . .
Experiment .
Botton ) layer . .
Experiment .
Botton ) layer . .
Experiment .
Botton ) layer . .
Experiment .
Botton ) layer . .
Experiment .
Botton ) layer . .
Experiment .
Botton ) layer . .
Experiment .
Botton ) layer . .
Experiment .
Botton ) layer . .
Experiment .
Botton ) layer . .
Experiment .
Botton ) layer . .
Experiment .
Botton ) layer . .
Experiment .
Botton ) layer . .
Experiment .
Botton ) layer . .
Experiment .
Botton ) layer . .
Experiment .
Botton ) layer . .
Experiment .
Botton ) layer . .
Experiment .
Botton ) layer . .
Experiment .
Botton ) layer . .
Experiment .
Botton ) layer . .
Experiment .
Botton ) layer . .
Experiment .
Botton ) layer . .
Experiment .
Botton ) layer . .
Experiment .
Botton ) layer . .
Experiment .
Botton ) layer . .
Experiment .
Botton ) layer . .
These results are shown graphically in .
The results of Heyn are marked , , those of Table I , , those of Table II , , and those of Table III , FIG. 1 .
The figure shows that the system is similar to that of phenol and tel The melting point of pure cuprous oxide is about 1210o C. Ab temperatules above 1195o mixtures having a composition between 20 per cent. and 95 per cent. cuprous oxide separate into two layers .
The above results show that up to 1400o C. there is only a slight } of this range of concentration , that is to say increase of temperature only slightly increases the Messrs. R. E. Slade and F. D. Farrow .
[ Sept. 24 , one liquid phase in the other .
It is , however , just possible that the quenching was not rapid enough and that in all the experiments the equilibrium obtained was approximately that at 1195o .
Dissociation Pressures.\mdash ; From the melting point diagram we can , by means of the phase rule , determine what type of ( pressure , temperature ) diagram will be obtained .
Since the system contains two components , copper and oxygen , there must be three phases present for one degree of freedom , or in the usual notation of the phase rule That is to say , if there are three phases present there will be a definite pressure corresponding to each temperature , but if there are only two phases present\mdash ; e.g. liquid and gas\mdash ; the pressure will depend on the composition as well.as upon the temperature .
The diagram ( projection on the surface ) will be of the type shown in fig. 2 .
, FIG. 2 .
The lines represent the pressures of the mono-variant systems:\mdash ; ab , system solid Cu , solid , gas .
, , , solid Cu , liquid , gas .
, , , solid , liquid , gas .
, , , liquid ( 1 ) , liquid ( 2 ) , gas .
The point represents the non-variant system solid Cu , solid , liquid , gas ; the point the system solid , liquid ( 1 ) , liquid ( 2 ) , gas .
It was found that below the pressure of the system was so small and equilibrium was attained so slowly that it was impracticable to determine any points on ab , , or .
Nor were any points on obtained owing to the short range both of temperature and composition of this line .
1912 .
] Investigation of the System Copper-Cuprous Oxide .
529 \mdash ; The furnace described by one of us in the preceding paper ( p. 519 ) was used .
The tube was sealed to a tube which could be dipped in liquid air and which led to the vacuum gauge and Topler pump .
The arrangement is shown in fig. 3 .
FIG. 3 .
During all the experiments the portion of the tube was kept immersed in liquid air to condense any and evolved from the magnesia boat and so prevent them from affecting the measurements of the oxygen pressure .
Behind the vacuum gauge was a glass millimetre scale illuminated by a lamp and milk.glass screen .
The readings were made with a telescope ; they were accurate to mm. The magnesia boats used at first were made as follows : Pure magnesia was fused in an electric arc or resistance furnace , ground up until it passed through a sieve with 90 meshes to the inch , and then made into a paste with magnesium chloride solution .
A carbon mould having been made for the boat , it was lined with the paste and then dried , first at , then at The boat had now become quite hard owing to the formation of magnesium oxychloride and adhered firmly to the mould .
Mould and boat were then gradually heated in a granular carbon resistance furnace up to 1800-200 C. On opening the furnace the boat was quite hard and had become loose from the mould .
* Ihese boats were quite refractory , but were unsuitable for the work in hand because the liquid mixtures of Cu and rapidly absorbed by the porous magnesia .
Besides this it was found that these boats gave off large quantities of .
This obviously comes from the sulphur absorbed by the nesia from the retort carbon in which it was baked .
One of these boats having a volume of about 4 .
of magnesia on heating in vacuo to 1400o C. gave off .
of Vide bSlade , ' Chem. Soc. Journ vol. 93 , p. 327 .
VOL. LXXXVIJ .
Messrs. R. E. Slade and F. D. Farrow .
[ Sept. 24 , These two defects were overcome by making the boats in the following way : A vertical carbon electrode made an arc with the bottom of a carbon crucible ; nesia was then fed into the crucible to smother the arc .
* In three or four minutes , when the magnesia had been well melted by the high power arc of 30-40 kw .
, the current was cut off .
A piece of solid magnesia , like irregularly-shaped teacup glazed on the inside , was found in the crucible .
In such a lump one or two portions suitable for a boat , when cut away from the mass , would be found .
The lump was carefully broken to these portions , and the boats finally shaped by grinding on an emery wheel .
These boats were taken from the lump in such a way that the inside of the boat was formed of the glazed surface of the magnesia round the arc .
After the tube had been in use for some and a deposit of had formed on the cool parts , a run was made with the furnace empty .
The pressure rose only to mm. in one hour at C. The cuprous oxide was prepared as described in the first part of this paper .
In most of the experiments a small quantity of electrolytic copper was added to the cuprous oxide , so that if the euprous oxide had been slightly oxidised we should , after heating up , have the system and not the system .
The boats held about .
of cuprous oxide .
results of experiments on the dissociation pressure are shown in fig. 4 , where the are plotted as ordinates against the time as abscissae .
Each continuous curve is an isotherm .
The temperature , during an experiment lasting up to , was usually kept within 1o C. and always within a range of , and are curves of the system liquid ( 1 ) liquid ( 2)-gas .
It is seen that after about three hours the pressure becomes quite steady , when the temperature is , but a much shorter period is necessal for equilibrium to be attained at ( Curve III ) .
Curve is the dissociation urve of the -variant system liquid-gas at 1240o .
In this case , where there was not sufficient copper present to form two liquid phases , the pressure was still rising after five hours ; no equilibrium was reached .
The explanation of this is that Cu was being volatilised more rapidly than from the liquid phase , which thus became richer in , and so had a ] oxygen pressure .
From analogy with other metals we should expect the metal to have a greater vapour pressure than the oxide .
In those experiments in which there were two liquid phases present volatilisation would only affect the quantity of the two Both the eyes and face of the operator must , of course , be suitably protected from the ultra-violet light of such an arc .
1912 .
] of the System -Cuprous Oxide .
531 liquid phases and not their composition ; therefore so as neither of the liquid phases had completely disappeared the system had a definite oxygen pressure .
The quantity of copper and cuprous oxide left in the boat after an experiment was , in only one case , enough for an analysis of sufficient accnracy to determine whether there had been one or two liquid phases present during the experiment .
Usually more than half of the mixture had been volatilised from the boat .
An analysis of the boat at the conclusion of one experiment ( Curve II ) gave Cu .
Tlus corresponds to a mixture cent. cent. .
Such a mixture would form two liquid phases at the temperatul.e of experiment , , as may be seen reference to fig. 1 .
The vapour of copper at these temperatures Dlay be calculated with a fair degree of as follows : has deternJined the boiling point of copper at one atmosphere to be 2310o , and has shown that the effect of pressure on the point of copper is sinilar to its effect on Thus where and are the absolute boiling points of } ) and mercury respectively at one atmosphere pressure , and and their boiling points at some other pressure .
Let this latter pressure be that exerted by copper 'Zeit .
Phys. Chem vol. 76 , p. 487 .
Messrs. R. E. Slade and F. D. Farrow .
[ Sept. 24 , at 1300o C. , that is 1573o absolute .
Then the temperature on the absolute scale at which mercury would have this same pressure is The pressure of mercury at this temperature\mdash ; 115o C.\mdash ; is approximately 1 mm. This is , therefore , also the vapour pressure of copper at 1300o C. It might be expected that the would not be appreciably volatile se , but that it would only volatilise by dissociating into copper and oxygen which , when they have diffused into the cooler parts of the apparatus , recombine , but this does not seem to be the case , for the authors find that a small piece of can be volatilised from a platinum strip at 1300o C. in a few minutes , even in air where the oxygen pressure is too great for diQsociation into copper and oxygen to take place , and would cause partial oxidation to cupric oxide .
Curve shows the results of an experiment in which a small piece of platinum was added to the mixture of cuprous oxide and copper to determine whether it would raise the dissociation pressure .
This was found to be the case , a steady pressure of 16 mm. being obtained , whilst at the same temperature\mdash ; 1240o C.\mdash ; without the platinum the dissociation pressure was 10 mm. This experiment was undertaken to explain an earlier experiment , in which an abnormally high pressure had been obtained .
and where it was found that a little of the oxide had been upset on to the hot part of the platinum tube .
The four values obtained for the pressure of the system liquid ( 1 ) liquid ( 2)-gas are given in Table and plotted in fig. 5 .
This is a portion of the curve of fig. 2 .
FIG. 5 .
1912 .
] Investigation of the System Copper-Cuprous Oxide .
533 Table In one experiment at 1230o the system liquid-gas gave a pressure of 39 mm. after five and a-half hours , but the pressure was still steadily rising , owing to volatilisation of copper from the liquid phase , making the latter continually richer in cuprous oxide .
Thermodynamic Theory.\mdash ; Allmand* has calculated the dissociation pressure of the system solid -solid Cu-gas at C. from measurements of the E.M.F. of the cell .NaOH/ Pt. and found atmosphere .
He has also calculated this pressure by means of the Nernst formula , which in this case is where and If Using this same formula Stahl has calculated that at 1662o C. atmosphere .
For 1250o C. , about which our experiments were made , we get atmosphere mm. This is the pressure we should expect for the system solid -solid Cu-gas at 1250o C. , if it could exist at this temperature , and assuming that the heat of reaction did not vary with the temperature .
For the system liquid ( 1)-liquid ( 2)-gas at 1250o C. we get from our experimental results 11 mm. There are no data available for applying Nernst 's mula to this equilibrium , for we should require to know the heat of the reaction Liquid ( 1 ) \mdash ; liquid ( 2 ) oxygen , where liquid ( 1 ) is the phase rich in cuprous oxide and liquid ( 2 ) that rich in copper .
Allmand ( loc. cit. ) points out that the law of mass action applied to the equilibrium gives the equation 'Chem .
Soc. Journ vol. 95 , p. 2163 .
'Metallurgie , ' vol. 4 , p. 682 .
Investigation of the System Copper-Cuprous Oxide .
so that at a iven temperature we should expect greater , if in place of the solid system we had the system solid -liquid-gas since would be lower for liquid thau for solid , the pressure of the liquid copper would be lowered by the formation the solution .
In the system of which we have measured the pressure , liquid ( 1)-liquid ( 2)-gas , both and will be lower than they would be if both the metal and oxide remained solid up to the temperature under consideration .
Since , however , is proportional to , and inyersely proportional to if the ratio in which and are lowered is the same in both cases , the relative lowering of the value of vould be much greater than that of the value of should therefore expect to be greater for the liquid than for the solid systems .
As is shown above , the experimental value for the liquid systems reater than that calculated on the assumption that the system is solid at that temperature .
If the heat of dissociation does not vary with the temperature , we may apply the formula of va n't Hoff to calculate from our measurements at two temperatures .
We find from the values at 1205o and 1260o C. cals .
, and from the values at 1260o and 1324o cals .
At dinary temperature , the yalue of for the dissociation of solid into solid copper and is cals .
From the two values calculated from experiments it is obvious that is not independent of the temperature , and this is what we should expect if the composition of the two liquid phases changed with the temperature .
In our experiments we found a small change of composition with temperature , though , as is pointed out on p. 528 , this effect may be somewhat greater than is indicated in fig. 1 .
The authors ' best thanks are due to Prof. F. G. Donnan for his kind interest and encouragement during the course of this investigation , and to Mr. R. Kingan for assistance in the analyses .
Part of the expenses of this research were met by a rant from the Government Grant Committee of the Royal Society , to whom the authors wish to express their thanks .
That is to , the pressure curve for liquid lies below that of superheated solid .
|
rspa_1912_0108 | 0950-1207 | On a method of finding the conductivity for heat. | 535 | 539 | 1,912 | 87 | Proceedings of the Royal Society of London. Series A, Containing Papers of a Mathematical and Physical Character | Prof. C. Niven, F. R. S.|A. E. M. Geddes, B. Sc. | article | 6.0.4 | http://dx.doi.org/10.1098/rspa.1912.0108 | en | rspa | 1,910 | 1,900 | 1,900 | 3 | 82 | 2,264 | http://corpora.clarin-d.uni-saarland.de/surprisal/6.0.3/?id=rspa_1912_0108 | 10.1098/rspa.1912.0108 | null | null | null | Electricity | 34.755813 | Thermodynamics | 15.930975 | Electricity | [
11.820470809936523,
-65.6314926147461
] | 535 On a Method of Finding the Conductivity for Heat .
By Prof. C. Niven , F.R.S. , and A. E. M. Geddes , B.Sc. ( Received November 2 , \#151 ; Read November 21 , 1912 .
) 1 .
The method to be described for finding the conductivity for heat of a \#166 ; class of bad conductors may be considered to be an extension of a method given by one of us for finding the conductivity of substances mostly in the form of powder or small grains .
In that paper the conductivity is inferred from the fall of temperature at different points from the axis of the mass , and the heat supplied to it by an electric current passing through a wire .
In the present paper the body was in the form of flat layers , and the heat was supplied by passing an electric current through a thin metallic layer-in our case a piece of Dutch leaf .
The leaf in the form of a rectangle was gummed to a piece of thin paper , and the current passed into it by two sheets of tinfoil also gummed to the paper and to the Dutch leaf along its \#166 ; opposite sides , the foil overlapping the leaf by spaces of about 1-2 mm. , the two pieces of foil and the Dutch leaf forming a rectangle about 18 cm .
long and 8 cm .
wide , of which the Dutch leaf occupied the length of about 8 cm .
The current was introduced and removed by soldering copper wires along the outer edges of the foil , which was then covered for about 1 or 2 cm .
with strong tissue paper so that the whole could be handled freely .
The potentials at the ends of the leaf were obtained by cutting the foils so as to leave two tags attached to the main foils by thin shreds and connecting thin wires to them in the same way as the main current leads were attached .
The whole appearance of the heating arrangements would be somewhat as in the figure .
P a. p e r This paper , with a similar sheet laid over the thin metallic sheets , will be called the " heater .
" 2 .
In our first experiments the " heater " was placed in the centre of a system made as alike above and below it as possible , the outer members Prof. C. Niven and Mr. A. E. M. Geddes .
[ Nov. 2 , of which were two brass boxes 19'7 cm .
long by 14*8 cm .
wide and 3-6 cm .
deep , through which tap water was allowed to flow , thus keeping the surfaces at a constant temperature , the same for both .
The other parts reckoned from the heater were ( 1 ) a thermo-electric junction made from No. 39 wires of iron and eureka ; ( 2 ) a slab of the material whose conductivity was to be found , usually |-1 cm .
thick ; ( 3 ) another thermal junction ; ( 4 ) a sheet of blotting paper , and then the flat surface of the cooling box .
On the other side of the heater the parts were exactly the same so far as we could make them , but there would probably be always some slight inequality in the thicknesses of the two slabs .
This , however , is of no consequence to the final result .
3 .
If wTe could assume that the Dutch leaf is uniformly warm when the heating has been so long continued that the temperature has become everywhere steady , the mathematical problem of the flow of heat from it on both sides would be the same as that of finding the lines of force between the plates of a plane condenser .
That is to say , the lines of flow would be perpendicular to the surface of the leaf and to the parallel surfaces of the coolers , and if the leaf were uniform we might , in any case , expect this to .
be true for an area near the centre of the leaf .
Assuming such a state of things to exist , and h to be heat produced by the current in one second per unit area , we should have h \#151 ; K(0#i where a and b are the thicknesses of the two slabs , d0i , dd2 the difference of temperatures on opposite sides of the slabs , and K is the conductivity .
4 .
To satisfy ourselves on this point we arranged a number of thermal junctions at equal distances along the Dutch leaf and separated from it by a thin layer of paper , and plotted the change of temperature along the leaf .
The results for two leaves are here given , one of the figures showing the change for points above and below the leaf ; in this case the curves above and below are alike , as we should expect .
A glance at the figures shows that there is no region of equal temperature 1912 .
] On a Method of Finding the Conductivity for Heat .
537 near the centre of the leaf , the reason being that the latter is by no means of uniform thickness all over .
As this want of uniformity presented itself in all the thin metallic leaves which we tried , we looked for a means of overcoming the difficulty .
After some trials with tin foil , we finally adopted the plan of placing above and below the heater two plates of copper of about the same area as the Dutch leaf .
On testing the variation of temperature as before , we found that , with a copper plate 0'45 mm. thick , the variations from point to point were very small and irregular in sign , and that with a plate 055 mm. thick there was no appreciable change of temperature at all along its surface .
The latter plates were accordingly used in our work ; and to keep the system of the same thickness throughout , they were placed in a hole of the same size cut out of a number of sheets of paper having the same aggregate thickness as the copper plates.* 5 .
These copper plates ( or equalisers ) receive all the heat from the Dutch leaf and deliver it to the conducting slabs beyond from surfaces at a uniform temperature , except what may escape by conduction through the tin foils or along the paper margins of the heater .
The loss of heat along the tin foils we have endeavoured to estimate by finding the distribution of temperature along the foils in the same way as was done over the surface of the Dutch leaf .
The accompanying diagram shows this distribution , the ordinates * Prof. Lees in his paper in the ' Phil. Trans. , ' 1898 , A , vol. 191 , had already used a hat coil between two copper discs ; and , indeed , he figures a system of plates very similar to the one we have employed , the difference between our methods being one of detail in the arrangement of the rest of our apparatus .
VOL. LXXXVII.\#151 ; A. 2 P 538 On a Method of Finding the Conductivity for Heat .
representing the rise of temperature from the ends to the junction of the Dutch leaf on an arbitrary scale .
I is taken without equalisers , II with equalisers of the same size as the Dutch leaf which they guard , III with equalisers extending ^ cm .
at each end over the tin foils .
In the last case the gradient is less than in either of the other cases and is approximately uniform under the plates ; we have therefore adopted this size for the plates .
The thickness of the tin foils is 0*02 mm. , their breadth 8 cm .
, and the temperature gradient at the edge of the equaliser is about 5*8 ' C. per cm .
; if then we take the conductivity of tin foil to be about 1/ 11 , the heat passing out along each foil is 0*0084 grm.-cal .
per second , and for both foils would be double this amount .
6 .
From the heat thus found has to be deducted that produced by the passage of the current through J cm .
of the foils at each end .
We proceed to estimate this amount and to find the proportion which it bears to the whole heat generated in the Dutch leaf .
The current in our experiments being kept at 5 amperes ( this being as much as the heaters would stand without burning ) the fall of potential along the Dutch leaf was found to be 0*659 volt , that down one of the foils 0*0498 volt , so that the heat produced in each foil was about 1/ 13 of that in the leaf .
In absolute measure these amounts were respectively 0*783 and 0*06 gramme-calories per second .
As the part of the foils under the equalisers was 1/ 10 of the whole , the heat directly generated under these is about 0*006 grm.-cal .
, which goes to neutralise the heat lost by conduction , leaving 0*0024 as the total heat lost at each end .
The loss at both ends is therefore 0*0048 , which is about 1/ 163 part or 6/ 1000 of that produced in the leaf .
If we treat the flow of heat across the paper margins of the heater as negligible , we may take the heat generated as taken from the Dutch leaf , diminished by about 0*6 per cent. 7 .
As an example of the determination of K we may give the case of glass:\#151 ; Current ... ... ... ... ... ... ... ... ... ... ... ... ... ... 5 amperes Fall of potential along leaf ... ... ... ... ... ... ... 0*641 volt Heat produced in grm.-cal .
per cm.2 of equaliser ... 1*06 XlO-2 Ditto corrected for conduction by foils ... ... ... 1*054 XlO-2 Mean thickness of two slabs ... ... ... ... ... ... ... .
1*306 cm .
Fall of temperature in crossing upper slab ... ... .
3*684 ' C. " " lower " ... ... ... . .
3*472 ' C. Value of K ... ... ... ... ... ... ... ... ... ... ... ... . .
19*234 x lO"* Studies of the Processes Operative in Solutions .
Thermal Conductivities .
Paper 3-27 x 10-4 C.G.S. Cork carpet 2-645 x 10-4 C.G.S. Plate glass 19234 " Linoleum 3513 5 ) Norwegian pine ... 3076 " Leather 3-286 Mahogany 3-42 Fire clay brick ... 14-354 Ash 3-651 Polished clay the. .
17-415 Canary pine 3-916 " Vulcanite 4-210 )\gt ; Teak 3-974 Sulphur 6-151 55 Oak 5-011 " Paraffin wax 6-649 55 Felt ( green ) 0-74 to 0-8 " Studies of the Processes Operative in Solutions .
XX*.\#151 ; The Conversion of Ammonic Cyanate into , especially as influenced by Alcohols .
By E. E. Walker , B.Sc. ( Communicated by Prof. H. E. Armstrong , F.R.S. Received July 29 , \#151 ; Read December 5 , 1912 .
) In view of the importance of a knowledge of the precise effects produced by ordinary alcohol and its homologues on the course of chemical change , it is remarkable that so little has been done to elucidate , by systematic inquiry , the nature of their influence .
Attention has been drawn , in earlier studies of this series ( Nos. XI , XIII , XVIII ) , to the marked difference in the behaviour of the various homologues of alcohol , especially to the fact that the higher alcohols are the more active agents .
Moreover , it is well known to physiologists that the higher alcohols have lethal properties which are scarcely met with in their lower and more soluble homologues .
Unfortunately , in many cases , the results obtained by previous workers do not afford satisfactory information on the subject , as the conditions have been such that the alcohol has not been the only variable but has been substituted for water , the amount of water being decreased as that of alcohol was increased ; the effects produced might be due to either or both of these variations .
* I , ' Roy .
Soc. Proc. , ' 1906 , A , vol. 78 , pp. 272\#151 ; 295 ; II\#151 ; V , ibid. , 1907 , vol. 79 , pp. 564\#151 ; 597 ; VI\#151 ; X , ibid. , 1908 , vol. 81 , pp. 80\#151 ; 140 ; XI , ibid. , 1910 , vol. 84 , pp. 123\#151 ; 136 ; XII , 'Chem .
Soc. Trans. , ' 1911 , vol. 99 , pp. 349\#151 ; 371 ; XIY , ibid. , pp. 371\#151 ; 378 ; XY , ibid. , pp. 379\#151 ; 384 ; XIII , XVI , XVIII , XIX , ''Chem .
News , ' 1911 , vol. 103 , pp. 97 , 121 , 133 , 145 .
VOL. LX XXVII.\#151 ; A. 2 Q
|
rspa_1912_0109 | 0950-1207 | Studies of the processes operative in solutions. XX.\#x2014;The conversion of ammonic cyanate into urea, especially as influenced by alcohols. | 539 | 554 | 1,912 | 87 | Proceedings of the Royal Society of London. Series A, Containing Papers of a Mathematical and Physical Character | E. E. Walker, B. Sc.|Prof. H. E. Armstrong, F. R. S. | article | 6.0.4 | http://dx.doi.org/10.1098/rspa.1912.0109 | en | rspa | 1,910 | 1,900 | 1,900 | 13 | 225 | 6,381 | http://corpora.clarin-d.uni-saarland.de/surprisal/6.0.3/?id=rspa_1912_0109 | 10.1098/rspa.1912.0109 | null | null | null | Biochemistry | 63.411428 | Chemistry 2 | 20.229645 | Biochemistry | [
-52.34346389770508,
-42.344730377197266
] | Studies of the Processes Operative in Solutions .
Thermal Conductivities .
Paper 3-27 xlO_4C.G.S .
Cork carpet 2-645 x 10~4 C.G.S. Plate glass 19*234 " Linoleum 3*513 Norwegian pine ... 3076 " Leather 3*286 Mahogany 3*42 " Fire clay brick ... 14*354 \#187 ; Ash 3*651 " Polished clay the. .
17*415 Canary pine 3*916 " Vulcanite 4*210 Teak 3*974 " Sulphur 6T51 Oak 5*011 " Paraffin wax 6*649 Felt ( green ) 0*74 to 0*8 " Studies of the Processes Operative in Solutions .
XX#.\#151 ; The Conversion of Ammonic Cyanate into Urea , especially as influenced by Alcohols .
By E. E. Walker , B.Sc. ( Communicated by Prof. H. E. Armstrong , F.R.S. Received July 29 , \#151 ; Read December 5 , 1912 .
) In view of the importance of a knowledge of the precise effects produced by ordinary alcohol and its homologues on the course of chemical change , it is remarkable that so little has been done to elucidate , by systematic inquiry , the nature of their influence .
Attention has been drawn , in earlier studies of this series ( Nos. XI , XIII , XVIII ) , to the marked difference in the behaviour of the various homologues of alcohol , especially to the fact that the higher alcohols are the more active agents .
Moreover , it is well known to physiologists that the higher alcohols have lethal properties which are scarcely met with in their lower and more soluble homologues .
Unfortunately , in many cases , the results obtained by previous workers do not afford satisfactory information on the subject , as the conditions have been such that the alcohol has not been the only variable but has been substituted for water , the amount of water being decreased as that of alcohol was increased ; the effects produced might be due to either or both of these variations .
* I , ' Roy .
Soc. Proc. , ' 1906 , A , vol. 78 , pp. 272\#151 ; 295 ; II\#151 ; V , ibid. , 1907 , vol. 79 , pp. 564\#151 ; 597 ; VI\#151 ; X , ibid. , 1908 , vol. 81 , pp. 80\#151 ; 140 ; XI , ibid. , 1910 , vol. 84 , pp. 123\#151 ; 136 ; XII , 'Chem .
Soc. Trans. , ' 1911 , vol. 99 , pp. 349\#151 ; 371 ; XIY , ibid. , pp. 371\#151 ; 378 ; XY , ibid. , pp. 379\#151 ; 384 ; XIII , XYI , XVIII , XIX , Chem. News , ' 1911 , vol. 103 , pp. 97 , 121 , 133 , 145 .
VOL. LXXXVII.\#151 ; A. Mr. E. E. Walker .
[ July 29 , The investigation carried on by James Walker and Kay* to determine the influence of alcohol on the formation of urea from amnionic cyanate may be taken as an example .
The method adopted involved the substitution of alcohol for water in a solution of ammonic cyanate , the amount of cyanate present being the same initially in all the mixtures examined .
The change was found to be accelerated , especially in the presence of large proportions of alcohol , the rate at which the transformation took place when 90 per cent , alcohol was used as solvent being about 30 times as great as when water alone was used .
On general grounds and taking into account the fact that , as James Walker lias shown , f ammonic cyanate is a stable substance except in the presence of water , it is scarcely to be expected that alcohol would cause so great a change in the rate at which urea is formed .
The remarkable conclusion arrived at by Walker and Kay may well be a consequence of the method they used and of the manner in which the observations were reduced .
There can be little doubt , in fact , that the procedure they adopted is not one by which a proper estimate can be formed of the influence exercised by alcohol , as it involves the proportion of water present relatively to the cyanate being lowered in proportion as the amount of alcohol is increased .
To ascertain the influence of alcohol on the transformation of ammonic cyanate into urea , the alcohol should be added in increasing quantities to a solution in which the proportion of cyanate to water is kept constant .
An opinion may be formed from Walker and Kay 's data of the manner in which alcohol acts on the rate at which the transformation takes place when added to an aqueous solution , if the concentration be expressed with reference to the weight of water present , disregarding volume , by multiplying the velocity coefficient by the weight of water in 1 c.c. of solution.^ The manner in which Walker and Kay 's velocity coefficient , kp2 , varies with the composition of the solvent when recalculated by this formula is as .
follows ( Table I):\#151 ; * 'Chem .
Soc. Trans. , ' 1897 , p. 489 .
t Ibid. , 1900 , p. 21 .
J The argument may be given shortly as follows : \#151 ; If C be the concentration in gramme-molecular proportions per litre , v the rate of change of concentration when the concentration is C units , W the number of grammes of water in one cubic centimetre of the alcoholic solution , then C/ W is the concentration in gramme equivalents of cyanate per 1000 grammes of water v/ W is the rate of change of concentration .
The velocity coefficient is therefore 1912 .
] Studies of the Processes Operative in .
Table I. Alcohol by volume .
W kp2 kp2 x W Per cent. 0 1-000 0 -00434 0 -00434 10 0-908 0 -0056 0 *00499 30 0 723 0 -00918 0 -00666 49 0*547 0 -0184 0 -0101 72 0*313 0 *0428 0 -0133 90 0-119 0-13L 0 -0156 It is obvious that whereas Walker and Kay were led to assume that the rate of change is increased 30 times in 90 per cent , alcohol , the values obtained by the method of reducing the results I have adopted indicate that the rate in such a solution is not more than about three times as great as when no alcohol is present .
This is shown graphically in Diagram 3 .
Walker and Kay also calculated values of k by taking into account the presumed degree of dissociation of the cyanate in the solution used , deducing this from the ratio The influence of alcohol appears to be far greater when this method of reducing the results is adopted , the rate in 90 per cent , alcohol being about 100 times that in water .
It is impossible to believe that alcohol can have such an influence .
The changes undergone by urea being of special interest on account of the behaviour of this substance towards the enzyme urease , at Prof. Armstrong 's request I undertook the extension of Walker and Kay 's work , primarily with the object of arriving at a valid method of studying such problems but with the ultimate purpose of comparing the influence of different alcohols on the formation of urea .
Walker and Hambly have shown* that the conversion of ammonic cyanate into urea is effected at a bimolecular rate and is to a slight extent a reversible change ; they observed that a subsidiary change took place at the same time which involved the formation of a small proportion of ammonic carbonate .
They explained the fact that the change followed a bimolecular law on the hypothesis that the urea is formed by the interaction of the dissociated ions , of ammonic cyanate ; on this hypothesis , Walker and Kay developed an equation to express the rate of change , involving the factor of dissociation ( p ) , by means of which they deduced what they supposed were true values , of the velocity coefficient K. Their equation is not only highly complex but also involves the introduction .
* Ibid. , 1895 , p. 746 .
2 q 2 Mr. E. E. Walker .
[ July 29 , of the factor p , which is of doubtful significance ; it also does not afford the means of comparing the actual velocity at particular corresponding concentrations in different experiments .
For the purpose I had in mind it was necessary to compare the actual velocities with which the cyanate is transformed into urea in the presence of alcohol and its homologues when the ratio of cyanate to water remained fixed .
The graphic method of reducing the results appeared to be particularly well adapted for the purpose , as the rate of change of concentration could be obtained from the tangent to the curve at the required point .
The points established experimentally were plotted on squared paper , a smooth curve was then drawn and the tangents determined at the desired points by means of a stretched thread , the mean of two or more readings being taken .
The numerical values thus obtained expressed the rate of change of concentration ( in gramme-molecular proportions of cyanate per 100 gramme-molecular proportions of water per minute ) ; the velocity coefficient was obtained by dividing this rate by the square of the concentration .
The rate of change of concentration divided by the concentration represents the rate at which cyanate disappears in the fractions changed per minute .
In studying the influence of alcohols , their effect on this rate was compared , the ratio of cyanate to water being kept the same in all cases .
It is claimed that the graphic method is not only very much simpler in application than that adopted by Walker and Kay but that it has other important advantages .
The actual rates of change at definite concentrations are arrived at without any assumption being made and can be compared with the concentrations of the changing substances on various assumptions ; the effect on the rate produced by added quantities of the products of change or of other substances can also be arrived at easily , which is not the case when Walker and Kay 's method is used .
Temporary divergences from the normal course of change are rendered apparent immediately by the graphic method but may escape notice if the mathematical method be used , as this involves the assumption that the action follows the postulated course of change over the entire interval considered .
The experimental procedure adopted was , for the most part , that described by James Walker and Hambly.* In preparing silver cyanate , it was found that a cleaner product was obtained by boiling the solutions of silver nitrate and urea separately and then mixing them .
To prepare the ammonic cyanate , the silver salt , in slight excess , was violently agitated , by means of a mechanical glass stirrer , with the proper amount of a solution of ammonic chloride .
* Ibid. , 1895 , p. 746 .
1912 .
] Studies of the Processes Operative in Solutions .
The solution of ammonic cyanate was made up by weight , heated to within 0-2 ' of the temperature of the bath ( 40 ' ) and the first observation made about five minutes after it had been placed in the thermostat . .
At measured intervals of time , samples of the solution were transferred by means of a pipette to flasks containing weighed quantities of an N/ 10 solution of silver nitrate , in small , approximately constant excess of that required to precipitate the cyanate in the sample .
The flasks were then cooled as quickly as possible in running water , weighed and the excess of silver nitrate determined with ammonic thiocyanate in the manner described by Walker and Hambly .
The experiments were all carried out in a bath kept at 40 ' by means of a Lowry thermo-regulator .
* Table II.\#151 ; Experiments on the Influence of the Products of Change on the Transformation of Ammonic Cyanate into Urea .
I- II .
III .
IV .
i*~ - \#151 ; N H4CNO 0*20 Water 100 NH4CNO 0 *25 Water ... 100 NH4CNO 0 *25 ( NH4)2C03 0 *01 Water ... 100 NH4CNO 0 *220 Water 100 + 0 *05 urea.t .
Cyanate .
t. Cyanate .
Carbon- ate .
t. Cyanate .
Carbon- ate .
t. Cyanate .
Cyanate .
0 30 60 105 155 210 270 310 370 455 550 640 700 0 -1836 0*1758 0 *1697 0 *1617 0 *1535 0 *1445 0 *1365 0 *1319 0 *1249 0 *1166 0 *1075 0*1011 0 *0968 0 55 110 176 235 300 365 410 0 *2411 0 *2203 0 *2038 0 *1870 0*1742 0*1615 0 *1497 0 *1428 0*0023 0*0053 0 *0068 0 *0076 0*0084 0*0089 0*0097 0 25 60 110 160 200^ 250 290 0 *2387 0 *2297 0 *2193 0 *2029 0*1904 0 *1814 0 *1694 0 *1619 0 0143 0-0152 0 -0159 0-0167 0 0174 0 -0177 0 -0180 0 -0182 0 30 60 90 120 0 -2067 0-1975 0 -1901 0 -1827 0 -1764 0 *2051 0 *1966 0 *1888 0 *1810 0 *1750 The data obtained in the experiments without alcohol are given in Table II , those with alcohol in Table Y. The values given in other tables are deduced from the curves drawn with the aid of these data .
The Influence of the Products of Change.\#151 ; A few preliminary experiments at various concentrations confirmed James Walker and Hambly 's observation that the rate varied nearly as the square of the concentration , the velocity coefficient being higher in dilute than in more concentrated solution .
It soon became evident , however , that the rate was controlled by some other - m Mr. E. E. Walker .
[ July 29 , factor besides the concentration of the cyanate .
On examining the results ( Experiment 1 ) , it is seen that the velocity coefficient falls rapidly at first ( see Table III , Diagram 1 , Curve 1 ) , reaching a minimum at a concentration Diagram 1.\#151 ; Showing Influence of the Kate of Formation and Presence of Ammonic Carbonate .
.25 -20 -15 Concentration of cyanate .
of 0T5 and then rising again.* Moreover , the velocity coefficient obtained from Experiment 2 ( Table IY , Diagram 1 , Curve 2 ) varies in the same manner .
The only difference between the two experiments is that the initial concentration of the first is 0*20 , whilst that of the second is 0*25 ; yet the rate at a concentration of 0*18 is 0*0754 in Experiment 1 and 0*0670 in Experiment 2 .
Table III.\#151 ; Velocity Coefficients deduced from Experiment 1 .
Concentration of ammonic cyanate .
Velocity coefficient .
0*18 0 *0754 0 *17 689 0*16 682 0 *15 672 0*14 675 0*13 685 0*12 690 0*11 713 0*10 716 * Concentrations are expressed in Table I and elsewhere in molecular proportions of dissolved substance per 100 molecular proportions of water .
1912 .
] Studies of the Processes Operative in Solutions .
545 From experiments made with urea and ammonic carbonate to ascertain the nature of the influence exerted by these substances , it appears that the discrepancy under discussion is due , in all probability , to the formation and influence of the latter .
The Influence of Ammonic Carbonate.\#151 ; In the second experiment the carbonate was determined by titration with 1ST/ 20 sulphuric acid , using methyl-orange as indicator .
The solution was titrated after removing the precipitate of silver cyanate and the colour of the methyl-orange then destroyed by boiling with some of the ferric sulphate and nitric acid used as indicator in the subsequent titration with ammonic thiocyanate .
It is evident from the values arrived at ( Table IY , Column 3 ) that the formation of ammonic carbonate is comparatively rapid at first .
Table IY.\#151 ; Experiment 2 , showing the Eat of Formation and Influence of Ammonic Carbonate .
Concentration of cyanate , C Concen-tion of ( NH4)2C03 , C ' Rate of formation of ( NHOsOOj , Rate of change of concentration of cyanate , V V c* v \#151 ; y ' v \#151 ; v ' v\#151 ; v ' C2 0(0 + 20 ' ) 0*23 0-004P 0 *00054 0 *00374 0 -0710 0 *00320 0 *0605 0 *0585 0*22 053 43 338 699 295 610 582 0*21 064 27 297 675 270 612 576 oa-20 072 16 265 663 249 625 583 0*19 078 11 241 668 239 637 589 0*18 082 105 217 670 206 636 583 0*17 088 098 199 688 189 654 593 0*16 094 094 189 739 180 703 629 0*15 101 092 170 756 161 715 631 Mean values 695 \#151 ; 644 595 J It is clear that the disturbing effect of the carbonate will affect the velocity coefficient in two ways .
As the carbonate is formed very rapidly at the beginning of the experiment , it will make the velocity coefficient too high , since the rate includes the conversion of cyanate into ammonic carbonate .
Later on , as the amount of ammonic carbonate increases and that of cyanate decreases , the velocity coefficient will again be too high , as ammonic salts accelerate the change .
It thus appears that the falling off of the " constant " in the early stages of the experiment is due to the falling off in the rate at which carbonate is formed rather than to any abnormality in the rate at which the change into urea takes place ; moreover , that the subsequent rise is due to an actual increase in the amount of urea formed in consequence of the accumulation of ammonic carbonate in the solution .
Mr. E. E. Walker .
[ July 29 , This view receives some confirmation from Curves 3 and 4 in Diagram 1 .
Curve 3 represents the values of the velocity coefficient obtained by subtracting the rate at which the carbonate is formed from the rate at which the cyanate is transformed .
The greater part of the fall has been eliminated .
Curve 4 is the result of dividing the rate by the concentration of the cyanate multiplied by that of the ammonium radicle.* This last operation eliminates , to a considerable extent , the rise in value of the velocity coefficient .
The net result of the two corrections is to reduce the mean velocity coefficient from 695 to 595 .
The effect of the carbonate is shown graphically in the pair of curves from Experiment 2 , shown in Diagram 2 .
The abnormally high slope shown at the beginning of the upper curve is straightened out in the lower .
The Influence of Urea.\#151 ; Two short parallel experiments were carried out in one of which 0*05 gramme-molecular proportions of urea were added per 100 of water but none in the other .
The effect of the small addition of urea was to increase the mean velocity coefficient from 0*0698 to 0*0726 .
The work of Orme and Irvine Massonf possibly throws some light on this curious result .
These authors show that , in the case of the metallic cyanates , the urea and carbonate are formed apparently in a fixed ratio ; it is therefore reasonable to expect that the addition of urea would increase the quantity of carbonate formed and thus increase the total rate .
The case of ammonic cyanate is somewhat different but the ratio urea/ carbonate appears to fall to a constant value .
It was to be expected , therefore , that the addition of ammonic carbonate would reduce the formation of further quantities of this substance ; this was found to be the case in an experiment ( 3 ) in which about 0*01 of a gramme-molecular proportion of ammonic carbonate was added ; Table Y gives the results of this experiment .
The values in this table are arranged as are those in Table III and show ( 1 ) that , in presence of only 1/ 100th of a molecular proportion of ammonic carbonate , the rate at which carbonate is formed is diminished by one-half .
( 2 ) From the outset , the velocity coefficient in Column 6 rises instead of falling .
( 3 ) The mean value of the velocity coefficient in Column 7 ( in which correction is made for the rate at which the carbonate is formed ) is raised from 0*0644 to 0*0680 , thus showing the accelerative action of the added ammonic salt .
The value in Column 8 , however ( in which correction is made for this acceleration ) , is reduced from 595 to 558 .
, showing that the correction introduced is somewhat too high , as might reasonably be expected * Walker and Hambly have shown that this correction is applicable in the case of ammonic sulphate .
4 Zeit .
Phys. Chem. , ' vol. 70 , p. 290 .
1912 .
] Studies of the Processes Operative in Solutions .
Table V. Concentration of cyanate , C Concentration of ( NH4)3C03 , C ' Rate of change of concentration of ( NH4)2C03 , v ' Rate of change of concentration of cyanate , V v \#151 ; v ' V C* v\#151 ; v ' ~c*~ v \#151 ; v ' C(C + 2C ' ) 0*23 0 *0152 0 *00022 0 *00337 0 *00315 0 *0638 0 -0596 0 -0525 0*22 158 20 321 301 663 622 542 0*21 164 16 297 281 677 637 549 0*20 169 13 278 260 683 658 557 0*19 174 9 246 237 682 656 554 0-18 177 7 225 218 695 673 559 0*17 180 6 210 204 727 706 577 0*16 182 5 194 189 758 759 597 Mean values 690 680 558 Table YI.\#151 ; Experiments on the Influence of Alcohols .
iperiment No y. VI .
VII .
VIII .
lolecular proportions Ethylic alcohol Ethylic alcohol Ethylic alcohol Ethylic alcohol of alcohol added 2 40 70 100 t Cyanate t Cyanate Carbonate t Cyanate Carbonate * Cyanate 0 0 *2332 0 0 *2300 0 *0022 0 0 *2209 0*0031 0 0 *2337 35 O *2208 31 0 *2048 40 20 0 *1982 48 m 0 *2164 84 0 *2249 62 0 *1847 53 43 0 *1785 70 50 0 *1682 144 0*1883 116 0 *1574 80 70i 0 *1604 85 95 0 *1362 214 0 *1725 1601 0 *1436 83 110 0 *1384 93 160 0 *1056 259 0 *1632 225 0 *1230 92 175 0 *1100 97 211 0 *0886 260 0 *0772 Experiment No. Molecular proportions of alcohol added Ethylic alcohol 120 Propylic alcohol 10 Butylic alcohol 2 Cyanate Carbonate t Cyanate Carbonate * Cyanate Carbonate 0 0 *2320 0 *0071 0 0 *2309 0*0036 0 0*0022 22\#163 ; 0 *1909 101 50 0 *2067 59 5 0 *2322 049 45\#163 ; 0 *1640 117 100 0 *1862 75 30\#163 ; 0 *2241 073 92 0*1279 \#151 ; 150 0 *1695 83 70 0 *2094 090 , .
125 0 *1097 147 205 0 *1547 89 115 0 *1950 103 165 0 *0935 152 265 0 *1410 94 170 0*1791 118 201 \#151 ; 155 325 0 *1286 97 215 0 *1682 123 290 0 *1521 126 355 0 *1394 \#166 ; i Mr. E. E. Walker .
[ July 29 , as the ammonic carbonate is probably not all active .
This full correction is introduced , however , in the following experiments on alcohols for lack of further data .
The error thus introduced is small .
The Action of Alcohols .
Several experiments were made with different quantities of ethylic alcohol and its homologues , propylic and isobutylic alcohol ( Table VI ) ; the curves deduced from these experiments are reproduced in Diagram 2 .
Diagram 2.\#151 ; Showing Acceleration Produced on the Addition of Alcohols .
.2 *16 Time in minutes .
In Table YII the effect is shown of the addition of various proportions of ethylic alcohol , the velocity being expressed as the fraction of cyanate converted into urea per minute .
In Column 6 , the value of the rate is corrected for the formation and influence of ammonic carbonate by means of the data given in Columns 4 and 5 .
Walker and Hambly state that no carbonate is formed in alcohol of 72 per cent , strength ; on this account , therefore , also because of the great difficulty Studies of the Processes Operative in Solutions .
Table VII.\#151 ; Influence of Ethylic Alcohol .
Experi- meant .
No. of mols .
alcohol per 100 mols .
water .
Rate of disappearance of cyanate .
Rate of formation of ( NH4)2C03 .
No. of mols .
( NH4)"CO:i per 100 mols .
water .
Corrected rate of formation of urea .
Per- centage accelera- tion .
Percentage acceleration per mol .
of alcohol .
0*2 mol .
Cyanate per 100 mols .
Water .
II 0 0 0133 0*0008 0*0072 0 *0117 \#151 ; Y 2 145 \#151 ; \#151 ; \#151 ; 8-3 4 *1* VI 40 342 0 *0030 0 *0082 0 -0296 153 3*83 YII 70 507 47 48 439 275 3 93 Till 100 684 \#151 ; \#151 ; \#151 ; 419 4-19* IX 120 805 0*0048 0-0098 0 *0691 491 4*01 0*15 mol .
Cyanate per 100 mols .
Water .
II 0 0 *0111 0*0006 0 -00101 0 *00925 VI 40 248 09 082 215 132 3*3 YII 70 362 12 089 313 220 3*4 VIII 100 455 \#151 ; \#151 ; \#151 ; 344 3 *44* IX 120 546 0 -0032 0 *00126 0 *0467 411 3-42 * Not corrected for carbonate formation .
of titrating in the presence of so much alcohol , no determination of the ammonia was made in Experiment 8 .
No precipitate was formed on adding a barium salt at the end of the experiment ; the fall and subsequent rise of the velocity coefficient ( Table VIII ) , however , indicated that some such change did take place .
Another experiment ( 9 ) was therefore made in which the ammonia was titrated .
For this purpose , about an equal volume of water was Table VIII.\#151 ; Fall and subsequent Rise of Velocity Coefficient in Experiment 8 indicating presence of a subsidiary change .
Concentration of cyanate .
Rate of change of concentration .
Y elocity coefficient .
0*21 0 -01500 0-340 0*20 1370 0-342 0-19 1200 0*331 0-18 1068 0-329 0-17 936 0-324 0 16 792 0*310 0 15 684 0-304 0-14 614 0-313 0 13 526 0-312 0-12 462 0*319 0*11 390 0*321 o-io 342 0-342 0*09 285 0-352 0-08 226 0*353 Mr. E. E. Walker .
[ July 29 , added to the solution before titration , a blank titration with the same quantity of alcohol and water being first made and this solution then used as the standard tint .
Before titration with thiocyanate , the solution was reduced in bulk by distilling off the alcohol .
It was found that , although a considerable quantity of ammonia was formed , no precipitate was produced by a barium salt ; it is not improbable that the ammonia was present as carbamate rather than as carbonate .
It was also found that , though these corrections reduced the value expressing the rate by as much as 20 per cent. , they did not produce any great change in the final result , i.e. in the percentage acceleration , as the quantity of carbonate formed increases as the rate at which urea is formed increases .
The results obtained by the method described differ radically from those obtained by Walker and Kay .
In the first place , the increase in the rate of change is very nearly proportional to the weight of alcohol added ; in the second , the total increase , as pointed out in the introduction , is considerably less .
If the alcohol acted as a diluent , in the same manner as an equal volume of water , then the rate should vary inversely as the volume containing unit weight of cyanate .
Therefore , it can only be considered to act as a diluent if it be conceded that the molecular activity of the alcohol increases very nearly proportionally to its concentration .
It is improbable that its activity would thus increase and if we entirely neglect it as a diluent , then we find that the effect produced per molecule is practically constant for all concentrations of alcohol .
The effect of the alcohol appears rather to resemble that produced by an admixture of fine sand with a solution , the change taking place , as it were , within aqueous cells distributed throughout the liquid .
The alcohol so modifies the aqueous solution , however , that the rate of change is increased in proportion to the amount of alcohol added but even when alcohol and water are present in equal molecular proportions the transformation is effected only about five times as rapidly as in the absence of alcohol .
Ethylic alcohol , therefore , has but a very moderate effect .
It is submitted that this conclusion is rational and a justification of the method adopted .
The far higher value arrived at by Walker and Kay is due simply to the fact that when the solution is diluted with alcohol and the effect referred to the solution as a whole , the effect produced is multiplied in proportion to the volume of alcohol present .
Further , it is claimed that uniform values for the molecular effect of alcohol are obtained only when the proportion of cyanate to water is kept 1912 .
] Studies of the Processes Operative in Solutions .
551 constant .
Table IX gives the percentage increase in the value of x W obtained from Walker and Kay 's values for Jc .
In Diagram 3 these are compared with the percentage increase in the values of Jcp2x W ( see p. 541 ) Diagram 3.\#151 ; Showing Proportionality of v* to Weight of Alcohol added when the Ratio of Ammonic Cyanate to Water is kept constant and a comparison with curves deduced from Walker and Kay 's values .
^ 300 Molecular proportions of alcohol added .
and those of the actual rates obtained by the method described .
It is only this last curve ( 3 ) which clearly shows the proportionality between the quantity of alcohol added and the effect produced .
* * The rates uncorrected for formation of carbonate are used , so that all points on the curve are comparable .
This renders all values on the curve slightly higher but does not affect its form Mr. E. E. Walker .
[ July 29 , Table IX .
Alcohol bj volume .
Molecular proportions of alcohol per 100 of water .
Jc kxW Increase of kxW Increase of kp2xW per cent. 0 0 *00595 0 -00595 per cent. per cent. 10 3*42 0 -00774 0 -00702 18 15 *2 30 12 *9 0 -0129 0 *00935 74 53-3 49 27 *9 0 *0295 0-0161 171 155 72 71 -5 0-093 0 -0291 389 207 90 234 0*575 0 *0684 1050 259 The results obtained on using propylic and isobutylic alcohols are given in the following Table X. Table X. Alcohol .
Molecular proportions of alcohol added .
Rate ( fraction changed .
per minute ) .
Rate of formation of ( NH4)2C03 .
Concentration of carbonate .
Cor- rected rate .
Accelera- tion per cent. Accelera- tion per cent , per mol .
0*20 mol .
Cyanate per 100 mols .
Water .
0 0 *0133 0-0008 0 -0072 0*0117 Ethylic ... 40 342 30 52 296 15 *3 3-83 Propylic ... 10 212 35 65 185 58 -1 5-81 iso-Butylic 2 157 12 100 132 12 *8 6*4 0*15 mol .
Cyanate per 100 mols .
Water .
0 0 -0111 0*0006 0 -0101 0 *00925 \#151 ; \#151 ; Ethylic ... 40 248 9 82 215 132 3*30 Propylic ... 10 160 5 91 138 49 *2 4*92 wo-Butylic 2 131 8 103 106 14 -6 7-3 The difference in the activity of the three alcohols is very striking , ethylic being less active than propylic , this in its turn being less active than isobutylic alcohol .
It is to be noted that the order in which the alcohols act is that observed on contrasting their activity as precipitants of salts from an aqueous solution and their physiological activity as hormones .
The opinion has already been expressed ( these studies , No. XIII ) that the action of the alcohols is largely mechanical .
It is reasonable to suppose that the tendency of the simple molecules of water to combine among themselves is decreased by the interposition of neutral molecules .
On this hypothesis it is to be expected that the larger molecules would have the 1912 .
] Studies of the Processes Operative in Solutions .
*553 greater effect both on account of their size and their greater mobility by reason of their lower affinity for water .
In the case of the formation of urea from cyanate , the net effect of the addition of water is to increase the velocity coefficient ; whilst in the case of the hydrolysis of cane sugar the activity of the acid is diminished .
It would seem , therefore , that the effect alcohols have of rendering the water more active is comparable with that produced by adding more water .
It is probably not a mere coincidence that the retarding effect produced by one molecular proportion of alcohol on the hydrolysis of cane sugar is practically equal to the acceleration effect of the same quantity on the conversion of ammouic cyanate into urea .
( + 3-83 per cent , in the case of ammonic cyanate , \#151 ; 3'97 per cent * in the hydrolysis of cane sugar .
) The results now brought forward are probably not without value as throwing light on the process whereby urea is formed from ammonic cyanate , which was discussed in a recent communication to the Society on the enzyme urease.+ It is not improbable that initially the cyanate tends to undergo decomposition into carbamate and finally into carbonate and that a relatively large proportion of urea is produced as the influence of the ammonic salt thus formed prevails more and more .
While recognising that the fact that the formation of urea proceeds at a bi-molecular rate may be accounted for , either on the assumption that two molecules of a cyanate meet to form the urea or that the salt is resolved into cyanic acid and ammonia , Walker and Hambly have contended that these explanations must be set aside in favour of the assumption that the salt is dissociated into its ions , because the change is accelerated by ammonic salts though not by ammonia .
But this argument is not a valid one : taking into account the activity of ammonic salts in comparison with that of ammonia , whatever the explanation of this activity , it is only to be expected that the salt would prove to be the more active in promoting the change ; moreover , an increase in the total amount of either radicle of the changing substance in the solutions will necessarily be attended by an acceleration of the rate of change .
That alcohol and its homologues should somewhat accelerate the change is not difficult to understand if it be assumed that the transformation involves the formation of the hydrol 0 f(oh)2 L(nh2)2 ' * From figures given by Armstrong and Worley , these Studies No. XIII .
t ' Roy .
Soc. Proc. , ' 1912 , B , vol. 85 , p. 109 .
554* Studies of the Processes Operative in Solutions .
Whilst it is not to be supposed that alcohols promote the formation of this compound , it is probable that they would promote its resolution into urea and thus hasten the formation of the latter .
It may be added that the production of the diamino-dihydrol in question would involve the prior production , at some stage , of corresponding ammonic salts : hence the accelerative influence of ammonic salts .
Walker and Hambly and Walker and Kay have in no way taken into account the concentrating effect of the substances they added and have overlooked the circumstance that , in effect , they were using solutions that were more concentrated than they supposed in many of the cases they studied .
One result at which they arrived is very noteworthy in connexion with the results now put forward , viz. , that sugar and similar substances have an accelerating influence on the transformation of ammonic cyanate into urea .
Whilst the influence of sugar is to be accounted for on the assumption that it combines with a certain amount of the water and therefore concentrates the solution , the effect produced by alcohols , especially in the case of the less soluble , must he mainly of a different order ; it cannot well be accounted for , except on the assumption that the water is modified by their presence and that they are probably in some way active mechanically in reducing the extent to which the water can enter into association with the substances that are present in solution .
|
rspa_1912_0110 | 0950-1207 | Studies of the processes operative in solutions. XXI.\#x2014;The hydrolysis of cane sugar by dilute acids. | 555 | 563 | 1,912 | 87 | Proceedings of the Royal Society of London. Series A, Containing Papers of a Mathematical and Physical Character | F. P. Worley, M. A., M. Sc.|Prof. H. E. Armstrong, F. R. S. | article | 6.0.4 | http://dx.doi.org/10.1098/rspa.1912.0110 | en | rspa | 1,910 | 1,900 | 1,900 | 10 | 109 | 3,188 | http://corpora.clarin-d.uni-saarland.de/surprisal/6.0.3/?id=rspa_1912_0110 | 10.1098/rspa.1912.0110 | null | null | null | Biochemistry | 60.366675 | Tables | 34.774704 | Biochemistry | [
-54.17052459716797,
-43.64797592163086
] | ]\gt ; Studies of the Processes Operative in Solutions .
XXI .
Hydrolysis of Cane Sugar by Dilute Acids .
By F. P. WOBLEY , M.A. , M.Sc .
, New Zealand , Leathersellers ' Company 's Research Fellow , Chemistry Department , City and Guilds ( Communicated by Prof. H. E. Armstrong , F.R.S. Received July 29 , \mdash ; Read December 5 , 1912 .
) In Part XII of these studies an account was iven of a close and extended study of the hydrolysis of cane sugar by means of chlorhydric and nitric acids in aqueous solution and of the influence of corresponding salts on the rate of change .
In the course of the investigation , not only were unexpected sources of error discovered in the method used by workers in reducing their observations but it became obvious also that the accepted views by which enquirers in this field have been guided hitherto need modification in essential respects .
It was pointed out , in particular , that the usual method of applying the mass action equation , to say the least , is not the best : besides a possible general error due to an incorrect initial reading , it gives a spurious constancy to the values of , 1naking it difficult to detect actual departures from the unimolecular law ; it was shown that the following is a better form of equation to in which and are the sugar concentrations at times respectively , successive equal intervals of time taken as small the accul.acy of the observations allows or the rapidity of the change demands .
In the tion referred to , the hydrolytic activity of the acid studied was determined in solutions of moderate ; consequently it was desirable to consider whether the conclusions arrived at by previous workers who have usecl very dilute acids may not also odification .
The subject has been dealt with already in Part VI of the " " Studies on nzyme Action\ldquo ; published from the laboratory of the City and Guilds College , * by E. F. Armstrong B. J. Caldwell , whose experiments were made directly with the object of the action of ncids antl enzymes at low degrees of concentration .
As it had been found that when only a very small proportion of enzyme was present the course of the change approximated to a linear and not to a logarithmic function of the time , it appeared 'Roy .
Soc. Proc 1904 , vol. 74 , p. 195 .
VOL. LXXXVII.\mdash ; A. Mr. F. P. Worley .
[ July 29 , not unlikely that the same result would follow in the case of acids .
Armstrong and Caldwell used solutions of strength of hydrogen chloride and in order that hydrolysis be about half completed within 10 hours carried out their experiments at about .
The conclusion at which they arrived was that though the results they obtained did not proyide evidence that the proceeds at a strictly linear rate , the approximation to a straight line law during the first two and a half hours is very close , the first 10 or 15 per cent. of the change being practically linear .
They therefore regarded their results as proof that the hydrolytic action of a small proportion of an acid is comparable with that of a small proportion of an enzyme .
* Assuming this conclusion to be correct , it was hoped that by making a series of experiments and with the concentrations at which the rate of change was in accordance with the mass action law , subsequently increasing the ratio of sugar to acid , it would be possible to find the dilution at which the rate of change began to be a linear function of the time .
As the improvements that have been made , from time to time , in the apparatus permit observations being carried on during many days at a constant temperature , the experiments were all carried out at C. The hydrolyst used was dilute sulphuric acid .
In the first experiment , one-tenth of a molecular proportion of acid was used with 200 molecular } ) ions of water and one of sugar .
Readings were taken minutes and 30 minutes after mixing and then at intervals of 60 minutes , during 7 hours .
The solutions were mixed at .
The results are given in Table I. Each reading is a mean of five observations taken at intervals of 30 seconds at the time stated .
The first difference is low probably because the temperature in the tube was slightly low at first .
It will be seen that after the first two intervals , when but a small fraction of the is inverted , the rate of change decreases regularly as the action proceeds and that there is no indication of a linear relationship .
In a second experiment , the concentration of the acid was reduced to onehundredth of a molecular proportion .
The rate of was very slow .
* In view of the importance of the conclusions which E. F. Armstrong and R. J. Caldwell were inclined to draw from their observations on action of acids on cane sugar in dilute solutions , it appeared to me to be necessary to verify their results , utilising for this purpose the improvements effected by Mr. Worley in the polarimetric method and also in reducing the observations .
I am indebted to Mr. Worley for having undertaken the somewhat arduous task .
I may add that he completed the work last summer and that a preliminary verbal communication of the results was made to the Biochemical Club at their meeting on July 8 , 1911.\mdash ; H. Fi .
A. 1912 .
] Studies of the Processes Operative in Solutions .
The observations were continued\mdash ; with one or two interruptions caused by accidents to the temperature regulator\mdash ; during 13 days .
The results are given in Table II .
Again in this case the rate of change decreased as the action went on .
As the end-value was not determined , the value of could not be calculated .
On account of the interruptions , the time is iven as the interval between successive readings .
Table I. Table II .
In Experiments 3 and 4 the concentration of the acid kept the same as in the previous experiment , viz. one-hundredth of a molecular proportion , whilst that of the sugar was increased to two and four molecular proportions respectively .
The two experiments were carried out simultaneously on the two water circuits of the apparatus and were continued during a week with Mr. F. P. Worley .
[ July 29 , one interruption near the beginning .
The end values were obtained by a given weight of the original solution in a steam oyen and making up by addition of water any loss caused by evaporation ; they are at the best only approximate .
The great difficulty of obtaining correct end values has been already dealt with* and will be further discussed in a later paper .
Two-decimetre tubes were used in these experiments in place of the fourdecimetre tube used in the previous experiment .
The results are tabulated in Tables III and In the third columns are given the differences per 60 minutes derived from the consecutive readings ; the fourth contain the values of the velocity constant deduced in accordance with the formula the interval of time being the interval between the consecutive from which the values and are derived .
The differences per 60 minutes rise at first but the abnormally high value of the third difference in both experiments would seem to indicate an unobserved temporaly rise in the temperature part of that interval .
In any case , after the third difference , when only about of the had been , the fall in the value of the differences is obvious .
Table III .
Table In the fourth column in the tables the values of fluctuate to some extent , on account of the errors of reading due to the very small amount of change during each interval .
They rise as the action proceeds but the fact that * Part XII , ' Chem. Soc. Trans 1911 , p. 349 .
1912 .
] Studies of the Processes in Solutions .
practically the same value is obtained in the two experiments is absolute proof that the rate of , at these concentrations , is proportional to the amount of cane sugar in solution .
The experiments show that at the relative concentrations of sugar and acid considered thele is no indication of the action being a linear function of the time .
It now became necessary to consider whether rise in the values of deduced by Armstrong and Caldwell were not due to the method of experimental values which they adopted .
The values of were dednced in the manner almost univelsally followed by means of the equation As has been pointed out , this method is open to serious It ives a spurious constancy to and any in the value of affects all the separate values of unequally , those at the inning being most affected .
In the four experiments considered , was determined 10 or 15 minutes aftel the solutions had been run into the polarimeter tubes .
If , as is very possible , the temperature had not then attained its correct value but was somewhat low , an apparent rise in the early values of and their later on wss to be expected from this cause alone .
The values of have consequently been recalculated using the equation and keeping the intelval of time constant .
The results of recalculating the values given by .
F. and Caldwell in the of two of their experiments ( representative of the two concentrations examined ) are set forth in Tables and , along with their own values , for comparison .
The strength of the acid was in each case ; the sugar solutions contained 171 and 342 .
of cane sugar respectively per litre .
In Table the interval of adopted is 90 minutes and 60 minutes and in Table minutes .
A comparison of the numbers arrived at with those previously obtained by Armstrong and Caldwell shows very clearly the errors that may arise from applying the mass action equation in the way usually advocated .
In the first place , the marked rise ( on which Armstrong and Caldwell relied ) in the early values and constancy in later values disappears and there is apparently a small continuous rise throughout each series which is scarcely perceptible in Table .
The rise is most probably caused by an error in the final reading at the completion of the inversion .
In the second place , the actual yalues of obtained by the two methods al.e somewhat different and the Mr. F. P. Worley .
[ July 29 , Table Table 1912 .
] Studies of the Processes Operative Solutions .
irregularity of those obtained on using a constant time interval in the calculations shows that no importance can be attached to variations in the value of the constant when the interval is less than 60 minutes .
The first five or six values of , as originally determined in each series , consequently are not to be relied upon .
All evidence of a linear rate thus disappears completely .
The most conclusive evidence against it , however , is obtained on comparin the values of for solutions of different proportions of sugar .
If , as Armstrong and Caldwell supposed , there be a tendency towards a linear change in the more dilute sugar solution , i.e. , that the rate of change at this concentration tends to be independent of the concentration of the sugar , then increase in the concentration of sugar should not increase the rate of change in the same proportion and the value of should be much smaller in the case of the more concentrated solutions .
In point of fact , in the more concentrated solution , the value of , instead of less , was greater than in the more dilute .
It therefore appears that there is no reason to that the rate conditioned by a dilute solution of an acid differs in the manner suggested by Armstrong and Caldwell from that eHected by more concentrated acid solutions .
Consequently , there is not , at present , any evidence to show that the action of dilute acids is analogous to that of an enzyme used in small proportion .
This conclusiol ] , however , in no way affects the conclusion on which and Caldwell 's experiments were based , that a constant weight and not a constant prop ortion cf the total amount of cane sugar present is hydrolysed in unit time hen only a very small proportion of enzyme is used : the evidence adduced by Adrian Brown in support of this conclusion being decisive and in no way subject to the criticism which may be applied to the results obtained with acids .
Such a conclusion serves to accentuate the marked difference in behaviour of enzymes and of acids as hydrolytic agents .
The above account was written before the publication by Messrs. M. A. Rosanoff , .
H. Clark and R. L. Sibley*of the results of " " A tion of the Velocity of Sugar Hydrolysis These observers attribute the fall in the velocity coefficient found by Julius Meyer and the rise foumd by E. F. Armstrong and Caldwell to an erroneous value having been assigned to the initial rotation ; they show that values of the constant are obtained that neither nor fall by substituting for the observed initial values those 'Amer .
Chem. Soc. Journ Dec. , 1911 , p. 1911 .
Mr. F. P. Worley .
[ July 29 , deduced from the subsequent part of the change .
The .
therefore conclude that the ] ysis follows a strictly unimolecular course .
There is little doubt that in Julius Meyer 's experiments , Hudson has already pointed out , the fall in the value of the constant arrived at is due to errors in the initial values ; the rise observed by and Caldwell is doubtless due to a similar cause .
These errors , however , are attributable probably not to inaccurate observations of the rotation but to the fact that the temperature had llot becolne constant .
Although Rosanoff , Clark and Sibley have arrived at a right conclusion , they have done so by an unsound method , by calculating an initial value in correspondence with the assumption they set out to prove , namely , that the action proceeds at a strictly unimolecular rate from the start .
They have also ovel.looked the fact that and Caldwell 's values at time are not the rotations at the time of mixing but those observed 10 or 15 minutes later ; it is , in fact , distinctly stated by them that the first reading was taken 10 or , after mixing , when the temperature had attained to that of the thermostat .
The American observers say " " that Armstrong and Caldwell 's observed values of are erroneous and that calculated values are much more reliable is clearly indicated by the data reproduced in Tables and The solutions corresponding to these tables have identically the same final rotation , , hence must have been identical in composition .
Yet the observed initial rotations were respectively and .
On the other hand , our calculated values , and , are practically equal The difference in Armstrong and Caldwell 's values at time is obviously due either to a slightly different interval of time having elapsed between mixing and ' t , he first reading or else to the temperature at not having been exactly the same in both experiments .
Rosanoff , Clark and Sibley have used the equation which is so generally adopted and have not seen that the errors due to an erroneous initial observation may be avoided by using the equation They have also ignored the possibility of an error in the final rotation In Part XII ( loc. cit. ) it is shown that the observed end point may be 'Zeit .
Physik .
Chem 1908 , vol. 62 , p. 59 ; , 1910 , vol. 72 , p. 117 .
'Amer .
Chem. Soc. Journ 1908 , vol. 30 , p. 1165 ; ibid. , 1910 , vol. 72 , p. 17 .
1912 .
] Studies of Processes in Solutions .
erroneous to a considerable extent ; it is also pointed out that it is possible to deduce an end point which gives the appearance of constancy to the values of , when in reality they should show a steady rise or fall .
The argument may also be applied when the values of are deduced by the equation in the case of a calculated initial value , as it is possible to so adjust the initial value as to make the values of approximate to constancy , in reality they should rise or fall .
Studies of the ocesses Operative in Solutions .
XXII.\mdash ; The Hydrolysis of Sugar by : Acid ; on imetric A By F. P. Communicated by Prof. H. E. Armstrong , F.R.S. Received July 29 , \mdash ; December 5 , 1912 .
) In view of the fact that the acids used in the inquiries discussed Tart XII and the succeeding parts of these studies were all monobasic , it was desirable to rrate the hydrolytic activity of a dibasic acid , more especially with a view to following the progressive alteration in moleculal hydrolytic activity and apparent degree of hydration changes of concentration .
A series of experiments , sulphuric acid as the catalyst , has been carried out therefore on the lines of those described in Part Some of the complexities of the hydrolytic process and of the } ) olarimetric .
method of following its course were dealt with in that communication ; moreover , several disturbing factors were referred to , such as the change in the osmotic conditions as the action proceeds and changes in the optical activity of the various substances due to dilution , to their mutual interference , and to the influence of acids or salts ; the possible influence of\ldquo ; trotation however , was not mentioned , as there appeared to be no reason to believe that it in any way affected the results .
The study of the rates at which hydrolysis is effected by sulphuric acid of different degrees of concentration has shown that exactly the same complexities are met with in this case as were experienced in the case of
|
rspa_1912_0111 | 0950-1207 | Studies of the processes operative in solutions. XXII.\#x2014;The hydrolysis of cane sugar by Sulphuric acid; also a note on improvements in Polarimetric apparatus. | 563 | 581 | 1,912 | 87 | Proceedings of the Royal Society of London. Series A, Containing Papers of a Mathematical and Physical Character | F. P. Worley|Prof. H. E. Armstrong, F. R. S. | article | 6.0.4 | http://dx.doi.org/10.1098/rspa.1912.0111 | en | rspa | 1,910 | 1,900 | 1,900 | 18 | 231 | 6,720 | http://corpora.clarin-d.uni-saarland.de/surprisal/6.0.3/?id=rspa_1912_0111 | 10.1098/rspa.1912.0111 | null | null | null | Biochemistry | 54.321607 | Tables | 18.920218 | Biochemistry | [
-53.76645278930664,
-43.873783111572266
] | ]\gt ; 1912 .
] Studies of Processes in Solutions .
erroneous to a considerable extent ; it is also pointed out that it is possible to deduce an end point which gives the appearance of constancy to the values of , when in reality they should show a steady rise or fall .
The argument may also be applied when the values of are deduced by the equation in the case of a calculated initial value , as it is possible to so adjust the initial value as to make the values of approximate to constancy , in reality they should rise or fall .
Studies of the ocesses Operative in Solutions .
XXII.\mdash ; The Hydrolysis of Sugar by : Acid ; on By F. P. Communicated by Prof. H. E. Armstrong , F.R.S. Received July 29 , \mdash ; December 5 , 1912 .
) In view of the fact that the acids used in the inquiries discussed Tart XII and the succeeding parts of these studies were all monobasic , it was desirable to rrate the hydrolytic activity of a dibasic acid , more especially with a view to following the progressive alteration in moleculal hydrolytic activity and apparent degree of hydration changes of concentration .
A series of experiments , sulphuric acid as the catalyst , has been carried out therefore on the lines of those described in Part Some of the complexities of the hydrolytic process and of the } ) olarimetric .
method of following its course were dealt with in that communication ; moreover , several disturbing factors were referred to , such as the change in the osmotic conditions as the action proceeds and changes in the optical activity of the various substances due to dilution , to their mutual interference , and to the influence of acids or salts ; the possible influence of\ldquo ; trotation however , was not mentioned , as there appeared to be no reason to believe that it in any way affected the results .
The study of the rates at which hydrolysis is effected by sulphuric acid of different degrees of concentration has shown that exactly the same complexities are met with in this case as were experienced in the case of Mr. F. P. Worley .
chlorhydric and nitric acids .
Thus , in the more concentrated solutions , there is a gradual change in the final angle of rotation after hydrolysis is complete such as was observed in the inquiry described in Part XII ; this was allowed for as before when necessary , though in most of the experiments the concentration was not great enough for its effect to be noticed .
In the solutions , the value of the velocity coefficient calculated from the equation is found to increase as hydrolysis proceeds ; that is to say , the ratio of the rate of hydrolysis to the concentration of the oane sugar increases as the sugar is hydrolysed .
This increase was shown in Part XII to be due , in all , mainly to the using up of water as hydrolysis , whereby a decrease is brought about in the ratio of water to acid .
As a decrease in this ratio involves a considerable increase in the molecular hydrolytic activity of the acid , it is to be expected that in cases in which the proportion of water used up in the hydrolysis is appreciable , the ratio of the rate of drolysis to the concentration of the cane sugar would increase appreciably as the action proceeds .
In addition , ation of the change in rotatory power attending hydrolysis at different dilutions has thrown light on the variation in the amount of optical inversion at different deglees of .
this .
point will be more fully discussed at a later Possible Effect of " " Mutarotation.\ldquo ; \mdash ; In view of the great accelerating influence of acids on the rate at which the one modification of glucose passes over into the isodynamic form , there is little doubt that in the presence of the relatively large quantities of acid used the equilibrium would be rapidly ived at that the phenomenon known as mutarotation , involving a gradual change in the specific rotatory power , would not be perceptible to any appreciable extent and , therefore , would not have any measurable influence on the results .
The futility of attempting to attribute any , change in the value of the elocity coefficient as hydrolysis proceeds to ' mutarotation\ldquo ; scarcely need be pointed out .
The wonder is that in the presence of so many possible disturbing influences the from constancy is not greater than it is .
In the case of the more concentrated solutions the alteration in the specific molecular hydrolytic activity of the acid as the ratio of water to acid diminishes is sufficient to account for a considerable rise in the value of the constant as hydrolysis proceeds .
There is , further , the probability that , the products of change exert an appreciable influence ; such an influence is !
1912 .
] Studies of the Processes in Solutions .
likely to be of a very complex nature and the fact that the " " constant\ldquo ; is so little affected is an indication that the various effects of the glucose and fructose formed must to a great extent counteract one another .
Apart from an actual in the constant as hydrolysis proceeds , there is the possibility of an apparent caused , on the one hand by an incorrect value being taken as the end point through of the fact that the value of the final rotation may not remain constant , on the other by the adoption of an incorrect initial value such as Hudson*pointed out was the cause of the fall in the value of the constant found by Julius and attributed by him to " " mutarotation to Hudson , " " otation \ldquo ; should cause ) in the constant .
He has argued that the higher rotatory power of the first formed would make it appear that at any moment less cane had been inverted than was the case and that as this effect is greatest in the earlier of the action the constant would appear to rise .
This vument , however , is misleading , as it involves the assumption that the amount of change is measured from the very start or in any case before there is a maximum excess of in solution .
In the event of -glucose being first fo1med and equilibrium being soon attained , the excess of the more dextro-rotatory -glucose would rapidly attain to a probably long before an initial could be taken .
The excess would then decrease as the hydrolysis proceeded and the rate of inversion , instead of appearing less , would appear to be greater than the rate in the absence of " " mutarotation As the higher rotatory power of the -glucose would cause the concentration of the unhydrolysed sugar to be over-estimated , the ratio of the observed rate of inversion .
to the concentration of the cane the velocity coefficient , would probably be little , if at all , affected eithel in value or in constancy .
It will shown later that , except at the very of hydrolysis , mutarotation has no effect on the constant .
Experimental acid used Yyas purified by crystallisations of the monohydrate , .
The strength of the solution used was ascertained from its density : two determinations at gave the values and resl ) ectively ; hence 1 .
of the tion contained .
of the acid .
The cane sugar used was purified coffee sugar specially supplied by Messrs. Tate .
The molecular proportions of the various substances used in the experiments were 1 of sulphuric acid and from 30 to of water , ' Amer .
Chem. Soc. JourIl vol. 30 , p. 1160 ; vol. 32 , p. 885 .
'Zeit .
physik .
Chem 1908 , vol. 62 , p. 69 .
Mr. F. P. Worley .
[ July 29 , molecular proportions of being used in the experiment with 30 and 40 of water and in those in which the proportion of water was from 40 to 200 ; in the case of the experiments with 40 of water , the same value was obtained with of sugar as with .
The experiments at the different concentrations were not duplicated , as the subsequent of the results and still more the treatment to which they were subjected in obtaining the apparent hydration values of the acid would reveal any irregularity in the values of obtained .
As there appeared to be no flaw or irregularity in any of the experiments and as the subsequent treatment of the results showed that they were perfectly uniform , there appeared to be no necessity of duplicating the indiyidual experiments .
The solutions were nlixed and the experiments carried out in the manner described in Part XII .
By means of the heated chamber used to bring the solutions to the required temperature before mixing ( see p. 580 ) , it was possil ) to obtain readings of the optical rotation very near the inning of each experiment .
The values of for the clifferent experiments deduced by of the equation ' are given in Table I. In the case of the ments with the more concentrated solutions , in which the value of the velocity coefficient obviously increased as the hydrolysis proceeded , the value corresponding to the of the interaction was found by extrapolation as described in Part XII .
Table I. Molecular proportions Molecular proportions of cane sugar .
of From the numbers given in Table I the value of the apparent molecular hydration of the acid at different concentrations was deduced by the raphic method used in Part XII in the case of the hydrolysis of cane sugar by 1912 .
] Studies of the Processes in Solutions .
chlorhydric and nitric acids and in Part XXIII in the case of the hydrolysis of methylic acetate by chlorhydric acid .
Diagram 1 shows the results obtained by this method of analysis .
The apparent molecular hydration of the acid is equal to the number attached to any curve when the total number of molecular proportions of water present represented by the abscissae corresponds to the highest point of the curve when it is momentarily horizontal .
The values of the products iven by the Mols .
total water .
ordinates at these points are the corresponding lnolectllar hydrolyti activities .
The dark curve through the apices thus ives the values of the molecular hydrolytic activities of the acid at concentrations .
The results are set forth in Table II , the molecular olytic activity.of the acid determined in the manner described multiplied by one Lhousand .
* In Part VII of these Studies , Armstrong and Wheeler , in all investigation of the relative efficiencies of acids as deduced from their conductivities and hydrolytic activities , have described experiments carried out to determine the rate of hydrolysis of cane sugar by sulphuric acid at four concentrations , and .
Their results , however , are not suitable for the method of analysis under discussion , as an insufficient Mr. F. P. Worley .
[ July 29 , Table II .
Sulphuric acid being a dibasic acid , the results now brought forward are particularly interesting in comparison with those obtained previously with the monobasic chlorhydric and nitric acids .
As in the case of these latter , the degree of apparent molecular hydration of sulphuric acid increases to Mols .
total water .
number of experiments was made at the higher concentrations .
As the experiments were carried out before most of the improvements had been made in the apparatus and the method of carrying out the experiments , the accuracy attained to was probably insufficient for the purpose now in view .
Moreover , in calculating the molecular hydrolytic activities the concentration was reckoned as the proportion of acid to the total water present , not to the free water , as in the above improyed method .
Their general conclusion , however , is correct , namely : that the molecular conductivity and molecular ytic conductivity are altered in opposite directions by change of concentration .
1912 .
] lStudies of the Processes in Solutions .
a maximum as dilution proceeds , whilst the molecular hydrolytic activity of the acid decreases to a minimum .
To aid the comparison , the results are expressed graphically for the three acids and for the monobasic benzenemonosulphonic acids which I have examined recently ( Diagrams 2 and 3 ) .
It will be seen that the apparent molecular hydration values of chlorhydric and nitric acids do not reach a maximum nearly so soon as do those of acid but increase up to a dilution of 200 molecules of water per molecule of acid ; in the case of the sulphonic acids , however , this is not the case , the resemblance to sulphuric acid being very close .
It is Mols .
total water .
possible bhat the difference in the case of chlorhydric and nitric acids may be due to slightly low values been obtained for the velocity constant at the higher dilution , as these acids were the first examined ; it will , therefore , be desirable to check the results .
The curves representing the hydrolytic activities of the monobasic acids lie close together , there very little difference in the strengths of the acids ; that for the stronger sulphuric acid is higher , though of the same shape .
The similarity of the hydrolytic action of sulphuric and chlorhydric acids is further out in Diagram 4 , in which the curves represent the change in the value of the velocity coefficient with change of concentration .
In Curves and the concentration is expressed as the molecular proportions of acid to a given nber ( here 150 ) of molecular proportions of water , whilst in Curyes A and the dilution is expressed as the number of molecular proportions vater to one of acid . .
F. P. Worley .
[ July 29 , Curves A and reveal a point noted by Armstrong and Wheeler in Part which is not evident in Curves and .
The activity of sulphuric acid relatively to chlorhydric becomes somewhat greater as the dilution is increased .
This may be due to the radual coming into play of a second point of attack in the sulphuric acid .
Sulphuric acid in concentrated solution acts mainly , it must be supposed , as a monobasic acid .
Mols .
to 1 of acid .
( urves A and B. ) Mols .
acid to 150 of .
( Curves and It should be pointed out , however , that even though sulphuric acid in dilute solution act as a dibasic acid and be capable of hydrolysing two molecules of hydrolyte at the same time , the rate of hydrolysis will still be proportional to the concentration of the hydrolyte and not to its square , as each active point of attack of the sulphuric acid may act independently of the other .
The only observable effect will be in the degree of activity of the acid .
1912 .
] Studies of the Processes Operative in Solutions .
Change in the Degree of Optical Inversion sis at Dilutions .
On comparing the final negative rotation at the completion of hydrolysis with the initial positive rotation of the sugar , it was found that this ratio decreased very considerably as dilution was increased .
As the solutions were brought to exactly in the heated chamber ' and transferred immediately to the polarimeter tube , which was already on the water circuit at the right temperature , the initial readings could ) taken very near the inning of the hydrolysis , the time after mixing being noted ; consequently , it was possible to find by extrapolation the approximate rotation at the time of mixing .
the experiments were carried out , the idea of comparing the initial and final rotations had not occurred and the zero taken was that found in the absence of the polarimeter tube ; consequently , the snlall error due to the optic activity of the glass discs at the ends of the tube has not been avoided .
From the results , however , it is clear that the error of extrapolation and that due to the glass discs is negligibly small in comparison with the large amount of change in the above ratio attending change of concentration .
The variation in the ratio was from for the most concentrated solution to for the most dilute .
As the ratio of sugar to acid the same in most of the experiments , it is not possible to say definitely how much of the variation is due to the variation in the concentration of the sugar and how much to that of the acid .
From the experiments with 40 molecular proportions of water to 1 of acid and respectively of sugar , it appears that the change in the ratio is not due mainly to the sugar , as practically the same yalue , viz. , and was obtained in the two experiments , whilst in the experiment with 80 of water and of sugar the value was .
The only difference this experiment and the one with 40 of water and of sugar is that the concentration of the acid is twice as great in one as in the other .
It appears , then , that the in the ratio is due , in all probability , mainly to the change in the concentration of the acid .
Table III gives the values of the ratio of the final negative rotation to the initial positive rotation at the different dilutions .
One molecular proportion of sulphuric was used throughout .
In Diagram 5 the values of the ratio of the final ative to the initial positive rotation are plotted in Curve A as ordinates ainst the total original water as abscissae .
The values are seen to be perfectly regular and to lie evenly on a curve .
If the values of the ratio are plotted against the relative concentrations of the acid ( Curve B ) a line is obtained .
VOL. LXXXVII.\mdash ; A. 2 Mr. F. P. Worley .
[ July 29 , Table I II .
Mols .
to 100 .
( Curve B. ) Mols .
to 1 of .
( Curve A. ) This alteration in the degree of optical inversion attending in concentration is , with little doubt , to be attributed mainly to alteration of the rotatory power of one or more of the sugars present but further investigation is necessary before the exact manner in which it is brought about can be ascertained .
It is well known that though the specific rotatory power of cane sugar and of glucose is very little affected by increase of concentration , that of fructose is made considerably more negative .
Change of rotatory power due to of concentration , bowever , is far too small to account for the efl'ect observed above ; moreover , the effect appears not to be due mainly to the concentrations of the sugar .
It is , therefore , to be supposed that the acid is responsible for the alteration .
It has long been known that the specific rotatory power of invert sugar is greatly increased by the presence of sulphuric and chlorhydric acids .
1912 .
] Studies of the Processes in Solutions .
Gubbe*has shown that if different amounts of acid are used with the same quantities of sugar and water , the increase in the rotatory power of the invert is proportional to the amount of acid present .
Preliminary experiments I have made confirm the conclusions of earlier investigators that it is the fructose and not the glucose that is mainly influenced by the presence of the acid .
In the experiments described in the present communication , the proportions of acid and sugar were kept constant throughout , that of water alone being varied .
If the observed be due to the influence of the acid on the rotatory power of the invert , this influence must vary greatly with amount of water present .
From the fact that the specific rotatory power of fructose is influenced in the same direction by the presence of acids as by increase of concentration and from the fact that the change in the amount of optical inversion described above is apparently dependent on the aqueon concentration of the acid rather than on the ratio of acid to , it appears probable that the influence of acids on the rotatory power of fructose is greatly due to their concentratin , effect .
Support is given to this idea by the fact that oxalic acid , which has little concentrating effect , was found by Gubbe to have practically no influence on the rotatory power of invel.t sugar ; also by the fact that alcohol has an opposite eHect , reducing the laevo-rotatory power of invert The evidence at present available goes to show that the effect observed is due to changes in the rotatory power of the sugars , chiefly in that of the , caused by the action of the acid on the water .
large effect produced may be attributed to chan ges in the of molecular regation rather than to changes in the degree of hydration ; it seems probable , in fact , that the polymerisation of fructose\mdash ; attended by increase of rotatory power\mdash ; would be more likely to occur in concentrated solutions and in presence of acids , whilst simplification would be brought about by rise of telnperattlre or the presence of neutral sOlvents such as the alcohols .
It is proposed to study the effect of neutral solvents on the rotatory power of fructose from this point of view .
The Validity of the netric Mof following Course of a Chemical Changj .
In Part XII of these studies and in the present communication many of the complexities of the polarimetric method of following the COUl.se of the hydrolysis of cane sugar by solutions of acids have been dealt with at 'Ber 1885 , vol. 18 , p. 2207 .
Mr. F. P. Worley .
[ July 29 , some and it is now necessary to consider the degree of confidence that can be placed in deductions from results obtained by this method .
In Part XII it was shown that , in cases in which the proportion of water to sugar and acid comparatively small , difficulties are met with owing to the gradual change in the rotatory power of the solution after hydrolysis is complete and to the fact that the velocity coefficient increases in value as hydrolysis proceeds .
In less concentrated solutions , however , there is little change in the final optical value and within the narrow limits of experimental error the velocity coefficient remains constant hydrolysis proceeds .
That is to say , the rate of hydrolysis is strictly proportional to the concentration of the cane sugar when the latter , at any given time , is taken as proportional to the difference between the rotation at that time and the final rotation .
It is obvious that such possible infiuences as that of " " mutarotation\ldquo ; and of change of specific rotatory power , due either to changes of concentration or to the influence of the acid on the rotatory power of the various present , either have no effect on the constancy of the velocity coefficient or the sum of the various effects is zero .
It is none the less important to investigate the separate disturbing effects that and to ascertain whether the magnitude of the velocity coefficient be in any way affected by them .
1 .
The of an Increase in the Rotatory Power of , caused by the Presence of the Acid Catalyst.\mdash ; In the polarimetric investigation of the rate of the hydrolysis of cane sugar , the difference between the rotation at any moment and the final rotation , i.e. is taken as proportional to the amount of cane sugar remaining unhydrolysed at that moment .
[ November 28 , 1912.\mdash ; This is true even when the rotatory power of the invert is altered by the presence of the acid , provided that the rotations produced by the various sugars present are proportional to their concen trations an experiment .
For if , at ti1ne be the concentration the cane sugar and that of the invert sugar , their specific rotatory powers being and , the rotation produced by the mixture will be After complete hydrolysis , the rotation is a .
Hence .
That is to say , isproportional to the concentration of the unhydrolysed cane sugar and independent of the particular values of and ] The velocity coefficient is consequently affected neither in constancy nor in nitude by an alteration in the rotatory power of the invert sugar .
1912 .
] Studies of the Processes in Solutions .
This , however , is not the case if there be a gradual change , as hydrolysis proceeds , in the specific rotatory power of any of the sugars present changes in their concentration .
The fact that the rotatory power of fructose is made considerably more negative by increase of concentration , whilst that of cane sugar and lucose is but little affected , as Hudson*has pointed out , should cause a gradual in the value of the " " constant From iments made by Rosanoff , Clark and Sibley , however , it is not unlikely that in a sugar solution in process of hydrolysis the specific rotatory power of the invert sugar is constant .
This point is , however , in need of further investigation .
2 .
Effect of lutarotation.\mdash ; It is necessary to consider only the mutarotation of the glucose , the ument being exactly the same in the case of fructose .
On hydrolysis , each molecule of cane gives rise presumably to one of -glucose , the olucose so formed rapidly into the -form of lower rotatory power ntil equilibrium between the two forms is attained .
If the initial molecular concentration of the cane be and , at time molecules have been hydrolysed ; and if , of the molecules of -glucose that have been formed , have into the -form : then is the concentra- tion of the relnaining cane sugar , that of the -glucose and that of the -glucose .
The rate of hydrolysis of the cane is ooiven by , whence ( 1 ) and .
( 2 ) rate of of ucose into - , lucose is given by ' ( 3 ) whence .
( 4 ) The amount of glucose in equilibrium at time with of -glucose is from equation ( 3 ) equal to since when equilibrium is obtained .
Hence the amount of -glucose in excess of the equilibrium mixture is From ( 2 ) and ( 4 ) , ( 5 ) and from ( 5 ) and ( 1 ) 'Amer .
Chem. Soc. Journ 1910 , vol. 32 , p. 888 .
Ibid. , 1911 , vol. 33 , Mr. F. P. Worley .
[ July 29 , Now the velocity coefficient of ' ' mutarotation\ldquo ; is very much greater than that of the hydrolysis of cane sugar in acid solution .
Except , therefore , for very low values of is an extremely small quantity and may be .
The aOove ratio is thus equal to , i.e. to a constant quantity , except when is very small .
In other words , except very near the beginning of the hydrolysis , the excess of -glucose over the equilibrium mixture is proportional to the concentration of the unhydrolysed cane sugar .
In Diagram 6 , if the curve represent the change of rotation in the absence of any mutarotation effect , then when mutarotation occurs , a curve such as would be obtained , the intercepts and Time .
being proportional to the unhydrolysed cane sugar and present at times and .
As and are respectively proportional to the same quantities , it follows that .
That is to say , the difference between the rotation at any moment and the final rotation , viz. , , is still proportional to the concentration of the unhydrolysed cane sugar and the velocity coefficient except at the very beginning of hydrolysis is thus unaffected either in constancy or in magnitude by the effect of mutarotation .
It appears then that in spite of the many complexities of the polarimetric method of following the course of the hydrolysis of cane sugar , the results arrived at by the method may be accepted with a considerable degree of 1912 .
] Studies of the Processes in Solutions .
confidence .
In execution the method has nlany advantages over a chemical method ; nevertheless it is at a great disadvantage , as it is impossible , by its aid , to arrive at the true concentration of any of the changing substances and it is necessary to investigate all disturbing factors before the results arrived at can be accepted with anything like confidence .
is true of physical methods in and it must be admitted that after all , when it is possible to uleasure accurately by chemical means the amount of a substance present at a iven time , the chemical far superior to the physical .
Note on the Apparatus used in Determining the Rate of Chemical Change by Polarimetric Observations .
As the apparatus used has been altered in almost every detail and much improved , a brief account may be iven of the refinenlents that have been introduced and of the precautions that have been found in order to reduce to a the effect of the various possible sources of error .
DIAGRAM 7 .
* Originally put forward as No. XVII of these studies but withdrawn when electrical heating was introduced .
Mr. F. P. Worley .
[ July 29 , In Diagram 7 is given a eneral sketch of the apparatus , showing the thermostat in association with a polarimeter and water circuit on each side .
The apparatus erected in a dark room kept at constant temperature so as to minimise the variations in the fall of temperature in the circuits .
The thermostat is kept at , so that the temperature of the polarimeter tube may be , the fall in the circuit being about C. The arrows show the course of the water from the tank through the circuits into the tubes and on through the pump back to the tank ; the tubes are provided so that the temperature of the water urning to the tank may be taken by means cf a thermometer with the bulb immersed in mercury in an inner test-tube .
It is essential to have as resistance as possible in the circuits , so that the flow of water may be rapid .
The speed of the motor is regulated by a lamI ) resistance , the rate of flow of water through each circuit being nlaintained at about 5liCres a minute .
The lettered parts are as follows:\mdash ; , copper lined wooden tank of about , 60litres capacity ; , polarimeters ; , motor , horse power , 200 yolt ; Albany rotatory bronze pump ; lamp ; -regulator ; , stirrer ; , Beckmann thermometers ; -volt Osram lamps ; , Jena glass tubes , ' A description of the polarimeter used was iven by Caldwell and In place of the adjustable slit at the far end a slit has been inserted immediately in front of the triple field nicols and the light from the me1cury arc lamp reduced to an approxin ) ately parallel beam by means of a lens between the lamp and the polarising nicol .
By this means much Jreater illumination is obtained and the beam of light is more nearly parallel in the polarimeter tube .
The vernier is ated by a candle-power 2-volt Osram lamp partially covered with tin foil , in series with a similar lamp to illuminate the note book Diagram .
By this means , when adjustment has been obtained , the vernier can be illuminated and the result recorded hout the eye being dazzled and its sensitiveness impaired .
Clock.\mdash ; The error introduced by not taking the at the moment has been greatly reduced by the use of an extremely accurate and trustworthy eight-day clock of the marine clock pattern , specially made by Messrs. Benson .
The clock has a large centre second hand and an 8-inch dial which may be faintly illuminated by a beam from the vernier lamp .
As a " " Brush Quartzlite\ldquo ; mercury arc lamp burner supplied the necessary resistance for a 200-volt circuit Brush EIectrical Part IX , ' .
Soc. Proc , vol. 81 , pp. 112\mdash ; 117 .
1912 .
] Studies of the Processes Operative in Solutions .
Engineering Company , Limited , is used , all measurements made with the green line .
This lamp has proved very satisfactory .
The brilliance of the light allows of the use of a very small half-shadow angle , which greatly increases the accuracy of the readings .
To prevent the light from the room , the lamp is enveloped in a thick black velvet cover .
Te , nperature Regulation.\mdash ; The thermostat is heated electl.ically by means of a 16 candle-power carbon filament lamp , Diagram 7 and Diagram 8 ) , the temperature controlled by means of a small toluene regulator made a thin-walled test-tube , Dingram 7 and , Diagram 8 ) .
This is so rapid in its action that a delicate thermo- meter fails to record any change of temperature .
From the rate at which the temperature found to fall when the lamp is kept shut off and the length of time the lamp remains extinguished when in use , it is found that the maximum temperature variation is C. The , difficulty of electrical ulation is the fouling of the mercury surface in the thermoyulator and the contact of the relay due to sparking .
This has been DIAGRAM 8 .
: 580 Mr. F. P. Worley .
[ July 29 , overcome in an ingenious way , devised by Dr. Haworth of this College , which will be easily understood by reference to Diagram 8 .
The current that is made and broken in the thermo-regulator is very small , being less than 1 milliampere ; it is derived from a Leclanche cell circuit , in series with a resistance R. current actuates a Siemens Post Office relay , which makes and breaks a larger current .
The circuit carries a current from the mains ( volts ) through a 16 candlepower carbon filament lamp as resistance .
It is divided into three parts , one of which , , is made and broken in the relay ; the second , , is a resistance of about 30 ohms ; the third , , passes round an electromagnet taken from an electric bell .
The lesistance of is adjusted so that when contact is made in circuit in the relay , the current in is not sufficient to allow the electromagnet to hold down the armature but is powerful enough to do so when the circuit is broken .
The circuit is direct from the main and includes the heating lnmp H. When contact is made at in the circuit , the circuit is completed in the relay .
In consequence the armature of the up and the circuit is broken at the platinum contact , thus shutting off the heating lamp .
The current that is made and broken in the relay is only a portion of the current in the circuit B. In addition , the presence of the circuit without such as exists in prevents sparking at the contacts in the relay .
The current in the circuit passes on to a second system regulating the temperature of an air chamber kept at C. Constant Air \mdash ; In order that solutions may be brought as nearly as possible to the temperature before mixing and immediately transferred on mixing to the polarimetric tube , also to keep the tions at constant temperature several days , if necessary , in order to examine the end points , a constant temperature chamber is established near the polarimeter .
This is heated electrically and regulated in the same way as the tank .
A small electric fan is included in the chamber .
The heating circuit is made and broken every few seconds by the thermoregulator , showing that no measurable variation of temperature occurs .
Thjrmometers .
Beckmann thermometers are kept in the tank , the return water in ( Diagram 7 ) and in the heated chamber .
They are frequently compared with a standard of excellent quality made specially by Messrs. Casella and standardised at the National Physical Laboratory .
Some Precautions that must be taken against Possible Sources of Error.\mdash ; Too much care cannot be taken to ensure accuracy and constancy of temperature .
In the apparatus described the temperature may be kept constant without attention over long intervals .
It is always advisable to 1912 .
] of the Processes Operative in Solutions .
put the solutions into the polarimeter tubes at as nearly the required temperature as possible , as it is very easy to under-estimate the time required for equilibrium of temperature to be attained .
If the jacketed tubes supplied by Schmidt and Haensch are used , care must be taken that there is no liquid in the cup , as this is not heated by the water jacket and remains cooler and denser than that in the tube ; it radually or suddenly circulates with the warmer liquid , the temperature and rendering the field indistinct , errors which are hard to locate .
In experiments in which the rate of change of rotation is great , the error in the time of taking the readings is important , as it is impossible to observe the field and the clock at the same time .
This can be boreatly reduced by shutting off the light illuminating the clock five or ten seconds before the time at which an observation is to be made and counting the remaining seconds mentally or with the aid of a ticking apparatus while observing the field .
The zero of the instrument should be ascertained before and after an experiment and especially whenever the mercury lamp is touched , as a change of several hundredths of a degree may be made by the position of the lamp .
When optical rotatory power it is to be remembered that the glass discs at the end of the tube are generally slightly optically acCive .
The zero must then be determined with the tube in position empty or filled with the solvent without touching the screw caps .
In velocity experiments several readings must be made at long intervals at the end of the change to make sure that a constant end point is obtained .
In the case of the hydrolysis of cane sugar the final negative rotation gradually becomes less negative .
For the method of dealing with this difficulty , see Part XII of this series .
|
rspa_1912_0112 | 0950-1207 | Studies of the processes operative in solutions. XXIII.\#x2014;The hydrolysis of methylic acetate by acids. | 582 | 603 | 1,912 | 87 | Proceedings of the Royal Society of London. Series A, Containing Papers of a Mathematical and Physical Character | F. P. Worley|Prof. H. E. Armstrong, F. R. S. | article | 6.0.4 | http://dx.doi.org/10.1098/rspa.1912.0112 | en | rspa | 1,910 | 1,900 | 1,900 | 18 | 283 | 8,157 | http://corpora.clarin-d.uni-saarland.de/surprisal/6.0.3/?id=rspa_1912_0112 | 10.1098/rspa.1912.0112 | null | null | null | Biochemistry | 52.690429 | Tables | 30.342182 | Biochemistry | [
-53.91158676147461,
-43.847389221191406
] | ]\gt ; of the Processes in Solutions .
XXIII.\mdash ; The of Methylic Acetate Acids .
By F. P. WORLEY .
( Communicated by Prof. H. E. Armstrong , F.R.S. Received July 29 , \mdash ; Read December 5 , 1912 .
) A. luction .
One of the main objects in view throucrhoutD this series of studies of the operative in solutions has been to discover the nature of the which attend dissolution , particulal .
lie the extent to which substances undergo hydration when in water ; another primary object has been to unlavel the nature of the process of hydrolysis .
The evidence thus far obtained } been such as to show omena are far more complex ) is usually supposed and even to discl.edit the interpretation that it is now customary to give of them .
In Communication XII of the series , I have given an account of experiments made with improved apparatus and with extreme care of the behaviour of cane sugar towards chlorhydric and nitric acids and of the influence of certain chlorides and nitrates on the rate of change .
It was shown that the rate of hydrolysis could not be accurately expressed by any simple formula , as it was not even proportional to the concentration of the , though it was approximately so when the molecular ratio of sugar to water was not high .
Evidence was adduced to show that water as such , i.e. free water , did not play any part in the change but acted solely as solvent and that the active factor of the interaction besides the sugar was the drated acid catalyst .
A noyel method was devised whereby the apparent molecular hydration of the acid arrived at .
[ It was assulned that a certain number of molecules of water was combined with or controlled by one molecule of acid and that only the " " free\ldquo ; water acted as diluent .
The values of ] , expressing the velocities of hydrolysis when one molecular proportion of acid was used in the presence of rent numbers of molecular proportions of water , were multiplied by the total number minus of molecular proportions of water , being given a series of trial values .
The products were plotted against the total water , a curve being obtained for each value of ( see Diagram 3 and Diagram 1 , Par6 XXIII ) .
It will be seen from the diagrams that each curve rises to a maximum and then falls as the dilution is increased , the maxima Studies of the Processes in Solutions .
occurring at points corresponding to greater and greater dilution as the value of is increased .
If the of hydration increase with dilution , it is obvious that , until maximum hydration is reacbed , a particular value of can express the true degree of hydration only at one concentration , which has been taken to be that corresponding to the on the curve when it is horizontal ; in other words , when of change of the value of the product is momentarily nil .
The value of the product at each of the lnaxina is taken as the molecular hydrolytic activity of the acid ab the corresponding dilutions .
With increasing dilution the molecular hydrolytic ctivity decreases towards a minimnm , while the values of increase towards a maximum .
The values of ?
so obtained lave been intentionally called appar hydration values , as it must be nised that , they may possibly in the main rep.resent actual hydration , they arc probably dependent to a considerable extent on the balancing of opposed eHects and also on the method of expressing dilution .
oveJnber 2 , 1912 .
] it is probably far more rational to express dilntion in terms of the molecular proportions of solvent ( here free water ) to adopt the old volume method still fayoured by many chemists , yet , in the case of conc trated solutions , there is no method which is not open to objection .
A similar series of experiments with raffinose\mdash ; a sugar closely allied to cane but of higher molecular weight\mdash ; was described by Dr. Glover in munication X of the series .
Very milar v , representing the apparent degree of hydration of hydrogen chloride and chlorides of the alkali metals , were obtained by means of both , though , on using raffinose as hydrolyte , the values deduced for nitric acid and nitrates were slightly than those obtained by means of cane sugar .
By using methylic acetate as hydrolyte in place of cane sugar , Armstrong and Watson deduced apparent hydration values for a number of salts which were mnch lower than those found by means of cane The subject was further discussed in Communication VIlI and the conclusion formulated that " " hydr tion values\ldquo ; should from case to case and ) the highest values should be obtained by using hydrolytes and hydrolysts which form relatively stable hydrols in solution ( VIII , p. 109 ) .
Methylic acetate was spoken of in this communication as a " " weak hydrolyte One object in carrying out the series of experiments reported in the present communication was to verify the correctness of and Watson 's conclusions .
Another important object was to collfirm the validity of the method described above of finding the apparent molecular hydration of the acid .
As the two hydrolytes , cane sugar and raffinose , were so similar in 584 Mr. F. P. Worley .
[ July 29 , character and the method of following the course of change the same , it appeared to be essential to apply the method to the case of the hydrolysis of substances of entirely different character , such as would render it possible to evaluate the course of change by a purely chemical method .
It was expected that if the conclusion provisionally formulated by Armstrong and Watson were confirmed , namely , that the apparent hydration values of salts were lower when methylic acetate was used than when cane sugar was the hydrolyte , there would be a corresponding difference in the apparent hydration values of the acid .
mentat .
The ordinary materials used were purified in the manner described in previous communications .
Methylic acetate was obtained at first from Kahlbaum but as the purchased material contained a considerable amount of impurity from which it could not be separated in a satisfactory manner by fractional distillation , I prepared the ethereal salt myself in accordance with the directions given by Wade , *subsituting methylic for ethylic alcohol .
The product had the boiling point and density characteristic of methylic acetate and also gave satisfactory results on analysis , yielding molecular proportions of acetic acid when hydrolysed by a slight excess of baryta solution .
In making the experiments , the requisite amounts of water and chlorhydric acid were weighed into a conical 200 .
Jena flask ; instead of hing out the exact amount required , it was found to be more convenient to add approximately the desired proportion of methylic acetate and then at once close the flask with a caoutchouc stopper and again weigh in order to ascertain the amount of acetate added ; correction was always made for the air displaced .
In the experiments in which hydrolysis took place so rapidly that it was necessary to carry out the titration as soon as possible after mixing the substances , the methylic acetate was weighed into a short wide test-tube suspended in the flask and the solution was heated to the required tempera- ture in the thermostat before admixture was effected ; in other cases the substances were well mixed before placing the flask in the thermostat .
The experiments were carried out at Titrations were made at intervals of 10 or 15 minutes or at longer intervals in the case of the more dilute solutions .
A dilute solution of baryta was used as alkali .
The rather large error by which such determinations are usually affected was reduced to a minimum in the following manner:\mdash ; ' Chem. Soc. Trans 1905 , p. 1656 .
1912 .
] Studies of the Processes in Solutions .
The rubber stopper used to close the flask was provided with a hole just large enough to admit the stem of the pipette and this was closed with a small glass stopper ; there was , therefore , but little chance of vapour escaping into the air on removing the subsidiary stopper when taking out the sample of liquid from the flask .
The pipette was warmed to in a tube in the thermostat before it was introduced .
In taking samples , the desired approximate quantity of the solution was sucked up into the pipette and at once run into an excess of carefully neutralised solution of sodic acetate and the determined .
In this way , the time required to remove the sample and run it into the acetate solution ( which was used in order to preyent further hydrolysis of the sample ) was reduced to a few seconds and the error of a pipette measurement was avoided .
The titrations were effected by a very slight excess of baryta solution and estimating the excess by an solution of hydrogen chloride .
The strength of the baryta solution was determined for each experiment and for the end points by uleans of a quantity of the standard chlorhydric acid used in the experiments ; this precaution is rendered very necessary on account of the change of density from day to day in the baryta solution as the temperature varies .
In all the experiments water and methylic acetate were used in the proportion of 120 molecules of the former to 1 of the latter , ether with from to 4 molecules of drogen chloride .
C.\mdash ; Deduction of Velocit , f Coeffici The velocity coefficient , , of the interaction under the differetlb conditions was deduced from the equation in which is the ] concentration of the methylic acetate and the amount hydrolysed at time .
To avoid the unwieldy equation obtained on integrating this expression , the rate of change was estimated directly by , the percentage change oainst the time and determining the tangent to the curve at per cent. by means of a black silk thread\mdash ; a method which has many .
The value of in terms of was deduced from the quantities of the substances present at equilibrium , when , and consequently when is the amount at equilibrium .
The graphic method of obtaining velocity coefficients is very much simpler 586 Mr. F. P. Worley .
[ iuly 29 , and in every way more satisfactory than that of using the complicated mathematical formula in cases in which the expel.imental error is larger than that involved in estimating the value of the tangent .
It has been usual to assume that in dilute aqueous solution methylic acetate is almost completely hydrolysed and that undel such conditions the small amount of change in a reverse direction , viz. : COOH is negligible .
As the water remains practically unchanged in amount , the interaction in such a case may be treated as a case of simple unimolecular change in which , finally , the methylic is almost completely hydrolysed .
My experiments show , however , that even at the low concentrations used a considerable proportion of the methylic acetate remains unhydrolysed when equilibrium is attained , the of hydrolysis in no experiment exceeding 95 per cent. It consequently seems imperative to take into account the reverse of etherification in the velocity coefficients .
It should be pointed out that if this reverse be neglected , the magnitude of the velocity coefficient obtained is considerably altered , though its constancy may be affected but slightly ; whence it follows that the fact that a constant value is obtained for on the assumption that the interchange is complete and proceeds as a unimolecular is no proof that this assumption is correct .
To illustrate these points , values for the velocity coefficient in the case of an experiment when the degree of hydrolysis at equilibrium was per cent. ve been deduced , both taking into account the reverse change and omitting it .
In Table I , under are given the values ( multiplied .
by ) obtained on taking into account the two interactions .
Under are given the values arrived at by the reverse change and assuming that at equilibrium the whole of the methylic acetate has been hydrolysed .
This is the procedure that has been generally followed by previous observers .
In the particular experiment , as per cent. of acetate remained unhydrolysed , the values taken as the concentration of the acetate are lower to this extent than the true values throughout the experiment .
Nevertheless , it will be observed that the values under are almost as constant as the true values under , though of considerably greater magnitude .
Under ] are given the values obtained on neglecting the reverse action and considering the actual amounts of methylic acetate present , assuming also that the action is ultimately complete\mdash ; a course sometimes adopted .
The values are fairly constant at first but fall off as the interaction proceeds .
It is very much easier to consider only the acetate thaG can be hydrolysed 1912 .
] Studies of the Processes in Solutions .
than to estimate the total amount present ; for this reason the method by which the values under are deduced has been enerally adopted previously .
In the present series of experiments , however , as the solutions were made up by weight and practically pure methylic acetate was used and as weighed quantities were taken for titration , it has been possible to estimate the total amount of acetate left unhydrolysed after different tervals of time in each experiment .
Table I. Percenta.gechange It is , perhaps , well to call attention to these examples as an illustration of the difficulties the reduction of observations such as those undel discussion .
The data from a typical experiment are giyen in Table II .
Table II.\mdash ; Typical Experiment .
120 Molecular Proportions of 1 of , and of VOL. LXXXVII.\mdash ; A. 2 .
F. P. Worley .
[ July 29 , A gives the baryta solution equivalent to 1 .
of solution ( found by titrating from 5 to 10 ) .
CoJumnB gives the baryta solution equivaleut to the acetic acid in 1 .
of solution .
The values are obtained by deducting , the amount of baryta solution equivalent to the HC1 in 1 .
of solution , from the numbers in Column Column gives the calculated of the methylic acetate hydrolysed .
Column gives the pel.centage hydrolysis to the rates of in the following column determined from the curve .
Table III contains the velocity coefficients ( multiplied by ) deduced from the different experiments .
In Diagram 1 is shown graphically the relation of the velocity coefficients to the concentration of the chlorhydric acid , Curve A being that obtained when the concentration is expressed as the molecular proportion of chloride to 120 of water , Curve when the dilution is expressed in terms of the number of molecular proportions of water to 1 of hydrogen chloride .
Table III.\mdash ; Values of , from Experiments with 120 Molecular Proportions of , 1 of , and from to of 1912 .
] Studies of the Processes Operative in Solutions .
Mols .
to 1 of HC1 .
( Curve B. ) Iols .
HC1 to 120 in Degree of with the of Aeid st. The end values obtained in the experiments described are such as to show that the percentage of methylic acetate hydrolysed at the of equilibrium is not independent of the concentration of the chloride used as catalyst .
To make sure that there was a real displacement of the point of equilibrium and that the apparent lowering of the decree of hydrolysis by the presence of the hydrogen chloride was not due to the formation and escape of methylic chloride , several experiments were made in which the Mr. F. P. Worley .
[ July 29 , point of equilibrium was approached from the other end , beginning with methylic alcohol , acetic acid , water and different of hydrogen chloride .
The points of equilibrium were practically the same as those obtained by hydrolysis , showing that there was an actual displacement of the point of equilibrium and an apparent change in the ratio of to as the concentration of the acid catalyst was increased .
This point will be discussed in a later section .
In Table is given in Column A the percentage of methylic acetate hydrolysed in the presence of the different amounts of hydrogen chloride indicated in the first column , whilst in Column is given the percentage of acetic acid and methylic alcohol left uncombined in the etherification experiments .
In Diagram 2 is shown graphically the degree of hydrolysis attained in the presence of different amounts of hydrogen chloride .
Table \mdash ; Change in the Percentage of Methylic Acetate Hydrolysed at Equilibrium caused by Change in the Concentration of Hydrogen Chloride .
Mols .
HC1 to 120 1912 .
] Studies of the ocesses Operative in Solutions .
imitations of that bo made Results arrived at by the treat , nent of the to the le of Mass Action .
It is now necessary to consider the adequacy of the methods used heretofore in discussing the results of experiments such as have been described .
The view has been too enerally held perhaps that the catalyst is not a necessary component of the system within which occurs but only accelerates its rate ; and it has been wrongly assumed that the position of equilibrium is not by the presence of the talyst or by alteration of its concentration .
It has there been uniyersally held that water as such enters into the interaction , no distinction been made between the water which plays an active part in the change in conjunction with the catalyst*and the water which acts only as solvent or diluent .
The mass action equations expressing the relation between the rates of hydrolysis and esterification and the concentrations of the substances and that for the conditions at have too frequently been based on the conventional chemical equations which express only the initial and final states without reference to the course of the change and the part played by the catalyst .
Thus in the case of hydrolysis it has been generally assumed that because one molecule of water ( hydrone ) is used up for every molecule of hydrolyte hydrolysed , the rate of hydrolysis is therefore proportional to the product of the concentrations of the hydrolyte and the water .
Again , in the case of the equilibrium veen nlethylic acetate , water , acetic acid and methylic alcohol , the equation has always been considered to express the facts accurately , the bracketed quantities being the molecular concentrations ( strictly speaking , the active masses ) of the substances in equilibrium .
The constancy in the ratio of to that has been belicved to persist when the relative proportions of the various substances have been altered has appeared to confirm the assumption that the active masses of the interacting substances are tly expressed by the above equation .
The fact has apparently been overlooked , however , that even though the ratio of to remain constant , it does not follow that the factor of the mass action equation .
necessarily represents one of the substances entering directly into the interaction .
It may be a factor representing merely the degree of dilution .
For the purposes of this discussion the anhydrous acid is represented as the catalyst .
In actual fact , the active agent is probably some form of hydrated compound derived irom the anhydrous acid and water .
Mr. F. P. Worley .
[ July 29 , Confuslon has probably arisen through the substitution of relative molecular proportions of the interacting substances for their concentrations in the above equation .
When the four substances are dissolve in a given quantity of some solvent such as acetone or when one of the interacting substances is in large excess and may be regarded as constant , the concentration of the different substances is not lost sight of ; when , however , there is no outside solvent and none of the four substances is in large excess , it is much easier to consider their relative molecular proportions .
Provided that the equation express the interaction accurately and that the active mass of each substance be proportional to its total quantity , relatiye molecular proportions may be justly substituted for concentrations .
This follows from the symmetrical nature of the equation .
Whether we express the concentration as the number of molecular proportions either in a given volume or ( b ) compared with that of one of the interacting substances or ( c ) compared with the total number of molecular proportions present , this dilution factor is the same for both sides of the equation and so does not affect it .
If , howevel\ldquo ; the water function mainly as diluent and be not strictly a factor in the interaction , the equation becomes umsymmetrical and a dilution factor must be introduced .
In Part XII the view was put forward that in the case of the hydrolysis of cane sugar the interaction was between the sugar and the hydrated catalyst , the water uncombined with the catalyst functioning merely as solvent .
It is highly probable that this is the case also in the hydrolysis of ethereal salts .
If the action of the catalyst be considered , it is well known that the velocity coefficient for the rate of hydrolysis is nearly proportional to the concentration of the catalyst when the latter varies in concentration .
This is very clearly shown by the approximate straightness of Curve A in Diagram 1 , which shows the relation of the velocity coefficient to the concentration of the chloride .
It shows , further , from the part extl'apolated to zero concentration of acid , that in the absence of catalyst the rate of hydrolysis is reduced to zero .
In other words , water alone has probably no power of effecting the hydrolysis of methylic acetate .
This argument does not , of course , preclude the view that has been adopted , that the action is between the water and a compound of the acetate with the catalyst .
It appears far more likely , however , that the interaction is between the ethereal salt and a compound of the catalyst with water , i.e. with the hydrated catalyst .
mechanism of hydrolysis will be fully discussed at a later stage ; but , for the present , let us assume that hydrolysis is effected by the interaction of the ethereal sa.lt and hydrated catalyst and that the water uncombined with the lyst functions merely as solvent and diluent .
If the proportion of the solvent ( .
the free water ) be large 1912 .
] Studies of the Processes , in it makes little difference whether we reckon concentration as the number of molecular proportions either in a iven volume or compared with a iven lUmber of molecular proportions of the solvent .
The concentrations of the interacting substances may be expressed consequently as the ratio of their molecular proportions to those of the diluent water .
The equation expressing the conditions at equilibrium thus becomes hydrated catalyst ' yhen the bracketed quantities are the relative molecular proportions of the various substances .
On simplification this becomes in which the factor is merely dilution factor and does not stand for one of the interacting substances .
Any other expression for the dilution can be substituted equally well .
The above simplified equation is thus very liable to be misinterpreted and wrong deductions have frequently been made from the results obtained by its use .
If the water be not in large excess , it is obvious that it is not legitimate to use it as a dilution factor and the equation is valid only on the improbable sumption that the four factors represent the .
substances and that the active part of each is proportional to its concentration even when the degree of concentration is high .
Since the completion of this investigation , Jones and Lapworth* have published the results of an investigation of the action of hydrogen chloride on the between ethylic acetate , water , ethylic alcohol and acetic acid .
In all their experiments the proportion of water was small and could not possibly be regarded as .
a measure of the dilution .
They considered merely relative molecular proportions and found that the value of , where rose from 4 to at least when the concentration of the chloride used as catalyst varied over wide limits .
They assumed that this variation in the value of was due to some of the water forming a hydrate of the hydrogen chloride and calculated that approximately two molecules of water were associated with each molecule of chloride present , though the existence of higher hydrates in a partly dissociated condition ' Chem. So Journ 1911 , p. 1427 .
Mr. F. P. Worley .
[ July 29 , not excluded .
Apart from the improbability of the degree of hydration remaining the same and so low over large ranges of concentration , it is obvious that their conclusions can be in no way valid except on the assumption that water as such is one of the interacting substances ; that the active lnasses of each of the four substances are proportional even in strong solutions to their concentrations ; also that the active mass of the water is proportional to that part of it unassociated with the hydrogen chloride , .
proportional to the pure water present which no power to effect the hydrolysis of pure ethylic acetate .
It is obviotls that little weight cftl be attached to their conclusions .
In the following sections " " apparent hydl.ation values\ldquo ; for the hydrogen chloride will be deduced from the velocities of hydrolysis and also from the equilibrium data .
It must be pointed out , however , that although the proportion of water was always large , the values arrived at cannot be regarded as absolute , as they are dependent on the method of reckoning concentration .
Moreover , this difficulty must always exist except in the case of extremely dilute solutions , as there is no method of expressing the coucentrations and active masses of substances in concentrated solution that is free from defects .
The conditions in solutions are undoubtedly of so complex a character that the utmost must be exercised not to put too rigid an interpretation on results arrived at on any one hypothesis .
tion of Apparent Values of en the the Coefficients of the Case of cetate and the Concentration of the drogen The apparent hydration values of hydrogen chloride at different concentrations have been determined from the data of the experiments described earlier on the assumption that part of the water is associated with or controlled by the acid and that the free water acts merely as solvent .
The method used is the graphic one described in Part XII in connexion with the hydrolysis of cane .
Diagram 3 shows the process and the results obtained .
the horizontal axis are given the total number of molecular proportions of water present to one of hydrogen chloride and on the vertical axis the products of the velocity.coefficients and the molecular proportions of free water , i.e. water uncombined with the chloride , on the various assumptions as to the number of molecular proportions of water attached to the acid .
Each curve is based on the assumption that a number of molecular proportions of water equal to the number opposite the curve 1912 .
] Stnclies of the Processin have been removed from the sphere of solvent water .
This number expresses accurately the water so removed at some definite concentration which has been taken as that corresponding to the maximum on the particular cnrve when the curve is at the point horizontal .
It will be observed the maxima on the different curves correspond to different concentrations .
The Mols .
total water .
dark curve through the apices gives from the ordinates the specific molecnlar hydrolytic activity at different dilutions of the acid .
The apparent molecular hydration and molecular hydrolytic activity of the hydrogen chloride at different dilutions are given in the following table , in which are included for comparison the values deduced in the case of the hydrolysis of cane sugar ( Part XII ) .
( The hydrolytic activity values have been multiplied by to reduce them to the same unit as the 1uethylic acetate values since in their calculation the velocity coefficient used Mr. F. P. Worley .
[ July 29 , Table data used in the calculations are given in Table III .
A small error in any of the values of makes a considerable irregularity in the curves .
Thus , the values 354 and 443 produced ularities , which were removed if the very slightly different values 351 and 444 were substituted ; these values were consequently used instead of the mean values .
Inspection of the list of values of in Table III shows that probably they may be taken legitimately as the means .
The regularity of the curves is a confirmation of the uniformity of the results .
It will be observed that the apparent molecular hydration values are much smaller than those deduced from the rate of inversion of cane sugar .
This diH'erence will be discussed in a later section ( p. 601 ) , after dealing with the apparent hydration values of salts .
A constant value for the molecular hydration and the molecular hydrolytic activity is reached much earlier in the case of the hydrolysis of methylic acetate than in that of cane .
In this respect the results are very similar to those obtained from the hydrolysis .
cane sugar by sulphuric acid and the monobasic sulphonic acids referred to in Part XXII .
of Values Equilibrium Data .
In the section dealing with the change in the percentage of methylic acetate hydrolysed caused by changing the concentration of the chloride ( see p. 589 ) , it was shown that increase in concentration of the acid catalyst was accompanied by an increase in the proportion of methylic acetate left unhydrolysed at equilibrium .
If , therefore , the ratio of to be calculated from the equilibrium data by means of the equation on where 1912 .
] of the .
Processes Operative in tlus ratio must increase as the concentration of the chloride is increased , provided that it be assumed that the amount of solvent water ; not dinlinished by increase in the concentration of the hydrogen chloride , which could occur only if the acid were present in aqueous solution in an unhydrated condition .
As this is not the case , increase in the concentration of hydrogen chloride must undoubtedly be accompanied by an increase in the amount of water in combination with the acid and a corresponding decrease in the remaining solvent water .
By decreasing the initial ratio of the watel to the methylic acetate , a decrease in the percentage of the acetate hydrolysed , such as is observed in the experiments described above , is about .
'fhree experiments were carried out in which the ratio of water to ylic acetate varied considerably .
At the start there were approximatelv 5 , 10 , and 20 nlolecular proportions of acetate to 120 of water and 1 of chloride .
At equilibrium the percent of methylic acetate hydrolysed were approximately 80 , 68 , and 55 .
It would appear , then , that although there may possibly be an actual increase in the ratio of to ( which would mean that the etherification was accelerated to a greater extent than the hydrolysis by an increase in the concentration of the catalyst , the increase is mainly and probably entirely apparent only and , if the correct value were taken for the solvent water , the ratio of to would be constant .
Hydration values have been deduced on this last assumption from the ulibrium data on p. 590 .
It is to be noticed that the values obtained are not exactly comparable with those found in the previous section , in which the apparent hydration values are those of the in the presence of a great ) ) of the maltered -methylic acetate .
The values found from the equilibrium data are values for the various substances in solution at equilibrium , when relatively large amounts of acetic acid and methyl alcohol are present , both of which , no doubt , remove some water from sphere of solvent .
In the following calculations , the of hydrolysis at equilibrium was taken not directly from the experimental values but from the curve ( Diagram which also gives the extrapolated value for the degree of hydrolysis that would be obtained in the absence of hydrogen chloride .
From this latter value the true ratio of to is obtained .
At equilibrium 95 per cent. of the methylic acetate should be hydrolysed when no water is removed by hydrogen chloride .
As there were originally 120 molecular proportions of water to 1 of methylic acetate , we have at equilibrium of water , of acetate and of acetic acid and methylic alcohol .
Hence Mr. F. P. Worley .
[ July This value for the ratio of to is used to calculate the values of the factor for the solvent water in the presence of the different amounts of hydrogen chloride .
For example , when one molecular proportion of hydrogen chloride is used we have , since the percentage of methylic acetate hydrolysed is 94.6 , ; whence the molecular portions of solvent water are found to be As molecular proportions of water were used up for the hydrolysis , the apparent hydration value for the substances in solution at equilibrium ( viz. , one molecular proportion of hydrogen chloride and approximately one each of acetic acid and methylic alcohol ) is equal to Table gives the apparent hydration values so obtained for the different concentrations of hydrogen chloride used .
Table 40 30 0 .
87 .
8 .
0.25 Column A ives the molecular proportions of hydrogen chloride present to 120 of initial water .
Column the molecular proportions of water ( initial values ) to one of hydrogen chloride .
Column gives the molecular proportions of methylic acetate at equilibrium .
Column gives the molecular proportions of solvent water calculated above .
Column gives the molecular proportions of water removed from the sphere of solvent , i.e. the apparent hydration values of the substances in solution .
1912 .
] of the ocesses Operative in Columnl gives the apparent ydration values corresponding to one molecular proportion of hydl'ogen chloride and the other substances in solution ( the approximate amounts of total water to one of hydrogen chloride being given in Column B ) .
Column gives the approximate number of molecular proportions of acetic acid and methylic alcohol to one of hydrogen chloride .
To obtain the apparent hydration values of the hydrogen chloride , we should ] lave to deduct from the nbers in Column the unknown amount of water in combination with the number of molecules of acetic acid and methylic alcohol in Column G. This , however , would no doubt be small compared with that in combination with the hydrogen chloride .
It will be observed that the numbers are than those obtained in the previous section .
The conditions are not the same , however .
In this case the methylic acetate has been displaced ( almost entirely ) by methylic alcohol and acetic acid .
The complexity of the conditions at equilibrium and the large eH'ect produced by a very small experimental error preyent being attached to the actual values obtained .
They are of such an order , however , as to confirm the explanation advanced for the change in the degree of hydrolysis with change in the concentration of the catalyst .
of Salts .
In view of the fact that lower values were obtained for the apparent hydration of hydrogen chloride from the rate of hydrolysis of ] acetate than were obtained from the experiments on the rate of inversion of cane , it appeared all the more desirable , as was stated in the introduction , to confirm the conclusions arrived at and Watson iu Part that salts had a smaller effect in the former case than in the latter , i.e. that their apparent hydration values were smaller when methylic acetate was used as the hydrolyte than when cane sugar was used .
The apparent hydration values of the chlorides of sodium , potassium and ammonium were determined by a method similar to that described in Part XII in the case of the hydrolysis of cane .
Iu the experiments the molecular proportions used were 120 of water , 1 of methylic acetate , 2 of hydrogen chloride and 2 of salt .
The values of the velocity coefficients were determined in the same way as for the acid alone .
the case of the ammonium chloride , phenolphthalein could not be used as an indicator and litmus was far from satisfactory .
The results are consequently not very trustworthy .
The results of the three e , xperiments are given in the following table .
The value of the constant obtained when the same proportion 600 Mr. F. P. Worley .
[ July 29 , $ of chloride was used was 606 .
The apparent h.ydration $ values were obtained by taking the horizontal distances between the curve for the acid alone and those for the acid in the presence of the salts .
Since the velocity of hydrolysis in the presence of the salts was determined for one concentration only , the hydration values could not be determined for differe1lt concentrations .
The curves were assumed to be parallel to the acid curve at the point considered .
* The apparent molecular hydration values obtained when 60 molecular of total water were present for 1 of salt were approximately 3 for ammonium chloride and each for sodium and potassium chlorides , that for sodium chloride being slightly the larger .
The values obtained by rong and Watson were considerably larger , being 5 , 8 and 10 respectively in the presence of molecular proportions of water .
The general sion arrived at by Armstrong and Watson , however , is confirmed and the low values obtained for the salts are in complete harmony with the values obtained for the hydrogen chloride .
Table Percentage composition .
I.\mdash ; Discussion of the Apparent Hydration Values arrived at in the Preuious Sections .
The method by which the apparent hydration value of the salts was deduced in the previous section is entirely distinct from that used to calculate the corresponding values for chlorhydric acid in .
Sections and G. In the case of the salts no assumptions are necessarily made with regard to the actual cause of their observed accelerating effect on the rate of In Diagram 1 the values of the velocity coefficients for hydrolysis in the presence of the three salts are indicated by crosses .
1912 .
] Studies of the Processes Operatire in hydrolysis .
The values are deduced directly from the values found experimentally for the rate of hydrolysis in the absence and presence of salts and merely express the nccelerating effect of the salt in terms of the amount of water that would have to be removed from the system in order to produce the same effect on the rate of hydrolysis .
Whilst it is believed that the accelerating effect of salts is mainly due to the concentrating effect they exercise , still the fact has never been lost sight of that their influence is of a much more complicated nature , the effect observed being the sum of various effects .
In the case of the methods of deducing the apparent hydration values of the acid , however , the assumption was made that the acid removed water from the system\mdash ; that it actually reduced the amount of solvent water .
It has already been pointed out that it is not to be expected that the values arrived at in Section would be the same as those arrived at in Section but would be larger .
The comparatively large effect that quite small differences in the experimental values used for the deduction of the apparent hydration values have on their magnitude prevents too great stress being laid on the actual alues arrived at in Sections and ; still , taking in to account the differences in the conditions under which the apparent hydration values of the acids and of the salts were determined , the similarity of the order of magnitude of the values is of a most nature .
More interesting still is the comparison between the above results and those arrived at in the case of the hydrolysis of cane sugar .
In this case , also , there was a singularly close relationship between the values arrived at for the acids and those for the salts .
There is , however , a wide difference between the values arrived at both for acids and salts in the two cases , the use of cane much higher values than when methylic acetate is employed .
The cause of this difference is not easy to locate .
It may be due to some extent to difference in the two methods of following the course of the interaction .
The polarimetric method , whilst giving extremely uniform results , is full of complexities , some of have already been dealt with in Part ; others are discussed in Part XXII .
It is not impossible that the method does not give a perfectly true record of the rate of change .
On the other hand , there is much to show that there is an actual difference due to the character and influence of hydrolytes .
The effect of substances such as methylic acetate on other substances in solution is very different from the effect of cane sugar .
The large effect that substances which have no great affinity for water , such , for instance , as propylic alcohol , with which methylic acetate may well be compared , have in reducing the solubility of salts in water would tend to show that such substances have a Mr. F. P. Worley .
[ July 29 , effect on the condition of other substances in solution .
Cane sugar has an entirely different effect and it is highly probable that the actual condition of the salts and acids is different in the presence of even small amounts of acetate from what it is in the presence of cane With regard for the graphic method used to deduce the apparent hydration values of the acid , the results appear in every way to show that this form of treatment is valid in principle .
The curves in the case of the hydrolysis of methylic acetate resemble in every way those obtained when cane sugar is used , the difference in the magnitude of the apparent hydration values arrived at being in accord with the difference in the corresponding values for the salts arrived at by an independent method .
1 .
The rate of hydrolysis at C. of methylic acetate in dilute aqueous solution under the catalytic influence of chlorhydric acid has been studied with a view to determine the apparent molecular hydration of the acid by the method used in connexion with the h.ydrolysis of cane sugar ( Part XII ) and further to ascertain whether the magnitude of the apparent hydration values of the acid and of salts be dependent on the nature of the hydrolyte .
The molecular proportions of the substance used were 120 of water , 1 of methylic acetate and from to4 of hydrogen chloride ( Sections A and B ) .
2 .
It is that in no experiment did the of hydrolysis exceed 95 per cent. of the methylic acetate taken and that it is not justifiable either to adopt the usual assumption that in the presence of so large an excess of water the hydrolysis is practically complete or to treat the interaction as a case of simple unimolecular .
In the calculation of the velocity coefficients of hydrolysis , allowance has been made for the reverse change of ethelification , the equation used being in which is the initial concentration of the methylic acetate and the amount changed at time .
The rate of change corresponding to different concentrations of unhydrolysed acetate was found directly from the experimental curve , the ratio of to being found from the equilibrium data ( Section C ) .
3 .
When the initial proportions of water and methylic acetate are the same , the amount of the latter hydrolysed at equilibrium depends on the concentration of the chloride present , decreasing as the concentration of the catalyst increases ( Section D ) .
1912 .
] Studies of the Processes in Solutions .
4 .
In Section it is shown that the equation always used to express the conditions at equilibrium , viz. :\mdash ; has in the past been much misunderstood and that , even though the relation .
ship expressed hold good for different proportions of the various substances , the factor does not necessarily stand for one of the substances entering directly into the interaction but probably expresses the degree of dilution .
The view is advanced that hydrolysis is probably effected by the direct inberaction of a unit of hydrated hydrolyte with one of the hydrated catalyst , the water uncombined with the acid catalyst functioning merely as solvent .
5 .
Apparent molecular hydration values of the catalyst ( chlorhydric acid ) have been deduced from the velocity coefficients of hydrolysis by the method developed in Part XII and also from the equilibrium ata .
Corresponding values for various salts have been found from the increase they produce in the velocity coefficient , on the assumption that the increase is due mainly to their effect .
The values obtained both for the acid and for the salts are much lower than the corresponding values found when cane sugar and raifinose were used as hydrolytes .
This difference may be due to some extent to the difference in the method used of following the course of the interaction but it is probable that there is a considerable actual difference in the condition of the acid and of the salts in the presence of such different hydrolytes as methylic acetate and cane sugar ; furthermore that the hydrolytes are themselves different in character ( Sections ) .
The curves obtained in the deduction of the apparent hydration values of the acid are similar to those obtained in the case of cane sugar hydrolysis .
The apparent hydration values increase with dilution to a maximum , whilst there is a corresponding decrease to a minimum in the molecular hydrolytic activity of the acid .
The results appear to confirm in every way the validity of the method used .
With to the explanation of hydrolysis put forward in this communication and in Part XII , it should be said that it appears to be in complete agreement with all the experimental facts , many of which are not in harmony with the explanations that have been based on the ionic dissociation hypothesis .
The theory of the hydrolytic process is discussed more at length in the following communication .
VOL. LXXXVII.\mdash ; A.
|
rspa_1912_0113 | 0950-1207 | Studies of the processes operative in solutions. XXIV.\#x2014;The nature of the hydrolytic process. | 604 | 623 | 1,912 | 87 | Proceedings of the Royal Society of London. Series A, Containing Papers of a Mathematical and Physical Character | H. E. Armstrong, F. R. S.|F. P. Worley | article | 6.0.4 | http://dx.doi.org/10.1098/rspa.1912.0113 | en | rspa | 1,910 | 1,900 | 1,900 | 7 | 316 | 9,996 | http://corpora.clarin-d.uni-saarland.de/surprisal/6.0.3/?id=rspa_1912_0113 | 10.1098/rspa.1912.0113 | null | null | null | Biochemistry | 66.100682 | Fluid Dynamics | 15.171231 | Biochemistry | [
-52.85020446777344,
-42.448577880859375
] | 604 Studies of the Processes Operative in .
XXIY.\#151 ; The Nature of the Hydrolytic Process .
By H. E. Armstrong , F.R.S. , and F. P. Worley .
( Received July 29 , \#151 ; Read December 5 , 1912 .
) 1 .
The inquiry described in previous parts of these studies , as well as in the parallel series of studies ( I-XVIII)* on the action of enzymes and in that on certain osmotic phenomena ( I-IY ) , f was undertaken primarily with the object of elucidating the nature of the processes operative in solutions , especially of the phenomena of hydrolysis , whether conditioned by ordinary agents or by enzymes , though other important issues have also been dealt with .
It now appears to be desirable to consider the general character of the results and to discuss their bearing on current views , so much having-been done to throw light on the nature of the changes occurring in solutions .
2 .
At the outset , we would urge that it cannot be denied that the phenomena presented by solutions are complex in character and that on this ground alone the simple explanation advanced by the advocates of the ionic dissociation hypothesis is highly improbable .
3 .
It appears to us that many of the conclusions arrived at in the past are to be regarded with the gravest doubt , the assumptions made being of too simple a nature\#151 ; more especially because the all important part played by the solvent has been often either entirely neglected or insufficiently considered .
The very existence of the solvent has been tacitly ignored by a majority of workers in discussing the properties of solutions , the volume of the solution having been considered of greater importance than the proportion of solvent to solute .
This has been almost universally the case in discussions of rates of interaction based on the principle of mass action .
In too many instances , possible changes in the degree of molecular complexity , both of solute and of solvent , of the latter especially , have been disregarded ; moreover , influences have been overlooked which are not commonly recognised as chemical in character , such for example as the large and opposite influence exerted by cane sugar and butyl alcohol on the solubility of salts in water .
4 .
It may be urged here that the law of mass action , to which appeal is so constantly made , can only be postulated\#151 ; that it is a commonsense generalisation based upon kinetic principles alone , true of an ideally perfect gas but of no other condition .
Strictly speaking , the law cannot be deduced from the study of solutions , because these cannot afford the required conditions of * 'Roy .
Soc. Proc. , ' 1904-12 .
t Ibid.,1906-11 .
Studies of the Processes Operative in Solutions .
605 simplicity\#151 ; and if the results obtained appear to be open to a simple interpretation in accordance with the law of mass , it is because the disturbing effects counterbalance one another .
Such a law must hold good in effect\#151 ; the difficulty we have is in determining what are the active masses concerned ; we can only guess at these , as a rule .
Only in very dilute solution can the active mass of a solute be taken as proportional to its concentration .
In concentrated solutions probably the number of units in a given volume is never proportional to the assumed number of molecules present , to the concentration ; moreover , alteration of concentration probably changes the degree of activity of the active units .
Other causes also may condition divergence from constancy in the calculated velocity coefficient .
In the case of the hydrolysis of cane sugar , for instance , in which both sugar and acid must be supposed to be " hydrated , " it is not only in no way certain that the degree of hydration of the substances finally present is the same as that of the original substances but it is beyond doubt that as the number of molecules in solution changes , as the interaction proceeds , the " osmotic " conditions must vary throughout the process .
It can scarcely be supposed that such changes are without effect on the chemical process and the apparent constancy not infrequently observed may be due , in great measure , to the balancing of opposed effects .
In fine , it is beyond doubt that far too little care is used in interpreting the results arrived at by the application of the law of mass action and that many erroneous conclusions have been drawn .
5 .
Similar considerations apply to all cases in which physical methods of studying the changes in solutions are used\#151 ; for example , to determinations of molecular weight by the cryoscopic method .
Thus , it cannot be asserted that because two non-electrolytes produce the same depression of the freezing point of water when dissolved in it in certain proportions , they are therefore present in solution as molecules of the relative weight corresponding to the proportions used ; the more soluble is presumably the more hydrated and its solution more concentrated therefore than that of the less hydrated but this latter probably will have more effect in simplifying the complexes present in water : if the greater concentration produced by the one just serve to balance the greater effect on the water produced by the other , the molecular weights may well be in the expected ratio but the agreement between fact and hypothesis only apparent .
We call attention specially to this case in order to lay emphasis on the importance of taking into account both the function of the solvent and also of the changes produced in it ; the effect of these latter has been overlooked almost universally .
6 .
The contention originally advanced by A. Williamson in 1850 involved only the assumption that salts in solution were in a state of continual flux 2 u 2 606 Prof. H. E. Armstrong and Mr. F. P. Worley .
[ July 29 , and constantly interchanging radicles\#151 ; an assumption which is entirely in accordance with all subsequent observations on the physical properties of solutions ; it in no way involved the conception of dissociation .
Williamson was content to call attention to a process at work in solutions but did not attempt to explain its nature ; he only pointed out its general character and what must be its effect .
To account for the electrical conducting power of solutions , the conception of dissociation into separate ions was introduced by Clausius in 1857 but this philosopher attributed the change to kinetic causes-alone .
Influenced by Williamson and Clausius and especially by Helmholtz , , who meanwhile had introduced the conception that the atoms carry the number of unit charges of electricity ( Johnstone Stoney 's electrons ) corresponding with their valency , Arrhenius in 1883 first put forward the view that substances in solution are in many cases all but completely dissociated into electrically charged ions ; secondly , that these ions are the active part of the solution : or in other words , that electrical conductivity is to be correlated with chemical activity ; and thirdly , that the degree of " electrolytic dissociation " is the more nearly complete the more active the substance and the more dilute the solution .
It is well known that the view soon became popular .
7 .
Arrhenius paid no attention to the solvent and his disciple Ostwald , in-particular , asserted that\#151 ; as Kohlrausch had previously argued\#151 ; it merely played the part of a screen.* At a later date , when it became necessary to admit that the solvent was not inert , it was assumed that water was specially active as a dissociating agent on account of its high specific inductive capacity.f * In the discussion at Leeds in 1890 ( ' Brit. Assoc. Rep. , ' p. 335 ) , Ostwald , after referring to the fact that , at ordinary temperatures , no pure liquid is an electrolyte , remarked : " The theory of Arrhenius is still , on this point , the only one which explains this strange fact ; pure liquids do not conduct because their molecules have no space to resolve themselves into ions .
It is , therefore , not improbable that water would conduct electrolytically if we could find a suitable solvent for it .
" But no such solvent has been found\#151 ; or ever will be apparently .
Hydrogen cyanide\#151 ; a good solvent of water and a liquid of very high specific inductive capacity\#151 ; has been shown by Walden to be without effect on water ( ' Trans. Faraday Soc. , ' 1910 , vol. 6 , p. 71 ) .
+ It is far too frequently left out of account that the explanation put forward by J. J. Thomson and Nemst is one which involves merely a loosening of the bonds of attraction between the two ions of the " electrolyte " under the influence of water\#151 ; not an actual separation of the ions such as is required to account for the increased effect exercised by electrolytes in comparison with non-electrolytes , assuming the kinetic explanation of osmotic pressure put forward by va n't Hoff to be correct .
It is a noteworthy fact , on which we would here lay stress , that the substances which manifest high specific inductive capacity are all relatively simple compounds of compact structure and therefore such as are most likely to form molecular complexes\#151 ; it may well be that the high specific inductive capacity they possess is due to this circumstance .
1912 .
] Studies of the Processes Operative Solutions .
8 .
We venture to insist on the importance of attention being paid to the views advocated by so high and impartial an authority as the late Prof. FitzGerald in the Helmholtz Memorial Lecture which he delivered to the Chemical Society in 1896 .
To quote a few passages bearing specifically on our contention:\#151 ; " So far as we can deal with solids and liquids as statical systems , we may be quite certain that other than electrical forces must be postulated ... ... we must assume other forces than electrical ones or any others var}ring inversely as the square of the distance .
Take , for instance , the suggestion that when an electrolyte is subject to electrostatic induction the superficial induced charges are due to a layer of electrified ions upon its surfaces .
If there were no forces other than electrical ones , these ions would fly off the surface like dust .
The pressure of the surrounding gas would certainly not prevent this , for a gas never prevents the diffusion of atoms .
Hence we must suppose that there are other than electrical forces keeping these ions attached to the liquid .
Helmholtz himself states as a conclusion of his investigation of the action of reversible electrochemical actions\#151 ; ' A remarkable feature in these processes appears to me to consist in the fact that the attraction of the water to the salt to be dissolved can constitute so great a part of the chemical force acting between the oppositely propelled elements .
' There seems to be considerable danger that these forces may be neglected .
So much advance has been made by assuming that bodies in solution behave in some respects like the same body in the gaseous state that there has been a serious danger of assuming that the physical conditions are all alike .
" " It is , no doubt , a most remarkable thing that osmotic pressure should be even roughly the same as what would be produced by the molecules of the body in solution if in the gaseous state but to imply that the dynamical theory of the two is at all the same or that the dynamical theory of a gas is in any sense an explanation of the law of osmotic pressures is not at all in accordance with what is generally meant by the word ' explanation .
' These osmotic pressures are much more closely connected with Laplace 's internal pressure in a liquid , which is essentially dependent on the forces between the molecules , than with the pressui'e of a gas , which is essentially almost independent of the forces between the molecules .
" " It is almost impossible to explain dynamically the supposition that free ions with their electrical charges are meandering about in the liquid in a condition that can be at all rightly called dissociated .
The term ' dissociated ' should be confined to a condition in which the components of a molecule are not connected by any chemical bonds at all .
In that case they can diffuse freely and independently through porous diaphragms .
Hence the possibility of this independent diffusion is the simple and necessary test of the independence of the components which can rightly be called dissociation .
In an electrolyte there is not this independence . . . .
Without some other important actions existing at the same time such a condition is dynamically impossible and although to consider the matter from this point of view may help us very much , because it gives us a rough and ready analogy to work on , yet there is great danger that it may stop important advances by an illusive appearance of explanation .
" FitzGerald even speaks of the " so-called freedom " of the ions as " due to their being in complete bondage with the solvent .
" He goes on to say\#151 ; " That atoms or molecular groups within a molecule often can and do exchange places is quite in accordance with chemical phenomena .
That they should do so of their own accord when the molecules are arranged in a particular way is also quite in accord with 608 Prof. H. E. Armstrong and Mr. F. P. Worley .
[ July 29 , such phenomena as crystallisation , where the molecules , of their own accord , arrange themselves into the crystalline form if they are first polarised by near approach to the surfaces of a crystal but not otherwise , as is evident from the well-known phenomena of supersaturation .
These crystalline forces are able not only to arrange the molecules in the solution but to move massive crystals and it is an important matter for investigation whether they are simply electrical or of the more complex type of chemical action .
This is perhaps the simplest example of so-called catalytic actions where change is induced by the presence of a material which itself is unchanged and shows the extensive applicability of the general principle that chemical changes depend upon particular arrangements existing and go on of their own accord so long as the arranging power exists .
It is conceded that electrolysis and its consequences can be explained by this hypothesis and the only outstanding phenomenon that does not obviously come under this explanation is that of why osmotic pressure is the same or approximately the same as the gaseous pressure of the same number of molecules and which is supposed to be explained ' by saying that the molecules in the solution are free .
This so-called explanation is , however , as I have already pointed out , not a dynamical explanation at all , it is only a very far-fetched dynamical analogy .
Thus this supposed advantage of the free ion theory is not only illusory but misleading .
" 9 .
The methods of discussing experimental data advocated by Arrhenius and others are valid not only on the assumption they have made that the substance is dissociated into free ions which alone are active ; they are also valid on the more general assumption that a portion of the solute is in some way activated .
It is important , on this account , that the term ionisation should not be used except as an indication that a medium has acquired a conducting state\#151 ; it should in no way be used as an implication of dissociation into separated free ions ; nor should the term ion be used otherwise than to indicate the parts or radicles into which a substance is separable by an electric current\#151 ; the sense in which it was used by Faraday .
10 .
The hold that the ionic dissociation hypothesis has taken upon the imagination of late years is such , however , that almost all workers have applied the conception , particularly those who have sought to explain the phenomena of hydrolysis and etherification .
Even the view has been advanced that not only electrolytes but also nonelectrolytes\#151 ; ethereal salts and the complex sugars , for example\#151 ; may be regarded as dissociated into ions and that the function of the catalyst in hydrolysis is merely to increase the number of the interacting dissociated ions .
The chief advocate of this extreme view , Euler , * represented the equilibrium between ethylic acetate , water , ethylic alcohol and acetic acid in the following manner:\#151 ; [ CH3CO][OC2H5 ] + [ H][OH ] = [ CH3CO][OH ] + [ H][OC2H5 ] .
11 .
The literature of hydrolysis and of the reverse change ( etherification ) * ' Zeit .
phys .
Chem. , ' 1901 , vol. 36 , p. 405 ; ' Ofvers .
K. Yet .
Akad .
Stockholm , ' 1899 , vol. 56 , p. 309 .
1912 .
] Studies of the Processes Operative in .
is now overwhelming .
We thought , at one time , that it would be desirable to present a succinct summary of the numerous publications but after spending much time studying them and preparing such a summary , it must be confessed somewhat unprofitably , we have been forced to conclude that it is impossible to do justice to the subject within reasonable limits of space and that the barest reference only can be given to the various hypotheses that have been advanced .
12 .
The question at issue is one of great importance , as it concerns the whole field of aqueous solutions , including vital phenomena ; but it is one of broad principle rather than of detail .
Chemists have to decide whether or no dissociative or associative changes are at the origin of chemical processes .
Hitherto this issue has not been fairly faced .
13 .
The views of those who postulate the occurrence of ionic dissociation in hydrolysis may be broadly summed up as follows :\#151 ; ( 1 ) In the first stage of the change , a complex positive ion is formed from the acid catalyst and the hydrolyte : in the opinion of some , this is produced by the direct union of the dissociated hydrogen ion of the acid with the hydrolyte ; in that of others , by the combination of the hydrolyte with the two dissociated ions of the acid , the salt so formed being at once resolved into the negative ions of the acid and a complex positive ion containing the hydrogen ion of the acid .
( 2 ) The ultimate products of hydrolysis are formed in a second stage by the action of water on the complex positive ion formed in the first stage\#151 ; the water acting , some think , in a dissociated form whilst others suppose that the molecule as a whole is active .
The changes attending etherification are regarded as similar in character to those involved in hydrolysis .
Stieglitz , * for example , who is one of the chief workers on the subject , has represented the hydrolysis of methylic acetate in the following manner:\#151 ; CH3C(:0)\#151 ; 6\#151 ; CH3 + H + OH .HOCH3 CH3Cfo ; H OH CH3COOH + H\#151 ; 0\#151 ; CH3 H CH3COOH + HOCH3 + H. * 'Amer .
Chem. Journ. , ' 1908 , vol. 39 , p. 60 .
610 Prof. H. E. Armstrong and Mr. F. P. Worley .
[ July 29 , The formation of the acetate is represented by similar expressions\#151 ; thus moH ch3c^o|h och3 CH3COOCH3 + H\#151 ; 0\#151 ; H I H ch*cooch3+hoh+h .
14 .
The hypotheses referred to all involve the assumption that the rate at which hydrolysis proceeds is proportional to the concentration of the dissociated hydrogen ions present and the numerous supporters of this view are emphatic on the point that this deduction is in agreement with experimental fact .
Thus to quote Stieglitz , * " In the case of the catalysis of the esters we are certain of three main facts which have been proved experimentally : the action is accelerated in proportion to the concentration of the hydrogen ions present ; the acid appears to remain unchanged throughout the course of the action , to remain uncombined with any of the compounds involved ; and the ultimate condition of equilibrium is not measurably changed by the presence of the acid .
" Acree and Johnson , f whose views differ from those of Stieglitz in that they assume that the water acts in an undissociated form , referring to their explanation say , " The assumption explains ... ... why the velocity of saponification and of esterification increases directly in proportion to the concentration of the hydrogen ions .
It further makes clear . . .
the experimentally established fact that the equilibrium of the system is not appreciably changed by a change in the concentration of the hydrogen ions .
These ideas ... .
have received very good experimental verification .
" 15 .
We have no hesitation in asserting that the facts are not in accordance with these assertions .
The upholders of the ionic dissociation hypothesis have been forced to assume that the dissociated " hydrogen ion " is the effective agent in hydrolysis .
The contention that the rate of hydrolysis is proportional to the concentration of this ion , however , is based solely on the fact that in the case of a series of acids , their molecular activities , as Ostwald was the first to show , are roughly proportional to their molecular conductivities * Ibid. , 1908 , vol. 39 , p. 30 .
t Ibid. , 1907 , vol. 38 , p. 341 .
CH3CO\#151 ; 6\#151 ; H + H + OCH3 \#151 ; ^ I H 1912 .
] Studies of the Processes Operative in Solutions .
and therefore , ex hypothesi , to the degree of their ionic dissociation .
But those who have discussed the subject appear to have been so led astray by the dissociation hypothesis that they have ignored the well known fact that the rate of hydrolysis increases at a greater rate than the concentration of the acid , instead of at a lower rate , as it should if the rate were proportional to the concentration of the hydrogen ions\#151 ; in other words , the molecular hydrolytic activity of an acid increases with concentration while the presumed degree of ionic dissociation , deduced from conductivity measurements , decreases .
It is remarkable that this fact should be neglected so persistently , as it is at complete variance with the explanations based upon the ionic dissociation hypothesis that have been given of the phenomena of hydrolysis .
Ostwald himself appears to have been the first to draw attention to the fact that the rate of hydrolysis of methylic acetate increases more rapidly than the concentration of the acid .
Thus , after quoting his results , he remarks:\#151 ; " Die Geschwindigkeit nimmt also mit steigender Verdiinnung etwas schneller ab als die Sauremenge , was wohl aus der Schwachung der Saure durch die zunehmende Wassermenge erklart werden kann."* The following year , having been converted meanwhile to the views of Arrhenius , with the express object of contrasting the molecular invertive power of the acid with the molecular conductivity , he extended his observations to the hydrolysis of cane sugar by chlorhydric acid : he again found that the former decreased while the latter increased with dilution .
In order to explain the absence of the proportionality which the dissociation hypothesis led him to expect , he assumed that some secondary influence was at work .
Two years before Ostwald 's results were made known , Urech had drawn attention to the fact that the rate of inversion of cane sugar increased more rapidly than the concentration of the acid .
In a later communication]- he again discussed the influence of concentration of the acid , drawing attention at the same time to the fact that Wilhelmy , in his classical investigations published in 1850 , had specially pointed out that an increase takes place in the velocity constant which is not proportional to the increase in concentration but greater .
No better illustration could be given of the way in which pioneer work can be overlooked and in which preconceived opinion may operate in precluding discussion of an issue of importance .
No explanation has been given of the lack of correspondence between molecular hydrolytic activity and molecular conductivity by the supporters of the ionic dissociation * 'Jr .
pr .
Ch. , ' 1883 , ( 2 ) , vol. 28 , p. 449 .
t 'Ber .
deut .
chem .
Gesell .
, ' 1884 , vol. 17 , p. 2165 .
612 Prof. H. E. Armstrong and Mr. F. P. Worley .
[ July 29 , hypothesis ; the quotations given above are proof that the very existence of the discrepancy has been ignored of late .
16 .
With regard to the statement made so emphatically by Stieglitz and by Acree and Johnson that the condition of equilibrium attained to in the hydrolysis of ethereal salts is unaffected either by the presence or by the concentration of the catalyst , all that can be said is that the assertion is entirely unsupported by experimental evidence and has probably been made through overconfidence in the explanation .
In Part XXIII it is shown that the percentage of methylic acetate hydrolysed at equilibrium decreases to a marked extent as the concentration of the chlorhydric acid is increased ; and Lapworth has obtained similar results , using ethylic acetate .
17 .
Finally , it may be pointed out that the ionic dissociation hypothesis does not in any way account for the all important fact that the hydrolytic activity of acids is much increased in presence of their salts .
18 .
The various hypotheses based on dissociation that have been put forward in explanation of the phenomena of hydrolysis and etherification are not only not in harmony with the experimental facts but are also involved and make it necessary to postulate changes which are not only purely hypothetical but also improbable if not impossible ; their advocates also do not take into account the action of the solvent water on the various substances , except its supposed power of inducing " ionic dissociation .
" In confirmation of our view , we may point to the confusion that has arisen of late among the advocates of the ionic dissociation hypothesis and to the admission that has been made that it is to be supposed that the catalytic activity of acids is a composite effect to be ascribed not only to the dissociated hydrogen ion but also to the undissociated acid.* We are convinced not only that the processes of hydrolysis rationally explained without the aid of the ionic dissociation hypothesis but that the chemical activity of acids cannot be explained by means of this hypothesis .
19 .
The explanation that we desire to advocate here is that hydrolysis is an associative process initially and that it is effected by the breakdown of a system composed of the hydrolyte , the catalyst and water .
According to our present view , hydrolysis is due to the association and direct interaction of two complexes\#151 ; of a single unit of the hydrated hydrolyte with one of the hydrated catalyst .
We imagine that such systems are constantly being produced , broken * Report of meeting of German Bunsen Society , ' Chemiker Zeitung/ May 25 , 1912 , p. 587 ; 'Zeits .
Electrochem .
, ' 1912 , vol. 18 , p. 539 ; 'Amer .
Chem. Journ. , ' 1912 , vol. 48 , p. 352 .
1912 .
] Studies of the Processes Operative in Solutions .
613 down and re-formed in such manner that , while some give rise to their original components , others are resolved into the products of change ; in other words , only a fraction of the unions are effective .
Free water , i.e. water uncombined with the hydrolyte or catalyst , does not enter into the interaction .
Hydrolysis , according to this view , is a bimolecular interaction , the second factor being , however , not as is generally supposed , the concentration of the water but that of the hydrated catalyst .
The fallacy which underlies the usual interpretation of the mass action equation expressing the condition of equilibrium in the case of the hydrolysis of ethereal salts , in which the proportion of water is one of the factors in the equation , has been pointed out in Part XXIII .
Etherification is to be regarded as a direct reversal of the process of hydrolysis .
20 .
We would further affirm that the similarity of the results arrived at by the study of the various properties of solutions , such as conductivity , chemical hydrolytic activity and osmotic effects , is due to the fact that the determining factor in all these cases is the interaction involved in the production of the electrolyte from water and the solute .
Increase of molecular conductivity to a maximum on dilution appears to us to be due mainly to two causes\#151 ; ( 1 ) to the gradual increase in the extent of the interaction between the dissolved substance and water ; ( 2 ) the gradual simplification of the complexes of the dissolved substance .
There is a marked resemblance between the curves showing the increase in the apparent molecular hydration attending dilution ( see Diagram 2 , Part XXII ) and the well-known curves representing the increase of molecular conductivity .
In Diagram 1 the two curves in the case of sulphuric acid are superposed and fall sufficiently together to justify the suggestion that molecular conductivity is proportional to the apparent molecular hydration .
In the case of chlorhydric acid , the curves do not lie so close together , that representing the apparent hydration rising more rapidly in dilute solutions .
It is pointed out in Part XXIII , however , that the somewhat rapid rise in the values of the apparent molecular hydration in the case of this acid in dilute solution may possibly be due to experimental error .
Decrease of molecular chemical activity\#151 ; of the hydrolytic activity of acids for instance\#151 ; to a minimum on dilution appears to be the necessary outcome of a gradual weakening of the acid by further combination with water .
It is rational to suppose that the more the activity of the acid is used up in combining with water , the less residual activity it will have to 614 Prof. H. E. Armstrong and Mr. F. P. Worley .
[ July 29 , effect hydrolysis , for instance .
This is no new idea but one which has long been held by chemists and a necessary consequence of the fact that heat is evolved as solutions are diluted\#151 ; a circumstance in no way taken into account in the ionic dissociation hypothesis .
It is a great weakness in the Arrhenius hypothesis that it involves the eminently improbable assumption that not only is the change of activity on dilution in any particular solution the consequence of an alteration in the mere number of active units but that the activity of the active units of different substances is the same .
21 .
The body of evidence now available that the process of chemical change is associative , not dissociative , is very great indeed : it is impossible to dispute the conclusion that in order that interaction may take place conditions must prevail such as obtain in a voltaic system .
The work of Brereton Baker , for example , in particular , has shown that not water alone but conducting ( impure ) water\#151 ; i.e. an electrolyte\#151 ; must be present to determine change .
As the contact difference of potential is equal and opposite at the opposite junctions of two substances , no current can flow in a binary system ; to constitute a slope of potential , a third compound must be introduced and one of the three must be an electrolyte .
To take an example , there is good reason to suppose that , in all cases , oxidation is primarily a process of hydroxylation effected in a complex circuit such as is pictured in the expression :\#151 ; H HO(HX)H* 0 HOH HX HO i+HO(HX)H +0 HOH + HX + HO ' * This expression is not used as a representation of the-constitution of the electrolyte or of the manner in which it acts but merely as an indication that the electrolyte is necessarily included in the circuit .
1912 .
] Studies of the Processes Operative in Solutions .
22 .
As the processes of electrolysis and of chemical change , in general , cannot well be regarded otherwise than as reciprocal , inseparable processes , it is to be supposed that electrolysis also is effected in a three component system\#151 ; in other words , that it is essentially an associative process .
In this connexion , attention may once more be directed to FitzGerald 's remark in the Helmholtz Memorial Lecture on the importance that is to be attached to " suitable arrangements of molecules " \#151 ; and to the opinion he expressed that a modified Grotthus ' hypothesis will fit the facts.* The process of hydrolysis differs only from the process of liydroxylation ( oxidation ) in that the compound hydrolysed is one consisting of two sections , one of which is capable of acting as the positive , the other as the negative element in the voltaic system\#151 ; capable , therefore , of sharing the two ions of the water molecule between them , the OH radicle being delivered against the positive and the hydrogen radicle against the negative element of the hydrolyte .
23 .
The selective activity of enzymes and their extraordinary efficiency as hydrolytic agents has been overlooked in common with nearly all the evidence to be derived from the organic side of chemistry ; such selective activity is incompatible with the hypothesis that the hydrogen ion is the effective agent in hydrolysis .
But the selective activity of enzymes is not only incompatible with the dissociation hypothesis , it also appears to afford an unanswerable argument in favour of the conclusion that hydrolysis is a process in which hydrolyte and hydrolyst become associated , especially in view of the fact that enzymes which act on glucosides may be specially controlled and their activity diminished by the " glucose " from which the glucosides are derived .
24 .
The view put forward by one of us in explanation of the activation of " salts " by dissolution in water involves the assumption that solvent and solute are reciprocally active and has the advantage that no distinction is drawn between compounds such as hydrogen chloride ( HC1 ) and hydrone ( H20 ) , whilst the dissociation hypothesis involves the assumption that they are of an entirely distinct nature and that the one is almost completely dissociated whilst the other is all but unchanged when they are intermixed .
It is impossible , on chemical grounds , to admit this latter postulate .
It is assumed that when the two compounds are brought together , whilst the one is " hydrolated " the other is " muriated , " thus : / H / H HC1 + OH2 = KClf H20 + HC1 = H20\lt ; XOH XC1 * ' Brit. Assoc. Rep. , Bradford , ' 1900 , p. 654 .
616 Prof. H. E. Armstrong and Mr. F. P. Worley .
[ July 29 , Moreover , that on dilution both of the " associated " compounds become further hydrolated , thus HC1\ H , etc. XOH\lt ; xOH H20\lt ; ^ H , etc. XCl\lt ; f XOH 25 .
On general grounds and in view of the fact that , on dilution , a point is reached at which the specific electrical conducting power of the mixture is at a maximum , it is probable that in some way or other the two kinds of " associate " are reciprocally active in conveying the current and therefore in all cases of electrolysis ( i.e. of chemical change , if chemical change always involve electrolysis , as we assume to be the case ) .
The argument we have in mind in making this statement is not an easy one to appreciate and it will be difficult to determine its validity .
We consider that as chlorine and oxygen are in every way analogous elements , their hydrides will tend to behave similarly\#151 ; whatever is true of the one is true , within limits , of the other .
Hence it is to be supposed that when interaction takes place on mixing them , each becomes " distributed " against the other .
The new correlated compounds that are formed ( H20\lt ; ^| and HG1\OH and their hydrols ) must have similar properties .
One or other of two further assumptions must be made\#151 ; that , in conveying the electric current , either ( a ) each is active singly or ( ) they act in conjunction .
Each of the two complexes presumably is less stable than either of the simpler molecules from which they are derived , as the dominant element ( chlorine in the one case , oxygen in the other ) has a greater burden cast upon it .
In other words , H and OH in the complex HC1\lt ; ^qjj are less firmly held than they are in hydrone , whilst H and Cl in the complex H20\lt ; ^ are less firmly held than they are in hydrogen chloride .
This vi ew is not only rational but the facts appear to support it .
But the stability of the two hydrides is only lowered by their interaction in the manner pictured\#151 ; their ions are not free .
Apparently a lowering of stability is not sufficient to render a compound an electrolyte per se\#151 ; no single substance of simple molecular constitution is an electrolyte .
There is much evidence , in fact , to show that , in some way or other , electrolysis is the outcome of an interaction determined by an electromotive force not the consequence of the breakdown of a single substance .
1912 .
] Studies of the Processes Operative in Solutions .
26 .
To account for the changes that occur when salts are mixed , it is necessary to assume that electrolysis is always taking place within closed circuits in solution and that rearrangements are effected in consequence .
When electrodes are introduced , they but tap the circuits and it becomes possible to urge a current along the various chains of molecules normally existent in the solution and to attract the oppositely polarised radicles at the ends of the chains to the oppositely charged electrodes .
It is difficult , in the absence of all positive knowledge on the subject , to give any precise picture of the process .
Presumably , the circuit is constituted primarily through the operation of the residual affinity of the negative radicles ; once they are constituted , the breakdown involving rearrangement ( i.e. electrolysis ) is immediate in some of the systems , whilst others are merely resolved into their original components .
The rate of hydrolysis depends on the proportions in which these two changes take place .
The change may be formulated as follows , using double arrows to indicate the directions in which residual affinity tends to act and dotted lines to show the direction in which cleavage is effected ; if read the reverse way the scheme indicates the course of change in etherification :\#151 ; r/ C1H *\#166 ; \lt ; C\#151 ; O-OH^CKoh H T iX " - '\#166 ; \gt ; HydrolaTed hydro lyle Hydrolysf* 27 .
The scheme is that applicable to concentrated solutions , in which presumably the hydrolyst is present in its simplest forms ; as the concentration is diminished , these give place to more hydrolated and weaker forms , e.g. H H H H H HO-O-O 1 i HO-O Cl-OH .
H H 1 H 1 II I l H H * The oxygen junction of an etheric compound is represented in this scheme .
618 Prof. H. E. Armstrong and Mr. F. P. Worley .
[ July 29 , It is to be supposed that these are immediately active only at one terminal point of each , where presumably the free valencies are situate , so that to represent their action in the diagram it is necessary to lengthen the symbols of the hydrolyst " correlates " only in the direction indicated by the barbed arrows .
If this view be adopted , an interpretation is at hand of the fact on which emphasis is laid in paragraph 20 that molecular hydration and molecular electrical conductivity follow closely the same course , as the solute is shown to be extending its influence as dilution proceeds though it loses strength as an agent .
28 .
It is to be expected , on the other hand , that acids would be active in the order of their specific electrical , conductivity , though molecular conductivity and molecular hydrolytic activity vary on dilution in the case of any one acid in opposite directions , the one diminishing as the other increases .
Action within the molecular circuits must follow Ohm 's law ( C = E/ E ) but it is not possible to institute any direct or absolute comparison between actual conductivity and hydrolytic activity , owing to the disturbance effected by the hydrolyte and the impossibility of allowing for the amount of free water .
In the case of acids , as the concentration is increased , specific conductivity increases to a maximum and then falls .
Hydrolytic activity also increases though at a more rapid rate than the concentration , whilst specific conductivity increases at a less rate ; but it has not yet been ascertained that it reaches a maximum .
Presumably it does but whether the maxima coincide is open to question ; it is to be supposed that in the case of hydrolysis complications arise owing to the interaction of the alcohol and the acid catalyst .
29 .
J. Gibson has argued in a recent communication to the Eoyal Society of Edinburgh* that the point of maximum conductivity is an all important turning point .
He considers that interaction always takes place in such a way as to cause an increase of specific conductivity .
Thus an acid catalyst of lower concentration than that corresponding to maximum conductivity , according to Gibson , should favour hydrolysis of ethereal salts , whilst one of higher concentration should favour the reverse change of etherification .
Etherification takes place , however , in and is accelerated by very dilute acid solutions , though it does not proceed far : it is probable that hydrolysis also takes place in acid solutions of greater concentration than that corresponding to maximum conductivity .
Gibson 's view that acid solutions of maximum conductivity are practically without hydrolytic action on cane sugar does not appear to us to be correct , , * 'Roy .
Soc. Edin .
Trans. , ' 1911 , vol. 48 , p. 117 .
1912 .
] Studies of the Processes Operative Solutions .
though it seems probable that beyond this concentration of acid the rate of hydrolysis is decreased instead of being increased by further concentration .
In our opinion , there is a " tendency towards maximum conductivity " because maximum conductivity is reached when the two constituents of the electrolyte interact in the proportions in which they exercise their maximal reciprocal influence .
It seems to us that actions involving withdrawal of water will take place preferentially on the one side ( the acid side ) of the maximum and those involving hydrolysis on the other\#151 ; in other words , it is probable that the point of maximum conductivity is that at which the reciprocal changes are in equilibrium in maximum proportions and that when this point is passed other actions set in .
For example , the charring of cane sugar must be an effect produced by the more or less direct interaction of the acid and the cane sugar , as the effect is not observed when dextrose , for example , is acted upon by the acid .
30 .
According to our view , the process of " ionisation , " i.e. activation , which gives rise to the hydrolyst is that involved in the interaction of the hydrogen chloride and hydrone , whereby the two " reciprocal " salt forms are produced \#151 ; but just as no distinction is drawn between the two hydrides and it is assumed that both are activated , so also it is assumed that the hydrolyte is also acted upon in an activated form , namely the hydrol .
The rate of hydrolysis , from this point of view , is dependent on the degree of activation of the hydrolysed substance , as well as on the degree of activity of the hydrolyst .
It is necessary therefore to recognise the existence of strong and weak hydrolytes as well as of strong and weak acids or bases , the strength depending in both cases on the degree of activation through hydrolation ( or the reciprocal change ) .
To make this contention clear , it may be pointed out that hydrolytes generally , from the point of view here put forward , are to be regarded as more or less basic substances in presence of acids .
It is assumed that the degree of activation , both of acid ( catalyst ) and base ( hydrolyte ) , is proportional to the number of molecules in which hydrol is active : ethereal salts , in fact , may be pictured as acting as weak bases more or less comparable with ammonia though weaker .
31 .
The advocates of the ionic dissociation hypothesis assume that all ions of acids are of equal strength and that the variation in the strength of acids is simply due to variation in the number of ions .
This does not appear to be in harmony with general chemical experience\#151 ; every chemist must feel that sulphuric acid is intrinsically a strong and acetic a weak acid .
VOL. LXXXVII.\#151 ; A. 2 X 620 Prof. H. E. Armstrong and Mr. F. P. Worley .
[ July 29 , According to the view here put forward , the ( molecular ) strength of an acid depends primarily on its nature ; but presumably it will also vary with concentration , becoming gradually weaker as it is more and more hydrolated .
Weak acids which obey the so-called dilution law are those which are only slowly resolved on dilution into the fundamental molecules and therefore only slowly hydrolated .
The method adopted by the advocates of the ionic hypothesis of determining the degree of dissociation of an acid in a solution ( the ratio / xj deduced by taking into account the molecular conductivity at a particular strength and molecular conductivity at infinite dilution ) is only valid if the simple assumption be accepted as to the manner in which dissociation takes place on which the advocates of the dissociation hypothesis rely , namely that the whole of the solute is eventually active .
If , as argued in previous parts of these studies , " hydration " may take place in various ways and give rise to compounds which are not all active ( hydrones as well as hydrols ; compare Part VI , p. 82 ) , the activity of an acid deduced in the manner referred to cannot be regarded as having more than relative value\#151 ; the proportion of real acid will only reach a certain maximum .
32 .
In conclusion , we may refer briefly to some of the issues brought under notice in these studies to which special attention may be directed .
33 .
In the first place , it is claimed that an advance in the method of studying the properties of solutions was made in Part I by referring the concentration of substances in solution to a given mass of solvent ( 1000 grm. of water , i.e.55'5 molecular proportions ) instead of to a given volume of solution , the method previously in vogue .
In strong solutions especially , the quantity of dissolved substance in a given volume cannot be altered without greatly reducing the quantity of solvent present , thus introducing a second variable often of considerable magnitude .
Throughout the inquiry , volume has been disregarded in making up solutions , the relative molecular proportions of the dissolved substance to a given quantity of solvent being alone considered .
The results appear to justify the procedure and to show that the method adopted is that most calculated to bring out the true nature of the effects produced in solutions by alteration of concentration .
.The anomalies presented by concentrated solutions made up to a definite volume are either no longer obvious or tend to disappear , the changes produced by alteration of concentration being similar in character throughout the entire range of dilution .
The method has been used with like results by Morse and Frazer in their refined studies of osmotic pressure .
34 .
Though a great improvement , however , the method is not perfect , as 1912 .
] Studies of the Processes Operative Solutions .
621 the water which is combined with the dissolved substance in concentrated solutions is often a very considerable fraction of the total water .
Consequently , the amount of water actually free to act as such must be subject to variation , according as the nature of the substances present is varied and the proportions in which they are dissolved are altered .
On this account , it will be very difficult , if not impossible , to unravel all the complexities solutions afford .
35 .
Throughout these studies , the influence exercised by salts in accelerating hydrolytic changes has been attributed mainly to their concentrating effect\#151 ; in other words , it is supposed that they enter into combination with more or less of the water present , so that the hydrolytic action of the acid catalyst is effected in a solution the actual concentration of which is higher\#151 ; it may be to a relatively considerable extent\#151 ; than the apparent concentration .
The behaviour of salts , it is well known , is not in harmony with the postulates of the ionic dissociation hypothesis .
We submit that the explanation we have advanced is consistent with the facts generally .
36 .
One main object of the inquiry has been to determine the extent to which salts are hydrated in solutions on the assumption that the increase in the rate at which hydrolysis proceeds is due mainly to the concentrating effect of the salt .
The method first adopted ( cf Part I ) involved merely the determination of the number of molecular proportions of water that were necessary to reduce the rate of change in presence of a molecular proportion of the salt to that obtaining in the presence of the acid catalyst alone .
Subsequently ( cf. Part XII ) , the method was improved in a way which made it possible to deduce apparent molecular hydration values corresponding to different degrees of dilution and it was shown that the values increase with dilution\#151 ; an entirely rational conclusion .
It is realised that though the values referred to are mainly concentration values , they do not necessarily represent the actual degree of hydration of the salts but are rather a measure of the sum of the changes effected in the solution by its presence .
37 .
A method has been devised ( Part XII ) whereby also the apparent molecular hydration of the acid catalyst may be determined , at different degrees of dilution , on the assumption that the free water does not enter into the interaction .
( The values include the water combined with the hydrolyte , which , however , is very small in amount when only a quarter of a molecular proportion of cane sugar is used to one of acid .
) The apparent hydration values of acids are rather larger than those of the alkali salts and , as in the case of salts , increase with dilution towards 622 Prof. H. E. Armstrong and Mr. F. P. Worley .
[ July 29 , a maximum .
The molecular hydrolytic activities of acids , when their concentration is estimated with regard to the free water present , decrease with dilution towards a minimum .
This is an important fact , as when their concentration is referred to the total water present it is by no means certain to what extent the increase of molecular activity with concentration is due to the concentrating effect of the acid itself\#151 ; doubling the proportion of acid to a given quantity of water more than doubling its true concentration referred to free water .
38 .
It has been shown that when raffinose is used as hydrolyte ( Parts XIV and XV ) results are obtained very similar to those arrived at with sugar .
When , however , methylic acetate is used , the apparent hydration values that are found both of acids and of salts are much lowrer than when cane susar is used .
39 .
The results recorded in these studies show that the apparent hydration values of salts diminish in the case of a series of allied metals as the atomic weight of the metal becomes greater .
The apparent hydration values of nitrates are always smaller than those of the corresponding chlorides , bromides and iodides .
It is a well known fact that the general chemical activity of corresponding salts is greater the lower the molecular weight of the salt .
The greater activity is to be correlated with the greater concentrating effect of the salt of lower molecular weight .
40 .
The effect produced by substances other than salts on the hydrolytic activity of acids is in many respects remarkable .
Substances such as sugar , which presumably enter into association with a more or less considerable proportion of the wTater in a solution , apparently have little or no influence .
It is not improbable that there are compensating influences at work which involve a reduction in the activity of the sugar in a degree corresponding to that in which it is raised by the effect the sugar exercises .
41 .
The effect produced by alcohols and similar substances having slight affinity for water appears to be quite distinct and different from that exercised by salts and substances such as sugar .
This cannot well be ascribed to the withdrawal of water but rather to the mechanical effects produced by interposition of the neutral molecules , affecting both the water itself , the hydrolyte and the liydrolyst .
It is pointed out above that the apparent hydration values , both of acids and of salts , found by means of methylic acetate are much lower than those deduced by using cane sugar as the hydrolyte\#151 ; this observation is of primary importance , in connexion with the behaviour of non-electrolytes , which have slight affinity for water , to which attention is here drawn .
1912 .
] Studies of the Processes Operative in Solutions .
623 Metliylic acetate is undoubtedly a weak hydrolyte* in comparison with cane sugar and the result arrived at may be the consequence of this weakness , not of any considerable actual lowering of the degree of hydration of either the acid catalyst or the salt .
42 .
To state in a few brief paragraphs the view which we have been led to form\#151 ; Water is a complex mixture of various polymerides of hydrone , OH2 , in equilibrium .
The proportions in which these are in equilibrium is disturbed by the presence of any substance dissolved in the liquid .
" Salts " and other substances exist in solution in combination with hydrone in proportions which vary constantly with the conditions , much water being removed from the sphere of solvent .
The compounds postulated are present in various forms differing in type , only some of the forms being chemically active .
The degree of hydration ( hydrolation and hydronation ) may vary from the large values characteristic of salts such as calcium chloride to almost nil .
We do not believe that salts are ever present in solution in the dissociated condition postulated by Arrhenius .
In concentrated solutions , they undoubtedly exist , to some extent , in a polymerised condition ; such complex molecules are simplified as dilution proceeds , the simpler molecules become " hydrated " in various ways and to various extents .
The interactions that occur in solution , we imagine , are primarily in all cases associative processes and ultimately the consequence of rearrangements effected within complex molecular systems .
43 .
We venture to claim that the explanation here given of the process of hydrolytic change is simple , consistent , in harmony with the facts , in accordance with chemical experience and generally applicable .
In our opinion , the ionic dissociation hypothesis does not afford an explanation of the facts .
We go so far as to assert that there is now sufficient evidence that the hypothesis is a false one .
* As acids act simply as agents without themselves undergoing change , no difficulty attends the determination of their strength ; but the hydrolyte is not simply the reciprocal of the acid , as besides acting in conjunction with the acid it is broken down ; the readiness with which change occurs depends therefore not only on the specific activity of the hydrolyte but also on its internal stability .
|
rspa_1913_0001 | 0950-1207 | Address of the president, Sir Archibald Geikie, K. C. B., at the anniversary meeting on November 30,1912. | 1 | 12 | 1,913 | 88 | Proceedings of the Royal Society of London. Series A, Containing Papers of a Mathematical and Physical Character | Sir Archibad Geikie, K. C. B. | speech | 6.0.4 | http://dx.doi.org/10.1098/rspa.1913.0001 | en | rspa | 1,910 | 1,900 | 1,900 | 5 | 191 | 5,580 | http://corpora.clarin-d.uni-saarland.de/surprisal/6.0.3/?id=rspa_1913_0001 | 10.1098/rspa.1913.0001 | null | null | null | Biography | 90.92816 | Fluid Dynamics | 2.307995 | Biography | [
38.07540512084961,
77.51273345947266
] | PROCEEDINGS OF THE ROYAL SOCIETY .
Section A.\#151 ; Mathematical and Physical Sciences .
Address of the President , Si % Archibald Geikie , K.C.B. , at the Anniversary Meeting on November 30 , 1912 .
In reviewing the progress of the Royal Society since St. Andrew 's Day last year we have first to take note of the losses which during the interval have been inflicted on our ranks by the hand of death .
Though , perhaps , somewhat fewer in number than the average of recent years , these losses have included some of our most distinguished associates .
Four of our Foreign Members have passed away , and on our Home List we have to regret^ the death of twelve Fellows , among whom are two former Presidents of the Society and Copley Medallists .
While both the biological and the physical sides of science have shared in this bereavement , it is more especially on the former and particularly on the domain of botany that the losses have fallen .
Two of our recently deceased Foreign Members were eminent representatives of botanical science .
Jean B. Edouard Bornet , who was elected into our number only two years ago , died at the end of last year at the ripe age of 83 , having attained the highest distinction by his investigations into the structure and life-history of the Algae .
Eduard Strasburger , one of the most original and versatile botanists of his day , died last May , in his 70th year .
The brilliance of his researches in various departments of botany , more particularly in cytology and plant anatomy , placed him in the front rank of the science , and drew around him , in his laboratory .at Bonn , students from all parts of the world .
In Ferdinand Zirkel mineralogy , geology , and petrography have lost one of their foremost exponents , and his wide circle of friends mourns VOL. lxxxviii.\#151 ; A. B 2 Anniversary Address by Sir A. Geikie .
[ Nov. 30 , the death of a loyal and lovable man .
We had hoped that he would attend the Society 's Anniversary celebration last July .
He wrote , not uncheerfully , that he would gladly have come to London had the state of his health permitted , but he passed away on June 11 .
He was the first man of science on the Continent who realised the far-reaching importance of the work of our late distinguished Fellow , Henry Clifton Sorby , in the application of the microscope to the solution of the many problems presented by the composition and intimate structure of the rocks that form the crust of the earth .
Zirkel 's name will always stand associated with Sorby 's in the forefront of the pioneers who led the way in the transformation or re-creation of the science of petrography .
His own original contributions to this science were marked by their singular grasp and lucidity , while his massive ' Lehrbuch der Petrographie ' remains as a classic monument of his industry , his wide acquaintance with the literature of his subject in every language , and his admirably clear and orderly method of presentation .
He was elected one of our Foreign Members in 1897\#151 ; an honour which he keenly appreciated .
By the death of Jules Henri PoincarE at the comparatively early age of 58 , mathematical science has lost one of its most distinguished cultivators .
He had already come to the front as a discoverer in the domain of pure analysis , when his accession to a Chair of Mathematical Physics turned his attention towards the great concrete realm of natural philosophy .
This branch of knowledge he expounded from the mathematical outlook in a series of memoirs and treatises which established for him a new reputation .
His profound and highly trained mathematical intuition enabled him , in not a few cases , to give a fresh impetus to problems that were pending and for the time at a standstill , such , for example , as the question of the classification of the various forms possible for a self-gravitating rotating planet , on which Lord Kelvin shed much fascinating light without entirely unravelling it .
Poincare 's work on celestial mechanics , culminating in a formal treatise on that subject , is a masterly and illuminating attempt to bring the empirical and tentative solutions , which have proved to be adequate for practical calculations , within the domain of precision which belongs to the modern theory of expansions in series .
In the more complex physical subjects , such as thermodynamics and the theory of electricity , where mathematical reasoning has to be largely of tentative and inductive type , he was a keen student and a candid critic .
His wide studies in these fields afforded ample material for the philosophic workings of a mind interested , like those of many of the greatest mathematical discoverers , in probing the ultimate foundations of knowledge ; and the popular essays in which he gave rein to his criticism 1912 .
] Anniversary Address by Sir A. Geikie .
3 .and often to his fancy , always in exquisite literary form , brought him a seat in the French Academy and made his name familiar in wide circles which his constructive work could hardly have reached .
In Henri PoincarE we lose a colleague who had long been in intimate and cordial relations with his fellow workers in this country .
His name stands first in the awards of the Sylvester Medal ; he was a Medallist of the Royal Astronomical Society ; and at the time of his decease his nomination was ripening for the chief award of the Royal Society\#151 ; the Copley Medal .
Illness prevented him from attending our Anniversary Celebration last July ; we had heard that his health was improving , but on the last day of our festival news came from Paris of his sudden death .
In obedience to a widely-expressed desire our Secretary , Sir Joseph Larmor , and the Astronomer Royal wrere deputed to represent the Royal Society at his funeral .
By the death of Sir Joseph Dalton Hooker the Royal Society has been deprived of its oldest member , its most distinguished botanist , one of its long line of Presidents , and one to whom it had awarded all the honours which it could bestow .
Born as far back as the year 1817 , this great man began his illustrious career , at the early age of 22 , by accompanying Sir James Clark Ross in the famous expedition of the " Erebus " and " Terror " to the Antarctic regions in 1839 .
The publication of the results of this voyage in his ' Flora Antarctica9 placed Hooker at one bound in the first rank of the systematic botanists of the day .
Thenceforward he continued to enrich science with contributions marked at once by great originality and philosophical insight .
His keen interest in the problems of the geographical distribution of plants , and his ardent enthusiasm as an explorer of the botany of new or little known regions , combined to make him one of the most intrepid and accomplished travellers of his time .
His Antarctic experiences were followed before many years by his memorable journeys in the Himalayas , Tibet , Nepal , and Sikkim , from which he returned with so rich a harvest of important observations .
In later years he visited Palestine and brought back results interesting alike to the botanist and the geologist , explored the Atlas and the uplands of Morocco , and , eventually extending his surveys into the New World , traversed the Rocky Mountains in Colorado and Utah .
Sir Joseph 's association with Charles Darwin and the publication of the ' Origin of Species ' is a memorable incident in the history of modern science .
In recognition of the great value of his early botanical researches Hooker was elected into the Royal Society in 1847 at the age of 30 .
Seven years later further approbation of his work was marked by the award of a B 2 4 Anniversary Address by Sir A. Geikie .
[ Nov. 30 , Royal Medal in 1854 .
His genial character , his judicious temperament , and his business capacity , led to his being frequently chosen to serve on the Society 's Council .
He repeatedly filled the office of Vice-President , and he occupied the Presidential Chair for five years , from 1873 to 1878 .
The crowning honour of the Copley Medal was conferred upon him in 1887 , when he had reached his 70 th year ; and a few years later , when the Darwin Medal had been instituted , it was awarded to him in recognition of his association with the great naturalist whose name it bears .
Universally acknowledged to stand at the head of the botanists of his day , continuing to work at his favourite studies up to the very end of his long and brilliant career , beloved by all who knew him , and full of honours as of years , he passed to his rest on December 10 , 1911 , in the 94th year of his age .
In Lord Lister we have lost one of the most epoch-marking men of our time .
By patient and skilful investigations along a strictly scientific path , his intuitive genius enabled him eventually to transform the art of the surgeon , and thereby to lay mankind under an eternal debt of gratitude for his achievement in the lessening of mortality , the diminution of suffering , and the extension of successful surgical treatment to operations wdiich were previously considered too dangerous to be undertaken .
Few chapters in the history of the advance of experimental science are more fascinating than those which , in Lister 's published papers and in other publications , trace the long and laborious investigation , the difficulties and disappointments which accompanied it , and the opposition or indifference with which it was watched outside , before he emerged in triumph with his purpose accomplished .
At the beginning of his career , his kindly nature was shocked at the appalling mortality in the surgical hospitals with which he was acquainted , and , as he felt sure that some remedy might be found , he set himself deliberately to seek for it .
Convinced of the truth of Pasteur 's researches in regard to the origin of putrefactive changes , he conceived that if he could exclude or destroy the micro-organisms everywhere present surgical wounds would probably heal , and the pain and fatal results accompanying them would be diminished or even prevented .
Step by step , as his knowledge of this obscure subject widened , his methods were altered , improved , and simplified , until their undoubted success compelled the attention of the medical world .
His antiseptic treatment was , ere long , adopted in hospital after hospital with ever-increasing appreciation , until it is now in universal use all over the world .
Lister was himself a skilful surgeon , and as a man of science he made important contributions to surgery and medicine .
In particular , his suggestive work in regard to bacteria was largely instrumental in founding 1912 .
] Anniversary Address by Sir A. Geikie .
5 the important modern science of bacteriology. .
But , undoubtedly , the achievement which will hand his name down to the remotest posterity has been the creation of aseptic surgery .
The remarkable company of eminent and representative men who from all parts of the civilised world gathered round his bier in Westminster Abbey was a visible expression of the gratitude of all countries for his priceless services .
The value of Lord Lister 's early contributions to science was recognised by the Eoyal Society , which elected him a Fellow in 1860 , when he was 33 years of age .
After he left the professorship which he held in the University of Edinburgh and had settled in London , he served frequently on the Council of the Society .
He was Foreign Secretary from 1893 to 1895 , and he filled the Presidential Chair from 1895 to 1900 .
He received a Royal Medal in 1880 , and was awarded the Copley Medal in 1902 .
His kindliness and courtesy , his simplicity and modesty , endeared him to a wide circle of friends who warmly cherish his memory .
He died at Walmer on February 10 last , in the 85th year of his age .
There was a widespread desire that his remains should be laid in Westminster Abbey , but by his own direction he was buried beside his wife in the West Hampstead Cemetery .
From among the chemists on our List of Fellows we have lost during the past year Dr. Edward Divers and Dr. Humphrey Owen Jones .
Dr. Divers spent his earlier years in this country ; but having been induced in 1873 to accept the offer of a Professorship of Chemistry from the Government of Japan , he remained on active service in that country for twenty-six years .
On his return to England his long experience found useful employment in the councils of learned societies and other institutions .
He became a Fellow of the Royal Society in 1885 .
He died in April last , in his 75th year .
By the sudden and tragic death of Dr. Jones and his young bride in the Alps last summer , science has been deprived of one who , though only 34 years of age , had already distinguished himself as an original observer and an excellent teacher , and who would doubtless soon have risen to eminence among the chemists of his day .
His merits were recognised when he was elected into the Royal Society this year .
We lament that a career so full of promise should have been so suddenly cut short by an accident met with in a recreation in which he was one of the most noted leaders .
The representation of Engineering in our Fellowship has been diminished since our last Anniversary by the death of Henry Taylor Bovey .
Born in 1850 , he became 12th Wrangler at Cambridge in 1873 , and after engaging in various engineering works accepted in 1877 the Chair of Engineering at McGill University , Montreal .
His skill and energy transformed the teaching of applied science in that institution and made the College the most important Anniversary Address by Sir .
A. Geikie .
[ Nov. 30 , engineering school on the American continent .
In 1908 he was induced to return to England and to accept the rectorship of the Imperial College of Science and Technology in London .
Owing to failing health , however , he resigned that appointment at the end of the following year .
He died on February 2 last .
The late Major-General Edward Robert Festing connected the Royal Society with the Royal Engineers .
In association with Sir William Abney he communicated papers to the Society on a variety of physical subjects , especially on photometry .
He was elected a Fellow in 1886 .
For many years Admiral Sir John Dalrymple Hay , Bart. , wras one of the most regular attendants at the meetings of the Society .
He was born in 1821 , entered the Navy at the age of 13 , and had a varied and interesting career until he retired from active service afloat in 1859 .
He had early shown an interest in some branches of science , particularly in meteorology , and after he retired from the sea he had opportunities of advocating the application of science to the needs of the Navy .
In 186 L he was appointed Chairman of the Iron-plate Committee that was formed for the purpose of carrying on experiments on the application of armour to the sides of vessels of war .
In 1864 he was elected a Fellow of the Royal Society .
His reminiscences of his experience in the Navy and in official life , his exceptional descriptive faculty , his dignified presence and old-time courtesy and his keen sense of humour made him a special favourite in society .
He passed away on January 28 last , in the 91st year of his age .
In Osborne Reynolds we have lost one of our leading physicists and scientific engineers .
His original contributions to the kinetic theory of gases and the molecular theory of viscosity , those on the flow of liquids in channels , and on the determination of the mechanical equivalent of heat , have given him an assured place in the history of physical science .
His labours as a University Professor have brilliantly illustrated the intimate connexion which exists between physical experiment and practical engineering progress , and have endeared him to the wide circle of pupils who studied under him .
He was elected one of our Fellows in 1877 and was awarded a Royal Medal in 1888 .
Dr. Ramsay Heatley Traquair , who has just died at Edinburgh in his 72nd year , has long held a foremost place in the ranks of vertebrate palaeontologists .
His medical training , and his early devotion to the study of the anatomy of fishes , gave him a grasp of the ichthyology of past time such as few of his contemporaries could equal .
By concentrating his attention on the fossil fishes of the Old Red Sandstone and the Carboniferous system , he was enabled to throw much new light on the relations of these 1912 .
] Anniversary Address by Sir A. Geikie .
organisms to each other , while at the same time he showed how their specific forms could be utilised for the determination of problems in stratigraphy .
He joined the Royal Society in 1881 , and in 1907 received one of our Royal Medals .
Dr. John William Mallet , who was elected into the Society in 1877 , was the son of Robert Mallet , one of the pioneers of modern seismology .
He graduated in medicine , but specially interested himself in chemical studies .
Settling in the United States , he became a Fellow of the College of Physicians of Philadelphia , and was Professor of Chemistry in the University of Virginia .
But he retained his connection with this country , and in 1906 was one of the representatives of the Royal Society at the celebration of the 200th anniversary of the birth of Benjamin Franklin at Philadelphia .
Robert Holford Bosanquet was for some time a Fellow of St. John 's College , Cambridge .
His investigations in the theory of sound , especially in relation to music , attracted attention 20 years ago .
He became a Fellow of the Royal Society in 1890 .
The Report of the Council , now in the hands of the Fellows , presents a brief summary of the operations of the Society during the past year .
Among these , the most prominent incident has been the celebration of the 250th Anniversary of the foundation of the Society .
The programme of proceedings , which had been drawn up after much careful deliberation , was carried out in detail as arranged , and with a success on which , I think , the Society may well be congratulated .
Our invitation was responded to by nearly all the Universities and the chief learned Societies , both in the Old and in the New World .
These different institutions were , in almost all cases , personally represented by delegates , though a few forwarded by post their addresses of felicitation .
Never before in our history did so numerous a company of representatives of learning and science assemble under our roof .
No more striking evidence could have been given of the sympathy which draws together the students of natural knowledge , and unites them into a worldwide brotherhood , inspired by one common spirit of devotion to the study of nature and the search after truth .
Nor could a more gratifying tribute have been offered to the Royal Society , in recognition of the part which it has played in the development of science during its career of two and a half centuries , than the addresses which were presented to us in our Library on July 16 last .
These documents form a united and impressive testimonial which the Society will preserve with pride through the years to come .
Since the Delegates returned to their homes , I have received many letters from them expressive of their great appreciation of the pleasure 8 Anniversary Address by Sir A. Geikie .
[ Nov. 30 , which they had received , and their warm congratulations on the success of our Celebration .
As a permanent memorial of this interesting event in the history of the Society , the President and Council determined last year to begin the preparation of a volume containing a facsimile reproduction of the signatures in the first Journal-book and in the Charter-book from the year 1660 down to the present time .
As a series of the autographs of the most eminent men of science and learning who have lived during the last 250 years , this collection has probably no rival in the world .
The volume , which has been admirably produced at the Oxford University Press , was completed in good time before the advent of the Anniversary celebration .
A copy was at once presented to the Patron of the Society , His Majesty the King , who was pleased to express his appreciation of this interesting memorial .
A volume embracing nearly 100 folio plates and a complete index to the signatures is necessarily costly .
But in order that it may come into the possession of those who are most directly interested in its contents , the Council has ordered that each Fellow of the Society may obtain a copy at one-third of the published price .
Another volume has concomitantly been prepared and published , in the form of a newT , considerably expanded , and thoroughly revised edition of the ' Record of the Royal Society/ Containing a brief history of the Society , with an account of its Charters , Statutes , and organisation , lists of its Fellows and Officers from the beginning , its Medallists and Lecturers , its portraits , relics , and other property , the book forms a useful compendium of information regarding the Society .
It is embellished with twenty plates showing views of the successive apartments occupied by the Society since its foundation , and including also portraits of former Presidents and others .
This volume is also obtainable by the Fellows at one-third of the published price .
MEDALLISTS , 1912 .
The Copley Medal .
The Copley Medal is this year assigned to Prof. Felix Klein , of Gottingen , for his researches in mathematics .
Prof. Klein is , perhaps , most widely known in this country for his investigations in geometry , which attached themselves closely to the work of Cayley and other British mathematicians .
This work has expanded and systematised our conceptions of non-Euclidean geometry , and indeed the philosophy of geometry in general .
1912 .
] Anniversary Address by Sir A. Geikie .
9 Of at least equal importance have been his researches in the theory of functions .
In his earlier papers he dealt mainly with the transformation of elliptic functions and the related theory of modular functions .
The key to the most of what followed lies in the memoir , ' Never Beitrage sir Riemann-ischen Funetionentheorie , ' published in 1882 .
In this memoir , quite independently of Poincare , and from an entirely different point of view , Klein lays the foundations of the theory of automorphic functions .
He here considers for the first time the relations between an infinite discontinuous group of linear substitutions and the functions which are unchanged by it .
This brilliant and fertile idea underlies the greater part of his work , and with its developments must be regarded as among the most valuable contributions to function-theory in recent years .
In a series of masterly works , written partly alone and partly in collaboration with Prof. Fricke , he has extended this theory in detail , first for the case of algebraic functions , then for the modular functions , and finally for general automorphic functions .
No estimate of the debt that mathematical science owes to Prof. Klein would be satisfactory without some reference to his work as a teacher .
He has created a school of young mathematicians at Gottingen whose work is a continuation of his own .
His published lecture-courses on a variety of subjects are works of very great originality in method ; and indeed , some of them\#151 ; for instance , the course on the theory of numbers\#151 ; abound invaluable original investigations .
The Rumford Medal .
This year the Rumford Medal has been awarded to Dr. Heike Kamerlingh Onnes , of Leyden , in recognition of the great value of his contributions to low-temperature research , among which his liquefaction of helium is the most noted .
He has founded at Leyden the most thoroughly equipped laboratory in the world for investigations in low temperatures .
In that institution a series of researches has been carried out regarding the effects of such great cold as can be obtained by the use of liquid hydrogen and even helium on the properties of substances , such as their magnetic relations and the electrical resistance of pure metals and alloys , the results of which are most striking and important for future progress .
Prof. Onnes has also made valuable investigations on the nature of the transition between the solid and fluid states of matter .
10 Anniversary Address by Sir A. Geikie .
[ Nov. 30 , The Royal Medals .
The awards of the two Royal Medals annually given by our Patron the King have received His Majesty 's approval .
One of these medals has been assigned to our colleague , Prof. William Mitchinson Hicks , as a mark of the Society 's appreciation of the value of his contributions to physical science .
Among his researches may be specially mentioned those on hydrodynamics , and particularly on vortex motion , published in the ' Philosophical Transactions .
' As a preparation for this work , he had previously made a very complete study and added much to our knowledge of a class of harmonic functions called by him " toroidal functions .
" He has also investigated , with a view to ultimate physical theories , the forces which exist between spheres immersed in an incompressible fluid medium when the volumes of the spheres are subject to periodical alterations .
Of late years he has devoted much attention to the numerical relations which exist between the frequencies of lines belonging to the same spectral series , and has published expressions which give the relations between these frequencies with great accuracy .
These investigations , which have involved much labour , have materially increased our knowledge of the spectra of groups of elements , and may probably prove of fundamental importance in relation to theories of the production of spectra in general .
The other Royal Medal has been adjudged to Prof. Grafton Elliot Smith , in recognition of the value of his biological investigations , more especially in regard to the morphology of the brain as developed in amphibians , reptiles , birds , monotremata , marsupials , and nearly every group of placental mammals .
His researches have established the natural subdivisions of the cerebral hemispheres , and have shown that the development of the neopallium , in the co-ordination of sensory impulses , is the fundamental condition in the survival of mammals .
His numerous papers are marked by a thorough grasp of the physiological and histological aspects of the subject and by great clearness of exposition .
Prof. Elliot Smith 's work among the ancient cemeteries of Nubia may also be referred to .
Already it has brought to light many interesting anatomical features in the buried remains of the former population of the Nile Valley , and , doubtless , much additional information will be obtained by him from the large mass of material which he has gathered together and brought to this country for deliberate study .
1912 .
] Anniversary Address by Sir A. Geikie .
The Davy Medal .
The Davy Medal has been assigned to Prof. Otto Wallach for his researches in organic chemistry , particularly in regard to the essential oils .
Our present knowledge of these complex vegetable products is largely the result of the numerous analytical investigations which he has carried out in the laboratories of Gottingen .
He has made many important discoveries , more especially in connection with the cyclo-olefines and their derivatives , and his researches on these compounds have played a notable part in the general development of organic chemistry .
The Darwin Medal .
The Darwin Medal is this year awarded to one of the sons of the illustrious man in whose honour this Medal was founded twenty-two years ago .
Mr. Francis Darwin by his researches has done much to emphasise the importance of plant movements in relation to environment , and has shown how strong is the evidence for the view that these various movements are the expression of the plant 's own individuality in response to external stimuli , and that they have been developed or acquired by the plant as an adaptation to environment in the struggle for life .
It is pleasant to remember that these interesting researches have been a continuation of the work which he carried on , conjointly with his father , in the long series of observations and experiments which are recorded in that important treatise , ' The Power of Movement in Plants .
' Mr. Francis Darwin by his devotion to the Department of Vegetable Physiology at Cambridge has not only advanced botanical science by his own researches there , but through the stimulus of his enthusiasm has gathered round him a school of research which has attained a world-wide celebrity .
To him , too , science is indebted for the admirable ' Life and Letters of Charles Darwin , ' a work which by the vivid presentation of the life and character and work of one of the greatest naturalists the world has ever seen , by its modest self-effacement of the author , and by its literary charm , has unquestionably had a quickening influence on the advance of science in our time .
Anniversary Address by Sir .
A. Geikie .
The Buchanan Medal .
This medal is awarded every five years in recognition of distinguished services to hygienic science or practice in the direction either of original research or of professional , administrative , or constructive work , without limit of nationality or sex .
It has this year been adjudged to Colonel William Crawford Gorgas , for his remarkable services under the American Government , in combating the terrible scourge of yellow fever .
As chief Sanitary Officer at Havana , Cuba , he there for the first time applied those sanitary methods by which the yellow fever was almost entirely eradicated from the place .
This marked success led to his being entrusted in 1904 with a similar but greater task in the Panama Canal zone , where the same disease was rampant , and where he is still engaged .
His success in that region has been not less conspicuous .
Its attainment has required not only a complete knowledge of sanitary organisation in the Tropics , but also those administrative qualities which are necessary to ensure its practical enforcement .
In the battle against diseases carried by insects , he led the way in the practical application of the results of scientific discovery , employing still untried weapons , and showing great fertility of resource and much needful determination in the face of many difficulties .
He has earned the gratitude of mankind in having perfected a new method of saving human life on a large scale .
The Hughes Medal .
This medal has been adjudged to William Duddell , P.R.S. , in recognition of the value of his researches in technical electricity and , in particular , his investigations with the oscillograph on telephonic sounds , his work on radiotelegraphy with the thermo-galvanometer , his development of the vibration galvanometer , and his investigations on the production of currents of very high frequency by the electric arc and by mechanical means .
|
rspa_1913_0002 | 0950-1207 | The motion of viscous liquid due to uniform and periodic motion maintained over a segment of an infinite plane boundary. | 13 | 23 | 1,913 | 88 | Proceedings of the Royal Society of London. Series A, Containing Papers of a Mathematical and Physical Character | W. J. Harrison, M. A.|Sir J. Larmor, Sec. R. S. | article | 6.0.4 | http://dx.doi.org/10.1098/rspa.1913.0002 | en | rspa | 1,910 | 1,900 | 1,900 | 12 | 120 | 2,782 | http://corpora.clarin-d.uni-saarland.de/surprisal/6.0.3/?id=rspa_1913_0002 | 10.1098/rspa.1913.0002 | null | null | null | Fluid Dynamics | 55.110867 | Tables | 20.490093 | Fluid Dynamics | [
47.109867095947266,
-32.3623046875
] | ]\gt ; The Motion of Viscous Liquid due to Uniform and Periodic Motion Maintained over Segment of an Infinite By W. J. HARRISON , M.A. , Fellow of Clare College , Cambridge ; Assistant Lecturer in Mathematics , University of Liverpool .
( Communicated by Sir J. Larmor , Sec. R.S. Received October 14 , \mdash ; Read November 21 , 1912 .
) The author was led to a consideration of the whose solutions are presented in this paper by the attempt to solve a certain problem in the theory of lubrication .
But it was thought that these solutions have sufficient intrinsic interest to warrant their separate publication as examples in theoretical hydrodynamics , the more physical pplications to lubrication being reserved for further development .
In the first three problems infinite viscous liquid is maintained in motion by uniform or periodic tangential motion of a part ( a strip of infinite length ) of its plane boundary .
In the remaining two problems the liquid is further limited by a second plane boundary parallel to the first .
A departure , which may be more or less important , from the usual actual physical conditions is neoessitated by the result that it is impossible to maintain the condition of no relative velocity at the boundary .
The treatment of the problem with the condition of no slip leads to a discontinuity in the velocity of the liquid at the boundaries of the moving strip .
But , on the other hand , from the nature of the problem this condition of no slip is an impossible physical state of affairs in the of two hnes of the boundary .
This complexity is avoided if we take the more general condition of slip with tangential traction proportional to the relative velocity , and then the case of no slip will be approached by taking the ratio of traction to slip to increase indefinitely .
There are two other alternative suppositions which might be made and which seem to carry with them a more physical appearance .
Ihese will have to be examined before further applicatio.ns are made of these solutions , but the solutions in their present form are given for their own interest .
Problem 1 .
In this and the following calculations the motion is two-dimensional , and therefore be coniidered to take place in ths plane ; accordingly , the third co-ordinate will never be mentioned .
Mr. W. J. Harrison .
Motion of Viscous Liquid [ Oct. 14 , Viscous liquid occupies the part of the plane for which is positive , being bounded by the axis of .
This boundary is fixed , except that between it is given a uniform velocity in its own direction .
The effect may be produced by supposing the part of the axis cut away , and underneath in contact with it a second boundary is placed which moves with the given velocity .
It is required to determine the motion which is thus maintained .
The motion is steady and is , moreover , assumed to be slow .
* It follows that the stream function satisfies the equation If we assume a distm.bance depending on , then where is positive .
This form of the stream function is appropriate to a velocity along the bounding plane varying as .
Let the velocity of the boundary.in its own direction be It is impossible to satisfy the condition of no relative motion at the boundary owing to the discontinuity that would arise at the points in the final synthesis of the harmonic elements .
Accordingly , the assumption is made that the boundary exerts a traction on the liquid proportional to the relative velocity .
Thus , is the appropnate condition .
If be made very small the condition of no relative velocity is approximately satisfied in general .
The remaining boundary condition is These lead to .
If the distribution of velocity of the boundary in its own direction be given by , then Suppose The fact that the motion has to be assumed slow in order to obtain linear equations is a very serious limitation on the interest of the solution ; but it be noticed that when it is a question of motion between parallel planes which are very near together the non-linear terms are neglected by Osborne Reynolds in his paper on lubrication , for reasons , and the limitation of slow motion is thus removed .
This consideration applies to the last two problems .
1912 .
] over a Segment of Infinite Plane Hence A convenient method of evaluating the definite integral is to plot the integrand for particular numerical values of .
But it is to be noticed that if be small , say , then , except near the boundary , is given by the integrated terms to a high degree of approximation .
In fig. 1 the stream lines are shown for the case .
They are drawn for the equidistant values of the stream function .
They are , however , independent of FIG. 2 .
FIG. 1 .
In fig. 2 the stream lines are in the neighbourhood of for the same case .
The method of evaluating the integral is similar to one to be mentioned later .
The stream lines are drawn for Distribution of Vdocity along the Axis of Now ( provided ( ab ) ( ab ) .
Mr. W. J. Harrison .
Motion of Viscous Liquid [ Oct. 14 , Hence -Si Si where The distribution of the velocity along the boundary , of which the moving section is bounded by , is exhibited in the following table .
The evaluation has been performed by the aid of Glaisher 's Tables of the Sine and Cosine Integrals .
table shows the ratio of the velocity to In addition to the above values it is interesting to note , in the case of , how rapidly the velocity changes in the neighbourhood of . .
From the distribution of the relative velocity of the piece and the liquid in contact with it , the traction exerted by the one on the other can be directly obtained , where is the coefficient of viscosity .
The total traction exerted by the liquid on the sliding piece per unit of its length is given as follows : the values , 1 of has the values , the breadth being two units .
The total rate of flow in the direction of motion of the sliding piece is , and this is independent of .
This is to be explained by the fact that , although the sliding piece exerts less traction on the liquid the greater the value of , the liquid itself experiences resistance from the remainder of the boundary .
1912 .
] over of an Inflnite Plane Boundary .
Problem From the foregoing solution it is ible to deriye immediateJy the stream lines where there are two such sl , iding pieces in diffel.ent parts of the boundary .
In fig. 3 the stream lines are drawn for the case when the part of the boundary is given a velocity in the direction of , and the part is given an equal velocity in the opposite direction .
The stream lines are drawn for the equidistant values of the stream .
FIG. 4 .
In fig. 4 the stream lines are drawn for the case in which the velocity of the second sliding piece is half that of the first .
The lines are shown for the same values of as in the previous case , except that is drawn as well .
Problem 3 .
We proceed to consider the case in which the sliding piece , instead of having a uniform velocity , is given a periodic velocity pt .
The stream function must now satisfy the equation where is the kinematic coefficieI ) of viscosity .
The appropriate solution is , where leading to VOL. LXXXVIII.\mdash ; A. Mr. W. J. Harrison .
Motion of Viscous Liquid [ Oct. 14 , being taken positive .
Also , since we are concerned with a maintained motion , is real .
The axis of is a stream line , and therefore This solution is appropriate to the harmonic distribution of velocity of the boundary .
Hence the remaining boundary condition is This leads to Hence Taking real parts , we find where where The solution , following the notation of Problem 1 , is The work of calculating the stream lines for particular values of the constants involved is a matter of some complexity .
I have performed it for one case , but not sufficiently to give more than a rough idea of their form .
But it was possible to see that a vortex is pel'iodically formed and destroyed in the neighbourhood of the sliding piece in this particular case .
It would be interesting to trace the stream lines for a range of values of the time , and so exhibit the growth and decay of this vortex .
But at the present time I have not the requisite leisure .
Distribution of Velocity over the Sliding Piece.\mdash ; It can easily be shown that pt The numerical evaluation of this integral presents features of some interest .
Apart from the variables are has been taken equal to one unit as before , , and the integral has been evaluated for 1912 .
] over a Segment of an Infinite Plane The method of evaluation depends upon the magnitude of , and one or two illustrations of the methods employed will be given .
since is very small for .
At the same time , so that the second integral is capable of evaluation by the aid of the tables of sine and cosine integrals as in similar integrals in Problem 1 .
The first integral can be evaluated by plotting the integrand .
In this same case the coefficient of pt can be evaluated by plotting the integrand , since it decreases rapidly with The coefficient of pt for involves an integral which can be replaced by to a good of accuracy .
These integrals are easily evaluated .
The coefficient of for involves an integral which can be replaced by Or ( d ) .
for any value of between , except near these limits .
When is very great Bepresenting the velocity at the centre of the sliding piece by X pt , we have the following values for X and X ecreases from 1 to increases from to a maximum value and then decreases again to zero .
The velocity at the point is 1 or 2 per cent. Mr. W. J. Harrison .
Mation of [ Oct. 14 , below that at the centre , and at and practically Mlf their values at the centre .
The maximum ( as regards the time ) integral traction on the piece per unit of its length can easily be found .
It has the following values in units of the system of measurements omployod .
For water , corresponds to a period of sec. in C.G.S. units , so that for this period the traction is about 18 times that for steady motion .
Probl , This is the same as the first problem , except that the liquid is further bounded by , whioh is fixed .
The corresponding boundary condition is taken to be that no relative motion is possible over it .
A possible stream function is given by The conditions to be satisfied are oos ; .
These lead to , and Using Fourier 's theorem , we obtain the stream function in the form where In fig. 5 the stream lines are drawn for the case of Since calculating for the unpractical case of , I have lighted upon a method of evaluating the integral for , but the advantage of recalculation is not great in the ease of so great as 2 .
1912 .
] over a Segment of an Piane Boundary .
\mdash ; FIG. 6 .
Velocity of the Xiquid at the Centre of the Sliding ce.\mdash ; The expression for the velocity of the liquid along the boundary is The ratio of the velocity at the centre of the sliding piece to is given below :\mdash ; When is small , it is easily shown that the velocity at any point of the sliding piece is , except that the approximation breaks down when is small , and that at the velocity drops to half that at the centre .
Hence the traction exerted by the liquid on the sliding piece is ( per unit length ) As is decreased indefinitely , this approaches the limit .
This is the same limit as in the case of the rapid periodic motion of the last case .
The liquid is bounded by two parallel planes as in the previous case , but the sliding piece is given a periodic velocity pt .
The appropriate typical harmonic solution is with the same notation as in Problem 3 .
Mr. W. J. Harrison .
' Motion of .
Viscous Liqud [ Oct. 14 , The solution follows as in previous oases , and I proceed at once to discuss the velocity of the liquid at points on the sliding piece .
Consider If vary slowly with within the range ( say ) , the value of the integral is to a very fair degree of accuracy .
It is assumed that is decreasing and one-signed .
The rate of variation need not be very slow for the approximation to hold , for example may decrease practically- to zero in the interval .
The approximations which follow are based on this consideration , but it is not claimed that the inter- mediate results in the range are more than roughly correct .
where is the real part of divided by Now , provided be small , the variation in is s1nall for moderate values of .
Accordingly is replaced by .
Now , when , where ( say ) .
Put It is found that where ( a ) Approximation when is small.\mdash ; The velocity at the centre of the sliding piece is equal to the coefficient being the same as in the case of steady motion .
This approximation is valid if ( 1 ) , which gives for water a period of 5 mins .
and over , ( 2 ) cm .
, , which gives for water a period of 3 sec. and over .
1912 .
] over Segment of an Infinite Boundary .
( b ) Approximation when , so that and can be neglected , compared with , etc.\mdash ; This applies in the case of water to periods of second and under , and second and under , for the cases and respectively .
The velocity at the centre of the sliding piece is The folowing table includes the whole range of values of , for , in which case , and the above formula is simplified .
It follows that the traction exerted on the sliding piece bears a ratio to that exerted in the steady motion which lies between 1 and It be noticed in Problem 3 when the period of the motion is very small , and in both of the last two problems when is small , that the condition of no slip at the boundary is not approximately satisfied for .
If be taken sufficiently small , then it is easily shown that the maximum total traction per unit length on the piece has a value , in the case of very rapid motion in Problem 3 .
In the steady motion of Problem 4 , when the distance between the two planes is very small , the integral traction has the value .
In the periodic motion of Problem 5 , if be small and , the integral traction depends upon and not upon , and has the maximum value .
If , however , be small and sufficiently great , the traction is independent of and has the value .
This can be shown from the approximate expressions for , which are given above .
Thus in the case of periodic motion between two near parallel planes the integral traction is equal to or greater than , and less than or equal to , provided this second limit is greater than the first .
|
Subsets and Splits