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rspa_1913_0003 | 0950-1207 | A comparison of the spectra of fluorescent R\#xF6;ntgen radiations. | 24 | 37 | 1,913 | 88 | 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, O. M., F. R. S. | article | 6.0.4 | http://dx.doi.org/10.1098/rspa.1913.0003 | en | rspa | 1,910 | 1,900 | 1,900 | 7 | 167 | 4,644 | http://corpora.clarin-d.uni-saarland.de/surprisal/6.0.3/?id=rspa_1913_0003 | 10.1098/rspa.1913.0003 | null | null | null | Atomic Physics | 68.278199 | Tables | 15.17219 | Atomic Physics | [
11.172088623046875,
-77.48976135253906
] | ]\gt ; U4 A Cornparison of the Spectra of fVuorescent Rontgen By J. CROSBY CHAPMAN , B.Sc. , Layton Research Scholar of the IIniversity of London , King 's College ; Research Student of Gonville and Caius College , Cambridge .
( Coinmunicated by Prof. Sir .
J. Tbtns O.M. , October 22 , \mdash ; Read November 21 , 1912 .
) In a previous paper*published in the ' Proceedings of the Royal Society , ' it has been shown that there is a second group .
elements consisting of tungsten , gold , platinum , bismuth , and the radioactive elements uranium and thorium , which emit secondary fluorescent -radiation when excited by a suitable primary beam of rays .
The which the radia- tions of this group ( Group L ) have been shown to possess in common with the radiations of Group .
( elements ) , investigated some years by Prof. Barkla , are as follows:\mdash ; ( l ) The radiations emitted by any particular element when excited consist of two distinct types : ( a ) the scattered fadiation , having the saine penetrating p the and iildistingnishable it ; ( b ) the homogeneous -radiation characteristic of the .
element in question .
( 2 ) Each element exerts selective for adiations which are of such a degree of hardness li8 in the neighbourhood of an " " absorption band In the case of the elements Group , to demonstrate the hoinogeneity of the radiations , lowanoe had to be made for scatteivd radiation Which always actiompanies the homogeneous constituent , but whioh in the Oas6 of the heavier elements is present in such magnitude as to mask , if no correction is applied , the true hoinogeneity .
In the experiment in the paper referred to , the absorption in hium of radiations has baen meaSured .
In I and II the absorption [ ; oefflciehb is defined by the equation , where is the density of aluminium .
absorption fficients in aluminium of the radiations of Group ]re added eferenbe ( Table ) .
From these tables it will be that the penetratihg of the adiad tions in Group is of the same order as the penetrating power of the radiations in Group K The empirical equation connects the atomic weights of two elements , which , though in different groups , emit characteristic * Chapman , ' Roy .
Soc. Proc 1912 , , vol. 86 .
Barkla and Sadler , ' Phil. Mag Ootober , 1908 .
artson Spectra of Fluorescent Rbntgen Radiatiom .
25 Table I. Table II .
radiations which appear the same when measured simply by their absorption in aluminium:\mdash ; .
The results then up to the present can be stabed as follows : elements of different atomic weights and belonging to different groups as regards their periodic -ray can , if suitably excited by a primary beam of Rontgen rays , be caused to emit identical characteristic radiations , when the sole criterion of identity is the fact that the absorption coefficients of their radiations in aluminium are equal .
This second series ( Group L ) is of great importance from the point of view of -ray properties , but the results given in the previous paper cannot , without further experiment , be employed with any certainty for the purpose of throwing light on the internal structure of matter , which is one of the objects of detailed -ray study .
The results cannot be directly used , for this reason : the comparison of the radiations of both groups , and the only way in which both have been standardised , is by means of their property of being absorbed to different extents in aluminium .
Now this test by itself is far from sufficient ; the absorption in a single fact , absorption experiments alone\mdash ; cannot determine conclusively the -ray property of am element , for two radiations totally different in structure might conceivably Mr. J. C. Chapman .
A Compcirison of the [ Oct. 22 , be absorbed to the same extent in the one element aluminium .
In addition to this , even if equal absorptions take place , there is yet the possibility that the energy absorbed is not transformed in similar ways for the two radiations .
It is the object of the present paper to investigate in some detail the radiations of the two groups , so as to establish the identity or dissimilarity of the types of radiation .
If we imagine for a moment that two totally diIierent types of radiation can be produced in any way , yet having equal absorption coefficients in an element X , then , tested only by their absorption in X , they would appear identical .
Suppose now instead of measuring their absorption in X their absorption in another element be found .
If the two radiations are not identical or of very similar nature , there is no reason for supposing that their absorption coefficients in the new element would again be identical .
This method of investigating the radiations of the two groups was the first used in the experiment .
The absorption in aluminium of the radiations of Group and Group being known , the absorption of the radiations of both groups was measured in various elements other than aluminium , in order to see whether the absorptions of two radiations in different groups , having the same absorption coefficients in aluminium , were also equal in these other elements .
Absorption Experiments .
The apparatus was essentially similar to that used in the previous research .
The usual method of exhibiting the absorption of the spectrum of homogeneous radiations by any element is as follows:\mdash ; The ffisorption coefficients in the element X of the various radiations are plotted as ordinates , while the absorption coefficients in aluminium for the samoe diations are plotted as abscissae .
In this way a curve is obtained showing the relation between the absorption coefficients in the element X and in aluminium .
Since there are two groups of elements furnishing -ray spectra , this curve can be obtained in two different ways .
Suppose we consider that this curve has been plotted , using the elements of Group as the series of radiations absorbed , that is in X has been plottea ' against in aluminium ( Group K ) .
Now consider that another curve is drawn , but in this case the group of elements which furnish the series or spectrum of radiations must be ( iroup L When this is done we again have in X plotted against in aluminium ( Group L ) , the only difference being that in the latter case the various radiations having different values of in aluminium belong to the second Group and not to Group as in the first curve .
The point in question is whether the form of curve is the same in the two cases .
1912 .
] Spectra of Fluorescent Rontgen In order to test this , the following absorptions were successively determined .
The absorption by copper , silver , and platinum , of\mdash ; The characteristic radiations of Group K. ( 2 ) The characteristic radiations of Group Each of these three elements was selected because of its definite -ray significance .
The element copper belongs to Group , and its homogeneous characteristic radiation is excited by the whole series of radiations Group L ) .
the absorption of which was determined .
Silver also belongs to Group but its characteristic radiation is not excited by any element in Group The element platinum belongs to Group , and , in addition , platinum exerts a selective absorption for a range of radiations which falls in the spectra formed by both Group and Group L. In the case of the absorption of the radiations of Group , it is only necessary to determine those of bromine , strontium , and molybdenum radiations .
The other values have been previously found .
* As before , is defined by the equation , while is the density of the element absorbing .
ABSORPTION TABLES .
Table III.\mdash ; For Radiations of Group K. Table \mdash ; For Radiations of Group L. From results previously obtained , combined with the two tables just given , it is possible to show that , for the various radiations of Group , the ratio of in Cu of any radiation in Group to in Cu of radiation in * Barkla and Sadler , 'Phil .
Mag May , 1909 .
2@ Mr. J. C. Chapman .
A on of Group X having same in Al as radiation of Lis umity .
This ratio is found in fifth oolumh of Table V. It in Table for the silver and platinum absorptions .
Table roup L Rrho .
Table * The curve showing the relation between in Pt and in Al is so steep at this point that a small inat curaoy in observation would introduce this disorepancy .
The fact that the ratio in each of the three cases approximates to unity can be exhibited graphically by drawing the curves for copper , silver , and platinum respectively , showing the relation between the absorption in the particular element and the absorption in aluminium for the spectra of radiations formed by each group .
In the curves , the continuous lines indicate the absorptioi1 of the radiations of Group K. It will be seen that the points corresponding to the radiations of Group lie approximately on the same curve .
This fact , that a single curve results on which lie the values of the absorption coefficients for both series of radiations ( Group and Group L ) , proves that the radiations in the two groups are of a similar nature .
Had the radiations been dissimilar , and had it only been by that the absorption coefficients in aluminium bear a certain relation to one another , two ourves would have oesulted , otle corresponding to each spectrum , as explained above .
1912 .
] Spectra of Fiuorescent Al .
IO Group elements\mdash ; continuous line .
Group elements\mdash ; points .
80 Mr. J. C. Chapman .
A Cornparison of the [ Oct. 22 , Group elements\mdash ; continuous line .
Group elements\mdash ; points .
The results , as shown in the foregoing tables , can be stated as follows : Any particular radiation belonging to Group and having a certain penetrating power in aluminium , is absorbed by any other element , to the same extent as the radiation in Group which has the same penetrating power in aluminium .
Further Considerations .
The evidence given does not yet completely establish the fact that the two series of radiations are identical in nature , though pointing in that direction .
Owing , however , to the importance of the clearest proof of a property which depends on electronic structure , and which repeats itself in two elements of different atomic weights , it is essential that the comparative analysis of the two series of radiations should be carried further .
It has been proved that two radiations belonging to different groups , and having the same penetrating power in aluminium , are absorbed to the same extent in any other element .
This energy which is absorbed is in the most general case ( i.e. when the element absorbing is capable of emitting a characteristic radiation ) spent in producing various types of radiation in the substance in which the absorption takes place .
Some of these results are\mdash ; ( 1 ) Homogeneous radiation .
( 2 ) Scattered radiation .
( 3 ) Corpuscular radiation .
( 4 ) Ionisation .
1912 .
] of Fluorescent Rontgen The intensity of the scattered and the homogeneous radiation is in general too feeble to determine , but the intensity of the ionisation and the corpuscular radiation , produced under suitable conditions , is well within the limits of measurement .
In order , therefore , to make a more thorough study of the radiations in the two groups , one method is to take two radiations , one from roup , both having the same penetrating power in aluminium and therefore , as the first part of the research proves , the same penetrating power in all substances , and allow these radiations to be equally absorbed in various elements or compounds , which may be either in the metallic or gaseous state .
If then we can measure the amount of corpuscular radiation or the intensity of the ionisation produced under varying conditions by the absorption of these equal of energy , evidence will be obtained showing whether the distribution of total energy is the same in the case of the two radiations .
When the radiations in the two groups are compared as regards their absorption .
in different elements , it is found that there is only one common value of the absorption coefficient for which radiations actually exist in both groups .
Ihese are bromine and bismuth .
These values , it will be seen , are well within the limits of experimental error , when account is taken of the somewhat difficult scattering correction which has to be made when dealing with the radiations of Group L. If then we take the element bromine as representing Group and bismuth as representing Group , it is possible to examine in detail the radiations given by each , and evidence can be obtained of similarity or dissimilarity in the nature of the two radiations .
Any results yielded by this examination can then be applied to the whole spectrum of radiations common to both groups .
It is proposed to test these two typical radiations by determining:\mdash ; ( 1 ) Their power of producing corpuscular radiation in various substances .
( 2 ) Their ionising power in various substances .
The remaining portion the research therefore divides itself into measurements of corpuscular radiation and ionisation .
Mr. J. Chapman .
A Comparison of the [ Oct. Experiments on the Corpuscular The ionisation chamber was of brass , 8 .
in diameter and 2 em. in length .
Its ends consisted of thin parchment stretched on brass caps .
The fitting of thsse oaps was such that without disturbing the apparatus eaeh end of the chamber could be reversed .
Ths whole of the inside of the chamber was lined with paper , and a paper shield was placed on the electrode .
A difference of potential of 200 volts between the eleotrode and the vessel was suffioient to produce saturation .
The method of the riment was as follows .
one face of eaeh of the parchment sheets forming the end. .
of the chamber , a sheet of very thin foil was deposited , this foil was copper in the first experimeI } and was of such a thickness that while not absorbing any depable fraetion of the fluorescent radiations of the hardness used in the experiment ( bromine and bismuth radiations ) , no electrons produced at the back surface were able to penetrate to the front surfaoe .
The foil being depos ; ted on the parch-ments wlJich formed the ends of the chamber , the copper faces were first placed facing outwards , so that when a ray travelled through the ehamber it traversed successively copper , parchment , the air in the chamber , parchment , copper .
nder these conditions , neglecting the small of and corpuscular radiation emitted by the parchment , the ionisation in the chamber was due ( 1 ) The direct ionising effect of the -rays on the air .
( 2 ) The scattered and fluorescent rays from the copper .
That is , since parchment is such an inefficient radiator and the factor ( 2 ) is small , the resultant iottisation is almost wholly caused by the direct action of the -rays .
Now consider the effect of reversir } the endS of the chaInber , so that instead of having the parchment on the inside the two ends are now by the thin foil .
In this case an -ray passes successively : Parchment , copper , the air in the cbamber , copper , parchment .
The ionisation under these circumstances was caused ( 1 ) The direct ionising effect of the -rays on the air .
( 2 ) The scattered and fluorescent -rays from the copper .
( 3 ) The corpuscular rays from the copper .
The iouisatio1t caused by the scattered and fluorescent -rays is small , but in any case this factor counterbalances in the two parts of the experi- ments , for the absorption of the scattered and fluorescont radiation by the parchment is small .
The difference in the ionisation in two cases must be due to ( 3 ) the corpuscular rays from the copper , the other constituents 1912 .
] of Fluorescent Radiations .
being common to the two experiments .
Herein lies the excellence of this method , for by a simple mechanical device it was possible , by finding the difference in the ionisation in the two cases , to measuure at once the ionisation caused by the corpuscular radiation from the copper .
qing this apparatus the energies of the radiations from bromine and bismuth respectively were first compared in intensity by their power of producing ionisation in air .
Let us assume for the moment that the beams are of the same intensity as measured by t , heir absorption in air .
In the experiment equal amoun ts of energy of these two beams were then absorbed by the copper .
The point to decide was whether equal absqrptions of energy would yield the same amount of corpuscular rays , in other words , whether the energy which is absorbed is distributed in the same proportion in the two cases .
Ihe results are given in tabular form .
Copper as CorpuscuIar Radiator .
The same experiment was repeated using tungsten ( Group L ) in the place of copper ( Group K ) as the source of the corpuscular radiation .
The tungsten was deposited by means of gum and chloroform .
Iungsten as Corpuscular Radiator .
In each expsriment from the tinal column in the tables it seen that the intensity of corpuscular radiation produced by equal absorptions of the two radiations is the same .
VOL. Mr. J. C. Chapman .
A Comparison of the [ Oct. 22 , It is interesting to consider upon what ffictors the intensity of the corpuscular radiation emitted by a plate , and measured by its ionising power in air , depends .
Let be the intensity of the beam exciting the corpuscular radiator , which , since the latter is thin , we can consider constant ; let be the transformation coefficient of X-radiation into corpuscular radiation , then with the usual notation , being the amount of energy converted into corpuscular energy in a layer thickness and unit cross-section , If we assume that half the radiation produced at any layer goes forward and half backward , travelling normally to the surface , the total intensity of corpuscular rays emerging from one side of the plate if is the coefficient of absorption of the corpuscular rays If each corpuscle produces on the average ions in the air , the total .
ionisation be Then , considering one surface of the radiator alone , for the bromine *radiation , inserting suffixes which explain themselves , And similarly for the bismuth radiation:\mdash ; But the experiment has shown that when then Therefore ; ; ; That is , the bromine and the bismuth radiations , although belonging to different groups , have the following properties in common:\mdash ; ( 1 ) They are equally transformed into corpuscular radiation .
( 2 ) The corpuscles ejected by the radiations have the same ionising and penetrating power Ionisation Bxperiments .
The ionisation chamber was cylindrical in shape , 2 cm .
in length and 7 cm .
in diameter , and each end was of thin parchment .
The whole of the inside was lined with paper so as to minimise corpuscular radiation .
1912 .
] Spectra of Fluorescent Rontgen Radiations .
In the experiment two vapours were used , one nickel carbonyl , in which the homogeneous radiation of the heavy element was excited by the radiations bromine and bismuth , and the other ethyl bromide , in which the characteristic radiation was not stimulated by these two radiations .
The vapours were introduced by exhausting the ionisation chamber , and then from the bulb attached letting in the requisite amount of saturated vapour .
The results obtained are shown below .
Nickel CarbonyL Ethyl Bromide .
Thus the ratio of ionisation in compound to ionisation in air has the same value whether bromine or bismuth is used as the exciting radiation .
If we take ionisation in air to be a measure of the energy absorbed in the air , and therefore proportional to the energy absorbed in the vapour , which follows from the first part of the research , it is seen that the same proportion of the energy absorbed is converted into ionisation whether the energy is derived from the bromine or the bismuth radiation .
So that as regards the phenomenon of ionisation the two radiations , bromine and bismutb , although belonging to different groups , behave as though identical in type , thus again demonstrating a similarity in property of the radiations of the two groups .
Conclusions .
It may appear that more than sufficient evidence has been brought forward to prove that the two series of radiations , although arising from 36 Comparison of Spectra of rescent Rontgen Radiations .
different atoms , are identical in nature ; but it is necessary to establish this beyond doubt .
For it is agreed that the phenomenon of secondary characteristic radiation is connected with the electronic distribution in the atom .
Therefore the fact that the two series of radiations are identical in nature proves that properties which are dependent on electronic structure repeat themselves in atoms of different elements containing different numbers of electrons , and in this way furnishes one of the clearest examples which the subject of -rays affords , of the theory put forward by Sir Joseph Thomson , namely , that " " we should expect the corpuscles in the heavy atoms to be arranged , as it were , in bundles , the arrangement of the corpuscles in each bundle being similar to the arrangement in the atom of some lighter element Suppose that , as previously suggested , the fluorescent -radiation is produced by the electronic system in the atom settling down after that atom has ejected an electron or electrons as a result of the primary pulse passing over it .
Taking , first , the case of the light elements in Group , suppose in the simple case that the ejected electron is expelled from a bundle of a certain definite arrangement ; then , as the atomic weight of the radiating element increases , the arrangement of the " " bundles\ldquo ; alters , as well as their number , till eventually " " bundles\ldquo ; with the same definite arrangement of electrons appear in an atom of higher atomic weight .
Under these conditions two atoms differing in weight would , owing to their similarity in essential radiating structure , emit precisely the same type of fluorescent radiation .
This is purely hypothetical , but it serves to show the type of explanation demanded to explain the fact that two atoms differing in respect of chemical and physical properties , as well as in the number of electrons they contain , should yet emit the same type of fluorescent -radiation .
No relation between elements of different atomic weights emitting identical radiations can be found on the basis of Mendeleef 's table .
Summarly .
The radiations belonging to Group and Group respectively have been inYestigated as regards their X-ray properties .
In this connection the absorption of the various radiations of both groups in copper , silver , and platinum has been found .
In all cases it has been shown that if radiations from different groups suffer the same absorption in aluminium , then they are equally absorbed in any other element .
It be seen that bromine and bismuth , though in different groups , emit radiations of equal penetrating power , so that as regards total energy absorption they are identical radiations .
The iritensity of the corpuscular The Synthesis of and of a Fdspar .
37 radiation produced in tungsten and copper and the ionisation resulting in ethyl bromide and nickel carbonyl , when equal amounts of energy of the two radiations were absorbed in the various substances , have been measured , and were found in each case to be independent of the radiator .
The results prove that these two spectra of radiations , Group and Group , are identical in their nature , as is shown by measurements on radiations in both groups which test\mdash ; ( l ) their absorption in elements ; ( 2 ) their power of producing corpusoular radiation ; ( 3 ) their power of ionising .
This suggests that the mechanism of production is the same , although the elements emitting the radiation differ widely in atomic weight .
I wish to express my best thanks to Sir J. J. Thomson for his interest and advice throughout this research .
The Synthesis of a Silicalcyanide of Felspar .
By J. EMERSON BEYNOLDS , , Sc. D. , F.R.S. Received October Read ember 2 [ PLATE 1 .
] In the course of an investigation which has occupied much time during some years the writer has obtained a considerable number of definite compounds including silicon and the nitrogen of diverse organic groups in direct chemical uniou .
Several of these new substances resemble in composition and in their general relations certain well-known compouhds of carbon with nitrogen .
such as amides , imides , and nitriles , among them being a silicocyanogen group , , in combination .
The formation of such substances afforded complete proof that silicon has , like carbon , though in less degree , a marked affinity for trivalent nitrogen , even when the latter is associated with organic groups .
* *These substances have been described in detail in the ' Transactions of the Chemical Socisty ' in the following papers:\mdash ; " " The Action of Silicon Tetrabromide on Thiocarbamide ' Chem. Soc. Trans vol. 51 , p. 202 ; " " The Action of Silicon Tetrabromide on Allyl and Phenylthiocarbamides vol. 53 , p. 854 ; " " The Action of Alcohol on the Compound \ldquo ; vol. 63 , p. 868 ; " " On amide , para-and ortho-Sihcotetratolylamides , a- and -Silicotetranaphthylamides , \ldquo ; vol. 65 , p. 474 .
These compounds were the first of those obtained in which silicon is exclusively united with nitrogen and forming crystalline substances .
" " The Action of Substituted Phenylamines on Silicon Tetrachloride vol. 61 , p. 453 ; On Silicodiphenyldiimide and Silicotriphenylguanidine vol. 77 , p. 836 ; " " The Bromination of Silicophenylimide and -amide , and the
|
rspa_1913_0004 | 0950-1207 | The synthesis of a silicalcyanide and of a felspar. | 37 | 48 | 1,913 | 88 | Proceedings of the Royal Society of London. Series A, Containing Papers of a Mathematical and Physical Character | J. Emerson Reynolds, M. D., Sc. D., F. R. S. | article | 6.0.4 | http://dx.doi.org/10.1098/rspa.1913.0004 | en | rspa | 1,910 | 1,900 | 1,900 | 9 | 182 | 5,643 | http://corpora.clarin-d.uni-saarland.de/surprisal/6.0.3/?id=rspa_1913_0004 | 10.1098/rspa.1913.0004 | null | null | null | Chemistry 2 | 56.477064 | Atomic Physics | 13.286287 | Chemistry | [
-37.84708786010742,
-70.92182922363281
] | The Synthesis of a Silicalcyanide and of a Felspar .
radiation produced in tungsten and copper and the ionisation resulting in ethyl bromide and nickel carbonyl , when equal amounts of energy of the two radiations were absorbed in the various substances , have been measured , and were found in each case to be independent of the radiator .
The results prove that these two spectra of radiations , Group K and Group L , are identical in their nature , as is shown by measurements on radiations in both groups which test\#151 ; ( 1 ) their absorption in elements ; ( 2 ) their power of producing corpuscular radiation ; ( 3 ) their power of ionising .
This suggests that the mechanism of production is the same , although the elements emitting the radiation differ widely in atomic weight .
I wish to express my best thanks to Sir J. J. Thomson for his interest and advice throughout this research .
The Synthesis of a Silicaleyanide and of a Felspar .
By J. Emerson Reynolds , M.D. , Sc. D. , F.R.S. ( Received October 23 , \#151 ; Read November 21 , 1912 .
) [ Plate 1 .
] In the course of an investigation which has occupied much time during some years the writer has obtained a considerable number of definite compounds including silicon and the nitrogen of diverse organic groups in direct chemical union .
Several of these new substances resemble in composition and in their general relations certain well-known compounds of carbon with nitrogen , such as amides , imides , and nitriles , among them being a silicocyanogen group , SiN , in combination .
The formation of such substances afforded complete proof that silicon has , like carbon , though in less degree , a marked affinity for trivalent nitrogen , even when the latter is associated with complex organic groups.* * These substances have been described in detail in the ' Transactions of the Chemical Society5 in the following papers:\#151 ; " The Action of Silicon Tetrabromide on Thio-carbamide,55 ' Chem. Soc. Trans.,5 vol. 51 , p. 202 ; " The Action of Silicon Tetrabromide on Allyl and Phenylthiocarbamides , '5 vol. 53 , p. 854 ; " The Action of Ethyl Alcohol on the Compound ( H4N2CS)8SiBr4,55 vol. 53 , p. 868 ; " On Silicotetrapheny]amide , para- and or^Ao-Silicotetratolylamides , a- and / 3-Silicotetranaphthylamides , " vol. 55 , p. 474 .
These compounds were the first of those obtained in which silicon is exclusively united with nitrogen and forming crystalline substances .
" The Action of Substituted Phenyiamines on Silicon Tetrachloride,55 vol. 61 , p. 453 ; " On Silicodiphenyldiimide and Silieotriphenyl-guanidine,55 vol. 77 , p. 836 ; " The Bromination of Silicophenylimide and -amide , and the Dr. J. E. Reynolds .
The Synthesis of a [ Oct. 23 , In the mineral kingdom no definite compounds of silicon with nitrogen have yet been met with ; nor are they likely to be found at any part of the earth 's surface to which water has easy access , as it is probable that any such substances would be very speedily decomposed in presence of moisture into silica and ammonia , or their derivatives .
On the other hand , the existence of the great group of " ahimino-silicates , " which constitute so large a proportion of granitic and other similar rocks , affords clear evidence of the strong attraction of silicon for aluminium , which latter acts as an essentially trivalent element in its high temperature relations , and seems capable under such conditions of doing chemical work somewhat similar to that of nitrogen .
These considerations raised the question whether some at least of the aluminosilicates may not be regarded as fully oxidised products of silicides of trivalent aluminium , somewhat analogous to SiN , which had been formed at high temperatures in the first instance below the oxidised crust of the earth .
It is evident that such " nuclear " silicides should be obtained for study by the complete deoxidation of the corresponding native silicates , or by direct synthesis from the suitable elements .
The first method was found to be impracticable in the most important cases , i.e. of alumino-silicates including alkali or alkaline earth metals .
The application of the second or synthetic method has proved satisfactory , as it has led to the discovery of a substance of remarkable stability , provisionally named Calcium Silicalcyanide , and with which a new synthesis of the felspar Anorthite has been effected .
The results recorded in the following pages tend to support the view suggested above as to the nitrogen rdle of aluminium in certain silicides , and afford some further clues to the constitution and natural relations of the plagio-clasic felspars .
Experimental Part .
The reduction , or deoxidation , of silica and alumino-silicates is easily effected by several agents ; but the most convenient of these is metallic magnesium .
It is well known that the finely divided metal when heated with silica ( SiCy in suitable proportions readily removes all the oxygen of that substance , so that elemental silicon and magnesium oxide result , and the latter can then be removed by hydrochloric acid , in which silicon is insoluble .
All the " alumino-silicates " which I have treated in the same manner are also reduced , but not completely ; for example , anorthite , formation of a Compound including the Group SiN , " vol. 87 , p. 1870 ; " On Interactions of Silicotetraphenylamide and Thiocarbimides , " vol. 88 , p. 252 ; " On Silicon Thiocyanate : its Properties and Constitution , " vol. 89 , p. 397 ; " On Silicotetrapyrrole , " vol. 95 , p. 505 ; " The Action of Potassium-pyrrole on Silico-chloroform , " vol. 95 , p. 508 ; and " Silicon Halides with Pyridine , Acetonitrile , etc. , " vol. 95 , p. 513 .
1912 .
] Silicalcyanide and of a Felspar .
3 9 oligoclase , orthoclase , and scapolite , when heated with the proportion of magnesium suitable for the removal of the whole of the oxygen in each case , gave nearly black reduction products .
These were closely examined and found to be slightly coherent masses which did not afford any metal-like particles when broken up .
Treated with cold water , no gas was evolved , and very little even on boiling ; but the alkalies present in any of the minerals were not deoxidised , and dissolved in the water , along with much of the lime from anorthite and scapolite .
The alkaline substances were washed away and the black insoluble residue , which still contained magnesia but no visible traces of metal , was in each case treated with hydrochloric acid ; some hydrogen was given off , and the colour of the powder changed to the well-known brown of finely divided and amorphous silicon , while aluminium and magnesium passed into solution .
In all these cases it was evident that the chief effect was reduction to silicon with more or less of a black silicide of aluminium , which latter was subsequently decomposed by the acid\#151 ; a further proportion of silicon separating .
The reduction method , therefore , only partially attained the end in view ; hence , attention was next given to the second line of treatment .
The synthetic method consisted in attempts to combine the unoxidised elements under well defined conditions , and to study any definite products obtained .
On the hypothesis already suggested , that aluminium can , in certain cases , act in regard to silicon in inorganic nature much as nitrogen does to carbon in the organic division , we should expect the following series of compounds to exist:\#151 ; Cyanogen ... ... ... ... . .
C2N2 or ( CN)2 Silicocyanogen ... ... ... Si2N2 or ( SiN)2 Silicalcyanogen ... ... . .
Si2Al2 or ( SiAl)2 We know that the first term of this series\#151 ; ordinary cyanogen gas\#151 ; is formed with difficulty from its elements except at very high temperatures , but much more readily in presence of a third and more positive substance , such as an alkali metal , which can directly combine with cyanogen as it is formed and produce a cyanide .
The second term is not known in the free state , unless it is the white substance which is produced when silicon is heated to the temperature of the electric arc in an atmosphere of nitrogen ; but I have obtained the group SiN in organic combination .
The third term has not been recognised hitherto either in the free state or in combination .
It seemed probable , however , that Si2Al2 might be more easily formed by direct union of the elements than the others , because both are fusible solids ; hence the first experiments were directed to this point .
Dr. J. E. Reynolds .
The Synthesis of a [ Oct. 23 , It is well known that silicon dissolves freely in molten aluminium at moderately high temperatures , but that much of the former separates in crystals on cooling .
Winckler found that when the liquid from which excess of silicon had crystallised out and been removed was allowed to solidify , it consisted of nearly equal parts of silicon and aluminium .
As the atomic weights of the elements are Si == 28*3 and A1 = 27*1 , Winckler* was disposed to regard this " alloy " as a definite compound , and therefore to be represented by the formula SiAl .
On the other hand , Yigourouxf denies that any definite compound is formed when aluminium and silicon are fused together .
FraenkeljJ also , concludes from his thermochemical observations that there is little or no chemical combination .
The following experiments were made with a view to examine this point more closely .
100 grms. of the purest commercial aluminium were fused in a " salamander " crucible , and 104 grms. of graphitic silicon were added in small fragments to the molten metal .
There was no evidence of chemical action after each addition nor as the silicon slowly dissolved .
When complete solution was obtained the liquid was heated to full redness for half an hour , and the crucible with its contents were then allowed to cool slowly .
An apparently homogeneous grey metallic mass was broken out of the crucible which had but slightly oxidised at the surface exposed to the air .
A horizontal section made through the middle of this mass showed that the bright metallic surface was crossed by numerous long crystals .
A section of about a centimetre in thickness was half immersed in much diluted hydrochloric acid for a day , and deep etching was obtained owing to solution of aluminium .
The long crystals which were left in relief , as shown in fig. 1 , were found to consist of silicon only .
It will be seen , however , that a few crystalline and brilliantly reflecting plates are present in addition to the silicon crystals .
Some of these plates were carefully picked out and treated with much stronger acid than that used in etching ; the plates disintegrated , leaving pulverulent silicon , while aluminium dissolved .
These plates probably represent traces of combination between the two elements .
I next sought to ascertain the composition of the material in which the silicon crystals were embedded .
For this purpose a moderately thin section of the large mass , weighing some 30 grm. , was supported on edge in a bath of melted calcium chloride , which fuses between 717 ' and 723 ' ( Carnelly ) , or a little above the melting point of aluminium , i.e. about 700 ' .
Gradual liquation of the aluminium occurred and much crystalline silicon was left .
When cold * 4 Journ. fur Praktische Cheraie , ' vol. 91 , p. 193 .
t 'Comptes Eendus , ' vol. 141 , p. 951 .
t 4 Zeits .
fur Anorg .
Chernie , ' 1908 , vol. 58 , p. 154 .
Silicalcyanide and of a Felspar .
1912 .
] the metal-like product resembled aluminium in colour but was quite crystalline in structure throughout .
The composition proved to be\#151 ; Silicon ... ... . .
28*33 Aluminium ... ... 71*57 99*90 This product when treated with acid also left crystals of silicon .
The original mass contained 50*8 per cent , of silicon , and a portion of this when remelted and suddenly cooled gave a good ingot which was steel-grey in colour , and the fractured surface presented the minutely crystalline structure shown in fig. 2 .
A portion of the same ingot was again fused and maintained at a full red heat for nearly two hours and then slowly cooled as in the first instance .
A section of this product when etched presented much the same appearance as in fig. 1 , save that the plates already referred to seemed to be rather more numerous , as if the prolonged fusion had promoted a little further combination of silicon with aluminium .
It is evident that silicon and aluminium do not directly enter into chemical combination to any material extent , even when a liquid mixture in atomic proportions is heated to full redness for more than two hours .
Under similar conditions carbon and nitrogen do not evince any greater tendency to unite and form cyanogen ; but , in the latter case , if a third element be present , such as an alkali metal , then combination takes place and a cyanide of the metal is formed .
On the " silicalcyanogen " hypothesis I have suggested , the addition of an alkali metal , or its equivalent , to the fused alloy of silicon and aluminium should act in a similar manner and lead to the formation of a silicalcyanide of the metal .
A number of prospecting experiments were next made with the molten alloy of silicon and aluminium in atomic proportions , in which sodium , potassium , magnesium and calcium were added to separate parts of the fused alloy .
The alkali metals proved to be much too volatile for use in open crucibles* ; magnesium dissolved quietly in the alloy without affording much evidence of chemical combination either in process or product ; but calcium caused almost violent action as it dissolved in the SiAl alloy , and afforded a very characteristic product .
Further experiments having indicated the best conditions for a preparation on a comparatively large scale , this was made in the following manner:\#151 ; 100 grms. of the purest aluminium obtainable in commerce were fused in a relatively large-sized crucible , heated in a powerful gas blast furnace ; * It will be shown later on that in closed vessels union can be effected to a certain extent .
42 Dr. J. E. Reynolds .
The Synthesis of a [ Oct. 23 , 103 grms. of crystalline silicon , as free as possible from carbide , were introduced , and the heat was continued until complete liquefaction was obtained ; 74 grms. of metallic calcium , cut into small pieces , were then gradually added to the molten alloy ; each piece , when pressed under the surface of the liquid , caused energetic action , and after the latter had somewhat subsided the liquid was well stirred with a steel rod .
Owing to this frequent stirring it was easy to note that the mass became sensibly less fluid after the addition of about half the calcium , as if owing to the separation of less fusible material , and this thickening increased until the last addition was made , when it became nearly solid.* The temperature was then raised to the highest point attainable during half-an-hour , but without fusion , and the whole was then allowed to cool very slowly .
When cold the crucible was broken away and a clean metal-like mass of a dark grey colour was extracted .
This weighed 279 grms.\#151 ; the small increase in weight , about 2 grms. , being doubtless due to some oxidation during the vigorous interaction which took place on the addition of the calcium .
All traces of free aluminium had disappeared .
A vertical section through the mass presented smooth metal-like surfaces with markings indicative of crystal sections , and the material , which could be easily broken up by a hammer , presented a highly crystalline structure and seemed to be uniform in character .
The brilliant crystalline faces appeared to belong to octahedral forms , and to be of the same kind throughout the mass ; but at certain parts a dark powdery substance was found which evidently consisted of the mixed oxides already referred to , as having been formed in small quantity at the surface , and then become entangled during the final stirring of the somewhat thick alloy ; this powder , which owed its dark colour to mixture with the finely divided portions of the alloy , was easily brushed away , and the broken product then presented the appearance shown in fig. 3 .
Some of the best defined crystalline groups were taken from different parts of the mass and their densities determined at 16 ' in water , which does not sensibly act on the alloy at ordinary temperatures , unless after long contact .
Upper section ... ... ... 2*347 Middle " 2*351 Lower " 2*353 As the densities of the constituents varied between 2*71 for aluminium and 1*534 for calcium , there had not been any material separation , so confirming the essentially homogeneous character of the 44 alloy .
" * The proportion of calcium added was then nearly Ca : Si2 : Al2 .
1912 .
] Silicalcyanide and of a Felspar .
43 Notwithstanding the above evidence , and the known weights of the elements used in the preparation of the alloy , analysis was considered desirable , hence rather large portions were broken from about the middle of the mass ; these well crystallised specimens were brushed free from scoria and then finely powdered .
The method of analysis consisted in heating the substance , spread in a thin layer on a porcelain boat contained in a Jena glass tube , in a current of carefully dried chlorine gas .
The powder was soon attacked and the constituents were converted into chlorides ; calcium chloride , not being volatile , was left in the boat when aluminium and silicon , as chlorides , were volatilised by heat and the vapours wholly absorbed by water ; Si and A1 were then separated in the usual manner .
The results of two analyses so conducted are given below , and are compared with the composition of a compound consisting of CaSi2Al2 .
Theory .
I. II .
Silicon 37 63 36 *81 36-76 Aluminium 35 -92 \#151 ; 35 -8 Calcium 26 *45 25 *72 25-86 100*0 The slight oxidation which occurred during the preparation of the substance , as already explained , is doubtless the chief cause of the lower values obtained for silicon and calcium than those required by the formula.* The indifference of this substance to oxygen , even at comparatively high temperatures , is as remarkable as its infusibility .
In a special experiment , 2 grms. of the metal-like material , in a rather finely powdered condition , were strongly heated in a porcelain boat placed in a hard glass tube , through which a current of dry oxygen was passed for an hour , while the temperature was maintained as near as was safe to the softening point of the containing tube .
The powder did not fuse , and was very slightly altered in appearance ; when cold it was found to have gained only 0*08 grm. in weight .
When heated in air by the oxyhydrogen flame , the " alloy " melts , and immediately bursts into vigorous combustion , affording a white semi-fused product .
The substance is also remarkable in that water acts very slightly upon it at ordinary temperatures , and little more if boiling , thereby proving * Numerous silicides and alloys , including aluminium and other elements , have been formed , and are described in the elaborate treatise of M. Baraduc-Muller , 'Sur les Siliciures Metalliques ' ( Angers , 1910 , 4to ) , but no " alloy " resembling the above either in composition or properties appears to have been obtained .
Dr. J. E. Reynolds .
The Synthesis of a [ Oct. 23 , incidentally that the large proportion of calcium which is present is wholly in chemical combination .
It is readily attacked , and in part dissolved , by hydrochloric acid , with evolution of hydrogen silicide and free hydrogen , while much silicon separates , aluminium and calcium passing into solution .
Strong nitric acid is almost without action in the cold , but the boiling acid slowly attacks the substance ; sulphuric acid has little action even when hot .
On the other hand , sodium and potassium hydroxides in strong solution act readily in the cold and rapidly on boiling .
When dry chlorine is passed over the substance , action begins without the application of external heatr and the products are calcium , aluminium , and silicon chlorides .
Advantage was taken of this complete action in order to effect the analyses given above .
The substance presents the essential characters of a chemical compound , , and appears to be one which has been formed from its elements much in the same manner that a metallic cyanide can be synthesised , silicon and aluminium representing carbon and nitrogen.* The analogy with a cyanide is easily recognised when the respective formulae are written as under:\#151 ; CN SiAl Ca\lt ; , Ca\lt ; .
XCN SiAl Calcium cyanide .
Calcium salicalcyanide .
It has been mentioned above that calcium 'silicalcyanide is very slightly attacked by free oxygen until the temperature of the oxyhydrogen flame is reached .
I may add that even fused potassium chlorate produces little effect upon it , and fused nitre is partial in its action .
If heated with easily reduced metallic oxides , such as lead oxide , the compound is broken up , and a lead , calcium , and aluminium glass results from secondary changes .
There is no doubt , however , that the crystalline Ca(SiAl)2 is capable of combining with eight atoms of oxygen , and of producing therewith a compound of the same composition as the mineral anorthite , that is CaSi2Al208 .
Now , ordinary cyanides of alkali or alkaline earth metals are by no means easily affected by gaseous oxygen even at comparatively high temperatures , but , if water vapour be present along with oxygen , change takes place at comparatively low temperatures , resulting in the formation of a carbonate of the metal , while ammonia is formed and separated . !
Such a change effected in the case of calcium cyanide can be represented in the following manner :\#151 ; CN Ca\lt ; " +02 + 3H20 = CaC03 + 2NH3 + C02 .
XCN * It is possible that barium and strontium may give similar products , t Unless oxygen is present in excess , when ammonia is oxidised in its turn .
1912 .
] Silicalcyanide and of a Felspar .
The silicalcyanide should obviously be capable of somewhat similar hydrolytic oxidation , and that proved to be the case , although the inability of aluminium to form a volatile compound like ammonia necessarily led to a modification in the nature of the end product .
After several trials the most convenient mode of effecting the change proved to be the following:\#151 ; About 2 grms. of the finely powdered alloy were placed in a Rose crucible of rather large size with the usual perforated cover and clay delivery tube for conveyance of gas to the interior .
The tube was connected with a flask containing water through which a stream of oxygen was allowed to bubble on its way to the crucible .
By heating the water in the flask the proportion of water vapour carried along with the gas could be increased at will , and heating the clay tube prevented condensation before the hot crucible and its contents were reached .
Under these conditions the moist oxygen led over the powder , which was heated to low redness , gradually converted it into a nearly white mass .
Two successive quantities were treated in the same manner until sufficient of the white product was obtained ; the whole was then powdered , returned to the crucible , and again strongly heated in the current of moist oxygen until perfectly white .
This material proved to be infusible at the .
highest temperature attainable in a small gas blast furnace ; but when an oxyhydrogen flame was made to impinge on the surface complete fusion was effected of the greater part of the mass ; much care was taken to avoid fusing the material of the crucible as well .
When slowly cooled in order to permit crystallisation the surface presented the somewhat volcanic appearance shown in fig. 4 .
Under the crater-like top a good proportion of solid and highly crystalline substance was found .
The best crystallised portions of this product from calcium silicalcyanide were picked out for examination and analysis .
When compared with a specimen of opalescent anorthite from the Tyrol my synthetic product proved to be very similar in character , and it was gelatinised by acids in much the same way .
0*962 grm. gave 0*3996 grm. of Si02 , 0*3615 of A1203 , and 0*2045 of CaO .
These data lead nearly to the ratios CaO : A1203 : 2Si02 = CaAl2Si208 , or those of the mineral anorthite .
Mr. Herbert H. Thomas , of H.M. Geological Survey , has been so good as to examine a specimen of this product , and kindly allows me to quote his observations , as follows:\#151 ; " In thin section it presents the appearance of a mass of acicular crystals which radiate from a series of centres ; the Dr. J. E. Reynolds .
The Synthesis of a [ Oct. 23 , individual needles are twinned once in most cases , but in some instances it was possible to make out polysynthetic lamellae .
" The powdered mineral has a mean refractive index of about 1*582 and a specific gravity of about 2*75 to 2*76 ( heavy liquid method ) .
" The mineral has low birefringence , large extinction angle on the plane of the best cleavage , and is most certainly a felspar .
The high mean refractive index and specific gravity both point with certainty to anorthite .
" In the following table the percentage composition of my synthetic* anorthite is compared with theory for the pure substance , and with analyses of native specimens , in order to show the range of variation in composition .
For convenience of comparison all the monoxides present in the native minerals have been calculated into their equivalents of CaO and added to the percentages of the latter which were actually obtained .
No. 1 is of clear crystals from Monte Somma , analysed by Abich .
No. 2 is of the massive variety indianite .
No. 3 is of the variety named barsowite , analysed by Friederici:\#151 ; Theory .
No. 1 .
No. 2 .
No. 3 .
New synthetic .
Si02 43 *08 43 *96 42 -09 41 *56 41 -53 ai203 36 *82 35 -72 38 *89 36 *59 37 *3 CaO 20 *1 20 *26 19 -46 21 *42 21 *25 100-0 Whether formed by partially hydrolytic action at comparatively low temperatures , or by direct oxidation alone at much higher temperatures , the relations of calcium silicalcyanide and anorthite are simple , and are expressed in the constitutional formula for the mineral given below:\#151 ; Si = A1 Ca\lt ; XSi = A1 Calcium silicalcyanide .
Ca\lt ; ^ 0\#151 ; Si02\#151 ; Al= 0\#151 ; Si02\#151 ; A1= Anorthite .
0 0* If nitrogen were present in the unoxidised compound instead of aluminium then hydrolysis would have involved its removal as NH3 gas , and the residue would probably have been a calcium disilicate , which is a potentially acid salt .
Anorthite is , on the contrary , a markedly basic silicate , because aluminium does not form any such gaseous compound as NH3 , and in * The synthesis of anorthite has been effected from the oxides or other compounds of the component elements , but this one is obviously different in character from those which preceded it .
1912 .
] Silicalcyanide and of a Felspar .
presence of an excess of oxygen , is retained in the molecule as a distinctly electropositive constituent .
It is probably owing to the essentially basic character of anorthite that it is so rarely found in the pure state .
According to Tschermac 's well-known view , all the plagioclasic felspars are either isomorphous mixtures , or solid solutions , of basic anorthite and the acidic felspar albite in various proportions .
These transition minerals are the important rock formers\#151 ; labradorite , andesine , and oligoclase , with other minor varieties , which exhibit well known and gradual changes in chemical composition and in physical characters between the two extremes .
Notwithstanding the wide difference in composition between anorthite and albite , which becomes apparent when the simplest expression of the composition of each mineral is compared as under\#151 ; Anorthite ... . .
CaSi2Al208 Albite ... ... ... NaSi3A108 their known relations above mentioned indicate that there is some fundamental similarity in constitution .
If the unoxidised nuclei are considered in view of the information gained in the earlier part of this work , it is easy to trace such a relationship .
The simple silicalcyanide type underlying anorthite is \#151 ; SiAl ; that of albite is obviously more complex , but still includes at least one such member , if the nucleus be represented by the following constitutional formula :\#151 ; N\amp ; Si Ultimate oxidation of this to albite probably would not make any material change in the relations of the principal elements , and the constitution of that mineral may similarly be represented as under\#151 ; It is probable that the free molecule of albite should be represented by two 48 The Synthesis of a Silicalcyanide and of a Felspar .
such groups linked up by the residual valence of aluminium .
Orthoclase , KSi3A108 , may be similar in structure .
The synthesis of albite from the oxides of its component elements is well known to be attended with difficulty ; but the synthesis of the corresponding silieide is still more difficult , * owing to the volatility of sodium , and heating under pressure in presence of a considerable excess of sodium is necessary .
When the requisite materials were heated in a strong iron tube , closed by a tightly screwed cap , some combination was effected .
This tube and its contents , placed in an inclined position in a powerful muffle furnace , was heated to the highest attainable temperature for nearly two hours , and then allowed to cool in sand ; when quite cold it was cut into four pieces of nearly equal length .
The upper part was lined by some condensed sodium ; the next section contained some sodium also , and the third section was found to contain a grey metal-like mass .
This was somewhat crystalline in character , quite hard enough to require the use of a chisel in order to cut it out , but the material easily took fire on friction , and when thrown into water gave abundance of hydrogen gas and a little hydrogen silicide .
A portion of the grey crystalline alloy was picked out in as clean a condition as possible , and was found to contain silicon , aluminium , and much sodium .
It is probably a solid solution of NaSi3Al in sodium .
The lowest section of the tube contained more of the grey alloy and a little free silicon .
This alloy is the nearest in the way of an unoxidised albite nucleus that I have as yet been able to obtain .
It is evidently possible that somewhat similar relations may be traceable between alumino-silicides of other types and other classes of " aluminosilicates .
" Much of the work recorded in this paper was carried out in the Davy-Faraday Laboratory , and my grateful acknowledgments are due for the facilities afforded by that institution .
* Some chemists , including Deville and Yigouroux , were unable to secure the combination of silicon with sodium or potassium under any conditions ; but Moissan , in 1904 , easily effected superficial combination by passing the vapour of sodium over silicon at high temperatures .
Reynolds .
Roy .
Soc. Proc. , A , 88 , 1 .
Fig. 3 .
Fig. 4 .
|
rspa_1913_0005 | 0950-1207 | A determination of the radiation constant. | 49 | 60 | 1,913 | 88 | Proceedings of the Royal Society of London. Series A, Containing Papers of a Mathematical and Physical Character | H. B. Keene, B. Sc.|Prof. J. H. Poynting, F. R. S. | article | 6.0.4 | http://dx.doi.org/10.1098/rspa.1913.0005 | en | rspa | 1,910 | 1,900 | 1,900 | 11 | 154 | 3,541 | http://corpora.clarin-d.uni-saarland.de/surprisal/6.0.3/?id=rspa_1913_0005 | 10.1098/rspa.1913.0005 | null | null | null | Thermodynamics | 40.054234 | Tables | 16.973955 | Thermodynamics | [
0.029214559122920036,
-23.95668601989746
] | ]\gt ; A Determination of the By H. B. KEEN , , Assistant Lecturer in Physics in the University of Birmingham .
( Communicated by Prof. J. H. Point F.R.S. Received November 7 , \mdash ; Read December 5 , 1912 .
) According to the Stefan-Boltzmann law , the radiation emitted by a full radiator in surroundings at a temperature of absolute zero is proportional to the fourth power of the absolute temperature of the radiator , or where radiation in ergs per cm.2 per , absolute temperature of radiator , radiation constant .
If the radiator is in surroundings at absolute temperature , which are themselves full radiators , then where is the net radiation .
The first important determination of the radiation constant is due to Kurlbaum , obtained a value erg/ sec. cm.2 , recently corrected to erg/ sec. cm.2 Later investigations give results varying considerably from Kurlbaum 's and from one another , and , on whole , they indicate that Kurlbaum 's value is too low .
Some determinations are given in the following table:\mdash ; The essential conditions in a determination of are , either that both emitter and receiver are full radiators , or that the amount by which they fall short of full radiators is known\mdash ; an amount difficult to determine with certainty .
Hitherto , a measurement of in which both emitter and receiver were full radiators has not been made .
Fery and Fery and DrecqS , who have * Ann. .
Phys 1898 , vol. 66 .
'Ann . .
Phys May , 1912 .
'Compt .
Rend Apri16 , 1909 .
S 'Journ . .
Phys July , 1911 , p. 668 .
VOL. LXXXVIIL\mdash ; A. Mr. H. B. Keen .
[ Nov. 7 , obtained results and erg/ sec. cm.2 , used a blackened conical receiver , which is more nearly a full receiver than a plain black surface .
Fery has pointed out that the advantage of this eiver depends upon the large number of reflections made by the incident radiation within the cone .
At all points of incidence and reflection , diffusion , as well as reflection , takes place , which implies energy losses from the mouth of the cone .
In this respect the instrument used by Fery is not a full receiver .
The nearest approach which we can make in practice to a full radiator or receiver consists in a good radiating surface in the form of a uniform temperature enclosure , with an aperture small compared with the total internal area .
The present paper describes some experiments in which the receiver fulfilled the above conditions .
The emitter could only be considered an approximation to a full radiator .
It consisted of a small Heraeus furnace at a temperature of about 1000o C. The construction of such a furnace does not lend itself to the production of a perfectly uniform temperature enclosure .
Steps taken to improve the furnace in this respect will be described later .
One of the chief objects of the paper is to describe the full to show that it is capable of giving consistent results .
At present a furnace is being constructed which approximates more nearly to the ideal full radiator and it is intended to make further measurements with it when completed .
For the purpose of the experiment it is necessary to oalculate the energy exchange between two fully radiating coaxial circular apertures at different temperatures , and at a distance apart of the same order as the diameters of the apertures themselves .
This calculation is given in the appendix , where it is shown that where is rate of emission of energy from one of the apertures , is net radiation per c and the greatest and least distances between two points , one on each circle bounding the apertures .
In order to bring this expression into line with that used when the distance between the apertures is large compared with their diameters , it may be written as a first approximation , where are the areas of apertures ; , the radii of apertures ; , the distance between apertures .
If and are small compared with , then the expression takes the familiar form in which it has been used by those investigators who have confined themselves to such distances that the correction was negligible .
1912 .
] A Determination of the Radiation In the arrangement to be described this expression was of the order the radiation constant being calculated from the expression where is the radiation constant and is the absolute temperature of furnace .
The fourth power of the absolute temperature of the receiver was negligible in comparison with that of the furnace .
Description of Apparatus .
The receiver consisted essentially of an aniline thermometer with a bulb of about 2 litres capacity and a stem of 1 mm. bore .
The bulb had double walls , between which was the aniline , the inner hollow cavity being lampblacked and provided with a circular orifice A which served as the receiving FIG. 1 .
aperture ( see fig. 1 ) .
The bulb was constructed of thin spherical copper shells , the inner one being 15 cm .
in diameter , with an aperture of about 2 cm.2 .
A third copper shell was placed in the liquid between the inner and outer shell to serve as a screen to prevent initial heat losses by direct radiation through the aniline from the inner surface .
Radiation from the Mr. H. B. Keen .
[ Nov. 7 , furnace aperture was received by the aperture ( fig. i ) , and fell on the inner blackened surface at the back of the bulb .
In order to minimise energy losses by direct reflection , this region was occupied by a thin copper cone , so that no part of the receiving surface received rays normally .
Since the thermometer contained a badly conducting liquid and also a screen to prevent radiation losses to the outside , the initial march of the meniscus in the stem gave a measure of the energy received per second ; 1 mm. rise of the meniscus corresponded to a rise of temperature of C. In order to eliminate the effect of external temperature variations a companion thermometer was constructed , and both thermometer bulbs were enclosed in FIG. 2 .
the same heat-insulating jacket , one alone receiving energy from the emitter .
The jacket consisted of a double-walled zinc box well lagged on the outside with felt , the outer surface of which was covered with bright tinfoil see fig. 2 ) .
In this way the rate of change of temperature of the two thermometers was made as small as possible when the room temperature was changing .
The thermometers were now used differentially , allowance being made for the small difference in capacity and bore of capillaries .
The march of the two meniscuses was observed prior to admitting radiation from the furnace into one of the apertures , when the room temperature was changing slowly and , a screen was removed and the radiation 1912 .
] A Determination of the Radiation was admitted .
The observations were now continued every half minute for 12 minutes , and the differential effect due to the energy from the furnace alone was determined .
The emitter consisted of a cylindrical electric furnace of the Heraeus type , about cm .
in diameter and 20 cm .
in length .
Owing to the low conductivity of the porcelain tube on which was wound the platinum heating strip considerable temperature differences , visible to the eye at red heat , exist between each successive turn of the heating spiraL These differences were minimised by the introduction of a lining cylinder of nickel and two nickel plugs near the centre of the furnace ( see fig. 3 ) .
In spite of this precaution a considerable fall of temperature takes place from the centre of the furnace to the aperture , and although the extremity of this region near FIG. the aperture is not visible from the receiving aperture , such an enclosure does not constitute a full radiator .
For this reason the results of the present measurements are offered as preliminary observations pending the construcon- of a new high temperature full radiator .
Screens.\mdash ; Between the emitting and receiving apertures were two watercooled screens coated with paraffin black on their surface see fig. 4 ) .
In order to avoid heating of the furnace screen by the.furnace a continuous stream of cold water from the town mains was brought in at the centre of this screen and conducted by means of a spiral guide to the extremities .
To ensure an even flow of water through the screen placed before the receiver , the water was brought in at a number of peints at the bottom of the screen and taken out in a similar way at the top .
The aperture in each screen consisted of a blackened cone of thin spun copper .
FIG. 4 .
Method of Carrying out a Jfeasurement .
librat of Receiver.\mdash ; The receiver contained a bale insulated platinum wire attached to the inner surface by a number of glass hooks .
FIG. 5 .
1912 .
] A of the Radiation Constant .
The wire formed a polygon lying close to the inner surface of the receiver ; the plane of the polygon was symmetrically placed within the sphere and occupied a position parallel to the plane of the receiving aperture .
The wire was provided with current and potential leads , and served as a means of introducing electrical energy for the purposes of calibration ( see fig. 5 ) .
The calibration was carried out as follows : When the apparatus indicated that the room temperature was changing slowly and uniformly the electric FIG. 6 .
circuit was completed at a noted instant .
The march of the meniscus both of the thermometer containing the electric circuit and of the companion thermometer was now observed every half-minute for 12 minutes .
These readings were plotted against time , and the differential effect due to the energy received from the wire alone was determined .
Two actual curves are shown on a reduced scale in fig. 6 .
By varying the electrical energy Mr. H. B. , Keen .
[ Nov. a series of such curves was obtained .
It was found that the ordinates of the successive curves at a given time after the circuit waa completed were proportional to the given energy supplies .
This was true whatever the value of , except at the beginning of the curves , where slight irregularities were apparent .
Twenty-four hours were allowed to elapse between each experiment .
This was found to be necessary in order to allow both thermometers to come to the same temperature conditions .
( 2 ) of Energy Stream.\mdash ; Similar curves were obtained when energy was received by radiation from the furnace .
Such a curve is shown at , fig. 6 .
The energy per second corresponding to the curve could be readily obtained by ' interpolation from the neighbouring calibration curves .
The initial portions of the curves were discarded and interpolations carried out at each of four successive different values of the abscissae , viz. , after 5 , 8 , 10 , and 12 minutes , and the mean value taken .
Before the admission of radiation to the receiver from the furnace , the latter was allowed to run for four hours in order that it might reach a steady state .
During this time a water-cooled zinc diaphragm was in position immediately in front of the receiving aperture .
This screen , indicated by the dotted rectangle in fig. 4 , oonsisted of a flat cylindrical box 4 cm .
in diameter and 1 cm .
thick , and carried a stream of running water at room temperature .
Both sides of the screen were coated with paraffin black .
When the furnace had attained a steady temperature , as indicated by the thermocouple within , the water-cooled was swung out of position at a noted instant and the march of the meniscuses observed as already described .
( 3 ) Temperature of Furnace.\mdash ; This was measured by a platinum-platinumrhodium thermocouple and , the maximum error being from 1o to in the neighbourhood of 1100o C. After use the couple was calibrated at the National Physical Laboratory , and the calibration was used in the present calculations .
In order to minimise electrical leakage from the furnace heating spiral to he thermocouple and potentiometer , the cylindrical nickel liner contained in the furnace and separating the thermocouple from the porcelain furnace tube was earthed .
In spite of this precaution a small leakage was still evident .
The effect of this leakage was eliminated by placing a reversing switch in the furnace circuit and determining the balance point on the potentiometer wire for beth directions of the furnace current .
The difference in the balance point never exceeded 1o C. 1912 .
] A Determination of the Radiation Calculation of Results .
A series of ten curves was obtained for the purposes of calibration , the electrical energy supply varying from to watts .
A series of five curves was obtained by admitting radiation from the fiirnace , the calculated energy supply varying from to watts .
The areas of the radiating and receiving apertures remained constant , while their distance apart and the temperature of the furnace valied from one experiment to another .
The results are embodied in the following table:\mdash ; Table I. Area of furnace aperture cm.2 .
Area of aperture c Mean value , erg/ sec. cm.2 Discussion of Results .
An objection to the present method of experiment lies in the fact that the energy to be measured and the energy used for the purposes of calibration are not introduced into the receiver in the same manner .
An attempt to show that the objection is not serious was made by varying the position of the heating coil .
If the cavity were a perfectly " " black body the resulting effect should be independent of this position .
This point was tested in the following way : A separate heater , consisting of a single platinum wire , provided with the usual current and potential leads , was stretched across a diameter within the receiver .
This position is very different from that of the original heating coil already described .
A series of calibration curves was obtained , using this wire to carry the current , and the energy of the radiation streams from the furnace was calculated from these observations .
The results differed by less than 1 per cent. from those obtained with the original heating coil .
The small differences indicate thab the energy losses Mr. H. B. Keen .
[ Nov. 7 , through the aperture are slightly gleater when the diametric heating wire is used .
Such an effect is to be expected , since this wire is stretched across the middle of the receiver , a position more favourable for direct radiation losses through the aperture .
Owing to this fact , the calibration data obtained with the diametric heater were discarded .
It will be seen that the method of measuring the energy received is essentially the same as that used by Fery and Drecq , differs in two important respects .
Firstly , the energy falls on a full receiver , and , secondly , the difficulty of temperature variation is avoided by using two such receivers differentially .
Again , in Fery and Drecq 's conical receiver the heating coil used for calibration was wound on the outer surface of the cone and was in contact with the liquid in the thermometer bulb .
With a conical receiver the proportion of the calibrating energy retained will depend entirely upon the position of the .
heating coil , while in the present method there is evidence to show that this proportion is practically independent of the position of the coil .
This fact makes it highly probable that equal quantities of energy put in as electrical energy and as radiation would produce the same effect .
Sources of Error .
In all previous determinations of the value of the radiation constant the receiver has not been \ldquo ; black body In some cases the arrangement of the screens has been such as to allow of additional energy reaching the receiver by radiation from the screens .
The first point has already been discussed .
With regard to the second it has been pointe out by a previous writer that one of the most important screens in the arrangement of Fe'ry and Drecq was not water cooled , and that it consisted of thick blackened cork containing a cylindrical hole , and from the surface of the cork additional energy would reach the receiving aperture by reflection .
The additional received would make the resulting value of too high .
In the arrangement described in the present paper ( see fig. 4 ) additional radiation would reach the receiving aperture after undergoing two successive reflections .
The screen facing the furnace would refleqt some of the radiation it received from the furnace aperture to the screen facing the receiving aperture .
This , , would reflect to the receiving aperture .
If the screens were not blacked , but left with a tarnished metal surface , reflecting , say , 50 per cent. of the incident energy , the writer calculated that would be 20 per cent. too high .
This point was verified experimentally , the results of three such experiments being , and erg/ sec. cm.2 'Journ . .
Phys July , 1911 , p. 658 .
Shakespear , 'Roy .
Soc. Proc 1912 , , vol. 86 , p. 180 .
1912 .
] A Determination of the Constant .
In all the experiments in Table I the screens were blacked .
If it is assumed that the blackened surface used diffuses 5 per cent. of the energy it receives , then it may be shown by making similar approximations to those in the previous calculation that the value of would not be increased by more than 1 per oent .
Another source of error is due to the water-cooled cone of the furnace screen reflecting some radiation from the cooler part of the furnace into the receiving aperture .
The calculation of the additional energy received by this means presents some difficulty , but a rough approximation shows that it is not more than 2 per cent. of the whole .
The difficulty due to reflection from this cone may be oyercome by reversing the furnace screen .
This was impracticable in the present case , since the placing of the furnace farther back would diminish the pencil of radiation which must come from that region of the furnace in the neighbourhood of the thermocouple ; and the apparatus was not capable of dealing with smaller quantities of energy with a very high degree of accuracy .
For this and other reasons the screen was not reversed , but when the new temperature full radiator is constructed , arrangements be made to overcome the difficulty .
It may be pointed out that the error due to reflection from the cone will be compensated at least partially by that due to the furnace not being a full radiator .
The experiment has grown out of a suggestion made to me by Prof. J. H. Pointing , F.R.S. , that in the measurement of it was desirable that both radiator and receiver should be full radiators ; and to him and to Dr. Guy Barlow I wish to express my gratitude for their kindly interest throughout the work .
APPENDIX .
Calculation of Energy Exchange between Two Fully Radiating Circular Apertures at Different For the following I am largely indebted to Mr. C. J. Lay .
The mutual illumination*of two such apertures of intrinsic brightness I may be written where is the angle between the tangents at , and is the distance between the elements , of the boundaries .
In this case put and then , ab *Cf .
Hermann 's ' Geometrical Optics , ' p. 212 .
For integration round the first circle put .
Then and we A Determination of Radiation .
and we Now Now Therefore we have after the first integration , where and ab .
For the second integration the result must be the same whatever vaJue of we start with , hence we have only to replace by .
We then get gives the sign negative , which shows we ought to change the sign of ; we then get where Since , we have /
|
rspa_1913_0006 | 0950-1207 | Optical investigation of solidified gases. II.\#x2014; The crystallo-graphic properties of hydrogen and oxygen. | 61 | 69 | 1,913 | 88 | 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.1913.0006 | en | rspa | 1,910 | 1,900 | 1,900 | 6 | 137 | 4,239 | http://corpora.clarin-d.uni-saarland.de/surprisal/6.0.3/?id=rspa_1913_0006 | 10.1098/rspa.1913.0006 | null | null | null | Thermodynamics | 62.477264 | Optics | 14.114332 | Thermodynamics | [
-9.384977340698242,
-44.563323974609375
] | 61 Optical Investigation of Solidified Gases .
II.\#151 ; The Crystallographic Properties of Hydrogen and Oxygen .
By Walter Wahl , Ph. D. ( Communicated by Sir James Dewar , F.R.S. Received September 19 , \#151 ; Read November 21 , 1912 .
) In a recently published paper I have described a method and apparatus for the optical investigation of crystalline nitrogen and argon and other bodies solidifying at extremely low temperatures.* The determination of the general crystallographic characters of these bodies by crystal-optical methods was also described .
The following communication deals with the optical investigation of solid hydrogen and oxygen .
In order to liquefy and solidify hydrogen in the crystallisation vessel described in the paper mentioned it is necessary to use liquid and solid hydrogen as cooling agents , and the apparatus for the investigation of nitrogen and argon has accordingly had to be modified .
Fig. 1 shows the arrangement of the apparatus used for working with liquid hydrogen .
To mechanical pump To mechanical pump fo mechanic^ pump A is a silvered vacuum vessel provided with two observation slits .
Through a metal cap a long , narrow , test-tube shaped vacuum vessel , B , is fixed into the vacuum vessel A. Through the same cap a syphon , D , by which liquid * ' Roy .
Soc. Proe .
, ' 1912 , A , vol. 87 , p. 371 .
Dr. W. Wahl .
[ Sept. 19 , air can be admitted , and a tube connected with the mechanical pump and the mercury barometer-valve , E , are inserted .
The inner vacuum vessel , B , is also fitted with a metal cap provided with a T-piece tube through which the stem of the quartz-glass crystallisation vessel , C , leads .
Through another tube in this metal cap is inserted a syphon , F , by which liquid hydrogen can be admitted .
The vertical part of the T-piece tube is , as far up as the branch tube in the centre of the cap , wider than the quartz-glass stem of the crystallisation vessel .
This branch tube is connected with a mercury barometer valve , Y , and also to the mechanical pump , so that the liquid hydrogen in the inner vacuum vessel can be exhausted .
The stem of the quartz-glass crystallisation vessel is connected to a T-piece , G- , of glass , fitted with three stopcocks , by means of a short piece of rubber pressure tubing .
The one branch of the T-piece G is sealed on to a three-way stopcock , a , and a large charcoal bulb , H. The other branch is sealed on to a U-tube , I , containing a few grammes of charcoal , and to this is connected a narrow glass vessel , K , of the wash-bottle type , containing asbestos wool .
K is , in turn , connected to a small mercury gasometer , L , containing pure hydrogen .
A T-piece , M , the branch tube of which is connected to a vacuum pump , is inserted between the vessel K and the gasometer L. The connecting rubber tubes of this T-piece can be closed by two screw-clamps , so that the gasometer can , if necessary , be detached from the apparatus during the course of the investigations in order to fill it with more hydrogen .
Two more charcoal bulbs , each connected with the interior of one of the vacuum vessels surrounding the crystallisation vessel , were employed in order to dry the glass surfaces before the liquid air and liquid hydrogen were admitted through the syphbns , D and F. Afterwards , however , it was discovered that the moisture from the glass walls would condense into the liquid air on the bottom of the vessel and could be frozen out on the glass walls of the lower part of the vessel if only a few drops of liquid air were admitted through the syphon to begin with .
As in these experiments with hydrogen and oxygen the cooling liquids were not allowed to cover the crystallisation vessel it was not necessary for them to be absolutely clear , and the two charcoal bulbs were therefore omitted in order to render the apparatus more simple .
Before the apparatus was cooled , the charcoal bulbs IT and I , as well as the asbestos vessel K , were thoroughly heated and exhausted through the threeway stopcock , a. This three-way stopcock was then turned so that the charcoal in H remained in communication only with the interior of the crystallisation vessel and the tubes , I and K , containing charcoal and asbestos .
1912 .
] Optical Investigation of Solidified Gases .
The charcoal bulb , H , was now immersed in liquid air and in this way the crystallisation vessel and the tubes connected with it were thoroughly exhausted .
After the charcoal bulb had been turned off , hydrogen was admitted from the gasometer to the crystallisation vessel , and this latter again exhausted by the charcoal exhaust .
The crystallisation vessel and the tubes connected with it were in this way washed out with hydrogen several times by alternately admitting from the gasometer and exhausting .
The tubes I and K , containing charcoal and asbestos , were then immersed in liquid air and the charcoal in I saturated with hydrogen from the gasometer .
Liquid air was then admitted to the outer vacuum vessel through the syphon D\#151 ; at first only a few drops , as described above , but later sufficient to cover the lower part of the inner vacuum vessel .
After the liquid air in the outer vacuum vessel had been kept under exhaust for some time liquid hydrogen was admitted to the inner vacuum vessel through the syphon F , and was only allowed to cover the lower part of the crystallisation vessel .
By exhaustion with the mechanical pump , the liquid hydrogen in B could easily be cooled down sufficiently for it to crystallise .
Hydrogen .
Pure hydrogen is admitted to the crystallisation vessel from the gasometer , and is freed from any possible trace of moisture , hydrocarbons , or other impurities , by passing it through the tubes containing asbestos wool , K , and cocoanut charcoal , I , immersed in liquid air .
The hydrogen is then caused to liquefy in the crystallisation vessel by cooling this in the vapour of the hydrogen contained in the inner vacuum vessel , and which is in a state of evaporation due to reduced pressure .
When a sufficient quantity of liquid hydrogen is condensed in the crystallisation vessel , the stopcock b of the T-piece G is closed , and the liquid hydrogen cooled down as much as possible by exhausting the surrounding solid hydrogen in the inner vacuum vessel B. The crystallisation of the hydrogen is then easily effected by placing the crystallisation vessel in communication with the charcoal bulb H. In such circumstances crystallisation takes place almost instantly and a fine-grained crystalline mass is formed .
The crystals rapidly melt again when the charcoal exhaust is disconnected .
If liquid hydrogen is now admitted in small quantities through the syphon , while the hydrogen in the inner vacuum vessel is kept solid by exhaustion , each splash of hydrogen is instantly solidified and causes , when it strikes the outer walls of the crystallisation vessel , part of the liquid hydrogen in this to crystallise .
Under such conditions crystal growth-structures are formed , but melt Dr. W. Wahl .
[ Sept. 19 , again almost instantly .
Crystallisation takes place from one or more nuclei and crystal needles grow , with extreme velocity , in all directions , forming a cluster of radiating needles very similar in appearance to the well known " tourmaline suns , " as found , for example , in Cornish granite .
Sometimes one or more of these needles grow much longer than the others and are more hair-like and occasionally bent .
These experiments show that the velocity of the crystallisation of hydrogen is extremely great , in spite of the fact that crystallisation takes place at such a low temperature , only about 20 ' above absolute zero .
Both the fine-grained crystal mass obtained by charcoal exhaust , and the needle-shaped parts of the growth-structures are absolutely isotropic .
As these needle-shaped parts of the growth-structures cannot form part of a hexagonal or tetragonal crystal growth-structure parallel to the basal plane of the crystal , we are justified in concluding that hydrogen crystallises in the regular system .
The needle-shaped branches of crystal growth-structures usually grow at right angles to a crystal face of the fully developed crystal , and we may therefore conclude from the formation of bundles of crystal needles , radiating from one centre in a great number of directions , that the hydrogen crystals , when fully developed , belong to one of the forms of the regular system rich in crystal faces , i.e. ; the trisoctahedron or the hexoctahedron .
Oxygen .
Pure oxygen was prepared by heating potassium permanganate which had previously been dried in a charcoal vacuum .
The gasometer containing the oxygen over mercury was connected directly to the T-piece G , fig. 1 , leading to the crystallisation vessel , the tubes I and K , filled with charcoal and asbestos , not being necessary in this case .
When the apparatus had been exhausted and washed out with oxygen , liquid air was admitted to the outer vacuum vessel and liquid hydrogen to the inner one .
This was done as previously described in the case of hydrogen .
The stopcock \amp ; , of the T-piece G , was then opened , and oxygen from the gasometer liquefied in the crystallisation vessel .
The liquid oxygen easily solidified when cooled in the vapour of the liquid hydrogen .
In order to again liquefy the crystallised oxygen it was necessary to wait until most of the liquid hydrogen had evaporated from the inner vacuum vessel , which , on account of the good heat isolation at the bottom of the inner vessel , takes some considerable time .
In consequence it was not possible to make as many observations as would otherwise have been possible with the quantity of liquid hydrogen available .
1912 .
] Optical Investigation of Solidified Gases .
65 The solidification of oxygen was found to be a somewhat comp li-cated phenomenon , but of much interest .
When the liquid is cooled it becomes viscous before crystallisation sets in .
The crystals which are formed in this apparently stiffened mass are not well developed , and grow very slowly .
If the cooling takes place rapidly these crystals cease to grow altogether , the liquid probably becoming too viscous to permit any further growth .
The product obtained is , in such circumstances , a stiffened mass of liquid oxygen , with oxygen crystals embedded in it .
In order to obtain a homogeneous crystallised product the cooling must take place very slowly , which is not easy when a very small piece of apparatus , as the crystallisation vessel in this case , is cooled by a spray of liquid hydrogen from the syphon .
Liquid oxygen , on cooling , thus behaves in a manner analogous to most silicates and borates , which , when rapidly cooled , give a glass with varying quantities of crystals embedded in it .
The crystals of oxygen are dark between crossed nicol prisms , similar to the surrounding stiffened liquid .
When the oxygen in the crystallisation vessel is cooled further by liquid hydrogen vapour , a transformation of the whole mass into a fine grained crystal mass takes place almost instantaneously .
These crystal grains are strongly double refracting .
Oxygen is thus polymorphous .
The crystal grains resulting from the transition into this second modification are , however , so small and of such irregular shape that it was not possible to determine to what crystal system they belong .
During the experiments carried out so far , the liquid oxygen was not cooled sufficiently quickly to produce a homogeneous stiffened mass without any crystals of form I being embedded in it , and it is uncertain whether such a homogeneous oxygen glass could be obtained at all by rapid cooling .
It is possible , however , that the oxygen glass , if once produced without containing any crystals of form I , would remain as a glass at still lower temperatures , and the crystal modification II not be formed at all in the absence of crystals I. Or , the supercooled oxygen might at a low temperature crystallise ( " devitrify " ) directly as form II , just as liquid sulphur , when supercooled in certain circumstances , may crystallise directly as rhombic sulphur .
It is probable , however , that when both crystals of form I and residual parts of liquid are present simultaneously , the transition at first takes plaice in the crystal phase , and that as soon as the crystals II are formed in the crystals I they act as germs , and a kind of devitrification of the remaining stiffened liquid into form II takes place simultaneously with the transition in the crystalline phase .
On account of the rapidity with which the whole VOL. lxxxviii.\#151 ; A. F Dr. W. Wahl .
[ Sept. 19 , process of formation of this double refracting mass of crystals takes place , it was not possible to observe directly how the devitrification of the noncrystalline parts into form II actually took place .
Under the conditions in which these experiments were conducted a rapid transition into the fine grained modification II always took place at low temperatures .
When , however , the temperature was lowered as much as possible by exhausting the solid hydrogen , which reached just up to the lower part of the crystallisation vessel , no further alteration of the product of this first transition could be observed .
The above refers to observations on oxygen at diminishing temperatures .
At increasing temperatures it is easier to investigate both the transition from one form into the other and also the properties of form I. This depends partly upon the fact that it is not so easy to lower the temperature of the crystallisation vessel gradually and evenly , by admitting liquid hydrogen through the syphon into the vacuum vessel B , as it is to increase the temperature very slowly by letting the surface of the liquid hydrogen sink gradually by evaporation , and partly because it is easier to study the properties of form I , when it is obtained by transition from form II , than when it is obtained by the crystallisation of the stiffened liquid .
In the apparatus shown in fig. 1 the isolation of the crystallisation vessel is extremely good , and the liquid hydrogen at the bottom of the vacuum vessel B only evaporates very slowly .
When evaporation has gone on for some time a very marked vertical temperature gradient is formed above the surface of the liquid hydrogen .
Consequently the temperature in the crystallisation vessel rises very slowly , and a certain temperature will first reign in the upper part and then gradually move downwards as the surface of the liquid hydrogen sinks in the vacuum vessel .
Any definite temperature , as for instance that of the transition point or that of the melting point , passes therefore from the upper part of the crystallisation vessel slowly downwards .
The transition and the melting will thus occur along each of two horizontal lines which move slowly downwards .
If , as in this case , the two temperatures are not far apart , it is possible to see the two border lines simultaneously in the crystallisation vessel .
The border line between the second and first crystalline modifications is easily visible to the naked eye as a sharp line below which the preparation looks white and nearly opaque on account of its finely granular structure .
The modification I is quite clear and translucent , so that it is not so easy to observe the border line between it and the liquid with the naked eye , although it is easily visible under the microscope .
In the parts of the crystallisation vessel above the crystals I , where a temperature reigns only slightly above 1912 .
] Optical Investigation of Solidified Gases .
67 that of the melting point , the liquid appeared stiff .
Higher up , however , in the stem of the vessel it was quite fluid , while the border line crystals I\#151 ; crystals II was still in the lower part of the vessel .
The crystal field I , lying between the two horizontal border lines , appears in most cases quite homogeneous and is dark between crossed nicols .
Near the border line crystals\#151 ; liquid , however , where the temperature approaches that of the melting point , it can be seen that it really consists of a great number of crystal grains , quite uniform in size and of hexagonal shape .
Only in two instances did the crystal field appear differently : It consisted of long flat prismatic crystals standing at right angles to the border lines and growing at the lower end on the expanse of the strongly double refracting grains of modification II .
These prisms had no even border line between each other but were otherwise well developed .
The extinction is parallel to the prism axis , and the double refraction low , of about the same magnitude as that of ordinary quartz in sections parallel to the axis .
From these observations at rising temperatures the crystal modification I must be considered hexagonal .
On crystallisation from the liquid the crystals always grow parallel to the basal plane , and appear dark between crossed nicols , just as ordinary hexagonal ice , for example , always crystallises with the basal plane parallel to the water surface .
Again , when the modification I is formed by transition from form II , it also , in most cases , grows with the basal plane parallel to the glass surfaces , and appears dark between crossed nicols .
In two instances , however , the growth described above occurred at right angles to the glass surfaces .
The width of the double vacuum vessels unfortunately does not permit of an investigation in convergent polarised light .
The form of the crystal grains , however , which , as mentioned , becomes visible near the border line crystals\#151 ; liquid by a kind of " etching " on melting , confirms the conclusions drawn from the observations in parallel polarised light , that the crystals I are hexagonal .
The exact temperature of the transition point crystals I to crystals II has yet to be determined , but , from the fact that the two horizontal border lines between crystals II and crystals I , and crystals I and liquid , observed during the experiments at rising temperatures , lie so close to each other , we may conclude that the transition point temperature is not far below the melting point temperature .
The melting point of oxygen has been given by Estreicher* as \#151 ; 227 ' .
Quite recently Sir James Dewar and Prof. Kammerlingh-Onnes have , independently of each other , determined the melting point temperaturef * T. Estreicher , ' Bull .
Intern , de l'Acad .
des Sciences de Cracovie , ' 1903 , p. 836 .
t Dewar , 'Boy .
Soc. Proc.,5 1911 , A , vol. 85 , p. 597 .
Dr. W. Wahl .
[ Sept. 19 , and found a much higher temperature : \#151 ; 219 ' and \#151 ; 218*4 ' .
It appears not improbable that the temperature determined by Estreicher has been that of the transition point crystals I to crystals II and not at all that of the melting point .
Estreicher observed a halt in the rising of the helium thermometer and noticed also that the upper part of the oxygen in his vessel at the same time appeared clear and " molten .
" In a vessel like the one employed by Estreicher , the crystals II must have appeared quite white and opaque like a snowy mass , and , as the crystals I will form a comparatively translucent mass above this , the transition point might easily have been taken for the melting point , and the true melting point overlooked .
This is the more probable as Estreicher employed a single vacuum vessel which was closed only by a wad of wool , and the inner vessel containing the oxygen therefore could not have been very easy to observe .
Another indication that the transition point temperature is close to the melting point temperature is supplied by the observation of Sir James Dewar , * that\#151 ; " Under the continued exhaust of the charcoal the smooth surfacef of the oxygen became gradually broken up by numerous cracks penetrating but slowly down into the mass , and giving it the appearance of having a white , crystalline surface.^ This disappeared very rapidly on turning off the charcoal exhaust , and the surface became quite smooth , although , with the good isolation , no appreciable melting could be detected for 15 minutes or more .
" These observations quoted from the paper of Sir James Dewar seem to indicate that the transition point temperature crystals I\#151 ; crystals II can be reached by continued charcoal exhaustion on the solid oxygen , whereby the surface of the oxygen mass thus transformed into the crystalline form II becomes cracked and of a white appearance .
In four different series of experiments the pressure , when the charcoal vacuum was turned off , is given by Sir James Dewar as 0*467 , 0*43 , 0*4280 , and 0*465 mm. , rising rapidly and then remaining constant at about 1*11 to 1*12 mm. for some thirty minutes during melting .
The exhaustion had in all cases been carried to about 0*3 mm. , and the constancy of the value obtained immediately after the charcoal vacuum had been disconnected indicates that this value 0*46 mm. is the triple-point-pressure crystals I\#151 ; crystals II\#151 ; vapour .
The pressure then rises rapidly to 1*12 mm. , which must be regarded as the triple-point-pressure crystals I\#151 ; liquid\#151 ; vapour .
Most of the physical constants of solid oxygen are determined at the boiling point of hydrogen , and they must therefore be regarded as the constants of the second crystalline modification of oxygen .
The observations on the crystallisation and melting of oxygen described above indicate that * Dewar , loc. cit. , p. 594 .
t Crystals !
( ' ?
) .
J Crystals II( ?
) 1912 .
] Optical Investigation : of Solidified Gases .
6 9 in order to determine any constants of modification I , it would be necessary preliminarily to cool the oxygen below the transition point temperature , and then investigate the product obtained by transition from form II , as a mixture of super-cooled , stiffened liquid containing varying quantities of crystals\#151 ; depending on the conditions of cooling\#151 ; may be arrived at by crystallising the oxygen directly from the liquid state .
The cracking up of the mass during transition to form II , and the opaqueness of the product , indicate a not inconsiderable change of volume , the modification II being the denser one .
The same phenomena , however , will render it difficult to obtain correct values of the density of this modification of solid oxygen when contained in a closed and rigid vessel .
The latent heat of transition of the one form into the other is probably considerable , as Estreicher states that he observed a distinct halt in the rise of his helium thermometer , at what is here considered to be the transition point .
The existence of two crystalline modifications of oxygen is interesting with regard to the position of oxygen in the periodic classification of the elements , and the analogy existing between the compounds of oxygen and sulphur .
By the discovery of similar polymorphous relations , this analogy is now extended to the elements themselves .
The investigations have been executed in the Davy-Faraday Research Laboratory of the Royal Institution .
I am indebted to Prof. Sir James Dewar for kind advice regarding these determinations at liquid hydrogen temperatures , and for placing at my disposal the vacuum vessels , syphons , and the necessary quantities of liquid air and of liquid hydrogen .
I also wish to thank Mr. W. Green , B.Sc. , of the Davy-Faraday Laboratory , for valuable help during the experiments .
|
rspa_1913_0007 | 0950-1207 | The photo-electric behaviour of iron in the active and passive state. | 70 | 74 | 1,913 | 88 | Proceedings of the Royal Society of London. Series A, Containing Papers of a Mathematical and Physical Character | H. Stanley Allen, M. A., D. Sc.|Prof. C. G. Barkla, F. R. S. | article | 6.0.4 | http://dx.doi.org/10.1098/rspa.1913.0007 | en | rspa | 1,910 | 1,900 | 1,900 | 3 | 103 | 2,549 | http://corpora.clarin-d.uni-saarland.de/surprisal/6.0.3/?id=rspa_1913_0007 | 10.1098/rspa.1913.0007 | null | null | null | Electricity | 44.515726 | Biochemistry | 25.333744 | Electricity | [
8.158914566040039,
-62.22203063964844
] | 70 The Photo-electric Behaviour of Iron in the Active and Passive State .
By H. Stanley Allen , M.A. , D.Sc .
, Senior Lecturer in Physics at University of London , King 's College .
( Communicated by Prof. C. G. Barkla , F.R.S. Eeceived October 17 , \#151 ; Read December 5 , 1912 .
) The discoveries of Hertz and of Hallwachs showed that a polished metal plate exposed to ultra-violet light readily loses a negative electric charge , but retains a positive charge .
If an electric field is applied by making the metal form one plate of an air condenser , whose second plate is charged positively by a battery , the saturation current obtained may be regarded as a measure of the photo-electric activity of the metal .
It has been known for more than a century that ordinary iron , which is acted on energetically by dilute nitric acid , can be made to assume a passive condition by immersion in strong nitric acid .
The same condition can be produced by other powerful oxidising agents , or by using iron as the positive electrode in an electrolyte containing oxygen .
The nature of the change that takes place when iron passes from the active to the passive state has given rise to much discussion , but none of the explanations suggested has yet met with general acceptance.* The experiments to be described were carried out in order to compare the photo-electric activity of iron in the active state with that of the same sample in the passive state .
It was hoped that the results might throw some fresh light on the theory of " passivity .
" The experiments prove that iron which is chemically active is active in the photo-electric sense , while iron which is passive shows much smaller photo-electric activity , in some cases none that can be detected .
The bearing of these results on the nature of " passivity " will be discussed later .
Measurements of the Photo-electric Activity.f The photo-electric activity of the plate under test was measured by determining the rate of leak between the plate and a parallel gauze of iron wire charged to 100 volts .
The current was found by observing the * Useful summaries of the literature of " passivity 55 have been published by Heathcote ( 'Soc .
Chem. Ind. Journ. , ' 1907 , vol. 26 , pp. 899\#151 ; 917 ) and Byers ( 'Amer .
Chem. Soc. Journ. , ' 1908 , vol. 30 , pp. 1718\#151 ; 1742 ) .
t I am indebted to the Government Grant Committee of the Royal Society for some of the apparatus used in this research .
The Photo-electric^ Behaviour of Iron .
71 rate of movement of the needle of a Dolezalek electrometer with one set of quadrants in connection with the plate .
A mercury vapour lamp of fused quartz by Heraeus was used to illuminate the plate through the meshes of the gauze .
Before commencing a series of observations the lamp was allowed to burn at least 20 minutes so that it might assume a steady state .
In this paper the photo-electric activity of the iron plate is expressed in terms of the activity ( arbitrarily assumed as 100 units ) of a standard plate of pure silver supplied by Messrs. Johnson , Matthey and Co. Previous experiments by the author* proved that this silver plate showed no photo-electric fatigue when kept in an air-tight brass testing vessel.f The iron plates used in these experiments were cut from Kahlbaum 's sheet iron , 0'2 mm. thick .
They were in the form of circular discs 5T cm .
in diameter , a projecting piece 2 cm .
long and 1 cm .
wide being left at one part of the rim to serve as a handle .
In some cases smaller plates ( 3 cm .
in diameter ) of the same shape were used .
Eods of commercial iron and steel were also examined .
The rods , which were 5 cm .
long and 0#6 cm .
in diameter were polished in the lathe with fine emery paper .
As all the tests for photoelectric activity had to be made with a dry plate , it was necessary , after having rendered the iron passive , to dry it without destroying the passivity The method followed was that recommended by Heathcote .
The passive iron was washed by the following solutions in turn:\#151 ; 1 .
Saturated aqueous solution of potassium bichromate +2*8 grm. potassium hydrate per 100 c.c. solution of bichromate .
2 .
Water 100 c.c. , pure methylated spirits 10 c.c. , potassium hydrate ( by alcohol ) 2*5 grm. 3 .
Absolute alcohol , The solutions were sprayed or poured on to the plate as quickly as possible one after the other .
The manipulation was easier for the rods than for the plates , and easier for the small plates than for the large ones .
In Heathcote 's experiments the following test was employed in order to determine whether the iron plate was in the active or in the passive state:\#151 ; " The rod was regarded as passive when , after plunging in 1*2 nitric acid and shaking for a moment in the acid and then holding motionless , no .chemical action could be detected at the surface by the unaided eye , the temperature of the acid being about 15'\#151 ; 17 ' C. " In the present experiments little difficulty was found in applying this test in the case of wires , small plates or rods .
A passive wire or small plate could be kept in this dilute acid for some time without chemical action , but * ' Phil. Mag. , ' 1910 , vol. 20 , p. 570 .
+ ' Eoy .
Soc. Proc. , ' 1907 , A , vol. 78 , p. 484 .
72 Dr. H. S. Allen .
The Photo-electric Behaviour of [ Oct. 17 , with the larger plates chemical action generally set in after the iron had been immersed for 15 or 30 seconds .
A single spot of active iron is sufficient to start the reaction , and the difficulty experienced with the larger plates is probably due to the extent of the sharp edge forming the circular boundary of the plate .
Summary of Experimental Results .
The experiments in which plates of Kahlbaum 's iron were rendered passive by immersion in strong nitric acid ( specific gravity , 1*5 ) proved that such treatment reduced the photo-electric activity to considerably less than one-half of the value for the active plate , and that when reduction was most marked the plate was most distinctly passive .
The following extracts from the laboratory note-book illustrate the results:\#151 ; Photo-electric Plate F , diameter 5*1 cm.:\#151 ; activity .
Plate cleaned with nitric acid and water , washed under tap , and then with solutions 2 and 3 ... ... ... ... ... ... ... ... ... ... ... ... ... ... ... . .
144 Plate begins to dissolve at once in dilute nitric .
Transferred to strong nitric , where action soon stops .
Wash with solutions 1 , 2 , and 3 ... . .
11 Plate tested in dilute nitric , is passive for 30 secs .
Wash under tap and then with solutions 2 and 3 ... ... ... ... ... ... ... ... ... ... . .
70 Another experiment .
Initial activity of plate ... ... ... ... ... ... ... ... ... 98 Dry iron plate , immersed in strong nitric , then washed with solutions 1 , 2 , and 3 ... ... ... ... ... ... ... ... ... ... ... ... ... ... ... ... ... ... ... ... .
13 Plate tested in dilute nitric , remains passive about 5 or 10 secs .
Washed under tap , and while wet placed in strong acid .
Wash with solutions 1 , 2 , and 3 ... ... ... ... ... ... ... ... ... ... ... ... ... ... ... ... ... ... ... 18 Plate remains passive for 10 secs , in dilute acid .
Wash under tap and then with solutions 2 and 3 ... ... ... ... ... ... ... ... ... .4 ... ... 147 Eesults of a similar character were obtained with the rods of commercial iron and steel .
The photo-electric activity , measured after treatment with strong nitric acid , was extremely small , and in some cases too small to be detected .
Experiments were also carried out in order to compare the behaviour of iron after being used as anode , and after being used as cathode , in a voltameter containing dilute sulphuric acid .
According to Heathcote { loc. cit. ) : " The current density must be above a certain value for passivity to ensue .
Iron behaves as if one could teach it to become passive ; repeated trials end in success , and , once passivity has been produced , its reproduction is facilitated .
" " If the anode be sprayed with alkaline potassium bichromate solution as it is withdrawn from the sulphuric acid , it can be dried and kept 15 hours in a laboratory atmosphere without becoming active to 1*2 nitric acid .
" 1912 .
] Iron in the Active and Passive State .
By using small plates of Kahlbaum 's iron , I have been able to show that photo-electric activity after use as anode is extremely , small , but the experiments with the larger plates were not successful .
In consequence of the difficulties in manipulating these plates , the later experiments were carried out with cylindrical rods of iron and steel .
The rod formed one electrode , and was surrounded by a cylinder of thin sheet iron , which constituted the second electrode .
In this way all parts of the rod were acted upon similarly .
The rod was mounted so that it could be lifted vertically out of the voltameter , and washed with the solutions , without any risk of its coming into contact with the second electrode .
The current was supplied by four secondary cells , giving 8 volts , and an ammeter and adjustable resistance were included in the circuit .
Photo-electric Iron Bod:\#151 ; activity .
Initial activity ... ... ... ... ... ... ... ... ... ... ... ... ... ... ... ... ... 60 Iron rod made cathode for 1 min. , current 0*5 ampere , then washed with solutions 2 and 3 ... ... ... ... ... ... ... ... ... ... ... ... ... ... ... ... 80 Iron rod made anode for 1 min. , current 0*5 ampere , then washed with solutions 1 , 2 , and 3 ... ... ... ... ... ... ... ... ... ... ... ... ... Less than 4 Iron rod made cathode for 1 min. , current 0*5 ampere , then washed with solutions 2 and 3 ... ... ... ... ... ... ... ... ... ... ... ... ... ... ... ... .
70 Iron rod made anode for 1 min. , current 1*0 ampere , then washed with solutions 1 , 2 , and 3 ... ... ... ... ... ... ... ... ... ... ... ... ... Less than 2 Bod immersed in dilute nitric , not visibly acted upon at the moment of immersion , but action quickly begins .
A steel rod gave similar results .
Discussion of Results .
The results just recorded may be summarised by saying that processes which render iron active in the chemical sense give it large photo-electric activity , while processes which render iron passive tend to greatly diminish the photo-electric activity , in general to less than half the value observed with an active plate .
It must be borne in mind that in these experiments the photo-electric activity is measured with a.dry plate , while the chemical activity is tested in solution , and that the processes employed in changing the state of the iron are all wet processes .
We may extend our conclusions by including the observations of Muthmann and Frauenberger , * who state that " metals become passive on lying in the air , and their potentials ( in KC1 solution ) assume medium values , whilst vigorous mechanical cleaning of the surface renders them active .
" Here the reference is to chemical activity , but the statement is equally true if interpreted of photo-electric activity .
* ' Zeit .
Elektrochem .
, ' 1904 , vol. 10 , pp. 929 , 930 .
The Photo-electric Behaviour of Iron .
Metals exposed to the air show photo-electric fatigue , whilst polishing the surface gives rise to a large photo-electric current .
We appear to be justified in assuming a correlation between these two sets of phenomena and in saying that the chemical activity and the photoelectric activity vary together .
If this view be correct we see that there are degrees of activity and also of passivity , a conclusion which appears to be in accordance with the general experience of chemists .
Further , we may regard the photo-electric fatigue sometimes observed with iron as a gradual passage from the active to the passive state .
The experiments of the author* and others support the conclusion of Hallwachs that the principal cause of fatigue is to be found in the condition of the layer of gas at the surface of the plate .
We should , therefore , be inclined to attribute passivity to the surface film of gas .
The fact that from the photo-electric standpoint different degrees of activity can be obtained from the same iron plate does not harmonise well with the idea of an allotropic change as the cause of chemical passivity ; it agrees far better with the idea of a protective coating , whether of oxide or of gas , and best of all with the last named , i.e. a gaseous film .
... ... ... ... ... ... ... ... ... .
It must , of course , be admitted that such an explanation , whether applied to passivity or to photo-electric fatigue , cannot be regarded as final or complete until we are able to describe with greater definiteness the character of the modification in the gaseous layer to which the effects are attributed .
Conclusion .
1 .
The investigation into the photo-electric behaviour of dry iron shows that when the iron is chemically active it exhibits large photo-electric activity , while in the passive state this activity is greatly diminished .
2 .
It is held that this result is in good agreement with the theory which attributes passivity to the condition of the gaseous layer at the surface of the metal .
* 4 Brit. Assoc. Bep .
, ' 1910 ; 4 Phil. Mag. , ' 1910 , vol. 20 , p. 572 .
|
rspa_1913_0008 | 0950-1207 | The penetrating power of the \#x3B3;-rays from radium C. | 75 | 82 | 1,913 | 88 | Proceedings of the Royal Society of London. Series A, Containing Papers of a Mathematical and Physical Character | Alexander S. Russell, M. A.|Prof. E. Rutherford, F. R. S. | article | 6.0.4 | http://dx.doi.org/10.1098/rspa.1913.0008 | en | rspa | 1,910 | 1,900 | 1,900 | 8 | 170 | 2,970 | http://corpora.clarin-d.uni-saarland.de/surprisal/6.0.3/?id=rspa_1913_0008 | 10.1098/rspa.1913.0008 | null | null | null | Atomic Physics | 38.558882 | Thermodynamics | 28.751787 | Atomic Physics | [
9.293315887451172,
-77.30803680419922
] | ]\gt ; The Pouer of the -Rays from Radium By ALEXANDER S. RUSSELL , M.A. , Carnegie Research Fellow of the University of Glasgow .
( Communicated by Prof. E. Rutherford , F.R.S. Received November 14 , \mdash ; Read December 5 , 1912 .
) The primary object of the present research was to find out if there is any residual radiation from radium after the -rays of ordinary penetrating power have been entirely absorbed .
In the course of the work it was necessary to measure the absorption of the -rays by mercury .
This , also , has therefore been investigated in some detail .
Only experimental results are given in this paper .
A discussion of the theoretical meaning of the results will be given in a subsequent paper dealing with hardening and scattering of -rays .
A very penetrating radiation may be looked upon either as a new type of radiation , resembling the -ray in that it is uncharged , but possessing a much greater penetrating power , or , if the assumption be made that the -rays are heterogeneous , as the most penetrating constituents of the -ray beam .
The recent work of Danysz*has shown clearly that some of the -rays from radium are ejected with a velocity not less than 99 per cent. of that of light .
It is not unreasonable to expect that there are -rays corresponding to these , and possessing , therefore , a much greater penetrating power than the average penetrating power of ordinary -rays .
This radiation , if it exists , would be present in the -ray beam only in very small amount , and detectable , therefore , only when a large source of radium is used , and special precautions taken .
In a previous paper it has been shown by F. and W. M. Soddy and the author that , when measured ditions such that no scattered radiation of any kind enters the electroscope , the -rays are absorbed , apparently according to a strictly exponential law , over a range of thickness of lead of 2 to 22 cm .
; or , expressed mathematically , if , be the intensity of the -rays after traversing a thickness of metal , the intensity after traversing a thickness , it was found experimentally that where is the base of the natural system of logarithms , and is a constant , * J. Danysz , ' Count .
Rend 1911 , vol. 153 , pp. 339 , 1066 ; 'Ls Radium , ' 1912 , vol. 9 , p. 1 .
F. and W. M. Soddy and A. S. Russell , ' Phil. Mag 1910 , , p. 725 .
Mr. A. S. Russell .
The Penetrating [ Nov. 14 , the absorption coefficient .
is constant from 2 to 22 cm .
of lead , and has the value c il .
In this work , difficulty was experienced in making accurate measurements from the 18th to the cm .
, owing to the smailness of the ionisation from the source of radium used .
For this reason , it was impossible to say with certainty , whether or not there was any radiationwhich etrated the greater of these thicknesses .
The result found indicated that the effect due to these rays,.if it exists at all , must be very small .
It was desirable therefore to repeat the work under : favourable conditions with a large quantity of radium C. To detect this very penetrating radiation , the following conditions were thought most likely to give the desired result:\mdash ; ( 1 ) A strong source of radium to be placed as near .
the detecting vessel as possible .
This requires the use of as dense a metal as possible as an absorbent of ordinary -rays .
( 2 ) Iotal exclusion of any scattered radiation from entering the electroscope through the sides .
and top .
( 3 ) A detecting vessel which is sensitive and possesses a very low natural leak .
It is essential that the ionisation chamber be large , in order that the air it contains may have a good opportunity of ben ionised by the rays .
The reasons for these conditions are sufficiently obvious , and need not be discussed at length .
The source used at the commencement of the experiments was about 300 millicuries of emanation .
Mercury was employed as absorber of the -rays , as it has a greater density than any Other common metal ; and , therefore , a given thickness of this metal absorbs more -rays than the same thickness , say , of lead .
The effect of scattered radiation was obviated by surrounding the source of rays on every side by at least 10 cm .
of mercury .
This reduced the rays moving in every direction to a very small percentage of their original ensity .
Any scattered radiation , produced by the rays which escaped , completely absorl , ed by the thick lead walls of the electroscope .
On p. is given a of the apparatu:s the chief experiment .
A is a cylindrical pot of cast iro .
, of inside diameter cm .
, and height cm .
When filled to the top it held kgrm .
of me On top of this pot was laid a.oircular disc of lead cm .
in diameter and 1 cm .
in thickness .
A large electroscope of the ordinary type was placed on the disc .
The lead used for the disc and for the electroscope was the oldest procurable , in order that the latter might have .
as low natural leak as possible .
The electroscope had an inside diameter of 20 cm .
, an inside height of cm .
, and a wall thickness of sides and top of 1 cm .
It contained litres of air .
The leaf system consisted of a strip of brass , 1912 .
] Power of the -Rays from Radium 7 cm .
long , to which was attached a gold leaf , 6 cm .
long .
Insulation was effected by means of a small bead of sulphur .
Two cylinders of lead , 6 cm .
long and 3 cm .
inside diameter , and 1 cm .
wall thickness , encircled the windows to prevent any scattered radiation from entering .
The windows were circular and of the wme diameter as the lead cylinders .
The latter were just large enough to allow the reading microscope to be inserted .
The microscope used had a nification of about The source of radium emanation was contained in two sealed glass tubes , , which could be attached by means of string to one end of an iron rod .
The rod was connected by a clamp at to a stand , and bent in such a way that , by raising or lowering , the radium could be raised or lowered centrally in the mercury .
By means of the glass apparatus , which contained a tap , the-mercury could be added to the pot by pouring it in through , or withdrawn by siphoning it off through F. The pot was carefully made and had .
very uniform diameter .
From the weight added or withdrawn from the pot , therefore , the increase or decrease of thickness of the mercury covering the radium could be easily calculated .
The natural leak of the electroscope was division per minute , which was considered low for an instrument of these dimensions .
One millicurie of emanation at a distance of 25 cm .
below the lead base of the electroscope gave a leak of 36 divisions per minute .
Mr. A. S. Russell .
The Penetrating [ Nov. 14 ; Attempts to Detect the very Penetrating Radiation .
Two different experiments were made to detect the very penetrating radiation .
The first was done at atmospheric pressure with the apparatus described above , the second was done with an ionisation chamber at high pressure .
The first experiment was carried out as follows : The pot was filled to the top with mercury , and the natural leak measured three times for intervals of about 40 minutes each , with the source of radium removed entirely from the laboratory .
The radium was then inserted to a depth of 20 cm .
below the meroury , and the leak measured a period of 20 minutes .
The value of the leak obtained was considerably higher than the natural leak .
The radium was then lowered to various depths , the leaks being carefully measured at each position , until a depth was reached at which there was no difference between the leak measured and the natural leak .
The results actually obtained are given in the accompanying table:\mdash ; Table I. Natural leak , division per It is seen that at a depth of 25 cm .
the ionisation due to the -radiation is only 7 per cent. of the natural leak of the electroscope .
At greater depths this leak disappears entirely .
There is , therefore , no -radiation capable of penetrating 27 cm .
of mercury and of being detected in the electroscope used .
The experiment shows also the complete absence of any secondary radiation entering the electroscope otherwise than through the base .
An ionisation chamber capable of withstanding a pressure of 80 atmospheres , was next used instead of the electroscope as a debecting vessel .
The apparatus was kindly placed at my disposal by Mr. D. C. H. Florance , .
who employed it in a research whioh will soon bs published .
Inside the pressure chamber were mounted centrally two concentric cylinders of brass .
The outer one was cm .
long and cm .
in diam.eter .
inner one cm .
long and cm .
in diameter .
The former was charged to a 1912 .
] Power of the Radium potential of 1500 volts , the latter was connected to one pair of quadrants of a sensitive Dolezalek electrometer .
The pressure chamber itself was earthed .
Ionisation took place in the space between the cylinders .
The pressure in the chamber was kept constant at 80 atmospheres .
This arrangement is not so sensitive as the large electroscope , but it was used for two reasons .
It is possible that the very penetrating rays might ionise dense ases only .
Secondly , a large quantity of incident and emergent -radiation from the very penetrating -rays might be produced when they strike the brass cylinders .
Such radiation when produced would be an efficient ioniser of a gas at high pressure .
When the radium was sunk to a depth of 26 cm .
in the mercury , however , the leak of the electrometer was exactly the natural leak .
No trace whatever of any radiation could be detected .
I have to thank Mr. Florance for kindly making the necessary measurements for me .
The Absorption of the -Rays by Mercury .
The absorption of the -rays of radium by mercury over a lange of thickness of cm .
was next investigated .
The radium was inserted centrally below the electroscope at a distance of 25 cm .
and the pot filled with mercury .
The leak was then measured .
Ten kilogrammes of mercury were then siphoned off , and the leak agairi measured .
More mercury was then siphoned off , and again the leak taken .
This was continued until the leak was too large to measure .
Smaller quantities of radium were then substituted for the larger quantity , and the absorption measurements continued till only 6 cm .
covered the radium .
At this stage a smaller lead electroscope , having a volume one-fifth of that of the , was substituted for it , and used for the absorption measurements from 1 to 6 cm .
This was necessitated by the powerful nature of the source used .
Experiments were conducted usually so that the leak was about 10 divisions per minute at the commencemen , and about 1 division per minute or less at the end , of the range of thickness investigated .
With the larger electroscope it was essential that the leaks should not be too great , owing to a possible lack of saturation in so great a volume of air .
The results obtained are given in the table that follows : In the first column is put the range of thickness density of mercury covering the radium .
The values given are obtained directly from the weight of mercury and the dimensions of the pot .
In the second column are put the values of the absorption coefficient divided by density of mercury .
All thickness $es in the tables which follow are given in centimetres , and all values of are c .Mr .
A. S. The Table IL The values of were obtained as follows : logarithms of the ionisation were plotted against the product of thickness and density .
OIi the average there was a point for every 12 units of thickness density .
From this line the mean value of over the range under investigation was obtained .
Each of the five experiments was separately carried out , and is quite distinct from the other four .
It is seen that the values of do not diffel by more than about 2 per cent. over the entire range investigated .
Two examples showing how closely the exponential law of absorption holds are given in the two following tables .
The first table deals with the first part of the range investigated , the second with the last part .
In the first column of each table is given the absolute thickness density of mercury over the radium , in the second the observed values of the ionisation , and in the third the calculated values .
For convenience , the observed value of the ionisation for the smallest thickness density is in both tables put at I000 .
The theoretical values are obtained from the usual equation , Table III.\mdash ; Range of Thickness Density , to 1912 .
] Power of the -Rays from Radium Table \mdash ; Range of Thickness Density , to 307 .
Since for mercury , is c thickness density of , or a thickness of cm .
mercury , therefore , cuts the -rays of radium down to half value .
Over the range to 307 of thickness density , the -radiation is reduced in the ratio of 360,000 to 1 .
Under the conditions of experiment , the leak due to the -rays from 300 millicuries of emanation in the electroscope was divisions per minute through a thickness density of 183 , and of division per minute through 307 .
The radiation from 300 millicuries , if unabsorbed by mercury , would produce10,800 divisions per minute in the electroscope .
The radiation , capable of penetrating thicknesses greater than cm .
of mercury , is therefore less than :10800 , i.e. is less than of the initial -ray beam .
The value of for mercury , cm .
, is 7 per cent. less than a value given in a previous paper by Soddy and Russell .
* In the former research the source of radium used was less than half a milligramme , and the absorption over the first 3 cm .
only could be investigated .
The mean value of for mercury , cm .
, is very similar to the mean value obtained in a previous research for a range of 2 to 22 cm .
of lead , namely c. The results of this paper , both with regard to the absence of a very penetrating radiation , and to the absorption of the rays by an element of high atomic weight , confirm and extend the results previously obtained with lead as an absorbent .
Beyond a thickness of cm .
of mercury it will be difficult to detect -rays even if large quantities of * F. Soddy and A. S. Russell , ' Phil. Mag 1909 , vol. 18 , p. 644 .
VOL LXXXVIIL\mdash ; A. The Penetrating Power of the -Rays from Radium radium are forthcoming .
the electroscope used in these experiments , the leak due to the -rays from 10 .
of radium would be only 4 per cent. of the natural leak , after they had penetrated cm .
of mercury .
Summar ?
y. ( 1 ) The -rays of radium are absorbed by mercury over a range of thickness of 1 to cm .
strictly according to an law .
The mean value of is .
Over this range the intensity is diminished in the ratio of 360,000 to 1 .
2 ) No trace of any radiation more penetrating than -rays could be detected .
If any exists , and is capable of ionising air , its intensity is less than of that of the initial -ray beam .
I have to express my warmest thanks to the Castner-Kellner Alkali Company of Runcorn for loaning me .
of pure mercury , and for making for me the cast iron pot which contained it .
But for their generosity in this matter , the present research could not have been carried out .
I have also to express my thanks to Prof. Rutherford , in whose laboratory this work was carried out , for his gestions and advice .
|
rspa_1913_0009 | 0950-1207 | On the scattering and absorption of light in gaseous media, with applications to the intensity of sky radiation. | 83 | 89 | 1,913 | 88 | Proceedings of the Royal Society of London. Series A, Containing Papers of a Mathematical and Physical Character | Louis Vessot King, B. A. (Cantab.)|Sir J. Larmor, Sec. R. S. | abstract | 6.0.4 | http://dx.doi.org/10.1098/rspa.1913.0009 | en | rspa | 1,910 | 1,900 | 1,900 | 6 | 101 | 2,830 | http://corpora.clarin-d.uni-saarland.de/surprisal/6.0.3/?id=rspa_1913_0009 | 10.1098/rspa.1913.0009 | null | null | null | Tables | 29.214635 | Atomic Physics | 24.110728 | Tables | [
13.047917366027832,
-75.54889678955078
] | ]\gt ; On the Scattering and Absorption of Light in Gaseous with Applications to the Intensity of Sky Radiation .
By LOUIS VESSOT KING , .
( Cantab .
) , Lecturer in Physics , McGill University , Montreal .
( Communicated by J. Larmor , Sec. R.S. Received June 7 , \mdash ; Read November7 , 1912 .
) ( Abstract .
) Sections 1 and 2.\mdash ; Lord Rayleigh* showed , in 1871 , that when radiation travels through a medium containing small particles whose dimensions are small compared with the wave-length , each of these sets up a secondary disturbance which travels in all directions at the expense of the energy in the original direction .
Various hypotheses of the aether and of the molecule in giving for the scattered radiation near an ele meant of volume an expression of the form , ( 1 ) where is the intensity contained in a small solid angle in a direction with the dilection of the original beam is the refractive index of the gas , the number of molecules per unit volume , and the wave-length of the incident radiation .
In a later paper Lord Rayleigh gave reasons for believing that the molecules of a gas are themselves able to scatter radiation in this way , and that both the attenuation of light by the earth 's atmosphere and the blue of the sky could be thus accounted for .
These results were applied by Lord to the problem of sky radiation , and this seems to have been the most recent theoretical contribution to the subject .
S Recent observations on sky radiation seem to have thrown some doubt on the sufficiency of the simple Rayleigh law to account for facts .
Seeing that * Rayleigh , ' Phil. Mag 1871 , vol. 41 , pp. 107 , 274 , 447 ; 'Collected Works , ' pp. S7 , 104 , 518 .
Bayleigh , 'Phil .
Mag 1899 , vol. 47 , pp. 375\mdash ; 384 ; CoJlected Works , ' vol. 2 , pp. 397\mdash ; 406 .
Kelvin , ' Baltimore Lectures , ' 1904 , p. 311 .
S The writer is indebted to Dr. Otto Klotz , of the Dominion Observatory , Ottawa , for calling his attention to the work of Exner along these lines .
Exner , ' Sitzungsbericht Akad . .
Wissen .
, Wien , M.-N .
Klasse , ' 1909 , vol. 118 , IIa .
A summary of results is given by Abbot C. in his recent book , ' The Sun , ' p. 299 ( Appleton and Co. , 1911 ) .
VOL. LXXXVIIL\mdash ; A. 84 Mr. L. V. King .
On the Scattering and [ June 7 , the phenomenon of molecular scattering is now well established , the 6 : subject has a very wide scope of application to a great variety of astrophysical problems .
It has therefore seemed desirable to investigate the subject in as general a manner as possible , and apply for verification to existing numerical data on absorption and scattering of radiation by the earth 's as well as by the sun 's atmosphere .
The two main extensions of the existing theory which form the basis of the present investigation are as follows:\mdash ; ( i ) The introduction of a second term in the differential equation for loss of intensity in a beam of radiation which allows for attenuation by absorption ( without scattering ) , i.e. the absorption gives rise to a direct conversion of radiant energy in the aether into thermal molecular agitation in the gas .
The introduction of this term leads to an equation of the form , where , ( 2 ) and A and are constants depending on the density of the gas .
The existence and magnitude of the term A can then be inferred from observations on atmospheric attenuation , and in this way a numerical estimate made of the distribution of energy between the aether and the molecular velocities of the gas .
The second feature of the present investigation consists in the mathematical consideration of effects due to nation .
Suppose a mass of gas exposed to external illumination : as a result of scattering the whole mass of gas will be luminous as is the case in the earth 's atmosphere .
Thus each element of volume besides being subject to the external incident illumination is also subject to the scattered radiation from the entire volume , and this factor will add considerably to the scattered intensity from the element of volume .
The mathematical expression of this effect gives rise to an integral equation which may be written I I is the intensity of scattered radiation per unit solid angle in a direction with the incident radiation and emanating from an element of volume at the point .
The accented symbols refer to the corresponding quantities with reference to another element of volume at The exponential expresses the attenuation of the scattered radiation from in travelling along to .
The integral is taken throughout the volume enclosed by the surface 2 drawn so as to include the entire mass of gas .
A differential equation for completes the analytical 1912 .
] Absorption of Light in Gaseous Media .
expression of the problem .
The total scattered intensity received from a small solid angle in any direction is given by , ( 4 ) where the integrals are taken so as to include all the elements of volume in the small solid angle .
The importance of self-illumination on the intensity of sky radiation is recognised both by Kelvin and Rayleigh , although no attempt seems to have been made to calculate its effect .
Schuster*in a paper on\ldquo ; Radiation through a Foggy Atmosphere\ldquo ; draws attention to the importance of the effect in astrophysical problems and obtains a representation of its magnitude by means of differential equations ; the results are applied to problems of the reversal of hnes in certain stellar spectra to be attributed to absorption and scattering in the stellar atmospheres .
The application of the theory of integral equations to problems of this type seems to offer a means of attacking a great numbel of physical problems .
3.\mdash ; An immediate application of the general equations just discussed can be made to the problem of absorption and scattering of solar radiation by the earth 's atmosphere .
The general integral equation can in this application be reduced to one in a single variable and by means of a perfectly general transformation of variables can be further reduced to the case of a homogeneous atmosphere contained between two parallel planes at a distance apart .
This transformation is independent of any law of density or temperature gradient in the atmosphere and only requires that planes parallel to the earth 's surface be planes of equal density .
The integral equation for the scattered radiation can then be written down , and by a consideration of the rate of accumulation of energy in an element of volume the result is shown to be consistent with the well-known law of attenuation , , ( 5 ) being the intensity of solar radiation of wave-length reaching a level X ; is the intensity outside the earth 's atmosphere and is the zenith distance of the sun ; is the generalised coefficient of attenuation in equation ( 2 ) referred to normal pressure and density .
Section 4.\mdash ; Progress towards the solution of the integral equation requires the development of a special method of approximation .
It is shown in a general case that the solution must lie between two limits called the extreme solutions , and an intermediate value called the mean solution is obtained which * Schuster , ' Astrophys .
Journ January , 1905 , vol. 21 , p. 1 .
Mr. L. V. King .
On the Scattering [ June 7 , represents a value probably not far from the correct one in the applications considered .
Section \mdash ; The approximate solution of the integral equation leads to a number of transcendental functions which recur so frequently that they are designated by a special notation and tabulated ; among these are ( 6 ) where is exponential integral , denoted by Section 6.\mdash ; The intensity of sky radiation corresponding to any direction of sun and sky can now be obtained in terms of the coefficient of attenuation for a particular wave-length .
Formulae are developed giving the total sky radiation on a horizontal plane and rough estimates of the degree of polarisa- tion of the light from different regions of the sky .
Section 7.\mdash ; Numerous observations on the attenuation of solar radiation have been made by the Smithsonian Astrophysical in connection with the determination of the solar constant .
At any station at a height above sea-level the law of attenuation may be written ( 7 ) where and and are constants for all stations and have the values and , while is the height of the " " homogeneous atmosphere The term expresses the attenuation by absorption alone .
If the observed values of the coefficients of attenuation are plotted against the inverse fourth power of the wave-length for different we should obtain a family of lines all passing through the same point .
The coefficients of attenuation for Mount Whitney ( 4420 metres , Mount Wilson ( 1780 metres ) , Potsdam ( 100 metres ) , and Washington ( 10 metres ) , are analysed in this way ; the result gives rise to a family of straight lines shown in the diagram .
The results for sea-level stations require special interpretation owing to Glaisher , ' Phil. Trans 1870 , p. 367 .
A summary of the most recent resuIts of the Smithsonian Astrophysical Observatory is given by Abbof ( C. " " The Sun 's Energy , , and Temperature ' Astrophys .
Journ October , 1911 , vol. 34 .
1912 .
] Absorption of Light in Gaseous the effect of ' ' atmospheric dust A disoontinuity in the straight lines occurs in the neighbourhood of .
Wave-lengths greater than this oonstitute -wave radiation , while shorter wave-lengths constitute short-wave radiat ; the two classes demand separate discussion .
-wave Radiation.\mdash ; For the longer waves the ' dust\ldquo ; present in the atmosphere is able to absorb as well as to scatter : the fact that the straight lines intersect in the same point leads to the result independently of any law of distribution of ' ' dust\ldquo ; : the presence of " " dust ' Variation of Coefficients of Atmospheric Attenuation with Wave-Length .
Curve L\mdash ; Mount Whitney .
II.\mdash ; Mount Wilson .
III.\mdash ; Potsdam .
IV.\mdash ; Washington .
gives rise to the constants of absorption and scattering denoted by accented letters .
This result can be expressed in the form : the ratio of energy scattered to energy absorbed and converted into heat is constant for any wave-length and is independent of the nature of the scattering particle whethe ' dust\ldquo ; or molecules .
( ii ) Short-wave Radiation.\mdash ; In this case we may suppose that " " dust\ldquo ; attenuates radiation of all wave-lengths without scattering , so that the scattering which exists is due entirely to air-molecules .
In order to test this conclusion we measure the slope of the straight lines of the diagram over the 88 Mr. V. King .
On the [ June 7 , portion corresponding to short-wave radiation , and so obtain values of , the barometric pressures at the stations being supposed known at the time of observation .
From a knowledge of the optical constants of air , we may make use of these values of to obtain an estimate of , the number of molecules per cubic centimetre of a gas at standard temperature and pressure .
The results are as follows:\mdash ; Potsdam .
, Mt .
Wilson Washington , Mt .
Whitney These are in tolerable agreement with the values obtained by Rutherford and and by Millikan Another numerical result of some interest is obtained from the observations on attenuation of solar radiation in the comparatively dust-free air above Mount Wilson and Mount Whitney .
From the straight lines in the diagram we find , so that .
( 9 ) represents the fraction of radiant energy travelling through air at normal pressure and temperature , which is converted into thermal molecular agitation per centimetre of path .
If direct sunlight is travelling through air under these conditions , the above value of leads to an increase of temperature of C. per hour .
The effect of ' ' dust\ldquo ; as at Washington is to increase this value about six-fold .
Section 8.\mdash ; The intensity of sky radiation can be calculated in terms of the coefficients of attenuation ; the results for zenith sky are calculated for Mount Wilson for comparison with observations .
and for Washington as typical of a sea-level station .
The former results agree as regards both quality and total intensity of sky radiation sufficiently well with experiment to indicate that molecular scattering when taken in conjunction with selfillumination is sufficient to account for all the phenomena of sky light .
The hitherto neglected factor of self-illumination is responsible for about 33 per cent. of the whole effect at in the violet and for about 5 per cent. at in the red .
Sky intensities at sea-level are interesting iu enabling us to calculate the total radiation from the sky on a zontal surface , a magnitude of some importance in meteorology .
At Washington it is found that this quantity is about per cent. of the normal solar radiation reaching the earth , and is approximately constant for all zenith distances of the sun .
Thus , if the sun 's zenith distance is , the contribution of sky radiation to the heat available Rutherford ( E. ) amd Geiger H. ) , ' Roy .
Soc. Proc 1908 , , vol. 81 , p. 171 .
MiUikan ( R. ' Phys. Rev April , 1911 , vol. 32 .
1912 .
] Absorption of Light in Gase.ous Media .
for heating the earth is 16 per cent. of the sun 's heat ; for a zenith distance of the proportion is 24 per cent. , and for the proportion reaches 44 per cent. Sky radiation is thus a feature of some importance in the meteorology of northern labitudes where the altitude of the sun remains small during the winter months .
Summary.\mdash ; The analysis of the present investigation seems to support the view that , at levels above Mount Wilson , molecular scattering is sufficient to account completely both for attenuation of solar radiation and for the intensity and quality of sky radiation .
Even at sea-level the effect of atmospheric dust\ldquo ; can be taken into account in a simple manner in the formulae for absorption and scattering .
Should future observations support the validity of the simple law expressed by equation ( 2 ) connecting the coefficient of attenuation with the wave-length , we may with considerable assurance make use of the law to obtain the coefficients for very short or very long wave-lengths when the direct method of calculation from high and low sun observations leaves room for considerable uncertainty owing to the small intensities in the solar spectrum at these wave-lengths , and owing to other experimental difficulties .
Schuster .
cit. ) points out in this connection the extreme importance of determining accurately the form of the solar intensity curve outside the earth 's atmosphere for short wavelengths , since the effect of a solar atmosphere in absorbing and scattering radiation is to give rise to an intensity-curve which does not agree with that given by Planck 's formula , especially for short wave-lengths .
Absorption and scattering of radiation by the sun 's atmosphere , taken in conjunction with effects of self-illumination , constitutes a problem analogous to that just considered for the earth 's atmosphere .
By making a com- parison between the calculated variation of intensity of radiation of different wave-lengths over the solar disc and the results of observation it will be possible to determine from the intensity-curve of the normal solar spectrum outside the earth 's atmosphere the intensity-curve at the radiating layer of the sun .
This corrected curve may then be compared with that given by Planck 's formula , and a closer approximation made to the temperature of the sun tha1i the values now given .
This investigation the writer hopes to be able to deal with in a future
|
rspa_1913_0010 | 0950-1207 | Some electrical and chemical effects of the explosion of azoimide. | 90 | 99 | 1,913 | 88 | Proceedings of the Royal Society of London. Series A, Containing Papers of a Mathematical and Physical Character | Rev. P. J. Kirkby, M. A., D. Sc.|J. E. Marsh, M. A., F. R. S. | article | 6.0.4 | http://dx.doi.org/10.1098/rspa.1913.0010 | en | rspa | 1,910 | 1,900 | 1,900 | 5 | 160 | 4,182 | http://corpora.clarin-d.uni-saarland.de/surprisal/6.0.3/?id=rspa_1913_0010 | 10.1098/rspa.1913.0010 | null | null | null | Electricity | 35.046234 | Thermodynamics | 33.03813 | Electricity | [
-15.157613754272461,
-49.60496139526367
] | ]\gt ; Some Electrical and Chemical Effects of the Explosion of Azoimide .
pressures wompared wumber oecules oectricity 1iberated boding eytic gertainIntroduetio ished sears amount o By Rev. P. J. KIRKBY , M.A. , D.Sc .
, and J. E. MARSH , M.A. , F.RS .
( Received November 23 , 1912 , \mdash ; Read January 16 , 1913 .
) formed by the explosion .
It was found that about molecules of water were formed for every pair of gaseous ions that reached the electrodes , and that the energy required to produce the observed quantity of electricity was extremely small fraction of the energy set free by the explosion .
The present investigation was undertaken to see whether these results would be substantially modified in case of the explosion of azoimide .
The explosion of this gas differs from that of electrolytic gas iu two important particulars from the point of view of these experiments .
In the first place it is disruptive , and secondly it is not productive of water-vapour , whioh with its well-known influence upon the motion of gaseous ions may , by promoting their re-combination , greatly obscure the electrical effects of the explosion .
Jlethod of Besearch.\mdash ; The method consisted in exploding the gas at various low pressures between two electrodes charged to a potential difference and in measuring the quantity of electricity thrown on to one of the electrodes .
Then , the volume of the gas contained between the electrodes being known , and its pressure , it is easy to find the ratio between the number of pairs of gaseous ions that find their way to the electrodes and the total number of molecules of the gas disrupted .
Preparation of the \mdash ; The gas was generated oy admitting dilute sulphuric acid into an exhausted vessel containing barium azoimide .
The latter was prepared in the following way .
Nitrous oxide was passed over sodamide at the temperature 19 C. The product of this reaction was dissolved water , and excess of acid was added to it .
From this solution the azoimide was distilled into barium hydroxide , forming barium azoimide , the excess of barium hydroxide was precipitated by carbon dioxide , and the solution after filtering was evaporated to dryness .
The residue was redissolved in water to remove a small amount of carbonate , and on evaporation the pure salt was obtained , which after drying was analysed ; * C. E. HaseIfoot and P. J. Kirkby , ' Phil. Mag October , 1904 .
and Effects of the Explosion of Azoirnide .
91 .
of the salt gave .
of , from which numbers the percentage of barium was found to be calc .
Description of the \mdash ; The salt having been thus prepared , about a gramme was placed in a small vessel , illustrated in fig. 1 , which shows the apparatus in diagrammatic form .
is a drying vessel containing calcium chloride , is a vessel for oeceiving the gas and I is a -tube manometer , which when the tap was opened was in connection with the little explosion chamber S. The tube was connected with a Fleuss oilpump .
To generate the gas , normal solution of sulphuric acid in excess of i the salt in was placed in the funnel , and with the taps open except .
FIG. 2 .
the air in was pumped out ; was then closed and the sulphuric acid admitted through , and the reaction having been accelerated by surrounding with hot water , the gas produced was dried in , colleoted in and sometimes pressed back into for further drying .
Before an experiment was exhausted by the pump and azoimide admitted and then immediately exploded .
The object of the tap was to economise the gas .
The explosion chamber , which consisted principally of two co-axial cylinders separated by ebonite , is illustrated in fig. 2 , drawn to scale , which represents a section of it by a plane through the axis of the cylinders .
The shaded parts of the diagram represent ebonite : is the end of a glass tube leading to the apparatus just described , is a brass tube leading to the pace sbetween tinders.inders , which wrass wnother beans oocks ofebonite through which tnner cinder passed , rass rings cirkby aarsh S merely , to prevent the ebonite from being displaced by the explosion .
The spark-gap is between the thick aluminium wires and , which are fixed in an ebonite sleeve fitting the tubes , accurately .
All the joints were made with black elastic glue .
The outer diameter of the inner tube was cm .
, and the inner diameter of the outer tube was .
The length of the outer tube was cm .
Hence the volume between the electrodes was Electrical Arrangenents.\mdash ; These were very simple .
The outer cylinder was connected to one of the Oxford City mains voltage about 105 ) , and the inner through a low resistance ballistic D'Arsonval galvanometer to the other main .
The spark-gap terminals and were connected to the ends of a small induction coil .
Method of Experiment.\mdash ; The explosion chamber was exhausted by the oil pump to as low a pressure as possible .
( The " " vabuum\ldquo ; attained was about 2 mm. or less , most of the residual pressure being most probably due to water-vapour .
) Then the gas was admitted from the adjoining chamber and exploded , and the resulting throw of the galvanometer determined .
It was verified that no part of the throw was due to the sparking .
Results.\mdash ; The results of three series of experiments are given iu the following tables , " " series\ldquo ; being a number of experiments carried .
out continuously in the order given upon the same sample of gas .
In every case recorded in the tables the difference of potential of the cylinders was nearly 105 volts .
Notation of the Tables.\mdash ; pressure of the gas in millimetres of mercury .
observed quantity of electricity in micro-coulombs .
number of molecules of gas exploded divided by the number of pairs of ions that reach the electrodes .
( It is easy to prove that by means of the well-known equation No , where is the number of molecules of a gas in 1 .
at 760 mm. pressure and temperature , and is the charge ( on an electron in electrostatic units ; for the volume of gas exploded between the electrodes was ) Previous to the series of experiments in Table I the gas had been dried ( in the vessel of fig. 1 ) by contact with calcium chloride for 24 hours .
The first explosion at the pressure 151 mm. produced much more electricity 1912 .
] Chemical Effects of the Explosion of Table I. than the rest , and seven times the amount produced by the third explosion under apparently the same conditions .
It is impossible to attribute this to any extra dryness ; it is an instance of a curious phenomenon repeatedly observed , consisting in the production , not necessarily at the first explosion , ' of an abnormal amount of electricity for no apparent reason .
Each of the ' three tables given shows an instance of it.* Thus in Table II at the pressure 82 mm. the value of is 59 , and in Table III , pressure 214 mm. , the value of is 87 .
In both these latter cases the throw of the galvanometer was so large that only a estimate , noted as less than the true value , was possible .
Table II gives another series of experiments upon azoimide after it had been allowed to remain a few minutes over phosphorus pentoxide in a little Table II .
* The same effect was observed in the explosion of ( loc. and though this was thought to be due to a higher degree of dryness , yet prolonged attempts to dry the gas wholly failed even approximately to reproduce the greater quantities of electricity than ither cases Ithough , exhibit arough constancy iindependent oKirk Marsh .
VeSsel between tbservations recorded iable Iuter cinder positive that this additional drying made no perceptible difference , pressure .
This table also appears to show that at the lower pressures more electricity resulted from an explosion when the outer cylinder was negative than when it was positive .
This latter conclusion is also supported by Table , in which the values of , when the outer cylinder was negative descend from ) to , which last agrees with the values of in Table II corresponding to a negative outer cylinder .
It does not seem possible to account for this conclusion by means of any known effects .
If the were lower and the inner cylinder much smaller it would be easy to do so .
For in that case , if the inner cylinder were positive , the negative ions in moving towards it would pass through the intense field of force surrounding it and so would generate others by collision ; whereas , if the inner cylinder were negative , the positive ions in passing through the similarly intense field would produce no appreciable similar effect .
* In the present case , however , the field of force was of the same order of intensity between the cylinders .
Its value at the inner cylinder was 236 volts per centimetre , and at the r186 .
Now , for a given ratio of electric force to pressure , the number of ions generated by the collisions of an electron per centimetre of its motion is proportional to the pressure of the gas .
It is clear , therefore , that if the increase in the values of at the lower pressures , when the outer cylinder was negative , were due to collision effects , aggravated by the abnormal condition of the gas , an increase of the same order would have been observed at the lowest pressures with a positive outer cylinder .
In fact , in some cases the ratio of electric force to pressure near the outer cylinder , when that cylinder was positive and no increase in the value of was observed , exceeded the same ratio near the inner cylinder when , the inner cylinder positive , striking increase was observed .
( See Table II , pressures 20 , 11 , where the ratio in question , applying to the region close to the positive electrode , through which all gative ionS had to pass , was 12 and 17 Effeet of Introducing a Resistance.\mdash ; The effect of a resistance between one end of a battery and one of the cylinders is shown in Table III .
* J. S. Townsend , 'Ionisation of Gases by Collision , ' p. .
; or P. J. Kirkby , 'Phil .
Mag February , 1902 .
Townsend , ibid. , p. 18 .
1912 .
] Chemical Bffects of the Explosion of Azoirnide .
Table III .
( Outer cylinder connected through resistance to the positive pole .
) The effect is very marked .
The explanation is , probably , that the electric force between the cylinders is reduced to such an extent during the passage of the current , when there is a considerable resistance , that the of recombination of ions is greatly increased , and the quantity of electricity that reaches the electrodes thereby greatly diminished .
In fact , the differ .
ence of potential of the electrodes is diminished by CB volts when the current amperes is flowing ; and it is not difficult to show that CR approximated to the voltage of the battery , i.e. the voltage difference of the cylinders when no current was passing .
To show this , let us suppose that the quantity micro-coulombs observed was carried in time by a stream of ions of constant density and constant velocity to one electrode .
Then , if denotes the distance between the electrodes , and .
Now , the electric force under which the ionoe moved was , roughly , .
Hence where is the velocity of the ionic stream moving under 760 mm. pressure and 1 volt per centimetre .
Therefore .
( ) This equation since ) makes the ratio equal to , respectively , in the case of the first three observations of Table III .
Now is probably greater than , and cannot be much less than , unity* ; therefore is substantially less than V. This result has been obtained on the assumption that the current was constant and the field of force undisturbed by the flow of ions .
But the conclusion at least indicates that in the actual case CR * See Sir J. J. Thomson 's ' Conduction of Electricity through Gases .
' difference oinders seduced taccount fbecame course oischarge , irkby aarsh Slectrical values of Q. Hence the smaller values of observed when a resistance was in the circuit may be attributed to the reduced difference of potential between the electrodes , which permitted a greater amount of recombination to take place .
But it does not follow that when the resistance was absent there was no recombination .
For the above equation ( a ) shows that the current , if assumed to be uniform , was throughout of the order of nitude 1 when so that it was quite large enough to produce polarisation of the electrodes , involving recombination .
eneral Conclusion.\mdash ; The general result of these experiments is to show that the number of pairs of ions generated by an explosion of azoimide is exceedingly small compared with the number of molecules dissociated by the explosion .
The observed proportion is so small ( always less than 1 to 100,000 ) as to lead to the conclusion that dissociated atoms do not in general carry electrostatic charges ; for , if in general they are charged , it is difficult to how tion could be so complete in such a strong field of force as in the present case\mdash ; a field which would impart a high velocity to such electrified atoms .
The same conclusion can be drawn from the experiments already alluded to on the electrical effects of exploding electrolytic gas in a field of force .
* In fact the latter effects are not so great as the effects of exploding azoimide .
What then is the explanation of the formation of .
ions during the explosion The explanation is probably to be foumd in the mutual collisions of the dissociated atoms as they unite in forming the product of the explosion .
The energetic nature of those collisions is shown by the evolution of heat .
Under favourable conditions of impact , including a sufficiently high relative velocity , ionisation may take place , just as Iownsend has shown that a positive ion , which is either of atomic or molecular dimensions , is capable under such conditions of impact of breaking up a molecule which it strikes into ions .
* See also P. J. Kirkby , 'Roy .
Soc. Proc 1911 , , vol. 86 , where a definite proof is given that separated atoms of oxygen are uncharged .
comparison of the two greatest effects observed in exploding and makes the number of ions , per gramme-molecule of each gas exploded , just 100 times greater in azoimide than in electrolytic .
It is possible , however , that the battery used in the experiments upon the latter gas may have been earthed through a resistance ( 100,000 ohms or less ) , in which case the electrical effects may have been greater than they were observed to be .
Townsend , ' Ionisation of Gases by Collision , ' p. 38 .
1912 .
] Chemical Effects of the Explosion of Azoimide .
Lowest Pressure of Bxplosion.\mdash ; The lowest pressure at which azoimide was observed to explode in the apparatus described above was 11 mm. No explosion took place at pressures of 10 mm. or less .
Observations made with different specimens of the gas were very consistent in this respect .
Hence mm. was very nearly the pressure-limit of explosions .
This limit would probably be lower still for pure azoimide .
For , in view of the imperfect evacuation of the oil pump , it cannot be asserted that more than 80 per cent. of the gas at the pressure 10 mm. was azoimide .
In this respect azoimide presents a sharp contrast with electrolytic gas , which does not explode at pressures much below 80 contrast that illustrates the highly explosive nature of azoimide .
This striking difference might , perhaps , be modified if electrolytic gas were exploded when not drier than the azoimide was .
But the contrast in any case would be great , for electrolytic gas was found to combine under the electric discharge with perfect regularity at the pressure 39 mm. , so that even when mixed with water-vapour its pressure of explosion must exceed 39 mm. It is natural to conclude from these two cases that all explosive gases cease to explode even partially when their pressure is below a certain critical pressure , depending , of course , upon their temperature .
The explanation is probably that the heat radiated from the molecules , formed as the product of the explosion in that region of where the explosion originates , plays an important part in , the adjacent portions of the gas , namely , by raising its temperature and thus facilitating its disintegration by molecular or atomic collisions .
If that is the case , when the pressure is reduced below a certain point , the molecules will be so far apart that the intensity of this radiation , diminishing as the inverse square of the distance , cease to have the same effect , and the reaction will not be propagated .
It should be added that the least pressure at which explosion occurs seems to depend partly on the apparatus and partly .
on the manner of starting the explosion .
Thus in one apparatus consisting of two brass discs about 7 cm .
in diameter , and insulated from each other by an ebonite ring about 5 mm. thick , the azoimide did not explode by the heating of a platinum wire fixed between the discs until a pressure of over 200 mm. was reached , when the gas exploded with great violence , wrecking the apparatus and destroying the adjacent vessel in which a supply of azoimide had been collected over mercury Absorption of Azoimide by Phosphorus Pentoxide.\mdash ; The first efforts to dry * Haselfoot and Kirkby , P. J. Kirkby , ' Phil. Mag January , 1906 , p. 182 .
aJso absorbed azoimide wreat rapidity Izoimide isabsorbed bhosphoric acids , into which Pformed bbsorp ished bubstitution oresh pWhen teries oosion einished aheabsorbed.dmitted trying vThis effect , hosphorus pentoxide wICirkby aMarsh .
Formation ozoimide olosion explosion chamber opened , it was found that part of the gold surface had been attacked .
In the part which lay in the direct line of fire from the ignition point the surface was covered with a dark-coloured deposit .
The rest of the gold was .
The small amount of the deposit rendered a quantitative analysis impracticable .
A little scraped off the side was found to be transparent and crystalline when examined under the microscope .
When held in the flame it exploded with a green-coloured flash .
It was apparently not acted on by water , but hydrochloric acid dissolved it .
This solution was found to contain azoimide , which was recognised by its characteristic smell and by giving , when into silver nitrate solution , a white explosive precipitate .
The solution did not contain gold , but copper in the cupric state was recognised by the ordinary tests .
A cupric azoimide is thus formed in the explosion chamber .
It seemed surprising that an explosive substance could be formed under such conditions and could survive after a long series of subsequent explosions .
A hydrated cupric salt of azoimide has been obtained by Curtius ( the discoverer of azoimide ) and Rissom .
* It is precipitated on mixing a solution of a salt of azoimide with a solution of a cupric salt , and has a reddishbrown colour .
Curtius and Rissom describe it as crystalline and highly explosive , even when moist , " " eines der gefahrlichst zu handhabenden Salze des Stickstoffwasserstoffs It was not obtained by them free from water , even when kept in a desiccator .
Azoimide does not attack gold , nor when dried by calcium chloride does it appreciably attack clean brass .
But in presence of air and water-vapour it attacks brass with the formation , after a few hours , of a black deposit which explodes with a green flash and dissolves in ammonia with a blue colour .
This deposit is undoubtedly a cupric azoimide , but , as formed in this way , it is not crystalline and transparent , but amorphous and opaque , very different from the deposit in the sion chamber .
Copper is also 'Journ . .
Chem. ' ( 2 ) , vol. 58 , p. 261 .
1912 .
] Effects of the Explosion of Azoimide .
attacked by moist azoimide vapour , giving the same black deposit .
Zinc also is not attacked by dry azoimide , but in the moist gas it gives a white deposit which explodes with a bluish-white flash .
We hay now to consider how the cupric azoimide comes to be formed in the explosion chamber .
In the first place , it is unlikely that the formation is due to the action of the azoimide before explosion , since azoimide does not attack gold and hardly attacks brass when dry.* Nor is it likely that the gold helped the azoimide to attack the brass ; otherwise the whole of the gold surface would have been attacked , whereas a considerable portion was ; bright and free from deposit .
Moreover , no diminution in volume was noticed when the charges of azoimide were admitted into the explosion chamber .
For the same reasons the explanation is precluded that the gold coating was ripped off by the first explosions , and that the azoimide then * : attacked the exposed brass .
The deposit , moreover , was crystalline , while that formed slowly on brass by exposure to moist azoimide was found to be amorphous , though it is , perhaps , possible that an amorphous deposit formed in the first instance might be hammered into crystals by a series of explosions .
It seems , on the whole , most probable that the copper azoimide was S formed during the actual explosions , and itself escaped explosion owing to its comparative stability , and to the fact that it was in contact with metal which would easily absorb the energy of subsequent explosions .
From the above description given by Curtius and Rissom of the hydrated copper salt , it would appear that the salt obtained by explosion is much more stable than the one they observed , and this may be due to its the anhydrous salt .
If , then , copper azoimide is formed by the explosions , it follows that a fair degree of stability belongs to the group .
Hence it is not unlikely that the first stage of the explosion is to break up into and , some of the groups escaping further decomposition by being driven through the gold into combination with the copper .
It might be supposed that the groups , being the same as the electrolytic chemical ions , were the cause of the electrical effect .
But this is improbable , since the quantity of copper azoimide formed , though small , was much larger than could be accounted for by the very slight electrical effect on the assumption that the atomic charge .
* An absorption of azoimide was noticed by us when a brass explosion chamber was used , instead of the gilded one .
This absorption was , no doubt , due to the presence of oxide or other impurity on the brass .
No absorption was ever noticed with the gilded brass even after many explosions had been made with it , when some of the gold surface may have been torn off .
dVOL .
LXXXVIIL\mdash ; A I
|
rspa_1913_0011 | 0950-1207 | On a new method of measuring the torque produced by a beam of light in oblique refraction through a glass plate. | 100 | 102 | 1,913 | 88 | 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.1913.0011 | en | rspa | 1,910 | 1,900 | 1,900 | 2 | 40 | 1,039 | http://corpora.clarin-d.uni-saarland.de/surprisal/6.0.3/?id=rspa_1913_0011 | 10.1098/rspa.1913.0011 | null | null | null | Optics | 30.069839 | Tables | 27.709271 | Optics | [
34.58324432373047,
-39.61074447631836
] | ]\gt ; 100 Torquae produced by a Beam On a New Method of suring tTorquae produced by a Beam of Light in Oblique through a Glass Plate .
By GUY BARLOW , D.Sc .
( Communicated by Prof. J. H. Pointing , F.R.S. Received November 29 , 1912 , \mdash ; 7 Read January 16 , 1913 .
) In a recent paper*an experiment was described in which the torque exerted by a beam of light in passing obliquely through a cube of glass was measured directly by the twist produced in the suspending quartz fibre .
Since the light was incident at a constant angle , about , the resulting torque was constant also , and the method may therefore be termed statical .
Another form of the experiment , which we might call the dynamical method , will now be described .
Consider a parallel beam of light having energy unit length , and let it pass through a parallel plate of glass of thickness and refractive index .
If the angle of incidence is small , the beam be displaced laterally through a distance , and on the assumption that the beam possesses momentum of amount : ( velocity of light ) per unit length , it at once follows that the torque produced should be Hence according to theory the torque is directly proportional to , and always tends to increase .
If the plate has a moment of inertia I and is suspended vertically by a quartz fibre giving a torsion couple per radian , the action of the light will virtually decrease the restoring torque due to the fibre with the result that the natural period of small oscillations , will be altered to , when the plate is traversed by the where .
Hence for the ratio of the periods we find In practice the change in period is very small , so putting we obtain We can regard this result as giving us a new method of verifying the existence of the torque exerted by light , since it will suffice for the purpose if , instead of measuring the torque for any given angle , we compare the value of calculated as above with the value actually observed as obtained from the periods with the beam of light respectively traversing the plate * Barlow , ' Roy .
Soc. Proc 1912 , , vol. 87 , p. 1 .
Torque produced by Light in Oblique Refraction .
and out off .
Further verification of the torque may seem unnecessary , but as this method possessed some novelty I have thought it worth while to make the experiment which is here described .
The above calculation shows that should be proportional to , the energy corresponding to the volume traversed in the plate .
The former apparatus using a cube of 1 cm .
edge was , therefore , quite suitable for the new experiment .
With the strongest beam available the expected value of was not more than per cent. ; it was therefore evident that this dynamical method could not compare favourably with the statical as regards the accuracy obtainable .
However , the new method possesses the distinct : advantage that no especial care is needed either in adjusting the cross-section of the beam or in setting the angle of incidence .
Theoretically we might irst , hose devices wracticefaces.mitted beakened intensity , ffect beturning tfixed moying asecond braversing tight a S beams give rise to torques also proportional to .
If we take the reflection , coefficient of the glass as for normal incidence it can be shown that the factor must be applied to the expression for if is to refer to the incident beam .
The apparatus used was exactly the same as in the earlier experiment ( lo .
The cube was set normally to the light , and the section of the beam was then reduced to a square of about 9 mm. edge in order to give good clearance .
The experiments were made with hydrogen at a pressure of about 10 cm .
Hg .
in the experimental case , as these conditions were known to be favourable for avoiding the effects of gas action .
To test the elimination of disturbing effects the cube was allowed to come to rest and then exposed to the beam for several minutes , but no appreciable deflection was ever observed .
Small torsional oscillations of the cube were conveniently set up by gently pumping out a little , or by letting a little more in .
The transits of the centre of swing , occurring at intervals of 54 seconds , were observed for an hour and recorded on a chronograph .
Ihese transits consisted of 5 sets of 12 , the sets 1 , 3 , and 6 being taken with the light off , the alternate sets 2 and 4 with the lighl on .
The damping reduced the amplitude to 1 per cent. of its initial } in the course of one hour , so that the time of observation could not be usefully extended .
The mean periods and for the alternate sets were obtained by applying Gauss 's method\mdash ; thus each set gave six independent values of the period .
Finally , was - obtained by taking the .
difference between the mean period for a set with on , Torque pOblique andRefraction after .
light on , and the mean period , with light off , for the sets before and after .
This treatment eliminates any error due to a possible effect of amplitude or temperature variation on the period of the cube .
The torsion head was I rotated so that all four sides of the cube were used in succession as incident faces .
The results are given in the following table:\mdash ; Final mean sec. The energy , measured as in the former experiments , was found to be erg/ cm .
Hence , making the correction for reflections , the theory gives see .
, a value which is in satisfactory agreement with the above value given by the experiment .
|
rspa_1913_0012 | 0950-1207 | The effect of junctions on the propagation of electric waves along conductors. | 103 | 110 | 1,913 | 88 | 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.1913.0012 | en | rspa | 1,910 | 1,900 | 1,900 | 4 | 118 | 2,737 | http://corpora.clarin-d.uni-saarland.de/surprisal/6.0.3/?id=rspa_1913_0012 | 10.1098/rspa.1913.0012 | null | null | null | Fluid Dynamics | 52.62126 | Electricity | 15.005601 | Fluid Dynamics | [
42.769439697265625,
-45.613224029541016
] | ]\gt ; * The Effect of Junctions on the of Blectric Waves along Conductors .
By LORD RAYLEIGH , O.M. , F.R.S. ( Received December 2 , 1912 , \mdash ; Read January 16 , 1913 .
) Some interesting problems in electric wave propagation are suggested by an experiment of Hertz .
* In its original form waves of the simplest kind travel in the positive direction ( fig. 1 ) , outside an infinitely thin conducting cylindrical shell , AA , which comes to an end , say , at the plane Co-axial with the cylinder a rod or wire BB ( of less diameter ) extends to infinity in both directions .
The conductors being supposed perfect , it is required to determine the waves propagated onwards beyond the cylinder on the positive side of , as well as those reflected back outside the cylinder and in the annular space between the cylinder and the rod .
: FIG. 1 .
So stated , the problem , even if mathematically definite , is probably intractable ; but if we modify it by introducing an external co-axial conducting sheath CC ( fig. 2 ) , extending to infinity in both directions , and if we further suppose that the diameter of this sheath is small in comparison with the wave-length ( ) of the vibrations , we shall bring it within the scope of approximate methods .
It is under this limitation that I propose here to consider the present and a few analogous problems .
Some considerations of a more general character are prefixed .
If , be components of electromotive intensity , , those of magnetisation , Maxwell 's general circuital for the dielectric give , ( 1 ) " " Ueber die Fortleitung electrischer Wellen durch Drffite 'Wied .
Ann 1889 , , p. 395 .
' Phil. Trans 1868 ; 'Maxwell 's Scientific Papers , ' vol. 2 , p. 128 .
and two similar equations , and , also wimilar equations , eing telocity oropagation .
Froml 0Lord Eayleigh.unctions o ( 1 ) and ( 2 ) we may derive ; and , further , that , ( 4 ) where .
( 5 ) At any point upon the surface of a conductor , regarded as perfect , the condition to be satisfied is that the vector be there normal .
In what follows we shall have to deal only with simple vibrations in which all the quantities are proportional to , so that may be replaced by It may be convenient to commence with some cases where the waves are in two dimensions only , supposing that , vanish , while , are independent of .
From ( 1 ) and ( 2 ) we have At the surface of a conductorP : : : , , are proportional to the direction cosines of the normal ; so that the surface condition may be expressed simply by , ( 6 ) which , with suffices to determine .
In ( 7 ) .
It will be seen that equations ( 6 ) , ( 7 ) are identical with those which apply in two dimensions to aerial vibrations executed in bounded by walls , then denoting velocity potential .
When is known , the remaining functions follow at once .
It may be remarked by the way that the above analogy throws light upon the question under what circumstances electric waves are guided by conductors .
Some high authorities , it would seem , regard such guidance as uing in all cases as a consequence of the boundary condition fixing the direction of the electric force .
But in Acoustics , though a similar condition holds good , there is no guidance of rial waves round convex surfaces , and it follows that there is none in the two-dimensional electric vibrations under consideration .
Near the concave surface of walls there is in both cases 1912 .
] Propagation of Electric Waves along Conductors .
a whispering gallery effect .
* The peculiar guidance of electric waves by wires depends upon the conductor being encircled by the magnetic force .
No such circulation , for example , could ensue from the incidence of plane waves upon a wire which lies entirely in the plane containing the direction of propagation and that of the magnetic force .
Our first special application is to the extreme form of Hertz 's problem ( as modified ) which occurs when all the radii of the cylindrical surfaces concerned become infinite , while the differences CA , AB remain finite and indeed small in comparison with .
In fig. 2 , then represent ..\mdash ; - . . .
FIG. 2 .
planes perpendicular to the plane of the paper and the problem is in two dimensions .
The two halves , corresponding to plus and minus values of are isolated , and we need only consider one of them .
Availing ourselves of the analogy , we may at once transfer the solution given ( after Poisson ) in ' Theory of Sound , ' S264 .
If the incident wave in CA be represented by and that therein reflected by , while the waves propagated along , AB be denoted by , we have ( 8 ) AB and .
( 9 ) The wave in AB is to be regarded as propagated onwards round the corner at A rather than as reflected .
As was to be anticipated , the reflected wave is smaller , the smaller is AB .
It be understood that the validity of these results depends upon the assumption that the region round A through which the waves are irregular has dimensions which are negligible in comparison with 'Phil .
Mag 1910 , vol. 20 , p. 1001 ; ' Scientific Papers , ' vol. 6 , p. 617 .
Lord Rayleigh.unctions oimpler example iketched i where f : FIG. 3 .
various lines represent planes or cylindrical surfaces perpendicular to the paper .
One bounding plane is unbroken .
The other boundary consists mainly of two planes with a transition at AB , which , however , may be of any form so long as it is effected within a distance much less than .
With a notation similar to that used before , may denote the incident positive wave and the reflected wave , while that propagated onwards in is .
We obtain in like ma1mer , ( 10 ) When AB vanishes we have , of course , .
A little later we shall consider the problem of fig. 3 when the various surfaces are of revolution round the axis of Leaving the two-dimensional examples , we find that the same general method is applicable , always under the condition that the region occupied by irregular waves has dimensions which are small in comparison with Within this region a simplified form of the general equations avails , and thus the difficulty is turned .
An increase in means a decrease in .
When this goes far enough , it justifies the omission of in equations ( 1 ) , ( 2 ) , ( 3 ) ) .
Thus become the derivatives of a simple potential function , which itself satisfies ; that is , the electric forces obey the laws of electrostatics .
Similarly are derivatives of another function satisfying the same equation .
The only difference is that may be multivalued .
The magnetism is that due to steady electric currents .
If several wires meet in a poin , the total current is zero .
This expresses itself in terms 1912 .
] Propagation of Electric Waves along Conductors .
107 : 3 virtue oanother bonditions which.argins oegion iorming tutions which aarts adistance oation between tations.\ldquo ; ethod tonsistsides fregion oarity , ccommodating t ection)onsidered iformer pndent vressi tectric conditionsi oethod iemconductors aution.round zthough titation iication t ; ( 12 ) also and vanish .
In the present case we have for the negative side , where there is both a direct and a reflected wave , , ( 13 ) where is the distance of any point from the axis of symmetry , and are arbitrary constants .
Corresponding to ( 13 ) , .
( 14 ) In the region of regular waves on the positive side there is supposed to be no wave propagated in the negative direction .
Here accordingly , ( 15 ) V , ( 16 ) being another constant .
We have now to determine the relations between the constants , hitherto arbitrary , in terms of the remaining data .
For this purpose consider cross-sections on the two sides both near the origin and yet within the regions of regular waves .
The electric force as expressed in ( 13 ) , ( 15 ) is purely radial .
On the positive side its integral between the radius of the inner and that of the outer conductor is , with omission of having the value proper to the section .
On the negative side the corresponding integral is ' Phil. Mag 1897 , vol. 44 , p. 199 ; 'Scientific Papem , ' vol. 4 , p. 327 .
dentified wnity Airst ration isrecognise these turther theconsider tntermediate rwhere ebeing tadius onner conductor aLord Reigh . .
( 17 ) In like manner the magnetic force in ( 14 ) , ( 16 ) is purely circumferential .
And the circulations at the two sections are as and H2 .
But since these circulations , representing electric currents which may be treated as steady , are equal , we have as the second relation\mdash ; .
( 18 ) The two relations ( 17 ) , ( 18 ) give the wave propagated onwards and that reflected in terms of the incident wave .
If , we have of course , If we suppose all great and nearly equal and expand the logarithms , we fall back on the solution for the two-dimensional case already given .
In the above the radius of the outer sheath is supposed uniform throughout .
If in the neighbourhood of the origin the radius of the sheath changes from to , while ( as before ) that of the inner conductor changes from to , we have instead of ( 17 ) , , ( 19 ) while ( 18 ) remains undisturbed .
In the logarithmic functions are proportional to the reciprocals of the electric capacities of the system on the two sides , reckoned in each case per unit of length .
From the general theory given in the paper referred to we may that this substitution suffices to liberate us from the restriction to symmetry round the axis hitherto .
The more general functions which then replace on the two sides must be chosen with such coefficients as make the circulations of magnetic force equal .
The generalisation here indicated applies equally in the other problems of this paper .
In Hertz 's problem , fig. 2 , .
the method is similar .
In the region of regular waves on the left in CA we may retain ( 13 ) , ( 14 ) , and for the regular waves on the right in CB we retain ( 15 ) , ( 16 ) .
But now in addition for the regular waves on the left in AB , we have , ( 20 ) : : 1912 .
] Propagation of Electric Waves along Conductors .
109 Three conditions are now required to determine in terms of We shall denote the radii taken in order , viz. , , SAA , , by respectively .
As in ( 17 ) , the electric forces give .
( 22 ) The magnetic forces yield two equations , which may be regarded as expressing that the currents are the same on the two sides along BB , and that , since the section is at a negligible distance from the insulated end , there is no current in AA .
Thus .
( 23 ) From ( 22 ) and ( 23 ) , ( 24 ) .
( 25 ) If exceeds but little , tends to vanish , while and approach unity .
Again , if the radii are all great , ( 24 ) , ( 25 ) reduce to , ( 26 ) as already found in ( 8 ) , ( 9 ) .
The same method applies with but little variation to the more general problem where waves between one wire and sheath divide so as to pass along several wires and sheaths ( etc. , always under the condition that the whole region of irregularity is negligible in comparison with the wave-length .
* The various wires and sheaths are , of course , supposed to be continuous .
With a similar notation the direct and reflected waves along the first wire are denoted by , and those propagated onwards along the second , third , and other wires by , etc. The equations are\mdash ; , ( 27 ) It is hardly necessary to detail obvious particular cases .
The success of the method used in these problems depends upon the assumption of a great wave-length .
This , of course , constitutes a limitation , but it has the advantage of eliminating the irregular motion at the junctions .
* This condition will usually suffice .
But extreme cases may be proposed where , in spite of the smallness of the intermediate region , its shape is such as to entail natural resonances of frequency agreeing with that of the principal waves .
The method would then fail .
110 Hon. R. J. Strutt .
Duration of Luminosity of [ Dec. 19 , In the two-dimensional examples it might be possible to pursue the approximation by determining the character of the irregular waves , ab least to a certain extent , somewhat as in the question of the correction for the open end of an organ pipe .
Duration of Luminosity of Electric Discharge in Gases Vapours .
By the Hon. R. J. STRUTT , F.R.S. , Professor of Physics , Imperial College of Science , South Kensington .
( Received December 19 , 1912 , \mdash ; Read January 16 , 1913 .
) S1 .
Introduction .
electric discharge produces luminosity in any gas or vapour through which it passes .
The question presents itself , Does the luminosity persist after the current has ceased , or does it stop immediately ?
A full answer is likely to be of great importance in unravelling the cause and mechanism of the luminosity .
There are existing observations bearing on the subject , but these are somewhat scattered in the literature , and , so far as I am aware , their mutual relations have not been pointed out .
It is hoped in this paper to do something towards systematising and extending them .
The most conspicuous phenomena in this connection are the various forms of afterglow which have been discussed in previous papers .
* But these are not really relevant to the present subject , for they are due to secondary causes of a chemical nature .
Some of them , produced in gaseous mixtures containing oxygen , are due to the interaction of ozone with other substances present .
Others , again , are connected with the formation of an active modification of nitrogen .
In none of these cases can after-luminosity be considered continuous with the luminosity of the discharge which produced it .
For it is always much less brilliant , even at first , and always has a quite different spectrum .
Several experimenters have found , by examining the leyden spark with a rotating mirror , that its luminosity may persist much longer than the 'Phys .
Soc. Proc 1910 , vol. 23 , pp. 66 , 147 ; 1911 , vol. 24 , p. 1 ; 'Roy .
Soc. Proc 1911 , , vol. 85 , pp. 219 , 377 , 633 ; 1912 , vol. 86 , pp. , 106 , 262 , ; 1912 , vol. 87 , pp. 179 , 302 .
|
rspa_1913_0013 | 0950-1207 | Duration of luminosity of electric discharge in gases and vapours. | 110 | 117 | 1,913 | 88 | 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.1913.0013 | en | rspa | 1,910 | 1,900 | 1,900 | 2 | 180 | 3,738 | http://corpora.clarin-d.uni-saarland.de/surprisal/6.0.3/?id=rspa_1913_0013 | 10.1098/rspa.1913.0013 | null | null | null | Atomic Physics | 35.825203 | Thermodynamics | 26.334453 | Atomic Physics | [
6.021728038787842,
-55.020179748535156
] | 110 Hon. R. J. Strutt .
Duration of Luminosity of [ Dec. 19 , In the two-dimensional examples it might be possible to pursue the approximation by determining the character of the irregular waves , at least to a certain extent , somewhat as in the question of the correction for the open end of an organ pipe .
Duration of Luminosity of Electric Discharge in Gases and Vapours .
By the Hon. B. J. Strutt , F.R.S. , Professor of Physics , Imperial College of Science , South Kensington .
( Received December 19 , 1912 , \#151 ; Read January 16 , 1913 .
) S 1 .
Introduction .
The electric discharge produces luminosity in any gas or vapour through which it passes .
The question presents itself , Does the luminosity persist after the current has ceased , or does it stop immediately ?
A full answer is likely to be of great importance in unravelling the cause and mechanism of the luminosity .
There are existing observations bearing on the subject , but these are somewhat scattered in the literature , and , so far as I am aware , their mutual relations have not been pointed out .
It is hoped in this paper to do something towards systematising and extending them .
The most conspicuous phenomena in this connection are the various forms of afterglow which have been discussed in previous papers.* But these are not really relevant to the present subject , for they are due to secondary causes of a chemical nature .
Some of them , produced in gaseous mixtures containing oxygen , are due to the interaction of ozone with other substances present .
Others , again , are connected with the formation of an active modification of nitrogen .
In none of these cases can the after-luminosity be considered continuous with the luminosity of the discharge which produced it .
For it is always much less brilliant , even at first , and always has a quite different spectrum .
Several experimenters have found , by examining the leyden jar spark with a rotating mirror , that its luminosity may persist much longer than the * 'Phys .
Soc. Proc. , * 1910 , vol. 23 , pp. 66 , 147 ; 1911 , vol. 24 , p. 1 ; 'Boy .
Soc. Proc. , ' 1911 , A , vol. 85 , pp. 219 , 377 , 533 ; 1912 , vol. 86 , pp. 56 , 105 , 262 , 529 ; 1912 , vol. 87 , pp. 179 , 302 .
Ill 1912 .
] Electric Discharge in Gases and Vapours .
electric current which gave rise to the luminosity.* This effect is observed when the electrodes are formed of a metal more or less easy of volatilisation .
If a non-volatile metal like platinum is used , the spark current passes only through air , and no persistence of luminosity is observed .
For this reason such sparks are suitable as a source of light for the photography of flying bullets .
So far I have referred to the case of negligible inductance in the spark circuit .
If the inductance is considerable , the ( alternating ) current is , of course , prolonged thereby .
In this case new streams of luminous vapour come off from the volatile electrodes at each oscillation , and add their effect to that of the luminous vapour already accumulated there .
These are the " streamers .
" The term is conveniently extended to the case of an almost non-inductive circuit .
Here there are , of course , still a number of streamers ; but they cannot be separated at any practicable speed of the mirror , and therefore appear to form one single stream of luminous vapour from each electrode .
The streamers , and the persistence of luminosity , can also be shown by a method due to Hemsalech.f He uses a coil with an iron core ; the hysteresis losses in the core reduce the spark to one single oscillation ; and the duration of the luminosity is observed by blowing the luminous vapour away by a rapid current of air .
The luminous track can be followed for an appreciable distance , and spectroscopic observations show which lines last longest .
The connection of the streamers with another known phenomenon does not seem to have been explicitly pointed out .
This is the so-called " aureole " of the mercury vapour lamp.$ If an arc discharge is passed between mercury electrodes in an exhausted vessel , intense luminosity is produced , and enough heat developed to raise considerable vapour pressure over the mercury electrodes .
If provision is made for allowing the mercury vapour to distil away into a cooled receiver , the moving stream of vapour is found to carry its luminosity with it .
The intensity diminishes as the vapour gets further from the lamp , owing to the lapse of time during its journey ; but it is important to notice that there is perfect continuity in intensity from the * Boys , 'Nature , ' vol. 47 , p. 416 , 1893 ; l Schuster and Hemsalech , 'Phil .
Trans. , ' 1900 , A , vol. 193 , p. 189 ; Schenck , 'Astrophys .
Journ. , ' 1901 , vol. 14 , p. 116 ; Milner , 'Phil .
Trans. , ' 1909 , A , vol. 209 , p. 71 .
+ 'Comptes Rendus , ' 1910 , vol. 150 , p. 1743 ; 1910 , vol. 151 , p. 220 .
X Stark and Reich , ' Phys. Zeit.,5 1903 , vol. 4 , p. 324 ; Stark , ' Phys. Zeit .
, ' 1903 , vol. 4 , p. 440 ; Stark , ' Ann. d. Pliys.,5 1904 , vol. 14 , p. 522 ; Stark , Retschinsky , and SchnaposnikofF , 'Ann .
d. Phys. , ' 1905 , vol. 18 , p. 231 ; W. Matthies , 1910 , 'Verh .
d. Deut .
Phys. Gesell.,5 1910 , vol. 12 , p. 754 .
112 Hon. R. J. Strutt .
Duration of Luminosity of [ Dec. 19 , point where it leaves the lamp until it is completely extinguished.* Immediately after it has left the region where the arc is passing , it is not appreciably less luminous than in the arc .
How far the luminosity will travel depends on the size of the tube , and the resulting velocity of flow .
Under favourable conditions , the luminosity may be made to travel 50 cm .
, or even more .
If the channel is anywhere less than about 3 mm. diameter , the luminosity hardly travels any appreciable distance from the arc .
The mass of mercury distilled in a few minutes amounts to several grammes , and consequently the linear velocity of the rarefied vapour must be very great It is estimated by Stark as of the order of 3 x 104 cm .
per second .
This method of observing the duration of the luminosity is much more advantageous than the preceding , where it can be applied .
Great practical difficulties stand in the way of applying it to cases other than mercury , though they may , perhaps , be overcome in some instances .
S 2 .
New Method of Observing the Streamers .
The principle is as follows : The electrodes are wires of the metal under investigation , aa } bb , fig. 1 .
They are inserted into the opposite ends of a Fig. 1 .
glass tube c of 1*5 or 2 mm. internal diameter ( Sprengel tubing ) so that the ends are about 5 mm. apart .
A hole d is blown in the side of the tube , between the ends of the wire , and when the jar spark passes , the metallic vapour formed is blown out of this hole , and out of the region of electric force between the electrodes .
The volume of vapour formed is not enough * Under some experimental conditions there are alternations of light and darkness .
These are due , as Matthies has pointed out , to alternations of higher and lower pressure produced by hydrodynamical causes .
1912 .
] Electric Discharge in Gases and Vapours .
113 to distinctly exude from the hole at atmospheric pressure ; hut the tube is arranged inside a receiver e which can be exhausted , and the effect becomes conspicuous at a pressure of a few millimetres of mercury .
The vapour is shot out of the side hole in a distinct jet several millimetres in length , visible by its own luminosity , which is seen to be continuous with that of the spark .
The jar is charged by an induction coil and an air gap is used in series with the apparatus of fig. 1 .
When the metal is difficult to obtain in the form of wire , iron wires may be used , and a fragment of the volatile metal under investigation introduced into the gap , and in contact with the end of one wire .
The same method is applicable to non-metals , such as sulphur and iodine .
The apparatus must be placed with d upwards in this case .
At pressures of a few millimetres of mercury the luminous jet is of small volume , the vapour making its way out in a comparatively narrow and sharply defined stream .
The outlines of the mass of luminous vapour are curiously hard , and not infrequently ragged and irregular .
Under these conditions , the residual air in the spark gap is driven out along with the metallic vapour , and gives the characteristic greenish-yellow afterglow , due to the reaction of ozone with nitric oxide .
This luminosity ts far more persistent than that due to the metal , and is perceptible right across the vessel , as a prolongation of the stream of metallic vapour .
The metallic glow is much the more brilliant , during the short time for which it lasts .
In fig. 2 the shading a represents the luminous metallic Fig. 2 .
vapour , b the greenish-yellow afterglow , which flattens itself out against the glass wall , as shown .
As the air pressure is reduced the greenish-yellow afterglow just mentioned disappears , and the metallic glow spreads out and becomes more diffuse .
At moderate vacua , say 1 mm. or less pressure , it issues almost 114 Hon. R. J. Strutt .
Duration of Luminosity of [ Dec. 19 , equally over a wide angle from the aperture ; and its outline is rounded ( fig. 3).* At high vacua the vapour may expand enough to fill nearly the whole of a 300 c.e. flask : but in this case the luminosity is diluted to extreme faintness .
\gt ; \#166 ; ! .
A t'-irr* ' ; : Fig. 3 .
At these low pressures it is difficult or impossible to prevent stray electrical discharges through the outer vessel , of the kind called ( not very correctly ) electrostatic .
These give rise to a faint luminosity of their own , particularly in the connecting tubes leading to the pump .
It is certain , however , that the metallic glows described are not connected with this , since there are no stray discharges when air is present to a pressure of a few millimetres ; and the phenomena can be traced continuously from that stage .
S 3 .
Effects with Vapours of Various Elements .
The vapours investigated all gave line spectra exclusively : \#151 ; Sodium.\#151 ; Bright yellow glow .
Could be made to fill large volume .
Thallium.\#151 ; Bright green glow .
Conspicuous .
Calcium.\#151 ; Good orange glow .
Zinc and Cadmium.\#151 ; Well developed , greenish glows .
Mercury.\#151 ; Amalgamated copper electrodes were used , which , however , only carried enough mercury for a short time .
Glow much more brilliant and voluminous than in most other cases , on account of the brilliancy of the mercury discharge and the volatility of the metal .
Colour , greenish .
Arsenic.\#151 ; Dull yellow glow , not very striking .
Glass soon obscured by the deposited metal .
Magnesium.\#151 ; An interesting effect wTas observed in this case .
As the surrounding air was removed , the glow which first emerged was bright green .
As , however , the pressure diminished , a blue glow was seen at the base of the luminous cloud ( see fig. 3 ) , where x is the blue portion , surrounded by the outer green envelope y. The glow at this stage was focussed on the slit of a spectroscope , and it was seen that the luminosity of the blue line 4481 from the side hole extended a short distance only , while the green * The significance of the shading is not the same in fig. 3 as in fig. 2 .
For explanation of the different shading of the inner part of the mass of metallic vapour in fig. 3 see below .
1912 .
] Electric Discharge in Gases and Vapours .
triplet 5172 extended two or three times as far .
The former line is characteristic of the spark discharge only ; the latter appears in the arc as well .
Lead.\#151 ; A similar effect is noticed in this case .
The light which first issues from the side hole is blue ; this expands to the usual rounded form ( fig. 3 ) as the air is removed , and eventually an inner zone of greyish light ( x , fig. 3 ) emerges very clearly distinct from the outer reddish blue one ( y , fig. 3 ) .
The spectrum of this glow was photographed , and , as before , the spark lines were confined to the inner zone , while the arc lines extended right through to the limits of the outer one .
The principal spark lines photographed were 4386 and 4246 , while the chief arc lines were 4062 , 3740 , 3683 , and 3572 .
These results for magnesium and lead confirm the conclusions obtained by Milner.* Using a revolving mirror to draw out the spectrum of the spark , he found that the arc lines were much the most persistent .
Probably a closer spectroscopic scrutiny of the various glows I obtained would show other instances .
In the particular cases cited , the difference is conspicuous by direct colour observation , without the spectroscope .
Selenium gave a fine , well-developed glow , filling a great part of the outer vessel with brilliant luminosity .
The red deposit of sublimed selenium on the glass soon hindered observation , and made it necessary to clean the outer vessel .
Sulphur gave an extensive blue glow , showing , like selenium , the line spectrum .
It is clear that phenomena of this class are not confined to the metals , as I was at one time disposed to think .
Phosphorus also gave a glow .
Iodine gave a not very extended glow .
The colour of the spark itself was green .
Many of the lines in this green light did not penetrate any appreciable distance out , and the glow due to the remainder had a buff colour , with a blue outer fringe .
There is room for a more detailed investigation of this and the other halogens in connection with their general spectroscopy .
S 4 .
Effects with the Common Gases .
Substantially the same method is applicable in this case .
The discharge tube may have an internal diameter of 5 mm. , and the electrodes may be 1 cm .
apart .
The latter may be of iron , which does not volatilise appreciably under the conditions .
They should be large enough to fill the entire diameter of the tube .
The gas , heated by the discharge , will not then have any means of escape , except through the lateral hole .
It is forced out , and shows luminosity , as do the metallic vapours .
* 4 Phil. Trans. , ' 1909 , A , vol. 209 , p. 77 .
VOL. LXXXVIII.\#151 ; A. K 116 Dura tion of Luminosity of Electric Discharge in Gases .
Since it is necessary to have an appreciable quantity of the gas in the region between the electrodes , we cannot reduce the gas pressure in the surrounding vessel very low , as was possible when experimenting with the vapours of solids .
Such vapours are formed inside the inner discharge vessel when the spark passes .
The gases , on the other hand , must be present in the inner vessel to begin with , and therefore necessarily in the outer one too , which is in communication with it .
For this reason no great expansion of the exuded glow can be obtained in the outer vessel .
Partly on this account , but much more , I believe , owing to the inherently short life of their luminosity , the exuded glow obtained with the permanent gases is a comparatively inconspicuous effect .
I have never got the glow to travel out more than about 5 mm. from the orifice .
Hydrogen shows the effect best .
The most suitable pressure with this , as with the other gases , is about 1 cm .
of mercury , at least , with the above dimensions of apparatus .
The luminosity is fiery red ( due mainly to Ha ) and not much less brilliant than the spark itself .
It dies out very abruptly .
Under some conditions it is succeeded by the blue afterglow of Hertz , after the fashion of fig. 2 .
The latter I have shown to be connected with a sulphur impurity.* Nitrogen or air do not show the effect at all conspicuously .
The luminosity scarcely exudes perceptibly from the orifice , presumably owing to its very short duration .
What there is of it shows the nitrogen line spectrum .
When pure nitrogen is used , the glow of long duration , due to active nitrogen , may sometimes be seen extending right across the vessel .
But this is not very conspicuous , for , as shown previously , !
a discharge giving only the line spectrum does not excite it .
J Oxygen gives the effect almost as well as hydrogen .
The exuded glow shows the line spectrum .
Carbon dioxide also shows the duration of its luminosity by the exuded glow .
This gives a band spectrum identical with that of the discharge\#151 ; the only band spectrum observed in these experiments .
S 5 .
Summary .
The luminosity of the electric discharge appreciably survives the current not only in metallic vapours but also in the vapours of non-metals , and in the permanent gases .
The luminosity fades away in a continuous manner , * See ' Proc. Boy .
Soc. , ' 1912 , A , vol. 86 , p. 529 .
t Fowler and Strutt , 'Roy .
Soc. Proc. , ' 1911 , A , vol. 85 , p. 385 .
J Presumably some trace of the band spectrum is present in these experiments , or it would not be excited at all .
Positive Ionisation Produced by Platinum tvhen Heated .
117 and without immediate change of spectrum , when the current ceases .
Sometimes , however , a change of spectrum eventually results from unequal decay of the lines .
These effects , which last less than 1/ 1000 of a second , are distinct , not only in degree , but in kind from the afterglows in nitrogen , in gaseous mixtures containing oxygen , and in gaseous mixtures containing hydrogen , previously investigated .
These have durations extending in some cases to several minutes , and their spectra are from the first radically different from those of the exciting discharges .
As previously shown , they are due to secondary chemical actions of substances produced by the discharge .
The Positive Ionisation Produced by Platinum and by Certain Salts when Heated .
By Frank Horton , M.A. , D.Sc .
, Fellow of St. John 's College , Cambridge .
( Communicated by Prof. Sir J. J. Thomson , O.M. , F.R.S. Received November 28 , 1912 , \#151 ; Read January 16 , 1913 .
) In the 'Proceedings of the Royal Society ' for 1910 , * there is an account of a spectroscopic investigation of the nature of the carriers of positive electricity when an electric current is sent from a glowing platinum strip covered with aluminium phosphate to a surrounding platinum electrode , the whole being contained in a highly evacuated vessel .
It was found that aluminium phosphate heated under these conditions evolved carbon monoxide gas , and as a molecule of this gas carrying a single electronic charge gives a value for ejm which agrees fairly well with the mean value found for the carriers of positive electricity from heated metals , it was concluded that the positive ions are charged molecules of carbon monoxide .
Hydrogen was also detected in the gas evolved by the hot electrode in this experiment , and it now seems probable that atoms of hydrogen also take part in carrying the current , for Garrett has found that about 10 per cent , of the positive ions present when aluminium phosphate is heated on a platinum strip in a vacuum have a mass corresponding to that of the hydrogen atom.f A different view of the nature of the positive ions from glowing metals and metallic salts is held by Prof. O. W. Richardson .
As the result of * Series A , vol. 84 , p. 433 .
t A. E. Garrett , ' Phil. Mag.,5 1910 , VI , vol. 20 , p. 582 .
|
rspa_1913_0014 | 0950-1207 | The positive ionisation produced by platinum and by certain salts when heated. | 117 | 146 | 1,913 | 88 | Proceedings of the Royal Society of London. Series A, Containing Papers of a Mathematical and Physical Character | Frank Horton, M. A., D. Sc.|Prof. Sir. J. J. Thomson, O. M., F. R. S | article | 6.0.4 | http://dx.doi.org/10.1098/rspa.1913.0014 | en | rspa | 1,910 | 1,900 | 1,900 | 7 | 446 | 14,947 | http://corpora.clarin-d.uni-saarland.de/surprisal/6.0.3/?id=rspa_1913_0014 | 10.1098/rspa.1913.0014 | null | null | null | Electricity | 38.799724 | Thermodynamics | 27.356305 | Electricity | [
5.565377235412598,
-63.425071716308594
] | Positive Ionisation Produced by Platinum tvhen Heated .
117 and without immediate change of spectrum , when the current ceases .
Sometimes , however , a change of spectrum eventually results from unequal decay of the lines .
These effects , which last less than 1/ 1000 of a second , are distinct , not only in degree , but in kind from the afterglows in nitrogen , in gaseous mixtures containing oxygen , and in gaseous mixtures containing hydrogen , previously investigated .
These have durations extending in some cases to several minutes , and their spectra are from the first radically different from those of the exciting discharges .
As previously shown , they are due to secondary chemical actions of substances produced by the discharge .
The Positive Ionisation Produced by Platinum and by Certain Salts when Heated .
By Frank Horton , M.A. , D.Sc .
, Fellow of St. John 's College , Cambridge .
( Communicated by Prof. Sir J. J. Thomson , O.M. , F.R.S. Received November 28 , 1912 , \#151 ; Read January 16 , 1913 .
) In the 'Proceedings of the Royal Society ' for 1910 , * there is an account of a spectroscopic investigation of the nature of the carriers of positive electricity when an electric current is sent from a glowing platinum strip covered with aluminium phosphate to a surrounding platinum electrode , the whole being contained in a highly evacuated vessel .
It was found that aluminium phosphate heated under these conditions evolved carbon monoxide gas , and as a molecule of this gas carrying a single electronic charge gives a value for ejm which agrees fairly well with the mean value found for the carriers of positive electricity from heated metals , it was concluded that the positive ions are charged molecules of carbon monoxide .
Hydrogen was also detected in the gas evolved by the hot electrode in this experiment , and it now seems probable that atoms of hydrogen also take part in carrying the current , for Garrett has found that about 10 per cent , of the positive ions present when aluminium phosphate is heated on a platinum strip in a vacuum have a mass corresponding to that of the hydrogen atom.f A different view of the nature of the positive ions from glowing metals and metallic salts is held by Prof. O. W. Richardson .
As the result of * Series A , vol. 84 , p. 433 .
t A. E. Garrett , ' Phil. Mag.,5 1910 , VI , vol. 20 , p. 582 .
118 Dr. F. Horton .
Positive Ionisation Produced [ Nov. 28 , numerous experiments by himself and his pupils , * Richardson has come to the conclusion that the positive ions emitted by heated salts are charged atoms of the metallic constituent of the salt under test , and that in the case of incandescent metals the carriers of positive electricity are charged atoms of sodium or potassium which are present as impurities in the form of salts .
It was in order to obtain further evidence of the origin of the positive ionisation from incandescent bodies that the experiments described in the present paper were undertaken .
The paper contains the results of an investigation of the effect of the surrounding gas upon the thermionic currents from different substances .
The general method of experiment was as follows:\#151 ; The positive leak from a strip of platinum foil was first carefully investigated .
Observations were made of its rate of decay with time , of its variation with the potential difference used , and with the gas pressure in the apparatus .
The strip was then covered with the salt to be tested , and the observations were repeated .
When the experiments with this salt were complete , the strip of platinum was carefully cleaned and another salt substituted .
In this way observations were made of the thermionic emissions under exactly similar conditions from platinum , from four samples of aluminium phosphate , from two samples of sodium ortho-phosphate , and from one sample of sodium pyro-phosphate .
Comparisons wTere made , in particular , at the two temperatures 1080 ' and 1190 ' C. In an earlier paper , f in which the discharge of positive electricity from sodium phosphate heated in different gases was examined , 800 ' C. was used as the temperature of comparison , and reasons were given why it is best to work at as low a temperature as possible .
In the present experiments , however , it was found in some cases that even at 1080 ' C. the thermionic current became so small on long-continued heating as to be hardly measurable with the galvanometer used , and it was on this account that the comparisons were finally made at 1190 ' C. These earlier experiments with phosphates of sodiumf and lithium^ have shown that the nature of the surrounding gas has a considerable effect on the magnitude of the thermionic current .
In the present experiments the gas in the apparatus was^usually air , but in one instance , with a sample of pure aluminium phosphate , some experiments were made in carbon monoxide .
The positive leak in this gas was found to be larger than that under the same conditions in air , but in other respects * O. W. Richardson , 4 Phil. Trans. , ' 1906 , A , vol. 207 , p. 1 ; 4 Phil. Mag. , ' 1908 , VI , vol. 16 , p. 740 ; O. W. Richardson and E. R. Hulbirt , 'Phil .
Mag. , ' 1910 , VI , vol. 20 , p. 545 ; O. W. Richardson , 'Phil .
Mag. , ' 1910 , VI , vol. 20 , p. 981 ; 'Phil .
Mag.,5 1911 , VI , vol. 22 , p. 669 ; C. J. Davisson , 'Phil .
Mag. , ' 1912 , VI , vol. 23 , p. 121 .
t 'Camb .
Phil. Soc. Proc.,5 1911 , vol. 16 , p. 89 .
J 'Camb .
Phil. Soc. Proc. , ' 1911 , vol. 16 , p. 318 .
1912 .
] by Platinum and by Certain Salts ivlien Heated .
119 similar results were obtained with the two gases .
It was therefore thought undesirable to prolong the research by repeating experiments with different gases in the case of the other substances .
A description of the apparatus used and an account of the results obtained will now be given .
Description of the Apparatus .
The discharge tube used in these experiments is represented in fig. 1 .
It is made of glass , and consists of two parts which fit together by a ground joint with a mercury seal .
The platinum strip A can thus easily be removed for covering with the salt to be experimented on .
When in position it is situated vertically in the centre of the tube between two parallel platinum plates P , P , which together form the negative electrode .
The strip A is of thin foil 2 cm .
long and 2 mm. wide .
It can be heated electrically by means of the thick platinum leads B and C , the current being supplied from eight accumulator cells , and regulated by wire resistances .
The temperature of the central portion of the strip is obtained by a thermocouple consisting of two fine wires , one of pure platinum and the other of platinum with 10 per cent , of rhodium .
These wires are 0*0025 cm .
in diameter , and are fused together at one end , the junction being lightly welded on to the centre of one side of the platinum strip as indicated in the diagram .
The wires are insulated for the greater part of their length by fine glass tubes , and are sealed through the lower portion of the discharge tube at E. The thermo-electric current is measured by a d'Arsonval galvanometer , and the deflections are standardised from observations of the melting point of pure potassium sulphate , making use of the curve given by Callendar* for this purpose .
The welding of the thermojunction on to the platinum strip is an operation requiring great care .
A very small junction has to be made , and this must be welded to the strip * Callendar , ' Phil. Mag. , ' vol. 48 , p. 519 .
Fig. 1 .
A , platinum strip forming the anode ; B , C , leads of heating circuit ; E , wires of thermocouple ; P , P , platinum plates forming the cathode .
120 Dr. F. Horton .
Positive Ionisation Produced [ Nov. 28 , without any part of the fine wires becoming affixed , otherwise they may tap off a portion of the E.M.F. of the heating circuit and thus invalidate the temperature observations .
Before standardising the thermo-couple used in these experiments , it was ascertained that the galvanometer used to indicate the temperature gave the same deflection when the direction of the heating current was reversed .
The two platinum plates P , P , are made of stout metal , and are 2*5 cm .
long by 1 cm .
wide .
They are connected together by a wire outside the discharge tube .
The plates were about 1 cm .
apart , and were at equal distances from the anode A. The thick platinum wires B and C of the heating circuit were covered with glass in order to make them more rigid and to keep them cool .
The whole apparatus was very carefully cleaned out with hot chromic acid and with boiling nitric acid , and then washed with distilled water and dried before being fixed on to the mercury pump .
A drying tube with phosphorus pentoxide was between the discharge tube and the pump , and the latter was also connected to a McLeod gauge for registering the gas pressure .
In order to facilitate the gradual alteration of the pressure in the apparatus , there was in connection with it a large vertical glass tube 5 cm .
wide and 50 cm .
long , which could be filled with mercury by raising a cistern of mercury attached by indiarubber tubing to its lower end .
For obtaining a thermionic current the platinum strip A was connected to the positive pole of a set of small accumulator cells .
The platinum plates P were connected to the negative pole of the battery through a fine tinfoil fuse and a sensitive d'Arsonval galvanometer .
The galvanometer was well insulated on paraffin blocks ; it gave a deflection of one scale division for a current of 3*68 x 10"10 ampere , and could be shunted for measuring larger currents .
The Experiments with Platinum .
Before being finally fitted up for experimenting , the platinum strip was boiled in strong nitric acid and then carefully washed with hot water .
The first observation of the thermionic current was made with a potential difference of 40 volts , and an air pressure of 3*42 mm. in the apparatus .
As the temperature of the platinum strip was gradually raised a current was first detected at 700 ' C. ; at higher temperatures the current was larger , but it decreased very rapidly with time in the manner which has already been described by Richardson.* A comparison of the rates of decay of the positive emission from platinum , and from the salts experimented on , will be given in a later part of this paper , but it will be convenient to point out here that * O. W. Richardson , ' Phil. Mag. , ' 1903 , VI , vol. 6 , p. 80 .
1912 .
] by Platinum and by Certain Salts when Heated .
121 although the current under given conditions of voltage and gas pressure became roughly constant after about five or six hours ' heating , it continued to decrease slowly throughout the series of experiments with the platinum anode , and if the heating had been continued for some hours longer 1 believe the positive leak would have been too small to measure on the galvanometer used , It should also be mentioned that after leaving the platinum strip cold overnight , a much larger current was obtained when first testing on the following morning .
This effect was most noticeable when the gas pressure in the apparatus was very low , and I thought it was possibly due to phosphorus vapour coming over from the phophorus pentoxide drying tube , for commercial phosphorus pentoxide often contains free phosphorus .
I investigated this point by having a mercury barometer tube so arranged that by raising the cistern I could cut off the connection between the discharge tube and the rest of the apparatus .
Doing this , I found that the largely increased leak was still obtained on allowing the strip to remain cold for several hours , although there was no possibility of it having come in contact with phosphorus vapour .
This effect is exactly similar to that which was obtained when investigating the negative leak from platinum at higher temperatures , * and I believe it is due to the mercury vapour from the pump forming some compound with the platinum .
The abnormally high value of the thermionic current only lasted for a short time ; in a few minutes the leak had decreased to a steady value , usually somewhat smaller than it had on the previous evening .
This decrease in the leak was accompanied by a slight increase in the electrical resistance of the strip , which suggests that some volatile product was subliming from its surface .
Even at the highest temperature of these experiments no negative leak could be detected while this process was going on .
When the thermionic current had been reduced to its nearly constant value , a series of observations of the relation between the current and the applied E.M.F. were made .
A typical curve showing this relation is given in fig. 2 .
This was obtained with the anode at 1190 ' C. , and with a pressure of 0*01 mm. * 4 Phil. Trans.,5 1907 , A , vol. 207 , p. 149 .
122 Dr. F. Horton .
Positive Ionisation Produced [ Nov. 28 , of air in the apparatus .
The values of the current obtained when the potential difference was being gradually increased are marked \#169 ; , and those obtained on decreasing the voltage are marked x .
These fall slightly below the first set\#151 ; a result which was obtained with each of the anodes used in these experiments .
The difference in the two readings is not much in the case of platinum , but when this is covered with aluminium phosphate a larger hysteresis effect is obtained .
This will be referred to again when the experiments with aluminium phosphate are being considered .
The shape of the curve in fig. 2 is similar to that given by Eichardson* for platinum at 976 ' C. in air at atmospheric pressure .
It will be seen that up to 320 volts the current is never completely saturated , but that after about 120 volts it increases approximately proportionally to the voltage .
At higher pressures the linear part of the curve did not begin until a somewhat larger E.M.F. was reached , indicating that it was more difficult to saturate the current under these conditions .
In my earlier experiments with sodium phosphate , which were performed with an apparatus of similar construction , and of about the same dimensions , as that used in the present research , fairly complete saturation was obtained with 40 volts potential difference , even with a pressure of 2 cm .
of air in the discharge tube .
This difference is no doubt due to the different temperatures used in the two cases .
The sodium phosphate anode in the earlier research was only heated to 800 ' C. , whereas the curve of fig. 2 corresponds to a temperature of 1190 ' C. In his experiments with platinum , already referred to , Eichardson also found that it was more difficult to saturate the current at high temperatures , and he states that this may possibly be due to the relatively greater magnitude of the negative ionisation , which would make recombination a factor to be reckoned with .
In the present experiments I could detect no negative emission at 1190 ' C. , and I think the difficulty in saturating the current may be due to the presence of slowly-moving ions at this high temperature .
Eutherford , f when measuring the velocity of the positive ions from a sheet of platinum heated electrically in air at atmospheric pressure , found that slowly-moving ions were formed in increasing numbers as the temperature of the platinum was raised .
These ions probably owe their origin to the dust which is produced by the disintegration of hot platinum , and may be formed by gas ions sticking to the dust particles .
With each of the anodes used in the present apparatus it was found that when the applied potential difference had been raised to 200 volts , the thermionic current was well within the stage when the increase with * O. W. Eichardson , 'Phil .
Trans./ 1906 , A , vol. 207 , p. 40 .
t E. Butherford , ' Pliys .
Eev .
, ' 1901 , vol. 13 , p. 321 .
1912 .
] by Platinum and by Certain Salts when Heated .
increasing voltage is small and uniform , and this voltage was used for the purpose of comparing the various thermionic emissions .
In the experiments with different gas-pressures in the apparatus , it was found that the form of the current-pressure curve was the same whether a potential difference of 40 volts or of 200 volts was used .
This was tested in several cases in order to make quite sure that the applied voltage was not an important factor in the results obtained .
Before the series of observations of the variation of the positive emission from the hot platinum strip with the pressure of the residual air in the apparatus were begun , a test was made to see whether the same value of the current could be obtained if the platinum strip was allowed to cool down for a few minutes , and was then reheated to the original temperature .
It was found that after reheating for a few minutes the original steady value of the current was obtained .
In taking a series of observations at different pressures it was usual to begin at the highest pressure , and gradually pump the air out of the apparatus .
After each observation of the thermionic current , while the pressure was being reduced , the heating current was cut off , and the platinum strip was allowed to cool down .
On reheating at the lower pressure , a few minutes were allowed for the current to become steady before the new reading of the galvanometer deflection was taken .
By cutting off the heating current during the alteration of pressure one is able to guard against accidentally overheating the anode\#151 ; a most important precaution , for if the temperature is raised too high , the thermionic current at the lower temperature is at first larger than the normal value , and it takes some time before the steady state is obtained .
In this way observations of the thermionic current under different potential differences were made at pressures between about 60 mm. and a good vacuum , the temperature of the anode being in the first experiments 1080 ' C. , and in the later ones 1190 ' C. It was found that there was very little difference in the magnitude of the current at pressures between 60 mm. and 30 mm. The relation between the current and the pressure at lower pressures wilWoe seen from the curve of fig. 3 , which was obtained with the anode at 1190 ' C. , and with a potential difference of 160 volts .
Pressure : mm. Dr. F. Horton .
Positive Ionisation Produced [ Nov. 28 , The current decreases steadily with the pressure until a pressure of about 1 mm. is reached , after which there is a sharp increase in the current as the pressure is still further reduced .
At pressures below 0*03 mm. the current was always rather irregular , but usually tended to decrease as the pressure was lowered .
These irregularities are possibly due to an inaccurate knowledge of the pressure in the discharge tube containing the glowing platinum , which is continually evolving gas .
At low pressures this evolution may conceivably cause the gas-pressure in the discharge tube to be much greater than that registered on the McLeod gauge .
Another difficulty in making observations at very low pressures is the mercury vapour which comes over from the pump , and which at the ordinary temperature of the laboratory has a pressure of about 0*001 mm. , * so that observations cannot be taken at pressures lower than this unless arrangements are made to prevent mercury vapour from entering the discharge tube .
It seems not improbable that the rapid increase in the positive leak with diminishing pressures below about 0*5 mm. is due to chemical action between the mercury vapour and the hot platinum , and it would be interesting to repeat the observations , taking care to exclude mercury from the discharge tube .
It should be mentioned that observations of the thermionic current made at gradually increasing pressures gave curves which were similar to the curve of fig. 3 .
The Experiments with Aluminium Phosphate .
Sir J. J. Thomson found that aluminium phosphate heated in air at atmospheric pressure gave rise to a much larger emission of positive ions than any other salt of the large number he tested under similar conditions.* ) In the present research four samples of aluminium phosphate wrere tested , and for convenience these will be numbered in the order in which they were used .
Sample No. II was from the same bottle as that tested by Sir J. J. Thomson ; it was the ordinary commercial pure salt .
Sample IY was also sold as pure by the chemist from whom it was obtained .
The spectroscopic test showed that each of these specimens contained sodium .
Richardson holds that the positive emission from commercial aluminium phosphate\#151 ; which he did not find to be remarkably large\#151 ; is due to the presence of alkaline impurities .
In the 'Philosophical Magazine ' for November , 1911 , he has described some experiments made with aluminium phosphate prepared from materials all of which had undergone distillation , hoping in this way to obtain the salt quite free from the alkali metals .
It * T. H. Laby , ' Phil. Mag./ 1908 , VI , vol. 16 , p. 789 .
t J. J. Thomson , ' Camb .
Phil. Soc. Proc.,5 1907 , vol. 14 , p. 105 .
1912 .
] by Platinum and by Certain Salts when Heated .
125 was found that with this pure phosphate the positive emission , even at 1050 ' C. , was very small , and Richardson therefore attributes the large emission from the commercial phosphate to the presence of alkaline impurities .
Sir J. J. Thomson found that of all the classes of salts he experimented with the phosphates gave by far the largest emission of positive ions , which suggests that the emission is increased by the presence of phosphorus in the salt , and does not depend mainly upon the metal which happens to be combined with it .
The importance of this point is so great that I decided to test some aluminium phosphate prepared in the same way as that used by Richardson .
I am indebted to Mr. F. R. Ennos , B.A. , and to Mr. W. W. P. Pittom , B.A. , who prepared the salt for me in the Chemical Laboratory of this University .
The precipitated phosphate , after washing with boiling distilled water , was divided into two parts , one of which was kept in a moist condition and the other was dried in an air oven .
The former of these was the first sample of aluminium phosphate tested in these experiments , the dried portion was Sample No. III .
It was found that each of these samples of pure aluminium phosphate gave an initial positive emission , which was considerably smaller than that given by either of the impure specimens .
This confirms the observations of Richardson .
It was also found , however , that after long-continued heating there was not much difference between the emissions from the different specimens .
In preparing the first aluminium phosphate anode tested , the platinum strip was covered on both sides with some of the pure sample which had been preserved in a moist condition .
The strip was then gently heated in the air by means of an electric current , and the phosphate was thus dried and formed a thin uniform layer over the surface of the platinum .
Anodes of the other samples were prepared in a similar manner ; the platinum strip was first cleaned by careful scraping and washing , it was then covered with an emulsion made by mixing some of the new specimen with distilled water , and dried by gentle heating .
In all cases when a new anode was fitted into the discharge tube , the air-pressure was reduced to a few millimetres , and the apparatus was left overnight in order that any moisture present might be absorbed by the drying tube .
With each of the aluminium phosphate anodes the first observations which were made were those of the rate of decay of the thermionic emission with time .
The temperature of the anode was usually 1080 ' C. , the potential difference was either 40 or 200 volts , the gas pressure in the apparatus was about 16 mm. With Samples I , III , and IY the current decreased continuously from the commencement of the experiment , but with 126 Dr. F. Horton .
Positive Ionisation Produced [ Nov. 28 , Sample II\#151 ; the impure aluminium phosphate used by Sir J. J. Thomson in his experiments\#151 ; the current steadily increased during the first half hour .
It then gradually decreased for over an hour , when some sudden disturbance seemed to take place and in the next 20 minutes the current rose rapidly to its highest value , after which it decreased continuously to a fairly steady value in about three and a half hours .
The rise in the current on first heating and the subsequent decay to a steady value is in agreement with the results obtained by Garrett , but this effect was not obtained with the other impure specimen tested in these experiments ( Sample IY ) .
This point will be referred to again later in the paper .
In all cases after the first few hours ' heating there was a gradual diminution in the emission throughout the experiments , but on leaving the apparatus overnight the current on the following morning was usually larger than when last tested .
If the air pressure were several millimetres , the current at first would be about two or three times the normal value , and it would decrease to a steady value in about an hour .
If an air pressure of only a small fraction of a millimetre had been left in the apparatus overnight , the effect already referred to with platinum was obtained , and the initial current on the following morning was perhaps 100 times the normal value .
This large current always decreased very rapidly during the first few seconds of heating , afterwards falling off gradually to a steady value as in the case when the pressure was higher .
It must be understood that the " steady " values were never quite constant ; the current was always slowly decreasing as time went on , but when a " steady " value had been reached there was no appreciable alteration in the galvanometer deflection in the course of 5 or 10 minutes .
With both of the specimens of impure aluminium phosphate a curious effect was observed on first testing the emission after the anode had been left for some time in air at a pressure of several millimetres .
Under these circumstances it was found that the initial current gradually increased for a few minutes before the usual decay to a steady value began .
This effect was only noticed on one or two occasions when the pure salt was being tested ; but , as will be seen later , it was also found to occur when a sodium phosphate anode was being used .
When , after reheating an anode , a steady state of the emission had been obtained , the thermionic current was always slightly less than the steady value when last tested .
It was therefore decided to test whether the current would decrease to a further extent if the anode were allowed to remain cold for several days .
This was tested with Samples III and IV , and it was found that a very considerable diminution in the steady emission was produced by leaving the anode cold for two or three weeks with the air in the apparatus at a few millimetres pressure .
It thus 1912 .
] by Platinum and by Certain Salts when Heated .
appears that the change which causes the decay of the positive leak with time goes on even in the cold , though at a very much slower rate than when the anode is hot .
It seems probable that this change is the evolution of gas by the anode , which one would expect to take place most rapidly at high temperatures .
With all four samples of aluminium phosphate the variation of the thermionic current with the potential difference was studied at different temperatures and with different gas pressures in the apparatus .
The curves given in fig. 4 will serve to illustrate the results obtained .
The points marked \#169 ; were obtained when the voltage was being gradually increased , those marked x were obtained afterwards , on decreasing the voltage .
It will be seen that the currents under an increasing voltage were rather larger than those obtained under the corresponding decreasing voltage .
There are two causes which tend to produce this effect .
The first of these is the slow but gradual diminution of the emission with time , but that this does not account for the whole of the effect was proved by commencing the series with the highest E.M.F. , gradually reducing it to zero , and then gradually raising it again to the initial value .
Taking the observations in this order , the values of the current at increasing voltages were still much larger than the corresponding values with decreasing voltages , although the decay of the leak with time tends to equalise the values in this case .
The second cause , and the one which seems to be mainly responsible for the hysteresis , is the fact that a sudden increase in the applied potential difference gives rise to a current which is at first larger than the normal value for that voltage , and which gradually decreases to the normal value in the course of 5 or 10 minutes .
If the voltage is suddenly decreased the opposite effect takes place , the current to begin with is too small and gradually increases .
A hysteresis effect similar to this was obtained by Pdchardson in his experiments with platinum* In making the observations for a current-E.M.F .
curve the readings have to be taken without much delay , firstly on account of the time-lag effect , secondly , because of the difficulty of maintaining the * O. W. Eichardson , 'Phil .
Trans. , ' 1906 , A , vol. 207 , p. 10 .
128 Dr. F. Horton .
Positive Ionisation Produced [ Nov. 28 , temperature constant for a long time .
At each change of the applied potential difference the new voltage was left on for about 2 minutes before the corresponding reading of the current was taken .
The indications of the galvanometer showed that in this time a great part of the effect due to the sudden change of voltage had subsided , but it is probable that the current had not quite settled down to the steady value , and this causes each of the readings at increasing voltages to be slightly too high , and those at decreasing voltages to be slightly too low , thus accounting for the difference in the curves obtained under the two conditions .
The curves in fig. 4 were obtained after the anode ( Sample I ) had been heated for several days at 1190 ' C. , and the emission had become very small .
The air pressure in the apparatus was 0*035 mm. ; at higher pressures the curves rose more gradually , showing that a greater E.M.F. was required to produce approximate saturation of the current .
The relation between the thermionic current from aluminium phosphate and the air pressure in the apparatus has been investigated by Garrett , * who found that as the pressure was lowered from about 150 mm. the positive emission increased to a maximum value at somewhere between 15 mm. and 5 mm. , according to the temperature of the phosphate , the maximum being at a lower pressure the higher the temperature .
After passing through the maximum value the current rapidly decreased with the pressure and became very small in a good vacuum .
In the present experiments a result similar to this was obtained with both specimens of impure aluminium phosphate , but with the pure salt the curves obtained were very similar to those given by platinum , and between 100 mm. pressure and a good vacuum there was no sign of the current attaining a maximum value .
With all the samples experiments were made at 1080 ' C. and at 1190 ' C. At each temperature a series of readings was taken as soon as the positive leak became fairly steady , and other series were taken after the anode had been heated for many hours so that the emission at the particular temperature had been reduced to a low value .
With Samples I and III of pure phosphate it was found that the current decreased gradually as the air pressure was reduced , from its highest value ; there was , however , little change in the emission at pressures above about 30 mm. At pressures lower than this there was a steady fall in the current to a minimum value between 1 mm. and 2 mm. pressure , followed by a slight increase as the pressure was still further reduced .
When the observations were made at gradually increasing pressures precisely similar current-pressure curves were obtained .
That the applied potential difference makes no appreciable difference to the general form of the current* A. E. Garrett , ' Phil. Mag. , ' 1910 , YI , vol. 20 , p. 573 .
* 1912 .
] by Platinum and by Certain Salts when Heated .
129 pressure curves will be seen from the observations recorded in fig. 5 .
Here the temperature of the anode was maintained at 1190 ' C. and the air pressure in the apparatus was gradually decreased from 30 mm. to a low value .
At each pressure observations were taken first with 40 volts and then Pressure : mm. with 200 volts applied potential difference .
It will be seen that under both conditions the current gradually decreased to a minimum value at about 1 mm. pressure , after which it increased slightly as the pressure was still further reduced .
When Samples II and IY of impure aluminium phosphate were used as anodes the current pressure curves resembled those obtained by Garrett , but at low pressures the current increased with diminishing pressure .
This is well shown in fig. 6 , which was plotted from observations at decreasing pressures made with the anode ( Sample II ) at 1190 ' C. , and with an applied potential difference of 200 volts .
On pumping down from a pressure of 83 mm. the current slowly increased to a maximum value at about 19 mm. pressure , after which it decreased rapidly with diminishing pressure , attaining a minimum value at a pressure of about 1 mm. , and then increasing somewhat on further pumping .
It was found that after an impure aluminium phosphate anode had been heated for a long time , the prominence of the maximum in the current-pressure curve became much less marked , and in the final set of readings , when the current had become very small , it increased continuously as the 130 Dr. F. Horton .
Positive Ionisation Produced [ Nov. 28 , air pressure in the apparatus was increased from about 1 mm. to 100 mm. At pressures below 1 mm. the curves were always similar to the corresponding portion of the curve in fig. 6 .
It seems , therefore , that the cause of the maximum current at a certain pressure gradually disappears on long-continued heating , whereas the cause of the increased leak at very low pressures still remains .
This latter effect is the same as that recorded in the case of a platinum anode , an explanation of which has already been suggested .
A pressure of maximum thermionic emission had been obtained in these experiments only in the earlier stages of heating the impure aluminium phosphate ; it was not observed in the experiments with the platinum anode , nor with the pure phosphate .
It had , however , appeared to a very marked extent in some earlier experiments which had been made by the author with sodium phosphate , and thus it seemed possible that the maximum emission at a certain pressure was connected with the presence of sodium in the anode .
In this case the gradual disappearance of the maximum on continued heating of the impure phosphate , ought to be accompanied by a disappearance of the sodium which is known to be present as an impurity in the fresh sample .
In order to test this , at the conclusion of the series of current-pressure observations with Sample IY of impure aluminium phosphate , the apparatus was taken down , and the platinum strip , which was still covered with a white powder , was introduced into a non-luminous Bunsen flame .
The flame did not give any evidence of the presence of sodium , but when a few grains of the original dry powder were placed on the strip , a yellow sodium flame was at once obtained .
It thus appears that in the course of the experiments the sodium leaves the impure phosphate , an effect which may be due simply to volatilisation , or it may be an essential part of the mechanism of the large positive emission from the freshly heated anode .
After this flame test the anode was refitted into the apparatus , which was evacuated to a pressure of about 6 mm. , and the thermionic current at 1190 ' C. was again tested by applying a potential difference of 200 volts .
The initial current was 1*26 xlO-6 ampere ; this decreased in the manner which is characteristic of the positive leak from freshly heated substances , and after about 90 minutes ' heating was only 6*3 x 10"8 ampere , a value which was still somewhat greater than the last reading at this pressure before the flame test was made , namely , 2*2 x 10"8 ampere .
The largely increased emission on first heating might possibly have been due to some of the powdered phosphate which had been heated in the Bunsen flame on the strip of platinum adhering to it and thus introducing a fresh supply of sodium .
I did not consider this likely to be the cause , on account of the 1912 .
] by Platinum and by Certain Salts when Heated .
131 small amount of fresh phosphate which was placed on the strip , but it seemed worth while to test the effect of heating in the Bunsen flame without risking contamination with sodium .
Accordingly , on the following day , the anode was again heated to 1190 ' C. , and was maintained at that temperature for nearly five hours , during which time the thermionic current decreased]to 2*5 x 10"8 ampere .
The apparatus was then taken down and the platinum strip was quickly and carefully introduced into a non-luminous Bunsen flame .
Again there was no sign of the presence of sodium .
After a few minutes ' heating in the flame the anode was placed in position in the apparatus , and after pumping down the emission was tested under the same conditions as before .
The initial current was greater than in the last experiment , being of the order of 10-5 ampere , but it decreased more rapidly , and in half an hour was no larger than it had been after 90 minutes ' heating on the former occasion .
On leaving the anode overnight , the emission was found to be less on the following morning , showing that , as usual , the change had gone on in the cold , and after heating for about an hour longer the current was reduced to a nearly steady value , 29 x 10-8 ampere , which is about the same as that obtained before repeating the flame test .
We thus see that simply heating the platinum strip in the Bunsen flame had the effect of increasing the positive emission to a value which is about that of the freshly heated anode .
It is well known that when platinum ] is heated in a flame it absorbs some of the flame gases , notably hydrogen , and there can be no doubt that it is the emission of these gases on subsequently heating in a vacuum which is responsible for the large current observed .
This view is , at all events , in agreement with the rapid decay of this induced activity on continued heating , and with the fact that the decay is more rapid on repeating the experiment , for it would be expected that continually Ailing and emptying the platinum would have the effect of rendering the escape of the occluded gas more easy .
That the sodium disappears from the anode during the experiments is extremely interesting , although it has been shown that the presence of this metal is not necessary in order to obtain a large positive emission , for there seems undoubtedly to be a connection between the presence of sodium in the anode and the variation of the thermionic current with the gas pressure in the apparatus .
At all events , as far as these experiments go , on reducing the pressure of the air from about 60 mm. , the thermionic current always increased to a maximum value at a certain pressure , depending on the temperature of the anode , when the latter contained sodium , and it did not do so in the absence of this metal .
VOL. LXXXVIII.\#151 ; A. L 132 Dr. F. Horton .
Positive Ionisation Produced [ Nov. 28 , The Experiments with Sodium Phosphate .
Experiments were made with two samples of Kahlbaum 's sodium phosphate , and with one sample of Kahlbaum 's sodium pyrophosphate .
A long series of observations was only made in the case of one of the samples of sodium phosphate , for the tests made with the other salts showed that there was practically no difference in the thermionic emissions from the three samples .
The results of a series of experiments with sodium phosphate at a temperature of 800 ' C. have already been published.* For purposes of comparison with the results for aluminium phosphate it was necessary to repeat the observations with sodium phosphate in air , at the higher temperatures 1080 ' C. and 1190 ' C. The platinum strip after being carefully cleaned was covered with sodium phosphate by evaporating a water solution of the salt upon it .
It was heated electrically during this process and the temperature was taken to a bright red heat to make sure that the salt was firmly attached to the platinum before the anode was placed in position in the apparatus .
The thermionic current at 1080 ' C. under a potential difference of 200 volts was tested at a pressure of 55 mm. after an interval of 24 hours for the absorption of moisture by the phosphorus pentoxide drying tube .
The initial current was 1*7 x 10-7 ampere , and this gradually increased during the first 40 minutes to 8*4 x 10"6 afflpere , after which it decreased in the usual manner .
The alteration of the initial current with time is thus similar to that which was found with one sample of the impure aluminium phosphate ; it will be referred to again in the next part of this paper .
Throughout the experiments it was found that after leaving the anode cold for some time with a considerable air pressure in the apparatus the effect which has been mentioned in connection with impure aluminium phosphate occurred , the current on retesting increased for the first few minutes and then the decay continued .
The maximum current was usually smaller than the last reading of the previous evening , showing that the change which causes the decay of the emission had gone on in the cold .
The proportional amount by which the activity of the anode was reduced by allowing it to remain cold was somewhat variable , but it seemed to depend in the main upon two things , firstly , upon the total length of time during which the heating had been kept up , and , secondly , upon the interval since the last observation was made .
The experimental results were in agreement with the assumptions that the freshly heated anode evolves a gas which takes part in carrying the current , and that the gas is also evolved , though at a very much slower rate , when a new anode is allowed to remain cold in a good vacuum .
* ' Camb .
Phil. Soc. Proc.,5 1911 , vol. 16 , p. 89 .
1912 .
] by Platinum and by Certain Salts when Heated .
133 On those occasions when the apparatus was left unused for some time with the gas pressure very low , the initial current was usually very large but decreased in a few seconds to a much smaller value , which gradually increased and then decreased in the manner described above .
This large leak at the start is the effect which was nearly always obtained on leaving any anode cold for some time in a good vacuum , and which I have suggested is due to the action of mercury vapour upon the platinum strip .
The relation between the current and the applied potential difference was investigated with different gas pressures in the apparatus , at both 1080 ' C. and 1190 ' C. The general character of the results obtained was precisely similar to that of the results recorded in the account of the experiments with aluminium phosphate .
Measurements of the positive emission under a constant potential difference of 200 volts were made with both increasing and diminishing pressures of air up to about 60 mm. The first series of observations was made at 1080 ' C. after about 10 hours ' heating at that temperature , and a maximum value of the thermionic current occurred at a pressure of 12 mm. when the pressure was being gradually reduced , and at about 15 mm. with increasing pressures .
Similar results were obtained at the higher temperature , 1190 ' C. , but here the pressure of maximum emission was not so well marked , probably because the anode had been heated for a long time before observations at this temperature were made .
A similar effect was noticed in the experiments with aluminium phosphate containing sodium , but in that case the pressure of maximum emission could not be detected after long-continued heating , whereas in the present case the thermionic current always had a maximum value at a pressure of about 10 mm. when the temperature of the anode was 1190 ' C. That the variation of the current with the gas pressure became much reduced by continued heating at 800 ' C. was pointed out in the account of my earlier experiments with sodium phosphate .
In the case of impure aluminium phosphate , the removal of the pressure of maximum emission by continued heating was accompanied by the disappearance of sodium from the anode .
In the present experiments , although the amount of sodium phosphate on the anode was less at the conclusion of the experiments than it had been at the beginning , it did not completely disappear\#151 ; a fact which was also obvious from the magnitude of the positive emission .
The thermionic current from impure aluminium phosphate is at first larger than that from sodium phosphate under similar conditions , but on continuing the heating for some time , the current from aluminium phosphate falls off to a much lower value than that from sodium phosphate .
At the end of the experiments with the latter salt the current at 1190 ' C , in an air pressure of 10 mm. was about 450 times the final value from impure aluminium L 2 134 Dr. F. Horton .
Positive Ionisation Produced [ Nov. 28 , phosphate .
The existence of this large emission from an anode which has been heated for so long that most of the occluded gas must have been driven out of it , is evidence in favour of the view that at this stage the current is largely carried by sodium atoms .
At low pressures the thermionic current from sodium phosphate always decreased continuously as the pressure was reduced .
There was never any sign of the increasing current obtained in other cases .
This is accounted for by the greater emission in the case of this anode , which would completely mask an increase of the magnitude usually observed .
The Decay of the Positive Emission from .
Freshly Heated Anodes .
The thermionic emissions from the various anodes , when freshly heated , cannot in all cases be compared , because the conditions under which the initial tests were made were not always the same .
In the case of platinum itself , and of the first samples of aluminium phosphate , observations were made at the lowest temperature at which a conveniently measurable current was obtained , whereas with the later salts the observations were commenced at 1080 ' C. With a view to comparing the initial currents from the different anodes , and the rates of decay under similar conditions , a fresh series of observations was made at the highest temperatures used in these experiments , 1190 ' C. , the air pressure being in all cases 15 mm. , and the potential difference 200 volts .
The platinum strip was well washed to free it from sodium phosphate .
It was then dried , and the absence of sodium was proved by heating it in a Bunsen flame .
The anode was replaced in the apparatus and the decay of the initial current from platinum under the standard conditions was investigated .
The values of the currents during the first two hours are plotted in Curve I , fig. 7 , and in the same diagram the corresponding curve for pure aluminium phosphate is given ( Curve II ) .
In this latter case , the current during the first few minutes was too large to be included in the figure , but the emission decreased continuously from the start , very rapidly at first , and the curve when plotted to a smaller scale was exactly similar to the curve for platinum .
The decay curves for the emission from sodium phosphate , from sodium pyro-phosphate , and from impure aluminium phosphate are given in fig. 8 , the curves being numbered in that order .
The Curves I and II for the sodium salts show the characteristics which have already been described , namely , an emission which increases to a maximum value during the first few minutes and then decays away .
The curve for impure aluminium phosphate ( Curve III ) is similar to those given in fig. 7 for the pure phosphate and for platinum ; there is an enormous decrease in the current 10~6 ampere 1912 .
] by Platinum and by Certain Salts token Heated .
135 s c3 \#163 ; 3 ' \lt ; P u Q 1\#174 ; ( \ Fig. 7 .
o v V S\#177 ; y^e_2 Curve 1 O 20 40 60 80 100 Time from beginning of heating ( minutes ) .
Curve 3 Time from beginning of heating ( minutes ) .
136 Dr. F. Horton .
Positive Ionisation Produced [ Nov. 28 , during the first few minutes .
The salt with which this curve was obtained was from the same bottle as Sample IV in the experiments already described , and the decay curve is similar to that which was obtained before with the anode at 1080 ' C. It will be remembered that the other specimen of impure aluminium phosphate ( Sample II ) gave a result resembling that obtained with the phosphates of sodium , the decay being preceded by an increase in the current to a maximum value .
This initial increase in the current before the decay sets in was not only obtained with these anodes when new , but also , to a smaller extent , on reheating after they had been left cold for some hours in a pressure of several millimetres of air .
A preliminary increase of the emission on reheating under these conditions was also occasionally noticed when the anode consisted of pure aluminium .
phosphate , or of platinum , although the magnitude of the effect in these cases was very small .
The aluminium phosphate used by Garrett in his experiments* also gave an initial current which increased to a maximum in about eight minutes , and then decreased rapidly .
He points out that the form of the curve seems to indicate that the first effect of the high temperature is the production on the anode of an unstable substance , which does not itself emit ions , but which gives rise to a second unstable substance which is the origin of the ionisation .
In the following table I have collected together the values of the thermionic currents from the different anodes at the commencement of the heating , and after the temperature ( 1190 ' C. ) had been maintained for 1 , 2 , 10 , 50 , and 100 minutes :\#151 ; Anode .
Current in 10 8 amperes .
At start .
1 min. 2 mins .
10 mins .
50 mins .
J 00 mins .
Platinum 183 18 0 6*9 2 5 1 *74 1-24 Pure aluminium phosphate Sodium phosphate 2040 201 87 18 *0 5*6 3-6 2550 3350 4430 5650 3750 1600 Sodium pyro-phosphate ... 3380 5220 5600 5270 2400 940 Impure aluminium phosphate 7560 3220 1450 250 59 32 The values of the current at the start must be taken as being approximate only , for the rapidity of the alteration during the first minute makes the observation very difficult .
The numbers given for platinum and for the phosphates of aluminium were obtained from the largest deflection of the galvanometer , and the rapidity with which this indicates changes in the * A. E. Garrett , 4 Phil. Mag.,5 1910 , YI , vol. 20 , p. 573 .
1912 .
] by Platinum and by Certain Salts tvhen Heated .
137 current depends on the extent to which it is shunted .
The instrument was shunted to the same extent for the measurements with platinum and with pure aluminium phosphate ; a shunt of smaller resistance was used in the cases of impure aluminium phosphate and of the phosphates of sodium .
From the numbers in the above table it will be seen that the decay of the current during the first minute of heating is much the greatest with a platinum or a pure aluminium phosphate anode ; with the aluminium phosphate containing sodium the decrease is considerably smaller , and in the case of the phosphates of sodium the current increases .
Now it is remarkable that when an impure aluminium phosphate anode which had been used for so long that all traces of sodium had disappeared from it was heated for a few minutes in a Bunsen flame , the emission on retesting was found to be of the same magnitude , and to decay during the first few minutes in the same rapid manner , as the initial discharge from the freshly heated pure salt .
The increase of the current after heating in the Bunsen flame is , no doubt , due to the emission of gases which have been absorbed from the flame , and this points to the conclusion that the large initial currents from freshly heated platinum and from pure aluminium phosphate are also due to the emission of gases by these anodes .
There is doubtless an emission of gas also in the case of the other anodes used , and this is probably responsible for carrying some of the observed current , but in these cases there is apparently some other source of ionisation which increases either in amount or in activity , or in both respects , during the first few minutes ' heating , and the most probable origin of this effect seems to be the sodium which these anodes contain .
In the case of impure aluminium phosphate this second source is not very large , and serves only to decrease the rate of decay of the total emission ; with the phosphates of sodium , however , the decay is completely overcome , and there is an increasing current during the first few minutes .
It will be remembered that an initial increase in the current was also observed with Sample II of impure aluminium phosphate .
This would seem to indicate that Sample II contained a greater amount of sodium impurity than Sample IV , which was used in obtaining the figures in the above table .
After a very few minutes ' heating the decay of the emission from the impure salt is more rapid than the decay of the activity of the pure phosphate , a state of affairs which can readily be explained by the gradual disappearance of the sodium , in addition to the falling off of the gas emission , in the case of the former anode .
The numbers recorded in the table give the relative activities of the different substances at 1190 ' C. The observations which had been made at lower temperatures gave the same general result .
The largest initial current 138 Dr. F. Horton .
Positive Ionisation Produced [ Nov. 28 , was always given by impure aluminium phosphate , and next in order of thermionic emission come the phosphates of sodium , pure aluminium phosphate , and , last of all , platinum .
The initial increase in the emission from sodium phosphate was relatively larger , and continued for a longer time , when the anode was at 1080 ' C. than when it was heated to 1190 ' 0 .
, a result which is probably due to the rate of evolution of gas from the heated anode increasing very rapidly with rise of temperature .
A comparison of the final values of the thermionic currents from the different anodes after heating for a long time is given in the following table .
In all cases the applied potential difference was 200 volts , and the temperature 1190 ' C.:\#151 ; Anode .
Thermionic currents ( 1 = 10 9 ampere ) at various air pressures .
0*005 mm. 1 mm. 2 mm. 5 mm. 10 mm. 20 mm. Platinum 5*2 1 *65 1 *65 2*2 2 *9 3*9 Pure aluminium phos- 0*7 0*6 0*7 0*9 1 *2 2*0 phate Impure aluminium phosphate Sodium phosphate 2*9 1*5 2*0 3 *1 41 5*0 1080 1500 1630 1750 1810 1740 The numbers given are interesting as indicating the order of magnitude of the emission from the different anodes at the conclusion of the experiments , but too much importance should not be attached to the actual figures , for it must be remembered that there was every indication that continued heating would have reduced the emission still further , although the rate of decay of the current had become so small that , in the case of the salt anodes , it might perhaps be accounted for by the phosphate gradually becoming detached from the platinum .
From the table it would appear to be doubtful whether the small emission given by pure aluminium phosphate is due to that salt at all , for it will be seen to be smaller than the emission from the platinum strip itself at the beginning of the experiments , but this would have decreased considerably during the extra heating .
At the conclusion of the experiments with the phosphates the platinum strip was cleaned and tested alone ; it was found that after heating at 1190 ' C. for several hours , the thermionic currrent was reduced to a smaller value than any recorded in the above table , and I am therefore inclined to think that the numbers given for pure aluminium phosphate are in part due to some remaining small emission from that salt .
After heating for about the same length of time , the final current measured from the impure aluminium phosphate is not much greater 1912 .
] by Platinum and by Certain Salts when Heated .
139 than that from the pure salt , although during the course of the first few minutes ' heating it was more than fifteen times as great .
It has already been stated that this seems to be due to the disappearance of the sodium which was present as an impurity in the former anode .
The outstanding feature of the above table is the relatively enormous emission from sodium phosphate , which is obtained although the anode had been heated for at least as long as either of the specimens of aluminium phosphate .
The Nature of the Carriers of the Positive Thermionic Current .
The experiments described in this paper have shown that there are considerable variations , both in the magnitude , and in the permanence , of the positive emission from different substances .
In the case of platinum , and of pure aluminium phosphate , we have an initial thermionic emission which decreases very rapidly with time , and in the course of a few hours ' heating at a high temperature becomes extremely small .
With sodium phosphate , on the other hand , the emission at first increases , and then decreases much more slowly than with the other substances tested , so that even after many hours ' heating a very considerable thermionic current can be obtained .
The impure aluminium phosphate falls between these two cases .
At the commencement of the heating the alteration in the emission with time resembles that given by phosphate of sodium , whereas the final low value more nearly corresponds to the current from the pure phosphate or from platinum .
The experiments have shown that this is accounted for by the fact that in the beginning the impure phosphate contains sodium , but that this gradually disappears from the anode in the course of the heating .
The author is of opinion that the ionisation from platinum ( and from metals generally ) is largely due to the emission of absorbed gases on heating , but that in the case of sodium phosphate a considerable part of the emission consists of positively charged sodium atoms , the final value of the current in a good vacuum after long-continued heating being almost entirely due to this cause , although at first there is no doubt also a large current due to the evolution of ionised gas , which probably conies partly from the salt and partly from the platinum upon which it is heated .
That certain salts of sodium when heated and used as anodes in vacuum tubes emit positively charged sodium atoms was demonstrated by Gehrcke and Reichenheim in the year 1906 , * but the experimental conditions were somewhat different from those described in this paper .
In their earlier experiments the salts were heated upon platinum foil , but the cathode of the discharge tube was also heated electrically , and consisted of a platinum * Gehrcke and Reichenheim , 'Deutsch .
Phys. Ges .
Verb .
, ' 1906 , p. 559 .
Dr. F. Horton .
Positive Ionisation Produced [ Nov. 28 , strip covered with barium oxide .
The potential difference applied was 110 volts , and under these circumstances a bundle of yellow rays was seen proceeding from the salt on the heated anode .
These rays Gehrcke and Eeichenheim called " anode rays , " and subsequent experiments proved them to consist of positively charged sodium atoms .
In later experiments* Gehrcke and Reichenheim obtained better results by using much higher potential differences across the tube and having neither electrode heated by an external current ; the current sent through the tube by the applied E.M.F. gradually warmed up the salt anode , and when this attained a bright red heat a luminous pencil of rays could be seen proceeding from it .
The discoverers of these rays found that they were given particularly well by the haloid salts of the alkali metals .
In each case the value of the specific charge of the ions , which was measured by two different methods , agreed with the value calculated on the supposition that they consist of atoms of the metallic constituent of the salt under test , conveying a charge equal to that carried by the hydrogen ion in electrolysis .
Anode rays were also obtained from salts of the divalent elements strontium and calcium , and in these cases the carriers appeared to be doubly charged atoms of the metal used ( Sr++ or Ca++ ) .
For a full account of the methods of obtaining these anode rays reference must be made to the original papers , but it will be convenient to mention here some of the conditions which seemed to favour their production .
In the earlier experiments , in which the salt was heated upon platinum foil and a low potential difference was used , the rays lasted for a very few minutes only .
In the later form of apparatus , in which a small stick of the fused salt formed the anode , the rays could be obtained for several hours , although the activity diminished with time .
The length of the luminous ray was greater the higher the vacuum in the discharge tube , but where the path was non-luminous it could be traced by the fluorescence produced on the glass .
The most copious supply of rays was obtained when easily dissociating or volatile salts were used as anodes , and some mixtures of salts seemed to work better than either of the constituents alone , possibly because the mixture had a lower melting point .
Anode rays could not be obtained from a cold anode , and in the form of apparatus where no external heating was used it was necessary to wait some time after the high E.M.F. was applied , until the current through the tube had raised the extremity of the anode to a red heat , before the rays appeared .
It occurred to the author that the anode rays of Gehrcke and Reichenheim were essentially the same as the thermionic emission from heated salts .
Sir J. J. Thomson had found that the greatest emission was given by phos-* Gehrcke and Reichenheim , 'Ann .
der Phys. , ' 1908 , p. 861 .
1912 .
] by Platinum and by Certain Salts when Heated .
141 phates , and that aluminium phosphate was particularly active .
It was therefore attempted to obtain anode rays from this substance , but without success.* A mixture of phosphates of sodium and lithium was also tried , and in this case some curious luminous effects were obtained , but I was unable to see the fine bright pencils of light described by their discoverers as characteristic of anode rays .
It was , however , obvious that positively charged sodium was being shot off from the anode , for , although the cathode was behind the anode , so that anything shot out by the glowing phosphates was projected away from it , yet a bright yellow sodium light began to appear on the cathode as the tube was worked , appearing first on the edge nearest to the anode , and gradually spreading all over it .
The impossibility of obtaining anode rays from these salts , which were then thought to be the most copious emitters of positive electricity when heated , led the author to the conclusion that there was no close connection between the two phenomena .
Recent researches , however , have modified this opinion .
Richardson has determined the specific charge of the carriers of the thermionic current from a number of different salts when heated in vacuo , and has concluded that these carriers are atoms of the respective metallic constituents minus a single electron .
He also found that aluminium phosphate is by no means the most active salt in producing positive ionisation when heated in a vacuum , a result which is confirmed by the experiments recorded in the present paper .
In the light of these results it seems probable that the anode rays of Gehrcke and Reichenheim are essentially the same as the emission , in a good vacuum , from a positively charged salt which has been heated until the steady state is reached .
There is , however , the difference that in the anode rays the emitted atoms are travelling much faster owing to the fact that they are liberated into a much stronger electric field .
Gehrcke and Reichenheim have shown that it is necessary to have a large fall of potential at the anode in order to obtain luminous anode rays .
Under ordinary circumstances , with such gases as oxygen or nitrogen in the discharge tube , the anode fall of potential is about 20 volts , and the velocity which the ions attain is too small for luminosity to result , but if a small quantity of any halogen vapour is introduced into the tube , the anode fall increases enormously , and may become many thousands of volts .
This fact explains why anode rays are readily obtained when haloid salts are used which have the property of dissociating when strongly heated .
Now Richardson has concluded from his experimentsf that what is required for a salt to be a good emitter of positive ions " is a * ' Camb .
Phil. Soc. Proc. , ' 1909 , vol. 25 , p. 329 .
+ O. W. Richardson , ' Phil. Mag. , ' 1911 , YI , vol. 22 , p. 669 .
142 Dr. F. Horton .
Positive Ionisation Produced [ Nov. 28 , combination of volatility in the possible compounds formed , together with high electro-positiveness of the metallic constituent .
" The salts of the alkali metals he found to be particularly active , and if only a trace of either sodium or potassium were present as an impurity in the salt under test , the values of e/ m obtained for the positive ions always indicated that they consisted of atoms of these metals .
Volatile salts were found to be more efficient than non-volatile salts ; for instance , zinc haloids were very active , and barium sulphide was more efficient than barium sulphate .
It will thus be seen that the class of salt which is best from the point of view of thermionic emission with low potential differences is precisely that which was found by Gehrcke and Eeichenheim to be most efficient for the production of anode rays .
The carriers of electricity in the two cases are identical , the only difference seems to be in the velocity with which they travel .
It should , however , be mentioned that whereas Gehrcke and Eeichenheim found that the anode rays from salts of strontium and calcium consisted of atoms of these metals carrying double charges , Davisson* obtained a value for the specific charge of the carriers of the thermionic current from these salts corresponding to a single unit of electronic charge per atom .
In some more recent determinations of \lt ; s/ m for strontium anode rays by measurements of the Doppler effect , Eeichenheimf obtained from certain lines of the spectrum a value corresponding to Sr+ , and from other lines a value more nearly corresponding to Sr++ .
Also Eichardson has concluded that there are ions of the type Zn++ present in the thermionic emission from the zinc haloids .
There is evidence , therefore , both in the case of anode rays , and of the ordinary thermionic emission , that polyvalent atoms may carry either single or multiple charges , but further investigation of this point is required before it can be regarded as fully established .
My experiments on the discharge of positive electricity from sodium phosphate heated in different gases led me to the view that the gas present in the discharge tube takes an active part in carrying the thermionic current\#151 ; probably by diffusing into the anode and being emitted in an ionised condition .
This view has been criticised by Eichardson , J who holds that the carriers of the thermionic current are in all cases atoms of the metallic constituent of the salt under test ; a conclusion which he bases upon his determinations of the value of the specific charge of the carriers in a good vacuum .
I think there can be little doubt that when a salt anode has * C. J. Davisson , 'Phil .
Mag. , ' 1912 , VI , vol. 23 , p. 121 .
t O. Reichenheim , ' Ann. der Phys. , ' vol. 33 , p. 747 .
t '* w* Richardson , 'Phil .
Mag. , ' VI , vol. 22 , p. 669 .
1912 .
] by Platinum and by Certain Salts when Heated .
143 been heated for so long that the thermionic emission has decreased to what I have called its " steady value , " the carriers of the current in a good vacuum are mostly metallic atoms\#151 ; the ions which have been found by Gehrcke and Reichenheim to constitute the anode rays .
At higher gas-pressures there is a considerable increase in the thermionic current , corresponding presumably to an increased emission of positively charged ions from the heated anode .
On the view which is advocated by Richardson no part of the current is carried by the gas , and this increased emission consists solely of positively charged atoms of the metallic constituent of the salt , but , so far as the author is aware , no theory has been advanced which explains how the presence of the gas increases the emission of these atoms .
The theory that the ions are entirely metallic atoms seems to rest upon some experiments of Davisson , * by which he claims to have proved ( 1 ) that the gases emitted by a heated anode are uncharged , ( 2 ) that the increased thermionic emission from a salt which is caused by the presence of a gas is not due to the cause which I suggested in the paper referred to above .
The first of these conclusions is in direct opposition to the results of other observers .
In the case of aluminium phosphate heated upon platinum , Garrett , from observations of e/ m , concluded that some of the carriers were charged hydrogen atoms , and the earlier work of Richardson on the positive discharge from heated platinum led him then to the view that the gas emitted by the hot metal was ionised .
Richardson investigated the positive leak from the outer surface of a platinum tube heated electrically in air at atmospheric pressure , while hydrogen was diffusing through the walls of the tube from the inside .
The results showed that the effect of the hydrogen was " to produce an additional number of positive ions proportional to the amount of hydrogen diffusing out , " from which Richardson concluded that " the hydrogen inside the metal , which is known from other considerations to be in the atomic state , is positively charged , " although " only a small fraction of it comes out in the ionic form."f These experiments are strong evidence in favour of the view that the carriers of positive electricity from heated platinum which is evolving hydrogen consist , partly at all events , of charged atoms of that gas , and it would seem to be extremely probable that the carbon monoxide gas which is generally evolved by a heated anode is also emitted in an ionised condition .
Of course , it does not follow that since the gases emitted by a metallic anode are ionised , that those emitted by salt anodes are also ionised , though I think this is usually the case , but it must be remembered that in the usual method of testing the thermionic emission , the salt is heated * C. J. Davisson , 4 Phil. Mag. , ' VI , vol. 23 , p. 139 .
+ O. W. Richardson , ' Phil. Trans. , ' 1906 , A , vol. 207 , p. 58 .
144 Dr. F. Horton .
Positive Ionisation Produced [ Nov. 28 , upon a strip of platinum and there is doubtless a liberation of ionised gas from this .
It was probably hydrogen evolved in this way from the platinum strip which was detected in the determinations of e/ m for the ions in Garrett 's experiments .
Davisson 's second conclusion\#151 ; that the increase in the thermionic current from a salt which is caused by the presence of gas , is not due to the emission of gas atoms or molecules which have been absorbed by the salt and are emitted in a charged condition\#151 ; rests upon determinations of the specific charge of the carriers from impure aluminium phosphate , in air and in carbon monoxide at pressures of about 0*1 mm. , and in hydrogen at about 1 mm. pressure .
The temperature of the anode was 600 ' C. ; the first observed value of e/ m in a good vacuum was taken to indicate that the ions were charged potassium atoms .
After longer heating the value found was much nearer the specific charge for sodium , and the ions were taken to be atoms of this metal .
On allowing gas to enter the apparatus the difficulty of measuring the specific charge of the carriers increased , owing to the scattering which occurs on collisions with the gas molecules , and Davisson concludes that this effect is responsible for the much smaller values which are then obtained .
From the curves given it appears that , with carbon dioxide , for example , the value of e/ m decreases from about 435 in a good vacuum to 280 at a pressure of 0T3 mm. ( The value of ejm for Na+ is 421 , and for C02+ is 243 .
) If an alteration of this magnitude is produced by the interference of the gas with the free passage of the ions , it is obvious that the method employed is quite unsuitable for determining the value of the specific charge of the carriers at the higher pressures .
Moreover , previous to these experiments of Davisson , Garrett had shown that in the case of an aluminium phosphate anode at 1005 ' C. , an increase in the gas pressure of the order used by Davisson produces only a very slight increase in the thermionic emission , and the increase would be very small indeed at the much lower temperature used by Davisson .
In the experiments recorded in this paper it was found that the emission actually decreases slightly as the gas pressure is gradually raised to about 1 mm. , so that if accurate measurements of e/ m could be made at this pressure they would not be expected to indicate that the gas is carrying any larger proportion of the current than it does at lower pressures . ?
Reference has been made at the commencement of this paper to the view recently advocated by Richardson as to the nature of the positive ions from incandescent metals .
Richardson obtained values of the specific charge of the ions from different metals varying from 486 to 337 , the mean value from measurements with 13 metals giving 25*7 for the mass of the carriers 1912 .
] by Platinum and by Certain Salts when Heated .
145 as compared with the mass of the hydrogen atom , from which he concludes they are atoms of sodium or potassium.* My experiments with impure aluminium phosphate have shown that if when first heated an anode is contaminated with sodium impurities , these disappear after the thermionic emission has been going on for some time , so that it is improbable that the value of the specific charge measured under these conditions refers to sodium atoms .
As the result of a determination of e/ m for the carriers of positive electricity from a hot platinum wire , Sir J. J. Thomson some time ago came to the conclusion that the current is carried both by atoms of the metal and by atoms or molecules of the surrounding gas.f Richardson , in his experiments , did not detect any ions of the former type , but his value of ejm for the carriers is not inconsistent with their being molecules of carbon monoxide carrying single charges ( CO+ ) .
It is known that many metals evolve this gas when heated , and that it is continually being set free in an evacuated vessel which contains traces of wax or grease , so that its presence in the apparatus used by Richardson is easily accounted for .
I think there can be little doubt that the large emission on first heating a clean platinum anode is due to escaping gas which comes from inside the metal in an ionised condition .
The connection between the gas emission from heated metallic wires and the emission of positive electricity from them has been carefully studied by Klemensiewicz.| He found that wires which had been heated in a good vacuum until the thermionic emission was very small , regained their activity when they were allowed to stand for some time in a gas at a pressure of several atmospheres , and that the recovery was aided by keeping the wires at a temperature of about 200 ' C. so as to assist the diffusion of the gas into the metal .
On the other hand there was no recovery of activity when the wires were allowed to remain for a much longer time in an evacuated glass tube .
There is thus a very close connection between the positive ionisation and the emission of absorbed gas , and this connection is most simply explained by the view that gas coming from the interior of the wire is ionised .
It is difficult to see any explanation on the supposition that the ions are atoms of sodium or potassium .
If the gas actually carries the current , we see at once the cause of the rapid fall of the emission from a new wire , for when the wire is heated the gas pressure inside it is increased and the gas diffuses out until there is equilibrium between the internal and the external conditions .
When , after * O. W. Richardson , ' Phil. Mag. , ' 1910 , VI , vol. 20 , p. 545 .
t J. J. Thomson , 4 Conduction of Electricity through Gases , ' Camb .
Univ. Press , 1903 , p. 185 .
1 Z. Klemensiewicz , 4 Ann. der Phys. , ' 1911 , vol. 36 , p. 796 .
146 Positive Ionisation Produced by Platinum when Heated .
long-continued heating , equilibrium is attained , there are as many gas atoms or molecules entering the wire in a given time as there are emitted by the wire .
The latter are ionised , a certain proportion of them ( probably a very small proportion of them ) is positively charged , and it is the charges carried by these which constitute the small " steady " current which is given by a wire which has been heated for a long time .
This is the view of the emission of positive ions from heated metals which the author thinks is most in agreement with the experimental results ; at the same time , if the metal is not perfectly clean , or if there are gases or vapours present which have chemical action upon it , there is probably , a certain amount of ionisation produced in other ways .
If there is a trace of sodium or of potassium impurity on the anode , then it is probable that atoms of these metals assist in carrying the current as they do when a salt anode is used .
In the experiments with platinum described in this paper the metal was very carefully cleaned before being tested , and later in the research it was found that the usual large emission on first heating was obtained after the platinum had been heated in a Bunsen flame , although the flame gave no evidence of the presence of sodium .
I think , therefore , that the ions cannot be sodium atoms in this case .
A small amount of chemical action may give rise to considerable ionisation , and so if gases or vapours are present which have a chemical action on the anode there may be electrification produced while this action is going on .
It seems probable that some of the ionisation which is produced when certain salts are heated has its origin in chemical actions between vapours produced by these salts and the platinum on which they are heated .
This view has already been put forward by Richardson to explain certain ionisation effects which he obtained when various salts were heated to a high temperature in a platinum tube .
The author wishes to acknowledge his indebtedness to the Government Grant Committee of the Royal Society for the means of purchasing some of the apparatus used in these experiments , and also to Prof. Sir J. J. Thomson for his advice and kindly interest in the research , which was carried out in the Cavendish Laboratory .
|
rspa_1913_0015 | 0950-1207 | Ionic size in relation to molecular physics, together with a new law relating to the heats of formation of solid, liquid, and ionic molecules. | 147 | 169 | 1,913 | 88 | Proceedings of the Royal Society of London. Series A, Containing Papers of a Mathematical and Physical Character | W. R. Bousfield, M. A., K. C.|Sir J. Larmor, Sec. R. S. | article | 6.0.4 | http://dx.doi.org/10.1098/rspa.1913.0015 | en | rspa | 1,910 | 1,900 | 1,900 | 4 | 227 | 5,499 | http://corpora.clarin-d.uni-saarland.de/surprisal/6.0.3/?id=rspa_1913_0015 | 10.1098/rspa.1913.0015 | null | null | null | Tables | 45.933852 | Biochemistry | 26.052712 | Tables | [
-18.205167770385742,
-63.27928161621094
] | ]\gt ; 147 : Ionic Size in to Molecular Physics , together Law Relating to the of of Solid , Liquid ; and Ionic Molecules .
By W. R. BOUSFIELD , M.A. , K.C. ( Communicated by Sir J. Larmor , Sec. .
Received October 18 , \mdash ; Read Vovember21 , 1912 .
) CONTENTS .
PAGE 1 .
Introduction 147 2 .
Components of Heats of Formation of Solid , Liquid , and Ionic Molecules 149 3 .
ljerimental Work 156 4 .
Deduction of Ionic Yolumes and Empirical Volume lations 158 5 .
Comparative Values of Ionic Volumes 160 6 .
AnalyticaI Treatment of the Empilical Equations 161 7 .
The Empirical Relation between )oint Depression and Ionic Volume , and Deduction of Constants 165 8 .
Application to Ionic Volumes at Infinite Dilution 1 .
Introduction.\mdash ; The greater part of this communication is concerned with obtaining the volumes and densities of the ions and ionic nuclei of three salts from conductivity , viscosity , and -point data , a process which is of limited interest and is therefore reserved for later sections of this communication .
The deductions which are drawn from the values so obtained , in conjunction with other data already available , lead to certain conclusions as to the heats of formation both in the solid and ionic state which are of much wider interest and are dealt with in the next section .
In two former communications* there was developed a theory with reference to the ascertainment of the relative sizes of ions which was based upon a consideration of various physical data relating to KC1 and .
In the present paper the necessary data are given for extending the results to .
In the former papers an empirical linear relationship was found between the solution volumes calculated from density measurements and the ionic volumes deduced from conductivity and viscosity measurements , which is now extended to .
In the present paper a new empirical relation will be found between the ionic volumes and the reciprocals of the effective * I shall have necessity to refer from time to time to these papers , and will do so under the short names " " Ionic Sizes I\ldquo ; and ' ' Ionic Sizes II An abstract of the former is to be found iu 'Roy .
Soc. Proc 1905 , p. 563 , but the references herein given are to the full paper , which was published , with some additions , in the 'Zeit .
fur Phys. Chem 1905 , vol. 53 , p. 257 .
The second paper was published in ' Phil. Trans 1906 , vol. 206 , p. 101 .
For the understanding of the later sections of the present communication it is necessary that the reader should have the second paper before him .
VOL. 148 Mr. W. R. Bousfield .
ombination interesting information aoint dhree Sations aound t relative volumes and densities of the ions and of the ionic nuclei . !
The three salts above mentioned are compounded of some of the most : compressible of the elements , and are therefore admirably suited for a consideration of volume changes in relation to heats of formation .
Now that we are coming to regard an atom as being itself composed of hundreds of more minute bodies ( which we will designate as corpuscles , in order to adopt a neutral term ) there is no a priori improbability in the theory of the compressibility of atoms .
We shall therefore express our results in terms of this hypothesis , to which they appear to give considerable support .
In ordel to correlate changes of atomic volume with heaCs of formation , it was necessary to consider a wider erroup of compounds of the same class as the three salts above mentioned .
For this purpose certain available data exist within a sufficient area to enable a useful generalisation to be made .
These data lead us to a new law relating to the heats of formation of the solid and liquid compounds formed from the elemerits and radicles of the ubstances considered , which may be enunciated as follows:\mdash ; The heat of formatio due to the combination in the liquid ' solid state of any of electro-positive elements with any of the electro-negative elements or radicles is approximately equal to the sum of certain calorific constants of the two elements or radicles , together with , where is the change of atomic volume produced by the combination .
This leads us to the conception of the internal energy of an atom as the sum of the kinetic energy of the corpuscles and of their potential energy under their mutually attractive forces .
On this view , the heat component , , represents the change in the internal energy of the atoms due to their volume changes on combination .
The heats of ionisation of , and are apparently irregular and have not hitherto been regarded as periodic functions of the atomic volumes .
The application of the factor to the contraction of volume of the nuclei will be found to show the heats of ionisation as periodic functions .
It appears probable that we can briug he heat of ionisation into complete subordination to the same general law as that above enunciated for the solid and liquid compounds of the same class .
* In a former paper ( Ionic Sizes II , p. 142 ) I used this expression to indicate the so-called molecular depression divided by , where is the ionisation coefficient .
The effective molecular depression of the freezing point may be shortly indicated by the .
letters E.M.D. , so that the E.M.D. is .
* .
1912 .
] Ionic Size in Relation to Molecular Physics .
149 2 .
Components of Eeats of Formation of'Solid , Liquid , and Ionic Molecules.\mdash ; Sufficiently complete data are available for most of the compounds of Na , and Li , with the radicles Cl , Br , I , , to enable us to arrive at a generalisation within this limited area as to the relation between heats of formation and atomic volumes .
The values of the atomic volumes of the elements in the uncombined state are indicated by the letter , and are set out at the foot of the table .
The values are those given by Mendele'eff , with the exception of those for , Na , and Li , for which the values are those given by Richards based on his own density determinations .
* The atomic volumes of the positive elements of each compound are set out in the column headed and those of the negative radicles in the column headed .
The values given for the compound radicles , such as , are merely the sums of the atomic volumes of their components .
The column headed gives the sums of the atomio volumes of the elements in each compound .
Under are given densities of the solid and liquid compounds , and under their atomic weights .
The quotient .
is therefore the actual ular volume of each compound .
The difference is the contraction of volume for each molecule which takes place on combination , and is set out in the column .
The actual heats of formation in -calories from Thomsen 's data are given in the column headed H.F. It will now be seen from the table that each heat of formation is the sum of three quantities , viz. , a part which is proportional to the total contraction , and is expressed by a remainder which is the sum of two components and , which have approximately the same value for each adicls in every combination .
To split the additive components into parts and we require a definite starting-point , which is wanting .
It is obvious , however , from the heats of formation of HC1 , , and that the calorific constant for the hydrogen atom is comparatively small .
If we place it at 1 then the calorific constants for the other radicles are those given under ' Values of \ldquo ; at the foot of the table .
If the value of for hydrogen were 3 instead of 1 we have only to diminish the heat components for each of the negative radicles by 2 , and increase the heat components for the positive radicles by the same amount .
It must , therefore , be understood that the value of 1 for the heat component for hydrogen is arbitrary , but it makes no difference to the additive scheme .
The is that all the heats of formation may be approximately expressed as separate components are set out in three columns of table and the 'Journ .
Amer .
Chem. Soc 1909 , vol. , 156 W. R. Bousfield .
[ Oet .
18 , 1912 .
] Ionic Size in Relation to Molecular Physics .
151 sum in the column headed 2 .
The column headed " " Diff shows the differences between the observed and calculated heats of formation .
The principle which is involved in the relationship which thus comes to light is probably capable of wider application , but data for extending the generalisation are very difficult to obtain .
At the suggestion of Prof. Sir J. Larmor data have been collected for another group .
They are set out in Table II .
The errors between observed and calculated values are about * twice as great as in the first group , but the heats of formation of the bivalent .
salts are also about twice as great .
Within the area of both these groups we can say that the heat of formation due to the combination of one of the electro-positive atoms with one of the electro-negative atoms or radicles is the sum of three components , two of which are constants to the several combining atoms or radicles , and the other of which is approximately , where is the contraction which takes place on combination .
The last component possesses reat interest in connection with the theory of the compressibility of the atom .
It appears probable that the component represents the change of internal energy due to the contraction of the atoms S on combination .
Let us conceive the corpuscles of a free or uncombined atom as vibrating in a certain maximum space with a maximum average amplitude at a given temperature , the volume of the atom being determined by an equilibrium between attractive forces , which tend to approximate the corpuscles and to reduce the volume , and the energy of motion of the corpuscles , which tends to increase the volume .
If we suppose such an atom to contract or to be compressed isothermally , the internal kinetic energy would be diminished , owing to the reduction of the amplitude of the corpuscular vibrations with reduction of volume , and the internal potential energy would be diminished , owing to the approximation of mutually attractive corpuscles .
This reduction of internal energy appears to be expressed by , or at all events included in , the component , which would thus represent the heat so developed .
This , in the case of , amounts to more than a quarter of the total heat of formation , and in the case of the nitrates and iodates to a still larger fraction .
We have spoken of a reduction of internal energy due to compression , but it must be observed that in the cases of HC1 and , to which the law also extends , there is an increase of atomic volume on combination , and a resulting increase of internal energy .
We may now apply the result obtained as regards to consideration of the heats of formation of ions .
The ession of the atoms in the ionic state is even greater than in the solid state , as we may see the values of Mr. W. R. Bousfield .
[ Oct. 18 , 1912 .
] Ionic Size in Relcition to Physics .
set out below , which deduced from the values of obtained in Section 7 .
: This is probably due to the superiority of the attractive foroes which come toms themselves oteinto petween ttoms a ter , over the mutual forces between The heats of formation of the solid salts , which are in the order of their $ atomic weights and volumes , being 105 .
may be regarded as periodic functions .
On the other hand , the heats of ionisation appear to be irregular , It seems clear that the heat component due to atomic compression , which probably expresses the reduction of the internal energy of the atom due to the approximation of its corpuscles , should equally be a component of the heat of ionisation .
The application of this consideration at once the heats of ionisation .
If , 13 , 21 , respectively be the numbers of water molecules combined with the solute see the last section of this paper ) , and if we attribute to each molecule of combined water a calorific constant , we may express the heats of ionisation of the three salts by one formula .
Heat of ionisation It will be noticed that in this scheme the idiosyncrasies of the ions Na , Li have disappeared except so far as they affect contraction and water combination , no place having been found for their individual calorific constants and , as to whose values it may be observed that they are so qmnu a ?
1 uaqA AttiI xapun I \mdash ; : oIlOfl buaqos ?
uauod -moi ) S1 } xatBI SIItIA 4 uo 8 . ? . . . . . . . . . . .
quIOO 30 eJOJj -uoo SI( UBO eq lsnm A )'JJOO $ ?
a{I ) $uuodmoo ?
addle $I AtOU SUOO onoJQ q a $deoxBJJUOO IIOS SI ?
SUOO 9 gsnog The last column shows the value of which results from these figures on the assumption that the whole of the water is in combination with the acid .
Thus up to a value for is yielded which is very nearly equal to the value deduced from the ions of the three salts above mentioned .
For 'Principles of Chemistry , ' Ed. 1905 , vol. 2 , p. 271 .
' ' Ionic Sizes I p. 304 .
Wiss .
Abhand .
der Phys. Tech .
Reichsanstalt , ' 1905 , vol. 4 , p. 246 .
uo pestq Jadtd pam$ ?
tqo dapuI Oenba S oq sqns pue $ U10J ; }Isuap a aas S1 sJaded : Relations between and KC1 . . . . . . . .
The molecular solution volumes are obtained by multiplication by the equivalent weights , which are ( old atomic weights ) 58 .
These lead to the empirioal volume relations in the form in which they are required for KC1 . . .
These equations are of the form the constants and for each salt being as shown .
from the viscosities it was that , both in the case of KC1 and , we were led to the result that the ctive molecular freezing-point depression , over a certain range of concentration , came out as a constant when reckoned upon the free water in } solution , that is , after deducting from the total water the amount of combined water calculated from the ionic volumes .
In the present paper this is taken as starting point for the determination of .
A new and more convenient empirical relation between ionic volume .
and freezing-point depression enables the factors to be worked out upon a systematic basis .
This relation is of the form , where is the effective molecular freezing-point depression , is the number of cules of solute per 1000 .
water , is the ionic volume reckoned in the old units , and is the volume of the ionic nuclei in the same units , and being constants .
By the use of this empirical relation in combination with that between ionic volume and solution volume it is possible to evaluate and to obtain the volumes both of the ions and of the ionic nuclei .
One theoretical defect in this process must not be overlooked .
" " Ionic Sizes II p. 156 .
" " fonic Sizes II p. 139 .
' fouic Sizes II p. 149 .
1912 .
] Ionic Size in Relation to Molecular Physics .
161 This is that we are using ionic volumes based on conductivities measured at C. as applicable to the solutions in the hbourhood of the freezing point .
To make our deductions strictly accurate , the ionic volumes should be based on conductivities also measured in the neighbourhood of the freezing point .
But no sufficiently accurate data of this kind are in existence .
The general character of the deductions of this paper will not be seriously modified by this defect .
It should be remembered that though a different factor is required for each salt to make the ionio volumes derived from the mobilities comparable as between the different salts , yet for any given salt the ionic volumes are strictly comparable through a certain rang of concentration .
Each set of ionic volumes , calculated as in the former papers from conductivity and viscosity data , must be considered as being given in its own arbi rary unit , the factor in each case reducing the arbitrary unit to ordinary units .
It should be noted that though we use the separate radions and of the positive and negative ions to arrive at the joint ionic volume of the solute , our factor , being applied to the joint volumes , cannot be used to obtain the absolute values of the radions .
These are not wanted for our present purpose , but to indicate that and require different factors to reduce them to absolute values it is better to term and the " " mobility radions 6 .
Analytical Treatment of the Equations.\mdash ; Before we are in a position to evaluate the required constants of the new empirical relation it is necessary to consider its physical meaning in combination with that of the other empirical relation It will be conyenient at this stage to collect together the symbols used in A tabulated form for reference .
Symbols Solution volume of 1 grm. of solute .
Volume which 1 .
of solute occupies in solution .
Weight of 1gramme-molecule of solute .
Weight of 1 gramme-molecule of water .
Density of free or uncombined water .
Average density of water which is in combination with the solute .
Volume of 1 gramme-molecule of free water .
Volume of 1 gramme-molecule of combined water .
We found formerly*that the E.M.D. , when reckoned upon the free water of the solution only , came out as a constant .
The E.M.D. is when this is reckoned upon the total water .
We shall still keep express this fraction .
The fact that the E.M.D. when reckoned upon the free water is a constant will then be expressed by , ( 1 ) where is a constant , and is equal to , or whatever number we decide to adopt as best for the limiting value of the E.M.D. The volume of water combined with 1 gramme-molecule of solute is , where is the volume of the ionic nuclei .
If is the factor required to reduce ionic volumes to litres and is the average density of the combined water , the weight ( in grammes ) of water combined with gramme-molecule of solute is 1000 , so that Hence equation ( 1 ) may be expressed as .
( 2 ) ' ' Ionic Sixes II p. 149 .
1912 .
] lonic Size in Relation to Molecular Physics .
Our empirical relation is Hence we have and S and we thus get for the required value of But there is still an unknown quantity , the density of the combined water , involved in this equation and an unknown quantity is required for the deduction of and .
We can obtain these by a concurrent consideration of the other set of empirical relations To interpret this equation we must remember that , the solution volume of a molecule of solute , is the volume which the molecule of solute occupies in solution less the contraction of the water which combines with the solute , that is to say , where is the volume which 1 .
of solute occupies in the solution , is the average contraction which 1 molecule of water undergoes in combination with the solute , and is the number of molecules of water combined with 1 molecule of solute .
It must further be noted that the volume of 1 molecule of the hydratedt solute , that is of 1 molecule of the ions and partly ionised molecules , is the volume which 1 molecule of solute occupies in solution plus the volume of the combined water , that is to say , where is the weight of a molecule of water .
By elimination of between ( 6 ) and ( 7 ) and noting that where is the density of the uncombined water , we get If we assume that at high dilutions , the density of the combined water , .
and , the density of the free water , are constants we may now compare our empirical equation ( 5 ) with equation 8 ) , and equate coetflcients .
But it is likely that there may be a change in the density both of the free watel and VOL. Mr. W. R. Bousfleld .
[ Oct. 1@ , .
the combined water in passing from high to low dilutions , and this limitation must , therefore , be borne in mind .
Equating coefficients we get , ( 9 ) .
( lO ) Now is the volume of the ionic nuclei in the same units as , and , therefore , from ( 9 ) and ( 10 ) we get .
( 11 ) From ( 4 ) and ( 10 ) , by eliminating , we get .
Whence also .
( 12 ) is thus expressed in terms of the constants of the empirical equations .
Also from and ( 10 ) by eliminating we get ' ( 13 ) and from ( 4 ) , ( 9 ) , and 13 ) ( 14 ) is thus expressed in terms of the constants .
By reason of 12 ) the last equation may be written in the interesting form .
( 15 ) Finally , the density of the combined water is given by ( 9 ) , which may be written .
( 16 ) For the simple calculation of from the experimental data we obtain from equations ( 3 ) and ( 12 ) the relation .
( 17 ) It will be noticed that we have treated and as if our conductivity data were taken at the same temperature as the freezing-point data .
This may in some equations produce an error of nearly two parts per thousand .
but the error produced on the value of is inappreciable .
It should also Ionic Size in Relation to Molecutar Physics .
be notieed that by treating and as constants in the region of high dilution we bring out as a constant .
This would introduce a small error at low dilution , as must probably be larger at such dilutions , owing to the reduced pressure on the nuclei when the ions are smaller and the water combination is less .
We have also neglected the difference in the value as between C. and C. 7 .
The Empirieol Bptation between Freezing-Point Depress and Volume , and of Constants.\mdash ; We are now in a position to obtain the empirical relations between freezing-point depression and ionic volume for the three salts under consideration .
Let us first take the identical set of figures set out iu the former paper*for KCL These were there shown to lead to the relation within the limits of experimental error .
* They equally lead to the new relation within the same limits .
The choice of the new relation instead of the old one is determined by the fact that it admits of a precise theoretical interpretation as was shown in the preceding section .
In the following table , the first , second , third , and fourth columns are set out the same figures as were formerly given for .
The values for the molecular depression of the freezing point are those given by Jahn .
The figures given for the calculated values of are obtained by taking Table VIII.\mdash ; Empirical Belation between Freezing-point Depression and Ionic Volume for * Ionic Sizes II p. 143 .
' Zeit .
Phys. Chem 1904 , vol. 60 , p. 136 .
166 Mr. W. R. Bousfield .
ahn 's [ Oct. 18 , If we look at the values of derived from Jahn 's duplicate differences oated vuesof lrder adifferences , aywithin timits oerror Aoncentration , which the , refore sithout doubt tation i is the most important for determining the limiting value of , Jahn 's results give a difference of on .
But such experimental differences at low concentration cannot be avoided , and , as a consequence , we find that Jahn 's figures for the three salts , yield three different values for the constant , which should theoretically be the same for each .
It seems clear that these differences in the value of , which is the limiting value of at infinite dilution , can only be due to experimental errors , and we shall , therefore , take a fixed value for which is the same in all three cases .
The reciprocal of the value which is yielded by the above figures is .
This is a higher value than that which is usually accepted .
Bedford 's figures*seem to be the most recent and the most reliable .
The highest figures which he obtained for the molecular depression of the freezing point with KC1 solutions were and , corresponding to effective molecular depressions of and .
We shall assume as the of our calculation the right figure , instead of .
This gives the value of our constant , instead of .
Taking this value of we might deduce from Jahn 's figures for each salt a value of for the salt which would be the mean value yielded by all the figures .
Since , however , the probable error in the value of given by any particular ation is inversely proportional to we shall deduce the value of from the mean of the two highest concentrations given in each case by Jahn .
As we are dealing with a straight line law this will be likely to give us the best values .
The figures which Jahn gives for these concentrations are as follows:\mdash ; Table IX.\mdash ; Jahn 's Values for Depression of Freezing Point .
Using the values of the hydration numbers and ionisation constants before given we arrive at the following figures by taking the mean of each pair of observations .
' Roy .
Soc. Proc 1910 , , vol. 83 , p. 464 .
is the number of molecules of vater per gramme-molecule of solute .
From these figures , taking , we arrive at the values for and * which are given in the following table:\mdash ; Table X.\mdash ; Values of the Constants and The values of are easily obtained by the use of equation 17 ) , taking the given data and putting , and taking the value of furnished by the empirical volume relation .
Our complete table of the constants of the empirical equations and of the values deduced from them by means of equations ( 4 ) , ( 12 ) , 13 ) , ( 14 ) , 15 ) , and ( 16 ) is as follows:\mdash ; Table XI.\mdash ; Constants Derived from the Empirical Equations .
8 .
Application to Ionic Votumes at Infinite Dilution.\mdash ; We are now in a position to complete the data required , in order to at the analysis of the ionic heats which is contained in Section 2 of this paper .
For this purpose it is only necessary to apply the figures obtained to deduce approximately the number of molecules of water combined with each pair of ions .
The toral volume of a gramme-molecule of ions in cubic centimetres is 1000 From this we must deduct the volume of the ionic nuclei to get the volume of the combined water , and multiply by the mean density of this water to get 168 Mr. W. R. Bouffield .
[ Oct. 18 , the weight .
Hence the weight of water combined with a gramme-molecule of ions of the so.lute at infinite dilution is Using the data given above the weights of combined water deduced are as follows:\mdash ; which expressed in molecules of water are 21.3 These numbers should be integers at infinite dilution , and taking the nearest integers we get for the molecules of water combined with the pairs of ions at infinite dilution , It has , of course , been observed that our analysis has not given us any means of separating the volumes of the several ions , or of the amounts of their separate water combination .
Our faotor is a factor which deals with the sum of the ionic volumes , and our quantity is the sum of the volumes of the nuclei .
But having regard to the mobilities of and Cl and to the transference numbers , we may reasonably conclude that the and Cl ions are of nearly equal size .
we took the Cl ion to be combined with five molecules of'water , we should have for the water combination of the other ions .
Na .
This is a very attractive looking series and there is something to be said for it .
Let us compare certain corresponding properties of the and Cl atoms and ions\mdash ; Now the joint contracted volume in the ionic state is 30 .
This is of the original joint volume 72 .
If the compressibilities were equal and the internal pressures in the ions equal , the respective contracted volumes would be ; nearly This would allow the Cl ion to have one more molecule of water than the ion , and yet have a less volume and greater mobility .
Unfortunately , Washburn 's transference experiments in order to determine the relative hydration*indicate that the numbers should be the other way , and that the ion has one more molecule than the Cl ion , in which the numbers for the separate ions yielded by our figures would be .
Cl. Na .
5 9 17 Whether Washburn 's method , which rests on the mixture with the solution a non-electrolyte , such as sucrose or raffinose , is completely reliable ia possibly open to some question .
If the Cl ion be taken to be combined with four molecules of water , the figures which his experiments yield are which may be compared with those above .
His figures are only relative , as * his method does not.yield absolute results , and the figures are for concentra- .
: tions of about normal instead of infinite dilution .
The division of the combined water between the separated ions is a matter of great interest , but fortunately it is quite unnecessary for the main purpose of this paper , which was deyeloped in the second section .
In conclusion , we may again refer to the fact that the precise figures .
depend , according to this method , on what is to be taken as the true value of the freezing-point constant .
If the low value be taken instead of the value , the figures come out as follows:\mdash ; but the general results of the second section of this paper are not affected thereby , though the value of the calorific constant for the water molecule in combination would be slightly altered .
* Technological Quarterly , ' 1908 , vol. 21 , p. 288 .
|
rspa_1913_0016 | 0950-1207 | On the new theory of integration. | 170 | 178 | 1,913 | 88 | Proceedings of the Royal Society of London. Series A, Containing Papers of a Mathematical and Physical Character | W. H. Young, Sc. D., F. R. S. | article | 6.0.4 | http://dx.doi.org/10.1098/rspa.1913.0016 | en | rspa | 1,910 | 1,900 | 1,900 | 6 | 145 | 4,905 | http://corpora.clarin-d.uni-saarland.de/surprisal/6.0.3/?id=rspa_1913_0016 | 10.1098/rspa.1913.0016 | null | null | null | Formulae | 88.177203 | Biography | 6.121247 | Mathematics | [
75.8311996459961,
-29.131328582763672
] | 170 On the New Theory of Integration .
By W. H. Young , Sc. D. , F.R.S. , Professor of Mathematics , University of Liverpool .
( Received November 28 , 1912 , \#151 ; Read January 16 , 1913 .
) S 1 .
In a paper published in the ' Proceedings of the London Mathematical Society/ * addressed to persons already acquainted with Lebesgue integration , I endeavoured to show that the method of monotone sequences enabled us to recognise intuitively the extensibility to Lebesgue integration of results known to be true for Riemann integrals .
For this purpose I naturally employed known results in the Theory of Sets of Points ; and , of course , also pre-supposed the proofs of the classical theorems whose generalisation was in question .
In the present communication I propose to indicate briefly how the method of monotone sequences enables us to prove , at one and the same time , these theorems and their generalisations .
For this purpose we have only to employ a slight modification of the procedure indicated in the paper cited ; one which , however , avoids all reference to the Theory of Sets of Points , f and assumes no results whatever in the Theory of Integration .
A careful study of the classical treatment of the theory of the integration \#166 ; of a continuous function shows that it is based on two principles , which are , however , not explicitly alluded to :\#151 ; ( 1 ) The function whose integral is required is approached as limiting function by discontinuous functions , whose integrals are already known , being in fact synonymous , if there be only one independent variable , with the sum of a finite number of rectangular areas ; these functions , which are constant in each of a finite number of stretches , by a natural and convenient choice of values at the points , necessarily finite in number , at which there is ambiguity , are , at our will , upper or lower semi-continuous functions.^ ( 2 ) The mode in which the limiting function is approached is by means of monotone sequences of these functions , and it is shown that , whatever * " On a New Method in the Theory of Integration , " ' Lond. Math. Soc. Proc./ 1910 , \#166 ; Ser. 2 , vol. 9 , pp. 15-50 .
t It is at the request of a distinguished mathematician of the older school that I have undertaken to explain the possibility of doing this .
I hope that the novelties in the present account will be regarded as sufficiently justifying the publication of this \#166 ; communication .
f For the definition and properties of semi-continuous functions see my tract " On the Fundamental Theorems of the Differential Calculus , " 'Camb .
Univ. Press , ' 1910 , pp. 6 , 7 .
On the New Theory of Integration .
monotone sequence of functions of the elementary type in question be employed , the limit of their integrals is necessarily the same .
If we then turn to the work of Darboux , to whom , and not to Riemann , our theory in its most generalised form is chiefly indebted , we find that he tacitly replaces the discontinuous function of which he is desirous to define the integral by two functions , one a lower semi-continuous function not greater than the given function , and the other an upper semi-continuous function not less than the given function .
To each of these functions he may be said to apply one half of the process employed in the classical theory in the case of a continuous function .
The lower semi-continuous function is approached from below , and the upper semi-continuous function from above only .
It follows , however , from the theory of such functions ; and , in particular , ^ from the fact that , if we divide an interval into a finite number of parts , and select a point in each part at which the function assumes its minimum value in that part\#151 ; supposing it to be a lower semi-continuous function\#151 ; or its maximum in that part\#151 ; supposing it to be an upper semi-continuous function\#151 ; and then subdivide each of the parts so obtained , and carry on the process indefinitely , the value of the function at every point is the unique limit of these minima , or maxima , respectively in its neighbourhood\#151 ; it follows , I say , from this fact , that the upper and lower semi-continuous functions in question are actually the limits of the discontinuous functions approaching them .
Moreover , the mode of approach is a monotone one ; and , as Darboux virtually shows , the limit of the integrals of the auxiliary functions approaching from below , and the limit of the integrals of the auxiliary functions approaching from above , are each of them unique and independent of the particular auxiliary functions , of the types specified , chosen to approximate to the given function .
These two limits are not , however , in general the same , and Darboux gives to them the names of integrate par dtfaut and integrate par exc\amp ; s respectively .
It lies in the nature of things to call these integrates par dtfaut et par exces the integrals of the lower and upper semi-continuous functions respectively which the generating functions have as limits .
Yet , as soon as we have done this , we have already taken a step into a domain which was closed to Riemann .
If further justification for this step is needed , it is easy to give it .
The extension to unbounded functions of the theory of integration in its most successful form , as developed by de la Vall4e Poussin , involved monotone sequences before the idea of Lebesgue integration had been mooted .
On the other hand , if for a moment we turn to the Theory of Sets of Points , we shall find that the definition we have just given of the integral of an Prof. W. H. Young .
[ Nov. 28 , upper semi-continuous function , for example , corresponds precisely , in the Theory of Sets of Points , to the convention by which we attach to a dosed set of points a content .
Now , even Riemann and his disciples have , implicitly or explicitly , always admitted the logical character of this convention .
The identity in question is evident , if we reflect that the function which is unity at every point of a closed set of points in the interval of integration , and zero elsewhere ( i.e , in the complementary intervals ) is an upper semi-continuous function , and that the definition we have given of integral is at once seen to be concomitant with that of the content of the closed set in question .
The matter becomes still plainer if we take the internal points of any non-# overlapping set of intervals , infinite in number , and not in general abutting , and suppose a function to be defined to have the value unity at each such point , and zero elsewhere .
The function so obtained is lower semi-continuous , and its integral , as we have defined it , is nothing more nor less than the sum of the series , necessarily convergent , of the lengths of these intervals .
The moment , however , that our definitions of the integrals of upper and lower semi-continuous functions have been accepted , the whole theory develops itself without a hitch .
In the first place we naturally formulate the following principle , which is perfectly general , and applies equally to bounded and unbounded functions:\#151 ; ( I ) A function is said to have an integral if it can be expressed as the limit { finite or infinite with determinate sign ) of a monotone succession of functions , belonging to a class of functions whose integrals have already been defined^ provided only that the limit of the integrals of the functions of every such succession is the samef and this limit is then called the integral of the given function .
It is convenient to add the gloss that the integral is not regarded as existing unless it is finite .
Denoting for brevity upper and lower semi-continuous functions by the letters u and Z , we are thus led to examine the nature of the functions generated as limits of monotone sequences of Z-functions and ^-functions .
A descending sequence of it 's gives us an u , an ascending sequence of Vs gives us an Z , but an ascending sequence of u 's gives us a new function in general , which we call a lu , and a descending sequence of Z 's gives us a new function which we call an ul , A repetition of this process leads , on the one hand , to a re-appearance of the lu- and ^Z-functions , and on the other to two new types of functions , which we may call lul- and i6Zw-functions .
It is clear that the process may be extended indefinitely , in such a manner , moreover , as to obtain functions for which a modified system of nomenclature is essential .
Confining our attention in the first instance to bounded functions , we have 1912 .
] On the New Theory of Integration .
173 to show that all bounded functions of the classes of types obtained in the manner explained possess integrals , in accordance with our principle ( I ) .
A theorem remarkable in itself , though intuitive in the light of recent theory , enables us to prove this once and for all , and at the same time gives us a different definition of integration , different in form , though equivalent in essence .
The theorem follows so simply from the considerations I have exposed , that I propose to state and prove it here .
S2 .
We shall suppose that the definition of the integrals of id- and / ^-functions as the limit of the integrals of descending successions of / -functions , and of ascending successions of ^-functions respectively , has been shown to be in accordance with principle ( I ) , and that this proof has been further supplemented by a proof that , if a function is both an ul and a lu , its integral defined by both of these two distinct processes is the same .
We shall also assume that term-by-term integration of monotone sequences involving functions which are lu- or ^/ -functions has been shown to be allowable .
The proof then turns on two lemmas:\#151 ; Lemma 1.\#151 ; Given a bounded lu , we can always find an ul , nowhere less than the lu , and having the same integral , and given a bounded ul , we can always find a lu , nowhere greater than the id , and having the same integral .
It is evident that the one half of the statement turns into the alternative half , if we change the signs of the functions .
Let/ i(^)^/ 2(^)^ ... be a monotone ascending succession of ^-functions , whose limit is the given / ^-function f(x ) .
Since fn { x ) is an ^-function , we may regard it as the limit of a monotone descending sequence of the elementary / -functions , and its integral as the limit of their integrals .
We may , therefore , take an / -function bn ( x ) ^ fn ( x ) , where J bn ( x ) dx ^ |/ w ( x ) dx+ 2~n~1e , If the succession bi ( x ) , b2 ( x ) , ... is not monotone ascending , we make it so , as follows .
Wherever bi(x)^\gt ; b2(x ) , we replace the value of b2(x ) by b\(x ) .
Let us denote the modified function by c2{x ) .
Then c2(x ) will still be ~ h ( x ) , also it remains an / -function .
Moreover C2 ( x)\#151 ; f2 ( x ) - \b2 { x)\#151 ; f2(x ) ] + [ \amp ; !
( x)\#151 ; fi ( x ) ] , whence , since both sides of this inequality represent / -functions , | [ C2 ( x)\#151 ; f2 ( x ) ] dx^e ( 2"2 + 2~3 ) \lt ; \e .
Similarly we modify bs , b\#177 ; , ... We thus get a monotone ascending sequence of / -functions c2(x ) , c%(x ) , ... , cn(x ) , ... such that Cn(x ) \#151 ; fn { pd ) , \[cn(x)-fn(x)]^^e .
( 1 ) [ Nov. 28 , Prof. W. H. Young .
Since the functions cn(x ) and fn(x ) are / -functions , this gives \fn ( x)dx^\ cn ( x)dx^\e + \fn ( x ) dx .
( 2 ) Hence , if gi ( x ) is the / -function which is the limit of the ^-succession , we get , by the definition of the integral of the / ^-function f(x ) , from ( 2 ) , \f(x ) dx^^gi(x ) dx - i\amp ; + \f ( x)dx , while , from ( 1 ) g\ { x ) -f(x ) .
Now let us again perform the same construction , taking \e , instead of \e , and choosing each of the / -functions which we employ to be ^gi(x ) .
We thus obtain an / -function g%(x)^f(x ) and -g\{x ) , and such that \f(x ) dx ^ |^2 ( x ) dx ^ \ e -f J/ ( x ) dx .
Continuing thus we obtain a monotone descending sequence of / -functions , gi(x)^g2(x)\#177 ; ... ^gn(x)\gt ; each ==/ ( # ) , and such that , for each value of n , J f(x ) dx == |gn ( x)dx^ 2~ne + J f(x ) dx .
If g ( x ) be the limiting function of the ^-sequence , then g ( x ) is ==/ ( x ) and is , by definition , an ^/ -function , and its integral , being the limit of J gn(x)dx is , as is evident from the last inequality , equal to that of f(x ) .
This proves the theorem .
Lemma 2.\#151 ; Given a bounded lul , we can always find an u.1 , nowhere less than the lul , and having the same integral ; and given a bounded ulu , we can always find a lu , nowhere greater than the ulu , and having the same integral .
The argument is precisely the same as the proof of Lemma 1 , except that the functions bn ( x ) are general / -functions , instead of elementary / -functions .
S 3 .
We can now at once prove the theorem which I have in mind .
Theorem.\#151 ; Given any bounded function , formed by any monotone process , such as those here described , we can find an ul-function not less than it , and a lu-function not greater than it , which have the same integral .
Suppose , for definiteness , that the monotone succession defining the function f(x ) is an ascending one , say , / iO ) -M%)- ... .
Then , without loss of generality , we may suppose that the theorem has been proved to be true for each function fn ( x ) of the sequence .
Let us take a / ^-function , g n ( x ) \lt ; fn ( x ) , and having the same integral .
Doing this for each integer n , we get a new succession , which , if not already monotone increasing , we modify as follows:\#151 ; At any point where g'i { x ) \gt ; g2 ( x ) , let us increase the value of the latter to that of the former .
Denoting the modified function by g2 ( x ) , it is still a fe-function ; and , since g'2(x ) ^g2(x ) 1912 .
] On the New Theory of Integration .
175 it has the same integral as before , equal to that of f2(x ) .
We then proceed to similarly modify g\ , and so on .
Thus we have a monotone ascending sequence of / ^-functions gn ( x ) , whose integrals are equal to those of the functions fn ( x ) .
The limiting function g ( # ) of this succession is an llu , that is a / ^-function , and is , of course , like every gn( % ) , not greater than f(x ) .
Also its integral may be obtained by term-by-term integration of the ^-sequence ; and is , accordingly , the limit of J fn ( x ) dx , that is J f(x ) dx .
Thus we have found such a / ^-function as was required .
Again , let us take an ?
^/ -function h'n ( # ) ^fn ( x ) , and having the same integral .
Doing this for each integer n we get a new succession , which , if not already monotone increasing , we proceed to modify as follows:\#151 ; Let hi ( x ) be the function whose value at each point is the lower bound of h\ ( x ) , h'2(x ) , ... , h'n{x ) , ... This function is easily seen to be an ^/ -function , since it is the limit of a monotone descending sequence of ^/ -functions , got by taking the lower bound of a finite number of the functions h'n ( x ) .
Similarly , let h2 ( x ) be the function whose value at any point is the lower bound of h'2{x ) , h'z(x ) , ... , h'n ( x ) , ... , and so on .
We thus get a monotone ascending sequence of W-functions hn ( x ) , such that fn { x ) \#151 ; hn ( X ) \#151 ; h n ( x ) , so that the integrals of these three functions are the same .
The limiting function h(x ) is a / ^/ -function , whose integral is , by definition , the limit of that of hn ( x ) , that is of fn ( x ) , and is therefore the same as that of f ( x ) .
S 4 .
We are thus able to show immediately that all the functions of the types we have introduced possess integrals in accordance with the principles we have laid down .
This is , however , not all that the theorem just proved enables us to do .
It gives us an entirely new definition of the concept of integration , which includes what we may , for convenience , call that of Darboux as a particular case .
Our new definition is as follows:\#151 ; Form the integrals of all upper semi-continuoUs functions less than the given function , and take the upper bound of these integrals ; form the integrals of all the lower semi-continuous functions greater than the given function , and take the lower bound of these integrals ; then , if the upper bound of the former , and the lower bound of the latter agree , the function is said to possess an integral , and the value of the integral is the common value of that upper bound and that lower bound .
The superiority of this definition over that of Darboux ( or that of Riemann ) consists in the fact that all bounded functions which may , in a sense easily Prof. W. H. Young .
[ Nov. 28 , understood , be said to be expressible mathematically , possess an integral in accordance with the new definition .
Darboux 's definition fails , in fact , because it is in general impossible to find an / -function and an ^-function having the given function between them , and possessing the same integral .
The new definition succeeds because it is always possible , in all the .circumstances which can arise in mathematical investigations , to find a Z^-function and an ^/ -function between which the function to be considered lies ( provided only it is bounded ) having the same integral .
S 5 .
When we come to consider unbounded functions no fresh difficulty arises in the application of our original principle , provided always we consider separately the modulus of the function , and the excess of the modulus over the function , or , which comes to the same thing , the two positive functions / i and / 2 , whose difference is / and whose sum is the modulus of / As in the other theories non-absolutely convergent integrals require separate treatment .
This treatment may be the same as in the older theory , except that a limitation is removed , corresponding to the restriction implied in the Riemann definition .
In discussing unbounded functions , we may , therefore , in considering the new theory , confine our attention to positive functions , and it is clear , from what has gone before , that this is the case also with bounded functions .
In *other words , in the proof of all our theorems in the new theory of integration we are at liberty to suppose that the functions with which we are concerned are positive , and we need not restrict them to be bounded .
In the case of an unbounded positive function , we can no longer enclose it between an ul and a lu , we can , however , always enclose it between an unbounded lul and an unbounded lu .
If we include infinity ( + oo ) as a possible value of the integral , we can then prove that all unbounded positive functions which can present themselves in mathematical reasoning necessarily possess an integral in accordance with both our definitions .
S 6 .
I have now completed my sketch of the theory , regarded from the point of view of monotone sequences .
If the exposition may seem somewhat long , two things are to be observed:\#151 ; One is that all reference to the Theory .of Sets of Points , with the various difficulties which it presents to many .students , is avoided in it : and the second is that , if the development of the theory is tedious , it is not so with the applications of it .
It remains to show that this is the case .
For this it will be sufficient to consider two examples .of different types .
I take first the theorem that change of order of integration is always allowable in the case of an unbounded positive function .
As passage by monotone sequences is always permissible when we are dealing with positive quantities , it is at once evident that the theorem is true 1912 .
] On the New Theory of Integration .
always , if it is true for the simple bounded upper or lower semi-continuous functions with which our chain of monotone sequences began .
But these functions are constant in rectangles , and their double integrals consist of the sum of the volumes of a number of rectangular parallelopipeds .
Hence , in the case of these simple functions , the repeated integrals are both equal to the double integral .
Hence , they must be equal in the case of any bounded , or positive unbounded function of two variables whatever .
As another example I take Schwarz 's inequality , namely , that ( Juv dx)2 ^\v ?
dx\v2dx .
It is clearly sufficient to prove it for the simple functions .
Let ai , a2 , ... , an be the values assumed by one of these simple functions u , -corresponding to a division of the interval of integration into n equal parts , each of length A ; bi , b2 , ... , bn the corresponding values of v. Then J uvdx = ( ad\gt ; \ + \amp ; 2\amp ; 2 + ... + Ctrln ) A , ju2dx = ( cti2-{-a22+ ... +an2)h , lv2dx = ( b12 + b22+ ... +bn2)h .
Thus the theorem is shown to be nothing more nor less than the assertion in the language of integrals of the well-known algebraic inequality , )(2\amp ; !2 ) .
S 7 .
This is not an occasion to dwell on the usefulness of the new concept , which is sufficiently evident to anyone who has had an opportunity of consulting recent mathematical literature .
It will suffice if I remind my readers that one of the reasons for its original introduction was that it enabled us to find the inverse differential coefficient of a bounded function in cases when the Riemann theory failed to help us .
That any bounded sequence may be integrated term by term follows , indeed , from the fact that it can be replaced in two ways by a pair of monotone sequences , the one pair consisting of a descending one followed by an ascending one , and the remaining pair by an ascending one followed by a descending one .
We may , therefore , in the case supposed , integrate the sequence [ f(x+h)-f(x)\/ h term by term , since the incrementary ratio and the differential coefficient have the same upper and lower bounds .
Denoting then by F ( x ) , the indefinite integral of f(x ) , and integrating between the limits x and a , we thus get Lt / F ( # +A ) \#151 ; F ( x ) F(q + A)-F(a)\ 2 .
* n ' Jl .
h. h\#151 ; ?O f f(x ) dx , J a 178 Prof. W. H. Young .
[ Dec. 19 , whence , bearing in mind that f{x ) , being continuous , is the differential coefficient of its integral , we get at once f(x)-f(a ) = [ J a Here the sign of integration refers to integration of the generalised Lebesgue type , and it will be sufficiently evident from what precedes , that this equation is only then in general true when the sign of integration is interpreted in this sense .
It may be remarked that f(x ) is both a lu and an ul , and is , therefore , of a very elementary type in our scheme of functions .
On the Formation of Usually Convergent Fourier Series .
By W. H. Young , SeJD .
, F.R.S. , Professor of Mathematics , University of Liverpool .
( Received December 19 , 1912 , \#151 ; Read January 30 , 1913 .
) S 1 .
Series which converge except at a set of content zero , or , using the expression very commonly adopted , series which converge usually , possess many of the properties which appertain to series which converge everywhere .
It becomes , therefore , of importance to devise circumstances under which we can assert the consequence that a series converges in this manner .
The subject has recently received considerable attention .
So far as Fourier series are concerned no result of even an approximately final character has been obtained .
It may be supposed , indeed , that the results* of Jerosch and Weyl were at first so regarded , f but , if we examine them closely in the light of the Riesz-Fischer theorem , which was known previously to the results of these authors , it becomes evident that they are merely equivalent to the statement that the Fourier series of a function , whose square is summable , is changed into one which converges usually , if the typical coefficients an and bn are divided by the sixth root of the integer n denoting their place in the series .
Now it is difficult to believe that the question of the usual convergence of a Fourier series can depend on the degree of the summability of the function with which it is associated , * ' Math. Ann. , ' vols .
66 and 67 .
t The result due to Fatou that a series of Fourier converges usually if nan and nbn converge to zero is still more special , being of course included in Jerosch 's condition .
For Fatou 's paper , see ' Acta Mat .
, ' vol. 30 .
|
rspa_1913_0017 | 0950-1207 | On the formation of usually convergent Fourier series. | 178 | 188 | 1,913 | 88 | Proceedings of the Royal Society of London. Series A, Containing Papers of a Mathematical and Physical Character | W. H. Young, Sc. D., F. R. S. | article | 6.0.4 | http://dx.doi.org/10.1098/rspa.1913.0017 | en | rspa | 1,910 | 1,900 | 1,900 | 9 | 114 | 2,926 | http://corpora.clarin-d.uni-saarland.de/surprisal/6.0.3/?id=rspa_1913_0017 | 10.1098/rspa.1913.0017 | null | null | null | Formulae | 69.942668 | Tables | 22.928202 | Mathematics | [
70.23941802978516,
-47.141395568847656
] | ]\gt ; 178 Prof W. H. coefficient of its integral , we get at once interpreted iense.emarked tnthis equation itrue wntegration isLebesgue Gvident frecedes , bearing ibeing continuous , Here tntegration refers tntegration o , and is , therefore , of a very elementary type in our scheme of.functions .
On the Formation ofConvergent Fourier Series .
By W. H. YouNG , Sc. D. , F.R.S. , Professor of Mathematics , University of Liverpool .
Received December 19 , 1912 , \mdash ; Read January 30 , 1913 .
) S1 .
Series which converge except at a set of content zero , or , using the expression very commonly adopted , series which converge usually , ossess many of the properties which appertain to series which converge everywhere .
It becomes , therefore , of importance to devise ciroumstances under which we can assert the consequence that a series converges in this manner .
The subject has recently received considerable attention .
So far as Fourier series are concerned no result of even an approximately final character has been obtained .
It may be supposed , indeed , that the results* Jerosch and Weyl were at first so regarded , but , if we examine them closely in the light of the -Fischer theorem , which was known previously to the results of these authors , it becomes evident that they are merely equivalent to the statement that the Fourier series of a function , whose square is summable , is changed into one which converges usually , if the typical coefficients and are divided by the sixth root of the integer denoting their place in the series .
Now it is to believe that the question of the usual convergence of a Fourier series can depend on the degree of the summability of the function with which it is associated , 'Math .
Anm vols .
66 and 67 .
The result due to Fatou that a series of Fourier converges usually if and converge to zsro is still more special , being of course included in Jerosch 's condition .
For Fatou 's paper , see ' Acta Mat vol. 30 .
1912 .
] Forvnation of Usually Convergent Fourier Series .
and it is still more difficult to see how precisely the sixth root of can have anything to do with it .
On the other hand Weyl 's method , which itself marks bn advance on that of Jerosch , does not obviously lend itself to any suitable modification which would secure a greater degree of generality im the result .
The mistake is frequently made of confusing theoretical interest withr practical importance in the matter of a necessary and sufficient test .
Testa which are only sufficient , but not necessary , are often much more convenient. . .
Still more frequently it is convenient to work from first principles , and not to use any test at all .
Instead of employing Weyl 's necessary and sufficient condition that a series should converge usually , I have attacked the problem directly .
The principles I have employed do not differ essentially from ! . .
those already exposed in previous communications to this Society , but the ' generality and interest of the results obtained in the matter in hand seem to justify a further communication .
These results are as follows:\mdash ; The Fourier series of any function uhatever , of any degree of summability , and its allied series , are both of them ( jhanged into Fourier which converge : usually , the coefficients and are divided by any power , however small , of the index denoting their place in the series , in other words , they are converted into such by the use of convergence factor , and by the of the convergence factor log More generally , they are converted into sueh series by the use of the convergence factor whose numerator unity , and whose denominator is , where and I have thought it .
sufficient to prove this latter theorem for the case in which .
With this before him the reader will easily be able , by induction or otherwise , to carry out the proof of the general result .
It will be remarked that , unlike Weyl , I have not considered general series of orthogonal functions .
The theory of these functions usually greater analytical difficulties , but not a greater wealth of ideas , and I have thought it best , with so many problems in the theory of Fourier series still unsolved , to confine my attention to this simpler class of seriesThe detailed study of the theory of Fourier series seems to me to form the best possible preparation for the larger theory .
Finally , it should be noticed that the results arrived at do not in any way strengthen the probability suggested by Lusin that the Fourier series of a function whose square is summable necessarily converges usuallyVOL LXXXVIIJ.\mdash ; A. 180 Prof. W. H. Young .
lusin 's statement that this is infinitely probable seems based that in any succession of partial summations of such a series a sub-succession $3 can be found which usually converges to the function .
This is , however , quite consistent with , for example , finite oscillation except at a set of content zero .
On the other hand , the results perhaps do suggest the possibility , though scarcely the infinite probability , of this latter circumstance presenting itself for all Fourier series .
If this be true , every monotone succession of constants , having zero as limit , would have the effect of the special series of constants employed in the theorems of the present communication .
These latter , however , are so far from being the most general successions of the monotone type that they are the Fourier cients both sine and of cosine series .
S 2 .
In the mode of investigaJion I have adopted , the following theorem and its analogue are fundamental:\mdash ; Theorem.\mdash ; liet be a summable function whose typical Fourier cosine a sine constants are and , and let , , , .
be a monotone descending sequence of constants with zero as limit , then the series boundedly at the point , provided a succession of constants can be found such that ( i ) bounded for values The series converges , ( iii ) is a function of Let denote the partial summation consisting of the first terms of 1 ) , and let .
( 2 ) Then , since , and , we get , rerarding f as periodic with period 2 Now 2 sin$u .
Formation of vergent Fourier Series .
Therefore , by and ( 4 ) , , ( 5 ) where Su \ldquo ; and is accordingly , to a constant factor pris , the n-th partial summation of " " lihe Fourier series of From ( 5 ) the truth of the theorem is at once evident , since by the hypothesis ( iu ) is a bounded function of , while the conditions ( i ) and are satisfied .
S3 .
The corresponding theorem .
for the allied series of is as follows:\mdash ; Theorem.\mdash ; Let be a summabte function , whose Fourier cosine and sine constants are and let , , , , be a monotone descending sequenee of constants with as limit , then the series ( 1 ) oscillates boundedly at the point , provided a succession of constants can be found , such that ( i ) is bounded for all values of ( ii ) The series 2converges , ( iii ) is a bounded function of Let denote the partial summation consisting of the first terms of and let Then , as in S2 , .
( 2 ) Now ( 3 ) Therefore , by ( 2 ) and ( 3 ) , ( 4 ) where ) 182 Prof. W. H. Young .
the allied series of the Fourier series of .
thesis ( bounded function oconstant factor psummation oying these theorems wrequire slementary r are bounded functions of in the convergence of series .
Lemma \mdash ; If where has posibive integral value , imjluding zero , and , then Writing we have But , which proves the lemma .
Cor.\mdash ; If , and has the same form as , with instead of , the series whose general converges .
Lemma \mdash ; If and the series 2convergent .
Writing we have ) ) .
But , whence .
Thus the series whose convergence is under discussion is not greater than the sum of two series both known to be convergent , namely , and This proves the lemma .
It should be remarked that if the index of the power of in the 1912 .
] Fonnation of Usually Convergent Fourier Series .
expression for be instead of , the series in question may be easily seen to be divergent .
Lemma and the seria 2 convergent .
Writing we have Hence , as in preceding proof , our series is the sum of series known to be convergent , which proves the lemma .
S5 .
In this and the next articles we shall prove certain properties as to the order of infinity of the partial summations of a Fourier series , and of its allied series , except at a set of content zero .
Theorem.\mdash ; Ifbe any surnmable fuwtion of , and , the integrals and are , for each value of not belonging to a certain set of zero content , bounded funetions of In fact the former integral may be written the absolute value of which is therefore where is a constant depending only on Here we have tacitly supposed that the integral just written down exists , which will certainly be the case , except for a set of values of of zero content , in virtue of a theorem that I have proved elsewhere , since and eosec are summable functions of In precisely the same way the second integlal is proved to be less in See W. H. Young , " " The gence of Certain Series Involving the Fourier Constants of a Function ' Boy .
Soc. Proc 1912 , , vol. 87 , p. 221 .
" " Sir la ralisation d theor6me de Parseval 'Comptes endus , ' 1912 , vol. 136 , p. 30 ; seance du ler juillet .
are , each value of not belonging to a certain set ' zero , bounded { $ functions of We have and therefore since llog is bounded in any closed neighbourhood of the origin , and remains bounded as increases indefinitely .
Hence since Sullog is summable in an interval enclosing the origin not containing the point the result stated with respect to the first integral is true , by reasoning similar to that employed in S2 , bearing in mind that it is clearly sufficient to prove the property in question for an interval of integration not including the point Precisely similar reasoning proves the statement with respect to the second integral , using the fact that is bounded .
S7 .
By a slightly more complicated process we arrive at the following result : Theorem.\mdash ; If be a summable function of , and log log , the integra and $ are , for valuof belonging to a certain set of zero , bounded functions of 1912 .
] Formation of Usualty Convergent Fourier Series .
We have For convenience of printing the quantities which now occur are to be supposed all taken in absolute magnitude .
Moreover , as in S6 , we may confine our attention to a conveniently small interval containing the origin , and not containing either the point unity , nor , and we need only consider the positive part of this interval .
We have then logJog log log Multiplying out , we get the sum of four terms , each of which is bounded , namely mu and mu , each multiplied by Hence , since is summable , the required result follows as before , for the first integral .
In a precisely similar way it follows for the second integral .
S8 .
The general theorem that I have been establishing step by step with regard to the order of infinity of the successions of our summations is now evident .
It is as follows:\mdash ; Theorem.\mdash ; If a mmable function of , the -th partial snmmation of the Fourier series of , and the corresponding summation connected with its allied series have an order of infinity which , for every and , is for every not belonging to a certain set of content zero , less them that of The reader may be left to complete the proof by induction , or otherwise .
S9 .
We are now able to prove the main theorems which form the subject of the paper .
We have only to take the fundamental theorems of SS2 and 3 instead of that of S2 .
Theorem 2.\mdash ; Under the same circumstances as in preceding theorem , the series , and converge usualty .
For since the condition ( i ) of SS2 and 3 is satisfied .
The condition ( ii ) is satisfied in virtue of the Lemma 1 of S4 .
Finally the condition ( iii ) is satisfied by S6 .
..Hence by SS2 and 3 and Abel 's Lemma the theorem is true .
Theorem 3.\mdash ; Under the same circumstances , the series converge usuatly .
1912 .
] Ynation of Converge.nt Fourier Series .
Hero we take and We then have showing that the condition ( i ) of SS2 and 3 is satisfied .
The condition ( u ) is satisfied in virtue of the Lemma 2 of S4 .
Finally the condition ( iii ) is satisfied by S7 .
Hence by SS2 and 3 the theorem is true , using once more Abel 's Lemma .
Theorem 4.\mdash ; Under the same circumstances the series 2 and 2 sin , where , usually .
Here we take We then have showing that the condition ( i ) of SS2 and 3 is satisfied .
The condition is satisfied in virtue of Lemma 3 of S4 .
Finally the condition ( iii ) is satisfied by S8 .
Hence by SS2 and 3 the theorem is true , using once more Abel 's Lemma .
S10.*If , instead of the theorem that exists as a function of almost everywhere , when and are summable functions , we employ the connected result that this function exists everywhere and is continuous , when the summabilities of and ars suitably connected , we obtain in a similar manner information as to the order of infinity everywhere of the partial summations of the Fourier series of the various types of functions .
In this way not only are results such as those exposed in my papers " " On the Convergence of Certain Series , etc. , \ldquo ; and\ldquo ; On the Fourier Series of Bounded Functions , \ldquo ; confirmed , but further new ones are obtained .
S11 .
On the other hand , Mr. G. H. Hardy points out that it is possible to slightly extend the results of this paper as regards Fourier series by utilising a theorem of Lebesgue 's instead of the above-mentioned theorem .
Indeed , we are thus enabled , in the case both of the Fourier series and its allied series , to replace the two 's by unities in the general convergence factor .
Moreover , in the case of the Fourier series\mdash ; as distinct , be it said , from the allied series \mdash ; we can , as he remarks , go still farther and obtain a further slight , but , as it *SS10-12 have been added during the passage through press , Feb. 8 , 1913 . .
supra .
'Lond .
Math. Soc. Proc 1912 , Ser. 2 , vol. 12 .
between the great mirror and its principal focus , is concave , and therefore shortens the effective focal length , in place of increasing it .
The deformations from spherical figures are also so great , especially for the great mirror , as to leave it doubtful whether the construction discussed could ever be the model for practicable instruments .
If we keep to the Cassegrain form , spherical aberration and coma may equally be corrected by deformations of the mirrors which , though large , are less extreme , but there remains a onounced curvature of the field .
For this reason I am led , in the present memoir , to consider more complicated systems produced by the interposition of systems of lenses .
Achromatism be preserved completely for a single focus if there are three lenses of focal length determined when their position are given , and if all are made of the same glass .
One of these lenses , which I 'lloy .
Soc. Proc 1912 .
' K. Gesell . .
Wissenschaften zu Gottingen , Math.-Phys.-Classe , ' Neus Folge , 1906 , vol. 4 .
|
rspa_1913_0018 | 0950-1207 | On a cassegrain reflector with corrected field. | 188 | 191 | 1,913 | 88 | 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.1913.0018 | en | rspa | 1,910 | 1,900 | 1,900 | 1 | 68 | 2,020 | http://corpora.clarin-d.uni-saarland.de/surprisal/6.0.3/?id=rspa_1913_0018 | 10.1098/rspa.1913.0018 | null | null | null | Optics | 39.894846 | Tables | 17.042932 | Optics | [
26.570205688476562,
-10.502854347229004
] | 188 Dr. R. A. Sampson .
[ Dec. 28y appears to me , important extension , by utilising an additional artifice already employed by Messrs. Hardy and Littlewood .
S 12 .
We may similarly , when desirable , instead of the connected result referred to in S 10 , use a property of an integral of a function of given kind of summability , such as follows from considerations exposed in my paper on " Summable Functions and their Fourier Series."* On a Cassegrain Reflector ivith Corrected Field .
By B. A. Sampson , F.R.S. ( Received December 28 , 1912 , \#151 ; Read February 13 , 1913 .
) ( Abstract .
) The purpose of this memoir is to discover an optical appliance which shall correct in a practical manner the faults in the field of a Cassegrain reflector , while leaving unimpaired its achromatism and the characteristic features of its design , which gives a focal length much greater than the length of the instrument , combined with a convenient position of the observer .
The question touches an investigation by Schwarzschildf as to what can be done with two curved mirrors the figures of which are not necessarily spherical .
With these he corrects spherical aberration and coma , but in order to secure a flat field he is led to a construction in which the second mirror , which is between the great mirror and its principal focus , is concave , and therefore shortens the effective focal length , in place of increasing it .
The deformations from spherical figures are also so great , especially for the great mirror , as to leave it doubtful whether the construction discussed could ever be the model for practicable instruments .
If we keep to the Cassegrain form , spherical aberration and coma may equally be corrected by deformations of the mirrors which , though large , are less extreme , but there remains a pronounced curvature of the field .
For this reason I am led , in the present memoir , to consider more complicated systems produced by the interposition of systems of lenses .
Achromatism can be preserved completely for a single locus if there are three lenses of focal length determined when their position are given , and if all are made of the same glass .
One of these lenses , which I * 4 Roy .
Soc. Proc. , ' 1912 .
t 'K .
Gesell .
d. Wissenschaften zu Gottingen , Math.-Phys.-Classe , ' Neue Folge , 1905 , vol. 4 .
1912 .
] On a Cassegrain Reflector with Corrected Field .
1891 call the reverser , is silvered at the back and replaces the convex mirror ; the other two are placed close together in the way of the outcoming beam , about one-third of the distance from the great mirror to the reverser ; the members of this pair , which I call the corrector , are of nearly equal but opposite focal lengths , introducing very little deviation in the ray but an arbitrary amount of aberration , according to the distribution of curvatures between the two-faces of each lens .
All the surfaces are supposed spherical except that of the great mirror .
The essential problem is to bring the necessary work into a form that will allow unknown quantities which express the distribution of curvature between the faces of each lens to be carried forward algebraically .
The methods employed are those of a recent memoir by the author , * and a part of the paper is occupied in working out expressions to which this theory leads , for thin lenses , systems of thin lenses , mirrors , reversers and the like , , and it may be regarded as an expansion and working illustration of that memoir .
This part does not lend itself to summary .
When the expressions are obtained the solution proceeds in a straightforward manner , by approximation , which is somewhat complicated owing to the number of considerations which it is necessary to keep in view , but is not otherwise difficult .
The solution is completed at the stage where the unextinguished aberrations are considered negligible .
Before determining the aberrations the system was made achromatic in respect to the normal , that is to say , the linear or ideal scheme , both in respect to position and magnification of the image .
Hence , at the end of the above steps , there might remain chromatic differences of the various aberrations , and it is a necessary condition that these also should prove inconsiderable .
When the curves of the lenses were given by a final solution the aberrations were calculated , to the third order without approximations , for the whole system for two different refractive indices , viz. , ^ = 1*5200 and I* = 1*535200 .
The object aimed at was to extinguish spherical aberration , coma , and curvature of the field , and to keep astigmatism down to very narrow limits .
The field whose curvature is contemplated is the field which passes through the circular images that lie midway between the two focal lines in a system which is free from coma .
Hence , in the system sought , the images of all points at the focal plane would be strictly circles , which increased in diameter with the square of the angular breadth of the field .
Distortion comes into the system with the separated lenses , but this does-not impair the images of points , and so long as it does not reach an * " A New Treatment of Optical Aberrations , " 4Phil .
Trans. , ' vol. 212 , pp. 149-185 .
190 On a Cassegrain Reflector with Corrected Field .
unmanageable amount it may be dealt with as a correction , calculated and applied to any measures that are made .
In the following particulars of the construction , together with its outstanding defects , the notation , though not exactly in the standard form , almost explains itself ; thus all the quantities with suffix 2 , for example , relate to the reverser , a2 being its semi-aperture , t2 its thickness , R2 , R2 ' the radii of its anterior and posterior surfaces .
Similarly , the suffixes 4 , 6 , relate to the first and * second lenses of the corrector , while the quantities d are the distances from surface to surface .
The unit employed is 1 inch .
The quantity e gives the departure of the great mirror from a parabolic figure , on such a scale that e0 = 1 would give a sphere .
Hence the figure is five-sixths of the way from a sphere to a paraboloid .
The greatest angle between the ray and the normal to any surface is 11 ' , at emergence from the second surface of the first lens of the corrector .
For comparison the particulars of a Newtonian of equal focal length and aperture and paraboloidal mirror are also given .
It may be remarked that if the solution had been made originally for the greater refractive index in place of the smaller , the residual aberrations shown by the other would apparently have been less in place of greater , so that those for which the solution was made are to be regarded as the significant ones .
Grjeat mirror\#151 ; Aperture ... ... ... ... ... ... ... ... ... ... ... ... ... ... 2a0 = 40*0 Radius of curvature ... ... ... ... ... ... ... ... ... ... R0 = - 400*000 Figure ... ... ... ... ... ... ... ... ... ... ... ... ... ... . .
e0 = +016468 d , = +132-013 Reverser\#151 ; Aperture ... ... ... ... ... ... ... ... ... ... ... ... ... ... 2 a2 = 16*2 First surface ... ... ... ... ... ... ... ... ... ... ... ... R2 = +211 *603 Silvered surface ... ... ... ... ... ... ... ... ... ... ... . .
Ra ' = +221*289 Thickness ... ... ... ... ... ... ... ... ... ... ... ... ... ... .
t2 = 2*000 o ?
3 = +90*676 Corrector , first lens\#151 ; Aperture ... ... ... ... ... ... ... ... ... ... ... ... ... ... .
2a4 = 12*2 First surface ... ... ... ... ... ... ... ... ... ... ... ... R4 = -144*298 Second surface ... ... ... ... ... ... ... ... ... ... ... ... R4 ' = +48*824 Thickness ... ... ... ... ... ... ... ... ... ... ... ... ... ... .
t4 \#151 ; 1*250 d5 = +0*500 Ditto , second lens\#151 ; Aperture ... ... ... ... ... ... ... ... ... ... ... ... ... ... 2 a6 = 12*2 First surface ... ... ... ... ... ... ... ... ... ... ... ... .
R6 = - 4138*559 Second surface ... ... ... ... ... ... ... ... ... ... ... ... R6 ' = - 38*285 Thickness ... ... ... ... ... ... ... ... ... ... ... ... ... ... .
t6 = 1*500 Distance to principal focus ... ... ... ... ... ... ... ... ... .
d7 \#151 ; +71*377 Focal length ... ... ... ... ... ... ... ... ... ... ... ... ... ... f7 ' = +508*802 Distance of principal focus beyond surface of great mirror + 33*290 Whole length of instrument ... ... ... ... ... ... ... ... ... 167*3 Diurnal Variation of Terrestrial Magnetism .
191 Specification of Field at Angular Radius 34*4 ' = tan 1 0*01 .
At - 1*5200 .
At 1*5352 .
[ Newtonian .
] Radius of least circle of aberration 0 *000 " -0 -007 " 0 *00 " " comatic circle -0*005 + 0-069 + 0*80 " focal circle + 0*370 + 0-566 -0*41 Distortional displacement + 6*75 , / + 7 -13 " 0*00 Curvature of field -1/ 16282 -1/ 542 -3 -1/ 508*8 On a New Analytical Expression for the Representation of the Components of the Diurnal Variation of Terrestrial Magnetism .
By George W. Walker , M.A. , A.R.C.Sc .
( Communicated by Prof. J. H. Pointing , F.R.S. Received January 8 , \#151 ; Read January 30 , 1913 .
) In any enquiry as to the cause or causes that contribute to daily or seasonal change of a periodic character in any observational quantity , the primary step is the determination of a simple and comprehensive expression for the dominant features of the phenomenon .
The periodic character of the variations of an element of terrestrial magnetic effect , such as declination , horizontal force , or the equivalent geographical components of force , is evident on almost every daily record obtained .
When the hourly values are set out and properly cleared from non-periodic change ( a problem of considerable subtlety ) , the historic method is to compute the Fourier harmonic components .
Another method that appears to possess great power is that so successfully carried out by Dr. W. Shaw in representing the daily and seasonal changes of meteorological elements by means of " isopleths If a Fourier analysis reveals the existence of a limited number of dominant terms , that is so far satisfactory and provides definite material on which the theorist may work .
But , in the case of the terrestrial magnetic elements , there is abundant evidence to show that even four Fourier terms give a very inadequate representation of the facts , and , with the exception of Dr. Schuster 's valuable memoirs based on consideration of the first two terms in the diurnal variation , the subject is in rather a dismal state .
The problem has attracted my attention for several years , and the following
|
rspa_1913_0019 | 0950-1207 | On a new analytical expression for the representation of the components of the diurnal variation of terrestrial magnetism. | 191 | 194 | 1,913 | 88 | Proceedings of the Royal Society of London. Series A, Containing Papers of a Mathematical and Physical Character | George W. Walker, M. A., A. R. C. Sc.|Prof. J. H. Poynting, F. R. S. | article | 6.0.4 | http://dx.doi.org/10.1098/rspa.1913.0019 | en | rspa | 1,910 | 1,900 | 1,900 | 2 | 34 | 1,017 | http://corpora.clarin-d.uni-saarland.de/surprisal/6.0.3/?id=rspa_1913_0019 | 10.1098/rspa.1913.0019 | null | null | null | Tables | 52.226878 | Meteorology | 26.90263 | Tables | [
45.86167526245117,
3.5836310386657715
] | ]\gt ; Diurnal riation of Terrestrial Magnetism .
Specification of Field at Angular Radius On a New Expression for the Representation of the Components of the Variation of Terrestrial lllagnetism .
By GEORGE W. wALxBIt , A.R.C.Sc .
( Communicated by Prof. J. H. Pointing , F.R.S. Received January 8 , \mdash ; Read January 30 , 1913 .
) In any enquiry as to the cause or causes that contribute to daily or seasonal change of a periodic character in any observational quantity , the primary step is the determination of a simple and comprehensive expression for the dominant features of the phenomenon .
The periodic character of the variations of an element of terrestrial magnetic effect , such as declination , horizontal force , or the equivalent geographical components of force , is evident on almost every daily record obtained .
When the hourly values are set out and properly cleared from non-periodic chan , ( a problem of considerable subtlety ) , the historic method is to compute the Fourier harmonic components .
Another method that appears to possess great power is that so successf.ully carried out by Dr. W. N. Shaw in representing the daily and seasonal changes of meteorological elements by means of " " isopleths If a Fourier analysis reveals the existence of a limited number of dominant terms , that is so far satisfactory and provides definite material on which tloe theorist may work .
But , in the case of the terrestrial magnetic elements , there abundant evidence to show that even four Fourier terms give a very inadequate representation of the facts , and , with the exception of Dr. Schuster 's valuable memoirs ased on consideration of the first two terms in the diurnal variation , the subject is in rather a dismal stnte .
The problem has attracted my attention for several years , and the following at once occurred as going a good way towards a rough representation .
The Curve I on the diagram ( fig. is aotually We note that as is required .
To plot the corresponding curve an obvious step .
In order now to make we require to shift the origin of , and so Curve II represents FIG. l.\mdash ; Graphs of the functions .
The curve III is obtained by the simple addition of I and II .
We have only to look at the curves*to see that III represents the characteristic features of the declination or west component for either Kew , Potsdam , or Paris .
' The essential feature of a declination curve is that the morning minimum is less in magnitude than the afternoon maximum , and that the curve is flatter at the minimum than it is at the maximum .
: The turning points be shifted by changing and the relative propor$ tions of I and II .
A great variety of curves can be obtained in this way , and : I am satisfied that any component , west , north , or vertical , can be imitated in essential features .
The general form suggested is thus wherein and are at our disposal and the origin of is also arbitrary .
It seems to me rather remarkable that curves essentially unsymmetrical can be imitated in this way .
Doubtless there are many other expressions of a similar type which could be used and the above is probably only the principal part of the correct formula .
It is not at once clear how a term in the denominator can arise physically , but the following tentative suggestion is worth considering .
There are some reasons for supposing that the magnetic field of the earth is in some way connected with the intensity of solar radiation in the upper regions of the atmosphere .
Now the intensity of radiation is approximately represented by a term of the form , where is the zenibh distance of the sun , and as , where is the latitude , the sun 's declination , and the hour angle , the occurrence of the term is suggested , but , of course , careful examination of local and seasonal effect is required before it can be accepted .
The curves of diurnal variation of the magnetic elements always indicate * Arrhenius , ' Cosmical Physics , ' or Chree , ' Phil. Trans 1903 , , vol. 202 .
194 Variation of Terrestrial twice ihours , imum aained bnother tithSented thief features bpresent tusion iated mhose different constants .
We may now indicate how the constants in the formula would be chosen so as to get the closest representation of the experimental curve .
The general scale of the curve fixes the most important relation of all between the constants .
It would be most natural to take the extreme range as fairly accurately known .
Again , the times of occurrence of zeros are given by and those of the maximum and minimum by We shall not be able in general to satisfy all these relations , for when the scale is prescribed only three more conditions can be satisfied .
In any particular case we should have to decide what points are most accurately given by the curve .
For instance , with declination in these latitudes there would be little hesitation in taking the maximum and the minimum with the zero occurring about noon as much more accurately determined than the zero towards midnight , and so we should take these three to determine the constants and let the remaining zero take care of itself .
The divergence will in fact be a measure of the correctness of the representation .
I had intended to reserve these considerations for inclusion in an extended examination of magnetic diurnal variation which I have in progress ; but as this method of considering functions that recur only once in 24 hours , and are capable of representing unsymmetrical curves , is of considerable interest , and I believe novelty , this account is now .
|
rspa_1913_0020 | 0950-1207 | A spectro-photometric comparsion of the emissivity of solid liquid copper and of liquid silver at high temperatures with that of a full radiator. | 195 | 205 | 1,913 | 88 | Proceedings of the Royal Society of London. Series A, Containing Papers of a Mathematical and Physical Character | C. M. Stubbs, M. A., M. Sc.|Prof. F. G. Donnan, F. R. S. | article | 6.0.4 | http://dx.doi.org/10.1098/rspa.1913.0020 | en | rspa | 1,910 | 1,900 | 1,900 | 2 | 227 | 5,064 | http://corpora.clarin-d.uni-saarland.de/surprisal/6.0.3/?id=rspa_1913_0020 | 10.1098/rspa.1913.0020 | null | null | null | Thermodynamics | 49.473953 | Tables | 13.334815 | Thermodynamics | [
0.5018436908721924,
-25.225614547729492
] | 195 A Spectro-photometricComparison of the Emissivity of Solid and Liquid Copper and of Liquid Silver at High Temperatures with that of a Full Radiator .
By C. M. Stubs , M.A. , M.Sc .
( Communicated by Prof. F. G. Donnan , F.R.S. Received January 9 , \#151 ; Read January 30 , 1913 .
) ( From the Muspratt Laboratory , University of Liverpool .
) Introductory .
In a paper which appeared recently in these c Proceedings'* Dr. Prideaux and the author communicated the results of a spectro-photometric comparison of the emissivity of solid and liquid gold at high temperatures with that of a full radiator , or " black body .
" Por solid gold , the curve for relative emissivity against wave-length was shown to be similar to , but not identical with , that for absorptivity at low temperatures determined by other workers ; whether the difference was due to a difference in the structure of the surfaces examined , or to a real temperature coefficient of the absorptivity , remained an open question .
At the high temperatures employed no appreciable temperature coefficient of the relative emissivity could be discovered , for either the solid or liquid metal .
At the melting-point , however , there is an abrupt change in omissivity , the curve for the liquid differing considerably from that for the solid .
In the present paper is described a similar investigation of the emissivity of copper and silver .
Apparatus and Method .
The general method pursued and the apparatus used were the same as described in the former paper , with the exception of such changes and modifications as will now be referred to .
The " black body " used in the present research was of the Lutnmer-Kurlbaum type.f It had certain peculiarities which perhaps are worthy of description .
Instead of the usual porcelain tube , an iron tube 58 cm .
long , 5 cm .
in internal diameter , and with walls 3 mm. thick was used ; the radiating surface consisted of a well-fitting iron block , 2 cm .
in thickness ; the radiating chamber was 4*7 cm .
in length , the nearest diaphragm to the radiating surface being of iron , 4 mm. thick , and with an aperture 1*6 cm .
in diameter .
* ' Roy .
Soc. Proc. , ' 1912 , A , vol. 87 , p. 451 .
t ' Ann. d. Phys. , ' 1901 , vol. 5 , p. 829 .
VOL. LXXXVIII.\#151 ; A. P 196 Mr. 0 .
M. Stubs .
Emissivity of Solid and Liquid [ Jan. 9 , In front of the radiating chamber were four other diaphragms , made of sheet nickel , which withstands oxidation well .
The temperature was measured by a thermocouple , enclosed in a thin-walled tube , which passed through the diaphragms immediately below the apertures , and fitted into a hole bored in the radiating block ; on the reverse side , a second checking thermocouple passed through suitable diaphragms and fitted into a hole bored in the centre of the radiating block .
The various diaphragms and radiating block were kept in their relative positions by stout iron rods , but could be moved collectively along the iron tube ; the radiating chamber could thus by actual trial be made to coincide with the region of uniform temperature .
The heating was by means of two windings of " nichrome " No. 22 resistance wire , on independent circuits , insulated from each other and from the iron tube by several layers of asbestos paper ; the outer one was , as suggested by Waidner and Burgess , * wound more closely at the ends than in the middle .
To sum up the advantages obtained , these were ( 1 ) evenness of temperature distribution through the nature of the winding , the conductivity of the walls of the radiating chamber , and the freedom of movement of the latter relative to the tube , and ( 2 ) automatic lining of the walls of the chamber , on heating , with iron oxide , which possesses a good degree of " blackness .
" The fact that at high temperatures a narrow hole bored in the centre of the radiating surface was invisible showed that very approximately full radiation was obtained .
The whole " black body " might probably with advantage have been made on a somewhat smaller scale .
Both copper and silver had to be kept in a reducing atmosphere , in order to avoid surface oxidation of the former , and the dissolution of oxygen in the latter , resulting in a considerable lowering of freezing-point and consequent uncertainty in temperature-measurement , and possibly also in a change in emissivity .
In the case of copper , the metal was contained in a silica pot inside a vertical iron tube 40 cm .
long and 5 cm .
in internal diameter , and closed at the bottom .
This tube possessed a hollow water-cooled cap which could be screwed tightly on .
Through the centre of the water-chamber was soldered a tube sufficiently wide to allow spectro-photometric observation of the copper ; other smaller tubes passing through the water-chamber were for the thermocouple , and for ingress and egress of hydrogen .
Over the central aperture was laid a thin microscope cover-glass , vaselined down at the edges , through which observations were taken .
A suitable tap allowed the observation-tube to be closed from the air when the cover-glass was removed for cleaning .
This arrangement proved quite satisfactory , and a slow stream of hydrogen passing * 4 Bull .
Bur .
Standards/ 1907 , vol. 3 , p. 165 .
1913 .
] Copper and of Liquid Silver at High Temperatures .
197 through the tube and out without burning kept the copper from oxidation , -The width of the iron tube was such that the reflection of its walls was not visible in the copper mirror .
The image of the under surface of the water-cooled cap , illuminated by the light of the furnace , would , however , be visible .
This surface was , therefore , lampblacked ; though as a matter of fact a simple calculation showed that the glowing parts of the heated tube were so far from the top that no appreciable influence would be exercised on the apparent emissivity of the copper , even if the bottom of the water-cooler were far removed from blackness .
In order to balance the loss of heat by conduction to the water-cooled end , the wall of the upper half of the iron tube was turned thin , and the whole tube then wound with " nichrome " resistance wire over asbestos paper , and placed within a large vertical platinum-wound resistance furnace whose heating-tube was 22 cm .
long and 12 cm .
in diameter .
With the aid of the heat generated by the passage of an auxiliary current through the winding on the tube , the desired temperatures were easily obtained .
In the case of silver , where access of oxygen below a red heat has not to be avoided , the metal was heated in a furnace whose heating-tube was a silica one wound with " nichrome " wire .
On to this tube fitted closely the water-cooled cap described above .
Any appreciable access of air was thus avoided^ and a reducing atmosphere was kept by placing a quantity of powdered graphite beneath the crucible containing the silver .
The metal was observed , as in the case of copper , through a thin cover-glass .
As was necessary for comparative purposes , the " black body " also was viewed through this glass .
The latter was in all cases cleaned from time to time .
The same care as described in the former paper was taken to calibrate and check the thermocouples , and the speetro-photometer with its comparison lamp .
Any change in the latter wTas checked and allowed for by making observations of " black body " radiation several times during the course of the experiments .
In measuring the temperature of the metals only one thermocouple was used , which was inserted about 1*5 cm .
into the metal .
Owing to the sharp temperature-gradient above the surface the temperatures indicated were a little too low , but were corrected , as described in the former paper on gold ( p. 456 ) , by observing the indication at the melting-point.* The corrections necessary were small , usually about 3 ' .
* In the case of oopper , allowance was made for the depression of freezing-point caused by dissolved hydrogen .
The latter amounts to 0*54 mgrm .
per 100 grm. of metal , according to Sieverts and Krumbhaar ( ' Zeits .
phys .
Ohem./ 1910 , vol. 74 , p. 292 ) .
From the depression constant given for copper by Heyn ( ' Zeits .
anorg .
Chem. , ' 1904 , vol. 39 , p. 20 ) , this would involve a depression of freezing point of less than 0*5 ' .
P 2 198 Mr. C. M. Stubs .
Emissivity of Solid and Liquid [ Jan. 9 , A method was devised of compensating automatically for the troublesome variable thermal E.M.F. of the potentiometer , mentioned in the former paper ( p. 457 ) , which , as such thermal E.M.F. 's occur frequently in these instruments , may be worth a brief description .
AiA2 and BiB2 ( fig. 1 ) are two of the pairs of circuit terminals on the potentiometer .
The thermal E.M.F. of the instrument tends to create a small difference of potential between Ai and A2 , or between Bi and B2 , whichever pair may be .
put into the potentiometer circuit by the circuit switch .
Ei is a battery which runs down through the high resistance R and the low slide-resistance XY .
With the circuit switch on AiA2 , and the main potentiometer current temporarily disconnected , the slider Z is adjusted so that the fall in potential along ZY is equal to that between Ai and A2 , due to the thermal E.M.F. ; the galvanometer will accordingly give no deflection .
If now E2 be the source of the E.M.F. to be measured , and connections be made as in the diagram Fig. 1.\#151 ; Diagram of method of compensating for thermal E.M.F. it is clear that between Bi and B2 there will be a fall in potential equal to E2 , together with the fall along ZY ; this latter will exactly balance the thermal E.M.F. , and consequently the reading of the instrument will correspond with the true E M.F. E2 .
Results and Conclusions .
( 1 ) Copper.\#151 ; About 400 grm. of pure electrolytic copper were used , the internal diameter of the containing pot being 4*2 cm .
and the depth of metal about 3*5 cm .
The solid copper surfaces whose emissivity was measured were prepared as follows :\#151 ; The block of previously fused electrolytic copper was turned flat in the lathe , then treated successively with four grades of emery paper , and finally polished on chamois leather with a little " Globe " metal polish , the surface being washed with benzene after polishing .
The use of rouge was avoided , as it is liable to tarnish soft metals , and actually did so in the previously investigated case of gold .
Brilliant mirrors were obtained which , on heating , showed practically no trace of filming due to impurity .
1913 .
] Copper and of Liquid* Silver at High Temperatures .
199 Even the best mirror was , however , marked with a few fine scratches .
Tate , also , * has recently found it impossible to get a perfect copper mirror by polishing .
The area occupied by these scratches would , however , be so small as scarcely to affect the emissivity ; and , in fact , they were invisible when the metal was heated to glowing .
The surface showed no apparent deterioration until within about 10 ' of the melting-point , when re-crystallisation rapidly set in , involving reflection of light from the furnace walls by the roughened surface .
A perfect mirror surface of liquid copper , free from film , was obtained without difficulty .
In Table I are given the values obtained for the relative emissivity of solid and liquid copper , calculated as shown in the former paper ( p. 458 ) .
The capitals at the head of the columns indicate , in alphabetical order , the order of the experiments .
The approximate temperatures are also given .
In this and subsequent tables emissivities and absorptivities are stated in percentage numbers .
Table I.\#151 ; Relative Emissivity of Copper .
Wave-lengtk " \#171 ; * .
Solid .
Liquid .
D. 989 ' .
c. 991 ' .
p. 1053 ' .
Mean .
B. 1090 ' .
A. 1127 ' .
c. 1X74 ' .
Mean .
700 10 -i 7*7 9*4 8*7 10-6 13*0 12 *4 11 *8 675 10 -7 95 11 *1 10 -2 12 -3 13 9 13 -0 12-9 650 11 *6 10 *4 12 *4 11 *2 14 *8 15 2 14 *6 14 *8 625 14 *7 13 *0 15 '0 13*9 17 *1 17 *8 16 7 17 -1 600 19 *3 17 -3 20 *1 18*5 21 *0 21 -0 19 *7 20 *5 575 24 *6 23 *7 25 *7 24 *4 25 *1 25 *0 24 *4 24 *8 550 .
31*7 30 *8 31 *9 31 *3 29 *8 29 *5 28 -6 29 *3 525 35 *2 35 *5 36 *7 35 -7 33 0 34 -0 34 *9 34 *0 500 41 *5 38'9 42*1 40*4 37 *4 38*1 40 *2 38 *7 475 \#151 ; \#151 ; \#151 ; \#151 ; 37 *4 47 *3 \#151 ; 42 *4 The solid copper mirror used for experiment D was not so perfect as that used for C , and one or two small red spots due to markings on the surface were visible amid the otherwise greenish light from the copper .
In calculating the mean , therefore , only half weight is given to the numbers in the first and third columns .
It is probable that even so the " mean " values err on the high side .
In calculating the mean values for the liquid only half weight is assigned to experiment A , there being reason to suspect the corresponding " black body " readings of less accuracy than usual .
The * 'Phys .
Rev. , ' 1912 , vol. 34 , p. 321 .
200 Mr. C. M. Stubs .
Emissivity of Solid and Liquid , [ Jan. 9 , mean values of the relative emissivity at the various wave-lengths are shown graphically by the Curves II and III in the diagram ( fig. 2 ) .
It is evident that , as in the case of gold , the emissivity of copper is discontinuous at the melting-point , the difference , however , between that of the solid and of the liquid being less marked .
No previous quantitative I. Absorptivity , solid copper ; II .
Relative emissivity , solid copper ; III .
Relative emissivity , liquid copper ; IY .
Relative emissivity , liquid silver .
measurements have been made of the radiation from solid copper ; but some on liquid copper have been made by Burgess.* The following table embodies his results :\#151 ; * Wave-length Relative emissivity of liquid copper at in ma .
1075 ' .
1125 ' .
1175 ' .
.1225 ' .
650 17 15 14 13 550 47 38 32 28 * 'Bull .
Bur .
Standards , ' 1909 , vol. 6 , p. 111 .
1913 .
] Copper and of Liquid Silver at High Temperatures .
201 The wide disparity between his values and the author 's is apparent ; nor in the author 's results is there any evidence of such a decrease of relative emissivity with rise in temperature as Burgess shows .
His results are undoubtedly in error , due largely to lack of monochromatism of the coloured glasses used in his pyrometer ( which in a case such as the present , where emissivity varies rapidly with wave-length , might introduce considerable errors ) , and probably also to the far less favourable experimental conditions of his work .
The reflectivity of copper at ordinary temperatures has been measured by several , the surface being prepared by polishing in the work of Hagen and Rubens , * Minor , f and Tool .
J The first named determined the reflectivity directly , the other two by calculation from other optical constants .
The following values for the absorptivity ( 1 \#151 ; R , where R = reflectivity ) are given by their results :\#151 ; Wave-length in / i/ x. Hagen and Rubens .
Minor .
Tool .
Wave-length in Hagen and Rubens .
Minor .
Tool .
700 9*3 575 29*8 i 660 \#151 ; \#151 ; 15 *4 560 \#151 ; \#151 ; 39 *9 650 11 *0 \#151 ; \#151 ; 550 40 *5 41 *6 \#151 ; 640 \#151 ; \#151 ; 15*9 540 \#151 ; \#151 ; 42 *4 630 \#151 ; 19 *5 \#151 ; 535 \#151 ; 43 *8 \#151 ; 620 \#151 ; \#151 ; .
17 *2 520 \#151 ; \#151 ; 44-0 600 16-5 \#151 ; 18 -6 500 46 -7 44-5 44 *9 589 *3 \#151 ; 25 *9 \#151 ; 480 \#151 ; \#151 ; 46 *1 580 \#151 ; \#151 ; 23 *3 450 51*2 49 *5 \#151 ; \#166 ; The values of the different workers do not agree very well , the differences being no doubt largely due to variation in the conditions of preparation of the surface .
All agree , however , in deviating strikingly from the values for the relative emissivity of the solid metal given in Table I. Hagen and Rubens ' values are shown graphically by the curve I in the diagram .
The deviation is in all cases greatest for the shorter wave-lengths .
Thus for wave-length 550 fifi ( green ) all three workers agree in placing the absorptivity at about 41 per cent. ; the author 's value for relative emissivity is 31 per cent. Again , in the region 560 to 590 the author 's curve does not show the remarkable flexure which is characteristic of the others ' , though there are signs of a slight bend .
As may be shown by a simple calculation , the discrepancy cannot be due to the temperature of the surface being lower than indicated by the thermo* 4 Ann. d. Phys. , ' 1902 , vol. 8 , p. 17 .
t 4 Ann. d. Phys. , ' 1903 , vol. 10 , p. 609 .
+ 4 Phys. Rev. , ' 1910 , vol. 31 , p. 14 .
202 Mr. C. M. Stubs .
Emissivity of Solid and Liquid [ Jan. 9 , couple .
For at ( say ) 1000 ' C. the total energy radiated by a " black body " is , by Stefan 's law , 5*3 x 10"5 x 12734 ergs per square centimetre per second .
The thermal conductivity of copper at ordinary temperatures is such that , with a temperature-gradient of 1 ' per centimetre , 0'91 grm. calories , or 4*2 xl07x 0*91 ergs , pass per square centimetre per second .
Thus , if X be the temperature-gradient in degrees per centimetre which a " black body " at 1000 ' and with the conductivity of copper would need for radiated energy to be continually replaced , 5*3 x 10"5 x 12734 = X x 4-2 x 107 x 0*91 , whence X = 3*7 .
Since now most of the energy radiated by a " black body " at 1000 ' C. is in the infra-red , where the reflectivity of copper is very high , and emissivity therefore very low , it is safe to say that copper would radiate less than 1/ 10 as much as a " black body " ; and the temperature-gradient necessary is reduced to less than 0*37 ' per centimetre .
Or , making every allowance for change in conductivity with temperature , etc. , a temperature-gradient of less than 1 ' per centimetre would be required , whereas an error of 17 ' would be needed to explain the difference given above between the values at wave-length 550 yaya .
Again , loss of polish on heating would result in reflection from the furnace walls , and therefore a greater instead of a less value for the relative emissivity .
The conclusion is unavoidable that the absorptivity in the visible spectrum of a polished copper surface changes on heating .
Such a change in the case of gold was suggested , though left open to question , by the results given in the former paper ( p. 461 ) .
It is significant that the relative emissivity curve for solid copper tends to approach the absorptivity curve at long and short wavelengths , but to make the intermediate flexure which is characteristic of all copper surfaces , even unpolished ones , * much less marked .
This tendency is carried out to a much greater degree in the curve for liquid copper , which is without flexure , but still approaches the absorptivity curve at extreme wavelengths .
Similar remarks apply in the case of gold .
It seems at least plausible that , however invariable optical constants may be with temperature in the case of such metals as platinum , *)* the atomic or molecular peculiarities which cause the rapid variation , in the visible spectrum , of the optical constants of copper and gold are diminished as the temperature rises and the kinetic energy of the atoms increases , a further diminution appearing suddenly when inter-molecular constraint is further relieved at the melting-point .
An investigation which the author has not the facilities for carrying out , * For an example of these , the recent work of Tate ( 4 Phys. Rev. , ' 1912 , vol. 34 , p. 321 ) may be referred to .
t Rubens , 4 Phys. Zeits .
, J 1910 , vol. 11 , p. 139 .
1913 .
] Copper and of Liquid Silver at High Temperatures .
203 but which may be suggested as a way of definitely settling the behaviour of copper , would be , after determining the emissivity of a heated solid copper surface , to let it cool down , and directly determine its reflectivity , or better still , to determine the reflectivity at various temperatures up to the melting-point .
The experimental difficulties , though great , should not be insuperable .
II .
Silver.\#151 ; About 400 grm. of silver were used .
A good mirror was easily prepared , but lost its polish on heating to redness , reflecting light from the furnace walls , and preventing measurement of the true emissivity .
This instability of the surface was noted by Drude , even when the metal was heated in hydrogen .
It is perhaps connected with the noticeable volatility of the metal .
The emissivity of a clear surface of liquid silver was , however , measured .
The results are tabulated below , along with Hagen and Rubens ' ( loc. cit. } p. 16 ) directly and Minor 's ( loc. cit. , p. 614 ) indirectly obtained values for the absorptivity ( 1\#151 ; R ) of solid silver mirrors .
Table II .
Wave-length in fx/ ji .
Relative emissivity of liquid silver .
Absorptivity of solid silver .
1004 ' .
1060 ' .
1117 ' .
Mean .
Hagen and Rubens .
Minor .
700 6*66 7 -22 6 99 5 -4 675 \#151 ; 6-90 7-41 7*15 \#151 ; - .
650 6-87 7 22 7 '30 7*18 6*5 \#151 ; .
' 625 6-77 6*97 7 '37 7*09 \#151 ; ' \#151 ; 600 7 -03 7*17 7'58 731 7*4 5*0 ( for 589 '3 ju/ i ) 575 7-39 7*75 7'74 7*67 \#151 ; \#151 ; 550 7-77 8-06 8-27 8-09 7 3 5*8 525 7'63 8*49 9 '03 8*53 \#151 ; \#151 ; 500 \#151 ; 8*17 9'48 8*82 8*7 6*8 450 \#151 ; \#151 ; \#151 ; ' \#151 ; 9*5 8*3 The relative emissivity of liquid silver is shown graphically in the diagram .
Since the reflectivity of silver is very high , a small error in its determination would involve a large error in the absorptivity , as given above ; because of this uncertainty the values for the absorptivity are not shown graphically .
It will be seen that the relative emissivity of the liquid is throughout somewhat greater than the absorptivity of the solid .
There is no other remarkable feature about the emissivity of liquid silver , except its extreme smallness throughout the visible spectrum , as might be anticipated from the high reflectivity of the metal .
This lowness of emissivity made measurements , especially near the melting-point , very difficult ; it is therefore doubtful Emissivity at High Temperatures .
whether the apparent slight increase in relative emissivity with rise in temperature , shown in the table , is real .
On this account also only half weight is given to the measurements at 1004 ' , in calculating the mean .
As in the former paper for gold , it is thought of interest to calculate the " black body " temperature , S , of the metals at their respective melting-points .
Table III.\#151 ; " Black Body " Temperature of Copper and Silver at their Melting-Points .
Wave-length in fx/ x. Copper .
Melting-point 1083 *4 ' C. Silver .
Melting-point 960 *7 ' C. S ( solid ) in 'C .
S ( liquid ) in 'C .
S ( liquid ) in 'C .
700 896 917 792 675 912 928 799 650 924 942 804 625 943 956 808 600 966 973 816 575 988 989 823 550 1007 1003 831 525 1018 1015 838 500 1028 1026 845 475 \#151 ; 1033 \#151 ; * Summary .
1 .
The emissivity of solid and liquid copper and of liquid silver at high temperatures , relative to that of a full radiator at the same temperatures , has been measured throughout the visible spectrum .
2 .
As in the case of gold , the emissivity of copper is discontinuous at the melting-point , the " relative emissivity " curve of the liquid showing no flexure .
3 .
The curve of " relative emissivity " of solid copper at high temperatures differs considerably from that of absorptivity at low temperatures ; it possesses a much less marked flexure in the green , and it is suggested that this is due to the same causes which ultimately bring about the total absence of a marked bend in the curve for the liquid .
4 .
Contrary to Burgess 's results , no appreciable temperature coefficient of " relative emissivity " was found for liquid copper over a range of 100 ' .
5 .
The " relative emissivity " of liquid silver is throughout remarkably low , but seems to be somewhat greater than the corresponding values of the absorptivity of solid silver at ordinary temperatures .
Crystallisation of Substances which form Mixed Crystals .
205 6 .
" Black body " temperatures of solid and liquid copper and of liquid silver at the respective melting-points are calculated .
The author desires to express his thanks to Prof. F. G. Donnan for his advice and help , and to Mr. L. Spencer for his invaluable assistance in making some of the measurements .
On the Spontaneous Crystallisation and the Melting- and Freezing-point Curves of two Substances which form Mixed Crystals and whose Freezing-point Curve exhibits a Transition Point.\#151 ; Mixtures of p-Bromnitrobenzene and p-Chlornitro-benzene .
By Miss Florence Isaac .
( Communicated by Sir Henry A. Miers , F.R.S. Received January 18 , \#151 ; Read January 30 , 1913 .
) The following paper is a continuation of two previous papers in which the melting- and freezing-point curves for two pairs of substances , each of which forms mixed crystals , have already been determined .
In the first of these papers* mixtures of naphthalene and / 3-naphthol were examined and found to form a continuous series of mixed crystals and to give curves of Roozeboom 's Type I , in which the melting and freezing points of all mixtures lie between the melting points of the pure substances .
In the second paperf mixtures of azobenzene and benzylaniline were examined and found to form mixed crystals of two kinds , whose melting-and freezing-point curves exhibit a minimum or eutectic point ( Roozeboom 's Type Y ) .
The present paper deals with mixtures of a pair of substances\#151 ; p-brom-nitrobenzene and jp-chlornitrobenzene\#151 ; which form mixed crystals and give freezing-point and melting-point curves belonging to Type IV of Roozeboom , in which , though the melting and freezing points of all the mixtures lie between those of the pure substances , the curves show a break or discontinuity corresponding to the existence of two kinds of mixed crystals , as in Type V. * ' Journ. Chem. Soc. , ' 1908 , vol. 93 , I , p. 927 .
+ 'Roy .
Soc. Proc. , ' 1910 , A , vol. 84 , p. 344 .
|
rspa_1913_0021 | 0950-1207 | On the spontaneous crystallisation and the melting- and freezing-point curves of two substances which form mixed crystals and whose freezing-point curve exhibits a transition point. -Mixtures of \lt;italic\gt;p\lt;/italic\gt;-bromnitrobenzene and \lt;italic\gt;p\lt;/italic\gt;-chlornitrobenzene. | 205 | 216 | 1,913 | 88 | Proceedings of the Royal Society of London. Series A, Containing Papers of a Mathematical and Physical Character | Miss Florence Isaac|Sir Henry A. Miers, F. R. S. | article | 6.0.4 | http://dx.doi.org/10.1098/rspa.1913.0021 | en | rspa | 1,910 | 1,900 | 1,900 | 3 | 177 | 4,780 | http://corpora.clarin-d.uni-saarland.de/surprisal/6.0.3/?id=rspa_1913_0021 | 10.1098/rspa.1913.0021 | null | null | null | Thermodynamics | 45.383957 | Chemistry 2 | 20.933745 | Thermodynamics | [
-31.926013946533203,
-73.33596801757812
] | Crystallisation of Substances which form Mixed Crystals .
205 6 .
" Black body " temperatures of solid and liquid copper and of liquid silver at the respective melting-points are calculated .
The author desires to express his thanks to Prof. F. G. Donnan for his advice and help , and to Mr. L. Spencer for his invaluable assistance in making some of the measurements .
On the Spontaneous Crystallisation and the Melting- and Freezing-point Curves of two Substances which form Mixed Crystals and whose Freezing-point Curve exhibits a Transition Point.\#151 ; Mixtures of p-Bromnitrobenzene and p-Chlornitro-benzene .
By Miss Florence Isaac .
( Communicated by Sir Henry A. Miers , F.E.S. Received January 18 , \#151 ; Bead January 30 , 1913 .
) The following paper is a continuation of two previous papers in which the melting- and freezing-point curves for two pairs of substances , each of which forms mixed crystals , have already been determined .
In the first of these papers* mixtures of naphthalene and / 3-naphthol were examined and found to form a continuous series of mixed crystals and to give curves of Roozeboom 's Type I , in which the melting and freezing points of all mixtures lie between the melting points of the pure substances .
In the second paperf mixtures of azobenzene and benzylaniline were examined and found to form mixed crystals of two kinds , whose melting-and freezing-point curves exhibit a minimum or eutectic point ( Roozeboom 's Type Y ) .
The present paper deals with mixtures of a pair of substances\#151 ; p-brom-nitrobenzene and jp-chlornitrobenzene\#151 ; which form mixed crystals and give freezing-point and melting-point curves belonging to Type IV of Roozeboom , in which , though the melting and freezing points of all the mixtures lie between those of the pure substances , the curves show a break or discontinuity corresponding to the existence of two kinds of mixed crystals , as in Type V. * ' Journ. Chem. Soc. , ' 1908 , vol. 93 , I , p. 927 .
+ 'Roy .
Soc. Proc. , ' 1910 , A , vol. 84 , p. 344 .
206 Miss F. Isaac .
Crystallisation , etc. , of two [ Jan. 18 , Mixtures of ^-bromnitrobenzene and ^-chlornitrobenzene have already been studied by Kremann* in a paper on isomorphous mixtures .
This author has traced the freezing-point curve for mixtures of these substances , and has shown that they form mixed crystals , and he also obtained five points lying on the melting-point curve .
Kremann obtained his freezing- and melting-point curves from observations made on the rate of cooling of various mixtures .
Liquid mixtures of known composition were allowed to cool , and a curve was obtained for each mixture by plotting temperature against time .
It was found that these cooling-curves showed two distinct kinks , one when crystallisation commenced and the second at what Kremann describes as the end of crystallisation .
From these cooling-curves Kremann obtained his freezing- and melting-point curves for the mixtures , the freezing-point curve or liquidus being given by the upper kinks , at which crystallisation started in the various mixtures , and the melting-point curve or solidus being given by the lower kinks , at which Kremann states that crystallisation ends .
In this manner he obtained curves of Roozeboom 's Type IY .
Since , however , he only obtained five points on the melting-point curve , none of which lie in the neighbourhood of the transition point , his curve is to some extent imaginary .
The following experiments were therefore undertaken with a view to verifying his results , and to determining a more complete set of melting points , and also in order to obtain the supersolubility curve or curve of spontaneous crystallisation for a series of mixtures of Roozeboom 's Type IY , in the same manner that this curve has already been obtained for mixtures of naphthalene with / 3-naphthol , and azobenzene with benzylaniline , which afford examples of Type I and Type Y respectively .
Crystalline Form of p-Bromnitrobenzene and p-Chlornitrobenzene .
Crystals of p-bromnitrobenzene have been examined by Fels , f who describes them as melting at 126 ' or 127 ' , and having a specific gravity of 1*934 at 22 ' , and states that p-bromnitrobenzene is isomorphous with p-chlornitrobenzene .
He obtained , from a solution in a mixture of acetone and ether , crystals which were colourless or slightly yellow , prismatic in the direction of the c-axis , and showing only n { 210 } and c { 001 } .
He found the crystals to be monoclinic , having a:b :c= 1*9336 : 1 : ?
; / 3 = 97 ' 57 ' .
* ' Jahrb .
der k. k. Geol .
Reiclisanstalt , ' 1908 , vol. 58 , p. 659 .
t 1 Zeitschr .
fiir Kryst .
u. Min .
, ' 1900 , vol. 32 , p. 375 .
1913 .
] Substances which form Mixed Crystals , etc. 207 The extinction on a prism face was 22 ' .
He also states that a crystal of ^-bromnitrobenzene will continue to grow when placed in an alcoholic solution of ^-ehlornitrobenzene , and that crystals of the latter which form in the neighbourhood will arrange themselves parallel to the jp-bromnitro-benzene crystal introduced.* ^-Bromnitrobenzene has also been examined by Kekule , f who describes the crystals as needles having melting point 125 ' ; and by Fittig , * who describes the crystals as long colourless needles , line as a hair , slightly soluble in cold alcohol , and having melting point from 126 ' to 127 ' .
Fels also examined ^-chlornitrobenzeneS and obtained the melting point of this at 83 ' to 84 ' , and its specific gravity as 1*520 at 18 ' .
He found the crystals to be monoclinic , having a : b : c \#151 ; 1*9577 : 1 : 1*1203 ; = 97 ' 11 ' , the plane of the optic axes being ( 010 ) .
The crystals were colourless and prismatic in habit , showing the forms a{100 } , m{110 } , c{001 } , r{101 } .
When grown from alcohol they usually showed as end faces only { 101 } , whilst those grown from ether , acetone , or benzene showed the form { 001 } .
Since the crystals become dull quickly in the air , Fels states that the reflections are always poor .
The extinction angle on a prism face was here 16*5 ' .
^-Chlornitrobenzene has also been examined by Jungfieisch , || who obtained it in the form of large plates derived from a rhomboidal prism of 125^ ' , but without end faces .
Microscopic Examination of p-Bromnitrobenzene , ^p-Ghlornitrobenzene , and their Mixtures .
No goniometric measurements of ^-bromnitrobenzene and p-chlornitro-benzene were undertaken , but both substances were examined under the microscope while growing from solution on a microscope slide .
jp-Bromnitrobenzene , dissolved in a drop of alcohol , ether , or benzene on a slide under a cover-glass , gave fine feathery needles branching in all directions .
The needles showed no end faces , so no angles could be measured .
The extinction was inclined at 18 ' or 20 ' to the length of the needles .
In convergent light no optic axis could be seen , but only a dark brush crossing the field as the nicols revolved .
jp-Chlornitrobenzene dissolved in a drop of benzene , alcohol , toluene , or * An attempt to confirm this observation did not lead to any positive result , t ' Liebig 's Annalen der Chemie , ' 1866 , vol. 137 , p. 167 .
t 'Ber .
deutsch .
Chem. Ges.,5 1874 , vol. 7 , p. 1175 .
S 'Zeitschr .
fur Kryst .
u. Min .
, 1900 , vol. 32 , p. 375 .
|| 4 Ann. de Chirnie et de Phys./ 1868 ( 4 ) , vol. 15 , p. 223 .
Miss F. Isaac .
Crystallisation , etc. , of two [ Jan. 18 , acetone , gave under the same conditions crystals which grew in a feathery manner in long branching needles having straight extinction .
These needles had no end faces and therefore no measurable angles .
Examined in convergent light these needles showed an optic axis visible on the edge of the field .
The birefringence is positive , and the plane of the optic axes along the length of the needles .
This would correspond to the different habit of the two substances noted by Fels , the face a being only found on the chloro-compound .
A few experiments made with mixtures of these substances under the microscope yielded somewhat indefinite results , no angular measurements being possible since the crystal needles had no end faces , but they seemed to show that mixtures containing up to 27*5 per cent , of ^-bromnitrobenzene gave crystal needles showing the same straight extinction and the same optic axial figure as pure ^-chlornitrobenzene .
Mixtures having more than 27*5 per cent , of p-bromnitrobenzene , on the other hand , gave crystal needles having the oblique extinction ( about 20 ' ) of pure ^-bromnitrobenzene , and they also show no optic axis when viewed in convergent light .
These experiments would indicate therefore that a change of some sort probably occurs in the crystals growing from these mixtures at the composition 27*5 per cent , ^-bromnitrobenzene , 72*5 per cent , p-ehlornitrobenzene , and subsequent experiments to be described in this paper show that at this composition there is a break or change in direction in the freezing-point curve , which would indicate a change in the nature of the crystals .
The Freezing-point Curve .
Mixtures of ^-bromnitrobenzene and ^-chlornitrobenzene were examined .in sealed glass tubes , and the freezing point for each mixture was obtained by the method which has been already employed by the author in the papers referred to above .
Each tube was heated in an oil bath with glass windows until the contained mixture was completely melted ; it was then held outside the bath a few seconds to induce one or two small crystals to start growing .
The tube was then re-immersed in the oil bath and these small crystals watched while the temperature of the bath was varied until a temperature was attained at which equilibrium existed between the liquid and the small crystals , and this was taken as the freezing point of the mixture .
The following are the tabulated results obtained for the freezing points of the various mixtures examined :\#151 ; 1913 .
] Substances tvhich form Mixed Crystals , etc. Percentage by weight of ^\gt ; -bromnitrobenzene in the mixture .
Freezing point .
100 *0 o 124 -0 90 *016 119-4 79 -886 115-2 75 -175 112-8 70 *0 110 -3 64 *888 107 -5 59 *874 104-8 54 *645 101 -5 45 *22 96 -75 44 *355 96-3 40 *339 93 -8 37 *747 92 -2 32 *849 89 -5 29 *952 87 -7 ( 0 ) 84 -5 ( a ) 29 *915 87 *7 ( j8 ) 84 *5 ( a ) 27 *478 84-5 25 *041 84-5 19 *94 84 -2 14 *957 83 -8 14 *935 83 -8 9*972 83 -0 5*024 82 -8 0 82-0 It will be seen that for mixtures containing about 30 per cent , of \#163 ; \gt ; -brom-nitrobenzene two freezing points have been obtained for the same mixture .
These correspond to two different sorts of mixed crystals , u and ft , two kinds being distinctly visible and having different melting points , at 87*7 ' and 84*5 ' respectively .
The crystals a , growing in the liquid mixture at the lower temperature ( 84-5 ' ) , are wide , transparent , quickly growing blades , and occur in all the mixtures having less than 30 per cent , of ^-bromnitro-benzene .
The crystals ft , which are in equilibrium with the liquid at 87*7 ' , are extremely fine small hair-like needles , growing very slowly .
In all mixtures containing over 30 per cent , of p-bromnitrobenzene , these very fine hair-like crystals only are to be seen .
Both sorts of crystals , a and ft , may be found also in a liquid mixture containing 27*5 per cent , of _p-bromnitro-benzene , but in this case they are both deposited at the same temperature and the existence of two sorts is therefore not so noticeable .
At this point , corresponding to 27*5 per cent , of ^-bromnitrobenzene , it will be seen that the freezing-point curve shows a break or transition point .
For mixtures containing above 27*5 per cent , of _p-bromnitrobenzene the freezing-point curve rises much more rapidly than for mixtures containing a smaller percentage , the curve for mixtures containing between 0 per cent , and 27*5 per cent , of _p-bromnitrobenzene being very flat and only rising by 2*5 ' .
210 Miss F. Isaac .
Crystallisation , etc. , of two [ Jan. 18 , It is to be expected that in the neighbourhood of this transition point the melting-point curve also will show discontinuity .
Comparing the values here obtained for points on the freezing-point curve with those observed by Kremann it will be seen that the new values are throughout somewhat higher than the old ones , although Kremann 's transition point was found to correspond to a mixture of almost the same composition as that obtained above .
Thus Kremann 's freezing points for mixtures with 100 , 70*8 , 39*6 , and 23*1 per cent , of p-bromnitrobenzene are 123 ' , 108 ' , 91*5 ' , and 84*5 ' respectively ; while the values here obtained for mixtures of the same composition are 124 ' , 111 ' , 93*3 ' , and 84*3 ' respectively .
This discrepancy may probably be due to slight supercooling having taken place before the first separation of crystals in Kremann 's cooling experiments .
The Melting-point Curve .
The freezing-point curve having been determined , an attempt was now made to fix the position of the melting-point curve for the same mixtures .
The method used was the same as that adopted in the case of mixtures of azobenzene and benzylaniline already referred to ( loc. cit. , p. 349 ) .
The same tubes of mixtures were , for the most part , used that had been used to determine the freezing-point curve .
The mixtures were heated until they were completely liquid , and they were then allowed to cool slowly in the bath until they had completely recrystallised , the crystals adhering to the sides of the tubes .
At least 24 hours were allowed , to enable the mixtures to solidify completely .
They were then heated again very steadily in the oil bath , and as the temperature rose the crystals were examined continually with a lens , until , when it had reached a certain point , some of the crystals in the tube began to look slightly sticky , and a further rise in the temperature of about half a degree caused a small stream of liquid to run down the sides of the tube .
The point at which melting was first observed was taken as the melting point of the mixture .
This method of obtaining the melting-point curve for mixed crystals has also been used by A. Stock.* This method may be expected to give satisfactory results in fixing the melting-point curve or solidus , since , according to the theory , when mixed crystals grow ' from a liquid mixture the crystals first deposited differ in composition from the original liquid ; but if solidification proceeds with sufficient slowness , the crystals approximate , as the temperature falls , more and more nearly in composition to the original liquid taken , until finally the last crystals which form should have the exact composition of the original liquid .
The method was found to give satisfactory results in the case of mixtures of azobenzene and benzyl* ' Ber .
deutsch .
Cliem .
Ges .
, ' 1909 , vol. 42 , p. 2059 .
1913 .
] Substances ivliich form Mixed Crystals , etc. 211 aniline , the curve obtained in this manner being confirmed by actual analysis of the mixed crystals ( loc. cit. , p. 352 ) .
The method , therefore , having been tested , there is no reason to doubt that the results described below for the melting-point curves of mixtures of p-bromnitrobenzene and p\gt ; -chlornitro-benzene are very approximately correct .
All the determinations have been very carefully made and each been repeated several times with concordant results .
The following table gives the melting points obtained:\#151 ; Percentage by weight of ^\gt ; -bromnitrobenzene in the mixture .
Melting point .
100 *0 o 124 -0 90 016 107 -0 80 -033 99 -0 75 *175 92-5 70 -0 89 -0 64 *690 86-5 ' 59 *874 84 -5 54 -645 84 -5 45 *22 84*5 44 *355 84-5 40 *339 84 -5 37 *747 84 -5 32 *849 84 -5 29 *952 84 -5 29 -915 84 -5 27 *478 83 -0 25 -041 82 *4 19 -94 82 -2 14 *957 81 -5 9*972 81 '5 5*024 81 *4 0 82-0 The melting-point curve plotted from these figures appears in the diagram .
Examination of the complete figure formed by the freezing- and melting-point curves for these mixtures shows that they form an example of Roozeboom 's fourth type of curves for mixed crystals .
The two branches AC and CB of the freezing-point curve or liquidus have each a corresponding melting-point curve or solidus , AD and EB respectively .
At the temperature 84-5 ' of the transition point C , two solid phases , a and / 3 , may exist in equilibrium with the liquid containing 27'5 per cent , of p-brom-nitrobenzene and 72-5 per cent , of p-chlornitrobenzene .
These two solid phases will contain respectively 30 and 60 per cent , of the bromo-eom-pound .
C is therefore an invariant point , and the transition from one series of crystals to the other , indicated by the horizontal line CDE , takes place at constant temperature .
All liquid mixtures to the left of C solidify vol. lxxxviii.\#151 ; A. Q 212 Miss F. Isaac .
Crystallisation , etc. , of two [ Jan. 18 , as a-crystals , and all liquid mixtures to the right of E solidify as / 3-crystals Mixtures between , D and E first form some / 3-crystals and then a-crystals , 1913 .
] Substances which form Mixed Crystals , etc. 213 which will have the compositions E and D respectively .
Varying the composition of the liquid between the limits D and E will change only the relative proportion of the two phases , a and / 3 , without altering the composition of either .
Mixtures between C and D also first form / 3-crystals , but on cooling slightly past the transition point these are all converted into a-crystals .
It has been seen that for mixtures containing 0 to 27*5 per cent , of p-bromnitrobenzene the rise of temperature in the freezing-point curve is very slight , viz. only 2*5 ' .
According to the theory of mixed crystals of Roozeboom 's Type IV , addition of ^-bromnitrobenzene should raise the melting point of the mixture .
It may be seen , however , that for mixtures containing from 5 to 15 per cent , of p-bromnitrobenzene the melting points of the mixtures are actually slightly lowered by the addition of j9-bromnitro-benzene .
The lowering is , however , very slight , amounting nowhere to more than 0*6 ' .
This slight lowering cannot be accounted for otherwise than by the assumption that one or both of the substances may -contain some small quantity of impurity .
The melting points obtained for them , namely 124 ' and 82 ' , seem to indicate that - this may be the case , since Fels obtained 126 ' to 127 ' as the melting-point of p-bromnitrobenzene , and 83 ' to 84 ' as the melting point of p-chlornitrobenzene .
Comparing the results here obtained for the melting-point curve with the five melting points obtained by Kremann it will be seen that there is a wide discrepancy in the results .
Percentage by weight of ^ ?
-bromnitrobenzene in the mixture .
Melting point .
Kremann .
Isaac .
83 *7 o 111 -o o 101 -o 70 -3 108 *0 89 '0 56-1 100 *0 84 *5 46*1 94 *8 84 *5 24 -2 84 *3 82 -0 It would appear , therefore , from the above values that Kremann 's melting points , obtained from the second kink in the cooling-curves for mixtures , are too high ; and this would seem to indicate that the mixtures could not have been completely solid at the time this second kink in the cooling-curve appears .
In the experiments described in this paper it has been found that the mixtures cannot be regarded as completely solid until several hours after the crystals first appeared in the liquid ; and , as stated Q 2 214 Miss F. Isaac .
Crystallisation , etc. , of two [ Jan. 18 above , at least 24 hours were allowed to elapse before the melting point of any mixture was taken .
The Spontaneous Crystallisation of Mixtures of p-Bromnitrobenzene and p - Chiornitrobenzene .
Finally , the methods described in the previous papers have been applied to mixtures of p-bromnitrobenzene and ^-chlornitrobenzene , in order to trace their supersolubility curve or curve of spontaneous crystallisation .
The mixtures were enclosed in sealed glass tubes which also contained some fragments of corundum to produce friction , and the tubes were heated for some time in the oil bath and shaken thoroughly as the temperature of the bath was raised , until all trace of solid had disappeared .
After heating further to at least 10 ' above the freezing-point curve the temperature of the bath was allowed to fall very slowly , the oil being constantly agitated in order to keep its temperature uniform throughout .
Thermometers placed at top and bottom of bath showed this to be the case .
The tube containing each of the liquid mixtures was shaken continuously ( by hand ) in the bath as the oil cooled , until at a certain temperature a shower of very fine crystal needles suddenly appeared in the tube , and thickened very rapidly until the whole tube was opaque .
The temperature at which crystals first appeared in each tube was noted as the temperature of spontaneous crystallisation for that mixture .
The results are tabulated below , and from Percentage by weight of p .bromnitrobenzene in the mixture .
Temperature of spontaneous crystallisation .
100 -o 0 120 *2 90 *016 115 *1 79 *886 111 *0 75 -175 108 *3 70 *0 105 *3 64 *888 102 *8 59 -874 101 *0 54 -645 96 *7 45 *22 92 *3 44 *355 92 *2 40*339 89 *8 37 *747 88 *2 32 *849 85 *5 29 *915 84 *0 27 *478 84 *0 25 *041 83 *4 19 *94 82 *7 14 *957 82 *2 14 *935 82 *1 9*972 81 *8 5*024 81 *7 0 81 *7 1913 .
] Substances which form Mixed Crystals , etc. 215 them the complete supersolubility curve is obtained which is shown on the diagram .
The goniometric method of plotting the supersolubility curve from observations of the refractive index , which was used in the research on mixtures of azobenzene and benzylaniline , was not used for the present mixtures , since the high temperatures at which they crystallise render them unsuitable for use in the goniometer trough .
* An examination of the supersolubility curve as it appears on the diagram shows that it , too , exhibits a break or bend for mixtures containing from 27*5 per cent , to 30 per cent , of p-bromnitrobenzene , corresponding to the transition point on the freezing-point curve .
It follows the direction of the freezing-point curve very closely , lying about 4 ' below it on the right-hand side of the transition point , and about l|- ' below on the left-hand side of that point .
It lies entirely above the melting-point curve except just at both the extreme ends , when it crosses it .
In a paper by Vanstone* the author states that the freezing-point curves as usually obtained for mixed crystals from the rate of cooling are in reality the temperatures of spontaneous crystallisation .
This suggests that Kremann 's freezing-point curve , obtained from observations of the cooling-curves , might coincide with the supersolubility curve here obtained .
Comparison with Kremann 's figures shows , however , that his freezing-point curve lies between the freezing-point curve and the supersolubility curve , though on the whole it lies slightly nearer to the latter .
Thus it would appear that in Kremann 's experiments crystallisation started in a supersaturated mixture , but before the mixture actually arrived at the labile temperature .
This is what might have been expected , unless special care were taken to prevent inoculation of the mixture by a crystal germ , by enclosing the mixtures in sealed tubes or other means .
The bath used in all these experiments consists of a square-shaped copper vessel of sufficient depth to allow the sealed glass tubes to be completely immersed .
It was filled with cotton-seed oil and heated by means of a Bunsen burner placed immediately beneath it .
Two round plate-glass windows were inserted in the sides of the bath immediately opposite each other , and held in place by means of brass rings and screws .
The bath was illuminated by means of a ground-glass electric bulb placed behind one of the windows , and the crystals were examined as they grew in the tubes with a lens held at the opposite window .
* ' Journ. Chem. Soc.,5 1909 , vol. 95 , I , p. 599 .
216 Crystallisation of Substances which form Mixed Crystals .
Conclusions .
The results obtained in this paper may be briefly summarised .
1 .
p-Bromnitrobenzene , / \gt ; -chlornitrobenzene and their mixtures have-been optically examined under the microscope .
2 .
The freezing- and melting-point curves for these mixtures have been determined .
It has been found #that these substances form mixed crystals and give curves of Roozeboom 's Type IY .
The freezing-point curve shows two branches corresponding to two different sorts of mixed crystals and meeting in a transition point at 84*5 ' , for a mixture containing 27*5 per cent , of ^-bromnitrobenzene and 72*5 per cent , of ^-chlornitrobenzene .
The freezing-point curve was found to correspond very nearly to that already obtained by Kreeman for these mixtures , though Kremann 's curve lies somewhat below it .
The melting-point curve also shows two branches , corresponding to the two branches of the freezing-point curve , and on each of these a different kind of mixed crystal is in equilibrium with the liquid .
At the temperature marked by the dotted horizontal line , both sorts of mixed crystals may exist together in equilibrium with a liquid containing 27*5 per cent , of j9-bromnitrobenzene .
The melting-point curve here obtained differs widely from that obtained by Kremann , a large part of the curve lying considerably below the latter .
3 .
The supersolubility curve or curve of spontaneous crystallisation has been determined for these mixtures , and it has been found that each mixture possesses a definite temperature of spontaneous crystallisation .
This curve lies almost Completely between the melting- and freezing-point curves , and , like them , it shows a break in the neighbourhood of the transition point .
My sincere thanks are due to Prof. H. L. Bowman for his kind help and interest throughout this research .
|
rspa_1913_0022 | 0950-1207 | The excitation of \lt;italic\gt;\#x3B3;\lt;/italic\gt;-rays by the \lt;italic\gt;\#x3B1;\lt;/italic\gt;-rays of ionium and radiothorium. | 217 | 229 | 1,913 | 88 | Proceedings of the Royal Society of London. Series A, Containing Papers of a Mathematical and Physical Character | J. Chadwick, M. Sc.|A. S. Russell, M. A.|Prof. E. Rutherford, F. R. S. | article | 6.0.4 | http://dx.doi.org/10.1098/rspa.1913.0022 | en | rspa | 1,910 | 1,900 | 1,900 | 5 | 206 | 4,078 | http://corpora.clarin-d.uni-saarland.de/surprisal/6.0.3/?id=rspa_1913_0022 | 10.1098/rspa.1913.0022 | null | null | null | Atomic Physics | 62.66744 | Tables | 11.561501 | Atomic Physics | [
6.679625988006592,
-77.67265319824219
] | ]\gt ; The Excitation of -Rays by the of Ionium and diothorium .
By J. CHADWICK , M.Sc .
, Beyer Fellow of the University of Manchester , and A S. RUSSELL , M.A. , Carnegie Research Fellow of the University of Glasgow .
( Communicated by Prof. E. Rutherford , F.R.S. Received January 25 , \mdash ; Read February 13 , 1913 .
) In t.oducilon .
It has been shown by one of us*that the -rays of radium , wl en they impinge upon matter , excite a small but detectable amount of -radiation- Owing to the presence of the intense primary -radiation whioh accompanies the -rays of radium , however , a detailed investigation of this excite -radiation was not possible .
With an intense source of ionium placed at our disposal by Prof. Rutherford it has been possible for us , not only ) show clearly that -rays are excited by the -rays of ionium , but also , to the absence of products emitting and -rays , to make a detailed study of the nature of this excited -radiation .
The results of these experiments are given in this paper .
We have found also that -rays are emitted from radiothorium , and a short of the work which led to this result is given here also , although , as will be explained later , it was not possible for us to make a systematic study of their nature .
The from Iomum .
The preparation of ionium used in these experiments consisted of a mixture of the oxides of thorium and ionium separated by Prof. Boltwoocl from the " " actinium residues\ldquo ; loaned by the Royal Society to Rutherford .
Its activity was such that 1 .
expelled -particles per second , i.e. 1 .
of the mixture contained a quantity of ionium equivalent to the amount of ionium in radioactive equilibrium with of radium .
The quantity of oxide used in most of the experiments weighed It is obvious that if definite evidence of the existence of -rays from ionium is required , the ionium in the mixture must be freed from every trace of bodies which emit or -radiations .
Besides thorium and iouium , the preparation contained all the products of the thorium series , and , in addition , radium and its products .
The radium had , of course , been * Chadwick , ' Phil. Mag 1913 , vol. 25 , p. 193 .
and -rays , measured under the same conditions as before : purification , was now 13 divisions per minute .
The activity remained practically constant for a period of 10 days , showing that it could not be due to radium or any other of the products of radium .
equal weight of old commercial thorium treated by exactly the same chemical methods , when measured immediately after purification , was found to be quite free from and -rays .
A month later , when the thorium X and its products had been formed in equilibrium amount , the activity due to the and -rays was only 2 divisions per minute .
The -ray activity of the ionium preparation cannot therefore be ascribed to the thorium that it It was thought not impl.obable that some unknown product enutting -rays might have been inally present , and a small portion of it still remained unseparated from the ionium .
The preparation was therefore into solution as before , precipitated three times with ammonia , and once with meta-nitrobenzoic acid , and finally ignited .
It was found that the -ray activity of the preparation had not been changed appreciably by this second series of chemical operations .
It was concluded from these experiments that this and -radiation must be due , either to the ionium itself , or to some unknown product which is chemically very similar to it .
A detailed study of the rays was then commenced .
A large electroscope of the ordin type , 17 cm .
cm , , was placed immediately above -Rays by the -Rays of Ionium and Radiothorium .
219 the pole pieces of a very powerful electromagnet .
The base of the electro- scope was of lead in which was cut an opening 10 cm .
cm .
, covered by very thin aluminium foil .
The faces of the pole pieces were 10 cm .
cm .
, and 9 cm .
apart .
They were covered with thick cardboard to minimise diffuse reflection of and -rays from them .
The active material was .
placed between the pole pieces at a distance of 9 cm .
below the base of the electroscope .
It was in the form of a film spread evenly over an area of about 15 sq .
cm .
on a shallow platinum dish .
Under these conditions the in the electroscope due to and -rays was divisions per minute .
When a etic field of about 1000 gauss was applied , the leak in the electroscope was 12 divisions per 1ninute .
The -ray activity of a film of uranium oxide , measured under the same conditions , was reduced by the same netic field to less than 1 per cent. The activity of 12 divisioDs per minute due to the ionium preparation must therefore be due to -rays .
Only 10 per cent. of the total activity can be due to -rays , and this small amount may be due entirely to -rays from thorium products , though probably part at least is due to the ionium .
It is to note that Boltwood , discoverer of ionium , stated that ionium emitted -rays as well as -rays .
Keetman showed , however , thaC these rays were due entirely to the presence of uranium X , which , non-separable from ionium , had been separated with it by Boltwood from the mineral .
Keetman , working with an ionium preparation comparable in intensity with ours , found no evidence of any radiation more than -rays .
His failure to detect the -rays must be ascribed to lack of sensitiveness of his methods of measurement .
The amount of -radiation from ionium is very small , and of quite a erent order , relative to the amount of -radiation , from that of a product emitting both and -rays such as radium C. The amount , however , is of the same order as that excited by the -rays of radium when they impinge upon matter .
Not only is the value of the to ratio abnormally low , but the to ratio is abnormally .
The ratio of the ionisations due to the and the -rays from a radio-element in an ordinary electroscope is in the most favourable case 1/ 50 .
In the case of ionium this ratio is at least 10 .
The existence of a new product , therefore , and -rays in this proportion , and chemically difficult to separate from ionium , is in the highest degree improb- able .
For these reasons it musG be concluded that the -rays from ionium are excited by the -rays , either the ionium itself , or in the surrounding atoms of thorium .
Boltwood , ' Amer .
Journ. Sci 1908 , vol. 22 , p. 537 .
Ksetman , ' Jahr .
tivitat , ' 1909 , vol. 6 , p. 269 .
FIG. 1 .
is not detectable after it has passed rough 0 cm .
of aluminium , and thethird , , of a small amount of a still harder type which can be detectecL even after it has passed hrough 4 cm .
aluminium .
The absorption of each type has been studied separately , and the absorption curves obtained are given in figs. 2 , 3 , and 4 below .
Absorption of the Softest Type.\mdash ; The active preparation was placed 9 cm .
below the electroscope , and the aluminium used for absorbing was laid directly on the preparation .
The sheets were very thin , each weighing .
per square centimetre .
After 12 of these sheets had been laid on , all the softest type of radiation had been completely absorbed .
The ionisation is then due to the two remaining types of rays .
Measurements .
* made with more than 12 sheets showed that each of the next few sheets beyond this amount absorbed about division per minute .
This remaining radiation is really absorbed exponentially , but , owing to the extremely small absorption taking place in so small a thickness , it is approximately linear .
It is , therefore , a simple matter to calculate the ionisation due to the rays which penetrate lsheets , hickness hanthis fifferent sheets aiven isheets.alues ofthird column oable I below .
In the first column is given the number of the sheets useci for absorbing , in the second the total ionisation measured , and in the fourth theionisation due to the softest type alone .
From these results a value of mass absorption coefficient ) in aluminium of about 500 is obtained .
Values deduced from other curves obtained in this way varied from to Table I. It is apparent from these values of for the softest type of rays , that a large proportion of these rays must be absorbed in the active material itself , .
and in the air between the electroscope and the active material .
A film of a small quantity of the material should , therefore , give an ionisation due to the soft rays large compared with that due to the other types .
About 25 .
of the active material , in the form of chloride , was carefully evaporated to dryness in a large platinum dish .
The film was about 20 sq .
cm .
in area .
When placed about 2 cm .
underneath the base of the electroscope , its activity was divisions per minute , 50 of which were due to the soft -rays , and the remainder , it was found , due chiefly to -rays .
It is seen from these results that the activity of the soft -rays has been increased very much by preparing the substance in a thin film .
Because of the proximity of the preparation to the electroscope , the -rays could not be deflect'ed away from the electroscope .
After correcting for their absorption , the absorption curve shown in fig. 2 was obtained .
It is seen that it is exponential within the error of measuremenb .
The value of obtained from this experiment .
Messrs. Chadwick and Russell .
Exeitation of [ Jan. 25 ; was 520 .
The leak due to these soft rays measured , under these special conditions , but at a distance of 9 cm .
from the electroscope , as mentioned above , was divisions per minute , i.e. 32 per cent. of the total ionisation .
Absorption of the Hardest Type.\mdash ; The absorption of the hardest type of radiation was determined very carefully over a range of thickness of 1 to 5 cm .
aluminium .
The leak due to this radiation if unabsorbed by aluminium was only division per minute , so that the determination of the absorption coefficient is by no means easy .
The absorption curve is shown in fig. 3 .
It is seen that the absorption is exponential .
The value of obtained from the curve is Absorption of the Rays of filedium Penetrating Power.\mdash ; The absorption curve of this type of radiation was determined over a range of thickness from that necessary to absorb the softest type totally , to a thickness of 2 mm. , beyond which , as further measurements showed , ths hardest type alone could be detected .
The amount of ionisation , due to the hardest type after traversing any t , hickhess within this range , could be calculated from the data given in the last paragraph .
By making the necessary corrections , the ionisation due to the rays of mediunr penetrating power alone was easily obtained for any thickness , and from these results the curve in fig. 4 was plotted .
The -Rays by the of Ionium Radiothorium .
223 en dium FIG. 4 .
where is known as the Exponential Integral : and is mean values of for the three )types of radiation , after correcting for the obliquity of the beam , are given in Table II .
Table II .
Radiation .
I. Soft type II .
Medium III .
Hard type Aluminium .
It is well that the value of lor any metal and for any -radiation that is absorbed exponentially varies somewhat according to the particular disposition used for measuring the absorption .
The -rays of radium , for instance , have a value of in aluminium of when the absorbing material is laid directly over the source and the base of the electroscope is 1 cm .
of lead , and when the absorbing material * Soddy ( F. and W. M. ) and Russell , ' Phil. Mag 1910 , vol. 19 , p. 725 .
King , ' Phil. Mag 1912 , vol. 23 , p. 242 .
See Russell , ' Jahr .
Radioaktivitat , ' 1912 , vol. 9 , p. 444 .
-Rays the a-Rays of Ionium .
225 itself the base of the electroscope .
The absorption of the hard -rays of radium was therefore investigated under the same conditions those used for the absorption of the ionium rays .
A plate of lead , cm .
thick , was laid immediately over a source of radium bromide .
This absorbs all the soft -radiation .
Immediately over this lead plate were laid the plates of * aluminium .
After correcting for the obliquity of the beam the value of for aluminium was found to be , which agrees very satisfactorily with 4 the values obtained for ordinary dispositions .
The ) of given in Table 2 may therefore be used in making quantitative comparison of the penetrating ers of the rays of ionium with those of X-radiations and -radiations , measured in the usual way .
No radiation more penetrating than the hard type whose coefficient is given in Table II is .
given out in detectable amount by the ionium preparation .
Relative of the Three of Radiation .
A rough calculation of the relative energies of these three types of radiation has been made .
The calculation is necessarily , for it involves assumptions which at present , the lack of data , cannot be verified .
If we assume , however , that the absorption of any of these types of radiation is , weight for , the same in aluminium as it is in air , and secondly , that the ionisation in air is proportional to the absorption , an approximate idea of the relative energies of the three types can easily be obtained .
It is probable that neither of these assumptions is strictly true , but it not likely that they are sufficiently erroneous to lead us to an entirely wrong result .
In making the calculation , account must be taken of absorption in the active material itself , in the air between the material and the base of the electroscope , and in the base of the electroscope .
The fraotion of the energy spent in the air of the electroscope is readily calculated from the dimensions of the electroscope and the absorbability of the radiation in air .
When the active material , weighing , and uniformly spread over a surface of 15 sq .
cm .
, was 9 cm .
from the electroscope , only 3 per cent. of the total soft -radiation escaped from the material .
Only per cent. of this amount is able to enter the electroscope and produce ionisation .
In doing so the radiation is totally absorbed .
The ionisation produced was 4 divisions per minute .
The total unabsorbed radiation would , therefore , produce , i.e. 15,000 divisions per minute .
Of the medium type of rays , 68 per cent. emerge from the material ; per cent. of this amount entels the electroscope , and 16 per cent. of this is absorbed in ionising .
The produced was divisions that prol ) ably the -rays of radioactive bodies are the charactelistic radiations of these bodies .
The characteristic radiations of ] ements of high atomic weight have been investigated in detail by Chapman .
He finds that the characteristic X-radiation of thorium , in what Barkla has called series , has a mass absorption coefficient in aluminium of .
This is so far the only characteristic radiation which has been found for thorium .
since the atomic weight of thorium is , and that of ionium is 230 , the characteristic -radiations of these elements will probably differ so little in penetrating power that it would be difficult to distinguish between them .
It will be noticed that this characteristic -radiation of thorium has approximately the same value of as the medium type of -radiation ( II ) found for ionium .
It is therefore natural to suppose that all three types of -radiation are characteristic radiations , either of thorium or of ionium , of different series .
Types I and III belong to no series of characteristic -rays at present known .
It is probable that type III belongs to a series intermediate between series and , while type I belongs to a series or in Barkla'sS nomenclature .
It is of interest to * Gray , ' Roy .
Soc. Proc , vol. 87 , p. 489 .
Rutherford , ' Phil. Mag 1912 , vol. 24 , p. 453 .
Chapman , ' Boy .
Soc. Proc , vol. 86 , p. 4$9 .
S Barkla , ' PhiL Nag 1911 , vol. 22 , p. 396 .
-Rays by the a-Rays of Ionium .
227 rote that , from Rutherford 's theory of the constitution of the atom and the mode of production of the -rays , it is to be expected that characteristic radiations of several different series are capable of being produced in the atom by suitable agencies .
The number of different types of radiation and their relative intensities would vary with the nature of the exciting agency and with the structure of the atom .
The question whether these -radiations are excited in the ionium atom .
itself , or in the surrounding atoms of thorium , is at present quite an open \amp ; : : one .
One would naturally suppose that , whatever the mechanism of excitation may be , the chance of producing a -ray would be much greater inside the atom emitting the -ray than in any other atom .
If , however , a large part of .
the radiation is excited in the thorium atom , it is bo be expected that some radiation would be excited in the platinum upon which the active material is placed .
To test this point the active material was : translerred to a paper dish equal in area to the platinum dish , and the intensity of the radiation measured for different thicknesses of aluminium .
No certain difference in the radiation could be detected .
This result does not prove that no radiation was excited in the platinum , for , taking Chapman 's value of for the characteristic -radiation of platinum , it was calculated that 85 per cent. of the radiation would be absorbed in the active material before it reached the electroscope .
This important point can be settled by making experiments with the source of -rays exciting the -rays in the form of a very thin film .
We hope to do this by depositing a thin film of polonium on different metals , and determining the quality of the -radiation in each case .
-Rays from A quantity of thorium oxide containing radiothorium equivalent in -ray activity to mglm .
radium bromide was purified from all and -ray products by the following method .
The oxide was obtained in solution by the same methods used for ionium .
The active thorium hydroxide was completely freed from thorium X by repeated precipitations with ammonia .
It was then dissolved in hydrochloric acid , and to this solution was added some lead nitrate and some bismuth nitrate .
No precipitate was allowed to form in this solution .
The lead and bismuth were precipitated as sulphides by .
The sulphides contained all the thorium and thorium C. The filtrate containing the radiothorium was evaporated on a water bath till all fumes were driven off .
The solution was acidified , some lead and bismuth salt in solution added to it , and again passed through it .
This operation removes the VOL. LXXXVIIL\mdash ; A. and -radiation is due , of course , to the thorium , and , formed by the thorium X grown from the radiothorium .
The fact tRat the to -ray $ ratio varies so considerably ths first after preparation , shows that there is some body present initially which emits a much greater proportion of -rays to -rays than the products grown from the radiothorium .
: body must be radiothorium .
If this body emitted -rays only , the ratio of to -rays would be constant with time , no matter how much thorium X and subsequent products were present with it after partial purification .
Some weeks later the radiothorium was again purified as oarefully as possible , and again a small amount of -radiation was found to be " " nonseparable\ldquo ; from it .
The amount of -radiation emitted by radiothorium is of the same order as that emitted by ionium when preparations of equal -ray activity are measured under the same conditions .
No absorption measurements of this .
-radiation have been undertaken , partly on .
account of the small amount , of it , and partly because of the rapid formation of products expelling intense and -radiation .
It is at present difficult to say whether the small -radiation emitted by radiothorium is due to that body , or to a product grown in the time which elapses between the last precipitation and the first measurement .
It is plain that the discovery of the excitation of by tays haa by the Ionium and .
229 opened up a new and interesting field of work , the results of which should have an important bearing , not only on the theory of the nature of the -rays and their mode of excitation in atoms , but also on the theory of the constitution of the atom .
We are continuing this work by studying in detail the and -radiations emitted by polonium , radium , and other -ray products .
Summary .
( 1 ) The work on the excitation of -rays by -rays has been extended to ionium .
It is shown that the -rays of ionium excite -radiation , and the nature of this exoited -radiation has been studied in detail .
There is also some slight evidence of the excitation of -rays .
( 2 ) The -radiation from ionium consists of three types .
The first of these has a value of in aluminium of 400 , the second of , and the third of .
The energy of the radiation is mainly confined to the softest type .
( 3 ) It is probable that these three radiations are characteristic radiations , either of thorium or of ionium , of different series .
( 4 ) Radiothorium emits also a small quantity of -radiation , too small , however , to be studied in detail with the quantity of active material at our disposal .
We wish here to express our great indebtedness to Prof. Rutherford , not only for the valuable preparations he has placed at our disposal , but also for his stimulating interest and advice throughout the whole course of the work .
|
rspa_1913_0023 | 0950-1207 | Re-reduction of dover tidal observations, 1883-84, etc. | 230 | 233 | 1,913 | 88 | Proceedings of the Royal Society of London. Series A, Containing Papers of a Mathematical and Physical Character | Edward Roberts, I. S. O., F. R. A. S.|Lord Rayleigh, O. M., F. R. S. | article | 6.0.4 | http://dx.doi.org/10.1098/rspa.1913.0023 | en | rspa | 1,910 | 1,900 | 1,900 | 3 | 70 | 2,247 | http://corpora.clarin-d.uni-saarland.de/surprisal/6.0.3/?id=rspa_1913_0023 | 10.1098/rspa.1913.0023 | null | null | null | Meteorology | 56.531914 | Tables | 29.800874 | Meteorology | [
44.56948471069336,
27.519824981689453
] | 230 Re-reduction of Dover Tidal Observations , 1883-84 , etc. By Edward Roberts , I.S.O. , F.R.A.S. { Communicated by Lord Rayleigh , O.M. , F.R.S. Received February 11 , \#151 ; \#166 ; Read February 27 , 1913 .
) In the ' Proceedings of the Royal Society/ vol. 45 , is contained a " Second Series of Results of the Harmonic Analysis of Tidal Observations/ ' collected by G. H. Darwin , LL. D. , F.R.S. In Table I , p. 567 , of this paper are included the harmonic constants obtained from the reduction of tidal observations at Dover for the three years 1883 , 1884 , and 1885 .
This tidal record was frequently interrupted , and there are wanting 34 days in 1883 , 57 days in 1884 and 72 days in 1885 .
The gaps are generally of short duration , except in 1885 , where there is no record from September 24 to October 26 .
The results generally show far more divergence than is usual , and in consequence many of the smaller tides have been altogether rejected and many of those retained are really bad .
In 1911 there was available a further record of observations , from which a period of one year commencing from 1910 , October 1 , was selected and reduced by me for the Hydrographic Department of the Admiralty .
A comparison of these new results with those contained in the above paper showed a very strong probability that if the gaps in the observations of 1883-85 could be filled in and the observations re-reduced , a much better agreement would be obtained between the results of the three years .
On my representation to Sir George Darwin he fully agreed to the desirability of the re-reduction , stating that at the time he had not realised the necessity of filling in the gaps even with rough approximations if the ultimate results were to be fairly reliable .
Accordingly Sir George made application and obtained a small grant from the Royal Society fund for the necessary work and obtained for me the original calculations for revision .
On examination of the records it would appear that , in addition to the gaps in 1885 , at least , there was evidence of some displacement in time of the actual observations , judging from the value found for the phase of the chief lunar semidiurnal tide ( M2 ) .
The value ( 344 ' ) would make the chief tide about 30 minutes later than those found for 1883 and 1884 , a wholly incredible amount .
From a close scrutiny of the observations an error appeared probable about 1885 , April 16 .
On this day the last four hourly readings are wanting , and the readings begin again at noon of April 17 .
The sequence of the heights , however , would indicate that the previous Re-reduction of Dover Tidal Observations , 1883-84 , etc. 231 readings should end , at least , not later than 19 h. of April 14 .
As the rectification of this displacement would entail virtually a re-reduction of the whole year , coupled also with the uncertainty of the correction , it was decided to confine the work to the years 1883 and 1884 .
Accordingly , with the newly-found constants , the whole of the curves for the two years were run off on my latest designed machine for tidal predictions , and the heights for the missing days filled in with the values on the machine curves .
The whole of the summations were then corrected and the resulting series re-analysed .
For the sake of comparison the results found from the 1910-11 observations are appended .
The values are now as follow:\#151 ; Harmonic Tidal Constants at Dover ( Long. 1 ' 19 ' E. ) .
Year f beginning \ A0 = 1883 .
January 1 .
deg. ft. 9*163 1884 .
January 1 .
deg. ft. 9-112 Mean of 1883-1884 .
deg. ft. 9*138 1910 .
October 1 .
deg. ft. : 8 -337 Si .
{ r. 244 0*030 { ?
: 285 0-013 { ?
: 264 0 -022 { = : 328 0*020 S2 \#166 ; { ^ : 20 *5 2*357 { ?
: 21 -9 2-297 21 -2 2-327 { ?
: 21 -4 2-326 S4 .
{ ^ : 332 0-047 18 0*068 { ?
: 355 0-057 349 0*058 T - r.z { ?
: 33 0-317 ^ M , -j rr .
137 0-013 ^ [ " - 17 0*019 [ \#174 ; - 77 0-016 ^ rr .
111 0 -014 m2 - 329 -0 7-553 ^ 329-0 7-445 ^ [ ?
: 329 -0 7-449 h !
\#171 ; : 331 -5 7*085 Ms ] rH = L * = 24 0-041 ^ l*r- 27 0-036 ^ [ = : 25 0-039 ^ I*.- 337 0-018 M4 -j H = .
K = 215 0*840 J H = .
K = 219 0-827 J fH = L * = 217 0-834 H = K = 222 0-720 m6 \ H = K \#151 ; 90 0-211 H = K = 93 0-190 r H = K = 91 0*200 rH = 95 0T53 Ms j H = _ K = 0 0-079 j H = fC = 1 0*069 j 'H = _ K = 1 0*074 j H = K = 351 0*040 K , H = K = 48 0*145 j H = K = 31 0-118 | H = K = 39 0T32 | H = K = 39 0T54 | H = fC = 24 *5 0-607 j H = K = 14 *2 0-682 j H = fC = 19-4 0-645 | H = K = 22 -0 0*704 ' I H = .
K = 182 0T90 j H = _ K = 163 OT77 j H = K = 172 0T84 | H = K \#151 ; 180 0-325 P 1 H = K = 17 0-065 j H = w K ~ 37 0*045 j H = K = 27 0-055 | H = K = 55 0-058 Note.\#151 ; The values of mean sea-level ( A0 ) are referred to the zero of the tide-gauge , which is said to be 8 *67 feet below the Ordnance datum .
The phases of the tides are referred to Greenwich time throughout .
Mr. E. Roberts .
Re-reduction of [ Feb. 11 , Harmonic Tidal Constants at Dover ( Long. 1 ' 19 ' E.)\#151 ; continued .
Year 1883 .
1884 .
Mean of 1910 .
beginning \ January 1 .
January 1 .
1883- -1884 .
October 1 .
deg. ft. deg. ft. deg. ft. deg. ft. T J rH = 0-014 j m \#151 ; 0-027 ^ fH = 0-021 ^ rn =B L - = 182 L \#171 ; = 231 l * = 207 L K = Q. ^ rn = 0-047 I fH \#151 ; 0-032 j rn \#151 ; 0-040 J rH = L K = 106 1 L i = 99 L * = 102 1 L \#171 ; = T J rH = 0-441 J H = 0-455 ^ rn = 0-448 i rH BS 0*585 L 1 L * = 330 1 L K = 331 L * = 331 1 L * = 323 i\r J rH = 1-418 J rH \#151 ; 1-392 J rH = 1-405 J rH = 1-392 L * - 308 *4 1 L - = 309*0 1 L K = 308 -7 1 L K = 313 -9 2N j rH \#151 ; 0-083 j rn = 0-179 ^ rs = 0-131 h rs = 0-299 L \#171 ; = 252 i * = 265 L * = 258 i\#171 ; = 313 " J H = 0-494 J rH \#151 ; 0-241 ^ ra SB 0*363 j rH = 0-521 r 1 L * = 293 1 L * = 272 t\#171 ; = 282 1 l \#171 ; = 343 * \ H \#151 ; 0-210 ^ ra = 0-269 j rn = 0*239 i rH = 0-420 L \#171 ; = 45 i\#171 ; = 45 L \#171 ; = 45 1 L * = 41 2SM j rn \#151 ; - 0-125 J H \#151 ; 0-113 J :h = 0-119 J H SB 0-119 L * = 231 i = 200 1 K = 215 1 = 216 MS -J rH = 0-528 J H \#151 ; 0-537 J ' H 0-533 J H = 0*732 L * = 270 1 _ K = 275 i .
K = 273 1 K = 285 MN .
fH \#151 ; 0-282 J H \#151 ; 0-316 J H = 0*299 J " H = 0*230 l - = 196 i K = 197 1 K = 197 1 = 160 2M2K , -1 rn 0-014 J rH = 0-020 , rH = 0-017 J rH = L \#171 ; = 125 1 L K = 50 1 L * = 88 i L \#171 ; = MjKj \#166 ; fH = 0-087 j rH = 0-102 i rH = 0*095 ^ rn as l * = 308 * ] L * = 4 1 L * = 336 L \#171 ; = Mm - fH = 0*056 ^ rs \#151 ; 0-174 , ra SB 0-115 ^ rn = 5 0*177 l* - 270 i * = 226 L \#171 ; = 248 L - = 267 Mf \#171 ; fH SB 0*112 ^ rn = 0-231 _ rn 3= 0*172 , rn \#151 ; 0-082 l - = 134 i\#171 ; = 261 i* = 198 L * = 163 MS/ - fH \#151 ; 0-057 ^ r h \#151 ; 0 -073 .
_ rs ss 0-065 rH = 0-130 l \#171 ; = 171 i\#171 ; = 336 i* * 254 4 L * = 330 S\lt ; * - fH \#151 ; 0-978 ^ fH 3= 0-570 _ fH = 0-774 _ fH as 0-283 l - = 213 1\#171 ; = 326 1 * = 270 i. \#171 ; = 272 S sa L * = 0 -460 ^ rs = 0-528 _ fH as 0-494 _ rn = 0*097 = 161 i\#171 ; = 192 L - = 177 L * = 328 It will be seen that the agreement throughout is now very good and all the tides originally rejected can now be retained as fairly accurate .
The long-period tides have been re-determined , but the very irregular character of the tides at Dover precludes the assumption of their reliability .
The mean value , however , of the phase of the solar annual tide accords with the new value of 1910-11 , and may be accepted as approximately correct .
It also agrees with the phases found for British ports generally .
In connection with this irregularity the following mean daily levels of the water above the zero of the tide-gauge may be noted .
The day is the astronomical day commencing at noon :\#151 ; 1913 .
] Dover Tidal Observations , 1883-84 , etc. 1884 .
ft. 1884 .
ft. .1884 .
ft. September 5 12 *22 September 17 6*38 September 29 7*17 " 6 9-88 " 18 6*04 " 30 6*31 " 7 8-56 " 19 5*85 October 1 7*20 " 8 7-90 " 20 6*12 " 2 6*28 " 9 7-04 , " 21 6*63 " 3 7*23 " 10 , 6-98 " 22 6*91 " 4 6*16 " 11 7-08 " 23 6*54 " 5 8*12 " 12 7-09 " 24 6*49 " 6 8*44 " 13 7-32 " 25 6*63 " 7 8*66 " 14 7-27 " 26 7*08 " 8 9 *20 " 15 7-09 " 27 6*98 " 9 9*63 " 16 6-77 " 28 6*74 " 10 10 *40 The mean level of the water determined for 1884 is 9T1 feet above the tide-gauge zero .
The above table shows an excess of over 3 feet on September 5 and a defect of about the same amount on September 19 , or a difference of mean level of over 6 feet within a period of 14 days , and for the whole period the mean level of the water is much below the average and only in excess of it on the first two and last three days .
The weather conditions during the period are normal and on only one day , September 7 , is the atmospheric pressure about three-tenths of an inch below the average with a strong W.S.W. gale , with a wind pressure of over 16 lbs. on the square foot .
The average for this day is 8*56 feet , or actually below the yearly average by 0'55 foot , when it would be anticipated to be considerably above it .
From this and other considerations it appears probable the heights have been measured from a base 2 feet too high from about September 6 to October 4 .
The effect of these misreadings on the Results will be very little except for the long-period tides , for which it may account in some measure for the divergence of the results obtained for 1883 and 1884 .
|
rspa_1913_0024 | 0950-1207 | Studies of the processes operative in solutions. XXV. -The influence of non-electrolytes on solubility. The nature of the processes of dissolution and precipitation. | 234 | 245 | 1,913 | 88 | Proceedings of the Royal Society of London. Series A, Containing Papers of a Mathematical and Physical Character | H. E. Armstrong, F. R. S.|J. Vargas Eyre, Ph. D. | article | 6.0.4 | http://dx.doi.org/10.1098/rspa.1913.0024 | en | rspa | 1,910 | 1,900 | 1,900 | 7 | 222 | 5,573 | http://corpora.clarin-d.uni-saarland.de/surprisal/6.0.3/?id=rspa_1913_0024 | 10.1098/rspa.1913.0024 | null | null | null | Biochemistry | 57.960747 | Chemistry 2 | 35.868632 | Biochemistry | [
-52.56667709350586,
-42.44828796386719
] | 234 Studies of the Processes Operative in Solutions .
XXV.\#151 ; The Influence of Non-Electrolytes on Solubility .
The Nature of the Processes of Dissolution and Precipitation .
By H. E. Armstrong , F.R.S. , and J. Vargas Eyre* Ph. D. ( Received January 1 , \#151 ; Read February 13 , 1913 .
) The subject of " competitive solubility " has been dealt with in two previous communications of this series , Parts II and XI.* In both of these , emphasis was laid on the fact that electrolytes and non-electrolytes are alike active as precipitants of salts from aqueous solutions and it was implied that no " theory " of the process of dissolution which does not take this fact into account can be satisfactory .
The activity of the several precipitants studied was expressed .
in terms of their apparent molecular hydration\#151 ; that is to say , the method of treatment adopted involved the evaluation of the amount of water thrown out of action as solvent water by the precipitant : care was taken , however , to point out that this artifice was introduced merely on the ground of convenience and that the expression " apparent molecular hydration " was not to be interpreted literally .
It was contended , in fact , that the precipitant does not act merely by attracting water to itself but that the condition of the solvent water must also , in some way , be changed by the introduction of the precipitant , especially in the case of a neutral substance such as propylic alcohol .
This was a novel conception , based on views previously brought under the notice of the Society , in 1906 , in a communication on the " Origin of Osmotic Effects " and subsequently in Parts II and VI of these studies .
The conception has since been extended to other phenomena in Parts XIII , XIV , XV , XVIII , XIX and XX of these studies and a large body of evidence has been brought forward to show that solute and solvent are in all cases reciprocally modified .
The experiments now described were instituted mainly in order to ascertain the effects of non-electrolytes on slightly soluble salts , as the hypothesis introduced by Nernst , in 1889 , in explanation of the precipitation of one salt by another , was based more particularly on the results obtained with such salts\#151 ; the hypothesis , namely , that the solubility of a salt is depressed by the presence of another salt if the two have an ion in common .
According to the view put forward by Nernst , the concentration of the " undissociated " part of a salt in a solution saturated with the sarlt is constant , * 'Roy .
Soc. Proc. , J 1907 , A , vol. 79 , p. 564 ; 1910 , vol. 84 , p. 123 .
Studies of the Processes Operative in Solutions .
235 even in the presence of another salt , at each particular temperature ; it is also proportional to the product of the concentrations of the ions of the salt ( the ionic solubility product ) .
If a second salt be introduced which has an ion in common with the salt with which the solution is saturated , a certain proportion of the common ion will be derived from each salt and to maintain the constancy of the solubility product each salt must be re-formed to a certain extent , so that the salt with which the solution was saturated originally is in part precipitated .
As Stieglitz has pointed out , * the hypothesis is based upon premises which are not valid in the case of salts ; moreover , though the results obtained with a few slightly soluble salts may appear to substantiate it , the behaviour of soluble salts is in no way in accordance with such an assumption .
To take a case in point , when hydrogen chloride is added to a solution of sodium chloride , the latter is all but entirely displaced from solution .
An even more striking case is that observed by Etard , f who has shown that potassium chloride is insoluble in a solution saturated with potassium bromide and iodide .
The complete command of the water exercised , in the one case , by hydrogen chloride , in the other , by the two haloids is very remarkable .
Peculiarities such as these did not escape the notice of the older workers , as witness the following statements made by Graham in 1850 in his Bakerian lecture on Diffusion :\#151 ; " In the consideration of solubility attention is generally engrossed entirely by the quantity of salt dissolved .
But it is necessary to apprehend clearly another character of solutions , namely , the degree of force with which the salt is held in solution or the intensity of solvent attraction , f quite irrespective of quantity dissolved .
" In the solutions of two salts which are equally soluble in point of quantity , the intensity of the attraction between the salt and water may be very different .
* " Besides being said to be small or great , the solubility of a substance has therefore to be described as weak or strong .
" The difficulty of evaluating the exact influence one soluble substance will exercise over another in solution must be very great , owing to the existence of peculiarities such as are referred to by Graham .
Indeed , to repeat a statement made in Part II , " It can scarcely be doubted that the forces at work in solutions are too complex in character to be expressed as simple mathematical laws .
The fact that water is itself a complex material , which varies greatly in composition as the conditions are changed , has been left almost wholly , if not entirely , out of account in discussing electrolytic and * ' Journ. Amer .
Chem. Soc. , ' 1908 , vol. 30 , p. 946 .
t 'Ann .
Chim .
Phys. , ' 1894 , ( 7 ) , vol. 3 , p. 275 .
1 This conception is embodied in the term Haftdruclc , proposed by Traube .
Prof. H. E. Armstrong and Dr. J. V. Eyre .
[ Jan. 1 , hydration phenomena ; and far too little attention has been paid also to the existence of salts in solution in various states of molecular aggregation/ ' If it be granted that solvent and solute are reciprocally active in the process of dissolution and that the dissolved substance in an aqueous solution is associated with " water , " it follows of necessity that when a solution saturated with a particular salt is mixed with a second soluble salt which , ex hypothesi , is also hydrated in solution\#151 ; the second salt being of such nature that no interaction of the two can take place\#151 ; some of the salt with which the solution was originally saturated must be precipitated , unless the affinity of this salt for water be so strong that it cannot be overcome by that of the added second salt , as in the case observed by Etard : precipitation must continue up to the point at which the two salts share the solvent in certain characteristic proportions .
But any neutral soluble substance which either combines with water on dissolving or in any other way exercises a dehydrating effect ( cp .
S 9 ) should act in this manner when introduced into the solution and therefore should cause precipitation .
On account of the importance attached by Nernst and others to the behaviour of slightly soluble salts , we have thought it desirable to extend our experiments to the two slightly soluble salts lead chloride and silver acetate and to determine the influence of a number of neutral precipitants not previously studied at the time when the experiments were instituted , though in the interval several accounts have been published by other workers who have had the same problem under consideration .
It may be added that the work now recorded was completed in the spring of 1911 .
The determinations were all made at 25 ' C. The substances used were prepared from materials sold as pure ( cp .
XI , p. 124 ) .
It was not found possible to estimate with certainty the small quantities of lead chloride present in the solutions by gravimetric methods nor was it possible to effect the determination by the usual volumetric method of titration with a solution of silver nitrate in the presence of potassium chromate as indicator , as a precipitate of silver chromate was formed at once ; but by modifying this method , so that all the lead was precipitated as chromate and a slight excess of potassium chromate left to serve as indicator , it was possible to estimate the chloride in the solution by gradually adding a solution of silver nitrate in the ordinary way .
If the titration be carried out in a white porcelain basin , satisfactory results are obtained without difficulty .
This was established by careful experiments with saturated solutions of lead chloride ; the results obtained differed among themselves by less than 1 per cent. 1913 .
] Studies of the Processes Operative in Solutions .
237 When hydrogen chloride was used as precipitant , the amount of acid present in the pipetted portion of the saturated solution was first determined by titration against standardised alkali ; the total chloride present was then determined in the neutral solution by titration with a standardised solution of silver nitrate and the amount of lead chloride present deduced from the two values .
The method used in estimating the amount of silver acetate in the saturated solutions was that known as Pisani 's method , which is based upon the fact that an aqueous solution of iodised starch is decolourised by solutions of silver salts .
A suitable solution for the purpose was prepared by adding to half a litre of hot water from 10 to 12 grm. of soluble starch made into a paste with water ; after boiling the liquid during a few minutes , it was diluted to about 1 litre and mixed with a few drops of an alcoholic solution of iodine , so as to render it ' a deep blue colour .
As it is necessary to use only very dilute solutions of silver salt , the samples of saturated solution were always diluted to 500 c.c. ; the diluted solution was titrated against 500 c.c. of the iodised starch solution after this had been standardised against a solution of silver nitrate of suitable strength .
With practice , very satisfactory results can be obtained by this method .
The extent to which the determinations are in agreement is shown in the following table .
The results of separate experiments with different samples of salt are given in sections I and II , whilst A and B represent those obtained with two samples of the same solution , the difference being that B was withdrawn an hour later than A:\#151 ; .
100 grms. of water at 25 ' C. dissolve Lead chloride .
Silver acetate .
grms. TfA 1*1024 A 1 B 1 -1030 ttJA 1-1026 11 \B 1*1021 grms. T/ A 1-096 \#177 ; tB 1-104 tt/ A 1*114 A\#177 ; 1B 1-117 The results are recorded in the table on p. 238 and are also represented graphically in the diagrams on p. 239 .
The effects on the solubility of potassium chloride of a variety of precipitants not previously studied are also recorded in the table and in the graphs .
Prof. H. E. Armstrong and Dr. J. Y. Eyre .
[ Jan. 1 Precipitant .
Molecular concentration of precipitant per 55 *5 mols .
of water .
Solubility in 1000 grin , of water at 25 ' .
Relative density , d 2\#151 ; 25 Molecular solubility .
Apparent molecular hydration of precipitant .
\#165 ; Lead Chloride .
__ 11 *0276 1*0098 0 *0397 Ethylic alcohol 4 10 *6609 1 *0069 0 *0383 7*39 Glycol " i 11*0352 1 *0116 0 *0397 - 0*15 1 11 *7035 1*0170 0 0421 - 3*41 Acetaldehyde i 10 *7638 1 *0097 0 *0387 + 5*31 ... i 10 *2451 1 *0095 0 *0368 5*25 Paraldehyde i 10*3910 1 *0114 0 *0313 12*83 11 *0210 1 *0098 0 *0396 Paraldehyde Ta 10 *7185 1 *0101 0 *0385 18*28 Glycerol i 11 *3658 1 *0152 0*0409 - 6*95 11 *0321 1 *0104 0 *0397 Propylic alcohol 4 10 *3266 1 *0066 0 *0371 14 *20 1 10 *0262 0 *9984 0 *0324 10 09 Hydrogen chloride ... 4 4 *2849 1 *0058 0 *0154 135 *85 i 3 *6833 1 0098 0 *0132 73*97 Methylic acetanilide It 10 *6567 1*0111 0 *0383 9*85 Lead nitrate 4 14 *2079 1 *0816 0 0510 -63 *91 55 .
To 11*6515 1 *0383 0 *0420 -31 *17 35 To 10 *7144 1 0170 0 *0386 + 79 *92 35 jio 11 1192 1 *0118 0 *0400 -43 *82 Silver Acetate .
10*2350 1 *0081 0 *0613 Glycol 1 9 0145 1 *0154 0*0540 6*62 Glycerol 1 9 *5420 1 *0277 0 *0572 3*76 Propylic alcohol 1 8 *5795 0 *9981 0 *0514 8*98 Paraldehyde Ta 9 *1015 1 *0084 0 *0535 24 *59 \#151 ; 11 *1780 1 *0085 0 *0669 Isobutylic alcohol ... s 8 *1080 0 *9996 0 *0486 20 *33 Propylic alcohol i 10 *1335 1*0059 0 0607 18 *75 Glycol i 11 *1570 1 *0099 0 *0668 0*42 10 *4250 0 *0625 Acetaldehyde 4 10 -3361 \#151 ; .
0 *0619 1*45 Paraldehyde i 9 *5478 .
~~ 0 *0572 18 *20 Potassium Chloride .
367 -700 1 *1820 4 *9315 .
Acetaldehyde 4 375 -119 1 *1791 4 *8968 1 *56 Paraldehyde A 363 -051 1 *1786 4 *8692 1 *42 Glycol i 365 -134 1 *1802 4 *8970 1 *51 l 359 100 1 *1762 4*8160 1*30 Glycerol i 366 -700 1*1830 4 *9194 0*56 Mannitol i 367 -455 1 *1903 4 *9285 0*15 33 A 368 -000 1 *1884 4 *9360 - 0 *22 Molecular proportion of precipitant per 55*5 mol .
prop , water .
1913 .
] Studies of the Processes Operative in Solutions .
Lead Chloride as Solute .
\ \ GLYCOL \ ACETALDEHYDE \ PROPY If \ GLYCEROL \ ETHYUC ALCL HOL \ A A \gt ; METHYL \gt ; ACETANILIDE PARALDEHYDE -to -3 O 5 / O / S 20 25 30 Silver Acetate as Solute .
JSO-BUTYUC A '.COHO/ .
GLYCOL PROPYUC AH ACETALDEHYDi ' Potassium Chloride as Solute .
J/ 4 '/ a \#171 ; . . . .
i * \#171 ; . .
\#171 ; B 1 \#151 ; 1 .
1 . . .
1 i GLUCOSE* CLP .
\#171 ; .
:ol 1 " ETHYL/ \amp ; ALCOHc\ 1 1 { PROPYLIC ALCL .
1 HO* HYDROGEN C .
C HLORiDE I .
S .
S CLY .
TERO , [ / .
' l t .
\#166 ; . . .
MANN/ T\amp ; ~ ''ACETALDEj rrDE PARALDEH X WE -to '5 0 3/ 0 / 5 20 23 30 Apparent molecular hydration of precipitant .
Prof. H. E. Armstrong and Dr. J. V. Eyre .
[ Jan. 1 , 1 .
Taking into account the observations of other workers as well as those brought forward in this and the two previous communications , it is clear that , in principle , no distinction can be drawn between slightly soluble salts and soluble salts .
Owing to the difficulty which attends the determination of solubility in the case of slightly soluble salts , we do not attach weight to the smaller differences observed between the lead and the silver salt , the more as we found it impossible to obtain constant values in the case of the latter , different samples giving different values\#151 ; whether on account of surface changes due to the action of light or to differences in the state of aggregation ( cp .
XI , p. 125 ) .
For example , we are not prepared to regard propylic alcohol and paraldehyde as more active precipitants of the silver than of the lead salt but are inclined to think that the activity of both precipitants , when present in small proportions , may have been overestimated in the case of the silver salt .
2 .
Non-electrolytes and electrolytes alike act as precipitants of salts ; though in both cases substances are to be found which increase solubility instead of depressing it .
3 .
As the activity of non-electrolytes as precipitants is inconsistent with the postulates of the ionic hypothesis , it is obvious that the explanation of the behaviour of precipitants in general must be based upon some broader hypothesis .
4 .
It is necessary , in all cases , to take into account the changes which affect the solvent as well as those that affect the solute ; to neglect consideration of the changes in the solute\#151 ; the almost universal habit of those who postulate the existence of dissociated , separate ions in solutions of electrolytes\#151 ; is an indefensible practice .
5 .
If it be admitted that both solids and liquids are formed by the association of the fundamental molecules characteristic of the gaseous state , dissolution must be regarded as in large measure a process of " depolymerisation " not of the solute alone but also of the solvent .
6 .
It is also necessary , far more than has been customary of late , to take into account the reciprocal changes which attend dissolution , other than those which involve disturbance of molecular complexity , namely , those which involve the formation of new molecular species , whether as the outcome of interactions or of mere association of solvent and solute .
7 .
One of the most striking facts brought out when the evidence now available is considered , is the remarkable antithesis presented by the activity of electrolytes and non-electrolytes as precipitants : whereas , in aqueous solutions , the former are usually the more active the more soluble they are , in the case of non-electrolytes the relationship is of the reverse order .
1913 .
] Studies of the Processes Operative in Solutions .
241 8 .
The simplest case to be considered is that of carbon dioxide ; as the molecules of this gas are unlikely to be present in solution in any other form than as simple molecules such as are represented by the formula C02 , any increase in its solubility cannot well be interpreted otherwise than as due to an increase merely in the number of molecules undergoing some form of hydration which renders them soluble .
Usher 's determinations of the solubility of this gas in presence of various organic substances* are , therefore , of particular value .
From experiments made with semi-normal solutions , he has deduced the results displayed in the-following table , the value given being the number of cubic centimetres of gas dissolved by 1000 grin , of water at 20 ' in presence of the substance quoted :\#151 ; W ater . .
878 8 .
Pyrogallol 894 1 .
Cane sugar . .
797 9 .
w-Propylic alcohol 902 2 .
Mannitol . .
833 10 .
Acetamide 906 3 .
Dextrose . .
841 11 .
Urethane 907 4 .
Glycine . .
864 12 .
Catechol 908 5 .
Carbamide . .
884 13 .
Quinol 928 6 .
Thiocarbamide ... . . .
885 14 .
Antipyrine 935 7 .
Acetic acid . .
893 15 .
Resorcinol 945 9 .
In the case of the three substances first on the list , the observed lowering of the solubility cannot well be regarded otherwise than as a direct dehydration effect , that is to say , as due to a diminution in the amount of free water present owing to the association of a certain amount of the water used with the added solute .
Excluding Nos. 4 , 5 , 6 , 10 , 11 and 14 , which conceivably may exercise an influence as basic compounds , though perhaps scarcely to the extent observed , , the remaining substances apparently all serve to render the water more active as a solvent of carbon dioxide\#151 ; more effective , that is to say , in converting it into a " hydrated " form .
Now the view advocated in previous communications of this series involves the assumption that when neutral substances are dissolved in water they serve to increase the proportion of simpler molecules in the liquid\#151 ; i.e. , molecules of hydrone , OH2\#151 ; and , therefore , to render it a more active agent .
' 10 .
Confining our attention to propylic alcohol , the only one of the substances under consideration of which we have experience , which is an active precipitant of salts\#151 ; more active , in fact , than ethylic alcohol\#151 ; the increase in the solubility of carbon dioxide in its presence , amounting to 24 c.c. , cannot well be ascribed to the direct dissolution of the gas in the alcohol .
* 'Chem .
Soc. Trans. , ' 1910 , p. 66 .
Prof. H. E. Armstrong and Dr. J. V. Eyre .
[ Jan. 1 , Ethylic alcohol depresses the solubility of carbon dioxide in water .
The coefficients found by Findlay and Shen* are as follows ( at 25 ' , 737-747 mm. ) Water ... ... ... ... ... ... ... ... ... ... ... ... ... ... ... 0*825 " containing 2*95 grm. alcohol ( in 100 c.c. ) ... .
0*812 " " 3*01 " " ... .
0*814 " " 8*83 " " ... .
0*786 As ethylic alcohol undoubtedly has a greater affinity for water than propylic , it may be supposed that it is far more completely hydrated and more under the control of the water than is propylic alcohol : consequently , that more molecules of the latter alcohol may be active in promoting dissociation of water molecules in the sense of the expression ( OH2 ) ; c \#151 ; \#166 ; - xOH2 .
On this assumption , a larger proportion of the molecules of carbon dioxide would be subject to hydration in a solution of propylic than in one of ethylic alcohol : hence the increase in solubility .
The argument is of general application .
1L When the results we have obtained with silver acetate , lead chloride and various haloids and those obtained by Eothmundf with silver sulphate , potassium bromate , potassium perchlorate and lithium carbonate\#151 ; four sparingly soluble salts which are more soluble than the two we used but less soluble than the remainder of those we have studied\#151 ; are contrasted , the same substances are seen to act as precipitants and , with certain marked exceptions , the order of their activity is the same .
12 .
In cases in which direct comparison is possible , the less soluble nonelectrolyte is always the more active precipitant : thus the activity of the monhydric alcohols is in the order of increasing molecular weight .
Paracet-aldehyde is more active than acetaldehyde , whether comparison be made of equal weights or of moleeularly similar proportions .
The activity of polyhydric alcohols diminishes as their hydricity and solubility increases .
Thiourea is more active than urea .
13 .
The experiments carried out by Fox and Gauge on the solubility of potassium sulphate^ and by Eothmund on the salts above mentioned are of special interest in this connexion .
The solubility of potassium sulphate is at first unaffected by the presence of cane sugar and is only slightly diminished as the proportion of sugar is increased ; obviously , therefore , as it must be supposed that cane sugar * 'Chem .
Soc. Trans.,5 1911 , p. 1313 .
t ' Zeit .
phys .
Chem.,5 1909 , vol. 69 , p. 523 .
X 'Chem .
Soc. Trans.,5 1910 , p. 377 . .
1913 .
] Studies of the Processes Operative in Solutions .
243 becomes associated with a certain proportion of the water , it must serve from the beginning to promote the solubility of the salt .
Mannitol , glycerol , glycol , pyridine , ethylic alcohol and acetone are active as precipitants from the beginning , in the order mentioned .
Most unfortunately , Rothmund 's experiments were carried out with volume normal solutions : consequently , no two solutions contained the same molecular proportion of precipitant and water , so that the results are not comparable among themselves .
Nevertheless , it is obvious , when strictly neutral precipitants such as the monhydric alcohols are considered , that these maintain their position in order of activity whatever the salt used may be .
The cases in which the precipitants vary in behaviour are significant .
Thus , whilst glucose promotes the dissolution of silver sulphate and of lithium carbonate , it hinders that of potassium bromate .
Similar differences are observed in the case of cane sugar .
Obviously therefore the behaviour of the salts of the " dibasic " acids is different from that of the monobasic : both sulphuric and carbonic acids , however , appear to be in reality monobasic acids upon which a slight extra activity is imposed ; it may well be that an exchange of radicles takes place between such salts and basic substances such as the sugars .
On the other hand , whilst phenol increases the solubility of silver sulphate , it depresses that of potassium bromate and perchlorate\#151 ; but acetic acid acts as a weak depressant in all cases .
It is significant also , from this point of view that acetonitrile promotes the solubility of silver sulphate whilst acting as a precipitant of lithium carbonate : it is well known that nitrogen compounds have a specially strong affinity for silver salts .
# * Similar interpretations may be given of other cases of " irregularity .
" 14 .
Propylic alcohol , which promotes the solubility of carbon dioxide , is a powerful precipitant of salts .
The assumption made previously ( S 8 ) , it may be pointed out here , is a satisfactory explanation of this difference .
In the case of carbon dioxide , an increase of solubility may be explained as the consequence of an increase of the active agent in the solution , that is to say in the number of molecules of hydrone , OH2 .
In the case of salts , however , though an increase in the proportion of molecules of hydrone would render the liquid a better solvent of the salt , it would also favour the tendency of the fundamental molecules of the salt to combine among themselves , as action would set in between hydrone molecules in the solution and those attached to the salt ; in other words , an increase in the number of hydrone molecules wmuld render the solution a dehydrating medium .
vol. lxxxviii.\#151 ; A. s Prof. H. E. Armstrong and Dr. J. V. Eyre .
[ Jan. 1 , 15 .
In the case of salts , an additional force is operative which cannot come into existence in a case such as that of carbon dioxide .
In the solid state , all salts presumably are " polymerised " forms of their fundamental molecules and on entering into solution , such molecules are more or less , if not entirely , dissociated .
The solubility of a salt may be said , in fact , to be determined by the two sets of affinities pictured in the expressions ( EX ) , ^ nBX x(RX ) + y( OH2 ) ^ ( RX)*(OH2V the solubility in each particular case depending on the extent to which the two opposite tendencies come into play .
Both forms of dissociative change shown in the equations would be promoted by those precipitants especially which have but slight affinity for water , as such molecules would be most effective mechanically .
The difference between salts generally and the corresponding acids is probably due to the fact that the acid radicle is more effectively held in check or neutralised by hydrogen than by any metal ; and the differences in salts may be attributed to the different extents to which the metals " saturate " the acid radicles .
On such a hypothesis , it is possible to understand that a metal should have the relatively constant effect which it is known to have in salts .
In the case of a very difficultly soluble salt such as is silver chloride , the affinity of the individual fundamental molecules for one another appears to be very great .
It is not improbable that in so far as such a salt is soluble at all , it enters into solution only in its simplest form represented by the symbol AgCl .
This molecule may be very active ; it may be so fully activated , in fact , as to be completely " dissociated " \#151 ; to use the now conventional term .
The solubility of the salt is slight because the affinity between the fundamental molecules is so special that it prevails almost entirely over the affinity which hydrone has for these molecules .
In the case of soluble salts the balance is far more nearly even .
The fact that salts generally are not precipitable by neutral substances in the inverse order of their solubility is probably to be explained by considerations of this order .
16 .
It will be noticed that in the case of lead chloride and silver acetate the graphs of propylic alcohol and paraldehyde slope backwards\#151 ; in other words these substances are the more active as precipitants the smaller the proportion present .
In all probability , as the amount present is increased , they tend more and more to promote the dissociation of the complex molecules of the salts into simpler more soluble molecules .
17 .
There can be little doubt that the polyhydric alcohols and sugars especially act mainly when not entirely as direct dehydrating agents .
1913 .
] Studies of the Processes Operative in Solutions .
245 In cases in which solubility is increased by such substances there can be little doubt that this is because more soluble substances are formed by the interaction of the substances present .
It is well known that the sugars form compounds with salts.* 18 .
In all cases , a soluble substance must exercise some influence directly as a dehydrating agent ; but the influence it exercises in this way must diminish and the effect it lias on the solvent must increase as the solubility of the substance diminishes ; in so far , however , as the added substance induces the dissociation of complex molecules of the solute , its action will be to increase solubility .
19 .
In fine , complex as the phenomena with which we have to deal in aqueous solutions undoubtedly are , it appears to be possible to interpret them on broad and general grounds by the application of ordinary chemical principles .
Little more is required than to extend to oxygen the conceptions which are accepted in the case of carbon .
20 .
It is only necessary to assume that water is a complex material consisting of a variety of molecular species in proportions which vary with the temperature , some comparable with the polymethylenes , others with hydrols ( cp .
Parts VI , XIX , XXIV ) .
Further , to assume that when substances are dissolved in water they are hydrolated and hydronated in various ways and to various extents and at the same time produce variations in the water ( XVIII ) .
Lastly , to admit that the several forms of " hydrated " compound are not all active chemically and that those which are active are not all equally so\#151 ; as in the case of the polymethylenes .
Such assumptions made , it follows that every variation in the conditions will involve variation not only in the active but also in the inactive constituents of the solution ; in other words , both components of a solution must vary as the conditions are varied .
[ The authors are indebted to Mr. F. W. Jackson for the assistance which he has given them in carrying out their experiments .
] * The greater solubility of lead chloride in presence of lead nitrate cannot well be accounted for otherwise than as the consequence of the formation of a mixed salt , PbCl(N03 ) .
|
rspa_1913_0025 | 0950-1207 | Studies of the processes operative in solutions. XXVI. -The disturbance of the equilibrium in solutions of fructose by salts and by non-electrolytes. | 246 | 252 | 1,913 | 88 | 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.1913.0025 | en | rspa | 1,910 | 1,900 | 1,900 | 5 | 99 | 3,114 | http://corpora.clarin-d.uni-saarland.de/surprisal/6.0.3/?id=rspa_1913_0025 | 10.1098/rspa.1913.0025 | null | null | null | Biochemistry | 77.524323 | Chemistry 2 | 12.995162 | Biochemistry | [
-54.09990692138672,
-43.346214294433594
] | 246 Studies of the Processes Operative in Solutions .
XXYI.\#151 ; The Disturbance of the Equilibrium in Solutions of Fructose by Salts and by Non-electrolytes .
By E. E. Walker , B.Sc. * ( Communicated by Prof. H. E. Armstrong , F.R.S. Received January 1 , \#151 ; Read February 13 , 1913 .
) One of the main objects in view throughout these studies has been to determine the manner in which non-electrolytes influence the course of change in solutions : it has been shown that they affect the rate at which cane sugar is hydrolysed ( XII ) ; also the rate at which urea is formed from ammonic cyanate ( XX ) ; and to judge from the behaviour of methylic acetate as a hydrolyte in comparison with that of cane sugar , it is probable that the degree of " hydration " of acids and salts in solution is lowered by their presence ( XXIII ) .
At Prof. Armstrong 's request , to throw further light on such phenomena , I have ascertained the effect produced by a variety of non-electrolytes on fructose in aqueous solutions .
The further study of this substance was desirable on various grounds , especially on account of the important part it plays in plant metabolism .
It is known to vary in optical activity to a marked extent , the temperature coefficient of an aqueous solution being larger than that observed in the case of any other sugar , viz. [ a]D = 0'*70 per degree Centigrade .
The rotatory power of the sugar in solution is decreased both by heating and by the addition of alcohol but increased by concentration , by salts and by acids ; it appeared therefore to be a specially suitable substance to use , as the course of any change could be followed with the polarimeter .
Little is known at present of the behaviour of fructose towards salts in comparison with that of glucose and cane sugar ; it was desirable , therefore , that it should be studied from the point of view from which these sugars have been considered ( X and XV ) .
Mr. Worley has drawn attention recently to the alteration in the degree of optical inversion which attends the inversion of solutions of cane sugar of different degrees of concentration ( XXII , p. 571 ) and has pointed out that probably an explanation is to be found in changes in the rotatory power of the fructose in presence of the acid .
The further study of fructose appeared to be of importance also in this connexion .
The material used was KahlbaunTs crystalline fructose prepared from inulin .
Except when stated otherwise , all measurements were made in Studies of the Processes Operative in Solutions .
a 400 mm. jacketed tube , the temperature being maintained at 25 ' + 0''005 .
The observations were carried out in mercury green light with the polari-meter and apparatus described in Part XXII .
It is commonly admitted that glucose exists in solution as an equilibrated mixture of the two stereoisomeric forms and it has been supposed that fructose also occurs in corresponding forms.* The change from the one isodynamic form into the other may be pictured as taking place in one or other of two ways ( R = CHVOH ) :\#151 ; C\#151 ; C I I OH EHC 0 / \/ XE 0 / \ HO H C---c + oh3 EHC C \ OH OH OH / \ HO H -OH2 || E EHC C\lt ; \/ xOH 0 / \ HO H C\#151 ; c I I OH EHC C\lt ; \/ XE O / \ HO H -OH2 c\#151 ; c I I EHC C\#151 ; E 0 HO C\#151 ; C + OH2 || E EHC C\lt ; \/ XOH 0 / \ HO H Whether , in the process of interconversion , the intermediate ( ketohydrol or ethenoid ) compound is ever formed in any considerable proportion must be left an open question at present .
Whilst the oxygen atom in the ring system may be pictured as in the plane of the ring in the one form of fructose , it is to be supposed that in the isomeric form , this oxygen atom is deflected out of the plane of the ring : hence it is , Hudson contends , !
that the one form is dextrorotatory , the other kevorotatory .
Presumably the two forms of glucose are similarly related : in point of fact , though both forms are dextrorotatory ( / 3-glucose [ \#171 ; ]d20 ' = +20 ' ) , the / 3-glucosides are all kevorotatory compounds , thus:\#151 ; / 3-methyl-glucoside ... ... ... ... . .
\#151 ; 32 ' / 3-ethyl " ... ... ... ... .
-33'4 ' / 3-propyl " ... ... ... ... .
\#151 ; 34-9 ' / 3-butyl , , ... ... ... ... .
\#151 ; 3 5-4 ' / 3-isobutyl " ... ... ... ... .
\#151 ; 34-9 ' / 3-allyl " ... ... ... ... .
-40-3 ' / 3-benzyl " ... ... ... ... .
-49-8 ' * Compare E. F. Armstrong 's The Simple Carbohydrates and the Glucosides , ' Long mans and Co. t ' Amer .
Chem. Journ. , ' 1909 , vol. 31 , p. 0G .
Mr. E. E. Walker .
[ Jan. 1 , To avoid periphrasis , it is proposed to speak provisionally of the one form of fructose as fructodextrose and of the stereoisomeric compound as fructo-Icevose rather than as a- and / 3-fructose .
Assuming that the active compound in a solution is the " oxonium hydrol , " in whatever way they are hydrated , to account for the difference in stability of the two forms , it is almost necessary to suppose that fructolsevose forms a more stable " hydrate " than fructodextrose , as the passage from the former into the latter is promoted by heating .
The fact established by H. T. Brown and S. U. Pickering that the heat of conversion from the ( / 3 ) kevo- into the ( a ) ( ?
) dextro-form is a relatively high negative value may be regarded as strong evidence in favour of this view , * thus:\#151 ; According to Hudson , cane sugar is resolved initially into a-glucose and fructodextrose ( [ a]D = +17 ' ) , that is to say , it is derived from corresponding forms of aldose and ketose .
Both forms of fructose and glucose undergo " mutarotation " at unimolecular rates , though the change takes place much more rapidly in the case of the former , f My own observations confirm those made by Hudson that the large temperature coefficient of fructose is due to a change in the proportions in which the two isodynamic forms are in equilibrium at different temperatures .
The same constant was obtained by following the course of the mutarotation in a solution which had been quickly prepared as in one which had either been cooled , then suddenly heated to 25 ' and brought under observation or had been heated and then quickly cooled to 25 ' before observation ( Table I ) .
Suspecting that the change in rotatory power produced by alcohol is due to a similar cause , a solution of fructose was prepared by dissolving the sugar in the proportion of two molecular proportions to 100 of water ; after a couple of hours , the solution was cooled quickly to 22 ' , then mixed with 35 molecular proportions of ethylic alcohol which had been weighed out separately .
The temperature rose almost to 25 ' ; it was quickly adjusted to 25 ' and the rise in rotatory power followed in the polarimeter .
Subsequently the solution was cooled in the ice chest , then heated rapidly to 25 ' and observations made as before .
The results are given in Table II .
The mean constants are practically identical : whence it follows that the change in rotatory power caused by alcohol is due to the same cause as that Fructose ... . .
ft \#151 ; * a-f/ 3 Glucose ... ... .
a \#151 ; a-f/ 3 Milk sugar ... a. \#151 ; \gt ; a -f- / 3 \#151 ; 835 calories 106 " 34 " * 4 Chem. So .
Journ. , ' 1897 , p. 750 .
t Hudson , ' Amer .
Chem. Soc. Journ. , ' 1908 , p. 1564 .
1913 .
] Studies of the Processes Operative in Solutions .
249 produced by heat .
It may be pointed out that the rate of change in presence of alcohol is lower .
Table I. Mutarotation .
* Cooling .
t ( minutes .
) a. a " aao .
* log ttl \#151 ; - ^ .
t " ax\gt ; t. a. a-ax .
\#151 ; log a ' a ' ' .
* a2"a30 0 112 *25 6*06 0 110 *68 4*49 2 110 *03 3*34 0*099 l* 109 *41 3*22 .096 4 108 *68 2*49 .094 5 107 *73 1 *54 .092 6 107 *82 1 *63 *092 7 107 *16 .97 TOO 8 ( 107 -21 ) ( 1 -02 ) \#151 ; 9 106 *82 .63 .094 11 106 *75 .56 .094 11 106 *61 .42 *086 14 106 *48 .29 *097 13 106 *46 .27 .095 17 106 *34 T5 .095 16 106 *23 T4 *099 22 106 *25 .06 20 106 *16 .07 44 106 T9 33 106 T9 86 106 T9 80 106 T9 Mean 0 *0951 Mean 0 *0946 Table II .
Alcohol .
Cooling .
t. a. a-ax .
] log '1 '* .
t. a. a-ax .
1 log a'~a* t a2~acc t a.2 - ax 0 97 -36 6 23 .044 2 99 *25 7*92 1 96 *76 5 63 45 2 98 -21 6*88 *041 4 95 -24 4T1 435 34 97 *08 5*75 .052 6 94 *50 3-37 46 5 96 *33 5-00 .040 8 93 *91 2 *78 42 7 95 *33 4*00 *048 10 93 *41 2*28 43 9 ( 94 *80 ) ( 3 *47 ) \#151 ; 13 92 -83 1 *70 425 11 94 01 2*68 .0435 16 92 *375 1 *245 45 14 93 -345 2 *015 *042 20 91 *93 .80 48 18 92 *535 1-305 *0465 24 91 655 .525 46 23 92 -095 .765 .0435 32 91 *36 .23 30 91 *66 .33 42 91*205 .075 50 91 *33* 62 91 T3 120 91 *32 75 91 T3 Mean 0 -0445 t i Mean 0 *0444 i * This higher value is probably due to the escape of alcohol , which is liable to be gradually absorbed by the cork closing the aperture in the polarimeter tube .
From experiments in which alcohol was added in various proportions up to that of 50 molecules to 100 of water , the solution containing half a molecular Mr. E. E. Walker .
[ Jan. 1 , proportion of fructose , it appears that the change in rotatory power is nearly proportional to the amount of alcohol added .
The results obtained with various substances are collected in Table III .
As it has been observed in other cases that the effects produced by nonelectrolytes are not quite proportional to the quantity added , the calculated values given in the fifth column are not to be regarded as strictly comparable but rather as indications of the order of activity of the substances .
Table III .
Substance added .
; ; .
\#166 ; \#166 ; \#166 ; ; Molecular proportion per 100 mols .
water .
Whs- Observed change .
Change per molecular proportion .
Fructose alone 1 -oo -105 *02 o O 2*00 -106 *30 -1 *28 -1 *28 ^Sodium chloride 2-00 -108 *77 -3*75 -1*88 .
*Potassium chloride 2 *00 -109 *12 -4*10 -2*05 Cane sugar 0*788 -108 26 - L *76 -2*50 Phenol 1 *53 -107 T7 -0*87 -0*59 Methylic alcohol ; 8*48 -102 *93 + 3*37 + 0 *397 Ethylic alcohol 5 *00 -102-06 + 4*24 + 0 *848 Propylic alcohol 5*00 -100 *60 + 5*70 + 1 T4 Isobutylic alcohol 1 *50 -103 *95 + 2*35 + 1 *57 Amy lie alcohol ( fusel oil ) 0*37 -105 *62 + 0*68 + 1 *84 Ally lie alcohol 5*44 -102*16 + 4*14 + 0 *762 Methylal 1 *22 -105 *26 + 1 *04 + 0 *853 Paraldehyde 0 *89 -105*13 + 1 *17 + 1*32 # These solutions contained only one molecular proportion of sugar ; the rest contained two .
It will be noticed that the alcohols of the ethylic series , as well as methylal and paraldehyde , appear to have promoted the formation of fructodextrose ; phenol , cane sugar , fructose itself and sodium and potassium chlorides , so far as alteration in rotatory power is concerned , appear to have the opposite effect .
The question to be considered is whether the apparently opposite effects produced by the two sets of substances are due to the occurrence of opposite changes in the solutions .
* Taking into account observations made in other cases , there is reason to suppose that , as pointed out above , the effect produced by the alcohols is the same as would be produced by heating\#151 ; that is to say , they exercise a dissociating and " dehydrating " effect ; the fact that the activity of the alcohol is greater the higher its molecular weight and the less soluble it is in water is in harmony with this conclusion .
But salts and even cane sugar should also produce a concentrating and dehydrating effect , as they withdraw water from the solution ; it might , 1913 .
] Studies of the Processes Operative in Solutions .
therefore , be expected that the proportion of fructodextrose would be increased , not diminished as it appears to be , in their presence .
The mere concentration of the solution will account only for part of the increase in negative rotatory power ; but in this connexion , the question arises whether the negative increase which attends concentration should be ascribed to an increase in the proportion of fructolaevose present rather than to the formation of an increased proportion of complex molecules of higher negative rotatory power ; in any case , it is scarcely probable that the rotatory powers observed are those produced entirely by substances present in the state of simple molecules .
It is reasonable to suppose that , in the case of the salts examined , the change in rotatory power is in part , it may be in large part , due to the formation of compounds of salt with sugar .
It is well known that such compounds exist and a large body of evidence in favour of the view that even cane sugar will combine with salts in solution was brought forward in Part X of these studies .
The magnitude of the effect produced by potassium chloride in the case of several sugars is as follows , the values given being those observed in solutions containing a single molecular proportion of salt , half a molecular proportion of sugar and 50 of water:\#151 ; Fructose . .
410 ' Lactose ... 0-17 ' Glucose ... 1-33 Melibiose ... 0-31 Cane sugar ... .
... 0-96 Raffinose ... .
0-04 It will be observed that the value is relatively high , not only in the case of fructose but also in that of cane sugar\#151 ; which itself contains a fructose residue , though not one derived from fructolaevose .
Taking into account the observations recorded in Part XY that / 3-methyl-glucoside is a more active compound than the isomeric a-eompound and that in presence of salts its rotatory power suffers the greater change , it is possible that fructokevose would be the more active and the more likely to combine with salts .
It therefore appears not improbable that the dehydrating tendency of the salt may be overcome by the tendency of the salt to combine with the fructose and that in consequence the salt may determine the formation of a larger proportion of fructolsevose .
Acids may be supposed to act similarly ; moreover , the peculiar behaviour of the acid-alcohol , phenol , lends support to such a view .
It was to be expected that this compound would behave like one of the less soluble alcohols of the ethylic series ; such is not the case , however .
It is only logical to extend the explanation here advanced to cane sugar ; it should be mentioned that the value arrived at in the case of this sugar is VOL. LXXXVIII.\#151 ; A. T 252 Studies of the Processes Operative in Solutions . .
based on the assumption that it retains its own specific rotatory power in presence of fructose .
If it be granted that the increase in the rotatory power of fructose on concentration is due to the formation of an increased number of polymerised molecules , it must be admitted to be possible that molecules of fructose can combine with the fructose section in cane sugar and that in this case also fructolaevose may be the more active substance .
It is hoped that it may be possible to throw further light on the problem and to test the explanation now offered provisionally by extending these observations and particularly by studying the behaviour of the methyl-fructosides in comparison with that of fructose .
[ It is obvious that if so delicate a difference as that which distinguishes the two isomeric forms of fructose can determine a difference in their behaviour towards salts\#151 ; and salts can therefore determine the formation of the one form rather than of the other , we are brought face to face with conditions of special interest on biological grounds .
It is to be supposed that the systematic study of such refined cases of chemical change will be of material service in enabling us gradually to interpret mysteries presented by vital phenomena .
The influence of potassium salts in particular on the formation of carbohydrates in plants and the special value of such salts in promoting animal metabolism are cases in point.\#151 ; H. E. A. ]
|
rspa_1913_0026 | 0950-1207 | Publication announcement | 253 | 253 | 1,913 | 88 | Proceedings of the Royal Society of London. Series A, Containing Papers of a Mathematical and Physical Character | null | publication-announcement | 6.0.4 | http://dx.doi.org/10.1098/rspa.1913.0026 | en | rspa | 1,910 | 1,900 | 1,900 | 1 | 15 | 217 | http://corpora.clarin-d.uni-saarland.de/surprisal/6.0.3/?id=rspa_1913_0026 | 10.1098/rspa.1913.0026 | null | null | null | Biography | 62.063184 | Biochemistry | 25.60774 | Biography | [
-19.074617385864258,
-21.399642944335938
] | 253 Factors Affecting the Measurement of Absorption Bands .
By H. Haktridge , M.A. , Fellow of King 's College , Cambridge .
( Communicated by Prof. J. N. Langley , F.R.S. Received November 1 , 1912 , \#151 ; Read January 16 , 1913 .
) [ This paper is published in Series B , vol. 86 ( No. B 585 ) .
] An Apparatus for Liquid Measurement by Drops , and Applications in Counting Bacteria and .
other Cells , and in Serology , etc. By E , Donald , B.Sc. ( N.Z. ) , D.P.H. ( Oxf .
) .
( Communicated by Dr. L. Hill , F.E.S. Received November 21 , 1912 , \#151 ; Read January 16 , 1913 .
) [ This paper is published in Series B , vol. 86 ( No. B 586 ) .
] The Liberation of Ions and the Oxygen Tension of Tissues during Activity .
( Preliminary Communication .
) By H. E. Eoaf , M.D , D.Sc .
( Communicated by Prof. C. S. Sherrington , F.R.S. Received January 10 , \#151 ; Read February 20 , 1913 .
) [ This paper is published in Series B , vol. 86 ( No. B 586 ) .
] VOL. LXXXVIII.\#151 ; A. u
|
rspa_1913_0027 | 0950-1207 | An investigation into the magnetic behavior of iron and some other metals under the oscillatory discharge from a condenser. | 254 | 280 | 1,913 | 88 | Proceedings of the Royal Society of London. Series A, Containing Papers of a Mathematical and Physical Character | E. W. Marchant, D. Sc., M. I. E. E.|Prof. S. P. Thompson, F. R. S. | article | 6.0.4 | http://dx.doi.org/10.1098/rspa.1913.0027 | en | rspa | 1,910 | 1,900 | 1,900 | 15 | 300 | 5,376 | http://corpora.clarin-d.uni-saarland.de/surprisal/6.0.3/?id=rspa_1913_0027 | 10.1098/rspa.1913.0027 | null | null | null | Electricity | 67.644964 | Tables | 24.983047 | Electricity | [
9.767762184143066,
-53.46400833129883
] | ]\gt ; ' Accad .
Lincei Atti , ' vol. 15 , pp. 63-74 .
' Nature , ' vol. 62 , p. 413 .
3 .
'Wied .
Ann vol. 26 , p. 427 .
S 'Soc .
Int. Elect. Bull 1911 , Ser. 3 , vol. 1 , pp. 49-57 .
'Ann . .
Physik , ' vol. 27 ( 1 ) , pp. 64-82 .
'Deutsch .
Phys. Gesell .
Verh vol. , pp. 185-204 ; 'Phi ] .
Mag. ' ) , vol. 3 , pp. 500-512 .
'Comptes Rendus , ' vol. 132 , pp. 917-920 .
'Ann . .
Physik , ' vol. 12 ( 4 ) , pp. SS 'Roy .
Soc. Proc vol. 70 , p. 398 .
'Comptes Rendus , ' June , 1894 .
lr 'Recent Researches in Electricity and Magnetism , ' p. 302 .
Phif .
Mag. ' 5 ) , vol. 38 , p. 426 .
'Wien .
Akad .
Sitz , p. 330 .
'Ann . .
Physik , ' vol. 12 ( 4 ) , pp. 869-874 .
SSS 'Comptes Rendus , ' June 11 , 1894 .
, etc. , under .
255 Method of Observation .
2 .
The method adopted in this investigation was to photograph the image .
of the spark produced by the condenser discharge reflected from a mirror ( see fig. 1 ) .
This method was similar to that originally adopted by : : : FIG. 1.\mdash ; Diagram to show arrangement of circuit .
Feddersen and Schiller , but in this case the surface of the mirror was flat and the light from the spark was focussed by a lens on to the photographic plate .
The mirror used in most of the experiments was formed with four silvered glass plates supported in a square aluminium frame , each milTor being 1 inch by 4 inches .
This could be run with safety up to 100 revolutions per second .
For higher speeds a small silver mirror was used with a reflecting face inch by 2 inches , which was run up to 230 .
revolutions per second .
The speed of the mirror was determined by a contact wheel driven by a worm cut in the shaft of the mirror , the contacts being arranged in one of the circuits of a double chronograph , the second circuit was connected to a clock giving seconds , and the speed could be measured to within* .
per cent. The spark gap was made with brass balls and its length was measured by a micrometer .
The circuit of the spark was closed through a contact-maker formed of a brush of fine wires attached to the frame of the mirror , which rubbed against a brass plate .
This contact-maker gave excellent results , chiefly because of the high speed at which the brush was revolved .
3 .
The condensers used consisted , in the first experiments , of a number of Leyden jars each having approximately microfarad capacity .
A second small condenser , sometimes used , consisted of nine plates of glass , 2 feet square , on which were pasted sheets of tinfoil 18 inches square , the glass being carefully shellacked and the whole well insulated .
The third condenser ( the one chiefly used ) consisted of 10 sets of 10 glass plates 3 feet square , coated with tinfoil 2 feet square , the glass being FIO .
2 .
Iron , etc. , under the Osciltatory Discharge .
257 different layers .
Each side of the square coil contained 90 turns , the diameter of each turn being approximately cm .
( see fig. 2 ) .
The object of using a square coil was to obtain , as far as possible , a closed magnetic circuit of the substances which were introduced , generally iron wire cores , as by this means calculation would be simplified .
With the assistance of Mr. Duddell , to whom the author is much indebted , $ very .
sensitive measuring apparatus was arranged , with the permission of 1 the late Prof. Ayrton , at the Central Technical College , for the measurement of this self-induction .
With this apparatus the value henrys was obtained correct to per cent. for the single-layer coil .
The resistance of this coil at C. was ohm .
Another square coil was used to obtain lower frequencies ; in this there were seven layers of wire on each side of the square , the whole containing 2670 turris of wire .
The self-induction of this coil was also carefully measured with a secohmmeter , found to be millihenrys .
The resistance of coil at C. was ohms .
A coil , used chietly preliminary experiments , consisted of a single bobbin of the same wire wound in seven layers ; this contained 750 turns of wire , and had a self-induction of app 1 millihenry .
Its self-induction was not measured by the secohmmeter , but was obtained by comparison with the square seven-layer coil by means of the air condenser .
The results of these experiments are iven later .
Measurement of the Pfates .
: 5 .
In order to obtain accurate measurement of the spark photographs , alarge mea microme'ter with a low-power microscope , with a oross wire in the eye-piece .
In most cases it was found possible to obtain measure- ments of not very quickly damped sparks accurately to within 2 per cent. , but with sparks whose period varied the acCuracy was very much lower , as black spots were often spread out and asymmetrical .
Theory of nents .
6 .
From the fundamental equations for the ischarge of a oondenser of farads capacity through a coil of self-induction henrys , and with a total resistance of ohms in the circuit , the-frequency of is given by .
The current at any instant pt amperes , where frequency and damping of the oscillations ; while even with fine iron wire cores the number of vibrations in many cases is reduced from 10 or 15 to 3 or 4 .
According to the investigation given above the damping factor is ; and accordingly , as increases , remaining constant ( the change caned by introducing the iron wire is minished , and hence the damping should be less rapid with the larger self-induction .
It is clear , therefore , that Phil. Mag January , 1903 , .
lffi .
'Recent Researches in Magnetism and Electricity , ' p. $04 .
Iron , etc. , umder the Oscillatory the cause of the very rapid damping must be the absorption of by the cores introduced , either by hysteresis or by eddy currents , or both .
Using the same notation as above , in .
which the magnetic force is represented by the real part of , the magnetic induction being assumed uniform along the axis of the wire , the rate of heat production per unit length of wire due to eddy currents is equal to the mean value of\mdash ; Sa real part of ) pt , where magnetic permeability , frequency , specific resistance of iron , radius of iron wire .
When is small the heat produced per unit length of core per second , being the number of wires and the maximum magnetising force .
The experiments of Sir J. J. Thomson .
( loc. cit. ) appeared to show that the hysteresis of iron accounted for a considerable part of the absorption of energy .
In these experiments it will be shown that hysteresis loss is almost negligible as compared with eddy-current loss .
Results of Experiments .
Part I. 9 .
The first series of was made in order to find how nearly the frequency determined by experiment agreed with that calculated from the observed self-induction and capacities used in the tests .
The tests made with the air condenser may first be considered .
The capacity of the air condenser was obtained both by calculation and by comparison with the standard 12-microfarad condenser .
The capacity found in this way microfarads .
On account of the bending of the plates , lt was found impossible to obtain a spark more than mm. long , and some difficulty was found in photographing this , as well as in maintaining the discharge by the large Wimshurst machine .
A series of determinations was first made of the self-induction of the circuit apart from the coil .
Using the small coil , the time for a complete 'Recent Researches in Electricity and Magnetism , ' J. J. Thomson , p. $20 .
These results are not given at great length as the paper by Battelli and Magri ( ' Phil. Mag June , 1903 , p. 620 ) covers the subject quite fully .
0.654 8.18 I-VII-V 0 s.5584 0.96 4.2 4.46 1.22 4.68 1.35 In all these experiments the spark was mm. and the values of are accurate to within 2 per cent. 11 .
In order to see whether the resistance .
of the circuit can have any effect on the frequenoy of the oscitlations ; the ce or the Iron , etc. , under the Oscillatory wire has been calculated from the expressions originally given by Lord Rayleigh .
For the highest frequencies used\mdash ; ( resistance to steady current ) .
Since ohm , ohm .
For this frequency , and The effect of the resistance of the circuit in this case is therefore negligible .
For the lower frequencies , when using the single-layer square coil , the total resistance neglecting the spark may be taken ohm , and so that in this case also the correction is less than 1 per cent. When the coil is used with an iron core , the value of is increased , and the co1Tection will therefore be smaller still .
It will be shown later that when the maximum current during an oscillation of the spark falls to less than 200 amperes , the resistance of the spark increases to about 2 ohms , and may be expected to become larger still as the current through the spark diminishes still further .
Under certain conditions , therefore , the spark resistance will have to be taken into account .
Part II .
12 .
The results of the experiments made to determine the effect of currents at high frequencies on iron may now be considered .
With freuencies .
from 100,000 to 5000 per second , the effect of an iron or nickel wire core is to produce a spark discharge which has no constant frequency , but in which the period for a half-oscillation rapidly increases as the discharge becomes damped by energy absorption .
* Having observed the effect , the explanation is obvious .
It is clear that at these frequencies iron retains very much the same properties as it does under a steady magnetic field , i.e. the permeability of the iron increases as the flux density in the iron diminishes .
13 .
Experiments have been made with a variety of soft iron wire cores , and it will be convenient first to consider the effects produced with discharges from the set of ten large condensers through the single-layer coil , when the latter is arranged with an iron wire core .
* This phenomenon has now been Battelli and Magri To obtain the " " effective permeability\ldquo ; of the iron the lines of force may be assumed to be uniform density ; on the introduction of an iron *The reason for this is clear from the curves drawn graphically in fig. 5 .
Phil. Mug Jsnmry , Iron , etc. , urbder the Oscillatory Dischvxrge .
263 oore a certain number of lines go through the iron .
We may put , there fore , , where is the area of one turn of the coil ( calculated from the mean value of the self-induction ) and is a constant .
When a core is introduced , where is the of the iron core , and is a quantity which may be designated the 1 " " effective\ldquo ; permeability .
Hence The quantity may be defined as the permeability of the iron which * would give the same period of oscillation for the spark as is obtained 4 experimentaly , the " " effective permeability\ldquo ; being constant and independent .
of the value of the magnetising force .
With the single-layer square coil sq .
cm .
sq .
cm .
( 1 ) Area of section of the No. 28 S.W.G. iron wire core ( 2 ) ( 3 ) ( 4 ) , , , 28 , , nickel , , 14 .
In the table are shown the results obtained when the discharge from No. 1 set of the large condenser flows through the singlelayer square eoil into which a core [ ( 1 ) above ] made up of 660 No. 28 S.W.G. iron wires has been inserted , the spark gap is mm. , corresponding to a P.D. before discharge of 9400 volts .
Large condenser , No. I set .
sec. , , volts sec. T. Lx 18.4 164.0 .
In the first place , the value of the maximum current during the first half-oscillation was estimated , and was found to be 210 amperes .
The corresponding value of the magnetising force due to this current C.G.S. units approximately .
The value of corresponding to this , obtained from Ewing 's results for Low Moor cvht iron , giving a value of approximately , a result which is of the same order of magnitude as the effective permeability calculated above .
M. Klemencio* and others that the hysteresis loss is greater at high ' Wien .
Akad .
Sitzberg , ' 1898 , vol. 107 , pp. 330-360 .
M. Klemencic seems to have determined the hysteresis loss by a of the decrement of in a Leyden jar discharge .
No allusion is made to which to be ced for eddy current losses .
also Warburg and Honig , -Wied .
, p. ; ' Phil. Mag Sspt9 1889 ; Battelh and Magri , [ Aecad .
} Atti , ' vol. 15 , pp. 485-492 ; Corbino , 'Accad .
Lincei Atti , ' vol. 16 , pp. ; 'Atti dell ' ASSOG Elett vol. 7 , p. 606 ; F. Piola , ' Elett .
Romi , ' vol. 6 , pp. 4-6 .
Iron , etc. , under the Oscilla tory frequencies than low .
Now , the total volume of the iron in the cores .
approx. Hence the total loss of energy due to hysteresis for the half-oscillation .
This loss is quite small as compared with the eddy-current losses .
The loss due to eddy currents during the first half-oscillation calculated from the formulae given above ergs .
Adding to this the hysteresis loss as calculated above , the total iron loss The ohmic loss due to the resistance of the coil is compalatively small .
In this case , assuming the root mean square value of the current to be of the maximum value , it amounts to ergs .
for the first half-oscillation .
The total energy stored ergs .
The value given above shows that the eddy-current and hysteresis losses amount to more than one-third of the total energy of the discharge during the first half-oscillation , whereas the loss due to ohmic resistance is only of the total energy .
The damping of the oscillations with iron cores might be expected to be much more rapid than when the cores are not present , and this is precisely what is observed .
The total number of half-oscillations on the plate with the iron cores is three , whereas without them ten half-oscillations , and even more , have been photographed .
This result nfirms the observation that the permeability of the iron is not very different at this frequency from that observed under similar conditions with a steady magnetising force , for , if the magnetic induction were very different from the value that has been assumed , the total calculated eddy-current loss would not have agreed so nearly with experiment .
19 .
The other results obtained with the set of large condensers may now be dealt with .
Ihese will correspond with lower frequencies than those considered in the preceding paragraphs .
The results are tabulated according to the method described in S13 .
Large condensers , Nos. , volts . .
llaximum ourrent during first oscillation amperes .
Naximum magnetising force , , , , C.G.S. units .
Estimated maximum magnetising force first oscillation - C.G.S. units .
Considering , in the first instance , the first half-oscillation of the spark after the discharge begins , it will be noticed that when iron cores are intro duced the change in frequency produced by using different capacities is comparatively slight , varying from 28 , per second with microfarad to 18,800\mdash ; per second with microfarad .
It will also be noticed that the decrease of effective permeability with increase of capacity is not quite uniform , but this is amply accounted for by possible errors in observation . !
: Iron , etc. , under the .
267 curve has been plotted between the values of the effective permeability maximum magnetising force , and is shown in fig. 4 .
20 .
Considering next the half-oscillations of the spark other than the first it will be seen that the same law holds .
Increase in capacity diminishes the apparent effective permeability .
Thus the second half-oscillations with microfarad corresponds with a greater value of the effeotive permeability .
It is noticeable from these figures that the damping of the discharge is of sine wave shape .
6 Fromtheresultsobtainedwiththelargestcondenseranattempthasbeenpercent.fromthatobtainedbyassumingbhecalculated\ldquo ; current t made to determine the magnitude of the resistance of the spark itself .
From the values calculated from the\ldquo ; effective\ldquo ; permeability the corresponding value of\ldquo ; \ldquo ; for each half-oscillation of the spark can be found , and hence the maximum value of the current , assuming a sine wave shape for the curve as a first approximation .
From this value for the current , the maximum voltage at the condenser at the beginning of each half-oscillation has been determined , and hence the loss of energy during each half-oscillation * The values of spark reeistance referred to later have been taken account of in drAwing this perceptible difference in the frequency of the oscillation .
* Large condenser , \mdash ; Capacity N.B.\mdash ; If the value of the spark tance for the 4th half-oscillation be assumed equal to 2 ohms , the total energy loss during the 4th half-oscillation becomes ergs .
Similar calculations have been made on other typical discharges , in particular , with the discharge of a condenser of 1 microfarad at an initial potentia ] difference of 7800 volts ; the average resistance for the spark- which it is necessary to assume to bring the energy losses into greement is 048 ohnl at 770 amperes , ohm at 440 amperes , and ohms at 230 amperes .
The accuracy of these figures is not great , and they are of value as showing the order of magnitude of the quantity involved , and in this respect they confirm the results which have been ooiven above .
21 .
Experiments were made in order to determine how the spark and , consequently , the potential difference at the spark gap just before the discharges , affected the observed effect .
It is clear that a shorter spark will give a smaller maximum current during the first half-oscillation , and hence , to the above results , the apparent self-induction of the coil should be increased .
Below given the results obtained with spark gaps 2 mm. and .
in length .
This result is in accordance with that obtained by Battelli and Magri , 'Phil .
Mag June , 1903 , vol. 5 , pp. 620-643 .
VOL. X lron , etc. , under the Discharge . .
Large condenser , No. sec. , volts T. Lx 0.048 6.5 5463 4443 0 .
lIaximum ourrent during first half-oscillation amperes .
Maximum magnetising force , , , , C.G.S. units .
Large condenser , .
Nos. sec. , volts sec. T. 6 .
54.1 45.0 Maximum current duriug half-ost illation amperes .
Maximum magnetising folce , , , , C.G.S. units .
aec .
Large condensers , Nos. sec. , volts T. Lx 0 10$x6..8x 0.158 Maximum magnetising fMaximum current during , , ation Large condenser , Nos. sec. , volts k- sec. T. Lx 7 .
' 16.4 0.12 0.139 8 .
21.0 16.6 ' Maximnm current during first hation resMaximum magnetising force , units .
Large condenser , Nos. VIII .
sec. , volts sec. T. Lx 0.06 12.6 8.5 0.150 0.17 9 .
16.0 0.20 0.24 ' 51.0 41.0 0.36 20 .
86.0 0.48 ?
225.0 193.0 Maximum current during first hation esMaximum magnetising force , nits .
Large condeIlser , Nos. sec. , volts sec. T. 0.14 8 .
11.7 0.18 16.6 0 .
42.0 34.0 52.0 Maximum current during first oscillation 570 amperes .
Maximum magnetising force .
, , , C.G.8 .
units .
Large condenser , Nos. sec. , volts sec. . .
0 .
0.0 8.6 4.4 18.2 11.4 0.24 ll Maximum magnetising force , unitsMaximum current during first , tion 24 .
These results appear , at first sight , somewhat remarkable , as it will be seen , on comparing them with the results obtained with a core composed of much finer wire , No. 28 S.W.G. , that there is very little difference in the value of in the tables .
On comparing the areas of the surface of the wires per centimetre length of the core , it is seen that , whereas for the No. 28 core the surface is sq .
cm .
, the surface for the No. 18 core is sq .
cm .
; Iron , etc. , under the Discharge .
snd since it is the surface of iron in the core which would appear to be most important , it might be expected that the change in frequency produced by the core would be much less noticeable .
The explanation , however , is obvious .
With the larger diameter wire core the loss due to eddy currents is greatly increased .
According to the approximate formula given above ( S8 ) it depends on the fourth power of the diameter , hence the loss of energy during the first half-oscillation would be more than ten times as great for a core having the same amount of iron in it , and made of the No. 18 wire , as it would be for one of No. 28 S.W.G. wire .
The actual magnetising current rapidly falls off , therefore , on account of this loss in energy .
There is another tending to diminish the magnetising force inside the iron , what is called the self-demagnetising force due to the magnetisation on the surface of the wire , at the place where the netic lines leak .
This netising force is increased with increase in diameter of the wire .
The diminution in the magnetising force owing to these causes will correspond with a greater permeability in the iron , which ( although the increase in permeability of the iron diminishes the depth to which the magnetisation penetrates ) is sufficient to counterbalance the much greater surface of iron exposed , with ] the finer core .
As in this case the permeability must clearly be higher than in the previous cases , we may assume taking into account the ratio of the surfaces ) , as a first approximation , [ As the results obtained with the large condenser , No. I , seem to be in very fair accordance with those given for the other sparks , the result for the first half-oscillation has been used as a basis of calculation .
] Proceeding exactly as in S16 , Hence cm .
The total induction through the core since the area of the iron sq .
cm .
This gives a value for the effective permeability , instead of as found by experiment .
It is of interest to observe the comparatively great lag in the maximum magnetic induction behind the maximum magnetising force .
With these The radius of the finer No. 28 is } cm .
, and of the No. 18 wire is cm .
The energy loss for the same mass of iron will be proportional to the squares of the diameters of the wires .
larger and smaller diameter .
The results have been arranged below the same way as the previous ones .
The notation of S13 has been adopted .
Large condenser , No. ' sec. , volts seo .
' .
3 .
0.11 0.12 Maximum magnetising force , lfaximumcurrent during ftion Large condenser , Nos. sec. , volts sec. T. 0.110 4 .
14.6 4 .
15.4 Maximum mgnetising force , ximum current during first hlation Large condenser , Nos , sec. , volts sec. T. 0.143 5 .
12.0 21.6 16.4 24.1 19.0 Maximum current during first half-oscillation amperes .
Maximum magnetising for , , , , C.G.S. units .
Large condenser , Nos. sec. , volts sec. Lx 12.8 0.20 0.216 8 .
20.0 16.4 0.228 8 .
22.4 18.0 0.34 21.0 Maxi netiMaximum oduring first half-oscillation The value of , the area of iron in this core , is equal to sq .
cm .
TIME IN OF A SECOND FIG. 5.\mdash ; Curves showing increase in permeability during successive oscillations of discharge ( from condenser ) of iron wire ( No. 28 B.W.G. ) core placed in coil through which discharge passes .
Numbers opposite are maximum magnetising forces during first half-oscillation .
Part III .
lVickpl Wire Cores .
29 .
Besides the experiments made on iron as described in Part II , a series !
of through coils having cores of nickel wire was photographed , the results from which are tabulated below .
It will be seen that the phenomena are similar to those obtained with iron cores , though the effects : : are less marked with the nickel wires .
The core consisted of 500 No. 28 wires , sq .
cm .
Maximum magnetising force , nits .
Large condenser , Nos. sec. , volts * Maximum current during first half-oscillation amperes .
Maximum magnetising force , , , , C.G.S. units .
Large condenser , Nos. , volts sec. 1 . . .
0 .
4 .
1.7 ' ll Maximum current dul:ing first half-oscillation S80 amperes .
Maximum magnotising force , , , , ) C.G.S. units .
30 .
We may proceed in exactly the same way as in the case of the No. 28 iron wire cores to determine more exactly the actual permeability necessary to produce the observed results , making allowances for the " " skin effect First , calc.ulating the value of may be assumed as a first approximation , C.G.S. units , whence cm .
Hence the magnetic induction through a single wire oos , where , giving an effective permeability which does not differ appreciably from 7 .
The lag in maximum netic induction behind maximum magnetising force is 1leglecting ysteresis .
mental error .
: When a similar core of iron wires was inserted , all the characteristic effects both of change of frequency and of damping were observed .
When a core of solid brass was introduced , the time for a complete oscillation seconds , thus showing an increase in frequency as found by Hemsalech .
With solid soft iron core the number of half-oscillations visible on the plate is reduced to two , thus showing the very great eddy-current loss ; while * Results published by Hemsalech confirm some of these observations .
'Journ .
Phys 1908 , pp. 76-90 ; 'Comptes Rendus , ' vol. 140 , pp. 1322-1326 .
'Comptes Rendus , ' vol. 140 , pp. 1322-1325 .
indicate a slight decrease in frequency , due to the permeability of the iron .
With the solid iron core , the permeability , therefore , is sufficiently great to overcome the effect of eddy currents , and tends to.increase the selfinduction , and to produce a slight decrease in the frequency .
32 .
It may be of interest here to notice some experiments in which a coil similar to the above was wound on a brass tube , about 1/ 32 inch thick .
In this case the brass seemed to screen off the action of the iron entirely , and no difference whatever could be observed when the iron cores were introduced , either in damping or in change of frequency , this result is also in agreement with that obtained by Hemsalech using a tube of zinc ( loc. cit Genered .
1 .
With an air condenser , the capacity of which was measured ballistically , and an air-core self-induction coil of known value , the frequency of the oscmations of the condenser discharge agrees ( within limits of experimental error ) with the values calculated by Kelvin 's formula .
2 .
The resistance of a spark between spheres of 1 inch diameter , mm. apart , has been estimated ; the resistance of such a spark when the maximum current is greater than 200 amperes does not exceed 2 ohms .
If the maximum current through the spark is greater than 500 amperes , the resistance does not exceed ohm .
Effecf , Produced by an lron Wire Core in the Self-induction .
3 .
When an iron wire is inserted in the self-induction coil , the time for each consecutive half-oscillation increases with the duration of the discharge .
4 .
With a series of discharges from a given condenser in which the maximum value of the magnetising current varies , the time for the first oscillation decreases with in the strength of the current .
5 .
The increase in the time of a half-oscillation with the duration of the discharge is due to the increase in the permeability of the iron , as the current , and consequently the magnetisin force , dies away .
6 .
The permeability of the iron wires calculated from the observed increase in the self-induction of the coil , decreases with increase of the magnetising force .
The curve connecting the ' effective\ldquo ; permeability , , the netising force , agrees , within limits of experimental error , with that obtained on the assumption that the permeability of the iron is the same as it is under a steady magnetising force .
oduced by of other Jfaterials . .
: 10 .
Nickel wire cores produce similar effects to those observed with iron , but of diminished intensity , the permeability of the nickel wire with rapidly oscillating magnetic force similar to that found with steady magnetising forces .
11 .
With cores made up of insulated copper wires , no , either in damping or self-induction , are apparent .
In conclusion , the author 's best thanks are due to the late Lord Blythswood for the loan of the apparatus described above , and to the late Lord Kelvin for the kind encouragement given by him during the early stages of the research , to Mr. Duddell for the measurements of the self-induction of the various coils used , and for his criticisms , and to Dr. Silvanus Ihompson for his criticisms and suggestions .
|
rspa_1913_0028 | 0950-1207 | Load-extension diagrams taken with the optical load-extension indicator. | 281 | 288 | 1,913 | 88 | Proceedings of the Royal Society of London. Series A, Containing Papers of a Mathematical and Physical Character | W. E. Dalby|Prof. H. E. Armstrong, F. R. S. | article | 6.0.4 | http://dx.doi.org/10.1098/rspa.1913.0028 | en | rspa | 1,910 | 1,900 | 1,900 | 4 | 164 | 3,916 | http://corpora.clarin-d.uni-saarland.de/surprisal/6.0.3/?id=rspa_1913_0028 | 10.1098/rspa.1913.0028 | null | null | null | Measurement | 73.7761 | Tables | 17.119403 | Measurement | [
45.873390197753906,
-60.00703048706055
] | 281 Load-Extension Diagrams taken with the Optical Load-Extension Indicator .
By W. E. Dalby , City and Guilds Engineering College .
( Communicated by Prof. H. E. Armstrong , F.R.S. Received January 24 , \#151 ; Read February 13 , 1913 .
) [ Plates 2 and 3 .
] This paper may be regarded as a continuation of that communicated in January , 1912 , * wherein I described a new optical apparatus by means of which it is possible to obtain load-extension diagrams free from the inertia effects of the parts of the testing machine in which the materials are strained and broken .
The apparatus is automatic in its action and gives a true record of the physical properties of the materials .
The curve corresponding to the straining and breaking of a specimen is drawn by means of a spot of light moving over a photographic plate placed in the camera which forms part of the instrument .
There is no practical limit to the speed at which a diagram can be taken other than that imposed by the " rapidity " of the plate .
When fracture of a specimen takes place , the spot moves across the plate so rapidly that no impression is made , and hence the actual load carried by the specimen at the instant of fracture is determined without ambiguity , because the spot of light ceases to record at the instant of fracture .
Even if a plate were used so rapid that the quick movement of the spot across the plate after fracture of the specimen were brought out , the discontinuity in the curve and the difference in intensity would fix the point accurately .
This property of the instrument , namely , its power of recording the true load-extension curve at any speed of loading , opens up a new field of research in the subject of the strength of materials , as is indicated below by the results obtained by the almost instantaneous straining of a piece of mild steel beyond its elastic limit .
The diagrams given in my previous paper related to mild steel , iron , and copper .
The present paper relates to the physical properties of gun-metal , brass , and phosphor-bronze , as disclosed by their respective load-extension diagrams and the corresponding micro-photographs of their molecular structure ; to further experiments on mild steel , with the instrument arranged somewhat differently in order to magnify the extension so much that the photographic record exhibits the elastic part of the diagram ; and * ' Roy .
Soc. Proc. , ' A , vol. 86 , p. 414 .
282 Prof. W. E. Dalby .
[ Jan. 24 , also to diagrams obtained by the application of load so quickly that the straining of the material up to the elastic limit may almost be regarded as done by an impulsive load .
Group 1.\#151 ; Copper-Tin and Copper-Zinc Alloys .
A piece of phosphor-bronze which was turned to a diameter of 0*54 inch was broken in the testing machine by a load applied so that the rate of straining was approximately constant .
The composition of the specimen was:\#151 ; Copper , 89*7 per cent. ; tin , 8*85 per cent. ; lead , 1*21 per cent. ; phosphorus , a trace .
The load-extension diagram is shown in fig. 1 , together with the microphotograph showing the structure of the material .
The magnification is 1500 diameters .
( See Plate 2 .
) The form of this diagram is in marked contrast to the form obtained from mild steel .
There is no period of molecular instability between the breaking-down point and the plastic yielding , as in the case of mild steel .
The curve is smooth and continuous from the commencement of the loading to the point of fracture .
There is a quasi-elastic stretching of the material up to a load of about 7 tons , followed by a plastic yielding with a continually falling load .
Reckoned on the original area of the bar , the load at fracture corresponds to a stress of 22*9 tons per square inch .
The reduction of area at the point of fracture was , however , 69 per cent , of the original area of the bar , so that the actual load carried by the bar at the instant of fracture was 74 tons per square inch .
The extension of the bar measured on a gauge length of 5 inches was 9*4 per cent. The peculiar scythe-shaped diagram of this material is different in almost every respect from the characteristic diagrams obtained from iron and steel .
Gun-Metal.\#151 ; A load-extension diagram from a specimen of gun-metal is shown in fig. 3 and the corresponding microphotograph in fig. 4 ; magnification , 750 diameters ; diameter of specimen , 0*6 inch ; distance between the gauge points , 5 inches .
The composition of the metal was:\#151 ; Copper , 85#4 per cent. ; tin , 12*4 per cent. ; lead , 2*41 per cent. There is a general resemblance in form between the curves in figs. 3 and 1 , but the gun-metal has a considerably increased plastic limb .
The quasielastic line in each diagram is very much the same in character , but the difference between the maximum load and the breaking load is not so great in the gun-metal as in the phosphor-bronze specimen .
The stress on the gun-metal specimen at the instant of fracture , reckoned on the original area of the bar , was 21*2 tons per square inch , but reckoned 1913 .
] Optical Load-Extension Indicator Diagrams .
283 on the actual area corresponding to a reduction of area of 55 per cent. , it was 45*8 tons per square inch , considerably lower than in the case of phosphor-bronze .
On the other hand the extension on 5 inches was 14 per cent. , considerably greater than in the extension of phosphor-bronze .
It is noteworthy that a not very great difference in chemical composition of the two materials results in a considerable difference in the physical properties .
Brass.\#151 ; The load-extension diagram of a piece of brass rod is shown in fig. 5 , and the corresponding microphotograph in fig. 6 .
Fig. 7 shows the load-extension diagram of a second specimen cut from the same brass rod , and fig. 8 shows the corresponding microphotograph .
The magnification in both figs. 6 and 8 is the same , namely , 190 diameters .
The first specimen ( fig. 5 ) was tested just as it was cut from the rod .
The second specimen ( fig. 7 ) was annealed in a muffle furnace before testing .
The specimen was heated to a dull red , and then allowed to cool in the furnace , the cooling lasting about four hours .
( See Plate 3 .
) Comparing the two load-extension diagrams together and also the two corresponding microphotographs together , it will be seen that the process of annealing has exerted a marked influence on the physical properties and on the molecular structure of the material .
In fact , the annealing process has destroyed entirely the quasi-elastic part of the load-extension diagram .
Whereas the unannealed bar carried a load of nearly 7 tons before passing into the plastic state , the annealed bar begins to approach that state before a load of 2 tons is reached .
Further , if the diagram for the annealed bar is compared with the load-extension curve of the copper bar given in my previous paper it will be seen that there is a striking resemblance in form .
The resemblance is so close that at a first glance the load-extension diagram of the annealed brass bar would be mistaken for a diagram from a copper bar .
The composition of the bar is as follows :\#151 ; Copper , 58'6 per cent. ; zinc , 40*8 per cent. ; lead , 0*6 per cent. There is a marked contrast also in the crystalline structure .
In the unannealed state ( fig. 6 ) the metal appears to be constructed of two kinds of material , roughly equal in size and uniformly distributed ; the lighter areas represent one kind of crystal , and the darker areas another kind .
After annealing ( fig. 8 ) , it will be observed , the dark areas have grown and the lighter areas have almost disappeared .
The magnification is the same in each figure , hence it is clear that the substance represented by the darker area has grown into aggregates of relatively large size .
These large aggregates seem to indicate that the long period of annealing has probably resulted in the formation of a true eutectic alloy .
284 Prof. W. E. Dalby .
[ Jan. 24 , Another peculiar characteristic of brass will be seen on the diagrams for both the annealed and the unannealed specimen , namely , the peculiar discontinuities in the curve as the specimen draws out .
These discontinuities appear earlier on the diagram of the unannealed specimen than on that of the annealed specimen .
The bar itself gives evidence that the internal stress has been somewhat differently distributed than in the case of the other metals tested , because after it has been drawn out to a length approaching the breaking-point the bar is no longer round but veined .
To the hand it feels as though the original smooth , circular , and apparently homogeneous bar has been drawn out into a bundle of thick strings .
The effect of annealing is also shown by comparing the ultimate stress and elongation of the specimens , though the annealed specimen extended so much that the end of the curve did not appear on the plate ; consequently the actual load at fracture could not be measured .
Unannealed .
Annealed .
Percentage elongation on 5 inches 20 -0 42 *4 Percentage reduction of area 18 *8 46 *0 Maximum load per square inch carried by the bar , reckoned on the original area 29 *2 25 '7 tons .
Load per square inch carried by the bar , reckoned on the actual area at fracture 42 *8 A common characteristic of all the alloys tested was the absence of a true elastic modulus .
The load line begins to bend away very soon after extension begins .
Mild Steel Specimen Broken with Suddenly Applied Load .
One of the most interesting diagrams I have ever taken with the apparatus is that shown in fig. 9 .
A mild steel specimen was put with the apparatus into the shackles of a 30-ton testing machine .
The straining cylinder of the machine was connected directly to the hydraulic main of the works .
The accumulators were pumped to the top of their strokes , and the pumps were then stopped .
The regulating valve on the testing machine admitting water to the straining cylinder was then opened wide , as quickly as it was possible to turn it , with the result that the whole break occupied only 10 seconds .
Notwithstanding this extremely rapid break , the whole of the load-extension diagram was obtained with the apparatus , with the exception of just the end , which came off the plate .
Everything worked perfectly , and after the fracture the spot of light came back to its initial position .
Although the whole period of the break was small , namely 10 seconds , 1913 .
] Optical Load-Extension Indicator Diagrams .
285 the time occupied by the purely elastic extension was a very small fraction of the whole time .
This is indicated by the relative intensity of the line in the elastic and in the plastic part of the diagram in the actual photograph .
The time occupied by the elastic extension was certainly less than 1/ 10 second .
Fig. 10 is placed beside fig. 9 for the purpose of comparison .
The curve is the load-extension diagram of a second specimen cut from the same bar as that from which the specimen broken in 10 seconds was cut , the load-extension diagram of which is shown in fig. 9 .
The time occupied in breaking this second bar was 2\ minutes .
The effect of the rapidity of the straining on the apparent properties of the material can be estimated by a comparison of the two figures .
Each bar was 0*55 inch diameter , and in each case the gauge points were 5 inches apart .
The scale of extension is practically the same in each case , namely , 3f to 1 , whilst the load scale is just the same , and is practically 1 ton = 9 mm. on the original diagrams .
The following results are found by measurement from the diagrams and the bars .
10-second break ( fig- 9)- 150-second break ( fig. 10 ) .
Original diameter Original area Fractured area Reduction of area Gauge length Extension Elongation Maximum load reckoned on the original area of the bar Load at yield point 0 '55 in .
0 '238 sq .
in .
0 '071 " 70 per cent. 5 in .
1 '45 in .
29 per cent. 26 '5 tons per sq .
in .
25 '2 " " 0 '55 in .
0 '238 sq .
in .
0*081 " 65 per cent. 5 in .
1 '22 in .
24 '4 per cent. 25 '2 tons per sq .
in .
24 *0 " " Comparing these results , it will be seen that the rapidity of breaking has little effect on either the yield-point or the maximum loads , but has a more marked effect on the plastic properties of the material .
With quick loading the extension of the material on 5 inches increases from 24 to 29 per cent. , and the reduction of area is increased from 65 to 70 per cent. A third specimen cut from the same bar was broken in 9 seconds , and the curve obtained was essentially the same as that shown in fig. 9 .
Load-Extension Diagrams of the Elastic Part of the Curve .
A specially designed extensometer and a modified arrangement of the instrument were used to obtain a diagram of just the elastic part of the VOL. LXXXVIII.\#151 ; A. Y Prof. W. E. Dalby .
[ Jan. 24 , curve .
Fig. 11 shows a diagram taken from a piece of mild steel in which the extension is so magnified by the instrument that only 0*01 inch extension appears on the diagram .
The scale of extension is such that 2T inches on the diagram represents an actual extension of 0*01 inch of the specimen .
By measurement of this diagram it was found that the bar extended 0*0804 inch on 5 inches for a change of load of 6 tons , the area of the bar being 0*282 square inch .
From these data E = 13,240 .
A similar diagram is shown in fig. 12 for a piece of electrolytic copper .
From this it appears that copper has no true modulus of elasticity , since it begins to curve away directly the load is applied .
It would almost appear that for materials of this kind another definition of the modulus of elasticity should be used , if the term is used at all .
For example , it might be defined as the ratio between unit stress and unit strain measured from a tangent at the origin of the diagram .
The difficulty of taking diagrams with this great magnification of the extension is chiefly that , with the ordinary testing appliances , it is difficult to get a true axial pull on the specimen .
For this kind of work it is necessary to use the device of crossed knife-edges instead of the ordinary spherical joints usually found in testing machines .
The diagrams shown in this and the preceding paper sufficiently illustrate the use of the apparatus as an instrument of research in determining the strength of materials , and indicate that many lines of investigation may be followed in connection with the determination of the physical properties of materials .
Summarising the points of advance made :\#151 ; ( 1 ) The diagrams are obtained free from inertia of the heavy mass of the beam of the testing machine and the jockey weight usually used as part of an autographic recording apparatus .
( 2 ) Pencil friction is entirely eliminated , since the diagram is obtained by the movement of a spot of light over a photograph plate , the movement of the spot being determined by small angular displacements of small light mirrors .
( 3 ) The load on the specimen is measured by a weigh-bar placed in series with it .
A variation of 1 ton on the specimen causes an elongation of about 0*001 inch on the weigh-bar .
This movement is multiplied by the mirror and beam of light to a movement of about 1 cm .
on the photographic plate .
( 4 ) An extensometer is placed on the bar to measure its extension , and up to the elastic limit the specimen extends a distance of the order 0*01 inch on a 5-inch length .
This movement is multiplied by a mirror and beam of light to about 4 cm .
on the photographic plate .
( 5 ) The accuracy of the multiplication and the sensitiveness of the mirror 1913 .
] Optical Load-Extension Indicator Diagrams .
gear and extensometer are shown by the results obtained in fig. 11 .
Fig. 11 may be regarded as a refined test of the instrument , since the slightest deviation from true proportionality in the multiplying mechanism of the instrument would be apparent on the elastic curve of a piece of mild steel .
As shown on the diagram , the line is straight and has a slope which gives an elastic modulus known to be correct from independent measurements .
The accuracy of the instrument being established by this test , the accuracy of the curve in fig. 12 for copper , which was obtained by the instrument , is also established .
( 6 ) The accuracy with which the instrument will follow the quick variations of stress in the specimen , that is to say , the freedom of the apparatus from lag due to inertia of the parts , is indicated by the diagram fig. 9 , which shows how every detail of the variation of load and corresponding extension is brought out , even when the loading is so rapid that it is almost impulsive .
The elastic part of the curve in this figure was described in certainly less than 0*1 second .
From other evidence I know that the instrument will follow quicker variations than this , the first limit to the speed being the speed of the plate .
( 7 ) The elastic line is drawn by the instrument continuously without a stop .
An elastic line plotted from observations in the usual way is drawn through points which correspond to periods of dead loading .
The loading is , in fact , intermittent , a stop being necessary at each load added to measure with an extensometer the elongation produced by the load .
( 8 ) In the diagrams of the whole curve up to the break , as in fig. 10 , the load on the bar at the instant of fracture is recorded .
Comparison of the Physical Characteristics of the Materials Tested .
When compared together the diagrams of gun-metal , brass , phosphor-bronze , copper , steel , and iron show two distinct parts : the elastic or quasielastic part , and the plastic part .
There is , hovrever , a sharp distinction between the alloys of copper , tin , and zinc and irons and steels .
The distinction lies in the manner in which the material passes from the elastic into the plastic state .
In the case of pure copper and its alloys , it is impossible to say where the elastic state ends and the plastic state begins .
The elastic diagrams of the alloys of copper , tin , and zinc all show a quasielastic line ( a line which in fact may almost be mistaken for an elastic line in those diagrams which show the whole of the break ) with a perfectly smooth join on to the plastic part .
With the iron and steels , the elastic part of the diagram ends not quite suddenly but with a quick change into a curve where there appears to be y 2 Optical Load-Extension Indicator Diagrams .
some struggle going on in the bar between the broken crystals , a struggle which apparently is settled , after an extension of about OT inch , in favour of a predominating plastic partner .
The curves obtained from annealed and unannealed brass rod , when considered with the micro-photographs and the curve from pure copper , show that the plastic properties of the materials are profoundly modified by the size of the aggregates from which the material is built up .
And if steel is assumed to be an alloy of iron constructed of iron aggregates of large size through which is distributed a network of crystalline structure , the peculiar characteristic diagram which is always obtained from steel may be explained on the assumption that it is the resultant load-extension diagram of two separate materials , the one material being present as a hard crystalline structure , the other being the iron with which it is associated .
The material breaks down in the elastic sense when this crystalline network gives way , but it continues yielding in the plastic sense and even carries a greater load than was carried at the time the network failed before local yielding begins .
The giving way of the crystalline network is probably only a slip of the crystals , because , as is well known , annealing in boiling water appears to restore the elastic properties of the bar , though this boiling does not cause the bar to return to its original length , it merely permits the reconstitution of the network into a resisting system in the new relative position of the crystals produced by the first slip .
It would be interesting to obtain the diagram of a piece of chemically pure iron .
The load-extension diagram would probably be the same in character as that of pure copper .
I should like finally to express my thanks to Mr. W. H. Merrett , of the Royal School of Mines , for making the micro-photographs which are used to illustrate the paper .
Dolby .
Roy .
Soc. Proc. , A , 88 , Plate 2 .
Fig. 2 .
Fig. 9 .
Fig. 10 .
Roy .
Soc. Proc. , A , 88 , Plate 3 .
Dolby .
Fig. 11 .
Fig. 12 .
|
rspa_1913_0029 | 0950-1207 | On a fluorescence spectrum of iodine vapour. | 289 | 296 | 1,913 | 88 | Proceedings of the Royal Society of London. Series A, Containing Papers of a Mathematical and Physical Character | Prof. J. C. McLennan|Sir J. Larmor, F. R. S. | article | 6.0.4 | http://dx.doi.org/10.1098/rspa.1913.0029 | en | rspa | 1,910 | 1,900 | 1,900 | 6 | 120 | 4,076 | http://corpora.clarin-d.uni-saarland.de/surprisal/6.0.3/?id=rspa_1913_0029 | 10.1098/rspa.1913.0029 | null | null | null | Atomic Physics | 63.115969 | Thermodynamics | 16.715863 | Atomic Physics | [
5.409276008605957,
-48.295249938964844
] | 289 On a Fluorescence Spectrum of Iodine Vapour .
By Prof. J. C. McLennan .
( Communicated by Sir J. Larmor , F.R.S. Received March 11 , \#151 ; ^ Read April 17 , 1913 .
) ( Plate 4 .
) In a number of most interesting papers Prof. R. W. Wood* has shown that it is possible to obtain from iodine vapour at ordinary room temperatures , under the stimulation of light from the mercury arc , a fluorescence spectrum , consisting of a number of lines ranging from A , = 7005*5 A.U. to X = 5337*63 A.U. Further , he has shown that these lines can be divided into three series , one of which is stimulated by the light from the green line A = 5460*74 A.U. , another by the light from the yellow line A = 5769*60 A.U. , and a third by the light from the yellow line A = 5790*66 A.U. Up to the present , he has identified in his photographs some 23 members in the series stimulated by the mercury green line , 10 members in that excited by the yellow line of shorter wave-length , and 13 members in the series arising from the excitation of the yellow line of greater wave-length .
Moreover , by using apparatus of high resolving power , he has recently been able to show that in nearly every case the members of the green line series are complex and are in reality close doublets accompanied by a number of fainter companions .
The members of the series due to the yellow line A = 5769*60 A.U. are also complex , he finds , but they appeared as doublets when a Cooper Hewitt arc was used as the source of the stimulating light , and as triplets when the light from a quartz-mercury arc lamp was used as the source of excitation .
The series of lines stimulated by the line A = 5790*66 A.U. he also finds to be complex , but the constitution of the members of this series is not uniform , some of them being single lines , others doublets , and one even a triplet .
The three lines X = 546074 i.U. , X = 5769-60 A.U. , and X = 5790-66 A.U. , which Prof. Wood used in his investigation , as is well known , are among the strongest in the mercury arc spectrum , and the absence of any resonance lines of wave-lengths shorter than A = 5337*63 A.U. suggests that , possibly , had a more intense source been used , or a modification in the method of illumination been adopted , some evidence might have been obtained of the excitation of additional series of resonance or fluorescence lines by the light * R. W. Wood .
'Phil .
Mag. , ' Oct. , 1911 , p. 469 , and Oct. , 1912 , p. 673 .
Prof. J. C. McLennan .
[ Mar. 11 , from other lines in the mercury arc spectrum , and especially by that from the stronger lines in the ultra-violet region .
In view of the possible existence of such an excitation , it seemed to the writer worth while to see if any indication of such resonance or fluorescence spectra could be obtained , and the following paper gives a short account of some experiments arranged with that end in view .
First of all , however , it seemed advisable to repeat Prof. Wood 's experiments , and efforts were directed to see if any improvement could be made in the method of illumination used by him , so as to reduce , if possible , the time of exposure to obtain good photographs .
After trying a number of arrangements , it was found that very satisfactory results could be obtained by illuminating the iodine vapour by the light from a number of Cooper Hewitt mercury arc lamps , placed parallel to each other and as close together as possible .
Each of these lamps , it is known , furnishes a luminous discharge from 50 to 60 cm .
in length , and when from four to six of them are used one can very conveniently obtain an exceedingly powerful illumination , as well as one of considerable extent .
With this arrangement it was found that very good results could be obtained with about two hours ' exposure , and fig. 1 , Plate 4 , is an example of a photograph obtained with this arrangement in that time .
The iodine vapour was contained in a highly exhausted glass tube , about 70 cm .
long and 3 cm .
in diameter , which was illuminated by the light from four Cooper Hewitt lamps , placed parallel to it and as close to it as they could be set up .
The photograph was taken with a Hilger constant deviation spectroscope , with the collimator directed towards the rounded end of the iodine tube .
The figure shows quite clearly the resonance lines stimulated by the green line , and a number of the members of the two series due to the two yellow lines .
Several plates were taken similar to this one with two-hour exposures , and they all showed quite clearly 20 out of the 23 members cited by Prof. Wood as belonging to the green-line series .
On most of them , however , it was possible to make out only seven members of each of the series stimulated by light from the two yellow lines .
This was owing in part to their relative faintness , and in part , at least in the case of several members of the series , to their close proximity to the relatively much stronger lines stimulated by the light from the green line .
No doubt , with the use of screens to cut out this latter series , and with exposure of longer duration than two hours , the yellow line series could have been brought out with much more distinctness ; but , in view of a point of special interest cropping up in another direction in the course of the work , the investigation of this matter was deferred for a time .
The point referred to came out while using a tube for illuminating 1913 .
] Fluorescence Spectrum of Iodine Vapour .
291 purposes , whose form is shown in fig. .
2 .
It consisted of an outer part AHC made of glass of the ordinary Cooper Hewitt design , and a second part DB made of clear fused quartz which was sealed into the former by wax joints ]c / Fig. 2 .
at Gr and F. The glass tube was furnished with mercury terminals at A and C , and carried the mercury arc .
Iodine in crystals was inserted in the tube BD , which w^as then highly exhausted and afterwards sealed off at E. With this apparatus it was possible to subject the iodine vapour in the inner tube to intense illumination by light whose wave-lengths extended beyond X = 7000 JL .
U. and down to approximately X = 1850 A.U. On examining the light emitted by the tube containing the iodine vapour by means of a quartz spectrograph directed at the exposed end I ) , it was found that in addition to the ordinary mercury lines coming from the arc in the outer tube the spectrum contained a number of narrow bands extending from about 4600 A.U. down to about 2100 A.U. With exposures of two or three minutes these bands could be readily seen on the photographs , but exposures of 15 minutes brought them out more clearly .
With an hour 's exposure they were brought out still more distinctly , but on increasing this to two hours it was found that the density of the bands was not greatly enhanced .
A photograph of the spectrum illustrating the distribution of these bands is shown in Plate 4 , fig. 3 , A. This shows a set of seven well marked bands between X = 3341*7 A.U. and X = 3131*7 A.U. , and also sets approximately equally spaced on either side of the line X = 4358*3 A.U. A limited series of bands in pairs is distinguishable between X = 3131*7 A.U. and X = 2893*7 A.U. , and a number of single bands can be seen between X = 2893*7 A.U. and X = 2536*7 A.U. Below X = 2536*7 A.U. the bands are spaced at intervals of approximately 20 A.U. , and can be seen extending down to the limit of the photograph .
The bands vary somewhat in width , but a majority of them have a width of approximately 10 A.U. A close examination was made of a number of photographs , and it was found possible to pick out over 80 bands in this new spectrum .
The positions of these were determined as closely as possible by comparison with 292 Prof. J. C. McLennan .
[ Mar. 11 , the more prominent of the mercury lines and their approximate mean wavelengths are given in Table I. Table I. Approximate mean wave-lengths of bands in Angstrom units .
Remarks .
Approximate mean wave-lengths of bands in Angstrom units .
Remarks .
4608 From A \#151 ; 4608 A.U. 2900 In the region from 4550 to A = 3365 A.U. the 2883 A = 2900 A.U. to 4505 bands are faint in 2853 X = 2545 A.U. the 4452 places and the group- 2825 bands are quite dising is somewhat irre- 2799 tinct , but their spac- 4290 gular .
2774 ing is irregular .
4250 2760 4210 2737 4170 2727 4130 2715 2697 4015 2685 3925 2667 3870 2638 3800 2628 3725 2622 3625 2617 3585 2612 3555 2594 3520 2590 3475 2580 3445 2560 3420 2545 3395 3365 2515 The bands below A = 2495 2515 A.U. are spaced 3315 The group of seven 2476 at intervals of about 3290 bands obetween X = 20 A.U. , and each 3268 3315 \#163 ; .U .
and X = 2450 band is about 10 A.U. 3245 3175 A.U. are parti- 2426 in width .
3220 cularly well marked 2408 3195 and appear to be 2382 3175 equally spaced at in- 2360 tervals of about 24 2340 3107 A.U. 2320 3090 2300 2277 3065 There are four well- 2254 3047 marked pairs of bands 2237 3009 in the regioq between 2218 2993 A = 3065 0A.U .
and 2195 2960 A = 2915 A.U. 2179 2946 2162 2930 2148 .
2915 2129 After obtaining the new band spectrum in the manner described , the tube BD was opened and air admitted .
The iodine was then all dissolved with methyl alcohol and thoroughly washed out of the tube .
The latter was then carefully freed of all moisture by forcing through it a current of dry air .
Finally , it was exhausted once more and sealed up again .
The mercury arc 1913 .
] Fluorescence Spectrum of Iodine Vapour .
was re-established in the outer tube , and photographs taken with the spectrograph again directed at the end of the tube D. One of these is shown in Plate 4 , fig. 3 , B. The bands , it will be seen , are entirely absent , and the only lines which are in evidence are those of the ordinary well-known mercury arc spectrum .
The disappearance of the band spectrum with the removal of the iodine vapour made it clear that the spectrum had its origin in this vapour .
It did away , moreover , with the possibility of ascribing the spectrum to any fluorescence of the quartz tube under a stimulation by the ultra-violet light of the arc , or to a fluorescence of any mercury vapour which might have found its way in minute proportions into the iodine tube during the process of its evacuation by the mercury pump .
After having ascertained in the manner just described that the iodine vapour was the origin of the band spectrum , an experiment was made to see if the spectrum could still be obtained if the tube BD were provided with a window of crystalline quartz attached with sealing-wax or mastic at Ik This was done to make certain that the mastic or wax of the joint did not give off any gas even in small quantities which might act upon the iodine vapour and so lessen its power to emit the band spectrum .
When the end of the tube was cut off at D and the crystalline quartz window attached in its , place , it was found , on repeating the experiment , that the bands , and , in fact , , the mercury lines , too , came out with even greater clearness than when the end of the tube was made of fused quartz .
In the next experiment the tube was modified by making the portion BD of ordinary combustion glass tubing and providing it with a window of crystalline quartz , sealed on at D in the manner just described .
After inserting the iodine crystals in the tube and exhausting it and sealing it off at D , the arc was struck in the outer tube and an exposure made with the quartz spectroscope , as before .
In these experiments , although they were made repeatedly , no trace was obtained at all of the band spectrum .
This will be seen from Plate 4 , fig. 3 , C , which is taken from one of the photographs obtained with this glass modification of the original tube .
The mercury lines come out quite distinctly down to X = 2893*7 A.U. , it will be seen , but there is not the slightest indication of any bands in the region immediately to the right or to the left of the line X \#151 ; 4358*3 A.U. , or in the region between1 X = 3341*7 A.U. and X == 3131*7 A.U. , while in both of these regions in fig. 3 , A , the bands stand out most distinctly .
Moreover , in none of the plates was there any indication of bands in that part of the spectrum lying below X = 2893*7 A.U. This interesting result shows , in the first place , that the emission of the Prof. J. C. McLennan .
[ Mar. 11 , band spectrum by the iodine vapour could not have been due to an elevation of the temperature of the vapour by the heat from the arc , for the experimental conditions for obtaining a temperature spectrum were precisely the same with the combustion glass tube closed by a quartz window as with the fused quartz tube closed by the same window .
It is known from the experiments of Konen , * * * S Friedrichs , t Puccianty Evans , S and others that iodine vapour , when heated in an exhausted tube , emits a band spectrum at temperatures ranging about the same as the temperature of the iodine vapour in the tubes used in this investigation , but this temperature spectrum appears to be entirely confined to the region above that of the spectrum obtained in the present experiments , and so does not appear to have any direct relation to it .
It seems , therefore , that one must conclude that the emission of this new band spectrum by the iodine vapour is a true resonance or fluorescence effect stimulated by the light from one or more lines in the mercury arc spectrum ( doubtless in the ultra-violet region ) to which the combustion glass tubing is not transparent .
Up to the present , it has not been possible to pick out , with any certainty , the lines in the ultra-violet spectrum of the mercury arc which emit the light which gives rise to this new resonance or fluorescence spectrum from the iodine vapour .
Owing to its strong intensity , however , the line X = 2536*7 A.U. seems to be a likely one .
The experiments of Hughes|| indicate that a line or lines of comparatively strong intensity exist in the spectrum of mercury near the region X = 1850 A.U. , and as quartz is still transparent to light of this wave-length , it is possible that the light from such line or lines may contribute , in part at least , to the effect .
It is known that mercury vapour absorbs the light of wave-length X = 2536*7 A.U. , and it should not be difficult to use this fact to see if the new resonance bands are excited by the light from this line or by the light from the lines close to it .
By a modification of the tube shown in fig. 2 it should be quite easy to insert a third exhausted tube of fused quartz containing a little mercury between the quartz tube BD and the glass one AHC .
With the arc established in AHC this intermediate tube would be heated , the mercury in it would become vaporised , and so as a vapour act as a screen to cut off the light emitted by the lines at and in the neighbourhood * Konen , ' Wied .
Ann. , ' 1898 , vol. 65 , p. 297 . .
t Friedrichs , 'Zeit .
fur Wissen .
Photographic , ' 1905 , vol. 3 , p. 154 .
{ Puccianti , ' Atti della Reale Aceademia dei Lincei , ' 1905 , vol. 14 , 1st semestre , p. 84 .
S Evans , 'Aat .
Phys. Journ. , ' July , 1910 , p. 1 .
|| Hughes , 'Camb .
Phil. Soc. Proc. , ' 1912 , vol. 16 , p. 428 .
1913 .
] Fluorescence Spectrum of Iodine Vapour .
295 of X = 2536*7 A.U. from the iodine vapour .
By the use of this third tube , therefore , with mercury vapour or other absorbing medium in it , there should be no great difficulty in locating , with considerable definiteness , the region or regions in the spectrum of the mercury arc from which the light comes which stimulates the iodine vapour to the emission of this somewhat extensive band spectrum .
Experiments with this end in view are now being carried out , and it is expected that information will soon be obtained which may throw some light upon this point .
A matter of interest in connection with these experiments is the complete absence from the plates , obtained with the new type of tube , of any indication of the lines belonging to the resonance or fluorescence spectrum from iodine vapour which has been so fully investigated by Prof. Wood .
The explanation of this absence , however , seems evident .
The tube BD , as is shown in fig. 2 , projected for some distance beyond the end of the tube AHC .
In consequence of this there would be a temperature gradient in the iodine vapour contained in it , the hottest portion being at the end B and the coldest at the other end .
If the light from the mercury green and yellow lines stimulated the iodine vapour , or any part of it , at the heated end to the emission of the spectrum studied by Prof. Wood , the light which constitutes this spectrum would have to pass through a considerable column of comparatively cool iodine vapour before it fell upon the slit of the spectroscope .
These are just the conditions under which one should expect to obtain an absorption of the resonance or fluorescence lines , and consequently their absence from the plates should not cause any surprise .
This explanation gains support , too , from the fact that there was considerable absorption by the iodine vapour of light corresponding to the green and the yellow lines of the mercury arc , for these appeared by visual observation very much sharper and narrower when viewed through the spectroscope with the iodine vapour in the tube BD than they did when this vapour was removed .
This can also be seen from the reproductions in fig. 3 , where the green and the two yellow lines are considerably sharper and somewhat narrower in A than they are in B. On the other hand , one cannot help asking why the bands of the new spectrum come out so clearly when those of the Wood spectrum do not .
Doubtless the fact that they do would seem to show that these bands have their origin in a system of atomic or molecular vibrations quite distinct from those responsible for the lines of the Wood spectrum .
One must remember that that portion of the iodine vapour upon which the light fell was raised to a considerable temperature by the mercury arc , and that it is highly probable , from the facts which have been brought out in connection with the investigation of the high temperature spectrum of Mr. F. B. Pidduck .
[ Mar. 13 , iodine vapour referred to above , that the molecular constitution of the iodine vapour at these higher temperatures is in all probability different from what it is at ordinary room temperatures .
It might , therefore , happen that the molecules of the heated iodine vapour would not be stimulated to emission at all by the light from the green and the yellow lines of the mercury arc spectrum .
If this were so , the lines in the Wood spectrum could not then appear on the plates .
At the same time , it might be possible that the molecules of the heated vapour would respond to a stimulation by the light from a line or lines in the ultra-violet portion of the mercury arc spectrum .
If such a stimulation had the effect of causing the heated vapour to emit a fluorescence spectrum , the light constituting this spectrum might easily pass through the cold vapour without any absorption and so give rise to the bands obtained in the present investigation .
In conclusion , I wish to acknowledge the services of my assistants , F. Mezen and P. Blackman , the one in quartz-blowing and the other in preliminary work on the photographs .
The Abnormal Kinetic Energy of an Ion in a Gas .
By F. B. Pidduck , M.A. , Fellow of Queen 's College , Oxford .
( Communicated by Prof. J. S. Townsend , F.R.S. Received and read March 13 , 1913 .
) 1 .
In a paper on " The Charges on Ions in Gases , and the Effect of Water Vapour on the Motion of Negative Ions , " Townsend* showed that when a stream of ions is moving in an electric field the extent to which it spreads out as it advances depends on the dryness of the gas as well as on the electric force , indicating that the rate of diffusion in dry air is abnormally great in comparison with the velocity under an electric force .
It was suggested ( loc. cit. , p. 469 ) that this could be explained on the supposition that the ions were not in " thermal equilibrium " with the molecules of the gas , but that their mean kinetic energy exceeded that of an equal number of gas molecules in the ratio k to unity , where k depends on the pressure and the electric force .
Townsend mentioned a possible means by which this abnormal energy might arise , namely , that the extra velocity acquired by an ion in an interval * J. S. Townsend , 4 Roy .
Soc. Proe .
, ' 1908 , A , vol. 81 , p. 464 .
McLennan .
Roy .
Soc. Proc. , A , vol. 88 , Plate 4 .
h-H fin L- . . .
ft Er L9\#163 ; Sz ' ' 1 MMSi i , A 8 99 co Fig.
|
rspa_1913_0030 | 0950-1207 | The abnormal kinetic energy of an ion in a gas. | 296 | 302 | 1,913 | 88 | Proceedings of the Royal Society of London. Series A, Containing Papers of a Mathematical and Physical Character | F. B. Pidduck, M. A.|Prof. J. S. Townsend, F. R. S. | article | 6.0.4 | http://dx.doi.org/10.1098/rspa.1913.0030 | en | rspa | 1,910 | 1,900 | 1,900 | 1 | 40 | 904 | http://corpora.clarin-d.uni-saarland.de/surprisal/6.0.3/?id=rspa_1913_0030 | 10.1098/rspa.1913.0030 | null | null | null | Fluid Dynamics | 44.057629 | Tables | 43.739133 | Fluid Dynamics | [
7.224172115325928,
-69.33161163330078
] | ]\gt ; in comparison with the velocity under an electric force .
It was suggested ( loc. cit. , p. 469 ) that this could be explained on the supposition that the ions were not in " " thermal equilibrium\ldquo ; with the molecules of the gas , but that their mean kinetic energy exceeded that of an equal number of gas ] ecules in the ratio to unity , where depends on the pressure and the electric force .
Townsend mentioned a possible means by which this abnormal energy might ] arise , namely , that ' extra velocity acquired by an ion ih an interval * J. S. Townsend , ' Boy .
Soc. Proc 1908 , , p. 464 .
, energy might accumulate for some time .
The effect has been further studied by Haselfoot , *both observers showing that is , at any rate approxi ; mately , a function of only , where X is the electric force and the pressure of the gas .
It seemed to the author that it would be desirable to investigate the matter quantitatively on the basis of the kinetic theory of gases , since we are here dealing with the validity or non-validity of the law of equipartition of energy .
It is shown in this paper that it is easy enough to obtain theoretical support for the assumption of abnormal kinetic energy ; in fact , the values of predicted by pure theory are considerably in excess of those actually observed .
In order to prevent misunderstanding , it may be stated that the law of equipartition of in the kinetic theory is only proved to be true when the molecules are left to themselves in the absence of external 1 forces .
2 .
The most satisfactory way of treating these questions is that developed by Maxwell in his later papers , and carried out by him on the assumption of an inverse fifth-power law of repulsion between molecules .
Where not otherwise stated we shall follow the notation used by Jeans in his account of Maxwell 's theory .
Let mber of ions per cubic centimetre of the gas , small in comparison with Number of molecules of gas per cubic centi1netre .
Electric force .
Absolute ture of the Velocity of an ion .
the mass-velocity of a group of ions .
Writing , w , is called the velocity of agitation of an ion , so that Velocity of agitation of a gas molecule .
Mass .
ion and molecule respectively .
Average kinetic energy of agitation of a gas molecule .
average kinetic energy of agitation of the ions in a specified small region .
C. E. Haselfoot , ' Roy .
Soc. Proc 1912 , , vol. 87 , p. 350 .
J. C. Maxwell , ' PhiL Trans , ' vol. 167 ; 'Collected Papers , ' , p. 26 .
'Dynamical Theory of Gases , ' Chap. XV .
3 .
The immediate problem with which we are concerned is to find the kinetic energy in a stream of ions advancing in a fixed direction , for example } the axis of , the motion depending on the co-ordinate alone .
Then constant , ( 9 ) , ( 10 ) , ( 11 ) , ( 12 ) .
( 13 ) * Jeans , p. 277 .
'Collected Papers , ' vol. 2 , pp. 47-48 .
motion tends wtream h. some distance .
In this case Substituting for X from this equation in ( 11 ) , ( 12 ) , and ( 13 ) , we find S These latter equations yield on addition ; ( 16 ) or , if is the " " root-mean-square value\ldquo ; of the velocity of agitation of the gas molecules , 4 .
The inverse fifth power law has the advantage of allowing a perfectly rigorous solution of the present problem , free from all considerations of approximation .
As , however , the formula ( 17 ) is not in agreement with experiment it is desirable to consider another law of force , namely , that both ion and molecule are elastic .
Some useful information is given by equations ( 15 ) as to the distribution of velocities of agitation in val.ious directions .
In general are unequal , and their differences are of the order of magnitude of .
In two cases , however , the differences are small in comparison with the absolute value of any of the quantities ; namely , when is nearly unity , and when is small in comparison with M. We shall , therefore , not be far wrong in Maxwell 's law of distribution as a first approximation .
Let represent the fraction of the whole number of ions which have velocities of agitation in the range and : then Maxwell 's law is expressed by .
( 18 ) There is no doubt as to the corresponding function for the molecules of the gas , namely , We shall suppose for the sake of generality that the collision of ion and molecule is not perfectly elastic , an assumption which allows roughly for a possible loss of energy on collision , it renders the validity of ( 18 ) more doubtful than it might otherwise be .
Under these conditions
|
rspa_1913_0031 | 0950-1207 | The influence of chemical constitution upon interfacial tension. | 303 | 313 | 1,913 | 88 | 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.1913.0031 | en | rspa | 1,910 | 1,900 | 1,900 | 2 | 94 | 2,381 | http://corpora.clarin-d.uni-saarland.de/surprisal/6.0.3/?id=rspa_1913_0031 | 10.1098/rspa.1913.0031 | null | null | null | Fluid Dynamics | 29.026443 | Biochemistry | 20.730485 | Fluid Dynamics | [
-3.006654977798462,
-32.5129508972168
] | ]\gt ; with spread over the surface of ; the tension of the composite surface so formed is less than that of pure , otherwise spreading would not When the film of A has become sufficiently thick two independent surfaces are formed , one of pure , the ) the interface between A and B. .
these respectively by and the energy of the two for each ?
unit of the oliginal surface of pure is and this quantity is not affected by further addition of A. Therefore in the spreading of A upon we have , as the limits of the change of sm.face energy , and In an earlier paper*I gave reasons for believing that the changes in the value of between these limits depend mainly upon the chemical constitution of A. Between the limits and , lies a series of values when A is not present in mass .
The phenomena over this are complex , therefore , in order to obtain a simpler presentation of the influence of chemical constitution it is necessary to have A as well as present in mass .
The equation then reduces to the simple form .
It is with measurements of the quantity that we are concerned in this paper .
Following Dupre ' we may write , ( 2 ) in which is the done per nnit of area of interface by the attraction of A for when a surface of A is allowed to approach normally and touch a surface of B. Since the quantity is the total work expended in forming unit area of interface by the molecular forces which operate between A and it follows that evidence of the influence of chemical constitution upon surface must be looked for in a comparison of this quantity when different fluids A form an interface with a constant fluid 'Roy .
Soc. Proc 1912 , , vol. 86 , p. 610 .
orie Mecanique .
Chaleur , ' Paris , 1869 , p. 369 .
See also Lord Rayleigh , ' Phil. Mag 1890 , [ 5 ] , vol. 30 , p. 461 .
Putting in equation ( 3 ) we see is ) gain in surface energy per degree of temperature .
An equation precisely to for an interface would have as its zero of tempersture , not the critical points of the pure fluids A and , but the temperature at which A and become completely miscible .
This ature is unknown .
the pairs of substances used ; an equation for ) interface may , however , be derived fro equations ( and ( 3 ) , namely Wied .
Annal .
, vol. 27 , p. 452 .
' Phil. Trans 1893 , , p. 647 .
previously cleansed with sulphuric and chromic acids and washed out with distilled water , was dipped into the lower layer ( distilled water ) and enough ayer , ontents whowed slowly trops which wountedfluid drawn uoint oeing raised spper while .
of fluid left the tube .
The operation was repeated with this .
result:\mdash ; Temperature , .
Tabe 1 .
Capacity , number of drops , 44 , Tube 2 , bent at angles , was next filled with the upper layer ( oleic acid ) and drops allowed to form and float up when the point was immersed in the layer ( water ) .
Tube 2 ; capacity , .
No. of drops , Tube 1 was then cleaned , dried , filled with oleic acid at and a series of 10 drops allowed to fall into a weighed stoppered weighing bottle .
Weight of 10 drops , .
Mean , Loss of weight by evaporation , determined by control experiment , From these data we now have to calculate the quantities and .
The formula frequently used to compute the surface tension from ) the weight of a drop delivered by a tubs is , when is the weight of the drop and the radius of the tube ; but his formula gives little more than half the true surface tension .
The of the drop cannot be calculated from statical consideration : the detachment of the drop is a dynamical effect .
complete solution of the dynamical problem is impracticable .
It was attempted by Dupre ' the argument has been restated by Lord Rayleigh , who found the formula to be a close approximation for thinwalled tubes .
The tubes used by myself had the following dimensions at the orifice:\mdash ; No. 1 .
External radius , cm .
Internal radius , No. 2 .
, , , , , , , , , , , , .
cit. , p. 327 .
Mag 1899 , [ 5 ] , , p. 321 .
Returning to the actual experiment , when the lower layer forms drops in the upper layer since water wets the glass of the capillary tube they detach themselves from the whole face of the end of the tube , therefore is here the ! .
external radius or cm .
But when oleic acid is delivered into water by tube 2 it does not wet the walls and the drops are detached from the lumen , and is the internal radius or cm .
When oleic acid is delivered from tube 1 in air , however , it wets the walls and the external radius must be used .
We therefore have : Tube 2Tube 1 Mean number of drops , Mean , Tube 1 .
Weight of one drop of oleic acid in air , Rigorous circumspection is necessary both in the handling of the water , and of the other fluids , and in their preparation .
The effect of a trace of impurity is hardly to be credited .
Cyclohexane , a saturated hydrocarbon , does not spread upon water .
In some of it per cent. by weight of oleic acid was dissolved , a normal solution .
The fluid now flashed over a water surface and the tension of the interface with water was found to have fallen from , that of pure cyclohexane-w.ater , to .
It cannot be without interest to notice that the concentration of oleic acid employed is of the order of concentration needed in the case of such physiologically active substances as adrenalin reckoned as percentage of the body weight of the animal ; also , if FitzGerald 's view be true that the force of contraction of a muscle is derived from changes in the tension of internal surfaces , such a concentration of a similarly active body would reduce the absolute force by about 50 per cent. While dealing with the question of chemical purity certain special cases must be mentioned .
A sample of octane purchased from Kahlbaum gave the following values , .
As these differed widely from the values obtained for other saturated bodies the sample was freed from unsaturated substances , by shaking for four weeks with many changes of concentrated sulphuric acid .
It was then washed with water and distilled from metallic sodium , and the fraction which came over at now gave the values which accord wound fheraturated bodies .
fraction gperfectly constant boiling point.eries o was therefore undertaken and two fractions collected , ( A ) , Bar .
758 .
The B.P. of octylene is given in Beilstem as , and as at mm. Fraction A gave Fraction The mean of these values is the best that can be got for octylene by fractional distillation .
The substances employed were for the most part purchased from Kahlbaum and , when possible , distilled to a constant point just before use .
Some specimens were lent to me by Dr. Ruhemann , to whom I owe also a reat debt for his kindness in directly superintending and helping in the purification of each substance .
Without the aid which his profound technical knowledge afforded I could not have succeeded in making the measurements .
The effect of any slight degree , of mutual solubility of the fluids A and upon the quantity needs consideration .
Let and be respectively the tension of the solution in A and of A in can form contiguous phases .
We theu have Since in all the cases dealt with , , and , the relation of to so far as magnitude is concerned is umcertain , terms of opposite sign being introduced by the presence of A and on both sides of the interiace .
When the two solutions are brought into contact the work done is derived from ( 1 ) the attraction of A for A and of for across the interfaoe , and ( 2 ) the attraction of A for B. When pure A and come into contact ( 1 ) is zero , and any degree of increases the work due to ( 1 ) and decreases that due to ( 2 ) .
Therefore , since mutual miscibility introduces effects of )osite s into the right-hand members of equation ( 2 ) , the relation of to cannot be predicted .
* Whatever the theoretical conclusion practically the value of under the conditions of measurement was found to be sensibly independent of the state of the phases .
obviously does not include the loss of potential due to the mixing of A and except at the interface , for , if it did , would be a function of the ratio surface/ ( mass of of B .
whichIhaveincludedToillustratethiswehavethefirstgroupofsaturatedsubstances , inoilC , \ldquo ; COInposedmainlyofhighboiling-point : paraffins .
lies between and 24 .
The introduction of an unsaturated linkage into the paraffin octane raises the value to 36 ( octylene ) .
] But in the case of a ring compound unsaturated linkages produce a smaller effect , the number rising only to ( benzene ) .
The introduction of the OH group into a ring compound increases the quantity by 20 cyclohexane cyclohexanol , ; but the effect in the case of the paraffin chain is only about one-half .
The presence of the carboxyl group produces the same effect as the OH group , the quantity being increased in the case of capryllic acid by For the esters we for ethyl hydrocinnamate .
The introduction of one more unsaturated linkage increases this only slightly , namely , to the 43 of ethyl cinnamate , and the double ester ethyl phthalate again is only slightly higher , namely , 46 .
Other relations nught be pointed out , but the figures speak for themselves .
I prefer to pass on to the more important negative relations .
In the saturated bodies there is a very small but I believe real difference between the paraffin chain and the ring formation , and again between these and the compounds and .
The two cyclic alcohols have practically will be complete and independent of the molecular volumes , since the mass of the fluids on either side of the is practically infinite .
ainst this view , however , it is be noted that chemical action between water and such stable substances as paraffin or cyclohexane , both in mass , is unknown .
If it did occur at an interface it could only be as the result of great stresses .
: Table III shows most clearly that the quantity increases with what may be called the chemical reactivity of the fluid , and especially that it is greatest when the molecules are of the salt type\mdash ; acids , alcohols , or esters .
Such molecules by their constitution readily exhibit electric polarisation , and we have here additional evidence for the fact mentioned in the earlier papers that the chief modifying factor in all interfaces is the development of a contact difference of potential , due to polarisation of the molecules by stresses normal to the interface .
If the quantity represents mainly the specific electric polarisation of the interface , then its vahae for paraffin , cyclohexane , etc. , may represent polarisation due to the water molecules , which are of this salt type .
For a surface ween two saturated substances not of salt type the quantity might well be zero , in which case we should have molecular volume and , following the usual notation , , being respectively the molecular volumes , and the axis normal .
to the interface .
Then on Young 's hypothesis , that molecular attraction is a .
force which is of constant value over the range , we have for two similar chemical substanoes , for which therefore is the same , That is to say , the would be proportional to the molecular volume .
The alternative assumption , that the attractive force of a molecule of A for one of falls off according to some power of the distance which separates them , yields result that for similar chemical substances , since is equal , the molecular volumes vary inversely with this power .
Thus , if the attractive force be put then The Tension of Composite Fluid .\mdash ; No. II .
By W. B. HAliDY , F.R.S. ( Received October 19 , 1912 , \mdash ; Read January 16 , \mdash ; Revised hIarch 11 , 1913 .
) With the Figures in Table III of the preceding paper ( p. 311 ) as a uide the problem of the spreading of one fluid over the face of another may be approached with some sense of security .
In an earlier ) the equation of a composite surface was found to be when is the tension of the composite surface , and a term depending upon gravity .
Putting , it is seen that spreading will occur only when and , at the limit , that is to the tension of pure water in the experiments under consideration .
Taking , the tension of pure water , we have from the last paper Table I. TA .
TAB. Cyclohexane Octane Oil " " Carbon tetrachloride * Boy .
Soc. Proc 1912 , , vol. 86 , p. 610 .
|
rspa_1913_0032 | 0950-1207 | The tension of composite fluid surfaces.\#x2014;No. II. | 313 | 333 | 1,913 | 88 | 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.1913.0032 | en | rspa | 1,910 | 1,900 | 1,900 | 6 | 235 | 5,870 | http://corpora.clarin-d.uni-saarland.de/surprisal/6.0.3/?id=rspa_1913_0032 | 10.1098/rspa.1913.0032 | null | null | null | Fluid Dynamics | 36.360228 | Biochemistry | 17.113185 | Fluid Dynamics | [
-3.034154176712036,
-32.69423294067383
] | ]\gt ; molecular volume and , following the usual notation , , being respectively the molecular volumes , and the axis normal .
to the interface .
Then on Young 's hypothesis , that molecular attraction is a .
force which is of constant value over the range , we have for two similar chemical substanoes , for which therefore is the same , That is to say , the would be proportional to the molecular volume .
The alternative assumption , that the attractive force of a molecule of A for one of falls off according to some power of the distance which separates them , yields result that for similar chemical substances , since is equal , the molecular volumes vary inversely with this power .
Thus , if the attractive force be put then The Tension of Composite Fluid .\mdash ; No. II .
By W. B. HAliDY , F.R.S. ( Received October 19 , 1912 , \mdash ; Read January 16 , \mdash ; Revised hIarch 11 , 1913 .
) With the Figures in Table III of the preceding paper ( p. 311 ) as a uide the problem of the spreading of one fluid over the face of another may be approached with some sense of security .
In an earlier ) the equation of a composite surface was found to be when is the tension of the composite surface , and a term depending upon gravity .
Putting , it is seen that spreading will occur only when and , at the limit , that is to the tension of pure water in the experiments under consideration .
Taking , the tension of pure water , we have from the last paper Table I. TA .
TAB. Cyclohexane Octane Oil " " Carbon tetrachloride * Boy .
Soc. Proc 1912 , , vol. 86 , p. 610 .
When the fluid A is a pure chemical substance , or when it is composed of spreadingarealwaysofthesimplest .
Thefirstaddedsubstanceshavingidenticalinfluenceuponthetension'thefluidforms.aphenomenaof .
continuous sheet on the surface of the water ( B ) , which may be thickened until spreading ceases , when the excess remains as a single lens .
I have met no exception to rule that , when pure A spreads on water , the equilibrium state is a single lens in tensile balance with a uniform composite sheet of A spread evenly on B. This follows from experiment and also from a consideration of vapour pressures ; for let the space above be enclosed , and * Cantor ( ' Wied .
Annal 1895 , vol. 56 , p. 492 ) is wrong in his conclusion that the vapours of fluids which do not " " wet\ldquo ; the surface of water will not condense on to the surface .
Ths saturated vapours of the substances mentioned in Table I will condense on to tap water at the same temperature , as a dew of fine lenses , though in the case of carbon bisulphide owing to the high value of the dew forms only with .
difficulty .
same curvature could co-exist , but the equilibrium would probably always be .
unstable .
The condition of equilibrium therefore is twofold , that the lens and the plane surface are in tensile equilibrium according to tha equation , and 2 ) that the vapour tension of the lens and of the plane surface shall be the same .
When a large lens of a fluid whose vapour pressure is negligible is placed : on water if it is capable of spreading the lens is at once extended to form an irregular sheet , which then proceeds to contract to one or more lensea which are in tensile equilibrium with a composite surface .
] ibrium is reached quickly when salts are present in the water and slowly when the water is of low conductivity .
Taking , for instance , ricinolic acid as an example , equilibrium is reached with tap water in 20 seconds , and with distilled water only after perhaps 20 minutes .
When distilled water is there appears to be a large tangential viscosity which impedes contraction of the excess oil .
As I have already pointed out*the film is at a different .
electrical potential to the underlying water , and the viscosity may be due to the low conductivity of distilled water cklaying the dissipation of electrical energy .
Whatever be the true explanation the contrast is remarkable .
When distilled water is the viscosity is so .
great as to allow the sheet of acid to develop wrinkles and folds as though it were a solid .
What we may picture as happening in all cases is that since the lens is at once pulled out to form a sheet .
From the visible edge of the sheet fluid is spreading on to the surface of , at first rapidly , then more slowly , the flow being impeded by the viscosity of the film and possibly by other causes .
As a consequence of this streaming from the edge the tension of the plane composite surface falls , and as it does so the extended lens contracts .
The sheet formed by the first rapid extension of the lens of frequently is unstable and ruptures .
Circular spaces appear which are occupied by a composite surface similar to the composite surface outside the lens .
The chief features on which I would insist here are ( 1 ) .
the relatively formation of the composite surface by increase in the mass of A per unit area until it is in tensile equilibrium with a convex lens of and ( 2 ) the fact that when a lens of A is extended form a sheet , the sheet is unstable if its thickness fall below a certain quantity .
When the fluid A has a sensible vapour tension\mdash ; such as benzene or ' Roy .
Soc. Proc 1911 , , vol. 84 , p. 220 ; also 1912 , .
, p. 608 .
occupied in forming the lenses , and the relative duration of particular stages depend upon the ratio of the components of , upon their nature , and upon the concentration of electrolytes in the water .
Increasing the i number of components as a rule lengthens the total time and the complexity the phenomena , and the vivid play of Newtonian colours is then very beautiful .
By increasing the number of components a composite sheet may be formed of films of different thicknesses which pass abruptiy into each $ other .
The whole surface shows sharply determined coloured areas , red , blue , green , bronze , etc. , which enduoe for days .
The Tension of Composite Fluid .
317 The phenomena ultimately depend upon the accumulation by diffusion of the most active constituents at the interface , and their complexity and durability are due to ths slowness with which tangential diffusion can occur owing to the small depth of the film .
The phenomena , occurring as hey do on the surface of water , may be said to take place in two S dimensions .
If they occupied the mass of the fluid , that is to say , if they were in three dimensions , the unstable sponges , films , and lenses would yield the phenomena of the colloidal state , and especially of gelation .
The horizontal networks which appear , and which are in an unstable state so far as surface eIlergy is cerned , must represent in a crude way the mechanism of a muscle reduced to two dimensions , for there can be .
little doubt now that the force of muscular contractionl is derived from in the energy of surfaces in the interior of each muscle fibre .
Curves of the change of tension produced by the spreading of A upon water , obtained by Wilhelmj 's method of measuring surface tension , were given in an earlier paper ( loc. cit. ) and it was noticed that , when disturbanoe due to hysteresis of the surface is avoided , the curve for certain substances consists of a series of straight lines .
I add here the curve for pure oleic acid ( fig. 1 ) .
The vapour pressure is so low as to render the error due to FIO .
1 .
vaporisation from the surface negligible , but , unfortunately , the acid leaks past the barriers used to contract the film by diffusion through the body of the water , so that the observed tension tends always to be too high .
In time , the oleic acid completely escapes from the control of the barriers , thus a contracted surface of tension was left overnight , two barriers close VOL. LXXXVIII.\mdash ; A. 2 stl'aight line .
the fuller knowledge now in my possession I regard FIG. 2 .
such curves as characteristic of films composed of two substances at least , an effect on the tension of the surface less than that of the } Measnrenlents of the tension throw some upon the singular features of these curves .
Let it first be supposed possible by the formation of a lens ( as .
by allowing vapour to condense on the surface iu the absence of nuclei ) continuously to increase the mass of per unit of surface area , a point will be reached when an independent surface of pure A is formed .
The therefore at and ends at Ts , both points determinable by experiment .
Of the intervening curve the first portion AB is horizontal or slightly undulating .
Lord Rayleigh interpreted it to be the region in which the quantity of A placed on the surface is insufficient to form a continuous * The sample of cymene used previously was found to contain a small percentage of an impurity with a high boiling point .
'Roy .
Soc. Proc 1912 , , vol. 86 , p. 623 .
The Tension of Composite Fluid .
319 sheet .
The objection to this interpretation is the sions of the molecule which follow from experiment .
Taking , for instance , pure oleic acid , the * : depth of the film of acid at the point is of the order cm .
Putting as the diameter of the hydrogen atom , a molecule of the acid regarded as a sphere would have by the Barlow-Pope theory a diameter of only cm .
Perhaps a way out of the difficulty may be found ultimately .
by the point as a critical point in the electric polarisation of the surface , also the calculated thickness of the film of A may be largely in excess of the real thickness , for complete immiscibility of A and cannot be postulated , and some loss must occur owing to diffusion into the mass of B. Lord Rayleigh remarks that " " an essentially different result would seem to require a repulsive force between the molecules ( of oil ) , resisting\ldquo ; contraction film .
There have already ointed out , evidence to show that : the oil spread on the surface is at a different electrical potential to the water .
A repulsion due to the charge on each molecule of oil must therefore exist .
: But this only increases the difficulty , since such a tangential repulsion would , if it operated alone , bring about a fall in the tension before a continuous layer of oil was formed on the surface .
It is open to us to suppose that one of the first effects of the oil is to undo a state of affairs at the surface of the water , namely , an average orientation of the water molecules themselves under the influence of the inwardly directed force of attraction , and thereby to increase the tension of the water , but a hypothesis which goes so far beyond ascertained fact cannot be so satisfactory as the direct explanation offered by Lord Rayleigh .
The significance of the inflection at fig. 1 ) is , I clear .
It is the point where the continuous uniform sheet of A spread on ceases to be stable and any further added quantity gathers into a lens .
This occurs when the tension of the composite plane surface is equal to .
The following table confirms this conclusion .
is the tension at the point as measured by Wilhelmj 's method .
Castor oil. .
Oleic acid Ricinohc acid Ethyi hydrocinnama .
( between and ) Benzene *Camphor is still active on a surfaoe on which a lens of this ester is standing , th6 space above being saturated with the vapour .
lbyleigh fixes the camphor point at order to maintain the surface against loss by evaporation it is necessary to have a flat lens of benzene , th refore Kg has a sensible value , and the tension observed is slightly lower than Tc .
The slope of the line CD is determined partly by the form of the lens or lenses on the surface , that is to say , by the quantities , and the density 'Roy .
Soc. Proc 1912 , , vol. 86 , p. 630 .
' The Tension of Composite fluid Surfaces .
321 satisfied .
This would make equal to the range of the attractive force between the fluids and A if the density of A on the composite surface be put equal to that of A in mass .
is the mass of A per unit area of surface .
The part of the curve , of unknown slope , would then relate entirely to the work expended in forming a layer of a new phase , namely pure and the process is complete at when the tension of the upper face becomes , and that of both faces .
The two tensions are now equal to the tension at , which , however , is that of a single true composite surface .
The diagram ( fig. 3 ) serve to make the explanation clearer .
On it are shown curves for four substances , the point being in each case put equal to .
The scale of the abscissae and the slope of the lines is entirely arbitrary .
At the point on each curve the tension of the composite surface has fallen to the equality , save in the case of the chemically saturated substance , when is always From to the composite surface is stable with resp to infinitesimal variations of the mass of A per unit area , but unstable with respect to finite variations .
That is to say , a lens cannot form spontaneously , because any tendency to a local accumulation of the fluid A will be resisted by the tension of the surface .
But if suitable nuclei are present , or if a lens of A be placed on the surface , condensation must occur .
If the curve from to be a straight line we have , as the equations of this part , ( 1 ) and , ( 2 ) being the mass of A per unit area of surface .
The part is a region of complete instability , hence , as has already been pointed out , when a lens of A is extended to form a sheet , the sheet ruptures when its depth is diminished below a certain minimum .
The form and slope of this part are entirely unknown .
The changes of the vapour pressure of A in equilibrium with the composite surface cannot be followed with any certainty , though something may be said about them .
At A on the curve the vapour pressure of the fluid equation which can be integrated only if we know the form of the function 4 ! .
Equations connecting the vapour pressure with the tension of the cpmposite surface are given by Warburg and Cantor , they cannot be trusted owing to faulty reasoning .
In both cases they are derived by equating the balance of work gained to the change in the potential of the surface when fluid is evaporated from A and condensed on to the surfaoe of , the series of operations performed upon A being essentially those used by HelmholtzS in his calculation of the change of free energy when a quantity of water is evaporated from the plane surface of a mass of pure water , and condensed into a solution of salt in water .
In the final process , when the water vapour is condensed into the salt solution , Helmholtz puts the pressure constant , and the work therefore simply equal to .
This is correct only if the mass of the salt solution be infinite .
Warburg and Cantor follow the procedure of Helmholtz in that they put the pressure of the vapour of A constant while it is being condensed on to the surface of B. This is equivalent to putting constant throughout the operation , and is obviously wrong .
Something may be said in answer to two questions , namely , ( 1 ) at what 'Trans .
Conn. Acad 1878 , vol. 3 , p. 398 .
'Ann .
Physik .
Chem 1886 , TOU .
, 1895 , vol. 66 , p. 492 .
S 'Mem .
Phys. , Part II .
Since is necessarily positive the curve would begin to ascend when becomes negative\mdash ; that is , when for any further addition of A to the surface its vapour pressure falls .
This would happen along ; and \amp ; the fall in vapour pressure would be strictly analogous to that which occurs when spheres of fluid in equilibrium with vapour about them fuse ; to form a larger sphere or a plane sheet .
At therefore , the vapour pressure of A would be maximal .
It vould also be supersaturated with reference to a plane surface of , since along it is falling to the pressure of saturated vapour at E. ; Passing backwards from towards the vapour tension of A at the composite surface is at first greater than the vapour pressure of pure and the surface would be in both tensile and vapour equilibrium with a convex lens of A. At some point the tension of the vapoul at the composite surface falls to an equality with that of a plane surface of pure A. The point at which this happens will depend upon the pressure of the saturated vapour and , since changes only slowly with temperature , the point would fall lower and lower on the line CE ' as the temperature rises .
: That this is so appears from measurements made by Clark* of the tension at the interface of ethyl ether and glycerine , and of a surface of glycerine in contact with a vapour space in which the vapour was maintained in equilibrium with the pure ether .
The quantity is always except near the critical point of ether , when it is .
It is interesting that in both cases the curves which connect temperature and and respectively are sensibly straight lines .
The curve for is at ordinary temperature high above that of but , falling more rapidly , it cuts the latter at about \mdash ; the critical temperature of ethyl ether being The way in which vapour is as it were flung off a surface during spreading points very decisively to a large rise in the tension of the of A at some stage in the process .
Ethyl hydrocinnamate boils at according to Beilstein , and as it is immiscible with water I hoped this ester would serve for measurements of the change of tension produced by thin films spread on water .
It proved , however , to be quite impossible to obtain any measurements owing to the fact that quite large quantities of the ester 'Proc .
Amer .
Acad. of and Sciences , ' 1906 , vol. 41 , p. 361 .
lenses being formed by and cast off from the edge of the main sheet .
The result in the main is that the potential energy of a lens of ester standing on 44 ; : a surface of high tension is partly expended in boiling the ester off the surface .
Any explanation of the variation of tension with the varying depth of the film of A to be adequate must include an explanation of the kable movements of e.g. a pair of lenses of carbon bisulphide on a clean water surface .
To exhibit the movements to perfection the lenses must be small and highly convex .
If they come within about 1 or 2 cm .
of each other they are violently attracted and move directly towards each other until the edges are nearly in contact , when equally violin ropulsion occurs .
In this way rapid alternate attraction and repulsion ocours , always , if undisturbed , accurately along a line joining the centres .
The explanation is I think as follows :Consider each lens when out of the sphere of influence of the other .
Vapour is being condensed on to the water face to form a film which spreads as a film centrifugally until it is destroyed by evaporation .
The lens is thus the centre of an area of lowered tension , which therefore forms a depression .
When two lenses come sufficiently close together these depressed areas fuse and a trough is formed between the centres along which they move\mdash ; the trough deepening as they approach .
With the near approach of the lenses the vapour sheet is thickened until and a repulsion .
The obstacle to the fusion of the lenses which is so obvious is the portion of the curve and a pair of lenses must acquire S a critical quantity of kinetic energy before they can break through it .
A relation found by Antonoff from measurements of interfacial tensions would , when it holds , fix the vapour pressure of the fluid A at the point on the curve as very near to that of a saturated solution of A in B. Using partially miscible substances , Antonoff*finds that the interfacial tension is equal to the difference between the tensions of the two phases .
That is , in !
our notation , , ( 4 ) ; and at the limit when the fluids are immiscible Clearly the relation is not universal , nor even a very common one , for , ffiking fluids sensibly immiscible with water , we have Table II .
Cyclohexane 65 Carbon tetrachlol : id 50 Octane 5 } 53 Castor oil 23 Oil " " \ldquo ; 61 Ethyl cinnamate 24 Carbon bisulphide 56 hydrocinnamate 24 It be noted that cyclohexane , oil " " and carbon bisulphide are exceptions to Quincke 's that TAB is always less than I am at a loss how to criticise Antonoff 's values , since they purport to be ealoulated by the erroneous equation .
This would results 40 to 50 per cent. wrong , but his figures with mine in the very low value for the quantity for alcohols , and in the value found for benzene .
The values for calculated from his figures also with those found by me for alcohols . .
It is possible that though the faulty equation is quoted with approval , the experimental results were obtained with tubes standardised by measuring the tension of some pure fluid whose tension is known .
The explanation of Antonoff 's relation is simple , and its theoretical significance not great .
If water is saturated with a fluid which causes the tension of water to fall , the surface will also become saturated with this fluid .
When this happens is reduced to the tension at on the curve , 'Journ .
de Chim .
Physique , ' 1907 , vol. 5 , p. 372 .
show that the more accurately and rapidly the series of measurements are made the more closely does the curve approximate to a straight line .
The most successful series I was able to obtain with oleic acid is plotted in fig. 4 , and the constants are given in the third column of Table III .
barriers were used to c*ontain the film and , as far as possible , kept touching each other throughout .
The water used was carefully cleaned tap water .
The readings were taken rapidly and were very steady until the first inflection of the curve at ; here , owing to some unknown cause , leakage occuroed , !
the tension rising while the weight was being recorded .
At the tension rose abruptly to owing to the formation of exceedingly fine lenses , each of which appeared under a hand lens as little more than a point .
A further slow rise from to occurred in nine minutes , and during this nine minutes some lyoopodium dust drifted .
away from the barriers on the side 4 'Phil .
Mag 1899 , [ 6 ] , vol. 48 , p. 331 .
Ibid. , 1892 , vol. 3$ , p. 468 .
6 Ts .
26188 27892 28652 67 .
27460\mdash ; 65.4 26503\mdash ; 20046 56.5 55.0 54.6 58 .
49.9 44 .
\mdash ; 40.9 ' Composite Fluid Surfaces .
327 lm of oleic acid .
The rise OP therefore was the bal'riers .
Table IIL 15.658 15.127\mdash ; 15180 15.562 15830\mdash ; 15198 15262 16.694 15.587 16.796 15.486 \mdash ; \mdash ; 14.831 14.467 refer to three separate measurements made with pure oleic acid .
to castor oil .
, the constants are in arbitrary units .
, the units are dynes per linea centimetre and cm .
and we have and But therefore .
and , ( 6 ) ; ( 7 ) and , since is by aeriment equal to a constant , , ( 8 ) where is another constant .
constant the form of these functions must be the same .
We may perhaps proceed a further .
Laplace assumed that the .
function of the attractive force between matter at minute distances is the same in all cases , " " the attraction differing merely by coefficients to densities in the theory of gravitation On this assumption we may write 3 equation ) and is then seen to be a constant , a result which is in agreement with :cS the suggestion of Young that molecular attraction is a force which is constant .3 in magnitude over the very minute range through which it acts .
But the range.in question must be less even than the thickness of the films of oil .
which when spread upon water reduce the tension , for , if be constant , then since ) this last function is equal to .
The physical significance of this last relation would be that each layer of molecules of A spread on the surface is attracted only by the layer of molecules previously there with which it comes into contact , a result not inconsistent with many aspects of this difficult question but altogether inconsistent with the view that the attraction of for A ceases only at the point in the curve .
Though such conclusions , based as they are upon an assumption of uniform density throughout an interface , cannot have great value , they are interesting as pointing to an unexpected simplicity in molecular forces .
The simple spatial relations which are the essence of the Barlow-Pope theory of the molecular structure of close-packed forms of matter also seems to demand some simple law .
If there were , for instance , alternating zones of attraction and repulsion about each molecule , more than one arrangement in space would satisfy the condition of minimal potential , and it would be possible by adequate pressure to compress a fluid to a } which it would continue to occupy when the pressure was lowered .
The unexpectedly simple relation a constant would appear to hold for an interface between solid and fluid .
A large amount of work has shown that when a solute such as iodine is condensed on bo the surface of , for instance , animal charcoal , the equilibrium reached is given by the empirical equation , where is the mass of the solute condensed on to the surface , the final concentration of the solution , and and are parameters .
Putting the area of the surface of the solid as unity , this may be written attraction of for A. When the structure is complete the tension is reached and any further addition of molecules of A to the surface does $ not disturb the architecture .
But , just as there are in many cases two arrangements of the same molecules in the solid state , that of the glass , and , that of the crystal , the former containing the greater quantity of energy per unit of mass , so in the formation of these films of matter the architecture actually reached may not always be that of least potential .
iption of Figures.\mdash ; Save for the diagram fig. 3 the scale of the ordinates is dynes per linear centimetre , that of the abscissae 1 ?
cm .
Lord ( ' Phil. Mag 1892 , vol. 38 , p. 309 ) has shown that the deviations irom Fresnel 's formula for the reflection of light at a liquid surface may be traced to the presence of a fllm of impurity on the surface .
The residual deviation which persists when all such films are swept away may , perhaps , be attributed to the real surface film the pure fluid .
to say with the purest acid which Kahlbaum prepares , further purified by fractional crystallisation .
The line BC has been followed by Miss Pockell 's method into the unstable region , until the end of the continuous line .
The izontal line through marks the tension which is equal to the sum of the tension of the pure acid and that of the interface between acid and water or .
Fig. 2 illustrates a prolonged experiment with oleic acid .
The curve is interrupted at one point where there was an accident to the the result being to alter the slope of the curve .
The curve was : followed without pause , save for the accident just alluded to , to the point [ when the barriers were left in position .
The tension rose in 10 minutes to first dot , and 20 hours later it was found to be at the top of the vertical line .
By again concentrating as much as possible of the oleic acid on to the same area the tension fell to the point marked with a thick cross .
The contraction of the surface from to was made very rapidly .
The ringed dot marks the tension when mgrm .
of oleic acid was spread on to a surface of clean distilled water c in extent .
For this tension therefore grnL and .
The scale of the cissae is based upon this measurement .
The remaining ures are adequately explained in the text .
1.\mdash ; In a previous paper*I pointed out that the mechanical stability of a composite surface is maximal just beyond the point in the curve when the tension begins to fall .
The measure of mechanical stability was the time which elapsed between the formation and bursting of bubbles of a particular size on the surface .
The rise in mechanical stability from zero to a maximum was found to occur at a point some distance lower on the curve than B. The reason for this displacement is simple .
When a film is formed at the surface by allowing a bubble of air to ascend from below , the surface is stretched and the quantity , that is the conoentration of the fluid A spread upon the water , thereby diminished .
The effect is to put the state of the surface backwards along the curve towards the inflection at B. If the film is sufficiently stretched , that is if the bubble is large enough to make , the bubble at once bursts .
The amount of displacement of the rise of mechanical stability forwards along the curve is thus a function of the radius of the bubble of air .
With infinitely small bubbles it would coincide with the inflection at , where theory would place it .
Appendix 2.\mdash ; An attempt to measure the tension of a composite surface in 'Roy .
Soc. Proc 1912 , , vol. 86 , p. 627 .
a convex lens which slowly flattens out .
The flattening cannot be due to an increase in above since the condensed vapour lowers the tension , as is readily seen by admitting a little air sO as to relieve the concentration of the vapour of , when the flattened lens at once contracts .
Append 3.\mdash ; The arguments employed in this paper throw light upon a suggestion put forward by Laplace , and incidentally on that vexed point .
$ the physical significance to be attributed to the term " " density\ldquo ; as used by Laplace .
By the Young-Laplace theory we have for the intrinsic pressure and the surface tension of a fluid respectively ( 10 ) and .
( 11 ) Laplace assumes that , like gravity , is a function depending only on the density of the substance , and we may therefore write ( 12 ) and .
( 13 ) From ( 10 ) and ( 12 ) follows It has been objected that the facts do not accord with this relation .
This The Tension of Cornposite Fluid Surfaces .
833 is true , but the cause may lie either in the fact that is constant only for similar fluids\mdash ; that is for fluids of the same chemical type , or in the difficulty in identifying the density of Laplace 's theory with a particular physical property .
Comparing equations ( 3 ) of the paper preceding and ( 12 ) we get If the density be taken as a molecular quantity then and .
From this we can derive equation ( 4 ) of the preceding paper as the expression for the interfacial tension .
The expression is now seen to be wrongly derived , the false assumptions being the identity of with , and of with \amp ; .
And for a similar reason the expression is inadmissible .
A- VOL. LXXXVIIL\mdash ; A.
|
rspa_1913_0033 | 0950-1207 | A simple method of finding the approximate period of stable systems. | 333 | 335 | 1,913 | 88 | 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.1913.0033 | en | rspa | 1,910 | 1,900 | 1,900 | 1 | 19 | 640 | http://corpora.clarin-d.uni-saarland.de/surprisal/6.0.3/?id=rspa_1913_0033 | 10.1098/rspa.1913.0033 | null | null | null | Fluid Dynamics | 44.82838 | Tables | 38.777011 | Fluid Dynamics | [
45.957340240478516,
-28.135744094848633
] | ]\gt ; true , but Approximate Periodof Stable 333 is true , but the cause may lie either in the fact that is constant only for similar fluids\mdash ; that is for fluids of the same chemical type , or in the difficulty in the density of Laplace 's theory with aparticular physical property .
: ions ( 3 ) of the paper preceding and ( 12 ) we get If the density be taken as a molecular quantity then and .
From this we can derive equation ( 4 ) of the preceding paper as the expressiofi for the interfacial tension .
The expression is now seen to be wrongly derived , the false assumptions being the identity of with , and of with .
And for a similar reason the expression is inadmissible .
A Simple Method of Finding the Approximate Period of Stable Systems .
By A. MALLOCK , F.RS .
Received February Read March In practical engineering work it is often a great convenience to be able to find the period of a structure , the calculation of which , by ordinary mathematical processes , would be difficult or even impossible .
To find the period of a structure for any particular mode of vibration involves a knowledge of its stiffness ( regarded as a spring ) and of the distribution of the mass , but if the latter is known , even approximately , a knowledge of the period gives the stiffness , and the defleotions for a given load can be found by simple arithmetic .
In nearly every case likely to occur in practice a stable ructure can b9 represented , as far as its elastic displacements are concerned , by an equivalent pendulum , a pendulum , that is , which has the same period as the particular mode of vibration under consideration , and an effective mass equal to that part of the mass of the structure which is subject to vibration , but concentrated at what , for the present purpose , may be called the centre of oscillation .
The proposition on which the simple determination of period above referred to depends is as follows:\mdash ; VOL LXXXVIII .
1913 .
] Finding the Period of Stable Systems .
335 first of these corrections is small for ships of ordinary proportions , and decreases with the ratio of draught to length .
The second increases the period ( as calculated from the formula ) by something like 10 per cent. The precise amount depends on the ship 's " " lines ( 5 ) If a vertical column when struck is found to give a note of a certain pitch , the principle here used allows of the immediate determination of its flexure under any given lateral force , and if the nature and dimensions of the column are known , the pitch under no load can be determined from first principles. .
As the load on the ends increases , the natural period increases also , becoming infinite when the unstable condition is approached and hence the observation of the actual pitch gives a measure of the load which is borne .
I first noticed the relation here stated in 1878 , and since that time have found it of great use in almost countless investigations , but except for one case ( involving the same principle ) referred to by D. Bernoulli it does not , so far as I am aware , appear to have been stated in any publication .
[ April 10 , 1913.\mdash ; Dr. Schuster has pointed out to me that there were mistakes in the original text of examples ( 2 ) , ( 3 ) , and ( 4 ) .
These have now been corrected.\mdash ; A. M. ]
|
rspa_1913_0034 | 0950-1207 | The motion of electrons in gases. | 336 | 347 | 1,913 | 88 | Proceedings of the Royal Society of London. Series A, Containing Papers of a Mathematical and Physical Character | Prof J. S. Townsend, F. R. S.|H. T. Tizard | article | 6.0.4 | http://dx.doi.org/10.1098/rspa.1913.0034 | en | rspa | 1,910 | 1,900 | 1,900 | 3 | 88 | 2,546 | http://corpora.clarin-d.uni-saarland.de/surprisal/6.0.3/?id=rspa_1913_0034 | 10.1098/rspa.1913.0034 | null | null | null | Fluid Dynamics | 40.104731 | Tables | 25.969469 | Fluid Dynamics | [
7.06660795211792,
-67.8831558227539
] | ]\gt ; received by the three insulated electrodes , and .
These were portions of a disc 7 cm .
in diameter , the central section being mm. wide and separated from the two equal side plates and by air gaps mm. a wide .
The narrow gaps between the electrodes were parallel to the direction of the slit in B. In the calculations it will be supposed that the electrode is 5 mm. wide , and that the side plates and come within mm. of the central line .
When no magnetic force is the charges and received by the electrodes and were equal and the centre of the stream fell on the centre of .
If be the charge received by the ratio depends on the electric force and the velocity of agitation of the ions .
In the previous experiments the factor by which the energy of agitation of the ions exceeded that of the surrounding molecules was deduced from observations of the lateral diffusion of a stream of circular section after traversing a distance of 7 cm .
under the action of the electric force .
The stream was received on a small circular electrode in the centre of a large metal ring , so that the proportion of the charge received by the small disc diminishes rapidly as the motion of agitation increases .
The apparatus was therefore suitable for determining the smaller values of the quantity The apparatus described above was better suited for the determination of large increases in the velocity of agitation and the values of may easily be found from the ratio , as is seen from the following investigation .
3 .
Let the origin of co-ordinates be taken in the centre of the slit , the axis of being normal to the plate and the axis of parallel to the length of the slit .
Since the central electrode is much than the slit the diffusion in the direction does not affect the number of ions that are received on the electrode , and it will only be necessary to find the motion in the directions and Considering the ions that pass at a uniform rate through a narrow section in the centre of the slit parallel to the axis of , the distribution in the electric field when the motion becomes steady is given by the equation* No When the electric force is measured in volts per centimetre , and the values of the constants No and are subsbituted , the equation becomes * J. S. Townsend , ' Boy .
Soc. Proc 1908 , , vol. 81 , p. 469 .
by neglecting the term is probably smaller than the experimental error .
It thus appears that the distribution of the quantity as expressed in terms of and is the same as the distribution of temperature , in terms of and , in an infinite solid initially at zero temperature throughout , except at the plane where the temperature has a constant value when The temperature is obtained from the equation .
and the solution given by Fourier is In the problem of the distribution of ions in the space between the plates $* and the sulface conditions are when for all values of except , so that in terms of and is given by the equation !
: $ The distance of the electrodes from the origin was 4 cm .
and the central } electrode was 5 mm. wide , so that the ratio , of the charge received by ] the central electrode to the total , is 1913 .
The Motion of Electrons in Gases .
339 $ where When various values are given to the quantity the corresponding ratios may be obtained from the tables of the values of the integrals .
It is necessary to take into consideration the width of the slit , since with the larger values of the proportion of the ions coming through a section of the slit near the edge that arrive on the central electrode is somewhat less than the proportion of those that come through at the centre .
The exact proportion for any section of the slit is easily calculated and the ratio when the ions come through all sections of the slit equally may be found in terms of The curve , , gives the values of in terms of 4 When the ratio is determined experimentally with an electric force acting between and may be found from the curve , fig. 2 , and the corresponding value of may be determined .
The curves , fig. 3 , give the values of found for air at various pressures .
The ratio corresponding to a given force and pressure depends on the dryness of the gas .
When the pressure is reduced to the required value , may be observed at intervals while the small quantity of moisture in the apparatus is removed slowly by the phosphorus pentoxide .
As the air dries the value of diminishes and after some weeks a constant minimum value is attained .
The continuous curves , fig. 3 , represent the minimum values obtained for dry air with different forces and pressures .
Several experiments were made with air which had not been dried very completely .
The values of are then practically the same as those obtained the amount of water vapour present , provided the amount exceeds a certain $ small value .
The dotted curve , fig. 3 , illustrateH the behaviour of air containing a small quantity of moisture , the pressule being mm. With a force of 1 volt per centimetre , which is the value of in the theoretical : curve at the point .
The two curves continue to coincide for some distance as increases , but when becomes 2 volts per centimetre , , as determined experimentally , is , the theoretical curve giving when .
The value of corresponding to the ratio is , so that when .
The value of reaches a maximum at and an increase in the force is accompanied by a remarkable increase in the divergence of the stream .
The ratio attains a minimum value 03 at the point where , the value of being .
Further increases in the force cause the divergence to diminish , and gradually the dotted curve takes a place between the two curves for dry air at and mm. pressure .
For values of exceeding 30 the values of are practically the same as for dry air at pressure .
' small .
For large forces the effect of the water vapour , and the .
electrons move freely with akinetic energy of agitation exceeding that of the surrounding molecules by the factor .
In the particular example illustrated by the dotted curve the effect of the water vapour disappears rapidly between the points A and and when the force exceeds 30 volts per centimetre the electrons move as in dry air .
When the amount of water vapour increases , the ratios and the forces corresponding to the maximum and minimum points A and , increase .
For different pressures , when the amount of moisture is approximately : proportional to the total pressure , the forces corresponding to the points .
and are also approximate]y proportional to the pressure .
This is interesting , : ; from a theoretlcal point of since these properties of the electrons depend on the velocity acquired between collisions with molecules , so that any particular effect should be obtained with the same value of if the proportion of the different gases that are present is not altered when the total pressure is altered .
5 .
The values of for dry air were obtained from the curves , fig. 3 , and it was found that depends on the ratio .
This is shown by the following examples of the numbers obtained from experiments at different pressures when is approximately constant:\mdash ; The agreement .
between the different determinations for values of between and was not as accurate as with the higher values .
This is probably due to the fact that small quantities of impurities have more effect when the lower forces are acting .
The results of the experiments on the lateral diffusion may be represented by a single curve giving as a function of .
The smaller values of from to are given in the curve , fig. 4 , and the larger values from to are given in the curve , fig. 5 .
Prof. J. S. Townsend and Mr. ] FIG. 4 .
FIG. 5 .
values obtained by Haselfoot for ions generated by ultra-violet light .
The conclusions to be drawn from these experiments depend on certain formulae that have been obtained for cases in which the velocity of agitation of the ions is large compared with the velocity under an electric force .
It will be seen from these investigations that when exc , eeds the ions in dry air are in the electronic state , so that the value of may be taken as .
The value of for a molecule of air being , the masses in the proportion , so that the velocity of agitation of an electron in thermal equilibrium with air is 230 times the velociby of agitation of a lectric forces acting exceed talue bactor rder thatmolecule oecond.ctual velocities ogitation w the ordinary formulae derived from the kinetic theory of gases should apply to the motion of the electrons it is necessary that the velocity in the direction of the electric force should be considerably less than the quantity .
: ' 6 .
The velocities were with the same apparatus for the same forces and pressures A transverse maguetic force was produced by a current in a pair of large circular coils outside the apparatus , the direction of the force being parallel to the slits .
The stream was then deflected so that the centre no longer fell on the centre of the electrode and the charge acquired by the electrode inc'reased with the force G. In these experiments the electrodes and were joined and the current in the coils was adjusted until the charge received by the electrodes and was equal to the charge acquired by the electrode .
The centre of the stream was thus deflected through mm. ( half the width of the central plate ) while the electrons travelled 4 cm .
in the direction of the electric force .
The magnetic forces required to deflect the centre of the stream through the angle when the ions are moving under the electric force X are given by the curves ( fig. 6 ) .
The different curves correspond to the different pressures of the air , which varied from to mm. The velocity under the electric force is given by the equation which expresses the condition that the direction of motion of the centre of the stream is along the resultant of the forces and We .
The latter force being small , the velocities may be assumed to be the same as those in the experiments on the lateral diffusion when the forces were acting . .
It follows that is a function of and the velocities may be expressed by means of a single curve .
The portion of the curve corresponding to values FIG. 8 .
7 .
The following table gives a comparison between the velocity of agitation and the velocity in the direction of the electric force , in terms of The velocity of a charged particle moving under an electric force is given proximately by the formula , when the mass of the particle is small compared with that of a molecule of the gas , and the velocity of gitation u is large compared with being the mean free path of the particle .
When the pressure is constant is also constant , and the velocity is proportional to when and are independent of .
In these cases is constant , being the mass of an electron , but increases with so that does not increase in proportion to the force .
The results of the experiments are thus in accordance with the theory , since increases less rapidly than when is constant ; in fact , the where is the mass of the charged particle , that of a molecule of the gas , the sum of the radii of the particle and a molecule , the number of molecules of the gas per cubic centimetre , and three-fourths of the reciprocal of the kinetic energy of agitation of the particle or a molecule of the gas .
Since the mass of the electron is small compared with a molecule the ratio reduces to , and is the mean free path of the electron .
The velocity of an electron thus becomes being the velocity of agitation of the electron .
The velocity is therefore independent of the mass of the molecules and is proportional to , the mean interval between collisions .
Langevin 's formula is deduced on the hypothesis that the mean energy of agitation of the particle is the same as that of a molecule of the gas .
When the masses are of the same order of magnitude the interval between P. Langevin , ' Ann de Chim .
et de Phys 1906 , , p. 246 . ! .
; must baken actual velocity ogitation , which exceeds that of agitation oarticle mHence iealing wlectrons telocity corresponding to a particle in thermal equilibrium with the molecules of tha .
gas by the factor a- : The value of for the electrffied particle may be obtained from the above .
equation by eliminating the quantity .
Thus mean faken awhere Nlimetre pressure t that tlectronand eiven bormula is cm .
Hence .
The values of thus obtained from the determinations of and corresponding to the different values of are given in the above table ( p. 345 ) .
The numbers obtained for do not differ very much from the value found by the more acourate methods uuder conditions in which the effects of collisions between electrons and molecules may be neglected .
The differences between the values found for for different values of are not entirely due to experimental errors , although the probable error in the final results is greater than that in the direct measurements , since the square of the velocity is involved in the formula for .
The nature of the collisions between electrons and molecules may not resemble the collisions between elastic spheres to the same extent for different values of the velocity * Mr. F. B. Pidduck ( p. 296 , supra ) has made a theoretical investigation of the motion of ions in gases ; he shows that when the negative ions are in the eIectronic state their velocity of agitation may become abnormally large , and the above values of and may be explained on the hypothesis that the collisions between electrons and molecules are such as would occur between imperfectly elastic spheres .
|
rspa_1913_0035 | 0950-1207 | Optical investigation of solidified gases.\#x2014;III. The crystalline properties of chlorine and bromine. | 348 | 353 | 1,913 | 88 | 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.1913.0035 | en | rspa | 1,910 | 1,900 | 1,900 | 4 | 114 | 2,856 | http://corpora.clarin-d.uni-saarland.de/surprisal/6.0.3/?id=rspa_1913_0035 | 10.1098/rspa.1913.0035 | null | null | null | Thermodynamics | 34.529757 | Optics | 31.616088 | Thermodynamics | [
-9.22829532623291,
-44.949073791503906
] | 348 Optical Investigation of Solidified Gases.\#151 ; III .
The Crystalline Properties of Chlorine and Bromine .
By Walter Wahl , Ph. D. ( Communicated by Sir James Dewar , F.R.S. Received February 26 , \#151 ; Read March 13 , 1913 .
) ( From the Davy-Faraday Laboratory of the Royal Institution .
) Of the crystalline properties of the halogens only those of iodine are known .
Of bromine , Arctowski has , at \#151 ; 78 ' , obtained red needles from a solution in carbon bisulphide , * but these have not been further examined .
Dewar , quite early in his researches at low temperatures , stated that solid bromine gets much lighter in colour when it is cooled to the temperature of liquid hydrogen .
Chlorine and fluorinef behave similarly ; beyond this nothing is known as to the crystal properties of solid chlorine .
Chlorine and bromine have , therefore , been investigated in continuation of the work described in ' Proc. Roy .
Soc. , ' A , vol. 87 , p. 371 , and A , vol. 88 , p. 61 .
Chlorine .
In order to obtain pure chlorine the gas was prepared from gold chloride and generated in the same piece of apparatus as was subsequently used for crystallising it .
The device is shown in the figure .
The stem of a quartz-glass crystallisation vessel ( C.Y. ) of the kind To pump To pump * Arctowski , * Zeitschrift fur Anorgan .
Chemie , ' 1895 , vol. 10 , p. 25 .
+ Moissan and Dewar , ' Comptes Rendus , ' 1903 , vol. 136 , p. 642 .
Optical Investigation of Solidified Gases .
349 previously described was first passed through a rubber stopcock fitting into a small vacuum vessel , and to this stem was then sealed a kind of small fractionating bulb of quartz-glass ( see fig. ) , the connecting tube being bent at right angles .
The bulb itself had a capacity of about 50 c.c. About 15 grains of gold chloride were brought into the bulb , and by means of a short piece of rubber pressure-tubing the side-tube was then connected to a U-tube , which again was connected to a charcoal bulb ( right-hand portion of figure ) .
The U-tube and the charcoal bulb were then immersed in liquid air and the interior of the entire quartz-glass apparatus was thus dried in high vacuum for a considerable time .
The quartz-glass bulb containing the gold chloride was subsequently heated in an oil bath , the temperature being raised gradually up to 125 ' .
In this high vacuum the gold chloride began to give off some chlorine at about 100 ' , and at 125 ' the chlorine was so freely given off that the heating was discontinued .
The moisture and HC1 , resulting from the action of chlorine on the moisture , together with the quantity of chlorine already given off by the gold chloride and any products possibly arising by the action of the chlorine on the rubber connection between quartz and glass , were in this way condensed and solidified in the U-tube immersed in liquid air .
The quartz-glass bulb was then allowed to cool , the charcoal vacuum being maintained all the time , and the quartz-glass apparatus sealed off at a ( see fig. ) by an oxygen blowpipe .
A syphon and a tube connected with a mercury barometer valve , and through this to the vacuum tank of the laboratory , were then inserted into the rubber stopcock , and this fixed into the vacuum vessel ( left portion of figure ) .
The liquefaction and solidification of the chlorine was effected in the following manner .
The crystallisation vessel was first cooled to some extent by admitting a small quantity of liquid air into the vacuum vessel and letting it boil off .
The quartz-glass bulb containing the gold chloride was then gently heated with a burning match , the heat from three or four matches being quite sufficient to generate the small quantity of chlorine needed to fill the minute space between the discs of the crystallisation vessel and the lower part of its stem .
When the crystallisation vessel had been cooled strongly before the gold chloride was heated , the chlorine was condensed in the form of quite minute isometric crystals on the walls of the discs of the crystallisation vessel .
These small crystals were very sharp and perfect , showed very brilliant light reflexes ' and seemed to possess a high refractive index .
Between crossed nicols they showed bright interference-colours and are thus double-refracting .
Owing to their small size it was not possible to make out anything as to their crystalline form .
vol. lxxxviii.\#151 ; A. 2 c Dr. W. Wahl .
[ Feb. 26 , If the crystallisation vessel is slowly cooled while the chlorine is generated , this can easily be condensed as a liquid and subsequently crystallised by further cooling .
It then solidifies in the form of very beautiful crystalline growth-structures .
These grow chiefly in the direction of a principal axis , simultaneously sending out branches to each side , at an angle of about 40 ' to 50 ' with the principal axis .
The space between the branches of the growth-structure is filled up , in a later stage of the crystallisation process , and in this way homogeneous crystal fields result .
When cooled further , a distinct cleavage parallel to the principal axis of the growth-structure is formed .
In spite of the thinness of the crystal film between the discs of the crystallisation vessel , the crystal fields appear distinctly pale yellow in colour .
The polarised light travelling parallel to the cleavage and principal axis is more strongly absorbed , and the transmitted light is of a deeper yellow , with a greenish tint , than is the polarised light passing in directions at right angles to the principal axis .
There is a slight difference in the degree of absorption in the two directions at right angles to the principal axis , but in such a thin crystal layer no difference in colour is noticeable between these directions .
The crystallised chlorine is , in sections both parallel and at right angles to the principal axis , strongly double-refracting .
The extinction between crossed nicols is parallel to the principal axis , as indicated by the cleavage .
Chlorine thus belongs to the orthorhombic system .
When the crystallised chlorine is further cooled the cleavage is further developed , but no polymorphic change has been observed at temperatures between that of the melting point and that of liquid air .
The absorption in the direction parallel to the principal axis gradually diminishes when the preparation is cooled , and at liquid-air temperatures scarcely any difference in colour in different directions is noticeable , the crystals appearing quite pale , scarcely coloured at all .
Bromine .
Some preliminary tests were made with ordinary bromine , brought directly into the stem of a crystallisation vessel and then sucked into the narrow space between the quartz-glass discs by alternately gently heating and cooling these .
As it was found that solid bromine is quite sufficiently transparent in such thin layers , a small sample of pure dry bromine was investigated in the piece of apparatus used for the investigation of chlorine .
A quantity of pure bromine ( " Kahlbaum " ) and some phosphorus pentoxide were brought into a small glass bulb provided with two tube-necks .
One of these was drawn out so as to fit into the open end of the 1913 .
] Optical Investigation of Solidified Gases .
small side-tube , ay of the quartz-glass apparatus .
The joint was made secure by slipping a piece of rubber pressure-tubing over it .
This acted as a spring , pressing the parts together .
The other tube of the bulb was connected with a U-tube'immersed in liquid air , and this with a charcoal bulb .
The bromine contained in the glass bulb was frozen by applying to it a wad of cotton-wool drenched in liquid air .
The apparatus was then exhausted by means of the charcoal and sealed off between the glass bulb containing the bromine and phosphorus pentoxide and the U-tube .
The quartz-glass apparatus and the bromine were in this way left to dry in vacuum over phosphorus pentoxide .
Subsequently , part of the bromine , about 1 c.c. , was sublimated over into the quartz-glass bulb by cooling this with liquid air .
The quartz-glass apparatus was then sealed off .
The bromine was sublimated over into the crystallisation vessel by cooling this with liquid air , and investigated as described in the previous cases .
Crystallised bromine is very similar to crystallised chlorine , only all the properties appear more pronounced .
The most striking feature is the strong pleochroism .
The crystal grains and fields show a tendency to develop in prismatic forms , and a prismatic cleavage is very distinct .
There is also an indication of a basal cleavage , but this becomes distinct only at low temperatures .
The prismatic cleavage angle is about 70 ' .
The double refraction is strong , and the extinction is parallel to the cleavage\#151 ; that is , to the principal axis\#151 ; and in sections at right angles to the principal axis it is parallel to the line bisecting the cleavage angle .
The absorption is : dark brownish red in the direction of the prism axis , yellowish red in the direction of a line bisecting the smaller prism-angle , and pale yellowish green in the direction of the line bisecting the larger prism-angle .
On cooling , the strong absorption ' in the direction parallel to the prism-axis rapidly diminishes , and at the same time the transmitted light gradually becomes more yellowish red , and subsequently yellow .
Also , in the direction of yellowish-red absorption a similar change takes place , resulting in a pale yellow colour at liquid-air temperature .
In the case of the third principal direction of absorption it is difficult to observe if a change takes place or not , as the colour is already so light at temperatures close to the melting point .
The change in colour of solid bromine from brownish red , nearly black as it appears near the melting point , to very pale yellow at the temperature of liquid air , and subsequently to quite a pale tint at the temperature of liquid hydrogen , as described by Sir James Dewar , is thus principally due to a gradual disappearance of the strong trichroism which it possesses at temperatures close to the melting point , the crystals assuming at low temperatur 2 c 2 Dr. W. Wahl .
[ Feb. 26 , more or less the colour they exhibit at high temperature in one certain crystallographic direction .
An alteration of the pleochroism with change of the temperature has been observed by Kirchhoff in the case of green tourmaline.* * * S The above optical characters , as well as the cleavage , show that bromine crystallises in the orthorhombic system .
No polymorphic change has been observed in the temperature range comprised between the melting point and that of liquid air .
The Relations between the Crystalline Properties oj Chlorine , Bromine , and Iodine .
Iodine has been investigated crystallographically by Mitscherlich , who found that it crystallises in the rhombic system and with a prism-angle of 67 ' 12'.f Recently , v. Fedorow , investigating iodine crystals that had sublimated on the asbestos stopper of a reagent bottle , found that these consisted both of the ordinary rhombic tablets and of prisms which belong to the monoclinic system .
J Both kinds of crystals are very similar in colour and general appearance .
Iodine is thus dimorphic .
Both forms can be obtained from solutions in CS2 , CHC13 , alcohol , and petrol-ether , the monoclinic being formed when the solution is very rapidly evaporated , the ordinary rhombic form when the solution is allowed to evaporate slowly .
Y. Kurbatoff found , in addition , that on sublimation of iodine the ordinary form is produced when the temperature is above + 46'5 ' , and that monoclinic prisms are formed when the temperature at which the sublimation is carried out is lower .
S With regard to the optical properties of iodine hardly anything is known .
Jorgensen states , however , that extremely thin dendritic crystals , obtained on a glass plate by the evaporation of an iodine solution in ether , act as polarisers ( " artificial tourmalines " ) and appear in polarised light either black or light brown , according to the direction of their principal elongation with reference to the polarisation plane.|| Sufficiently thin crystal-layers can also be obtained simply by melting a small crystal of iodine between two glass plates and squeezing these firmly together while the preparation is cooling and the iodine crystallising .
I am able to corroborate the statements of Jorgensen and to add that total absorption takes place when the direction * G. Kirchhoff , ' Pogg .
Ann./ 1860 , vol. 109 , p. 299 .
t See v. Groth , ' Chemische Krystallographie/ vol. 1 , p. 33 .
I v. Fedorow , ' Bull .
Acad. Petersburg/ 1907 , ( 5 ) , vol. 22 , p. 287 .
S v. Kurbatoff , ' Zeitschrift f. Anorg .
Chemie/ vol. 56 , p. 230 .
|| S. M. Jorgensen , ' Berichte Chem. Ges .
Berlin/ 1869 , vol. 2 , p. 465 .
1913 .
] Optical Investigation of Solidified Gases .
353 of the principal axis is parallel to the plane of polarisation .
The light transmitted at right angles to the principal axis is , in these extremely thin growth-structures , either light reddish-brown , or light leather-brown , there being no great difference of absorption visible between these directions , probably on account of the thinness of the crystal-layer .
It was further found that the colours appeared considerably paler in the direction at right angles to the principal axis , when the preparation was cooled in liquid air .
The absorption in the direction parallel to the principal axis remains , however , even at low temperature , strong enough to extinguish the polarised light totally in this direction .
No transition into a monoclinic form takes place when the rhombic growth-structures are cooled to about \#151 ; 180 ' , as is clearly seen from their behaviour in polarised light .
It seems , therefore , not probable that the monoclinic form is the one stable at low temperatures , the rhombic at high temperatures , the transition point being +46*5 ' , as suggested by Kurbatoff .
The ordinary rhombic modification of iodine is probably the modification stable at all temperatures , the monoclinic prisms belonging to a monotropic form with a marked temperature-limit of formation , and apparently low velocity of transition at ordinary temperature .
Their opaqueness and metallic character render it impossible to know if the monoclinic crystals investigated by v. Fedorow and Kurbatoff wTere pseudomorphosed or not .
The formation of the monoclinic form by rapid evaporation of solutions indicates also that it is a sporadically formed monotropic modification , and that a transition-point between the two modifications does not exist .
If we compare crystallised chlorine , bromine , and iodine with each other , we thus find that all three elements are rhombic .
From the investigation of the melting points of the systems chlorine-bromine , chlorine-iodine , * and bromine-iodine , f we are enabled to conclude that they form a continuous series of mixed crystals , and may thus be regarded as perfectly isomorphic .
The pleochroism of the three members of the series is of particular interest , as it occurs in all members of the group , and its strength and character\#151 ; like the other physical and chemical characters of the group\#151 ; change and increase as the atomic weight increases .
It is , however , specially remarkable that the colour in thfe direction of principal absorption in chlorine should be so closely the same as the colour in the direction of weakest absorption in bromine , and that the colour of strongest absorption in bromine should be about the same\#151 ; as far as determination is possible\#151 ; as that of weakest absorption in iodine .
* B. J. Karsten , ' Zeitschr .
f. Anorg .
Chemie , ' 1907 , vol. 53 , p. 365 .
t Meerum Terwogt , ' Zeitschr .
f. Anorg .
Chemie , ; 1905 , vol. 47 , p. 203 .
|
rspa_1913_0036 | 0950-1207 | The relation between the crystal-symmetry of the simpler organic compounds and their molecular constitution.\#x2014;Part I. | 354 | 361 | 1,913 | 88 | 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.1913.0036 | en | rspa | 1,910 | 1,900 | 1,900 | 3 | 161 | 3,917 | http://corpora.clarin-d.uni-saarland.de/surprisal/6.0.3/?id=rspa_1913_0036 | 10.1098/rspa.1913.0036 | null | null | null | Chemistry 2 | 39.585431 | Thermodynamics | 28.314036 | Chemistry | [
28.76881980895996,
-77.42503356933594
] | 354 The Relation between the Crystal-Symmetry of the Simpler Organic Compounds and their Molecular Constitution.\#151 ; Part I. By Walter Wahl , Ph. I ) .
( Communicated by Sir James Dewar , F.R.S. Received March 21 , \#151 ; Read April 17 , 1913 .
) ( From the Davy-Faraday Laboratory of the Eoyal Institution .
) Introduction .
Certain relations between the chemical composition of bodies and their crystalline forms indicate that the crystallographic properties depend in a simple way on the chemical constitution .
There are three distinct relations which principally point towards such a connection .
1 .
The Isomorphism shows that similarly constituted compounds , even of a very complicated chemical composition , crystallise in a very similar way when certain atoms in the molecule are replaced by chemically related atoms .
There are probably few subjects in the whole field of chemistry upon which so much separate evidence has been collected .
As a result of all this research upon isomorphic relationship and isomorphic series , from that of Mitscherlich up to the recent work of Tutton , it may be concluded with a great amount of certainty that to a definite molecular edifice belongs a certain crystalline edifice .
In consequence , the replacement of one or several atoms in such a molecular structure by atoms chemically closely related does not imply more than a slight alteration in the crystal form .
2 .
The Morphotropy ( in the sense of v. Groth ) implies that , if a certain atom or group in a large molecular-complex is replaced by another group , a definite alteration of the crystal-form in a certain crystallographic direction may take place .
This shows that changes in the constitution of a molecule are accompanied by corresponding changes in the crystal-form of the body , and thus also serves to establish the existence of a general relationship between molecular and crystallograpbical build .
* 3 .
The Enantiomorphism.\#151 ; All the substances which in the liquid state or in solution exhibit the property of rotating the plane of polarisation , crystallise as two " enantiomorphic " forms ( Law of Pasteur ) .
When the molecular edifice s hows a lack of symmetry , as a result of which right- and left ' handed modifications exist , the two being mirror-images of each other , a similar lack of symmetry , accompanied by the occurrence of crystals which form mirror- Crystal-Symmetry and Molecular Constitution .
images of each other , also exists between its crystallisation products .
Enantiomorphism , therefore , may be regarded as a proof of the existence of a general relationship between molecular and crystallographical properties .
There are , however , at present few data which may be used to correlate the evidence as established separately by isomorphism , morphotropy , and enantiomorphism .
Most of the work on isomorphism has been done on salts and double salts of a complicated nature ; the investigations on morphotropy on organic bodies with a large molecule , mostly those of the aromatic series ; and in those cases in which the crystal-forms of optically active organic bodies have been investigated the molecules are nearly all of great complexity .
The circumstance that nearly all organic bodies of simple chemical composition at ordinary temperatures are gaseous or liquid , and their crystalline properties therefore hitherto unknown , must , of course , be regarded as one of the principal difficulties to be overcome in establishing the facts governing the relationship between their molecular constitution and crystal-form .
As an illustration of how little is really known with regard to the crystalline properties of the simpler organic compounds , it may be noted that in the ' Chemical Crystallography/ edited by von Groth ( of which the recently issued third volume contains all crystallographic data hitherto obtained concerning aliphatic and hydro-aromatic compounds ) , only three methane derivatives are quoted ( carbon tetrabromide , iodoform , and di-isonitramido-methane-dimethylether ) which have not the character of salts containing metallic atoms , such as , for instance , the formates .
In connection with the recent investigations by the author on the crystalline properties of the elements gaseous at ordinary temperature , which have been described in the ' Proceedings of the Eoyal Society/ * some observations were made on certain of the simpler organic compounds of low melting point .
As some interesting observations were made on the relations between the crystalline properties of similarly constituted compounds , and also on the occurrence of polymorphic modifications , the investigation was extended to a larger number of the simpler organic compounds .
The experimental data concerning the aliphatic hydrocarbons are presented in this paper .
The results with regard to the halogen- and nitro-derivatives of methane , together with the general conclusions to be drawn from all these experimental data , will be given in a further communication .
* W. Wahl , ' Boy .
Soc. Proc./ 1912 , A , vol. 87 , p. 371 ; 1913 , A , vol. 88 , p. 61 ; 1913 , A , yoI .
88 , Feb. 26 .
356 Dr. W. Wahl .
Relation between [ Mar. 21 , Experimental Investigation .
In investigating the bodies , gaseous or liquid , at ordinary temperatures , practically the same methods were employed as have been described in ' Proc. Eoy .
Soc. , ' A , vol. 87 , pp. 371-374 and 376-378 .
The solid bodies were brought into the stem of the crystallisation vessel , melted and sucked into the narrow space between the polished quartz-glass plates , and their crystallisation and behaviour on cooling to liquid-air temperature investigated as in the case of the liquids . .
As pointed out in the case of methane , it is necessary to use the substances to be investigated in a very high state of purity in order to be able to study properly their manner of crystallising .
All the gases have therefore been fractionated by using liquid air or solid carbonic acid to condense them , a middle fraction being collected in a small glass gasometer over distilled mercury and used for these investigations .
The liquids were in most cases distilled immediately before investigation , a Young 's still-head in three sections being employed .
The solids were in some instances purified by sublimation in a charcoal-vacuum in a way similar to that described in the case of bromine.* .
Methane.\#151 ; Methane crystallises in the regular system .
The account of the investigation of methane has been published in ' Proc. Eoy .
Soc/ , A , vol. 87 , p. 377 .
It is therefore sufficient to refer to that paper for details .
Ethane.\#151 ; Ethane was prepared in the way described by Frankland , f by reducing ethyl iodide with coppered zinc .
The gas was passed through potassium hydroxide solution and through concentrated sulphuric acid , and then condensed and again boiled off and collected over water in a glass gasometer of the type designed by Bunsen , and of a capacity of about litres .
From here it was passed , for final purification , through a series of small wash-bottles containing bromine under water , a solution of potassium hydroxide , and concentrated sulphuric acid .
From the wash-bottles the gas passed through a tube fitted with a stopcock into a condensing vessel of the wash-bottle type , where it was condensed by cooling with liquid air .
The outlet tube of the condensing vessel was provided with a two-way stopcock leading to a barometer mercury-valve and to a T-piece , which again was in communication through the one branch with a mercury-gasometer of about 100 c.c. capacity and through the other branch , which was provided with a stopcock , with a large Fleuss pump .
When all the gas from the large gasometer condensable at liquid-air temperature had been condensed , after having passed through * 'Eoy .
Soc. Proc. , ' A , vol. 88 , Feb. 26 .
t E. Frankland , 'Liebig 's Ann. , ' vol. 71 , p. 203 ; vol. 85 , p. 360 ; vol. 95 , p. 53 ; and 'Chem .
Soc. Journ. , ' 1885 , vol. 47 , p. 236 .
1913 .
] Crystal-Symmetry and Molecular Constitution .
357 the absorption bottles , the stopcock between these and the condensation vessel was closed .
The ethane in the condensation vessel remained liquid in spite of this being immersed in liquid air , which shows that ethane prepared in this way cannot be obtained in a pure state by simply passing it through the absorbing agents mentioned above , and even condensing it once .
When the condensation vessel , however , was evacuated by means of the Fleuss pump , the liquid solidified .
It is probable that the ethane prepared in the above manner contains some methane , but it may also be that when it is condensed in presence of hydrogen , or perhaps also of air , it dissolves a sufficient quantity of the lighter gas to remain liquid at \#151 ; 180 ' .
These circumstances account for the statement concerning ethane , often to be found in the literature , that its melting point lies below the boiling point of liquid air .
All the lower members of the methane series behave in a very similar way , that is , they remain liquid at temperatures very much below their true melting point if purified only by passing through bromine , and condensed for the first time from the gaseous reaction products mixed with air .
By the evacuation following upon the solidification the lighter volatile products were pumped away .
The solid was then melted and the liquid was allowed to boil off gradually from the condensation vessel , the first portions being boiled off through the mercury barometer valve .
A further small portion was then used to wash out the tubes and connections with the mercury gasholder , these being subsequently evacuated .
About 100 c.c. of the middle fraction of the ethane were then collected into the mercury gasholder .
The ethane purified in this way was used for the crystallisation investigations .
It crystallises very readily in fern-like broad blades , growing rapidly in one principal direction .
If rapidly cooled , the liquid can be supercooled and becomes at about \#151 ; 200 ' a glass traversed by numerous cracks .
When the temperature is then allowed to rise spherulitic crystallisation sets in .
If the surface of the liquid air in the Dewar-vessel surrounding the crystallisation vessel is kept about 1 cm , below this , it is easy to crystallise and melt the ethane alternately by simply turning on and off the exhaust on the liquid air .
The crystal-fields of ethane show no cleavage at a temperature close to that of the melting point .
When the preparation is further cooled by evacuating the liquid air a very marked cleavage in two directions is developed .
The double-refraction varies very much in different directions , the maximum value , however , not being much higher than that of quartz .
Crystal fields occur also which remain isotropic when the nicols are revolved .
The direction of extinction in the double-refracting sections bisects the angle Dr. W. Wahl .
Relation between [ Mar. 21 , between the two cleavage-directions .
Judging from the occurrence of isotropic sections , and from the cleavage , which must be regarded as rhombo-hedral , ethane is hexagonal .
Propane.\#151 ; Propane was prepared in a similar manner to ethane by reducing isopropyl iodide with coppered zinc .
Judging from the fact that nearly half the volume of the reaction product was absorbed when passed through bromine , a very large proportion of olefinic hydrocarbons are formed in this case .
The fractionation was effected in the same way as described in the case of ethane .
When cooled in the vapour of evaporating liquid air the liquid propane does not crystallise .
If liquid air is admitted through the syphon until the crystallisation vessel is partly submerged in the liquid air , and the temperature is still further lowered by exhausting the liquid air , crystallisation after some time sets in .
The liquid is at this temperature not yet supercooled sufficiently to become stiff or glassy ; the crystalline phase , however , grows very slowly and spreads in most cases in one single homogeneous crystal-field over the whole field of the microscope .
By variation of the exhaust , that is the temperature of the liquid air , a growth in the form of prismatic needles can be obtained at the fringe of the crystal field .
This crystalline form of propane is strongly double-refracting and apparently rhombic .
When the exhaust on the liquid air is turned off and the temperature allowed to rise , a transition into another form takes place .
This form , which appears to be stable at higher temperatures , grows very slowly in the other modification , but in precisely the same way as crystals grow in a liquid .
This crystalline form is also strongly double-refracting , and either rhombic or monoclinic .
When the temperature rises further it begins to melt , and if only a portion is melted and the preparation then again cooled , recrystallisation takes place in the form of very narrow , sharp needles , projecting from the margin of the crystal-field into the molten mass .
If the crystals are , however , totally melted , supercooling of the liquid invariably takes place on cooling , and the crystal modification formed spontaneously in the supercooled liquid is always the form stable at lower temperatures .
Thus in propane we meet with a polymorphic substance which behaves in a similar way to sulphur\#151 ; and in a certain sense to oxygen\#151 ; in this respect , that the modification stable at low temperature is formed directly by the crystallisation of the supercooled liquid , i.e. , in the case of oxygen , the glassy liquid .
In all three cases the transition-point temperature lies only slightly below that of the melting point , and all three substances strongly tend to become supercooled , and also show little velocity of crystallisation in the case of the modification stable at higher temperature .
1913 .
] Crystal-Symmetry and Molecular Constitution .
359 Trimethyl-methane ( Tertiary Butane).\#151 ; Trimethyl-methane was prepared from tertiary butyl iodide in a way similar to that described in the case of the preparation of ethane and propane , and the reaction product treated as described in the case of ethane .
The gas obtained after the first condensation was absorbed , however , to the extent of about 80 per cent , when passed through bromine , showing that principally olefinic hydrocarbons are formed in this case .
Trimethyl-methane crystallises very beautifully in large crystal-fields and prismatic columns .
These are strongly double-refracting .
On further cooling with liquid air a very regular cleavage in one direction is developed .
The extinction is parallel to this cleavage direction .
It is therefore possible that trimethyl-methane is rhombic , but it may also be that the crystal-fields are always developed parallel to one and the same crystal face , as , remarkably enough , the interference colour in all cases was the same .
These observations , therefore , cannot be regarded as conclusively determining to which crystal system trimethyl-methane belongs .
Tetramethyl - methane ( Quaternary Pentane).\#151 ; Tetramethyl-methane was prepared according to Lwow , * i.e. by the action of a calculated quantity of zinc-methyl on tertiary butyl iodide .
It was found that the reaction is very treacherous , and it is not safe to work with more than quite small quantities .
If the iodide is not sufficiently cooled while the zinc-methyl is added , the reaction product is , for the greater part , absorbed when passed through bromine .
If more strongly cooled , reaction does not take place at all , and , when the mixture of the iodide and zinc-methyl is allowed to get gradually warmer , the reaction does not commence gradually , but sets in quite suddenly and a most violent explosion takes place .
The raw gas was purified by passing successively through bromine , caustic potash solution , and concentrated sulphuric acid , and was then frozen and subsequently fractionated .
Lwow states that the tetramethyl-methane crystallises in similar grille structures to ammonium chloride . .
Investigated in the same manner as the substances described above tetramethyl-methane has been found to crystallise in very beautifully developed cubical growth-structures , which are later filled up , and become homogeneous crystal-fields .
These are absolutely isotropic between crossed nicols .
When the preparation is cooled , a cubical cleavage is first developed , and at low temperature a transition into another modification of low doublerefraction takes place , which , to judge by its optical characters , is probably tetragonal .
* Lwow , ' Zeitschr .
f. Chemie , ' 1870 , vol. 6 , p. 520 ; and 1871 , vol. 7 , p. 257 .
360 Crystal-Symmetry and Molecular Constitution .
Normal Butane.\#151 ; Normal butyl iodide is not acted upon at ordinary temperature by coppered zinc and alcohol .
The reaction product obtained at higher temperature does not seemingly contain any appreciable amount of %-butane .
Lebeau has described a method for the reduction of alcoholic iodides by sodium dissolved in an excess of liquid ammonia .
He claims this method to be generally applicable to the synthesis of saturated aliphatic hydrocarbons .
I have tried to prepare the 72-butane as described by Lebeau.* The action of the deep blue sodium solution on the iodide takes place readily , but instead of a reduction taking place the reaction proceeds according to the Wurtz reaction , that is sodium iodide and octane are formed .
Only an insignificant quantity of gaseous reaction products was formed , and a slight smell of amines was noticeable.^ Finally , the Grignard reaction was tried and gave a good yield of the hydrocarbon .
This was then purified by condensation , passing through bromine and solidification , followed by fractionating .
72-Butane crystallises readily , and large crystal-fields are formed .
Both double-refracting sections showing parallel extinction and isotropic sections are observed .
The uniaxial character of the crystals in this case was also confirmed by observation in convergent polarised light .
72-Butane must thus be regarded as hexagonal .
At a temperature close to that of liquid air , boiling at ordinary pressure , this modification changes into another which exhibits a stronger double refraction and is rhombic .
On heating the reverse change into the hexagonal modification takes place .
Normal Pentane ( Kahlbaum 's , from petroleum).\#151 ; The commercial product did not crystallise , and it was not possible to obtain by fractionation a quite homogeneously crystallising preparation .
Only a certain middle fraction crystallised fairly well , and this was further fractionated and investigated .
On cooling , it at first became supercooled , but could be brought to crystallise by rubbing the inner wall of the stem of the crystallisation vessel with a metal wire .
It at first crystallises in the form of spherulites , but can be recrystallised , and is then obtained as long needles and prismatic fields of parallel extinction , and low double-refraction , which belong to the rhombic system .
Crystalline growth-structures , very similar to those of olivine , as * P. Lebeau , ' Bull .
Soc. Min./ [ 3 ] , vol. 33 , p. 1089 , and \#163 ; Bull .
Acad. Belgique , ' [ 3 ] , 1908 , vol. 46 , p. 300 .
t The reaction occurred twice in this way ; I have , however , not had the time to study the case further .
Quite recently E. Chablay ( 'Compt .
Bend .
, ' January 27 , 1913 ) stated that the hydrocarbons of the ethylene-series may also be obtained in a similar way .
Bemarkably enough the reaction between sodium dissolved in liquid NH3 and the alcoholic iodides thus seems to be able to proceed in three different ways , in each case giving good yields .
The conditions under which the one or the other product is obtained are , however , not known .
Ammonium Ferrous Sulphate and its Alkali-metal Isomorphs .
361 seen in basaltic rocks , were also observed .
A small quantity of the liquid did not crystallise at all , but became glassy at low temperature .
Normal Hexane ( Kahlbaum 's , from propyl iodide).\#151 ; 72-Hexane crystallises in needle-shaped prisms which exhibit extinction angles of very different degree .
The double-refraction is moderately high .
At liquid air temperature a very distinct longitudinal cleavage is developed .
No polymorphic change takes place above \#151 ; 200 ' , but at low temperature sparse twinning lamellae are formed , lying at an angle of about 80 ' to the prism axis ; 72-hexane is thus monoclinic or triclinic , probably monoclinic .
Normal Heptane ( Kahlbaum 's , from petroleum).\#151 ; The commercial product does not crystallise well , and a homogeneous preparation could no more be obtained in this case than in the case of 72-pentane .
The principal crystallisation product of the middle fractions consisted of long monoclinic or triclinic needles .
Normal Octane ( Kahlbaum 's , from 72-butyl iodide).\#151 ; 72-Octane crystallises well and in large prismatic columns of moderately high double-refraction .
It is monoclinic or triclinic .
No polymorphic transition has been observed above \#151 ; 200 ' .
Ammonium Ferrous Sulphate and its Alkali-metal Isomorphs. .
By A. E. H. Tutton , D.Sc .
, M.A. , F.R.S. ( Received March 11 , \#151 ; Read March 13 , 1913 .
) Ammonium ferrous sulphate , ( NH^Fe^O^.GFGO , although one of the commonest double salts in everyday laboratory use , and noted for its excellent , comparatively stable , clearly transparent , pale greenish-blue crystals , has never yet been subjected to a thorough crystallographic and optical study .
Since the year 1859 , when a few of its principal angles were measured by Murmann and Rotter , * and an approximate idea of its optical properties for red , yellow , and green light of no specific wave-lengths briefly indicated , just adequately to confirm that the salt belongs to the monoclinic series of double sulphates crystallising with 6H20 , no accurate measurements have been made .
The substance has , however , formed the subject of several special researches from a different point of view , such as those of von Hauerj* on the parallel growths of this salt on crystals of other salts of the series , of * Murmann and Rotter , 6 Sitzungsber .
d. Akad .
d. Wiss .
Wien/ 1859 , vol. 34 , p. 153 .
t K. von Hauer , 1860 , ibid. , vol. 39 , p. 611 .
|
rspa_1913_0037 | 0950-1207 | Ammonium ferrous sulphate and its alkali-metal isomorphs. | 361 | 387 | 1,913 | 88 | Proceedings of the Royal Society of London. Series A, Containing Papers of a Mathematical and Physical Character | A. E. H. Tutton, D. Sc., M. A., F. R. S. | article | 6.0.4 | http://dx.doi.org/10.1098/rspa.1913.0037 | en | rspa | 1,910 | 1,900 | 1,900 | 5 | 181 | 5,510 | http://corpora.clarin-d.uni-saarland.de/surprisal/6.0.3/?id=rspa_1913_0037 | 10.1098/rspa.1913.0037 | null | null | null | Atomic Physics | 34.968475 | Chemistry 2 | 27.087314 | Atomic Physics | [
-29.112438201904297,
-76.66403198242188
] | ]\gt ; above Ammonium Sulphate and its Alkali-metal Isomorphs .
By A. E. H. TUTTON , D.Sc .
, M.A. , F.B.S. ( Received March ll , \mdash ; Read Iarch13 , 1913 .
) Ammonium felTous sulphate , , although one of the commonest double salts in everyday laboratory use , and noted for its .
excellent , comparatively stable , clearly transparent , pale greenish-blue crystals , has never yet been subjected to a thorough crystallographic and optical study .
Since the year 1859 , when a few of its principal angles were measured by Murmann and Rotter , an approximate idea of its optical properties for red , yellow , and green light of no specific wave-lengths briefly indicated , just adequately to confirm that the salt belongs to the monoclinic series of double sulphates crystallising with , no accurate measurements have been made .
The substance has , however , formed the subject of several special researches from a different point of view , such as those of von Hauer on the parallel growths of this salt on crystals of other salts of the series , of * Murmann and Rot , ' Sitzungsbr . .
Akad .
' 1859 , vol. 34 , p. 163 .
K. von , Hauer , 1860 , ) , vol. 39 , p. Axial .
Value of Murmann and Rotter , ibserved .
Habit.\mdash ; Chiefly tabular parallel to ently elongated along the edge , or ; occasionally with , ) , and more or less equally developed .
Murmann and Rotter also observed a tabular form parallel to , prolongation along the edge , and predominating development of , and with subordinated , and , the latter type being shown in fig. 1 .
The salt is thug characterised by predominating development of the pair of parallel faces of the form , which is usually only a subordinate one for the series in general .
Ihree typical crystals measured by the author are in figs. 2 , 3 , and 4 .
The types 3 and 4 are clearly tabular H. Baumhauer , ' Pogg .
Ann. .
Phys 18/ 3 , , p. 619 .
St. Meyer , ' Sitzungsber . .
Akad . .
Wiss .
Wien , ' 1899 , vol. 108 , p. G. Wullf , ' Zeitschr .
fiir Kryst 1901 , vol. 34 , p. 486 .
S E. von Fedorow , 1909 , , vol. 46 , p. 258 .
FIG. 4 .
Typical of Ammonium Ferrous Sulphate .
the edge , so that the -faces are long and narrow .
Good little faces of the hemipyramid were present on two of the measured crystals , and very narrow faces of were discovered on one but their signalimages were neither sufficiently clear nor adequately free from diffraction to be of use other than for identification purposes .
Twelve excellent crystals were measured , of which ten were small and very perfectly formed , while two were larger , but yet gave excellent single images of the Websky signal .
The crystals were selected from four different crops , which had been grown umder ideal conditions of slow deposition and freedom from disturbance .
These measured crystals in general yielded splendid]y sharp and clear images of the signal , as will be obvious from the excellent agreement between the measured and calculated in the following table of angles .
Other crops were considerably influenced by striation of the c- and -faces , an occurrence which has been shown to be general throughout this series of double salts .
Table of \mdash ; The , table presents the results of the measurements and calculations .
The values of Murmann and Rotter , and also some earlier ones of Kopp , included in the last two columns .
* Cited in Rammelsberg , ' Handbuch .
kryst .
phys .
Chemie , ' Leipzig , 1881 , vol. 1 , 364 Dr. A. E. Interfacial FIG. Crystal of Ammonium FerrousSulph.ateSulphate growing on one of Ammonium Zinc sulphate , with precisely equally developed faces , in a slightly supersaturated / solution of ammonium ferrous sulphate .
The crystal was suspended in the solution by means of a platinum wire hook .
According to the experience of both von Hauer and Wulff ammonium ferrous sulphate is the most soluble : double sulphate of the series , so that a crystal of ammonium zinc sulphate does not dissolve in a saturated solution of ammonium ferrous sulphate , but , on the contrary , the latter salt at once begins to crystallise as a layer or zonal overgrowth on the crystal of the ammonium zinc salt .
Instead , however , of the equal continuation of growth on the equally grown different faces of the latter salt , the lesulbing crystal at the end of another similar period of time shows the relative development of faces represented in which is drawn from the correct relative amounts of development already described as having been by Wulff .
First comes largely * St. Meyer , ' Sitzungsber . .
Aknd . .
Wiss .
Wien , ' 1899 , vol. 108 , , p. 613 .
G. Wulff , ' Zeitschr .
fur Kryst 1901 , vol. 34 , p. 486 .
VOL. LXXXVIII.\mdash ; A. 2 faces of and following closely after in relative extent of development Wentions ttcrystals ommonium zevendoes rmmonium ferrous sphate pates oheHe aifference a rowth oalts ivesselThose ommonium zsually gither p in contact with the bottom of the vessel , and very rarely on , a form $ which is singularly seldom well developed , as regards extent , throughout the whole series .
Moreover , the ammonium zinc salt never grows upon an face .
On the other hand , ammonium ferrous sulphate crystals grow best of all on the -plane , as well as readily upon and but never upon .
It would thus appear that Wulff is correct as regards this explanation of the difference of habit .
and its -metal It is interesting to remark that this fact of ready growth on the -plane may be connected with St. Meyer 's observation , that when ammonium ferrous sulphate is crystallised in a magnetic field the crystals take the form of plates parallel to .
For , as this salt is highly magnetic , there can be no surprise if the earth 's magnetism should produce the same effect as an artificial magnetic field , and cause the deposition of tabular crystals parallel to Moreover , as regards habit , it has been sflown by the author that the alkali base esent , in the cases of potassium , rubidium , and caesium , has a definite influence on the habit , which is most marked in the case of the basal plane ; the faces of this form are , as a rule , relatively very large in ths potassium salt , very narrow in the caesium salt , and of intermediate size in the rubidium salt .
This influence is absent in the nonmetallic ammonium salt , other influences more free to act .
The " " setting\ldquo ; of the crystals of the saIts of this series has been gone carefully into by von Fedorow .
* The setting employed by the author , in this and all previous communications this series , is that which was given by Murmann and Rotter , and , as it is ths most natural one in precise keeping with the undoubtedly holohedral monoclinic symmetry of the crystals , was adopted by the author in the absence of any opposing reason .
It has been shown that this setting is preferable to that proposed by Wulff , when the development of faces yhout the whole series is generally considered , and V011 Fedorow confirms this view from the standpoint of the rule regarding reticular density .
Both the of Wulff and of the author agree with monoclinic symmetry , but Wulff rotates the crystal about the symmetry axis until becomes the basal plane instead of , both these planes being in the orthozone at right angles to the symmetry plane .
Von Fedorow , however , yet another setting , which he finds to agree better with the rule of reticular density .
But it is , in the opinion of the author , much to its disadvantage that the reason for it is really based on the peculiar form of the geometrical theory of crystal structure which has been anced by von Fedorow , and particularly on that part of it which is not so rrounded as that which refers only to the derivation of the 230 possible point-systems concerned in crystal structure ; this more part refers to the nature of what the points represent , and to von Fedorow 's idea that all crystals are of either cubic or hexagonal type or of one of those types more or less deformed , which he terms pseudo-cubic * E. von Fedorow , ' .
fur Kryst 1909 , , p. 258 .
' Journ. Chem. Soc 1893 , , p. 337 ; see fig. 1 , p. 343 , for stereographic projection .
versed , he regards the various poles from an altogether different stand .
point .
He ignores the monoclinic symmetry , except as being a deformation .
in one direction , and states that the crystal complex appears to be a hexagonaloid one of cubic type , that is , one of trigonaloid character , which he expresses , in accordance with a method of concise symbols which he S employs , thus : The letter in the top line indicates the octahedral main structure ; the 3 in front of it represents the trigonaloid character , which is similar to the .
rhombohedral one of calcite , but considerably deformed in one direction ) from the form of the regular rhombohedron ; the signifies the number of degrees of monoclinic deformation , on the side of the trigonal axis that is , the angle between the centre of projection , which in a truly trigonal crystal like calcite is occupied by the pole ( 111 ) , and the actual position of the pole of the possible face which is analogous to ( 111 ) on the deformed crystal .
The central number represents the number of degrees in the principal angle ( 111 ) : ( 001 ) , that is , between the basal plane and one of the faces of the primary rhombohedron , on the supposition of trigonaloid character and after imaginary re-deformation of ( 111 ) back to true trigonal symmetry , that is , to the centre .
The lower number represents the ular deviation from .
of the poles on the primitive circle , that is , of the poles in trigonal symmetry would correspond to and ; these are adjacent faces of the two varieties of hexagonal in a truly trigonal crystal , and are in the latter apart , bub in the neighbourhood of ( the angle ) in this series of double sulphates in ammonium ferrous sulphate ) .
Von Fedorow gives the following transformation equations for the conversion of the indices , of any face according to the monoclinic setting of the author , to the corresponding indices according to von Fedorow 's onaloid setting : or the determinants : without pole-dots : { 111 } the basal plane ; four .
of the six faces of the hexagonal prism of the first order , for only two , and , are ; generally developed , which are the -faces ( 100 ) and of the author 's : monoclinic setting , the other four faces , , , and , having only been seeh developed to measurable extent on one or two crystals of six of the 38 ated salts of the series as the minute faces namely , sulphates ) ; and two of the .
three faces of the primary rhombohedron itself { 100 } , for only one , ( 001 ) , is present , while ( 010 ) and ( 100 ) are generally entirely absent , and ) only been seen by the author as minute faces ( the -faces ) on three of the 38 salts of the series investigated , namely , KNiRbCu- , and -sulphates .
there , which is even more significant , while it is true that all six faces of the hexagonal prism of the second order ) are developed , four of them are the largely and generally predominatingly developed faces of the primary prism of the author 's monoclinic setting , while the other two are vely small and frequently absent faces of the clinopinakoid ; that is , two clearly different and very unequa ] developed forms make up the six faces which von Fedorow proposes to consider as a hexagonaloid prism .
Again , the cleavage is only developed parallel to one plane , that of the pair of parallel faces of , that 1913 .
] Sulphate and its Atkali-metal Isomorphs .
371 only parallel to one of the three planes of the pseudo-rhombohedron of 4 von Fedorow .
Thus , while it may be true that the faces of the pseudo-rhombohedron possess the maximum reticular densit still there appear to be so many deficiencies as regards development of primary planes , either as Iaces or cleavage planes , that the author much .
to aocept the simple and obvious monoclinic symmetry of both faces and as determinative of the setting ; and as Wulffs setting is still less to be preferred , both for the reasons given by the author and for the additional ones also advanced by von Fedorow , it is considered to retain the setting which has been adopted throughout all these investigations .
If a clearly hexagonal habit were presented , and all the essential fnces well developed , such as in the cases of the simple rhombic sulphates and selenates of the alkalies , where the differences from exactly are only a .
few minutes , the presence of a pseudo-hexagonal spaoe-lattice could with reason be accepted , and in the descriptions of those salts the author has : given the dimensions of the elementary cells of the space-lattice on sucl } an assumption .
But in this monoclinic series of double salts such is not the case . .
Etch-Figures.\mdash ; The investigation by Baumhauer* of the ures produced by a small quantity of water on the principal faces afforded results conclusively indicating the presence of holohedral monoclinic symmetry .
Besides ammonium ferrous sulphate two other salts of the series were studied , namely , potassium and ammonium nickel sulphates .
Two illustrations are reproduced from Baumhauer 's memoir , in figs. 8 and 9 , but with his lettering of the faces replaced by the letters now assigned to those faces .
FIG. 8.\mdash ; Etch-figures on Ammonium Ferrous Sulphate .
Fig. 8 shows the character of the etch-figures on the predominating taces of in the of ammonium ferrous sulphate .
Fig. 9 reproduces those * H. Baumhauer , Pogg .
Ann. .
Phys 1873 , vol. 160 , p. 619 .
presence of a digonal axis of symmetry perpendicular to the plane of symmetry ( parallel to the shorter edges of the page ) .
They possess , consequently , both the elements of monocliuic , and therefore the crystals are holohedral .
Moreover , the etch-figures are quite different from such as are usually afforded by a crystal of trigonal symmetry .
on of the Constants of the Four Salts of the Group.\mdash ; The crystal-angles , axial angles , and axial ratios of the potassium , rubidium , , and ammonium ferrous sulphates are compared in the next two tables .
As the monoclinic axial angle , its value for the ammonium salt is almost identical with that for the caesium salt .
It is noteworthy that a like fact has been observed in all the other groups yet studied , the sulphate and selenate groups containing zinc and nesium respectively , and the magnesium group of double chromates .
With reference to the axial ratios , it is only possible to infer that the values for the ammonium salt are so similar to those for the analogous alkali-metal salts that true isomorphism undoubtedly exists .
It is somewhat singular that the -values are identical for three of the salts , potassium , rubidium , and ammonium ferrous sulphates .
lsomorphs .
373 From the table of crystal angles and a derived the following facts : In the cases of angular change introduced by tho replacem occurs in the same direction ( increase or dec : or caesium is the replacing element , and th , and occur in cases where th effect of the replacement of potassium by genera ] an alteration in the crystal angles of It is thus clear that both the average and the maximum changes of angle which occur when potassium is replaced by ammonium are almost exactly identical with those evoked by the introduction of caesium instead I of potassium , and twice as great as when rubidium is the replacing element .
Identical conclusions were also drawn from the investigation of the $ magnesium and zinc groups of double sulphates and selenates .
They 2 accord completely with the eutropic character of the relationships between the three alkali-metal salts , and with the merely isomorphous and not eutropic nature of the occurrence of the ammonium salt in the group .
As , regards the average and maximum changes of crystal angle , the three eutropic salts show direct proportionality to the atomic weights of the three metals .
Volume .
Relative Density.\mdash ; Seven determinations of specific gravity were made with small perfect crystals selected from five differeIlt crops , by the Retgers immersion method , using a mixture of methylene iodide and benzene as the .
immersion liquid .
The following results for the heaviest crystal in each ca se- were obtained:\mdash ; 1913 .
] Density f IIIIV .
1.86168627 : 1.8639 1.8635 1.8644 The value accepted for is thus Earlier values ( none of then ] recent ) by various workers have varied as much as from to .
Considering the excellent unanimity of the above results this wide difference is difficult to understand .
Iotecular Volume .
Molecular Distance Ratios ( topic axial ratios : of the of Potassiurn , Rubidium , Ferrous Sulphates.\mdash ; In order to render valid all comparisons between the volume constants of these four salts of the ferrous iron group , a series of redeterminations of the specific gravities by the Retgers immersion method have been carried out for the three alkali-metal salts ; for the earlier determinations recorded in the author 's 1896 memoir*were carried out by the pyknometer method , which is liable to afford lower values for the density , owing to the result being an average one for a large number of crystals in the finely powdered condition , whereas the Retgers method affords the density of the heaviest and therefore most cavity-free crystal .
The results are yiven below : Potassium Ferrous Sulphate , I. Density for 2 1797 For II .
, , , , III .
, , , , .
, , 2 .
, , 2.1751 In determination I the heaviest crystal showed a tendency to rise in the immersion liquid , and in determination III to sink .
In determinations II and the heaviest crystal remained in the middle of the liquid .
The accepted value is therefore , for Rubidium Ferrous Sulphate , I. Density for For II .
, , The accepted value is thus for * Journ. Chem. Soc 1896 , , p. 344 .
It will be clear from this table that the molecular volume and topic axial ratios of the ammonium salt are very close to those of the rubidium salt , a result in keeping with the facts derived from the zinc and magnesium sulphate , selenate , and chromate groups previously investigated .
As regards the molecular volume , the value for ammonium ferrous sulphate is about one unit higher than that for the rubidium salt , and in the oases of the topic axial ratios the values for and are slightly higher and for very slightly lower .
These small differenoes between the volume constants of the ammonium and rubidium salts are very much smaller than the differences between the values for the three alkali-metal salts ; between the potassium and caesium salts there is a difference of molecular volume of no less than units , and between the potassium and rubidium salts of units .
It is thus clear that the replacement of potassium by .
ammonium accompanied by practically the same amount of extension of the crystal structure as when rubidium is introduced for potassium , and by a very much smaller change of volume than when caesium is introduced instead of potassium .
Obviously also , there is scarcely any change at all of volume or orientation of the Axes of the Optical Ellipsoid .
rubidium , and caesium successively replace the ammonium , the rotation being a function of the atomic weight of the alkali metak in the cases of these 3 ?
three metallic salts .
These rules are exactly similar to those found for the magnesium and zinc groups , both double sulphates and double selenates .
Refractive Indices.\mdash ; Six excellent -prisms were ground by means of the cutting and grinding goniometer , rom perfectly clear and transparent crystals , selected from three different crops .
Each prism two :$ indices directly .
three of them gave and , two yielded and , and the sixth prism furnished and .
The results are compiled in the next : According to Murmann and Rotter the -indices for red , yellow , and- .
green light are lespectively , and The intermediate index , corrected to a vacuum ( correction ) , is expressed for any wave-length by the following general formula : The -inchces are also reproduced by the forruula if the constant is reduced by , and the -indices if it is increased by 1913 .
Sulphate and its Alkati-metal Isomorphs .
379 Refractive Indices of Ammonium Ferrous Sulphate .
Mean of , and for Na light Change of Refraction by Rise of Temperature.\mdash ; Determinations of refractive index at C. were carried out with two of the prisms , which furnished and , and and respectively .
The results are combined in the table ; the two series of -values were practically identical , the greatest deviation for any one wave-length being only , so that the table is a very trustworthy one .
These values are lower than those for the ordinary temperature , the -values being on the average lower , the -values smaller , and the -values less .
Comparison of the Refractive Indices of the Salts of the Iron The indices of ammonium , potassium , rubidium , and caesium ferrous sulphates are compared in the next table .
1913 .
] Sulphate and its -metal lsomorphs .
381 -axis of the potassium salt is taken as unity , in order in the latter case to llipsoidsascertain tffect o replacing one alkali base by another on the dimensions : Axial Ratios of the Optical Indicatrix .
RbFeKFe sulphate .
9979:1 : 00390.9970 : 1:1.0050 RbFe , atios.tical Velocity Epsoidp : : FeNH F These numbers unite in indicating that the dimensions of the optical ellipsoid , whether it be the indicatrix or the velocity ellipsoid , in the case of the #L$ ammonium salt of the iron group lie between those of the rubidium and caesiUm salts , and when the total change of dimensions is considered , as given by the right-hand set of ratios for each ellipsoid , the values lie much closer to those of the rubidium salt than to those of the caesium salt .
It must be remembered , however , that the ellipsoid rotates about the symmetry axis on each replacement , in the order given in the table on p. 378 and illustrated in fig. 11 .
Molecular Optical Constants.\mdash ; These constants have been calculated for the ammonium salt , from the specific gravity and the refractive indices , and the values are compared in the next three tables with the corresponding values for the three alkali-metal salts of the iron }roup .
These latter values have been recalculated , employing the new values for the specific gravities given in this memoir , the results of the redetiations by the immersion method .
Table of Specific Refraction and Dispersion ( Lorenz ) .
VOL LXXXVIIL\mdash ; A. 2 From these tables the following facts are to be derived:\mdash ; } The specific refraction and dispersion of the ammonium salt are considerably higher than those of the alkali-metal salts of the group , which three latter salts exhibit values progressively diminishing with the atomic weight of the alkali metal .
The molecular dispersion of the ammonium salt lies between the values for the rubidium and caesium salts , and nearer to those of the caesium salt .
The molecular refraction of the ammonium salt , whether calculated by means of the formula of Lorenz or by that of Gladstone and Dale , is very close to , and very slightly higher than , the as regarda direction in the crystal and the optical ellipsoid ) value for the rubidium salt .
The mean molecular refraction , in which the influence of direction in : the crystal is eliminated , follows precisely the same rule .
The rule is , indeed , common to all the double sulphate , selenate and chromate groups of } this series yet investigated .
Optic Axial Angle.\mdash ; Three excellent pairs of section-plates to the first and second median lines were obtained by grinding , with the aid of the cutting and grinding goniometer , each pair from crystals belonging second median 1ates 1nterference figures iirst eations opider 1ines feasurement oEand sswhen immersed iwith vinner reparate cThey arnished mgnificent interference figuresb prought quite uuine , with hates 1oThe riven i Apparent Optic Axial Angle in Air , , of AmFe Sulphate .
Murmann and Rotter obtained for the middle part of the spectrum .
Optic Axial Angles of the Iron Group .
The optic axial angle of ammonium ferrous sulphate is thus slightly larger that of caesium ferrous sulphate , which is the largest of the optic axial angles of the alkali-metal salts .
This was also found to be the case in the zinc double sulphate group , while in the corresponding zinc double selenate group the value for the ammonium salt was found to be htly less than that for the caesium salt .
In all three groups the value for the ammonium green crystals are distinguished from other members of the series by the exceptionally predominant development of the orthopinakoid of the second order S The same facts have been found to apply in this double sulphate iron #S group of salts of the series as were deduced from the previous investigalions of the magnesium and zinc double sulphate and selenate groups , *namely , that the ammomum salt of any group is truly a member of the isomorphous .
series , but not eutropic with the potassium , rubidium , and caesium salts of : the group , which three latter salts are strictly eutropic with one another , and follow the rule of progression of the crystal properties with the atomic weight of the alkali metaL The \mdash ; Small but definitely measurable changes in the magnitude of the crystal angles occur when the potassium in potassium 9 ferrous sulphate is replaced by ammonium , and they are mostly in the same direction as those which accompany the replacement of potassium by either rubidium or caesium .
Both the average and the maximum changes of interfacial angles for the ammonium interchange ( for potassium ) are almost exactly the same as for the replacement of potassium by caesium , and twice as great as when rubidium is introduced instead of potassium ( the average and maximum of angle being directly proportional to the atomic weights of the alkali metals ) .
Also the monoclinic axial angle ( the axial angle , between the vertical and inclined axes ) of ammonium ferrous sulphate is almost identical with that of caesium ferrous sulphate .
The Morphological Axial Ratios of the ammonium salt are very similar to those of the analogous potassium , rubidium , and caesium salts , and adequately so to prove true isomorphism in the usually accepted sense , that is , subject to the small variations of crystal angles referred to in the last paragraph .
The Constants.\mdash ; The molecular volume and topic axial ratios of 'Journ .
Chem. Soc 1905 , , p. 1123 .
clusions of a similar nature derived from the previous work on the magnesium and zinc groups .
of the al Ellipsoid.\mdash ; Rotation of the optical ellipsoid about the symmetry axis occurs when one base is replaced by another in this iron group of salts , and the order of the rotation is : Ammonium salt , { 9 potassium salt , rubidium salt , and caesium salt .
The direction is forwards from the vertical axis , to which one of the axes ( or a ) of the ellipsoid is adjacent ( only removed ) in the case of the ammonium salt .
Befractive \mdash ; The whole of the refractive indices for all wavelengths of visible light , and also the mean index , of ammonium ferrous sulphate are near to and slightly higher than those of rubidium ferrous sulphate , and in no case so high as for the caesium salt .
Also the dovlte refraction for the ammonium salt lies between the values of this constant for the rubidium and caesium salts , but in this case nearer to the value for the caesium salt .
The dimensions of the axes of the optical ellipsoid also lie between thos6 for the rubidium and caesium salts , and much nearer to those of the rubidium salt .
The Molecular Optical Constants.\mdash ; The specific refraction and dispersion of the ammonium salt are.much higher than those of the alkali-metal salts , which three latter salts arrange themselves as regards these constants in the $ ; 3 1913 .
] and its Isomorphs .
387 order of the atomic weights of the metals .
The molecular dispersion of the : ammonium salt lies between that of the rubidium and caesium salts , and nearer to that of the latter .
The molecular refraction corresponding to each of the three refractive indices , and also the mean molecular refraction , ) , for the ammonium salt is very nearly the same as , and a very slight amount higher than , the corresponding value for the rubidium salt .
All these results have been experimentally shown to be independent of the temperature .
Opiic Axial Angles.\mdash ; The optic axial angle of ammonium ferrous sulphate is slightly larger than the largest for the metallic salts , that of caesium ferrous sulphate , and the dispersion , both of the optic axes and of the median lines in the symmetry , is small between the two extremes of the spectrum , and very similar for all four salts of the group .
Chief Condusion.\mdash ; The principal conclusion to be emphasised , as the result of this investigation , and in further coufirmation of the deductions from the previous investigations of the zinc and magnesium groups of double sulphates and selenates , and those still more recently*derived from the study of the magnesium group of double chromates , is the following : The ammonium salts are truly isomorphous with the potassium , rubidium , and caesium salts of this large monoclinic series of salts having the general formula , but not eutropic with them , the three latter salts alone being eutropic ( following the law of progression with atomic weight of the alkah metal ) amongst themselves ; also , it is a singular and very interesting fact that scarcely any change in structural dimensions occurs when ammonium and rubidium are interchanged for each other , that is , when ten atoms replace two atoms , for they do so without appreciably altering the dimensions of the unit cell of the space-lattice .
'Mineralogical Magazine , ' 1912 , vol. 16 , p. 169 .
|
rspa_1913_0038 | 0950-1207 | Studies of the processes operative in solutions. XXVII.\#x2014;The causes of variation in the optical rotatory power of organic compounds and of anomalous rotatory dispersive power. | 388 | 403 | 1,913 | 88 | Proceedings of the Royal Society of London. Series A, Containing Papers of a Mathematical and Physical Character | H. E. Armstrong, F. R. S.|E. E. Walker, B. Sc. | article | 6.0.4 | http://dx.doi.org/10.1098/rspa.1913.0038 | en | rspa | 1,910 | 1,900 | 1,900 | 5 | 107 | 3,381 | http://corpora.clarin-d.uni-saarland.de/surprisal/6.0.3/?id=rspa_1913_0038 | 10.1098/rspa.1913.0038 | null | null | null | Biochemistry | 39.902417 | Tables | 25.378432 | Biochemistry | [
-31.51603889465332,
-43.82966613769531
] | ]\gt ; one of us pointed out ( p. 1208 ) that\mdash ; " " Two optically active , chemically indifferent bodies of opposite rotatory power , having rotatory dispersive potvers , if mixed in certain proportions , would ( as Biot has shown for a solution of dextrorotatory camphor in laevorotatory turpentine oil ) exhibit phenomena similar to those manifested by tartaric acid solutions ; hence the most ] probable explanation of the anomalous rotatory dispersive power of solutions of tartaric acid would appear to be that they contain , besides the acid , a compound of opposite rotatory power of the acid with water , in proportions varying according to the concen- ) tration and ature of the solutions But that this explanation was not regarded as altogether satisfactory is apparent from a sentence written at about the same time which appears in the edition of Miller 's 'Elements of Chemistry , ' Part III , " " Organic Chemistry\ldquo ; ( p. 992 ) , published in 1880:\mdash ; " " The anomalous rotatory dispersive power of aqueous solutions of tartaric acid almost necessitates the assumption that the acid forms a compound with water opposite to itself in rotatory power ; the formation of a body having a reversed rotatory power as ompared with that of the parent substance from a compound like dextrotartaric acid , whidh , according to Hoffs hypothesis , has the constitution , is composed of two similar dextrorotatory groups\mdash ; is , however , not easy to understand In those days , of course , our knowledge of structure was far less developed !
than is now the case .
Meanwhile , notwithstanding the attention devoted to ; the study of optically active substances since the introduction of Va n't Hoff 's 'Ann .
Chim Phys 1868 , ( 3 ) , vol. 64 , p. 415 .
light of other degrees of refrangibility .
T. M. Lowry has since improved the method and by the use of photography has extended it so that the measurements can now be made without difficulty not only in the visible but also throughout the ultra-violet region ; this work , it may be added , was undertaken mainly in consequence of the suggestion made to him by one of , us several years ago that it was desirable to reinvestigate the subject of anomalous rotatory dispersion from the point of view of Biot 's suggestion . .
The method has been in use during several years past in our laboratory and in that of Prof. Pope .
It is safe to say that it is no longer legitimate to confine the measurements : of rotatory power to yellow light .
It is remarkable that so little attention should have been paid to rotatory dispersive power and to the anomalous behaviour of some substances .
Walden , his comprehenslve survey of the of actlvlty , the lecture he delivered to the German Chemical Society in mentions almost casually the abnormal behaviour of tartrates without reference to Biot 's explanation and this has been disregarded also by Frankland , Patterson and other recent workers , even by Winther , who has discussed change in rotatory power particularly in relation to the changes in the " " solution-volume\ldquo ; and the " " internal pressure\ldquo ; of solutions .
S Winther , following Biot , considers that abnormalities in dispersive power are due to the presence of forms ering in rof , atory power but supposes that these are complex molecules and compounds of solute and solvent .
The effect of solvenbs on the rotatory power of certain tartrates has been made the subject of most exhaustive study during the past 12 years by T. S. Patterson , who , in a series of 20.communications to the Chemical Society , has shown that different liquids produce extraordinarily different effects in changing the rotatory power especially of tartrates .
He has summarised the results which he and others have obtained *Compare Frankland , Presidential Address , 'Chem .
Soc. Trans 1912 , p. 654 .
PhiL Trans 1912 , , vol. 212 , p. 261 .
'Berichte , ' pp. 366-408 .
S 'Zeit .
Phys. Chem vol. 60 , pp. 663 , 590 , 641 , 766 .
An attempt to harmonise qualitatively the relations between temperature and rotation for light of all refrangibilities of certain active substances both in the homogeneous state and in solution , ' Chem. Soc. Trans 1913 , p. 146 .
rotating with the angular velocity of the earth but in the opposite direction .
with tdata.heory tropose aheir obeyondregions otmosphere.urther donfirm trise fconductivity oerwhich wccount froceed tecondterms , atter txpress tegard tconductivity required ivery cature We have thus formed a simple specification of the .
terms which seem to fit -composition diagrams .
Fructose.\mdash ; Passing from ideal cases to actual facts , the case of fructose may now be considered .
There is every reason to suppose that this compound is present in solution in two isodynamic forms and it has been shown in Part XXVI of these studies that the proportions in which these are presumably present in equilibrium may be altered to a considerable extenl by the addition of alcohol or other substances .
In order to determine under which of the above four cases fructose comes , a solution was made up containing two molecular proportions of fructose and 100 molecular propor .
tions of water and the rotatory power of this solution was determined using the light of the yellow , green and blue lines emitted by a mercury vapour lamp .
Various quantities of alcohol ( .taining per cent. water ) were then added and the specific rotatory powers determined as before .
The results are given in Table II .
It will be noticed that the values given in the last two columns represent ing the dispersion are practically constant , except in the most dilute solution in which the experimental error is large .
The values for blue light cannot be regarded as so nearly accurate as those for yellow and green ; on account of the spectroscope being in the eye-piece of the polurimeter , the flood of yellow and green light is so great that when the rotation is considerable the blue is obscured .
Therefore in the case of solutions 1 and 2 , a blue filter was used to cut out the yellow and green bands ; this rendered the blue fainter also . .
If the assumption be made that the composition of the mixture studied is S a linear function of the specific rotatory power in the case of a given coloured ' light , all the points representing the specific rotatory power in other colours : should fall on straight lines when placed on the appropriate ordinates ; the abscissae should then represent the composition to an unknown scale .
Tot construct the diagram characteristic of a substance , a reference line is drawn with a slope of unity and on this are plotted the various specific rotations of light of any one of the refrangibihties observed .
The points for other refrangibilities are then plotted on the ordinates passing through the points previously located on the reference line .
The observations may be those made either at different temperatures or in different solvents or at different concentrations .
It is proposed to call the portion of the rotation-composition diagram in the manner described the Characterutic Diagram , as it shows under which of the cases discussed on p. substance comes .
When the characteristic diagram of fructose ( fig. 2 ) is drawn from the data given in Table II , it is clear that this sugar comes under Case III and that it is to be supposed therefore that the two isodynamic forms have the persion vited shows tubstance i as coming under Case .
The slope of the lines is no longer a measure of the dispersion ss it is in the case of fructose but gives what is practically identical with Winther 's " " solution dispersion coefficient.\ldquo ; * The value of this coefficient calculated from the various pairs of solutions is ' remarkably constant in comparison with the apparently irregular variation : of the dispersion coefficient ( cp .
Tables I and ) .
Table * Winther ( ' Zeit .
Phys. Chem vol. 41 , p. 207 ) has shown that the increase in the rotatory power of the ethereal salts of tartaric acid can be represented as a parabolic function of the temperature .
If and are the values of for light of two different wave lengths , then Winther called the ratio the rational dispersion coefficient ; this was shown to be to a large extent independent of the concentration and the solvents .
Subsequently , he vol. 45 , p. 373 ) used what he termed the " " solution-dispersion coetiicien ; this was calculated from the expression:\mdash ; wbre and are the changes in rotatory power of light of two different wave lengths occasioned by a given change in concentration .
( The " " rational dispersion coefficient\ldquo ; was determined from a similar expression when the constants of the parabolic equation were not known .
) It is clear that this latter ratio is identical with the ratio of the slopes of the lines of the characteristic diagram ; in fact the slope of these lines represents this quantity The characteristic diagram ( fig. 4 ) drawn from these data shows that methylic tartrate also comes under Case .
The comparatively low values at which the lines cross is probably an indication that there is considerably less difference between the magnitude of the dispersion of the two forms than in the case of the quinaldine derivative and probably also a correspondingly smaller difference in constitution .
A point of great significance in this diagram is the fact that the values for the ethereal salt alone at various temperatures lie practically on the ] projection of these curves , the whole forming one complete diagram .
These values were deduced from Winther 's data*by graphic interpolation from the dispersion curves ; the values so obtained are given in Table directly when the line of unit slope is chosen as denominator .
It therefore appear $ desirable to designate the ratio:\mdash ; : by a single term , whether the change in equihbrium be caused by an alteration either in : temperature or in concentration or solvent ; for this purpose the term " " rational dispor sion coefficient\ldquo ; might well be retained .
*Op .
cit. , vol. 41 , p. 17 ' .
1913 .
Studies of the Processes Operative in Solutions . .
4.\mdash ; Equilibrium varied by the addition of FI 5.\mdash ; Ethylic tartrate .
Equilibrium alcohol to the aqueous solution and by heating varied by change of solvent and con the original substances .
centration at constant temperature20o C. Table Ethylic Tartrate.\mdash ; Fortunately Winther has supplied very complete data for this substance .
* The characteristic diagram is given in fig. 5 ; some of points have been omitted , as they come so close ether .
Excepting those for solutions in water , the values all lie very close indeed to straight lines .
The solution in benzeme ( not included ) also appears to afford slightly exceptional values .
2-Nitrotoluene-4-sulphonyltetrahydroquinaldine.\mdash ; The characteristic diagrams *Op .
, vol. 60 , p. 582 .
VOL. LXXXVIII.\mdash ; A. 2 Being quinonoid , the second of these would doubtless be the more dispersive .
Passing to tartaric acid , we have to account for the fact that the rotatory power of the acid and of its ethereal salts is more or less affected by variation in the temperature ; morever , that not only water but also " " neutral\ldquo ; solvents modifythisrotatorypower , often tconsiderable extent ; and 9Studies orocesses Oolutions.that t rotatory sive power of the solutions is generally anomalous .
According to Biot , no such abnormal dispersive power is noticeable in solutions of the metallic tartrates ; this statement has been confirmed by Winther .
Although it has been customary to regard carboxylic acids as compounds containing the free carboxylic radicle , the evidenoe that such is always the case is in no way sufficient , let alone conclusive .
The behaviour of monocarboxylic acids , especially their recognised tendency to form double molecules , as in the case of acetic acid , is clear proof that the carboxylic radicle is far from being saturated .
Taking into account the views that now prevail that valency has direction $r and the conclusion which is the outcome of this conviction that carbon atoms are not united as mere links in a chain but tend to form re-entering systems , such systems being formed preferentially from either five or six atoms ; moreover , that oxygen atoms may take the place of carbon atoms : it is both possible and probable that the fundamental molecule of tartaric acid can exist not only in the " " open\ldquo ; form commonly pictured ( I ) but also in various isodynamic " " closed\ldquo ; formoe CO(OH ) OH H(OH ) H.OH CH(OH ) HO HO .
HC / CO 1 .
II .
III .
IV .
It cannot be demed that there is little to guide us in choosing between these formula or in deciding which is the mosb likely form to preponderate .
* The third obviously a marked resemblance to that of fructose\mdash ; in which , in place of the four-membered ( tetraphane ) ring there is a fivemembered ( pentaphane ) .
The fourth is similar to the third .
It is scarcely probable , we think , either that any alteration in the degree of a substance represented by formula I or that the passage from * It is remarkable that possibilities such as these have not been taken into account by Walden , who has recognised that structural changes may in some cases underlie the alterations in rotatory power observed in solutions .
Taking the ethereal salts of tartaric acid as an example , he has postulated changes which appear to us not only to be improbable , but altogether insufficient to account for the magnitude of the effects observed , especially the change in sign of the rotatory power , accompanied by a sufficient difference in dispersive power to give rise to the phenomenon of anomalous X and may be either other molecules of the tartrate or molecules of the solvent .
) COOR H.O\mdash ; CH .
COOR H.O\mdash ; C.COOR It is well known , that gluconic and similar acids derived.from the sugars are very readily converted into the corresponding lactones\mdash ; a change precisely similar to that attending the conversion of the carboxylic form of tartaric acid into the tetraphane form ; and if gluconic lactone be regarded as present in solution in a hydrated form , the behaviour of the two acids is in correspondence .
Gluconic and similar lactones , moreover , have high rotatory powers , whilst the acids derived from them have low rotatory powers of opposite sign\mdash ; which is precisely the difference we have postulated in the case of the two isodynamic forms of taric acid .
Il may also be pointed out here that in the case of the ethereal saIts of tartaric acid two stereoisomeric modifications of the tstraphane and pentaphane forms are possible : this is also true of the quinonoid form of the -nitroquinaldine derivative examined by Pope and Winmill .
As " " asymmetric influsnces\ldquo ; are likely to be operative in such cases , the proportions in which the two isomerides are in equilibrium may be very different and one form prevail to the almost entire exclusion of the other .
1913 .
] are Studies othe Operative in Solutions.istinctio :Asimilar formula has been suggested for maleic acid in contradistinction to the dicarboxylic formulaassignedOH to the isomeric fumaric acid COOH .
CH Maleic acid .
Fumaric acid .
: Such a formula is justified not only by the fact that maleic and fumaric acids differ considerably in strength but especially because maleic acid is converted into fumaric acid by mere contact with chlorhydric or bromhydric acid\mdash ; a change which is easily accounted for by the assumption of this mula but with difficulty in any other way .
OH OH HC .
COOH : COOH .
CH If therefore tartalic acid existed in form under ordinary conditions , it is to be expected that it would be easily converted into its optical isomeride ; actually this change only takes place under special conditions and at relatively high temperatures .
Malic acid resembles tartaric acid in its optical behaviour and a similar explanation may be given of its pecuharities .
It is in accordance with our hypothesis that the rotatory power of methoxysuccinic acid , COOH .
COOH , is subject to but slight variation , as the formation from this compound of a closed tetraphane system corresponding to form III of tartaric acid is impossible ; it is nevertheless conceivable that the two compounds in esse in the original substance may rise to the corresponding derivative : but this argument would not apply to the case of chlorosuccinic , for example .
In this latter oase , however , two forms are still possible , related to one another as are maleic and fumaric acids , viz. , OH CIHC .
COOH COOH .
1 .
It is well known that the acid chloride derived from succinic acid has a owards solutes generally , apart fcasessphere action , olvents behave rwaysl 9Studies orocesses O in which some special property of the solute comes into operation to disturb ases brought forward binmiuthis rarity ooteworthy though totatory power oubstance varies the dispersive power of each set of solutions is practically identical .
By considering the of solvents generally and by further study of cases such as that afforded by the orthonitroparasulphonyl-derivative frequently referred to , in which case the activity of benzene as a solvent is quite out of the normal order , we hope that we shall be able to throw further light on this part of our subject .
But taking into account the numerous factors involved , the equilibrium arrived at in each case cannot well be otherwise than the outcome of a variety of changes which balance one another .
lt is not likely , therefore , that a simple solution of the problem can be found .
The difficulty is all the greater because of the difficulty of arriving at any proper basis of comparison .
Hitherto it has been customary to contrast the values arrived at by observations made in light of the refrangibility of the sodium hne but this is obviously insufficient ; even , however , when the observations are extended to rays of other refrangibilities , it possible that the difficulty of making proper parisons met with in the case of other physical properties will still not be overcome .
To state our views , in a few words:\mdash ; The variations in rotatory power met with in optically active compounds may be ascribed to alterations in molecular size and to the formation of compounds between solvent and solute ; ( b ) to the occurrenoe of changes giving rise to the presence of reversibly related isodynamic forms .
The charjges included under ( a ) are common to all optically active substances ; those included under ( b ) can occur only in special cases .
In these special cases , if the change involve the formation of compounds so different in chemical type that they not only differ in rotatory power in sign but also in rotatory dispersive power , the product might have anomalous dispersive power ; in other cases , it would behave normally . .
Winther , op .
, vol. 60 , p. 702 ; Walden , op .
, p. 397 .
|
rspa_1913_0039 | 0950-1207 | On the luminosity curves of persons having normal and abnormal colour vision. | 404 | 428 | 1,913 | 88 | Proceedings of the Royal Society of London. Series A, Containing Papers of a Mathematical and Physical Character | W. Watson, D. Sc., F. R. S. | article | 6.0.4 | http://dx.doi.org/10.1098/rspa.1913.0039 | en | rspa | 1,910 | 1,900 | 1,900 | 4 | 198 | 5,024 | http://corpora.clarin-d.uni-saarland.de/surprisal/6.0.3/?id=rspa_1913_0039 | 10.1098/rspa.1913.0039 | null | null | null | Optics | 58.741521 | Tables | 34.799195 | Optics | [
12.428780555725098,
-16.74764633178711
] | ]\gt ; fixed width .
Light of sensibly one wave-length , i.e. monochromatic light , * ?
will pass this slit , and by meaus of a lens placed in the beam of this light an image of the first face of the prism which is used to form the spectrum can be formed on a screen .
In this way a monochromatic patch of light is obtained , the brightness of which depends on the nature of the somce of light , the width of the collimator slit , the width of the slit placed in the spectrum , which for short will be called the moyable slit , and the dimensions of the lenses employed .
Further , if alongside this coloured patch is formed a white patch of light produced by light which proceeds from the same source but has not undergone dispersion , and that by some means or other the intensity*of this white light is altered till the coloured and white patches appear to the eye equally bright , then the intensity of the white light , ured in any arbitrary units , measures the luminosity of the light of that colour which is passing through the movable slit .
Since the unlt in which the white light is measured is arbitrary , we are not concerned * The physical brightness of a light , i.e. the stimulus , will be spoken of as the ntensity , the term being rved for the sensation produced when the light nters the eye .
Luminosity Curves of Colour Vision .
405 with the absolute intensity of illumination of the white patch , and may use screen satio ouantity oightany e given person tement ouminosity ogiven cight iemployed iifferent experiments.urther bbserved t patch appears tctrum iomparison orightness olouredhim wrightness obite patch a appears timThe above definition of what is meant by the luminosity of a colour in the spectrum of a given source is equivalent to that employed by Sir William Abney in all his work , and the only reason for , it is that to follow the S reasoning used in this paper it is essential that this definition should be kept in mind .
A convenient arrangement for conducting measurements of empl ebservati iveIlluminosit hescribed bFesti eThis iardly tlace tiscuss tccuracy which w :judge of the comparative brightness of , say , awhite and agreen light .
It is admittedly a difficult operation , but the results which are quoted below show that if the conditions are suitably chosen the measurement can be performed with considerable consistency .
The difficulty of comparing the obviated iflicker method employed , hich toloured ahitelights auccessively occupy tcreen ahebrightness ocoloured light wwhite light ilmost completely intensity of the white is altered till the flicker vanishes .
If suitable precautions are taken even quite inexperienced observers are found to be capable of making quite consistent measurements by the flicker method , and a satisfactory piece of apparatus for such measurements is described later .
If the movable slit described above is placed in different parts of the spectrum and the intensity of the white which appears equally bright is measured in each place , on plotting these intensities as ordinates , the abscissae prism deviations , a luminosity curve is obtained , that is a curve which gives the luminosity of the different colours in the spectrum of the source and for the particular prism employed .
As has been mentioned , the unit in which the intensity of the white is measured is quite arbitrary , and throughout this paper it is taken as such that for a eye the maximum luminosity in the spectrum of the brightness employed is The abscissae of the luminosiby curves given are also 'Phil .
Trans 1886 , Part II , p. 455 .
The intensity of illumination of the screen corresponding to 100 is throughout about , or candle-feet .
been shown ) Abney , Tufts , Ives and others*that , etc. *This statement requires a certain amount of limitation , and must be held only to apply to spectra of moderate brightness and to sources of light such that the light is not ?
chiefly due to the blue and violet .
The proposition that the luminosity of the sum of two lights is equal to the sum of the separate luminosities does not apply to very bright : lights , and in the case of very small intensities may not apply in the blue and violet .
having Normal and .
407 That is , the luminosity of the recombined spectrum is equal to sum of the luminosities of its parts .
, Now the sum , etc. , is proportional to the area enclosed by the luminosity curve .
Hence the area of the luminosity curve represents the totalbrighbnessofthelightwhichisformedintothespectrumandis , therefore , aconstanbwhate.vertheconditionofthevisionofthepersonwhomakestheobservationsThisisatonceapparentifwerememberthatifthe brightness of the whole recombined spectrum is compared with the comparison white , since these whites are derived from the same source and must , therefore , have exactly the same composition , a setting which appears correct to one person must also appear correct to any other , whatever the differences which may exist between their vision .
The fact thaG with a given spectroscope and source of , if the scale .
used for measuring the white is the same for all measurements , the area of the luminosity curve will be always the same is of great utility , since it allows us to correct for any variation in the unit in terms of which the white is measured , such as may occur owing to the mirrors , lenses , etc. , becoming tarnished .
It may be mentioned here that when a colour-blind observer makes a luminosity-curve determination I have often obtained my own curve at the same time .
The two sets of measurements being made immediately one after the other there is no time for the instrument to alter , and thaareas of the curves obtained have always been the same , although the shapes of the curves are often entirely different .
S 2 .
Calculation of the Form of the Curve for Cotour-Deficient Observers.\mdash ; Before giving the luminosity curves obtained in the case of colour- deficient observers , it will be convenie1lt to calculate what would be the for1n of the curves on certain assumptions .
We shall then be in position to judge of the accuracy of these assumptions by comparing the calculated curves with those obtained by observation .
Starting from the well-established fact that all colours can be matched by a combination , in suitable proportions , of three properly selected colours , Thomas Young and Helmholtz developed a theory of colour vision which supposes that the machinery by which oolour is perceived consists of three sets of mechanism , and that the sensation produced by of any .
is the sum of due to the individual mechanisms .
Or , as we may say , the sensation produced is the sum of the separate sensations produced by these separate mechanisms .
It is hardly necessary here to consider the line of reasoning by which the amount of each sensation produced by the different colours of the spectrum can be derived from experiments in which a coloured light of one wavefor the electric arc Area of red sensation curve 579 Area of green sensation curve 248 Area of blue sensation curve 'Phil .
Trans 1906 , , p. 333 .
having and Abnormal Colour Vision .
409 We have now to consider the manner in which the sensation curves of a person who has defective colour vision differ from the normal .
In several papers , Abney has forward evidence that , at any rate , in the case of the more dinary forms of colour defect , either the red sensation curve or the green sensation curve is modified , and that this modification is such that the shape of the curve remains unaltered , each ordinate being reduced in the same proportion .
* Thus , if the red sensation is deficient , and , say , the ordinate of the red sensation curve for any given wave-length is half the corresponding ordinate for the normal , then for all other wave- lengths the ordinates of the red se1lsation curve are also half those of the normal red sensation curve .
Hence it follows that the area of the red : sensation curve musb also be half the area of the corresponding curve for the normal .
If we possessed any method of measuring in absolut , units the sensation produced when light of a given intensity enters the eye , we should be ] to tackle the question as to whether the maximum ordinate of the sensation : curves was the same for all persons .
A certain amount of evidence on this matter has been obtained by Abney by the study of the minimum intensity of light required for vision .
For the present , however , we are confining ourselves to a study of the relative sensations produced by given amounts of light of dtfferent colours for each observer separately .
Thus we take some one kind of light as a standard and compare the relative stimulation of the sensations produced by other kinds of light with that produced by this standard light .
This is what is done when detsrmining a luminosity curve , the particular light chosen as a standard being white light , i.e. the light which we are going to use to produce the spectrum which supplies the different colours which are to be used iu the measurements .
Having to use white light as a standard , when we come to compare the measures made by a person having defective colour vision with those made by a normal , the matter is complicated by the fact that the unit with which the comparison is made , that is the'white , is pot the same for both .
The defective sensation will not only affect the sensation received from the coloured light , but also that received from the Abney 's theory as to the way the sensation curves of persons having defective colour vision differ * Another way in which we might have a departure from the normal would be if , say , the green sensation curve were displaced in such a way that its maximum occurred at a different wave-length .
There seems evidence that such a displacement may occasionally be met with , and the author hopes shortly to discuss this question in another communica- tion .
He has calculated the luminosity curves corresponding to such displacement and finds that they all intersect at neighbouring points , which do not coincide with the point referred to on p. 411 .
the wave-length is , and that and are the ordinates of the normal ] red and green sensation curves for this colour , the ordinates q for the observer will be and .
The total sensation produced by the !
colour will be the sum of the two sensations , that is , for the normal it will be and for the observer The sensation produced by the comparison white in the luminosity measurement will be proportional to the sum of the areas of the red and green sensation curves .
Hence , if we represent the areas of these curves for the normal by and respectively , the sensations produced by the white for the normal will be , and for the colour-deficient will be Thus the brightness of the coloured light is for the .
observer reduced in the ratio ) , while that of the white is reduced in the ratio .
Let be the intensity of the white when the normal observer makes the luminosity setting and the intensity of the white when the colour-deficient observer makes the setting .
Then we have .
( 1 ) and , ( 2 ) where is a constant which depends on the unit used to measure the intensity of the white light .
the case of a normal eye the total luminosity due to the blue sensation when white light enters the eye is only about 1/ 200 of that due to the red sensation .
results together with the normal luminosity curve are shown in fig. 2 .
It will be observed that all the luluinosity curves intersect at one point , , which corresponds to S.S.N. or a wave-length .
The i- condition that the luminosity should be the same for the normal as for , say , the .
observer is that [ equations ( 1 ) and ( 2 ) ] or or , ( 4 ) that is at a wave-length such that for both observers the ratio of the ordinates of their red and green sensation curves is the same as the ratio of ersons [ orresp nntersection independent o amount or kind of the deficiency in colour sensation of the observer .
FIG. 2 .
The curves given in fig. 2 depend on\mdash ; ( 1 ) Ths accuracy of Abney 's sensation curves .
( 2 ) The correctness of Abn ey 's theory that in the case of the ordinary types of total or partial red or Jreen colour-blindness the ordinates of one of the sensation curves are all reduced in the same proportion , and ( 3 ) The additive property which has been assumed and which involves the corollary that the areas of the luminosity curves obtained by normal and colour-deficient persons are the same .
Thus if it can be shown that the observed luminosity curves of persons who are colour deficient agree with the calculated curves it is strong evidence in favour of the correctness of the above three assumptions .
To test this point the observed luminosities obtained by colour-deficient observers will be shown plotted on diagrams containing the calculated curves in fig. 2 , so that it will be possible to see at a glance whether ( 1 ) the observed points all lie on one of these curves or lie uniformly between two adjacent curves indicating that the observer belongs to a class intermediate The wave-length at which all the curves will intersect depends on the distribution of light in the spectrum employed in the experiments , i.e. on the source of light .
them were published* before the sensation curves used in the calculations had been obtained .
It is also open to anyone to check the results by reference to the original papers .
[ Secondly , use is made of a selection from a large number of fresh measurements obtained in a different manner .
Since the equality of brightness method of obtaining the luminosity curves described above , involving as it .
does the comparison of the brightness of two lights which differ greatly in colour , is a process which requires considerable practice , although given such practice Abney 's numbers show that concordant measures can be obtained , : the flicker method originally described by Ferry , has been utilised for the : determination of luminosity curves .
In one arrangement which has been found to give good results , even with quite inexperienced observers , cylinder of diameter rotating about a horizontal axis is placed between the movable slit and the screen on which the light is received .
Segments are cub out of the circumference of the cylinder so that the screen is alternately illuminated by the coloured light and the comparison white , both kinds of light falling on the same part of the screen .
In order to obtain satisfactory measurements it is essential that the alternations from colour to * Sir W. Abney has stated in one of his papers that the numbers given in the papers which are quoted were all obtained before he had determined the sensation curves .
'Amer .
Journ. Sci 1892 , vol. 44 , p. 192 .
VOL. LXXXVIIL\mdash ; A. 2 FIG. 3 .
'Roy .
Soc. Proc 1910 , , vol. 83 , p. 472 .
In figs. 3 and 4 we have examples of persons who have R.S. and : G.S. respectively .
In fig. 6 observer has G.S. and observer has R.S. .
In figs. 6 and 7 we have two examples of persons having R.S. and one having G.S. It will be noticed that when the observed points are plotted on such a scale that the area of the curve drawn through them is the same as the *All the numbers given in this paper were obtained when the observer was dark adapted .
On plotting the numbers iven in the ' Philosophical Transactions ' for V. H. , it was obvious that some error had crept in , and on submitting the matter to Sir W. Abney , he said he had already moticed that , owing to a mistake when reducing the scale readings of the instrument to S.S.N. , the numbers as given were erroneous .
He has kindly looked up the original asurements and the points given in fig. 6 are obtained from these numbers .
FIG. 6 .
Roy .
Soc. Proc 1910 , , p. 460 .
, ' Roy .
Soc. Proc 1910 , , p. 472 .
Abnormal Cobur Vision .
417 FIG. 6 . .
B. , ' PhiL Trans 1892 , p. 556 .
V. H. , ' Phil. Trans 1892 , p. 555 .
FIG. 7 .
, ' Boy .
Soc. Proc 1910 , , vol. 83 , p. 466 .
FIG. 8 .
No. 2 .
curves were obtained with an arc in which the positive carbon was horizontal , so that the crater is directly facing the slit of the spectroscope .
The equality of brightness curves were obtained using an arc with nearly vertical carbons , so that the crater was turned more or less edgeways towards the slit .
Most of the difference between the two curves is , however , a real difference , due to the difference of method .
Tbis difference is most marked in the green and May 6 , 1913.\mdash ; This is the mean obtained by 10 observers .
* , foveal .
No. 6 , parafoveaL rightness oparts opectrum omparison white varies tntensity ooured light Hence , oted tarying tintensiGy oxamined bseries o the comparisons with white were made , while , in my experiments , the brightness of the coloured light , and hence also of the comparison white , was very much less at the ends of the spectrum than at the middle .
$ In fig. 8 , Observer 1 has about , while Observer 2 has about In fig. 9 , Observer 4 has about , and Observer 3 , .
In fig. 10 , the points marked by ashow that Observer 5 has a little over Observer 1 has a shortened spectrum , a neutral point , and he mistakes red for green , and vice .
He matches a mixture of green and violet light with white , and any amount of deep red could be added to the mixture without his being aware that any change had been made , although this addition of red caused the mixture , to a normal eye , to change from a bluishgreen to a bright red .
He is quite unable to correctly distinguish the colours of ships ' lights .
Observer 2 has a neutral point , and calls the green of this part of the spectrum white .
He often calls a green light white or a white light green , and , with lights of small intensity and small angular magnitude , he occasionally confuses green and red .
Observer 3 frequently calls white green and green white , and , with lights of small angular magnitude , he occasionally calls red green .
Observer 4 has a shortened spectrum and confuses red and green .
With ships ' lights , at distances up to 2 sea miles , he made over 20 per cent. of mistakes .
Observer 5 has a neutral point and calls green white and white green .
If a little white light is added to any green , he calls the mixture white , although to a normal eye it still appears a fairly saturated green .
S 5 .
In the preceding two sections examples have been given of what may be termed " " normal\ldquo ; luminosity curves for persons having both normal and defective colour vision .
The great majority of the luminosity curves obtained belong to this class .
In a few , cases , however , both of persons possessing normal colour vision and of those possessing defective colour vision , the luminosity curves differ in that they do not agree with any of the curves given in fig. 2 , nor do they lie uniformly between any adjacent pair .
Taking first the case of abnormal curves given by persons who have normal colour vision .
In and 12 , the points marked by , and through 'Phil .
Mag July , September , and December , 1912 .
through toint Purve passing cbove toint ahements mbservers Ieither curves passwhich tdotted 1correspond tosity m ' * FIG. 11 .
, foveal .
No. 6 , parafoveal .
FIO .
12 .
, foveal .
No. 7 , parafoveaL border subtended an angle of at the eye of the observer , while the external border subtended an angle of .
A small white dot at the centre served to fixate the eye .
Although this arrangement is more difficult to use than the small square , yet with a little practice fairly good .
settings could be obtained .
The points marked in figs. 11 , 12 , and 14 give the results obtained for the parafoveal region for Observers 6 , 7 , and the author .
The first thing that strikes one is that in the case of Observer 7 the luminosity curve is practically the same for the parafoveal and the foveal regions , and that both of these agree with the author 's parafoveal curve .
Next , in the case of Observer 6 , the parafoveal curve more nearly agrees with the foveal curve for the normal .
This distinction is brought out very clearly in fig. 15 , where the ratio of the parafoveal luminosity to the foveal for No. 7 and W. W. are shown .
It will be seen that for Observer 7 the rati is practically constant and equal to unity throughout the spectrum , .
while for W. W. the ratio increases rapidly as the blue end of the spectrum is reached .
It would thus appear that Observer 7 has no more pigment at 'Phil .
Trams 1860 , vol. 160 , p. 76 .
S. S. N. FIG. 16 .
1o Observer 6 cannot make reliable settings beyond the blue-green , the light 3 appearing to him too feeble .
requireslittleornoviolet , eason being twing tacular absorptionmatching awhite beans omixture ogreen , iolet light hObserver 6appears tuite normal colour 8ense , although w the white is to him much\ldquo ; yellower\ldquo ; than to a normal eye , and hence the ; mixture of red and green which to the normal looks yellower than ; S white appears to him a correct match .
He is quite good at matching blues ] and violets .
Observer 7 has also normal colour sense , although for his white match he uses more violet than the normal .
In figs. 16 and 17 are shorn the flicker luminosity curves of two observers who have defective colour vision , the green sensation being in each case in defect , and who , in addition , appear to have more than the normal amount of pigmentation of the fovea .
In fig. 18 Observer has more pigmentation than the normal , and his G.S. is practically zero .
Observer N. W. , on the hand , is defective as to red sensation but has less pigmentation than the normal .
It would be very interesting to examine the parafoveal luminosity curves for these colour-deficient observers , but unfortunately up to now it has been impossible to get them to devote the necessary time to make the observations .
The parafoveal curve for Observer 5 is indicated by the points marked in fig. 10 .
The pigmentation of this observer appears to be normal .
In fig. 19 are given the luminosity curves of two persons who were * The values given in figs. 18 , 19 , 20 were all obtained by the lity of brightness method .
A displacement of the green sensation curve towards the red end of the spectrum would give a luminosity curve very like those ined by Observers 8 and 9 .
A study of their parafoveal luminosity curves might enable one to say whether they are cases of green deficiency plus abnormal macular pigmentation or cases oi such dkplacement .
: ; having and Abn : S. ; FIG. 16 .
, foveaL FIG. 17 .
, foveal .
suffering from tobacco scotoma , and it will be observed that the curves are of an entirely different type to any of those previously given .
In fig. 20 FIG. 19 .
, ' Roy .
Soc. Proc 1891 , vol. 49 , p. 502 .
C. , ' Roy .
Soc. Proc 1891 , vol. 49 , p. 493 .
having and are given the curves for two observers due to disease ( atrophy of the optic ner very nearly rees with the normal , A resembles that of Observer 7 .
It disease Ghe colour-blindness which is to that which is found in cases of case comparison of the luminosity curv seems as if it might give us valuaOle in perceiving apparatus .
9 .
' : Sg Miss W. , ' Roy .
, vol. 49 , p. 507 .
W. S. , ' Boy .
Soc. Proc 1891 , , p. 498 .
The examples of the luminosity rVeS of different colour-deficient persons which have been given form only a small proportion of the cases which the author has examined .
They will , however , be sufficient to show that the : assumptions on which the calculated curves are based must , in the main , be true .
Abney 's theory that the different classes of the more commonly occurring forms of congenital colour defect are due to different degrees of deficiency in the red or green sensations is so strongly supported as to practically amount to a complete proof .
It must be remembered that the *The eye tested had become " " colour blind\ldquo ; after a stroke of paralysis ; the other eye was still normal .
VOL. LXXXVIIL\mdash ; A. 2 428 Prof. W. H. Brag and Mr. W. L. Brag .
[ Apr. investigation given above has been confined to that portion of the on the red side of the blue .
If we wish to extend our investigation into blue and violet then we should have to take account of the effect of the blue sensation .
Further , although it seems quite clear that the major part of luminosity perceived in that part of the spectrum including the red , yellow and green , at any rate with fairly bright spectra , is due to the red and greeq sensations , there is much evidence to indicate that , at any rate in the green and blue , there is a fourth sensation which may be called the fundamental : .
white sensation .
This probably corresponds to the rod-effect of von Kries , which would have to be taken into account if extremely minute differences of luminosity were under consideration , or were with spectra of .
small intensity .
The Reflection of -rays by Crystals .
By H. BRAG , , F.B.S. , Cavendish Professor of Physics in the University of Leds ; and W. L. BBAGG , B.A. , Trinity College , Cambridge .
( Received Apri17 , \mdash ; Read April 17 , 1913 .
) In a discussion of the Laue photographs it has been shown*that they may conveniently be interpreted as due to the reflection of -rays in such planes within the crystal as are rich in atoms .
This leads at once to the attempt to use cleavage planes as mirrors , and it has been found that mica gives a reflected pencil from its cleavage plane strong enough to make a visible impression on a photographic plate in a few minutes ' exposure .
It has also been observed that the reflected pencil can be detected by the ionisation method .
For the purpose of examining more closely the reflection of -rays in this manner we have used an apparatus resembling a spectrometer in form , an ionisation chamber taking the place of the telescope .
The collimator is replaced by a lead block pierced by a hole which can be stopped down to slits of various widths .
The revolving table in the centre carries the crystal .
The ionisation chamber is tubular , 15 cm .
long and 5 cm .
in diameter .
Tt can be rotated about the axis of the instrument , to which own axis is perpendicular .
It is filled with sulphur dioxide in order to increase the ionisation current : both air and methyl iodide have also been used occasionally to make sure that no special characteristics of the gas W. L. Brag , ' Proc. Camb .
Phil. Soc vol. 17 , Part I , p. 43 .
W. H. Brag , ' Nature , ' Jan. 23 , 1913 .
|
rspa_1913_0040 | 0950-1207 | The reflection of X-rays by crystals. | 428 | 438 | 1,913 | 88 | Proceedings of the Royal Society of London. Series A, Containing Papers of a Mathematical and Physical Character | W. H. Bragg, M. A., F. R. S.|W. L. Bragg, B. A. | article | 6.0.4 | http://dx.doi.org/10.1098/rspa.1913.0040 | en | rspa | 1,910 | 1,900 | 1,900 | 3 | 125 | 3,053 | http://corpora.clarin-d.uni-saarland.de/surprisal/6.0.3/?id=rspa_1913_0040 | 10.1098/rspa.1913.0040 | null | null | null | Optics | 40.668309 | Atomic Physics | 31.859081 | Optics | [
17.56589698791504,
-24.16006851196289
] | ]\gt ; 428 Prof. W. H. Brag and Mr. W. L. Brag .
[ Apr. investigation given above has been confined to that portion of the on the red side of the blue .
If we wish to extend our investigation into blue and violet then we should have to take account of the effect of the blue sensation .
Further , although it seems quite clear that the major part of luminosity perceived in that part of the spectrum including the red , yellow and green , at any rate with fairly bright spectra , is due to the red and greeq sensations , there is much evidence to indicate that , at any rate in the green and blue , there is a fourth sensation which may be called the fundamental : .
white sensation .
This probably corresponds to the rod-effect of von Kries , which would have to be taken into account if extremely minute differences of luminosity were under consideration , or were with spectra of .
small intensity .
The Reflection of -rays by Crystals .
By H. BRAGG , , F.B.S. , Cavendish Professor of Physics in the University of Leds ; and W. L. BBAGG , B.A. , Trinity College , Cambridge .
( Received Apri17 , \mdash ; Read April 17 , 1913 .
) In a discussion of the Laue photographs it has been shown*that they may conveniently be interpreted as due to the reflection of -rays in such planes within the crystal as are rich in atoms .
This leads at once to the attempt to use cleavage planes as mirrors , and it has been found that mica gives a reflected pencil from its cleavage plane strong enough to make a visible impression on a photographic plate in a few minutes ' exposure .
It has also been observed that the reflected pencil can be detected by the ionisation method .
For the purpose of examining more closely the reflection of -rays in this manner we have used an apparatus resembling a spectrometer in form , an ionisation chamber taking the place of the telescope .
The collimator is replaced by a lead block pierced by a hole which can be stopped down to slits of various widths .
The revolving table in the centre carries the crystal .
The ionisation chamber is tubular , 15 cm .
long and 5 cm .
in diameter .
Tt can be rotated about the axis of the instrument , to which own axis is perpendicular .
It is filled with sulphur dioxide in order to increase the ionisation current : both air and methyl iodide have also been used occasionally to make sure that no special characteristics of the gas W. L. Bragg , ' Proc. Camb .
Phil. Soc vol. 17 , Part I , p. 43 .
W. H. Bragg , ' Nature , ' Jan. 23 , 1913 .
hamber affect tonisation currentis measured dance method hound ieflect aortion orimary r oduce affect c The slit which the primary pencil of -rays emerges from the box iner .
Since tfrom tnticathodee engular width obout athird odegree i the latter case .
In the same way a slit 2 mm. wide and mm. long admit , S the reflected pencil to the ionisation chamber when preliminary measurements are being made , or when the whole effect is feeble ; and this width can be cut down to mm. when desired .
The distance from either slit .
to the axis of the apparatus is 8 cm .
We have foumd it best to keep the bulb ver .
" " soft The cathode stream has often been visible over its whole length .
As will be seen later it is desirable to determine angles of incidence and reflection with great accuracy .
This was not anticipated , and the circular scale was only divided into rees , and was made too small .
Nevertheless , it is possible to read tenths of a degree ; a better and more open scale is now put in .
Let us suppose that a crystal is placed on the revolving table so that the cleavage face passes through the axis of the instrument .
Let the incident pencil fall on the face and make an with it ; and let the crystal be kept fixed while the ionisation chamber is revolved step by step through a series of angles including the double of , the ionisation current being measured at each step .
The results of such a set of measurements are shown in fig. 1 .
In this case the crystal is FIG. 1.\mdash ; Begular reflection from rock-salt ; and it has been so that the cIeavage face of rock-salt , incident pencil makes an angle of \mdash ; as glancing angle given by the apparatus\mdash ; with the incident beam .
The points marked in the figure show the result of setting the ionisation chamber at various angles and measuring the current in each case .
chamber spparatus trotation of the chamber or .
The figure that these limits are actually observed ; the whole curve lies well within the range to .
The source must therefore be nearly a point .
ation chamber hetermined , irror ahamb beWhen trelation between tngles orystal mirror a swept together through an extended range , the relation between the angles such that the chamber always shows the maximum current for each setting of the crystal .
It is convenient to use the wide slits for a preliminary examination of this kind .
When the effect is small the wide slits can alone : be used .
But in a number of cases it is possible to use the narrow slits in ordel to make a closer survey , and where this is done much more information , can be obtained .
The curve in fig. 2 shows the results of a sweeping movement of this kind , the crystal being iron pyrites .
Curves for rock-salt are drawn in figs. 3 , I , and 3 , II .
It will be observed that there are peculiar and considerable : variations in the intensity of the reflection at different angles .
The three u peaks marked , and are common to the curves of all crystals so far : investigated , e.g. zinc blende , potassium ferrocyanide , potassium bichromate , quartz , calcite , and sodium ammonium tartrate .
They are readily distinguishable by their invariable form , relative magnitudes , and spacings .
: Moreover , the absorption coefficients of the rays reflected at these separate 1 angles do not vary with the nature of the crystal or the state of the bulb .
It happens that the actual angles of reflection of the three sets of rays nearly the same for several crystals .
The use of the narrow slits permits a closer examination of these 5 Degrees .
FIG. 3.\mdash ; Reflection ( I ) from face ( 100 ) and ( II ) from face of rock-salt .
The curves show the variation of strength of reflected beam with angle of incidence .
effects ; but , of course , it takes much longer time to make , and more space to exhibit .
The results for iron pyrites are shown in the series of curves of fig. 4 : a series in which each curve is obtained in the same way as the curve of fig. 1 , the crystal being set at some definite angle which is altered in going from curve to curve .
The curves are arranged so that the vertical distance between the horizontal lin es of reference of any pair is proportional to the difference in the angles of setting of the crystal in the two cases .
In comparing the curves at the different angles two principles must be borne in mind .
In the first place if there is a general reflection of rays throughout the whole range of the pencil which is emerging from the slit near the bulb , the curves show , as in fig. 1 , a maximum with similar slopes Prof W. H. Brag and Mr. FIG. 4.\mdash ; Detailed examination of reliection Here is the bulb slit , the axis of the instrument , and the chamber slit .
When the crystal face is in the position PR , let us say , the ray OP strongly marked homogeneous pencils of sharply defined quality ; they occur 1 at ( uncorrected chamber angles ) , and .
What we have called ; the general reflection may comprise many other definite pencils , but they are scarcely resolved at all in this series of curves .
Their presence is , however , fairly obvious .
A series of potassium ferrocyanide curves shows them much more clearly .
Three of this series are shown in fig. 4 , and their peculiar forms indicate to what extent interpretation has yet to be carried .
When these neous beams are isolated by the use of narrow slits , it is possible to determine their absorption coefficients in various substances .
In the end , there is no doubt , this will be done with great acculacy ; for the present , our results must only be looked on as provisional .
They are , perhaps , right to 5 per cent. for many purposes this is quite sufficient .
In the case of rock-salt we find the mass absorp , tion coefficients in aluminium of , and to be , and respectively , the last being the most doubtful and probably too low .
The absorption coefficient of the -rays in Ag is 74 , in Cu 140 , in Ni 138 ; these values are approximate .
We have made no exhaustive determination of the coefficients in the case of various crystals , but in a number of cases , all those tried , we have found them to be the same .
There can be little doubt the three peaks are , in all cases , due to the same three sets of homogeneous rays , rays which do not change with the state of the bulb , but may well do so with the nature of the anticathode .
It atinumis vound bhapman fharacteristic radiation oefection observed tbsorption coefficient oeast penetrating s hows Tetermined wreat accuracy ; enwith haratus twithin 1 The angles at which the special reflections of these rays take place are not \amp ; : The readings for zinc blende and calcite are not corrected for errors of setting .
The difference in the case of the two faces of rock-salt gested an attempt to find a repetition of the characteristic three peaks at multiples or sub-multiples of those at which they were first observed .
For the sines of and ( half the angles of the chamber settings of the peak in the two cases ) are and respectively .
These are very nearly in the ratio 1 : .
If the effects are true diffraction effects such a lelation might be expected .
The { 111 } planes are further apart than the { 100 } planes in the ratio 2 : ; the sines of angles of special reflection should be in the inverse ratio , : 2 .
True , the sines of the angles have been increased in the ratio 1 : , instead of diminished in the ratio 2 : , but it is not at all unlikely that a spectrum in one case is being compared with a spectrum of higher or lower order in the other .
We , therefore , made a search for other spectra and found them at once .
In the case of rock-salt we found traces of a third .
The full rock-salt curves are shown in fig. 3 for the two kinds of face .
The peaks first found are marked , and their repetitions there is a trace of also .
The corrected positions of are , and .
The sines of the halves of these angles are , and , and are very nearly in the proportion 1 : 2 : 3 .
The absorption coefficient of the rays at is the same as that of the rays at In the case of the rock-salt section { 111 } a spectrum occurs at half the angles first found .
This is shown in fig. 3 , II .
It is not at all strongly beyond that of wave.length .
These results do not really affect the use of the corpuscuIar theory of X-rays .
The theory represents the facts of the transfer of energy from !
electron to -ray and vice , and all the phenomena in which this transfer is the principal event .
It can predict discoveries and interpret them .
It is useful in its own field .
The problem remains to discover how two hypotheses so different in appearance can be so closely linked together .
It is of great interest to attempt to find the exact wave-length of the rays to which these peaks correspond .
On considering Curve I , fig. 3 , it seems evident that the peaks are analogous to spectra of the first and second orders , because of the absence of intervening sets of peaks .
The value of in the equation seems clear .
The difficulty of assigning a definite wave-length to the rays arises when we atcempt to determine the value of , the distance of plane from plane .
* We learn that Messrs. Moseley and Darwin have lately been making similar to some of those recorded here .
Their resuIts , which have not been published , : agree with ours .
1913 .
] The Reflecbion of -rays by rystals .
437 3 .
There is strong evidence for supposing that the atoms of a cubic crystal like rock-salt , containing two elements of equal valency , are arranged parallel to the planes { 100 } in planes containing equal numbers of sodium ; and chlorine atoms .
The atoms in any one plane are arranged in alternate rows of each element , diagonal to the cube axes , successive planes having these rows opposite ways .
The question arises as to whether the value of is to be taken as that between two successive planes , or two planes identical in all respects .
The value of in the one case is twice that in the other .
The centres of the atoms of sodium and chlorine , regarded for the time being as identical , are arranged in a point system , having as unit of its pattern a cube with a point at each corner and one at the centre of each cube face .
The dimensions of this elementary cube can be found in the following If the side of the cube is of , the volume associated with each point in the point system will The mass of a hydrogen atom being .
and the density of rock-salt , we have This gives The distance between planes passing through atoms identical in all respects is this distance .
The wave-length , as calculated in this way , is for the peak B. But half-way between these planes which are identical in all respects are situated planes containing the same number of sodium and chlorine atoms , though the arrangement is not in all respects the same .
Possibly this tends to make the odd spectra due to the first lot of planes disappear , and , if this is the case , we must halve the first estimate of the wave-length , and put The difference between these two values corresponds to as a unit of the point system\mdash ; ( 1 ) The group , the smallest complete unit of the crystal pattern .
( 2 ) The individual atom of either nature , associated with only one-eighth of the volume of the complete unit .
We have also examined the reflection from the ( 110 ) face of the rock-salt , and have found the peaks situated such angles as indicate that the ratio of The wave-lengths to be associated with the spots in the photographs taken by Laue of the diffraction of -rays by crystals are much smaller than these 1 values .
They belong to the region in which we have found reflection to take plaoe at all angles , a region in which the peaks do not obviously occur .
This } : agrees with the distribution of intensity amongst the spots .
The experimental method can be applied to the analysis of the radiation from any soulce of -rays .
It may , however , be able to deal only with intense radiations .
The three sets of rays issuing from the bulb we have been using have angles of reflection whose sines are The reciprocals of these are , 5 , and .
The frequencies , and therefore , according to Planck , the corresponding quantum energies , are in arithmetical progression .
In this there is some hint of analogy with .
's recent work on the of the various types of -ray from Prof. Barkla has lately communicated to the Physical Society an account of certain experiments in which a diffuse pencil of -rays , when reflected on the cleavage plane of a crystal , acted on a photographic plate , producing a series of bands .
The effect which we have been describing is clearly identical in part with that which Prof. Barkla has described .
It is impossible , of course , to criticise a communication of which we have seen an abstract only .
But it seems probable that the ionisation method can follow the details of the effect more closely than the photographic method has so far been able to do : and that in this way it is possible to distinguish between those bands which represent distinct sets of rays , and those which are repetitions of one and the same set .
|
rspa_1913_0041 | 0950-1207 | Studies of the processes operative in solutions. XXVIII.-The influence of acids on the rotatory power of cane sugar, of glucose and of fructose. | 439 | 443 | 1,913 | 88 | 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.1913.0041 | en | rspa | 1,910 | 1,900 | 1,900 | 2 | 45 | 1,221 | http://corpora.clarin-d.uni-saarland.de/surprisal/6.0.3/?id=rspa_1913_0041 | 10.1098/rspa.1913.0041 | null | null | null | Biochemistry | 43.77928 | Tables | 20.256597 | Biochemistry | [
-54.1552734375,
-43.7035026550293
] | ]\gt ; Studies of the Processes in Solutions .
XXVIII .
Tfoe Influence of Acids on the Rotatory Power of ugar , of Glucose and of Fructose .
By F. P. WORLEY .
( Conlmunicated by Prof. H. E. Armstrong , F.R.S. Received April 15 , \mdash ; Read May 1 , 1913 .
) It is shown in Part XXII of this series of studies that when cane is rationshydrolysed , inthepresenceofsolutionsofsulphuricacidofdifferentcon-theratioofthefinalvalueoftherotationoftheinvertsugarto the initial value due to the cane sugar becomes very considerably greater as the concentration of the acid is increased .
The effect was attributed to : an increase in the optical rotatory power of the sugars caused by the acid ; from the fact that the ratio of acid to sugar was the same in most of the experiments , it was argued that the determining factor was the ratio of acid to water , the alteration in the rotatory power being due mainly to changes in the water .
Judging from the results of preliminary experiments and the work of previous investigators , it was probable that the fructose was the sugar chiefly affected but that the observed change in the above ratio could not be attributed to this cause alone .
In the course of experiments recently carried out to determine the hydrolytic activity of benzenesulphonic acid at different degrees of dilution , data have been accumulated which confirm the results arrived at when sulphuric acid was used as the hydrolyst .
Experiments have also been [ carried out to determine the effect of the acid on the rotatoly power of cane sugar , glucose and fructose .
It will be seen on reference to the following table that as the concentration of the acid is increased from one molecular proportion in two hundred of ( Observations vrere made in the light of the meroury green line .
) 80 I20 160 Z00 Mols .
to 1 of acid .
Curve A. ) DIAGRAM I. In the experiments carried out to find the effect of acid on the rotatory power of cane sugar , glucose and fructose , the molecular proportions used were very approximately of sugar and 40 of hydrone in the presence and absence of 1 of benzenesulphonic acid .
cane sugar used was carefully purified coffee sugar , specially supplied by Messrs. Tate and Sons .
Kahlbaum 's first quality glucose and ' ' crystallised\ldquo ; fructose were used .
The water of crystallisation of the glucose was removed by desiccation in vacuo over concsntrated sulphuric acid at 10 C. No special precautions were taken to purify the glucose and fructose , as the object of the experiments was to find the change in rotatory power caused ever , vident there wmpurity present.hief eresence ojudging fotatory powers arrived aStudies operative iolutions .
notdiffelwasthat.thesamplesusedintheexperimentswithandwithoutacidshouldinrotatorypower ; toensurethis , aweighedquantityofthesugar was lved in water and portions of this solution were used in making up the solutions for the experiments .
Care was taken that mutarotation was always complete .
The same polarimeter tube was used throughout .
k$k In order to deduce the value of the initial rotatory power of the cane sugar in the presence of the acid , it was necessary to make observations as soon after mixing as possible and by extrapolation to deduce the value of the rotation produced at the time of mixing .
The solutions were contained unmixed in the mixing apparatus , described in Part XII , consisting of two 100 .
Jena conical flasks connected by a short wide -tube ground into the necks .
After being brought to C. in the constant temperature air chamber described in Part XXII , the solutions were quickly mixed while still in the chamber , the time being noted ; they were then immediately transferred to the polarimeter tube which was already at on the water circuit .
Readings of the rotatory power were taken at half-minute intervals and from these it was easy to find with a close approach to accuracy by extrapolation the value of the rotatory power at the time of mixing .
The initial rotatory powers given above were obtained in this malmer .
Table II .
Time in minutes after mixing Rotation NUTES AFTER M IXINC DIAGRAM IL 62.45\mdash ; 104.40 and The value of the ratio found when the molecular proportion of water to acid was 40 to 1 was .
In the absence of acid , therefore , it should be This value is practically identical with that found from Diagram I by extrapolation to zero concentration of acid , viz. , ; that found when sulphuric acid is used is Velocity of a-Partides in through Matter .
443 It is therefore clear that the large alteration produced by the acid in the value of the ratio of the final to the initial rotation in the experiments on : the hydrolysis of cane sugar oan be completely and satisfactorily explained by the changes produced by the acid in the rotatory powers of the three sugars involved .
The Decrease in yelocity of a-Partides in through Matter .
By E. MARSDEN , M.Sc .
, Lcturer , and T. S. TAYLOR , Ph. D. , John Harling Fellow , University of Manchester .
( Communicated by Prof. E. Rutherford , F.R.S. Received Apri122 , \mdash ; Read May 1 , 1913 .
) It is becoming recognised that one of the most fruitful sources of information as to the internal structure of atoms is provided by the phenomena attendin the passage of swift electrified particles through them .
In particular from a consideration of the scattering of -particles it has been found that the atom consists essentially of a very concentrated charge at the centre of the atom*surrounded by electricity of the opposite sign , probably electrons , distributed throughout the remainder of the atom .
Further , Darwin and have attempted to obtain information as to the number and distribution of electrons in the atom by a consideration of the absorption or loss of velocity of the -particles in passing through matter .
The only data for this purpose so far obtainable aoe provided by the velocity curves , or relations between velocity and thickness of matter traversed , in aluminium as determined by Rutherford , S and in mica as determined by It seemed , therefore , of interest to make a more complete investigation of the velocity curves in various ances , more particularly as the earlier observations are subject to slight errors due to the assumption that equal thicknesses of matter have the same air equivalent at different parts range of -particles .
In the present experiments the velocity curves in gold , copper , aluminium , mica and air have been determined , using as source the -particles of E. Rutherford , ' Phil. Mag 1911 , vol. 21 , p. 669 .
C. G. Darwin , ' Phil. Mag 1912 , vol. 23 , p. 907 .
N. Bohr , ' Phil. Mag 1913 , vol. 26 , p. 10 .
S E. Rutherford , ' Phil. Mag 1906 , vol. 12 , p. 138 .
Geiger , ' Roy .
Soc. Proc 1910 , , vol. 83 , p. 605 .
VOL LXXXVIIL\mdash ; A. 2 I
|
rspa_1913_0042 | 0950-1207 | The decrease in velocity of \#x3B1;-particles in passing through matter. | 443 | 454 | 1,913 | 88 | Proceedings of the Royal Society of London. Series A, Containing Papers of a Mathematical and Physical Character | E. Marsden, M. Sc.|T. S. Taylor, Ph. D. |Prof. E. Rutherford, F. R. S. | article | 6.0.4 | http://dx.doi.org/10.1098/rspa.1913.0042 | en | rspa | 1,910 | 1,900 | 1,900 | 2 | 166 | 4,032 | http://corpora.clarin-d.uni-saarland.de/surprisal/6.0.3/?id=rspa_1913_0042 | 10.1098/rspa.1913.0042 | null | null | null | Atomic Physics | 33.545579 | Tables | 27.569479 | Atomic Physics | [
7.449884414672852,
-79.11833190917969
] | ]\gt ; Velocity of a-Partides in through Matter .
443 It is therefore clear that the large alteration produced by the acid in the value of the ratio of the final to the initial rotation in the experiments on : the hydrolysis of cane sugar oan be completely and satisfactorily explained by the changes produced by the acid in the rotatory powers of the three sugars involved .
The Decrease in yelocity of a-Partides in through Matter .
By E. MARSDEN , M.Sc .
, Lcturer , and T. S. TAYLOR , Ph. D. , John Harling Fellow , University of Manchester .
( Communicated by Prof. E. Rutherford , F.R.S. Received Apri122 , \mdash ; Read May 1 , 1913 .
) It is becoming recognised that one of the most fruitful sources of information as to the internal structure of atoms is provided by the phenomena attendin the passage of swift electrified particles through them .
In particular from a consideration of the scattering of -particles it has been found that the atom consists essentially of a very concentrated charge at the centre of the atom*surrounded by electricity of the opposite sign , probably electrons , distributed throughout the remainder of the atom .
Further , Darwin and have attempted to obtain information as to the number and distribution of electrons in the atom by a consideration of the absorption or loss of velocity of the -particles in passing through matter .
The only data for this purpose so far obtainable aoe provided by the velocity curves , or relations between velocity and thickness of matter traversed , in aluminium as determined by Rutherford , S and in mica as determined by It seemed , therefore , of interest to make a more complete investigation of the velocity curves in various ances , more particularly as the earlier observations are subject to slight errors due to the assumption that equal thicknesses of matter have the same air equivalent at different parts range of -particles .
In the present experiments the velocity curves in gold , copper , aluminium , mica and air have been determined , using as source the -particles of E. Rutherford , ' Phil. Mag 1911 , vol. 21 , p. 669 .
C. G. Darwin , ' Phil. Mag 1912 , vol. 23 , p. 907 .
N. Bohr , ' Phil. Mag 1913 , vol. 26 , p. 10 .
S E. Rutherford , ' Phil. Mag 1906 , vol. 12 , p. 138 .
Geiger , ' Roy .
Soc. Proc 1910 , , vol. 83 , p. 605 .
VOL LXXXVIIL\mdash ; A. 2 I The source consisted of a fine platinum wire cm .
in length and mm. in diameter which had been exposed to a strong source of radium emanation so as to become activated with a deposit of about 20 millicuries radium C. Twenty minutes after the wire was withdrawn from the emanation the radium A had practically disappeared , so that the -particles emitted came from radium only .
The source fitted with its ends in a support attached to the pIatform , which also held the slit wire being adjusted so as to be parallel to the slit and about 8 cm .
from it .
The platform could be slipped into the brass chamber and against a stop as shown in the figure , the opening being closed by a ground glaSs plate I , and the whole evacuated through a tube by means of a Fleuss pump and cooled charcoal : The foils whose absorption was under inveitigation were placed over windows in a " " laddtr\ldquo ; , and by means of a pie66 of thread attached 3 1913 .
] Velocity of rticles in passing through Matter .
445 round a tube projecting from a ground-glass joint any particular window : could be placed opposite the source without altering the exhaustion in any way .
The absorption foils were weighed in the form of single sheets and a number of layers taken , so that successive windows differed from one another by convenient amounts .
In all cases the air equivalents of the windows were also obtained by the scintillation method , these measurements affording a useful .
check on the weighings .
The pencil of -particles passed through the slit and fell on the zinc sulphide screen , producing a fine line of scintillations , the position of which could be easily read to 1/ 20 mm. by means of a travelling microscope K. The magnetic field was then applied perpendicular to the plane of the diagram and the position of the line of scintillations again read .
The successive windows were then moved in front of the source and the new positions of the line of scintillations determined .
Similar observations were made with the same value of the magnetic field , but reversed , and the double deflections obtained by subtracting the corresponding readings .
Measurements were continuedwith different field strengths up to9000 gauss , until the radium had decayed to such a small activity that observations were difficult to make .
The relative velocities were calculated by substituting in the formula , where , and are the respective values of the mass , velocity , and charge of the -particles , the field strength and the radius of curvatule of the path of the particles obtained from the relation .
In the latter formula is the deflection produced by the magnetic field as measured on the screen , and and the distances of the slit from the source and screen respectively .
This formula applies to th .
experiments , as the whole of the path of the particles was in the magnetic field , which was uniform to less than 1 per cent. throughout the whole of its length .
In all cases the ratios of the velocities , with and without absorption sheets , were ted , and these are practically inversely proportional to the double deflections in the same magnetic field , a small correction being necessary , depending on the tudes of the deflections .
An example of a set of readings is given in Table I. The velocity curve obtained in the case of gold is shown in fig. 2 , the ordinates represent relative velocities and abscissae the mass per unit area , or thickness density , of the foils used .
For foils greater than about 6 cm .
air equivalent the velocity changes rapidly with thickness , and the method generally adopted was to place a foil of about cm .
air equivalent directly over the source , and to use additional foils for the windows of the " " ladder\ldquo ; increasing thickness by very small amounts .
446 Mr. Marsden and Dr. Taylor .
The Decrease in [ Apr. 22 , : Mass of gold per sq .
cm .
FIG. 2 .
The curve shown is seen to be smooth down to a velocity of of the initial velocity corresponding to a mass per square centimetre of or an air equivalent of cm .
at C. and 76 cm .
Hg .
Here a somewhat unexpected difficulty was encountered , for with additional thickness of foil no further diminution in velocity could be detected .
The line of scintillaiions apparently remained stationary although steadily decreasing in intensity with increasing thickness .
Similar results were obtained with Cu , Al , and mica ; in no case could we obtain with certainty a velocity less than about of the initial velocity of expulsion .
This question will be discussed more fully in a later section of the paper .
Table II gives the results of the experiments , the masses per unit area of arious meing given which wsary tVelocity ortides ihrough M velocity of the -particles to the fractions given in column 1 .
The values are taken from smooth curves drawn through the experimental points .
For gold and mica the values are probably correct to 1 per cent. , although the t$ results for copper and aluminium are not quite so reliable , owing to the unhomogeneity of the foils used .
As the velocity changes comparatively [ slowly with the thickness , especially for thicknesses up to about 3 cm .
air @ equivalent , the values of the velocity corresponding to any given thickness ' will have a considerably greater percentage accuracy .
The foils were in all cases commercially pure .
The values given for velocity are taken from the curves as the smallest mass per square centimetre necessary to give this velocity .
The values given in the last line of the table are the masses per square centimetre necessary to completely absorb the -particles in the various materials .
These numbers were not determined directly , but by extrapolation from the values necessary to cut down the range by about cm .
in air , using for the remainder of the range the numbers given by Richardson and one of u The method by which the values for air given in the last column were obtained is given in the next section .
Table II .
In connection with the above experiments the value of for the unabsorbed -particles was determined by substitution of the various values in the formulae given above .
The distances of the source from the slit and screen were and cm .
respectively .
With six values of the field varying between 4000 and 8500 gauss , the values of determined * Marsden and Richardson , ' Phil. Mag 1913 , vol. 25 , p. 184 .
*Cf .
Geiger and Nuttall , ' Phil. Mag October , 1912 , vol. 24 , p. 647 .
: rtides ihrough Mssumed ising tbove dparticles absorbed similarly by the various materials , i.e. either that the emergent -particles @# are homogeneous in velocity or that they are " " straggled\ldquo ; or sorted out in velocities to the same extent .
This question has been discussed by Richardson and one of us ( loc. cit and further evidence will be given in the next section of this paper .
It appears to us that we are justified in obtaining the air velocity curve in this way , at any rate to an accuracy within the .
possible experimental error , especially for velocities above of the initial velocity .
A difficulty arises measuring the air equivalents of foils greater than that corresponding to about cm .
If the experiment is done in air at ordinary pressure either by ionisation or by the scintillation method this difficulty is due to the large variation in intensity of the -particles at the end of the range with the source uncovered ( i.e. at about 7 cm .
distance ) , and the end of the range when such a thick foil is interposed ( i.e. less than 1 cm .
distance ) .
In our experiments the scintillation method was used , with radium as source .
A zinc sulphide screen was adjusted at the end of the range with and without the various foils interposed .
For the very thick foils the source was sometimes allowed to decay to a small intensity before making the adjustment with the foil covering the source .
The difference between the distances of the zinc sulphide screen from the source with and without the foil over it gives the air equivalent required .
As a check on the values for the thicker foils the source , foils , and screen were enclosed in a chamber which could be evacuated .
A constant distance separated the source and the screen , and the pressure was adjusted until the -particles just failed to reach the screen .
Even with these precautions a difficulty was encountered owing to the unhomogeneity of the foils , and for this reason more reliance is placed on the values obtained with mica .
The values are all reduced to C. and 76 cm . .
The masses per unit area corresponding to any air equivalent are in general a few psr cent. less than the values determined by Richardson and one of us from the variation of air equivalent along the range of foils of the order of 1 cm .
air equivalent .
For this reason the masses given by these authors for the equivalents per centimetre at various points of the range will require diminishing by a factor constant for each substance .
A direct determination of the air velocity curve was also made , although owing to the nature of the experiment the values obtained are probably not quite so accurate as those deduced by the above method .
The apparatus of fig. 1 was used , the slide holding the source and slit being modified as shown in fig. 3 .
The plate held a fine slit covered airtight by a thin mica window equivalent to about cm .
air , and the whole was waxed so as to The main chamber was evacuated completely , and the pressure varied in the bell-jar .
In this way the range of the -particles entering the magnetic deflecting chambe could be varied .
The air equivalent of the mica window was known at different parts of the range , and by adding the equivalent at and 76 cm .
Hg .
of the air between and at the various pressures the exact reduction of range could be calculated .
The reason that two slits were necessary arose from the considerable " " compound\ldquo ; scattering of the beam of -particles , which would otherwise cau se a spreading out of the pencil received on the zinc sulphide screen .
Even with the above arrange- ment a certain amount of spreading of the beam due to scattering is unavoidable , and also for the same reason there is a considerable reduction in the intensity of the -particles for low velocities where the scattering becomes considerable .
Thus measurements of a high degree of accuracy could not be obtained by this method .
The results are given in Column 4 of Table III , and they prove the substantial accuracy of the values calculated by the former method .
As in the expeliments with metal foils no certain evidence could be obtained of velocities below of the initial velocity .
Attempts to Obtain Velocities below of the Initial Velocity .
It has already been mentioned that with foils of any material , of thickness from cm .
air equivalent upwards , no reduction in velocity could be obtained below of the initial velocity .
This result is in agreement with Prof. Rutherford 's original experiments ( loc. cit in which a lower limit was obtained .
Rutherford used aluminium foils and a photographic plate to register the deflected bands of -particles , and it has generally been assumed that his failure to obtain low velocities arose from the want of uniformity of his foils .
Geiger ( loc. cit using mica as absorbing substance and the scintmation method , obtained two values of velocity as low as and of the initial velocity respectively .
1913 .
] Velocity of a-Particles in passing through .
451 ncreasi gfraction oheorder 2cattering wthen increase wheets otraversed iique direction through teeth phenomena oompound scattering , there jreater tbout 6This decrease arises f Observations at the end of the range are difficult owing to several causes : expected that there would be a variation in velocity in the -particles ' which do emerge .
Further , not only is the number of -particles in the beam greatly reduced , but the brightness of the scintillations themselves decreases considerably , and observation becomes difficult .
: From these considerations it will be seen that for low velocities it is necessary to use a very intense source , and to place uniform absorption sheets directly over it so as to keep the spreading of the beam at a minimum .
However , with these precautions , and using the arrangement of sliding absorption windows , we were unable , as has already been stated , to obtain velocities below of the initial velocity .
In all cases the deflection caused by a netic field remained constant for foils greater than cm .
air equivalent .
An experiment was tried in which the increase of thickness was obtained by rotating a sheet of mica of about 6 cm .
airequivalent about an axis parallel and very near to the source .
The same result was obtained ; after a certain rotation the deflected beam remained stationary until it was too faint to observe .
This result was obtained whether the whole of the apparatus was in the magnetic field or only that part from the slit to the zinc sulphide screen .
In another experiment the apparatus was cut down to half its length , and a source of radium equivalent to the amount in equilibrium with 15 millicuries of radium emanation was used , on a wire of 1/ 10 mm. diameter , with a slit 1/ 10 mm. wide .
Three foils of mica , equivalent to , and cm .
of air , were employed successively and placed directly over the source with a separate evacuation for each experiment .
The resultant double deflectiqns were and mm. respectively , and the double deflection for the bare wire was mm. These values are constant within the limits of experimental error due to the extreme faintness of the bands , the mean value of the velocity being of the velocity with the source uncovered .
The cross wire in the microscope was set in each case on the centre of the band of scintillations .
* H. Geiger , ' Roy .
Soc. Proc 1910 , , vol. 83 , p. 492 .
452 Mr. Marsden and Dr. Taylor .
The Decrease in [ Apr. Owing to the faintness of the bands there was some difficulty in estimating appeared narrower freater thicknesses.quivalent toany possible unhomogeneity ielocity.eflected b cm .
the measurements indicated that -particles of 39 to 47 per cent. of the initial velocity were present .
However , a lower limit of velocity was not at all evident even with the thicker micas .
Discussion of Results .
It will be more convenient first to discuss the results of the last section .
It is possible that in the beam of -particles after passing through cm .
air-equivalent , the velocities are distributed within the limits 39 to 47 per cent. , just mentioned .
With further absorption the particles of higher velocities may become degraded in velocity .
However , we are faced with the difficulty of accounting for the absence of -particles of lower velocities .
It is possible that they no longer produce scintillations .
This point was investigated with different zinc sulphide screens but with negative results .
But even if they no longer produce scintillations then it is probable that they also no longer ionise , for the ranges of -particles determined by the scintillation method are the same as those determined by the ionisation method .
The results may possibly be explained by assuming that when the velocity of an -particle falls below a certain value it is subject to a new special type of scattering , possibly by some kind of sub-central arge present in the atom .
From an examination of the large number of -particles in the photographs of C. T. R. Wilson*which exhibit large angle deflections in the last 2 mm. of the range as shown by the cloud trails we have calculated that this number is far in excess of the number to be expected on the laws of single scattering of Rutherford , experimentally proved by and one of us .
However , with such an hypothesis one might expect some difference in the limiting velocity with different substances unless it is supposed that the sub-centres are present in all atoms .
An alternative explanation may , of course , be obtained on the assumption that at this particular velocity the -particle takes on an electron and then has only one positive charge .
This would account for the limiting velocity coming practically the same in all the substances .
An attempt was made to detect such singly charged -particles but only one line of scintillations in the magnetically deflected beam could be observed .
It must be remembered , however , that Geiger apparently obtained one * C. T. R Wilson , ' Roy .
Soc. Proc 1912 , , p. 277 .
E. Rutherford , ' Phil. Mag 1911 , vol. 21 , p. 669 .
H. Geiger and E. , ' Phil. Mag 1913 , vol. 26 , p. 604 .
Velocity ohrough M there mdoes nurve ahing morea reement wWith aocit cuand ixcept focities 1they socity curve Geiger deduced fwhereV iocity , constant aange omergingfrom tbsorbing fPutting iotal range aiven ieducedthe paper focity curves iarious mocity radium Crrect ohere mchang.companying thewere ubtain socity .
Whether Geiger srove xpressed bubstances oncreasin.tomicweight .
This indicated bnergy curve fhown iDarwin ( firstattemptedtodeduceexpressionsforthevelocity S curve in various materials , the assumption being that the -particle loses energy by setting in motion the electrons in the atoms of the absorbing substance .
To avoid , as far as possible , any hypotheses as to the structure of atoms Darwin also assumed that an -particle only acts on the electrons in : an atom when it actually passes through the atom .
Bohr has extended Darwin 's results and removed the objection of limiting the action of the -particle .
Bohr arrives at a formula which may be reduced to where is the velocity of an electrified particle , the distance traversed through the absorbing material and A and are constants .
We have applied this formula to our results , but the agreement is only good for velocities greater than about of the initial velocity .
This , however , does not altogether contradict the theory , for certain assumptions used by Bohr in integrating his formula do not hold for low velocities .
For instance , the formula depends on the assumption that a certain distance exists , which is very small in comparison with * Bohr 's actual formula is ) .
and are the charge and mass of the electrified particle , and the corresponding quantities for an electron .
is the number of atoms per unit volume , and a constant .
The frequencies of the electrons in each atom are denoted by 454 Velocity of rtides in passing through Matter . .
This assumption comes in in the consideration of the effect of the atomic forces on the motion of the electrons disturbed by an -particle .
If we consider the variation in the velocity of an -particle when , say , i.e. , it can be calculated that must be extremely small compared with for this assumption to hold .
For oxygen , Bohr calculates from data of Planck and of Whiddington that for some electrons in the atom , and that for materials of higher atomic weight electrons of much higher frequencies must exist .
Thus Eohr 's conditions probably do not hold for low velocities , and this possibility he has himself already pointed out .
It is interesting to note that no theoretical explanation has so far been given for Bragg 's law that the absorption of -particles per atom of different substances is proportional to the square root of the atomic weight .
This law is not strictly accurate , as it cannot hold for all velocities of -particles , yet its wide range of approximate application seems to suggest that it has some simple theoretical foundation .
We are deeply indebted to Prof. Rutherford for his helpful encouraging interest in these experiments , and for supplying us with the large quantities of radium emanation necessary .
|
rspa_1913_0043 | 0950-1207 | Synthesis of the anhydrides of \#x3B1;-aminoacyl glucosamines. | 455 | 461 | 1,913 | 88 | Proceedings of the Royal Society of London. Series A, Containing Papers of a Mathematical and Physical Character | Charles Weizmann|Arthur Hopwood|Dr. A. Harden, F. R. S. | article | 6.0.4 | http://dx.doi.org/10.1098/rspa.1913.0043 | en | rspa | 1,910 | 1,900 | 1,900 | 2 | 131 | 3,196 | http://corpora.clarin-d.uni-saarland.de/surprisal/6.0.3/?id=rspa_1913_0043 | 10.1098/rspa.1913.0043 | null | null | null | Chemistry 2 | 82.580481 | Biochemistry | 14.010822 | Chemistry | [
-55.519771575927734,
-44.99018478393555
] | 455 Synthesis of the Anhydrides of a-Aminoacyl Glucosamines .
By Charles Weizmann and Arthur Hopwood .
( Communicated by Dr. A. Harden , F.R.S. Received April 5 , \#151 ; Read June 19 , 1913 .
) The behaviour of the albumin glucosides and the mucus bodies known as mucins , mucinogens , mucoids , and hycdogens , on hydrolysis suggests the probability that these complex proteins would bear the same relation to the condensation products of the sugars or the amino-sugars with the amino-acids as the simpler proteins bear to the polypeptides .
Consequently , the authors decided two years ago to make a start in the synthesis of the glucoproteins by preparing the condensation products of glucosamine with the amino-aliphatic acids , in order that their properties and behaviour towards ferments could be ascertained and compared with those of the degradation products of the glucoproteins and thereby throw some light on the constitution of these complex and important organic bodies .
After many failures , the method of synthesis which we eventually adopted for the condensation of glucosamine with amino-aliphatic acids was somewhat similar to one of the methods employed , by Emil Fischer and his co-workers* in the synthesis of the polypeptides .
In brief , the method consists in condensing a-bromoacyl haloids with glucosamine hydrochloride in the presence of sodium hydroxide , and then displacing the halogen in the resulting a-bromoacyl glucosamines by an amino-group through the action of cold aqueous ammonia , viz.:\#151 ; a-Bromoacyl Haloid + Glucosamine Hydrochloride .
sodium a-Bromoacy^ aqueous hydroxide .
Glucosamine .
ammonia .
Anhydride of a-Aminoacyl Glucosamine .
Numerous difficulties were encountered in carrying out these changes .
In coupling the a-bromoacyl haloids with glucosamine hydrochloride in the presence of sodium hydroxide , it was found that good yields were obtained only when molecular proportions of the reacting substances were employed and when the mixture was vigorously shaken and maintained about the temperature of melting ice .
Further , in the subsequent treatment of the a-bromoacyl glucosamines with aqueous ammonia , the temperature had also * ' Ber .
, ' 1903 , vol. 36 , p. 2982 , et seq. 456 Messrs. Weizmann and Hop wood .
Synthesis of the [ Apr. 5 , to be kept low both during the interaction of the bodies and the subsequent evaporation under reduced pressure , otherwise much decomposition took place and sticky brown masses resulted .
It should be observed here that when molecular proportions of a-bromoacyl haloids and glucosamine hydrochloride are condensed together in the presence of cold alkali hydroxide , the whole of the bromoacyl group of the substituted acid chloride appears to unite with the amino-group and none with the hydroxyl groups of glucosamine .
This is shown by the fact that the condensation product made from molecular proportions of a-bromolauryl chloride and glucosamine hydrochloride in the presence of normal sodium hydroxide is practically insoluble in dilute or concentrated hydrochloric acid , an almost conclusive proof that only the amino-group present in glucosamine is attacked when the condensation process is carried out under the above conditions .
Moreover , this view is also supported by the analogous behaviour of the a-bromoacyl haloids towards serine , isoserine , tyrosin , and other hydroxyamino-acids in the presence of alkali hydroxides.* It should also be noted that when the a-bromoacyl glucosamines interact with cold aqueous ammonia , they do not yield the expected a-aminoacyl glucosamines but the anhydrides of a-aminoacyl glucosamines .
The action appears to consist in the replacement of the bromine atom in one molecule of the a-bromoacyl glucosamines for an amino-group , and the simultaneous or subsequent withdrawal of the elements of water .
The analyses of the products formed by the action of ammonium hydroxide on a-bromopropionyl glucosamine and a-bromoisohexoyl glucosamine demand this conclusion .
Moreover , it seems that whenever ammonia or alkalies act upon glucose or its derivatives the change which takes place is generally accompanied by the loss of a molecule of water.f In concluding this introduction , we should state that since we published a preliminary note on the condensation of a-bromoacyl haloids with glucosamine , J we find that other chemists have also been working simultaneously on the derivatives of glucosamine with a view to developing the synthetic chemistry of the glucoproteins .
S We should like to state that we are experimenting from an entirely different point of view , and no overlapping has so far * * * S * Of .
E. Fischer , 'Ber.,5 1904 , vol. 37 , pp. 2486-2571 ; ibid. , 1907 , vol. 40 , pp. 37043717 ; E. Fischer and W. F. Koelker , 'Ann .
, ' 1905 , vol. 340 , pp. 180-190 ; E. Fischer and H. Roesner , 'Ann .
, ' 1910 , vol. 375 , pp. 199-206 .
t Cf .
Lobry de Brnyn , 'Ber .
, ' 1895 , vol. 28 , p. 3082 ; Emil Fischer and Karl Zack , 4 Ber .
, ' 1912 , vol. 45 , pp. 456-465 , 2068-2074 .
f Cf .
A. Hopwood and C. Weizmann , ' Chem. Soc. Proc. , ' 1912 , vol. 28 , p. 261 .
S Cf .
J. C. Irvine and A. Hynd , 'Trans .
Chem. Soc. , ' 1913 , vol. 103 , pp. 41-46 .
1913 .
] Anhydrides of a-Aminoacyl Glucosamines .
457 taken place either in the methods adopted or in the products obtained by synthesis .
ot-Bromopropionyl Glucosamine , CH3*CHBrC0*NH*C6Hii05 .
a-Bromopropionyl glucosamine is prepared by the condensation of a-bromopropionyl bromide and glucosamine hydrochloride in cold alkaline solution .
For this purpose , 4 grm. of a-bromopropionyl bromide ( 1 mol .
) and 18*6 c.c. of N sodium hydroxide ( 1 mol .
) are added gradually and alternately , with vigorous shaking after each addition , to a well-cooled solution containing 4 grm. of glucosamine hydrochloride ( 1 mol .
) dissolved in 18-6 c.c. of N sodium hydroxide ( 1 mol .
) .
There is much frothing and a colourless precipitate separates out immediately after the condensation begins to take place .
The mixture is kept cool for about two hours by surrounding the containing vessel with melting ice , and when the odour of a-bromopropionyl bromide has disappeared a slight excess of concentrated hydrochloric acid is added .
After standing for about 30 minutes , the impure a-bromopropionyl glucosamine is collected , washed with a little cold water , and dried in air on a porous plate .
A further crop of crystals is obtained by evaporating the mother liquor at ordinary temperatures , which like the former are purified by recrystallisation from hot absolute alcohol .
Total yield , 4T grm. a-Bromopropionyl glucosamine crystallises from alcohol in colourless prismatic needles which melt and decompose at 200-201 ' when slowly heated , and at 210-211 ' when quickly heated , yielding a black liquid .
The crystals are readily soluble in hot and moderately soluble in cold water .
They are readily soluble in dilute alcohol ( 50 per cent. ) , but are difficultly soluble in cold and only moderately soluble in hot absolute alcohol .
They are insoluble in ether , but dissolve instantly in cold ammonia or alkali hydroxides , forming yellow solutions .
The warm aqueous solution of a-bromopropionyl glucosamine readily reduces alkaline copper solutions , yielding red copper oxide , or ammonio-silver nitrate solution , giving a silver mirror ; but when an aqueous solution of the bromide is shaken and warmed for two hours with a little more than one molecular proportion of either semicarbazide hydrochloride dissolved in excess of sodium acetate solution or phenyl hydrazine dissolved in dilute acetic acid no semicarbazone or phenylhydrazone is formed , and the resulting solutions on evaporation under reduced pressure yield most of the original bromide unchanged .
0-6201 gave 24*1 c.c. N2 at 14*0 ' C. and 751 mm. N = 4*57 .
0-1793 " 0*1073 AgBr .
Br = 25*47 .
C9Hi606NBr requires N = 4*46 ; Br = 25*45 per cent. 458 Messrs. Weizmann and Hopwood .
Synthesis of the [ Apr. 5 , Alanyl Glucosamine Anhydride , C9Hi605N2 .
Alanyl glucosamine anhydride is prepared by the action of cold ammonium hydroxide on a-bromopropionyl glucosamine .
For this purpose 1 grm. of a-bromopropionyl glucosamine is mixed with excess of concentrated aqueous ammonia in a pressure bottle and then shaken for five days at the ordinary temperatures of the laboratory .
The resulting solution is evaporated whilst cold in a vacuum desiccator over concentrated sulphuric acid until crystals of impure alanyl glucosamine anhydride separate out , which are then collected and washed with cold absolute alcohol in order to remove brown decomposition products .
Further crops of crystals are obtained by evaporating the aqueous mother liquor and the alcoholic washings at ordinary temperatures under reduced pressure .
The crude products are then dissolved in hot water and boiled with animal charcoal until the solution becomes colourless .
On cooling , alanyl glucosamine anhydride separates from the aqueous solution in colourless prismatic needles , which are further purified by recrystallisation from hot water .
Yield , 0*3 grm. Alanyl glucosamine anhydride when heated quickly turns pale brown at 245-250 ' and melts at 269-272 ' , yielding a black liquid .
It is moderately soluble in cold and readily soluble in hot water , but it is almost insoluble in cold and only sparingly soluble in hot absolute alcohol .
On prolonged heating , the aqueous solution of alanyl glucosamine anhydride slowly reduces Fehling 's solution , yielding red copper oxide , or ammonio-silver nitrate solution , giving a silver mirror ; but when an aqueous solution of the anhydride is shaken and warmed for two hours with a little more than one molecular proportion of either phenyl hydrazine dissolved in dilute acetic acid , or semicarbazide hydrochloride dissolved in excess of sodium acetate solution , no phenyl hydrazone or semicarbazone is formed , and the resulting solutions on evaporation to crystallisation under reduced pressure yield most of the original anhydride unaltered .
As a primary amine , the anhydride is readily soluble in dilute or concentrated hydrochloric acid , and when heated with alcoholic potash and chloroform yields an unpleasant earbylamine odour ; but when an aqueous solution of the anhydride is mixed with an aqueous solution of picric acid and afterwards evaporated to crystallisation under reduced pressure no picrate is formed and most of the original anhydride crystallises out unchanged .
0*1194 gave 0*2041 C02 and 0*0694 H20 .
C = 46*61 ; H = 6*50 .
0*1322 " 13*8 c.c. N2 at 14*2 ' C. and 752 mm. N = 12*27 .
C9Hi605N2 requires C = 46*51 ; H = 6*94 ; N = 12*07 per cent. 1913 .
] Anhydrides of a-Aminoacyl Glucosamines .
a-Bromoisohexoyl Glucosamine , CHMe2CH2*CHBr*C0*NH*C6Hii05 .
Four grammes of glucosamine hydrochloride ( 1 mol .
) dissolved in 18*6 c.c. of N sodium hydroxide ( 1 mol .
) , when treated with 4*8 grm. of a-bromoisohexoyl bromide ( 1 mol .
) and 18*6 c.c. of N sodium hydroxide ( 1 mol .
) in the same way as previously described for a-bromopropionyl glucosamine , and afterwards acidified with hydrochloric acid , yield 6*5grm .
of a-bromoisohexoyl glucosamine .
The product crystallises from absolute alcohol in colourless rhombic plates melting and decomposing when heated quickly at 178-181 ' , and crystallises from water in colourless prismatic needles , melting when heated quickly at 192-195 ' , yielding a black liquid .
The crystals are slightly soluble in cold , and readily so in hot , water or alcohol , either of these liquids being suitable solvents for purifying the solid by crystallisation .
They are insoluble in ether , but dissolve slowly in cold ammonia or alkali hydroxides , yielding yellow solutions .
The warm aqueous solution of a-bromoisohexoyl glucosamine readily reduces alkaline copper solutions , yielding red copper oxide , or ammonio-silver nitrate solution , giving a silver mirror ; but , like a-bromopropionyl glucosamine , does not appear to react with either phenyl hydrazine or semicarbazide .
0*6189 gave 21*0 c.c. 1ST2 at 13*8 ' C. and 746 mm. N = 3*96 .
0*2240 " 0*1175 AgBr .
Br = 22*33 .
Ci2H2206lSTBr requires N = 3*93 ; Br = 22*45 per cent. Leucyl Glucosamine Anhydride , Ci2H2205172 .
One gramme of a-bromoisohexoyl glucosamine , when treated with concentrated aqueous ammonia in the same way as described for a-bromopropionyl glucosamine , yields 0*25 grm. of leucyl glucosamine anhydride , which crystallises from water in colourless prismatic needles .
When quickly heated , it sinters about 205 ' and melts at 213-215 ' , yielding a brownish black liquid .
It is moderately soluble in cold , and readily soluble in hot , water , but it is difficultly soluble in cold , and only slightly soluble in hot , absolute alcohol .
On prolonged heating , the aqueous solution of leucyl glucosamine anhydride slowly reduces Fehling 's solution , yielding red cuprous oxide , or ammonio-silver nitrate solution , giving a silver mirror , but , like alanyl glucosamine anhydride , does not appear to react with either phenyl hydrazine or semicarbazide .
The anhydride is readily soluble in dilute or concentrated hydrochloric acid , and , when heated with alcoholic potash and chloroform , VOL. LXXXVIII.\#151 ; A , 2 K 460 Messrs. Weizmann and Hop wood .
Synthesis of the [ Apr. 5 , yields an obnoxious carbylamine odour , but , like alanyl glucosamine anhydride , does not appear to unite with picric acid .
0-2193 gave 0*4217 C02 and 0*1492 H20 .
C = 52*44 ; H = 7*62 .
0*1905 " 16*0 c.c. N2 at 13*8 ' C. and 761 mm. N = 10*01 .
Ci2H2205N2 requires C = 52*52 ; H = 8*09 ; N = 10*22 per cent. x-Bromolauryl Glucosamine , CiiH22Br*C0*NH*C6Hii05 .
Four grammes of glucosamine hydrochloride ( 1 mol .
) dissolved in 18*6 c.c. of N sodium hydroxide ( 1 mol , ) , when treated with 5*6 grm. of a-bromo-lauryl chloride ( 1 mol .
) and 18*6 c.c. of FT sodium hydroxide ( 1 mol .
) in the same way as previously described for a-bromopropionyl glucosamine , and afterwards acidified with hydrochloric acid , yields 7*6 grm. of a-bromolauryl glucosamine .
The product crystallises from hot absolute alcohol in colourless rhombic plates , which , when heated quickly , turn brown at 183-186 ' , and melt with frothing at 194-196 ' , yielding a dark brown liquid .
The crystals are insoluble in hot or cold water , but moderately soluble in hot absolute alcohol .
They are insoluble in ether and almost insoluble in concentrated ammonium hydroxide , but they dissolve in hot solutions of sodium or potassium hydroxide , with evolution of ammonia and formation of brown solutions .
The crystals are insoluble in dilute hydrochloric acid , and only slightly soluble in hot concentrated hydrochloric acid , showing that the amino-group , and not the hydroxyl groups of glucosamine , has been attacked during the condensation .
Like the other a-bromoacyl glucosamines , it readily reduces hot alkaline copper solutions , yielding red cuprous oxide , or ammonio-silver nitrate solution , giving a silver mirror .
0*5855 gave 16*8 c.c. N2 at 12*0 ' C. and 747 mm. N = 3*38 .
0*2055 " 0*0885 AgBr .
Br = 18*32 .
CigH^OeNBr requires N = 3*18 ; Br = 18*15 per cent ct-Aminolauryl Glucosamine Anhydride , C18H34O5N2 ' Owing to the insolubility of a-bromolauryl glucosamine in ether or in aqueous ammonia , the preparation of the anhydride of a-aminolauryl glucosamine is a process of considerable difficulty .
One gramme of a-bromolauryl glucosamine and 500 c.c. of concentrated aqueous ammonia when shaken for 14 days at ordinary temperatures , or allowed to stand for one year at ordinary temperatures , or heated for four hours at 100 ' C. in a pressure bottle , yield a soapy emulsion , but only a very small quantity of the bromide goes into solution , and almost all of it is recovered unchanged on filtration .
The brown ammoniacal solutions on evaporation to dryness under reduced pressure left small brown residues , which on being washed with absolute 1913 .
] Anhydrides of a-Aminoacyl Glucosamines .
461 alcohol yielded colourless crystals , but too small in- quantity to establish their composition and properties , though obviously the anhydride of a-amino-lauryl glucosamine .
Constitution of the u-Bromoacyl Glucosamines and the Anhydrides of u-Aminoacyl Glucosamines .
The analyses and properties of the a-bromoacyl glucosamines are in strict accordance with their representation by aldehydic or glucosidic formulae similar to those generally adopted for glucosamine , * viz.:\#151 ; H H OH H H H OH H I I I I III !
OH CHsC\#151 ; C\#151 ; C\#151 ; C CHO or OH*CH2C\#151 ; C\#151 ; 0\#151 ; C-CHOH ( a or A ) OH OH H NHAc OH H NHAc -0 \#151 ; where Ac is a bromoacyl group of elements .
The representation of the anhydrides of a-aminoacyl glucosamines by constitutional formulae is , however , a more difficult matter , inasmuch as no satisfactory explanation has yet been given of the much simpler anhydrides formed by the action of ammonia or alkalies on glucose and its derivatives.f It is a matter of conjecture to state from what part of the molecules the elements of water are abstracted when the a-bromoacyl glucosamines react with aqueous ammonia .
The feebly basic and slightly reducing properties of the anhydrides of a-aminoacyl glucosamines may be explained by assuming that the elements of water are withdrawn between the amino- and the aldehydic groups with the consequent formation of a linkage between them , which linkage is only broken by the prolonged action of hot alkaline copper solutions .
But , on the other hand , as the elements of water seem to disappear so often when glucose and its derivatives react with ammonia or alkalies , it is more probable that when a molecule of an a-bromoacyl glucosamine interacts with aqueous ammonia a molecule of water is abstracted from the glucose portion of the molecule in much the same way as in other anhydro-derivatives of glucose .
We mean to continue further this investigation .
In conclusion we desire to express our thanks to the Research Fund Committee of the Chemical Society for a grant which defrayed the greater part of the cost of this investigation .
* Cf .
J. C. Irvine and A. Hynd , 'Trans .
Chem. Soc. , ' 1912 , vol. 101 , p. 1128 .
t Cf .
J. C. Irvine , R. F. Thomson , and C. S. Garrett , ' Trans. Chem. Soc. , ' 1913 , vol. 103 , pp. 238-249 ; E. Fischer and K. Zack , 'Ber .
, ' 1912 , vol. 45 , pp. 456-465 , 2068-2074 .
2k2
|
rspa_1913_0044 | 0950-1207 | The transition from the elastic to the plastic state in mild steel. | 462 | 471 | 1,913 | 88 | Proceedings of the Royal Society of London. Series A, Containing Papers of a Mathematical and Physical Character | A. Robertson, M. Sc.|G. Cook, M. Sc.|Prof. J. E. Petavel, F. R. S. | article | 6.0.4 | http://dx.doi.org/10.1098/rspa.1913.0044 | en | rspa | 1,910 | 1,900 | 1,900 | 1 | 96 | 2,749 | http://corpora.clarin-d.uni-saarland.de/surprisal/6.0.3/?id=rspa_1913_0044 | 10.1098/rspa.1913.0044 | null | null | null | Measurement | 58.455213 | Tables | 21.799533 | Measurement | [
47.366050720214844,
-61.02444076538086
] | ]\gt ; were eliminated , and obtained , as a result , a reduction of stress immediately after yield of about 16 per cent. Since the experiments here described by the present writers were carried out , Prof. W. E. Dalby has published an account of an optical raphic recorder , in which the measurement of the load is effected in a manner similar to that adopted by Kennedy , and in tests carried out on mild steel has observed a reduction of stress of about 13 per cent. * .
Soc. Proc vol. 65 , p. 172 .
'Proc .
Inst. Mech. Eng 1886 .
'Roy .
Soc. Proc , p. 414 .
) Transition from Elastic to Plastic in Mild Steel .
463 In neither of these cases were any special precautio other than the use of spherical seatings ) taken to ensure that the stress distribution across the section of the test specimen was uniform ; such precautions are , indeed , unnecessary when it is desired merely to obtain a record of the load-strain relation throughout the plastic stage .
Prof. C. A. M. Smith has pointed out , *however , the importance of securing concentric loading of the specimen ( and consequent uniformity of stress ) in experiments dealing with the determination of the elastic limit and yield point , and has shown that even when the specimen is supported by nuts resting on spherical such a condition is nor necessarily guaranteed .
An arrangement whereby a much closer approaeh to truly axial loading is secured has been described by the authors in a previous paper , and has been used in the present work .
By this means , and also by hmiting the extension of the specimen immediately after yield to a very small amount , the authors have observed at this point a reduction of stress greater than 23 per cent. in 11 specimens of mild steel .
A sketch of the complete apparatus is shown in fig. 1 .
The specimen , of carefully annealed mild steel machined to about inch diameter , was screwed at each end into a hollow rectangular block of steel to which the load was transmitted through a steel ball co-axial with the centre line of the specimen and resting on the hardened surface of a stout steel cross-bar A. Care was taken in machining the block to ensure that the centre line of the hole into the specimen was tightly screwed passed the centre of the spherical cavity resting upon the steel ball .
The whole was attached to two heavy castings machined to fit the testing machine grips .
Two bars of mild steel inch diameter were supported by nuts bearing on machined surfaces at each side of the casting , and extensometers attached to them , by means of which the load occurring at any time in them was determinable , both bars having previously been independently calibrated .
The manner of carrying out a test was as follows:\mdash ; 'Engineering , ' Dec. 10 , 1909 , , p. 796 .
'Engineering , ' vol. 92 , p. 786 .
The specimens were made from ordinary mild steel , and the variations in the results of the tests may be due to a number of causes , of which the chief are ( 1 ) slight differences in composition or annealing , ( 2 ) slight deviations from true axiality in the applied load .
It may be mentioned here that a deviation of one five-hundredth of an inch of the resultant load $ from the axis of the specimen would cause the stress on one side of the specimen to be 4 per cent. in excess of the mean lred ) stress , and the 1913 .
to the Plastic State in Mild Steet .
465 observed stress at yield might therefore be below the true yield stress by an amount which would considerably affect the value of the stress reduction .
A confirmation of the results arrived at is , however , obtained by experiments on bending and torsion to be described later .
In the of the experiments it was considered desirable to determine the actual extensions in the test specimen immediately after yield in order to construct a stress-strain diagram .
The short of the specimen , however , prevented the use of any of the laboratory extensometers .
special apparatus was constructed for the purpose , the principle of which was that of Marten 's extensometer .
The diagram shown in fig. 2 has been constructed from observations taken with this instrument on specimen 1oo zoo FIG. 2 .
No. 8 .
The point A is limit beyond which it was impossible to carry the extension without readjustment the apparatus , on ount of the necessity of keeping the stress in the side bars well below the elastic limit .
Al this point the load was therefore relieved , the necessary adjustment made , and a second test performed of the same specimen .
It be seen that the stress now required to cause further deformation is not appreciably different from that existing in the specimen at the oonclusion of the previous test .
It would appear , therefore , that the " " drop\ldquo ; is a phenomenon associated solely with the breakdown from the inif , ial elastic state , and that the reduced stre remains at a fairly constant value over a total strain equal to several times the magnitude of the elastic strain .
urther evidence in confirmation of the results arrived at in the above cases , making certain assumptions , quation cbtained ewhen subjected tuniform stress Torsion furnish tstress distribution Ioers titude oeduction wehavi ' the relation between the moment , displacement , and stress duction after yield has taken place .
The magnitude of the reduction may therefore be obtained from the experimental observation of tffi moment and displacement .
Consider first the case of a bar of rectangular section subjected to a uniform bending moment .
If the stress at every point is below the elastic limit , its magnitude is proportional to the distance from the neutral plane , and is therefore a maximum at the extreme surfaces .
The displacement at the middle point is given by where stress at outer fibres , length , depth , 's modulus .
When the bending moment is increased beyond a certain amount , yield occurs in those parts subjected to the greatest stress , namely , the outer fibres .
It be assumed:\mdash ; ( 1 ) That plane sections remain plane .
( 2 ) That the stress in the overstrained part is uniform .
This assu ption is allowable , in view of the fact that the total strain in those parts is comparable to the elastic strain , and the stress variation has been shown to be very small for extensions of this magnitude ( see fig. 2 ) .
( 3 ) That the greatest stress in parts still elastic is equal to that required to initiate the yield .
That the stress distribution is symmetrical about the neutral plane .
* Let AB ( fig. represent the normal section of the beam , and be the maximum direct tensile stress the material is capable of withstanding without overstrain .
If to some scale , the stress at any point in AB , when the * This involves the assumption that the stresses at yield and the reduction of stresses after yield are the same in tension and compression .
If these two values are different , the reduction of stress actually occurring on the tension or compression sides must greater than the estimate from the following analysis .
1913 .
] Elastic to the Plastic in Mild Steel .
467 maximum bending moment consistent with perfect elasticity in all parts is applied , will be given by the ordinate at that point to the line t- If the bending moment is increased to some value , the extreme fibres will be overstrained , and the beam may be considered as made up of two parts , acentral elastic portion of depth in which the maximum stress still be , and ( 2 ) two portions , one at the upper and one at the lower : surface , in which the stress is assumed uniform , and in magnitude equal to .
The new distribution may be represented diagrammatically by the lines EE'C'D'F'F ( see fig. 3 ) .
The displacement produced by may be obtained by considering the equilibrium of the central elastic portion , and is given by But , the maximum displacement when the whole of the beam is elastic is given by and , therefore , , .
Now is equal to the sum of the moments of resistance of the different parts the beam .
Hence A number of tests were made on bars of annealed mild steel machined accurately to a rectangular section about 48 inch deep and inch wide .
A uniform bending moment was secured by applying the load outside the supports which were 3 inches apart .
The displacement of the central point relative to two fixed points situated in the neutral plane over the supports was obtained by observing the rotation of a 1mrror attached to a tripod resting with one leg on the beam and the other two on supports rigidly connected to the two points of reference .
The load was applied gradually , and the displacement read after each addition .
While the whole of the bar was elastic the position of equilibrium was reached immediately .
When yield occurred , the displacement continued to increase for a short time without the application of further load .
A diagram is given in fig. 4 showing the relation of bending moment to displacement throughout the test .
The relation , as will be seen , is a linear one until yield takes place , the latter being very definitely located by the ( 1 ) The probability that yield does not occur over the whole length of ths bar at the same time , but is at first localised at some point , from which it extends gradually , producing the slow continuous increase in the displacement under constant load .
( 2 ) The probability that yield in tension and compression do not occur simultaneously .
1913 .
Elastic to the Plastic State in Steel .
469 Both effects would make the displacement less than if yield took place simultaneously over the whole of the tension and compression surfaces .
Therefore it is probable that the position of the curve in the earlier stages of yield does not correspond with the true value of the stress reduction , and that the comparison of the theoretical and experimental curves is more legitimate in the later stages when yield has probably taken effect over the whole length .
Thus , in fig. 4 , although the double bend following on the yield point might correspond to a difference in the yield stress in tension and compression , it cannot be regarded as conclusive evidence on this point .
Though no definite value for the magnitude of the stress reduction can be looked for from the bending experiments , they suggest limits between which it may lie .
These limits would appear to be 25 and 33 per cent. The yield phenomenon in ductile materials is probably due mainly to shearing stress , therefore it was expected that some definite information on the value of the stress reduction at yield would be obtained from the consideration of a round bar subjected to torsion .
In this case the stress on every normal section is one of pure shear and varies uniformly from zero at the to a maximum at the surface , provided that the elastic limit is not exceeded .
An analytical investigation carried out in a precisely similar manner to that of a beam leads to the equation where and are twisting moments , and and the corresponding angular displacements at and after yield .
It will be seen from this equation that if is less than , or , in other words , if the stress reduction is greater than 25 per cent. , the angular displacement when the yield point is reached will continue toincrease without further increment in the twisting moment until the true plastic state is reached .
In experiments carried out on annealed mild steel bars inch diameter , it was found that this actually took place .
When the yield point was reached , the angular displacement increased at a slow but uniform rate under the same torque : The in in which the experiment was carried out only permitted a limited angular displacement , and when this was reached , the displacement was still increasing .
A diagram showing the experimental relation between twisting moment and angular together with the theoretical curves for various values of the percentage reduction is given in fig. 5 .
J. J. Guest , " " The Strength of Ductile MateriaIs under Combined Stress 'Phil .
Mag July , 1900 , Series V , vol. 60 .
that the hole was quite central , and that , therefore , the phenomenon was not due to eccentricity .
An explanation may be given in the following manner .
Owing to lack of homogeneity , yield may first take place on one side of the hole .
The stress at that part may thereby be relieved to the extent of per cent. , and the effect upon the rest of the cylinder will be the same as if the hole were elliptical .
If the defornlation of the external surface were measured on the diameter passing through the centre of the yielded part , *A similar effect has been observed by Mr. L. B. Turner , vol. 92 , p. 117 .
The innwnt of High Potentials by the Use of Radium .
471 contraction would probably be observed , which would not be converted into an extension until the whole of the internal surface had yielded .
Petavel , valuable 8uggestions iourse oorkBy HoSELEY , John Harling Fellow , University oanchesterThe.esire tecord their indebtedness tinment o ( Communicated by Prof. E. Rutherford , F.RS .
Received April 22 , \mdash ; Read May 1 , 1913 .
) ' The original aim of the work described in this note was to measure the energy and numerical importance of each of the many distinct kinds of -particles emitted by a single radioactive substance .
Calculation of the energy of a -particle from observation of its deflection in a magnetic field* involves assumptions which are as yet insufficiently supported by experi- meant .
Theoretically both the energies and distribution of the particles could be directly measured by giving a gradually increasing positive charge to the source of radiation ; for , when the potential of the source is electTons possessing energy less than will be drawn back to the source of radiation .
Unfortunately , more than a million volts would be necessary to stop the fastest -particles , and no method is at present known of maintaining such a high potential in .
It was thought that this difficulty might possibly be overcome by using the active material itself in order to produce the high potential according to the inciple employed in Strutt 's radium clock .
If the source of radiation were perfectly insulated its potential would rise until the swiftest -particles could no longer escape .
The present note deals with made to test whether this method were practicab.le .
It was found that high potentials were readily obtained , but the attempt to attain to a million volts failed through the difficulties of insulation encountered .
But few experiments were completed , and many failed as the result of accident .
This shows that , even if perseverance had been rewarded by greater success , technical difficulties , accentuated by * Planck , ' Phys. Zsit 1906 , vol. 7 , p. 753 .
Strutt , ' Phil. Mag 1903 , vol. 6 , p. 688 .
A preliminary account of these experiments was communicated to the Manchester Literary and Philosophical Society , November 12 , 1912 .
|
rspa_1913_0045 | 0950-1207 | The attainment of high potentials by the use of radium. | 471 | 476 | 1,913 | 88 | 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.1913.0045 | en | rspa | 1,910 | 1,900 | 1,900 | 4 | 119 | 3,019 | http://corpora.clarin-d.uni-saarland.de/surprisal/6.0.3/?id=rspa_1913_0045 | 10.1098/rspa.1913.0045 | null | null | null | Thermodynamics | 42.141789 | Electricity | 30.253003 | Thermodynamics | [
4.2395405769348145,
-77.44401550292969
] | The Attainment of High Potentials by the Use of Radium .
471 contraction would probably be observed , which would not be converted into an extension until the whole of the internal surface had yielded .
The authors desire to place on record their indebtedness to Prof. J. E. Petavel , F.R.S. , for many valuable suggestions in the course of this work .
The Attainment of High Potentials by the Use of Radium .
By H. G. J. Moseley , B.A. , John Harling Fellow , University of Manchester .
( Communicated by Prof. E. Rutherford , F.R.S. Received April 22 , \#151 ; Read May 1 , 1913 .
) The original aim of the work described in this note was to measure the energy and numerical importance of each of the many distinct kinds of / 3-particles emitted by a single radioactive substance .
Calculation of the energy of a / 3-particle from observation of its deflection in a magnetic field* involves assumptions which are as yet insufficiently supported by experiment .
Theoretically both the energies and distribution of the particles could be directly measured by giving a gradually increasing positive charge to the source of radiation ; for , when the potential of the source is + Y , electrons possessing energy less than eV will be drawn back to the source of radiation .
Unfortunately , more than a million volts would be necessary to stop the fastest / 3-particles , and no method is at present known of maintaining such a high potential in vacuo .
It was thought that this difficulty might possibly be overcome by using the active material itself in order to produce the high potential according to the principle employed in Strutt 's radium clock.f If the source of radiation were perfectly insulated its potential would rise until the swiftest / 3-particles could no longer escape .
The present note deals with experiments^ made to test whether this method were practicable .
It was found that high potentials were readily obtained , but the attempt to attain to a million volts failed through the difficulties of insulation encountered .
But few experiments were completed , and many failed as the result of accident .
This shows that , even if perseverance had been rewarded by greater success , technical difficulties , accentuated by * Planck , ' Phys. Zeit .
, ' 1906 , vol. 7 , p. 753 .
t Strutt , 4 Phil. Mag. , ' 1903 , vol. 6 , p. 588 .
+ A preliminary account of these experiments was communicated to the Manchester Literary and Philosophical Society , November 12 , 1912 .
Mr. H. G. J. Moseley .
The Attainment of [ Apr. 22 , every effort to improve the insulation , would probably have prevented the practical application , of the method .
It seemed , therefore , useless to pursue the matter further , until more is known of the reasons why the insulation of a vacuum breaks down .
In these experiments the source of / 3-radiation was 20 millicuries or more of purified radium emanation contained in a thin bulb\#151 ; marked B in fig. 1\#151 ; Fig. 1 .
of about 1 cm .
diameter .
The bulb , which was just thick enough to stop all a-radiation , was supported by a fine silica rod R inside an exhausted glass flask F of 1 litre capacity .
The rod , of diameter about 0*8 mm. , was freshly drawn from transparent fused silica .
The surface of the bulb and the flask was coated with silver , which was found to retain a trace of conductivity when subsequently heated to 400 ' C. , though it then became almost transparent .
The potential gained by the bulb was measured by a simple form of attracted disc electrometer , a circular aluminium disc being hung from the arm of a horizontal silica spring , the other end of which was soldered with aluminium to a projection from one of the glass walls of the flask .
By observing with a microscope the .
displacement of the disc , the force of attraction exerted on it by the bulb was measured , and from this it was .
easy to calculate the charge and the potential acquired by the bulb .
The force of a dyne displaced the spring by about 0T mm. The disc was hung just at the entrance to the mouth of the flask , so that the remainder of the flask wall served the purpose of a guard-ring .
In order to diminish the risk of discharge through any trace of gas left in the vessel , the greatest care was taken in the exhaustion of the flask .
Instead of an attempt being made to measure the residual pressure in the apparatus , methods of exhaustion were followed which , in the hands of 1913 .
] High Potentials by the Use of Radium .
473 others , have yielded the highest attainable vacua.* To remove water and other volatile substances the entire apparatus was subjected to prolonged heating at 400 ' C. , and exhausted by a Gaede mercury pump .
Everything was heated electrically , the main flask F being surrounded by a cylinder of sheet asbestos wound with nickel wTire and insulated with kieselguhr , while the charcoal bulbs A and C and the connecting tubes were enclosed in small tube furnaces .
At first , almost as soon as pumping ceased , the hydrogen and carbon monoxide lines appeared in the discharge tube D , which was used to test the degree of exhaustion .
After some hours ' heating , and after repeatedly filling the whole system with dried nitrogen and then re-exhausting , a few minutes ' pumping sufficed to prevent the passage of a discharge in D , and this condition was then maintained for an hour or more after pumping had ceased .
To obtain this result it was necessary to employ a U-tube cooled in liquid air to condense the vapours of mercury and tap-grease , and the charcoal in A and C , which was being heated all the time , had to be properly prepared .
The preparation , which followed the directions given by Hupka , f consisted chiefly in heating freshly-made coconut charcoal to 450 ' in vacuo , until gas was no longer evolved ; a tedious process , since the hydrocarbons are very slowly volatilised and decomposed .
Before the final exhaustion the wide by-pass Y was sealed off .
Then after five hours ' pumping the tap T was closed , and C cooled in liquid air .
After a further five hours the apparatus was sealed off at X , and quickly removed from the furnaces .
A was then kept in liquid air during the course of an experiment .
If all went well the exhaustion was completed in about 24 hours .
As soon as the apparatus had had time to cool , it was seen that the bulb was abruptly discharged every few minutes .
The disc of the electrometer was first displaced by an amount which showed that the bulb was very highly charged , and then suddenly flew back to its original position , while in a dark room a yellowish-green flash was seen to light up the bulb , the rest of the interior of the flask remaining dark .
The displacement of the disc immediately recommenced , at first slowly , since the force of attraction depended on the square of the attracting charge , then at an ever increasing rate , until the maximum was approached .
The disc then began to move more slowly , at times it would falter or fall back a little , as if some slight discharge were taking place .
Finally , without warning , came the complete discharge , the time occupied by the cycle being erratic , but * Heuse and Scheele , ' Zeitschr .
f. Instrumentenk .
, ' 1909 , vol. 29 , p. 46 ; Pointing and Barlow , 4 Roy .
Soc. Proc.,5 1910 , A , vol. 84 , p. 534 .
t Hupka , 'Ann .
d. Physik , ' 1910 , vol. 31 , p. 169 .
474 Mr. H. G. J. Moseley .
The Attainment of [ Apr. 22 , corresponding roughly with the interval expected having regard to the quantity of active material and the capacity of the system .
The thin disc , if not in metallic connection with the flask , gained a free positive charge , which pulled it hack towards the neighbouring silvered surface ; a difficulty easily overcome by occasionally tilting the apparatus slightly .
The bulb could be discharged at will by directing on to the apparatus a powerful beam of X-rays , the necessary charge being doubtless carried to the bulb by the swarm of electrons released from the surface of the flask .
A preliminary experiment made with simpler apparatus showed that a potential of the order of 150,000 volts could readily be obtained .
In the first successful attempt to use the apparatus described above , the bulb , of diameter 9 mm. , was made of quartz .
As soon as the apparatus was completely exhausted a spark perforated the bulb and the radium emanation began to diffuse out and condense on the cooled charcoal .
It was several days before the greater part of the emanation had been transferred , so that the size of the hole , calculated* from the rate of effusion , must have been only of the order of 10"4 mm. This accident appeared not to affect the discharge potential , which was found to be 1*5 x 105 volts , and remained the same even when most of the emanation had left the bulb .
The experiment was repeated with a glass bulb of 1 cm .
diameter through which a platinum wire was sealed , in order to prevent the passage of a spark through the glass .
The tip of the bulb was fixed by the wire into a small silica tube fused on to the silica rod .
The maximum discharge potential observed was 1*7 x 105 volts , but this figure was probably slightly over-estimated , since the silica tube if charged would itself have attracted the disc appreciably .
In each case the discharge potential decreased as soon as the charcoal was heated to room temperature , but was still of the order of 105 volts .
This decrease is a strong indication that the sudden discharge , which always limited the potential , took place through the residual gas and not along the silica rod .
The slow and irregular rate of charging at high potentials may have been due in part to conduction along the silica .
The number of particles escaping must also have been somewhat diminished , since 160,000 volts will turn back any particle emitted with velocity less than 0*65 that of light .
Study of the experimental circumstances of discharge in high vacua has been singularly neglected .
The only systematic work on the subject is that of Madelung.f This author , working with parallel electrodes at distances up to 0*4 mm. , concluded that in the highest vacua a discharge takes place as .
* Knudsen , 'Ann .
d. Physik , ' 1909 , vol. 28 , p. 999 .
f Madelung , ' Phys. Zeit .
, ' 1907 , vol. 8 , p. 68 . .
1913 .
] High Potentials by the Use of Radium .
soon as 4die electric force at the surface of the electrodes exceeds 3 or 4 x 105 volts per centimetre .
The highest potential used by him was only about 12,000 volts , but his results showed clearly that under his conditions the discharge could not be explained by the ordinary theory of ionisation by collision in gases .
In the present experiments there can be no doubt that the process of exhaustion wTas really effective , as special tests were made to guard against the possibility of mistake .
The residual pressure was therefore so small that ordinary ionisation by collision was out of the question .
When a bulb of 9 mm. diameter is charged to a potential of 1*5 x 105 volts , the electric force at the surface is 3*3 x 105 volts per cm .
, and the agreement between this figure and that found by Madelung may well be more than a coincidence .
Again , in the one experiment the tip of a platinum wire projected from the glass bulb , and the failure of this point , at which the electric force must have been enormous , to promote discharge is paralleled by Madelung 's observation that the discharge potential was much higher between pointed electrodes than between parallel plates at the same distance .
The nature of this discharge at very low pressures is still obscure , but it is probably essentially the same as the discharge found by many observers to pass in air at less than the minimum spark potential between electrodes very close together .
This latter discharge has been the cause of much controversy ; partly because some observers have looked for a visible spark , while others have been content with the passage of a minute current ; partly on account of experimental difficulties introduced by the use of air and consequent restriction to minute spark-gaps ; and partly because the discharge seems to be much influenced by the nature and condition of the electrodes .
With varying length of spark-gap the discharge takes place when the electric force at the electrodes reaches a fixed limiting value , which is apparently uninfluenced by the presence of any kind of gas.* Various observersf using different electrodes have found values ranging from rather more than I06 up to 107 volts per centimetre , while AlmyJ obtained no visible discharge with an electric force of nearly 2 x 107 volts per centimetre .
It is not clear why the maximum electric force found by Madelung and in the present experiments should be so much lowTer , but very possibly the area of the electrode surface is here a factor of importance .
For these reasons it was hoped that the discharge might be prevented by * Hobbs , 'Phil .
Mag. , ' 1905 , vol. 10 , p. 617 ; G. Hoffmann , ' Phys. Zeit .
, ' 1910 , vol. 11 , p. 961 .
t Hobbs , loc. cit. ; G. Hoffmann , loc. cit. ; Earhart , 'Phil .
Mag. , ' 1901 , vol. 1 , p. 147 ; Shaw , 'Roy .
Soc. Proc. , ' 1903 , vol. 73 , p. 337 ; Kinsley , ' Phil. Mag. , ' 1905 , vol. 9 , p. 692 ; Rother , 'Phys .
Zeit .
, ' 1911 , vol. 12 , p. 671 .
I Almy , ' Phil. Mag. , ' 1908 , vol. 16 , p. 456 .
VOL. LXXXVIII.\#151 ; A. 476 The Attainment of High Potentials by the Use of Radium .
increasing the size of the bulb , and so reducing the surface intensity of electrification .
An experiment was , therefore , tried using a bulb of 5 cm .
diameter .
The electrometer spring was made very much stronger in anticipation of a much greater force of attraction , but otherwise nothing was altered .
Mr. Baumbach , the University glass blower , successfully undertook the difficult task of assembling the apparatus .
Owing to the increased capacity of the bulb it charged up much more slowly than before .
Instead , however , of discharging itself at intervals , it now became charged to an almost constant potential , which it retained , except when artificially discharged by the use of X-rays , for at least three weeks .
During that time this potential gradually rose from 105 to IT x 105 volts , while the current carried away by the / 3-particles fell from about 10"11 amperes to 2 per cent , of that value , owing to the decay of the radium emanation .
The potential was uninfluenced by the temperature of the charcoal bulb , and there can be little doubt that it was limited by a leak along the silica support , which was now stouter and less scrupulously cleaned than before .
This curious case of the potential being independent of the current carried by the silica strongly resembles conduction in a gas at a potential just below that required to produce a spark .
There variation of the current over wide limits is accompanied by very slight change in the potential , and perhaps the conduction in the silica had a similar origin .
In the event of this method of maintaining a constant high potential proving of practical use , much time could probably be saved by cutting short the process of exhaustion .
We see then that a radioactive substance may by the emission of / 3-radiation charge itself positively to a potential difference of more than 150,000 volts from its surroundings .
This fact provides a striking direct proof of the large amount of energy involved in the expulsion of a / 3-particle .
It also extends somewhat our knowledge of the insulating properties of a vacuum .
Previously Hupka ( loc. cit. ) had shown that two plates could in a highly exhausted chamber be maintained by means of an influence machine at a potential difference of 90,000 volts , without any discharge taking place .
1 am indebted to his paper for many useful suggestions .
In conclusion I wish to thank Prof. Rutherford for his kind interest in the progress of this work .
|
rspa_1913_0046 | 0950-1207 | On the recombination of the ions produced by R\#xF6;ntgen rays in gases and vapours. | 477 | 494 | 1,913 | 88 | Proceedings of the Royal Society of London. Series A, Containing Papers of a Mathematical and Physical Character | H. Thirkill, M. A.|Prof. Sir J. J. Thomson, O. M. F. R. S. | article | 6.0.4 | http://dx.doi.org/10.1098/rspa.1913.0046 | en | rspa | 1,910 | 1,900 | 1,900 | 61 | 150 | 3,687 | http://corpora.clarin-d.uni-saarland.de/surprisal/6.0.3/?id=rspa_1913_0046 | 10.1098/rspa.1913.0046 | null | null | null | Electricity | 37.811469 | Tables | 28.978792 | Electricity | [
4.048162460327148,
-68.59722137451172
] | ]\gt ; takes the simple form the solution of which is , ( 2 ) being the concentration of the ions initially , and the concentration after an interval of time .
In what has been said above the effect of diffusion is supposed to be negligible .
The coefficient of recombination is of fundamental importance in the theory of the ionisation of gases , and an experimental verification of equation ( 2 ) serves as a general test of the theory .
Methods of measuring the coefficient have been devised by Rutherford , *Townsend , Langevin , and others , and many determinations have been made by different observers .
S The results obtained present some rather wide divergences , both as regards Butherford , ' Phil. Mag 1897 , vol. 44 , p. 422 .
Townsend , ' Phil. Trans 1899 , vol. 193 , p. 129 .
Langevin , ' Annals de Chimie et de Physique , ' 1903 , vol. 28 , p. 433 .
S McClung , PhiL Mag 1902 , vol. 5 , p. 283 ; Hendren , 'Phys .
Rev 1905 , vol. 21 , p. 314 ; Retschinsky , ' Ann. der Physik , ' , 4 , vol. 17 , p. 518 .
values are liable to present wide divergences , and there is some difficulty in weighing up the results .
In the second place , the distribution of the ionisation in the vessel is of no small importance .
On account of the secondary radiation which is always present in these experiments , and which may produce intense local ionisation , it is impossible to know in an exact manner the distribution of the ionisation in the vessel .
Finally , the effects of the diffusion of the ions to the walls of the vessel are important , and there is some di[ficulty in correcting for this effect .
Langevin*has shown the importance of diffusion in McClung 's experiments .
At ordinary 'Journ .
de Physique , ' 1906 , vol. 4 , p. 322 .
Rontgen Rays in Gases Vapours .
479 pressures diffusion accounted for about 10 per cent. of the observed recombination , and , at a pressure of one-eighth of an atmosphere , the values obtained were probably five or six times too large .
In Langevin 's method these are avoided , and this was the'one used throughout these experiments .
Before giving a short account of the method , it may be useful to consider the significance attached by Langevin to the term ' number of colIisions.\ldquo ; Suppose that round each negative ion in an ionised gas a surface is described , the dimensions of which are arbitrary , except that its largest dimension is large compared with the mean free path of an ion , and small compared with average distance between two ions .
The number of positive ions which , in a time , penetrate into the interior of these surfaces , as a result of the attraction of the negative ions inside , is independent of the dimensions of the surface and of the eJectric field existing in the gas due to the neighbouring conductors .
This number Langevin defines to be the number of collisions between ions of opposite sign in the time The number of these collisions is by the expression in which and are the mobilities of the positive and negative ions respectively , and are the concentrations of the positive and negative ions , and is the charge on an ion of either sign .
This expression contains neither the dimensions of the surface supposed to surround the ion nor the strength oectric fdchange oositive aegative itokinetic energy oemented bnergy dheir meparate again after havingapproached , ravitated tround ther .
Afraction necess inity , umber oisions w If each collision results in a recombination of the two ions , the rate of But recombination does not necessarily follow a collision .
The initial Comparing this with the expression ; we have and .
( 3 ) in which and Experiment gives the relative values of the quantities and : : are proportional to the quantities of electricity received by the electrode in the two cases after one discharge from a Crookes tube , and and are propor : uantities olectricity induced olectrode aProduced bontgen R when tectrio fangevin.onvenieIhce oanation 1ater , onvenientto describe triefly hhich Qatios Qgiven bationx aurve irawn weing The points corresponding to and have a known rence of abscissae . .
The corresponding ordinates are and and their difference is also a known quantity In order to determine and , it is sufficient to determine on the curve two points and , the abscissae and ordinates of which differ respectively by the known quantities and .
By ving a transparent pa:per over the curve it is possible to find these points with both ease and accuracy .
The abscissae and ordinates of these points are and , and we have An example will illustrate this .
In an experiment on dry carbon dioxide at a pressure of 614 mm. of culy and a temperature of C. , th6 following results were obtained:\mdash ; ' necessary modifications were introduced .
A momentary discharge was produced in the Bontgen-ray bulb by the breaking of the contact at , which was in the primary circuit of a Marconi induction coil .
The contact at was between two pieces of platinum which could be separated very suddenly .
For effective action at this break it was necessary to have the platinum pieces held together by a steady , firm pressure .
A capacity of about 8 microfarads was inserted in order to suppress .
the spark which would occur when the circuit 1913 .
] Produced by Rontgen Rays in Gases and .
483 was broken .
A small spark here gave great irregularities in the -lay flash ; however , when this was entirely eliminated , and with a constant as measured by the ammeter , in the primary , the ionisation produced in the chamber by a single flash of rays was very constant , and readings could be repeated with great ease .
The ionisation chambers are denoted by AB and .
The upper electrodes A and , by means of a key , could be connected , either separately or together , with the insulated pair of quadrants of the electrometer .
Two exactly similar ionisation chambers were used and the Rontgen-ray bulb was adjusted so that the ionisation produced in each chamber by a single flash of the rays was the same .
With electric fields of opposite sign in the two chambers , the electric charge received by the electrometer when connected with both chambers was zero .
The quantity received in either of these chambers gives the charge If the electric field in one chamber be now increased , one electrode receives a quantity of electricity QL and the other a quantity of opposite .
If the two electrodes are both connected to the electrometer , the latter will suffer a deflection proportional to the difference of these charges , that is to .
This difference is a very small fraction of either of the charges or ( \amp ; and the error in is approximately proportional to the error in .
It is better , therefore , to measure and rather than and separately .
may be only 1 or 2 per cent. of , and some special device is necessary if both quantities are to be measured with the same electrometer .
Langevin used an electrometer with a condenser of variable capacity .
similar method was first tried in these experiments but was not found to be very satisfactory .
The variable capacity employed consisted of two sets of 10 parallel plates fixed to two axes .
One set , which was connected with the electrometer , remained fixed ; the other , which was kept at zero potential , could be rotated into or out of the fixed set , thus increasing or decreasing the capacity .
In measuring the quantity , the condenser was The accumulation of the ions in the neighbourhood of the electrodes affects the electric field , which is no longer uniform but is of greater intensity in the vicinity of the electrodes .
In the case of a uniform ionisation between the electrodes , Langevin has shown that the relative error resulting from the modification of the fieJd by the ions has for its principal term and , at the same time , its upper limit , the value .
The error , therefore , will be less than 1 per cent. so long as does not exceed .
With a non-uniform ionisation the modffication of the field by the ions becomes more important .
At low pressures with small values of and becomes very small , and it is necessary to have arger values of the ratio .
In general , however , voltages were ohosen so as to render the effect of the nisation on the field practically negligible .
In fig. 2 , A and are the ionisation chambers .
The plates 1 and 4 can be connected , either separately or together , to the electrometer , and the potential of the lower plate 2 can be varied .
The outer case of the ionisation chambers , receives auantitiesLet qoefficients oapacity anduction oystemsto beasured aatios ( where 4ductors , uffixes referl iumbers iigurethe eectrostatic fetween tates 1irst chamberexperiment .
Suppose tiash oontgen rthemeter , part oonductor kthroughout thethe guard tubes Tuadrants , oduced biontgen Rectrometer bated a disconnected ; the charge on the conductor 1 is given by the relation in which and , are the potentials of 1 , 2 and 3 , respectively .
Initially , and are both zero , so that the equation may be written .
( 4 ) When the charge is given to 1 , let the potential of the electrometer become .
Then we have .
( 5 ) Suppose now that the potential of 2 is changed to , and that , in consequence , the potential of the electrometer becomes , then , since there is no increase in the charge on 1 , we have , whence , subtracting ( 4 ) , If be adjusted so that the potential of the electrometer is brought back to zero , then .
( 6 ) Similarly , when 1 and 4 are both connected to the electrometer and therefore , since is zero .
( 7 ) When the charge is given to 1 , let the potential of the electrometer become .
Then we have Suppose now , that the potential of 2 is changed to , and that the electrometer , in consequence , assumes a potential .
We have and subtracting ( 7 ) from @ method it was unnecessary to have the plates charged for any appreciable time , and therefore the effects of slight insulation leaks were reduced to a minimum .
The manner in which the changes were brought about can be seen from the figure .
The electrode ( fig. 1 ) was connected to the point When and and and were connected , was at the potential of the plate of the battery of cells .
By breaking the contact between and , and joining and , the potential of could be changed to that of the point N. was a potentiometer consisting of 100 equal resistances .
The current from a small number of accumulators passed through this , and , by moving 1913 .
] Produced by Rontgen in Gases Vapours .
487 round the pointer , any fraction of this small potential could be added to or subtracted from that of the battery .
By connecting to instead of to , the potential of the electrode could be changed by a small known amount .
This was used in measuring the quantity .
The potential of the electrode was determined by that of the battery .
The small change of potential required to balance was measured by means of a potentiometer and a Weston cell .
An experimental difficulty may be noticed here .
If the gas between the plates was ionised while the plate A was insulated and the plate was connected to earth , a deflection corresponding to a positive charge was produced in the electrometer .
This effect was not due to a difference in the coefficients of diffusion of the positive and negative ions because an effect of a similar order of magnitude was obtained in carbon dioxide , in which the coefficients of diffusion of the two kinds of ions are very nearly the same .
The effect was probably due to the emission of electrons from the upper electrode under the influence of the Rontgen rays .
It was shown , however , that this effect did not influence the results obtained .
The charge received by the upper electrode , when a flash of Rontgen rays was used , was measured for increasing electric fields , first in one direction and then in the opposite direction .
For small values of the electric field the curves obtained were unsymmetI'ical , but this lack of symmetry decreased very rapidly as the potential increased , and for the large fields used in these experiments the two curves for electric fields of opposite sign were identical .
4 .
Preparation of ihe Gases The atmospheric air was thoroughly dried before being admitted to the apparatus by allowing it to remain in contact with phosphorus pentoxide for some time .
The carbon dioxide was liberated by the action of hydrochloric acid on calcium carbonate and was dried by allowing it to remain in contact with phosphorus pentoxide for some time .
The carbon monoxide was liberated by the action of sulphuric acid on formic acid and was dried over phosphorus pentoxide .
The sulphur dioxide was obtained from a cylinder of the liquid and was dried over phosphorus pentoxide .
The nitrous oxide was obtained from a cylinder of the gas and was dried over phosphorus pentoxide .
In some cases the gases were passed a spiral tube immersed in liquid air .
The ionisation chambers were exhausted by means of a Topler pump , and the remaining gas was absorbed by means of charcoal immersed in liquid air .
The dry gas was then admitted to the apparatus .
In every case great care was taken to make the gas or vapour dust-free .
variations , however , were within 6 or 6 per cent. of the mean value .
The values apply to a mean temperature of about C. The temperature at the time of the observations was always recorded , but no correction was made as it was considered that such a correction would almost certainly be within the limits of error of the experiment .
6 .
Discnssion of Results .
this table it will be seen that the coefficieni is very nearly proportional to the square of the pressure over a fairly wide ange of pressures .
At higher pressures this rate of increase becomes smaller .
1913 .
] Produced by Rontgen in Gases .
489 Table I. Pressure in mm. Air .
0.272 0.272 0.272 0.272 0.272 0.272 0.272 0.272 0.272 0.272 0.272 0.272 0.272 0.272 0.272 630 Carbon Dioxide .
0.151 0.078 0.038 0.151 0.078 0.038 0.151 0.078 0.038 0.151 0.078 0.038 0.151 0.078 0.038 0.151 0.078 0.038 0.151 0.078 0.038 0.151 0.078 0.038 0.151 0.078 0.038 0.151 0.078 0.038 0.151 0.078 0.038 0.151 0.078 0.038 0.151 0.078 0.038 0.151 0.078 0.038 0.151 0.078 0.038 Carbon Monoxide .
364 Sulphur Dioxide .
0.466 0.019 0.466 0.019 0.466 0.019 0.466 0.019 0.466 0.019 0.466 0.019 0.466 0.019 0.466 0.019 0.466 0.019 0.466 0.019 0.466 0.019 Nitrous Oxide .
Such a departure is to be expected if we accept Langevin 's interpretation of , for it would tend to approach a limit when every collision is accompanied by recombination .
Under these circumstances would be unity , and a further increase in the pressure would produce no increase in the value of .
This limit appears to be reached for compalatively small pressures : air at a pressure of about 4 or 5 atmospheres ; in sulphur dioxide at an even lower pressure .
Pressure 757 690 Coefficient of recombination 1820 1600 Sulphur Dioxide .
Pressure 680 504 444 338 200 Coefflcient of recombination 2740 2260 1900 1510 876 548 Nitrous Oxide .
Pressure 749 596 480 204 200 Coefflcient of recombination 28$0 2400 1690 1110 690 Townsend McClung Langevin Air .
Carbon dioxide .
There is a good agreement between the results obtained by different observers working with air and carbon dioxide at atmospheric pressure .
This is more striking when one considers the great difference between the method employed in the experiments described in this paper for example , and that employed by McClung .
At low pressm.es , however , there are wide divergences .
From the curves * ' Phil. Trans , vol. 209 .
Produced by Rays in Gases and Vapours .
491 Fi it can be seen that , for a considerable range of pressure , depending on the gas , the coefficient of recombination is proportional to the This VOL. LXXXVIIL\mdash ; A. moving particles ejected by the Rontgen rays would disappear almost instantaneously in the presence of the large electric fields used .
This is supported by the agreement between the results of the experiments made under different experimental conditions ; large variations of the electric field and of the intensity of the ionisation do not seem to produce any appreciable effect on the coefficient of recombination .
Although for this reason the results obtained by Plimpton cannot be compared with those here , one point may be noticed .
As would be expected , Plimpton 's values are in every case very large , but these values decrease when the time-interval during which diffusion is allowed to take place is increased .
The final slopes of the curves obtained from Plimpton 's data , however , are too steep to enable one to deduce a limiting value with any degree of accuracy .
This is especially so in the case of carbon dioxide , in which the coefficient of much smaller than it is in air .
The final value obtained is 4880 compared with an initial value of 10,000 , and the value is still decreasing .
In the case of air the lowest value for is 3960 .
This value is about 10 per cent. higher than the result given here .
The values of obtained at low pressures in these ximents may be 'Roy .
Soc. ' 1912 , , p. Produoed by Rontgen Rays in Gases and .
493 briefly mentioned here .
The observations at low pressures are much difficult than those at higher pressures , especially in those gases in which the ionisation is small .
The important quantity which has to be measured is , the difference between the quanli of electricioy which reach the electrode for two different values of the field .
This quantity depends on the value of the coefficient and on the ionisation in the gas .
Both these decrease when the pressure decreases , the former being approximately inversely proportional to the square of the pressure .
At low pressures , therefore , the difference becomes very small .
This difficulty can be obviated to some extent by using more than one flash of the rays , but this is not so satisfactory .
The results obtained do seem to indicate departures from the linear law at lower pressures , but in view of the increased difficulty of the experiments it is perhaps well not to lay too much emphasis on these variations .
It is significant , however , that the changes appear in the region of pressure in which other experiments seem to suggest that some modification takes place in the negative ion .
The constancy of the results that have been obtained in these experiments under conditions which have been very widely varied seems to be in favour of the simple law of recombination or in its more general form , Among the modifications of this law which have been proposed , perhaps ths best known is that of Sutherland It is not always easy to distinguish between these two laws , and the results of some observers seem to fit in almost equally well with both formulae .
Experiments in which ionisation of very widely varying intensity is used seem most promising .
It is hoped to give a more detailed account of some experiments on this point at a later date .
tion .
Regarded from this point of view alone it is of advantage , in the construction of a reflecting telescope , to make the mirror of as large a size aa the mechanical difficulties incident to the construction of large mirrors allow , difficulties , that is to say , such as that of obtaining the glass of the necessary homogeneity throughout , in order to avoid distortion owing changes of temperature , and the difficulties of grinding , shaping , and polishing .
There is , however , another factor to be considered which affects the problem .
The mirror , even if perfect in other respects , will , when partially supported , be distorted by its weight , to a greater or less extent according to the nature of the support .
This distortion will cause a diminution in the resolving power , ffie of which will evidently increase with the size of the mirror , and so will tend to counteract the advantage accruing from the larger aperture .
It is conceive .able even that there will , for any
|
rspa_1913_0047 | 0950-1207 | The flexure of telescope mirror-discs arising from their weight, and its influence upon resolving power. | 494 | 522 | 1,913 | 88 | Proceedings of the Royal Society of London. Series A, Containing Papers of a Mathematical and Physical Character | H. Spencer Jones, B. A., B. Sc.|Sir Joseph Larmor, F. R. S. | article | 6.0.4 | http://dx.doi.org/10.1098/rspa.1913.0047 | en | rspa | 1,910 | 1,900 | 1,900 | 30 | 258 | 7,606 | http://corpora.clarin-d.uni-saarland.de/surprisal/6.0.3/?id=rspa_1913_0047 | 10.1098/rspa.1913.0047 | null | null | null | Fluid Dynamics | 34.677417 | Tables | 24.085834 | Fluid Dynamics | [
27.736501693725586,
-9.841693878173828
] | ]\gt ; Mr. .
H. S. Jones .
The Flexure of Telescope [ Apr. 26 , 7 .
Conclusions .
( 1 ) Recombination appears to take place according to the simple law or more generally ( 2 ) The coefficient of recombination with the pressure and throughout a considerable range of pressure is proportional to the pressure .
In conclusion I desire to express my appreciation of the kindly interest which Prof. Sir J. J. Thomson has shown throughout this work .
The Flexure of Telescope Mirror-discs Arising from their Weight , and its upon Resolving Power .
By H. SPENcElt JONES , B.A. , , Jesus College , Cambridge , Isaac Newton Student .
( Communicated by Sir Jossph Larmor , F.R.S. Received Apri126 , \mdash ; Read June 19 , 1913 .
) The resolving power of a reflecting telescope is proportional to its aperture , the mirror being supposed accurately a paraboloid of revolution , sa a bundle of parallel rays pass through a geometrical focus after reflection .
Regarded from this point of view alone it is of advantage , in the construction of a reflecting telescope , to make the mirror of as large a size as the mechanical difficulties incident to the construction of large mirrors will allow , difficulties , that is to say , such as that of obtaining the glass of the necessary homogeneity throughout , in order to avoid distortion owing changes of temperature , and the difficulties of grinding , shaping , and polishing .
There is , however , another factor to be considered which affects the problem .
The mirror , even if perfect in other respects , will , when partially supported , be distorted by its weight , to a greater or less extent .
according to the nature of the support .
This distortion will cause a diminution in the resolving power , the ifect of which will evidently increase with the size of the mirror , and so will tend to counteract the advantage from the larger aperture .
It is conceivable even that there will , for any 1913 .
] Mirror-discs from their Weight .
given mebhod of support , be a critical aperture , an increase of the size of the mirror beyond which will actually produce a decrease instead of an increase in the resolving power .
The object of the presenb paper is , firstly , to calculate the nature and amount of the distortion which is produced by the weight for various methods of support , and , secondly , to investigate to what extent this distortion will affect the resolving power of ths instrument , and whether any limitation is thereby placed upon the size of the mirrors which are likely to be practically attainable .
The types of support which are considered are necessarily comparatively simple and somewhat ideal : the difficulties of the mathematical analysis impose these limitations , but it will be seen that they are sufficient to enable us to give a definite answer to the problem as to whether the critical size of aperture is one which is likely to be reached in the construction of large mirrors , or as to whether this critical size is so large as to be of no practical significance .
Since the equations of elastic are ]inear it is sufficient to consider the flexure of the disc for the two cases in which it is horizontal and vertical .
The case in which it is inclined at any angle can then be obtained by a combination of these .
The notation used hout will be that used by Prof. Love in his ' Mathematical Theory of Elasticity.'* We will discuss first the case in which the plane of the disc is horizontal , and will treat it as a circular plate of uniform thickness .
This is nearly true for large mirrors and will be a sufficient approximation for the present discussion .
We consider several different supports .
( 1 ) The disc is held in a horizontal position , being supported at its centre , its edge being free .
We obtain the solution by a combination of various stress systems , which together are to the correct body forces and are to be so adjusted as to satisfy the terminal conditions .
The conditions in this case are that the normal displacement at the centre should vanish , and that the stress resultants , and stress couples , should vanish at the edge .
We use the following systems of stress\mdash ; A system in which all the stress components vanish except , being the weight of the plate per unit volume , and the axis being vertically upwards , and the origin in the central plane .
2 is the thickness of the plate .
*Camb .
Univ. Press , 1906 , 2nd Edition .
Love , loc. , S 294 .
Mr. H. S. Jones .
The I ?
exure of Telescope [ Apr. 26 , The corresponding displacements may be taken to be given by Also all stress resultants are zero .
The axes of and are in the plane of the plate ; are the components of displacement parallel to the three axes ; , as usual , denote Poisson 's Ratio and Young 's Modulus of Elasticity for the material of the plate .
A stress-system in which there is a pressure 2 on the face of the plate .
The solution for a plate bent by a uniform pressure over one face is given in Love , S307 ; we must in the solution there given put and so obtain whxy .
These give , in the central plane , a radial displacement of amount , and a nolmal displacement where is the igidity of the plate .
If the radius of the plate be , we have also at the edge 1913 .
] Mirror-discs Arising from their Weight .
( ) We need other solutions which give no resultant body forces in order to adjust the boundary conditions .
We may take giving For this system the normal displacement of the central plane vanishes , but there is a radial displacement in the plane of amount We finally take the solution corresponding to a system of generalised plane stress , given in Love , SS303 and 304 The components of displacement in the central plane vanish .
If is the normal displacement of the central plane it is shown that satisfies where is Laplace 's Operator in two dimensions , and that the stress resultants are derived , when is known , from the formulae . .
We have given by an expression of the fornl since vanishes at the centre .
Therefore Combining these four solutions , the conditions that vanish at the edge give .
The total value of at any point is i.e. there is a downward displacement at any point of amount Mr. H. S. Jones .
The Flexure of Telescope [ Apr. 26 , Putting 2 , the weight of the plate , the downward deflection at the is given by .
The second term in this expression is small compared with the first , the relative magnitudes being of the order , which is comparatively small , since the usual order of magnitude of the thickness is 1/ 10 of the aperture .
The correctness of the first term of this expression oan be proved by the use of the approximate theory which holds for the flexure of plates .
This approximate theory is very useful in obtaining solutions for more complicated cases of support , when the more exact theory would either be very tedious or else impracticable .
It is shown by Love* that for a plate slightly bent by transverse forces only the stress couples at the edge are given by , where denotes differentiation along the outward normal at the edge , and the edge , is the radius of curvature .
If is the acting force per unit area , is determined by We therefore have for the case of a circular plate under the action of its own weight , ; that using the facb , where necessary , in the integration that vanishes at the centre of the plate : so that when we must have , since vanish at the boundary , and ) These values of agree in magnitude with those previously obtained , provided that the term in which involves be ected .
We therefole obtai the deflection at the edge iven by the approximate expression .
, S 313 .
1913 .
] Mirror-discs Ari.sing from their Weight .
( 2 ) We now take the case in which the plate is held horizontally and clamped at the rim .
Then we must havs both and vanishing at points on the rim ; and the radial displacement in the plane of the disc must also vanish on the rim .
If we combine the system of solutions above , the resudtant radial displacement is and so vanishes at all points .
We may take for the solution of in in this case Since is not infinite at the centre , we must have , and in order that may not become infinite at centre , we must have Thus the conditions at lire that and the depression at any point is given by , the central depression being In this case the exact theory agrees with the approximate theory.* The reason is that no terms upon are involved .
( 3 ) If the plate is supported at the edge , we must have vanishing there .
Ths first two evidently do so .
We can take the same solution for as in ( 2 ) , and the remaining conditions give and , giving for the value of at any point , a downward displacement , * See solution , in Love , p. 467 ( ii ) .
Mr. H. S. Jones .
The Flexure of Telescope [ Apr. 26 , The first term agrees with that obtained by means of the approximate theory .
Combining these three results we have , for the relative depressions of centre and rim , ( 1 ) When supported at the centre , .
( 2 ) When clamped at the rim , .
( 3 ) When supported at the rim , .
Neglecting the small second term , the ratios of these expressions depend only upon the value of .
If we put , which is approximately the case for glass , we have the relative deflections in these three cases given by the ratios 93 : 15 : 63 .
The deflection is thus much smaller in the case of the clamped rim .
( 4 ) It is to be expected that the more complete the support at the back of the mirlor the less will be the effect due to the flexure .
We will accordingly consider the case in which the plate is not only supported at the centre , so that there , but is , in addition , supported at the edge .
A sufficiently close value of the flexure is obtained by using the approximate theory , and since the work is much shortened by so doing , that is the course here adopted .
We have Thus Since at the centre , we must put ; and since at the edge , we obtai1l Also must vanish at the edge .
The second boundary condition is accordingly 1913 .
] Mirror-discs Arising from their Weight .
From these two equations we obtain and the value of at any point of the plate is given by which vanishes\mdash ; as it should\mdash ; when ( 5 ) We consider finally , as an example of a still more complete support , the case in which the disc of radius is supported at the centre and the edge , and also round the circumference of a concentric circle of radius We must now assume different solutions which hold according as If we may assume If we take We have here six c , onstants Ting .
Ihese are uniquely determined from the six boundary conditions , which are that , should vanish when when when , , , The condition that when has been satisfied already by our choice of From these equations we deduce that , Mr. H. S. Jones .
The Flexure of Telescope [ Apr. 26 , and also that These equations suffice to determine the deflection at any point of the disc in this case .
We have still to consider the solutions of the stress equations which are appropriate to the case in which the disc is held vertically .
The body forces are now in the plane of the disc , and there are no normal components .
We take the and axes in the plane , the origin being at the centre , and the positive direction of the axis being vertically downwards .
We will consider several simple solutions , by a combination of which the solutions appropriate to various boundary conditions may be obtained .
We take the simple solutions of the state of plane stress:\mdash ; If we assume we have a system stresses which give a body force parallel to the axis of amount , the weight per unit area .
The remaining solutions will , therefore , be such as to give no resultant body forces .
From these values we deduce the following particular solutions for the displacements , and the stress resultants are -why , which give and , etc. , all zero .
( ) A particular solution which gives no body forces is one in which the stress resultants and the components of displacement are iven by and 1913 .
] Mirror-discs Arising from their Weight .
and the rest zero .
Thus ( ) There are also a series of particular solutions for forces in the plane of the disc which are given by ' where is any plane harmonic nction .
These values give If we take ) , a plane harmonic of the third yree , we obtain \mdash ; cos2 and then the displacements are If the plate is held at the centre there must be a force applied there which is equal in magnitude to the weight of the disc .
The simplest case of a singularity arising from the application of a force at a point inside the body is given in Love , S148 .
The components of displacement are A and the stress components are given by , ? .
These are easily shown to give Mr. H. S. Jones .
The Flexure of Telescope [ Apr. 26 , ( 1 ) We combine these solutions by adding to the first , the second multiplied by a constant times the third , and times the fourth .
Then the stress components are found to vanish all round the edge provided that l , The coefficient in the stress resultants in the solution is then .
The resultant of the tractions on the surface of a small cavity taken round the point of application of the applied force must be equal and opposite to that force , and therefore independent of the shape of the cavity in the limit when its dimensions are taken very small .
The resultant is easily found to be parallel to the positive direction of the axis , and is therefore equal in magnitude and opposite in direction to the weight of the body , and so is correct .
The solution thus obtained is therefore the correct solution for the case in which the disc is supported at its centre with its edge free .
The displacement components are given by const .
The constant occurring in the expression for has to be determined from the condition that should vanish when vanishes ; but on account of the logarithmic term becomes infinite at the centre .
The reason for this is that the force cannot be applied at an exact mathematicai point : it must be distributed over a small area , and the value of the constant will depend upon the mode of this distribution .
The difference of the displacements in the direction of the force at any two points on the disc can , however , be uniquely determined by this formula .
( 2 ) If the disc is clamped at the and held vertically the displacements there must be zero .
To obtain the appropriate solution we combine the cases , ( ) , ( ) above , determining the constants introduced by means of the boundary conditions ; we obtain const .
1913 .
] Mirror-discs Arising from their Weight .
We choose so that the coefficients of in the expression for are equal , and so that vanishes , i.e. ' .
The constant in is so chosen that is zero on the rim .
We thus obtain ' and the corresponding stress components are easily shown to be which give the correct body force , and so all the conditions are satisfied .
The displacement at the centre is given by This displacement is entirely in the plane of the plate and is small compared with the displacement in the direction 11ormal to the plate , when it is horizontal , for in the latter case there is a term involving in the denominator .
( 3 ) For the case in which the disc is held vertically in a groove at the rim in such a manner that the normal displacements there are zero , but tangential displacements are possible , the boundary conditions are that the normal displacement and the tangential stress resultant must vanish at the rim .
Our previous solutions cannot be combined in any manner so as to satisfy these conditionsi .
We can obtain another solution for the case in which there are no body forces in the following We may express the stress components in terms of a mcCion , which satisfies , in the form .
We try a solution Mr. H. S. Jones .
The Flexure of Telescope [ Apr. 26 , and then we have cos3 , whence we deduce that , , , whence These three equations are satisfied by The normal component of the displacement at any point is We combine this solution with the solution above , for which the normal displacement at any point is Then , when , by putting , and equating the coefficients of to , we obtain ' 1913 .
] Mirror-discs Arising from their Weight .
so that the components of displacement at any point of the disc are iven by .
The central deflection is given by ' In the case in which the plate is inclined to the vertical there will be a superposition of the two effects .
There is now a component of gravity the plane of the plate and a component normal to it .
This produces the normal which is , in general , the chief distortion .
The component of the force in the plane of the plate produces small displacements in the plane , .
accompanied by very slight normal displacements , which are symmetrical about and vanish on the central plane .
We can obtain some information as to the tive magnitudes of these effects from the results which have been already obtained .
When the plate is supported horizontally at the centl'e it has been that the deflectio11 at the is .
Ths ratio of the two terms which occur in this expression is If we put , and , which gives ratio of aperture : ness equal to 10 , we obtain ratio of the two terms to be 1 : , so that the second term is tolerably small when compaled with the first .
When the plate is supported ab the rim the deflection at the centre is , and the ratio of th second term in this expression to the first mlder the conditions is 1 : VOL. LXXXVIII .
Mr. H. .
Jones .
The Flexure of Telescope [ Apr. 26 , the case in which the plate was held vertically and clamped at the edge we have seen that the central displacement is and the ratio of this to the small term occurring in the normal displacement when supported at the centre is and so is very small indeed .
The displacement in the plane of the disc when this is held vertical is in this case only about 1/ 16,000 of the normal displacement at the edge when the disc is supported horizontally at the centre .
If the disc is vertical and held at the centre the relative displacement for points on the same radius at distances from the centre is If cm .
and cm .
, then has a maximum value when , and this maximum is approximately which is rather larger than the small term ) which occurs in in the first horizontal case considered .
When the disc was vertical and supported round the rim the central deflection was .
This is about 5/ 4 the value when the edge is clamped .
It follows that , unless the disc when horizontal is very well supported at the back , the displacement normal to the disc which is produced by its weight is very large compared with the displacement in the plane of the disc when it is held vertically .
We have now to apply the results which have been obtained to discuss the extent to which resolving power is affected by the flexure .
We suppose the undistorted mirror to be accurately paraboloidal with a focal length and take a system of rectangular axes such that the axis is the axis of the mirror , and the vertex is at the origin .
Then the equation of the paraboloid is 1913 .
] Mirror-discs Arising from their Weight .
A bundle of rays all parallel to the axis will after reflection all pass through the point of intersection of the axis with the focal plane , i.e. through the point We consider now another parallel bundle , each ray of which makes a small angle with the axis .
The ray which passes through the point of the surface has the equation Then the reflected ray may be represented by Since the direction cosines of the normal to the surface are proportional to , and since the incident and reflected rays make equal angles with the normal , and are all in the same plane , we have the conditions ; and also together with Since has been assumed so small that its square and powers may be neglected , and since also we obtain for the values of the expressions , correct up to terms including and , to the same order of approximation , the co-ordinates of the point in which the reflected ray cuts the focal plane are given by or the distance from the axis of the point in which the reflected ray through cuts the focal plane is For a iven value of this is greabest when , i.e. for the point in the Mr. H. S. Jones .
The flexure of Telescope [ Apr. 26 , plane through the axis which contains the direction of the bundle .
For points in this plane the greatest value is at the edge , and is where is the edge value .
Since even for points on the rim will be comparatively small we may take this distance to be approximately Now two points of light , one of whioh is on the axis and the other at a small angular distance be resolved provided that where is the wave-length of the light , and is the semi-aperture of the telescope , for when this condition is satisfied the angular separation of the spots is of cient magnitude to prevent their first diffraction maxima overlapping Hence if two stars are to appear distinct , the breadth of the central image for parallel rays must not exceed Suppose now that the undistorted surface has for its equation Then , the components of the displacement of the point , are functions of and , and the co-ordinates of the displaced point are given by Since are all small we can in them put , so that they become functions of and .
The equation of the deformed surface is therefore .
We consider first , for simplicity , the deformation which is produced when the disc is horizontal .
In this case , the only displacement being norrnal to the disc and symmetrical , so that we can proceed in two dimensions .
The section of the surface by the plane has for its equation .
The equation of an incident ray parallel to the axis is , and since the ( lirection cosines of the normal to the surface at the point are proportional to it follows that , the reflected ray being and are given by the equations 1913 .
] Mirror-discs Arising from their Weight .
and the reflected ray is If , i.e. if the mirror is undistorted , there is perfect focussing at We suppose then that the nearest approach to focussing when the mirror is bent is on the plane , where is a small quantity which has to be determined .
Then the corresponding value of is given by where has been used to denote ( w/ \amp ; ) , and where squares of have been neglected .
On expansion , retaining only first power of , there results ( 1 ) In the case when the diso is clamped at the edge it has been shown that , where By differentiation of the above value of it is found that the condition for a stationary intercept is where , and then we get .
The condition for a stationary value becomes in the case at present under discussion , For a given value of there are two values of .
In the case in which , these combine to give an inflexional tangent at The value of at any point is The part which is independent of vanishes at the two edges , and the two parts add as shown in the diagram .
Mr. H. S. Jones .
The Flexure of Telescope [ Apr. 26 , The position of the stationary points depends upon the value assigned to and the values at the ends may be either greater or less than the maxima .
The most favourable case , the least breadth , will occur when the two are equal .
Retaining only the most important terms the maxima are given by and to the same order are equal to The end values when are equal to Hence the condition that this is equal to the maximum is which is satisfied by , giving a breadth of image 2 , equal to 4 , and this gives the limiting condition that The following approximate mean values for glass are sufficient to determine the magnitude of the permissible limits for , viz. :\mdash ; C.G.S. units , cm .
, and Putting , the condition is that , or If the mirror is so constructed that , then the limiting value of is cm .
, and so in this case the resolving power is lost for a very small breadth of aperture .
Since the limiting condition is const .
this result is also an example of the general law that the thicker the mirror the larger is the permissible breadth of the aperture .
1913 .
] Mirror-discs Arising from their Weight .
In the case when the disc is horizontal and supported at the , the value of was found to be ( say ) , where has the same value as above .
Proceeding exactly as above it is easily found that the stationary values are given by : and when The maxima and minima are again , and so the condition that these are equal to the end values is which is satisfied by a breadth equal to exactly as before , and so\mdash ; since has the same valne\mdash ; the limiting value of in order that the resolving may still increase with increase of aperture has the same as before .
( 2 ) Coming now to the nex6 case considered , in which the plate was supported both at the ce1ltre and at the edge , the value of was shown to be where were determlned , and here Then the intercept on the plane is approximately , ectin g all terms of higher order .
The maximum value of the intercept is determined by the condition and for this value of If we adjust so that the maximum and the value at the are equal and Mr. H. S. Jones .
Flexure of Telescope [ Apr. 26 , opposite , then the from the two halves of the mirror overlap .
This requires that where the value of determined by the maximum condition has been used .
Since the focal length is usually about five times the aperture , i.e. the ratio of the terms is , and so very little error will be caused by working with the approximate first terms .
Then for the determination of the value of at the maximum we have the equation Now , approx. , so that ; or , putting By trial it is found that nearly satisfies , so that we write where is small .
A second approximation gives , so that it is sufficiently acourate to take at the maximum .
Since the first terms are now comparatively small , we include also the next order terms on substitution of this value of , and by writing , and it is found that the breadth of the image is 2 therefore the limiting condition is that or , using the same values for the constants as before , this condition ives , and if cm .
, or inches , and so the limiting permissible value of the radius , in this case , the thickness being of the aperture , is about 4 feet .
1918 .
] Mirror-discs Arising]Weight .
If we use a thicker plate we can use a mirror of aperture , e.g. if , then inches , or the permissible radius is nearly 7 feet .
By comparison with the preceding cases , it is at once apparent how great is the advantage which is obtained simply by supporting the mirror at the centre in addition to the edge .
( 3 ) It now remains to discuss the last mode of support considered , when the disc was horizontal , viz. , when it is supported at the centre , round the circumference , and round a concentric circle of radius the values of the displacement which were found for the two portions of the disc we obtain for the values of the intercept on the plane the values , according as or respectively , Jog which are continuous at , as they should be .
We can abbreviate the work and at the same time illustrate the advantage given by the additional support if we take a special value for .
The simplest value to take is , and then , by putting , we have givetl by and also On investigation , it is found that the conditions cannot be satisfied by supposing the maximum deflecLion to fall in the inner portion , and by making it equal to the end dellection .
We therefore make the maximum in the outer portion equal to the end deflection .
The condition for the maximum is and the corresponding maximum is .
H. S. Jones .
The Flexure of Telescope [ Apr. 26 , and the equation to determine is ab On substitution of the numerical values , we get 2.02 By trial it is found that nearly satisfies , and by substituting , and retaining first powers only of , a nearer approximation is .
Including now the next order the total breadth of the image is found to be 4 ak , and the limiting condition is that , so that , or cm .
inches , if The limiting value of the radius of the mirror is thus increased to about 10 feet , as compared with the 4-foot radius obtained in the case in which the support at half the radial distance is abssnt .
The cases which have now been discussed are sufficient to enable us to conclude that as far as the displacement normal to the plane of the disc , produced by the component of gravity in that direction , is concerned , the effect on the resolving power may be practically nullified if care is taken to support the mirror well at the back .
Although the methods of support considered above are necessarily somewhat ideal , it is certain that with a mirror well supported at the back , as e.g. is the case in the method devised by Ritchey for the large reflecting telescope at Mount Wilson Observatory , it is possible to use mirrors of an aperture which is far beyond the limits which at present are practically attainable .
This discussion has also shown how , for a given mode of support , larger apertures may be used provided that the thickness of the mirror is increased sufficiently .
The bhickness to be used must of course be determined by practical considerations , such as the possibility of obtaining a homogeneous mirror , or by the question of the weight which the supports are designed to bear .
For the remainder of the discussion we shall suppose the mirror to be well enough supported at the back for the normal component of gravity to have no effect upon the resolving power , so that it only remains to discuss the effect of the displacements whicf ] occur in the plane of the disc .
We will 1913 .
] -discs Arising from their Weight .
therefore consider the case in which the disc is vertical , as then these displacements will have their maximu value .
The nature of the back support does not now concern us , and whatever this may be the disc must also be held in some manner at the edge and it will be impossible to prevent the displacement in the plane of the disc from taking place .
Putting , the equation of the mirror becomes The equation of the normal at is where and it is easily shown that corresponding to a ray incident at the point of the surface parallel to the axis , the reflected ray is where are given by ; and as far as the first order only in the displacements , by substituting for in terms of , and putting , we have ; and , similarly , For simplicity of discussion , we will consider first the case in which .
we consider for the present only the rays which are incident at points on the mirror in the vertical plane through its axis .
For the case of the mirror which is clamped at the where and so , and Neglecting the term in and all terms of a higher order , we see that , for a given value of is a maximum when Mr. H. S. Jones .
The Flexure of Telescope [ Apr. 26 , We suppose that positive : then the intercept is positive and is equal to The value of steadily diminishes with increase of , since is supposed positive , and so the greatest negative intercept is from and is , so that the total breadth of the band is and to this order is least when we put A similar result is obtained if is supposed negative , since then the greatest negative from Thus the least value of the intercept on a plane perpendicular to the axis produced by the reflection of a beam incident parallel to the axis in the vertical plane through the axis is 3 .
The upper limit for in order that the resolving power may not decrease with increase of the size of the mirror is given by 3 or and if the focal is five times the aperture , , we obtain the limiting value of to be cm .
inches , and so the limiting radius of the mirror is about feet , and quite a lar .
size is permissible .
Whereas , in the cases previously considered in which the mirror was horizontal , the determining factor was the ratio of the aperture of the mirror to its thickness , the limiting value of the radius being found from an equation of the type constant ; in the present case the determining factor is the ratio of the aperture to the focal length , the limiting value of being found from an equation of the type constant .
If it was desired to construct a mirror of given focal length and of as large an aperture as possible , the limit for the aperture could be determined from the above .
Thus , if the required focal length were 50 feet , the largest radius which may be used is 280 cm .
, or about 9 feet .
In the more general case when is zero we have for a first approximation Or , since we have , Corresponding to the centre , we have , and the radius vector from this point to any other point of the patch is given by 1913 .
] Mirror-discs from their Weight .
and this attains its greatest value when and have their greatest values , i.e. at the two points on the circumference in the verlical plane through Che axis , and then .
This gives the 1naximum extent of the swing for light incident at any point , and is the case discussed above .
In the obher cass considered , in which the normal component of the displacement at any point of the edge vanishes , the normal component of the displacement at any point of the disc , using the values of 2 , previously obtained , is given by -S The poinl in which the reflected cuts the focal plane is iven by giving a normal component of amount , and , since , we obtain so that and so is given by 2 Or , , where is constant for Mr. H. S. Jones .
The Flexure of Telescope [ Apr. 26 , definite radial direction , the normal component is The variation of this expression with for a definite value of , i.e. along a definite radius , is and the radial component of the intersection with the focal plane is found to be , on substitution for There are two cases to be considered , according as If , the radial intercept continually decreases with increase of so that the extreme values arise from the centre and circumference , and are at the centre and at the edge , and the maximum extent of the displacement is the difference of these , and is very nearly .
This expression decreases with increase of and so has its maximum value when , i.e. in the plane , and is then .
If , then the radial intercept has a stationary value the value of given by and this value of will be less than provided that Thus if , the radial intercept continuously decreases from to .
If , however , it reaches a minimum for a certain value of which is less than and is given by the above equation .
After this it will commence to increase , and the extreme values are at the centre and at this minimum .
For this value of the intercept is 1913 .
] Mirror-discs Arising from their Weight .
and the maximum breadth of the image on the focal plane in the definite direction , , is Consideriug now the variation of this expression with , as increases from to , we find that it decreases , and so has its greatest value , viz. , This is less than the greatest when and so the limiting condition for is that , ' and on riting this gives a linliting value for of 358 cm .
, or 141 ches , so that the disc may have with this mode of support a radius of nearly 12 feet .
This method of support corresponds closely to that used by Ritchey , who , in addition to the back support which prevented the normal displacements from being appreciable , placed the mirror in a circular metal band supported on the outside .
In this way , can be no normal displacements at the edge , but there is perfect freedom for tangential displacements to occur .
It has been assumed in the discussion immediately preceding that mirror is held vertically .
The displacements in this case necessarily attain their greatest possible values , and so if the radius is less than the critical value for this case , it will be so any augle of inclination .
The resuIts obtained in the present discussion may be briefly summarised as follows:\mdash ; 1 .
The components of the displacement of any point of the mirror-disc arisin from its weight have been calculated for various modes of support , both in the oase when the mirror is he , ld horizontally , and also when it is held vertically .
2 .
It is found that in all cases the displacements in the former case are very much larger than the latter , and that if the mirror were not well supported at the back , the lesolving power would begiu to decrease as the aperture was increased for comparatively small breadths of aperture .
The more complete is the back support , the larger of course is the critical size of mirror , and with simple forms of support this critical size is far larger than is likely to be practically reached .
3 .
It is also shown thnt for any given mode of support the critical size of the mirror may be increased by increasing at the same time its thickness .
522 Drs. J. A. Harker and G. W. C. Kaye .
Electrical [ May 6 , 4 .
When the mirror is held vertically the displacements are small , but the support cannot be so arranged as to rid of them , as was the case with the normal component .
It is shown , however , that the critical size of mirror is comparatively large , very much larger in fact than any mirrors at present in use , the limiting radius being somewhere in the hbourhood of 12 feet in the two cases which are discussed in detail , when the telescope is so constructed that its focal length is five times its aperture and the aperture ten times the thickness of the mirror .
For a given mode of support a larger aperture may be used by increasing the focal length .
On the Electrical Emissivity and of Hot Metals .
By J. A. HARKER , D.Sc .
, F.R. , and G. W. C. KAYE , B.A. , D.Sc .
, National Physical Laboratory .
( Received May 6 , \mdash ; Read June 19 , 1913 .
) lntroductory .
In February , 1912 , the authols communicated to the Royal Society an account of some experiments on the emission of electricity from carbon at high temperatures .
* In this investigation all the experiments were conducted at atmospheric pressure , and some evidence was forward that under these conditions the carriers of electricity appeared to consist almost wholly of ' ' spnttered \ldquo ; matter , and that corpnscles\mdash ; the carriers of negative electricity in high vacha\mdash ; played in these experiments but a minor or at any rate an indirect part .
It was shown that , even in the absence of any applied potential , it was possible for charged particles to escape in sufficient number from a hot carbon surface to give rise , at temperatures , to currents of ammeter raf , her than electrometer magnitude .
The particles appeared to be emitted with considerable velocity and the emissivity of the radiating surface sending out the particles seemed to depend primarily on the temperature alone .
It was , however , influenced to some degree also by the nature of the surrounding gas .
Depending on this emissive property of carbon , a kind of ionic dynamo was constructed , capable of lighting intermittently a small group of glowlamps ( 2 volts , 3 amperes ) .
* Harker and Kaye , ' Roy .
Soc. Proc 1912 , , vol. 86 , p. 379 .
|
rspa_1913_0048 | 0950-1207 | On the electrical emissivity and disintegration of hot metals. | 522 | 538 | 1,913 | 88 | 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.1913.0048 | en | rspa | 1,910 | 1,900 | 1,900 | 8 | 239 | 5,497 | http://corpora.clarin-d.uni-saarland.de/surprisal/6.0.3/?id=rspa_1913_0048 | 10.1098/rspa.1913.0048 | null | null | null | Electricity | 37.658745 | Thermodynamics | 33.731747 | Electricity | [
28.050119400024414,
-10.022997856140137
] | ]\gt ; S 522 Drs. J. A. Harker and G. W. C. Kaye .
Electrical [ May 6 , : 4 .
When the mirror is held vertically the displacements are small , but the support cannot be so arranged as to get rid of them , as was the case with the normal component .
It is shown , however , that the critical size of mirror is comparatively large , very much larger in fact than any mirrors at present in use , the limiting radius being somewhere in the hbourhood of 12 feet in the two cases which are discussed in detail , when the telescope is so constructed that its focal length is five times its aperture and the aperture ten times the thickness of the mirror .
For a given mode of support a larger aperture may be used by increasing the focal length .
On the Electrical Emissivity and Disintegration of Hot Metals .
By J. A. HARKER , D.Sc .
, F.RS .
, and G. W. C. KAYE , B.A. , D.Sc .
, National Physical Laboratory .
( Received May 6 , \mdash ; Read June 19 , 1913 .
) Introductory .
In February , 1912 , the authors communicated to the Royal Society am account of some experiments on the emission of electricity from carbon at high temperatures .
* In this investigation all the experiments were concted at atmospheric pressure , and some evidence was brought forward that under these conditions the carriers of electricity appeared to consist almost wholly of ' sputtered \ldquo ; matter , and that corpuscles\mdash ; the carriers of negative electricity in high vacha\mdash ; played in these experiments but a minor or at any rate an indirect part .
It was shown that , even in the absence of any applied potential , it was possible for charged particles to escape in sufficient number from a hot carbon surface to give rise , at high temperatures , to curoents of ammeter rather than electrometer magnitude .
The particles appeared to be emitted with considerable velocity and the emissivity of the radiating surface sending the particles Qeemed to depend primarily on the temperature alone .
It was , however , influenced to some degree also by the nature of the surrounding gas .
Depending on this emissive property of carbon , kind of ionic dynamo was constructed , capable of lighting intermittently a small group of glowlamps ( 2 volts , 3 amperes ) .
* Harker and Kaye , ' Roy .
Soc. Proc 1912 , , vol. 86 , p. 379 .
reproduced wther substanoesP aarbon ceincentive cent interesting researctles oiamquesCion osputtering ottention seems tophenomenon onvestigated , thehave bbservers tccompanying etake furth rexperiments with aview tscertaining txtent tEmissivity ookes , atinum group , interest ohigh temperature phenomena except in high vacua .
It would appear also that of the experiments on metals at high temperatures , a very large proportion have been made on platinum , and , so far as we are aware , nearly all were carried out on a someil what small scale , generally with fine wires .
The present experiments , made at the National Physical Laboratory during the early part of last year , have been interrupted and are still incomplete , but nevertheless we have been led to believe that , there is much involved in the work which is obscure and demands further investigation , enough facts have been elicited to warrant the publication of a preliminary paper .
More especially does this seem desirable as considerable attention is now being given to the nature and properties of the emissions from hot bodies .
Thermal Sputtering .
The volatility of metals at temperatures well below their melting points is a familiar phenomenon to most workers .
A homely example is provided by the blackening which a common enough feature of carbon filament lamps and is occasionally displayed by tungsten lamps , especially when over-run .
Sputtered images of a definite outline depending on the shape of the filament can sometimes be traced on the bulbs of carbon lamps .
The abnormal volatility of iridium has been known to high temperature workers , in connection with its employment in thermocouples , furnace tubes and gas thermometer bulbs ; the extent of the effect is suffioient to prohibit the use of iridium or its alloys at temperatures much above 1000o C. Platinum is also known to exhibit a similar though much less marked * Crookes , ' ) .
Soc. Proc 1912 , , p. 461 .
A detailed account and discussion of the phenomena of ionisation by incandescent solid bodies is given in ) IX of Sir J. J. Thomson 's 'Conduction of Electricity through Gases , ' second , 1906 .
A more recent summary in considerable detail ma be found in H. A. Wilson 's ' The Electrical Properties of Flames and Incandescent Solids , ' 1912 .
It has therefore not been deemed necessary to give here any account of the work or a bibliography of the subject .
VOL. LXXXVIIL\mdash ; A. 2 524 Drs. J. A. Harker and G. W. C. Kaye .
Electrical [ May 6 , volatility ; examples of sublimed platinum crystals are often found on the : tubes of platinum-wound furnaces which , ha.ve been subjected to prolonged use at temperatures up to 1400o or so .
The thermal disintegration of the platinum metals was first investigated gravimetrically by a group of workers\mdash ; Berliner , Elster and Geite ] , and Stewart in 1887-9 .
Holborn , Hemming , and Austin , *took up the matter at the Reichsanstalt in 1903 , from the point of view of the high temperature : worker .
In Sir William Crookes'experiments ( loc. cit samples of the platinum metals were heated still air at atmospheric pressure .
His esults indicate a decreasing volatility in the order Ru , Ir , Pd , , and Bh ; the effects were unexpectedly large .
The volatilisation of a metal increases rapidly with the temperature .
In the case of platinum , iridium , and rhodium , the disintegration lessens as the pressure of the surrounding gas is reduced , and the effect would not there .
fore seem in these instances to be one of true subhmation .
Roberts has recently brought forward evidence that with these metals the volatilisation is effected through the intermediary of endothermic oxides more volatile than the metals themselves .
It may be added that almost all workers are agreed that the presence of oxygen is essential to bring about the disintegration of most metals .
Hydrogen and nitrogen are in general unfavourable to the effect .
Experimental .
After one or two preliminary trials , the apparatus described below was constructed and used in practically all the experiments .
It is shown in fig. 1 .
Through a round iron plate , forming the support of a large glass belljar , were fitted near the circumference two insulated vertical brass electrodes capable of carrying for short periods some hundreds of amperes without undue heating .
Projecting inwards some 15 cm .
from each electrode toward the centre of the jar was a stout iron strip with its inner end bent upwards .
To these iron strips were clamped adjustable jaws of the same material .
The strip of metal ( S ) to be heated was gripped between these jaws in a horizontal position , edge upwards .
The strips employed were of uniform thickness and width but varied somewhat from sample to sample .
The currents employed to heat them varied from about 50 to 250 amperes and the voltage across the strip from to a maximum ( rarely * Phil. Mag 1904 , vol. 7 , p. 388 .
PhiL Mag February , 1913 , , p. 270 .
When necessary to prevent contamination of the metal of the strip touched the jaws , which sometimes became considerably heated , a platinum lining was fitted to the part where the metals in contact .
other oetalscylinder ( provided woles ( iewing ttrip barger specimens water itudy oomewide.long between tlamps ; mitting aboutreached)bout 6Most otrips wpproximately 5mlnl 9ssivity.ounding ttlip ansulated cetely fmetal means of an optical pyrometer .
with suitable adjntments from an insulated support ( r ) passing through the base-plate of the apparatus .
One pole of the strip was connected through a currentmeasurer to the cylinder , the whole of the circuit being everywhere carefully insulated earth .
Eeat Supply .
The cylinder carried on an arm ' In order to avoid any local effects due to a different polarity at different parts of the strip , alternating current was always used for heating purposes .
This was taken from a step-down transformer iving a number of variable ratios and voltages from upwards .
The primary current to the transformer was supplied from a motor-alternator , usually at a frequency of about 90 cycles .
The field windings FIG. 1 .
of the alternator were excited from a direct-current 100-volt supply .
In series with the usual field regulator on the switchboard was arranged a convenient portable rheostat having a large number of segments .
This could be manipulated by the observer at the optical pyrometer , who regulated the temperature of the strip as required .
The control of the temperature was thus rendered extremely easy and accurate , and it was possible to maintain a strip at any given temperature to within a few degrees or even on the verge of melting for a considerable period .
In the later experiments the heating current and volts , and hence 526 Drs. J. A. Harker and G. W. , Kaye .
[ May 6 , approximately the expended in the hot strip , were measured by suitable alternating instruments .
Measurement of the Ionic Currents Produced .
ments caken osame gvanometer owing tanydifferent ranges oensitivity , arge aeflection wways aoyed designed study oheabout 1npere Fower ranges aresistance movin.ivan gvanometer igher .
ITangementThe ionic current.enerated vfrom afractiou omicroampere t means of this instrument , continuous and accurate current and volt measureif required , at any value of the current or voltage to be measured .
On account of the very rapid changes in the currents obtained in most cases with rising temperature , some device of this kind was essential to convenient work .
Employed .
In practically the whole of the experiments now to be detailed the gas employed was nitrogen of the ordinary commercial quality supplied by the British Oxygen Company and made from liquid air by the Linde process .
The usual procedure , after mounting the strip in position , was to exhaust , by means of a rotary oil-pump , the large -jar , which served to cover the whole apparatus , and rinse out twice with nitrogen direct from the cylinder before the final filling and pressure adjustment .
No special precautions were taken to secure either dryness of the gas used or great constancy of pressure during a run .
Owing to the energy dissipated in the strip , amounting in some cases to a kilowatt or more , the upper parts of the apparatus usually became quite warm after five or ten minutes ' run , and the pressures given are therefore only to be considered as approximate mean values .
Pressures below a few millimetres of mercury were intentionally not employed , as it was desired to avoid pressures so low that the vative ion became the unencumbered negative electron .
The experiments were conducted in nitrogen with the idea of using a gas which would be chemically inert to most of the metals .
We were aware from the outset that it was more than probable , from the experiments of Strutt and other workers , .
that the same kind of effects as we were seeking could be obtained at relatively low temperatures if more delicate means of detecting minute currents had been adopted .
We resolved , however , to study only the phenomena from the point of view of the currents generated of ammeter rather than electrometer order , and therefore more sensttive cuIxent measurers were intentionally not adopted .
1913 .
] Emissivity and of Hot Metals .
Measurement of Temperature .
The temperatures were measured by an optical pyrometer of the HolbornICurlbaum type made by Messrs. Siemens Bros. This instrument consists of a telescope of rather short focal length , iu the focal ] of which is fixed the filament of a small incandescent lamp .
In series with the lamp are a four-volt accumulator , a regulating resistance and an accurate ammeter .
In taking an observation , the central portion of the horseshoe-shaped filament is matched in brightness with the object whose temperature is to be measured and the current through the lamp noted .
Previous calibration of the arrangement serves as the basis of a table showing the connection between the current through the lamp and the temperature of the radiating object , applying , if necessary , the appropriate correction for want of " " blackness\ldquo ; in the surface of the radiator .
The observations are taken through an eyepiece consisting of one or more red glasses .
The absorbing device supplied with the instrument , consisting of two black glass mirrors , was used before the object glass in all cases , a few of the observations at the lowest temperatures .
In this arrangement the beam of light from the hot body is reflected twice at an angle of incidence and thereby weakened to about of its original intensity , thus allowing continuous observations to be made up to about C. without risk of over-running the pyrometer lamp .
Observations even to the highest temperatures are easy and a practised observer can follow continuously the temperature of the strip to within a few degrees up to its melting point .
Experience showed that , except the last two or millimetres at each end , the temperature of the strips was generally very uniform .
The temperatules recorded are , of course , black-body temperatures and are to some extent a function of the predominant wave- length in the red glass used in the pyrometer .
In some of the curves below these black-body temperatures are reduced to true temperatures .
As a rule , the error ( of the order of or so at ) due to absorption in the glass walls of the bell-jar was unimportant .
Employed .
We happened to have by us a number of suitable specimens of the platinum metals in the form of strip .
On account of their relative chemical inertness , high melting-point and , as Crookes showed , their large volatility , we decided to use these for the earlier work .
In the present experiments , platinum and iridium were employed ; and , later on , the metals iron , tantalum , copper , nickel , and brass .
The behaviour of the different metals is dealt with below .
\mdash ; The platinum strip when heated showed small positive currents 528 Drs. J. A. Harker and G. W. ( at about 110 : at higher temperatures th the relation between temperature and experiment ; the pressure was about 40 current increased rapidly as the pressure example of this ; the temperature of the Te ( Bl body ) FIG. 2.\mdash ; Platinum in Nitrogen at 40 mm. Pressure .
Relation between Negative Ionisation and Temperature .
1460o B.B. : there was practically no sputtering either on the bell-jar or elsewhere .
Iridium.\mdash ; At atmospheric pressure the iridium strip , when heated to high temperatures , emitted a black cloud of smoke , which ceased to be noticeable as the pressure was lowered .
The volatility of iridium under such conditions is course well known .
In one experiment with nitrogen at 4 mm. pressure iridium gave a maximum positive current\mdash ; about ampere\mdash ; at 1200o C. , which , on cooling and reheating , did not attain 1nore than a quarter of this amount .
At 1300o the negative current was plainly evident : it increased to 20 microamperes at , and steadily rose until when the trip burnt out 1913 .
] Ernissivity and Disintegration of Hot Metais .
Pressure FIG. 3.\mdash ; Platinum in Nitrogen .
Relation between Negative Ionisation and Pressure .
about 2300o C. ) the current had attained 80 milliamperes .
shows the growth of the current with temperature in this run .
The higher temperature readings are somewhat doubtful owing to the increasing deposit on the bell-jar .
Iron.\mdash ; Transformer iron was used in most of the experiments .
The heating currents ranged from 40 to 150 amperes at voltages up to 2 or 3 .
No measurable ionisation current was detected at temperatures below 1100o in nitrogen at atmospheric pressure .
At lower pressures a small positive current showed itself in some cases at about 1150o to 1250o .
Occasionally for some reason the positive effect would persist right up to the meJting point .
Fig. 5 shows the relation between current and temperature at a pressure of 9 mm. The sputtering of the iron during this particular run was very great .
As will be seen , the negative current increases very rapidly in the neighbourhood of the melting point .
Fig. 6 shows a similar run at a rather pressure and somewhat lower temperatures .
Our experience certainly seemed to be that the greater the volati the greater were the currents recorded .
In those experiments in which for this changed to negative at about .
At .
the negative current had increased to about 220 .
Fig. 7 shows the variation of the ionisation current with temperature .
The tantalum on this ocoasion yielded a very considerable deposit , which when analysed proved to be nearly all tantalum with a trace of iron .
@ 1913 .
] and Disintegration of Hot Metals .
Te pe a.tu re FIG. 6.\mdash ; Iron in Nitrogen at 9 mm. Pressure .
Relation between Negative Ionisation and .
Large Sputtering .
Tem perafure body FIG. 6.\mdash ; Iron in Nitrogen at 12 mm. Pressure .
Relation between Negative Ionisation and Temperaturs .
Slight Sputtering .
C. Kaye .
Electrical [ May 6 , Black -body ) FIG. 7.\mdash ; Tantalum in Nitrogen at 1 mm. Pressure .
Relation between Negative Ionisation and Temperature .
On a second heating at a slightly higher pressure there was very little sputtering , and the highest current recorded at about 1660o B.B. was about 50 microamperes .
Heating currents up to 80 amperes and volts were employed .
Nickd.\mdash ; Nitrogen at 4 mm. pressure .
Heating current up to 80 ampe]es .
There was no sputtering .
Small positive currents were recorded from 1200o upwards ; they increased suddenly to about 1 microampere as the strip melted ( 1440o Copper.\mdash ; Nitrogen at 4 mm. pressure .
Heating current up to 200 amperes .
Small positive currents from 1000o upwards ; a larger positive current flashed on the galvanometer as the copper melted At higher pressures , this final CUl'rent was smaller , e.g. 5 at 55 mm. Hg .
Brass.\mdash ; Nitrogen at 3 mm. pressure .
Heating current up to 110 amperes and volts .
There was no noticeable sputtering .
At temperatures of upwards small positive currents were noticed , which at the instant when the brass melted ( about ) became momentarily much larger .
The fused ends of the strip showed very plainly the copper present .
Carbon.\mdash ; From our experience with carbon at atmospheric pressure we 1913 .
] Emissivity and Disintegration of Hot Metals .
anticipated that the sputtering would be greatly enhanced by a reduction of pressure .
On trying the experiment with a carbon rod of unusually high purity , in a good vacuum , we were surprised with the result , for only a very slight deposit was obtained , and this was whitish and obviously due to traces of silica , etc. , present in the carbon .
The copper cylinder was absent and the temperature employed was about 2000o C. A similar negative result was obtained from an experiment oonducted with Acheson graphite in a hydrogen vacuum , and a temperature probably exceeding 2500o C. Incidentally , evidence was obtained in these experiments of the softening of carbon at temperatures from about 2500o upwards .
special clamps were made , and as they were not quite in alignment the carbon rod was clamped under lateral strain .
At the end of the run it was found that the rod , originally straight , was now crooked ; the carbon had evidently been plastic enough to accommodate itself to the strain .
The result is interesting having regard to a recent controversy on the subject .
Fig. 8 shows the carbon rod before and after the experiment .
FIG. 8 .
We were tempted to return for the moment to an experiment at atmospheric pressure .
AB ( fig. 9 ) is a rod of specially pure carbon Am meter FIG. 9 .
containing only about per cent. of impurity ( chiefly silica ) .
The ends were mounted in graphite blocks , and the rod was surrounded by a carbon cylinder ( CD ) insulated with bushes of mabor brick .
The cylinder served as the " " cold\ldquo ; electrode , and was joined through an ammeter to the inner rod , which was heated by transformer current and made as hot as our resources would permit ( probably not far from 3000o C The current used was of the order of 1000 amperes , the energy about 10 kilowatts .
The outer cylinder rose to about 1100o C. , and under these conditions the ammeter recorded a steady ionisation current of about 3S amperes .
The degree of conductivity akin to that of a metal .
heated bternati otook tcarbon tdown tentre ohich assed aisation oetween tectrod iurse , tsbeen removed beontinued heati rithdrawing theWas pHarker atition omention d metal tube at the end of half an hour or so it was found to be coated with a I deposit of carbon , hard enough and coherent enough to be slid off in short lengths .
Fig. 10 shows two examples of such carbon .
The method is of FIG. 10 .
interest as furnishing a possible means of obtaining by fractional distillation carbon of a purity unattainable by other methods- During experiment ionisation currents up to about 1 ampere were recofded .
It certainly seems that the ionisation effects obtained with carbon at higher pressures are due to the chemical activity of the carbon , for which the presence of gas in quantity is essential .
Positive Currents .
The emission of positive electricity was found to occur between ) and 1400o C. In the case of metals which melt within this range a sudden and striking increase in the positive current at the melting point was sometimes remarked with samples which had not been heated for more than a few minutes .
There were two factors which helped to display this effect to ; one , the nicety of control over the heating , by which it was possible to hold the temperature just below or on the melting point for some time ; the other , the large size of the samples which served both to enhance the effect and to give the metal some ability to hold together at the melting point .
In some instances the slow local fusing of part of the strip was watched in the pyrometer while temperature measurements were being taken .
The positive currents obtained from most bodies at moderate temperatures are now pretty generally attributed\mdash ; at any rate in part\mdash ; to the escape of occluded gas , which leaves the metal in an ionised condition .
The escape of this gas would naturally be greatly facilitated when liquefaction of the 1913 .
] Emissivity Disintegration of Hot Metals .
metal occurred , and it is to this cause we think the momentary increase in the positive current at the liquefying point is due .
En passant , we may note that our general experience with most of the metals we have tried has been that the positive current is augmented by the presence of oxygen .
The positive current readings were not steady or reproducible under specified conditions\mdash ; the currents usually drop considerably after a few minutes ' heating , and this without altering the temperature or pressure in any perceptible way .
Yegative Currents .
As will have been remarked , the negative ionisation increases rapidly with the temperature : the various curves shown above , connecting temperature and current , are all exponential in character .
It should be pointed out that in all cases the currents are unsaturated ; no potential whatever is applied to the hot metal apart from the small variable potential due to the alternating current .
The negative ions must accordingly derive their velocity directly or indirectly from the heat of the strip , or from some chemical reaction between the strip and the gas .
Sir J. J. Thomson*showed that charged particles of metal were among the carriers of current in the positive discharge from a hot platinum wire .
We believe that they are also often present in the negative discharge obtained from metals at higher temperatures , and that while the negative current at moderate pressures is usually due mainly to the negative gas ion , the current is ] augmented if the conditions are such that particles of metal also cross between the two electrodes .
These conditions are probably secured by the presence of a gas to which the metal is chemically responsive \mdash ; with most metals oxygen is so effective .
Thus the ionisation current is to be regarded as a direct manifestation of the chemical energy of combination .
With this view in mind we tried to gerate the effect by burning iron and magnesium wire in oxygen , the wire being surrounded by au outer cylinder , with a galvanometer in circuit between the wire and the oylinder .
We tried various forms of apparatus , but the experiments were interrupted before we were completely assured of their success .
If it should be that , at any rate at higher pressures , the ionisation current from hot metals is in some instances carried chiefly by particles of the metal , we have the means of deriving a mean value for the ratio of the charge to the mass for the particles .
For example , in one experiment with iridium , conducted in nitrogen at a pressure of about 20 mm. and a temperature of 1360o B.B. , the iridium strip lost mgrm .
in 11 minutes ; of this * J. J. Thomson , ' Conduction of Electricity through Gases , ' 1906 , second ed. , p. 217 .
eceived bHarker aKaye.onisation ourrent during this time was microampere .
Whence E.M.U. , and assuming that each particle can.ies unit charge , Now the mass of the iridium atom is about , so that the average number of iridium atoms in one particle is 1200 .
Apropos of the source of the ionisation current , it may be added we have repeatedly noticed that if the metal is hot enough to be giving out negative electricity , and is allowed to come into actual contact with the surrounding colder cylinder , the galvanometer shows a large current in the reverse direction .
The thermal E.M.F. is thus opposed to the ionisation potential .
This remark holds equally well for a hot carbon rod in an outer cylinder of cold carbon .
Straight Line Projection of Particles .
While there is no doubt that a good deal of the deposit which we obtained in these experiments was due to volatilisation and condensation as ordinarily understood , we think that this is not the whole explanation , and that the effect is partly due to the straight line emission of particles of matter from the heated metal .
* Under most conditions , it is true , this rectilinear propagation is confused by general sublimation , but we have noticed it on several occasions when the circumstances were favourable .
In one experiment a strip of iridium ( S ) was heated , edge upwards , in nitrogen at about 20 mm. pressure .
At the end of the run it was noticed that there were two horizontal bands of deposit on the inside of the copper enclosing cylinder , each one opposite and roughly the same width as the vertical face of the strip .
At points and opposite the edge of the strip there was little or no deposit .
Fig. 12 is a photograph of the iron deposits FIG. 11 .
obtained on the bell-jar , in the proximity of the brass uprights fig. 1 ) .
In this experiment there were two holes siik by side in the cylinder C. The photograph is possibly to be regarded as showing much distorted projections of the uprights and , by particles of metal shot from the heated strip , through the holes in the cylinder .
But this is probably not a complete explanation of the photograph .
The pressure during this run was about 2 mm. , not too low to prevent convection See , in this connection , Reboul and de Bollemont , 'Journ .
de Phys July , 1912 .
1913 .
] Ernissivity and Disintegration of Hot currents controlling the sublimed iron vapour , which , as the deposit all over the bell-jar shows , was everywhere present .
In this experiment , the iron FIG. \mdash ; Iron Deposit .
strip was heated for some minutes and the brass uprights , and iron strips , got appreciably warm\mdash ; warm enough doubtless to cause an upward current of gas to oppose the descending iron vapour , and to cause it to deposit on the glass adjoining .
The successive bands of deposit at each of the crests are certainly interesting and suggestive of a kind of spectrum which might be produced by a magnetic or electric field acting on charged particles of metal with velocities grouped around certain values .
But the only possible source of such a field is the alternating heating current , and even taking the maximum values of the current and potential the strength of the magnetic or electric field which could be produced is entirely inadequate to deflect and disperse charged particles whose masses are as large as we FIG. Iridium Deposit .
believe them to be .
We are not in a position to explain the various pec , uliarities the photograph displays ; fig. 13 is a corresponding photograph in the case of iridium .
538 Emissivity and Disintegration of Hot Metats .
Summary .
Preliminary experiments have been carried out on the volatiIisation and electrical emissivity of a number of metals , mostly in nitrogen at reduced pressures .
The metals were heated by alternating current and no appIied ] potential was employed .
( 1 ) The emission of positive electricity occurs at temperatures from about : ; 1000o to 1400o C. For metals which melt within this range , a sudden and marked increase in the positive current often occurred at the liquefying point\mdash ; due probably to the sudden release of occluded gas .
( 2 ) Oxygen appears to augment the positive current .
( 3 ) At higher temperatures , negative electricity predominates and increases rapidly with the temperature .
The negative current.attained with iridium at the melting point was 80 milliamperes , with 1670o C. 220 microamperes , with iron at the melting point 90 micronmperes .
In the case of carbon in air at atmospheric pressure , an current of amperes was obtained .
( 4 ) The negative current at moderate presures appears to be increased if the conditions are such that considerable sputtering of the metal occurs .
( 5 ) The negative currents are probably a consequence of chemical reaction between the metal and the surrounding gas .
( 6 ) Carbon becomes plastic* in the neighbourhood of 2500o C. At such temperatures it also readily sublimes .
We should like to thank Mr. H. C. Booth , of the National Physical Laboratory , for his sketch of the apparatus ( fig. 1 ) .
|
rspa_1913_0049 | 0950-1207 | An active modification of nitrogen, produced by the electric discharge.\#x2014;V. | 539 | 549 | 1,913 | 88 | 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.1913.0049 | en | rspa | 1,910 | 1,900 | 1,900 | 7 | 272 | 5,110 | http://corpora.clarin-d.uni-saarland.de/surprisal/6.0.3/?id=rspa_1913_0049 | 10.1098/rspa.1913.0049 | null | null | null | Chemistry 2 | 41.316916 | Thermodynamics | 25.902141 | Chemistry | [
-0.5477331876754761,
-47.60559844970703
] | 539 An Active Modification of Nitrogen , Produced by the Electric Discharge.\#151 ; V* 1 By the Hon. R. J. Strutt , F.R.S. , Professor of Physics , Imperial College of Science , South Kensington .
( Received May 9 , \#151 ; Read June 19 , 1913 .
) S1 .
Improved Technique .
Experience has led to certain modifications of detail in preparing nitrogen for the experiments .
Commercial nitrogen.from cylinders is still used , but instead of passing it over phosphorus it is allowed to stand in contact with it for some hours .
The former method does well enough when the phosphorus is freshly cut , but in time the surface deteriorates , owing , in part at least , to the accumulation of oxides of phosphorus , which tend to obstruct access of the gas .
Two 15-litre aspirator bottles are arranged as a gasholder in the usual way , the gas being displaced by water .
In the gas space is hung up a muslin bag containing chopped phosphorus .
On filling the gasholder with commercial nitrogen the phosphorus fumes freely , and all traces of oxygen are removed in the course of two or three hours .
The fumes subside , and the gas is ready for use .
It merely requires drying on its way to the discharge tube .
This 15-litre supply is more than enough for most experiments .
When it is used up the water rises and drowns the bag of phosphorus , dissolving out the oxides which have been formed , and leaving it in good condition for use next time .
It is advisable to cover the gasholder with a jacket of black cloth to exclude light , which spoils the phosphorus surface .
With this precaution such an apparatus will remain in good order for a year or more .
Air should not be drawn into it .
If this is done the phosphorus will probably catch fire .
It may be thought inconvenient to intermittently fill up the gasholder , instead of working straight from the supply in the cylinder .
In practice this disadvantage is more than compensated .
In using the gas it is convenient to be able to measure the rate of intake , which is readily done if the gasholder is graduated.f * I , 'Roy .
Soc. Proc. , ' A , vol. 85 , p. 219 ; II , ibid. , A , vol. 86 , p. 56 ; III , ibid. , A , vol. 86 , p. 262 ; IV , ibid. , A , vol. 87 , p. 179 .
t The bottle holding the displaced water is the most convenient one to graduate , as it does not need to be kept covered from the light .
VOL. LXXXVIII.\#151 ; A. 2 P Hon. It .
J. Strutt .
[ May 9 , Moreover , it is advantageous to dispense with the automatic gas regulators , which , as obtained commercially , give an inconveniently high gas pressure , and are apt to leak , so that more nitrogen is wasted than is used .
S 2 .
Effect of Impurities in the Nitrogen used .
It has been thought by some of those who have repeated my experiments* that the phenomena of active nitrogen are not obtained in the absence of traces of oxygen .
Othersf have confirmed the original conclusion that nitrogen alone is concerned .
For my own part I am more than ever confident of the correctness of this view .
Since the question has been raised I shall enter into my reasons more fully than would otherwise have been thought necessary .
As explained ( S1 ) the nitrogen used habitually in the experiments has stood over phosphorus until all action is over and all fume has subsided .
Moreover , the issuing nitrogen is saturated with phosphorus vapour , as is shown by letting it blow off into the air in a dark room , when the issuing jet of gas becomes luminous by mixing with atmospheric oxygen .
The question then arises , how much oxygen at the most can be present in such nitrogen ?
To settle this a flask of 1500 c.c. capacity was filled with commercial nitrogen , and allowed to stand over water in a pneumatic trough .
A piece of phosphorus was supported in the middle of the flask , and in the course of a few hours removed most , at any rate , of the residual oxygen .
The gas volume was then quite free from fume , and in the dark no luminosity whatever could be seen in it .
A bubble of air , 1/ 20 c.c. in volume , was then passed up into the flask , J which was enough to produce distinctly visible streaks of white fume .
These were distributed throughout the greater part of the volume , showing that the oxygen introduced was no longer locally concentrated .
With 1/ 10 c.c. of air the streaks were most conspicuous , and could not escape even careless observation .
From this experiment it appears that the addition of a 1/ 150000 part of oxygen produces a distinct reaction .
It seems pretty safe therefore to conclude that not more than 1/ 100000 part of oxygen can remain when the phosphorus has done its work .
Probably even this fraction would be an enormous overestimate of the actual amount .
* See F. Comte , ' Phys. Zeit .
, ' 1913 , vol. 14 , p. 74 ; also E. Tiede , 'Ber .
d. Deutsch .
Chem. Gesell .
, ' 1913 , p. 340 .
+ Konig and Elod , 4 Phys. Zeit .
, ' 1913 , vol. 14 , p. 165 .
J It is scarcely necessary to describe the simple arrangement used to measure out and deliver this small quantity of air .
1913 .
] An Active Modification of Nitrogen .
541 Thus the phosphorus purification seems to secure the complete absence of oxygen .
In addition the gas has been passed on occasion through a tube 80 cm .
in length , tightly packed with rolls of fine copper gauze , and heated to full redness .
The gauze had been oxidised and reduced beforehand to make its surface spongy .
I do not find that the copper makes any difference whatever to the phenomena .
Naturally therefore it has been discarded .
This result with copper is in direct contradiction with one of my critics ( Comte ) .
How to account for his result I do not know .
The whole weight of the decision as to whether oxygen is necessary must rest on direct experiment .
But I would ask those who may not have an opportunity of seeing or repeating the experiments to give a little consideration to the a priori probabilities .
The active gas is capable of forming nitrides from the metals , and hydrocyanic acid from hydrocarbons .
What possible r6le is there for oxygen , admittedly in infinitesimal proportions only , in such a process ?
We may next consider the effect of intentionally adding oxygen to the nitrogen used , starting with nitrogen which had been purified by phosphorus .
The unfavourable effect of oxygen has already been considered.* It was now systematically investigated , mixtures of known composition being made up and passed through the discharge tube .
One per cent , of oxygen ( by volume ) was found to very materially diminish the volume and brilliancy of the active nitrogen glow ; 2 per cent , obliterated it altogether .
With 5 per cent , of oxygen a totally different phenomenon , the ozone-nitric oxide glow , f begins to come in .
These experiments indicate that to get good results the nitrogen should certainly not contain more than 1/ 10 per cent , of oxygen .
As already shown , nitrogen purified in the cold by phosphorus more than fulfils this condition .
The effect of other impurities likely to be present was also studied .
The addition of 20 per cent , of hydrogen extinguishes all glow ; \#163 ; per cent , of hydrogen , on the other hand , scarcely does any harm .
It is seen that traces of hydrogen produce far less effect than traces of oxygen .
Practically if the Ha line cannot be distinctly seen in the exciting discharge , outshining the nitrogen bands in the same region of the spectrum , it may be concluded that no prejudicial quantity of hydrogen is present .
Carbon dioxide hinders the glow about as much ( or as little ) as hydrogen .
The presence of water vapour is much more prejudicial .
Scarcely any glow is obtained from nitrogen drawn straight from the gasholder without drying , and therefore saturated with water vapour.t * I , p. 224 ; II , p. 56 .
+ ' Phys. Soc. Proc.,5 December 15 , 1910 .
J It is of course no longer saturated after it has passed the regulating stopcock , and is many times expanded .
Hon. R. J. Strutt .
[ May 9 , To get the best results very good drying is required .
Two alternative drying tubes were arranged in parallel .
A two-way stopcock made it easy to exchange one for the other .
Each contained well packed phosphorus-pentoxide ; one column of this material measured about 6 cm .
x 2 cm .
, the other about 3,0 cm .
x 5 cm .
The glow was markedly better developed with the second .
Even when this had done its work a further slight improvement was obtained by passing the gas through a tube cooled to liquid air temperature , and packed with copper gauze , to provide a large condensing surface .
It has not been determined whether the advantage of this last purification is in further drying , or in removal of traces of hydrocarbons and phosphorus-vapour .
The latter certainly is removed .
S 3 .
Chemical Action on Elements\#151 ; Metallic and Non-Metallic .
In the earlier work* the proofs of chemical union with active nitrogen chiefly relied upon were increase of weight in the substance acted upon , and disappearance of the gaseous nitrogen used .
I have now gone over most of the ground by the alternative method of testing for ammonia when the products are boiled with water or caustic potash solution .
This method has proved much easier and more powerful than the previous ones .
Mercury , it will be remembered , ]- gave an explosive compound when its-vapour was allowed to mix with active nitrogen .
Shaking the product with water , and filtering , a strong reaction of ammonia is obtained with Nessler's-solution .
] It was observed , too , that specimens of the compound which had lain exposed to the air for some days no longer gave the characteristic crackling explosions on heating .
Presumably the nitride had been decomposed by atmospheric moisture .
Zinc and cadmium distilled below a red heat in a current of active nitrogen also yield nitride , which is not explosive , however .
Boiled with water the contents of the tube give a strong Nessler reaction in each case .
Blank experiments , in which the conditions are in all respects the same , , except that the stream of nitrogen is not made active , gave absolutely negative results .
With all these metals the product forms an adherent black coating on the-walls of the tube , and apparently retains mechanically an excess of the metal condensed from its vapour .
* I , pp. 222-225 .
f I , p. 225 .
| J In this and the following experiments , the indication obtained was not merely a discoloration , but an abundant red precipitate making a quantity of liquid quite opaque .
1913 .
] An Active Modification of Nitrogen .
Sodium vaporised in the nitrogen stream also gave a nitride , decomposable by water , and detected as before .
This action appears to be somewhat less energetic than those just mentioned .
But the first part of the distillate from the alkaline solution gave a strong Nessler reaction .
It was thoroughly verified that sodium from the same stock , not treated with active nitrogen , gave no such reaction .
Arsenic sublimed in active nitrogen and boiled with potash solution gave ammonia , readily detected in the distillate .
Sulphur did the same .
Occasionally traces of the blue compound obtained so abundantly with carbon disulphide ( see below ) appeared in this instance .
More commonly the product was not visibly distinguishable from the excess of sulphur .
It probably consists of the ordinary yellow sulphide of nitrogen .
A quantity of iodine was allowed to sublime at room temperature , in a , stream of active nitrogen .
The usual brilliant blue glow was produced.* The iodine , together with any product that might have been formed , was frozen out with liquid air and dissolved in potash .
No trace of ammonia could be obtained from the solution .
S 4 .
Chemical Action on Inorganic Compounds .
When carbon disulphide vapour is fed into a stream of active nitrogen , it is-soon noticed that a solid deposit forms on the walls of the vessel .
This deposit forms evenly over a considerable area , and has a deep indigo blue colour .
In the experimental arrangement the gas stream was laid on through a tube cooled in liquid air to remove excess of carbon disulphide .
Here it was observed that a further deposit of brown colour was formed on the cooled surface .
First , as regards the blue deposit .
This oxidised with strong nitric acid yields sulphuric acid , identified by its action on barium chloride solution .
Sulphur , then , is one constituent element .
Heated with potash solution the blue substance dissolves ] and ammonia is liberated , indicating the presence of nitrogen .
The blue substance is identified with the blue sulphide of nitrogen obtained by Burt , ] to which he assigned the composition ( NS)* .
Like his preparation , , it proved insoluble in benzene and in chloroform .
The brown deposit separated on the cooled condenser remains to be considered .
It was soluble in hot concentrated sulphuric acid to a * I , p. 227 ; see also coloured plate , p. 228 .
t A thin colourless skin is left on the glass , which has not been investigated further .
] ' Trans. Chem. Soc. , ' 1910 , vol. 97 , p. 1171 .
Hon. R. J. Strutt .
[ May 9 , brown-purple solution , and in concentrated nitric acid to a red solution .
This behaviour , taken in conjunction with its formation from carbon disulphide , identifies it as the polymeric carbon monosulphide obtained by Dewar and Jones* by the action of the silent discharge on carbon disulphide vapour .
Apart then from the unknown molecular weight of the solid product , the action may be represented thus CS2 + N = NS+CS .
Yapour of chloride of sulphur , fed into active nitrogen , yields a light yellow deposit , which consists , at all events in part , of ordinary sulphide of nitrogen .
Heated with potash , it yields ammonia in abundance .
Hydrogen sulphide behaves similarly .
In each case the luminosity developed is blue and shows bands due to sulphur .
The magnificent luminous effects obtained with stannic chloride have already been mentioned.]- The energy of the chemical action does not seem to be proportionate .
A small quantity of white deposit forms on the tube walls , but it is difficult to collect enough for examination .
Titanium tetrachloride , which develops a brilliant titanium line spectrum on mixing with active nitrogen , gives a much more abundant white deposit .
This yields ammonia when boiled with potash , but is not dissolved .
It is soluble in acids and appears to be a compound of titanium , chlorine , and nitrogen .
Its further study may be undertaken later .
S 5 .
Chemical Action on Vapours of Organic Substances .
It was previously shown ] that acetylene reacted with active nitrogen to yield a cyanogen compound .
The proof was : ( 1 ) development of the cyanogen spectrum ; ( 2 ) formation of a cyanide by absorption in alkali .
Other organic compounds also develop the cyanogen spectrum , and it was assumed that they also form cyanogen .
The subject has now been examined more fully , though much still remains to be done .
In order to condense out the products of reaction , the gases were passed through the vessel shown in fig. 1 , with the result that they were frozen on the outside of the test-tube .
This could be withdrawn after the experiment , and quickly inserted into another larger test-tube , by means of the same rubber cork ( fig. 2 ) .
In the bottom of the outer tube was a little potash solution .
As the products evaporated they were absorbed by agitation in this solution , which could then be examined .
* 4 Roy .
Soc. Proc./ 1910 , A , vol. 83 , p. 527 ; 1911 , A , vol. 85 , p. 574 .
t I , p. 226 ; also Strutt and Fowler , 'Roy .
Soc. Proc. , ' 1911 , A , vol. 86 , p. 110 .
' ] I , p. 228 .
1913 .
] An Active Modification of Nitrogen .
The advantage of this method is that the cooled test-tube is readily taken out and replaced for the next experiment without disturbing other parts of the apparatus .
The following compounds were tested and gave the Prussian blue reaction strongly : acetylene , benzene , pentane , methyl bromide , ethyl -T\#151 ; GAS stream ENTRANCE LIQUID air EXIT W Fig. 2 .
chloride , ethyl iodide , chloroform , bromoform , ethylene dichloride , ethylidene dichloride , and ether .
Carbon tetrachloride and carbon disulphide , in sharp contrast with the above , gave no trace of it .
No evidence was brought forward in previous papers to decide whether the compound formed in these cases is cyanogen gas or hydrocyanic acid .
The reactions of these substances with alkali are as follows :\#151 ; HCN + KOH = KCN + H20 , C2N2 + 2KOH = KCN + KCN0 + H20 .
We may therefore hope to decide between the two alternatives by looking for a cyanate in the liquid .
The test for cyanate used was very kindly shown me by Dr. M. 0 .
Forster , F.E.S. The liquid ( as concentrated as possible ) is just acidified with acetic acid , and a cobalt solution added .
In the presence of cyanate a brilliant blue colour is produced .
This test was applied to the product from three hydrocarbons , pentane , acetylene , and benzene , * and gave absolutely negative results .
It is * In the two latter cases the solutions had to be decolorised with animal charcoal before the test could be applied .
546 Hon. R. J. Strutt .
[ May 9 ?
concluded that the product from hydrocarbons is hydrocyanic acid , not cyanogen gas .
Compounds containing the halogens behave differently .
With chloroform and carbon tetrachloride , * a strong cyanate reaction was obtained .
It seems probable that in these cases cyanogen chloride is formed , which ( as is known ) yields cyanate when treated with alkali .
The evidence above presented is not enough to determine completely the course of the reaction when active nitrogen acts on these organic vapours .
We need not hesitate , indeed , to represent it in the case of acetylene by the equation C2H2-f2N = 2HCN , and similarly in the case of benzene .
This , however , is not a complete account of the matter .
More complex solid or liquid products of dark colour are formed in addition .
With benzene these have a characteristic odour .
Dr. Forster , to whom they were submitted , felt fairly certain that cyanobenzene , C6H5CN , was present , and probably also the isomeric phenylcarbylamine C6H5NC .
It seems not improbable that there is here the germ of a new method of organic synthesis , which I hope may be taken up by those competent to pursue it .
With pentane and similar bodies the question remains unanswered\#151 ; what becomes of the surplus hydrogen , over and above that required for the formation of hydrocyanic acid ?
The probable alternatives are ( 1 ) it is set free , or ( 2 ) it unites with more of the active nitrogen to form ammonia .
Neither possibility lends itself very easily to experimental test .
Ammonia is indeed easily obtained from the products by the action of caustic alkali , but this proves nothing , for it may come wholly from the decomposition of hydrocyanic acid by the caustic alkali used .
Little or no dark-coloured matter is produced when active nitrogen acts on pentane vapour .
Chloroform does yield a little , however , under some conditions .
It is of interest to inquire what fraction of the nitrogen passed through the apparatus is converted into hydrocyanic acid , when allowed to react with excess of some organic vapour .
In a typical experiment light petroleum , mainly pentane , was used .
Six litres of nitrogen were passed , the products frozen out , and afterwards absorbed in potash .
The excess of petroleum floated as a layer on the alkaline solution , and was got rid of by burning it off .
The cyanide was estimated by Liebig 's volumetric method ; 15'5 c.c. of decinormal silver solution sufficed to just give a permanent turbidity .
* The latter , it will be remembered , gives no cyanide .
1913 .
j An Active Modification of Nitrogen .
547 This indicates about 37*4 c.c. of combined nitrogen , measured as nitrogen gas at room temperature , i.e. 0*62 per cent , of the nitrogen passed .
This is about the same as the yield of combined nitrogen obtained in earlier experiments in the reaction with phosphorus , * but much less than in the reaction with nitric oxide , j* I do not now look on any of these estimations as indicating the percentage of active nitrogen generated under the experimental conditions , though of course they are inferior limits to it .
Probably much of the active nitrogen reverts to ordinary nitrogen without entering into chemical union with the reagent presented to it .
S 6 .
Luminosity Accompanying these Actions .
It was remarked^ that the various organic vapours differ very much in the intensity of the cyanogen spectrum which they yield when mixed with active nitrogen .
In cases like benzene the spectrum is scarcely to be seen , and this was thought ( loc. ait .
) to indicate that very little hydrocyanic acid was formed .
The chemical tests have shown , however , that it is formed quite as abundantly from benzene , which scarcely gives the cyanogen glow , as from acetylene , which gives it magnificently .
Again , if ready-made cyanogen is fed into active nitrogen we get the cyanogen glow brilliantly , but anhydrous hydrocyanic acid vapour gives little or nothing of it in the same circumstances .
These cases are of interest because in them we have to do with ready-made molecules , and are independent of any special phenomena which may occur at the moment of their formation .
Not only does the absolute intensity of the cyanogen glow differ very much from one compound to another , but also the relative prominence of the red series of bands .
S Further investigation has shown that a special development of the red bands is always associated with the presence of the halogens .
Carbon tetrachloride , chloroform , bromoform , ethylene dichloride , and ethylidene chloride all gave a strong orange cyanogen glow .
Ethyl chloride and methyl bromide gave one of intermediate character , while in all the cases examined , in which halogens were not present , the glow was lilac .
I am inclined to associate the orange glow with cyanogen chloride or bromide .
This view is strengthened by the observation that vapour of cyanogen chloride fed in directly yields it in great intensity .
* * * S * I , p. 223 .
t II , p. 58 .
X I , p. 228 .
S I , p. 228 ; also Strutt and Fowler , \#163 ; Roy .
Soc. Proc. , ' 1911 , A , voJ .
86 , p. 113 .
VOL. LXXXVIII.\#151 ; A. 2 Q An Active Modification of Nitrogen .
In spite of the large number of additional facts accumulated it is still difficult to decide definitely what connection exists between the luminous phenomena developed by active nitrogen , and its chemical actions .
The following points may be noted : When the nitrogen stream acts on elementary bodies the spectrum of the element developed may be one of lines ( mercury , sodium , the metals generally ) or of bands ( sulphur , iodine ) .
In the former case chemical action appears always to be traceable .
In the latter it is traceable in some cases ( sulphur ) ; in others not ( iodine ) .
When the action is on a compound the spectrum developed may be a band spectrum of the compound introduced ( cupric chloride , tin tetrachloride , mercury haloids ) , a line spectrum of one of the elements contained in it ( titanium tetrachloride ) , a band spectrum of one of the contained elements ( hydrogen sulphide ) , or a band spectrum of a compound formed in the reaction ( cyanogen spectrum from acetylene ) .
Finally , an energetic action may be going on without any very distinct emission of light ( benzene ) .
There is evidently no simple generalisation to be extracted from such facts as these , and it is best perhaps provisionally to regard the luminous effects as quite independent of the chemical ones .
On this view , if a suitable substance , elementary or compound , happens to be present , it will draw energy in some way from the active nitrogen , and emit a characteristic spectrum ; and this no matter whether the substance is introduced in the first instance as such , or results from chemical combination or decomposition .
S S 7 .
Summary .
( 1 ) An improved practical method of preparing and storing nitrogen for the experiments is described .
( 2 ) It is shown , notwithstanding criticisms of certain other experimenters , that the presence of traces of oxygen in the nitrogen used is not essential , or even favourable , to the phenomena .
The nitrogen used , purified by cold phosphorus , does not contain oxygen to the extent of one part in 100,000 .
Passing it over red-hot copper in addition makes no difference .
The intentional addition of oxygen does harm ; 2 per cent , obliterates the effects altogether .
Hydrogen and carbon dioxide as impurities are much less harmful , but traces even of water vapour have a very bad effect .
( 3 ) Nitrides are formed by the admixture of active nitrogen with vapour of mercury , cadmium , zinc , arsenic , sodium , and sulphur .
These are decomposable by water or potash solution , yielding ammonia .
( 4 ) Carbon disulphide yields a blue polymeric nitrogen sulphide , and polymeric carbon monosulphide .
Chloride of sulphur gives ordinary yellow The Capacity for Heat of Metals at Different Temperatures .
549 nitrogen sulphide .
Stannic chloride and titanium .tetrachloride also yield solid products .
In the latter case nitrogen was proved to be present .
( 5 ) All organic compounds tried , except carbon tetrachloride , yield hydrocyanic acid freely , but not cyanogen , as was proved by chemical tests .
When chlorine is present , cyanogen chloride is formed .
Benzene yields ( almost certainly ) cyanobenzene .
( 6 ) The intensity of the cyanogen spectrum with organic compounds is no index of the quantity of hydrocyanic acid being formed .
Preponderance of the red cyanogen bands is associated with cyanogen chloride or bromide .
On a general view of the evidence , there does not appear to be any definite connection between the development of spectra by active nitrogen and the chemical actions in progress .
I take this opportunity of thanking my colleagues , Prof. H. B. Baker and Dr. M. 0 .
Forster , for constant help and advice .
The Capacity for Heat of Metals at Different Temperatures .
By E. H. Griffiths , Sc. D. , F.R.S. , and Ezer Griffiths , B.Sc. , Fellow of the University of Wales .
( Received April 1 , \#151 ; Read May 1 , 1913 .
) ( Abstract .
) The object of this investigation was the determination , with the closest approach to accuracy , of the specific heat of certain metals , and the changes therein caused by changes in temperature .
The work , including the necessary preliminary standardisations , has occupied our attention during the last two years and we feel unable , in this abstract , to describe with any clearness the various precautions adopted , or the somewhat elaborate process of reducing the results .
We , therefore , here content ourselves with a brief indication of the methods of experiment , a statement of the results , and a short discussion of certain suggestive features which they present .
I. The method of experiment is briefly indicated in the following numbered paragraphs :\#151 ; VOL. LXXXVIII.\#151 ; A. 2 R
|
rspa_1913_0050 | 0950-1207 | Obituary notices of fellows deceased. | 0 | 0 | 1,913 | 88 | Proceedings of the Royal Society of London. Series A, Containing Papers of a Mathematical and Physical Character | Samuel Hawksley Burbury | article | 6.0.4 | http://dx.doi.org/10.1098/rspa.1913.0050 | en | rspa | 1,910 | 1,900 | 1,900 | 2 | 383 | 11,353 | http://corpora.clarin-d.uni-saarland.de/surprisal/6.0.3/?id=rspa_1913_0050 | 10.1098/rspa.1913.0050 | null | null | null | Biography | 72.613111 | Fluid Dynamics | 10.401558 | Biography | [
32.432403564453125,
77.18705749511719
] | OBITUARY NOTICES OF FELLOWS DECEASED .
VOL. LXXXVIII.---A .
5 ' CONTENTS .
Page Samuel Hawksley Burbury ... ... ... ... ... ... ... ... ... ... ... i Frederick John Jervis-Smith ... ... ... ... ... ... ... ... ... .
iv John Brown ... ... ... ... ... ... ... ... ... ... ... ... ... ... ... .
vi Edward Divers ... ... ... ... ... ... ... ... ... ... ... ... ... .
viii Henry Taylor Bovey ... ... ... ... ... ... ... ... ... ... ... ... ... x Bight Hon. Sir John Charles Dalrymple-Hay , Bart. , G.C.B. xii Osborne Reynolds ... ... ... ... ... ... ... ... ... ... ... ... ... .
xv i SAMUEL HAWKSLEY BURBURY , 1831\#151 ; 1911 .
Mr. Burbury was born at Kenilworth in May , 1831 , and was educated at Shrewsbury School , where he gained the highest prizes for his studies .
He subsequently entered at St. John 's College , Cambridge , where he graduated in 1854 as fifteenth Wrangler and second Classic , having previously gained the Craven Scholarship ( for Classics ) as well as the Porson Prize .
About five years later he was called to the Bar , and it was not till about twenty years later that he commenced to specialise in mathematical science .
He was elected a Fellow of the Royal Society in 1890 .
His first substantial contribution , written in collaboration with the late Rev. H. W. Watson , Sc. D. , F.R.S. , was a treatise , published in 1899 , on * An Application of Generalised Co-ordinates to the Dynamics of a Material System/ The alliance with Watson was a successful one , for we find the same two writers bringing out ' The Mathematical Theory of Electricity and Magnetism/ in 1883-5 , a book intended to give greater definiteness and precision to the deductive portions of the subject than was to be found in Clerk Maxwell 's two volumes .
The first edition of Dr. Watson 's ' Kinetic Theory of Gases ' was published at the end of 1876 , just three years before the first joint work with Burbury .
The subject always appears to have had a fascination for Burbury .
About the year 1890 mathematical physicists were turning their attention to the statistical molecular distribution commonly referred to as Maxwell 's Law , and we find Burbury taking an active part in a controversy in which Boltzmann , Lord Kelvin , Lord Rayleigh , and several other physicists were involved .
This controversy , briefly speaking , turned on the two questions , first , whether the Boltzmann-Maxwell distribution is always a possible one , and secondly , whether it can be proved to be the only possible one .
It may perhaps be correct to say that the general result of these investigations has been to leave Maxwell 's Law somewhat in a similar position to Euclid 's eleventh axiom , a possible hypothesis , but not necessarily a unique one .
Among Burbury 's contributions at that time we notice papers\#151 ; " Some Problems in the Kinetic Theory of Gases " ( ' Phil. Mag./ Oct. , 1890 ) , and " The Collision of Elastic Bodies " ( ' Phil. Trans./ 1891)\#151 ; in the latter of which he criticises the test *cases previously proposed by Lord Kelvin and Burnside , and proves that the conventional proofs of Maxwell 's Law and Boltzmann 's Minimum Theorem can be extended to doublets , lop-sided spheres , and systems of colliding rigid bodies generally .
In a further paper ( 'Phil .
Mag./ Jan. , 1894 ) , Burbury extended the proof to groups of molecules under each other 's influence , while subsequently ( 'Phil .
Mag./ June , 1894 ) he traced the relation between the law of distribution and the assumed property that c^Q/ T is a -complete differential .
b 2 ii Obituary Notices of Fellows deceased .
In these papers Burbury appears in the light of counsel for the defence , but when it comes to the question of proving the uniqueness of the Boltzmann -Maxwell distribution he takes up the opposite line , and shows that Boltzmann 's Minimum Theorem , and the deductions following from it , are based on a certain assumption , which he calls " assumption A. " This line of argument receives its fuller development in Burbury 's treatise on ' The Kinetic Theory of Gases ' published in 1899 .
As applied to collisions between two different kinds of molecules , the assumption is that the probability factor of a given distribution of co-ordinates and momenta between pairs of colliding molecules , previous to collision , is of the form Ff where F depends on the molecules of one kind and f on those of the other , in other words that the distributions of the two kinds , previously to collision , are independent of each other .
This will no longer be true after the collisions have taken place , so that if F ' and f are the subsequent separate probability factors for the two systems , the probability factor for the combined system is not really F'/ ' .
It thus becomes necessary to assume that between collisions a process of mixing takes place so that the distributions of the molecules which are about to collide again become independent and the new probability factor assumes the form F'f .
if assumption A be made , Burbury admits that Boltzmann 's Minimum Theorem can be proved , but not otherwise .
The question of reversibility has also been used by Burbury and others in this connection , who contend that for every motion which makes as the result of a collision , an equally probable reversed motion must exist in which the opposite occurs .
In a letter to the present writer , dated December 17 , 1901 , Burbury says : " Now I say that the law has never been proved at all , except as a deduction from Boltzmann 's assumption A. If it has ever been proved , or attempted , will you tell me where ?
Tait , Watson , Maxwell , Weinstein , all make Boltzmann 's assumption .
Further , there is no evidence whatever for Boltzmann 's assumption , except that it leads to the law of equal partition .
We are in a vicious circle .
The tortoise is supported on the back of the elephant , and when I ask what the elephant is supported on they say it is suspended from the tortoise .
" In his treatise Burbury considers the result of abandoning " assumption A. " and making " assumption B , " according to which " the chance of a given molecule having at any instant assigned velocities is not independent of the positions and velocities of other molecules at that instant .
" This leads him , at any rate for the simpler cases of elastic spheres , to a distribution in which the probability factor is an exponential function of an argument containing not only squares but also products of velocities .
In other words , he finds that the velocities of neighbouring molecules become correlated .
This would happen particularly in a dense medium , thus affording some theoretical explanation for the physical differences between such a medium and an ideal gas subject to Maxwell 's Law .
From this time onwards , Burbury devoted a large amount of attention to* Samuel Hawksley Burbury .
iii tracking and exposing assumption A , or its equivalent , in all the papers written on the kinetic theory .
The late Willard Gibbs ' ' Statistical Mechanics/ Jeans 's papers , Planck 's investigations , all fell under Burbury 's critical eye ; and it was not long before most writers found this part of their argument attacked in a short paper by Burbury .
One of the recent questions which attracted Burbury 's critical mind was the loss of available energy accompanying the diffusion of two gases at constant volume , a subject dating back to a paper by Lord Rayleigh , published in 1876 .
Burbury 's criticisms were published in the 'Phil .
Mag. ' for July , 1907 , and in ' Science Progress .
' The difficulty in the problem lies largely in the fact that it is impossible to assign a quantitative value to any irreversible transformation unless it is possible to restore the system to its original state by a compensating transformation , and further , unless the latter transformation is reversible , it is impossible to obtain a measure of anything but the sum total of the irreversible effects of the direct and reverse transformations .
If there is one thing to be said in criticism of Burbury 's views it is that he hardly appreciated\#151 ; or if he did appreciate it he did not sufficiently emphasise the fact\#151 ; that the whole question depends essentially on experimental evidence regarding the processes of separation of mixed gases .
If we express the belief that the entropy of a gas mixture is the sum of the entropies of its components when each component occupies the same volume as the original mixture , this belief is founded on statements which experimental physicists give us and which they can only prove to be approximately true .
If , however , we consider ideal perfect gases we find that this entropy property is independent of the other definitions of such a medium , just as Euclid 's axiom of parallels is independent of the other axioms of geometry , and it is possible to formulate a theory of media the mixtures of which are defined as satisfying a different entropy property .
Burbury frequently reverts to the argument , Why should two different gases behave differently to two different portions of the same gas ?
Those who have entered into friendly controversies with Burbury on similar knotty points will well appreciate the zeal with which he would follow up a line of argument , till in many cases his opponent would have to give up the contest , often owing to lack of opportunity to continue it .
He was a typical example of a school of mathematical physicists essentially characteristic of the second half of the nineteenth century .
Most of his fellow workers have passed away , such as Maxwell , Kelvin , Boltzmann , Watson , Stony , Willard Gibbs , all of whom devoted either the whole ora considerable part of their attention at one time or other to unravelling these difficult problems .
Such work is usually described as theoretical .
In reality it has every right to be called experimental .
To find out what conclusions follow from certain assumed hypotheses is no less an experiment because it is conducted on paper instead of with apparatus .
For many years previous to his death Burbury suffered from deafness .
Perhaps this was the reason for his abandoning his legal career and taking to iv Obituary Notices of Fellows deceased .
mathematical physics as a scientific recreation .
He had four sons and two daughters .
He died in August , 1911 , and shortly afterwards one of his sons died when on active service in India .
It will be seen that Burbury 's work consisted largely in an attempt to secure logical rigour of treatment in the branches of mathematical physics in which he was interested .
It has certainly led to a closer examination of the foundations of statistical dynamics , and at the same time , when taken in conjunction with other contemporaneous investigations , has opened up a wide field of study which may well attract the attention of future workers . .
G. H. B. FREDERICK JOHN JERVIS-SMITH , 1848\#151 ; 1911 .
The Reverend Frederick John Jervis-Smith , the only son of the Reverend Prebendary Smith , of Taunton , was born at Taunton on April 2 , 1848 .
He was educated at Pembroke College , Oxford .
While still a boy at home he had the great advantage of meeting constantly William Ellis Metford , by whom his natural aptitude for science and mechanics w'as stimulated so that his genius , which was so marked in these directions , forced him at a later date to break away from the narrower life which his father wished him to follow .
In obedience to this wish he entered the Church and acted for some years as his father 's curate and organist , becoming later Yicar and Patron of the living of St. John 's , Taunton .
It must have been at this time also that with the help of Sir John Stainer he attained that knowledge of music and skill at the organ and piano that his friends so greatly admired , for a touch such as his could not have been acquired in later life .
While at Taunton he followed the bent that was so strong in him and carried on experimental work in his own workshop , acquiring by various means an intimate knowledge of workshop practice such as the amateur rarely possesses .
In 1886 he was invited to take charge of the Millard Engineering Laboratory attached to Trinity College , Oxford , and it was here that his best work was done .
A good indication of the variety of Jervis-Smith 's investigations may be found by reference to the c Philosophical Magazine ' in the twenty years from 1882 to 1902 .
The subject to which he devoted himself most particularly was that of work-measuring machines and integrators , and many of the papers are on this subject .
Several papers refer to the measurement of the torsion of rotating shafts with a view to determine the power being transFrederick John Jervis-Smith .
v mitted , and one of his early papers describes the means now adopted on large steamships , where , owing to the engines being turbines , indicated power cannot be ascertained and the torsional method is the only one available .
Other enquiries which interested him were the magnetic properties of metals as affected by mechanical stress or by heat ; electric sparks and the influence on them of flame or pressure .
Under this heading , probably , should be mentioned his beautiful electrically produced images of coins that he called inductoscript .
One of the most valuable results of Jervis-Smith 's ingenuity and mechanical aptitude is his tram chronograph .
Those who have used the old pendulum myographs so usual in physiological laboratories , where the time records are rendered tiresome by the variable speed of the recording surface , should be the first to appreciate this beautiful instrument , in which trouble from this cause is entirely eliminated .
A still greater value has been given to this instrument by the perfection of the electromagnetic styles that he invented and made .
By making his electromagnets extremely small and the yoke relatively short and thick he reduced the latent period so that this chronograph is now not only the most convenient but the most accurate instrument for ballistic and other measurements of the kind .
Other subjects of less interest perhaps in which Jervis-Smith made investigations or inventions were in relation to mercury pumps and means for raising the mercury continuously and automatically , quick distillation of mercury in vacuo , recalescence of iron , and high resistances made of graphite and plaster of Paris .
During the last few years since his retirement to his charming house near Lymington Jervis-Smith was greatly interested in glowing phenomena in vacuous bulbs moved or spun in electric and magnetic fields .
On these he made numerous original experiments , but up to the present these results are not well understood .
Jervis-Smith was awarded a medal at the Paris Exhibition of 1878 for a dynamometer , and at the Inventions Exhibition at South Kensington he was awarded a silver medal for his work on dynamometers .
He also received a medal from the Royal Humane Society for rescuing a person in danger of being drowned .
He was a member of the Committee on Explosives appointed by the Home Office in 1895-96 .
He became a Fellow of the Royal Society in 1894 .
He was keenly interested in the historical side of Physical Science , and often brought to light curious anticipations of more recent inventions .
He found , for instance , that the telephone had been made and described in Italy as an instrument for recording taps upon it by movement at the receiving end .
The former inventor had apparently invented the same instrument as Bell , but he never thought of speaking into it .
This historical appreciation made the selection of Jervis-Smith to represent the University of Oxford at the tercentenary of Torricelli at Faenza in 1898 singularly appropriate .
Throughout his career one subject was constantly receiving his atte ntion vi Obituary Notices of Fellows deceased .
and that was dynamometry in its widest sense .
On this he had been collecting papers all his life , and in his later years he was putting these in order in the hope of seeing the great work completed which had gained so much from his originality .
It is hoped that this will appear this year .
He married Annie Eyton , second daughter of T. Taylor , Esq. , who with one surviving son remains to mourn his loss .
The singular charm , humour , and modesty of Jervis-Smith , no less than his genius , made his friendship a valued possession .
The writer of this notice found in addition a community of taste and a mutual sympathy , and he has lost his closest and most valued friend and counsellor .
C. V. B. JOHN BROWN , 1850\#151 ; 1911 .
John Brown , who died on November 1 , 1911 , at his residence , Longhurst , Dunmurry , Belfast , was born close by , at Edenderry , in 1850 , eldest son of John Shaw Brown , the proprietor and largely the developer of the well-known Edenderry flax spinning and weaving works .
During the seventies of last century his father took a conspicuous and public-spirited part in social and political life in Ulster , several times contesting the Parliamentary representation of divisions of Belfast on moderate Liberal principles , as understood in those days .
His son 's interests from earliest years were mechanical and philosophical .
After the usual school education at the Royal Academical .
Institution at Belfast , he went into the work of the firm .
In his leisure time he kept in touch with the progress of physical science , largely through the correspondence columns of the ' English Mechanic,5 a journal then at the zenith of its usefulness in keeping the workshop in touch with the laboratory , before the modern period when the rise of electric engineering has turned the professional societies into scientific institutions .
In this way he made and retained the acquaintance of other practical mechanicians of scientific taste , some of whom have taken a notable part in subsequent developments .
In particular , he became fascinated , at a time when the primary battery was still a main electric source of power , with the problem of the seat of the transformation of the chemical into electric energy .
Is the measured potential difference between copper and zinc due to a sudden transition between the metals where they are in contact , or is it mainly due to such transitions between each metal and the surrounding atmosphere in which the measuring apparatus must be immersed ?
The reasonings of Volta and John Brown .
Vll Faraday and Kelvin\#151 ; necessarily general and somewhat vague up to the nineties because the existence and role of electrons as the agents of all electric change were still unrecognized\#151 ; strongly fascinated him .
Where the chemical affinity lay , there , as he thought , should the potential difference be , at any rate in the state of equilibrium when no current passes\#151 ; for the passage of a current necessitates its own special distribution of driving force in accordance with Ohm 's law , which must be brought about by the superposition of transient distributions of free charge on the intrinsic transitions of potential aforesaid .
It was left to Brown to put these ideas to direct test : and the paper ( 1878 ) in which he announced that replacement of air or oxygen as the surrounding medium by sulphuretted hydrogen gas at once changed the direction of the potential difference between zinc and copper , attracted immediate attention and discussion .
He became a refined and diligent experimenter in the field of voltaic combinations , stoutly adhering against all comers to the indications of Faraday , whom he took as his mentor ( cf. obituary notice in ' Nature/ November 16 , 1911 ) , and -encouraged by the interest and friendship of George FitzGerald , Oliver Lodge , J. D. Everett , and other friends and colleagues .
When the resources , mostly self-constructed , of his own laboratory at Edenderry were inadequate , he worked for long spells in Everett 's physical laboratory at the Queen 's College , Belfast .
At a later stage he was attracted to Trinity College , Dublin , to the laboratory of his friend FitzGerald ; and while there , an explosion in chemical preparations , relating to his work on primary batteries , cost him the loss of an eye .
Later he resumed similar work at Belfast .
He had little instinct for publicity ; yet during these years he produced , besides many local papers and lectures at Belfast , an extensive general experimental paper on contact electricity in f Boy .
Soc. Proc. , ' and a later one in 1902 on the effect of a heated bath of petroleum in modifying this phenomenon .
He seems to have been the first to publish the remarkable patterns produced by electric discharge on photographic plates .
He became interested also in the Hertzian electric waves , whose qualities were being explored and verified extensively in the Dublin laboratory by FitzGerald and Trouton and others about the time he was there\#151 ; just as , later , the results of the introduction by Marconi of the aerial antenna , which was needed to effect the copious radiation necessary for telegraphic signalling , were first publicly verified by them at a regatta in Dublin Bay , as tested by the transmission of press messages to the shore .
On the introduction of internal combustion engines , Brown at once grasped the new possibilities which they brought , and he spent much time experimenting on the development of the motor car ; but an isolated worker , far from the resources of capital and factories , could hardly much affect practical evolution in such a subject .
He also worked on the development of a spring wheel to absorb shock .
His experiences in this direction led him on to a cognate topic , on which he became a public force .
The badness of the roads , especially in Ireland , was a main obstacle to the introduction of the new viii Obituary Notices of Fellows deceased .
type of locomotion .
He invented an instrument , attachable to a ear , to take* a trace of the inequalities of the road ; and he circulated the graphs thus obtained , to the occasional confusion of the road authorities .
He pointed out the evils of the slipshod methods of road-repair , by loosely spreading macadam stones mixed with mud , that were then in vogue .
He established the Irish Eoad Improvement Association , which brought pressure to bear on public bodies with considerable success , and later worked in touch with enlightened road engineers in Great Britain .
In these ways he was a pioneer in a development which now , under Government direction , is producing fundamental improvement in the facilities for communications and for country life .
He grudged no time or effort to the stimulation of scientific interests in the community among whom he lived .
He was one of the main forces which kept fresh and active in recent years the old-established Belfast Literary and Philosophical Society ; and when the British Association last visited Belfast in 1902 he was the expert and indefatigable local Secretary of the meeting .
He was elected a Fellow of the Royal Society in 1902 .
J. L. EDWARD DIVERS , 1837\#151 ; 1912 .
Edward Divers , M.D. , D.Sc .
, F.I.C. , after an operation followed by a painful illness , died at his residence at Kensington on April 8 .
He was born in London on November 27 , 1837 , and therefore at the time of his decease had attained his 75th year .
He was educated at the City of London School , the Royal College of Chemistry , and Queen 's College , Galway .
From this time onwards he was increasing his own knowledge , and by his numerous investigations added to that of others .
In 1870 he received the appointment of Lecturer on Medical Jurisprudence at the Medical School of the Middlesex Hospital .
The experience he gained whilst holding this position stood him in good stead in after life , and invested him with authority in connection with criminology .
A great event in his career took place when he accepted a Professorship in Chemistry in the service of the Imperial Government of Japan .
This was in 1873 , at which time that country issued invitations to all nations that could give her assistance in acquiring the material civilisation of the West .
On his arrival in Japan , Divers had to attend to the building of his own laboratories , around which grew the palatial buildings of the Imperial College of Engineering .
In 1882 he was appointed Principal of this Edward Divers .
IX Institution .
It was here , in consequence of an explosion in a test tube , that for some time he practically lost his sight .
This , however , was partially regained , and , although with one eye he could read at a short distance from his face , he could not recognise acquaintances in the street .
Notwithstanding this misfortune , contrary to expectations , Divers ' power for work , rather than growing less , grew greater .
Memoir followed memoir and paper followed paper .
Many of these were written in conjunction with a colleague , an assistant , or some promising student .
Amongst these the names of Haga , Takamine , Shimidzu , Nakamura and others will be familiar to many chemists .
His work has appeared in the f Transactions ' and * Proceedings ' of the Royal Society , the 'Journal of the Chemical Society/ and particularly in the ' Journal of the College of Science of the Imperial University of Japan .
' In the latter we notice papers on Mercury Sulphites , the Composition of Tori mochi or Japanese birdlime , Oxyamidosulphonates and their conversion into Hyponitrites , the Manufacture of Calomel in Japan , Sulphazotates , Sulphate of Hydroxylamine , Imidosulphites , Nitrilosulphates , and Sulphamide .
In the ' Transactions of the Asiatic Society of Japan 5 we find contributions relating to Japanese meteorites and hot springs .
The accident which cut him off from pleasures which nearly all enjoy seems to have increased the time he had for original investigations .
He gave himself but short holidays ; and during the Long Vacation , when the halls of the College of Science were supposed to be deserted , the echo of a footstep or the hum of some quaint old melody told the intruder that Divers loved his laboratory better than hills he could not see .
At the entrance to that college a large bronze bust reminds many in Japan of a teacher they admired .
He went to Japan with an engagement for five years ; but he found an environment so fascinating and a bondage so agreeable , that he remained in that country without once leaving it for 26 years .
On his retirement he was made Emeritus Professor of the University of Japan , received the Second Class of the Order of the Sacred Treasure and the Third Class of the Rising Sun .
On reaching England his activity continued .
In 1902 he was President of the Chemical Section of the British Association .
He also became President of the Society of Chemical Industry , and represented that Society on the governing body of the Imperial College of Science and Technology .
In addition to these offices he was a VicePresident of the Chemical Society and of the Institute of Chemistry .
In 1865 he married Margaret Theresa FitzGerald , of Mayfield , County Cork .
His only son , who joined the Chinese Customs service , succumbed to an illness in Amoy .
His two daughters , the Comtesse de Labry and Mrs. Tilden , in common with all who knew him , mourn his loss .
He had a genial and generous disposition , was full of humour , was always ready to give assistance or advice , and was esteemed by all .
His high forehead and grey beard gave him a dignified appearance , while the kindly expression on his face was an invitation to friendship .
He did very much more than any other X Obituary Notices of Fellows deceased .
individual to found the present School of Chemistry in Japan , and his colleague , Professor Sakurai , writing from Japan , says Divers " will be for ever remembered in this country as the great promoter of chemical science .
" J. M. HENRY TAYLOR BOYEY , 1850\#151 ; 1912 .
Henry Taylor Bovey was born at Torquay on March 7 , 1850 .
He received his school education at Clevedon College , Northampton , a private school , many of whose pupils distinguished themselves afterwards at the University .
A scholarship from this school carried him to Queens ' College , Cambridge , where he read for the Mathematical Tripos .
In those days it was considered necessary , if a man aimed at a high position among the Wranglers , to read during the whole of his three years with one of a few leading coaches , college and University lectures taking a secondary position .
He became a pupil of W. H. Besant , F.R.S. , of St. John 's College , and graduated as Twelfth Wrangler in 1873 , shortly afterwards being elected to a Fellowship at his college .
Deciding to become a civil engineer , he entered the office of Sir George Lister , who was at that time the engineer of the Mersey Docks and Harbour Board .
He afterwards joined the staff of that Board as assistant engineer , in which capacity he had charge of some of the most important structures then in progress .
It was , however , as a Professor of Engineering that Bovey was to make his mark .
A severe accident in the football field , with broken ribs and a damaged lung , was the proximate cause of the change in his career .
He was advised to spend some time in a dry climate , and this induced him to accept the offer of the Chair of Engineering at McGill College , Montreal , which was made to him at this time by Sir W. Dawson , and he went to Canada in the autumn of 1877 to take up this post .
But at the end of the first year he appears to have been so dissatisfied with the organisation of the teaching that he sent in his resignation with the intention of returning to England .
He was persuaded , however , by the Principal to reconsider his determination , and receiving from the latter a promise of support in a reorganisation of the department , he decided to remain .
Although he did not know it at the time it was the opportunity of his life .
In a few years the Engineering School at McGill was transformed .
It became the leading institution of the kind on the American Continent , and his pupils were always sure of going straight from college into good engineering posts .
But it was not by any means all plain XI Henry Taylor Bovey .
sailing .
There were difficulties of organisation within , and the want of means to ensure development , until at last Sir W. Macdonald came to the rescue with princely donations .
His first fight was to free his subject from the domination of the Arts Faculty , and to obtain recognition of an independent Faculty of Applied Science .
In 1890 the Engineering building was begun , and he and the donor\#151 ; Sir Wm. Macdonald\#151 ; made a tour of Engineering schools in the States .
From what# they saw there it was easy to convince Sir William that McGill needed adequate buildings and Chairs for Physics and Chemistry , and Bovey 's ideas of adequacy were wide and large .
One who knew him well writes : " He found a subordinate department of the Faculty of Arts .
He freed it and made it a great Faculty .
I think he did it first by reason of boundless energy .
When he came over to the Imperial College he was already ill , and a mere shadow of himself , and could give no idea of what he was in the eighties and nineties .
He was then sanguine and self-confident , and full of go .
He had a real fund of geniality and kindness of heart .
Everyone who came out was sure of a most kind welcome and helpfulness of every sort .
He really had ideas that were worth while so far as the concrete creation of a great Faculty went , and from 1890 to 1900 he had practically a free hand .
In working out his ideas another marked gift appeared .
He always knew the right man to go to to get a thing done .
He enjoyed meetings and remembered people , and had that mysterious way of knowing what was going on by instinct .
His real gifts were practical organisation , knowing the right man , how to set about it , and no limit to what he wanted for the Faculty .
" In 1907 an offer was made to him of the rectorship of the Imperial College of Science and Technology in London , and he was definitely appointed to it in May , 1908 .
But his health had commenced to break down before this , and after two years ' work in the organisation of the new College , he resigned the post in December , 1909 .
He passed away at Eastbourne on February 2 , 1912 , and lies buried in Eastbourne Cemetery .
He married on May 5 , 1880 , Miss Emily Eedpath , youngest daughter of Mr. John Eedpath , of a well-known Montreal family .
He is survived by his widow , two sons , and three daughters .
The Eoyal Society elected him a Fellow in 1902 , and his old College in Cambridge conferred on him an honorary fellowship in 1906 .
He was one of the founders of the Canadian Society of Civil Engineers , and at one time or another held all the offices from Secretary to President .
He was also one of the founders of the Liverpool Society of Civil Engineers .
In 1896 .
he became President of Section III of the Eoyal Society of Canada .
He was author of several text-books on Engineering .
W. M. IL Xll EIGHT HON .
SIE JOHN CHAELES DALEYMPLE-HAY , Bart. , G.C.B. , 1821\#151 ; 1912 .
John Charles Dalrymple-Hay , third baronet , was born in Edinburgh on February 11 , 1821 .
He spent his early boyhood at home until sent to Eugby in 1833 .
Entering the Eoyal Navy in 1834 , he joined H.M.S. " Thalia , " serving in her on the West Coast of Africa .
From 1839 to 1842 he served in H.M.S. " Benbow , " on the Mediterranean Station , being present at the capture of St. Jean d'Acre by Sir Eobert Stopford in 1840 , and " being gazetted for gallantry at the attack on Tortosa .
Having passed his examination for Lieutenant in 1841 , he attained that rank in 1844 , and serving on the China Station became Flag Lieutenant to Admiral Sir Thomas Cochrane , who , in 1846 , promoted him to a vacancy as commander of the " Wolverene .
" Hay 's next appointment was to H.M. Brig " Columbine , " proceeding in her to the China Station in 1849 .
The opportunity now occurred for him to show the result of the excellent training he had received in ships commanded by able officers , animated by the great traditions of the Naval service .
The Chinese coasts were infested by pirates , and it was by the squadron\#151 ; two of which were paddle steamers\#151 ; under Hay 's command , that the most notable were destroyed in Bias Bay and the Tonquin Eiver , places then uncharted and requiring great audacity and perseverance to navigate .
It was here that the value of steam propulsion in war vessels came home to him .
For this service he was promoted to Captain and presented by the merchants in China with a service of plate .
During 1846-50 Hay undertook observations in meteorology , and communicated to the Indian Government papers on the cyclone theory , remarks on three typhoons in the China seas , and on two hurricanes off Mauritius , besides papers on storms in the Atlantic off Bermuda and the Western Islands , neither of which appears to have been published .
After serving in H.M.S. " Hannibal " during the Crimean War he became Captain of H.M.S. " Indus , " one of the last sailing line-of-battle ships commissioned for sea service , and on leaving her in 1859 his career at sea ended .
This was not intentional on his part , for trusting to his long service and existing regulations he fully counted upon being given an Admiral 's command .
But , being one of those officers of his day who appreciated the value of science when applied to his profession as a sailor , he saw an opening for utilising his energies in that direction for a time on land .
The construction of iron-built ships for war purposes which was attempted in the early forties was almost immediately discontinued as being quite unsuitable , and wood-built ships propelled by steam or sail , or both , as required , formed our Navy for several years .
However , the use of iron as a valuable protection to wood-built floating batteries was shown by the Sir John Charles Dalrymple-Hay .
xiii French when bombarding Kinburn in 1855 .
Then , in 1860 , was launched the French wood-built armour-plated frigate " La Gloire , " responded to in the same year by the British iron-built armour-plated frigate " Warrior .
" The latter vessel sounded the death-knell of the wood-built ship .
The early failure , and subsequent success and progressive use , of iron in the construction of warships when armour-plated had been favourably noted by Hay , enabling him to cast aside the strong predilection for the wood-built ship , which affected many able officers of his time , and he put all his strength into furthering what he considered to be the inevitable future .
In 1861 Hay became Chairman of the Iron-plate Committee appointed in 1860 to carry out experiments in armour and other proposals for introduction into the Navy .
For this he had many qualifications , actual experience of the value of armour for ships during the Crimean war , considerable war service afloat , and a mind open to genuine improvements .
Moreover , he possessed great tact and ability in smoothing the difficulties which presented themselves when presiding over a Committee consisting of eminent scientific members dealing with inventions and proposals , good , bad , or indifferent , often strongly pressed for adoption .
Following this , the Institution of Naval Architects elected him a VicePresident in 1862 , and later on he became Chairman of the Mill wall Shipbuilding Company , and also of Keuter 's Telegraph Company .
The work he had so far undertaken was not enough for Hay 's activities , for he sought other opportunities for promoting naval progress by entering Parliament .
He was successively Member for Wakefield , 1862-65 ; Stamford , 1866-80 ; and Wigton Burghs , 1880-85 .
In 1866 he accepted a seat on the Board of Admiralty , a post he held for two years and a half .
It was during this period that Hay , now a Bear-Admiral , successfully contended for a large addition of armour-plated ships to the Navy , in spite of considerable opposition , even tendering his resignation of a coveted position rather than give way upon a question he considered vital to the strength of the Navy .
It was with deep regret that , at the age of 49 , Sir John was obliged to relinquish all prospects of active service at sea .
A new scheme of compulsory retirement for all officers who had been unemployed afloat for specified periods was ordered , and Hay , refusing the offer to be made an exception to the rule , had to go .
If he could not serve his country in the way of his choice , he was , at any rate , free to do so in other directions .
Thus , not only in Parliament , but at the meetings of the Institution of Naval Architects , he was a keen debater on naval questions , and he did good work as VicePresident of the Boyal United Service Institution .
Of his published writings , the following may be mentioned : 1868 , ' Lines from my Log Book ' ; 1876 , The Flag List and its Prospects ' ; 1878 , 'Ashanti and the Gold Coast ' ; 1883 , 'Our Naval Deficiencies ' ; 1889 , 'Piracy in the China Seas .
' In 1903 , when seismology was much to the front , he contributed to the ' Proceedings ' an interesting paper , written from xiv Obituary Notices of Fellows deceased .
his own naval experiences , " On Central American Earthquakes , particularly the Earthquake of 1838/ ' Sir John was the recipient of various distinctions .
In 1852 he became a Fellow of the Eoyal Geographical Society , and in 1864 was elected a Fellow of the Royal Society .
Ten years later he was appointed a Privy Councillor .
Oxford and Glasgow conferred on him the honorary degrees of D.C.L. and LL. D. respectively .
He was created K.C.B. in 1885 and G.C.B. in 1902 .
Sir John married the Hon. Eliza Napier , third daughter of the eighth Lord Napier , in 1847 , and by her had three sons and six daughters .
She died in 1901 .
The eldest son having died in 1908 , the next , William Archibald , succeeded to the baronetcy , which his father had held since 1861 .
As a naval officer Hay was a strict disciplinarian , tempered with tact and full consideration for the welfare and happiness of those under his command , qualities fully appreciated by seamen .
Both in private and public life lie was remarkable for his genuine courtesy , coupled with the frankness of the sailor , and his memory will be long and warmly cherished by his acquaintances as well as friends , including many of the Fellows of the Royal Society , who much appreciated his regular attendance at the meetings and at other functions .
Admiral Sir John Charles Dalrymple-Hay died at his residence in London on January 28 , 1912 , in his 91st year .
E. W. C. XV OSBORNE REYNOLDS , 1842\#151 ; 1912 .
Osborne Reynolds was born August 23 , 1842 , at Belfast .
He came of a clerical family .
His grandfather and great-grandfather had been rectors of Debach-with-Boulge , Suffolk .
His father , the Rev. Osborne Reynolds , was thirteenth Wrangler in 1837 ( a year remarkable as being that of Green and Sylvester ) , and was subsequently Fellow of Queens ' College , Principal of the Belfast Collegiate School , Headmaster of Dedham Grammar School , Essex , and finally , in his turn , rector of Debach .
For his early education Reynolds was indebted chiefly to his father , first at Dedham and afterwards privately .
In 1861 , at the age of nineteen , he entered the workshop of Mr. Edward Hayes , mechanical engineer , of Stony Stratford , in order , as Mr. Hayes expressed it , " to learn in the shortest time possible how work should be done , and , as far as time would permit , to be made a working mechanic before going to Cambridge to work for Honours .
" The motives which guided the first steps in Reynolds ' career may be stated in his own words.* " From my earliest recollection I have had an irresistible liking for mechanics ; and the studies to which I have specially devoted my time have been mechanics , and the physical laws on which mechanics as a science are based .
In my boyhood I had the advantage of the constant guidance of my father , also a lover of mechanics , and a man of no mean attainments in mathematics and their application to physics .
" After referring to the year he spent with Mr. Hayes , he proceeds :\#151 ; " Having now sufficiently mastered the details of the workshops , and my attention at the same time being drawn to various mechanical phenomena , for the explanation of which I discovered that a knowledge of mathematics was essential , I entered at Queens ' College , Cambridge , for the purpose of going through the University course , previously to going into the office of a civil engineer .
" The decision to proceed to Cambridge appears to have been taken rather suddenly , for his previous education had not included Greek ; he succeeded , however , by the obstinate labour of a few weeks , in reaching the standard of the " Previous Examination .
" His mathematical studies were pursued with success , for he graduated in 1867 as seventh Wrangler , and was immediately afterwards elected to a Fellowship .
He then entered the office of Mr. John Lawson , civil engineer , of London .
In 1868 he was elected to the newly instituted professorship of engineering in the Owens College .
This professorship was almost !
the first of its kind in England , although similar chairs had existed for some time in Scotland and in Ireland , and had been illustrated by such names as those of James Thomson and Rankine .
It is possible that Reynolds was influenced to some extent by * Taken from his letter of application for the Owens College professorship .
+ Fleeming Jenkin had been appointed professor of civil engineering at University College , London , in 1865 .
VOL. LXXXVIII.\#151 ; A. C xvi Obituary Notices of Fellows deceased .
the tradition of these chairs .
With Eankine , at all events , for whom he always professed the greatest admiration , he had strong affinities , in the range of his scientific interests , in the directness of his intuitions , and in the courage and tenacity with which he attacked difficult and complicated problems .
He resembled Eankine also in his views as to the scientific character of the training to be given to engineering students .
The course of instruction which he arranged for his pupils , and to which he consistently adhered , was remarkable for the thoroughness and completeness of the theoretical groundwork .
On one point he was uncompromising .
In his mind all engineering was one , so far as the student is concerned , and the same fundamental training was required whatever the nature of the specialisation which was to come afterwards in practice .
As an ideal principle this can hardly be gainsaid , although the varied ramifications of mechanical science , and the increasing multiplicity of " subjects , " have in more recent times compelled a deviation from it .
The course laid out by Eeynolds was no doubt felt by many students to be severe , and there is testimony that his lectures were not always easy to follow .
It is therefore hardly to be wondered at if at first some shade of disappointment was felt by the eminent practical engineers , and other friends of the Owens College , who had worked for the creation of the professorship .
Few could have foreseen at that time how splendidly the appointment was destined to be justified , not only by the distinguished scientific career for which it served as a base , but also by the succession of students who derived stimulus and inspiration from the genius of their teacher , and who came afterwards to occupy important positions in the professional as well as in the academical world .
Both branches of his activity were greatly assisted by the establishment of the Whitworth Engineering Laboratory in 1888 , although some facilities for hydrodynamical experiments on a moderate scale had been secured at an earlier date .
Several of the more important appliances in the new laboratory , e.g. the triple-expansion engines and the hydraulic brakes , were specially designed by Eeynolds for purposes of study and research , and presented many novel features .
Shortly after his appointment Eeynolds entered on the career of original research which continued without interruption down to his retirement in 1905 .
The results of many of his investigations were communicated in the first instance to the Manchester Literary and Philosophical Society , which cherished the memory of Dalton , and was still distinguished by the presence of Joule .
In the affairs of this Society Eeynolds took a lively interest ; he was Secretary from 1874 to 1883 , and President for the term 1888-9 .
After the death of Joule he wrote for the Society a memorial volume , which was published in 1892 ; and he was the leading spirit in the movement for a public monument to Joule , which resulted in the beautiful statue by Gilbert which now adorns the Manchester Town Hall .
His scientific writings are a remarkable fulfilment of the plan traced out in the letter which has been quoted .
They deal almost entirely with mechanical Osborne Reynolds .
xvii questions , or with physical phenomena so far as these appear to be susceptible of mechanical interpretation .
Although they treat of subjects which are at first sight widely different in character , there are many underlying affinities , and trains of thought which constantly recur .
It is characteristic of Eeynolds that , even when they bear on questions of immediate practical import , there is a persistent endeavour to penetrate to fundamental principles , and to disregard what is accidental or adventitious .
It is probably for this reason , in part , that there was some delay in the recognition of his work by the practical world , even in cases where his ideas have since been proved to contain the germ of fruitful applications .
His work on turbine pumps , for example , is now recognised as having laid the foundation of the great modern development in these appliances , whilst his early investigations on the laws governing the condensation of steam on metal surfaces , and on the communication of heat between a metal surface and a fluid in contact with it , stand in a similar relation to recent improvements in boiler and condenser design .
About the year 1899 the Cambridge University Press suggested to Eeynolds that a collected edition of his papers would be valuable , and offered to undertake the publication .
This signal compliment on the part of his old University was greatly appreciated by him , and in due course two considerable volumes appeared .
Some idea of the extent of his scientific activity may be gathered from an inspection of the list of contents of this edition .
In the way of practical papers , we find , in addition to those already referred to , investigations on the " racing " of the screws of steamers , on the steering of screw steamers , on rolling friction , on the errors of indicator diagrams , and on the action of tidal currents in the silting of estuaries .
These , and others , may still be read with profit , and display , equally with the more impressive contributions to science , his skill in unravelling and explaining a mass of complicated detail by the light of some simple mechanical principle .
In the scientific world at large , however , the reputation of Eeynolds is most likely to rest in the future on his contributions to general physics , and , in particular , to hydrodynamics , although here also the suggestion came usually from some practical question of engineering .
The paper on " Lubrication " ( 1886 ) , for example , explains on familiar hydrodynamical principles how the presence of a film of oil is maintained between a rotating shaft and its bearings , in spite of enormous pressures between them .
The explanation , when given , is almost obvious ; but Eeynolds was the first to formulate it explicitly , and to submit it to the test of calculation .
To many minds it had not even occurred that there was anything to be explained at all .
In the paper " On the Law of Eesistance in Parallel Channels " ( 1883 ) , an experimental investigation is made of the circumstances which determine whether the flow of water through a pipe shall be smooth and regular , with a resistance varying as the velocity , as in Poiseuille 's experiments with capillary tubes , or irregular and sinuous ( or " turbulent , " to use Lord Kelvin 's happy xviii Obituary Notices of Fellows deceased .
description ) , with a resistance varying more nearly as the square of the velocity , as in most questions of practical hydraulics .
The conclusion , based on the dynamical principle of " dimensions , " and confirmed by the experiments , is that there is a certain " critical velocity , " depending on the ratio of the ( kinematic ) viscosity of the fluid to the diameter of the pipe , at or about which the transition takes place from one type of motion to the other .
The character of the motion , at any stage , was revealed by the behaviour of a filament of coloured water introduced into the stream , a device often used by Reynolds in the study of fluid motion .
The experiments described in the paper , and often repeated by Reynolds in his lectures , were of a beautiful and striking character .
Although much has since been written on the subject , and something still remains to be cleared up , the investigation has taken rank as a classic , and is perhaps the most widely appreciated amongst the decisive achievements of the author .
The most extensive piece of purely experimental work carried out by Reynolds was undoubtedly that bearing on the Mechanical Equivalent of Heat , and described in the Bakerian Lecture for 1897 .
This was prompted by a number of considerations .
The original determination of Joule depended ultimately on the properties of a particular thermometer .
More recent observers had endeavoured to refer their measurements to the absolute scale , but with somewhat discordant results .
Measurements of the heat generated in the hydraulic brakes in the Whitworth Laboratory had been conducted under Reynolds ' direction for some years , and compared with the work absorbed , but this had been done mainly by way of verification , and for practice .
He was at length led to recognise that he had at his command appliances which could be used on an unprecedented scale , and to solve a more definite problem .
The question which he attacked was to ascertain the total amount of work required to raise a pound of water from freezing point to boiling point , or in other words , the mean specific heat ( in terms of work ) between these two temperatures .
The object of the measurement thus became absolutely definite , and independent of any arbitrary thermometric scale ; and at the same time , owing to the great quantities which could be dealt with , the margin of error could be greatly reduced .
The principle of the method was simple in the extreme ; water was fed into the brake at the freezing temperature , there raised by friction to boiling point , and then carried off to a tank on the table of a weighing machine .
The work absorbed was given by the couple on the brake , multiplied by the total rotation of the shaft .
A good deal of preliminary work was required , and some improvements in the mechanism , before the method was brought to its ultimate degree of accuracy .
The final measurements , which extended over a considerable period , were undertaken by Mr. W. H. Moorby .
The definitive result was that the mean specific heat between freezing and boiling points , expressed in mechanical units , at Manchester , is 776*94 .
The whole investigation is a model of scientific method , and may claim to rank among the classical determinations of physical constants .
Osborne Reynolds .
xix Among the shorter writings which have played a part in the development of science mention may be made of the papers on the " Refraction of Sound " ( 1874 ) , and on " Group-Velocity of Waves " ( 1877 ) .
The effect of wind on the transmission of sound had been discussed by Stokes in 1857 .
Reynolds independently gave the same explanation , and confirmed it by a series of experiments ; he also added an examination of the various effects of a vertical temperature gradient , according as the temperature decreases or increases upwards .
As regards group-velocity , a geometrical explanation had been given by Stokes , but Reynolds brought in the very important and significant fact that the group-velocity gives also the rate of transmission of energy .
A word must be said as to the style and composition of his papers , if only because these elements have been the occasion of some injustice and neglect .
The leading idea is in nearly all cases simple ; his bias was , indeed , always to look for a simple explanation of a phenomenon , rather than to frame a theory based on the concurrence of a number of independent causes .
But when he came to write out the results of his researches , he appears to have aimed in the first place at a statement which should , accurately reflect his own experience of the matter .
Unfortunately , the joints which have given most trouble to the author are not always those which are most difficult to the reader , and vice versed .
When , on one or two occasions , he took up a subject for a second time , with a view to explaining it to a popular audience , he was lucid and forcible .
Like some other distinguished physicists whom one can call to mind , he was not a great reader of contemporary scientific literature .
When new theories were brought under his notice , he thought the questions out independently and in his own way .
He held to his own technical terms and phrases , even when there was an established usage , and sometimes employed familiar terms in a new sense .
Consequently , the reader of his papers will at times find it necessary to bring some patience to the task , if he means to extract the solid value which is to be found in them .
But , with one or two exceptions , there are no cases of obscurity which cannot be surmounted in this way .
Although he sometimes affected , not quite seriously , to despise mathematics , he had considerable mathematical power , and did not hesitate to apply it on occasion .
One or two of his calculations , if isolated from their context , would rank as considerable analytical achievements , even if they had been carried out with the help of modern and more expeditious methods .
Reference may here be made to the paper on " Dimensional Properties of Matter in the Gaseous State " ( 1879 ) , and to that on the " Dynamical Theory of Incompressible Viscous Fluids " ( 1894 ) .
The former paper , written in the early days of the radiometer , is important in relation to the theory of gases , and discusses , both experimentally and mathematically , the new phenomenon of " thermal transpiration .
" In the latter an attack is made on the very difficult problem of calculating theoretically the critical velocity , already referred to , at which the regular flow of a liquid through a pipe becomes unstable .
XX Obituary Notices of Felloivs deceased .
At the British Association meeting of 1885 , Reynolds read a short paper on the " Dilatancy " of granular media .
When an agglomeration of loose granules is closely packed , it cannot have its shape altered without increasing , at all events temporarily , the volume of the interstices .
Consequently , if such an aggregation is prevented from expanding , it becomes rigid .
These principles were illustrated by simple but striking experiments , and it was also pointed out that they lead at once to the explanation of a familiar but hitherto obscure phenomenon , viz. that when a foot is planted on the firm moist sand of the sea-shore , the space immediately around becomes relatively dry , whilst the space beneath the foot , when this is raised , is found to be abnormally wet .
This explanation , it may be mentioned , gave great delight to Lord Kelvin .
In spite of the interest of the experiments , Reynolds was careful to state that the theory was anterior to them .
He had long speculated on the possibility of a mechanical theory of matter and ether which should , amongst other things , resolve the riddle of gravitation .
He had convinced himself that a medium composed of smooth rigid grains ( e.g. spheres ) in contact was promising , and it was by reflection on the properties of such a medium that he was led to foresee the somewhat paradoxical behaviour of sand and other granular aggregations which %ras so beautifully confirmed by his experiments .
The results of the remarkable physical speculation referred to are recorded in the long memoir on the " Sub-mechanics of the Universe " which marked the close of his scientific career .
This was read before the Royal Society on February 3,1902 , and now constitutes the third and final volume of his collected papers .
Unfortunately , illness had already begun gravely to impair his powers of expression , and the memoir as it stands is affected with omissions and discontinuities which render it unusually difficult to follow .
Ko one who has studied the work of Reynolds can doubt that it embodies ideas of great value , as well as of striking originality ; but it is to be feared that their significance will hardly be appreciated until some future investigator , treading a parallel path , recognises them with the true sympathy of genius , and puts them in their proper light .
Prof. Reynolds , owing to the failing state of his health , withdrew from the active work of his chair in 1905 .
His last years were spent in retirement at Watchet , Somerset , where he died on February 21 , 1912 .
He had been twice married ; first , in June , 1868 , to a daughter of Dr. Chadwick , of Leeds , who died in July , 1869 ; and secondly , in December , 1881 , to a daughter of the Rev. H. Wilkinson .
A son by the first marriage died in 1879 .
By his second marriage he leaves three sons and a daughter .
The character of Reynolds was , like his writings , strongly individual .
He was conscious of the value of his work , but was content to leave it to the mature judgment of the scientific world .
For advertisement he had no taste ; and undue pretensions on the part of others only elicited a tolerant smile .
To his pupils he was most generous in the opportunities for valuable work which he put in their way , and in the share of credit which he assigned to them in cases of co-operation .
Somewhat reserved in serious or personal Osborne Reynolds .
xxi matters , and occasionally combative and tenacious in debate , he was in the ordinary relations of life the most kindly and genial of companions .
He had a keen sense of humour , and delighted in starting paradoxes , which he would maintain , half seriously and half playfully , with astonishing ingenuity and resource .
The illness which at length compelled his retirement was felt as a grievous personal calamity by his pupils , his colleagues , and by other friends throughout the country .
He was elected a Fellow of the Royal Society in 1877 , and received a Royal Medal in 1888 .
He was made an Honorary Fellow of Queens ' College , Cambridge , in 1881 , and received the degree of LL. D. from the University of Glasgow in 1884 .
An admirable portrait by Collier , presented by scientific friends and admirers from all parts of the kingdom , hangs in the hall of the Manchester University .
H. L.
|
rspa_1913_0051 | 0950-1207 | Errata | 0 | 0 | 1,913 | 88 | Proceedings of the Royal Society of London. Series A, Containing Papers of a Mathematical and Physical Character | null | errata | 6.0.4 | http://dx.doi.org/10.1098/rspa.1913.0051 | en | rspa | 1,910 | 1,900 | 1,900 | 1 | 10 | 91 | http://corpora.clarin-d.uni-saarland.de/surprisal/6.0.3/?id=rspa_1913_0051 | 10.1098/rspa.1913.0051 | null | null | null | Headmatter | 39.774911 | Reporting | 24.96991 | Reporting | [
31.119205474853516,
47.819305419921875
] | XXV11 Page 231 .
Page 254 .
Page i. ERRATA , Etc. In column headed " Mean of 1883-1884/ ' For 7*449 read 7*499 .
Paper by E. W. Merchant .
Reference to following paper should have been made :\#151 ; Ottavio Bonazzi , " Misura della Permeabilita del Ferro nel Campo Magnetico dell Scariche Oscillatorie/ ' ' Pubbl .
del 1st .
Fis .
del Univ. di Pisa/ 1910 .
Obituary Notice of S. H. Burbury\#151 ; Line 10 , For 1899 read 1879 .
VOL. LXXXVIIl.\#151 ; A. e
|
rspa_1913_0052 | 0950-1207 | The capacity for heat of metals at different temperatures. | 549 | 560 | 1,913 | 88 | Proceedings of the Royal Society of London. Series A, Containing Papers of a Mathematical and Physical Character | E. H. Griffiths, Sc. D., F. R. S.|Ezer Griffiths, B. Sc. | abstract | 6.0.4 | http://dx.doi.org/10.1098/rspa.1913.0052 | en | rspa | 1,910 | 1,900 | 1,900 | 4 | 153 | 3,438 | http://corpora.clarin-d.uni-saarland.de/surprisal/6.0.3/?id=rspa_1913_0052 | 10.1098/rspa.1913.0052 | null | null | null | Tables | 42.063827 | Thermodynamics | 29.998077 | Tables | [
-12.143450736999512,
-68.83930206298828
] | ]\gt ; The Capacity for Heat of Metals at Different Temperatures .
549 nitrogen sulphide .
Stannic chloride and titanium tetrachloride also yield solid products .
In the latter case nitrogen was proved to be present .
( 5 ) All organic compounds tried , except carbon tetrachloride , yield hydrocyanic acid freely , but not cyanogen , as was proved by chemical tests .
When chlorine is present , chloride is formed .
Benzene yields ( almost certainly ) cyanobenzene .
( 6 ) The intensity of the cyanogen spectrum with organic is no index of the quantity of hydrocyanic acid being formed .
Preponderance of the red cyanogen bands is associated with cyanogen chloride or bromide .
On a general view of the evidence , there does not appear to be any definite connection between the development of spectra by active nitrogen and the chemical actions in progress .
I take this opportunity of thanking my colleagues , Prof. H. B. Baker and Dr. M. O. Forster , for constant help and advice .
The Capacity for Heat of Metals at Different Temperatures .
By E. H. GRIFFITHS , Sc. D. , F.R.S. , and EZER GRIFFITHS , B.Sc. , Fellow of the University of Wales .
( Received April l , \mdash ; Read May 1 , 1913 .
) ( Abstract .
) The object of this investigation was the determination , with the closest approach to accuracy , of the specific heat of certain metals , and the changes therein caused by changes in temperature .
The work , including the necessary preliminary standardisations , has occupied our attention during the last two years and we feel unable , in this abstract , to describe with any clearness the various precautions adopted , or the somewhat elaborate process of reducing the results .
We , therefore , here content ourselves with a brief indication of the methods of experiment , a statement of the results , and a short discussion of certain suggestive features which they present .
I. The method of experiment is briefly indicated in the following numbered paragraphs :\mdash ; VOL. LXXXVIIL\mdash ; A. Griffiths aGriffiths .
dependent upon any assumption concerning the capacity for heat of bodies !
: other than those under consideration .
: 2 .
The substances were raised across a given temperature through very small ranges of temperature ( extreme limit of range , about 3 .
These temperature changes were measured by means of differential platinum thermometers , for which purpose these instruments are admirably adapted .
4 .
masses of the substances were used , ranging from 1 to 4 kgrm .
5 .
The apparatus was constructed with all the parts duplicated .
The metals examined were suspended by quartz tubes in similar air-tight brass cases , which were placed side by side in a large tank containing rapidly stirred water or oil .
This tank was electrically co1ltrolled with great constancy at any given temperature One of the metal blocks remained at the tank temperature throughoub an experiment , while the other , having been previously cooled below , was raised to a somewhat similar temperature above it by a supply of heat electrically developed in the centre of the block , the difference in the temperature between the two blocks being determined at regular intervals by means of the differential platinum thermometers .
Any changes in the surrounding conditions would , therefore , affect both blocks equally , and hence , by measuring the difference of temperature only , possible causes of error were eliminated .
6 .
equation connecting the various quantities is MS where total mass and its specific heat , the initial temperature and the final temperature , the potential difference at the extremities of the coil of resistance , and the number of thermal units lost , or gained , during time from sources other than the electrical supply .
In these experiments the values of and were so arranged that was in every case small or negligible , and , if necessary , could be ffitimated with sufficient accuracy .
7 .
With two exceptions ( Cu and Fe ) the samples of metals used were supplied by Messrs. Johnson and Matthey , to whom we wish to express our , sincere thanks for the trouble they have taken in the matter .
Each sample was accompanied by their certificate egarding its purity .
*For a full discussion of the reasons for selecting this value of see p. 110 of the Thermal Measurement of Energy , ' by E. H. ( .
Univ. Press ) .
1913 .
] for of Metals at fferent Ter 5 51 An analysis of the iron was supplied by the manufacturers , and Mr. C. T. Heycock has very kindly made an analysis of the copper .
8 .
Experiments on identical samples at the same temperature were repeated under very varied conditions .
Two separate methods of experiment , involving different data and methods of reduction , were employed .
Three different sets of platinum thermometers were used .
The rate of heat supply was varied in the ratio of 9 : 1 .
The determination of at a given temperature , with a particular sample , was in several cases repeated after the lapse of some months .
The quartz tubes and their cover were replaced by others of diflerent masses , etc. We were thus enabled to ascertain causes of error which would otherwise have remained undetected .
9 .
The results of our observations have been deduced from the actual experimental numbers and in no case from " " smoothed culves.\ldquo ; The most serious difficulty presented by this method of experiment is that of determining the mean temperature of the block of metal when its temperature is altering .
Temperature gradients must necessarily exist , since equalisation of temperature by stirring is an impossibility .
The manner in which this ifficulty was surmounted is described in full in the original paper .
When embarking on this investigation we proposed to extend our of temperature to the lowest point obtainable by means of liquid air , limiting the inquiry to a study of two or three metals only .
Owing , however , to delay on the part of the contractors in the delivery of the liquid-air plant , we were compelled to postpone that portion of our investigations dealing with temperatures below C. to a later date , and therefore we enlarged the scope of our inquiry so as to include the metals , namely : aluminium , iron , copper , zinc , silver , cadmium , tin , and lead .
As the data already accumulated concerning the capacity for heat of these metaJs over the C. to 10 may be useful to other observers , we have seen no reason for postponing the publication of the work already completed .
II .
Statement of In the following tables we have , in each case , inserted in Column IV the " " probable error expressed in percentages , as the resulting numbers are of a nature suitable for treatment by the " " method of least squares and this appeared to be the most concise way of indicating the extent of the discrepancies in the results .
This " " probable error\ldquo ; does not , of course , include persistent errors or those present in determinations of the various standards employed .
We have , however , no reason to suppose that 552 Dr. E. H. ffiths and Mr. E. Griffiths .
[ Apr. 1 , such errors are of sufficient magnitude to have any appreciable effect upon our conclusions .
In order to express the relation between and , many forms of equations were tried , but it was found that the mean path of the results was most closely expressed in all cases by a parabola .
In Column we give the differences ( expressed in percentages ) between our values as found by experiment and those deduced from the parabola given at the foot of each table .
We also give the previous treatment of the metal and its analysis .
With copper an unusually large number of experiments at C. were performed .
Two methods were employed which involved different data .
The close correspondence between the resulting numbers convinced us of the validity of both methods , and therefore , in our later work , we contented ourselves with the adoption of the more convenient , i.e. that which we termed the " " method of intersection The capacity for heat of the copper case appeared as a small correction in our determinations of the specific heat of all the remaining metals .
For the above reasons we made no less than 35 determinations of its specific heat at C. , and these were performed on different dates and under varied conditions .
In two cases , where a note of interrogation is placed after a group number , it is an indication that we regard the result as less satisfactory than usual .
* Although little weight should be attached to values thus indicated , we do not feel that we have evidence sufficient to justify us in discarding them .
The " " group numbers\ldquo ; ( Column II ) do not merely indicate repetition of the same experiment , for the rate of supply of heat differed in the individual members of the group .
For example , in Table I , Column II , the first group of 12 includes experiments performed with potential differences varying from 3 up to 9 Weston cells , hence the rate of heat supply was , in this group , changed in all the following proportions : 9 : 16 : 25 : 36 : 49 : 64 : 81 .
In no group in any of the tables are there less than three such changes .
Column indicates the close correspondence of results obtained under such conditions .
With the exception of Cu and Fe , Messrs. Johnson and Matthey state that the previous history of the blocks was as follows:\mdash ; " " The cylinders in every instance were cast and then allowed to cool , subsequently being turned in a lathe .
They were not annealed The weight of metal as given at the head of each table is only a rough We have some doubts as to the constancy of the bath temperature during these two groups .
1913 .
] for Heat of Metals at Different .
553 approximation , as the mass was , in some cases , slightly altered series of experiments .
The copper was electrolytically deposited .
Table I.\mdash ; Copper .
Weight .
Density Mr. C. T. Heycock writes as follows:\mdash ; " " Cu per cent. Remaining per cent. consists of traces Pb , Fe , and a very little .
You will be correct in stating that it is of high purity During the above experiments at , three different pairs of thermometers were employed , and two different covers to the copper case .
The quartz tubes holding the block were also altered .
The frequent repetition of group experiments was considered necessary in order to ascertain the effect of such changes .
With reference to the sample of aluminium employed ( Table II ) Messrs. Johnson and Matthey state : " " Aluminium we have reason to believe to be exceptionally pure , say per cent. , with a trace of iron With the exception of the first group of 3 , these experiments were extremely satisfactory , so much so that the fifth figure appears to have some real gnificance .
The perfect agreement of the experimental and curve values is very noticeable .
554 Dr. E. H. Griffitf Weighi .
1913 .
] for Heat of at Diferent Temperatures .
This specimen was presented to us by the American Rolling Mm Company , Middletown , Ohio , U.S.A. , who state : 'Material rolled from an ingot into a billet ( 4 in .
by 4 in .
) on 'blooming mill , ' forged into round section at blacksmith 's shop .
Same had no further annealing nor additional treatment other than when rolled and forged The specimen was turned down to size in the laboratory workshop .
Analysis supplied by the manufacturers:\mdash ; Iron .
Mn .
Sitrace . .
Cu Table Zinc .
Weight .
Density .
*Where the " " value adopted\ldquo ; is not the mean of the numbers in Col. III in this , or other , tables , the reasons are dicated in the original paper .
Messrs. Johnson and Matthey state " " approximately per cent. zinc The agreement between the results , on repetition at the same temperature , was less satisfactory than usual ( see Column III ) , the extreme difference from the adopted value at C. being per cent. 556 Dr. E. H. ffiths and Mr. .
Griffiths .
[ Apr. ] , Table Silver .
Weight .
Density .
Messrs. Johnson and Matthey state : " " Better than fine Table Cadmium .
Weight .
Density .
Messrs. Johnson and Matthey state : " " Fully per cent. pure , with very slight traces of iron and zinc 1913 .
] for Heat of Metals at Different Table Weight .
Density experiments igroupNIoIof.roup .Messrs .
Johnson and Matthey state : " " Probably analyse to per cent. with trifling quantities of arsenic , lead , and iron Table VIII .
Lead .
Weight .
Density .
Messrs. Johnson and Matthey state : " " Approximate to per cent. , with inappreciable traces of arsenic and bisnluth The numbers in Column indicate that the agreeme1lt between the individual membsrs of a group in Table VIII is distinctly inferior to that attained with metals .
This is probably effect of the low conductiviby of lead and the consequent steepness of the thermal radients within the cylinders .
558 Dr. E. H. Griffiths and Mr. E. Griffiths .
[ Apr. 1 , III .
An inspection of these results will show that the curvature in the case of Al and Fe is far more marked than in the metals .
The curves of Sn and present certain interesting features .
The specific heat of Sn at appears , for reasons given elsewhere , to be exceptionally high .
This may in some way be connected with the fact that Sn at temperatures not much below readily assumes the " " grey powder\ldquo ; form and it is possible , therefore , that at its physical condition is an exceptional one .
The curvature in the case of shows distinct alteration as the temperature approaches , the rate of increase being much diminished .
In consequence , in this case , we pushed our inquiry to a temperature exceeding 12 C. The results confirmed the indications observed at somewhat lower te , nlperatures .
In this connection it should be remezubered that becomes malleable about 12 C. and we have some indication of a physical cause for its abnormal behaviour .
The range of atomic weights covered by the metals enumerated above is from ( A1 ) to ( Pb ) .
At the conclusion of our experiments , we proceeded to plot our values of at C. as ordinates and the atomic weights as abscissa .
The resulting points lie very closely on the curve [ deduced from the values of Al , the mean of Cu and , and Pb ] which is represented by where atomic weight .
The value of for Sn , however , exceeds the curve value by as much as per cent. ( i.e. , as against We have endeavoured to ascertain how nearly the values of obtained from this curve are in harmony with the experimental results of observers in the case of elements not examined by us .
In a large number , no satisfactory information is procurable and , where information exists , it is difficult to estimate its true value .
Again , few observers have used a ange of temperature including C. , and , in such cases , we have had to reduce their results to by means of the values given them at other temperatures , assuming the changes to be of a linear order .
In our full paper we have stated , in every case , the authority and the data by which we ascertained the most probable values at C. The following table shows the results of the ation : Column I gives the percentage difference between the calculated and the experimental values ( a positive sign indicating the latter as the greater ) in those cases where the difference does not exceed 3 per cent. In the case of 1913 .
] for Heat of Metals at Different Temperatures .
all gases , however , the experimental values have been doubled before making the comparison .
Column II .
Elements whose differences lie between 3 and 16 per cent. Of , however , we do not consider the values of , Na , and to be sufficiently established to warrant any conclusions , and we may state that , in order to test this point , we are now engaged in the determination of the specific heat of Na .
Column III .
* Elements whose experimental values differ so greatly from the calculated as to exclude the possibility of agreement .
A couple of curious coincidences , however , present themselves .
The calculated value of is almost exactly four times that of the diamond .
The mean value for amorphous is very closely half the calculated .
Table IX .
We are aware of the serious difficulties in the way of accepting any such relation as that given by the above equation between the atomic weights and specific heats at an arbitrary temperature such as C. It is , however , possible that the large majority of elements are in a stable condition at that temperature , and , if such is the case , some definite connection may exist between their atomic weights and specific heats .
However this may be , one thing is evident , , that the curve gives , throughout the whole range of atomic , valuss of in the case Column III the actual numbers , insead of percentage differences , are given .
The expression " " Atomic heat \ldquo ; is evidently an alternative manner of expressing the same relation .
560 The for Heat of at Different Temperatures .
of which , in a very majority of cases , are within 2 per cent. of the most probable values .
* It has already been pointed out that the curvature of the curve in the case of Al and Fe differs markedly from that of the remaining metals on our list .
If we take those six remaining metals , and , from the parabolic formulae given supra , deduce the point of intersection with the ordinate at , and , assuming the values of , find their atomic heats at absolute zero , we obtain as the mean of our results the number , their differences from the mean surprisingly small , when we consider the effect of any error in the values of the coefficients over the to 10 C. If then , assuming the values of at given by , and the experimental values of at and l00o , we construct the resulting parabolas and ascertain the differences between the experimental and the calculated values at the various points ally determined by us , we find that in no instance does the difference exceed per cent. , and that it is , in cases , much less .
The remarkable approximation between the hypothetical value of the atomic heat at C. of a body with atomic weight 1 and the likewise hypothetical value of the atomic heat of the group of metals at absolute zero is probably a coincidence , but may possibly be of real significance .
If we assume the value of Dulong and Petit 's constant as , the deduced values for the elements in Column I would , in some cases , differ from the experimental ones by as much as 30 per cent.
|
rspa_1913_0053 | 0950-1207 | On Fourier series and functions of bounded variation. | 561 | 568 | 1,913 | 88 | 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.1913.0053 | en | rspa | 1,910 | 1,900 | 1,900 | 6 | 106 | 2,904 | http://corpora.clarin-d.uni-saarland.de/surprisal/6.0.3/?id=rspa_1913_0053 | 10.1098/rspa.1913.0053 | null | null | null | Formulae | 77.265972 | Tables | 19.602414 | Mathematics | [
71.23878479003906,
-48.8157844543457
] | ]\gt ; On Fourier Series Functions of Bounded Variation .
By Prof. W. H. YouNG .
Sc. D. , F.B.S. ( Received April 10 , \mdash ; Read June 19 , 1913 .
) S1 .
In a previous communication to the Society I have pointed out that the succession of constants obtained by multiplying together two suocessions of Fourier constants in the manner which naturally gests itself is a succession of Fourier constants , and I have discussed the summability of the function with which the new constants are associated .
We may express the matter in another way by saying that I have shown that the use of the Fourier constants of an even function as convergence factors in the Fourier series of a function changes the latter series into a series which is still a Fourier series , while the summability of the function which is associated with the new series is increased .
The use of the Fourier constants of an odd function as convergence factors , on the other hand , has the effect of changing the allied series of the Fourier series of into a Fourier series , even when the allisd series is not itself a Fourier series .
It at once suggests itself that the former of the two statements in this form of the result is not the most that can be said .
Indeed , the series , whose general term is , and whose coefficients are accordingly unity , may clearly take the place of the Fourier series of , although it is not a Fourier series .
the other hand , it is the derived of the Fourier series of a function of bounded variation , which is , moreover , odd .
We are thus led to ask ourselves whether this is not the trivial case of a general theorem .
In the communication I propose to show , among other things , that the answer to this question is in the affirmative .
The theorems are , in fact , true : If the coefficients of the derived series of a Fourier series of odd function of bounded variation be used as convergence factors , the Fourier series of a general summable function will remain the Fourier series of a summable function , while the degree of summability of the function will in general be unaltered .
On the other hand , if the function of bounded variation used be even , the corresponding convergence factors obtained by its Fourier series will have the effect of ming the allied series of a Fourier series into the Fourier series of a fmlction having the same of summability as the function corresponding to the original Fourier ssries .
These results appear to me to possess of themselves sufficient interest to justify my communicating them to the Society .
Apart , however , from their Prof. W. H. Young .
On Fourier [ Apr. 10 , intrinsic interest , the method by which I have been led to obtain them is , I think , at once suggestive and instructive .
In germ this method has already been employed by Stieltjes .
Properly handled and suitably developed , it constitutes a very effective tool in dealing with some of the finer } ctions in the Theory of Functions of a Real Variable .
For this .
purpose , however , we require to introduce the notion of the summability of a function with respect to a function of bounded variation , and not merely , as Stieitjes does , to employ an analytical expression , which may be interpreted as the Riemann integral of a continuous function taken with respect to a monotone function .
Moreover , we require to have a theory of integration with respect to a function of bounded variation which shall correspond to that of integration with respect to the independent variable , such as I have exposed in a recent communication to the Society .
* When this has been done we may integrate sequences and successions with respect to any assigned function of bounded variation , whether continuous or not , under conditions which are analogous to those in the known theory .
particular , we have a theory of the integration of Fourier series term by term with respect to a function of bounded variation of the most general type .
We are thus led to a variety of results of interest , and , among others , to those I have stated above .
I have not attempted to give a complete account of the theory , but I have thought it well to take the opportunity to enunciate and give indications of proof of some of the connected results so obtained .
Among these may be mentioned the one which states that if a series has the property that its integrated series converges everywhere boundedly , then term-by-term integration of the trigonometrical series is allowable after it has been multiplied by any function of bounded variation whatever , the sum of the latter integrated series being expressible in terms of the integral of the function of bounded variation with respect to Added June , 1913.\mdash ; In the order of ideas there indicated various slightly fferent but equivalent modes of treatment are possible .
If we start with simple and functions and define , as we evidently may content ourselves with doing , their integraIs with respect to a monotone increasing function , special attention must be paid to the discontinuities of , unless we hypothecate that the simple functions are so chosen that none of their disco.ntinuities coincide with those of .
We may also , if we please , start with the integral of a continuous function , using for this purpose the formula of Stieltjes ; this corresponds to the treatment suggested in my paper , ' On a New Method in the Theory of Integration cited below .
I am , by request , writing out a systematic account of these matters , and propose to present the paper containing it to the London Mathematical Society .
All turns on the use of monotone sequences .
Another , but far less intuitive form of treatment , has been briefly indicated by Lebesgue .
He employs , but evidently with great reluctance , the process of change of the independent variable .
See H. Lebesgue , ' Comptes Rendus , ' 1909 .
1913 .
] Series and Functions of Bounded Variation .
563 the function which is the sum of the integrated trigonometrical series itself .
Again , it appears that the coefficients of the derived series of the Fourier series of respectively an odd and an even function of bounded variation , when employed as convergence factors , change the Fourier series of a continuous ction and its allied series into the Fourier series of continuous functions .
The theory of the summability of a function with respect to a function of bounded variation is , it be noted , only part of a still larger theory .
Even Stieltjes was led to consider integration with respect to a continuous function , owing to the necessity of formulating a theorem of integration by parts .
In general , however , the generalisation in this direction involves difficulties of a naturs analogous to those which arise when we are dealing with non-absolutely convergent integration with respect to the independent variable .
I do not propose , therefore , in the present communication , to enter on these matters .
S2 .
It will not be necessary on this occasion to enter into details with regard to the theory of ration with respect to a function , and in particular with respect to a function of bounded variation .
It will be evident that a function which is summable may , or may not , be summable with respect to au assigned function of bounded variation , and a sequence or succession which is integrable term by term may , or may not , remain integrable term by term when the integration is with respect to a function of bounded variation .
The rules , however , which enable us to recognise such possibilities in the general case are usually completely analogous to the known ones in the special case .
Thus we have merely to remark that the repeated integral with respect to two monotone increasing functions of a positive function is necessarily independent of the order in which the integration is performed , to see that , if is any function of bounded variation whatever , and is any summable function , the integral of with respect to c , ertainly exists except for a set of values of of content zero .
Using Stieltjes ' notation , and interpreting it in the extended sense above explained , we may accordingly write , ( 1 ) where is an indefinite integral of .
We thus see that the right-hand side of ( 1 ) is an integral with respect to , and that the inside integral on the left certainly exists , except at it set of content zero , while it consbitutes a summable function of S3 .
Again we see immediately that sequences that converge uniformly can certainly be iutegrated with respect to any function of bounded variation .
Prof. W. H. Young .
On Fourier [ Apr. 10 , In fact let be the general of a sequence which approaches uniformly .
Then it is plain tb.at has , as , the unique limit zero .
For we can find an so that is less than for all points in the interval of , and we may suppose expressed as the difference of two positive monotone functions .
Each the corresponding integrals will then be less than a certain finite multiple of , and is therefore as small we please .
Hence the limit of our integl.al , as , is zero .
But , more generally , it is cient that the sequence should converge boundedly for the same to be true .
To see this we have , in fact , merely to retrace the steps of the reasoning by which , in a recent communication to the Society , I showed that the process is allowable when integration is .
taken in the new generalised sense there explained .
Mutatis mutandis the whole argument applies .
S4 .
Let , and consider the series where , ( 3 ) being an odd function of bounded variation , so that is the typical coefficient of the trigonometrical series got by differentiating term by term the Fourier series of .
We are about to prove that the series ( 2 ) is the Fourier series of the following function\mdash ; .
( 4 ) We have by ( 4 ) .
In fact , of order of integration with respect to and is permitted when the factor is omitted , and is therefore , by a theorem , analogous to a known theorem in ordinary repeated integration , allowable when is present .
Now the inside integral on the right-hand side is evidently equal to nt .
We can , in the further evaluation of the right-hand side of ( 5 ) , almost without leaving the realm of Stieltjes ' ideas , employ an obviously allowable generalisation of the ordinary theory of integration by parts .
The term evidently contributes nothing to the result , since is odd ; and 1913 .
] Series Functions of Bounded since vanishes at the limits of integration*with respect to , of the two parts involving , one vanishes identically .
Hence ( 5 ) becomes .
( 6 ) Similarly The equations and ( 7 ) show that the series ( 2 ) has the Fourier form , .
and that the corresponding function is , as was stated .
S5 .
Next consider the series , ( 8 ) .
where being an even function of bounded variation , so that is the typical coefficient of the trigonometrical series got by differentiating term by term the Fourier series of .
We are about to prove that the series ( 8 ) is the Fourier series of the following function\mdash ; We have , as before , equations ( 11 ) and ( 12 ) show that the series ( 8 ) has the Fourier form , and that the corresponding function is .
S6 .
We may next discuss the summability of the functions and , and the mode in which this depends on the summability of .
There is no difficulty in seeing that both these functions belong in general to the * In fact , as we suppose periodic and odd , its values when and must be both zero .
VOL. 566 Prof. W. H. Young .
On Fouri'er [ Apr. 10 , ) same class of functions as .
If we consider in particular the case in which the power of is summable , we have only to use the inequality where and are any positive functions of the independent variable More generally we may use the inequality where is the indefinite integral of any positive function whose differential 'coefficient is positive This inequality may evidently be proved in a manner analogous to that used in proving the corresponding inequality when is itself the independent variable , with whose limits of integration we are concerned .
Pntting then and equal to the total variation of , or as the case may be , and taking to be the independent variable , the required results immediately folow .
S7 .
It may also be remarked that the corresponding reasoning shows that the effect of integrating the Fourier series of a function of bounded variation , and its allied series , with respect to an odd function of bounded variation and an even function of bounded variation respectively is , in the former case , to preserve the character of being the Fourier series of such a function ; and , in the latter case , to transform the allied series into such a Fourier series .
Or , as we may otherwise express it , the convergence factors and have these effects respectively .
S8 .
If , on the other hand , we perform the process of integration with respect to a function of bounded variation on the Fourier series of a continuous fimction , we easily prove that the following result holds good : If and are the typical coefficients of the derived series of the Fourier series of respectivdy an odd and an even of bounded variation , then the tvergence factor transforms the Fourier of a continuous function into the Fourier series of a function , whde the convergence factor jhanges the allied series of the Fourier series of such a function into the Fourier series of a continuous function .
fact , the argument is precisely the same as that employed in SS4 and 5 , * On Classes of Summable Functions and their Fourier Series 'Roy .
Soc. Proc 1912 , , p. 227 .
' ' On the New Theory of Integration 'Roy .
Soc. Proc 1912 , , vol. 88 ; see also 4 ' On a New Method in the Theory of Integration 'Lond .
Math. Soc. Proc 1910 , , vol. 9 , pp. 16-60 .
1913 .
] Series and Functions of Bounded and shows that the functions with which these series , as Fourier series , are associated are respectively and , where and are respectively the odd and even functions of bounded variation .
The theorem stated follows immediately from the known property of a continuous function of being uniformly continuous .
may indeed find a quantity , independent of ( and of ) , such that for this and all smaller values , is less than a fixed quantity , as small as we please .
Hence , for which , as the total variation of is finite , proves the continuity of ) .
Similarly , is seen to be continuous .
Or , more simply , we may remark that the sequence converges uniformly to as , whence the required result follows by S3 .
S9 .
Finally we shall prove the following theorem , which , it will be seen , is { of a slightly different type .
If and are the typical Fourier constants of a function of bounded variation , and and the typical coefficients of a trigonometrical series whose integrated series converges boundedly to , then the series whose general term is ( eonverges boundedly and has for sum .
To prove this we have only to employ the theorem to which allusion has been made in the last few lines of S3 .
In fact , since the series whose general term is onverges boundedly to , it is the Fourier series of , and to prove the result we have merely to integrate term by term the Fourier series of with respect to .
We shall then get the right-hand side of the equation to be proved with its sign changed onlthe right of our equation , while on the
|
rspa_1913_0054 | 0950-1207 | On a condition that a trigonometrical series should have a certain form. | 569 | 574 | 1,913 | 88 | 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.1913.0054 | en | rspa | 1,910 | 1,900 | 1,900 | 3 | 77 | 2,075 | http://corpora.clarin-d.uni-saarland.de/surprisal/6.0.3/?id=rspa_1913_0054 | 10.1098/rspa.1913.0054 | null | null | null | Formulae | 82.490481 | Tables | 17.080226 | Mathematics | [
70.63803100585938,
-48.09889602661133
] | ]\gt ; On Condition that a Trigonometrical Series should have Certain Form .
By Prof. W. RYouNG , Sc. D. , F.R.S. Received Read June S1 .
In a recent communication to the Society I have illustrated the fact that the derived series of the Fourier series of functions of bounded variation play a definite part in the theory of Fourier series .
Some of the more interesting theorems in that theoly can only be stated in all their generality when the coefficients of such derived series take the place of the Fourier constants of a function .
I have also recently shown that Lebesgue 's theorem , whether in its original or in its extended form , with regard to the usual convergence of a Fourier series when summed in the Cesaro manner is equally true for the derived series of Fourier series of functions of bounded variation .
I have also pointed out that , in considering the effect of all known convergence factors in producing usual convergence , it is immatelial whether the series considered be a Fourier series , or such a derived series .
We are thus led to regard the derived series of the Fourier series of fuuctions of bounded variation as a kind of pseudo-Fourier series , possessing properties which are identical with or analogous to those of Fourier series , properly so-called .
In particular we are led to ask ourselves what is the necessary and sufficient condition that a trigonometrical series should have the form in question .
One answer is of course immediate .
The integrated series must converge to a function of bounded variation .
This is merely a statement in slightly different language of the property in question .
We require a condition of a simpler formal character , one which does uot require us to solve the difficult problem as to whether an assigned trigonometrical series not only converges but also has for sum a function of bounded variation .
I have already indicated the corresponding answer in the case when the trigonometrical series is required to be the Fourier series of a function of a particular class .
If the class be the class of functions whose power is summable , this condition is that should be a bounded function of , where denotes the Cesaro partial summation of the series considered .
of the Fourier series of a function of bounded variation is that ious reasons.ustrates tfunction , aboutsu Cdition tseri serived sProf .
Young.ondition tThis reems torthy ottention oSociety forIn tresent communication Ipropose tshow tecessary a should be a bounded function of which all that we know is that it is summable , is necessarily more than merely summable , but it of itself justifies our regarding such derived series as having their definite place in our theory .
Moreover , the method by which it is obtained has an interest of its own .
It involves the consideration of bounded successions of integrals of positive functions , and we are led by the exigencies of the reasoning to conclude a priori the probability of such successions of integrals containing sequences .
It was , in fact , in this way that I was led to remark that this result is immediately deducible from easoning which I had already employed .
We have , in fact , the following theorem : the integrands of a bounded succession of are bounded below in their ensemble , there is in every sub-succession of the succession of the integrals a sequence which converges to a lower semi- continuous upper semi-integral , in other words , to an asymmetrically continuous function of bounded variation of a certain type .
The cases in which we can assert that an oscmating succession contains a sequence are very few in Jlumber .
Almost the only one known is that discovered by ArzelA , and which , in the extended and modified form given to it by myself , the condition of uniform and homogeneous oscillation on one side at least .
Such successions have come to have a considerable theoretical importance in the abstract theory of sets , as well as in the applications to the theory of functions of a real variable .
It is noteworthy that in the present instance , though this does not come out in the proof , there is uniform and homogeneous oscillation on the left .
This follows indeed from a fact that I long ago signalised , viz. , that the non-uniformity of the oscillation of a succession of monotone continuous functions is always visible .
With regard to the main result of the paper it will be noted that it gives us at the same time the necessary and sufficient condition that a trigonometrical series should be the Fourier series of a function of bounded variation .
It may finally be remarked that if instead of expressing the Fourier coefficients of the Fourier series as ordinary integrals involving the function ntegrand , xpress terms oespect tndefinite integral othat function tiven tourierFourier series tifference being tunction wespect toseries identical wesponding oerived series ogonomet which the integration is to be performed is in the latter case a function of bounded variation which is not in general an integral .
S2 .
We first prove the theorem with respect to successions of integrals to which reference has been made .
Theorem.\mdash ; If a of integrals of functions which ( above ) in .
ensemble oscillates boundedly , there is in every sub-succession sequence of the integrals , converging to a lower semi-continuous uppe ( lower ) semi-integral .
It be sufficient to prove the former of the two alternative statements in the theorem .
Since the succession of integrals is bounded and that of the rands f is bounded below , the latter succession is semi-integrable below ; therefore all the upper functions and all the lower functions of the succession of integrals are upper semi-integrals .
* Again , from the fact that the succession is bounded below , it follows that has no negative double limit , as and , and accordingly thab the succession of integrals oscillates uniformly and homogeneously below .
Hence all the upper and all the lower funotions of the succession of integrals are lower semi-continuous functions .
Now an upper semi-integral is the sum of an integral , which is a con- tinuous function , and a monotone .
function , which , in our case , is accordingly a lower semi-continuous function , and therefore continuous the left .
But I have proved that , if all the upper , or all the lower , functions of a succession are continuous on one side at least , the same at each point for all such upper or lower limiting functions , then a sequence of the functions can be found having an unique limiting function .
In our case the functions are the integrals , so that , by this theorem , we can find a succession of integers , .
such that converges , as , to an unique limiting function , which , being one of the lower and upper limiting functions of the succession of integrals , is , by what has been W. H. Young , " " Semi-integrals and Oscillating Successions of Functions 'Lond .
Math. Soc. Proc 1910 , Ser. 2 , vol. 9 , pp. 300-301 , SS 15-16 .
W. H. Young , " " Successions of Integrals and Fourier Series , 1912 , vol. 11 , p. 51 .
W. H. Young , " " On Homogeneous Oscillation of Successions of Functions ibid. 1912 , vol. 8 , p. 366 , Cor. 4 .
First , to prove the sufficiency of the condition .
Since J is a bounded function of , the same is true of .
The integrands of these two integrals being positive , we can apply to each of them the theorem of S2 .
Thus we can find such a succession of integers , , that , for this succession of values of , the first of the integrals describes a sequence .
The corresponding values of the second integral form a sub-succession to which we again apply the theorem , and find .
succession of integers , , from among , so that as describes these values , the second describes a sequence .
Therefore as describes the succession , , both the integrals describe sequences , and therefore their difference , namely also describes a sequence .
By S2 , the limiting functions of the two first sequences are semi-integrals , and therefore functions of bounded variation .
Hence the limiting function of the last sequence , say is a function of bounded variation , and we have , say , ( 2 ) where 1913 .
] Series should have Form .
57.3 Since , ( x ) is a bounded function of , we may integrate term by term after multiplying both sides by .
Thus .
( 4 ) Similarly , multiplying ( 2 ) by mx and integrating term by term .
( 5 ) From ( 4 ) and ( 5 ) , const .
This shows that our trigonometrical series ( 1 ) is the derived series of the Fourier series of the function of bounded variation , provided the given condition is satisfied .
The condition is therefore sufficient .
Next to prove that it is necessary .
Let be the function of bounded variation , corresponding to which the series ( 1 ) is the derived series of the Fourier series .
Since is the difference of two monotone increasing functions , and therefore , where , 1 ( x ) and , 2 ( x ) are the Cesaro partial summations of the derived series of the Fourier series of these monotone increasing functions , it is only necessary to prove the necessity of the condition when the function of bounded variation is a monotone increasing function .
Now , when is a monotone increasing function , is positive , for Therefore , in this case is , and is given by the righthand side of ( 3 ) .
Denoting by the Cesaro partial summation of the Fourier series of which our series is the derived series , we have , therefore , where is the upper bound of the Cesaro partial summations of the Fourier series of , which , as is known , *converges boundedly in the Cesaro manner , since has bounded variation .
Thus the condition is necessary when is monotone increasing , and therefore also , in the general case , when ) is a function of bounded variation .
W. H. Young , " " On the Integration of Fourier Series 'Lond .
Math. Soc. Proc 1910 , Ser. 2 , vol. 9 , pp. , S3 .
Series .
S4 .
Bearing in mind what has been said in S1 , it will be seen that the following theorem completes the set of tests of the type considered:\mdash ; Theorem.\mdash ; The no ( jessary and suffic nt condition that a given trigonometrical series should be the Fourier of a bounded is that for all values of and being a constant .
That this condition is necessary is evident from mere inspection of the usual expression for .
That it is sufficient follows from reasoning of a similar but simpler character to that employed in the analogous theorems .
In fact , if is a bounded function of , the integrated series necessarily oscillates uniformly and homogeneously when summed in the Cesaro manner , index unity .
Accordingly , a sequence of these Cesaro partial summations can be found converging to an integral , since has the unique double limit zero when .
In other words , we have where , moreover , is a certain bounded function .
* Multiplying both sides of this equation by , or by , and integrating term by term , we see that the rated series is a Fourier series , having for corresponding function ; that is , the rated series is the Fourier series of the integral of a bounded function , whence the theorem follows .
' ' Successions of Integrals and Fourier Series , p. 31 .
|
rspa_1913_0055 | 0950-1207 | On a method of measuring the viscosity of the vapours of volatile liquids, with an application to bromine. | 575 | 588 | 1,913 | 88 | Proceedings of the Royal Society of London. Series A, Containing Papers of a Mathematical and Physical Character | A. O. Rankine, D. Sc.|A. W. Porter, F. R. S. | article | 6.0.4 | http://dx.doi.org/10.1098/rspa.1913.0055 | en | rspa | 1,910 | 1,900 | 1,900 | 12 | 181 | 4,974 | http://corpora.clarin-d.uni-saarland.de/surprisal/6.0.3/?id=rspa_1913_0055 | 10.1098/rspa.1913.0055 | null | null | null | Thermodynamics | 49.967514 | Tables | 39.733246 | Thermodynamics | [
-8.539999961853027,
-36.184417724609375
] | ]\gt ; On a Method of suring the Viscosity of the Vapours of Volatile Liquids , with an Application to Bromine .
By A. O. RANKINE , D.Sc .
, Fellow of and Assistant in the Department of Physics in University College , London .
Communicated by A. W. Porter , F.R.S. Received Apri122 , \mdash ; Read June 19 , 1913 .
) The determination of several of the physical properties of the halogens is rendered difficult by reason of their great chemical activity .
This is particularly the case where pressure measurements are involved , it almost impossible to choose a gauge fluid which is unacted upon by these elements .
It was in order to surmount this difficulty that the following method was devised , and this paper deals with its application to the determination of the viscosity of gaseous bromine at various temperatures .
It be seen that in the apparatus used the only possibility of chemical action is between the bromine and the glass , and the author has been given to understand that this does not occur to any appreciable extent .
Although originally designed for the purpose of avoiding chemical action , the method to be described appears to form a very suitable means of determining the viscosity of the vapour of any volatile liquid , the only data required being the saturation vapour pressures over a small temperature range and the densities of the liquid over the same range .
JIethod of The method is based upon O. R Meyer 's transpiration formula , and the modifications of the older methods consist in the special devices adopted for estimating the pressures at the two ends of the capillary tube , and for measuring the quantity of gas passing through it .
Fig. 1 shows an ideal form of the apparatus , which will suffice to indicate the principles involved .
A and are two glass bulbs connected by a capillary tube , and the FIO .
1 .
peratures oespective eosures Traversing theapparatus contains nothing biquid aapour.estrict tecure thecondense iWith adpressures iwere taturation vapour pressures aspecified tstimated either fumetained ahigher temperature tiquid wporate iRankine .
Method osuring t of liquid disappearing from A or from that condensing in , provided that $ the of the liquid be known .
All the data for measuring the viscosity of the vapour would then be available , and by maintaining the capillary tube at various temperatures higher than that of ( this to secure that no condensation should occur elsewhere than in B ) , the viscosities at those temperatures could be determined .
Further , the apparatus being symmetrical , measurements in alternate directions could be performed successively .
In practice , however , the experiment is scarcely so simple as this .
Owing to the smallness of the volume of liquid corresponding to a large volume of vapour , it is clearly desirable that the vessels A and should not be bulbs , but should take the form of graduated tubes , narrow in bore , although not of course , comparable in this respect with the capillary itself .
When this is the case it is found that with a capillary whose bore is of sufficient size to permit of accurate measurement , the pressures at the two ends are no ger equal to the saturation vapour pressures for the temperatures of the baths in which A and are immersed .
This is , of course , to be to the fact that when the rate of distillation through the capillary is large , heat can neither enter A nor leave rapidly enough to secure equilibrium between the liquid clnd its vapour .
The consequence is that the pressure in A is less than , and that in greater than the corresponding saturation pressures , and in order to find the true pressures means have to be adopted for estimating the above differences .
A consideration of the diagram of the apparatus actually used show how this was achieved .
It will be seen ( fig. 2 ) that the vessels A and are -tubes , sealed at the ends remote from the capillary .
They are enclosed in water baths , the temperatures of which differ by several degrees .
Let us suppose that that containing A is at the higher temperature .
temperature of the bath containing A must be lower than that of any other part of the apparatus except , and , with this restriction , the temperature of the bath containing the capillary tube may be maintained at the value at which it is desired to determine the viscosity of the vapour .
The vapour which evaporates from A passes through the glass spiral in order that it may be raised to the desired 1913 .
] Viscosity of the of Volatite Liquids .
temperature before the capillary .
After emerging from the other end it is eventually condensed to liquid in B. Now let us consider what happens in the closed limbs of the vessels A and B. The variations of level to which the liquid is subject in these limbs is not such as to involve appreciable evaporation or condensation Temp. , Temp. FIG. 2 .
there ; consequently the saturation pressures are maintained .
In the limbs adjacent to the capillary , however , owing to rapid evaporation and condensation , the pressures differ from the saturation values , but by amounts which can be easily estimated by the differences of level in the two limbs of the -tubes .
Thus suppose and are the temperatures of the baths containing A and respectively , and the densities of the liquid at these temperatures , and the pressures at the two ends of the and and the differences of levels of the liquid in the respective -tubes , .
( saturation pressure at ) ( saturation pressure at ) Thus , provided that the saturation vapour pressures and the liquid densities over a small temperature range are known , the pressures controlling the transpiration can be found without using anything in the nature of an ordinary pressure gauge .
Furbher , a of the specific volumes of vapour and liquid provides means of determining the rats of flow through the capillary , from observations of the volume evaporation and condensation of the liquid .
Although the results recorded here are confined to bromine , the method will probably be found suitable for measuring the viscosity of the vapours of such elements as iodine , phosphorus , and sulphur , besides many volatile organic substances .
The adjustment was , however , wholly effected in this manner , and it was rather surprising to find that the rate of evaporation was not greatly diminished .
The explanation lies in the fact that the pressure difference between the ends of the capillary assumed a higher value ; in other words , the experiment approached more nearly to the ideal case referred to in the beginning of this paper .
The -tubes A and were about 2 mm. in internal diameter , and each li was about 20 cm .
long .
They were graduated in millimetres and carefully calibrated .
The length of the capillary tube was about 39 cm .
, and the radius approximately cm .
In transpiration experiments , however , the dimension required is the effective value of , where is the length and the radius of the equivalent uniform capillary .
In orcler to allow for the oonical ends and other irregularities in the tube , calibration with a short thread of mercury was used in order to determine the sum , where is any short length and the radius in that neighbourhood .
The advantage of this method is that it gives proper weight to the retarding effects of the various portions of the tube , and indicates how far it is justffiable to ignore the viscous retardation in parts of the apparatus other than the capillary Viscosity of the Vapours of Volatile Liquids .
itself .
In the apparatus in question no correction comparable with the experimental error was necessary on this account .
The actual value of was c The method of obtaining the data necessary for calculating the rate of flow of gas and the pressures at the two ends of the capillary was to take time readings of the positions of the four liquid levels\mdash ; two on the evaporation side and two on the condensation side .
The masses of bromine evaporating and condensing in the same given time were always found to be nearly equal , but calculations have been made from the rate of evaporation only , since there was no guarantee that the whole of the condensed vapour found its way at once into the liquid already there ; in other words , the amount of liquid in the process of flowing down the walls of the condensation tube at ven instant was not necessarily constant .
The readings on the condensation side were , however , necessary for the estimation of the pressure , and the difference of level both on this side and on the evaporation side throughout an experiment were found in.each case .
An experiment usually lasted rather more than an hour , 12 or 14 observations of each level being taken in this time .
The temperatures both in the baths A and and in the tank were obtained by means of thermometers specially standardised for the purpose , the probable accuracy bsing C. in the case of A and , and an amount varying from C. to C. according to the temperature in the case of C. The apparatus was entirely devoid of taps both in its final form and during the process of filling , absence of tap grease being regarded as necessary in order to avoid the production of impurities due to chemical action upon it by the bromine .
The bromine used was of the purest quality supplied by Kahlbaum .
Some difficulty was experienced in securing that the contents of the apparatus consisted only of the liquid and its vapour .
Eventually the following method of procedure was adopted with success .
The was first of all evacuated as far as possible by means of a mercury pump , the latter then being sealed off , leaving charcoal tubes which could be placed in liquid air to remove final traces of permanent gas .
The liquid bromine was then introduced by breaking off the end of a narrow tube placed below its surface .
When a sufficient quantity had entered , the narrow tube was sealed off .
With the charcoal tubes now in liquid air , a portion of the bromine was allowed to evaporate so as to rid it of gases which might be dissolved in it , and finally the charcoal tubes were sealed off , and the liquid distilled into the -tube A. It was noticed that , even after this procedure , a small quantity of permanent gas had survived ; indeed circumstances at this stage seemed to Dr. A. O. Rankine .
Method of Measuring the [ Apr. indicate that the bromine vapour exercised a displacing action upon gases condensed in the charcoal , and it was only by making use of a series of separate charcoal tubes that the impurity was reduced to an amount which would not seriously affect the measurement .
Although a small admixture of foreign gas would not greatly alter the viscosity , it was important to remove any trace of it from the closed limbs of the -tubes , otherwise the pressures , at these points would not have the estimated values , namely , the saturation of the bromine .
This was done by successive condensation and evaporation of the bromine in the -tubes , and that the process had been successftll was evident from the fact that afterwards , if the closed limbs were cooled , they would become completely filled with liquid .
Calculation of Results .
Meyer 's transpiration formula , upon which the present method of measurement is based , is where is the viscosity , the radius and the length of the capillary tube , the time during which a volume enters the tube , and and the respective pressures at the ends where inflow and outflow cur .
This formula is developed upon the assumption that the gas in question obeys Boyle 's law .
It is quite possible , therefore , that if we are dealing with a gas which is only slightly superheated , we may not be justified in using this means of finding the viscosity .
Indeed , this very fact may be the cause of certain irregularities which are observed in the'case where the temperature of the capillary tube is only a few degrees above that of the evaporating bromine .
For lack of precise information on this question , however , there was nothing to be done but to assume the validity of the formula in all cases .
The same objection possibly applies also to the assumption that Charles ' law is true for the vapour in the rarefied condition in which it was used , as has been done in order to connect the volume of liquid evaporating with that of the gas entering bhe capillary .
Both these points will be treated more fully later in the paper .
With the above assumptions we may write in the transpiration formula where absolute temperature of the capillary , and being normal pressure and temperature , and the volume of gas reduced to N.T.P. Further where is mass of gas traversing the capillary and its density at N.T. 1913 .
] Viscosity of the of Volatile Liquids .
Meyer 's formula therefore becomes the quantities variable from one experiment to another being and The density of bromine at N.T.P. , i.e. , was estimated from the value of the atomic weight , , relative to oxygen .
The value obtained and used was .
per cm.3 .
As has been shown , the vapour pressure of bromine and the density of the liquid over a temperature range from C. to about C. were needed in order to calculate and from the experimental observations .
The densities were necessary to obtain in terms of the volume of liquid evaporating .
For the former purpose the vapour pressures due to Ramsay and Young* were taken , and to their observations was fitted , by the method of least squares , over the small necessary temperature range a parabolic formula , so as to be able to interpolate .
The values of the densities of liquid bromine at various temperatures were taken from the mutually consistent results of Pierre , Quincke , .
D. van der Plaats , S and Andrews and Carlton They range from c at C. to c at C. Small corrections were also applied for the expansion of the capillary tube with temperature and for the slipping of the gas over its internal walls .
The former correction amounted to about per cent. at the highest temperature at which observations were taken ; the latter , which would have been almost .
igible had the gas been at atmospheric pressure , was comparatively important by reason of the fact that the average pressure in the experiments was of the order of 10 cm .
of mercury only .
The correction for slipping , aa is well known , amounts to multiplying the original Meyer 's expression by the factor , being the radius of the capillary and a quantity which differs little from the mean free path of the gas molecules under the conditions of the experiments .
The value of needs to be known only approximately for correction purposes , and in the present cases a sufficiently accurate value was obtained by adopting the method used by the author in previous determinations , namely , to calculate from the approximate value of the viscosity , using the customary formula based on the kinetic theory .
Ramsay and Young , ' Chem. Soc. .Tourn .
, ' 1886 , vol. 49 , p. 453 .
Pierre , 1848 .
Quincke , 1868 .
Andrews are obtained from Landolt and Born'Roy .
Soc. Proc 1910 , , vol. 83 , p. 617 .
VOL. LXXXVIII.\mdash ; A. 2 582 Dr. A. O. Rankine .
Method of suring the [ Apr. 22 , More accurate values of can , if required , be subsequently obtained by the method.of repeated substitution .
Owing to the rarefied condition of the gas esent morrections occount oippingwere ceater , ounting taccordingVa othat tiscosit othough evidence wiven 1ater tromine to the temperature .
range , independent of the pressure , it has been thought desirable to record the values of and and their mean value .
These are given ( in centimetres of mercury ) in Columns 2 , 3 , and 4 of Table I , where the results of all the experiments are tabulated .
The rates of transpiration , i.e. the number of grammes of vapour traversing the capillary per second , are also given in Column 5 .
It may be mentioned , in this connection , that calculations were made to see whether an appreciable reduction in driving pressure was brought about by the velocity of transpiration of the vapour , but the amount was found to be much below the probable accuracy of the measurements .
Table I. It will be noticed that , in each of the groups indicated above , the temperatures are approximately the same , and that the variations in values of the 1913 .
] Viscosity of the of Liquids .
viscosity in any group amount to about 1 per cent. This , indeed , represents very nearly the degree of accuracy which could be expected from the form of apparatus used .
In Table II there are collected the mean values deduced from the previous table , and the same data are shown graphically in fig. 3 .
Table Il .
FIG. 3 .
In view of the number of separate observations taken at the various temperatures , the probable error is considerably less than 1 per cent. Discussion of Results .
There are several points of interest in connection with the results which been obtained .
the first place , it is possible to compare one of resent determinations wRankine.orresponding determinationMethod osuring t ifferent apparatus aethod 1eems jbtained iemperatures onder cifferent feasured beans oiscosity iound tbtain.uthor bdifferent mityThe vbtained wresent caseof bromine.vapo.easured aatmo.spheric pressureat.emperatur .
therefore , to conclude that the viscosity of this vapour is independent of the pressure , at any rate , through the range from 9 to 76 cm .
of mercury , notwithstanding the fact that it may be only comparatively slightly superheated .
It is worthy of notice also that the accordance of these two results suggests that within the degree of accuracy attained in these viscosity measurements it is probable that Boyle 's law is valid , and its use in the calculation of these results permissible , at and above the temperature in question .
When we come to consider the mode of variation of the viscosity with temperature , we are met with the , at first sight , surprising result that the viscosity increases more and more rapidly as the temperature rises ( fig. 3 ) .
The experimental points lie on a curve which is at first concave upwards and becomes practically straight at the higher temperatures .
As far as the author is aware , no previous viscosity determinations with any gas have indicated this type of variation with temperature .
No gas even approximately obeys the law deduced from the simple kinetic theory over the temperature range which has up to the present been treated experimentally ; but the departures from this law hitherto served have not been sufficiently emno doubt , emperatures tiscosity overy gdgreat turvature oyinteresting tbserve tquation which Sroposed doesthe connecting viscosity wemperature.onnection iquare remperature , departures from this law are great enough to produce an actual inflexion in show such an inflexion .
The curvature of his curve ( and being constants ) changes sign at or C. This has , the author believes , not been called attention to previously , probably because no such variation has been found experimentally .
For , for 'Boy .
Soc. Proc 1912 , vol. 86 , p. 166 .
1913 .
] Viscosity of the Vapours of Liquids .
instance , the value of which ) been found is 113 , and assuming Sutherland 's equation to be valid at such temperatures , measurements of the viscosity at absolute would be necessary to reach the point of inflexion , and at still lower temperatures to indicate the upward curvature .
In this region the nitrogen would be normally liquid ; indeed , speaking generally , all gases are so at the absolute temperature , so that from this point of view experiments with the vapour at low pressures would be required to indicate this type of variation .
This is , in fact , what has been done in the present case , and although it turns out , upon closer consideration , that the correspondence , from other standpoints , between the experimental results for bromine and Sutherland 's equation is by no means close , yet the very fact that the inflexion of the curve appears both practically and theoretically seems to favour the view that the modifications of the simple kinetic theory introduced by Sutherland are upon the right lines .
However , the attempt to fit Sutherland 's equation to the experimental points as they stand is unsuccessful .
The equation involves that at absolute zero the slope of the curve is zero , and a reference to fig 3 will show that the positions of the points are not such that a continuation of the curve through them would satisfy this condition .
If , however , the two lowest temperatures are omitted from the calculation , very good agreement with Sutherland 's equation is shown by the remaining four .
The full curve in fig. 3 represents the equation fitted to the upper four points , and it has been continued down to absolute zero , both to show the divergence for the lower points and the point of inflexion previously referred to .
In the following table ( Table III ) are given the observed values of the viscosity and the values calculated according to the equation Table IIL Dr. A. O. Rankine .
Method of Measuring the [ Apr. 22 , There is obviously more probability that the equation of Sutherland will approximate more closely to the facts at higher than at lower temperature .
Indeed he made no claim that it would be valid where the gas was only slightly superheated .
The changes necessary to be made in the gas theory of inflexion .
owest point ibservations uhichmust aretain aaise tointAn aternative eanation ocurve this value is based the vapour was so slightly superheated ( a few degrees only ) , and that consequently it could not be treated as a perfect gas in the calculation of the viscosity .
It seems unlikely , however , considering the fact that the pressure was so low , that an error so large as 6 per cent. would be introduced on this account .
One other point , perhaps , also deserves mention .
No data are available to show what degree ( if of association exists in the bromine vapour under the circumstances of the experiments .
Obviously this might have an important effect , particularly if , as is almost certain , dissociation occurred with rise in temperature .
The agreement between the values at C. , but at considerably different pressures , previously referred to is distinctly against the occurrence of appreciable association , at any rate , at that temperature .
These considerations only apply to the lower temperatures , and we may take it that at the higher temperatures Sutherland 's law fits in with the facts to a considerable degree of accuracy .
It is possible , therefore , to test the agreement or otherwise of the data presented in this paper with the two laws in connection with gaseous viscosities which the author has previously shown to apply in other cases .
* The first of these is that , for a large number of gases , Sutherland 's constant is proportional to the critical temperature , the relation being expressed by the equation The critical temperature of bromine , according to Nadejdine , is absolute , and the above ratio has the value .
This ratio is distinctly higher than , and in this respect bromine is similar to chlorine , the ratio for which is It appears , therefore , that although various gases without distinction of kind obey this law approximately , still better agreement is obtained when the application is confined to a single group in the periodic system .
'Roy .
Soc. Proc 1910 , , vol. 84 , p. 190 ; 'Phil .
Mag January , 1911 , p. 47 .
'Roy .
Soc. Proc 1912 , , vol. 86 , p. 166 .
1913 .
] Viscosity of the Vapours of Volatile Liquids .
The second law may be stated as follows : the group of inert gases the square of the viscosity at the critical temperature is proportional to the atomic weight , or constant In this numerical valne is in C.G.S. units and A is the atomic weight relative to oxygen .
It should be pointed out that is not the viscosity in the critical state , but merely the viscosity at the critical temperature , when the pressure has such values that the viscosity is independent of it .
Using the values of the viscosity of bronnne given in this paper , and those for chlorine communicated in a previous paper , it is possible without violent extrapolation ( some C. in the case of chlorine , and C. in the case of bromine).to obtain by means of Sutherland 's equation the viscosities at the critical temperatures .
These values are based upon Knietsch 's determination abs .
for the critical temperature of chlorine , and Nadejdine 's determination ) for bromine .
Applying these estimates to the test under consideration the results are as follows:\mdash ; It will be at once seen that the numbers in the last column are practically identical , although not at all the same number as that for the inert gases .
This suggests the possibility of the law in question being of wider application than merely to the inert gases , with the restriction that the constant of proportion is not universal , but has values peculiar to each group in the periodic table .
Finally , the values of the viscosity have been used to estimate the molecular dimensions of the two gases .
For this purpose the number of molecules per cubic centimetre at N.T.P. has been taken as , and Sutherland 's correction arising from the intermolecular attractions has been applied .
The molecular diameters and volumes are both recorded in Table Mr. A. E. Oxley .
[ May 8 , Table V. BromineCblorine 3 .
1..30169 Apparently the dimensions of the molecules do not differ to any great extent , and this , of course , involves that the density of the atom of bromine is something like twice as great as that of chlorine .
The Hall Effect in Electrolytes .
By A. E. OXLEY , M.Sc .
, B.A. , Senior Scholar and Coutts Trotter Student , Trinity College , Cambridge .
( Communicated by Sir J. J. Thomson , O.M. , F.RS .
Received May 8 , \mdash ; Read June 19 , 1913 .
) Introduction .
The distortion of the lines of flow of an electric current in a thin metal plate by the action of a magnetic field was discovered in 1879.* Hall attributed this to the action of the magnetic field on the molecular currents in the metal film , which were deflected to one side or the other and accompanied by a corresponding twist of the equipotential lines .
This explanation did not pass without criticism , and another theory of the effect found by Hall was published in 1884 .
In that paper the author seeks to explain the effect by assuming a combination of certain mechanical strains and Peltier effects , a thermo-electric current being set up between the strained and the unstrained portions .
The effect of such strain was to produce a reverse effect in some metals , and these were precisely the metals for which the Hall effect was found to reverse .
' Aluminium was the only exception .
In other respects , however , as shown by Hall in a later paper , S Bidwell 's * E. H. Hall , ' Amer .
Journ. Math vol. 2 , p. 287 ; 'Phil .
Mag 1880 , , p. 225 .
S. Bidwell , ' Roy .
Soc. Proc 1884 , vol. 36 , p. 341 .
'Nature , ' vol. 29 , p. 614 ; 'Chem .
News , ' vol. 49 , p. 147 .
S 'Science , ' vol. 3 , p. 387 ; 'Phil .
Mag 1885 , vol. 19 , p. 419 .
|
rspa_1913_0056 | 0950-1207 | The hall effect in liquid electrolytes. | 588 | 604 | 1,913 | 88 | Proceedings of the Royal Society of London. Series A, Containing Papers of a Mathematical and Physical Character | A. E. Oxley, M. Sc., B. A.|Sir J. J. Thomson, O. M., F. R. S. | article | 6.0.4 | http://dx.doi.org/10.1098/rspa.1913.0056 | en | rspa | 1,910 | 1,900 | 1,900 | 15 | 283 | 5,196 | http://corpora.clarin-d.uni-saarland.de/surprisal/6.0.3/?id=rspa_1913_0056 | 10.1098/rspa.1913.0056 | null | null | null | Electricity | 60.349549 | Tables | 15.598126 | Electricity | [
-15.428869247436523,
-64.44414520263672
] | ]\gt ; Mr. A. E. Oxley .
[ May 8 , Table V. BromineCblorine 3 .
1..30169 Apparently the dimensions of the molecules do not differ to any great extent , and this , of course , involves that the density of the atom of bromine is something like twice as great as that of chlorine .
The Hall Effect in Electrolytes .
By A. E. OXLEY , M.Sc .
, B.A. , Senior Scholar and Coutts Trotter Student , Trinity College , Cambridge .
( Communicated by Sir J. J. Thomson , O.M. , F.RS .
Received May 8 , \mdash ; Read June 19 , 1913 .
) Introduction .
The distortion of the lines of flow of an electric current in a thin metal plate by the action of a magnetic field was discovered in 1879.* Hall attributed this to the action of the magnetic field on the molecular currents in the metal film , which were deflected to one side or the other and accompanied by a corresponding twist of the equipotential lines .
This explanation did not pass without criticism , and another theory of the effect found by Hall was published in 1884 .
In that paper the author seeks to explain the effect by assuming a combination of certain mechanical strains and Peltier effects , a thermo-electric current being set up between the strained and the unstrained portions .
The effect of such strain was to produce a reverse effect in some metals , and these were precisely the metals for which the Hall effect was found to reverse .
' Aluminium was the only exception .
In other respects , however , as shown by Hall in a later paper , S Bidwell 's * E. H. Hall , ' Amer .
Journ. Math vol. 2 , p. 287 ; 'Phil .
Mag 1880 , , p. 225 .
S. Bidwell , ' Roy .
Soc. Proc 1884 , vol. 36 , p. 341 .
'Nature , ' vol. 29 , p. 614 ; 'Chem .
News , ' vol. 49 , p. 147 .
S 'Science , ' vol. 3 , p. 387 ; 'Phil .
Mag 1885 , vol. 19 , p. 419 .
1913 .
] The Hall Effect in Liquid Electrclytes .
theory did not stand the test of experiment , and results lend no support to his theory , while they are in complete accordance with the explanation that the molecular currents are disturbed by the action of the magnetic field .
On the electron theory of metallic conduction , the mechanism of the Hall effect is more obvious , but at present no satisfactory explanation of the reversal found in some metals is known .
Furth experiments have made it clear that there is a real deflection of the elementary currents , due to the application of the magnetic field , independent of any effect due to strain .
The first attempt to measure the Hall effect in gases was made by Marx in 1900 .
* The velocities of the ions from flames are about one million times the ionic velocities in liquids , and , is very important , there is in this case a considerable difference between the velocities of the two kinds of ions .
Marx succeeded in showing that a small though appreciable Hall effect existed in such flame ases and verified completely the predictions of the convective theory .
In 1902 , H. A. Wilson showed that the Hall effect was large in the positive column of the discharge tube , at low pressures , the effect being proportional to the intensity of the magnetic field .
There are certain considerations which lead us to suppose that a true Hall effect exists in liquid conductors .
In the first place , a liquid conductor contains ions which , owing to their motion , constitute elementary molecular currents .
In the second place , it has been established that the presence of strains is not an essential factor in the production of the effects sought .
Although the effect will necessarily be small , on account of the low value of the mobility of the ions in electrolytes , still there is reason to suppose that it does exist and that the difficulty lies in our not being able to appreciate the small effects , which are likely to be masked by disturbing forces .
Review of Past Work on liiquids .
RoitiJ in 1882 , attempted to observe the 'Hall effect in a thin liquid amina , the liquid being enclosed between two plates of glass ( 55 mm. mm. ) separated by a distance of mm. The results obtained were complex and difficult to interpret .
Roiti holds the opinion that they are due to local variations of concentration .
In 1896 Roiti 's research was repeated by Bagard , S who claimed to establish ' Ann. der Phys 1900 , vol. 2 , p. 798 .
'Proc .
Camb .
Phil. Soc 1902 , vol. 11 , p. 249 .
'Atti R. Accad .
Lincei , ' 1882 , vol. 12 , p. 397 .
S ' Count Rendus , ' 1896 , vol. 122 , p. 77 ; 1896 , vol. 123 , p. 1270 .
590 Mr. A. E. Oxley .
[ May 8 , the existence of the Hall effect to a high degree in liquids .
In Bagard 's experiment the liquid layer was horizontal and the bounding plates were 53 mm. mm. , the distance between the plates being mm. A water bath wrevent disturbances demperature variations .
Thepole pieces olectromagnet hquare plates ( side)attachedto tlates weparated bdistance oagard considered that the field was uniform in the central region of the lamina .
Here it is important to consult a research by concerned with the alteration of the concentration of a salt solution placed in a non-uniform magnetic field .
The effect of such variations of concentration , even if they occur at the boundary of the lamina only , will be sufficient , in a short time , to produce diffusion of the salt from the central region .
This may give rise to a potential difference which is considerably greater than the estimated value of the Hall effect .
As Boiti had found , the effect was not produced instantaneously ; the rate of growth was large at first and small afterwards and varied with the concentration of the solution .
Both Bagard and Roiti used a capillary electrometer to measure the transverse potential difference .
Shortly afterwards , Bagard 's research was repeated by Florio , under precisely the same conditions .
He obtained a negative result , and attributed the large effects found by Bagard partly to disintegration of electrodes and partly to disturbances produced by vibrations .
The dimensions of the lamina used by Florio were 11 cm .
cm .
mm. , and the pole pieces had a diameter of 13 cm .
The experiments of Bagard have been further tested by Chiavassa , who took every precaution to reproduce the original conditions as accurately as possible .
He concluded that the effect observed by Bagard was spurious and due to variations of temperature and of concentration , the latter being caused by non-uniformity of the magnetic field over the region occupied by the lamina .
Chiavassa found that a small liquid film exposed to a uniform netic field gave no indication of a Hall effect .
A capillary electrometer , which would detect volt , was used to measure the transverse potential difference .
Two more attempts have been made to discover the existence of the Hall effect in liquids .
Ihese were made in 1904 by HeilbrunS and in 1908 by Delvalez Heilbrun used a triple cathode and investigated the redistribution ' Gott .
Nach 1910 , p. 646 .
'Nuovo Cimento , ' 1896 , vol. 4 , p. 106 ; 1897 , vol. 6 , p. 108 .
'Nuovo Cimento , ' 1897 , vol. 6 , p. 296 .
S 'Ann .
der Phys 1904 , vol. 15 , p. 988 .
'Journ .
de Phys 1909 , vol. 8 , p. 360 .
1913 .
] The Hall Effect in Liquid Electrol.ytes .
of the deposit on each portion under the action of a magnetic field .
The small variations observed were attributed to movements of the electrolyte .
Delvalez used an alternating primary current and a telephone as indicator in the transverse circuit .
He showed that the Hall coefficient , if it exists , does not exceed the value 5 , amagnitude nearly ten thousand times greater than that which theory indicates .
* The question of the existence of a true Hall effect in liquid electrolytes is therefore an open one .
It seems probable , however , that such an effect exists , and that itis because the methods hitherto adopted to detect it have not been delicate enough that no satisfactory confirmation of the theory has been made .
Mr. H. L. P. Jolly , of Trinity College , placed his galvanometer , designed by Prof. Paschen , at my disposal , and I resolved to make an attempt to detect the effect indicated by theory .
With the aid of such a delicate instrument it was hoped at least that the upper limit of the value of the Hall coefficient , , obtained by Delvalez , would be considerably reduced .
The value of the expected effect will now be considered .
If the potential gradient of the Hall effect along the axis be denoted by , and the potential gradient between the primary electrodes by , then Donnan has shown that , ( 1 ) where is the strength of the magnetic field , and are the velocities acquired under unit force byl -mol .
of positive and negative ionic matter , is the valency of each ion and is the quantity of electricity per gramme- equivalent of ionic matter .
and NI are two factors depending for a partially dissociated electrolyte on the equilibrium equation , and are connected with the concentration of the dissociated salt and of the undissociated salt , by the relations Writing and , where and are the velocities aoquired by a gramme-molecule of positive or negative ionic matter under unit potential gradient , the coefficient of the Hall effect is * Donnan , ' Phil. Mag 1898 , vol. 46 , p. 465 ; Larmor , Bther and Matter , ' p. 301 ; van Everdingen , ' K. Akad . .
Wetensch .
Amsterdam , ' vol. 1 , p. 27 .
is the velocity acquired by -moL of undissociated salt when acted on by unit force .
Mr. A. E. Oxley .
[ May 8 , Donnan shows that the value of the Hall coefficient , assuming that the elecGrolyte is completely dissociated is and the transverse potential difference due to it will be for a fall of 1 volt per centimetre between the primary electrodes .
If gauss and cm .
, then volt .
Superposed on this effect is the difference of potential due to change of ionic concentration*and this is shown by Donnan to have the value .
( 2 ) Taking cm .
, and volG per centimetre , we have , for a field of gauss , volt , for a completely dissociated electrolyte .
is larger than .
Nevertheless this potential difference , if it can be measured , will be as true an indication of the existence of a Hall effect as the potential difference is .
Further , on the above theory , the existence of implies that of In the experiments described later it was found difficult to make observations within 15 seconds from the moment of exciting the magnetic field , so that probably the resultant of the two effects was observed .
It is impossible to measure the initial Hall effect , which is twice as large as the stationary Hall effect , because the stationary state has been reached by the time an observation is taken .
The effect arising from ( 1 ) will , in what follows , be referred to as the true Hall effect , while that arising from ( 2 ) will be called the concentration Hall effect .
Description of Apparatus and Method .
Fig. 1 is a diagram showing the arrangement of the apparatus .
are the pole pieces of the electromagnet and is the liquid lamina placed between them .
The primary circuit through the cell containing the liquid a is completed by the resistance and the primary current is supplied by the battery The electromagnet circuit contained three rheostats , a reversing key , and a Siemens-Halske ammeter A. A battery of 20 large cells supplied the current .
Vide Donnan , .
cit. , p. 468 .
1913 .
] The Hall Effect in Liquid Electrolytes .
represents the Paschen galvanometer .
is a control magnet fixed vertically above the galvanometer so that the sensitiveness could be varied by raising or lowering it , while the zero could be adjusted by turning it round .
The distance from the electromagnet to the galvanometer was 25 metres .
At this distance the effect of the permanent field when the magnet was excited was small and varied from one experiment to another , depending upon the distance between the pole pieces and the intensity of the exciting current .
Throughout an experiment this small change of zero remained of constant amount .
This form of galvanometer possesses advantages over the Broca galvanometer in that its period of swing for maximum sensiliveness is secs .
only , as compared with secs .
, while its normal sensitiveness is 10 times that of the Broca galvanometer .
The galvanometer was mounted on a stone slab supported by pillars which are built into the foundation of the Cavendish Laboratory .
But during the day time the galvanometer zero unsteady and therefore the observations were made at .
On one evening only were slight erratic disturbances noted , otherwise the zero was very steady .
The suspended system of the galvanometer consists of a fine glass rod about 8 cm .
long , to the centre of which is attached a plane rectangular Mr. A. E. Oxley .
[ May 8 , mirror ( fig. 2 ) .
The system was 1nade almost perfectly astatic by two groups of nets M and M2 , each consisting of 15 small magnets fixed to the glass rod .
The system was suspended by a fine quartz fibre , so that and each filled an.oval-shaped cavity formed by a pail of coils .
When all the four coils are connected in series , as in the present experiments , the resistance of the galvanometer is 16 ohms .
The Cells .
For Liquids : The outside dimensions of the cell are mm. To construct one , a micro-square was taken and four small blocks of ebonite , cut from the same ring and approximately 1 mm. thick , were fixed at the four corners by specks of Canada balsam .
A second micro-square was cemented to the tops of these , and three sides of the skeleton so formed .a adjustmentTh eransverse eectrodes oopper wireebonite bocks , rimary eectrodes oopper wirewere swith beeswax aesin .
Sulphate Gopper sphate g prepared , placed upon the table of a microtome and frozen with ether .
Thin sections of the gel were cut , thrown into water for a few moments , withdrawn and mounted on sheets of mica .
The edges of the gelatine film were trimmed so as to form a square of about 2 cm .
side .
Fig. 4 is a diagram of the cell .
The adjustment of the transverse electrodes FIG. 3 .
FIG. 4 .
to the same equipotential was made by scraping away the gelatine .
In order to secure good contact of the electrodes with the gel , the electrodes were laid in position on the microtome section and a layer of warm gel was 1913 .
] The Hall Effect in Liquid painted over them .
The positions of the thicker layers of gelatine are shown by the shaded areas of the figure .
The type ( a ) of cell was mounted on a rigid brass support ( fig. 5 ) , which was fixed to a heavy lead block B. The latter rested on a slate bed , which had square rails sorewed to it , and on these rails slid a brass carrier , whose position could be adjusted by a screw motion .
The movable electrode was attached to the glass rod , and adjustments corresponding FIG. 5 .
to 1/ 1800 of the applied primary potential gradient could be made by the pointer over one division of the scale D. A Grassot fluxmeter was employed to measure the intensity of the magnetic field and , with the search coil used , the full scale deflection corresponded to 22,300 gauss .
The creep of the pole pieces was prevented by a wedge of brass .
To ensure that the temperature in the neighbourhood of the cell remained constant during an experiment , a small platinum thermometer was inserted just inside the gap .
This thermometer was provided with compensating leads , and the temperature measured as shown at ( fig. 1 ) .
A very small primary voltage was applied to the cell and the movable electrode adjusted or the equipotential lines twisted until the galvanometer gave a small deflection only .
The primary potential gradient was now increased , and the same operations repeated until a voltage was reached beyond which the galvanometer zero was unsteady owing to irregularities in the action of the cell .
The constancy of the zero was tested carefully in each case .
The galyanometer circuit was now opened for a few seconds until induction effects due to the application of the magnetic field had died away , and the new zero of the galvanometer due to the presence of the magnetic field was noted .
Several deflections were taken , each about 10 seconds after closing the galvanometer circuit .
A similar series of observations was taken with the magnetic field reversed .
The importance of a uniform magnetic .
field cannot be overstated , for gravity , the lower layer is more dense than the upper one .
To avoid disturbances due to air currents the cell was surrounded with pads of cotton wool and the junctions in the galvanometer circuit enclosed in glass tubes .
The solutions were transferred to the cell by means of a capillary tube , and the presence of air bubbles thereby prevented .
A syphon was provided in the later experiments to keep the cell fulL Experiments .
Copper Sulphate Solutio ?
b.\mdash ; An estimation by the iodine method was made and the solution was found to contain .
of copper sulphate per litre .
In the following table is the zero position on the scale when the galvanometer circuit is open , is the deileoted position when the circuit is closed and the primary current is flowing , is the deflected position when , in addition , the magnetic field is applied .
A preliminary experiment was made on arch 1 , 1912 , the observations being taken to the nearest scale division only .
1913 .
] The Hall Effect in Liquid Electrol.ytes .
Field direct .
March 16 , 1912.\mdash ; Field direct .
Field reversed .
March 18 , 1912.\mdash ; The cell was washed out with copper sulphate solution and refilled .
The following readings were taken:\mdash ; Field direct .
* The alteration of the zero was produced by the fields of the electromagnet and the exciting circuit .
Ihe change of sign of in this and the two following experiments , for a direct field , is due to a reversal of the galvanometer terminals .
Field reversed .
VOL LXXXVIII.\mdash ; A. Mr. A. E. Oxley .
[ May 8 , March 19 , 1912.\mdash ; The cell was cleaned and refilled .
Field direct .
Field reversed .
March 22 , \mdash ; The cell was cleaned and refilled .
Field direct .
Field reversed .
Field direct .
1913 .
] The Effect in Laquid Electrolytes .
An examination of the tables given above shows that the mate value of the deflection is 1 cm .
for a field of 14,000 gauss .
This value may be taken as indicating the true order of the effect .
calibration of the galvanometer showed that one scale division ( i.e. 1 mm. ) represented ampere .
The resistance of the cell between the transverse terminals was found to be 615 ohms and as that of galvanometer is 16 ohms , the total resistance in the galvanometer circuit is 631 ohms .
Hence 1 mm. on the scale represents volt .
A deflection of 1 cm .
corresponds therefore to a transverse potential difference of volt .
The potential applied between the plimary electlodes was volt and as the distance ween the electrodes is cm .
, the primary potential gradient is volt per centimetre .
The distance between the transverse electrodes is cm .
From equation ( 1 ) we find , using these numbers , that the potential difference due to the true Hall effect will be volt , while from equation ( 2 ) the Hall ation effect will be volt .
This latter effect*is probably the one which ha been measured , and the former , which would give rise to a deflection of one or two scale divisions , is included .
These calculations are based on the assumption that the coppel sulphate solution is completely dissociated , but whatever the extent of the dissociation the order of the calculated effect is the same as that of the experimental effect ; for the function is continuous and steadily inoreases with the concentration .
Although the large disturbing forces which gave rise to the effects observed by Bagard have been much reduced , there is still the possibility that the small effect in the experiments may be due to a similar but far less effective cause .
But if so , it is difficult to see how any effect due to disturbances could give rise to such consistent resuIts as those found .
For not only was the liquid lamina changed for each experiment , the pole pieces were further apart in some cases than in others , and any erratic effect due to local disturbances would have had a opportunity of itself , if it had existed .
The effect observed appeared to grow for a short time but soon attained a steady value .
It was impossible to observe the early of the deflection because several seconds were needed for the netic field to attain its steady value and on the galvanometer circuit a reading could be taken only after an additional 10 seconds had elapsed .
When the netic It must be noted that in the calculation we have assumed that the solution is completely dissociated .
It can be shown that if , then becauHc .
Hence the calculated value is too low .
The solution contained .-equivalent per litre , and was therefore by no means completely dissociated .
Mr. A. E. Oxley .
[ May 8 , field was taken off , the deflection on closing the galvanometer circuit gradually became smaller .
At the suggestion of Sir Joseph Thomson , the following experiments were made on cells of copper sulphate gelatine in which movements of the solute as a whole are prevented .
Drude and Nernst*have carried out experiments on gelatine laminae , and they found that the large effect observed by the early experimenters did not exist .
Their means of investigation was not delicate enough , however , and it seemed interesting to test the above experiments on liquid copper sulphate by examining a gelatine film of the same salt .
To a strong solution of cQpper sulphate , estimated by the iodine method and found to contain 83 .
of copper sulphate per litre , was added sufficient gelatine to enable thin sections to be cut .
The gel contained 8 per cent. of copper sulphate by weight .
Two cells of the type ( b ) were constructed , and an experiment made with each .
The potential difference between the primary electrodes was 38 volts .
The following observations were taken:\mdash ; May 6 , ] 912.\mdash ; Field direct .
Field reversed .
Temperature C. Wiedemann Ann 1891 , vol. 42 , p. 668 .
1913 .
] The Hall Effect in Electrolytes .
May 7 , 1912.\mdash ; Field reversed .
Field direct .
The thickness of the laminae in the last two experiments was 30 .
From the tables it is seen that a deflection of 5 mm. was found on applying a magnetic field of 15,000 gauss .
This deflection disappeared within a minute from takino oflo the magnetic field .
The sensitiveness of the galvanometer was tested and 1 mm. was found to correspond to ampere .
The resistance of the lamina between the transverse electrodes was 2300 ohms , and therefore 1 mm. deflection corresponds to volt .
Hence the magnitude of the transverse effect is volt .
Using ( 1 ) , where volts centimetre , gauss , cm , we find that the transverse potential difference is volt ; while ( 2 ) gives a transverse1 potential difference of volt .
Experiments on ( a ) Silver lVitrate Solution , ( b ) Cadmium Sulphate Solution.\mdash ; ( a ) A solution containing 10 per cent. of silver nitrate was used .
This was contained in a cell made of mica , the inside dimensions of the cell being cm .
cm .
cm .
The primary electrodes were of silver , cm .
diameter ; the transverse electrodes , also of silver , had a diameter mm. The cell was mounted on a large sheet of mica which was fastened to one pole piece of the electromagnet .
The following readings were taken : \mdash ; Mr. A. E. Oxley .
[ May 8 , May 25 , 1912.\mdash ; Field direct .
Field reversed .
Temperature C. The deflection observed on applying a field of 14,800 gauss was 10 mm. The resistance of the cell between the transverse electrodes was 1200 ohms , and as 1 mm. deflection corresponded to ampere , the value of the transverse potential difference is volt .
The primary potential gradient was volt per centimetre , and the transverse electrodes were cm .
apart .
From these data the calculated value*of the transverse potential difference , assuming it to be a Hall concentration effect , as represented by ( 2 ) , is volt .
( b ) A 15-per-cent .
solution of cadmium sulphate was prepared .
The dimensions. .
of the cell were cm .
cm .
cm .
, and the electrodes were of cadmium wire drawn out to convenient thicknesses , the diameter of the primary electrodes being cm .
, that of the transverse electrodes 0 .
The following readings were taken:\mdash ; The values of for copper sulphate solution , silver nitrate solution , and cadmium sulphate solution are each equal to .
for a potential gradient of 1 volt per cm .
1913 .
] The Hall Effect in Liquid Electrolytes .
October 23 , 1912.\mdash ; Field direct .
Field reversed .
Temperature C. unequal values of are probably due to a small diffusion effect which would not reverse with the magnetic field .
The ection obtained on applying a field of 11,400 gauss was 7 mm. The resistance between the transverse electrodes was 220 ohms and as 1 mm. deflection was found to correspond to ampere , the transverse potential difference is volt .
The distance between the transverse electrodes was 2 cm .
and between the primary electrodes cm .
and the primary voltage applied was .
Using these data in ( 2 ) , the calculated value of the transverse potential difference is volt .
Conclusion .
In the above experiments the Hall concentration effect contributes the greater part of the potential difference , and the true Hall effect , which would give rise to a deflection of 1 or 2 mm. , is included .
It was hoped at the outset that some information as to the nature of the process of reversal would be obtained by an examination of electrolytes whose differences of ionic velocities vary considerably .
But the preponderance of the concentration effect , depending on the sum of the ionic velocities , has prevented this .
Eight experiments have been made and all the potential differences are of the calculated order , they reverse with the magnetic field and act in the same direction , while the experimental conditions vary widely .
These results are regarded as establishing the existence of a Hall effect in liquid electrolytes .
[ Note added January , 1913.\mdash ; The observations on copper sulphate solution are plotted in fig. 6 .
For low magnetic fields ( 8000 gauss ) the error of The Hall Effect in Liquid olytes .
observation amounts to 20 per cent. of the total deflection .
This error is attributed to disturbances in the cell .
The point A departs from the linear relation by 27 per cent. , while the point is approximately 10 per cent. out .
The points and correspond to a field of 14,000 gauss and the error of observation is smaller .
The mean positions of the pairs of points A-B and C-D are marked , and these lie approximately on a straight line passing FIQ .
6 .
through the origin .
Hence within the limits of experimental error the transverse potential difference is proportional to the znagnetic field .
It has been shown by Florio that the proportionality of the magnetic field and the large effect observed by Bagard may be due to the presence of vortical motions in the solution , and for this reason more reliance is placed on the uniformity of the effects observed and on the quantitative agreement with theory , in identifying the Hall effect , than on showing that a linear relationship exists between the netic field and the effect .
] The above experiments were made in the Cavendish Laboratory between Octobe .
, 1911 , and November , 1912 .
I wish to express my indebtedness to Sir Joseph Thomson for advice and criticism during the progress of this research and to Mr. H. L. P. Jolly for the loan of the galvanometer .
|
rspa_1913_0057 | 0950-1207 | \lt;italic\gt;Bakerian Lecture\lt;/italic\gt;:\#x2014;Rays of positive electricity. | 1 | 20 | 1,913 | 89 | Proceedings of the Royal Society of London. Series A, Containing Papers of a Mathematical and Physical Character | Prof. Sir J. J. Thomson, O. M., F. R. S. | lecture | 6.0.4 | http://dx.doi.org/10.1098/rspa.1913.0057 | en | rspa | 1,910 | 1,900 | 1,900 | 20 | 287 | 9,609 | http://corpora.clarin-d.uni-saarland.de/surprisal/6.0.3/?id=rspa_1913_0057 | 10.1098/rspa.1913.0057 | null | null | null | Atomic Physics | 37.249971 | Electricity | 20.315134 | Atomic Physics | [
11.1516752243042,
-73.03044128417969
] | ]\gt ; PROCEEDINGS OF THE ROYAL SOCIETY .
TICAL AND ScIEyCES .
BAKERIAN CTIJRE :of Electricity .
By Prof. Sir J. J. , O.M. , ] Lecture delivered received June [ PLATES 1\mdash ; 3 .
] In 1886 , Goldstein obseryed that when the cathode in a tube was pierced with holes , the electrical discharge did not stop at the cathode ; behind the cathode , beams of could be seen streaming through the holes in the way represented in fig. 1 .
He ascribed these pencils of light to rays FIG. 1 .
through the holes into the gas behind the cathode ; and from their associatlon with the channels through the cathode he called these rays Kanalstrahlen .
The colour of the light behind the cathode depends upon the gas in the tube : with air the light is yellowish , with hydrogen rose with neon the gorgeous neon red , the effects with this gas being exceedingly striking .
The rays produce phosphorescence when they strike ainst the VOL. LXXXIX .
Sir J. J. Thomson .
walls of the tube ; they also affect a photographic plate .
Goldstein could not detect any deflection when a permanent magnet was held near the rays .
In 1898 , however , W. Wien , by the use of very powerful magnetic fields , deflected these rays and showed that some of them were positively charged ; by measuring the electric and magnetic deflections he proved hat the masses of the particles in these rays were comparable with the masses of atoms of hydrogen , and thus were more than a thousand times the mass of a particle in the cathode ray .
The composition of these positive rays is much more complex than that of the cathode rays , for whereas the particles in the cathode rays are all of the same kind , there are in the positive rays many different kinds of particles .
We can , however , by the following method sort these particles out , determine what kind of particles are present , and the velocities with which they are moving .
Suppose that a pencil of these rays is moving parallel to the axis of striking a plane at right angles to their path at the point ; if before they reach the plane they are acted on by an electric force parallel to the axis of , the spot where a particle the plane will be deflected parallel to through a distance given by the equation where , are respectively the charge , mass , and velooity of the particle , and A a constant depending upon the strength of the electric field and the length of path of the particle , but quite independent of , or If the particle is acted upon by a netic force parallel to the axis of it will be deflected parallel to the axis of , and the deflection in this direction of the spot where the particle strilces the plane will be giveu by the equation where is a quantity depending on the magnetic field and length of path of the particle , but independent of .
If the particle is acted on simultaneously by the electric and magnetic forces , the spot where it strikes the plane will , if the undeflected position be taken as origin , have for co-ordinates B. ( 1 ) Thus no two particles will strike the plane in the same place , unless they have the same value of and also the same value of ; we see , too , that if we know the value of and , we can , from equation ( 1 ) , calculate the values of and , and thus find the velocities and character of the particles composing the positive rays .
Rays of Positive From equation ( 1 ) we see that .
( 2 ) all the particles which have a given value of strike the plane on a parabola , which can be photographed by allowing the particles to fall on a photographic plate .
Each type of particle in the positive rays will produce a separate parabola , so that an inspection of the plate shows at a glance how many kinds of ) articles there are in the rays ; the measurement of the parabolas , and the use of equation ( 2 ) , enablefi us to find the values of corresponding to them , and thus to make a complete analysis of the gases in the positive rays .
To compare the values of ?
to the different parabolas , we need only measure the values of on these parabolas corresponding to a constant value of .
We see from equation ( 2 ) that the values of are proportional to the squares of the values of Thus , if we know the value of for one parabola , we can with very little labour deduce the values of ) for all the others .
As the parabola corresponding to the hydrogen atom is foumd on practically all the plates , and as this can be at once recognised , since it is always the most deflected parabola , it is a very easy matter to find the values of for the other particles .
] made by the positive rays after they have suffered electric and ynetic deflections are reproduced in figs. 2 and 3 ( Plate 1 ) .
The apparatus I have used for the rays is shown in A is a bulb of from 1 to 2litres capacity in which the discharge passes , the cathode placed in the neck of the bulb .
The position of the front of the cathode in the bulb and the shape of the bulb where it joins the neck have a very considerable influence on the brightness of the rays and the distribution of velocities among the particles .
If the cathode projects into the bulb , the pressure of the in the bulb when the rays are the brightest is apt to be inconveniently low , and the same is true when , FIG. 4 .
FIG. 5 .
Sir J. J. Thomson .
though the cathode is kept in the neck , the bulb swells out gradually from the neck instead of off abruptly .
I have got the best results by 1naking the transition from the neck to the bulb as abrupt as possible and putting the front of the cathode flush with the junction of the neck and the bulb , in the way shown in fig. ; this gives better results than the cathode is placed as in The form of cathode which I have found to the best pencil of rays is shown in fig. 4 .
The front of the cathode is an aluminium cap , carefully worked so as to be symmetrical about an axis : this cap fits on to a cylinder made of soft iron with a hole bored along the axis ; the object of making the cathode of iron is to screen the rays from magnetic force while they are passing through the hole .
A case fitting tightly into this hole contains a long narl .
OW tube which is the channel though which the rays pass into the tube behind the cathode .
This tube is the critical part of the apparatus , and failure to obtain a good pencil of rays is generally due to some defect here .
As the length of this tube is very long in proportion to its diameter\mdash ; the length of most of the tubes I have used is about 6 and diameter from to mm.\mdash ; it requires considerable care to get it straight enough to allow an unintelTupted passage to the rays .
The method we use is to start with a piece of fine copper tubing and draw it out until the diameter is reduced to the right value , the proper length is cut off , and this is rolled between two surface plates , until optical examination sbows that it lets a pencil of light pass without obstruction through the tube ; it is useless to attennpt to experiment with positive rays unless this tube is exceedingly straight .
The rays themselves exert a sand blast kind of action on the tube and disintegrate the metal ; after prolonged use the metallic dust may accumulate to such an extent that the tube gets silted up , and obstructs the passage of the rays .
The cathode is fixed into the glass vessel by a little wax ; the joint is made so that the only channel of communication from one side of the cathode to the other is through the tube in the cathode .
The wax joint is surl.ounded by a water jacket to prevent the wax being heated by the discharge .
The arrangements used to produce the electric and magnetic fields to deflect the rays are shown at and M. An ebonite tube is turned so as to have the shape shown in fig. 4 , and are two pieces of soft iron with carefully worked plane faces , placed so as to be parallel to each other , these are connected with a battery of storage cells and furnish the electric field .
and are the poles of an electromagnet separated from and by the thin walls of the ebonite box : when the electromagnet is in action there is a strong magnetic field between and ; the lines of magnetic force and electric force are by this ement parallel to each other and the electric of Positire Electricity .
and netic fields are as nearly as possible coterminous .
This arrangement was adopted for a special investigation in which it was desirable that the fields should not overlap ; for many purposes , for example , the analysis of the gases in the tube , this condition is not important , and the simpler arrangement shown in fig. 6 answers all the requirements .
Here the ebonite box is done away with , the electric field is produced between two parallel plates of , and the UneCic field is produced by an ynet w poles are on opposite sides of the tube .
The arrangement used for the rays is that designed by Mr. Aston and described in the 'Phil .
Mag 1911 , vol. 21 , p. 227 .
Plates of soft iron are placed between the electroand the discharge tube to prevent the discharge ected by the gnetic field .
The pressure in the tube behind the cathode must be kept low , this is done by means of a tube containing charcoal cooled by liquid air .
The pressure on the other side of the cathode is much higher .
A typical photograph taken with this apparatus is reproduced in fig. 7 .
It will be noticed that in addition to the parabolic arcs whose origin has already been discussed , thele are a series of lines approximately These secondary lines are due to particles which have been charged for a part only of the time they were in the electric and magnetic fields and are therefore not so much deflected as those which were charged for the whole time which produce the parabolas .
Some particles which are when they enter those fields lose their charges before they get through , while others which are uncharged to begin with gain a charge before they leave the fields .
We can distinguish between these cases in the following way .
Make the magnetic field M. ( fig. 8 ) overlap the electric field , so that in the region EM the particles are exposed to but not to electric forces .
Sir J. J. Thomson .
A particle which begins by being uncharged and first picks up a charge in this region will experience a magnetic without an electric deflection , so that the trace made on the photograph by the particles which pick up a charge will resemble fig. 9 , Now , consider the trace made by the particles which started with a charge but lost it before they got through : these , when they are in the EM , will have already experienced a considerable deflection so that the place where they get a magnetic without an electl'ic deflection will be at the most deflected end of the line and the shape of the trace they make on the plate will be somewhat like An example of this effect is shown in the photograph reproduced in fig. 10 .
Unless the pressure in the observation chamber is very low , few of the particles remain charged during the whole of the journey through the electrostatic and magnetic fields , and in this case the parabolas disappear , and only the lines due to the secondaries appear on the plate .
The parabolas are determined by the values of , thus an atom with a single charge would produce the same parabola as a diatomic molecule with a double ] .
We can , however , by the following method distinguish between parabolas due to particles with a single and those due to particles with more than one charge .
The parabolas are not complete parabolas , but arcs starting at a finite distance from the vertical , this distance is by equation ( 1 ) inversely proportional to the maximum kinetic energy possessed by the particle .
This maximum kinetic energy is that due to the arge on the pal'ticle falling from the potential of the anode to that of the cathode in the discharge tube .
Consider now the particles which have two : these acquire in the discharge tube twice as much kinetic energy as the particles with a single charge .
Some of these doubly charged particks will lose one of their charges while passing the long narrow tube in the cathode , and will emerge as rticles with a single charge ; they will , however , possess twice as much kinetic energy as those which have had one charge all the time .
Thus the stream of singly charged particles from the tube will consist of two sets , as much kinetic energy as the other ; the particles having twice the kinetic energy will strike the plate nearer to the vertical than the others , and will thus prolong beyond the normal length the arc of the parabola corresponding to the singly eharged particle .
An example of this is shown in the photograph reproduced in fig. 11 , where the line , due to a singly charged en atom for which , is prolonged until its emity is only half the normal distance from the verticil .
line on Rays of Positive Etectricity .
the gives , hence we conclude that this line is due to an atom of oxygen with two charges , whereas if the oxygen line had not been we should have concluded that was due to a singly charged atom with an atomic If the atom acquired more than two charges the prolongation of the atomic line would be still longer .
If , for example , it could acquire eight charges it would be prolonged until its extremity was only one-eighth of the normal distance from the vertical .
An example of this is shown in fig. 12 ( Plate 2 ) , where is the line due to the charged mercury atom , this approaches to within one-eighth of the normal distance , and the theory is verified by the appearance on the plate of the lines , , which correspond to mercury atoms with 2 , 3 , 4 , 5 , 6 , 7 charges .
The lines due to the one with 8 cannot be detected , but the intensity of the lines diminishes as the charge increases , and it is perhaps itimate to conclude that with more sensitive apparatus the line corresponding to the atom with charges be detected .
Using this method to uish between singly and multiply systems we find that the particles which produce the parabolas on the raphic plates may be divided into the following classes:\mdash ; 1 .
Positively electrified atoms with one charge .
2 , Positively electrified molecules with one 3 .
ified atoms with multiple 4 .
atively electrified atoms .
5 .
atively electrified nlolecules .
The production of a charged molecule involves more than the detachment of a corpuscle from the molecule , that of a atom reqnires the dissociation of the molecule as well as the electrification of the atom .
As the results are so different we naturally ask , Is the mechanism by which the charged atoms are produced the same as that which the charged molecules ?
There seems to me to be evidence that the charged atoms and molecules are produced by different ents .
We not infrequently find that some of the parabolas have characteristic peculiarities such as abrupt changes in intensity .
An example of this is shown in figs. 13 and where several of the lines broaden at points which are all in the same vertical line , showing that the particles where the broadening commences have all the same kinetic energy .
This indicates that at certain places in the discharge tube there is an abnormally large production of the pSrticles corresponding to these parabolas .
It will be noticed , however , that it is only some of the parabolas which show this effect , there are others which Sir J. J. Thomson .
are of approximately the same intensity bout .
The measurement of the parabolas shows that the uniform ones correspond to atoms while those with the swellings correspond to molecules .
Thus we may at certain places in the dark space have great changes in the production of charged molecules without any change in the production of charged atoms .
This proves , I think , that ) two are produced by different agencies .
Another ument in favour of this view is the great variation that occurs in the relative intensities of the lines due to the atoms and molecules of the same element when the conditions of discharge are slightly altered .
I will confine myself to the case of the lines due to the atoms and molecules of hydrogen .
By altel.ing the } ) osition of the cathode in the neck of the discharge tube we can make the line due to the atom either more or less intense than that due to the molecule .
Thus if the cathode is well inside the neck line due to the atom is more intense than that due to the molecule , while if the cathode is pushed forward into the bulb the line due to the molecule is more intense than that due to the atom .
Examples of this difference are shown in figs. 14 and 15 .
These changes in the position of the cathode involve changes in the pressure of the , for to get the positive rays well developed the pressure has to be higher when the cathode is in the neck than when it rudes into the bulb , so that it would seem that reduction of pressure favours the formation of charged molecules more than that of charged atoms .
In the discharge tube we have cathode rays , positively electrified atoms and molecules , and rays analoo.ouso to soft rays ; all these are known to ionisc a gas when they pass through it .
As far as my observations have gone the properties of the positive rays indicate that the cathode particles produce the positively charged molecules , while the moving positively electrified particles produce the positively electrified atoms .
I do not mean by this that under no tances can a cathode particle produce a positively atom , for it would probably do so if it struck one of the structural corpuscles , i.e. one of those which bind the two atoms in the molecule together .
The number of molecules struck in this way would , however , be only a small fraction of those struck by the rays , so that if this were the only source of ionisation the number of charged atoms would be small compared with of charged molecules .
This , however , is not the case , so that we conclude that moving positively charged atoms and molecules are in the main responsible for the dissociation which produces the positively charged atoms occurring in the positive rays .
I will now pass on to the consideration of another very interesting type of positive ray\mdash ; the multiply charged atom .
I say atom advisedly , because of Etectricity .
it is doubtful whether we get among the positiye rays multiply charged molecules .
The indication of a multiple charge is that the line to the charged carrier is abnormally towards the The only case of a line due to a molecule for which I have observed a suspicion of such a prolongation is that of the line which corresponding to a molecule of nitrogen or carbon monoxide .
There is reason for doubting whether this is agenuine prolongation of the molecular line , as , since for aluminium , if any aluminium atoms from the cathode got into the discharge tube , the prolongation might be that of the atomic line of aluminium rather than that of the line due to the molecule of The rarity of the doubly charged molecule seems to indicate that the shock which produces the double charge is sufficiently intense to dissociate the molecule into its atoms .
The uniformity of the intensity of the parabolas corresponding to the multiply atoms shows that they acquire this at one operation and not by repeated ionisation on their way to cathode .
The occurrence of the multiple charge does not seem to be connected with the valency or other chemical property of the atom .
Of all the elements whose lines I have studied , hydrogen and ( see p. 14 ) are the only ones which have never appeared with a double .
Elements as different in their chemical properties as carbon , nitrogen , , chlorine , helium , eon , a new gas whose atomic weight is 22 , argon , crypton , mercury , all give multiply charged atoms .
The fact that these multiple charges so frequently occur on atoms of the inert gases proves , I think , that they are not produced by any process of chemical combination .
All the esults point to the sion that the occurrence and nitude of the multiple charge is connected with the mass of the atom rather than with its valency or chemical properties .
We find , for example , the atom of mercury , the heaviest atom I have tested , can have as many as 8 charges , crypton can have as many as 5 , argon 3 , neon 2 , and so on .
There is evidence that when these multiple occur the process of ionisation is generally such that the atom starts either with one charge or with the naximum number , that in the ionisation of mercury vapour , for example , the mercury atom begins either with 1 or with 8 , and that the particles which produce the parabola corresponding to 5 charges , for example , started with 8 and lost 3 of them on its way through the tube in the cathode .
The intensity of the lines corresponding to multiply atoms varies greatly with what are apparently but small alterations in the condition of the discharge , a slight alteration in the pressure or in the Sir J. J. Thomson .
position of the cathode may make all the difference between the lines being quite or so faint as to be hardly visible .
We shall now pass on to consider the negatively electrified particles which are found mixed with the positive rays .
These have much the same energy as the positively electrified ones ; they are , in fact , positively electrified until they reach the cathode , they get neutralised after passing through it , and attract another corpuscle , thus negatively electrified before reaching the electric and magnetic fields .
As are moving past the corpuscJes at a very speed , in some cases as fast as 2 cm .
, it is evident that their attraction for the corpuscles must be very considerable , otherwise they could not grip and hold fast a corpuscle under such conditions .
The power of a particle to get negatively electrified may thus be taken as an indication of the strength of the electric field round it , if the electric field is small , .
if the chemical affinities of the particle are saturated , it will not be able to pick up a corpuscle and become negatively electrified , yhile it may be able to do so if it is unsaturated and the electric field around it intense .
Now I have not yet found a case where a molecule of a compound acquires a negative , and only two cases , which will be considered later on , where a molecule of an elementary gas does so .
Again , there are some elements whose atoms , when in the positive rays , never acquire a negative charge , such as nitrogen , heJium , neon , argon , crypton , and mercury vapour , while negative charges are found on the atoms of , carbon , oxygen , sulphur , chlorine .
In oxygen the parabolas due to the atively charged atoms are exceptionally strong ; an example of this is shown in the photograph reproduced in , which was taken when the gas in the discharge tube was very pure oxygen .
Another photograph , showing the lines due to negatively electrified oxygen and carbon atoms , is reproduced in The two cases where I have found a molecule of an element to be atively c are oxygen and carbon .
The electrified molecule of oxygen does sometimes occur , although it is by no means common ; the conditions for appearance have not beeu worked out with certainty , it is probably connected with the presence in the discharge tube of some oxygen compounds of a special type ; the negatively charged oxygen atom , on the other hand , occurs in nearly every case when oxygen is present in the tube .
It is not perhaps inconsistent with the chemical properties of oxygen to suppose that in some compounds we may have two oxygen atoms united ether so as to for a system with a good deal of residual affinity , hydrogen peroxide is perhaps an example of this .
Rays of Positire Electricity .
The conditions which regulate the appearance of the atively charged carbon molecule have been worked oub and are very interesting .
The ative molecule does not occur in compounds like marsh-gas , carbon dioxide , carbon monoxide , phosgene , and so on , where there is no linking between carbon atoms .
On the other hand , it does occur with compounds like acetylene , ethylene , ethane , where there are two carbon atoms linked together by one or more bonds .
This is interesting from the chemical point of view because it shows that in such compounds two carbon atoms are held so firmly together that they remain united when the molecule is broken up by the rough treatment it in the discharge tube ; and secondly , that the system consisting of the two carbon atoms is a highly unsaturated one , as there is an electric field round it strong enough to catch and hold a corpuscle moving past it at a speed .
In benzene vapour we get negatively electrified triplets of carbon atoms , and I have etiules thought that I could detect the ative quartet .
The Use of Positive as Iethod of Chemical alysis .
Since each parabola on the photograph indicates the presence in the ( tube of particles ) aving a known of , and as by the methods described above we can determine what multiple is of the unit charge , we can , by measuring the parabolas , determine the masses of all the particles in tube , and thus identify the contents of the tube as far as this be done by a knowledge of the atomic and molectl ] veights of all its constituents .
The raph of the positive rays thus gives a of the atomic and molecular weights of the elements and compounds in the tube .
This method has several advantages in comparison with that of spectrum analysis , especially for the detection of new substances ; for , with method , when we find a new line we know at once the atomic or molecular of the particle which produced it .
Spectrum analysis would be much easier and more efficient if from the wave-length of a line in the spectrum we could deduce the atomic weight of the element which produced it , and this virtually is what we can do with the positive-ray method .
Again , in a mixture the presence of one gas is apt to swamp the spectrum of another , necessitating , in many cases , considerable purification of the gas before it can be analysed by the spectroscope .
This not the case to anything like the same extent with the positive rays ; with these the presence of other gases is a matter of comparatively little importance .
With regard to the sensitiveness of the positive ray ethod , I have made , as yet , no attempt to design tubes which would give the maximum sensitiveness , but with the tubes actually in use there is no difficulty in the Sir J. J. Thomson .
helium contained in a cubic centimetre of air , even though it is mixed with other gases , and I have not the slightest doubt a very much greater degree of sensitiveness could be obtained without much difficulty .
I will illustrate the use of the method by some applications .
The first of these is to the detection of rare gases in the atmosphere .
Sir James Dewar kindly supplied me with some gases obtained from the residues of liquid air ; the first sample had been treated so as to contain the heavier constituents .
The positive-ray photograph reproduced in fig. 17 gave the lines of xenon , crypton , argon , and a faint line due to neon ; there were no lines on the photo- raph umaccounted for , and so we may conclude that there are no heavy unknown gases in the atmosphere occurring in quantities comparable with that of xenon .
The second sample from Sir James Dewar contained the hter gases ; the photograph ( fig. 18 ) shows that , in addition to helium and neon , there is another gas with an atomic weight about 22 .
This gas has been found in every specimen of neon which has been examined , including a very carefully purified sample prepared by Mr. E. W. Watson and a specimen very kindly supplied by M. Claud , of the raph of this specimen , fig. 19 ( Plate 3 ) , is remarkable , as it shows , in addition to this line and the helium line , a line to a substance with atomic , whose properties are discussed later on .
The substance giving the line 22 also occurs with a double charge , giving aline for which .
There can , therefore , I think , be little doubt that what has been called neon is not a simple gas but a mixture of two gases , one of which has an atomic about 20 and the other about 22 .
The parabola due to the heavier gas is always much fainter than that due to the lighter , so that probably the heavier gas forms only a small percentage of the mixture .
Another application of the method was to the analysis of the gas in a small glass tube in which 30 mgrm .
of radium bromide had been sealed for more than 10 years .
The raph showed that , in addition to helium , the tube contained considerable quantities of neon , or some gas with about the same atomic weight , some gas of the atomic weight 3 mentioned before , and also a trace of argon , a little more than I should have expected from the volume of air in the tube , although the difference was not very great .
The photograph is shown in fig. 20 .
The last application of the method I shall bring before you is to the investigation of the gas for which .
The most convenient way of producing this gas is by bombarding solids by cathode rays .
The arrangement used for this purpose is shown in fig. 21 .
A is a vessel communicating by a tube with the bulb , in which the positive rays are produced ; a tap is placed in the tube , so that the communication between the vessels can be cut Rays of Positive off if desired .
A is provided with a curved cathode , like those used for Rontgen-ray focus tubes , and the catbode rays focus on the platform on which the substance to be bombarded is placed .
After the solid to be examined } ) been placed on the platform , the tap between A and is turned so as to cut off the connection between them , A is exhausted until the pressure is low enough for the cathode rays to be produced , the electric discharge is sent through , and the cathode rays bombard tloe solid ; the result of this is that in a very short time so much gas , mainly and , is driven out of the solid that the pressure , too high for the cathode rays to be formed ; to reduce the pressure a tube containing charcoal cooled ) .
liquid air is connected with , and the gases given off at the commencement of the bombardment are absorbed by the charcoal ; after the first rush of has come off , the charcoal is cut off from A by the tap .
To analyse the gases ( riveno off from the solid , a photograph is taken before the connection between A and has been opened ; after this is finished and when the bombardment has been for some hours , the tap is turned and a little of the gas from A is allowed to go into : another is taken , and the lines in the secondphotograph which are not in the first represent the ases which have been liberated by the bombardment .
The solids tested include platinum , lead ( both old and some chemically pure , procured from Kahlbaum ) , gold , silver , copper , iron , nickel , nickel oxide , zinc , aluminium , magnesium , uranium , palladium , graphite , calcium carbide , diamond.dust , mica , lithium chloride , potash , potassium iodide , potassium chloride , fluorspar , specimens of meteorites , mouazite sand , volcanic dust .
In every case , Sir J. J. Thomson .
except the two last , a whose atomic is 3 was found to have been liberated by the bombardment with cathode rays ; in some cases the parabola corresponding to it was very well marked , as in the photograph reproduced in fig. 22 , which is taken with the gas driven out of platinum ( the line is the third from the top ) ; of the substances tried , the line corresponding to the gas with atomic weight 3 , which I shall denote henceforth by , was with platinum , lithium chloride , and potash .
The gas continues to come off , even though the bombardment is for some hours , but in all the cases I have tried it ceases if the bombardment is for the working hours of several days , and the metal arrives at a state when it can be bombarded without liberating the .
The metalbefore bombardment can be heated to a high temperature without producing much diminution in the supply of this gas given off under the cathode rays , but by heating copper auze , made of very fine wire , in a vacuum in a quartz tube to a red heat for about 40 hours reduced to a state when it no off under bombardment .
Helium and in some cases neon or a approximately the same atomic weight are given off along with the when solids are bombarded by cathode rays .
Almost every substance I have bombarded gives off sufficient helium to be detected by this method .
After long bombardment , however , the supply of helium gives out , generally long before the is exhausted .
This is hardly to be wondered at , for in most cases the amount of is much greater than that of helium .
In minerals like thorianite , monazite , the two meteorites I examined , and a specimen of volcanic dust , the helium is in excess , in monazite and thorianite the is but a small fraction of the helium .
method is a very convenient one for analysing the gases in minerals .
I may say in passing that helium in small quantities is by no means an infrequent impurity in gases .
I have detected it as well as in some oxygen obtained from a cylinder .
I do not mean , however , to imply that all such oxygen contains helium .
With regard to the origin of the gases given out on bombardment , the fact that the emission of gas ceases after prolonged bombardment , and that thin copper wire by long continued heating can be brought to a state in which it ceases to emit the gas , favours the conclusion that in such cases the gas is originally present in the solid , or at any rate is not manufactured de novo by the action of the cathode rays alone .
The question arises , Are the gases merely absorbed by the solid in the same way that air is absorbed by water or are they constituents of atoms or molecules which are decomposed by the cathode rays ?
The gas is certainly held with surprising firmriess by the metal , the only case in which I have been able to get rid of it by heating is that of Rays of Electricity .
the fine copper wire heated to redness for a week .
I have heated lead in a vacuum until two-thirds of it were boiled away and yet the remainder still gave off some helium and when bombarded by the cathode rays .
I tested given out from the lead when heated and found traces of and also of helium ; the quantities obtained in this way were , however , very small compared with those produced by bombardment with cathode rays .
If the gases were absorbed in the solids we should expect to be able to eliminate them b the solid in water or acid and the solution to dryness ; in some cases , however , this treatment does not reduce the quantity of liberated by the cathode rays .
A conspicuous instance is lithium chloride : a sample of this when bombarded gave off and helium , it was then dissolved in water and the solution evaporated to dryness , the freshly deposited lithium chloride gave off and helium as freely as it did before solution , indeed the helium line seemed to be stronger than before .
This process was repeated nine times without leading to any diminution in the gases given out .
Similar results are obtained when the is dissolved in alcohol instead of water and when KHO is substituted for .
It would seem very improbable that any gas merely absorbed or imprisoned by the solid would have been able to withstand this treatment , which , would not have eliminated any soluble compound of these gases .
This persistence after solution suggests that the is in a state of chemical combination and is not merely absorbed in the usual meaning of the term .
We shall see that the gas has some power of entering into chemical combination so that the existence of it as a compound is not impossible .
The lithium chloride , howeyer , ives off helium after solution , as well as , so that , assuming that the solution and subsequent heating would eliminate any helium in the free state , the helium must either be generated from ) the bombardment of cathode rays , or else it must exist in some compound sufficiently stable to admit of dissolved without decomposition .
In some cases , though not as we have seen in all , solution has the effect of the metal into a state in which it does not boive off either or helium when bombarded .
Thus I could get no gas from lead freshly deposited as a " " lead tree\ldquo ; ; again , iron which off gas when bombarded ceased to do so when dissolved and re-precipitated .
Again , platinum dissolved up in acid and con verted into spongy platinum five times in succession , though it did not altogether cease to give off gas under bombardment , did not emit like so much as it did before bombardment .
The differences in the effects produced by the solution of the metal .
in different cases would be readily intelligible if these gases formed compounds of different qualities with the different metals .
Sir J. J. Thomson .
Though the largest quantities of are obtained by bombardment with cathode rays , this is by no means the only source of the gas .
It and are obtained when the discharge from a Wehnelt cathode passes through an exhausted tube .
Indeed I had observed the line corresponding to it on several occasions on the photographic plate long before I tried bombarding the solids ; its appearance was , however , very sporadic and although I tested a great variety of gases I was never able to get it at will until after a tedious search I hit upon the method of bombarding solids .
I will now pass on to describe the experiments I have made to test the nature of the substance The most obvious suggestion is that it is a carbon atom with four charges of electricity .
This , however , is not tenable , for the following reasons .
The first are based on physical principles .
We have seen that a multiply charged atom involves a prolongat , ion of the line due to the singly charged one ; in the case of an atom with four charges the primary line would be prolonged until it reached up to one-quarter of the normal distance from the vertical .
Now I have never observed .
a prolongation of the line due to the carbon atom beyond the half distance , this corresponds to a doubly charged atom , and the line for this atom is frequently found on the plate , though always fainter than the primary line .
Again , on many of the plates where the line is strongest there is no ation of the line due to the carbon atom at all , and no line corresponding to the doubly charged atom .
In some cases , indeed , the line is than the imary carbon line , and in all cases when the gas is enerated by bombardment ( than the doubly carbon line .
This is the argun ) from the physical side ; there is , however , another argument based on consideration of a chemical character .
The gas can be stored and tested weeks after the bombardment has taken place .
If then the line is due to the carbon atom with four charges it must be that some carbon compound is produced by the bombardment which , when introduced into the discharge tube , gives a plentiful supply of carbon atoms with four chal'ges .
Now I have put directly into the tube all the gaseous carbon compounds I could get , including marsh-gas , carbon dioxide , carbon monoxide , rbon tetrachloride , phosgene gas , carbon bisulphide , cyanogen , acetylenc , ethylene , ethane , the vapours of a number of alcohols and , benzene , coal gas , without getting a trace of the line .
can resist treatment with hot copper oxide and potash , which would remove the carbon compounds .
For these reasons we may , I think , put aside the idea that is due to carbon .
If does not contain a new element and is not carbon with four charges Rays of Positive Electricity .
it must be triatomic hydrogen .
From the physical side there is considerable evidence in favour of this view ; for example , whenever is freely produced by bombardment , it is always accompanied by large quantities of hydrogen : we may , however , have large quantities of hydrogen without .
The chemical properties of , however , in no way , so that if it is manufactured from that gas its relations to hydrogen must be very different from those of ozone to oxygen .
The properties of brought to light by these experiments are as follows:\mdash ; It can be kept over mercury for several weeks , although it is diminished in amount at the end of that time .
It can be heated in a quartz tube for several hours without any appreciable chan the quartz is at a red heat .
It can be sparked with oxygen and also with phosphorus without being .
destroyed .
It is not affected when passed over cold metallic sodium , and when heated with sodium vapour it does not combine with it .
It can withstand the action of red-hot copper oxide and potash .
This experiment was tried seven times , in two cases there was an appreciable diminution in the quantity of , in the others there was no effect .
The exceptional cases , I am inclined to think , were due to some of the copper being reduced , as hot copper combines , to some extent , with .
Fig. 23 ( 3 ) is from a raph when the gas had passed over hot copper oxide ; 23 ( 2 ) and ( 4 ) of the same which had not been treated .
23 ( 1 ) is the check taken before the gas was admitted ; it does not show the 3 ' line or the helium , which would come just under the strong line the top , which is due to the hydrogen molecule .
It can stand over potash for several days without being absorbed These properties point to its being a very inert substance , and are not those we should expect an allotropic form of hydrogen to possess .
I have found , however , two cases where it enters into chemical.combination\mdash ; ( 1 ) It combines with mercury vapour when an electric discharge is sent through the mixture .
( 2 ) It combines , to some extent , with red-hot copper .
This is illustrated the photograph reproduced in fig. 24 ; ( 1 ) is the check before the , ( 2 ) and ( 4 ) that of gas not passed over copper ; ( 3 ) that of the gas after passing the copper , in this the 3 ' line is fainter than in ( 2 ) and ( 4 ) .
These properties point to the conclusion that if is an element it has considerable resemblance to the inert gases helium and argon , although its chemical properties are slightly more energetic .
The absence of parabolas corresponding to and shows that if it is an element it VOL. LXXXIX.\mdash ; A. Sir J. J. Thomson .
is monatomic .
Mendeleeff predicted the existence of an element of atomic weight 3 , and attributed to it properties similar to those of fluorine , but of greater intensity .
The chemical properties of are much too lethargic to be consistent with the view that it is a kind of super-fluorine .
If is elated to such an element , that element must have an atomic weight 2 and not 3 , and must be a stable compound of it with .
If this were the case , since the line corresponding to the element would coincide with that due to the hydrogen molecule , which is always on the plate , it would be difficult to get , by the study of the lines due to the positively charged particles , evidence as to its existence .
We should expect , however , that a substance possessing the energetic chemical properties of Mendele'effs element would be able to attract a negative charge , and that there would be on the negative side of the photographs a line for which .
I have not , however , as yet been able to detect the existence of such a line .
Again , with but three exceptions , , all the atomic less than 40 are of the form 4 or 4 ; if the atomic weight of were 2 it would be another exception to this law .
I have much pleasure in thanking Mr. F. W. Aston , B.A. , of Trinity College , and Mr. E. Everett , for the invaluable assistance they have given me with these experiments .
[ Note added , 1913.\mdash ; In the experiments described in the lecture the evolution of and helium from metals under bombardment by cathode rays was in most cases much smaller when the metals had been freshly deposited , and the solution evaporated to dryness , than it was with metals which had not been so treated .
The supply of helium , too , soon gave out under bombardment , indicating that the helium had been absorbed by the metal and was liberated by the bombardment .
There was one case , however , that of , in which solution produced no diminution in the amount of helium given out .
This result led me to examine within the last few days the effect of bombarding by cathode rays the salts of the alkali metals and of the alkaline earths ; these experiments have convinced me that when the salts of Li , Na , or Bb are bombarded by cathode rays there is a genuine production , as distinct from liberation of absorbed gas , of helium and potassium giving the largest supply .
The amount of helium obtained from these elements was much larger than that from any of the substances I have tried other than minerals such as monazite sand , thorianite , volcanic ash , or meteorites , which are known to contain free belium .
On the other hand , the salts of calcium , ammonium , and silver , have shown no special power of Rays of Positive Electricity .
out ] ; the very small amount obtained not more than could be accounted for by absolbed gas , they produce , however , quite freely .
The of using the salts instead of the metals themselyes is that , by solution in water or alcohol and snbsequent evaporation to dryness , they can be freed from absorbed helium and .
The salts examined were LiOH , ( this was a portion of a cylinder ) , and .
The lithium , sodium , potassium , and rubidium salts showed the helium line strongly , especially the potassium salts ; indeed , except with minerals which are known to contain helium , I have neyer seen the helium line so strong as it was when KI was bombarded .
The of the He line was not diminished by repeated solution and on the contrary , it was increased sometimes to a considerable extent .
I think this increase may be a secondary effect , due to the elimination from the salt of the ordinary absorbed yases , such as H2 and .
The result of this is that a naller amount comes off when the salt is bombarded , the in the bombardment chamber is lower , and the cathode rays are faster and more energetic .
The helium did not come from the electrodes , for when or was bombarded with the same electrodes , at the same pressure and for the same time , little or no helitun was produced .
As an additional precautiun , the cathode was scraped time to time .
All the nples of the salts I have tried giye the same esults .
This makes it that the effects are due to the presence of some helium-containing mineral like mollazite sand .
I have dissolved some of the salts in alcohol , and filtered the solution , without the supply of helium ; thus any helium-containing impurity must be soluble in alcohol .
On the plate on which the helium line was \mdash ; the ] was could see a very faint line to an atomic weight 35 or thereabouts .
I should have this was due to a trace of chloride .
the potassium iodide , except for the fact that when was substituted for this line was not thened .
I have not yet been able to get this line strong to measure it with sufficient to decide whether the article p it has an atomic weight exactly equal to the difference of the atomic of potassium and helium .
The tion of helium in exceptionally large amounts from the alkaline metals is interesting , since potassium , as Mr. Campbell has shown , is radioactive .
I am disposed to the emission of helium from these metals as supporting the speculation I gave in a letter to 'Nature , ' Feb. 13 , 1913 , that other elements besides radium , thorium , and the like , make to expel -particles ( atoms of ) .
In ordinary elements these particles have not enough energy to get away from the atom ; they are , however , as Rays of Positive Electricity .
it were , loosened , and can be detached by vigorous bombardment with cathode rays .
I now pass on to consider the effect of solution and subsequent evaporation on the evolution of , which all the salts , including the calcium , ammonium , and silver ones , gave off in abundance .
Solution and evaporation produced a marked diminution in the output of from .
It had little effect , however , on the output from LiUH , .
It will be noticed that these latter salts are very deliquescent , while those which are cted by solution are not .
l'his suggests that the diminution in , when it occurs , may be due to water being driven off when the salts are strongly heated after evaporation , the deliquescent salts recovering the water before bombardment , whilst the others do not .
The will come out of the salt with cathode rays which are not fast enough to liberate helium .
These results show , I think , that the liberated from the dissolved salts was not simply absorbed by them , but was either manufactured from hydrogen in the presence of water , or liberated from j atoms of one or more of the elements in the salt , and that the presence of water is an important , it may be an essential , condition for its production by atomic disruption .
If we suppose is made from hydrogen the function of the salt may be merely to supply the necessary water in a convenient form .
is produced when the discharge from a Wehnelt cathode passes through gas at a low pressure , though in this case the bombardment of the walls of the tube by cathode rays is feeble ; this and its sporadic appearance in tubes would be accounted for if it were produced from water vapour .
] [ Note added , 1913 .
find that disappears when a mixture of it with hydrogen is sparked with sufficient to give a violent explosion .
] FIG. FIG. 10 .
FIG. .
FIG. 7 .
Pro FIG. 12 .
FIG. 17 .
FIG. 16 .
|
rspa_1913_0058 | 0950-1207 | The magnetic materials in claywares. | 21 | 30 | 1,913 | 89 | Proceedings of the Royal Society of London. Series A, Containing Papers of a Mathematical and Physical Character | Arthur Hopwood|Prof. H. B. Dixon, F. R. S. | article | 6.0.4 | http://dx.doi.org/10.1098/rspa.1913.0058 | en | rspa | 1,910 | 1,900 | 1,900 | 9 | 126 | 5,096 | http://corpora.clarin-d.uni-saarland.de/surprisal/6.0.3/?id=rspa_1913_0058 | 10.1098/rspa.1913.0058 | null | null | null | Geography | 39.669647 | Chemistry 2 | 21.923252 | Geography | [
39.082271575927734,
-67.40363311767578
] | 21 The Magnetic Materials in Clayivares .
By Arthur Hopwood .
( Communicated by Prof. H. B. Dixon , F.R.S. Deceived May 14 , \#151 ; Read June 19 , 1913 .
) Robert Boyle* first observed the magnetic nature of burnt clays and found that a brick , after being heated in a fire and subsequently allowed to cool in the same position , became magnetised in the same direction as the earth 's magnetic field .
Later , J. B. Beccariaf observed that bricks or ferruginous stones which had been struck by lightning were also permanently magnetised in the same direction as the earth 's magnetic field .
But Gheradij was the first to make a systematic study of the magnetism of burnt clays .
He examined all sorts of clay articles made at different epochs and at various places in Italy and Egypt , and demonstrated the existence of permanent magnetism in all kinds of earthenware or stoneware .
Further , he observed that antique clay wares permanently retained the magnetism induced in them during the process of baking , irrespective of the positions they afterwards occupied with respect to the earth 's magnetic field .
In brief , the researches of Gheradi established the existence of permanent magnetism in all kinds of antique and modern claywares , and also demonstrated its influence on the measurements of the terrestrial magnetic elements in brick edifices .
Taking advantage of the property which clay possesses of becoming magnetised during the process of baking and of permanently retaining the magnetism acquired through the action of the earth 's magnetic field , Giuseppe FolgheraiterS advanced the view that the various claywares found in excavations and ancient tombs afford an indelible record of the state of the earth 's magnetism at the epoch and place of their manufacture , * * * S * ' Experimenta et Observationes Physicse , ' London , 1691 , Chap. I , Expt. 12 ; The Philosophical Works of the Honourable Robert Boyle , ' by Peter Shaw , 1st Edition , London , 1725 , vol. 1 , p. 504 ; 2nd Edition , London , 1738 , vol. 1 , p. 506 ; ' Works of the Honourable Robert Boyle , ' by Thomas Birch , New Edition , London , 1772 , vol. 5 , p. 573 .
t ' Observations et Memoires sir la Physique , ' par M. l'Abbe Rozier , Paris , 1777 , vol. 9 , pp. 382-384 ; vol. 10 , pp. 14-16 .
X ' II Nuovo Cimento , ' 1862 , vol. 16 , p. 384 ; 1863 , vol. 18 , p. 108 ; see further , Gage and Lawrence , ' Phys. Rev. , ' 1899 , No. 3 , p. 304 .
* S ' Roma , Real Accad .
Lincei Atti , ' 1896 , vol. 5 , pp. 66-74 , 127-135 , 199-206 , 242-249 , 293-300 ; 1897 , vol. 6 , pp. 64-79 ; 1899 , vol. 8 , pp. 69-76,121-129,176-183 , 269-275 ; see also 'Seances de la Societe Fra^aise de Physique , ' 1899 , pp. 118-123 .
Mr. A. Hopwood .
and thereby furnish us with an indirect means of enlarging our knowledge of the secular variation of the magnetic inclination of the earth .
From various parts of Italy and Greece Dr. Folgheraiter collected a large number of antique vases and other clay articles , which had been placed in an upright position during the process of firing , and of which were also known the dates and places of their manufacture .
He then determined the directions of the magnetic axes of these antique vases , which led him to assign definite values to the magnetic inclination at the time and place of their manufacture .
" Without entering into the numerous details of these indirectly interesting researches , it will be sufficient for our purpose to state briefly that the work begun by G. Folgheraiter , and more recently extended by B. Brunhes and P. David* and P. L. Mercanton , f had almost exclusively for its object the determination of the orientation of the magnetism in antique claywares as a means of extending the knowledge of the secular changes in the magnetic inclination of the earth .
In all these memoirs on the magnetism of burnt clays it is assumed that baked clays owe their magnetic properties entirely to the presence of magnetic oxide of iron , and that this is derived partly from the orientation of the magnetite originally present in the clays , and partly from the reduction of the ferric oxide of the clays during the process of burning .
Numerous observations on different kinds of claywares led the author to conclude that this view was too limited , and it will be shown in the following pages that white , cream , grey , yellow , buff , red , or brown claywares are feebly or moderately magnetic owing to the presence of black unfused grains of unchanged magnetic minerals and bluish-black fused globules of ferruginous silicates ; while flashed , brindled , or blue claywares are strongly magnetic owing to the presence of ferruginous silicates and magnetic oxide of iron .
Nature of the Magnetic Materials in Clay wares .
White , cream , grey , yellow , buff , red , or brown claywares when carefully examined , preferably on a fractured surface , are found to be more or less speckled with black unfused grains or more frequently with bluish-black fused globules , varying in size from minute bubbles to large blisters .
The unfused black grains are generally unchanged granules or concretions of either magnetic or non-magnetic ferruginous minerals originally present in the unbaked clays .
The more common bluish-black fused globules are never present in the unburnt clays , and are always strongly attracted by a magnet .
* 'Comptes Rendus , ' 1901 , vol. 133 , pp. 155-157 ; 1903 , vol. 137 , pp. 975-977 ; 1904 , vol. 138 , pp. 41-42 ; 1905 , vol. 141 , pp. 567-568 .
t ' Comptes Rendus , ' 1906 , vol. 143 , pp. 139-140 .
The Magnetic Materials in Claywares .
23 When heated to 1300 ' C. in the reducing atmosphere of a blue brick kiln , or to 1350 ' C. in the oxidising atmosphere of a china biscuit oven , the fused globules sometimes melt , but otherwise undergo no change .
The analyses of the fused globules from different kinds of claywares show them to be complex ferruginous silicates of slightly variable composition .
Hence white , cream , grey , yellow , buff , red , or brown claywares normally owe their magnetic properties , partly to the presence of black unfused grains of unchanged ferruginous minerals , and partly to the presence of bluish-black fused globules of complex ferruginous silicates .
Analyses of the Magnetic Globules in Claywares .
Globules from salt-glazed sewer pipes ( Burslem ) .
Globules from red bricks ( Hanley ) .
Globules from blue bricks ( Tunstali ) .
Silica per cent. per cent. per cent. 40 *52 42 *03 42 -83 Alumina 17*85 16 *50 15 *50 Ferrous oxide ( calc , from total iron ) 30 *73 31 *65 34 *27 Manganous oxide ... 0*92 0*74 0*83 Lime 4*33 4*55 2-74 Magnesia 4-82 3*53 2-93 Alkalies 0*58 0*90 0*72 99 -75 99 *90 t 99 *82 When grey , yellow , buff , red , or brown claywares have been flashed , i.e. partly reduced , in the baking process so that their surfaces become greenish-black or bluish-black in places , they invariably contain more fused globules of ferruginous silicates than the corresponding normally fired claywares , together with varying amounts of an unfused magnetic material present in the greenish-black or bluish-black patches .
In some claywares , these unfused bluish-black patches can easily be separated mechanically from the fused globules of ferruginous silicates , but as their magnetic constituent is so uniformly distributed throughout the bluish-black patches it cannot be separated mechanically from the main body of the claywares .
On analysis , a greenish-black patch on a * piece of slightly flashed terra-cotta gave 2T per cent , of ferrous oxide and 6-5 per cent , of ferric oxide , indicating that only part of the ferric oxide had been reduced to magnetic oxide of iron , while a bluish-black patch on a badly-flashed red brick made from the same clay gave 2'8 per cent , of ferrous oxide and 57 per cent , of ferric oxide , corresponding to the proportions of these oxides in magnetic oxide of iron .
Hence , the unfused magnetic material Mr. A. Hopwood .
present in the greenish- or bluish-black patches on grey , yellow , buff , red , or brown claywares is magnetic oxide of iron .
Blue claywares made by strongly heating a highly ferruginous clay , first in an oxidising and finally in a reducing atmosphere , consist of a blue-black unfused interior speckled with bluish-black fused globules , and an external perfectly fused blue film .
When a portion of a blue brick is heated to 1100 ' C. in the oxidising atmosphere of a red brick kiln , the external blue film and the internal bluish-black fused globules remain unaltered , while the blue-black unfused portion of the interior acquires the red colour of ferric oxide .
Both the bluish-black fused globules and the blue-black unfused interior are strongly magnetic , and in some speoimens they can be separated mechanically .
On analysis , the fused globules in blue claywares are found to be ferruginous silicates somewhat similar in composition as well as properties to those present in white , cream , grey , yellow , buff , red , or brown claywares .
On analysis , the unfused interiors of two strongly magnetic blue claywares gave 2-3 and 2'5 per cent , of ferrous oxide to 47 and 57 per cent , of ferric oxide respectively , corresponding to the proportions of these oxides in magnetic oxide of iron ; while the unfused interiors of two less magnetic blue claywares made from the same clays gave 47 and 4'5 per cent , of ferrous oxide to 2'8 and 3'0 per cent , of ferric oxide respectively , showing that the reduction in the latter cases had proceeded beyond the limits requisite for the production of magnetic oxide of iron , and that ferrous oxide as well as ferroso-ferric oxide may be present in the unfused blue-black matrix of blue claywares .
It follows from these analyses that flashed , brindled , or blue claywares always owe their strongly magnetic properties to the presence of complex ferruginous silicates and magnetic oxide of iron .
Origin of the Magnetic Materials in Claywares .
As ordinary clays contain but small amounts of magnetite only a small proportion of the magnetic oxide of iron present in flashed , brindled , or blue claywares can have been derived from the magnetite originally present in the clays , and consequently the larger proportion must obviously have been produced by the reducing action of the kiln gases on the finely divided oxides , hydroxides , or carbonates of iron distributed uniformly throughout the clays .
The derivation of the fused globules of ferruginous silicates is quite different from that of the magnetic oxide of iron .
While the latter would appear to be derived generally from the precipitated or colloid oxides , hydroxides , or carbonates of iron disseminated throughout the clays , the former would appear to be derived from the granules or concretions of ferruginous minerals like iron pyrites , cupriferous pyrites , siderite , haematite , The Magnetic Materials in Clay wares .
magnetite , menaccanite , chromite , glauconite , biotite , hornblende , etc. , which always occur in clays in masses varying in size from minute particles to large pieces .
It is well known by clayworkers* that when a clay containing granules or concretions of ferruginous minerals is easy-fired in a strongly oxidising atmosphere , these minerals are left in the product as unfused black grains , while if the clay be fast-fired or hard-fired in a slightly oxidising or neutral atmosphere , or better if the , clay be over-fired in a slightly reducing atmosphere , these minerals fuse with the surrounding matrix , producing small bubbles or large blisters of a bluish-black ferruginous slag .
In conformity with this , the author observes that easy-fired white , cream , grey , yellow , buff , red , or brown claywares are less magnetic than hard-fired claywares and considerably less magnetic than over-fired claywares made from the same clays .
To test these explanations of the origin of the magnetic materials present in claywares , six clays used in the manufacture of different kinds of claywares were heated separately in different kilns ranging in temperature from 600 ' to 1350 ' C. The clays selected for investigation were a china clay , a ball clay , a stoneware clay , a fireclay , a common brick clay , and a red terracotta clay , which contained 0*27 , 0*55 , 1*3 , 2*2 , 3*5 , and 5*5 per cent , of iron respectively .
The granular and concretionary ferruginous minerals were removed from portions of these clays by passing them through a fine sieve and subjecting them to an electromagnet , then elutriating the powders with water in a Schone 's apparatus , f and finally collecting the purified clays from the suspension in water by sedimentation .
The purified and the naturally occurring clays were then pressed separately into small tiles and heated whilst enclosed in seggars in the most strongly oxidising portions of ( 1 ) a ceramic thermoscope kiln raised to 600 ' C. in 12 hours ; ( 2 ) a white earthenware enamel kiln raised to 750 ' C. in 10 hours ; ( 3 ) a white earthenware majolica kiln raised to 1000 ' C. in 20 hours ; ( 4 ) a red terra-cotta kiln raised to 1100 ' C. in 80 hours ; ( 5 ) a reddish-brown roofing the kiln raised to 1180 ' C. in 80 hours ; ( 6 ) a white earthenware biscuit oven raised to 1250 ' C. in 40 hours ; and ( 7 ) a china biscuit oven raised to 1350 ' C. in 40 hours .
In every case , the purified clays gave white , cream , grey , buff , red , or brown non-magnetic bodies free from black specks of either unfused grains or fused globules , showing that the magnetisation of ordinary clays , when heated in strongly oxidising kilns , originates in the granular or concretionary ferruginous minerals and not in the precipitated or colloid oxides , hydroxides , or carbonates of iron present in the clays .
The naturally occurring clays heated * Cf .
E. Orton , ' Trans. Amer .
Cer .
Soc. , ' 1903 , vol. 5 , pp. 377-430 .
t Cf .
' Zeitschr .
f. Anal. Chem. , ' vol. 7 , p. 20 .
Mr. A. Hopwood .
to 600 ' , 750 ' , or 1000 ' C. in strongly oxidising atmospheres gave white , cream , grey , buff , or red magnetic bodies , which were speckled with black unfused grains of unchanged ferruginous minerals , but with no bluish-black fused globules of ferruginous silicates ; moreover , the amounts of magnetic materials they contained were rather less than those present in the unbaked clays , showing that ordinary clays , when heated in strongly oxidising kilns ranging in temperature from 600 ' to 1000 ' C. , become magnetised only by the orientation of the magnetic minerals originally present in the unburnt clays .
The naturally occurring clays , when heated to 1100 ' C. in the oxidising part of the red terra-cotta kiln , left white , cream , grey , buff , or red magnetic bodies speckled with many black unfused grains of unchanged ferruginous minerals and a few bluish-black fused globules of ferruginous silicates ; further , when the same clays were heated in the oxidising portions of the previously mentioned , higher temperature , clayware kilns they left similarly coloured magnetic bodies generally containing more fused globules of ferruginous silicates and less unfused grains of unchanged ferruginous minerals , showing that ordinary clays , when heated in oxidising clayware kilns ranging in temperature from 1000 ' to 1350 ' C. , become magnetic , partly owing to the orientation of unchanged magnetic minerals and partly to the conversion of granular or concretionary ferruginous minerals to fused globules of complex ferruginous silicates.* When the clays were heated in the slightly reducing portions of the above clayware kilns , or better when heated to 1300 ' C. in the strongly reducing atmosphere of a blue brick kiln , the purified clays yielded white , grey , or blue magnetic bodies containing unfused magnetic oxide of iron but free from fused globules of ferruginous silicates , while the naturally occurring clays yielded similarly coloured magnetic bodies containing unfused magnetic oxide of iron and also fused globules of ferruginous silicates .
This shows that ordinary clays when heated strongly in reducing kilns become highly magnetic due to the formation of complex ferruginous silicates and magnetic oxide of iron .
Amounts of the Magnetic Materials in Claywares .
In view of the fact that the magnetic disturbances existing in magnetic observatories and physical laboratories have in many cases been found to be due to the brickwork of the buildings , f magneticians and physicists have to * Cf .
G. Folgheraiter , ' Eoma , Real Accad .
Lincei Atti , ' 1895 , vol. 4 , 2 , pp. 78-85 ; 1897 , vol. 6 , 2 , pp. 368-376 .
t Cf Lamont , ' Abhandl .
d. K. Bayr .
Akad .
d. Wiss .
, Math. Phys. , ' 1847 , vol. 5 , p. 24 ; F. Kohlrausch , ' Wied .
Ann. , ' 1883 , vol. 19 , p. 142 ; R. W. Willson , ' Amer .
Journ. Sci. , ' 1890 , vol. 39 , pp. 87-93 , 456-470 .
The Magnetic Materials Claywares .
be very careful in the selection of building materials to be employed for such purposes.* In consequence , the author has determined the combined amounts of the magnetic materials present in the different kinds of claywares made in various parts of the country , in order to ascertain which would and which would not be suitable for the construction of such buildings .
The combined amounts of the magnetic materials present in each kind of clayware were determined by powdering separately several specimens , representing all grades from the best to the worst of each kind , and then weighing the black particles which adhered to a 12-inch horse-shoe magnet when its poles were moved repeatedly through the finely powdered mass placed upon a piece of glazed paper .
In the case of white , cream , grey , yellow , buff , red , or brown claywares , the complete separation of the black magnetic materials from the non-magnetic matrix was usually accomplished after subjecting their powders to the magnet for 5-10 hours , but in the case of flashed , brindled , blue , or black claywares the complete separation of the magnetic from the non-magnetic materials could not always be made even by a much more prolonged application of this process .
For convenience of description the claywares are roughly divided according to their colour into six classes , i.e. white , grey , yellow , red , blue , or black claywares .
Each of these classes contains widely different varieties , which are distinguished in this paper by brief statements of their uses or the clays and other materials employed in their production at the same time as the variation of the combined amounts of the magnetic materials in each variety is given .
( i ) White Claywares.\#151 ; Porcelain or china made either from a mixture of china clay and felspar , or from a mixture of china clay , ball clay , cornish stone , and calcined bones , is always feebly magnetic , f and contains from traces to 0'002 per cent , of black magnetic materials .
Glazed white earthenware or glazed white stoneware made for ornamental , household , or electrical purposes , from a mixture of china clay , ball clay , cornish stone or felspar , and flint , is also feebly magnetic , and contains from 0-0005 to 0'005 per cent , of black magnetic materials .
The coarser white or cream terra-cotta and also ornamental or facing bricks made from common ball clays are more magnetic , and generally contain from O'OOl to OT per cent , of magnetic materials ; while the still coarser white or grey firebricks made from china clay refuse or from disintegrated granite usually contain from 0'01 to l'O per cent , of black magnetic substances , although as much as 5 per cent. * Cf .
C. C. Marsh , ' Observations at the United States Naval Observatory , ' Washington , 1887 , Appendix I , pp. 1-37 .
t Cf .
M. Faraday , ' Phil. Trans. , ' 1846 , vol. 53 , Part I , p. 29 .
Mr. A. Hopwood .
is frequently found in badly-fired specimens having speckled bodies or flashed surfaces .
Further , the white , pink , green , or blue floor tiles for tesselated or mosaic pavements made by colouring white-burning clayey mixtures with a zinc , tin , nickel , chromium , or cobalt stain are technically and magnetically similar to the finer qualities of white earthenware , and contain from 00005 to 0'005 per cent , of black magnetic bodies .
( ii ) Grey Claywares.\#151 ; Glazed stoneware made from siliceous ball clays for culinary , preserving , bottling , or electrical purposes usually contains from 0 001 to 0-5 per cent , of magnetic materials , although more than 1 per cent , is often present in badly speckled or flashed bodies .
The coarser salt-glazed stoneware made from vitreous fireclays for sanitary purposes is generally more magnetic and usually contains from 0-015 to 5'0 per cent , of black magnetic materials , but in badly speckled , black-cored , or flashed specimens the proportion is often as high as 10 per cent. ( iii ) Bvff or Ycllovj Claywares.\#151 ; Cream or buff claywares made from various grades of tertiary or carboniferous buff-burning fireclays vary considerably in their magnetic qualities .
Glazed buff tiles , teapots , and similar goods made for ornamental or household uses usually contain from 0001 to 05 per cent , of magnetic materials , though those with badly speckled or flashed bodies , almost invariably covered with dark-coloured glazes , often contain more than 1 per cent. Buff floor tiles made from high grade buffburning clays for tesselated or mosaic pavements are always feebly magnetic , and usually contain from O'OOl to 025 per cent , of black magnetic materials ; but the ordinary buff quarry floor tiles , terra-cotta , and also paving , facing , or ornamental bricks generally contain from 0005 to 1'0 per cent , of magnetic substances .
The coarser buff fire-bricks , glazed bricks , and similar refractory wares made from lower grade fireclays are more magnetic , and generally contain from 0 01 to 5-0 per cent , of black magnetic substances , while 10 per cent , is often found in specimens having black cores , speckled bodies , or flashed surfaces .
Similarly , the cream or yellow claywares made from calcareous ferruginous clays or calcareous clayey mixtures vary somewhat like the refractory claywares in their magnetic properties , and usually contain from 0'005 to 5-0 per cent , of black magnetic substances .
Further , the grey or drab floor tiles for tesselated or mosaic pavements made from a high grade buff-burning clay and manganese dioxide or puddler 's tap cinder , are invariably more magnetic than the technically similar buff floor tiles , and usually contain from 0005 to 1*0 per cent , of black magnetic materials .
( iv ) Bed or Brown Claywares.\#151 ; Red or brown claywares made from highly ferruginous clays vary greatly in their magnetic properties .
Glazed red tiles , teapots , and similar wares made for ornamental or household purposes The Magnetic Materials Claywares .
generally contain from 0-001 to 1*0 per cent , of magnetic materials , though as much as 5 per cent , is often found in specimens having badly speckled or flashed bodies covered with dark-coloured glazes .
Salmon or red floor tiles made from high grade red-burning clays or clayey mixtures for tesselated or mosaic pavements , are always feebly magnetic , and contain from O'OOl to 0 3 per cent , of black magnetic materials ; but the ordinary red quarry floor tiles , plant pots , terra-cotta , and also ornamental , paving , or facing bricks , generally contain from 0*005 to 1*0 per cent , of black magnetic substances .
The coarser common red building bricks and red firebricks , as well as red and brown roofing tiles , are more magnetic and generally contain from 0'01 to 10 per cent , of black magnetic substances , but 20 per cent , is frequently found in badly fired specimens having black cores , speckled bodies , or flashed surfaces .
Further , the chocolate floor tiles for tesselated or mosaic pavements made from a high grade red-burning clay and manganese dioxide or puddler 's tap cinder , - are invariably more magnetic than the technically similar red floor tiles , and usually contain from 0*005 to 1*0 per cent , of black magnetic bodies .
( v ) Blue or Brindled Claywares.\#151 ; Blue , brindled , or flashed claywares made by heating ferruginous clays first in an oxidising , and finally in a reducing atmosphere , are always very magnetic , the intensity of their magnetisation depending upon the extent of the conversion of the finally disseminated oxides of iron and the grains of ferruginous minerals to magnetic oxide of iron and ferruginous silicates .
Brindled bricks and other partially reduced claywares like grey , buff , or red claywares having flashed surfaces , yield powders of which 10 to 50 per cent , usually adheres to a magnet , while blue bricks , blue quarry floor tiles , and other completely reduced claywares give impalpable powders , the whole of wdiieh often adheres to a magnet .
This shows that either the whole mass of a uniformly blue clayware is a ferruginous silicate having strongly magnetic properties , * or more probably that the magnetic oxide of iron produced by the reduction of the homogeneously distributed ferric oxide is uniformly disseminated throughout the mass of the clayware , making the separation of the magnetic from the nonmagnetic materials impossible by mechanical means .
( vi ) Black Claywares.\#151 ; The greatest variation in magnetic qualities is found in the black claywares used for ornamental or paving purposes .
Those made from a ferruginous clay , manganese dioxide , and ironstone , are usually feebly magnetic and generally contain from 0 01 to 1*0 per cent , of magnetic materials ; but those made from a ferruginous clay and * Cf .
E. Orton , ' Trans. Amer .
Cer .
Soc. , ' 1903 , vol. 5 , pp. 377-430 .
The Magnetic Materials Claywares .
puddler 's tap cinder are generally strongly magnetic , and usually yield powders the whole of which adheres to the poles of a magnet .
The general conclusions to be drawn from these analyses are that all baked claywares are magnetic , and that different kinds , as well as different specimens of the same kind , contain extremely varying amounts of black magnetic materials .
Black , blue , or brindled claywares , and also badly-fired grey , yellow , buff , red , or brown claywares having black interiors , speckled bodies , or flashed surfaces , are almost invariably strongly magnetic ; while white , cream , grey , yellow , buff , red , or brown claywares having none of these imperfections are always feebly magnetic .
Whenever claywares have speckled bodies , flashed surfaces/ or black cores , they are always much more magnetic than the corresponding ones free or relatively free from these defects ; and , consequently , the intensities of the magnetisation of any white , cream , grey , yellow , buff , red , or brown claywares can be roughly inferred from a cursory examination of the extent of the specking , flashing , or black-coring they exhibit .
Building Materials for Physical Laboratories and Magnetic Observatories .
The strongly magnetic nature of certain claywares shows that great care must be exercised in the choice of these materials for the construction of magnetic observatories and physical laboratories , or serious disturbances may take place during observations with delicate magnetic instruments .
The suitability of claywares for building purposes , or the choice between two or more claywares , can often be readily inferred from a cursory examination of their outward characteristics .
In other cases , the problem can be solved very readily by determining the combined amounts of the magnetic materials in their powders by extraction with a magnet .
Many physical laboratories are in existence in which greater care in the selection of the claywares used would have considerably reduced the magnetic disturbances existing in them .
Some are built with badly speckled and flashed bricks , and others even contain brindled and blue claywares .
These are not by any means the least magnetic of the claywares , and consequently on delicate magnetic instruments they will cause disturbances which could have been easily reduced to a negligible extent by a more careful selection of the building materials .
|
rspa_1913_0059 | 0950-1207 | On the force exerted on a magnetic particle by a varying electric field. | 31 | 35 | 1,913 | 89 | Proceedings of the Royal Society of London. Series A, Containing Papers of a Mathematical and Physical Character | J. G. Leathem, M. A., D. Sc. |Sir J. Larmor, F. R. S. | article | 6.0.4 | http://dx.doi.org/10.1098/rspa.1913.0059 | en | rspa | 1,910 | 1,900 | 1,900 | 7 | 53 | 1,649 | http://corpora.clarin-d.uni-saarland.de/surprisal/6.0.3/?id=rspa_1913_0059 | 10.1098/rspa.1913.0059 | null | null | null | Fluid Dynamics | 57.195615 | Tables | 17.057728 | Fluid Dynamics | [
38.97506332397461,
-47.0990104675293
] | ]\gt ; On the Force Exerted on a gnetic Particle by Varying Electric Field .
By J. G. LEATHEM , M.A. , D.Sc .
, Fellow of St. John 's College , Cambridge .
( Communicated by Sir J. Larmor , F.R.S. Received May 21 , \mdash ; Read June 26 , 1913 .
) With a view to explaining netism as a purely electrical phenomenon it is customary in the modern theory of electromagnetism to define force a solenoidal vector whose curl is 4 times the electric current , and the magnetisation of a material element as half the moment of the motion of electricity in the element .
* But it is clear that the definitions remain unjustified until it has been shown that the relations of these quantities to one another and to the quantities of the theoretical formulation are the same as the relations which experience indicates ils subsisting between the corresponding physical.quantities .
lt is , therefore , an essential part of the test of the theory to ascertain the theoretical value of the force exel.ted by a external field upon a etic particle .
The particle is supposed to contain , whether continuously or discretely distributed it is not necessary at the moment to specify .
This charge is supposed to be in motion relative to the particle , and the force exerted on the particle by the electromagnetic field is simply the resultant of the forces which the field exerts on the electric charge .
Let denote the velocity of an origin situated in the particle and moving with it , and let an element of electric charge de to the particle have co-ordinates referred to non-rotating axes with as origin .
Then the velocity of has components , and may be denoted by external field is specified by the magnetic intensity , and the ethereal displacement .
If these letters wiClwut suffix denote the values at , the value at is derived by means of the operator of Taylor 's expansion , namely In terms of the netic system of units the force on an element of is *Cf .
H. A. Lorentz , ' Encyk .
der Math. Wiss vol. , 2 , p. 181 ; and Larmor , ' fther and Matter , ' S64 .
Dr. J. G. Leathem .
Force Exerted on where is the velocity of light , and the square bracket denotes the vectorproduct .
Consequently the resultant force on the particle is the integral being extended to all the charges in the particle .
Here the exponential operator applies only to the components of and ; it will , of course , be expanded , and all but the earlier terms will be considered negligible .
The following notation is convenient:\mdash ; , .
Here is the algebraic total of the particle , are the components of its electric polarisation , while the 's are analogous to moments and products of inertia and may be called the ' second electric moments ' of the particle .
If we assume that the second moments are so small as to be negligible we get Now the components of netisation m , are defined by the relations ; and we note further that ; hence with other similar equalities .
Accordingly terms involving time-fluxes of the This formula is general .
With a view to considering a purely magnetic agnetic Particle by a Varying Electric Field .
particle we may suppose that the total charge is zero , and that there is no electric polarisation , so that the first term of is zero .
Let us further suppose that there is such permanence in the configuration average configuration of electric in the particle that there is a set of axes ( possibly rotating , provided the rotation be not extremely rapid ) , with as origin , with respect to which the second electric moments are constant , or have constant average values .
When this holds the time-fluxes of the 's are either zero or ( for rotating axes ) small of the same order of smallness as the 's themselves , and so may be neglected .
Thus , for a purely magnetic particle , , or , vectorially , The first term of is the ordinary formula for the force exerted on a magnetic particle , regarded as a polarised combination of positive and egative magnetism , by a field of magnetic force .
The second term is rather unexpected ; it represents a mechanical force exerted on a magnet by a current of ethereal displacement , perpendicular to the current and to the magnetic moment , and proportional to the product of the two and the sine of the between them .
If experimental evidence were definitely against the existence of such a force the theory would be at fault .
It might seem possible to test the matter by a small horizontally between the ho1izontal plates of a charged condenser and then effecting a non-oscillatory discharge of the condenser .
If the upper plate were originally charged with positive electricity , the displacement current on discharge would be upwards , and an eastward impulse on the magnet might be looked for .
But when it is remembered that the formula is in terms of units it will be seen that the charge on the condenser required to impart sensible motion to the magnet would probably VOL. LXXXIX.\mdash ; A. Dr. J. G. Leathem .
Force Exerted on be enormously great .
Thus an experimental test may well be out of the question .
* With regard to the hypothesis of the exact or average constancy of the values of the second electric moments of a magnetic particle , it is to be remarked that exact permanence of configuration in a whirling distribution of electricity is to be looked for only when the rotation is entirely about one axis round which the distribution is circularly symmetrical .
This does not seem to be a probable state of affairs in a magnetic particle .
On the other hand an average permanence of configuration may be claimed to exist for quite a complicated system of orbital motions of separate electrons proyided the geometrical configuration of the orbits be permanent .
All that is required for permanence of the average electric configuration is that the time-average be taken for an interval of time which is great compared with all the periods that the various electrons take to describe their respective orbits , or , if one orbit be described by several electrons , the interval between successive recurrences of the same electric configuration in that orbit .
If the velocities in the orbits are very great only a very minute interval of time need be taken in order to get constant timeaverages .
In the case of a magnetic particle possessing as a whole a rotatory motion of not very great rapidity the permanence of the timeaverages of the second moments would be with respect to moving axes .
It is indeed conceivable that the duration of any obtainable displacement current might be too short to permit the substitution of time-averages for a more accurate tracing of the changes in the configuration of charge in a single particle ; in the case , however , of a magnet made up of a large number of particles any resultanl effect would correspond to an average for all the particles , in which the fortuitous character of the instantaneous circumstances for a single particle would be obliterated by force of numbers and the probably quite irregular distribution of phase .
Sir Joseph Larrnor , to whom the writer is indebted for suggestions and criticisms , suggests as interesting the following aspect of the supplementary term in the above hypothetical expression for the force on a magnetic rticle : If a magnet were merely a whirling distribution of electncity then the forces acting on a region of it ought , like those on any other distribution of electricity , to be expressible as the result of a quasi-stress over the boundary and a quasi-momentum in the region .
But the commonly assumed forces Another possible difficulty is that the displacement current might alter the state of magnetisation , so that would be a function of and D. In so far as this held good the result would be uncertain .
Magnetic Particle by Varying Etectric Field .
on a medium of magnetic quality are not so expressible ; * consequently the force on a whirl of electricity is not completely expressed by the usual formula of magnetic type in terms of its equivalent magnetic moment .
The addition of the above obtained subsidiary term of much smaller order is just what is needed to restore the possibility of a stress-momentum specification .
The term being too small for any tht to be thrown upon its existence by direct experiment , there is no reason for excluding it ; if we postulate the universality of the stress-momentum representation we must retain it .
For the sake of completeness it may be mentioned that , to the degree of approximation above contemplated , the torque on a particle is terms involving time-fluxes of the second electric moments .
The part of this applicable to a purely magnetic particle is the same as is got from ordinary magnetic theory .
It is to be noted that the expressions here discussed refer only to the action of an external field on a particle .
They do not include the action upon an electron of its own field or of the field due to other belonging to the same particle .
Thus radiation and netic inertia do not enter into the discussion .
' Phil. Trans , 189 vol. 190 , S39 .
|
rspa_1913_0060 | 0950-1207 | On the luminosity curve a colour-blind observer. | 36 | 38 | 1,913 | 89 | Proceedings of the Royal Society of London. Series A, Containing Papers of a Mathematical and Physical Character | W. Watson, D. Sc., F. R. S.|Dr. F. W. Edridge-Green. | article | 6.0.4 | http://dx.doi.org/10.1098/rspa.1913.0060 | en | rspa | 1,910 | 1,900 | 1,900 | 1 | 60 | 1,218 | http://corpora.clarin-d.uni-saarland.de/surprisal/6.0.3/?id=rspa_1913_0060 | 10.1098/rspa.1913.0060 | null | null | null | Optics | 72.512934 | Tables | 21.965745 | Optics | [
9.664621353149414,
-13.637476921081543
] | 36 On the Luminosity Curve a Colour-blind Observer .
By W. Watson , D.Sc .
, F.R.S. , with an Appendix by Dr. F. W. Edkidge-Green .
( Received May 24 , \#151 ; Read June 26 , 1913 .
) In a recent paper communicated to the Society , the author gave the results of a long series of measurements which indicate that the luminosity curves of colour-blind persons can be deduced from the curve obtained by a person who has normal colour vision , by making the necessary allowance for their colour defect .
In the discussion on this paper , Dr. Edridge-Green mentioned that he had made measurements by a flicker method of the luminosity for a colourblind observer , and that he had found it to agree exactly with the normal.* This result being entirely opposed to the results obtained by the author , it seemed of great interest to investigate the matter further .
This , owing to the kindness of Dr. Edridge-Green and the gentleman ( Mr. C. ) , has been possible , as luminosity curves for Mr. C. and Dr. Edridge-Green have been obtained with the author 's apparatus , and in this note are given the results .
The measurements obtained in the bright part of the spectrum , extending from the red to the bluish-green , are given in the following table:\#151 ; Wave-length of coloured light .
A.U. Luminosity .
Difference .
Luminosity calculated for 0*4 Gr .
S. Mr. C. Dr. Edridge-Green .
6090 84 -0 75 -3 + 8-6 84 '8 5890 101 -o 94 -0 + 7-2 99-6 5800 100-0 99 -2 + 0-8 100 -o 5560 82 -6 91 -8 -9 -2 86 -5 5410 67 -3 74 -6 -7'3 67 -0 5270 49 -9 58 -0 -8 -1 49 -2 5140 35 *4 42 -3 -7 0 33 -7 The numbers obtained by Dr. Edridge-Green are in good agreement with those of the majority of persons having normal colour vision .
The only difference in his case is that his numbers in the blue and violet are somewhat higher than the normal .
This , as shown in the previous paper , is probably due to the macular pigmentation being rather less than the normal , which also accounts for his luminosity at wave-length 5800 A.U. being a little low .
Mr. C. 's luminosity , on the other hand , is decidedly different from the * Dr. Edridge-Green has been good enough to supply the particulars of the results he has obtained , and these are given in Appendix I. On the Luminosity Curve of a Colour-blind Observer .
37 normal , the luminosity being high on the red side of 5800 and low on the blue side of this point .
This is what one would expect if Mr. C. is partly green-blind , and in the last column of the table are given the values of the luminosity of a person who has only 04 of the normal green sensation obtained by the method described in the aforementioned paper .
It will be observed that these calculated values agree very fairly with Mr. C. 's observed numbers ; in only one case , namely , at 5560 A.U. , is the difference at all marked .
This difference is probably entirely due to errors of observation , Mr. C. never having used the apparatus before and only one series of measurements being taken .
It thus appears that Mr. C. is not an exception and that his case really supports the results given in the previous paper .
When Dr. Edridge-Green examined him red and green lights were compared , these lights being obtained by means of coloured glasses .
No doubt in this way a fairly pure red was obtained .
The green , on the other hand , would contain a considerable proportion of blue light .
It is quite possible that this blue light affected the results , as in the case of most observers the results obtained with blue or violet light by the flicker method are very variable and depend enormously on the brightness of the light employed .
Further , the experimental error when a red is compared directly with a green , as in Dr. Edridge-Green 's measurements , is very much greater than when either is compared with a white .
Further it is to be remembered that in the case of persons having a deficiency in the green sensation the effect produced on the luminosity can only be small , as is shown in the curves given in the previous paper .
Hence 1 think it quite possible that Dr. Edridge-Green 's apparatus may not have been sufficiently sensitive to detect the difference between Mr. C. 's luminosity and the normal , particularly when , owing to the mixture of blue with the green , the effect to be observed was probably partly masked by this blue .
Appendix I.\#151 ; Results of the Examination C. Dr. Edridge-Green .
Colour Perception Spectrometer.\#151 ; Light , petroleum , 180 metre-candles .
Eye light-adapted .
Saw two colours in brilliant spectrum , yellow and blue with grey interval between .
lied appeared as a darker yellow .
Neutral area , 5013-5040 .
Area of greatest luminosity , 5655-6319 .
38 On the Luminosity Curve of a Colour-blind Observer .
Monochromatic Designation of regions .
region by him .
754 -521-5 ... ... ... Yellow .
521-5-508 ... ... . .
Green or grey .
508 -501-3 ... ... ... Green or grey .
501-3-492 ... ... . .
Blue-green .
492 -483 ... ... . .
Green-blue .
483 -417 ... ... . .
Blue .
Saw small area of light 549-561 to same point of extinction as I did .
Lantern Test.\#151 ; Tested with large aperture , S inch in diameter , from a distance of 20 feet .
Called neutral , green ; red , yellow and green ; green , yellow , orange and red ; and yellow , red and green .
Recognised small points of coloured light on convex mirror from the same distance as I did , but could not tell their colours .
Bead Test.\#151 ; Put red , orange , pink and brown in red division ; orange , pink , and white in yellow division ; green , coral , pink , brown and grey in green division ; and blue and purple in blue division .
Rayleigh Equation ( 0 being full red , 25 full green).\#151 ; Made a match at 17*7 and 18 .
Said my match 15 was not correct , the mixed colour appearing to him darker and greener .
A Comparison of Red and Green by Flicker Method.\#151 ; The luminosities of a red and a green glass were compared with the Simmanee-Abady photometer .
The red glass transmitted rays 780-627 and feebly from 627 to 617 .
The green transmitted rays very imperfectly 605-575 and better the remainder of the spectrum 575-424 .
The filament of an osram incandescent light cannot be seen through both glasses combined .
His ratio was 4-1 R/ G for two consecutive observations , my ratio was 41 R/ G.
|
rspa_1913_0061 | 0950-1207 | Phosphorescence of mercury vapour after removal of the exciting light. | 39 | 44 | 1,913 | 89 | Proceedings of the Royal Society of London. Series A, Containing Papers of a Mathematical and Physical Character | F. S. Phillips|The Hon. R. J. Strutt, F. R. S. | article | 6.0.4 | http://dx.doi.org/10.1098/rspa.1913.0061 | en | rspa | 1,910 | 1,900 | 1,900 | 3 | 132 | 2,803 | http://corpora.clarin-d.uni-saarland.de/surprisal/6.0.3/?id=rspa_1913_0061 | 10.1098/rspa.1913.0061 | null | null | null | Atomic Physics | 32.860242 | Thermodynamics | 32.11671 | Atomic Physics | [
5.686584949493408,
-48.592037200927734
] | 39 Phosphorescence of Mercury Vapour after Removal of the Exciting Light .
By F. S. Phillips .
( Communicated by the Hon. R. J. Strutt , F.R.S. Received June 10 , \#151 ; Read June 26 , 1913 .
) [ Plate 4 .
] S 1 .
Introduction .
By means of Becquerel 's phosphoroscope the fluorescence of solids has been shown to be persistent , hut up to the present phosphorescence in the case of liquids and gases has not been observed .
That of solids has generally been explained as due to chemical reactions brought about by impurities , while in the case of gases it has been considered that damped vibrations of the rapidity of those connected with light could not be conceived as persisting for a sufficiently long time for the necessary observations to be made .
On the other hand , because of their relative simplicity , gases and vapours have been recognised as being eminently suitable for the study of fluorescence and kindred phenomena .
Wood has applied the phosphoroscope to the case of sodium vapour , with however a negative result .
In the present experiment I have attacked the problem in a different way .
The method used was to pass a beam of the exciting light transversely across a rapidly moving column of mercury vapour , obtained by distillation vacuo .
Then if the fluorescence of the vapour persists the luminosity should be carried along with the stream .
The fluorescence was excited by 2536 light which was obtained by means of a quartz mercury lamp .
Under suitable conditions the vapour could be seen to be still fluorescing , after it had passed a distance of some 18 inches from the point of excitation .
The fluorescence of mercury vapour was first observed by Hartley , * it has been further investigated by Wood.f The latter obtained the spectrum of the fluorescence excited by the light derived from the cadmium spark , and found that it was mainly continuous , but that under certain conditions the 2536 mercury line made its appearance .
Wood has shown in a later paperj that 2535 light produces resonant radiation even when the mercury vapour has only the very small density corresponding to ordinary temperatures .
Under these circumstances the exciting radiation could penetrate a distance * ' Roy .
Soc. Proc. , ' 1905 , vol. 76 , p. 428 .
t ' Phil. Mag. , ' August , 1909 .
J ' Phil. Mag. , ' May , 1912 .
40 Mr. F. S. Phillips .
Phosphorescence of Mercury \#166 ; of a few centimetres into the vapour , without total absorption taking place , but if the temperature was higher and the vapour consequently denser , the radiation could only penetrate a few millimetres .
S 2 .
Preliminary Experiments .
Wood does not appear to have stated that this 2536 light produces visible fluorescence in mercury vapour .
This , however , is the case and it is excited at a much lower pressure than when cadmium light is used .
This latter fact is of great importance , in making possible the present method of showing the phosphorescence .
The fluorescence may be easily shown in a small exhausted quartz bulb containing a globule of mercury .
If the bulb is uniformly heated to some 350 ' C. , and then while cooling a concentrated beam of 2536 light is passed through it , the following interesting changes take place .
At the highest temperature the vapour does not show any appreciable fluorescence , but as the bulb cools , the track of the beam gradually becomes illuminated with a bluish-green light .
The fluorescence may conveniently be divided into two parts , that along the main track of the beam and the portion that extends for about 1 mm. from the place where the beam enters the bulb .
At an early stage in the cooling the former reaches its maximum , and then begins to decrease in intensity .
But the spot of fluorescence at the commencement of the beam does not begin to decrease in brightness until all the rest has disappeared .
It then gradually fades away , and before the bulb reaches the temperature of the room all fluorescence has disappeared .
There are apparently three distinct phenomena excited by 2536 light in mercury vapour:\#151 ; ( 1 ) Resonant radiation , that exists over a long range of pressure from about one thousandth part of a millimetre to about 1 cm .
( 2 ) Ordinary fluorescence , which does not rapidly grow less bright as the beam passes through the vapour ; this exists when the pressure of the mercury vapour is about 1 cm .
; and ( 3 ) Local fluorescence at the point of entrance of the beam , that exists at much lower pressures than the ordinary fluorescence , but not at the very low pressure corresponding to ordinary temperature .
It is this local fluorescence that has been found to be persistent .
A roughly made quartz monochromator was used in conjunction with the mercury lamp , and in order to obtain as much light as possible the slit of the monochromator was arranged so that it was horizontal and parallel to the luminous tube of the lamp .
A Westinghouse Cooper-Hewitt lamp made of fused quartz was used in these experiments .
Wood had previously Vapour after Removal of the Exciting Light .
41 found that when such a lamp became hot it lost its efficiency for producing resonant radiation in about five seconds after starting .
The heating up of the lamp similarly affected the excitation of the persistent fluorescence , but in this case the falling off of intensity was not as rapid as that of the resonant radiation , yet after the lapse of one minute the effect was many times less powerful than at first .
This trouble was entirely overcome by water-cooling the lamp , both the resonant radiation and the fluorescence being as good after an hour 's run as when the lamp was first lit .
The reason for the hot lamp being less effective than the cold one has been pointed out by Wood .
It is illustrated in fig. 1 , Plate 4 .
This shows the spectra of the lamp when hot and when cold .
The 2536 line in the hot lamp is unsymmetrically broadened and shows a magnificent reversal , while the same line in the cold lamp can be obtained as sharp as desired even in the sixth order of a Rowland grating .
The upper spectrum shows the 2536 line as produced by the cooled lamp , while the lower one was obtained with the lamp hot , as it is ordinarily used .
The symmetrical lines in this latter spectrum are ghosts .
Both the resonant radiation and the persistent fluorescence were excited by no mercury lines other than the 2536 line .
Since the resonant radiation disappears as soon as the line broadens and becomes reversed , Wood inferred that it is only stimulated by radiations within very narrow limits of wavelength .
The limits of wave-length that excite the persistent fluorescence are also very narrow , although possibly not quite so restricted as those that produce resonant radiation .
There seems to be some connection between the two effects .
The cooling of the lamp was brought about by allowing water to run freely over both poles , while the tube between had a water-jacket half way round it .
In this way only the portion of the lamp adjacent to the slit of the monochromator was not in contact with a cold surface .
This portion became just sufficiently hot to prevent condensation taking place there .
The spectra in fig. 1 were photographed with a 10-foot Rowland grating , the fourth order being utilised .
The line marked by a dot in the photograph is a third order line at 3391 A.U. S 3 .
Persistence of the Luminosity .
The form of the silica tube used to obtain the moving column of mercury vapour is shown in the diagram .
After a convenient quantity of pure mercury had been placed in it , the tube was exhausted and sealed off .
The mercury placed at the beginning of an experiment in B was heated by means of a small electric heater , while the bulb C and part of the tube was kept in 42 Mr. F. S. Phillips .
Phosphorescence of Mercv.ry cold water .
With this arrangement the mercury completely distilled over in about\#171 ; 90 minutes .
The beam of ultra-violet light passed across the tube at the point A , its direction being indicated in the diagram by an arrow .
A screen was so placed as to prevent any light reaching directly the cold limb of the tube .
When the beam was passed across while the A whole apparatus was cold the resonant direction of beam radiation extended the width of the tube , but as soon as the bulb B was heated and the mercury began to distil over , the radiation became concentrated at the point where the beam entered .
This resonant radiation was quite bright enough to be viewed by means of a camera with a quartz lens , using a piece of uranium glass as a screen .
A stream of green fluorescent light , originating from the concentrated patch of resonant radiation , passed round the tube with the distilling mercury vapour .
A photograph of the tube under these conditions has been reproduced on Plate 4 , fig. 2 .
This photograph was obtained by means of an ordinary camera , so that it does not show the resonant radiation , which , though of course invisible , was really more intense than the green fluorescence .
The silica itself also fluoresced with a bluish-violet colour under the influence of the ultra-violet light .
The effect of this has been reduced to some extent by taking the photograph through a yellow screen .
Since the fluorescence of the mercury vapour is green ( the region of minimum sensitiveness of the photographic plate ) , this operation was somewhat difficult , and the resulting photograph is not a good reproduction of the actual effect .
However , it shows plainly that the stream of fluorescence passes up the tube from the point of excitation , while none passes downwards .
In the actual experiment the fluorescence clearly showed the stream-lines of the vapour passing through the patch of resonant radiation .
The glow passed up the hot limb of the tube as an attenuated band , but gradually spread out and filled the whole tube as it passed into the other limb .
Its course could be traced for about 18 inches , this was as long a path as it could be made to take in the particular tube used .
Further investigation on this point will be made with the idea of determining the length of time for which the fluorescence will persist .
Vapour after Removal of the Exciting Light .
The spectrum of the fluorescence carried over was obtained by means of a small quartz spectrograph at a point some distance down the cold limb of the tube .
It was found to be similar in character to the spectrum obtained by Wood for the fluorescence stimulated by cadmium light .
But , instead of the two bands of continuous spectrum that Wood obtained , there were four .
The 2536 line itself appeared in the fluorescent spectrum A , which is the upper one of the two reproduced in fig. 3 of Plate 4 .
The lower one was obtained under similar conditions except that a piece of glass was placed in the direct path of the beam , so causing the fluorescence to cease .
In this way it was shown that all the lines in the upper spectrum , except the 2536 line , were due to stray light .
This was deduced from the fact that in the original negative the three lines in the part of the spectrum , to which glass is transparent , were equally intense in both spectra .
This experiment also suggests a method of solving a problem raised by Wood , * in his paper on resonance radiation of mercury vapour .
He attempts to discover the mechanism of the secondary resonance radiation , which surrounds the beam of primary radiation under conditions of low pressure of the accompanying air .
The mercury vapour itself was of course at very low pressure , being kept at ordinary temperatures .
The secondary radiation may be due , as Wood pointed out , to one or both of two causes : ( 1 ) the light from the primary beam exciting the secondary radiation , or ( 2 ) the molecules of mercury diffusing from the primary beam and being still active , exhibiting the radiation in the neighbourhood of the beam .
A thin screen of quartz was used by Wood in his attempt to separate the two effects .
Such a screen would allow the light , but not the molecules , to pass through .
The experiment was only conclusive in as far as it showed that the greater portion of the effect was due to the action of the light radiated from the primary beam .
Wood thought it impossible to obtain a screen that would cut off the light and yet would allow the molecules to pass .
In effect a moving column of vapour , such as is used in the present experiment , achieves the desired object .
Certain observations during the course of the experiment seem to show that about one-twentieth of the secondary radiation in Wood 's experiment was probably due to moving molecules .
The rest of the radiation would be produced by scattered light from the primary beam .
S 4 .
Other Experiments .
Besides mercury the vapours of such substances as iodine , anthracene , and retene were experimented with , in order to ascertain whether the fluorescence * 'Phil .
Mag. , ' May , 1912 .
Phosphorescence of Mercury Vapour .
of the vapours persisted .
An attempt was also made to obtain the same effect in the case of the fluorescence of mercury vapour excited by cadmium light .
In all cases so far investigated , negative results have been obtained .
This is probably due to the fact that the fluorescence does not occur at a sufficiently low pressure to make the method feasible .
S 5 .
Summary .
( 1 ) The paper describes how phosphorescence of a vapour has been for the first time observed .
The method consists in passing a beam of the exciting-light across a moving column of the vapour .
If the fluorescence of the vapour persists it will be carried along with the stream .
( 2 ) The vapour chosen was that of mercury and the exciting light was the 2536 mercury line , obtained by means of a water-cooled silica lamp .
This light caused mercury vapour to fluoresce at a very low pressure .
( 3 ) The moving column of mercury vapour was obtained by distilling mercury in an evacuated tube .
When a beam of 2536 light was passed across the moving column the fluorescence was carried along with the vapour .
( 4 ) The fluorescence of some other vapours was also investigated , in order to ascertain whether in any case it was persistent , but no positive results were obtained .
In conclusion I have very great pleasure in thanking Prof , the Hon. R. J. Strutt , F.R.S. , for his kind interest and help during the course of this research .
It was at his suggestion that these experiments on the optical properties of mercury vapour were carried out .
I have also to thank Prof. Fowler , F.R.S. , for kindly permitting me the use of the instruments mounted in the Spectroscopic Laboratory of the Imperial College of Science and Technology .
DESCRIPTION OF PLATE .
Fig. 1.\#151 ; Showing the reversal of the 2536 line in the hot mercury lamp .
Fig. 2.\#151 ; Showing phosphorescence of mercury vapour .
Fig. 3.\#151 ; A. Spectrum of phosphorescence .
Phillips .
Poy .
Soc. Proc. , A , 89 , Plate 4 .
2534-9 2536-7 Fig. 1 .
Fig. 2 .
2536 3132 3655 40474359 Fig. 3 .
|
rspa_1913_0062 | 0950-1207 | The fluctuation in the ionisation due to \#x3B3;-Rays. | 45 | 57 | 1,913 | 89 | Proceedings of the Royal Society of London. Series A, Containing Papers of a Mathematical and Physical Character | P. W. Burbidge, M. Sc.|Sir J. Larmor, F. R. S. | article | 6.0.4 | http://dx.doi.org/10.1098/rspa.1913.0062 | en | rspa | 1,910 | 1,900 | 1,900 | 18 | 168 | 4,149 | http://corpora.clarin-d.uni-saarland.de/surprisal/6.0.3/?id=rspa_1913_0062 | 10.1098/rspa.1913.0062 | null | null | null | Tables | 42.474767 | Atomic Physics | 20.570734 | Tables | [
14.355731964111328,
-76.17768096923828
] | ]\gt ; 5 The in the due to By P. W. IDGE , lI .
Sc. , Government esearch and Jacob Joseph Scholar , Victoria College , Wellington , New Zealand .
( Communicated by Sir J. Larmor , F.R.S. Received April 2\mdash ; Read Jume 26 , 1913 .
) The work to be here considered is a continuation of a previous investigation by Prof. Laby and the present author , which the existence of fluctuations in the ionisation due to -rays from radium was demonstrated .
In the present paper the lantitative measurement of this fluctuation is described , its relation to the theory of -rays investigated .
At the present time two theories exist for the explanation of the Pontgen and -rays ( the two radiations exhibit so many properties in common that they are arded as phenomena differing only in degree ) , viz. , the pulse and entity theories .
According to the former , the rays are conceived as propagated from the source , with a continuous wave front , while the latter theory includes the corpuscular form of Brag , the pulse in a tube of force , or bnudle , theory of Sir J. J. Thomson , and the quantum form postulated by Planck and Stark .
In any of these last theories the disturbance has a discontinuous wave front and is ated from the source along a line .
Since both and -rays show many points of resemblance , on the hand , to and -rays , and , on the other , to light , it becomes of import- ance to investi their exact nature .
More especially is this so in view of the connection that has been recently demonstrated between -rays in the phenomena of fluorescence , reflection , and possibly of diffraction .
The possibility of discriminating between the two theories mentioned by the fluctuation in the ionisation due to -rays was pointed out Prof. and by von Schweidler , the experiments here described { leterlnine how the fluctuation varies with the ionisation:\mdash ; ( 1 ) When the solid angle of the rays used is valiel .
( 2 ) When the used in the ionisatiou vessel is changed .
absolute fluctuation in the number of ions fol.lned per second in the T. H. Laby and P. W. Burbidge , ' Roy .
Soc. Proc 1912 , vol. 86 , p. 333 .
In au application made , in 1908 , to the Royal Society for a grant towards.the research . .
von Schweidler , ' Phys. Zeit 1910 , vol. 11 , p. 225 .
Mr. P. W. Burbidge .
ionisation vessel , i.e. , , has been evaluated by means of the relation established by Dr. N. B. Campbell* where is the mean square deviation in millimetres of the of the fibre of the electrometer used from its mean position , is the capacity of the system in centimetres , is the resistance in E.S.U. between the fibre , etc. , and the earthed surroundings , is the sensitiveness measured in millimetres per E.S.U. of voltage , is the elementary in .
on an ion .
The present communication contains:\mdash ; ( 1 ) A note on the experimental ements .
( 2 ) An account of the method of evaluating , involving the measurement of , and 3 ) A discussion of the results in the light of the theory developed .
( 4 ) A criticism of some results on the same subject obtained by Dr. Meyer , of Aachen .
As these experiments will be continued the theory of them is only very briefly discussed in this communication .
jrimental A Most of the apparatus used in this work has already been described , the essential parts , the electrometer and he ionisation vessel , the same as were used before .
It was found necessary to make several alterations and additions .
The general scheme is shown in fig. 1 .
A Bronson resistance was connected to the fibre of the electrometer .
Some conductor , by which charges acquired by the central electrode of the ionisation vessel can leak away , is essential to enable the fluctuation to be evaluated .
This previously existed in the insulation leak , which arises from the radium acting on the air surrounding the wire connecting the central electrode to the electrometer .
A Bronson resistance was added as an additional conductor in order that the resistance not vary inversely as the ionisation in the can .
The resistance consisted of two brass plates , the lower .
coated with black uranium oxide , and the upper being connected to the fibre of the electrometer and air-insulated ( see fig. 2 ) .
The resistance so obtained was of the order of ohms , and the fluctuations arising from its introduction , * N. R. Campbell , ' Camb .
Phil. Soc. Proc 1909 , vol. 15 , p. 117 ; 1910 , vol. 15 , p. 310 ; and ' Phys. Zeit 1910 , vol. 11 , p. 826 .
Laby and Burbidge ( loc. cit Compare figs. 1 , 4 , 6 , 7 in this earlier paper .
The ionisation vessel had top and bottom of 2 mm. , sides of mm. tin-plate , back and front and fittings of mm. aluminium .
The in the due to as shown in the photographic records , vere small enough to be quite rlioible .
FIG. 1.\mdash ; Ionisation vessel , string electrometer and Bronson resistance .
FIG. 2.\mdash ; Bronson resistance .
The Source of \mdash ; The screen surrounding the 5 mgrm .
of radium was increased so as to cut off all -rays .
As determined experimentally the thickness for this was mm. of aluminium ; the equivalent thickness actually used was mm. , a thickness through which , ca]culating on the Mr. P. W. Burbidge .
exponential law of absorption , only per cent. of the fastest -rays could penetrate .
The photogrrecording apparatus was modified somewhat by the use of an extension to the bellows of the camera so that the movement of the fibre in the direction of the optic axis was not so detrimental to the sharp focus of the image , and by improvements to secure a uniform motion of the photographic film , as shown in fig. 3 .
REDUCING CEARINC FIG. ving mechanism for photographic film .
A. Weight to keep film in tension .
B. Weight giving constant resistance .
C. Rubber roller round which film passes , driven through reduction gearing by A.C. motor .
xsurement of the Fluctuatio The relation is true provided that the arithmic decrement of the motion of the fibre is large compared to ; this condition is amply fulfilled by the string electrometer used .
Since and are constant under the conditions used , in considering the variation of , the corrections and alone enter .
The justification of the latter is obvious , but the former has been called iu question and been proved not to hold for the quadrant electrometer .
* For the leaf electroscope , however , the correction has been justified and applies probably even more exactly in the case of the string electrometer .
The evaluation of *E .
Meyer , ' Phys. Zeit 1912 , vol. 13 , p. 73 .
Campbell , 'Camb .
Phil. Soc. Proc 1910 , vol. 16 , p. 310 .
The Fluctuation in the Ionisation due to from this expression requires the values of , and to be known .
These were determined as follows:\mdash ; was measured by finding the time required for a charge to leak through it .
Consider the theory of such a leak .
Tf mean potential on the central system in an interval of units ; mean current ; , in the infinitesimal time the fall in potential thus produced ; and capacity of system then The measurement consists in observing the time of leak of a charge over a given range of potential , about a known mean potential , .
In the observations made , volt and on either side .
The accuracy of the method was verified by a measurement of the Bronson resistance alone , first , by allowing the charge to leak from the top plate to earth , and then by up the top plate through the application of a potential to the lower plate .
The two methods gave concordant results .
, the sensitiyeness , was recorded by means of the potentiometer on the films see ; from these it was read in millimetres per volt .
\mdash ; The main part of each experimental observation consisted in otographic records of the variation in the potential ( as shown by the fibre of the electrometer ) of the central electrode .
For this purpose the small contact potential of the Bronson resistance was first neutralised by the application of an equal and opposite potential to the lower plate , and then the tube containing the 5 mgrm .
of radium used was adjusted symmetrically to the two compartments of the ionisation vessel ( see fig. 1 ) .
Equal and opposite potentials of 200 volts were applied to the two plates \mdash ; one in each compartment of the vessel\mdash ; and the ionisations in the gas in these compartments finally adjusted to exact equality by means of a lead screen moved across the front of one .
This adjustment was shown when the fibre , viewed from time to time for about 10 minutes , though varying continually in its , had its mean position approximately coincident with the zero .
The saturation current , with the Bronson resistance in ( which introduced no error ) , was then determined ; this gave the ionisation , and , after the sensiciveness had been adjusted and the photographic apparatus placed in position , the film was set in motion for obtaining the * Measured by method of " " mixtures usin standard cylindrical condenser with a capacity E. S.U. VOL. LXXXIX.\mdash ; A. Mr. P. V -X ul * .
Burbidge .
The in the lonisation due to record .
The order of events in taking each record ( compare fig. 4 ) , was as follows:\mdash ; Sensitiveness recorded .
Fibre earthed .
Fibre isolated ( radium present ) for 20 minutes .
Fibre earthed .
Sensitiveness recorded .
Fibre isolated ( radium absent ) .
After the completion of the raphic record , the radium was replaced in position , and the resistance determined as stated above .
A typical entry of an observation , film No. 68 , reads as follows:\mdash ; Date , 16.10.12 .
Fibre tension in arbitrary units , Screen ( see below ) .
For the evaluation of on film , the section of it recording the fluctuation was divided into several , usually seven , by the timing nals , and the mean position of the fibre in each determined by the use of a planimeter working from an arbitrary base line .
The mean line for the seven points representing these mean positions was then calculated by a least squares method , and its position ruled on the film .
By using a glass scale , about 120 of the deyiation of the fibre from this mean line were taken .
The mean square of these readings , , was then calculated .
Results .
The table fives the results of the work to date ; many other records have been taken but owing to fnorance of the exact conditions required for evaluation , the records are of little immediate value .
In this table , the screen A is that previously .
of aluminium , mm. of glass and part of the adjustable 2 mm. lead screen .
The italicised values for the total resistance in ohms in the table have been calculated from fairly accurate measurelnents of the Bronson resistance , and Mr. P. W. Burbidge .
Table I. a knowledge ( gained from later measurements ) of the leak in the ionisation vessel and the earth-shielded connections , due to the action of the radium in two positions used ; the most doubtful value is that for Film 66 .
The last four values are more accurate , being directly measured as described above .
The values of the ionisation were taken with the Bronson resistance in , as experiments showed that the ratio of the values in any two so taken was ( within per cent. ) the same as the ratio when the Bronson was not in .
The last column ives the absolute fluctuation , evaluated by means of the formula { given above .
The distance of the radium is given from the front end of the ionisation vessel .
The italicised values of the observed fluctuation have been corrected for the spurious fluctuation in those experiments .
The above table ives the results tabulated in the order they were obtained , and they illustrate the effect of varying the distance of the radium from the ionisation vessel , and varying the gas contained in the vessel .
The expressions connecting the fluctuation and the ionisation derived by Campbell* and von Schweidler have been investigated with the object of deducing what relations are to be expected under iven experimental conditions ; and the results of this examination , together with the theory and assumptions on which they are based , are given in the following table .
full discussion of the theory is not given here for the reasons stated in the introduction .
Table II provides the required theoretical relations between the fluctuatior and the ionisation under the experimental conditions used .
It remains to be seen how the experimental results can be elucidated in this way .
In Campbell , .
cit. E. von Schweidler , loc. cit. , and ' Phys. Zeit 1910 , vol. 11 , p. 614 .
Th in the Ionisation due to -Rays .
Table II.*\mdash ; Relation between the Ionisation and Fluctuation for varying Conditions .
eory umber orays p Table III some of the results are revabulated so as to show the effect on the fluctuation of varying the solid of the rays used .
( 1 ) Effect of Distance of Table III .
The above figures indicate that ; the difference between and is large , and the mean value of the fluctuation ratio , , is sufficiently * The suffixes denote the variation of the quantities with the va1iation of the solid angle of rays or of the gas ionised .
In view of the photographic evidence of C. T. R. Wilson Proc , direct ionisation alone is considered .
Campbell ( ' Phys. Zeit loc. cit. ) has deduced the relations holding for direct ionisation ; they are at variance with our experimental results .
Mr. P. W. Burbidge .
close to the mean value of the ionisation ratio , , to permit of easy distinction between relations ( 1 ) and ( 2 ) of Table II .
The observations support ( 1 ) and consequently the entity theory of -rays .
( 2 ) Effect of the Gas.\mdash ; Table uuattei)Ratio o Carbon Dioxide and Air .
2 2 2 2 2 Mean Carbon Dioxide and Coal Gas .
Mean Air and Coal Gas .
1.6 The means in the various experiments show that the ratio of the fluctuations is roughly equal to the ratio of the ionisations , but is consistently larger by about the same fraction in each case , e.g. for the three pairs of gases has the values The value of the fluctuation obviously differs greatly from that given by the expression , and thus relation ( 5 ) in Table II , based on the pulse The result for hydrogen is not considered in this table ; the values it gives for the ratio of the fluctuationf ; agree more nearly with the relation , but the degree of agreement varies widely according to the gas taken for comparison .
Since the value of the fluctuation for it is the smallest , consequently constant errors of evaluation would have most effect , and , further , since the coal-gas used contains probably 40 per cent. of hydrogen and shows no such marked departure , it was considered that confirmation of the result was needed before reliance could be placed upon it in deducing theoretical relations .
The in the Ionisation due to -Rays .
theory , does not hold .
To between the relations , ( 3 ) and ( 4)\mdash ; both derived from the entity theory\mdash ; requires a knowledge of the variation for the used of the number of ions formed in the vessel per , while only the ratio of the ionisation is known .
In both sets of experiments , then , the evidence , though not finally conclusive on account of insufficient data , supports decisively the entity theory of -rays .
The result is of interest , as recent experiments tend to demonstrate that -rays , X-rays and are but types of the same phenomena .
If experiments now conducted confirm the above result , an entity theory of light seems a necessary consequence.* Dr. Meyer 's Results .
Since the results obtained above do not with those of Dr. E. Meyer , of Aachen , who has been -rays by somewhat similar methods , it of interest to consider briefly his published results .
In a paper Dr. Meyer 's earliest on this subject was criticised in certain respects ; CampbellS has also advanced some criticism on other points , and the second publication by Dr. is an experimental [ This theoletical part of the paper is criticised by a referee as follows:\mdash ; " " In first place , the particular form of pulse theory which is compared with the entity theo1y is not one which is likely to be maintained .
It is assumed that on this pulse theory the number of -rays made by one -ray in the ionisation chamber is not small , and is larger than the number would be on an entity theory .
A pulse theory , seriously rivalling the entity theory , must suppose the number of -rays made by one -ray in the ionisation chamber to be very small ; and where this is done , such experiments as are made here cannot distinguish between them .
The fluctuations due to variation in the number of -rays entering the chamber are masked by the fluctuation due to variation in the number of -rays made by each -ray .
" " ln the place , when the gas is varied , ought to vary as on either the pulse or entity theory .
It is now clearly established that the ionisation in such a vessel as was used is due to -rays from the walls .
The fluctuations cannot depend on how these were produced , but only on the number of them , and this must be the same on either theory .
In fact , , the number of ions due to a , is proportional to the whole current ; and thus in Table II ( 3 ) is proportional to or to .
This has been overlooked in the endeavour to establish a basis of experimental comparison of the two theories .
" " Such experiments as are described in this paper are unable to decide between the rival theories .
In this respect the author has made no advance on Meyer 's work ; but the criticism of that work is probably just .
The fact that the present results can be interpreted in absolute measure , and shown to be of the order expected , gives theIn a weight much greater than previous experiments Laby and Burbidge , .
cit. E. Meyer , ' Berliner Berichte , ' 1910 , vol. 32 , p. 647 .
Campbell , 'Phys .
Zeit .
cit. E. Meyer , ' Phys. Zeit 1912 , vol. 13 , p. 73 .
Mr. P. W. Burbidge .
refutation of Campbell 's criticism of the method used for measuring the resistance , between the electrometer needle and its earthed surroundings .
No account is taken by Meyer of the point raised by Campbell and von Schweidler ( loc. cit. ) that the experiments , with the theory as then developed and used by him , afforded no decive distinction between the entity and the continuous pulse theories .
In a third publication , results of the previous work are taken as established , and new experiments made to ascertain if , in an ionisation vessel consisting of two similar compartments , there is any connection between the ionisation in the two sides .
His results lead him to assert a connection , but the work seems open to criticism on the grounds : ( 1 ) With the extreme sensitiveness of the electrometer used ( 10,000 mm. per volt ) and the small fluctuations observed ( 2\mdash ; 14 mm due evidence is not given for the accuracy claimed .
( 2 ) It is not clear that the test given by Meyer for spurious fluctuations included the Bronson resistance used ; the experimental conditions would appear to prohibit this .
It is known that the currents in such resistances fluctuate , and since the conductivity of the resistance by Meyer is from five to ten times as large as the one used in the present experiments , the absolute fluctuation due to it would be larger , but the fluctuation due to the radium would be smaller than in these experiments .
Unless the test for spurious fluctuations in an experiment involves all the arrangements used in the ation of the fluctuations , except that the -rays are absent , the experiment is open to criticism .
( 3 ) The correction for the resistance seems doubtful , e.g. in Tables , VIII , etc. , the resistance ( proportional to in his paper ) has almost the same value when the positive ions in both compartments are collected by the central electrode as when a differential method is used , as in our experiments .
It seems obvious that a much smaller resistance is needed in the former case than in the latter , but the ures do not indicate this .
Dr. Meyer concludes:\mdash ; ( 1 ) That one -ray liberates more than one ( 2 ) That a -ray occupies a solid angle not small compared with that occupied by the ionisation vessel ( i.e. a cone with vertical angle ) .
Buchwald on the grounds of Dr. Meyer 's experiments , has calculated that the probable angle of the cone of such a -ray is E. Meyer , 'Ann . .
Phys 1912 , vol. 37 , p. 700 .
Buchwald , ' Ann. .
Phys 1912 , vol. 39 , p. 41 .
The Fluctuation in the due to -Rays .
Summar.1/ I. Photographic records of the fluctuations in the ionisation due to -rays have been obtained , and the value of the absolute fluctuation estimated them .
II .
The fluctuation has been found almost proportional to the ionisation when either the solid angle of rays used or the in the ionisation yessel is varied .
III .
The theory evolved by Campbell has been confirmed ( a ) by the failure of six other methods of evaluation , none of which gave any constant relation between the fluctuation and the ionisation , even when all other conditions were constant , ( b ) by the concordant obtained by using the correction factor based on his theory . .
Using an extension of the theory of von Schweidler and Campbell , it has been found possible to discriminate between the continuous pulse and the entity theories of -rays .
The results appear to lead to the deduction that a -ray is an entity in the sense that it has a discontinuous " " wave-front.\ldquo ; .
The work of Dr. E. Meyer on the structtuie of -rays is briefly reyiewed and criticised .
The Royal Society of London lent the radium used ; this , and a New Zealand Government Research Scholarship , rendered the yation possible .
I wish also to record my gratitude to Prof. Laby the stimulating help he has given throughout the work .
My thanks are also due to Dr. G. W. C. lCaye for reading the proofs of this paper .
|
rspa_1913_0063 | 0950-1207 | The sublimation of metals at low pressures. | 58 | 67 | 1,913 | 89 | Proceedings of the Royal Society of London. Series A, Containing Papers of a Mathematical and Physical Character | G. W. C. Kaye, B. A., D. Sc.|Donald Ewen, M. Sc.|Dr. R. T. Glazebrook, F. R. S. | article | 6.0.4 | http://dx.doi.org/10.1098/rspa.1913.0063 | en | rspa | 1,910 | 1,900 | 1,900 | 6 | 203 | 4,955 | http://corpora.clarin-d.uni-saarland.de/surprisal/6.0.3/?id=rspa_1913_0063 | 10.1098/rspa.1913.0063 | null | null | null | Thermodynamics | 30.014443 | Atomic Physics | 23.410407 | Thermodynamics | [
-15.936606407165527,
-72.91264343261719
] | 58 The Sublimation of Metals at Low Pressures .
By G. W. C. Kaye , B.A. , D.Sc .
, and Donald Ewen , M.Sc .
( Communicated by Dr. R. T. Glazebrook , F.R.S. Received June 10 , \#151 ; ' Read June 26 , 1913 .
) ( From the National Physical Laboratory .
) [ Plate 5 .
] Introductory .
Many metals have been found to exhibit evidences of volatility at temperatures considerably below their melting points .
As long ago as 1872 , Merget* demonstrated that frozen mercury volatilised perceptibly in air in course of time .
Demar(}ay , 'f* in 1882 , conducted similar experiments vacuo and found that cadmium evaporated sensibly at as low a temperature as 160 ' , zinc at 184 ' , and lead and tin at 360 ' C. In 1887 , Zenghelioj obtained evidence of the volatility of lead , copper , zinc , etc. , even at room temperatures .
Spring , S in 1894 , working at atmospheric pressure , showed that zinc was appreciably volatile at 300 ' , and cadmium and copper at 500 ' .
Roberts-Austen and Merrett , in some unpublished experiments at the Royal Mint , in 1896 , detected the volatility of cadmium and zinc at 100 ' in vacuo , while Krafft|| in 1903 and 1905 investigated in some detail the volatilisation of a number of metals at low pressures .
Rosenhain , at the National Physical Laboratory , has obtained beautiful crystals of sublimed zinc by heating a piece of zinc to 300 ' C. for some weeks in a glass tube containing hydrogen at atmospheric pressure .
The notable phenomena of the interdiffusion of metals , with which Roberts-Austen 's name is associated , provide , of course , additional evidence of the vapour pressure that solid metals exert even at ordinary temperatures .
A familiar illustration of metallic volatilisation is furnished by the blackening of tungsten and carbonlf filament lamps .
Deposits of definite outline can occasionally be detected on the bulbs of the lamps ; a fact which seems to point to the projection of particles in definite directions from the filament .
* Merget , 'Ann .
Chim .
Phys. , ' 1872 , vol. 25 , p. 121 .
t Demargay , ' Comptes Rendus , ' 1882 , vol. 95 , p. 183 .
f Zenghelio , ' Zeit .
Phys. Chem. , ' 1887 , vol. 1 , p. 219 .
S Spring , ' Comptes Rendus , ' 1894 , p. 42 .
|| Krafft , 'Ber .
Deut .
Chem. Gesell .
, ' 1903 , vol. 36 , p. 1690 , and 1905 , vol. 38 , p. 254 .
IT Berthelot showed , in 1904 , that such vaporised carbon is not graphitic , but amorphous .
The Sublimation of Metals at Low Pressures .
59 The extent of the disintegration exhibited by a heated metal depends a great deal on its nature .
In the case of the metals of the platinum group , Crookes* found that when they were heated in still air at atmospheric pressure , they arranged themselves in the following order of increasing volatility : Eh , Pt , Pd , Ir , and Ru .
The marked volatility of iridium at temperatures above 1000 ' C. has long been known to users of platinum-iridium thermocouples .
The disintegration of a metal increases rapidly with a rise in the temperature , and almost all observers are agreed that the presence of oxygen serves to augment the effect , at any rate in those cases which have been investigated .
Hydrogen and nitrogen do not , in general , favour disintegration .
The platinum metals , with the exception of palladium , all disintegrate less as the pressure is lowered , and accordingly it does not appear that in these cases the effect is one of true sublimation .
Robertsf has recently conducted experiments with these metals , and infers that the volatilisation is not a simple process , but is brought about by the formation of endothermic oxides more volatile than the metals themselves , j With most other metals , however , we should naturally expect volatilisation to be facilitated by a reduction of pressure .
We have collected in the following table , the data for a number of metals for which information Metal .
Boiling point .
Volatilisation detectable at Melting point at 1 atmos .
At 1 atmos .
\#166 ; In vacuo .
0 c. 'c .
' c. ' c. Mercury 357 160 -39 -39 Potassium 760 370 63 63 Sodium 880 420 97 97 Cadmium 778 450 160 321 Zinc 918 550 180 419 Bismuth 1420 1000 269 269 Lead 1525 1150 360 327 Silver 1955 1400 ?
680 961 Copper 2310 1600 ?
400 1084 Tin 2270 1700 ?
360 232 Gtold 2530 ?
1800 ?
1370 1064 Iron 2450 \#151 ; 950 1500 Platinum 2500 ?
\#151 ; 1200 1750 * Crookes , ' Roy .
Soc. Proc. , ' May , 1912 , A , vol. 86 , p. 461 .
t Roberts , ' Phil. Mag. , ' February , 1913 , p. 270 .
I In this connection , see Goldstein ( ' Ber .
Deut .
Chem. Ges .
, ' 1904 ) and Magnus ( ' Phys. Zeit .
, ' 1905 , vol. 6 , p. 12 ) , who showed that Pt and Ir at a white heat rapidly absorb oxygen .
Dr. G. W. C. Kaye and Mr. D. Ewen .
regarding the effect of pressure on the boiling point is available .
The values of the higher boiling points are largely due to Greenwood.* Some of the volatilisation temperatures quoted have been recently determined at the National Physical Laboratory .
Columns 2 and 3 reveal the marked effect of pressure on the boiling point ; and Column 4 shows the temperatures at which volatilisation has been detected , mostly at low pressures .
These temperatures are intended to imply appreciable volatilisation ; if the experiments were sufficiently prolonged , volatilisation could be detected in some cases at temperatures even lower than those given , as will be gathered from p. 58 .
Column 5 gives the corresponding melting points and is added for the sake of comparison .
Rectilinear Emission of Particles .
Evidence has recently been obtained of the emission of particles of metal at right angles to the surface of a heated metal , in much the same way , for example , as particles of metal are ejected from the surface of a cathode in a discharge tube .
In most cases , this straight line emission is obscured by general volatilisation ; but when the circumstances were favourable its existence has been detected .
Keboul and de Bollemontj* have recently shown that small strips of either copper or silver , when heated in an electric furnace at temperatures from 400't to 900 ' C. yield black deposits which closely follow the outline of the emitting metal .
Thus when the latter was cut in the shape of a cross , the deposit also was cruciform .
The deposits were received on a platinum screen , and proved to consist either of the emitting metal or its oxide .
In air at atmospheric pressure , 3 mm. was the greatest distance at which such deposits were obtained ; the best results were obtained at about 1 mm. distance .
In oxygen , the effect was enhanced ; in a vacuum , the deposit gained in sharpness of outline .
Curiously enough , in hydrogen , the edges of the strip seemed to be the only active regions , so that the sputtered image reproduced merely the outlines of the strip .
S The rate of deposition increased very considerably as the furnace was made hotter .
On repeating the experiment with a sample of copper which had already been used , the deposit was much less dense than that obtained on the * * * S * Greenwood , ' Boy .
Soc. Proc. , ' 1909 , A , vol. 82 , p. 396 ; 1910 , A , vol. 83 , p. 483 .
+ Beboul and de Bollemont , ' Journ. de Phys. , ' July , 1912 , 5 , vol. 2 , p. 559 .
f Below 400 ' no deposits were obtained .
S A somewhat similar edge-effect was obtained by one of us in connection with the sputtered deposit from an aluminium cathode in a discharge tube ( Kaye , ' Phys. Soc. Proc. , Feb. , 1913 , vol. 25 , p. 198 ) .
The Sublimation of Metals at Low Pressures .
61 first heating .
Other metals\#151 ; nickel , iron , and aluminium\#151 ; were tried , but without success .
Experimental .
The present authors , during the early part of last year , obtained somewhat similar results which are recounted in this paper .
Iridium.__In one experiment , with which Dr. Harker was associated* a strip of pure iridium ( S , fig. 1 ) was heated by the passage of a heavy alternating current of low voltage .
The strip was arranged , edge upwards , within a C Fig. 1 .
Fig. 2 .
hollow metal cylinder of diameter about 18 mm. The gas was nitrogen and the pressure about 20 mm. At the end of the experiment two horizontal bands of deposit A and B were observed on the inner surface of the cylinder , each one facing a side of the iridium strip , and of roughly the same width .
The rest of the cylinder was not wholly free from deposit , but it reached a minimum at points C and D opposite the edges of the strip .
Copper.\#151 ; In a second experiment , a copper tube ( T , fig. 2 ) with a hole ( diameter 8 mm. ) in its side was heated from within by a strip of metal through which alternating heating current was passed .
As shown in fig. 2 , the strip was not in contact with the cylinder .
The pressure was about 1 mm. and the gas nitrogen .
After a few minutes the copper attained a visibly red heat ( 800 ' C. ) , and a black deposit rapidly formed some 4 cm .
away on an opal-glass plate ( P ) placed obliquely , as indicated in the figure .
The deposit approximated in shape to an elliptical ring .
This is to be ascribed to the sputtering action of the edge of the hole in the tube .
The outline of the sputtered ring was shortly afterwards largely obscured by general deposit from the body of the tube and the heating strip .
Fig. 3 gives a notion of the appearance of part of the elliptical band of deposit ; it has been strengthened slightly in the photograph ( see Plate 5 ) .
* See Harker and Kaye , ' Roy .
Soc. Proc. , ' 1913 , A , vol. 88 , p. 536 .
Dr. G. W. C. Kaye and Mr. D. Ewen .
Iron.\#151 ; In a further series of experiments , some interesting deposits have been obtained with iron .
Commercially pure Swedish wrought iron was used in the form of thin strips which were highly polished .
The arrangement of the apparatus is indicated in fig. 4 .
The iron strip A was mounted vertically and connected at its extremities to two stout copper leads , by which means the strip was heated electrically by direct current .
Parallel to , and at about 1 mm from , the polished surface of the iron was stretched a strip of platinum foil B , in the centre of which was a small hole about 3 mm. square .
A second piece of platinum foil C was welded on to B , and contained another similar hole so arranged that the two holes in B and C were opposite each other and about 5 mm. apart .
A third strip of platinum foil D was mounted opposite the hole in C and about 1 mm. away from C. Strips B and C were electrically insulated from the iron strip A , and the outermost strip D , which was intended to receive the deposit , was connected to the positive end of the iron " strip .
The whole was placed in a vessel which was highly exhausted , and the iron strip was then heated by passing through it a direct current of about 20 to 30 amperes at 50 to 100 volts .
The temperature of the iron was kept at about 950 ' C. for some 5 hours.* By this means , a dark brown deposit was obtained on the platinum strip D , and , as shown in the photograph ( fig. 5 ) , the deposit took the form of a well defined image of the square holes in the other pieces of foil .
The clearly defined edges of this shadow make it difficult to imagine that the method of transference of the material can be other than some kind of rectilinear propagation of the volatilised particles .
The slight distortion of the image is due in part to a want of alignment of the two holes in B and C , and partly to the shape of the hole in C. No deposit was found on the sides of B and C remote from the hot iron strip .
Big .
5 shows the black deposit on the side of B facing the iron * The temperature was measured by a hot-wire optical pyrometer .
Platinum Screen D Iron Strip A 1 2 3cm .
Fig. 4 .
The Sublimation of Metals at Low Pressures .
63 strip .
There was also some deposit on the corresponding face of C around the sides of the hole ; a feature which indicates that not all the particles are projected normally from the iron .
In some experiments , plate C was removed and only the one hole ( in B ) used ; the deposits in these cases were not quite so well defined .
The surface of the emitting iron strip , when examined under a fairly high power , shows regularly oriented etched pitting ( fig. 6 ) .
The method of heating by direct current seems to favour the development of these etched pits to an extraordinary degree .
As described later , specimens of iron were also heated in a tube furnace in vacuo to the same temperature as before , viz. , 950 ' C. In these cases , the etched pitting of the surface , although generally distinguishable , was not developed to anything like the same extent as in specimens heated under the same conditions by the passage of the heating current through the specimens themselves .
It would appear , therefore , that the electrical conditions which obtain in the latter case predispose the metal to disintegration , as evidenced by the etching effects.* It would be of interest to see if heating by the passage of an alternating current through a metal would also produce such marked pitting .
The frequent twinning , an example of which is shown in fig. 6 , is , of course , characteristic of the structure of iron at the temperature of the experiments .
The central and hottest portion of the iron strip , which was opposite the holes in the platinum strips , was afterwards found to be brown in colour .
The appearance suggested that a certain amount of oxidation had taken place in spite of the fairly high vacuum employed.f This is supported by the fact that on subsequently annealing the iron in hydrogen the brown colour disappeared and the iron reverted to its normal tint .
The deposit was found , when tested , to give a distinct iron reaction , thus proving that the shadow was due to the transference of particles from the iron .
The loss in weight of the iron specimen was too small to be detected by an ordinary chemical balance .
The adhesion of the deposits to the receiving strip of platinum was remarkable , vigorous polishing for some minutes being necessary for their removal .
Under the microscope , the surface of the platinum where the deposit was formed shows a reticular pattern resembling the structure obtained on polished and etched metallic surfaces .
* Fredenhagen ( ' Phys. Zeit .
, ' 1912 , vol. 13 , p. 539 ) found a parallel effect with the negative electrical discharge from a hot metal in vacuo .
The emission from a certain electrode , when the latter was heated in an electric furnace , was only 1 per cent , of that obtained on heating by direct current to the same temperature .
t The pressure was initially of the order of 0'004 mm. of mercury and during the course of the heating averaged about 0'035 mm. , the rise being accounted for by the evolution of gases from the heated iron .
Dr. G. W. C. Kaye and Mr. D. Ewen .
As the result of a number of experiments , it was found that the maximum range of the iron particles was about 1 cm .
in a good vacuum ; at higher pressures it would probably be less.* Deposits from iron were also obtained on non-metallic receiving surfaces , such as fused silica .
In order to examine more closely into the cause of this transference of material , some further experiments were carried out with iron , in which the arrangements were similar to those already described , but the heating was effected by an electric tube-furnace , wound with a spiral resistor of nichrome wire ; the iron specimen did not , therefore , in this case , carry any current .
The window in these experiments was a long slit parallel to and about 2 mm. from the strip ; only one window was employed .
As before , quite a sharp shadow of outline corresponding to the slit was obtained on a platinum screen , about 1 mm. distant from the slit .
This is shown in fig. 7 ; the illumination of the screen in the photograph causes the grey deposit to appear white on a dark ground .
With this arrangement , one hour 's heating produced only very faint indications of a deposit , whilst a clearly defined image was obtained from a run lasting three hours .
With direct-current heating , on the other hand , the rate of deposition was much more rapid , and in one experiment , 10 minutes sufficed to produce a fairly clear deposit ( see also p. 63 ) .
In the tube-furnace experiment the temperature was not quite uniform , so that both iron strip and platinum screen were a good deal hotter at one end than the other .
The deposit on the screen was found to be fainter at the hotter end ; this was probably due to the greater loss by evaporation from the hot end of the screen .
The deposit shown in fig. 7 did not possess the brown colour of the shadows obtained in the previous experiments , nor , as has already been remarked , did the surface of the iron show such characteristic etched pitting .
Thus , although more prominent deposits were obtained when there was slight oxidation , it would appear that the presence of oxygen\#151 ; at any rate , in quantity sufficient to cause visible oxidation\#151 ; is not essential to the process of transference .
Tungsten.\#151 ; Extensive deposits and corresponding shadow results were also obtained when tungsten was heated in vacuo to about 1800 ' C. ' Discussion .
From the foregoing results , and those obtained by Reboul and de Bollemont , it would appear that there are two main classes of vapour given out when a metal volatilises ; one kind , which is associated with * Cf .
Reboul and de Bollemont , above .
The Sublimation of Metals Low Pressures .
65 evaporation as usually understood by the term , the other , made up of particles of metal , which travel in straight lines from the surface of the metal , which they leave approximately at right angles , and which , as our experiments appear to show , have ( in the case of iron , at any rate ) a range of only a centimetre or so in vacuo .
Wliat may be the inherent cause of difference between these two kinds of particles we are not in a position to say at present ; we suggest that the " rectilinear " type consists of electrified particles of metal , while the ordinary vapour particles are electrically neutral .
It is well known that , if a liquid has its surface suddenly changed in area , a surplus charge of electricity makes its appearance , as , for example , in the splashing of water or mercury .
On the same grounds , the pitting of the heated surface , and the consequent alteration of area , would be expected to release a certain amount of electrification , which would , in favourable cases , accompany the liberated particles .
The repulsion of the charged particles at right angles to the surface of the heated metal would follow if the surface were also charged with like sign ; this , of course , is possible with a strip heated by direct current .
We have already remarked on the special efficacy of direct current in producing deposits .
The effect is not so easy to explain in the case of the tube-furnace and alternating-current experiments .
Reboul and de Bollemont suggest , in explanation of the phenomena , that the transference of the material is due to miniature eruptions caused by the explosive combination of occluded hydrogen and oxygen in the metal .
On this view , the effect would be expected to fatigue , and this is in accordance with their experiments ( p. 60 ) .
The explanation does not , however , seem to us convincing .
In our experiments with iron , the temperature did not exceed about 1000 ' C. , under which conditions we should expect that any electrified particles there might be would carry a positive charge ; and , in fact , Sir J. J. Thomson* showed some years ago that positively charged particles of metal were among the positive ions given off by platinum heated to moderate temperatures at low pressures .
It would be interesting to see if a difference could be detected in the intensity of the deposits obtained from either end of a strip of metal heated by direct current .
On the above hypothesis , the positive end of the strip might give an appreciably heavier deposit at such temperatures .
At higher temperatures than we have employed\#151 ; near and above the melting point of iron\#151 ; negative electricity predominates , and opposite results would accordingly be expected in such an experiment .
The effect of a ' magnetic field on the stream of particles would , of course , be a valuable * 'Conduction of Electricity through Gases , ' 1906 , p. 217 .
VOL. LXXXIX\#151 ; A. F Dr. G. W. C. Kaye and Mr. D. Ewen .
piece of evidence .
By such means , Owen and Halsall* find , however , that in a good vacuum , and over a wide range of temperatures all high enough to give negative ionisation , the thermionic current , in the case of Pt , Pd and Ir , is due almost entirely to electrons .
They conclude that the proportion of heavy and metallic negative ions is certainly less than 1 part in 2000 .
It should be remarked also that Eoberts , in the paper already referred to , did not find any evidence of particles which were electrified in the vapours of the platinum metals .
But , from his published account , we should gather that the fog-condensation chamber , by which he tested the point , was probably too remote from the heated metal to detect such short-range particles as we have described .
The influence of traces of oxygen in producing a kind of " weathering " of the surface of the metal is one on which stress has been laid by a number of experimenters , and it is reasonable to suppose that some such action would augment the disintegration to a marked degree with some metals .
It is significant that most workers are agreed that the presence of oxygen accentuates the positive electrical emission from hot metals ; in such cases we may regard the charged particles as the direct outcome of the energy of reaction between the metal and the gas .
We have elsewhere noted Eoberts ' conclusions as to the part played by oxygen in the volatilisation of the platinum metals , and it is a matter for further investigation to ascertain the extent of the effect with the baser 'metals .
Some evidence is afforded by the experiments on p. 64 .
f As an alternative to the charged-particle hypothesis it is not impossible that the distinction between the " rectilinear " particles and the ordinary particles is one chiefly of size .
We should expect that very small emitted particles of metal\#151 ; with dimensions not far from molecular\#151 ; would suffer appreciable scattering by the gas molecules and lose very speedily their original direction of projection .
But larger particles , projected with the same velocity , would travel farther before being similarly disturbed .
Possibly the range of the projected particles under the same temperature conditions varies considerably from metal to metal ; and this may account for the lack of success which attended Eeboul and de Bollemont 's efforts to obtain deposits with metals other than copper and silver at atmospheric pressure .
It may not be too far from the purpose of this paper to consider the possible source of such large particles .
Dr. Eosenhain and one of usj have * ' Phil. Mag. , ' May , 1913 , vol. 25 , p. 735 .
+ See also Humfrey , 'Iron and Steel Inst. Jonrn .
, ' 1912 , Carnegie Memoirs .
I " Intercrystalline Cohesion in Metals , " Rosenhain and Ewen , 'Inst .
Metals Journ , , Sept. , 1912 , Kaye and , Roy .
Soc. ProeA , 89 , Plate 5 .
Fig. 3.\#151 ; Copper Deposit .
B and C D Fig. 5.\#151 ; Photograph of Hole and Iron Deposit cast by it .
In the above figure , plate C is behind plate B. Full size .
Fig. G. Pitted Surface of Iron Str ip , x 500 diameters .
The Sublimation of Metals at Low Pressures .
put forward a theory as to the mechanism by which evaporation takes place from crystalline metals .
The view was adopted , from the observations of the behaviour of a number of metals in vacuo , that the volatilised metal consists initially of the intercrystalline amorphous material which cements together the crystal faces .
This amorphous cement is more volatile than the crystals themselves , and accordingly grooves or channels are formed along the crystal boundaries of metals subjected to prolonged heating in vacuo .
The increased liability to erosion along the sides of these channels may perhaps be the cause , directly or indirectly , of particles larger than those from the body of the crystals .
With polished specimens the channels are visible under the microscope ; the process is known as vacuum etching .
If there is any real analogy between the sputtering from a cathode in a low-pressure discharge tube , and thermal sputtering such as we have described , it may be that cathodic sputtering carried out under suitable conditions would similarly lead to the formation of patterns corresponding to the structure of the metal .
So far as evaporation from the crystals themselves is concerned , we may usefully employ the conception of a " crystal unit " adopted by some metallo-graphists .
The term implies a small ordered stable aggregate of molecules which serves as a brick from which to build up the crystal structure .
We may imagine that either through the application of heat or by chemical combination the stability of a surface unit is endangered by reason of the loss of individual outlying molecules .
The whole unit disintegrates and conies away piecemeal from the crystal in particles , may be , of appreciable size , and at the same time a pit is commenced in the crystal surface .
We should not be unreasonable in expecting that such particles coming from a stable crystal system would be electrically charged , in contradistinction to those coming from an unordered amorphous medium .
The results described in this paper are to be regarded as of a preliminary character ; it will be apparent that there is scope for further work in a number of directions .
|
rspa_1913_0064 | 0950-1207 | A peculiar form of low potential discharge in the highest vacua. | 68 | 74 | 1,913 | 89 | 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.1913.0064 | en | rspa | 1,910 | 1,900 | 1,900 | 5 | 109 | 2,535 | http://corpora.clarin-d.uni-saarland.de/surprisal/6.0.3/?id=rspa_1913_0064 | 10.1098/rspa.1913.0064 | null | null | null | Electricity | 66.416423 | Thermodynamics | 11.025781 | Electricity | [
6.390046119689941,
-58.4385986328125
] | A Peculiar Form oj Low Potential Discharge in the Highest Vacua .
By the Hon. R. J. Strutt , E.R.S. , Professor of Physics , Imperial College of Science , South Kensington .
( Received June 18 , \#151 ; Read June 26 , 1913 .
) Mr. C. E. S. Phillips has described a curious electrical electrodes Ei , E2 , fig. l , f were fixed in a glass bulb as shown .
effect* Iron The bulb was E , E Fig. 1 .
exhausted very highly ; a discharge was passed for a moment , and turned off .
The iron electrodes were then magnetised by exciting the electromagnets Mi , M2 .
On magnetisation , a luminous ring was observed in the equatorial plane of the magnet , which lasted for a few seconds , and then died out .
The effect excited considerable interest at the time , and careful experiments were made by the discoverer to elucidate its causes .
The following may be quoted from the concluding section of the paper as representing his views .
" The preceding experiments show that the principal effect of the magnets is to produce a concentration of negative ions at the strongest portion of the magnetic field , and centrally within the bulb ... ... ... . .
I consider that this concentration of negative ions is due to two main causes .
In the first place it is partly produced by the action of the magnetic field on ions already in motion within the bulb ... ... ... And secondly owing to the reaction resulting from the sudden excitation of the magnets , the comparatively dense cloud of ions situated at the ends of the bulb would , in rapidly turning about the magnetic axis , tend to move towards the pointed end of the electrodes , and so concentrate as observed .
" I find some difficulty in forming a clear idea of the theory here suggested but the effects are apparently attributed to ions left in the volume of the * 'Roy .
Soc. Proc. , ' 1898 , vol. 64 , p. 172 ; ' Phil. Trans. , ' A , 1901 , vol. 197 , p. 135 .
t This figure is taken from Phillips ' paper .
Lotv Potential Discharge in the Highest Vacua .
bulb , and to the electromotive force set up by the sudden growth of the magnetic held .
The latter point of view was favoured by Prof. S. P. Thompson* and by Lord Kelvin , f but the experiments described below cannot be reconciled with it , or with the idea that ions left in the gas by the preliminary discharge have anything to do with the phenomena .
In other passages Phillips attaches importance to charges of electricity left on the glass walls by the preliminary discharge .
In this , as I hope to be able to show , he is entirely right .
Fig. 2 .
To test the latter question , it was decided to repeat the experiments in a vessel lined internally with wire gauze , thus avoiding the uncertainty always encountered in experimenting with charged insulators .
The vessel employed is shown in fig. 2 .
The gauze lining was separated from the iron poles by a short length of glass , and communicated with the outside by a wire so that it could be brought to any desired potential .
The vessel was highly exhausted by a Gaede pump followed by cooled charcoal .
An induction coil was connected to the end caps A , B. The coil circuit was insulated , and the gauze lining connected to earth .
The coil discharge passed with difficulty , with occasional flashes of green phosphorescence .
It sufficed to pass it for a moment only .
Then , when the electrodes were magnetised , the equatorial ring described by Phillips appeared extending as far as the gauze sheath .
It * ' Electrician , ' 1899 , vol. 43 , p. 412 .
+ * Electrician , ' 1899 , vol. 43 , p. 532 .
70 Hon. B. J. Strutt .
A Peculiar Form of lasted 3 seconds or more and then became visibly intermittent , finally ceasing .
If the gauze sheath was electrically connected with the pair of poles AB , the ring was instantly extinguished , no trace of it remaining .
This experiment makes it certain that the ring is essentially connected with a difference of potential between the inner walls of the vessel and the pair of iron electrodes .
The potential difference must be attributed in this case to a charge left on the electrodes , and on the coil circuit connected with them , since the gauze lining is earthed .
Since a charge on the iron poles was necessary , it was an obvious step to maintain it by means of an electrical machine .
" When the iron poles ( connected together ) were kept negatively electrified in this way , the ring could be maintained indefinitely .
It was extinguished when the magnet was turned off , but reappeared when the magnet was turned on again , and then remained steady .
It is therefore evidently unconnected with induced electromotive forces produced during establishment of the magnetic field .
The preliminary induction coil discharge was not necessary .
The ring could be started at any time without it .
Finally , no ring was obtained when the iron poles were positively electrified .
Measurements of the potential difference between the iron poles and the gauze lining when the ring was formed showed that this only amounted to about 300 or 400 volts , varying somewhat with the exact conditions .
When the magnet current was turned off this potential difference at once leapt up to a very high value , far above the capacity of the measuring instruments available ( 12,000 volts ) .
The experiments just recorded indicate the following proximate explanation of Phillips ' phenomenon .
The preliminary induction coil discharge serves only to leave a static charge of electricity on the glass walls , or , if the induction coil circuit is nowhere earthed , on the electrodes .
Under ordinary conditions the electricity thus left is far from being able to discharge itself through the highly rarefied gas .
But when the magnetic field has been created its escape is very much facilitated .
The luminous ring indicates discharge .
That the discharge lasts some seconds is probably to be explained by the well-known gradual leaking out of the electric charge from insulators .
In the modified form of experiment with earthed gauze walls the charge is on the iron poles and on the secondary circuit of the Buhmkorff coil ( not in action ) .
The capacity is mainly in the condenser formed by the insulating tube on which the secondary is wound , the primary and secondary acting as coatings .
The charge of this condenser leaks out gradually , owing to " electric absorption .
" Lovj Potential Discharge in the Highest Vacua .
The question next to be faced is why the discharge potential is so enormously reduced by excitation of the magnets .
With the conical pole pieces so far used , it is difficult to determine whether the effective component of the magnetic force at the electrode surface is parallel to the lines of electric force , or perpendicular to them .
A piece of brass tubing was slipped over the pole pieces as indicated in fig. 3 , connecting them electrically , but not , of course , magnetically .
The low potential ring Fig. 3 .
ft MODS Fig. 4 .
discharge was equally well obtained in this case , starting from the portion 9f the brass tube midway between the poles .
The lines of electrostatic force are with this arrangement necessarily radial to the brass tube , and the lines of magnetic force in the equatorial plane are at right angles to them , as indicated by the dotted lines .
Let us consider what will be the path of an electron starting from the brass tube , used as cathode .
If the electric force alone were acting , the electron would , of course , go radially outwards towards the anode , which is concentric with the brass tube .
When , however , a transverse magnetic force acts as well , the electron will be deflected from its initial path , and will tend to curl round the brass tube from which it started , at the same time as it moves outwards under the influence of the electric force .
The resultant path will therefore be a spiral* and the electron will perhaps cross the radius of the cathode along which it started several times ( fig. 4 ) before reaching the anode .
In an ordinary vacuum discharge , without magnetic force , electrons starting from the cathode are not able to ionise the gas until they have travelled a certain distance , represented by the Crookes dark space .
Why this should be so , and , in particular , why the region of ionisation the negative glow ) is suddenly entered , is hard to understand .
Accepting it * The form of this spiral could he calculated if we regarded the motion as free and made simple assumptions as to the radial distr ibution of the electric and magnetic forces .
But it is , of course , useless to regard the distribution of electric force as undisturbed by the passage of the current .
Hon. R. J. Strutt .
A Peculiar Form however , as a fact , we can in a measure foresee the action of magnetic force with this disposition of electrodes in lowering the discharge potential .
The gas space in the neighbourhood of any element of area on the cathode is continually crossed by electrons from elements of area at some anaular distance away round the tube ; electrons which have already travelled some distance through the gas possibly in circulating more than once right round the cathode .
They , at any rate , are able to ionise the gas , and consequently to lower the potential gradient .
Thus the Crookes dark space , the un-ionised region in which the great expenditure of electromotive force occurs , is almost abolished , and the discharge potential drops accordingly .
Discharges of this kind can be conveniently maintained by a battery of say 300 cells , a telephone in the circuit is quite silent , unless the current exceeds a certain limit .
Additional and Confirmatory Experiments .
The spiral path of the electrons is clearly indicated by theory , and affords as satisfactory an explanation as can be expected of the great diminution of voltage drop at the cathode , having regard to the general level of our comprehension of such phenomena .
No spiral structure can be seen in the luminous effect , nor is it to be expected , since everything is symmetrical about an axis .
The spirals starting from different azimuths round the cathode overlap , the aggregate thus produced having circular symmetry .
We can , however , prove that the paths of the electrons have a tangential component by simply interposing a radial partition KJKl_ which stops tangential motion , though it Fig - does not interfere with direct passage of ions between the electrodes .
The low potential discharge then fails , and we can only force the current through at the enormous electromotive forces ordinarily required in high vacua , Low Potential Discharge in the Highest Vacua .
73 Fig. 5 shows the arrangement .
The brass tube A contains inside it the magnet poles ( not shown ) about 1 cm .
apart , separated by a brass distance piece .
The tube is cemented airtight right through the glass envelope and serves as cathode .
Its interior , however , is independent of the vacuum , so that the distance between the poles can be adjusted without difficulty .
The concentric ring anode B , 4'5 cm .
in diameter , is slit at c to admit the mica slip D. D can be lowered by means of a thread from the winch E , which can be operated from outside.* On lowering the mica slip , the effects are as follows : At first the rise of potential is small , not exceeding a hundred or two volts until the mica is half-way down .
It then begins to increase more rapidly until , when 2 or 3 mm. off the brass tube , it has risen to 1000 volts .
Finally , when nearly touching , the potential suddenly leaps up until capable of spaxking 2 or 3 inches in air ; this stage is conveniently demonstrated by an induction coil , though the steady voltage of an electrical machine or battery is necessary when the lower voltages are to be measured .
These changes in the discharge potential are accompanied by interesting luminous effects .
In the absence of the radial partition , the whole space between the electrodes in filled with luminosity .
As the mica descends , it cuts off the light in the sharpest and clearest manner from the whole circular ring into which it protrudes .
Beyond this limit nearer the centre , the luminosity remains unaffected ( fig. 6 ) .
The experiment proves most definitely that the circular movement of electrons ordinarily prevails as far * The winch is constructed by filing a groove for the thread round the plug of an ordinary stopcock ; this arrangement is copied from one devised by Mr. Aston for Sir J. J. Thomson 's experiments on positive rays .
VOL. LXXXIX.\#151 ; A. G Low Potential Discharge in the Highest Vacua .
out as the anode ring .
At the same time the character of the discharge is not fundamentally altered , unless circular movement in the immediate neighbourhood of the cathode is prevented .
When this occurs , the mica partition being right down , no more luminosity is to be seen in the gas , and green phosphorescence of the glass envelope , previously absent , suddenly becomes intense .
Summary .
The phenomenon originally described by Mr. C. E. S. Phillips is traced to its origin .
As an outcome of this a peculiar form of electric discharge is studied .
The cathode is a cylinder immersed in a magnetic field parallel to itself .
The anode is a ring concentric with the cathode .
In very high vacua the electrons travel from cathode to anode in a spiral path , whirling round the cathode .
The drop of potential over the cathode region is reduced from , say , 200,000 volts to 300 volts .
Further investigations are in progress , including the detailed study of potential gradient in these discharges at various gas densities .
|
rspa_1913_0065 | 0950-1207 | On the efficiency of selenium as a detector of light. | 75 | 90 | 1,913 | 89 | Proceedings of the Royal Society of London. Series A, Containing Papers of a Mathematical and Physical Character | E. E. Fournier d\amp;apos;Albe, D. Sc.(Birm).|Prof. J. H. Poynting, F. R. S. | article | 6.0.4 | http://dx.doi.org/10.1098/rspa.1913.0065 | en | rspa | 1,910 | 1,900 | 1,900 | 16 | 364 | 6,707 | http://corpora.clarin-d.uni-saarland.de/surprisal/6.0.3/?id=rspa_1913_0065 | 10.1098/rspa.1913.0065 | null | null | null | Optics | 33.742691 | Electricity | 32.429278 | Optics | [
25.295940399169922,
-44.95330810546875
] | ]\gt ; the Efficiency of Selenium as Detector of Light .
By E. E. FOURNIER D'ALBE , D.Sc .
( Birm .
) .
( Communicated by Prof. J. H. Pointing , F.R.S. Received bIay 7 June 19 , 1913 .
) The following investigation concerns the limits up to which minute quantities of light and minute variations of its intensity ma .
be discovered by means of seleninm .
There are two actions of on selenium which may be used\mdash ; ( l ) a change in the conductivity , first described by .
Smith in 1873 ; and ( 2 ) the generation of an E.M.F. in a yoltaic cell in which selenitun is an electrode ( Sabine , 1878 ) .
The of an apparatus for the detection of is the ratio of the amount of measurable effect it indicates to the of eceived by the apparatus .
Both the above actions static , the amount of light available is best stated in terms of the steady flux of , the unit the lumen , or the amount of falling upon 1 sq . .
distant 1 .
from a source of 1 candle-power .
Hitherto it has been customary to specify the sensitiveness\ldquo ; of a selenium preparation by stating the ratio in which its resistance is reduced by a iven illumination , reckoned in metre-candles lux This practice , however , ives no indication , the usefnl effect to be obtained from a restricted of , such as that out conically from a star , as this ) ends upon the extent of the sensitive surface to be coyered .
Since the obtainable with a given selenium preparation is directly proportional , as a rule , to its sensitive surface , the latter has to be taken into account in determining its efficiency , and this is done by specifying the in lumen rather than lux .
Voltaic elenium " " cells properly so called , are electrolytic cells in which illuminated selenium forms one of the electrodes and yenerates an E.M.F. Their efficiency should be defined as the E.M.F. in volts enerated per lume1l when the illumination is 1 lux .
The illumination must be specified , since the .
is proportional to the square root of the incident Thus , in the arrangement adopted for the selenium of stars , volt was obtained by .
a sensitive surface of sq .
cm .
means of a candle at a distance of .
The * G. M. Minchin , ' Bo Soc. Proc 189 vol. 58 , p. 142 ; and 1896 , vol. ) , 231 .
VOL. LXXXIX.\mdash ; A. Dr. E. E. Fournier d'Albe .
On the was lux .
With unit illumination , the E.M.F. would have been volt .
Then the flux of light intercepted by sq .
cm .
would have been microlumen , and the resulting voltaic efficiency is 1270 volts per lumen .
Th.e Galvanometric Effieiency .
Selenium " " cells\ldquo ; in which the action due to light is a in the resistance selenium are more properly termed selenium " " bridges\ldquo ; ( Minchin ) .
The problem here presented for solution is not so much to obtain the possible ratio of ' ' dark\ldquo ; to " " light\ldquo ; resistance , but the absolute increase of conductivity , i.e. the largest additional current on .
to light .
In this respect , the most " " sensitive\ldquo ; bridges may be comparatively useless unless they also have a reasonably low resistance , and this it has always been found difficult to secure .
The " " galvanometric efficiency\ldquo ; may be defined as the increase of conductivity produced in a selenium bridge under unit flux of light .
Conyenient nunlbers , applicable to most made , are obtained if the conductivity is reckoned in reciprocals of megohms micromhos and the flux of in lumen .
Thus , a selenium bridge 10 cm .
square , placed at 1 .
from a 100 candle-power source , would receive llumen of .
If , under those circumstances , its resistance changed just as it would if a megohm were connected in parallel with it , its " " galvanometric efficiency\ldquo ; uld be unity .
Observed Efficiencies .
The data hitherto published with to the results obtained by means of selenium preparations are often insufficient for their efficiencies .
M. Reinganum , * using photo-voltaic selenium cells with a sensitive surface of sq .
cm .
, obtained about volt with a Nernst lamp placed at 30 cm .
This gives a voltaic efficiency of about 6 volts per lumen at normal illumination if the square root law holds good for intense illuminations .
Low as this efficiency is , it is probably considerably above that obtained by .
Uljanin in 1888 , who observed volt in sunlight about .
As regards galvanometric efficiencies , the greatest interest , from the point of view of the present investigation , attaches to the figures given by Stebbins , recently studied the light-curve of Algol by means of a selenium bridge .
The light from the star was received by the 12-inch M. Reinganum , ' Phys. Zeitschr 1906 , vol. 7 , p. 786 ; and 1907 , vol. 8 , p. 293 . .
Uljanin , ' Wied .
Ann 1888 , vol. 36 , p. 241 .
J. Stebbins , ' Astrophys .
Journ 1910 , vol. 32 , p. 185 .
Efficiency of Selenium as Detector of Light .
objective of a refractor , and an extra-focal cm .
in diameter was formed on a Giltay selenium bridge having a " " dark\ldquo ; resistance of 3 megohms .
The illumination due to the star was thus increased 1,900 times .
Now , the illumination due to Arcturus is very nearly one microlux* .
The stellar magnitudes of Arcturus and Algol at maximum are given by the Nautical Almanac as and respectively .
Hence the unaided\ldquo ; illumin ation } ) Algol will be microlux , and the illumination of its extra-focal image 330 microlux .
This illumination , falling on a surface of area sq .
cm .
, gives a light flux of micro- lumen .
The deflection shown by the galvanometer was 8 diyisions .
The deflection represented a current of ampere .
The used was 6 .
Hence the additional conductivity was micromhos , and the galvanometric efficiency\ldquo ; was 20,200 micromhos per lumen .
That a alvanometric efficiency of 25,200 is unusually great will appear from a calculation of the efficiency of a cylindrical bridge described by Buhmer as the best out of a number of bridges tested .
The area exposed to an illumination of was sq .
cm .
, a flux of lumen .
resistance fell from 35,000 ohms to half that value , which means an additional conductivity of micromhos .
Hence the efficiency is micromhos per lumen .
Another Ruhmer , used by Korn for yraphy , had an efficiency of about 234 micromhos per lumen in " " diffused daylight\ldquo ; ( about .
Conditions In order to compare two selenium bridges under standard conditions , it is necessary to take into account a number of circumstances their indications .
These are the ( a ) Colour.\mdash ; For the ordinary sources of light , the maximum effect shown by selenium is that due to the visible red , and as the maximum shifts with the distribution of energy in the spectrum , this distribution must be specified .
In practice , it will be most convenient to adopt a standard istribution of energy in the spectrum , such as is offered by one of the } ) standards of rhtness .
I suggest , as the standard illumi]ation , that provided by the whole spectrum of Harcourt 's pentane standard , the distance from the .
M. Minchin ( C. Boys ) , 'Nature , ' , vol. 62 , p. 246 .
See also G. Muller , ' Die Photometrie .
Gestirne ' Engelmann , Leipzig ) . .
Ruhmer , ' Phys. Zeitschr 1902 , vol. 3 , p. 468 . .
Korn , ' Phys. Zeitschr 1904 , vol. 5 , p. 113 .
7 .
Dr. E. E. Fournier d'Albe .
On the source being such as to give one lux .
As an alternative , the Hefner lamp be adopted .
( b ) Temp found that the sensitiveness of a selenium bridge was considerably increased by its temperature permanently to C. found a reduction of 25 per cent. in the sensitiveness on plunging a bridge into liquid air .
I found a reduction of 10 per cent. under the same circumstances .
I propose to adopt C. as the most convenient standard temperature , freezing point being unsuitable for photo-Yoltaic selenium cells .
( c ) Voltage.\mdash ; The resistance of a selenium depends upon the , the percentage decrease of resistance being proportional to the logarithm of the applied I propose 1 volt as the standard voltage .
This has the advantage that the efficiency can be expressed in micro-amperes ( instead of micromhos ) per lumen .
The voltage does not sensibly affect the sensitiveness , unless it is so high that the Joulean heating produces a perceptible rise in the temperature of the , whereupon the sensitiveness decreases .
The wide divergence of results hitherto obtained with regard to the " " sensitiveness\ldquo ; of selenium is attributable to the differences in method of exposure and of interpretation .
The measurements are affected by the " " inertia\ldquo ; of selenium , shown in the slowness with which it acquires its final conductivity when illuminated , and the even greater slowness of recovery in the dark .
In selenium bridges with graphite electrodes , in which there is no chemical action between the electrodes and the selenium , the changes of conductivity during and after faint illumination closely approximate to what they would be if due to a progressive ionisation of the selenium under the action of light , the number of ions produced in unit of time being proportional to the flux , and the total number proportional to the total quantity of light , less whatever ions recombined .
The equation to the light-action curve is then where is proportional to the flux of incident energy and is the coefficient of recombination .
is the additional conductivity , and is proportional to the number of ions of both signs liberated .
In a steady state , or the final steady conductivity is proportional to the square root of the light intensity ( as actually found by Boss , Adams , Berndt , and Minchin ) . .
Stebbins , .
cit. Pocchettino , ' Rend .
R. Accad .
dei Lincei , ' 1902 , vol. 11 , p. 286 . .
E. Fournier d'Albe , ' Eoy .
Soc. Proc 1912 , , vol. 86 , p. 452 .
Efficiency of Selenium as a Detector of Light .
integration we get , or The -curve has an initial line portion inclined to the -axis , so that before recombination becomes considerable the change of conductivity on illumination is .to the incident , as is found to be the case for all feeble exposures .
For the recovery curve we have , by , the relation where is the additiorial conductivity at the moment of shutting off the light .
ma be most conveniently obtained from the recovery curve itself .
If the galvanometel deflection at the moment of obscuration is called zero , and are two taken at equal time-intervals after that moment , then This is the final value ained by the recovery after a very long time .
It is hereinafter called the " " total recovery and by .
It is , other conditions being equal , the net additional conductivity due to previous illumination , whatever may have been the method of exposure .
But since the rapidity of reaction varies greatly with the intensity of the tJht , it is best to adopt a method of exposure in which the light action has a definite relation to the recovery .
This is attained by alternately ) and obscuring for equal times until the curve oscillates between steady valuea Then the number of ions produced by illnmination is twice the number recombined in the same time , and if the number produced varies as the incident enelgy , the amplitude of ] ation will also vary as the incident energy .
This is shown below to be very approximately the case .
Thus the process proposed for ( the true increase of tlctivity for a given illumination is the following:\mdash ; Illuminate and darken for alternate periods of one minute each , and when the " " light\ldquo ; and " " dark\ldquo ; deflections have each become consistent , shut off the light finally and take readings after the first and second minute .
The conditions proposed for determining the normal galvanome efficiency of a selenium bridge may here be summarised:\mdash ; Dr. E. E. Fournier d'Albe .
On the Quality of : complete radiation from a standard pentane lamp .
( b ) Illumination : llux .
( c ) Voltage : 1 volt .
( d ) Temperature : C. ( e ) History : alternate and darkness for one minute each until steady state is attained .
( f ) Measurement : readings for successive minutes during recovery .
Evaluation of the ' normal alvanometric efficiency\ldquo ; in micromhos per lumen , in this case equivalent to micro-amperes per lumen , or micro-amperes per square centimetre of sensitive surface , divided by The Detection of Small Fluxes of Light .
A preliminary experiment to test the efficiency of selenium in detecting small fluxes of light was made as follows : thin rod of highly insulating porcelain was ground flat at one end , offering a circular surface sq .
cm .
in area .
Thick pencil lines were drawn along two opposite generators of the cylindrical surface , and a cap of selenium was thinly spread over one end .
The selenium was then sensitised in the usual manner by annealing , and the rod was inserted in a hole bored through a stick of ebonite , and fixed by means of binding screws .
When not exposed , the selenium was covered with a cap fitting over the aperture .
This miniature selenium is shown in fig. 1 .
Its resistance , when freshly prepared , was 50 megohms .
It was inserted into a circuit containing a battery of 20 volts and a Broca ( consequent pole ) galvanometer iving 0 division for ampere .
The " " dark\ldquo ; deflection was oompensated by suitably altering the netic field , Efficiency of Selenium as Detector of Light .
and the selenium was then exposed to various moderate illuminations .
The faintest illumination discoverable with certainty proved to be that due to a affin candle 5 .
from the selenium .
This illumination was lux , and the flux received on the sensitive surface was microlumen .
The deflection was 5 divs .
micro-ampere .
This means an additional conductivity of micromhos , and a galvanometric efficiency of omhos per lumen .
Both these efficiencies are low , and as the sensitive surface is of about the same area as the pupil of the eye , this method evidently falls far short of the ability of the human eye in detecting a candle at 5 Better results were obtained by a condenser through the selenium resistance and discharging it ballistically , but it was difficult to obtain consistent readings .
Electro ethods .
A Dolezalek quadrant electrometer giving 200 divisions per volt was used to measure the resistance of some resistance selenium brid , , either by Cardew 's method , or by inserting it in the galvanometer branch of a eatstone bridge .
A change of per cent. in the resistance was thus observed , due to an illumination of lux .
The galvanometric efficiency was of the order of 300 micromhos per lumen .
Results with : The best results , both as regards actual deflections and anometric efficiencies , were obtained with a Kelvin differential galvanometer coils of a total resistance of 6280 ohms .
In order to be able to vary the illumination measurably within wide limits , the arrangement shown in the diagram ( fig. 2 ) was adopted .
The Se No. 3 was fixed on the bottom of the box , which was optically blackened inside .
At a distance of 25 cm .
above the selenium was a circular ening 2 sq .
cm .
in area , closed by a plate of ground glass .
A metallic lamp was placed above the box at such a distance that the total candle-power of the ground-glass disc , as seen from the bottom of the box and determined photometrically , was .
The illumination at the bottom of the IJOX was thus when the ground glass was lighted to fiye candle .
By placing a small diaphragm on the surface , the ilhuuination could be reduced to any desired amount .
The faintest illumination so obtained was 10 microlux , or ten times that due to Arcturus unaided Since this was discovered by means of a selenium bridge , it means that it is possible to discover bright stars by means of selenium without the aid of any tical system whatever .
Dr. E. E. Fournier d'Albe .
On the As glass does not an illumination uniform over a wide angle , the precaution was adopted of picking out central , intermediate , and portions of the ground glass in turn .
Under the conditions here described no difference due to this shifting was discoverable , so that for the purposes of these measurements , as well as others described below , the rolmd may be considered as equivalent to a uniformly self-luminous surface .
One of the coils of the differential galvanometer was put in circuit with a battery of accumulators , giving 80 volts , and the selenium bridge .
The other coil , which had the same resistance , was tTaversed by a compehsating current of the order of 6 A set of was made by drilling ound holes of different diameters in a piece of sheet copper .
Complete series of measurements were made with four of these , called , and respectively .
Two smaller ones , called and somewhat uncertain results because the instrumental errors to be comparable with .
the quantities to be measured .
The table ives the dianoeters and areas of the apertures used , and the candle-power of the small of ground glass they exposed to the light , together with the illumination produced by that candle-power at the distance of the selenium bridge ( 25 cm Area .
BFED Illumina.tionmicrol .
The galvanometer having been made nearly aperiodic , readings were taken after half a minute 's exposure , then after half a minute 's recovery , and so on alternately until successive ' dark\ldquo ; and ' light\ldquo ; readings had become sensibly constant .
The exposures were made either by moving a cardboard shutter or by switching on the lamp , the room being otherwise in complete darkness .
Finally , the shutter having been closed , were taken for five or six half minutes in order to detel.mine points on the recovery\ldquo ; curve .
The timing was done by listening to the beats of a metronome marking seconds .
The accompanying diagram gives the so obtained in the of aperture A. On joining up the " " light\ldquo ; and ' dark\ldquo ; readings respectively , two curves Efficiency of Seleninm as a of Light .
are obtained whose vertical distance apart we may call the " " amplitude\ldquo ; of the alternating exposure culVe .
These readings , therefore , us two main results : the " " total recoyery\ldquo ; , calculated as explained , from ordinates in the recovery curve ; and the " " amplitude\ldquo ; P. Both these quantities should be plotted against the illumination I , in order to discover the laws of the action .
This is done in fig. 4 , which fives the total recoveries after ious illuminations , and , which gives the amplitudes FIG. 3 .
FIG. 4 .
The values for the apertures and were too small to be obtained in the way .
They were somewhat roughly estimated by waiting umtil the deflection in the light seemed to ) proach a final value , then , and until the ecovery seemed to do the same , and the mean of two deflections for the " " total recovery The conclusions can be drawn from these cllrves:\mdash ; ( n ) The amplitude is proportional to the illmnination .
The curve is a line , which , however , does not ) through the origin , and probably has a curved portion between and the origin ( lig .
5 ) .
( b ) The total recovery is proportional to the square root of the illumination .
This appears to hold idly down to the feeblest illuminations , as far as the Dr. E. E. Fournier d'Albe .
On the limits of accuracy allow one to judge .
These limits are indicated in the curve ( fig. 4 ) by rectangles including all admissible values of the illumination and of the total recovery .
( c ) The ratio of amplitude to total recovery is proportional to the square root of the illumination .
This follows from ( a ) and ( b ) , and is subject to the error specified under for very Saint illuminations .
One division ( 1 mm. at 1 of the galvanometer scale represented a current of micro-ampere .
This , with 80 volts , means that each millimetre of deflection indicates a gain or loss of conductivity amounting to micromhos .
Hence the " " galvanometric efficiency\ldquo ; of the selenium Se 3 is given by the following ures , which , of course show an efficiency inversely proportional to the square root of the illumination .
To discover still fainter illuminations , a minute hole , cm .
in diameter , was pricked in tinfoil , thus giving an illumination of 10 microlux ( about that due to Venus maided ) .
It was not discoverable with certainty by means of bridge Se No. 3 , but was easily discovered by means of a of resistance 20,000 ohms , which could be worked with 15 volts .
The " " amplitude\ldquo ; was divisions , derived from 20 alternate readings , during which , however , there was a strong drift owing to of temperature .
The efficiency is the same as in case of hole G. with Potassium Photo-electric Cell .
It is of interest to compare the above results with the best performance of a potassium photo-electric photometer described by Elster and Geitel .
* They placed a minute hole sq .
mm. in area in front of an amyl acetate lamp at .
The illumination thus received was 3 microlux .
The photoelectric current was then ampere .
With 10 microlux , in the Iast experiment , the current was -ampere .
Selenium , therefore , with the same illumination and extent of sensitive surface , is capable of , iving a J. Elster and H. Geitel , ' Pbys .
Zeitschr 1912 , vol. 13 , pp. 468 and 739 .
Efficiency of Selenium a Detector of measurable effect at least 100,000 times greater than that furnished by a potassium photo-electric cell .
Comparison with the The sixth magnitude is usually assumed as that of the faintest star cleal .
lie visible to the naked eye .
Zollner estimated the ratio of the htness of the sun and Capella as 55,700,000,000 .
The vertical illumination has been put at 50 , ( Exner ) .
This would make the illumination due to Capella ( magnitude ) microlux .
A star of would then give an illumination of microlux , and an illumination one-third of that would have to be considered the limit of human vision .
Let us call it 3 milli-microlux .
An attempt to test this limit experimentally was made as follows:\mdash ; A 10-volt 1 candle-power electric lamp was encased in a cylinder closed with a disc of ground lass .
To secure an even illumination of the latter , the cylinder was lined with white cardboard .
An image of this disc was thrown by a lens on to screen G. The lens was stopped down by an iris diaphragm until the whole luminosity emitted by the screen approached the limit of accurate comparison with a pentane lamp .
At that point , the candle power of , in the direction of the original beam produced , was to be , as compared with the pentane standard .
The experiments were conducted in a dark and the eye was carefully protected from all stray light .
Further reductions were then made by inserting small measured stops into the iris .
When the area of the stop was sq .
cm .
, the computed candle power of the illuminated surface of sq .
cm .
in area , was micro-candle .
A faint " " star " " was then produced ) a small stop on the ground glass G. A stop of area sq .
cm .
was not visible at all .
A stop of area sq .
cm .
was visible after 10 minutes ' accommodation to complete darkness , and a stop of area sq .
cm .
clearly visible .
Averted or " " rod\ldquo ; vision was employed in every case as a final test .
The object was 20 cm .
from the eye .
The candle powers were respectively , and 0.395 milli-micro-candles .
The illuminations at 20 .
were , and milli-microlux respectively .
Another observer obtained the same results , except that it was very difficult to perceive the second stop .
On the whole , the results show a satisfactory agreement with the star estimates .
It was next attempted to find the limit of visibility of a faintly illullinated .
The surface examined was the ground ho.lassG , with the iris diaphragm stopped down by means of very minute holes pricked in tinfoil .
Dr. E. E. Fournier On the The results showed that a surface becomes invisible when its intrinsic brightness is less than candles per square centimetre ; 1 sq .
cm .
of the barely visible surface gives an illumination of 10 milli-microlux at 20 cm .
If its brightness were concentrated at a point , that point would be clearly visible .
The eye , therefore , suffers in sensitiveness when the light is diffused .
The selenium detector does not .
If the two were equally tive to a point source , the selenium detector would be mor .
sensitive than the eye for faintly illuminated surfaces .
The fluxes of light discoverable by the are very minute .
In the dark , the diameter of the pupil is about 6 mm. , and its area sq .
cm .
With an illumination of 3 milli-microlux , the flux received is lumen .
This is , therefore , the minimum flux of light perceptible to the eye .
The Theoretical Instrument liimit .
The limit reached with the experimental arrangements described above is still very far removed from the limit theoretically attainable with the most sensitiye instruments now available .
This is evident from the faGt that a potassium photo-electric cell closely approaches the efficiency of the eye , although the current obtainable from it is 100,000 times feebler than the CUlTenG furnished by the selenium bridge .
Elster and Geitel worked with currents of the order of ampere , which represents approximately the present-day limit of current measurement .
Now if a current of the order of ampere is obtained with an illumination of 10 microlux , a current of ampere should , if the square-root law holds throughout , be obtainable with an illumination of microlux , or the unaided illumination of a star of the magnitude , which is invisible in the most powerful telescope hitherto constructed .
If , on the other hand , the current amplitude varies simply as the illumination , an illumination of milli-microlux should be discoverable , which is at least 100 times less than that discoverable by the eye , so that stars of the 11th magnitude s. hold show an electric effect unaided .
This advantage over the eye would be kept whatever the optical system , so that a telescope would give no advantage to the eye without giving it to the selenium detector to the same extent .
Selenium , therefore , offers an extension of our field of perception far beyond present optical or even photographic limits .
Bearing on the Theory of Quanta .
The efficiency of a lamp which converts the entire energy supplied to it into luminous radiation of the most visually advantageous type is 55 candles Efficiency of ium , as a Detector of Light .
per watt .
This value , given by Buisson and Fabry , intermediate between the values found by Drysdale and by Hyde , who obtained 17 and 72 respectively .
That portion of the total flux of energy from a Hefner lamp lies within the visible spectrum is about 200,000 ergs per second .
The portion intercepted by 1 sq .
cm .
at 1 .
is 16 erg per second .
This is the equivalent of 100 micro-lumen , and the illumination is llux .
The eye , as we have seen , can an incident luminous energy of 8 .
lumen , which is equivalent to ergs per second .
Planck'sf energy quantum for a frequency is .
For a frequency , which is that of maximum visibility , the quantum is erg .
The number of quanta received by the eye when receiving the minimum visible light is , therefore , about 360 per second .
Any instrument , therefore , which has a sensitiveness 1000 or more times greater than that of the eye may be effective in discovering discontinuities in the light emission at feeble illuminations .
As selenium is by far the most efficient detector known , the efforts in this direction made by N. Campbell with Na-K alloy cells should be repeated selenium of In.visible Radiatio In comparing the efficieucy of selenium with that of the eye or of other detectors , it is necessary to deduct the effect of the invisible spectrum .
The maximum energy of most terrestrial sources of is in the infra-red , and if selenium were , like the bolometer or the thermopile , simply a of radiant energy , its performances in sources of terlestrial radiation could not be arded as evidence of superiority in visible ions .
In order to study this question experimentally a new form of seleniurn bridge was constructed , consisting of a porcelain rod .
in diameter and 5 cm .
long .
Two thick parallel pencil lines were drawn thwise the rod , a clear white line cm .
wide and 4 cm .
between them .
The white line was then over with selenium , was then sensitised .
The result was a ' line \ldquo ; suitable for scopic vork .
After constructing such elements the most sensitive chosen .
It had a normal galyanometric efficiency of micromhos per lnmen .
This line was exposed to the spectrum of a Nernst lamp produced by flint glass prism .
The isible spectrum was cm .
* Buisson and Fabry , ' Comptes Pendus , ' 1911 , vol. .
Planck , ' Ann. der Phys 1901 , vol. 4 , .
Campbell , ' Camb .
Phil. Soc. Proc 1910 , vol. 1 ) Dr. E. E. Fournier d'Albe .
On the portion which affected the selenium was not longer than 8 cm .
It was divided into half centimetres , and the lin bridge was successively placed at eacf ] division .
Half minute " " amplitudes\ldquo ; were taken for each position , moving the bridge first from ultra-violet to infra-red and then in the opposite direction .
The mean amplitudes so obtained for each position were divided into two groups , those for the invisible spectrum and those for the visible spectrum respectively .
Expressed in percentages of the total radiation the effectivebnergies were\mdash ; Ultra-violet Visible Infra-red Although it is evident that the invisible radiations are not in the regate as effective as the visible rays , the above figures do not necessarily represent the quantitative distribution of the effective energies .
The latter cannot be accurately obtained without ascertaining the law of light action for each radiation separately .
This was done by Pfund* for short exposures and for two diff'erent intensities .
He found a somewhat abrupt transition at a wave-length of 6500 .
Below that wave-length the deflection was proportional to the square root of the energy , while from .
to the end of the spectrum it was simply proportional to the energy .
I have already mentioned that the deflections so obtained are not necessarily proportional to the total effect , and a more detailed investigation of the law of action will be necessary for each part of the spectrum .
Meanwhile , the following qualitative experiment shows that the dissymmetry found by Pfund does not apply to the final deflection .
The Nernst lamp spectrum was allowed to fall on a ground-glass screen closing the front end of a tube 43 cm .
long , lined with white cardboard .
Any portions of the spectrum could thus be recombined separately , and the selenium at the other end received a definite portion of the aggregate energy of whatever parts of the spectrum were transmitted through the ground glass .
The spectrum was divided into two portions which exerted equal actions .
The division proved to be slightly on one side of the line towards the blue .
The separate effects were always in the greater than the total effect , showing that the effect varies as a power of the energy below the first power .
The slit of the spectroscopic arrangement was then * A. H. Pfund , ' Phys. Rev 1912 , vol. 34 , Effi , ciency of Selenium as Detector of Light .
arrowed or widened , and the selenium exposed alternately to the two porvions , as before .
The intensity was thus varied in the ratio of at least , but the total deflections were sensibly equal for both portions .
shows that there is no great difference in the exponent of the for the two branches of the resonance curve .
The general result for the spectral distribution of the effective is that about three-quarbers of the total effect are due to visible radiations , eyen when the energy maximum is in the infra-red , as it is in most terrestrial sources .
This proportion is maintained , or exceeded , with faint illuminations .
If Pfund 's relation held , selenium would be sensible to none but those radiations which to the visible spectrum , if the were faint enough .
In any case , only some 30 per cent. at most need be deducted the obseryed effect in selenium in order to reduce it to visible light .
The Detect of Small Ch anges of Brightness .
The limit of accuracy in photometric estimates is enerally rnised to per cent. , and as there is no optical means of increasing the contrast of extended surfaces , a limitation is thus imposed upon the estimation of bri , htness such as physicists are not content to accept in other measurelnents .
Contrast can be increased by almost indefinitely , * it is a rocess , and gives no measure of the original contrast .
It is therefore of interest to inquire whether selenium , besides efficient as a detector of feeble , is superio to the eye as the appreciation of ulinlte differences of illnmination .
To take a concrete case .
A selenium of efficiency 1000 will 1000 micro-amperes with one volt if its surface is 1 sq . .
and the illnmination llux .
With an illumination of ( feeble the current will be 100,000 micro-amperes ( assuming the square-root law ) , or 10 microif the sensitive surface is only 1 sq .
cm .
A diffel.ence in the illumination lnting to 1 per cent. will make a difference of cent. in the current , a difference of micro-ampere ( say , 100 divisions on the scale of a sitive talvanometer ) .
There is , then , no reason why a difference of cent. should not be electrically discovel.ed , which , of course , is eyond the power of the eye .
This conclusion was confirmed by a nulnber of experiments , one of which the following:\mdash ; A disc , 21- ) .
cm .
in area , ated by a lamp from itbove .
The disc then transmitted a eqnivalent to 1/ 8 candle .
selenium bridge placed 25 cm .
below the disc was exposed to this , and *E .
E. Fournier d'Albe , ' Roy .
Dub .
Soc. Proc 1909 , 12 , vol. 11 , p. 97 .
Efficiency of Selenium as Detector of Light .
was connected up to a P.O. resistance box .
A battery of 8 volts and a Broca galvanometer adjusted to give 100 divisions per micro-ampere were also connected up .
Adjustment being made for equilibrium , a black thread mm. thick was drawn across in contact with the ground glass surface .
When passing across the centre of the disc it shaded off per cent. of its area .
A deflection of 8 divisions was obtained on the galvanometer .
With 20 volts a deflection of 20 divisions was obtained .
It was possible , then , to discover a variation of per cent. with this comparatively insensitive arrangement .
It is evident , therefore , that for such purposes as photometry and half-shadow polarimetry the selenium bridge must become a valuable accessory , capable of bringing these measurements up to the level of accuracy of other standard physical determinations .
1 .
The efficiency of seleninm preparations used for detecting is strictly defined , and standard conditions are chosen for determining it .
2 .
The efficiencies of some selenium preparations are evaluated from data yiven in previous publications .
3 .
Experiments are described which were made in order to detect minute quantities of light by means of selenium .
4 .
The minimum illumination reached is 10 microlux .
5 .
The law of light action is investigated , and shown to be , in the main , square-root law , down to the feeblest illuminations .
6 .
The theoretical limit of light action discoverable by means of presentday methods and apparatus is calculated , and shown to be , with selenium , very far beyond the power of the eye .
7 .
It is shown that this offers a means of the question of the discrete structure of radiant energy ( theory of quanta ) .
8 .
It is shown , theoretically and experimentally , that selenium apparatus is capable of differences and variations of luminosity quite inappreciable to the eye .
|
rspa_1913_0066 | 0950-1207 | Experiments on the flow of viscous fluids through orifices. | 91 | 99 | 1,913 | 89 | Proceedings of the Royal Society of London. Series A, Containing Papers of a Mathematical and Physical Character | G. F. Davidson, B. E. (Sydney), B. A. (Cantab).|Prof. B. Hopkinson, F. R. S. | experiment | 6.0.4 | http://dx.doi.org/10.1098/rspa.1913.0066 | en | rspa | 1,910 | 1,900 | 1,900 | 6 | 170 | 3,822 | http://corpora.clarin-d.uni-saarland.de/surprisal/6.0.3/?id=rspa_1913_0066 | 10.1098/rspa.1913.0066 | null | null | null | Fluid Dynamics | 30.901837 | Thermodynamics | 22.247644 | Fluid Dynamics | [
39.89291763305664,
-29.55422592163086
] | 91 Experiments on the Flow of Viscous Fluids through Orifices .
By G. F. Davidson , B.E. ( Sydney ) , B.A. ( Cantab .
) , 1851 Exhibition Research Scholar .
( Communicated by Prof. B. Hopkinson , F.R.S. June 26 , 1913 .
) Received May 23 , \#151 ; Read This paper deals with an experimental investigation of the flow of liquids through a round hole .
In most of the experiments a fairly thick oil was used , and by varying its temperature the kinematic viscosity could be varied about a thousand-fold .
It was possible by this means to change the character of the motion continuously from the type determined almost wholly by viscosity to the form in which the resistance was mainly due to ElecfrTcaf , time Sicjnals .
G ^.St AjJui Strip of blackened paper inertia , and to follow the corresponding change in the relation of resistance and flow .
When the experiments were first undertaken it was hoped by comparing experiments with orifices of different sizes , and in which the viscosity and rate of flow were suitably varied , to obtain confirmation of the law of similar motion in viscous fluids .
It was found , however , that this law did not hold , and the cause was discovered to be that the stress in this oil is not proportional to the rate of distortion .
Fig. 1 is a diagram of the apparatus used .
The tube A was 20 cm .
in diameter and 150 cm .
long , closed at the bottom by a horizontal brass plate with an orifice at its centre .
This tube was held in the centre of a tank 75 cm .
in diameter and 150 cm .
high .
The tank was a closed vessel with a small cock C for admitting air under pressure and an aperture B , 10 cm .
in diameter , by which the air pressure inside the tank could be suddenly released , he apparatus stood in a vertical position with the oiifice immersed , say , 10 or 20 cm .
below the surface of the fluid in the tank .
Aii pressure in the tank forced the fluid up in the tube A , so that the two sui faces of the fluid were about 100 cm .
apart .
On opening the aperture B the fluid in A flowed through the " drowned " orifice under a " falling head " until the two surfaces of the fluid came to the same level .
VOL. lxxxix.\#151 ; A. t Fig. 1 .
92 Mr. G. F. Davidson .
Experiments on the A float on the fluid inside the tube had a strip of paper attached to it which passed over a very freely running and evenly balanced aluminium wheel , and was held taut by a small weight attached to it .
This strip of paper was blackened and passed underneath an electrically operated stylus which marked on it equal intervals of time ( such as seconds for an orifice 2 cm .
in diameter ) as the level of the fluid fell in the tube A. The record was fixed with varnish , and from this the velocity of the surface of fluid in tube A can be found at any head , because zero head is iparked on the paper at the end of each experiment when the fluid is at the same level inside and outside the tube .
Corrections in head are made for the variation in level of the fluid in the outer tank as the column of fluid inside the tube falls .
Corrections in velocity are made for the velocity of approach .
The correction required owing to the retardation of the falling column giving a greater head than the record showed was quite negligible .
Knowing the dimensions of the tube and the velocity it was possible to calculate the actual discharge .
This divided by ^/ ( 2 \lt ; /H)* x area of the orifice gives the coefficient of discharge , which we call C^ .
Thus can be plotted against head .
Actually , the records were measured up and two curves drawn , showing velocity and head each to a time base .
Convenient readings of head were taken from these faired curves , and from the corresponding values the was calculated so that the C^ against head curves do not show experimental errors .
These errors were small , and the " fairing " of the original curves ( to a time base ) was \#166 ; almost unnecessary , the points being usually within 1 per cent , of the smooth curve .
Three orifices were used .
They were 4 , 2 , and 0'5 cm .
in diameter , and were made in plates 3'2 , 1*6 , and 04 mm. thick respectively .
They were made geometrically similar by having the edge of the orifice rounded to a semicircle whose diameter was the thickness of the plate .
The fluid used was a heavy engine oil of good quality , with a flash point of 260 ' C. About 60 gallons were used in these experiments .
It proved very suitable , and as it was kept in a closed vessel it remained perfectly clean and uniform during the 18 months it was under observation .
It showed no signs of streakiness , although , of course , considerable care was needed to get such a large quantity at a uniform temperature when it was very viscous .
In such cases it was " explored " with a resistance thermometer .
* Where H is the difference in level of the two surfaces of the fluid at any instant and a is the acceleration due to gravity .
Flow of Viscous Fluids through Orifices .
93 A wide range of viscosities was obtainable by varying the temperature .
The value of p/ p was about 200 at 11 ' C. , and 0T4 ( about the same as for air ) at 110'.* The viscosity was measured by allowing 126 c.c. of the oil to flow under a small head through a tube 6'2 cm .
long and 6T mm. in diameter .
The viscometer was simply a spherical bulb with two tubes attached to it opposite one another , and held in a vertical position .
Errors were looked for both with water and oil , on account of wall effect , vortex motion , and baffling action by the bottom of the tank .
The wall effect was examined by putting sleeves of various diameters inside the large tube A , and observing when a variation in the coefficient of discharge due to this cause became perceptible .
It was found to be negligible .
The absence of vortex motion , that is the fluid swirling round so that a particle follows a spiral path towards the orifice , was proved by observing small floating bodies .
A baffle plate , distant only one diameter of the orifice away from it on the downstream side , had no effect on the C\lt ; * .
Accordingly , the results are considered to be accurate within 1 per cent , for one infinite fluid flowing into another through this sort of round-edged orifice .
The working of the apparatus was tested with water flowing through sharp-edged orifices of 2 cm .
and 4 cm .
diameter .
The results agreed well with those obtained by other experimenters .
It is interesting to note that with this arrangement it is possible to measure the Gd at much lower heads than in the case of an orifice discharging into air , because the surface of the fluid can be remote from the orifice , and is not affected by the motion there .
For water the for a " drowned " orifice as compared with a " free " discharge is only reduced about 1 or 2 per cent. A non-viscous fluid would have a constant Cd at all heads ( somewhere about 07 for these orifices ) until the pressures are such as to produce appreciable changes of density .
The value which the Gd should have when flowing through an orifice in a thin plate into space has not been calculated for a circular orifice , although it has been for a long rectangular one .
Many experiments have been made to determine this C which is in the neighbourhood of 06 for circular orifices with sharp edges .
With viscous fluids at low heads viscosity becomes relatively important , and the effect of inertia negligible .
The velocity then is proportional to the Throughout the paper the word " viscosity " is used to signify the kinematic viscosity pjp .
denoted by v. Mr. G. F. Davidson .
Experiments on the head , and the curve Cd against head ( H ) should be a parabola , since Cd is really a measure of Results for Oil.\#151 ; Fig. 2 shows a set of curves of Crf against head for the orifice , 4 cm .
in diameter .
The dotted lines for the curves at viscosities of 24'5 , 497 , and 206 The numbers in brackets are the values of the kinematic viscosity of the fluid in C.G.S. units .
Orifice drowned Head cms .
3 2 mm.thick .
Fig. 2 .
C.G.S. units are the parabolas which the curve approximately follows under the low heads .
That it does not do so completely is due to the fact that the viscosity of the oil is not independent of the rate of distortion , a point which is referred to later .
It is interesting to note the relative effects of the viscosity and inertia forces .
Up to a Gd of , say , 0'3 the curve rises sharply , fulfilling more or less the parabolic law , but above this the inertia forces tend to flatten it until at a Cd of 065 the inertia effect is predominant , and the curve continues as an approximately straight line parallel to the H axis .
The general effect of viscosity is to turn the curves downwards .
Fig. 3 , however , shows a curve for water , whose viscosity is about O'Ol , which actually is curved in the opposite direction , and the flat part of its curve has a Cd below 066 , while the viscous oils rise to 07 .
Flow of Viscous Fluids through Orifices .
On this figure also are shown three curves for fluids discharging through this round-edged orifice into air .
It is interesting to note the small difference between the two curves for water .
The two curves for oil discharging freely WATER C-OI ) FREE .
WATER DROWNED ( -01 ) 4CM .
ORIFICE Discharging to air , and drownedr HEAD CMS .
Fig. 3 .
can also be compared with the corresponding ones for the drowned orifice , and it is to be observed that the difference becomes more marked as the viscous forces become more important .
One would expect the flat part of the C^-H curve to attain the same value for all fluids .
The curious thing is that , for a mobile fluid like water , flowing through a 4 cm .
orifice , the flat part of the curve is considerably lower than that for the viscous oils .
The water curve ( even for the drowned orifice ) also curves upwards , and at low velocities rises above the upper limit prescribed by inertia .
Another curious point is that at high heads with drowned orifices ( as with air* ) the curve is not truly flat , but varies slightly as the head increases .
These variations are probably caused by the viscous forces increasing the coefficient of contraction Cc , and decreasing the coefficient of velocity C\#187 ; .
For the coefficient of discharge , = Cv xCc .
A viscous medium round the issuing jet , and the viscous resistance near the surface of the plate in the neighbourhood of the orifice , will both tend to ^ Watson and Schofield , 'Proc .
Inst. Mech. Eng. , ' May , 1912 .
Mr. G. F. Davidson .
Experiments on the increase the contracted area of the jet by giving the fluid a rotation outwards .
In this way the Gc may be increased , while the inertia forces are so large as to keep C\#187 ; nearly unity .
Hence , at high velocities , the more viscous the fluid , the higher the flat part of the curve will be , as is shown by water and oil in these curves .
It is curious to find a friction effect like viscosity actually increasing the quantity discharged per second .
At low heads with water , this same effect causes the Cd to rise above the value for the flat part of its curve , but , with a more viscous fluid , the Gvis so reduced that it overcomes the increase in Gc\gt ; and so the Cd is reduced and the curve is concave downwards .
It is of interest to apply to these results the principle of dynamical similarity.* Consider the motion in an experiment in which the fluid has viscosity v and the orifice is of diameter d. If the length scale of the motion be altered in the ratio L , and the velocity at every point multiplied by a constant Y , a geometrically similar motion will be derived going through a similar orifice of diameter L d.This second motion will in general be dynamically possible if , and only if , the viscosity of the fluid in which it occurs is Ei\gt ; , where YL/ E is unity .
Further , if this condition be fulfilled , the pressure at corresponding points , and , therefore , the heads under which these two motions go on , will be in the ratio V2 .
Conversely , if H be the head in the first case , then the similar motion so derived from it will be that which actually occurs when fluid of viscosity Ei^ flows through a tube of diameter Ld under a head V2H .
And if in any two experiments the head , the viscosity , and the diameter are so related that d*yiL/ v is the same for both , then the motions must be similar in these two cases , and the velocities at corresponding points , and , therefore , the average velocities which then hold , will be in the ratio of the square roots of the heads .
Since Cd is equal to average velocity ( 2yH ) , it follows that it must be the same in both cases .
That is , Cd should be the same in all cases for which YL/ v is the same , where V might be taken indifferently as representing the average velocity of the flow , or the square root of the head , L as the diameter , and v as the kinematic viscosity .
In figs. 4 and 5 the values of Cd found in these experiments are plotted against VL/ *\ From these figures it is seen that Cd varies from 02 to 0-4 when VL/ = 2 , from 0'4 to 0'6 when YL / v = 10 , and so on .
The experimental errors are considered to be well within 5 per cent. * Dr. Stanton , 'Trans .
Inst. Nav .
Archs .
, ' March 22 , 1912 .
, Flow of Viscous Fluids through Orifices .
97 The variation of C a in different experiments for which YLJv is the same can only he explained by the failure of one or more of the assumptions underlying the application of the principles of dynamical similarity to fluid motion .
These assumptions are : ( 1 ) That the stress varies as the rate of distortion .
.5 .4 .2 I 0 2 4 6 8 v|_ 10 12 14 16 18 20 C.C.S. units Fig. 4 .
For values of Cd above -5 see Fiq 5 .
J______I ; i l i_____L Jj___A 1 i Vaiuesfortha '/ 2cm orifice J___________________________________________________i______________________________________________ !
_ __________________________________________________1___________________________________________________I \#166 ; L. T5 o Til T i ir l#T Val ues for the '6 .
cm .
orifice 60 vl so ~"=C-C-S units Fig. 5 .
( 2 ) That gravity does not determine the motion except in so far as it produces differences of pressure at points where the fluid is at rest .
That the second assumption is fulfilled in these experiments was proved by reversing the flow .
The same results were obtained whether the flow was upwards or downwards through the orifice .
That the first assumption is not fulfilled for this oil is suggested by the divergence of the C^-H curve ( fig. 2 ) from the parabola , when the inertia forces are unimportant .
In order to determine the amount of variation of viscosity and its possible 98 Experiments on the Flow of Viscous Fluids through Orifices .
effects an absolute viscometer was made .
It consisted of a glass tube 10| cm .
long , and 2 mm. diameter , through which 220 c.c. of oil were caused to flow by air pressure .
The air pressure came from a reservoir of 40,000 c.c. capacity , and was measured by a manometer .
The volume of oil was measured in a spherical bulb of 220 c.c. capacity .
There was one of these bulbs connected to each end of the capillary tube by about 4 cm .
length of piping 1-|- cm .
internal diameter .
The viscometer was contained in a large water-bath to keep its temperature constant .
The temperature was kept constant and the time of flow was measured .
The head varied from under 4 cm .
to over 52 cm .
of mercury .
The viscosity was calculated from the ordinary expression for flow in tubes and reduces in this case to v \#151 ; constant x time of efflux x head .
The critical velocity ( mean ) would be about x 105 cm./ sec. in this apparatus .
Since the actual mean velocity never exceeded 15 cm./ sec. , and v was over 9 , there was no possibility of eddying motion .
The apparatus was designed to give roughly the same average rates of distortion as occurred in the principal experiments with the orifices .
Owing to lack of time the variation of v was only thoroughly examined at one temperature , namely 25 ' C. A few readings were taken at 35 ' C. ( where v is about 4 ) which showed the same sort of variation as those at 25 ' C. , but not to such a marked extent .
The values of v found varied from 13-7 to 9'4 , and are shown on fig. 6 plotted against the rate of distortion , both being in C.G.S. units .
The value of v found in the first viscometer fits nicely on this curve .
-----value obtained in original experiment .
Oil at 25'C .
Rate of Distortion ( in secs .
) = 8V/ 3 ( Rad. of Tube ) .
Fig. 6 .
The variation of viscosity with rate of distortion precludes any application of the laws of similar flow to these experiments , because the rate of distortion varies from point to point , and the corresponding changes in v will alter the form of the flow .
But generally speaking the effect of the changing viscosity is that the values of v assumed in calculating the results exhibited graphically in figs. 4 and 5 , are too high , the error being greater at the higher viscosities If allowance be made for this by taking in each case the value of v correEffect of Rotating Magnetic Insulator Magnetic Field .
99 sponding to the actual average rate of distortion in that experiment , the result is to reduce somewhat the range of values of VL/ i ; corresponding to any \#171 ; iven Crf .
Thus the variation of viscosity may be said to furnish a qualitative explanation of the large divergences in this oil from the accepted laws governing similar motions .
It is perhaps worthy of notice that there were indications of a want of proportionality between stress and rate of strain in this oil even when it was as mobile as air .
This work was done at the Engineering Laboratory , Cambridge , and I wish to express my thanks to Prof. Hopkinson for his kind help and inspiring interest .
On the Electric Effect of Rotating a Magnetic Insulator a Magnetic Field .
By Marjorie Wilson , B.A. , M.Sc .
, and H. A. Wilson , D.Sc .
, E.R.S. , Professor of Physics , Rice Institute , Houston , Texas , U.S.A. ( Received May 26 , \#151 ; Read June 19 , 1913 .
) In a previous paper* by one of us it was shown that when an insulator of specific inductive capacity K rotates in a magnetic held there is an electromotive force induced in it equal to that in a conductor multiplied by 1 \#151 ; K-1 .
The object of the experiments described below was to measure the induced electromotive force in a magnetic insulator rotating in a magnetic held parallel to the axis of rotation .
According to the theory based on the " principle of relativity " this induced electromotive force should be equal to that in a conductor multiplied by 1 \#151 ; ( yaK)-1 , where / / .
is the magnetic permeability of the insulator , whereas on the theory of H. A. Lorentz and Larmor the appropriate multiplier appears to be 1 \#151 ; K-1 , as for a non-magnetic insulator.f Ao insulator is known for which yu , differs appreciably from unity , so that it was necessary to construct a sort of model of a magnetic insulator .
The insulator adopted consisted of wax , in which a large number of small steel spheres was embedded .
The spheres were \#163 ; inch in diameter , and each one * " On the Electric Effect of Rotating a Dielectric in a Magnetic Field , " by H. A. Wilson , ' Phil. Trans. , ' 1904 , A , vol. 204 .
t M. Abraham , ' Theory der Elektrizitat , ' vol. 11 , p. 322 .
|
rspa_1913_0067 | 0950-1207 | On the electric effect of rotating a magnetic insulator in a magnetic field. | 99 | 106 | 1,913 | 89 | Proceedings of the Royal Society of London. Series A, Containing Papers of a Mathematical and Physical Character | Marjorie Wilson, B. A., M. Sc.|H. A. Wilson, D. Sc., F. R. S. | article | 6.0.4 | http://dx.doi.org/10.1098/rspa.1913.0067 | en | rspa | 1,910 | 1,900 | 1,900 | 12 | 156 | 3,128 | http://corpora.clarin-d.uni-saarland.de/surprisal/6.0.3/?id=rspa_1913_0067 | 10.1098/rspa.1913.0067 | null | null | null | Electricity | 56.090582 | Tables | 19.918899 | Electricity | [
38.176658630371094,
-48.64742660522461
] | ]\gt ; of Iagnetic Iin xgnctic Field .
to the actual rate of distortion in iment , the result is to reduce somewhat the of values of respondin to iven C. Thus the variation of viscosity may be said to furnish a qualitative explanation of the large ences in this oil from the accepted laws sl It is vorthy of notice that there indications of a of proportionality between stress and late of strain in this oil even when it was as mobile as air .
This vork was done at the Laboratory , and I wish to express my thanks to Prof. Hopkinson for his kind help and inspiring interest .
the of Rotating in a Iognet i By , lf .
Sc. , anil H. A. , D.Sc .
, F.B.S. , Professor of Physic , , h'ice Institute , Houston , Texas , U.S.A. Received Read June In a previous paper*by one of ns ib shown that when an insulator of specific indnctive capacity in netic field there is an electromotive force induced in it to in a conductor multiplied by The jcct of the ) below was to measure the induced omotive force in a onetic ilsulator rotating in neCic field parallel to the of rotation . .
to the theory based on the " " principle of relativity\ldquo ; this induced electromotive force should be equal to that in a conductol multipJied here is the netic 1ermeability of the insulator , whereas on theory of H. A. Lorentz and Larmor the nrultiplier to be , as for a non-nlagnelic insulator .
insulator is known for which differs from unity , so that it was necessary to construct a sort of model of a lnagnetic insulator .
) ulator adopted consisted of wax , in which a number of ] steel embedded .
The spheres inch in diameter , and each one ' ' On the Effect of Rotating a Dielectl.ic in Iagnetic Field by H. A. Wilson , ' Phil. Trans 1904 : , vol. 204 .
M. ' Theory der ' vol. 11 , p. 322 .
100 Mrs. M. Wilson and Prof. H. A. Wilson .
Electric Effect was coated thinly with wax .
The coated spheres were packed htly and melted paraffin wax poured into the empty spaces between them so as to form a solid mass .
The insulator was in the of a hollow cylinder with inside and outside metal coatings , and was rotated in a magnetic field parallel to the axis of the cylinder .
The outside was connected to one pair of quadrants of a quadrant electrometer , the other quadrants of which were earthed .
If an electromoGive force is induced in the cylinder and this raises the potential of the outer coating by volts , then where is capacity between the inner and outer , and the capacity of the electrometer connecting wire and outside surface of the outer coating .
The inner coating is supposed earthed .
If the potential of the inner is raised by au amount , and this raises the potential of the outer coating by , then Let the electrometer deflection due to be and that due to be Then we have .
Thus can be found in terms of , and .
Another way is to earth the outer and charge the one to a potential , then insulate the outer coating and afterwards earth the inner one .
In this way a to outer coating which raises its potential to and -CE ' This second method has the that it requires ) outer to be earthed , so that errors may arise due to electric effects produced by the key the outer to the earth .
Also in the first method the potential Ji ' acts in exactly the same as the ced electromotive force , so that errors due to bad insulation affect both and equally , and so ilre eliminated .
The first was therefore adopted .
In the earlier experiments referred to above a small , standard condenser was used to give a known charge to the outer \ldquo ; and the capacity of the cylinder was found in ternls of that of the condenser .
This method was less direct than that now employed .
The inner was connected to earth a 10-ohm resistance which could be connected a 90-ohm resistance to a dry cell .
The potential difference between the ends of the 100 ohms was measured with of Rotating Magnetic Insulator in a Field .
a lVeston voltmeter .
When the cell was not conn ected the inner coatin .
was earthed , and when it was connected the inner as raised fo a potential one-tenth of that indicated by the volbmeter , which was usually volts .
The apparatus was that used in the earlier tion , with some improvements in detail .
The ylinder was .
external 2 cm .
internal diameter , and cm .
outside SUl.face of the cylinder was a tube ) .
thick , and another brass ) fitted the inside surface .
The inner tube mounted on a shaft , from which it was insulated , and the shaft was mon1l between fixed conical bearings and could be rotated by means of a by a .
motor .
The cylinder was surrounded by a la .
solenoid which a netic field parallel to the axis of rotation .
Two s1nall brass wire brushes made contact , one on the middle of the outel ' the othel on the inner tube close to one end of the cylinder .
ement of the brnshes is shown in .
Each brush was kept pressed FIG. 1 .
Outer coating of cylindel ' .
Innel of P. pull Solenoid .
Brush on outer cuating .
D. Brush on inner Conical xxxx .
Water jacket .
EEFiE .
Ebonite bushi tino on K. outer .
TTTT .
cell .
11 .
to istauces of 90 and 1 Key .
Dry cell .
Voltmeter .
tube shaft .
down htly but steadily by the of a bar fastened at angles to the end of the rod supporting the brush as shown .
The ineltia of these bars preven ted the brnshes from when the cylinder was Mrs. M. Wilson and Prof H. A. Wilson .
Electric Effect quickly and they could be adjusted so that the pressure on the brushes very small .
This new arrangement of the brushes caused a reat improvement in working of the apparatus .
The electrometer and the wire leading to it were completely enclosed in a metal case which , with the solenoid , formed a complete electrostatic screen around the insulated system .
The inside of the solenoid was kept cool by means of a water-jacket .
The speed of the cylinder was found with a revolution counter driven by a worm To make a deternIination of the induced electromotive force in the cylinder the electrometer deflection due to the potential of the inner by about volt was first observed and then the cylinder started and its speed found .
The effect of a known current in the solenoid was next .
The speed and sensibility were then measured .
The speed of cylinder remained constant within the limits of error .
The sensibility also remained constant over periods .
The electrometer scale reading was very steady while the cylinder was and the effect of the current could be easily and exactly observed .
In fact with the new ement of the brushes no difficnlty in the observations was experienced and the accuracy seemed to be limited only by the smallness of the deflections obtained .
The cylinder insulated well .
There was no effect due to running the cylinder in absence of a magnetic field and no effect due to reyersing the current when the cylinder was at rest .
The speed and sensibility were not by the current in the solenoid .
The sensibility the same when the cylinder was running as when it was at rest .
The following table contains a set of results obtained:\mdash ; It will be seen that the induced electromotive force is very nearly proportional to the current reyersed and to the nutnber of revolutions per second .
After these observations were made it was found thab running the cylinder had produced a narrow air gap beliween the inner tube the wax .
This of gnetic Insulator in gnetic Field .
was filled up by slightly warming the cylinder and forcing down the mixture of wax and balls at the ends of the cylinder so that the mixture was very htly pressed against the inner and outer tubes .
The best results could be obtained a6 about 100 reyolutions per second .
At greater speeds the electrometer reading was not vays quite steady and at smaller speeds the deflections were too small .
A set of concordant Uleasurements of the effect due to about 14 amperes at 100 revolutions per second was therefore obtained and the llean of these adopted as the result of the experiments .
The mean results were as follows : will be seen that this result rees closely with the others .
In order to compare the observed effect with that in a conductor , it is necessary to the ) .
induction the cylinder .
Corl.ections for the induced electromotive forces in the metal have also to be applied .
The change of induction the cylinder and its outer due to reversing a in the solenoid , } found by means of a spiral of fine wire wrapped round it from end to end .
Tbis spiral was connected to a alvanometer , nd the secondary coil of an accurately known mutual induction was included in the circuit .
The current in the primary of mutual induction was measured with the same ammeter that was used to measure the current in the solenoid .
The induction found to be proportional to the current from 5 to 15 amperes , and to be equal to 4210 per ampere reversed .
A second determination of this quantity was done , using a coil of two turns round the cylinder .
The induction this coil was found for a series of equidistant positions the cylinder and the mean induction through the cylinder calculated .
The sult 4200 .
The mean of f , he two results , 4205 , was adopted .
The difference between the mean area of the windings and the area of cross-section of tlJe cylinder was , of course , allowed for .
The field at the windings was taken equal to that due to the solenoid in the absence of the cylinder .
The mean induction in the hole the cylinder was found with a coil which could be slid inside when the cylinder was supported in its usual 104 Mrs. M..Wilson and Prof. H. A. Wilson .
Electric Effect position with the innel tube and shaft removed .
This was found to be equal to per ampere reyersed .
The field at the centre of the solenoid in the absence of the cylinder was found to be equal to 200- for a current of 2 amperes , which is the same as the value found in the earlier inyestigation done in the Cayendish Laboratory .
It was found that near the ends of the cylinder there was a stronger field than inside the hole through .
This , of course , was due to the magnetisation of the cylinder .
In consequence of this there was an induced electromotive force in the inner tube which diminished the effect observed .
The induction through the cross-section of the inner tube at the brush on it was found to be per ampere reversed , so that the potential of the inner tube was lowered by the electromotive force due to units of induction .
The induction through the outer covel was aken to be equal per unit cross-section to the field in the absence of the cylinder , which made it 143 per ampere reversed .
An error in this quantity would have practically no effect on the final result for the ratio of the effect to that in a conductor , because it is to be subtracted from both quantities .
The induction through the cylinder at the brush on the outer cover was found to be 5010 per ampere reyersed .
This is greater than the average induction through the cylinder by .
In consequence of this the potential at the was raised above the average potential of the outside of the cylinder by the potential due to 805 units of induction per ampere observed eHect , therefore , includes an induced electromotive due to units of induction per ampere l'eversed , acting in the metal coatings of the cylinder .
This gives volt per ampere reversed per revolution per second .
Subtracting this from the observed effect we get volt per ampere reversed per revolution per second as the observed effect in the insulator itself .
The average induction through the insulator is per ampere reyersed .
Tbis would give an induced electromotive force in a conductor equal to volt per ampere reyersed per reyolution per second .
The ratio of the observed effect to that in a conductor is therefore The value for the insulator was found* to be and that of to be , so that For method see earlier paper referred to abo ve .
of JIagnetic Insulator in gnetic Field .
The accuracy of the value found for the ratio of the induced electromotive force in the insulator to that in a conductor depends on of the voltmeter and ammeter employed .
The electromotive force was found in terms of the voltmeter reading , and the induction depends on the product of the mutual induction of the standard and current determined by the ammeter .
The primary of the itual induction consisted of a single layer of wire wound in a screw thread of 1 mm. pitch cut on a brass tube 5 .
in diameter and 90 cm . .
The screw was cut on an accurate and the number of threads was found to be 10 per cm .
to within 1 part in 5000 .
The secondary coil consisted of a layer of turns wound on an accurately turned brass cylinder , which fitted into the primary coil .
The area of the secondary coil was known to within 1 part in .
The induction was known to higher order of accuracy than the other mtities involved .
neter and anlDleter readings only enter into the final result the value of the ratio of the potential indicated by the voltmeter to the current indicated by the tmmeter , because the sa1ne ammeter was used to measure the currents in the solenoid and in the of the mutual induction .
The value of found by means of a standard one-tenth ohm resistance .
The table ives the results ained : Current by lumeter ( .
tmeter ( .
by lumetel ( .
tmeter ( .
by lumetel ( .
tmeter ( .
by lumetel ( .
tmeter ( .
by lumetel ( .
tmeter ( .
by lumetel ( .
tmeter ( .
0.1 The ratio is constant and to the resistance of the so that it seems certain that no sppreciable error could have been introduced by ammeter and yoltnleter , which were new Weston ) instruments .
It appears , efore , that the induced force in the rees approximately with that to be expected on the theol.y of relativity .
This theory no assumptions to the constitution the inslll , so that it is applicable to any 1nedium in bulk an biliby and inductive capacity K. The effect to be exlJected on the theol.y of H. A. Lorentz and Lalmor depends 011 assumptions as to the ltion of the mnterial medium so that it is whether to be regarded as necessarily to as the valne of the ratio of the otive in the compum to that in a These ] ) eriments therefore confirm the tbeory 01 ' re]ativity but do not Prof. W. B. Morton .
necessarily connict with the fundamental assumptions of H. A. Lorentz and Larmor 's theory .
They do , however , make it probable that the application of this theory to magnetic bodies has not yet been worked out in a satisfactory manner .
added , 1913.\mdash ; The specific in capacity and meability of any material medium are values over volumes large compared with the structural units ( molecules or bodies ) up the medium .
The medium employed has definite values of these quantities for volumes large compared with the olume of one of the spheres used in building it up .
It appears , therefore , to be allowable to apply any theoretical results expressed in terms of and to the medium used .
] Our thanks are due to the Government Grant Committee of the Society for a grant with a large part of the apparatus used in this investigation was originally purchased , and also to the Trustees of the Rice Institute for the facilities for experimental work which they have placed at our disposal .
On the cements of the rticles their Paths in some Ca.ses of Two-dimensional Motion of Frictionless Liquid .
By W. B. , Professor of Physics , Queen 's University of Belfast .
( Communicated by Sir J. Larmor , Sec. R.S. Received June 2 , \mdash ; Read June 19 , 1913 .
) The paths described by the individual particles of a liquid have been inyestigated only in a few cases , those in which the motion is steady , so that the particles ] the stream-lines .
Clerk Maxwell , , pnblished for the paths in an unbounded liquid disturbed by the passage of a circular cylinder .
The curves for particles in contact with the cylinder were plotted by calculation ; the other paths were drawn by eye from a knowledge of their terminal points and curvature .
From these curves were derived others , showing the successive in the deformation of a row of particles which , before the approach of the cylinder , lay in a straight line perpendicular to its motion .
In 1885 , Lord Kelvinl- investigated the paths of particles of a liquid ' Lond. Math. Soc. Proc vol. 3 ; 'Collected Papers , ' vol. 2 , p. 208 .
'Collected Papers , ' vol. 4 , p. 193 .
|
rspa_1913_0068 | 0950-1207 | On the displacements of the particles and their paths in some cases of two-dimensional motion of a frictionless liquid. | 106 | 124 | 1,913 | 89 | Proceedings of the Royal Society of London. Series A, Containing Papers of a Mathematical and Physical Character | W. B. Morton, M. A.|Sir J. Larmor, Sec. R. S. | article | 6.0.4 | http://dx.doi.org/10.1098/rspa.1913.0068 | en | rspa | 1,910 | 1,900 | 1,900 | 23 | 312 | 6,219 | http://corpora.clarin-d.uni-saarland.de/surprisal/6.0.3/?id=rspa_1913_0068 | 10.1098/rspa.1913.0068 | null | null | null | Fluid Dynamics | 66.844057 | Tables | 13.51219 | Fluid Dynamics | [
45.20197296142578,
-32.964210510253906
] | ]\gt ; Prof. W. B. Morton .
necessarily connict with the fundamental assumptions of H. A. Lorentz and Larmor 's theory .
They do , however , make it probable that the application of this theory to magnetic bodies has not yet been worked out in a satisfactory manner .
added , 1913.\mdash ; The specific in capacity and meability of any material medium are values over volumes large compared with the structural units ( molecules or bodies ) up the medium .
The medium employed has definite values of these quantities for volumes large compared with the olume of one of the spheres used in building it up .
It appears , therefore , to be allowable to apply any theoretical results expressed in terms of and to the medium used .
] Our thanks are due to the Government Grant Committee of the Society for a grant with a large part of the apparatus used in this investigation was originally purchased , and also to the Trustees of the Rice Institute for the facilities for experimental work which they have placed at our disposal .
On the cements of the rticles their Paths in some Ca.ses of Two-dimensional Motion of Frictionless Liquid .
By W. B. , Professor of Physics , Queen 's University of Belfast .
( Communicated by Sir J. Larmor , Sec. R.S. Received June 2 , \mdash ; Read June 19 , 1913 .
) The paths described by the individual particles of a liquid have been inyestigated only in a few cases , those in which the motion is steady , so that the particles ] the stream-lines .
Clerk Maxwell , , pnblished for the paths in an unbounded liquid disturbed by the passage of a circular cylinder .
The curves for particles in contact with the cylinder were plotted by calculation ; the other paths were drawn by eye from a knowledge of their terminal points and curvature .
From these curves were derived others , showing the successive in the deformation of a row of particles which , before the approach of the cylinder , lay in a straight line perpendicular to its motion .
In 1885 , Lord Kelvinl- investigated the paths of particles of a liquid ' Lond. Math. Soc. Proc vol. 3 ; 'Collected Papers , ' vol. 2 , p. 208 .
'Collected Papers , ' vol. 4 , p. 193 .
Two-dimensional ' Motion of Liquid .
enclosed in a rotating ellipsoidal shell .
He showed that they moved , relatively to the shell , along a set of similar ellipses in parallel planes , the period of this motion being the same for all the particles , so that after this period the configuration comes back to the initial one rotated through an Later ( 1889 ) , Riecke*gave diagrams for the cases of translation of a sphele and of a vortex-pair .
His method of procedure was the reverse of Maxwell 's .
He began with a straight row of particles , and , by giving them displacements proportional to the instantaneous values of their velocities , he obtained the approximate forms of the curves on which the particles lay from second to second .
From these the curves described by individual particles were deduced .
ReCently Havelock{ has discussed some points of difficulty in the case of translation of a circular cylinder , specially with regard to the conditions at infinity .
He has explained the uniform displacement forwards of the mass of the liquid .
From a different point of view , that of problem of the same nature has been ated by W. N. Shaw and in tracing the paths of individual particles of air in the course of actual atmospheric movements , supposed to be practically laminar , while the same problem , for vertical movement of the air , has been more recently treated by .
Bjerknes .
In the present paper I have rated the equations of motion and plotted curves for the paths of particles in the well-known simple cases of twodimensional motion , , for liquid contained in a rotating elliptic cylindel .
and in a equilateral ular prism , and for liquid to infinity and disturbed by the translation or rotation of an elliptic cylinder .
The use of the word " " particle\ldquo ; in this connection is convenient , but nires some explanation .
What is really ated is the motion of a mathematical point which moves at each instant with the velocity to its position in tlJe liquid .
If at any a small sphere be put round this point and the motion of points on its surface be followed in the same way , it will often be found that the volume is continuously as time goes on , being pulled out indefinitely in one direction .
This happens , for example , in the simple case of irrotational circulation in a " " free vortex It occurs in liquid contained in a .
triangular and in liquid outside a elliptic cylinder .
For liquid inside 'Wied .
Ann vol. 36 , p. 322 .
'Univ .
Durham Phil. Soc. Proc 1911 , vol. 4 .
' Life-History of Surface Air-Curreuts , ' Publications of Meteorol .
Office , 1906 , No. 174 , 1906 .
VOL. LXXXIX.\mdash ; A. Prof. W. B. Morton .
an elliptic cylinder , on the other hand , or more generally in Kelvin 's case of an ellipsoidal shell , the ' particles\ldquo ; are not continuously deformed , but come back periodically to their initial shapes .
In this case the term particle can fitly be applied to a volume element throughout the motion ; it is obviously inappropriate to the pulled-out filament .
This feature of the motion brings out the limitations inhelent in the conception of the liquid as a continuum in the hydrodynamical treatment , and enforces our instinctive ideas of a molecular structure in actual liquids .
This is pointed out by Havelock in connection with the deformation of volume ] ements in the immediate neighbourhood of a cylinder .
The same point is illustrated in a still more striking way by the occurrence in many cases of points on the solid boundary where the relative velocity of liquid to boundary is zero .
The " " particle\ldquo ; at this point moves with the boundary , particles on either side approach it or recede from it continuously , remaining in contact with the wall .
When there is approach from both sides toward this limiting position , the volume elements bounded on one side by the wall become extended indefinitely into filaments in the direction perpendicular to the wall .
General of Results .
( i ) Elliptic Rotating , Liquid \mdash ; Particles on the surface slide backwards along it , so that their excentric angles decrease by amounts proportional to the angle of rotation the cylinder .
Particles in the interior do the same thing similar ellipses , so that the same of particles constantly forms a radius vector of the ellipse .
The paths in space are thus a family of similar looped curves ( fig. 1 ) .
The apsidal angle and the width of the loops are found , and it is shown that consecutive loops intersect for ellipses less excentric than the form .
( ii ) Equilateral Triangular Prism Rotating , Liquid Inside.\mdash ; Particles on the walls move backward from one angular point to the other , and do not pass the corners .
Their path has a single loop and has the circum-circle of the triangle as asymptote .
Particles in the interiol describe looped paths , the loops becoming closer and smallel towards the centre .
Apsidal and width of loops are obtained ( fig. 4 ) .
( iii ) Elliptic linder with Motion of mslation ough Liquid at Rest at Infinity.\mdash ; The two particles on the surface which are carried in one piece with the cylinder , are those situated where the excentric angle is equal to the angle between the direction of motion and the major axis , and at the diametrically opposite point .
These are limiting positions between which the surface particles move in opposite directions round the two sides Two-dimensional Motion of Frictionless Liquid .
of the cylinder .
The paths of these surface particles in space are looped curves extending from to .
Between the limiting points on each side of the ellipse there are two points at which the velocity of the particle in space has no component in the direction of motion of the cylinder , and one point at which the perpendicular component vanishes .
Simple geometrical relations are found to connect these " " stationary points\ldquo ; and the limiting points on the surface .
For particles not in contact with the cylinder the paths are looped at the initial position occupied by the particle before the approach of the cylinder and the final position where it is left when the cylinder has passed off to infinite distance .
The line these end points is always parallel to the direction of motion of the cylinder and decreases rapidly in length at increasing distance from the line of motion .
The direction of the path at its ends makes with the direction of motion of the cylinder an angle which is the same for all particles , and depends on the shape of the ellipse as well as on its direction of motion .
The angle vanishes only for translation along a principal axis .
In this case it is shown that for a given breadth of cylinder , and for particles lying beyond a certain distance from the central line , there is a definite shape of ellipse which is most effective in displacing the partic ] forward .
Diagrams are given for direct motion of four different forms of cylinder ( figs. 5-8 ) and for oblique motion of a plane lamina ( fig. 9 ) .
Also , for the deformation of a row of particles originally on a straight line ( figs. 10-14 ) .
( iv ) Rotating Elliptr.uder , Liquid Outside.\mdash ; As regards the configuration of the stream-lines relative to the ellipse , it is shown that there are two different cases according as the ellipse is more or less excentric than the form .
For the less excentric forms the relative stream-lines completely surround the ellipse in all cases .
In the other class there is a mound of liquid carried round by the cylinder at each end of the minor axis ( fig. 15 Particles inside these regions describe closed paths relative to the cylinder and never escape from the neighbourhood of the minor axis .
There is one particle in the centre of each region which moves in one piece with the cylinder , and four particles on the surface of the cylinder , at the boundaries of the " " mounds which do the same thing .
These four points are limiting points at which the direction of motion of particles .
along the surface is reyersed , and the circle passing through them is approached asymptotically by threedifl.erent curves in space , viz. , the paths of particles coming in opposite directions along the surface together with the path to the outer boundary of the .
mound The other paths in this case , and all the paths in the less excentric case , show recurring loops .
rams are given for one ellipse of the less excentric kind , an1 Prof. W. B. Morton .
for the plane lamina ( fig. 17 ) .
Expressions are found for the apsidal angle of the paths which are examined in detail for the plane lamina ( fig. 18 ) .
It is shown that for certain paths in the latter case there are three different apsidal distances .
Method of Calculation .
If is the stream function for the motion of the liquid determined by the motion of a cylinder then the stream function for the motion relative to the cylinder is The curves const .
are the relative stream-lines .
The paths of the particles in space are got by combining a motion along these with the motion of the curves themselves as they are carried by the moving cylinder .
Tbus it is necessary to connect the position of a particle on its relative stream-line with the time or with the displacement of the cylinder from an initial position .
Let be expressed in terms of the appropriate orthogonal co-ordinates with length-elements , and let be chosen to fix the position on a stream-line .
The expression for the -component of velocity gives the equation When is removed from the right-hand side by aid of the equation const .
, the integral can , in the cases considered , be expressed by elliptic functions .
will contain or as a factor .
It is convenient to replace as independent variable by or The paths in space are got by to each point on a stream line the corresponding linear displacement , or displacement Liquid , Rotating Elliptic Cylinder.\mdash ; Here .
The relative stream-lines are similar ellipses .
Using the excentric angle to fix position on one of them we find .
Thus in miform rotation of the cylinder the particles slip back along their ellipses so that their excentric decrease at a uniform rate .
This is a particular case of Kelvin 's result for the ellipsoid .
When the cylinder has turned through the angle the particles are back in their original imensional Motion of Frictionless Liquid .
relative positions .
Each element of liquid has received a body rotation through this angle in consequence of a motion which is differentially irrotational at each instant .
Particles which at any instant lie on a radius of the ellipse continue to do so throughout the motion .
Thus , it is easy to follow the progressive deformation and restoration of form of a small volume-element bounded by two radii and two elliptic arcs .
FIG. 1 .
FIG. 2 .
shows the path of on the boundary of the ellipse in which .
For particles inside , the paths are similar curves .
apses of the path , of course , correspond to the ends of the axes of the ellipse ; the motion is " " direct\ldquo ; across the end of the major axis , " " retrograde\ldquo ; the minor axis .
The stationary points occur when the particle is on the radius vector bisecting the between the axes .
The following results are easily obbained : apsidal angle of path is , so that the mean ular motion of the particles in space bears to the motion of the cylinder the ratio The angular distance between the stationary points , i.e. ular width of the loops on the path , is In the apsidal and half-width of loop are plotted for different values of the axis ratio .
The curves intersect near the value showing that for an ellipse of this shape successive loops are in contact .
As the straight line limit is approached the width of a loop approaches a value of about , while the apsidal angle becomes infinite .
( ii)Iiquid Contained in Rotati , Here where the side of the triangle is The equation of the family of relative stream-lines For the curve breaks up into the sides of the Prof. W. B. Morton .
Using as the coordinate-fixing position on the stream-line , we have giving Let be the roots of the cubic in , then the solution of this equation is and are the apsidal distances on the stream-line , being the radius drawn in direction towards an angular point of the triangle , that drawn towards the middle point of a side .
The third root lies outside the limits of the triangle .
The expression for vanishes when .
It is convenient to identify a stream-line by the distance For particles in contact with the wall , then , the elliptic functions become hyperbolic and the inteo r takes the form , where is the distance from the middle point of a side .
For , i.e. the particles move backwards along the wall between one angular point and another , and do not pass the corners .
The path of a particle in space then approaches asymptotically to the circle of the triangle . .
FIG. 4 .
In fig. 3 the curves are drawn for , 1 .
A section of the relative stream-line is shown in each case , continued by the path in space .
The apsidal angle of the path is found to be The mean ular motion of the particle bears to tlJe motion of the prism the ratio of this angle to Two'- Motion of a rictiontess Liquid .
The stationary points are determined by , which leads to , etc. So here , as in the last case , the radius to the stationary position bisects the angle between the apsidal distances .
The ular width of the loops as seen from the centre is Fig. 4 shows how the apsidal angle and half-width of loop vary for streamlines at different distances from the centre .
It appears that successive loops come into contact when is about ( iii ) Translation of Elliptic linder.\mdash ; Let the velocity make angle with the major axis , then , in terms of the usual elliptic co-ordinates , , where on the surface of the cylinder .
Thus .
For the present purpose it is enient to replace the co-ordinate ) , say , and to write the equation of the family of stream-lines in the Then is the argument and the modular angle of the elliptic functions which occur in ) integral of the equation of motion .
The forms of these stream-lines are given in the text-books .
It is easy to show that the line whose parameter is , at points very distant from the ellipse , runs parallel to the line of motion of the centre at a distance from this line of : Particles which follow this particular stream-line will therefore have this for their initial and final distance from the line of motion of the centre .
The passage of the cylinder results in cases in a displacement of particles in the direction of its motion .
* The motion the relative stream-line is from when the cylinder is at infinite It seems clear that this will be the case no matter what is the form of the cylinder .
The statement is equivalent to saying that in the steady flow of a liquid past a cylindrical obstacle each straight stream-line , fter swerving round the obstacle , comes back to the prolongation of the same straight line .
This appears physically obvious if we think of two of the stream-lines so far from the obstacle on opposite sides as to be practically straight throughout their length .
The space between them , at great distances on the two sides of the obstacle , is filled across with straight intermediate lines of flow , so each of these inep , after deflection by the obstacle , must resume its former position .
The same argument does not apply to in three dimensions .
If we consider a tube of lines of flow so far removed from the obstacle on all sides as to be straight , and take sections of it at great distances on both sides of the obstacle , the same bundle of tubes of flow comes out as goes in ; but there is now the possibility of the tubes having been twisted together in passing the obstacle , e.g. , if it possessed a helical structure .
Prof W. B. Morton .
distance behind to when it has passed off to infinite distance in front .
The equation of motion in the original co-ordinate is , where is the distance the cylinder has moved from some fixed position .
Having obtained from the integral of this as a function of , the co-ordinates of successive positions occupied in space by the particle are found by applying the displacement to the corresponding points on the stream-line .
Let the origin be taken at the undisturbed initial position of the particle ; let the axis of X be perpendicular to the direction of motion of the cylinder , and the axis of parallel to it .
Then ( X , Y ) , the sideways and forward displacements of the particle , are found to be given by , .
The special stream-line includes the surface of the cylinder and the hyperbola .
The point on the ellipse and the diametrically opposite point are limiting points for the motion of part-cles the surface , i.e. points of zero relative velocity , as explained above .
The paths of surface particles have , as asymptotes in opposite directions , the lines described by these points on the ellipse .
The expressions for the co-ordinates X , become in this case , the igin now being at the poin corresponding to For the hyperbolic stream-line the co-ordinate must be used .
The values are cos2 which vanish for , and therefore give displacements from the initial position .
The following consequences can be deduced from the formulae:\mdash ; ( 1 ) The distance between the initial and final positions of a particle is got by putting in , which gives Two-dimensional Motion of Frictionless Liquid .
( 2 ) The form of the paths at a great distance from the line of motion .
When is small , X , , are small quantities of the same order , Elimination of gives the equation The paths , therefore , approximate to small circles , radius ( 3 ) Initial direction of motion of a particle .
On the expressions for X , , and putting , we get , which gives the tangent of the angle between the direction of motion of the cylinder and the direction in which a particle begins to move .
It is the same for all the particles , and vanishes only when motion is along one of the principal axes .
The greatest value is when .
For the case of a plane lamina , the in question is the complement of .
So , if the lamina is moving at to its plane , the direction of initial motion is parallel to the plane of the lamina .
This is shown in fig. 9 .
( 4 ) The critical points on the surface of the cylinder .
These are\mdash ; The lin]iting points , and , where the stream-lines diyide ; The point , where the -component of the velocity vanishes and the particle has its greatest sideways displacement ; The points , on opposite sides of , where -velocity vanishes .
The equation with ives and gives as roots of so that tau These equations show that and are pairs of conjugate points in the sense of Fagnano 's theorem on the ification of elliptic arcs .
They have the same length of intercept on the tangent between the point of contact and the foot of the central perpendicular .
Further , it is easy to show that if be the length of this intercept for the pair and for , the relation exists between these , i.e. the sum of the squares of the interoepts is equal to Prof. W. B. Morton .
the square of the maximum intercept at " " Fagnano 's point The symmetry of this shows that the of the two pairs of points can be interchanged .
( 5 ) Influence of the shape of the ellipse on the displacements of a particle , the motion along a principal axis .
Let the motion be along , keep constant , and let increase , beginning with , for the transverse motion of a plane lamina .
If undisturbed distance of a particle from the central hne of motion , maximum displacement sideways , reached when the particle is on the -axis , final displacement in direction of motion , then , in terms of the parameter , .
The first and second equations show that , as is increased , the same value of is found at distances from the central line proportional to .
So there is a continual increase of the sideways displacement of particles at given distance .
For the forward displacement we have If the function of bc plotted , it shows a maximum value about , and closer calculation places this at .
Therefore , to obtain the greatest forward displacement at distance we must have This gives a positive value for if .
For particles closer to the line , the plane disc is the most effective form for causing forward displacement .
Description of Diagrams.\mdash ; In fig. 5 I have drawn the paths of particles in liquid disturbed by the passage of a plane lamina .
The motion must be supposed very slow and the edges of the lamina rounded , so as to avoid the occurrence of discontinuity .
The direction of motion is perpendicular to its plane ; the line with the arrow shows the path of the edge , the dotted line at the bottom gives the half-breadth of the lamina .
The particles which are originally along a line parallel to the plane of the lamina have positions relative to it defined by the values of , so that , if the half-breadth be taken as unity , their initial and final distances from the line of motion of the centre are given by the ents of these angles , say , , and Two-dimensional Motion of Frictionless Liquid .
For comparison wit , this the following figures show the paths of -he same particles when the plane lamina is replaced by an elliptic cylinder FIG. 7 .
FIG. 8 .
of the same breadth , with axis in the direction of motion of , and respectively , as shown by the dotted quadrants .
The values of which would give maximum forward displacement to the five particles are , and .
In agreement with it will be seen Prof. W. B. Morton .
the first and second palticles are displaced farthest in fig. 5 , the third iu fig. 7 , and the fourth and fifth in fig. 8 .
For particles in contact with the cylinder the paths extend to infinity in both directions , and have loops of the same type as the other curves shown .
In the case of the plane lamina the loop contracts to a cusp .
It did not FIG. 9 .
Fig. 9 shows the paths for a plane lamina moving at with its plane .
I have drawn a path , lying to the left of the central one , to show the symmetrical relation between corresponding paths on opposite sides of the line of motion of the centre of the lamina .
It will be seen that one is got from the other by a double reflection .
It has already been pointed out that this is the only case in which the directions of the paths at their ends are parallel to the moving plane .
FIG. 10 .
Two-dimensional Motion of a Frictionless Liquid .
Figs. 10 , 11 , 12 , show the successive forms assumed by a row of particles which , before the approach of the cylinder , lie on a line perpendicular to the direction of its motion .
This initial position of the row is shown as a FIG. 11 .
Prof. W. B. Morton .
datum level in each figure ; the position of the moving solid is shown dotted , the final configuration when the cylinder has moved off to infinite distance is the curve drawn through the upper ends of the paths shown on figs. 5 , 6 , and 9 .
and 14 give the forms of a row of particles lying originally on lines parallel to the motion of a plane lamina .
The paths by which the FIG. 13 .
FIG. 13 .
FIG. 13 .
FIG. 13 .
FIG. 13 .
FIG. 13 .
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FIG. 13 .
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FIG. 13 .
FIG. 13 .
FIG. 13 .
FIG. 13 .
FIG. 13 .
FIG. 13 .
FIG. 13 .
FIG. 13 .
FIG. 13 .
FIG. 13 .
FIG. 13 .
FIG. 13 .
FIG. 14 .
particles have moved from their initial to their present positions are shown by dotted curves .
Diagrams like these can be constlucted by sliding a drawing of the relative stl'eam-lines over another , iving the paths in space .
This was the plan used by Maxwell .
It has the practical drawback that the required points are given as the intersections of curves which are often nearly parallel to each other , so that a error in the setting , or in the forms of the curves , causes a large displacement of the intersections .
I found it better to plot separately the co-ordinates X and against , the distance travelled by the cylinder , and then to lead off from these curves pairs of values for each ( iv ) Outsid a Elliptic lin The relatiye stream-lines const .
show peculiarities which I have not seen any reference to , although the above expressions are yely ] known .
The configuration of these curves is quite different for ellipses more excentric and less excentric than the critical form defined by , or Writing the equation of family as dimensional Motion of Frictionless Liquid .
the value gives the surface of the ellipse .
In the less excentric class this is the whole of the stream-line in question , but for the other class there is another part .
Solving the equation as a quadratic in with or The first value corresponds to the surface of the cylinder .
The second is also admissible , provided the point defined by it lies outside the cylinder , .
if or -cos2 If sinh2 , this gives a range of values of extending downwards from the value on both sides .
So here is an additional piece of the streamline over the end of the minor axis and meeting the ellipse at the points defined by .
These are evidently points of no relative motion .
The space between this additional piece of the stream-line and the end of the minor axis is filled by closed stream-lines to smaller values of A. These contract to a point ; the position of this point on the axis is given by .
Here also the particle of liquid remains in a fixed position relative to the rotating ellipse .
All the liquid in the region occupied by the closed stream-lines is carried round with the cylinder , and is kept distinct from the of the liquid .
Stream-lines for which encircle the ellipse .
For the less excentric forms all the lines of this type .
The arrangement of stream-lines above described is shown on fig. 15 for .
Also , for the limiting form of the plane lamina , in one quadrant of fig. 17 .
The arrows show the direction of motion , as seen by an observer moving with the cylinder .
The less complicated forms for the less excentric class are shown on fig. 16 for Prof. W. B. Morton .
To find the paths in space the co-ordinate is again used .
Its connection with , the of rotation of the cylinder , is given by , where is written for .
The reduction of the integral , when the right-hand side has been expressed as a function of , is rather tedious .
The result is In this A is the stream-line constant , as above .
, , with .
These formulae hold when .
When the of the radical is changed in the definition of the constant .
When ( in the more excentric class ) becomes greater than unity and Che reciprocal modulus is used .
On the surface of the cylinder reduces to This for the class .
For replaces A good deal of labour is needed in order to numerical values from the general formula .
* The elliptic functions were taken from 's tables .
I took the amplitudes of modular angles to the nearest minute so that double interpolation was necessary .
The functions were expressed by functions and these were calculated from the expansions in ascending powers of " " The values of were got from the tables of Jahnke and Enlde .
Apses on the Paths.\mdash ; When the particles right round the cylinder the apses are on the major and minor axes .
The apsidal in space comes out The particles which keep near the end of the minor axis in the more excentric class , have apses in the two positions where they cross this axis .
The apsidal angle is got from the expression just given by omitting the I am indebted to Miss Mary Beck for much help in the a1ithmetical work in connection with this case and the preceding one .
Motion of a Frictionless Liquid .
subtracted and replacing the denominator of the first term inside the bracket by Fig. 18 shows the variation of the apsidal angle for different values of the stream-line parameter , in the case of a plane lamina .
For a certain range of the closed stream-lines there is a third apse intermediate between the two which correspond to the transits of the particle across the minor axis .
This is where the particle is at maximum distance from the centre .
We have .
Differentiating with respect to and taking account of the equation of the stream-line which vanishes for .
For the maximum occurs at the point on the cylinder where the external part of the stream-line meets it .
As A decreases the position of maximum moves up the outer part of the stream-line until , for certain value of , it coincides with the more distant point on the axis .
This happens when the value of iven a is equal to For the plane lamina this gives .
So the third apse is found on the paths between and .
From to , when the stleam-line shrinks to a point , there are only the two apses corresponding to the positions on the minor axis .
FIG. 16 .
FIG. 17 .
Description of Diagrams.\mdash ; Fig. 16 shows the forms of the paths for an ellipse of the less excentric class .
As in preceding diagrams the first quadrant is occupied by the relative stream-lines with the VOL. LXXXIX.\mdash ; A. Two-dimensional Motion of Frictionless Liquid .
surface of the cylinder itself .
The two external lines are and .
These stream-lines are continued into the paths in space .
In fig. 17 the plane lamina is taken as the extreme case of the more excentric class .
Here , and the surface of the lamina with the external FIG. 18 .
loop corresponds to .
The other stream-lines drawn are for the values .
The paths are again shown as continuations of the relative stream-lines , except in the case of the outer portion of the lamina itself between the critical point and the edge .
The particles in contact with this move round the edge from the critical point on one side to that on the other side , the motion becoming infinitely slow near the limiting points .
The path has a cusp at the edge of the lamina and approaches the asymptotic circle from the outside .
It has been drawn , for the sake of clearness , from its cusp at the left-hand side of the diagram .
It will be seen that the same asymptotic is approached from the inside by the path corresponding to the external loop and also by the particles which slide along the central part of the lamina between one critical position and the other .
|
rspa_1913_0069 | 0950-1207 | A critical study of spectral series. Part III.\#x2014;The atomic weight term and its import in the constitution of spectra. | 125 | 127 | 1,913 | 89 | Proceedings of the Royal Society of London. Series A, Containing Papers of a Mathematical and Physical Character | W. M. Hicks, F. R. S. | abstract | 6.0.4 | http://dx.doi.org/10.1098/rspa.1913.0069 | en | rspa | 1,910 | 1,900 | 1,900 | 3 | 55 | 1,398 | http://corpora.clarin-d.uni-saarland.de/surprisal/6.0.3/?id=rspa_1913_0069 | 10.1098/rspa.1913.0069 | null | null | null | Atomic Physics | 51.649489 | Tables | 43.840412 | Atomic Physics | [
22.18269920349121,
-78.75944519042969
] | ]\gt ; A Critical Study of Series .
Part III.\mdash ; The Atomic Weight Term and its Import in the Constitution of Spectra .
By W. M. HICKS , F.B.S. ( Received June 7 , \mdash ; Read June 26 , 1913 .
) ( Abstract .
) The wave numbers of the lines in a spectrum which form any of the recognised series can be calculated , as is well known , from an expression of the form where and fraction , the fraction being in general a function of the integer .
The constant or triplet separations of and series are formed by the deduction of a quantity , or , in the case of triplets , from , and it has long been known that these quantities are very roughly proportional to the squares of the atomic weights when elements in the same group are compared .
The present communication deals with the actual relation between and the atomic weight , and with the part it plays in the general constitution of spectra .
It is shown that there is a definite , quantity in connection with each element which is of fundamental importalJce in the building up of its spectrum .
It is proportional to the square of the atomic : in fact , if ?
denote the atomic divided by 100 its value is This quantity is of such universal application that it is useful to have a special name for it , and it has been called the oun .
Its value is denoted by , but is used for the multiple , as it is of very frequent occurrence .
evidence for its existence is based on the arc spectra of He , the elements of the Groups I and II , the Al sub-group and Sc of and the , Se oi of the Periodic Table\mdash ; in other words , all those elements in which the series lines have been allocated .
It is found:\mdash ; ( 1 ) That the which give the doublet and triplet separations are all multiples of their respective ouns .
( 2 ) That the corresponding quantities , which give the satellite separations in the series , are also multiples of the oun .
( 3 ) That the series show satellites depending in a similar way on the oun .
* It will be convenient to refer to as V ( n ) and as .
A Study of Spectral Series .
( 4 ) That , in a large number of cases , lines are related in such a way that the differences of their denominators are multiples of the oun , and that frequently in place of an expected line which is not observed another occurs related to it in this manner .
It is said to be collaterally displaced .
After reviewing the evidence for the existence of the oun the paper deals in succession with : ( a ) The constitution of the series .
After establishing the dependence of the satellite separations on the oun , it is shown to be possible that the series may not depend directly on a formula involving , but that the of different orders may be given by the successive addition , or subtraction , of various multiples of the oun .
It is curious that in those cases where there are no satellites , these differences are multiples of the themselves .
Evidence is also given to show that the decimal part of , i.e. for the first line , is a multiple of , or for triplets , but that , in the case where satellites exist , the extreme satellite is to be taken .
( b ) The constitution of the series .
The series is one whose limit is the variable part in the formula for the series corresponding to the first of the lines ; in other words , it depends on the series in the same way that the limits for the and series depend on the first line of the P. For all elements , except the alkaline earths , the lines are far in the ultrared , and it is only recently that waves of extreme wave-lengths have been measured by Paschen .
It is probable that the for the first lines in each sub-group may be the same , and even possible that it may be the same in all , the earths excepted .
In the earths there are a very large number of strong well-defined lines which are connected collaterally with one another , or with the lines of the series themselves , the displacements proceeding by multiples of .
Ihese afford values of large multiples of , and hence of ; and , in consequence , give very exact values for the latter .
( c ) The preceding results are then discussed with a view to obtaining a better approximation to the value of the oun as a function of , on the supposition that it is always proportional to it .
A value is obtained ( see above ) which is probably correct to a few un its in the fifth nificanC figure .
With further knowledge it is probable that this degree of accuracy may be extended to the sixth , and even beyond .
It is clear that with such a knowledge of this constant , and with more definite and certain knowledge of spectral relations enabling values of of the same degree of accuracy to be obtained , it will be possible to determine atomic with extreme accuracy , an accuracy much beyond that attainable by methods depending on weighing .
The large atomic weight of Ag , combined with the fact that it may be A Band Spectrum attributed to Monosulphide .
127 regarded as the basis of other atomic weights , would point to it as the best element from which to deduce the value of .
The value of its doublet separation can be determined with extreme accuracy , to one or two units in the sixth significant figure .
But , unfortunately , the deduction of from this is subject to an uncertainty which quite upsets that degree of accuracy .
The most probable value is , however , very close to that obtained by the final discussion .
The uncertainty is due to a doubt as to the real relations of lines usually assigned to the , and series in Ag , and it is hoped to clear this up by a further consideration of the spectrum .
It is then shown how the ] indicated in the fore o discussion enable the doublet and the satellite differences for Au , and the limits of the series to be determined .
The value of for Sc is considered in Appendix I. In Appendix IT , the wave-lengths of the and lines treated of , together with short historical notes , are given .
A Band attributed to Carbon lphide .
By L. C. MARTIN , A.R.C.Sc .
, B.Sc. , Research Student Imperial College of Science and Kensington .
( Communicated by A. Fowler , F.R.S. Received June 10 , \mdash ; Read June 26 , 1913 .
) [ PLATE 6 .
] The experiments described in the present paper were made in connection with the investigation of sulphur spectra developed by the nitrogen in continuation of previous observations by Profs .
Strutt and Fowler .
* A result of considerable interest is the detection of a series of ultra-violet hands which appear to be characteristic of a compound of sulphur and carbon .
This band system extends from approximately .
It is , however , quite distinct from that deyeloped , in the same ion , by carbon disulphide in the .
afterglow , which is described in the paper to which the reference is given .
Further photographs were taken , and it was found that the two sets of bands had nothing whatever in common .
Confirnlation of Prof. Strutt 's work on the chemical actions taking place between carbon disulphide and the active nitrogen was obtained .
yreen deposit of nitrogen sulphide formed in the experimental tube , and also a .
Soc. Proc 1911 , , vol. 86 , p. 111 .
|
rspa_1913_0070 | 0950-1207 | A band spectrum attributed to carbon monosulphide. | 127 | 132 | 1,913 | 89 | Proceedings of the Royal Society of London. Series A, Containing Papers of a Mathematical and Physical Character | L. C. Martin, A. R. C. Sc., B. Sc.|A. Fowler, F. R. S. | article | 6.0.4 | http://dx.doi.org/10.1098/rspa.1913.0070 | en | rspa | 1,910 | 1,900 | 1,900 | 3 | 119 | 2,541 | http://corpora.clarin-d.uni-saarland.de/surprisal/6.0.3/?id=rspa_1913_0070 | 10.1098/rspa.1913.0070 | null | null | null | Atomic Physics | 59.45164 | Thermodynamics | 30.562008 | Atomic Physics | [
9.781700134277344,
-43.863407135009766
] | A Band Spectrum attributed to Carbon Monosulphide .
127 regarded as the basis of other atomic weights , would point to it as the best single element from which to deduce the value of The value of its doublet separation can be determined with extreme accuracy , to one or two units in the sixth significant figure .
But , unfortunately , the deduction of A from this is subject to an uncertainty which quite upsets that degree of accuracy .
The most probable value is , however , very close to that obtained by the final discussion .
The uncertainty is due to a doubt as to the real relations of lines usually assigned to the S , D , and P series in Ag , and it is hoped to clear this up by a further consideration of the spectrum .
It is then shown how the laws indicated in the foregoing discussion enable the doublet and the satellite differences for Au , and the limits of the series to be determined .
The value of A for Sc is considered in Appendix I. In Appendix II , the wave-lengths of the D and F lines treated of , together with short historical notes , are given .
A Band Spectrum attributed to Carbon Monosulphide .
By L. C. Martin , A.R.C.Sc .
, B.Sc. , Research Student Imperial College of Science and Technology , South Kensington .
( Communicated by A. Fowler , F.R.S. Received June 10 , \#151 ; Read June 26 , 1913 .
) [ Plate 6 .
] The experiments described in the present paper were made in connection with the investigation of sulphur spectra developed by the nitrogen afterglow , in continuation of previous observations by Profs .
Strutt and Fowler.* A result of considerable interest is the detection of a series of ultra-violet bands which appear to be characteristic of a compound of sulphur and carbon .
This band system extends from A. 2436-2837 approximately .
It is , however , quite distinct from that developed , in the same region , by carbon disulphide in the.afterglow , which is described in the paper to which the reference is given .
Further photographs were taken , and it was found that the two sets of bands had nothing whatever in common .
Confirmation of Prof. Strutt 's work on the chemical actions taking place between carbon disulphide and the active nitrogen was obtained .
A green deposit of nitrogen sulphide formed in the experimental tube , and also a * ' Roy .
Soc. Proc. , ' 1911 , A , vol. 86 , p. 111 .
Mr. L. C. Martin .
A Band brown one of polymerised carbon monosulphide , the latter only in the presence of a stray discharge .
Sulphur in the Carbon Arc. The new bands were first observed in an attempt to obtain the spectrum of sulphur in the carbon arc .
After some failures , successful results wTere obtained by using a hollow carbon , well charged with sulphur , as the upper pole , which was made positive .
In these circumstances a steady flow of melted sulphur into the arc was maintained .
In addition to overpoweringly strong bands of carbon and cyanogen , and faint bands recognised as belonging to sulphur , several of the photographs showed a fairly well developed system of bands in the region 2500-2700 of which no previous record could be found .
Like the sulphur bands , the new bands were degraded towards the less refrangible side .
Attempts to brighten the spectrum by surrounding the arc with sulphur vapour from a test-tube in which sulphur was boiled by a bunsen burner increased the intensity of this set of bands , but brought out a good many reversed sulphur bands in the region 2800 to red .
The band system 2500-2700 betrayed no tendency to reversal .
It therefore seemed probable that these bands were not due to sulphur itself , but to some compound produced in the arc .
Sulphur Vacuum Tube .
As a check on the previous result , experiments were made on the electric discharge through sulphur vapour .
Salet 's apparatus* is very suitable for the visible region of the spectrum , but fails for short wave-lengths , since it is generally constructed of glass , and would be difficult to make of silica glass .
An arrangement was accordingly devised ( fig. 1 ) with a quartz window ( Q ) .
The sulphur could be melted in side tube ( A ) by means of gentle heating with a bunsen burner .
The electrodes ( B ) were of aluminium , led into the discharge tube by quill tubing within the wider side tubes , and cemented in with sealing wax .
With apparatus of the dimensions shown , it was found that the quartz window was hardly at all clouded during the 15 minutes necessary for exposure .
The tube was first exhausted with a pump and the vacuum was subsequently maintained by means of charcoal cooled with liquid air ( see JD , fig. 1 ) .
The discharge , as described by Salet , is of a blue colour , and is luminous enough , even in the fairly wide tube , to require only a short exposure .
In the first experiments , with a less perfect form of apparatus , giving an * G. Salet , 'Analyse Spectrale , ' p. 220 .
Spectrum attributed to Carbon Monosulphide .
129 insufficient supply of sulphur vapour , the characteristic sulphur bands were accompanied by bands of nitrogen and the lines of carbon and mercury at 2478 , 2536 , respectively .
The new system of bands in the region 2500-2700 was also faintly present .
When the more perfect apparatus was employed , however , nitrogen , carbon , and mercury were eliminated and the new bands were also absent ; the SO C.m.Fig .
1 .
spectrum then only extended as far as 2829 into the ultra-violet and showed nothing but the broad , double-headed sulphur bands degraded towards the red .
It is clear that these bands 2500-2700 are not given by the discharge through pure sulphur vapour ; also that they are only developed to any strength when the carbon line 2478 is present .
They have nothing whatever to do with the ordinary spectra of carbon or nitrogen .
Discharge in Carbon Disulphide .
The spectrum of the electric discharge through the vapour of carbon disulphide was next photographed .
A similar apparatus to the previous one was used , the carbon disulphide being contained in a bulb , and the flow of the vapour was regulated by a tap .
The vapour was led into the tube at C ( fig. 1 ) .
As in the previous case it was easy to maintain a good vacuum by means of charcoal and liquid air , especially as in this case the action of the discharge tends to decompose the vapour and lower the pressure still further .
The discharge from a 10-inch coil immediately gave a heavy dark brown deposit on the walls of the tube , doubtless being a mixture of sulphur and polymerised carbon monosulphide as described by Dewar and others .
This deposit extended to the liquid-air tube .
It was found that by lengthening the discharge tube slightly , the quartz window could be kept free from deposit .
Mr. L. C. Martin .
A Band The spectrum was found to be very complicated .
In the first place it reproduces that of the sulphur vacuum tube perfectly , band for band , and it seems probable that this is due to free sulphur , one of the immediate products of the discharge .
Corresponding in intensity to the sulphur bands is a remarkable band system extending from X 2436-2837 , the brightest of the bands being identical with those previously shown by sulphur in the carbon arc .
Discharge in Disulphur Dichloride .
It was thought desirable to test whether or not these bands were due to sulphur in a different molecular condition from ordinary sulphur vapour , and for this purpose an unstable and volatile sulphur compound was necessary ; such a compound is disulphur dichloride .
An apparatus similar to that adopted for the carbon disulphide discharge was used , and was kept exhausted by means of cooled charcoal .
The defect in this apparatus was that the bulb containing the disulphur dichloride was connected to the discharge tube by means of a short piece of thick red rubber tubing such as is used for vacuum tube work .
The discharge produced a blue glow as in the two previous cases and a deposit was immediately formed on the walls of the tube , found on after examination to consist of sulphur and a higher chloride .
The spectrum of the discharge contained the usual sulphur bands and faint indications of the new bands .
The carbon line 2478 was present and the impurity was found to be due to the action of the disulphur dichloride on the rubber connection .
To make certain of this another tube was constructed and the bulb sealed on ; it could be filled with the liquid by a fine bent tube on removing the tap stopper .
On taking a photograph with an even longer exposure than before , the carbon line and the new bands were found to be eliminated , the sulphur spectrum only being left in its entirety .
Description and Wave-lengths of the New Bands .
As already explained , when fully developed , the new spectrum consists of a number of bands degraded to the less refrangible side .
With the spectrograph employed , giving a dispersion of about 10 A.U. to the millimetre in this region , a few of the bands were just resolved into their component lines .
Like the sulphur bands they appear fairly evenly spaced and double headed , and like those of the carbon arc they form groups in which successive heads diminish in intensity , although in the opposite direction to the carbon bands , which are degraded towards the violet .
The group with its head at 2579 is worthy of special mention .
Its Spectrum attributed to Carbon Monosulphide .
131 appearance varies greatly under different conditions , and it appears to be the best developed of all the bands only when the whole system is weak .
It is the strongest in the carbon arc spectrum of sulphur , and in cases where sulphur vapour is contaminated with carbon in the vacuum tube .
In the carbon disulphide discharge , however , where the whole of the bands are strongly shown , it is not so bright relatively , and is evidently superposed on another group with a fairly strong band near 2573 .
In this case the head at 2665 is the brightest of the system .
The wave-lengths of the bands were determined as accurately as possible by means of an iron comparison spectrum in the usual way .
Except in the extreme ultra-violet , where the resolving power is high , the heads of the bands were very diffuse and indistinct , and consequently very difficult to measure .
As the second-frequency differences are small it has not been at present found possible to give a Deslandre 's frequency formula for the band system .
Wave-length .
Intensity .
Group .
Remarks .
Wave-length .
Intensity .
Group .
Remarks .
2436 -00 0-5 A 2621 -52 ' 1 a 2444 -56 1 o B 2622 -53 r O E 2445-09 J Z 2629 -59 : i 4 ?
2453 -451 1 A 2630 -70 r 2454 -16/ 1 Jx 2638 *85 ' L A 77 2460 -02 1 9 B 2639-87 4 jl 2460 -07 J 2659 -34 2 ?
2473 *21 l A 2661*851 I Very diffuse .
2476-89 2 B 2664 -02 10 F 2493 -41 4 A 2674 -66 2 ?
2508 -14 \ 2509 -39 J 5 ?
Indistinct 2677 -44 ] 2679 -52 j i- 8 F Do .
2511 -29 6 C 2692 -66 ] L 8 T 2522 -971 6 Tk 2694 -51J r JJo .
2523 -79 J JJ 2709 -011 r* 2529 -90 2 c 2710 -41 1 O h 2535 -541 9 p 2726 -62 4 p 2536 * ] 2744 -49 2 F 2538 -55 1 r* Tv 2754 -731 i 2539 -29 J o JD 2756 -90 J I- 6 G 2549 -44 2 c 2769 -46 ] 6 Indistinct 2555 -74 \ a n 2771 -90J G 2556 -10 J o u 2785 -161 2569 -61 i c 2787 -59 J r 5 G 2572 -64 2 D 2801 -581 2579 -12 8 E 2803 -58 J \gt ; 5 G 2587 -26 4 ?
2818 -371 2590 -22 6 ?
2819 -29 1 4 G 1 2591 93 10 E 2837 -21 4 G 2605 -59 \ 2606-91/ 8 E 1 132 A Band Spectrum attributed to Carbon Monosulphide .
General Conclusions .
Sir J. Dewar and Dr. H. 0 .
Jones describe an experiment in which the volatile condensable compound produced by the action of the silent electric discharge on the vapour of carbon disulphide is condensed in a U-tube cooled by liquid air .
When the tube is removed from the Dewar vessel violent polymerisation occurs , and a flash is produced .
The spectrum of this flash is described as containing scattered bands from 2480 to 3620 , the sulphur bands between 3840 and 3920 , and indications of cyanogen and hydrocarbons .
It is probable that , apart from impurities , this spectrum is a reproduction of that produced by the discharge through carbon disulphide vapour , and contains the ordinary sulphur spectrum , together with the bands from 2436 to 2837 described in this paper .
The action of the discharge is to break up the vapour into free sulphur and carbon monosulphide .
Polymerisation of this monosulphide oocurs almost immediately and forms the dark deposit , but during this action the electric discharge , or the influence of great heat , or both as in the electric arc , produces the band system .
The different groups vary in their relative development with the conditions of experiment ; it is possible that they are due to successive compounds produced during the transition from the disulphide into the monosulphide and its polymers .
The author 's best thanks are due to Prof. Fowler , F.R.S. , for constant interest during the progress of the experiments , and valuable help during the preparation of the paper .
Band Spectrum Due to a Sulphide of Carbon .
3 .
Discharge through sulphur1 vapour .
4 .
Dischar ge through carbon disulphide vapour ( short exposure ) .
O. Sulphur ill carbon arc .
*0 \#169 ; \amp ; O o p 6 .
Iron comparison .
S ' vol. 89 , Pla
|
rspa_1913_0071 | 0950-1207 | New series of lines in the spark spectrum of magnesium. | 133 | 137 | 1,913 | 89 | Proceedings of the Royal Society of London. Series A, Containing Papers of a Mathematical and Physical Character | A. Fowler, F. R. S. | article | 6.0.4 | http://dx.doi.org/10.1098/rspa.1913.0071 | en | rspa | 1,910 | 1,900 | 1,900 | 5 | 69 | 1,793 | http://corpora.clarin-d.uni-saarland.de/surprisal/6.0.3/?id=rspa_1913_0071 | 10.1098/rspa.1913.0071 | null | null | null | Atomic Physics | 74.736767 | Tables | 24.926783 | Atomic Physics | [
14.223560333251953,
-48.05692672729492
] | ]\gt ; New Series of Lines in the Spectrum of ]gnesbum .
By A. , F.RS .
, Assistant Professor of Physics , Imperial College of Science and , South Kensington .
( Reoeived June 12 , \mdash ; Read June 26 , 1913 .
) Introdory .
A recent investigation suggested that the spectrum of hydrogen was unique in two Principal series of lines which are related to each other in the same manner as Diffuse and Sharp series .
* One of these series begins with a line at , and the other with a line at 3203 , the two series to the limit 48764 on the frequency scale .
The lines in question have so far only been produced by passing powerful discharges through helium tubes ( which also contain drogen ) , but in accordance with the work of Rydberg , they have been attributed to hydrogen on the ground of their series relationsbip with lines known to be due to In for further examples of such series , with hydrogen suggested spark spectra as the most promising sources .
One of the most remarkable spark lines is the well-known line of magnesium , which is ordinarily not visible at all in the arc , but is by far the strongest line in the spark .
Further , there is a series of single lines in the arc spectrum of nesium , first identified as such by Rydberg , which it seemed possibly be to the Balmer series of hydrogen lines .
Magnesium therefore appeared to be a suitable element for ation , but records of the spectrum were ether inadequate for the purpose in view .
There were , in fact , only two recorded lines which could possibly be connected in series with 4481 ; namely , the lines given by Exner and Haschek at and .
Other associated ultra-violet lines , howeyer , have now been photographed , and it results that the spark lines form two series like of hydrogen , 4481 being analogous to the first Principal line of hydrogen JIethod of The magnesium spark lines , as ordinarily obtained , are too diffuse for accurate measurement , and it appears from the present investigation that in the far ultra-violet they are even too diffuse to be recognisable .
The lines may be narrowed by the use of self-induction , but they are at the same time weakened , and the more refrangible lines were then too feeble for observation .
It is known , however , that the spark lines are also brought out when the arc ' Monthly Notices R.A.S. , ' 1912 , vol. 73 , p. 62 .
Mr. A. Fowler .
New Series of is passed in vacuo ; that is , in reality , in a low-pressure atmosphere of hydrogen liberated by the heated metal .
* Under these conditions the lines are well developed and sharply defined , and by this method it became possible to photograph five additional lines which were evidently related to the three spark lines already mentioned .
The apparatus employed was identical with thaG described in a previous paper for the observation of the spectrum of magnesium hydride .
In addition to the spark lines , the arc in vacuo also exhibits the arc and flame and the bands attributed to magnesium hydride .
The spark lines , however , are easily identified by comparison with the arc in air .
In the region beyond , the five new spark lines are , in fact , the only lines present in most of the photographs .
An iron arc comparison was utilised in the determination of wave-lengths , except for the extreme ultra-violet , where , in the absence of tabulated iron lines , the comparison spectrum was that of copper .
Series of Spark Lines .
Wave-lengths and other details relating bo the new series lines are given in the appended tables .
The wave-lengths are on Rowland 's scale , and the oscillation frequencies have been corrected to vacuum .
A mere inspection of the photographs suggests that the eight lines form a single series having the usual characteristics , but calculations show that they must be divided into two series by taking alternate lines .
As the new series consist of enhanced lines , they may be conveniently designated and , to distinguish them from the other nesium series , which already include Principal , Diffuse , and Sharp series of triplets in addition to the series of single lines .
The Hicks formula for the two series , as calculated from the first three lines in each case , are Observed minus computed values of the frequeucies ( 0\mdash ; C ) are iven in Column 6 of the tables .
* Fowler and Pain , 'Boy .
Soc. Proc 1903 , vol. 72 , p. 253 .
Fowler , ' Phil. Trans 1009 , , vol. 209 , p. 449 .
See plate accompanying paper by Fowler and Reynolds , this vol. , p. 137 Lines in the Spark Spectrum of gnesium .
Spark Series *Used in calculation of constants .
Spark Series * Used in calculation of constants .
It will be seen that the calculated limits of the two series are practically identical , and that the values of differ by very nearly , as is also the case with hydrogen .
The two spark series of magnesium are similar to the two Principal series attributed to , and run nearly parallel to them , as will be evident from the ison of the respective frequencies:\mdash ; Limits .
HPI Diff Mg HPII Diff Limits .
The similarity not only refers to the distribution of the lines in series , but also , to a considerable extent , to the manner in which the two sets of lines .are produced .
136 New Series of Lines the Spectrum of Magnesium .
Besides the above lines , there are four other magnesium spark lines which do not belong to the series .
They are very hazy in the spark itself , but are well defined in the arc in vacuo .
The wave-lengths of these lines are , and Discussion .
If the new magnesium lines are to be regarded as forming series , the -Schuster law of limits would lead us to expect associated Diffuse and Sharp series , with their common limit at 49776-22309 , i.e. 27467 .
The series of single lines , however , has its limit at 26618 , and there is apparently no other series which can be supposed to have any closer relation to the spark lines .
In the case of hydrogen there is a similar discrepancy , but of much smaller amount ; thus , 48764-21334 , while the limit of the Balmer series is actually at would thus appear that the -Schuster law , in its present form , does not accurately connect the spark series with series produced in the arc .
Or it may be that the law fails only when there are two Principal series converging to the same limit .
bion may be called , however , to another possible relation between the spark and the Bydberg series .
If , in the application of the RydbergSchuster rule , we use the iable part of the spark equation given by , in place of the actual limit of the series and , we get a much closer approximation to the limit of the Rydberg series .
Thus , , and , if the first line of series be subtracted from this , it gives 26482 , differing by 136 from the of the Rydberg series .
A still closer approximation is obtained if a simple equation be calculated for series E2 , namely , from the first two lines , This gives , and 22309 as before , the result is 26558 , differing by only 60 from the limit of the fiydberg series .
In view of the approximate character of all series equations , there is thus a strong suspicion that the spark series may be related to the Rydberg series in such a way that the limit of the latter is equal to the difference between the variable part of the equation for the second spark series with and the frequency of the first line of the first spark series .
It should be mentioned , however , that , in the case of hydrogen , the discrepancy is slightly increased if this alteration in the -Schuster law be made .
In this notation signifies " " variable part\ldquo ; of equation .
Series Lines in the Spectrum of gnesium .
Until other examples of spark series have been discovered , it is evident that no definite conclusion can be drawn .
An alternatiye view would be to suppose that the new series , both in magnesium and hydrogen , are series of a uew type , having no necessarily simple relation to other series in the respective spectra .
In that case the two series attributed to might equally be supposed to belong to helium , the presence of which is necessary for their production in the laboratory ; it is difficult to believe , however , that the close agreement of one of the series with the Principal series calculated for hydrogen by Rydberg is merely accidental .
Additional Triplets and other Series Lines in the Spectrum of By A. FOWLER , F.B.S. , Assistant Professor of Physics , Imperial College of Science and , South Kensington , and W. H. BEYNOLDS , B.Sc. , , Research Student .
( Received June 12 , \mdash ; Bead June 26 , 1913 .
) [ PLATE 7 .
] Recent of the spectrum of the rnesium arc in vacuo , taken primarily for the investigation of enhanced lines , *have revealed several additional members of the triplet and single line series .
For some of the previously known lines it has also been possible to obtain improved wavelengths on account of their greater sharpness under these conditions .
It is believed that the results will form a useful contribution to the general study of series lines , and they have accordingly been brought together in the present communication .
For the representation of the series , the formula , as modified by and Hicks , been employed , namely ' * See Fowler , this vol. , p. 133 .
' Roy .
Acad. Amsterdam Proc 1906 , vol. 9 , p. 434 .
'Phil .
Trans. ' 1910 , , vol. 210 , p. 57 .
|
rspa_1913_0072 | 0950-1207 | Additional triplets and other series lines in the spectrum of magnesium. | 137 | 145 | 1,913 | 89 | Proceedings of the Royal Society of London. Series A, Containing Papers of a Mathematical and Physical Character | A. Fowler, F. R. S.|W. H. Reynolds, B. Sc. | article | 6.0.4 | http://dx.doi.org/10.1098/rspa.1913.0072 | en | rspa | 1,910 | 1,900 | 1,900 | 8 | 112 | 2,398 | http://corpora.clarin-d.uni-saarland.de/surprisal/6.0.3/?id=rspa_1913_0072 | 10.1098/rspa.1913.0072 | null | null | null | Atomic Physics | 57.679269 | Tables | 42.057252 | Atomic Physics | [
15.228716850280762,
-48.42916488647461
] | ]\gt ; Series Lines in the Spectrum of gnesium .
Until other examples of spark series have been discovered , it is evident that no definite conclusion can be drawn .
An alternatiye view would be to suppose that the new series , both in magnesium and hydrogen , are series of a uew type , having no necessarily simple relation to other series in the respective spectra .
In that case the two series attributed to might equally be supposed to belong to helium , the presence of which is necessary for their production in the laboratory ; it is difficult to believe , however , that the close agreement of one of the series with the Principal series calculated for hydrogen by Rydberg is merely accidental .
Additional Triplets and other Series Lines in the Spectrum of By A. FOWLER , F.B.S. , Assistant Professor of Physics , Imperial College of Science and , South Kensington , and W. H. BEYNOLDS , B.Sc. , , Research Student .
( Received June 12 , \mdash ; Bead June 26 , 1913 .
) [ PLATE 7 .
] Recent of the spectrum of the rnesium arc in vacuo , taken primarily for the investigation of enhanced lines , *have revealed several additional members of the triplet and single line series .
For some of the previously known lines it has also been possible to obtain improved wavelengths on account of their greater sharpness under these conditions .
It is believed that the results will form a useful contribution to the general study of series lines , and they have accordingly been brought together in the present communication .
For the representation of the series , the formula , as modified by and Hicks , been employed , namely ' * See Fowler , this vol. , p. 133 .
' Roy .
Acad. Amsterdam Proc 1906 , vol. 9 , p. 434 .
'Phil .
Trans. ' 1910 , , vol. 210 , p. 57 .
Messrs. Fowler and Reynolds .
Additional Triplets where gives the oscillation frequencies of successive lines corresponding to integer values of is the convergence frequency , or limit , of the series ; 109,675 is the general series constant derived from the Balmer sel.ies of hydrogen lines ; and are constants to be determined for each senes .
In some cases , it has been necessary to introduce an additional term in the denominator , as found by Hicks , in order to represent the lines with greater accuracy .
The spectrum of the manesium arc vacuo , in the visible region , has already been described by Fowler and Pain .
* Photographs including the ultra-violet are reproduced in Plate 7 .
They show the bands attributed to ynesium hydride , together with the lines which are characteristic of the arc , spark , and flame .
In the spectrum the Rydberg series of single lines is well developed , while in the ultra-violet the triplets and spark lines are striking features .
Observations have shown that the spark lines are best developed on the ative pole , while the aro lines are especially conspicuous in the green flame .
In the tables which follow , the wave-lengths are on 's scale , and oscillation frequencies have been reduced to vacuum .
Diffuse ( Suborclinate ) Series of Details relating to the Diffuse series of triplets are given in Table I , Kayser and e 's values included for comparison so far as they go .
The formula calculated for the less refrangible components of the triplets , from the first two and last of the obse1ved members of the series , is The observed computed values of the frequencies ( 0-C ) are given in Column 8 and it will be seen that this formula does not represent the se1ies quite within the estimated limits of error , nearly so .
A more accurate representation of the lines is giyen by a term namely As shown in Column 9 the lines are very closely represented by equation . .
Soc. Proc 1903 , vol. 72 , p. 253 .
and other Series Lines the ) Table I.\mdash ; The Diffuse } of Triplets .
VOL. LXXXIX .
Messrs. Fowler and Reynolds .
Additional bordinate)of Details of the Sharp series of are given in Table IT .
The formula calculated for the less ible components from the first three and the last line is Following Hicks , a term has been introduced for the better represent of , and Ilas been taken reater than unity .
I will be seen that the lines are represented almost perfectly by equation givon ) the limit of the series only differs by lies of Triplets .
Remarks .
for the calculation of constants .
The in Column 4 for triplet { roltl the .
The triplet falls in a group of five relatively strong lines , { its components to be masked by lines for which wave-lengths are , 277 two neigl1bouring lines are 2779.94 , and Series Lines in of .
14 ] .
from the liDlit for the series th is introduced .
As regards the agreement of the observed and calculated values , an almost equally result is obtained by less than unity , that is 2 for .
Using the same lines as before the tion then becomes The limit is scalcely changed , and the differences O-C are respectively ( ?
) , .
Applying 's law tlris equation would lead us to expect ultra-violet series , the ] imit o obtained by would be at S5540 , and the first line of the triplet at 45780 .
ations include the region which would be occupied by this triplet , but the lines ve not been observed .
Hence , the first equation is probably correct , as indicates a principal series of triplets in the -red with its .
This series has apparently been obseryc by Paschen , the limit calculated from the actual lines observed is iven by hinl as From the data given the mean interval between the hrst and second members of the r , riplets in the Diffuse and Sharp sel.ies is , and between the second third .
The formula the seconlil and third components may bc deduced by and from the first of the equations 1 the first of the triplets given above .
As roduced in the in lines of the of lines are very diffne , especially on their less ) sidcs , for the first few lines the ths have not previously been with any great of accuracy .
) arc in ives them quite shal.ply , and has been taken of this to better values for the wave-lengths .
In Table IIT the lirst line is from 1aschen ; the next are from 's solar tables ; the next four determined from a photograph of the arc taken with a 10-foot concave , and the last three from photographs with a prismatic spectroscope .
This series has long been recognised as one which cannot be accurately by a formula , and the reyised -lengths a further 'Aun .
Phyb ( 4 ) , vol. ) essrs .
, er and Reynolds .
Additionat Priplets test .
The Hicks equation calculated from the first three and last lines of the observed spectrum is The differences , " " observed - computed\ldquo ; frequencies , are shown in Column S. able I of ingle Lines .
* Used in the calculation of constants .
It will be observed that even a four-constant formula does not represent all the observed within the limits of error , and that extrapolation to the infra-red member of the series is very defective .
Further , the negative value obtained by ) is , and this is far from being in agreement with the infra-red line of which chen regards as connected with the series .
If the infra-red line and the three following lines are used for calculation , the formula becomes giving .
The ative value obtained by ) utting is now , in place of the closer approximation to , which might have been expected from the lines eIIll ) loyed f calculation .
It is evident that the formulae given above do not well represent the Rydberg series as a whole .
The limit of the series , however , is not likely to be far from the value given by the first formula , namely , other Sei les Lines in the Spectrum of gnesium .
143 [ Notc.\mdash ; An result , which follows from the revision of the wave-lengths of the lines of the series , is the identification of four additional solar lines with lines of magnesium .
The details are as follows , including the three lines ) reviously identified by vland : It will be seen that the in the sun are consistently than the in the arc , but this may perhaps be accounted for by the unsymmetrical character of the arc lines , which are shaded towards the red , and would produce a displacement to the side of longer -lengths in the arc measurements .
There can be no doubt that the four important solar lines in question should be assigned to magnesium .
The lines of the series cannot be traced with tainty in the solar , on account of their ) on iron lines .
] Series ) Lincs .
There are two tJlher magnesium tlrc lines which ) pear to ) elated to the ydberg series , though no connection has hitherto been ised .
heir wave-lengths , as given by Kayser and Bunge , are and .
Assuming that the two lines are successive members of a series , a simple ydberg formula gives the limit of the series as , which is very nearly that of the ydberg series .
If the limit then be assumed to be identical with that of the Rydberg series , a Hicks formula indicates a third line about .
This line has not reviously been recorded , but it is readily seen in photographs of the ordinary magnesium arc taken with adequate ) osure and dispersion ; its waye-length is .
The three lines are all of the same character as those of the ydberg series , but much weaker , and their intensities diminish in Messrs. Fowler and Reynolds .
Additional iplets to the violet in the manner characteristic of series lines .
The first line is identified by Bowland with the solar line ; the second is doubtless identical with the solar line , though it is llot assigned to magnesium by Bowland ; and the third is probably identical with the solar line .
Adopting the solar wave-lengths as the best approximation to the true wave-leng6hs of the lines , the Hicks formula is Details as to the lines are given in Table The equation for this series that it is of the Sharp or second subordinate type , while the series is the associated Diffuse or first subordinate series .
If this be so , the variable part of the equation when be expected to approximate to the lillit of the , if such a series exists .
The variable ) is actually , and the line of the series would be ) eoted at .
at 3882 .
is , \ldquo ; no line 1leal ' this ) osition .
In anothel ) it is ested that Principal series may be the newly nised ) series finninUc at , but this is far reeing with the foregoing calculation .
It is not inll ) ossible that the first member of the ) series sought for may be the arc 35056 , but the discordance would then be even greater than for the spark series .
for1nula capable of more eneral application in the representation of series reatly to be desired .
For completeness , it should be recalled that there is a feebly leveloped series of lines which is also associated with the series. .
The waveFowler , .
cit. Fowler , ' Roy .
Soc. Proc 1903 , vol. 71 , p. 420 . . . .
other Series Lines in the of ) .
145 of heHe lines are about ) ) .
A Hicks , calculated from the first three lines , ives the limit of the ; as , while if the term be introduced by nsing all four lines the calculated limit is .
These are as near to the limit of the .
series as can be expected from the approximate which can alone be obtained .
The series may be arded as a third subordinate one .
1 .
triplets have been measured in the spectrtlll of the arc ) of which belong the ) iffnsP and two to the Sharp series .
For some of the preyionsly } lines illproved wavehaye also ) ined .
2 .
Four additional members of the of single lines been raphed .
a not ately represent this Heries . .
Four strong lines of previously ) been identified with lines of the , namely , 4 .
A unrecorded line at ) be united in a series with known lines and having th( linlit its the ) series .
This series probahly of the ) or seco R ) DESCRIPTION OF The photographs show the spectrunn of the magnesium.arc , between wavelengths and , and indicate the various in which ) lines have been classified .
The lettelH at the bide have the following :\mdash ; , Rydberg series of single lines .
, Probable second subordinate to ) series .
, Diffuse ( ltit sub .
) series of triplets .
, Sharp ( 2nd sub .
) series of triplets .
Series of spark lines .
In addition to lines of magnesium , the photographs show the magnesium hydride bands in the neighbourhood of 560 , , and 480 , and background of faint lines due to the same substance .
There are also a few lines due to impurities of calcium , iron , and manganese , the most prominent being those of calcium at 3934 , 4227 .
|
rspa_1913_0073 | 0950-1207 | A new band spectrum associated with helium.\#xAD; | 146 | 149 | 1,913 | 89 | Proceedings of the Royal Society of London. Series A, Containing Papers of a Mathematical and Physical Character | W. E. Curtis, B. Sc., A. R. C. S., D. I. C.|A. Fowler, F. R. S. | article | 6.0.4 | http://dx.doi.org/10.1098/rspa.1913.0073 | en | rspa | 1,910 | 1,900 | 1,900 | 2 | 84 | 1,649 | http://corpora.clarin-d.uni-saarland.de/surprisal/6.0.3/?id=rspa_1913_0073 | 10.1098/rspa.1913.0073 | null | null | null | Atomic Physics | 73.279105 | Thermodynamics | 17.959664 | Atomic Physics | [
13.55897045135498,
-49.80731201171875
] | 146 A New Band Spectrum Associated * By W. E. Curtis , B.Sc. , A.R.C.S. , D.I.C. , Demonstrator of Astropliysics at the Imperial College of Science , South Kensington .
( Communicated by A. Fowler , F.R.S. Received June 12 , \#151 ; Read June 26 , 1913 .
) [ Plate 8 .
] Introductory .
In the course of Prof. Fowler 's recent observations of the principal series of hydrogen lines in the spectra of helium tubesf traces were frequently seen of a band spectrum the origin of which was unknown , and of which no previous record could be found.j The most prominent features visually were bands having their heads at about XX .
6400 , 5732 , 4649 , and 4626 .
The band at 5732 was degraded towards the violet end of the spectrum , the opposite being the case with the other three .
Although in the first instance the new bands were always comparatively feeble , they were such a frequent and persistent feature of the spectra of the various tubes that it was thought desirable to investigate their origin , and to determine their positions .
It was soon found possible , by choosing suitable conditions of pressure and discharge , to obtain the new spectrum quite brightly , when a number of other bands were observed , some visually and others by photography .
These bands were evidently associated with those first noticed .
Conditions of Observation .
The discharge tubes employed were mostly of the ordinary Pliicker form , and were sealed on to an apparatus consisting of a tube containing cleveite , potash and phosphorus pentoxide tubes , and a charcoal bulb .
After the whole apparatus had been exhausted by means of a Gaede pump the cleveite was heated , and the gases given off were passed over the potash and * Shortly after this paper was communicated to the Society a reprint of a paper describing the same spectrum was received from Dr. E. Goldstein .
It bears the title " Uber ein noch nicht beschriebenes , anscheinend dem Helium angehorendes Spektrum " ( 'Deut .
Phys. Ges .
, ' vol. 15 , p. 10 ) .
Dr. Goldstein 's results appear to have been obtained under conditions very similar to those described in the present paper , and the two accounts of the spectrum are in close agreement .
t A. Fowler , ' Monthly Notices R.A.S. , ' 1912 , vol. 73 , p. 62 .
J While the present investigation was in progress it was found that a band spectrum had been observed by W. Heuse in the positive column of the discharge in a helium tube of wide bore ( ' Deut .
Phys. Ges .
, ' 1900 , vol. 2 , p. 16 ) .
The spectrum was there attributed to helium , but no description or measurements were given , A New Band Spectrum Associated Helium .
147 phosphorus pentoxide into the vacuum tube .
The charcoal was then cooled with liquid air , and absorption allowed to proceed until no further changes were observed in the spectrum .
The discharge was kept running for some hours in order to clear off as much gas as possible from the electrodes .
It may be mentioned that as far as carbon impurities were concerned this treatment proved very effective .
Several tubes prepared in this way and then sealed off show no trace of carbon bands after a great deal of use .
Hydrogen , however , could not be eliminated in this way .
The new spectrum was not seen until the carbon ( Angstrom ) bands had practically disappeared , leaving the helium lines the predominant feature of the spectrum , with hydrogen present in small quantity , and frequently some mercury .
The pressure of the helium in the tube depended upon the amount of heating to which the cleveite had been subjected .
In most cases it was reheated several times , and absorption allowed to proceed to the limit in each case .
As a result of the examination of a number of sealed tubes containing various gases ( helium chiefly in nine cases ) it appears that the following are the principal facts bearing on the development of the new bands:\#151 ; ( 1 ) The only substances common to all the tubes from which the new spectrum was obtained were helium and hydrogen , the former being the chief constituent in every case .
( 2 ) A moderately high pressure is desirable ; the best results wrere obtained when the pressure was just too high to permit of the formation of the Crookes dark space round the cathode .
( 3 ) With an uncondensed discharge ( i.e. , with no capacity in the secondary circuit ) the new bands were faintly visible both in the capillary and the bulbs .
They could be obtained very much more brightly , however , on introducing a little capacity and a short spark-gap ( 1 or 2 mm. ) , but then appeared only in the bulbs .
On increasing the current through the tube beyond a certain limit , either by lengthening the spark-gap or by increasing the capacity , the new spectrum began to decrease in relative intensity .
( 4 ) The evident association of the new spectrum with that of helium suggested that it might possibly occur in celestial spectra showing the lines of the latter element .
An examination of a number of such spectra lias accordingly been made , but without result .
Description of the New Spectrum .
The wave-lengths given are only approximate , as the bands are in many cases of such a nature that the precise positions of the heads could only be determined after a complete analysis of the spectrum .
The bands are VOL. LXXXIX.\#151 ; A. N Mr. W. E. Curtis .
degraded towards the less refrangible side in every case save one , this exception being that marked / 3 , and having its head about 5732 .
Wave-lengtli ( I.A. ) .
Reference letter in Plate .
Remarks .
( " 6399 [ 6310 6250 to 5750 5732 J 5133 *7 t 5112 5056 *1 J 4648 *55 \4625 -63 4546 '4 4500 to 4400 4157 '8 4050 to 3900 3777 / 3677 L 3665 / 3356 -5 t 3348 -5 J 3206 13201 f 3123 1 3118 Very strong head .
Companion head ill-defined , but probably about here .
Many obvious band-lines in this region , but no easily recognisable heads .
Yery strong single head ; band degraded towards violet .
Although weak in photographs , these heads are fairly conspicuous visually .
Faint single head .
Yery strong heads ; bands well developed .
Strong single head .
Many strong lines , but no obvious heads .
Fairly strong single head .
Many strong lines ; positions of heads uncertain .
Fairly strong single head .
Strong double head .
Fairly strong double head .
Rather weak double head .
Yery weak double head ; too faint to show in reproduction .
Probable Origin of the Spectrum : In the present state of the experimental evidence it seems reasonable to attribute the new spectrum to helium , but further work will be necessary before the question of its origin can be regarded as definitely settled .
The matter is complicated by the presence of hydrogen in all the tubes examined ; if this could be completely removed , and the new spectrum were found to persist , there would be no reason to suppose that any substance other than helium is concerned in its production .
Up to the present , however , attempts to get rid of the hydrogen have not been successful , so that it is necessary to admit the possibility of hydrogen being connected with the origin of the bands .
It may be remarked here that the presence of hydrogen may easily be overlooked unless a careful examination is made .
For example , a tube may show no trace of the hydrogen lines either in capillary or bulb when the uncondensed discharge is employed , and show them fairly strongly in the bulbs , on introducing the condenser , yet still give no trace of them in A New Band Spectrum associated with Helium A New Band Spectrum Associated with Helium .
149 the capillary .
An incidental illustration of such a case will be found in Plate 8 , I. # I am greatly indebted to Prof. Fowler for the constant interest he has taken in this work .
DESCRIPTION OF PLATE .
I ( a ) .
New spectrum , showing also the helium and hydrogen lines .
( b ) .
Helium comparison , obtained from capillary of same tube with uncondensed discharge .
Note complete absence of hydrogen lines in this case .
II ( a ) and III ( a ) .
Portions of new spectrum ( with lines of helium and hydrogen ) taken on a Littrow prismatic spectrograph .
II ( b ) and III ( b ) .
Iron arc comparisons .
IV .
Portion of new spectrum taken in first order of 10-foot Rowland ooncave grating , showing structure of bands 8 and e. Studies on the Processes Operative Solutions ( XXX ) and on Enzyme Action ( XX).\#151 ; The Nature of Enzymes and of their Action as Hydrolytic Agents .
By E. Frankland Armstrong and H. E. Armstrong , F.R.S. ( Received June 13 , \#151 ; Read June 26 , 1913 .
) [ This paper is printed in Series B , vol. 86 , No. 591 .
] yol .
lxxxix.\#151 ; A. o
|
rspa_1913_0074 | 0950-1207 | On trigonometrical series whose ces\#xE0;ro partial summations oscillate finitely. | 150 | 157 | 1,913 | 89 | Proceedings of the Royal Society of London. Series A, Containing Papers of a Mathematical and Physical Character | W. H. Young, Sc. D., F. R. S. | article | 6.0.4 | http://dx.doi.org/10.1098/rspa.1913.0074 | en | rspa | 1,910 | 1,900 | 1,900 | 9 | 106 | 2,501 | http://corpora.clarin-d.uni-saarland.de/surprisal/6.0.3/?id=rspa_1913_0074 | 10.1098/rspa.1913.0074 | null | null | null | Formulae | 78.546288 | Tables | 18.528746 | Mathematics | [
71.07917785644531,
-48.085811614990234
] | ]\gt ; On Trigonometrical whose Cesuro Partial Summations Oscillate Finitely .
By W. H. YOUNG , Sc. I ) .
, F.R.S. , Professor of Mathematics in the University of Liverpool .
( Received May 21 , \mdash ; Read June 19 , 1913 .
) S1 .
Riemann 's remarkable theorem , which , in the extended form given to it by Lebesgue , by virtue of the use of the concept of generalised integration , asserts that a trigonometrical series is a Fourier series if it converges everywhere , except at a reducible set of points , to a function which is summable and has a value , or values , everywhere finite , has been discussed , and still further extended , by a relatively large number of writers .
* The object of the present communication is to state and prove certain results which include all those at present known .
They are as follows:\mdash ; I. the upper lower fumtions of the succession of the Cesaro partial , index not them unity , of a trigonometrical series which is such that and as , are summable , and everywhere finite except possibly at a set of points which no perfect sub-set , then the series Fourier series .
II .
If the upper lower functions of the succession of the Cesaro partial summations , index , of a trigonometrical series , are summable and everywhere finite , then the series is a Fouriseries .
S2 .
In proof of these results all turns on the use of upper and lower derivates of a generalised character .
If denote the function , it is open to us to consider , not merely the limits of It will be sufficient for the purpose of the present communication to refer to the following:\mdash ; W. H. Young , " " On the Conditions that a ourier Series should have the Fourier Form 'Lond .
Math. Soc. Proc 1910 , Series 2 , vol. 9 , pp. 421-433 ; Marcel Riesz , " " IJeber summierbare trigonometrische Reihen 'Math .
Ann 1911 , vol. 71 , pp. 54-75 ; De la Vallee Poussin , " " Sir l'Unicit6 du Developpement Trigonometrique ' Bull .
de l'Acad .
Royale de Belgique , ' 1912 , pp. 702-718 , and , 1913 , pp. 9-14 .
We shall also have occasion to refer to L. Fejer , " " Untersuchungen uber Fourier'sche Reihen ' Math. Ann 1903 , vol. 58 , pp. 51-69 .
for example .
We may , as is well known , consider with advantage the limits of the expression obtained from this formally by integrating numerator and denominator with respect to separately between the limits and .
The expression so obtained , though not conceived of in this manner , has indeed formed the subject of considerable discussion .
No one appears , however , to have seen the advantage that could be obtained from the consideration of the expressions obtained when the process in question is repeated .
L. Fejer , in his very valuable paper , *employs in fact an entirely different expression which has not the simple properties of those here referred to .
By a known theorem in the theory of indeterminate forms such expressions as those made use of in the present communication have at each stage limits lying between the limits of each of the expressions obtained at a lower This fact enables us to see that the higher expressions share the striking properties shown by de la Vallee Poussin to be possessed by A modification of Feje'r 's reasoning is then all that is required to obtain the main theorem from which the first of the results iven in S1 immediately follows .
To obtain the second of the results we have then merely to make use of certain simple facts in the theory of Cesaro summation , due essentially to Knopp and Marcel Riesz , though not as far as I am aware explicitly stated by them .
S 3 .
As ards the importance of the results here exposed , this does not consist merely in the fact that they include previous results as special cases .
This will be evident if we reflect on the part played by Cesaro summation in the theory of Fourier series .
We know practically about the mode of convergence , or oscillation , of a Fourier series when summed in the ordinary manner , except in one or two isolated instances .
On the other hand , all such series converge almost everywhere when summed in any Cesaro manner .
Thus , the upper and lower functions of such Cesaro partial summations have the same degree of summability as the function corresponding to the Fourier series , differing , in fact , from it only at a set of content zero .
That the most general results hitherto obtained , those due to de la Vallee Poussin , remarkable as they are , are not final , is then at once evident .
It should not be necessary to have information with to the ordinary upper and lower functions , in order to say whether a .
cit. , supra .
Marcel Riesz 's interesting investigations loc. closely connected with .
cit. , supra .
Prof. W. H. Young .
Series whose trigonometrical series is a Fourier series ; it should be sufficient to have the corresponding information with regard to the Cesaro partial summations .
It is precisely this step which the results of the present communication enable us to take .
Moreover , in this way the investigations which took their rise in Riemann 's paper take a more or less final form which brings them into formal analogy in some sort with the necessary and sufficient conditions I have shown to hold that a trigonometrical series should be the Fourier series of a function of a certain type .
These necessary and sufficient conditions are , in fact , expressed in the language of Cesaro summations .
The interest is further enhanced if we appeal to the analogy between the properties of Fourier series when summed in the Cesaro manner with the properties of derivates .
The analogy is a striking one .
Thus we have the pair of theorems:\mdash ; If fcmction us an integrat , ?
upper and ivates agree except at a set.of content If a series converg to integral , upper and lower functions of its derived series , when summed any ro manner , agree except at a set of content zero .
's Theorem remains true when for an integral we write a function of bounded variation , and I have recently shown that the same is true of the theorem .
We are thus naturally led to inquire whether the counterpart of Lebesgue 's Theorem , also proved by him , has its correspondent in the tpeory of Fourier series .
The present paper enables us to answer this question in the affirmative , and in this way to complete the analogy .
We have , in fact , the following pair of theorems:\mdash ; If the of a and finite , the fnnction is an .
( Lebesgue .
) If the lower functions the dprived series of a trigonometrical series , uhen sumrned some Cesara of positive index less than unity , are snmmabl and finite , the trigonometrical series converges to an integral .
Moreover , corresponding to the known extension of Lebesgue 's Theorem to which I have called attention , in which exceptional points are permitted , we have a corresponding extension of its analogue in the theory of Fourier series .
CesSummations Oscillate Finitely .
S4 .
We shall now obtain the theorem which corresponds to that proved by Feje it in a which we can at once apply .
Theorem.\mdash ; If siu and .
scrics , pllld the second , of subsequent condition , if denote of th succession of tho modnli of ations o}}in .
thr Cesaro , then of as , arc ricall .
, ?
is a constant of it bjing that We have whence ( rh ) , say , so that Now write Hence ' since , by S5 , ?
is bounded , and ?
for fixed vanishes as .
Thus .
cit. , pp. ) .
theoretll states that " " if converges ( C1 ) and , and if when then ' ( nt ) converges for every positive value of , and if , the limit of its sum when is the Cesaro sum of the series Prof. W. H. Young .
Trigonometrical Series whose Now has finite upper and lower bounds at the point considered , while ( mh ) and have each the unique limit zero as , therefore the final term on the of the last expression vanishes as .
Hence Now we can find a point internal to the interval so that Therefore where is a number independent of , but depending on , such that , for values of lies between and , whence , denoting by the yreater of and , and is such that We can confine our attention to values of so small that , and therefore Now Therefore Hence for all values of , say , while , since we see that , for is numerically less than a certain corresponding number .
In particular , for values of , since , we have , provided .
Hence Cesaro Partial Finitely .
The first summation on the has , since is independent of , the unique limit zero as .
The second summation is , and has , therefore , the limit .
Finally , since the third smmmation is less than .
Hence , finally , , where vanishes with , for values of less than 1/ 3 , and less than where NI depends on , and is as small as we please .
Thus where is independent of .
If we next make the hypothesis that and have zero as limit when / , it at once follows that the series of which is the sum converges uniformly , and that accordingly is a continuous function .
It also follows that , as iemann has shown , has zero as limit , as Further , as we have already remarked , the upper and limits of lie between those of Hence , on the hypothesis stated in the first of the theorems stated in S1 , it follows that , if be any one of the limits of , it is one of the limits of the latter expression , and is slunmable and finite except at the points of a set which has no perfect sub-set .
In fact , by the theorem of S4 it is numerically less than a metion h these properties .
We have therefore only to apply Theorem / de la Vallee Poussin 's first paper , above cited , to see that our theorem is true .
* * Here we may conveniently make of the theorem that a trigonometrical series is a Fourier series , if its second integrated series converges to a repeated integral .
Moreover , the function of which it is the Fourier series is the second differential coefficient of this repeated integral .
See W. H. Young , .
cit. 156 Prof. W. H. Young .
Trigonometrical Series whose $ S6 .
Now let us omit the hypothesis that and converge to zero .
Then it will no longer be possible to assert a priori that the expression approaches zero as .
Thus the reasoning of S5 will no longer apply .
We can no longer indeed assert that is continuous , unless we suppose , which is the case in the enunciation of our second theorem , that the loriven trigonometrical series is summable ( Ck ) , where has some value less than unity .
It is then possible , as is shown below , to prove that the series of which is the sum converges uniformly , so that is continuous .
We are thus able to use de la Vallee Poussin 's Theorem 6 , and so obtain a proof of the latter of our two main results .
In our ument we make the tacit assumption that , if the upper and lower functions of a series are finite at an crned point , the same is true of the upper and lower functions ( Ck ' ) , where .
Moreover if the former are summable , so are the latter , these in fact less in absolute value than a numerical multiple of the former .
S7 .
It remains then to show that if the series oscillates boundedly ( Ck ) , and denote the ordinary partial summation of the series , then is bounded , while the series obtained by each term by the power of its place in the series oscillates boundedly when summed in the ordinary manner .
* Denote by the Cesaro partial unmation .
Then , in the case in which , the required result follows immediately from the equation and the equation When is not unity we write whence multiplying both sides by and comparing coefficients the second of the results follows .
The first result follows similarl by both sides by , and the fact that S8 .
We have also to obtain a relation between the partial summations From this follows that the first , and therefore the second , of the series in the enunciation of S4 converges everywhere .
Cesuro Oscillate and the partial summations .
For this purpose we have merely to use the equation .
Now write , and expand on both sides , and equate coefficients of Suppose a fixed number so that , for is less than its upper bound as a suitable small quantity has been added to the latter .
Then , for } the limits of the coefficient of on the left , taken in absolute value , are expressible in terms of the limits of the coefficient of on the -hand side , by means of an inequality .
The required result then easily .
Thus we obtain the result that the upper limit of the modulus of the Cesaro partial summations ( Ck ' ) is less than a numerical multiple , *independent of , of the upper limit of the modulus of the Cesaro partial summations .
It follows that , if the Cesaro partial unmations ( have the property hypothecated in the second theorem of S1 , the Cesaro sumnlations have the same property .
Thus the theolem of S3 is applicable .
It is of course not necessary for our purpose here to show that this numerical quantity is unity .
|
rspa_1913_0075 | 0950-1207 | Atomic specific heats between the boiling points of liquid nitrogen and hydrogen. I.\#x2014;The mean atomic specific heats at 50\#xB0; absolute of the elements a periodic function of the atomic weights. | 158 | 169 | 1,913 | 89 | Proceedings of the Royal Society of London. Series A, Containing Papers of a Mathematical and Physical Character | Prof. Sir James Dewar, F. R. S. | article | 6.0.4 | http://dx.doi.org/10.1098/rspa.1913.0075 | en | rspa | 1,910 | 1,900 | 1,900 | 4 | 198 | 4,647 | http://corpora.clarin-d.uni-saarland.de/surprisal/6.0.3/?id=rspa_1913_0075 | 10.1098/rspa.1913.0075 | null | null | null | Thermodynamics | 66.294472 | Measurement | 14.435121 | Thermodynamics | [
-9.897045135498047,
-30.405061721801758
] | 158 Atomic Specific Heats between the Boiling Points of Liquid Nitrogen and Hydrogen .
I.\#151 ; The Mean Atomic Specific Heats at 50 ' Absolute of the Elements a Periodic Function of the Atomic Weights .
By Prof. Sir James Dewar , F.R.S. ( Received May 29 , \#151 ; Read June 19 , \#151 ; Revised July 30 , 1913 .
) A method of determining the specific heat of substances at low temperatures was described in a paper on " Studies with the Liquid Hydrogen and Air Calorimeter/ '* also in the abstract of a lecture delivered at the Royal Institution entitled " Liquid Hydrogen Calorimetry , " .( .
where the apparatus then used is illustrated .
Continuing the use of the same method , but with some modification of the apparatus , the investigation has been extended to a large number of inorganic and organic bodies .
In this later series of experiments , the measurements of the specific heats of materials by the liquid hydrogen calorimeter were made over a range of temperature from boiling nitrogen to boiling hydrogen , a fall of temperature of some 57 ' Abs .
Weighed pieces of the material are cooled to the temperature of boiling nitrogen in a quartz cooling vessel of special design .
By a simple mechanical device they are then released from this vessel , and drop into liquid hydrogen in the calorimeter below .
The resulting volumes of hydrogen evaporated are measured .
From this value and a knowledge of the latent heat of the liquid hydrogen and the mass of the substance , the specific heat is calculated as follows :\#151 ; If V is volume of hydrogen at N.T.P. evaporated by the fall of 1 grm. of the substance through T degrees above the temperature of boiling hydrogen , and s its specific heat , L being the volume of hydrogen evaporated by 1 calorie , then Y .
Y sT = L ' S = Tl4 The latent heat of liquid hydrogen is taken as 115 calories , and therefore L = 97'05 c.c. ; also in these experiments T is constant ( 57''5 ) therefore s = Vx 0-0001792 .
Thus the hydrogen volumes measured are reduced to Y at N.T.P. and simply multiplied by the constant factor 0'0001792 , thereby giving the specific heat .
* ' Roy .
Soc. Proc. , ' A , vol. 76 , p. 325 .
t 'Roy .
Inst. Proc. , ' 1904 , vol. 17 , p. 581 .
Atomic Specific Heats .
159 * The following examples show the actual volumes of gas dealt with:\#151 ; The observations were : hydrogen measured over water at 14 ' C. , barometer 771 mm. ; calorimeter alone 8 c.c. per minute .
The hydrogen evolved by dropping any material into the calorimeter is all collected during about 15 seconds .
The volumes observed are corrected by 2 c.c. due to calorimeter alone .
1 grm. Pb gave 168 c.c. Frozen drops of normal propyl alcohol : 0234 grm. gave 219 c.c. ; 0275 grm. gave 254 c.c. Frozen bullets of acetic acid : 0*352 grm. , 282 c.c. ; 0*342 grm. , 268 c.c. Frozen bullets of benzene : 0*273 grm. , 188 c.c. Tabulated results ( factor for correction of gas to N.T.P. , 0*9499 ) :\#151 ; Substance .
Hydrogen volumes at N.T.P. from 1 gram .
s. Apparent values .
Lead 159 *6 0 *0286 5*92 Atomic specific heat .
^-Propyl alcohol 881 *2 0 *1536 9*47 Molecular " 869 *6 0 *1559 9-36 ) ) \#187 ; Acetic acid 754 *4 0 *1352 8-12 \gt ; \gt ; \gt ; \gt ; 737 *9 0 *1322 7 *44 \#187 ; \gt ; ) Benzene 648 *5 0 *1161 9-07 33 33 Applying the correction explained later on for heat absorbed in transit , when the neck of the calorimeter is not cooled with liquid air , the following are the mean results:\#151 ; Substance .
s. Keal values .
Lead 0 *0240 0 -1300 0 *1123 0 *0975 4 *97 Atomic specific heat .
7 *80 Molecular " 6 74 " 7 *62 w-Propyl alcohol Acetic acid Benzene In my earlier paper* the value of the latent heat of hydrogen was taken as 122*92 .
Five observations were given varying +5 about this mean value .
This was determined on the basis of 0*0291 being accepted as the mean specific heat of lead from 15 ' C. to 20 ' Abs .
Several Willard Gibbs vapour pressure formulae , however , calculated from the vapour tensions of liquid hydrogen , give a mean value of 115 for the latent heat of hydrogen , so that the specific heat of lead over this range would seem to be 0*0272 .
Accepting the value of 115 for the latent heat of hydrogen , the resulting * 'Roy .
Soc. Proc. , ' A , vol. 76 , p. 325 .
160 Sir J. Dewar .
Atomic Specific Heats between the value of the specific heat of lead from 80 ' Abs .
to 20 ' Abs .
is now 0*02399 .
This is the mean value of a series of nearly 30 observations .
The greatest variations from this mean value were 0*0247 and 0*0233 , but the majority of the values varied to a much less extent .
This is equivalent to an atomic specific heat of 4*965 .
It may be mentioned that a computation from Nernst and Lindemann's* real specific heats of lead within the same range of temperature gives the mean value 5*18 .
In the observations with the liquid air calorimeter the specific heats were calculated in each case by direct comparison with lead observed at the same time , , as explained in the earlier papers .
This is most convenient because liquid air varies in composition on standing , and therefore in the volume evaporated by unit amount of heat .
Liquid Air Calorimetry .
A few results obtained with the form of calorimeter used in 1904 with liquid air may be recorded .
They were all reduced by comparison with lead done at the same time , using the value for the specific heat of lead given in the earlier paper , viz. , 0*0290 from 195 ' Abs .
to 85 ' Abs .
and 0*0295 from 15 ' C. to 85 ' Abs .
Substance .
s. Atomic beats and molecular specific heats .
1 .
From 195 ' Abs .
to 85 ' Abs .
Nickel carbonyl , Ni(CO)4 0 *1653 28 *22 Iron carbonyl , Fe(CO)5 0 *1488 29 *17 Nickel 0 -0736 4-33 Iron 0 -0727 4-06 Para-cyanogen , ( CN ) " 0 -1162 3 *02 x Silver cyanide 0 -0680 9-11 Tantalum 0 -0280 5*07 2 .
From 15 ' C. to 85 ' Abs .
Silver cyanide 0 0925 12 -38 ( CN ) " ' 0 -1788 ( 4*65 ) " The values of the molecular specific heat of carbonic oxide by difference are 5*97 from the nickel carbonyl , and 5*02 from the iron carbonyl .
The relatively high values of the iron and nickel to that observed between 80 ' Abs .
and 20 ' Abs .
are also noteworthy , viz. , 4*06 and 4*33 , compared to 0*98 and 1*22 .
Some observations were done with liquid nitrogen instead of liquid hydrogen , under the same conditions , in the form of calorimeter now * ' Sitzungsber .
d. Berl .
Akad .
, ' 1911 , p. 494 .
Boiling Points of Liquid Nitrogen and Hydrogen .
described .
They were reduced on the basis of the value 48'9 for the latent heat of nitrogen at its boiling point , as given by Fischer and Alt in 1902 .
The method of calculation was thus similar to that employed with liquid hydrogen .
The values obtained , which are probably a little too high , were as follows:\#151 ; Substance .
s. Atomic heat .
1 .
From 15 ' C. to 77'3 ' Abs .
( B.P. of nitrogen ) .
Lead 0-0300 6-21 Bismuth 0 -0295 6-14 Thallium 0 -0311 6-36 Aluminium 0 1737 4-71 Magnesium 0 -2068 5-05 2 .
From 195 ' Abs .
to 77,3 ' ( solid COo to liquid nitrogen ) .
Mercury 0 -0313 6-26 Bismuth 0 -0291 6-06 Thallium 0 -0308 6 -30 Aluminium 0 -1540 4-17 Magnesium 0 -1550 3-78 The liquid hydrogen calorimeter is a glass cylindrical bulb vacuum vessel A ( fig. 1 ) of 50 c.c. capacity , silvered , with \#163 ; cm .
slit .
The inner diameter is 3 cm .
On to the neck , contracted to about 1*7 cm .
, is sealed a glass tube B of equal diameter and 38 cm .
long .
This projects about 8 cm .
through the brass coned fitting cap F of an ordinary slit silvered vacuum vessel in which it is supported .
A side delivery tube , 1 cm .
wide , provided with a stopcock D of 8 mm. bore , is sealed near the top of B. A short length of rubber tubing on the neck of F makes a gas-tight joint with B. To minimise splashing , and to reduce the impact of the falling pieces , a thin strip of german silver or lead E , bent out near the top into a shoulder about 1 cm .
square , stands centrally in the calorimeter A. The strip is cut from a thin tube of about the same diameter as the calorimeter neck .
A short length of the tube is left above the shoulder , and supports the strip by fitting loosely into the neck of A. The shoulder is arranged just above the level of the liquid hydrogen in A , which is at least three-quarters full .
Some such device is essential in the use of this form of the liquid hydrogen calorimeter .
The calorimeter in its turn is immersed in liquid hydrogen in the supporting vacuum vessel C , the neck of the calorimeter being 8 to 10 cm .
below the liquid hydrogen surface .
This vacuum vessel C is only slightly wider than the lower part of A , and is provided with a coned cap F , whereby it is also supported and completely immersed in a wider vacuum 162 Sir J. Dewar .
Atomic Specific Heats between the ... -L EVAPORATING H : CONNECTED TO 3-WAY STOPCOCK AT TOP F'-TO TO COLLECTING EXHAUST VESSEL PUMP TO MEASURING iBURETTE V w Fig. 1 .
Boiling Points of Liquid Nitrogen and .
163 vessel G- containing exhausted liquid air .
G- is also fitted with a brass coned cover , fitting vacuum-tight on to the cap F on C. .
Both caps are pierced by two thin tubes , one for fitting on to the filling syphons , the other , bent at right angles , serves for connecting to the exhaust in the case of the liquid air vessel , and in the case of the liquid hydrogen vessel to the stopcock leading the evaporating hydrogen through the upper part of the apparatus .
This arrangement thus charged only needs a little liquid air sucked in every one and a-half hours .
The liquid hydrogen vessel will not need replenishing for at least four hours .
The level of the liquid hydrogen in the calorimeter does not fall 1 cm .
in six hours with constant use .
The bulk of the materials added roughly compensates for the volume of the liquid hydrogen evaporated .
It is important that this level should not materially change , since , after striking the shoulder , bodies move more slowly , are deflected on to the cold wall , and low results are obtained due to longer cooliug of the materials in the vapour before being immersed in the liquid hydrogen .
The isolation of the calorimeter was such that less than 10 c.c. of hydrogen gas was evaporated from it per minute .
The whole apparatus is supported between the cork-lined spring jaws mounted on a heavy metal base , on which the outer vacuum vessel rests .
The cooling vessel H is connected by india-rubber tube to the top of the calorimeter .
It consists of an ordinary cylindrical slit silvered vacuum vessel , 20 cm .
long and 7 cm .
wide , with a central axial open tube K sealed in below .
This tube passes through the liquid in the vacuum vessel .
It has the same diameter below as the neck tube of the calorimeter .
Hear the top of the central tube a side tube J , of about the same diameter , and some 3 cm .
long , serves for the introduction of the weighed pieces of material , which are all cooled previously to the temperature of liquid air , and then fail on to a thin metal disc P fitting loosely the tube K , where they remain about 15 minutes .
P is supported by being hinged to two thin ebonite rods , L and M , fixed to a brass fitting cemented on to the top .
The rod L is not fixed directly to the disc but to a metal ring R. From the ring R two thin vertical steel wires are connected freely to two points on the circumference of the pan below .
This rod and the attached ring can be given a vertical motion by a crank N in the top fitting , thereby tipping the pan and releasing the piece of material , which then falls freely down into the calorimeter .
The level of the pan placed about H is approximately one-third the vertical height of the'cooliug vessel .
Quartz was found to be safer than glass for the construction of this vessel .
A high 164 Sir J. Dewar .
Atomic Specific Heats between the vacuum was maintained by a cross-tube S , opening to the annular space , filled with charcoal .
At the temperature of boiling nitrogen , the convection currents in the central tube of such a vessel , when connected to the calorimeter below , have no serious effect on the temperature in the tube at a reasonable distance from the bottom , provided the central tube be not wide .
The difference of temperature in the tube and in the surrounding liquid was found to be only 05 ' when the tube was 1*5 cm .
wide .
With a larger pattern vessel the width of the central tube was increased to 2'2 cm .
, and even here the difference was under 3 ' at the level of the pan .
These temperatures were measured by a small helium thermometer , consisting of a 4 c.c. bulb to which was sealed a small mercury manometer of fine capillary tubing .
The thermometer was filled with pure helium to 273 mm. pressure at 0 ' C. The reading of the mercury manometer thus gives , with slight corrections previously determined , the absolute temperature .
It is scarcely necessary to add that , by exhausting the liquid nitrogen , a lower initial temperature than 78 ' Abs .
can be secured .
The hydrogen evaporating from the liquid in the vacuum vessel C , in which the calorimeter is immersed , is employed in the interval of observations to maintain a hydrogen atmosphere through the neck of the calorimeter and the connected measuring tubes .
Risk of solid air in the calorimeter neck is thus obviated .
A simple arrangement of a three-way cock T , connected at the top of the brass fitting on the central tube of the cooling vessel , allows this to be manipulated .
The hydrogen thus passes continually in at the tubular top of the fitting on the central tube of the cooling vessel , and out through the stopcock on the calorimeter neck , and through the cocks to the measuring vessels .
When an observation is to be made , the three-way cock is turned to allow the hydrogen current to-escape to the laboratory , thereby closing off the calorimeter , which now only connects to the collecting and measuring vessels V and W. V consists of a glass tube 8 cm .
in diameter and 40 cm .
long , open at the bottom and provided with a wide T-piece at the top .
The tube is immersed to the neck in water in a glass cylinder , and is counterpoised by a weight and cord running over a pulley just above .
It is thereby readily raised during the time gas is being evaporated from the calorimeter ; this ensures that no back pressure is produced .
One arm of the T-piece is open and connects to the stopcock D on the calorimeter neck ; the other is provided with another small stopcock and connects to a 200 c.c. gas burette W similarly immersed in water .
This latter stopcock is closed during the collecting of the gas from a dropped piece of material .
This being completed , the calori- Boiling Points of Liquid Nitrogen and Hydrogen .
165 meter stopcock is closed while the evaporated hydrogen gas is measured by transference to the burette , the slight continual evaporation from the calorimeter meanwhile finding a vent through the three-way cock T at the top of the cooling vessel , which is now turned on .
These arrangements are necessary to secure the minimum impediment to the evaporating hydrogen , which is usually evolved in less than 10 seconds , any temporary back pressure being fatal to concordant results .
At least 15 seconds are allowed for collecting the gas given off , and even longer , in some cases , with badly conducting bodies .
A slightly different form of calorimeter vacuum vessel was used on some occasions , but without modifying the results .
Instead of the constriction at the top of A , a ground conical neck was used of the same diameter as the inner tube .
This neck was fitted with a similar ground conical hollow tube sealed on to the tube B. Anhydrous glycerin was used to make the ground joint tight at the low temperatures .
The wider neck in some ways simplifies the preliminary manipulations , and allows a more efficient arrangement to be securely fixed for preventing splashing , and breaking the fall of the bodies dropped into the calorimeter .
The arrangement is shown in the side sketch B. It consists of a light counterpoised trap door hinged at the lower end of a conical brass or german silver tube , supported in and fitting to the inner tube of the calorimeter .
A small lead ball on a wire soldered to the trap door keeps this closed until struck by a falling sphere , while shutting it again immediately after its passage .
The conical tube above the trap door is pierced with several small holes to leave a free passage for the evaporating hydrogen .
The addition of a gauze filter to intercept spray was found to be impracticable , the resistance introduced causing back pressure .
As far as possible the materials used were cast in the forms of spheres about 8 mm. diameter , and for this purpose the use of an ordinary bullet mould was found convenient .
In the case of liquid bodies , the mould was first cooled by liquid air .
Frequently liquids were frozen into solid cylinders in thin glass tubing , and pieces cut off after removing the glass mould .
The metallic materials were in some cases fused into buttons of convenient weight in an exhausted quartz tube .
The lead , however , of which many pieces were required , was cut from rod , and subsequently squeezed in a small spherical mould .
Yolatile bodies were weighed at a low temperature on a light german silver pan supported by a thin platinum wire suspension from the balance pan about 2 cm .
above the level of liquid air contained in a wide deep vacuum vessel .
Some materials would not make coherent bullets or cast sticks .
These were filled into very thin walled cylindrical metal capsules VOL. lxxxix.\#151 ; A. p 166 Sir J. Dewar .
Atomic Specific Heats between the of equal weight , so that a preliminary determination of the volume of hydrogen evaporated by the metal of the capsule gave the correction .
They were then cooled on an aluminium dish floating on liquid air , filled with the fluid , and weighed separately .
Materials which could not be fused were compressed hydraulically into small blocks and cut up into pieces of suitable dimensions .
At least three pieces of every substance were dropped .
The results rarely varied among themselves by more than 2 to 3 per cent. Very frequently the agreement was within 1 per cent. In order to ensure good results , uniformity of shape and size in the pieces of material used is desirable , so that the manner of release and fall shall be comparable : because in the use of this instrument the materials have to pass through a region of the neck , between the cooling vessel and the calorimeter , where a considerable gradient of temperature exists .
It is necessary that , as far as possible , the bodies used shall be subjected to this variable region in the same manner , so that the amount of heat absorbed in transit shall be nearly the same .
This value was determined in the following manner .
The warm portion of the calorimeter neck between the cooling vessel above and the vacuum vessels below was cooled by being surrounded with liquid air placed in a simple temporary fitting .
Observations with various kinds of bodies were then made .
The comparison of the reduced volumes now obtained with the values given by the ordinary use of this particular form of the instrument gives the correction factor .
Many confirmations of the specific heats were made with this addition to the instrument .
In the latest form of the calorimeter the neck is always surrounded with liquid nitrogen , thus abolishing all heat correction .
This improved calorimeter gives results differing but slightly from the corrected values of the old instrument .
The value of the atomic heat of lead is determined before and after any series of experiments as a check on the constancy of the instrument .
The values of the specific heats given will include any heat of transformation of glassy or crystalline modifications or other comparable change produced by the cooling to 20 ' Abs .
Another effect is produced by some materials when used in the form of hydraulically compressed blocks .
Such as are porous exhibit in varying degrees the phenomenon of heat evolution due to liquid hydrogen passing into the capillary spaces , thereby rendering the observed specific heat too great unless the proper correction is made .
Any air occluded during the preliminary cooling of the porous material to liquid air temperature before being introduced to the hydrogen calorimeter is also included .
Some of this air would be replaced by hydrogen through diffusion while in the hydrogen atmosphere in the central tube of the cooling vessel Boiling Points of Liquid Nitrogen and Hydrogen .
167 of boiling nitrogen ; but the true remedy is the preliminary cooling of such porous bodies in a hydrogen atmosphere to the temperature of liquid air .
That heat evolution continued in many cases for some time after the dropping of the material was shown by an increased rate of evolution of hydrogen from the calorimeter .
As stated above , this is* normally less than 10 c.c. per minute .
In some instances the introduction of porous material increased this for some time to more than 30 c.c. per minute .
The values set out in Table I for the mean atomic specific heats of 53 elements at about 50 ' Abs .
represent the results of some 200 calorimetric observations .
When plotted in terms of their atomic weights , they reveal definitely a periodic variation resembling generally the well-known Lothar Meyer atomic volume curve for the solid state .
The relation between the two curves is shown in fig. 2 .
If experiments were similarly made between the boiling points of hydrogen and helium then in all probability the atomic specific heats would be all very small and nearly constant .
Until more accurate values of the atomic heats have been reached , by the use of purer samples of the elements and the latest form of this calorimeter , it will be advisable to delay theoretical discussion .
The second part of this paper will contain the molecular specific heats of a series of inorganic compounds ; while a third part will include similar values derived from the examination of types of organic bodies .
Sir J. Dewar .
Atomic Specific Heats between the Table I. Element .
Atomic weight .
Specific heat .
Atomic heat .
Lithium 7-03 0 -1924 1 -35 Grlucinum 9 T 0 -0137 0-125 Boron 11 0 0 -0212 0-24 Carbon ( Acheson graphite ) ... 12-0 0 -0137 ' 0-16 Diamond 12 -0 0 -0028 0-03 Sodium 23 -0 0 -1519 3-50 Magnesium 24 -4 0 -0713 1 -74 Aluminium 27 *1 0 -0413 1 -12 Silicon , fused , elec , cruc 28 -4 0-0303 0-86 " crystallised 28 -4 0 -0303 0-77 Phosphorus ( yellow ) 31 *0 0 -0774 2-40 " ( red ) 31 0 0 -0431 1 -34 Sulphur 32 0 -0546 1-75 Chlorine 35 -45 0 -0967 3-43 Potassium 39 T5 0 *1280 5-01 Calcium 40*1 0 -0714 2-86 Titanium 48 T 0 -0205 0-99 Chromium 52 T 0 -0142 0-70 Manganese 55 0 -0229 1-26 Iron 55 -9 0 -0175 0-98 Nickel 58 *7 0 -0208 1 -22 Cobalt 59 -0 0 -0207 1-22 Copper 63 -6 0 -0245 1 -56 Zinc 65 '4 0 -0384 2-52 Arsenic 75 -0 0 -0258 1 -94 Selenium 79 -2 0 -0361 2-86 Bromine 79 -96 0 -0453 3-62 Rubidium 85 -1 0 -0711 6-05 Strontium , impure 87 -6 0 -0550 4-82 Zirconium 90 *6 0 -0262 2-38 Molybdenum 96 *0 0 -0141 1 -36 Ruthenium 101 -7 0-0109 1 -11 Rhodium 103 -0 0 -0134 1 -38 Palladium 106 *5 0 -0190 2-03 Silver 107 -93 0 -0242 2-62 Cadmium 112 -4 0 -0308 3 -46 Tin 119 0 -0286 3 -41 Antimony 120 -2 0 -0240 2-89 Iodine 126 -97 0 -0361 4-59 Tellurium 127 -6 0 -0288 3-68 Csesium 132 -9 0 -0513 6-82 Barium , impure 137 -4 0 -0350 4-80 Lanthanum 138 -9 0 -0322 4-60 Cerium 140 -25 0 -0330 4 -64 " Didymium " 142 0 -0326 4-63 Tungsten 184 0-0095 1 -75 Osmium 191-0 0*0078 1 -49 Iridium 193-0 0 -0099 1-92 Platinum 194 -8 0-0135 2-63 Gold 197 -2 0 -0160 3 -16 Mercury 200 0 -0232 4-65 Thallium 204-1 0-0235 4 " 80 Lead 207 0 -0240 4-96 Bismuth 208 0 -0218 4-54 Thorium 232 -5 0 -0197 4-58 Uranium 1 238'5 0 -0138 3 -30 Boiling Points of Liquid Nitrogen and Hydrogen .
During the course of this laborious work Mr. W. J. Green , B.Sc. , of the Davy-Faraday Laboratory , has rendered most efficient aid .
|
rspa_1913_0076 | 0950-1207 | The thermal effects produced by heating and cooling palladium in hydrogen. | 170 | 186 | 1,913 | 89 | Proceedings of the Royal Society of London. Series A, Containing Papers of a Mathematical and Physical Character | J. H. Andrew, M. Sc.|A. Holt, M. A., D. Sc.|Dr. G. T. Beilby, F. R. S. | article | 6.0.4 | http://dx.doi.org/10.1098/rspa.1913.0076 | en | rspa | 1,910 | 1,900 | 1,900 | 3 | 265 | 6,480 | http://corpora.clarin-d.uni-saarland.de/surprisal/6.0.3/?id=rspa_1913_0076 | 10.1098/rspa.1913.0076 | null | null | null | Thermodynamics | 68.097311 | Chemistry 2 | 10.902895 | Thermodynamics | [
-10.384538650512695,
-50.52145767211914
] | 170 The Thermal Effects produced by Heating and Cooling Palladium in Hydrogen .
By J. H. Andrew , M.Sc .
, Research Fellow and .
Demonstrator of Metallurgy , The University , Manchester , and A. Holt , M.A. , D.Sc .
, Reader in Physical Chemistry , The University , Liverpool .
( Communicated by Dr. G. T. Beilby , F.R.S. Received June 17 , \#151 ; Read June 26 , 1913 .
) It is agreed by all observers that a change in the extent to which hydrogen is occluded by palladium takes place at a temperature of about 100 ' C. This change might be the result of ( 1 ) a polymorphic transformation in the metal , or of its surface layer ; ( 2 ) the formation or dissociation of a compound or solid solution with hydrogen , and , further , the occlusion may be of a dual nature\#151 ; surface adsorption and diffusion into the metal\#151 ; these phenomena may take place at different temperatures .
Since the pressure-temperature-concentration relations of hydrogen to palladium have already been the subject of detailed investigations by Hoitsema(l ) , Roozeboom , and others , and the changes in electrical resistance resulting from occlusion of the gas have been examined by Fischer and Sieverts ( 2 ) , it appeared advisable to attack the problem from a thermal standpoint , since it has been found that occlusion of hydrogen by the metal is accompanied by an evolution of heat .
This aspect of the question has already been the subject of experiments by Ramsay , Mond , and Shields ( 3 ) , who argue that if the heat evolution is solely the result of condensation of the gas , the heat evolved during the condensation of equal volumes of hydrogen by different metals should be the same .
Calorimetric observations by these authors showed that this was not the case , at any rate for palladium and platinum , the values obtained exhibiting a greater divergence than could be accounted for by experimental error .
The above hypothesis assumes that the gas is condensed in a similar manner by the two metals , but the great difference in the volumes occluded by unit volume of each metal does not , however , support this contention .
For example , suppose the gas to be merely condensed on the surface of the one metal either as molecules , or molecular complexes , whilst in the other case it is dissolved in the atomic condition .
In both cases a certain amount of heat would be evolved , but in the latter this amount would be diminished by that absorbed in dissociating the gas molecules into atoms , the heat of solution of the gas in this , condition not being taken into account .
Thermal Effects in Palladium .
Little is known concerning the condition of the hydrogen occluded by palladium .
From density determinations it appears that the gas is present in a quasi-solid condition , whilst the experiments of Sieverts ( 2 ) , point to the probability that at temperatures up to the melting point of the metal the gas is dissolved in the atomic state .
Holt , Edgar , and Firth ( 4 ) have shown that a close analogy exists between the phenomena of occlusion of hydrogen by palladium , and by charcoal , and according to McBain the gas absorbed by charcoal is present as atoms .
Since any change in the condition of the gas must be accompanied by an evolution or absorption of heat , the study of heating and cooling curves of hydrogen-palladium should afford valuable data , and it is the study of such curves that constitutes the present communication .
Palladium in three different forms was used for the experiments : thin foil ( about Off mm. thick ) , black , prepared by strongly igniting palladium ammonium chloride , and fused metal in the form of a button .
The metal was heated in either hydrogen , air , or , in an electrically heated porcelain tube furnace .
The whole apparatus is illustrated in fig. 1 .
The TO PUMP ^ ; HEATING CIRCUIT TO HYDROGEN SUPPLY POTENTIOMETER Fig. 1 .
furnace was so constructed that a vacuum could be maintained on the outside of the heated portion of the tube , in order to give a uniform rate of cooling .
The outer jacket consisted of a hard drawn copper tube , to which gun metal ends were brazed .
Between these ends and the porcelain tube were inserted rubber rings , -which could be expanded by means of screw caps , thus forming air-tight connections between the tube and outer jacket .
The porcelain tube was surrounded by water coolers at both ends .
The leads for the heating circuit were passed through air-tight insulators in the outer jacket .
Upon 172 Mr. Andrew and Dr. Holt .
Thermal Effects produced by evacuating the space between the tube and outer jacket , it was found possible , on account of the vacuum and high reflecting power of the copper , to cool the furnace at a regular and comparatively rapid rate , even at low temperatures .
Full details of the furnace are to be found in a previous publication of one of the authors ( 5 ) .
For detection of thermal changes in the palladium , a platinum-platinum-iridium thermocouple , previously calibrated over the range of temperature concerned , was employed .
In the case of the fused button of palladium , contact was made by inserting the thermocouple into a small hole drilled in the specimen , whilst when using palladium foil or black , the metal was enclosed in a quartz tube and closely packed round the end of the couple , a pad of asbestos keeping the whole in position .
The wires from the thermocouple lying inside the furnace were insulated from each other by means of a two-hole fireclay tube , and passed through a rubber stopper , which made an air-tight joint at one end of the porcelain tube .
Outside the stopper they were soldered to copper leads , which in turn were connected through a Carpenter-Stansfield potentiometer to a d'Arsonval mirror galvanometer .
The cold junctions were kept at 0 ' C. by immersing in ice .
The other end of the porcelain tube was connected to a manometer , hydrogen reservoir , and an automatic sprengel pump with three fall tubes , the details of this portion of the apparatus being apparent from the illustration .
The experiments grouped themselves into five categories:\#151 ; ( I ) Heating and cooling the metal in vacuo .
( ii ) Heating and cooling the metal in hydrogen , after allowing it to occlude gas in the cold , until the initial heat evolution had ceased , and the metal had regained its normal temperature .
( iii ) Heating and cooling the metal in hydrogen immediately after the above treatment , and consequently without preliminary occlusion of gas and evolution of heat .
( iv ) After cooling in hydrogen and evacuating in the cold , the metal was heated , and the gas still occluded was continuously removed by the pump .
( v ) Admitting hydrogen to the metal heated in , and cooling in the gas .
In all experiments the hydrogen was maintained at a constant pressure , slightly higher than that of the atmosphere , in order to prevent inward diffusion of air through the rubber stoppers .
Heating and Cooling Palladium in Hydrogen .
173 The first series of experiments in which heating and cooling curves of the metal in vacuo were taken are illustrated in figs. 2 and 3 .
In the actual experiments , time readings were taken at constant intervals of temperature , and the differences in time taken to cool , or heat up , through this constant Fig. 2.\#151 ; Heating Curves of Palladium in vacuo .
Nos. 1-7 .
Palladium foil .
No. 8 .
Palladium black .
temperature interval , at different temperatures , are plotted against actual temperature readings .
The method of plotting is what is generally known as the " inverse rate method , " the values of At/ Ad being plotted against those of 0 , where t = time and 0 the temperature .
It will be seen from figs. 2 and 3 that , whilst no thermal effect of any 174 Mr. Andrew and Dr. Holt .
Thermal Effects produced by magnitude is indicated , small changes in the slope of the curve are apparent at certain temperatures .
These might be attributed to experimental error , since they are of very small order , were it not for the fact that the temperature ranges over which they persist are nearly coincident in all the Fig. 3.\#151 ; Cooling Curves of Palladium vacuo .
Nos. 1-7 .
Palladium foil .
No. 8 .
Palladium black .
curves .
More probably they are an indication of some transformation within the metal , since they represent heat absorption during heating and heat evolution on cooling\#151 ; complementary effects .
If a slow change over a wide range of temperature took place , no great deviation from normal heating and cooling curves would be apparent .
Though the results of the above curves are by no means conclusive , the Heating and Cooling Palladium in Hydrogen .
175 authors are inclined to believe that they do indicate an allotropic change , and this belief is strengthened by a consideration of the experimental work of other investigators on hydrogen-palladium .
Palladium black , even after an interval of many years , appears always to possess the property of immediately occluding hydrogen , with evolution of heat .
A sample of black which had been untouched for over 30 years was found to be in no way different from the freshly prepared substance .
If , however , a sample of black be melted into a metallic bead , this property is almost entirely destroyed .
Such an inactive bead can , however , always be reactivated by heating to a red heat in air .
The probable effect of this treatment is to produce a film of oxide , which in the presence of hydrogen is at once reduced , giving a surface of spongy metal intensely active towards hydrogen .
On long standing this property dies away , a phenomenon not observed in the case of palladium black .
The reduction of an oxide by hydrogen , or the decomposition by heat of such a compound as ammonium palladium chloride , gives rise to the production of amorphous palladium , which , if uncontaminated by the stable crystalline form , undergoes no change .
This would satisfactorily explain the activity of palladium , for whilst the pure amorphous black ( which alone appears to possess the property of rapid occlusion of gas ) would remain in the meta-stable condition , a film of spongy amorphous metal on a crystalline mass would gradually tend to crystallise , owing to the presence of the stable phase .
A somewhat parallel case is that of grey and white tin .
Each variety apart from the other is more or less stable , but if present together in physical contact ( as in the case of a mass exhibiting both varieties ) the meta-stable passes gradually to the stable form .
It is stated by Eamsay , Mond , and Shields that a unit mass of palladium in any form will occlude the same volume of hydrogen .
This occlusion may be , and probably is , an intrinsic property of the metal , but the extreme variation in the rate of initial occlusion of gas , as well as the decay of this rate with time , requires a separate explanation , and the above hypothesis appears to satisfy the experimental observations .
It has been pointed out that palladium black is probably amorphous , since -it has been produced by decomposing a compound at a temperature lower than that at which the metal melts , and crystallisation in the case of a metal is usually associated with cooling from the liquid state , and it is this form alone which is able to bring about rapid occlusion of the gas .
It is now usually believed from the work of Beilby(6 ) , Bengough(7 ) , Bosenhain ( 8 ) , and others , that under certain conditions the crystals of a metal are surrounded by an amorphous metallic cement .
Beilby showed 176 Mr. Andrew and Dr. Holt .
Thermal Effects produced by that this amorphous material is readily formed upon subjecting the metal to strain , the slipping of the crystals over one another giving rise to its formation .
Bengough , however , considers that this amorphous material is present in all metals and alloys , whether they have undergone any mechanical treatment or not .
Both , however , consider that this cement ultimately disappears with rise in temperature , the temperature at which it ceases to exist differing in each metal .
Bosenhain has carried the matter further still , and quotes experiments to prove the existence of this amorphous cement at all temperatures below the melting point .
If this be the case , it follows from what has been said that palladium cooled from the molten state will contain a minute amount of amorphous matter , and hence should exhibit the power of rapid occlusion of the gas very feebly .
It was found that the activity of palladium in .
the massive state was considerably affected by first allowing it to occlude gas and then pumping it off ; not only was its activity preserved , but it was increased .
In the May lecture of the Institute of Metals , 1911 , Dr. Beilby makes the following suggestion with regard to the action of gases upon crystallisation .
He says : " The gas molecules as they find their way among the metal molecules of the solid are quite capable of producing sufficient movement to arrest crystallisation , or even to flow the crystals which are already formed into the amorphous variety .
" Dr. Beilby 's theory offers a very likely explanation of this increased activity , the continual occlusion and extraction of the gas giving rise to the production of the active amorphous phase .
This view would certainly explain the great changes in the rapidity of the initial occlusion with alteration in the state of the metal .
The gas no doubt does subsequently diffuse right into the crystals of the metal , but extremely slowly .
A microscopical examination of the surfaces of the palladium before and after saturation with hydrogen exhibited no striking features .
In each case the metal was found to be highly crystalline .
The surface of the specimen which had been previously saturated with hydrogen had a distinctly pitted structure , dark blotches distributed in an irregular manner throughout the metal being evident .
It is quite probable that these dark markings are due to the presence of the amorphous metal farmed during the evolution of hydrogen .
Palladium black appeared as amorphous grains , with no trace of crystalline structure .
The second series of experiments ( in which the metal , after the preliminary heat evolution due to initial occlusion of gas had ceased , was heated and cooled in hydrogen ) will next be considered .
As has already been mentioned , palladium , in any form except black , will sometimes pick up gas .
with avidity , Heating and Cooling Palladium Hydrogen .
177 and at others with extreme slowness , the heat evolution varying in a parallel manner with the rate of occlusion .
Some measurements of this heat effect have been made , which although by no means accurate , on account of the unsuitability of pyrometric measurements for such determinations , are of interest as showing the great differences which occur .
Some values are given in the subjoined table .
Condition of metal .
: Temperature before admission of gas .
Bise in temperature after admitting gas .
'c .
'c .
Black 15 60 Black 310 5 Fused mass 15 3 Fused mass 310 7 Foil ( 0 *1 mm. thick ) 310 3 From these figures , it is evident that , when hot , the heat evolution is practically a constant , no matter what the condition of the metal may be , whereas at the ordinary temperature of the laboratory ( about 15 ' C. ) the condition of the metal makes an enormous difference .
Hence it may be concluded that when hot the amount of gas picked up by unit mass of metal is constant , and characteristic of the metal , whilst when cold some other influence comes into play .
It should be remarked that whilst the heat evolution in the case of the black remains fairly constant ( at about 15 ' C. ) , with the fused mass it varies somewhat according to the state of its surface .
Determinations were also made to ascertain the heating effect produced by admitting hydrogen to palladium black , at intermediate temperatures between the limits cited .
The results are as follows :\#151 ; Initial temperature at which hydrogen was admitted .
Eise in temperature .
'c .
'c .
15 53 103 21 120 15 258 8 The rise in temperature , therefore , decreases with the absolute temperature of the metal , as is to be expected from the temperature-concentration relations .
The initial heat evolution upon admission of hydrogen is followed by an extremely rapid cooling , more rapid indeed than could be expected from normal cooling , indicating the probability of an endothermic change .
178 Mr. Andrew and Dr. Holt .
Thermal Effects produced by After hydrogen had been admitted to the metal , in the cold , and after any nitial thermal effect had died away , the metal was then heated in the gas and heating curves taken .
Such curves are shown in fig. 4 .
Fig. 4.\#151 ; Heating Curves of Palladium in Hydrogen .
No. 1 .
Palladium foil which had evolved no heat upon admitting hydrogen at 15 ' C. No. 2 .
Palladium foil which had evolved heat and occluded hydrogen at 15 ' C. No. 3 .
Palladium black which had evolved heat and occluded hydrogen at 15 ' C. No. 4 .
Palladium button which had evolved heat and occluded hydrogen at 15 ' C. These curves can be divided into two classes , according as they do , or do not , exhibit any critical points , and it is remarkable that such points are only shown when there has been initial heat evolution upon admitting gas in the Heating and Cooling Palladium Hydrogen .
179 cold .
The critical points , whether for black , foil or fused button , all possess a similar character .
An absorption of heat begins at about 95 ' C. , and continues up to a temperature of about 135 ' C. , at which temperature a rapid evolution of heat begins .
The absorption of heat between 95 ' and 135 ' C. corresponds exactly with the range of temperature over which the great decrease in solubility of the gas in the metal occurs , for at 95 ' C. ( according to Hoitsema 's values ) about 750 volumes of gas at atmospheric pressure are retained by one volume of the metal , whereas at 135 ' C. the solubility has decreased to about 100 volumes .
When it is considered that critical changes are only observed when a heat evolution has followed the admission of hydrogen in the cold , and as condensation would cause such a thermal change , an absorption of heat over a temperature range during which most of the occluded gas is being evolved is a natural consequence .
In fig. 5 are shown the cooling curves obtained when the metal after heating in hydrogen was allowed to cool in the gas .
On cooling no prominent points were observed unless the metal had rapidly absorbed gas in the cold and given it off between 95 ' and 135 ' C. on heating .
On cooling a heat evolution commences at about 135 ' and ceases about 105 ' C. , this latter temperature varying somewhat with the condition of the metal .
Thus , for palladium black , the heat evolution ceases about 120 ' C. , whilst for palladium foil it ceases about 100 ' C. It is evident that whatever may be the nature of occlusion , the process is reversible , the evolution of heat on cooling , and absorption of heat on heating , taking place practically over the same temperature , the former heat effect being due to occlusion of gas , and the latter to its evolution .
After the metal had completely cooled in hydrogen , it was reheated in the gas .
The heating curves are shown in fig. 6 .
As might be expected , they are very similar in character to those of fig. 4 , but it is remarkable that the temperature of the critical points in the case of palladium foil and fused button varies greatly according to the time the metal has remained in contact with the gas in the cold .
If the re-heating took place almost immediately after the metal had cooled , the point coincided with a temperature of about 140 ' C. , whilst if it had remained a week after cooling the point was raised to about 235 ' C. , and intermediate temperatures were observed for shorter periods of time at room temperature .
In the case of palladium black , this effect was not observed .
It would 180 Mr. Andrew and Dr. Holt .
Thermal Effects produced by seem , therefore , that when the ratio of surface to mass of metal is not too great , a time limit affects the temperature at which the gas is given off on a somewhat rapid heating , for the point again coincides with rapid evolution Fig. 5.\#151 ; Cooling Curves of Palladium in Hydrogen .
No. 1 .
Palladium button only slightly active towards hydrogen .
No. 2 .
Palladium foil only slightly active towards hydrogen .
No. 3 .
Palladium foil more active towards hydrogen than in the case of No. 2 .
No. 4 .
Palladium foil very active towards hydrogen .
No. 5 .
Palladium black very active towards hydrogen .
Note.\#151 ; When the palladium button became active , a series of curves similar to Nos. 2 , 3 , and 4 were obtained .
of the gas .
With very slow heating this difference in temperature is found to be less apparent , so that the effect may be due to a difficulty experienced by the gas in rapidly escaping , otherwise it must be concluded that the Heating and Cooling Palladium Hydrogen .
181 pressure-concentration values vary with the length of time the metal has remained in contact with hydrogen .
A comparison of these curves with those of fig. 4 shows that , in the case of Fig. 6.\#151 ; Reheating Palladium in Hydrogen .
No. 1 .
Active palladium foil after remaining 1 hour in hydrogen at 15 ' C. No. 2 .
Active palladium foil after remaining 14 hours in hydrogen at 15 ' C. No. 3 .
Active palladium foil after remaining 8 days in hydrogen at 15 ' C. No. 4 .
Active palladium button after remaining a short time in hydrogen at 15 ' C. No. 5 .
Palladium black .
The temperature of the critical point being independent of the time of standing in hydrogen .
Note.\#151 ; A series of curves similar to Nos. 1-3 were also obtained with the palladium button .
palladium foil , exactly similar points are observed as in fig. 4 .
The palladium button , however , gave no point on first heating in hydrogen , and little evolution VOL. LXXXIX.\#151 ; A. o 182 Mr. Andrew and Dr. Holt .
Thermal Effects produced of heat was observed upon admitting the gas .
A point on cooling indicated , however , that some gas had been picked up .
A further series of curves in hydrogen was taken , but as the results were in every way similar to those already discussed no further comment is necessary .
After this second series of curves the procedure was varied .
It was originally observed by Graham , and confirmed by many other observers , that a portion of the occluded gas could be readily pumped off in the cold , whereas part of the hydrogen is held more tenaciously by the metal , and from the experiments of Holt , Edgar and Firth , it is probable that this easily removed portion represents the adsorbed layer , with no doubt some of the inner dissolved gas .
When the metal had completely cooled in hydrogen , the surrounding atmosphere of gas , together with this easily removable portion , was pumped off .
Heating curves were then taken , the pump meanwhile removing the rest of the gas as it was evolved .
The heating curves are shown in fig. 7 and are of considerable interest .
The curves are of four types .
In the case of palladium black , it seemed that all the occluded gas could easily be removed in the cold , and hence the heating curves are not characterised by any points .
The gas retained by the metal did not exceed ten volumes .
With palladium foil , two distinct types of curves were obtained , according to whether the metal had remained for a long or a short period of time in hydrogen at room temperature .
When it had only remained a short time , about 120 volumes of gas were evolved on heating , or about 0T molecule , and the heating curve showed an evolution of heat which attained a maximum at about 190 ' C. When , however , it had remained for a long period in contact with the gas , upwards of 890 volumes of hydrogen were found to have been picked up , which is equal to about 0'75 molecule , and the heating curve showed the familiar point at 190 ' C. , a gradual absorption of heat having taken place from about 130 ' C. The curve is indeed similar to that shown in fig. 6 for palladium after long standing in hydrogen .
It was remarked that , in the case when about 120 volumes of gas were occluded , the gas on heating was evolved at a rate which the pump could easily cope with .
When , however , the volume of gas was greater , it was evolved far too rapidly for the pump to remove , and pressures of 200 to 300 mm. were recorded on the manometer .
The failure of the pump to remove the gas as fast as it was evolved resulted in a condition similar to that existing in the experiments shown in fig. 6 where the heating was carried out in an atmosphere of hydrogen .
In the case of the fused button , a condition intermediate between these Heating and Cooling Palladium in Hydrogen .
183 two different cases was observed , a result quite borne out by the heating curves .
It has been shown by Hoitsema , that the portions of the pressure-coneenFig .
7.\#151 ; Heating Curves of Palladium in vacuo .
No. 1 .
Palladium foil after remaining a short time in hydrogen at 15 ' C. No. 2 .
Palladium foil after remaining a long time in hydrogen at 15 ' C. No. 3 .
Palladium button after remaining a short time in hydrogen at 15 ' C. No. 4 .
Palladium black .
The time of standing in hydrogen not affecting the curve .
tration curves for small concentrations of gas ( up to about 0T5 molecule ) can be represented by an expression C/ -v/ P = K , where C is the concentration and P the pressure of the gas , and hence it has been suggested that , at first , the hydrogen is dissolved as atoms .
This view is , perhaps , somewhat discounted by the work on absorption of hydrogen by charcoal carried out by 184 Mr. Andrew and Dr. Holt .
Thermal Effects produced Travers ( 9 ) , though , on the other hand , it is supported by the work of McBain .
It receives distinct confirmation from the heating and cooling curves just described .
If the gas was dissolved in atoms , there would be a considerable evolution of heat when it was expelled from the metal , in the ordinary molecular form , and this is precisely what has been observed when only small volumes of gas are pumped out of the metal upon heating .
No other simple explanation accounts for an evolution of heat .
Further , above a temperature of about 150 ' C. , the volume of gas retained by the metal does not greatly vary until the melting point is reached , and this volume of gas ( about 0'15 molecule ) is very rapidly absorbed .
It therefore appears probable that it is this gas which one is dealing with in the above experiments , and which causes the almost constant rise of 7 ' C. when hydrogen is admitted to palladium in the heated state .
In many of the heating curves of palladium in hydrogen , and also palladium in vacuo , after cooling in hydrogen , as in case ( vi ) , it is very noticeable that , after the preliminary absorption of heat indicated in the curve by a movement to the right , the curve , instead of returning to its normal position , moves abruptly towards the left .
This deflection in the curve can only be interpreted to mean that the initial absorption of heat is followed by an evolution .
This phenomenon is exactly the reverse of what takes place at 15 ' C. upon admitting hydrogen , when , as it has been remarked , the initial heat evolution is followed by a very rapid cooling .
This can be explained on the assumption that , whereas the absorption of heat on heating , and evolution of heat upon admitting hydrogen in the cold , are due to condensation of the gas by the amorphous material , the reverse thermal effects are due to the gas either going into or being driven out of solution of the crystalline mass of the metal .
The evolution of heat is most strongly evident in the curves taken after the metal has been in contact with hydrogen for a considerable time at room temperature , which is entirely what would be expected , the absorption of hydrogen by the crystalline particles having had time to take place .
Although the amorphous phase is meta-stable , and must disappear after being some little time in contact with the crystalline variety , its disappearance at 15 ' C. is not marked by any evolution of gas , all the gas condensed by the amorphous material being absorbed by the crystalline .
The amorphous material merely functions , therefore , as a vehicle conveying hydrogen to the mass of metal .
Any possibility of it remaining as a stable phase is contrary to phase-rule considerations .
Heating and Cooling Palladium in Hydrogen .
185 Discussion of Results and Conclusions .
The thermal behaviour of palladium when heated and cooled vacuo furnishes additional evidence of the dimorphic nature of the metal , the stability of the two forms depending upon the temperature .
Owing to the stability of the two modifications when existing separately , and the rate of change from one variety to the other being extremely slow , it seems impossible to bring about any rapid transformation , with the result that only a very slight thermal effect is observed upon heating or cooling through the point of transformation .
A consideration of the results of the heating and cooling curves of palladium in hydrogen , and of the relation they bear to the volume of gas evolved or occluded at varying temperatures , also shows that , whatever the nature of occlusion may be , there is every reason to suppose that the metal exists in two different states , depending upon the temperature and mode of treatment .
In the first place , the metal or its surface layer may be brought into a condition which will enable it to occlude large volumes of hydrogen , with evolution of a considerable quantity of heat , at normal temperatures , the magnitude of the heat evolution and volume of initially occluded gas increasing with the ratio of the surface to the mass of metal .
This rapid occlusion of gas by the metal is most probably due to the presence of an amorphous phase .
This portion of the gas which is occluded rapidly is probably present in the metal in the molecular state , or else exists as molecular complexes , for , upon heating , it is evolved with absorption of heat , the complementary effect to that which took place during occlusion .
The same remark applies to the large volume of gas which is slowly picked up by the metal on standing in kydrogen .
It is evolved for the greater part with absorption of heat , the evolution of gas taking place at a higher temperature than is the case when the metal is allowed to remain in contact with hydrogen for short periods of time only .
This alteration in the temperature at which it is evolved is probably the result of the gas having more thoroughly penetrated into the interior of the specimen , necessitating , therefore , greater energy to overcome the passive resistance offered by the metal , and cause it to be driven out .
In the absence of an amorphous film on the surface , palladium may be quite passive with regard to rapid occlusion of gas in the cold ; it is highly probable , however , that this passivity is apparent rather than real , and that if sufficient time were allowed for occlusion to take place , a volume of gas equal to that occluded by the active material might eventually go into solution .
Thermal Effects Palladium .
At temperatures above 100 ' C. , however , whatever may be the condition of the metal ( active or passive ) a rapid occlusion of a small quantity of hydrogen invariably takes place with the evolution of constant degree of heat .
If , after the occlusion of this small amount of gas , the metal is allowed to cool in hydrogen , no critical points present themselves in the cooling curve .
If the metal after being allowed to cool in this manner is now heated in vacuo , a small evolution of heat is found to occur .
The most feasible explanation of the above phenomena is that , following the initial occlusion of gas molecules , which gives rise to a small evolution of heat , there occurs a splitting up of the molecules into atoms .
When this gas is expelled , therefore , an evolution of heat will be indicated , owing to the combination of atoms to form molecules .
The cause of the complementary effect not being realised upon admitting the gas to the metal at this temperature is undoubtedly the initial heat evolution , due to adsorption of the gas in the molecular form , and also the fact that the breaking up of the molecules into atoms is not sufficiently spontaneous to give any observable effect .
Hydrogen may be dissolved by both the crystalline and amorphous varieties of the metal , but whilst in presence of the amorphous phase solution of hydrogen is extremely rapid , when this phase is not present solution takes place but slowly .
The amorphous phase appears to function as a vehicle for the transference of hydrogen to the crystalline phase .
That temperature is an important factor is quite evident , when it is considered that above a certain temperature all varieties of palladium cease to occlude hydrogen in any quantity .
In fact , it may be stated that above 150 ' C. all forms of the metal have an equal affinity for the gas .
In conclusion the authors wish to express their indebtedness to Prof. Carpenter for the kind interest he has taken , and for the facilities which have enabled them to carry out their investigation .
BIBLIOGRAPHY .
1 .
Hoitsema , ' Zeit .
f. Physik .
Chemie , ' 1895 , vol. 17 , p. 1 .
2 .
Sieverts , ' Zeit .
f. Electrochemie , ' vol. 16 , p. 709 ; ' Ber .
, ' vol. 43 , p. 897 ; ' Internat .
Zeit .
f. Metallographie , ' vol. 3 , p. 51 ( Table XII ) .
3 .
Ramsay , Mond , and Shields , 'Roy .
Soc. Proc. , ' 1897 , vol. 62 , p. 290 ; 'Phil .
Trans. , ' 1898 , A , vol. 191 , p. 105 .
4 .
Holt , Edgar , and Firth , ' Zeit .
f. Physik .
Chemie , ' 1913 , vol. 82 , p. 5 .
5 .
Andrew , ' Journ. Iron and Steel Inst. , ' 1911 ( Carnegie Memoirs ) , No. 3 .
6 .
Beilby , 'Journ .
Inst , of Metals , ' 1911 , No. 2 .
7 .
Bengough , 'Journ .
Inst , of Metals , ' 1912 , No. 1 .
8 .
Rosenhain and Ewen , 'Journ .
Inst , of Metals , ' 1912 , No. 2 .
9 .
Travers , 'Roy .
Soc. Proc. , ' A , 1906 , vol. 78 , p. 9 .
|
rspa_1913_0077 | 0950-1207 | Spectroscopic investigations in connection with the active modification of nitrogen. III.\#x2014;Spectra developed by the tetrachlorides of silicon and titanium. | 187 | 193 | 1,913 | 89 | Proceedings of the Royal Society of London. Series A, Containing Papers of a Mathematical and Physical Character | W. Jevons, A. R. C. Sc., B. Sc.|A. Fowler, F. R. S. | article | 6.0.4 | http://dx.doi.org/10.1098/rspa.1913.0077 | en | rspa | 1,910 | 1,900 | 1,900 | 33 | 126 | 2,287 | http://corpora.clarin-d.uni-saarland.de/surprisal/6.0.3/?id=rspa_1913_0077 | 10.1098/rspa.1913.0077 | null | null | null | Atomic Physics | 71.422756 | Tables | 14.099083 | Atomic Physics | [
1.3337268829345703,
-45.774288177490234
] | ]\gt ; Spectroscopic Investigations in Connection with the Active of Nitrogen .
III .
developed by the of Silicon tanium .
By W. , A.R.C.Sc .
, B.Sc. , Assistant Demonstrator of Astrollhysics , Imperia.1 of Science and } , South ( Communicated by A. Fowler , F.R.S. Received June 20 , \mdash ; Read June 26 , 1913 .
) [ PLATE 9 .
] In previous papers by Profs .
Strutt and Fowler , accounts were iven of the spectrum of the afterglow of nitrogen , of the spectra of various elements and compounds excited by the In the course of the latter investigation it was found that carbon introduced into the afterglow developed , in general , the spectrum of , the bands , however , a curious modification as compared }with the cyanogen bands produced by the carbon arc in air .
The present paper is primarily an of an .
which has revealed the interesting fact that tetrachloride of silicon , when brought in contact yith active nitrogen , produces a band of a nitride of silicon , as would be anticipated from the close resemblance of the elements silicon and carbon in their chemical behaviour .
An is also iven of experiments on titanium tetrachloride in the , in which , however , no spectrum attributable to a nitride has been noted .
The method of producing the was identical with that adopted in former work , and has been described fully by Three spectrographs have been A one-prism quartz instrument giving a linear dispersion .
from 35 to 60 strom umits per millimetre in the region ; ( 2 ) a Littrow spec t a dispersion of 9 to 12 ngstrom units per millimetre in the same ; ( 3 ) a10-foot concave grating mounted on the plan devised by and giving .
per millimetre in the first order .
'Roy .
Soc. Proc 1911 , , vol. .
Soc. Proc 1912 , , vol. 86 , p. 10 Bakerian Lecture , ' Roy .
Soc. Proc 1911 , , vol. , p. 219 .
S 'Astrophys .
Journ 1910 , vol. 31 , p. 120 .
Mr. W. Jevons .
Silicon Tetrachloride .
This substance is a colourless , volatile liquid ( boiling ) oint 5 C. ) which fumes in moist air .
On introduction of a suitable supply of its vapour , the became purple in colour .
The spectrum was found to consist of\mdash ; ( 1 ) Unquenched nitrogen bands .
( 2 ) Silicon lines .
Impurity lines mercnry and bands of cyanogen heads associated tails ) .
( 4 ) A new set of bands in the region ibuted to a nitrogen compound of silicon .
The examination of this complex spectrum was facilitated by a comparison with of the electric discharge through rarefied vapour of the tetrachloride at a pressure less than its own maximum vapour-pressure , which latter is too to allow the discharge to pass .
The was observed end-on\ldquo ; a quartz window , a continuous current of the vapour .
maintained out the exposure in order to minimise the deposit of solid matter on the window .
No trace of the bands attributed to the nitride was detected in this experiment .
The line spectrum of silicon was developed very strongly ether with probably due to the tetrachloride itself .
* Other lines present were due to aluminium ( from the electrodes ) , , and chlorine .
The silicon lines were present in the afterglow .
They occurred also in the discharge ether with well nised spark lines Scale .
Weaker than in , Weaker , , , , Very strong .
Very weak .
Weaker than in The flutings in the discharge attributed to the chloride occur in three clusters:\mdash ; ( 1 ) Between and 2865 , with heads fading off in the direction of diminishing wave-lengths .
2 ) Two triple heads , also degraded on the more refrangible side , at , 25 , 23 , and .
( 3 ) A very strong head at , fading off towards the red , with fainter heads on either side of it extending from to 2596 .
Active of Nitrogen .
( Rowland Scale ) .
Prominent group , occurring with about the same intensities as in roup.hree aeakerW than in Prominent group , equally vell developed in the ) ources .
The silicon lines of reater w than which occur in the were quite indiscernible in the afterglow .
This region in the aftero 1 is occupied by the new system of bands .
They are degraded towards the red , and the remarkable regularity in their distribution and character will readily be seen in the ( Plate 9 ) .
Some of the bands exhiI ) a sudden fall in intensity at a point about four tellthmetres frolu the head , followed by a recoyery in intensity before the final and more fadino .
off .
SoIne heads which under-exposed thus easily be mistaken for isolated lines .
Other bands have their heads suppressed , the intensity maxima occurring towards the less refrangi portions of the bands .
These phenomena have been noted } ) reviously in the case of the more bands .
engths of th New Bands .
The positions of the brighter heads were determined from taken with the rating , the comparison spectrtun being that of the iron For the fainter bands raphs taken with the quartz raph w utilised , and the limits of error are therefore considerably greater .
As many heads as possible were included in the measurements in order to make the discussion of the ularity of structure fairly complete .
In the table the wave-lengths are given in terms of the International ngstrom , and the oscillation-frequencies have been reduced to Mr. W. Jevons . .
The relative intensities have been estimated as nearly as possible a scale of 10 for the htest band .
The remaining columns refer to the analysis of the bands which follows later:\mdash ; Table I. 4211.9 3939.8 3949.8 4345.4 4211.9 4016.7 3939.8 3949.8 [ 22849 ] [ 25787 ] [ 26006 ] 2 20840 4 21244 5 21430 3 21596 5 22097 6 22.304 8 22500 8 22681 [ 22849 ] 3 22927 4239 .
4087 .
8 24459 8 24681 6 3949 .
4 25311 4 25556 [ 25787 ] [ 26006 ] 2 26212 2 20840 4 21244 5 21430 3 21596 5 22097 6 22.304 8 22500 8 22681 [ 22849 ] 3 22927 4239 .
4087 .
8 24459 8 24681 6 3949 .
4 25311 4 25556 [ 25787 ] [ 26006 ] 2 26212 IIII IIIIII IIIIIIIII VIIIII I Iy III IV IV V .
Iy V IV V IV V V VI V VT V VI VI VI VI quency given .
Head uoped An examination of the frequencies showed that it was possible to arrange them into rows and columns in the manner which has been adopted for classification of the positive bands of nitrogen , and of the less refrangible cyanogen bands .
* * Fowler and Shaw , ' Roy .
Soc. Proc 1912 , , vol. 86 , p. 118 .
Active Table II .
Regularity of the New Bands .
Oscillation Frequencies in vacno type ) ; Snccessive Frequency Intervals ( smaller type ) .
II Group 17 [ 260061* 23375 22097 20840 25082 lso2 23780 22500 1256 21244 24130 [ 22849 ] 1253 21696 * Masked by CN bands group .
Head undeveloped .
The frequencies in the brackets have been calculated from the formula .
The successive intervals of taken vertically and horiZOll t form arithmetical ression s ; that is to say , the frequencies in each vertical group may be represented by a formula , and in each row by where , A and are constants , and successive values given to and to , while are constant fractions .
The system of bands may therefore be esented by a Deslandres equation .
For the bands observed takes the years from 50 to 55 , and from 12 to 22 .
The more accurately observed frequencies have been in evaluating the constants , and the resulting equation is Mr. W. Jevons .
The degl'ee of approximation to which this formula represents all the bands can be seen from the column in Table I , headed " " Observed minus Calculated Evidence to the Origin of the New Bands .
The new afterglow bands are not present in the discharge spectrum , in which the chloride is characterised by entirely different bands ( see footnote , p. 188 ) .
It is probable , therefore , that the new bands are not due to a chloride , but to a compound .
In the afterglow reaction , chlorine is from the tetrachloride .
Prof. Strutt has tested qualitatively the white solid which was deposited on the inside of the afterglow tube in these experiments .
The deposit was put in caustic potash solution , and a small quantity of liquid distilled off ; this gave a Nessler reaction , while blank tests with the potash solution alone gave negative results .
This proof of the presence of nitrogen in the deposit confirms the spectroscopic evidence of the itride origin of the new bands .
It may be recalled that Welss and Engelhardt* have described the formation of a nitride , the approximate formula , by heating silicon in at 1300-1400o C. They have also prepared , by other means , another compound , , which , when ignited and washed with hydrochloric acid , ives rise to a white nitride , .
It is impossible to say what is the composition of the nitride the band spectrum until a analysis of the deposit has been un dertaken .
Tetrachloride .
In view of the chemical relations of titanium to carbon and silicon , and especially of the fact that metallic titanium unites very readily with forming a nitride , it was that titanium tetrachloride might behave in a similar manner to silicon tetrachloride and the carbon compounds in the afterglow .
The tetrachloride of titanium closely resembles that of silicon , being a colourless , volatile liquid ( boiling point fuming even more strongly on exposure to the atmosphere .
On introduction of its vapour into the active nitrogen , the afterglow became very pale blue in colour .
The spectrum was compared with those of titanium oxide in the carbon arc , and of the condensed discharge through the tetrachloride vapour itself , at a pressure less than that of its saturated vapour .
The afterglow gives a well developed line spectrum of titanium , with intensities about equal to those in the arc .
In addition , and in common with the discharge , it shows the group 'Zeit .
Anorg .
Chem 1909 , vol. 65 , p. 38 . .
CO I .
A ctive Modific of of bands due to the tetrachloride , *with three principal heads , at 4192.7 , and .
The enhanced lines of titanium , generally speaking , are not developed in the afterglow , the few which do occur being fainter than in the arc .
The condensed discharge t , hrough vapour of the tetrachloride , on the other hand , noteworthy as being an excellent source of enbanced lines .
No bands occur in the which can be attributed to a although it has previously been proved that is present in the compound which is deposited in apparatus .
Unlike the carbon compounds and silicon tetrach]oride , therefore , the tetrachloride of titanium to the class of substances which , ) introduced into the afterglow , do not develop the spectrum of the final product of the reaction .
1 .
The paper iyes an account of the } ) on the introduction of the vapours of and into the 2 .
The is notable for the occurrence or a new of bands between 3800 and 4950 , with heads raded towards the red .
The bands show intensity minina near the heads , .
to the moditications of the cyanogen bands .
3 .
The of the heads have lined and their frequencies have been arranged into rolll ) , silnilar to the classification of the bands and the positive bands of 4 .
The new ban( clo not occur 111 the characterised by a different system of bands ) and are therefore attributed to a nitride silicon .
Chemical eyidence in suppol.t of this has been obtained by Prof. Strutt .
5 .
The afterglo howeyer , develops no bands of a esponding nitrogen compoumd of titanium .
Its spectrum is merely that of titanium ether with the group of flutings stic of I am anxious , in conclusion , to great indebtedness to Prof. A. Fowler , F.R.S. , for his valuable hout this and to Prof. the Hon. B. J. Strutt , .S .
, for the apparatus which he placed at my sposal , and without which the task would have been impossible .
DESCRIPTION OF PLATE .
1 .
( a ) Two groups of the bands attributed to a nitride of silicon .
( b ) Iron comparison .
2 .
Smaller dispersion photograph showing nearly the whole system of nitl .
id bands .
* Fowler , ' Roy .
Soc. Proc 1907 , , vol. 70 , p. 509 . .
J. Strutt , Roy .
Soc. Proc vol. 88 ,
|
rspa_1913_0078 | 0950-1207 | On the passage of waves through fine slits in thin opaque screens. | 194 | 219 | 1,913 | 89 | 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.1913.0078 | en | rspa | 1,910 | 1,900 | 1,900 | 8 | 189 | 4,978 | http://corpora.clarin-d.uni-saarland.de/surprisal/6.0.3/?id=rspa_1913_0078 | 10.1098/rspa.1913.0078 | null | null | null | Formulae | 37.777204 | Tables | 20.912177 | Mathematics | [
36.989601135253906,
-40.34809875488281
] | ]\gt ; perpendicular to the length of the slit .
It appeared that if the width of the slit is very small in comparison with the wave-length ( ) , there is a much mOre free passage when the electric vector is perpendicular to the slit than when it is parallel to the slit , so that unpolarised light incident upon the screen will , after passage , appear polarised in the former manner .
This conclusion is in accordance with the observations of upon the very narrowest slits .
Fizeau found , however , that somewhat wider slits scratches upon silvered glass ) gave the opposite polarisation ; and I have wished to extend the calculations to slits of width comparable with .
The subject also a practical interest in connection with observations upon the Zeeman effect .
The analysis appropriate to problems of this sort would appear to be by use of elliptic co-ordinates ; but I have not seen my way to a solution on these lines , which would , in any case , be rather complicated .
In default 01 such a solution , I have fallen back upon the approximate methods of my former paper .
Apart from the intended application , some of the problems which present themselves have an interest of their own .
It will be convenient to repeat the general argument almost in the words formerly employed .
Plane waves of simple type impinge upon a parallel screen .
The screen is supposed to be infinitely thin and to be perforated by some kind of aperture .
Ultimately , one or both dimensions of the aperture will be regarded as small , or , at any rate , as not large , in comparison with the wave-length ( ) ; and the investigation commences by adapting to the present purpose known solutions concerning the flow of incompressible fluids .
" " On the Passage of Waves through Apertures in Plane Screens and Allied Problems ' PhiL Mag 1897 , vol. 43 , p. 269 ; 'Scientific Papers , ' vol. 4 , p. 283 .
'Annales de Chimie , ' 1861 , vol. 63 , p. 385 ; Mascart 's 'Traite d'Optique , ' S646 .
See also ' Phil. Mag 1907 , vol. 14 , p. 350 ; 'Scientific Papers , ' vol. 5 , p. 417 .
Zeeman , 'Amsterdam Proceedings , ' October , 1912 .
: where and is the velocity of propagation .
If we assume that the vibration is everywhere proportional to , ( 1 ) becomes , ( 2 ) where .
( 3 ) It will conduce to brevity if we suppress the factor .
On this understanding the equation of waves travelling parallel to in the positive direction , and accordingl incident upon the negative side of the screen situated at , is .
( 4 ) When the solution is complete , the factor is to be restored , and the imaginary part of the solution is to be rejected .
The realised expression for the incident waves will therefore be .
There are two cases to be considered corresponding to two alternative boundary conditions .
In the first ( i ) over the unperforated part of the screen , and in the second ( ii ) .
In case ( i ) is drawn outwards normally , and if we take the axis of parallel to the length of the slit , will represent the magnetic component parallel to , usually denoted by , so that this case refers to vibrations for which the electric vector is perpendicular to the slit .
In the second case ( ii ) is to be identified with the component parallel to of the electric vector , which vanishes upon the walls , regarded as perfectly conducting .
We proceed with the further consideration of case ( i ) .
If the screen be complete , the reflected waves under condition ( i ) have the expression .
Let us divide the actual solution into two parts , and ; the first , the solution which would obtain were the screen complete ; the second , the alteration required to take account of the aperture ; and let us distinguish by the suffixes and the values applicable upon the negative , and upon the positive side of the screen .
In the present case we have .
( 6 ) This -solution makes over the whole plane , and over the same plane the element of the aperture , and the integration is extended over the whole of the area of aperture .
Whatever functions of position may be , these values on the two sides satisfy ( 2 ) , and ( as is evident from symmetry ) they make vanish over the wall , viz. , the unperforated part of the screen , so that the required condition over the wall for the complete solution is already satisfied .
It remains to consider the further conditions that and shall be continuous across the aperture .
These conditions require that on the aperture .
( 8 ) The second is satisfied if ; so that , ( 9 ) making the values of equal and opposite at all corresponding points , viz. , points which are images of one another in the plane .
In order further to satisfy the first condition , it suffices that over the area of aperture , ( 10 ) and the remainder of the problem consists in so determining that this shall be the case .
It should be remarked that in ( 9 ) is closely connected with the normal velocity at .
In general , .
( 11 ) At a point ( x ) infinitely close to the surface , only the neighbouring elements contribute to the integral and he factor may be omitted .
Thus ; or ( 12 ) being the normal velocity the point of the surface in question .
In the original paper results were applied to an aperture , especially of elliptical form , whose dimensions are small in comparison with For our present purpose we may pass this over and proceed at once to consider The use of implies that the variation is in a fixed direction , while may be supposed to be drawn outwards from the screen in both cases .
through Fine in Thin Opaque Screens .
the case where the aperture is an infinitely long slit with parallel edges : whose width is small , or at the most comparable with The velocity-potential of a point-source , viz. , , is now to be replaced by that of a linear source , and this , in general , is much more complicated .
If we denote it by , ' being the distance from the line of the point where the potential is required , the expressions are* ( kr ) , ( 13 ) where is Euler 's constant , and .
( 14 ) Of these the first is " " semi-convergent\ldquo ; and is applicable when is the second is fully convergent and gives the form of the fimction when is moderate .
The function D- may be regarded as being derived fro1n by integration over an infinitely long and infinitely narrow strip of the surface S. As the present problem is only a particular case , equations ( 6 ) and remain valid , while ( 9 ) may be written in the form the integrations extending over the width of the slit from to .
It remains to determine , so that on the aperture At a sufficient distance from the slit , supposed for the noment to be very narrow , ) may be removed from under the inteolalb sign and also be replaced by its limiting form given in ( 13 ) .
Thus .
( 16 ) If the slit be not very narrow , the partial waves arising at different parts of the width will arrive in various phases , of which due account must be taken .
The disturbance is no longer symmetrical as in ( 16 ) .
But if , as is usual in observations with the microscope , we restrict ourselves to the direction of original propagation , equality of phase obtains , and ( 16 ) * See 'Theory of Sound , ' S341 .
VOL. LXXXIX.\mdash ; A. Lord Rayleigh .
On the Passage of Wavei remains applicable even in the case of a wide slit .
It only remains to determine as a function of , so that for all points upon the aperture ( ) , ( 17 ) where , since is supposed moderate throughout , the second form in ( 13 ) may be employed .
Before proceeding further it may be well to exhibit the solution , as formerly given , for the ease of a very narrow slit .
Interpreting as the velocity-potential of aerial vibrations and having regard to the known solution for the flow of incompressible fluid through a slit in an infinite plane wall , we may infer that will be of the form , where A is some constant .
Thus ( 17 ) becomes .
( 18 ) In this equation the first part is obviously independent of the position of the point chosen , and if the form of has been rightly taken the second integral must also be independent of it .
If its co-ordinate be , lying between ( 19 ) must be independent of .
To this we shall presently return ; but merely to determine A in ( 18 ) it suffices to consider the particular case of Here .
Thus , and ; so that ( 16 ) becomes .
( 20 ) From this , is derived by simply prefixing a negative sign .
The realised solution is obtained from ( 20 ) by omitting the imaginary part after introduction of the suppressed factor .
If the imaginary part of be neglected , the result is corresponding to 22 ) Writing , we have ( S ) Sb2 as we see by changing into in the second integral .
Since has disappeared , the integral is independent of .
In fact , * and we have , ( 23 ) as in the particular case of The required condition ( 17 ) can thus be satisfied by the proposed form of , provided that be small enough .
When is greater , the value of in ( 15 ) will no longer be constant over the aperture , but we may find what the actual value is as a function of by carrying out the integration with inclusion of more terms in the series representing D. As a it will be convenient to discuss certain definite integrals which present themselves .
The first of the series , which has already occurred , we will call , so that elow .
or , on integration by parts , Thus by which the integrals can be calculated in turn .
Thus , Similarly , and so on .
It may be that the series within brackets , being equal to approaches ultimately the limit .
A tabulation of the earliermembers of the series of rals will be convenient:\mdash ; Table I. The last four have been calculated in sequence by means of ( 25 ) .
Fine Stits in Thin Opaque Screens .
In ( 24 ) we may , of course , replace by throughout .
lf both and occur , as in , ( 26 ) where and are even , we may express by means of , and so reduce ( 26 ) to integrals of the form ( 24 ) .
The particular case where is worthy of notice .
Here .
( 27 ) A comparison of the two treatments gives a relation between the integrals Thus , if We now proceed to the calculalion of the left-hand member of ( 17 ) with , or , as it may be written , The leading term has already been found to be .
( 29 ) In ( 28 ) is equal to .
, as before , we have ( 30 ) As regards the terms which do not involve , we have to deal merely with , ( 31 ) where is an even integer , which , on expansion of the binomial and integration by a known formula , becomes co .
( 32 ) Lord Rayleigh .
On the Passage of Waves Thus , if .
If , and so on .
3 ) The coefficient of ( 31 ) , or ( 32 ) , in ( 30 ) is .
( 33 ) At the centre of the aperture where , ( 32 ) reduces to its first term .
At the edges where , we may obtain a simpler form directly from ( 31 ) .
Thus ( 31 ) For example , if ( 34 ) We have also in ( 30 ) to consider ( even ) being even .
In ( 36 ) S8i 1.2.3.4 and thus the result may be expressed by means of the integrals .
Thus if ( 35 ) If If ( 35 ) It is worthy of remark that if we neglect the small differences between the 's in ( 39 ) , it reduces to 4 , and similarly in other cases .
When is much higher than 6 , expressions corresponding ( 37 ) , ( 38 ) , ( 39 ) become complicated .
If , however , be either , or ( 36 ) reduces to a single term , viz. , or .
Thus at the centre from either of its forms ( 35 ) On the other hand , at the edges ( 30 ) In ( 30 ) , the object of our quest , the integral ( 35 ) occurs with the coefficient Lord Rayleigh .
On the Passage of Waves Thus , expanded in powers of 28 ) or ( 30 ) becomes { Scos } .
( 43 ) At the centre of the aperture , in virtue of ( 40 ) , a simpler form is available .
We have Similarly at the edges , by ( 34 ) , ( 41 ) , we have .
( 45 ) .
( 46 ) These expressions are the values of ( 47 ) for the values of We now suppose that .
The values for other particular cases , such as , may then easily be deduced .
For , from ( 44 ) we have , ( 48 ) since , log2 In like manner , if , we get still with .
( 49 ) If , we have .
( 50 ) ( 51 ) Similarly , if , we have And if , with diminished accuracy , .
( 53 ) As an intermediate value of we will select .
For from ( 46 ) Also , when .
( 55 ) When , only a rough value is afforded by , viz. , The accompanying table exhibits the various numerical results , the factor being omitted .
of .
In this case the condition ( 17 ) can be letely satisfied with , A being chosen suitably .
When is finite , ( 17 ) can no longer be satisfied for all values of .
But when , or even when the tabulated number does not vary greatly with and we may consider to be approximately satisfied if we make in the first case , ( 57 ) and in the second , .
( 58 ) The value of , applicable to a point at a distance directly in front of the aperture is then , as in ( 16 ) , .
( 59 ) In order to obtain a better approximation we require the aid of a second solution with a different form of .
When this is introduced , as an addition to the first solution and again with an arbitrary constant multiplier , it will enable us to satisfy ( 17 ) for two distinct values of , that is of , and thus with tolerable accuracy over the whole range from to Theoretically , of course , the process could be carried further so as to satisfy ( 17 ) for any number of assigned values of As the second solution we will take simply , so that the left-hand member of ( 17 ) is .
( 60 ) If we omit , which may always be restored by consideration of homogeneity , we have ( 60 ) same expression with the sign of changed .
The leading term in ( 60 ) is thus imaginaly part is independent of that variable .
The complete expression ( 60 ) naturally assumes specially imple forms at the centre and edges of the aperture .
Thus , when ( 60 ) ; ( 62 ) and , similarly , when ( 60 ) To restore we have merely to write for in the right-harul members of ( 62 ) , ( 63 ) .
The calculation is straightforward .
For the same values as before of and of , equal to , we get for ( 60 ) Table We now proceed to combine the two solutions , so as to secure a better satisfaction of ( 17 ) over the width of the aperture .
For this purpose we determine A and in , ( 64 ) so that ( 17 ) may be exactly satisfied at the centre and edges .
The departure from ( 17 ) when can then be found .
If any value of and the first tabular ( complex ) number is and the second , and for the first is and the second , the equations of condition from ( 17 ) are From ( 65 ) we get , ( 66 ) ' so that ( 67 ) Thus for we have whence and ( 67 ) The above values of and are derived according to ( 17 ) from the values at the centre and edges of the aperture .
The success of the method may be judged by substitution of the values for these in ( 17 ) we get , -for what should be , a very fair approximation .
In like manner , for ( 67 ) : and for ( 67 ) As appears from ( 16 ) , when is given , the lnodulns of may be taken to represent the amplitude of disturbance at a distant point immein front , and it is this with which we are mainly concerned .
The following table gives the values of Mod .
and Mod.2 for several values of The first three have been calculated from the simple formula , see ( 20 ) .
Table 1 The results are applicable to the problem of aerial waves , or shallow water waves , transmitted through a slit in a thin fixed wall , and to electric When is lalge , the limiting form of ( 67 ) may be deduced from a formula , analogous to ( 12 ) , connecting and .
As in ( 11 ) , in which , when is very small , we may take .
Thus , or Now , when is large , tends , except close to the edges , to assume the value , and ultimately ( 67 ) ( 69 ) which the modulus is simply , i.e. We now pass on to consider case ( ii ) , where boundary condition to be satisfied over the wall is .
Separating from the solution ( ) which would obtain were the wall unperforated , we have , ( 70 ) giving over the whole plane , S* and the point , at which are estimated , is equal to .
The form ( 71 ) secures that on the walls , so that the condition of evanescence there , already satisfied by , is not disturbed .
It remains to satisfy over the .
( 72 ) The first of these is satisfied if , so that and are equal at pair of corresponding points on the two sides .
The values of are then opposite , and the remaining condition is also satisfied if .
( 73 ) At a distance , and if the slit is very narrow , may be removed from under the integral sign , so that , ( 74 ) in which And , even if be not small , ( 74 ) remains applicable if the distant point be directly in front of the , so that .
For such a point ( 76 ) There is a simple relation , analogous to ( 68 ) , between the value of at any point of the aperture and that of at the same point .
For in the application of ( 71 ) only those elements of the integral contribute which lie infinitely near the point where is to be estimated , and for these .
The evaluation is effected by considering in the first instance a point for which is finite and afterwards passing to the limit .
Thus It remains to find , if possible , a form for , or , which shall make constant over the aperture , as required by ( 73 ) .
In my former paper , dealing with the case where is very small , it was shown that known than in case ( i ) , see ( 20 ) .
The realised solution from ( 78 ) is , corresponding to The former method arrived at a result by assuming certain hydrodynamical theorems .
For the present purpose we have to go further , and it be appropriaie actually to verify the constancy of over the aperture as resulting from the assumed form of , when .
is small .
In this case we may take , where .
From , the suffix being omitted , ; and herein const Thus , on integration by parts , In ( 81 ) and so long as is not equal to , it does not become infinite at the limits , even though .
Thus , if vanish at the limits , the integrated terms in ( 81 ) disappear .
We now assume for trial which satisfies the last-mentioned condition .
Writing we have ) .
Of the parts of the integral on the right in ( 83 ) the first yields when x. For the second we have to consider , from to where , and lastly from to .
In evaluating the first and third parts we may put at once .
And if Sin being omitted , the first and third parts together are thus where , and is to be made infinite .
It appears that the two parts taken together vanish , provided are so chosen that It remains to consider the second part , viz. , ' ( 85 ) in which we may suppose the range of integration to be very small .
Thus ( 85 ) and this also vanishes if , a condition consistent with the former to the required approximation .
We infer that in ( 83 ) , ( 86 ) so that , with the aid of a suitable multiplier , ( 73 ) can be satisfied .
Thus if , ( 73 ) gives , and the introduction of this into ( 74 ) gives ( 78 ) .
We have now to find what departure from ( 86 ) is entailed when is no longer very small .
Since , in general , we find , as in ( 81 ) , , ( 87 ) and for the present has the value defined in ( 82 ) .
The first term on the right of ( 87 ) may be treated in the same way as ( 28 ) of the former problem , the difference being that occurs now in the numerator instead of VOL. LXXXIX.\mdash ; A. term we have , and thus The latter integral may be transformed into and this by means of the definite integrals is found to be .
To this order of approximation the complete value is For the next two terms I find When , or , the calculation is simpler .
Thus , when ; , ( 92 ) the last term , deduced from , being approximate .
For the values of we find from ( 91 ) , ( 90 ) , ( 92 ) for , 1 , , 2:\mdash ; Table These numbers correspond to the value of expressed in ( 82 ) .
We have now , in pursuance of our method , to seek a second solution with another form of .
The which suggests itself with does not answer the purpose .
For ( 81 ) then gives as the leading term , ( 93 ) becoming infinite when A like objection is encountered if .
In this case The first part gives simply when becomes zero .
And ; so that , ( 94 ) becoming infinite when So far as this difficulty is concerned we might take , but another form seems preferable , that is .
( 95 ) With the same notation as was employed in the treatment of ( 82 ) we have .
( 96 ) Thus altogether for the leading term we get .
This is the complete solution for a fluid regarded as incompressible .
We have now to pursue the approximation , using a more accurate value of than that hitherto employ In calculating the next term , we have the same values of and as for ( 88 ) ; and in place of that equation we now have ( 98 ) The integral may be transformed as before , and it becomes ( 99 ) The evaluation could be effected by expressing the square bracket in terms of powers of , but it may be much facilitated by use of two lemmas .
If denote an integral function of ( 100 ) in which the doubled angles are got rid of .
Again , if be integral , .
( 101 ) ( 103 ) $ ?
ik ; * ' and thence , on introduction of the values of , for the complete value to this order of approximation , : .
( 104 ) To carry out the calculation to a sufficient approximation with the general , value of would be very .
I have limited myself to the extreme cases .
For the former , we have , ( 105 ) : and for the latter .
( 106 ) From these formula the following numbers have been calculated for the value of Table We may take the modulus of ( 108 ) as representing the transmitted vibrations , in the same way as the modulus of 67 ) represented the transmitted vibration in case ( i ) .
Using , as before , to denote the tabulated complex numbers , we have as the equations to determine A and so that .
( 110 ) For the second fraction on the right of ( 110 ) and for its modulus we get in the various cases And thence ( on introduction of the value of ) for the modulus of ( 110 ) representing the vibration on the same scale as in case ( i ) .
Table These are the numbers used in the plot of Curve , fig. 1 .
When is much smaller than 3 , the modulus may be taken to be 3 .
When is large the modulus approaches the same limiting form as in case This curve is applicable to electric , or luminous , vibrations incident upon a thin perfectly conducting screen with a linear perforation when the electric vector is parallel to the direction of the slit .
about one-third of the wave-length of yellow-green , there would be distinctly marked opposite polarisations at the ends of the spectrum .
These numbers are in good agreement with the estimates of Fizeau : " " Un ligne polarisee perpendiculairement a sa direction a paru de de millimetre ; un autre , beaucoup moins lumineuse , polarisee parallelement A sa direction , a e'te ' estimee a de millimetre .
Je dois ajouter que ces valeurs no sont qu'une approximation ; else peuvent eAtre en re'alite ' plus faibles encore , mais il est peu probable qu'elles soient plus fortes .
Ce qu'il a de certain , c'est que la polarisation parallele n'apparait que dans les fentes les plus fines , et alors que leur largeur est bien moindre que la longueur d'une ondulation qui est environ de de millimetre It will be remembered that the " " plane of polarisation\ldquo ; is perpendicular to the electric vector .
It may be well to emphasize that the calculations of this paper relate to an aperture in an infinitely thin perfectly conducting screen .
We could scarcely be sure beforehand that the conditions are sufficiently satisfied even by a scratch upon a silver deposit .
The case of an ordinary spectroscope slit is quite different .
It seems that here the polarisation observed with the finest ticable slits corresponds to that from the less fine scratches on silver deposits .
|
rspa_1913_0079 | 0950-1207 | Experiments on the temperature coefficient of a Kew collimator magnet. | 220 | 231 | 1,913 | 89 | Proceedings of the Royal Society of London. Series A, Containing Papers of a Mathematical and Physical Character | G. A. Shakespear, M. A., D. Sc.|Prof. J. H. Poynting, F. R. S. | experiment | 6.0.4 | http://dx.doi.org/10.1098/rspa.1913.0079 | en | rspa | 1,910 | 1,900 | 1,900 | 1 | 167 | 5,304 | http://corpora.clarin-d.uni-saarland.de/surprisal/6.0.3/?id=rspa_1913_0079 | 10.1098/rspa.1913.0079 | null | null | null | Electricity | 28.695743 | Measurement | 26.529376 | Electricity | [
43.990272521972656,
-1.3636165857315063
] | 220 Experiments on the Temperature Coefficient of a Kew Collimator Magnet .
By G. A. Shakespeare , M.A. , D.Sc .
( Communicated by Prof. J. H. Pointing , F.R.S. Received June 20 , \#151 ; Read June 26 , 1913 .
) It is usually assumed that the relation between the moment mt of a collimator magnet used in determining the horizontal component of the earth 's magnetic field is dependent on the temperature , the relation being given by the equation mt = m0 ( 1 \#151 ; qt\#151 ; q't The evidence , however , upon which this assumption is based not appearing conclusive , the writer was led to make an independent investigation of the subject , and the present paper is an account of the experiments carried out with that object on a Kew collimating magnet of the ordinary type about 20 years old .
One of the difficulties in any magnetometer observations arises from the variability of the earth 's field .
Variations may be either those of a widespread nature , such as are generally dealt with under the name of diurnal variation , or those of purely'local origin , due to the proximity of electric trams , dynamo-electric machinery , electric mains , or like causes Among these disturbances we may include those arising from earth currents , since these currents , to whatever cause they may be due , are often of much more considerable magnitude that is usually suspected .
It is therefore necessary to eliminate the errors which such disturbances might produce .
The method of attaining this end , which suggested itself to the writer , is the use of what may be called a compensating magnetometer .
The principle of the method is simple .
Let A and B be two plane mirrors .
Then , if a ray of light falling on one of these be reflected on to the other in the way indicated in the diagram ( fig. 1 ) , the direction of the emergent ray will make with that of the incident ray a certain angle dependent on the angle between the planes of the mirrors .
If , now , each of the mirrors be rotated through the same small angle in the same sense , the deviation of the ray brought about by the first mirror will be corrected by the second , and the emergent ray will still form the same angle with the ray incident on the first mirror .
Hence , if the ray comes from a very distant scale , and is received in a telescope , there is no displacement of the image of the scale in the field of view .
In practice it is often inconvenient to have the scale at a great distance , and to overcome this difficulty a collimator may be used , having a scale at Temperature Coefficient of a Kew Collimator Magnet .
221 the focus of the collimating lens .
A more convenient device , however , is to use an ordinary scale at a moderate distance .
But in this case there will be a movement of the image of the scale in the field of view , depending on the distance between the mirrors , and , to secure absence of such movement , the mirror B must he made to move through a slightly greater angle than the mirror A. If A and B be the mirrors attached to two magnetometers , this end can be attained by slightly weakening the controlling field of the magnetometer B by the use of a small subsidiary magnet so arranged as to weaken the field without altering its direction , in a manner to he described later .
In this way the image of a scale viewed with a telescope in the manner indicated may be made to remain stationary , though the direction of the field change considerably .
It is assumed that the disturbing force may be regarded as a second uniform field superposed on the general field of the earth .
But it is useful to note that if the disturbing field be not uniform ( as in the case of a neighbouring dynamo ) , it is still possible to arrange the strength of the field at the compensating magnetometer in such a way as to eliminate disturbance , provided the relative magnitudes of the disturbing field at the two magnetometers remain constant .
But if the field be thus arranged to compensate for a non-uniform field , which varies in a given ratio at the two magnetometers respectively , it will not be such as to compensate for a uniform disturbing field .
It is , for instance , possible to compensate for the effect of a dynamo at a distance of , say , 10 metres , but not at the same time for electric trams at a distance of 400 metres .
In the present experiments compensation was made for uniform disturbing fields , thus eliminating the effect of the trams and of the diurnal change .
Experiments were suspended while dynamos close at hand were being used , though the disturbances due to those were very greatly diminished .
Arrangement of Magnets and Magnetometers.\#151 ; A differential method was 222 Dr. G. A. Shakespeare .
Experiments on the used , in which the effect of the magnet to be tested was balanced by means of a compensating magnet at ordinary temperature .
Several dispositions of the apparatus were tried , which will be understood from the accompanying figure ( fig. 2 ) , where K and C represent the Kew magnet and compensating magnet respectively , and M and M ' the primary and compensating magnetometers .
Of these ( a ) was most satisfactory and was used exclusively in the later work , so that the description given must be taken to apply to this case unless otherwise stated .
Heating Arrangements.\#151 ; The Kew magnet was contained in a brass tube , being fixed therein by its middle point by means of a collar of brass provided with two projecting teeth at the bottom and a central screw at the top , as shown in section at P ( fig. 3 ) .
The collar was brazed to the brass tube at the t^ZZZZTSTZZZZZZTZZZSTi middle of its length , an aperture B being left above the screw to allow the latter to be screwed up when the magnet had been inserted in its place , by means of a gauge bar , through the open end A of the tube .
A short tube from this aperture to the exterior was closed with an indiarubber bung .
This magnet tube was fixed by means of two perforated annuli of brass , D and D ' , in the middle of a large tube EE , which served as a water jacket , through which water could be allowed to flow by means of inlet and outlet tubes as indicated by the arrows .
Brazed on the underside of the outer tube at the middle point was a short rod of brass ( F ) with a conical point .
At G two other hemispherical feet were attached .
These three feet rested on a brass plate which had a hole to receive the point of the cone F and a V groove to take the hemispherical end of one foot G , the end of the third foot resting on the plane surface of the plate .
This elaborate arrangement was necessary to secure that the centre of the magnet should neither approach nor recede from the magnetometer in the course of heating or cooling , for an extremely small movement would entirely mask the true nature of the effect to be observed .
The water jacket was covered with thick felt ; and a lump Temperature Coefficient of a Kew Collimator Magnet .
223 of lead ( L ) was fixed between the feet for greater stability .
The brass plate was cemented down to a slate slab on which the magnetometer and compensating magnet stood .
As an illustration of the necessity for elaborate precautions to avoid small changes of distance , it may be mentioned that the tilting of the floor due to change of position of the observer may be quite sufficient to produce an appreciable change of scale reading .
In fact the changes in humidity and temperature caused minute tilting of the wooden table and wooden magnetometers at first used , thereby producing irregularities which seemed inexplicable .
These troubles , however , were overcome by building up a table made of a slate slab on masonry supports standing on the concrete floor , from which the wooden blocks had been removed , and by making the magnetometers of brass .
The water supply from the main passed through a gas heater on its way to the water jacket and the temperature of the latter could be adjusted to any value between about 9 ' C. and 60 ' C. , and kept constant to about 0'01 ' C. The temperature of the magnet was given by the thermometer T which projected into the middle of the magnet through the rubber bung R. The range of temperature used in most of the experiments was about 10 ' C. to 35 ' C. , i.e.about such variations as a Kew magnet in ordinary use , and occasionally handled , might be subjected to .
In some of the experiments however , the range was considerably greater .
Compensating Magnet.\#151 ; The compensating magnet was contained in a brass tube fitted into a brass box , in which the tube was surrounded by about a litre of water .
In this way the temperature of the compensating magnet changed very slowly with the change of the room temperature .
It was necessary , as will be seen later , that the compensating magnet should be of as nearly as possible the same length and moment as the Kew magnet .
To secure this , the magnet was built up of a number of thin magnetised rods , each of the same length as the Kew magnet , the number being chosen to give approximately the same moment as that of the Kew magnet .
These rods were arranged in the form of a tube inside a brass tube and a thermometer projected into the middle of the compound tubular magnet thus formed .
Magnetometers.\#151 ; Each of these consisted of a box with three sides of glass , the framework and the remaining side being of brass .
This last side had a large circular opening .
When the magnetometers were in position , these two apertures faced one another and were connected by means of a cardboard tube covered with felt , so that a beam of light could pass from the mirror of the one instrument to that of the other without traversing any unnecessary 224 Dr. G. A. Shakespeare .
Experiments on the glass on the way .
The mirrors were sextant mirrors about 2'5 x 2 cm .
, silvered on both sides .
Each was fitted with eight small magnetised needles about 1 cm .
long , mounted on a small slab of cork through which passed a thin copper wire depending centrally from the frame of the mirror .
By this means the needles could be turned to any desired orientation with respect to the mirrors .
The copper wire was continued below the needles and w'as bent into the form of a horizontal ring about 1 cm .
beneath them .
This ring dipped into a dash-pot of oil , the size of* the ring being such as to make the motion of the magnetometers very nearly dead-beat .
The mirror and needles were suspended with a single fibre of cocoon silk about 10 cm .
long .
Adjustment.\#151 ; The two magnetometers were placed in the required position in the same N.S. line .
The mirror and telescope were then adjusted so that the scale was seen by reflection in both mirrors as shown in fig. 4 .
For making the final adjustment it was necessary to be able to superpose on each of the magnetometers equal fields transverse to that of the earth ; for this purpose a long bar magnet was placed at a distance of about 5 metres on the line bisecting the distance between the magnetometers at right angles .
By means of telescopes viewing a scale by reflection from the backs of the mirrors the position of the bar magnet was adjusted so that on rotation of the magnet through 180 ' about a vertical axis , equal deflections were produced in the two magnetometers .
The position of the magnet was then marked and the magnet removed .
The Kew magnet was next placed in position to the W. of the primary magnetometer so as to lie in an E.W. line passing through the centre of that magnetometer , but so as not to produce any deflection of the compensating magnetometer .
The compensating magnet was now brought into position to restore the primary magnetometer to its original direction , while at the same time giving no deflection of the compensating magnetometer .
This was rendered simple by the equality of its moment and length with those of the Kew magnet .
On now bringing into position the disturbing bar magnet , the two magnetometers , being in controlling fields of unequal magnitudes , were deflected through different angles and the image of the scale seen by reflection in both mirrors moved .
In the case represented in the diagram ( fig. 4 ) , the controlling field at M ' is too small .
A small subsidiary magnet , M " , of steel wire , about 3 cm .
Temperature Coefficient of Kew Collimator Magnet .
225 long , fixed in a brass support , was therefore brought to a suitable position S. of the compensating magnetometer to give an increase in magnitude of the controlling field ( without change in direction ) , so that on rotating the disturbing magnet no deflection was observed in telescope T. In this way the deflections due to the disturbing magnet were reduced to less than 1/ 400 of that which would have been given without the compensating device .
It is evident that if the moments of K and C remain constant , small changes in the direction of the earth 's field will not alter the scale reading .
But if the temperature vary , the moments of the two magnets will in general vary to differing extents .
It is necessary , therefore , to determine the change of scale reading due to each degree change of temperature of the compensating magnet , the Kew magnet being kept meanwhile at constant temperature .
This was done separately for each arrangement of the apparatus .
Course of an Experiment.\#151 ; The water was turned on through the water jacket of the K magnet and when the temperature indicated by the thermometer remained steady the scale was read and the temperatures of both magnets were taken .
The gas was now lighted in the heater through which the water passed on its way to the magnet .
The temperature of the magnet could thus be gradually raised to any desired temperature up to about 60 ' by adjusting the gas tap .
Headings of scale and thermometers were taken at suitable intervals of temperature ; the temperature of the magnet being-allowed to become steady before taking a reading .
To avoid rapid fluctuations in temperature the water after leaving the heater passed through a spiral of metal tube immersed in a vessel of water , to serve as a sort of temperature flywheel .
The temperature of the magnet thus could not be suddenly changed .
Value of Sw/ m.\#151 ; So far we have dealt with changes in the moment for a given change in temperature .
It is necessary to know the ratio of such changes to the original value of the moment .
Several ways of doing this were tried , but the following proved most satisfactory .
The primary magnetometer was fitted with a coil consisting of two single turns of insulated wire , one on each side of the needle , the common axis of the turns passing through the centre of the needle system ( as seen in fig. 6 ) , so that , when an electric current passed , a field was produced perpendicular to the horizontal component of the earth 's field and in the same direction as that due to the Kew magnet .
The Kew magnet and compensating magnet having been adjusted in position as already described , the Kew magnet was removed and a current was sent through the coil so as to restore the needle to its original position .
( The effect of the coil on the compensating 226 Dr. G. A. Shakespeare .
Experiments on the magnetometer was balanced by means of a single turn of wire in series with the coil , not shown in the diagram .
) The magnitude of the current C was measured by means of a potentiometer .
The current was then stopped and the Kew magnet was replaced in position and heated through any desired range of temperature , the small current SC necessary to restore the needle to zero position being determined .
It was assumed that Bm/ mwas equal to SC/ C. In this way the value of each scale division could be determined in terms of the total effect due to the Kew magnet alone .
In some of the experiments the results were obtained by means of the current at each temperature , in others by observing the scale deflection and deducing the ratio jm from the value of each division determined at the beginning of the experiment .
The advantage of this method lies in the elimination of the uncertainties introduced by torsion of the suspending fibre .
Separate experiments devised for the purpose showed that the effect of the current in the coil upon the Kew magnet and compensating magnet was negligible .
Results.\#151 ; The moment of the magnet is not simply a function of the temperature .
The relation is complicated by the fact that time enters into it .
Moreover , the moment at any given temperature depends on the previous history of the magnet ; e.g. , in general , the moment at a given temperature depends to some extent upon whether that temperature was preceded by a higher or a lower temperature and also upon the extreme temperature to which it has immediately previously been subjected .
The general effect may be illustrated by reference to two curves shown in fig. 5 .
These two curves are for two consecutive temperature cycles , the second covering a greater range than the first .
The arrows indicate the branches of the curves corresponding to rising and falling temperatures respectively .
The range of temperature in these curves is somewhat greater than in the majority of cases investigated , and in consequence the effects to be noticed are considerably greater , and thereby made clearer .
The dotted lines are straight lines .
It will be noted that the curve for falling temperature in each case lies below that for rising temperature .
The curve AB is represented by the equation mt = mn { 1-3-292 x 10~4(*-17)-l\L5 x 10~6(7-17)2 } .
The moment at 17 ' C. has been taken for convenience as 1000 .
In general , if the cycle has been performed at about the same rate throughout , the sagitta of the cooling branch is less than that of the warming branch .
In fact , the cooling branch is often indistinguishable from a straight line , the actual shape depending largely upon the rate of Temperature Coefficient of a Kew Collimator Magnet .
227 cooling at different parts of the range of fall of temperature .
If the first part of the fall is made rapidly and the last part slowly the curvature of the branch may be reversed , so as to be concave upwards .
It will be seen that in the case illustrated there is a subpermanent loss TEMPERATURE of moment on cooling to the final temperature in each cycle , the loss due to the second being very slightly less than that due to the first .
But if the second cycle had been for the same range of temperature ( instead of a greater ) the second loss would have been considerably less than the first .
228 Dr. G. A. Shakespeare .
Experiments on the For the experiments show that this subpermanent loss is dependent on the highest temperature reached .
In successive cycles of the same range this subpermanent loss rapidly diminishes , so that if , for example , we take three cycles in quick succession , the loss for the second is less than that for the first , while that for the third , is less than that for the second .
The subpermanent loss , however , gradually disappears after the cycle is ended if the temperature is kept constant .
Thus , in the case shown , after a rest of about 48 hours , the finishing point E would have risen so as to lie very nearly on the original curve AB , though it would still be slightly below .
In fact , the experiments show that it is highly probable that any cycle results in a very small permanent loss of moment , even if the range be only one of a few degrees centigrade ; but the higher the extreme temperature the greater the permanent loss .
In the case shown the curve CD lies entirely below the curve BC , but this is not always so ; the curve for the second heating may lie largely above that for the first cooling , especially if the interval of time between the two cycles be somewhat long ( say two or three hours ) .
To illustrate the gradual recovery of the subpermanent loss the result of a cycle in which the range of temperature was from 7 ' to 31 ' C. may be quoted .
At the end of the cycle the moment had at 7 ' C. the value which it previously had at 7'9 ' C. on the warming branch of the curve .
But in 48 hours it had recovered to such an extent that at 7 ' C. its value was that which it previously had at 7T ' C. If the magnet has been heated to , say , 60 ' C. and cooled quickly to , say , 15 ' C. and then quickly heated again to , say , 25 ' C. the recovery is facilitated , so that at the end of the second cycle the moment may be greater than at the beginning of that cycle , though less than at the beginning of the previous one .
In general we may say that the subpermanent effect Qf a cycle is always greater for the first cycle after a period of rest of several days than for succeeding cycles following at short intervals , the range of temperature in each case being the same .
In fact there is a striking analogy between this effect and the permanent lengthening of a wire which has been stretched with a load far below that required to reach the elastic limit .
For it has been shown that a wire does not accurately recover its length after being stretched with a comparatively small load and this subpermanent residual stretch is greater for the first load after a period of rest than for succeeding loads following at short intervals .
This fact suggests that part at least of the effect of a change of Temperature Coefficient of a Kew Collimator Magnet .
229 temperature on the moment of a magnet may be ascribed to the same kind of action as occurs in the stretching of a wire , i.e. to some change in the relative positions of the crystals of which the steel is composed .
Such a change would occur if the crystals had a coefficient of expansion slightly different from that of the matrix in which they were embedded , with a consequent minute amount of rupture on heating ; and the gradual recovery with time after cooling would be accounted for by the gradual growing together again of the crystals .
There can be little doubt that the magnetic properties of the steel depend to some extent on the crystalline structure of the metal .
It may be noted that permanent effects on the moment of the magnet tend to be masked by permanent effects of changes of temperature on the compensating magnet , but if the latter is kept at a fairly constant temperature the compensating device enables the experiments to be carried on continuously for months without appreciable change of zero .
Effect of the Magnetic Field , in which the Magnet lies , on the Temperature Coefficient.\#151 ; Experiments with different arrangements ( ) ( b ) ( c ) ( d ) , fig. 2 , suggested that the temperature coefficient might be slightly affected by the field in which the magnet lay .
To test this point the primary magnetometer alone was used .
This magnetometer was supported on a vertical rod attached to a fixed horizontal slab .
The Kew magnet was fixed on a second slab which was capable of rotating in a horizontal plane about the vertical rod .
The Kew magnet was first laid in an E.W. direction , as indicated at K , fig. 6 , in such a position as to produce no deflection of the magnetometer .
The slab was then rotated through 90 ' so as to bring the magnet to position K ' , when its field would of course be perpendicular to that of the earth .
The compensating magnet was placed at C , fig. 6 , to restore the magnetometer to zero ; the Kew magnet was then removed , and the current required in the coil to restore the magnetometer to zero once more was observed .
The Kew magnet was then replaced at K ' and heated through a certain range of temperature and the small current which was necessary again to restore the magnetometer was measured .
The whole experiment was then repeated with the Kew magnet reversed , end for end , i.e.with its S.-seeking pole to the northward .
Thus the mean coefficient over a given range of temperature could be found when the magnet was lying in fields differing by about 2 H. The results showed that for the magnet under investigation the temperature coefficient is not sensibly affected by changes of field of the order of H. VOL. lxxxix.\#151 ; A. T 230 Dr. G. A. Shakespeare .
Experiments on the Conclusions .
0 We may now give a summary of the conclusions to which the experiments lead:\#151 ; ( 1 ) For a steady rise of temperature , the relation between the moment mt at a temperature t ' above some standard temperature , 0 , may be approximately represented by an equation of the form mt = m0(l \#151 ; qt where q and q are constants , and for a subsequent steady fall a similar equation holds , but with different constants .
( 2 ) If the rise and fall of temperature be not steady , the relation cannot be represented by any such simple equation .
( 3 ) There is always , even for a change of temperature of only a few degrees , a residual weakening of the magnet , which diminishes with time , if kept at constant temperature , until after the lapse of about 24 hours the original value is very nearly ( though perhaps never perfectly ) regained .
( 4 ) It appears that it is easy to over-rate the degree of accuracy with which the moment of a collimator magnet at any temperature can be deduced from that at some other temperature , the application of the ordinary quadratic formula being likely to give an apparent degree of accuracy which is quite illusory .
Perhaps the following way of dealing with the question would be fairly satisfactory .
Suppose the magnet is generally to be used at temperatures in the neighbourhood of 15 ' C. Let the magnet be heated to , say , 30 ' C. , and the mean coefficient \#171 ; over this range be observed .
Then let it be cooled to , say , 0 ' C. , and the mean coefficient j3 over this range be ascertained .
How , let us suppose that we are doing magnetometer observations , and having done the oscillation experiment at temperature 0 we proceed to the deflection experiment .
If now the temperature has risen to d + t , we may put for the moment m0+\lt ; = me(l \#151 ; at ) If , on the other hand , the temperature has fallen to 6\#151 ; t , we may put me-t = me ( 1 + Probably some such method as this would lead to rather more accurate results than would be attained by the simple application of the quadratic formula .
But if the collimating magnet is to be regarded as an instrument of precision its temperature must not be allowed to vary more than a few degrees , and after being handled it should not be used for some hours , as Temperature Coefficient of a Kew Collimator Magnet .
231 such handling may give rise to a subpermanent change of moment which will not immediately disappear .
It is , moreover , necessary to take precautions to secure that the temperature of the magnet is known , especially as , in the ordinary use of a Kew magnetometer , an error of even half a degree in the estimate of the temperature is by no means impossible .
( 5 ) For differences of field of the order of +H the temperature coefficient is not sensibly affected by the field .
In conclusion , I wish to thank my assistant , Mr. E. Simpson , for help in construction and adjustment of apparatus throughout the work .
Note.\#151 ; The principle of the compensating magnetometer may be applied to needle galvanometers , and I have constructed an instrument consisting of two galvanometers to test the utility of such an application .
I have not yet had an opportunity of fully investigating its possibilities , but it seems likely that a high degree of sensitiveness may be attained with a fair immunity from effects of small local magnetic disturbances .
Moreover , for a given resistance , two galvanometers with this arrangement can be made more efficient than one .
On Light-Sensations and the Theory of Forced Vibrations .
By George J. Burch , M.A. , D.Sc .
Oxon , F.R.S. ( Received April 19 , \#151 ; Read June 26 , 1913 .
) [ This paper is published in Series B , vol. 86 , No. 590 .
] VOL. lxxxix.\#151 ; A. u
|
rspa_1913_0080 | 0950-1207 | On light-sensations and the theory of forced vibrations. | 231 | 231 | 1,913 | 89 | Proceedings of the Royal Society of London. Series A, Containing Papers of a Mathematical and Physical Character | George J. Burch, M. A., D. Sc. Oxon, F. R. S. | article | 6.0.4 | http://dx.doi.org/10.1098/rspa.1913.0080 | en | rspa | 1,910 | 1,900 | 1,900 | 1 | 13 | 274 | http://corpora.clarin-d.uni-saarland.de/surprisal/6.0.3/?id=rspa_1913_0080 | 10.1098/rspa.1913.0080 | null | null | null | Electricity | 27.792987 | Biography | 26.844522 | Electricity | [
43.97870635986328,
-1.375396490097046
] | Temperature Coefficient of a Kew Collimator Magnet .
231 such handling may give rise to a subpermanent change of moment which will not immediately disappear .
It is , moreover , necessary to take precautions to secure that the temperature of the magnet is known , especially as , in the ordinary use of a Kew magnetometer , an error of even half a degree in the estimate of the temperature is by no means impossible .
( 5 ) For differences of field of the order of +H the temperature coefficient is not sensibly affected by the field .
In conclusion , I wish to thank my assistant , Mr. E. Simpson , for help in construction and adjustment of apparatus throughout the work .
Note.\#151 ; The principle of the compensating magnetometer may be applied to needle galvanometers , and I have constructed an instrument consisting of two galvanometers to test the utility of such an application .
I have not yet had an opportunity of fully investigating its possibilities , but it seems likely that a high degree of sensitiveness may be attained with a fair immunity from effects of small local magnetic disturbances .
Moreover , for a given resistance , two galvanometers with this arrangement can be made more efficient than one .
On Light-Sensations and the Theory of Forced Vibrations .
By George J. Burch , M.A. , D.Sc .
Oxon , F.R.S. ( Received April 19 , \#151 ; Read June 26 , 1913 .
) [ This paper is published in Series B , vol. 86 , No. 590 .
] VOL. lxxxix.\#151 ; A. u
|
rspa_1913_0081 | 0950-1207 | A case of abnormal trichromatic colour vision due to a shift in the spectrum of the green-sensation curve. | 232 | 245 | 1,913 | 89 | 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.|W. Watson, D. Sc., F. R. S. | article | 6.0.4 | http://dx.doi.org/10.1098/rspa.1913.0081 | en | rspa | 1,910 | 1,900 | 1,900 | 7 | 213 | 5,910 | http://corpora.clarin-d.uni-saarland.de/surprisal/6.0.3/?id=rspa_1913_0081 | 10.1098/rspa.1913.0081 | null | null | null | Optics | 72.171143 | Tables | 22.671698 | Optics | [
9.472997665405273,
-12.686057090759277
] | 232 A Case of Abnormal Trichromatic Colour Vision due to a in the Spectrum of the Green-Sensation Curve .
By Sir W. de W. Abney , K.C.B. , F.R.S. , and W. Watson , D.Sc .
, F.R.S. ( Received June 13 , \#151 ; Read June 26 , 1913 .
) The authors have each separately dealt with the question of complete and incomplete colour-blindness caused by the absence of , or decrease in , the response to stimulation of the red or green perceiving apparatus which is functional in the case of vision .
We have shown that a large number of cases of defective perception of colour are simply explained on this hypothesis .
Abnormality of colour vision may also be due to a shift in , or an alteration in form of , one of the sensation curves .
In the present paper we discuss the effect of one type of shift on the colour perception and give the results of a series of measurements which show that such a shift , without any alteration of form , does sometimes occur .
In a paper which appeared in the ' Proceedings of the Royal Society , ' * one of us indicated how a shift , that is a displacement of the whole curve so that the maximum is displaced to a different wave-length , of one of the sensation curves could be detected by a simple spectrum test , which is as follows .
When yellow light of wave-length 5760 A.U. is mixed with blue light of wave-length 4610 in suitable proportions the mixed light looks to the normal eye exactly the same as the white light from the crater of the electric arc both in hue and brightness .
If a person who has a shift in one of the sensation curves is shown this match it will not appear correct to him nor can it be made correct by any alteration in the proportions of the yellow and blue lights .
There will , however , in every case be found a position of the slit through which the yellow light is obtained with which a satisfactory match can be obtained .
In other words the wave-length of the light which is complementary to the blue will be different to that of normal vision .
On the other hand , where the colour perception defect is due to a deficiency of one of the sensations the observer will agree that the match ' made by the normal is correct , although in most cases he will also consider correct matches made when the yellow slit is moved to one or other side of the normal setting , the range being the larger the greater the defect .
In order to see why in the case of colour defect due to a deficiency in one of the sensations the normal match appears correct it is necessary to * 'Roy .
Soc. Pioc .
, ' 1912 , A , vol. 87 .
A Case of Abnormal Trichromatic Colour Vision .
233 consider the sensation curves .
In fig. 1 are given the sensation curves of the spectrum colours for the normal eve , the source of light being the crater of an arc with a horizontal positive carbon , i.e. one in which the crater directly faces the slit of the spectroscope .
The sensations are given in terms of luminosity* so that the sum of the ordinates of the three curves for any wave-length ZZ 24 26 28 30 32 34 36 38 40 42 44 46 50 52 54 56 58 60 62 2000AJJ 5,000 5500 6,000 6500 Fig. 1.\#151 ; Scale of prismatic spectrum ( S.S.N. ) , showing wave-lengths .
is equal to the luminosity at that wave-length .
Since the luminosity of the blue sensation is so small compared to the others the blue sensation curve has been plotted on a scale 100 times as great as that adopted for the red and green sensations .
When considering the matches made between mixtures of different coloured lights it is , however , often convenient to adopt a different scale , namely , one in which the areas of the three sensation curves are all equal .
With this scale equal ordinates of the three sensation curves correspond to a mixture which will appear to the normal eye as white .
The areas of the three sensation curves on the luminosity scale are Eed = 579 , Green = 248 and Blue = 3'26 , and these correspond to the sensation produced by the whole combined spectrum , that is by white light .
If we multiply the ordinates of the green sensation curve by 579/ 248 or 2*21 , and those of the blue sensation curve by 579/ 3-26 or 117 , the green and blue sensation curves will have the same area as the red sensation curve , the three sensation curves plotted on this scale are shown by the full line curves in fig. 2 .
An explanation of what is meant by the luminosity of a coloured light is given on p. 404 of vol. 88 ( A , 1913 ) of the ' Proceedings .
' U 2 Sir W. de W. Abney and Dr. W. Watson .
Let ns now consider an observer who has , say , only half the normal green sensation , so that on the luminosity scale the ordinates of his green-sensation curve will he half those for the normal curve .
On the equal area scale , however , his green-sensation curve will be the same as the normal , for since ioo $ 20 \lt ; D H 60 3 50 o 40 30 *o ri2 20 m io 1 y s ; A 7 \ \ A ( / 4r l t A \amp ; \ \ u. \ d/ / / / \ V \ / / ,7 A \ A \ \ A \lt ; 4^00 Fig. 2.I I t i i i ] i 4500 5,000 -Scale of prismatic spectrum ( S.S.N. ) , showing wave-lengths .
i pi i i i | i 6,000 6,500 ^oooAU .
the area of the green-sensation curve on the luminosity scale is now 124 , to obtain the equal area scale we must multiply by 579/ 124 or 4*42 .
Hence , since the multiplier is twice as great as for the normal , the resulting curve will be the same as for the normal .
How if we take a yellow at S.S.N.* 48*4 ( 5760 A.U. ) , at a ( fig. 2 ) , and mix it with a violet at S.S.H. 9 5 ( 4235 A.U. ) , at b ( fig. 2 ) , the width of the violet slit being 2*5 times that of the yellow , and read off the three sensations at these places from the full line curves given in fig. 2 , the values in the violet being multiplied by 2*5 , we get the following numbers:\#151 ; * The values of the scale numbers given in the diagrams in terms of wave-length are as follows:\#151 ; S.S.N. Wave-length .
o A.U. S.S.N. Wave-length .
0 A.U. 62 6957 34 5002 60 6728 32 4924 58 6521 30 4848 56 6330 28 4776 54 6152 26 4707 52 5996 24 4639 50 5850 22 4578 48 5720 20 4517 46 5596 18 4459 44 5481 16 4404 42 5373 14 4349 40 5270 12 4296 38 5172 10 4245 36 5085 8 4198 A Case of Abnormal Trichromatic Colour Vision .
Table I. Position of slit .
Sensations .
Red .
Green .
Blue .
a 67 *9 69 -3 1 -6 b 1 -4 0 67 -7 Sums 69 3 69 -3 69-3 Since the sums for the three sensations are the same it follows that the mixture will look white to the normal eye .
Further , since the curves for the person who has half the green sensation are precisely similar , the sums will be equal for him also and hence he will match the mixed colour with his own white .
Similarly for any other case of colour defect , where the defect is due to a deficiency of one of the sensations , the equal areas of the sensations will be the same as those of the normal eye .
Although the person who has a defect of one of the sensations will agree with the normal match , it will be found that when making the match the position of the yellow slit can be moved some little distance from the correct position for the normal without the match becoming defective to him .
This want of definiteness of the mixture required for a match when one of the colour sensations is defective can be illustrated by fatiguing the normal eye ( say ) with red so that temporarily the red sensation is defective .
This effect is illustrated in the following matches made by one of us .
In each case white was matched by a mixture of red , green and violet light by altering the width of the slits through which the coloured light proceeded .
In the case of both the unfatigued and the fatigued eye not only was a correct match made but also one when the green slit was so much reduced that the deficiency in green was just observable and one where this slit was so much opened that the excess of green was just perceptible , the red slit being kept at a constant width throughout .
The numbers obtained for the width of the green slit are given in Table II .
The range between a noticeable excess and defect of green is for the unfatigued eye 4-5 , and for the fatigued eye 16-2 , and a match correct for the unfatigued eye is correct for the fatigued eye .
If the sensation curves are the same for a given observer as for the normal , except that one of them is shifted along the spectrum , quite a different result will be obtained .
Thus suppose that the green-sensation curve is shifted towards the red end of the spectrum by an amount equal to 236 Sir W. de W. Abney and Dr. W. Watson .
Table II .
Character of match .
Width of green slit .
Unfatigued .
Fatigued .
Correct 22 -7 23 -5 Too little green 20 5 11 -o Too much green 25 -0 27 -2 2 S.S.N. and occupies the position shown by the dotted curves in figs. 1 and 2 .
The sensations at the points a and b for such a person are as follows:\#151 ; Table III .
Position of slit .
Sensations .
Red .
Green .
Blue .
a b 67 -9 1-4 79 -2 0 1-6 67-7 Sums 69 -3 79 -2 1 69 -3 The sums of the blue and red sensations are still equal but the sum of the green sensation ordinates is greater , and hence the mixed colour will not match the white but will appear to such a person too green .
If , however , the yellow slit is moved towards the red to c , fig. 2 ( S.SJST .
49'8 , 5860 A..U .
) and the width of the violet slit is made 272 times that of the yellow slit we get Table IV .
Sensations .
Position of slit .
Bed .
Green .
Blue .
c 71 -8 73 -5 0 5 b 1 -7 0 73 0 Sums 73 -5 73 5 73 o The three sums are now equal and hence the mixed colour will match the white to such an observer , although it will appear orange to normal vision .
A Case of Abnormal Trichromatic Colour Vision .
237 Hence , if an observer does not agree with the normal when violet and yellow are matched to form white but requires that the yellow slit be moved towards the red to form a match , we conclude that his green-sensation curve is displaced towards the red and vice versa .
A movement of the red-sensation Qurve would produce a similar change but since we have not hitherto had an opportunity of finding such a case we shall in this paper only consider the effect of a shift of the green-sensation curve .
It may , however , be pointed out that a shift of the red-sensation curve would be accompanied by an increase or decrease in the luminosity of the extreme red end of the spectrum according as the shift is away from or towards the green .
As far as the shift of the green-sensation curve is concerned we have hitherto only met with displacements towards the red end of the spectrum .
In the case of a shift of the green-sensation towards the red amounting to 2 S.S.H. as indicated by the dotted curves in figs. 1 and 2 we should expect the following effects to be produced :\#151 ; 1 .
The part of the spectrum which to the normal appears yellow will appear greenish , for owing to the displacement the green sensation excited will be greater than in the normal .
In the same way what appears orange to the normal will appear yellow , and so on .
2 .
If we place three slits in the spectrum , one at the place of the red lithium line , d , fig. 2 , another at the b magnesium line e , fig. 2 , and the third in the violet at b , fig. 2 , and by varying the width of the three slits produce a mixture which to the normal appears to match the white , this match will not appear correct to the observer with the green shift ( whom , for short , we may designate by 0 .
, the normal being indicated by N. ) .
To 0 .
the match will be imperfect , for the green sensation he receives from the light passing through the green slit at e will not be as great as it is to 1ST .
By opening the green slit we can , however , obtain a match which is correct for 0 .
, but his match will appear green to N. , and he will never agree that the normal match is correct .
If now we move the green slit to f , fig. 2 , where the normal green-sensation curve cuts the displaced curve we shall find that a match which is correct for N. is also correct for O. , and that either can detect a small departure from this setting.* 3 .
The above is one arrangement of the three slits such that 0 .
and 1ST .
make the same match .
Another such position is obtained if the red slit is moved to g , fig. 2 ( S.S.H. 52'4 , 6000 JLU .
) .
The light which now comes through the red slit excites green sensation in the case of both N. and 0 .
, but * We have neglected any small variation in the amount of violet which may be necessary owing to small differences of macular pigmentation .
Sir W. de W. Abney and Dr. W. Watson .
to a greater extent in the case of the latter .
Since the red and blue sensations are the same for both it will be sufficient to consider the equality of the red and green in the two cases .
If the width of the red slit is 06 2 times that of the green we get the following values of the sensations on the equal area scales:\#151 ; Table Y. Sensations .
Position of slit .
N. 0 .
Red .
Green .
Red .
Green .
e 21 -1 48 -5 21 -1 34 -5 9 43 -8 16 *4 43-8 30 -4 Sums 64 -9 64 -9 64 -9 64 -9 where the sums are the same in the two cases and hence the mixture appears white to both 1ST .
and 0 .
Thus if the red and green slits are kept in a constant position and the red slit is gradually moved up towards the green the matches made by 0 .
appear to K at first too green , but the excess of green gradually decreases till the red slit is at S.S.N. 52*4 .
If the red slit is moved further towards the green the mixture which appears correct to 0 .
will then appear too red to N. 4 .
Owing to the displacement of the green-sensation curve O. 's luminosity curve will be higher than the normal on the red side of the point where the normal and displaced green-sensation luminosity curves cut and lower on the green side of this point , for the ordinates of the luminosity curve are the sums of the ordinates of the three luminosity sensation curves .
The resulting luminosity curve for a displacement of 2 S.S.N. towards the red is shown in fig. 1 by the dotted curve , the corresponding normal curve being given by the thick continuous line .
Up to quite recently those observers who gave indications of a shift of the sensation curves have not been able to devote the time necessary for a full investigation .
We have , however , been fortunate enough to have in the Senior Physics Class at the Eoyal College of Science this year a case of such a shift , and this gentleman ( R. ) has been good enough to devote the necessary time to carrying out a complete investigation of his colour sensations .
He has proved to be a most accurate observer , and we can place complete reliance on his observations .
He made a series of matches throughout the spectrum A Case of Abnormal Trichromatic Colour Vision .
239 from which his sensation curves have been deduced in the manner described by one of us in a previous paper.* His red and practically his blue sensation curves are identical with those of the normal , but his green-sensation curve is markedly different .
The numbers obtained for the green sensation are shown by the crosses in fig. 3 .
It will be observed that E/ s green-sensation curve is 'O 5/ )oo 5,500 6,000 6 , Fig. 3.\#151 ; Scale of prismatic spectrum ( S.S.N. ) , showing wave-lengths .
similar in shape to the normal , which is shown by the continuous line on the figure , but that it is displaced by about 2 S.S.N. towards the red end of the spectrum .
Thus to him the maximum for the electric arc light occurs at wave-length 5690 A.U. in place of at 5575 JLlL , which is that of the normal .
When white is matched by mixing light which passes three slits placed at the points d , e , and b , fig. 2 ( 6705 , 5190 , 4235 A.U. ) , E. requires very much more green than the normal , as is shown by the first line in Table VI .
If , however , the red slit is moved towards the yellow , the green and violet slits remaining fixed in position , the excess of green required by E. got less and less , till finally a position for the red slit was found where the mixture matched white both to E. and to the normal .
If the red slit is moved further towards the yellow E. required less green than the normal , so that his mixture looked slightly red to the normal .
The above changes indicated that in the case of E. we had to deal with a shift of the green-sensation curve .
The changes in the slit widths required to match white both by E. and by a normal ( W. W. ) are shown in Table VI .
The positions of the green and violet slits were kept constant , as w:as also the width of the green slit , the * ' Phil. Trans. , ' 1905 , A , vol. 205 , p. 333 .
Sir W. de W. Abney and Dr. W. Watson .
match being obtained by varying the widths of the red and violet slits and the brightness of the comparison white .
With the red slit at 52'5 the match made by either was correct for the other .
Table YI .
Position of " red " slit .
Slit widths .
R. W. W. S.S.N. A.U. Red .
Green .
Violet .
Red .
Green .
Yiolet .
59 '8 6710 28 -3 17 '2 26-0 62 *5 17 -2 26 -0 57 '1 6450 8-5 17 *2 26 -0 16 -5 17 -2 26 -0 54 -5 6200 7-2 17*2 26 -0 8-6 17 *2 26 -0 53 -0 6080 9*2 17 -2 33 -0 9-2 17 -2 33 -0 52 -5 6040 10 -4 17 *2 33 -0 9-5 17 -2 33 -0 52 -0 6000 14 -8 17 -2 45 -0 10 -o 17 -2 45 -0 When matching D-light with a mixture of red and green light , if the red is at the red lithium line , R. required considerably more green than did the normal .
If , however , the red slit were moved towards the yellow , just as in the case of the white matches , the excess of green gradually decreased , though , owing to the fact that the D-light in the case of R. excites the green sensation more strongly than the normal , we did not get the marked change in the appearance of R. 's match to the normal which has been referred to in the case of the white match .
For this reason the white match is preferable to the Rayleigh match for bringing out the characteristic changes when the position of the red slit is altered .
Another advantage of the white match is that the yellow produced by mixing green and red to match the D-light is less saturated than the D-light itself , and this causes considerable difficulty with some observers when making the match .
When matching white by a mixture of violet light ( 9'5 S.S.bL , 4235 A.U. ) and yellow light the following results were obtained:\#151 ; W. W. R. Position of yellow slit ... 48'9 S.S.N. or 5780 A.U. 50'0 S.S.N , or 5860 A.U. showing that the complementary to the violet is in the case of R. displaced towards the red , as has been shown on p. 237 , we should obtain if the green-sensation curve was shifted towards the red end of the spectrum .
Again it was found that if the red and violet slits were in the standard positions d and b , fig. 2 , a position for the green slit , / , fig. 2 , could be found such that the mixed light matched white both for R. and for N. A Case of Abnormal Trichromatic Colour Vision .
241 The luminosity curve obtained by R. , using the equality of brightness method , is given by the upper dotted curve in fig. 3 , the continuous line being the normal curve .
In fig. 4 are given the points corresponding to four sets of luminosity measurements made by the flicker method , the crosses giving 26 28 50 32 34 36 38 40 42 44 46 48 50 52 54 56 58 60 62 1 1 1 | 1 1 11 | 1 1 \lt ; 1 I .
1 1 1 1 I 1 1 1 1 | 5poo 5,500 6,000 6500 SO Fig. 4.\#151 ; Scale of prismatic spectrum , showing wave-lengths .
the values obtained by R. and the circles those obtained by one of the authors ( W. W. ) .
It will be observed that R. 's luminosity curve agrees with what it ought to be if his green-sensation curve is displaced towards the green by about 2 S.S.N. , such a calculated curve being given in fig. 1 .
Attention may be drawn to the fact that R. 's luminosity curve does not agree with the normal at S.S.H. 48'6 , as it would if R. 's abnormality were due to a deficiency of either the red or green sensations as has been shown in a recent paper by one of us.* It will thus be seen that the results obtained by R. agree in all respects with what we should expect if there is a shift of the green-sensation curve and which are given on p. 237 , so that they form a strong support not only of the green-sensation curve obtained by R. but also of the normal curves published by one of the authors .
Further , it is difficult to see how the various matches made by R. , which are simply and consistently explained on the trichromatic theory , can be explained on any of the other commonly held theories of colour vision .
* ' Roy .
Soc. Proc. , ' 1913 , A , vol. 88 , p. 404 .
242 Sir W. de W. Abney and Dr. W. Watson .
It is of practical importance to consider what effect a shift of the green-sensation curve such as that exhibited by It .
will have on the power of discriminating colours , particularly those colours which are used as signals at sea and on railways .
As has been mentioned , one effect of the displacement of the green-sensation curve is that the part of the spectrum which to the normal appears yellow , to such persons appears green or greenish .
Thus E. places the change from green to yellow in the spectrum at 49-9 S.S.N. or 5810 A.U. while to a normal ( W. W. ) this point appeared to be at 48-8 S.S.N. or 5780 A.U. One effect of this difference is that a light , such as that given by a paraffin lamp , which to the normal appears decidedly yellow appears to a person with the shift of a greenish hue and in fact E. often calls such a light green .
Another effect of the displacement is that the perception of a green light when diluted with white light is very much more difficult than for the normal .
The reason for this effect is at once apparent from a consideration of the sensation curves .
Consider a green at S.S.N. 36 ( 5090 A.U. ) .
At this point in the spectrum the red and blue sensation curves for N. on the equal area scales intersect .
Hence we may regard the effect produced by light of this wave-length as an amount of green sensation ( represented by the difference between the ordinate of the green-sensation curve and the ordinate of either the red or the blue-sensation curves ) diluted by white light ( this white light corresponding to the equal amounts of red , green , and blue sensation excited ) .
It will be observed that the amount of the diluting white is the same for the normal and the person with the displaced green curve ; but to 0 .
the amount of residual green sensation is less than half that of the normal .
In other words the green perceived by E when light of this wavelength enters his eye is very much more diluted than it is to a person having normal colour vision .
As a certain amount of dilution with white light will obliterate the perception of green in the coloured ray , it follows that to O. the amount of white light which will obliterate it is considerably less for O. than it is for a normal vision .
This effect is clearly indicated by some measurements made by E. that are shown in fig. 5 .
The experiment consisted in determining the amount of any given coloured light which could be added to a given amount of white light so that in the resulting mixture the colour was only just recognisable .
The ordinates in fig. 5 give the luminosity of the coloured light expressed as a percentage of the luminosity of the mixture , the crosses being the values obtained by E. and the circles those obtained by W. W. It will be observed that in the red the two agree as they also do in the blue .
In the green , however , E. requires more than twice as much green light to be mixed with the white than does a person having normal colour vision .
A Case of Abnormal Trichromatic Colour Vision .
243 To see whether the above given explanation is adequate to explain the effect observed in the case of E. we may calculate the proportion the residual green sensation bears to the total white , that is the added white plus the white due to the equal stimulation of the three sensations for the mixture of green at S.S.N. 35 .
The results are given in the following table:\#151 ; Luminosity of colour when just This colour consists of\#151 ; Total Ratio of residual colour to total white .
perceptible ( white = 100 ) .
White .
| Residual colour .
white .
R 27*7 24 '1 3 '6 124 *1 106 '6 0 029 0*031 w. w 9'9 6'6 3'3 It will be observed that the ratio of colour to white when the colour is just observable , when allowance is made for the want of saturation of the colour sensation is the same for E. as for the normal .
Another effect produced by this want of saturation is observed if the Fig. 5 .
Fig. 6 .
minimum brightness is determined at which a 'coloured light can be distinguished from a white light of the same intensity placed alongside , in other words , when the chromatic threshold is determined .
In fig. 6 are given the illuminations on a screen ( 3'2 x 1'6 cm .
) placed at a distance of 66 cm .
from the eye when the coloured light looks indistinguishable from a similar patch of white light alongside .
In the red and the blue E. and W. W. agree , but in the green there is a marked difference , E/ s threshold for colour being markedly higher than the normal .
The above results both as to the effect of dilution with white and as to 244 Sir W. de W. Abney and Dr. W. Watson .
the chromatic threshold are of great practical importance , for they both affect the power of an observer to identify green lights such as those used at sea .
These lights are never pure spectral lights , though they are spectral colours diluted with white .
Thus the Board of Trade standard light-green light can be matched by a mixture of spectral green at S.S.N. 37'4 or 5115 A.U. , with an equal amount of white ( arc light ) .
Further , if the size of the image of the coloured patch on the retina is diminished , it must be remembered that the amount of white required to extinguish a spectral colour is very much reduced .
The increased want of saturation of the green produced by a displacement of the green-sensation curve towards the red is clearly brought out by the curves given in fig. 7 .
In this figure the spectrum is represented in terms Fig. 7.\#151 ; Newton 's colour diagram of the arc-light spectrum .
The three colour sensations which make white light being shown as of equal value .
of sensations on a triangular Newton 's colour diagram .
The corners of the triangle represent the red , green and blue sensations , the scale adopted being the equal area scale used in fig. 2 , so that the centre W of the triangle represents white .
The amount of either of the sensations corresponding to A Case of Abnormal Trichromatic Colour Vision .
245 any point within the triangle is inversely proportional to the distance of this point from the corner corresponding to that sensation .
The spectrum , as it appears to the normal eye , is represented by the continuous line , the numbers written alongside the line representing the different parts of the spectrum expressed in S.S.K The dotted line gives the spectrum as it appears to a person who has the green-sensation curve displaced by 2 S.S.N. towards the red .
Even to the normal eye the green part of the spectrum corresponds to a green sensation diluted by much white , for the curve representing the spectrum passes about half-way between the green-sensation corner and the white point TV .
In the case of the green-sensation shift the curve passes much nearer the white point W , indicating that the colour seen is less saturated than it is to the normal eye .
If the green-sensation curve were shifted by 3'6 S.S.IST .
towards the red , the green-sensation curve on the equal area scale ( fig. 2 ) would pass through the point where the red and blue sensation curves intersect , and hence light of the wave-length ( 5090 A.U. ) corresponding to this point would produce the sensation of white to such a person .
In other words , there would be a neutral point in his spectrum .
In such a case the curve representing the spectrum on the Newton diagram would pass through the point W. As a result of our study of the case of R. , as well as of some more isolated observations made on others , we consider that it is extremely probable that the particular class of colour abnormality which was first investigated by Lord Rayleigh by means of his instrument for matching D-light by a mixture of red and green light , and which is generally referred to as anomalous trichromatism , is due to a shift of the sensation curves , and that green anomalous trichromates are persons who have the green-sensation curve displaced towards the red end of the spectrum .
It must , however , be remembered that abnormal matches may be obtained by persons who in place of a shift have a reduced sensation for red or green .
The two classes are , however , distinguished , as has been pointed out earlier , by the fact that in the case of a deficient sensation the accuracy with which matches can be made is less than in the case of either the normal eye or one in which one of the sensation curves is shifted .
In conclusion , the authors would like to express their obligation to Mr. R. , to whose careful measurements they are indebted for many of the results which are embodied in this communication .
|
rspa_1913_0082 | 0950-1207 | The reflection of X-rays by crystals. (II.) | 246 | 248 | 1,913 | 89 | Proceedings of the Royal Society of London. Series A, Containing Papers of a Mathematical and Physical Character | W. H. Bragg, M. A., F. R. S. | article | 6.0.4 | http://dx.doi.org/10.1098/rspa.1913.0082 | en | rspa | 1,910 | 1,900 | 1,900 | 3 | 59 | 1,472 | http://corpora.clarin-d.uni-saarland.de/surprisal/6.0.3/?id=rspa_1913_0082 | 10.1098/rspa.1913.0082 | null | null | null | Atomic Physics | 69.01427 | Tables | 11.383212 | Atomic Physics | [
12.680671691894531,
-81.13459777832031
] | 246 The Reflection of X-rays by Crystals .
( II .
) By W. H. Brag , M.A. , F.R.S. , Cavendish Professor of Physics in the University of Leeds .
( Received June 21 , \#151 ; Read June 26 , 1913 .
This note is a supplement to a paper on the reflection of X-rays by crystals which has been recently communicated to the Royal Society.* It is there shown that the wave-length of a homogeneous beam of X-rays can be found accurately in terms of the spacing of the elements of a crystal .
There has been some doubt as to the actual arrangement of the atoms in the crystal and in consequence it was not possible in the paper quoted to draw any final conclusions as to wave-length values .
From the work now described by W. L. Brag it appears that the reflection phenomena lead to a more definite knowledge of crystal structure , and we may now complete various quantitative determinations .
The elementary volume in rock-salt is a cube with 1 atom of sodium at each of four corners and 1 atom of chlorine at each of the other four .
In other words the number of elementary volumes in any space of measurable dimensions is equal to the number of atoms in that space .
The number of molecules in 1 c.c. of XaCl is 215/ 58*5 x 1*64 x 10~24 = 2*24 x 1022 .
( The weight of the H atom is taken to be 1*64 x 10-24 .
) The number of atoms is twice as great and the elementary cube volume is therefore 1/ 4*48 x 1022=2*23 x-10~23 .
The edge of the cube is 2*81 xl0~8 ; this is the distance between consecutive reflecting planes parallel to ( 100 ) .
The principal bundle of homogeneous X-rays from a platinum anticathode is stated in the paper quoted to be reflected at the ( 100 ) face of rock-salt at a glancing angle of 11*55 ' .
Recent observations with better apparatus show that this bundle is really double , consisting of two separate sets whose wavelengths differ from each other by a little less than 2 per cent , of either ; they also show that the first estimate was a little too high .
For the purpose of the present argument it is sufficiently accurate to ignore the division and assume the angle to be 11*3 ' .
This gives a wave-length ( 2 cl sin 6 ) = 2 x 2*81 xl0"8x 0*196 = 1*10 x 10"8 .
The wave-lengths of other homogeneous rays can then be found easily as soon as their angles of reflection are known .
* W. H. Brag and W. L. Brag , these ' Proceedings , ' A , vol. 88 , p. 428 .
The Reflection of X-rays hy Crystals .
A bulb having a nickel anticathode gives one weak beam of homogeneous rays reflected at a glancing angle of 17*2 ' ; the corresponding wave-length is 1-66 x 10"8 .
A tungsten anticathode gives a weak beam at an angle of 12-9 ' and the wave-length is therefore 1*25 x 10-8 .
An iridium anticathode gives a more complicated spectrum which is not yet completely analysed .
On the basis of existing theories certain numerical relations might be expected to subsist between these quantities , and it is interesting to see how closely they are fulfilled .
In the first place the " quantum " energy for a wave-length 1*10 x 10"8 is 6*55 x 10-27 x 3 x 1010/ 1*10 x 10~s = 1'78 x 10-8 ergs .
This should be the value of the energy of the cathode ray which can excite this particular X-ray , as well as of the cathode ray which it can excite .
The quality of the X-ray can be expressed in terms of its mass-absorption coefficient in aluminium .
The estimate of this quantity given in the first paper quoted was too low ; the influence of the scattered radiation was not effectively removed .
By taking the mean of the radiation on either side of the B peak and subtracting this from the radiation at the peak itself with and without an A1 screen a value 23-7 is found .
That the radiation is very homogeneous is ascertained in the usual way .
Now according to Barkla 's experimental results , X-rays of this quality are such as are given in the K series by a radiator of atomic weight 74 and in the L series by a radiator of atomic weight 198 .
The atomic weight of platinum is 195 , and this can hardly be a coincidence .
It may be calculated from Whiddington 's results* that the energy of the cathode ray required to excite the X-ray of the K series in an atom of weight 74 is about 2T4 x 10-8 ergs , which is in very satisfactory agreement with the " quantum " energy calculated above .
From the foregoing it seems reasonable to take the radiation of the B peak as equivalent to the characteristic radiations of an atom of atomic weight 74 ( or perhaps 72'5 , the equivalent of platinum in the K series ) , while the experiment with the nickel anticathode may be taken to show that the wavelength l*66xl0-8 belongs to nickel ( at .
wt. 59 ) and in the same way that of 125 x 10~s to tungsten in the L series or its equivalent ( at .
wt. 67 ) in the K series .
Now the quantum energies should be proportional to the frequencies and at the same time according to Whiddington to the squares of the atomic weight .
The squares of 59 , 67 , and 74 ( or 72*5 ) are in the ratio 100 :130 :157 or 150 , while experiment shows that the frequencies are in the ratio 1/ 1'66 :1/ 1*25 :1/ 140 , or 100 :132 :151 .
The frequency is therefore very nearly proportional to the quantum energy .
* ' Proc. Camb .
Phil. Soc. , ' vol. 16 , p. 150 .
VOL. LXXX1X.\#151 ; A. X Mr. W. L. Brag .
Th Structure of Some Lastly , though the absorption coefficient of the tungsten peak has not yet been satisfactorily measured , it may be doubtless supposed to be a little less than that of the A peak of platinum , since its wave-length is slightly less .
A recent measurement of the latter quantity gives the value 35'5 and the absorption coefficient of the characteristic radiation of tungsten is given by Barkla as 33 .
The Structure of Some Crystals as Indicated by their Diffraction of X-rays .
By W. L. Brag , B.A. ( Communicated by Prof. W. H. Brag , F.R.S. Received June 21 , \#151 ; Read June 26 , 1913 .
) [ Plate 10 .
] A new method of investigating the structure of a crystal has been afforded by the work of Laue* and his collaborators on the diffraction of X-rays by crystals .
The phenomena which they were the first to investigate , and which have since been observed by many others , lend themselves readily to the explanation proposed by Laue , who supposed that electromagnetic waves of very short wave-lengths were diffracted by a set of small obstacles arranged on a regular point system in space .
In analysing the interference pattern obtained with a zincblende crystal , Laue , in his original memoir , came to the conclusion that the primary radiation possessed a spectrum consisting of narrow bands , in fact , that it was composed of a series of six or seven approximately homogeneous wave trains .
In a recent paperf I tried to show that the need for assuming this complexity was avoided by the adoption of a point system for the cubic crystal of zincblende which differed from the system considered by Laue .
I supposed the diffracting centres to be arranged in a simple cubic space lattice , the element of the pattern being a cube with a point at each corner , and one at the centre of each cube face .
A simpler conception of the radiation then became possible .
It might be looked on as continuous over a wide range of wave-lengths , or as a series of independent pulses , and there was no longer any need to assume the existence of lines or narrow bands in its spectrum .
* W. Friedrich , P. Snipping , and M. Laue , 'Munch .
Ber .
, ' June , 1912 .
t 'Camb .
Phil. Soc. Proc. , ' November , 1912 .
|
rspa_1913_0083 | 0950-1207 | The structure of some crystals as indicated by their diffraction of X-rays. | 248 | 277 | 1,913 | 89 | Proceedings of the Royal Society of London. Series A, Containing Papers of a Mathematical and Physical Character | W. L. Bragg, B. A. |Prof. W. H. Bragg, F. R. S. | article | 6.0.4 | http://dx.doi.org/10.1098/rspa.1913.0083 | en | rspa | 1,910 | 1,900 | 1,900 | 16 | 383 | 10,653 | http://corpora.clarin-d.uni-saarland.de/surprisal/6.0.3/?id=rspa_1913_0083 | 10.1098/rspa.1913.0083 | null | null | null | Atomic Physics | 39.453066 | Optics | 26.305398 | Atomic Physics | [
12.404451370239258,
-79.14070892333984
] | ]\gt ; Mr. W. L. Brag .
The Structure of Some Lastly , though the absorption coefficient of the sten peak has not yet been satisfactorily measured , it may be doubtless supposed to be a little less than that of the A peak of platinmn , since its wave-length is slightly less .
A recent measurement of the latter quantity gives the value and the absorption coefficient of the characteristic radiation of tungsten is given by Barkla as 33 .
The Structure of Some Crystats as Indicated by their Diffraction of -rays .
By W. L BRAG , B.A. ( Communicated by Prof. W. H. Brag , F.R.S. Received June 21 , \mdash ; Read June 26 , 1913 .
) [ PLATE 10 .
] A new method of investigating the structure of a crystal has been afforded by the work of Laue*and his collaborators on the diffraction of -rays by crystals .
The phenomena which they were the first to investigate , and which have since been observed by many others , lend themselves readily to the explanation proposed by Laue , who supposed that electromagnetic waves of very short wave-lengths were diffracted by a set of small obstacles arranged on a ular point system in space .
In the interference pattern obtained with a zincblende crystal , Laue , in his original memoir , came to the conclusion that the primary radiation possessed a spectrum consisting of narrow bands , in fact , that it was composed of a series of six or seven approximately homogeneous wave trains .
In a recent paper I tried to show that the need for assuming this complexity was avoided by the adoption of a point system for the cubic cryStal of zincblende which differed from the system considered by Laue .
I supposed the diffracting centres to be arranged in a simple cubic space lattice , the element of the pattern being a cube with a point at each corner , and one at the centre of each cube face .
A npler conception of the radiation then became possible .
It might be looked on as continuous over a wide range of wave-lengths , or as a series of independent pulses , and there was no any need to the existence of lines or narrow bands in its spectrum .
W. Friedrich , P. Knipping , and M. Laue , ' Miinch .
Ber June , 1912 .
Camb .
Phil. Soc. Proc November , 1912 .
ystals as Indicated by their of .
249 It is the object of this paper to extend the analysis used in the case of the zincblende to some other crystals , particularly those of the simple alkaline halides .
In treating the diffraction of waves by a space point system such as a crystal , that case is the most simple in which the diffraction is caused by a series of points arranged in a space lattice , of one of the 14 Bravais types .
Here every point is identical with every other point of the arrangement , and it is always possible to find an element of the pattern consisting of a parallelepiped with a point at each corner : there will then be as many parallelepipeds as atoms in any space .
The points can be referred to three axes parallel to the edges of the parallelepiped , and if one of the points is taken as the the co-ordinates of the others may be written where are any integers , and are equal to the sides of the parallelepiped , and therefore proportional to the axial ratios of the space lattice .
When the axes are chosen in this way the co-ordinates of the points and the equations of the planes passing through given selections of points are expressed in the simplest manner possible .
Lt a series of pulses fall on this space lattice , the direction of ation yiven relation to the axes of the system .
As any one pulse passes over each point , a diffracted avelet spreads from it , and it will be shown that the wavelets from all the points due to one incident pulse will combine in certain directions to form trains of waves , rise to the patterns of spots appearing in Laue 's diffraction patterns .
This may be done in the way:\mdash ; If the axial ratios of the space lattice be denoted by , any plane which makes intercepts pa , , on the axis being is parallel to a whole set of planes on which the points of the ystem may be considered as arranged .
It is such planes as these which form the faces of a crystal .
When a pulse falls on a set of points on a plane the wayelets from the points combine to build up a wave front which will appear to be regularly reflected from the plane .
As there are a series of planes regularly spaced one behind the other , a single pulse on them gives rise to a reflected wave train .
When therefore a narrow pencil of -rays falls on a section of a crystal , part of its energy is transmitted undeviated , but there is also a part -hich is reflected on the crystal planes .
potentially in the body of the crystal .
is the series of narrow beanls arisio .
reflection in this which gives rise to the pattern of spots in the photograph .
Mr. W. L. Brag .
The Structure of Some There can be to each set of parallel planes integral dices , as when naming the faces of a crystal , and a spot can be classified as being reflected in the set of planes .
Here the integers , are reciprocal to the intercepts which a parallel plane makes on the axis of reference .
They are Millerian indices , the equation of the plane being They may be considered as the parameters of each spot of the pattern , and are exactly eqnivalent to the parameters employed by Laue in his original treatment of the subject .
Lane defines his parameters by that the diffracted wavelet from a point at the of co-ordinates , wave-lengths in the directions under consideration behind the wavelets proceeding from its neighbours along the axes respectively .
Thus the wavelets from all atoms in the plane are in phase with that from the origin , and , in general , the wavelets from all points in the plane integer are in the same phase .
We are led back to the same conclusion as before , that the direction of the diffracted wave front is one in which the primary beam is reflected by planes whose Millerian indices are .
But , as will appear presently , it is important to bear in mind the fact that crystal structure alone fixes the exact position of the interference maxima , quite independently of the existence of homogeneous components of definite length in the incident rays , and therefore a method of treatment has been adopted in which all reference to the wave-length has been avoided .
It is possible for a spot to appear in a position corresponding to reflection in any of planes having integral indices .
In an act , ual pattern obtained by allowing the diffracted -rays to fall on a photographic plate , since there is not an infinite number of spots , only a selection of the planes can be operative .
The spots forming the pattern are of very different intensities , and one can never say that spots are entirely absent but merely that in certain the rays are too weak to make an impression .
It would seem , however , that by classification of the planes which reflect the principal spots ol the pattern a clue can be got to the true point system arrangement of the diffracting centres .
The point system which affords the most simple interpretation of the pattern is that which ought to be taken as representing the crystal structure .
by their of -rays .
251 When a raph has been taken with a crystal an analysis is necessary in order to to each spot of the pattern obtained the correct parameters , the Millerian indices of the face from which the spot is rellected .
Having decided on the axes of reference of the crystal , the method will be to apply whatever their inclinations to each other and axial ratios may be .
The more important planes of the system are those densely packed with points , and from this fact it follows that these planes contain rows along which the points are closely packed .
These are the important \ldquo ; of the crystal , and each of these point-rows will have a set of important planes parallel to it .
The three axes themselves are the most obvious examples of these point-rows .
The " " zone axis\ldquo ; of planes .
to a common zone is also such a direction .
There is a convenient relation betw even the points which are reflected in the planes to any one zone .
The reflected beam always lies on a circular cone with apex at the crystal section , the zone axis as axis , and the direction of the primary beam as one enerator .
This cone cuts the photographic plate in an ellipse through the central point of the pattern , and all spots reflected in planes of the zone lie on it .
The arrangement of the spots on ellipses is very obvious in an interference pattern ( see fig. 11 ) , and the ellipses can immediately be drawn .
A little calculation shows to which zone axis each ellipse must be , and , by marking a given spot as on the intersection of two ellipses , the calculation of the indices , of that spot is made possible .
For each zone of planes we have the relation where is the zone symbol ; that is to say , the set of direction ratios of the zone axis .
When representing diagrammatically an interference pattern it is inconvenient to draw the ellipses at the intersections of which the spots of the pattern lie .
It is simpler to employ an extension of the usual stereorapllic projection of crystallography .
Reference to will make this clear .
Let the section of crystal be situated at , the centre of the sphere represented in the by the circle ABP , and let the direction of the incident rays be from to C. The rays traverse the crystal mdeviated fall on the photographic plate AD at A. Let represent the direction of a zone axis .
The beams reflected in planes of this zone lie on a circular cone with vertex at , of which is the axis , and CA , CB are two generators .
This cone cuts the sphere in a circle of which AB is a dianleter , and by the well known property of the stereographic projection , the projection of this circle on the plane AD from the pole is also a circle .
The centre of this circle is at , since , the point where the zone axis cuts the photographic plate .
Mr. W. L. Brag .
The Structure of Some Let the pattern of spots be supposed to be made by the diffracted beams on the sphere ABP , and this pattern projected on the plane AD from the pole P. Spots to reflection in planes of a zone now lie on a circle , having its centre at the point where the zone axis cuts the plate AD .
The spot at made by the reflected beam CB becomes a spot at of the FIG. 1 .
transformed .
The distortion of the pattern of spots by the transformation is very small except in the yions distant from the centre , and circles are much easier to draw than ellipses .
This has been done in all the diagrams iven in this paper .
In constructing a yram , a point is chosen as that in which the incident rays meet the raphic plate .
This is A in the figure .
Then the points such as , where the principal zone axes meet the plate , are found by a calculation , which is easy when the crystal is placed symmetrically to the pencil of -rays .
A circle is drawn With centre and radius .
This done for each zone axis , the intersections of the circles the stereographic projections of the reflected spots .
Let us take as an example of the application of this analysis the very simple case of potassium chloride .
The diffraction pattern obtained when the X-rays fall normally on a plate cut parallel to the cube face ( 001 ) is reproduced in fig. 2 , Plate 10 , and its stereographic projection in fig. 3 , which shows also the indices of the reflecting planes corresponding to the several points of the photograph .
Potassium chloride is cubic , and the indices given to the planes are those obtained when the edges of the cube are selected as axes of reference .
Crystals as by their of -rays .
253 The circles correspond to zone axes which and their intersections the spots reflected in all planes of the form where and have any of the values , 5 .
In the diagram of the KC1 pattern the spots are represented dots , the nitude of each dot the strength of the spot in the FIG. 3.\mdash ; Potassiu hotograph .
It will be seen how complete the pattern is , and how within a certain range each intersection is represented by a spot in the photograph .
This may be put in another way .
Below is a table of values of and being equal to 1 .
In the square corresponding to given values of and Mr. W. L. Brag .
The Structure of Some ; is placed a dot denoting the magnitude of the corresponding spot , the square being left empty if no spot is to be seen .
Table I. 1 This ) contains a list of all the spots in the raph .
It gests that the diffraction is due to a simple cubic space lattice , for when the elementary parallelepiped is a cube and its are taken as axes the indices of the planes naturally take these simple For , let a series of planes be taken , for which two indices are constant and one varies , such as the series 031 , , 231 , 331 , 431 , etc. These planes will be arranged in this order for all their properties , such as reticular density , distance apart , and so forth , if , and only if , the indices are referred to axes parallel to the sides of the elementary parallelepiped .
If this condition is satisfied , then all the properties of the planes vary in an orderly manner as one passes along the series .
The power of reflecting the -rays- is a particular property of the planes , which is seen from the to vary con- tinuously for any such series as the one iven above , therefore the diffracting system is a space lattice with axes at right angles , and a cube for its elementary parallelepiped .
It may be objected here , that it is conceivable that a complex structure , and a radiation consisting of eneous components , just happen in the case of potassium chloride to hoive a deceptively simple pattern .
That this is not the case can be seen by the crystal from its symmetrical position , and obtaining the distorted interference pattern .
It is still as htforward as before , of course no symmetrical .
Correspots in the two patterns are now made by different wave-lengths , and it is obvious that there can be nothing of the nature of homogeneous components of the incident radiation .
The contrast of this pattern with those characteristic of potassium bromide and iodide , of rock salt , and of inchlende , which will shortly be given , will tend to make this more clear .
Crystats as Indicated by their of -rays .
All the most intense spots of the raph are at about the same tance from the centre of the pattern .
A circle can be drawn such that the spot , which lie near to it are very intense , while those further away are weaker and those at great distances are too faint to appear .
All ellipse intersections near this circle are represented by a spot .
Those planes reflect most for which lancing a. lies between and and it is in seeking to explain this fact that it is necessary to consider the question of the\ldquo ; \ldquo ; of the diffracted rays .
This we must now do .
When a pulse falls on a series of planes arly spaced one behind the other , it is reflected as a way train , and the waves any one spot must be considered to be of the iven by where distance bveen successive planes , and an integer 1 , 2 , 3 , etc. An alternative way of arding the phenomenon is to consider the incident radiations as compounded of homogeneous of all , with a characteristic stribution of in the spectrum , when the parallel planes must ) considered as reflecting only that part of the spectrum for which the relation holds .
In the case of the cubic space lattice considered here , this relation reduces wherea is the distance between hbouring points the cnbic for a simple calculation shows that .
Since is equal to unity for all the spots of the potassium chloride photograph , spots which have the same , and lie at the same distance from the centre of the pattern , correspond to the same wave-length .
The ring of intense spots in the pattern indicates reflection of a certain part of the spectrum of the incident radiation .
Either conditions are for this , or the incident rays have a large of their energy in this part of the spectrum .
It is interestin to comp-are the simple pattern of otassium chloride with those of potassium iodide , potassium bromide , fluorspar , and zincblende .
The stereographic projection of KBr ( 100 ) is given in , that of KI being very similar .
Both of these are like the of zincblende and fluorspar , and are in marked contrast to that of * The most important condition in this connection is probably the thickness of the crystal section used .
As will be sllown later , the use of a crystal section -ours the reflection of the longer wave-lengths , spots coming out hile the use of a thick section favours the reflection of the shorter .
Mr. W. L. Brag .
The Structure of Some It is evident that some factor has now entered which destroys the simplicity of the arrangement of spots characteristic of potassium chloride .
Spots no appear at every intersection of the ellipses within a certain region , as FIG. 4.\mdash ; Potassium bromide .
in .
A tabulation of the intensities of the spots in the zincblende and potassium bromide patterns will make this clear .
( See Tables II and III .
) There are also in the case of zincblende several spots for which a value 3 must be to , if and are to be , but not many .
It was a consideration of Table II which led in a former paper*to the conclusion that the diffracting centres of the zincblende crystal are arranged on the facecentred cubic space lattice .
An examination of the planes in which reflection takes place shows that there is a differentiation between those whose .
indices are wholly odd and ' Camb .
Phil. Soc. Proc November , 1912 .
Crystats as Indicated by their Diffraction of -rays .
257 Table II .
Table III .
K.Br .
those which have one or more even indices .
If those planes alone are considered which have odd indices , as in the following table , the scheme is as complete as it was for the spots of the KC1 crystal .
Table Table Zn .
I3 5 9 Odd planes , .
Even planes , The same is true for those with an even index*except that the intense spots are all further removed from the centre of the picture .
This difference can be explained without our being forced to assume that the diffracting system is more than a simple system of identical poin It is sufficient to suppose that the point system has points at the centres of the ( jube faces as well as at the cube corners .
Let a cubic point system of the first kind be taken which has points at cube corners alone , and let points be introduced at the cube face centres in order to turn it into a * The spot 041 forms an exception , indeed evidence is not lacking that the assumption of diffraction by the face-centred space lattice does not completely account for the pattern .
The reason for this will appear when the parts played by the atoms of two kinds in the diffraction are discussed .
Mr. W. L. Brag .
The Structure of Some point system of the so-called " " third kind ( The " " second kind\ldquo ; is the centred cube .
) The spacing of the planes which have odd indices is not altered by the introduction of the new points , for they all lie on the original planes and only increase their point density .
On the other hand , in the case of planes having an even index , some of the new points lie halfway between the planes , the distance between the successive planes of this type must now be halved , and so must therefore the wave-lengths of the reflected beams .
The interpretation of the zincblende pattern is now simple .
We have seen that the planes with odd indices only are a complete set .
Ihere are fewer spots corresponding to reflection in planes with an even index , for these planes are , relatiyely to the former , less closely packed , and of a more complex nature .
Moreover , they are , at the same time , less widely separated , and therefore the intense spots with even indices are further from the centre ; the angle of incidence must be increased in order to make these planes reflect that region of the spectrum which gives intense spots .
By assuming the third cubic space lattice instead of the first , all the intense spots of the pattern again correspond to the same The difference between the diffraction by the two cubic space lattices may be put in a much clearer way on analysis of the patterns of threefold symmetry , obtained when the incident rays fall normally on a plate cut perpendicular to a trigonal axis .
If the points of the space lattices are considered from this aspect , they are special cases of the } rhombohedral space lattice , one of the Bravais types .
The axes to which the spots ought to be referred are not the same for the two cubic lattices .
When the points are at cube corners alone , the axes ( which they are nearest neighl ) ours are the cube edges , and the cube itself is the elementary parallelepiped .
When there are also points at the centres of the cube faces , three onals of cube faces meeting in a corner form three edges of the e]ementary parallelepiped .
The angles between the axes are angles in the first case , in the second they are . .
It will now be clear that when the stereographic diagram is constructed , giving the positions of the spots reflected from the simple planes of a rhombohedral space lattice , one such diagram will represent the patterns of all rhombohedral lattices , the alteration of the angle between the axes , i.e. , the rhombohedral angle , onlycausing an alteration of the scale of the diagram .
The radius of the sphere used in the projection is , of course , supposed to be always the same .
Given the points where the three axes of the lattice meet the rame , the corresponding points for the other zone axes can immediately be found and by their Di .
ff'raction of -rays .
259 the whole diagram drawn .
Such a diagram is shown in these axial points , Now , our study of the patterns of fourfold symmetry given by potassium chloride and zincblende has shown that the axes of the lattice , which is from this aspect a special case of the rhombohedral lattice , make angles of with each other in the first case , and of in the second .
Therefore it ought to be possible to refer the threefold patterns of potassium chloride and zincblende to the same trigonal lattice diagram , the scale being different , however , in the two cases .
This conclusion is exactly confirmed by experiment .
The pattern given by zincblende was published by Laue in his original memoir .
The stereographic projections of the zincblende and potassium chloride patterns are given in figs. 6 and 7 .
The ob , of this comparison is to show that the spots of the KC1 pattern fall naturally on Mr. W. L. Brag .
The Structure of Some a diagram twice the size of that on which the spots of the pattern are , the points where the axes making with each other cut the plate , being just twice as far apart as for axes making with each other .
FI 6.\mdash ; Zincblende .
The following table will illustrate the awkwardness of referring either pattern to the wrong diagram .
If the spots of the zincblende pattern are referred to the cubic axes , their indices become very much more complicated , and the pattern is no longer complete .
The converse is true for the potassium chloride pattern , the indices in this case simpler when referred to cubic axes .
In Table a list of indices of the spots of each pattern is set down referred to ( A ) the cube edges , ( B ) the cube face onals , i.e. , three edges of the regular tetrahedron , as axes .
It will be seen that in the case of zincblende it is the series , in the case of the potassium chloride the A series , which is simple , and which gives a complete series of indices over a certain range .
I do not think there can be any doubt which space lattice is the right one in either case .
Crystafs as Indicated by their Diffraction of -rays .
261 FIG. 7.\mdash ; Potassium chloride .
Table * The indices of the A series for the KC1 pattern may not , at first sight , appear simpler than those for the series .
] series , however , is curiously incomplete .
For instance , and occur but no and but no and 312 but no 322 .
In fact , there is tendency for the sum of the indices to be even , and such a selection of the simple planes as thi always implies that the wrong axes have been taken .
In the list for , indices such as ( 622 ) are intermediate between and Mr. W. L. Brag .
Thae Structnre of Some In the case of rock-salt , it is not possible to regard the pattern as completely characteristic of the one point system or the other .
obtained a thin section of crystal , ) mm. thick , cut parallel to a cube face , show a pattern very similar to that given by potassium chloride , in no case are they so simple as the pattern given by the latter crystal ; for a considerable amount of difference between the " " odd\ldquo ; FIG. 9.\mdash ; Rock-salt , mm. thick .
and " " even\ldquo ; planes is also evident .
A photograph taken with a section 6 mm. in thickness is more like one taken with potassium bromide or iodide , the difference between odd and even planes being more marked .
In fig. 8 , Plate 10 , is reproduced a photograph taken with a section of rock-salt , mm. thick , cut parallel to a face ( 100 ) , and in fig. 9 its stereographic diagram .
In the tables on the next page are set down the intensities of the spots when different thicknesses of crystal are used .
Crystals as Indicated by their action of .
263 Table .
Table VIII .
Table IX .
mm. , 1 mm. mm. I think these tables , especially the first one , that the rock-salt diffracting system is in some way intermediate between those of potassium chloride and potassium bromide .
The change of intensity of the spots with the thickness of the crystal is interesting .
It may be laid down as a general rule that increasing the crystal thickness increases the intensity of the inner spots as compared with that of the other .
This is to be expected , for the inner spots represent the shorter and more penetrating radiations .
If in passing through a thickness of the crystal a proportion of the radiation of a certain wave-length is reflected , and if the absorption coefficient of the radiation in the crystal is , then the radiation reflected in a slip of crystal of thickness will be proportional to to a rough approximation .
This is a maximum when , and since is very small , this means that to get a spot strongly marked a section of crystal should be used of such thickness that it absorbs a fraction of the incident radiation of that wave-length .
This would explain qualitatively the variation with thickness of crystal of the intensity distribution over the spots which is actually observed .
On comparing the evidence as to the nature of the systems in these crystals of sodium chloride , and of potassium chloride , bromide , and iodide , it seem that a very simple explanation of their curious difference may be arrived at when it is considered that in each case diffraction is caused by two different atoms , and that the relative efficiencies of the two vary from crystal to crystal .
Any explanation of these differences would be an extremely improbable one which did not assume a similar structure for the whole group of alkaline halides , for these crystals resemble each other very closely in their properties .
Yet it has been seen that the space lattice of diffracting points is the simple cubic one in ; it is the facecentred cubic lattice in KBr and , and that in the case of the VOL. LXXXIX.\mdash ; A. Mr. W. L. Brag .
The Structure of Some diffracting point system is in some way intermediate between the two space lattices .
Let us consider on what atomic properties the relative efficiencies might depend .
It has been firmly established that the absorption of -rays depends on the relative proportions of the various elements contained in the absorber .
It is a purely additive property of the weight of each element per cubic centimetre of the absorber , and does not depend on the manner in which the elements are combined .
Also the absorption of homogeneous X-rays increases steadily with the atomic weight of the absorber , except for a sudden discontinuity consisting of a large drop in the absorption coefficient when the atomic weight of the absorber passes through that of the element of which the eneous -rays are the characteristic radiation .
There are , however , no discontinuities in the absorption coefficient corresponding to the changes in chemical properties of the elements in the periodic table as one passes to higher atomic weights .
It is reasonable , therefore , to assume sionally that the weight of the atom in the main defines its effectiveness as a diffracting centre , and that two atoms of equal weight are equally effective .
In the case of potassium chloride the atoms of potassium and chlorine , of atomic weight 39 and respectively , are sufficiently close in atomic weight to act as identical diffracting centres .
For rock salt this is no longer true ; the atomic weight of sodium and chlorine differ considerably ( to 23 ) , and complications are introduced into the simple pattern characteristic of potassium chloride .
In potassium bromide and iodide one atom preponderates so greatly over the other in atomic weight that the diffracting system consists practically of atoms of one kind only , and the pattern can again be assigned to a simple space lattice , but one which is of a different nature to that of potassium chloride .
Yet the atoms of alkaline metal and halogen have precisely the same arrangement in all these cases .
Let us distinguish between two kinds of diffracting points by calling them black white .
Then the points must be arranged in such a way that\mdash ; 1 .
There are equal numbers of black and white .
2 .
The ement of points black and white taken all together is that of the first cubic space lattice .
3 .
The arrangement of blacks alone or of whites alone is that of the third cubic space lattice .
An arrangement which gives this result is shown in fig. 10 .
In this diagram we may associate black centres with the alkaline metal , and white with the , or vice versed .
The space lattice formed by the whites is the same as that formed by the blacks , being in each case the Crystals as by their of .
265 centred cube .
If black and white centres become identical , as in potassium chloride , the diffracting lattice becomes the simple cubic one .
The evidence for this arrangement in the alkaline halides seems very Strong .
' but this does not by any means complete the solution of their structure .
It yet remains an open question whether one atom alone is to be associated with each point of the system , so that , for example , the black and white centres actually represent sodium and chlorine atoms in rock , or whether the crystal structure is of a more complex nature .
It was with the object of the complexity of the unit of these and other crystals that the series of crystal pattern analyses , which will now be described , were made ; their results would seem to indicate clearly the association with each diffracting centre of a single atom .
It was shown above that the , giving the position of spots reflected in the planes of a trigonal rhombohedral lattice , is the same except for scale for lattices of any rhombohedral angle .
The completeness with which the spots of the zincblende pattern whose projection is iven in fig. 6 represent the intersections of the circles of the for the lattice would gest that in all cases in which centres were on a trigonal lattice , the pattern obtained would be very much the same .
At all events , this would be so when the rhombohedral angle is not very different from .
That this is actually the case is well shown by the stereographic projections in figs. 12 and 13 .
They are the projections of photographs taken with sections of fluorspar and calcite , cut perpendicular to a trigonal axis , the fluorspar photograph being given in fig. 11 , Plate 10 .
It is clear that in this case also , as in that of zincblende , every simple plane of the lattice reflects a spot when the angle of incidence lies within a certain range .
Corresponding spots in the three rams vary very much in intensity , but this is to be expected .
The point which it is desired to Mr. W. L. Brag .
The Structure of Some make clear is the certainty with which the correct axes of the lattice may be found from a study of the pattern .
In the case of fluorspar , that of zincblende , the rhombohedral angle of these axes is .
In the case of calcite it is slightly greater , a calculation of this angle and a comparison of the orientations of crystal and pattern making it clear that the axes of the lattice are three diagonals of rhombohedron faces meeting in an obtuse corner of the calcite rhombohedron , not the of the rhombohedron , FIG. 12.\mdash ; Fluorspar .
which are generally taken as the axes to which the faces of a calcite crystal are referred .
In these three cases , zincblende , fluorspar and calcite the diffracting centres are thus arranged on one space lattice .
But , since a space lattice is an arrangement in which each point is related to its neighbours in exactly the same way as every other point , it would be impossible to arrange complex molecules in a space lattice unless ] one point in each molecule is effective .
It is difficult to avoid the conclusion by their on of -rays .
267 that the molecule acts as a single point because it contains in each case one atom of much greater atomic weight than the others .
A comparison with.a case in which this is not so is afforded by the rock-salt pattern of threefold symmetry given in fig. 14 and Plate 10 , fig. 15 ; it will be seen how awkwardly it fits the diagram .
There is a certain want of symmetry in the figures , which must not be confused with the want of fit .
Its pattern is , in fact , intermediate between that characteristic of axes of rhombohedral angle FIG. 13.\mdash ; Calcite .
at and that of axes at , just as was the case with its pattern of fourfold symmetry .
Having found the nature of the simple*diffracting lattice in these three cases and that of the alkaline halides , the final step in the ument which would assign a single heavy atom to each diffracting centre is made below by a comparison of the scale of their lattices , that is , a comparison of the length of the sides of the elementary parallelepiped for different crystals .
Since the diffraction is caused by the heavy atoms , and there is only one in Mr. W. L. Brag .
The Structure of Some each molecule , this conclusion , if correct , will mean an association of one molecule with each parallelepiped of the lattice .
In a paper to the Royal Society , read in April , a method was described of analysing the radiations from an -ray bulb by reflecting them from the face of a crystal , and measuring the ionisation produced by the reflected beam .
The apparatus devised for this purpose resembled a spectrometer ; the 14.\mdash ; Rock-salt .
crystal was set on a revolving table at the centre of the instrument , and irradiated by a narrow beam of -rays passing through a collimator slit .
The reflected beam was received , and its ionisation measured , in a chamber mounted like the spectrometer .
By means of this instrument it was possible to measure the strength of the reflected beam when an approximately constant beam of rays fell on the face of the crystal ab varying angles of incidence .
The results of the measurement made with a crystal face may be summed up in a curve , in which the strength of the * W. H. Brag and W. L. Brag , ' Roy .
Soc. Proc July 1 , 1913 .
as by their ffraction of .
269 reflected beam is plotted against the glancing at which the fell on the crystal .
With most crystals , such a curve shows that at all angles there is a general reflection of the rays , the reflection being much stronger at the more angles .
Superimposed on this , as it were , there is at certain very sharply defined angles a special reflection of very great intensity as compared with the general reflection .
This special reflection shows itself as very marked peaks on the curve , the amount of ionisation in the chamber becoming perhaps 20 times as great as the chamber is } the region of peak , and then away to its normal value again , the whole taking place within settings a degree apart .
The results which we obtained with various crystals pointed to the existence of at least three components of the -ray beam of definite wavelength , reflected from a crystal face when the condition is satisfied for the component and crystal in question .
Here is the wavethe , and the distance between successive planes of the crystal structure parallel to the reflecting face .
The ntunber represents the " " order\ldquo ; of the reflection , for several peaks , which can be nised as to the same homogeneous radiation by the identity of their absorption coefficients , appear at a series of angles whose sines are in the ratio 1 : 2 : 3 .
It will possibly be objected here , that in the previous discussion of the interference patterns , the spectrum of the incident radiation has been taken to be continuous , the simplicity of the chloride Taph supporting the view ; while here direct evidence of the existence of homofeneous components of the radiation has been obtained .
This difficulty disappears when -lengths to be yned to the spots of the interference pattern , and to the peaks of the curve , are compared .
For instance , in the potassimn chloride pattern of fourfold symmetry the spot formed by the longest waves is reflected in the planes ( 221 ) , and if is the side of the elementary cube of the lattice of this crystal , the -length to be associated with the spot , from the formula is equal to .
On the other hand , the ) to the homogeneous radiation of shortest is reflected from the face ( 100 ) of the same crystal at an of about , and corresponds to a wave-length nearly .
The spots of the pattern thus correspond to a region of the spectrum well inside the peaks on the reflection curve , and , in eneral , this is true for all the patterns .
The reflection curve , indeed , bears Mr. W. L. Brag .
The Structure of Some out well the assumptions as to the continuous nature of the spectrum of the radiation giving the spots , for at all angles less than a strong reflection takes place which only falls away slowly as the glancing angle is increased .
The very fact that in most photographs the incident rays are parallel to an axis of symmetry ensures that no important planes occur making such an with the primary rays as to reflect the homogeneous components .
It is possible to nise the same three peaks , which will be referred to as , in the curves drawn for reflection in the faces of almost all crystals which have been tried .
They are always of approximately the same relative height , they have each a characteristic absorption coefficient , and they are spaced in the same way on the curves .
There appears to be no doubt that three lines*exist in the spectrum of the incident radiation , which give rise to the peaks .
This being so , one has a means of finding with some accuracy the ratio of the values of , the distance between successive planes of the structure , for different crystals and different faces of the same crystal .
angles at which these peaks are reflected from the various faces of a crystal , and from faces of different crystals , thus afford a great insight into the cry stal structure ; and , in fact , they supply just that information concerning the structure which the interference patterns do not , for by their means the dimensions of the lattices of different crystals can be accurately compared .
The interference patterns only supply information the nature of the lattices .
An analysis of the results obtained when different faces of the same crystal are used to reflect the -rays in the spectrometer will show how this comparison is carried out .
In the curves for reflection from the three primary planes of the rock-salt crystal ( 100 ) , ( 110 ) , ( 111 ) , ( two of which are shown in fig. 16 ) , the peaks occur for each face , but at different angles .
From the equation being the angle for the peak of the first order in each case , we have , for these three faces ' where is the distance between planes parallel to the face ( 100 ) , the angle at which the most prominent peak is reflected from the same face .
* By using narrow slits in the reflection apparatus , evidence of the existence of more than three lines has been obtained , the and peaks being really double .
See fig. 16 .
Crystals as Indicated by their Diffraction of -rays .
The angles for these three faces are .
This gives the result whereas 1 : : : 1 : these being the theoretical relations for the face-centred cubic space lattice .
This does not comprise all the information which a study of these three curves yields , they will be analysed more carefully below .
For the present , it is sufficient to indicate what strong reasons there are for assuming that the distances for the various faces can be accurately compared , by finding the at which these peaks occur .
It has been seen that the patterns ( given by potassium chloride , zincblende , fluorspar , and calcite can be ascribed to diffraction by points of a space lattice .
It is now desired to compare the dimensions of the lattices of these crystals ; since the absolute value of the wave-length of the radiation which forms the peaks is as yet unknown , the dimensions of each lattice will be expressed in terms of as unit .
Since now both the form and the dimensions ( in terms of ) of the elementary parallelepiped are known , for the space lattice arrangement of Mr. W. L. Brag .
The Structure of Some diffracting centres of these crystals , it is possible to calculate the volume of this parallelepiped ; the volume is that associated with each point of the lattice , it is the inverse of the number of points per unit volume .
A multiplication of this volume by the density of the crystal gives the mass associated with each diffracting centre , and it is to be expected that the comparison of these masses ( for different crystals ) will give some idea as to whether the centre consists of atoms , molecules , or groups of molecules .
The results of these calculations for the various crystals are set forth in the table below:\mdash ; In this table\mdash ; angle of peak , 1st order .
distance between planes parallel to the face investigated .
volume of elementary parallelepiped , calculated from this value of and a knowledge of the nature of the lattice .
density of crystal .
molecular weight of substance .
Table X. The last column gives the value of , the mass associated with each diffracting centre divided by the molecular weight of the substance .
This quantity is , therefore , proportional to the number of molecules associated with each centre .
For each of these crystals , with the exception of potassium chloride , this quantity is the same within the errors*of experiment , showing It must be remembered that in calculating this quantity , any percentage error in the value for is trebled , since is raised to the third power .
as Indicated by their of .
273 that in all these crystals the number of molecules associated with each diffracting centre is the same .
Taking into consideration the very different constitution of these crystals , this fact seems to point to the association of one molecule , one alone , with each diffracting centre ; and since in zincblende , fluorspar , and the molecule contains only one heavy atom , the conclusion is arrived at that the space lattice which the pattern inffiicates is that formed by the individual zinc or calcium atoms of these crystals .
Potassium chloride forms an apparent exception to this rule , for it has a value for half that given by the other crystals .
The reason for this is clear when it is remembered that in potassium chloride there are two atoms of very nearly equal atomic weights .
Each molecule provides two diffracting centres , these arranged on the simple cubic space lattice .
The mass associated with each centre is not that of a molecule , but half of this quantity , and again it is single atoms , but now of two kinds , which form the points of the diffracting space lattice .
It is clear that the argument given here cannot pretend to be a complete proof of this important point .
It is conceivable , for example , that in all these crystals it just happens that the molecules are grouped together in fours , and that these groups form the centres .
It is easy to picture such an arrangement for the alkaline halides , in fact this is the arrangement given to all such binary compounds by the theory of closest by Pope and Barlow .
Their arrangemenc would explain satisfactorily the patterns and peak relations of rock-salt , zincblende , and potassium bromide and iodide , for the black and white centres of the diagram given in are represented by tetrahedra composed four spheres corresponding to atoms of either nature .
This would also involve , however , the grouping in fours of the calcium atoms in calcite , and considerable difficulty is experienced in an arrangement which does this .
A similar difficulty arises in the case of fluorspar .
Potassium chloride is also hard to account for on this arrangement , if it is granted that in this substance potassium and chlorine act almost identically on the -rays , for the atoms are in the closest packed arrangement of the face-centred cube , while the diffraction pattern is characteristic of the simple cubic lattice .
Many more comparisons of crystals are necessary to confirm this point , in the meantime it will be assumed that the simple structure correctly represents the truth , and that the diffracting centres are single atoms .
It has been seen how the comparison of the angles of reflection of a peak from various faces of the same crystal gives information concerning the space lattice structure of the crystal .
Further information can be got by studying the dimensions of these peaks .
For instance , the curves for two of the three Mr. W. L. Brag .
The Structure of Some primary planes ( 100 ) , ( 110 ) , ( 111 ) of rock-salt are given in fig. and a reference to these curves will show the very marked difference which there is between the curves for the face ( 100 ) and that for the face ( 111 ) .
The ( 100 ) curve shows very marked.first-order peaks , much smaller second-order peaks , and the merest indication of the peaks of the third order .
The ( 111 ) curve on the other hand shows the second-order peaks very much stronger than those of the first order .
This difference of the curves corresponds to a difference in the nature of the planes parallel to these faces of the crystal .
In the arrangement of black and white points given in fig. 8 , it will be seen that the successive planes parallel to ( 100 ) contain equal numbers of black and white points ; the same is true for the planes ( 110 ) , which also give a first-order reflection .
The planes parallel to ( 111 ) , on the other hand , contain alternately all blacks and all whites .
The black points alone form a face-centred lattice , for which the ( 111 ) planes are further apart than the ( 100 ) planes in the ratio .
Thus small first-order peaks reflected from the ( 111 ) face of rock-salt correspond to a periodicity of black planes alone , parallel to ( 111 ) , the planes containing the heavy chlorine atoms .
The presence midway between these planes of the planes containing sodium atoms does not completely destroy this reflection of the first order , but it goes a way towards doing so , while of course the reflection of the second order is reinforced and ives a large second-order peak .
This explains the abnormal relative magnitudes of the ( 111 ) peaks of different orders as compared with those reflected from the faces ( 100 ) and ( 110 ) .
In accordance with this , it is found that if the sodium is replaced by potassium , the first-order peak reflected from the ( 111 ) face becomes too small to be detected , the ( 111 ) curve for sylvine appears to have a peak of the first order , at an angle , to planes as far apart as the planes parallel to ( 100 ) .
In fact , the peaks are where they should be for the simpIe cubic space lattice .
This argument may be summed up as follows : The arrangement of the heavy atoms of these crystals ( potassium chloride with its two equal atoms being an exceptional case ) is that of the space lattice which is the skeleton of the crystal , one molecule containing one heavy atom being associated with each point of the lattice .
The first order peaks of the reflection curves are in the positions which theory would give for this space lattice , but the relative nitudes of the peaks of the first and second orders on any curve are influenced by the positions of the lighter atoms in the crystal structure .
If * For the experimental evidence in support of this part of my argument I am indebted to my father .
Crystals as Indicated by their ffraction of -rays .
275 these lighter atoms are so disposed as to lie on the planes of the heavy atom space lattice parallel to the face ated , then the reflection curve may be said to be of the normal type , it will have ) eaks of the first order and small ones of the second .
If the hter atoms are arranged on planes situated halfway between the planes of the lattice , the first-order peaks will be dimimshed and those of the second order reinforced .
The curves for the faces ( 100 ) and ( 111 ) of fluorspar show this effect in a very marked manner .
This crystal has as its skeleton the facecentred cubic lattice , the points of the lattice being represented by the calcium atoms .
The fluorine atoms are so disposed that the reflection from , .
and FIG. 17 .
the ( 111 ) planes is now of the normal type , in strong contrast to the curves for rock-salt .
On the other hand , the first-order reflection from the face ( 100 ) has almost disappeared .
The fluorine atoms must be arranged so as to lie on or near the ( 111 ) planes of the fundamental lattice , not on the planes ( 100 ) as are the sodium atoms of rock-salt .
The calcite curves iven in fig. 16 show that for this crystal it is the ( 100 ) planes which normal reflection , the curve for the face ( 111 ) beinero very like that for the face ( 111 ) of rock-salt .
It is hoped that an examination of the reflection from various faces of all these crystals may lead to the discovery of the exact positions of the hter atoms in the crystal structure ; as yet the experimental results are very incomplete .
The results obtained so far seem to fix with some certainty the arrangement of the heavy atoms of these simple crystals , and in the case of the alkaline halides it is hoped that the positions to atoms of both kinds are at any rate close approximations to the truth .
A slight metrical distortion of the arrangement , which would reduce the crystal symmetry , would not affect any of the results which have been obtained here .
The analysis of crystal structures given here was initially lertaken with 276 Crystal Structure as by Diffraction of the object of discovering the absolute wave-length in centimetres of the geneous radiations issuing from the -ray bulb .
The positions of the peaks on the curves gave the wave-length of the corresponding radiations in terms of the dimensions of the crystal space lattice .
As long as the complexity of the unit associated with each point of the lattice is unknown , the absolute wave-length cannot be calculated .
If the arrangement here assigned to the alkaline halides is , the dimensions of the lattice can be given in centimetres , for the mass associated with each centre of the lattice can be calculated from the known mass in grammes of the hydrogen atom .
For rock-salt , mass of 1 molecule of ; therefore cm .
From the value for , and that for fiven in Table X , the dimensions of the lattice for any crystal in this table can be calculated .
Summary .
For a numb of simple crystals the interference patterns can be ascribed to diffraction of a " " white\ldquo ; radiation by a set of points on a space lattice .
Each of these points is a single atom ; if one atom in the molecule is at east twice as heavy as any of the others , it is the lattice formed by these atoms alone which the diffraction pattern reveals .
Two atoms of nearly the same atomic weight are nearly equivalent as diffracting centres .
The lighter atoms of the molecule are not grouped closely round the heavy atom forming the diffracting space lattice , but occupy intermediate positions .
For instance , in sodium chloride the sodium atom has six neighbouring chlorine atoms equally close with which it might pair off to form a molecule of NaCL The reflection curves and interference patterns given by the alkaline halides agree in assigning the same structure to these salts , the atoms being arranged on a simple cubic space lattice in such a way that rows parallel to the cubic axes contain alternate atoms of either kind .
The association of a single heavy atom with each point of the space lattice is indicated by the fact that the mass of each point is proportional to the molecular weight of the substance when each molecule contains one heavy atom .
This relation is got from the reflection curves of different crystals .
A knowledge of the mass of a hydrogen atom makes it possible to calculate the actual dimensions of a crystal lattice , and so to find the wave-length in centimetres of the homogeneous components of the -ray beam , this being the object for which these analyses of crystal structure were undertaken .
L. Brag .
6 .\mdash ; Potassium FIG. 11 .
\mdash ; Flnorspar .
floy . .
Proc. , , vol. 89 , Plate 10 .
FIG. -salt , ) mm. thicl FIG. \mdash ; Rock-sadt .
The Structure of the Diamond .
In conclusion I should like to express my indebtedness to Prof. Pope for his sympathetic interest and generous assistance .
Dr. Hutchinson , with the greatest kindness , has overcome the only experimental difficulties connected with this subject by supplying the necessary crystal sections ; but for his help it would have been impossible to obtain the very large umber of photographs used in the investigation .
These were obtained at the Cavendish Laboratory , and I wish to thank Prof. Sir J. J. Thomson for his kind interest in the experiments .
The measurements with the -ray spectroscope were , as already stated , made by my father in the laboratory of the University of Leeds .
The Structure of the By W. H. BRAG , M.A. , F.B.S. , Cavendish Professor of Physics in the University of Leeds , and W. L. BRAG , B.A. , Trinity , Cambridge .
( Received July 30 , 1913 .
) There are two distinct methods by which the -rays may be made to help to a determination of crystal structure .
The first is based on the Laue raph and implies the reference of each spot on the photograph to its proper plane within the crystal .
It then yields information as to the positions of these and the relative numbers of atoms which they contain .
The -rays used are the heterogeneous rays which issue from certain bulbs , for .
example , from the commonly used bulb which contains a platinum anticathode .
The second method is based on the fact that homogeneous X-rays of are reflected from a set of parallel and similar crystal planes at an ( and no other angle ) when the relation is fulfilled .
Here is the distance between the successive planes , is the glancing which the incident and reflected rays make with the planes , and is a whole number which in practice so far ranges from one to five .
In this method the -rays used are those homogeneous beams which issue in considerable intensity from some -ray bulbs , and are characteristic radiations of the metal of the anticathode .
Platinum , for example , emits several such beams in addition to the heterogeneous radiation already mentioned .
A bulb having a rhodium anticathode , which was constructed in order to obtain a radiation having about half the wave-length of the platinum characteristic
|
rspa_1913_0084 | 0950-1207 | The structure of the diamond. | 277 | 291 | 1,913 | 89 | Proceedings of the Royal Society of London. Series A, Containing Papers of a Mathematical and Physical Character | W. H. Bragg, M. A., F. R. S. |W. L. Bragg, B. A., | article | 6.0.4 | http://dx.doi.org/10.1098/rspa.1913.0084 | en | rspa | 1,910 | 1,900 | 1,900 | 15 | 199 | 5,179 | http://corpora.clarin-d.uni-saarland.de/surprisal/6.0.3/?id=rspa_1913_0084 | 10.1098/rspa.1913.0084 | null | null | null | Atomic Physics | 47.715126 | Optics | 19.113703 | Atomic Physics | [
12.254157066345215,
-79.78463745117188
] | ]\gt ; The Structure of the Diamond .
In conclusion I should like to express my indebtedness to Prof. Pope for his sympathetic interest and generous assistance .
Dr. Hutchinson , with the greatest kindness , has overcome the only experimental difficulties connected with this subject by supplying the necessary crystal sections ; but for his help it would have been impossible to obtain the very large umber of photographs used in the investigation .
These were obtained at the Cavendish Laboratory , and I wish to thank Prof. Sir J. J. Thomson for his kind interest in the experiments .
The measurements with the -ray spectroscope were , as already stated , made by my father in the laboratory of the University of Leeds .
The Structure of the By W. H. BRAG , M.A. , F.B.S. , Cavendish Professor of Physics in the University of Leeds , and W. L. BRAG , B.A. , Trinity , Cambridge .
( Received July 30 , 1913 .
) There are two distinct methods by which the -rays may be made to help to a determination of crystal structure .
The first is based on the Laue raph and implies the reference of each spot on the photograph to its proper plane within the crystal .
It then yields information as to the positions of these and the relative numbers of atoms which they contain .
The -rays used are the heterogeneous rays which issue from certain bulbs , for .
example , from the commonly used bulb which contains a platinum anticathode .
The second method is based on the fact that homogeneous X-rays of are reflected from a set of parallel and similar crystal planes at an ( and no other angle ) when the relation is fulfilled .
Here is the distance between the successive planes , is the glancing which the incident and reflected rays make with the planes , and is a whole number which in practice so far ranges from one to five .
In this method the -rays used are those homogeneous beams which issue in considerable intensity from some -ray bulbs , and are characteristic radiations of the metal of the anticathode .
Platinum , for example , emits several such beams in addition to the heterogeneous radiation already mentioned .
A bulb having a rhodium anticathode , which was constructed in order to obtain a radiation having about half the wave-length of the platinum characteristic Prof W. H. Brag and Mr. W. L. Brag .
rays , has been found to give a very strong homogeneous radiation consisting of one main beam of wave-length c , and a much less intense beam of wave-length cm .
It gives relatively little hetero- geneous radiation .
Its spectrum : as given by the ( 100 ) planes of rock-salt , is shown in fig. 1 .
It is very convenient for the application of the second method .
Bulbs having nickel , sten , or iridium anticathodes have not so far been found convenient ; the former two because their homogeneous radiations are relatively weak , the last because it is of much the same FIG. l.\mdash ; Spectra of rhodium rays : 100 planes of rock-salt .
wave-length as the heterogeneous rays which the bulb emits , while it is well to have the two sets of rays quite distinct .
The platinum homogeneous rays are of lengths somewhat greater than the average wave-length of the general heterogeneous radiation ; the series of eneous iridium rays are very like the series of platinum raised one octave higher .
For convenience , the two methods may be called the method of the Laue raph , or , briefly , the photographic method , and the reflection method .
The former requires heterogeneous rays , the latter homogeneous .
The two methods throw light upon the subject from very different points and are mutually helpful .
The present paper is confined almost entirely to an account of the application of the two methods to an analysis of the structure of the diamond .
The diamond is a crystal which attracts investigation by the two new methods , because in the first place it contains only one kind of atom , and in the second its crystallographic properties indicate a fairly simple structure .
We will consider , in the first place , the evidence given by the reflection method .
The diagram of fig. 2 shows the spectrum of the rhodium rays thrown by the ( 111 ) face , the natural cleavage face of the diamond .
The method of obtaining such rams , and their interpretation , are given in a preceding This value is deduced from the positions of the spectra of the rhodium rays in the ( 100 ) planes of rock-salt on the assumption that the structure of rock-salt is as recently described ( see preceding paper ) .
The Structure of the paper .
* The two peaks marked constitute the first order spectrum of the rhodium rays , and the angles at which they occur are of importance in what follows .
It is also a material point that there is no second order spectrum .
The third is shown at ; the line of the fonrth order is at , and of the fifth at The first deduction to be made is to be derived from the quantitative measurements of the angle of reflection .
The sines of the glancing FIG. 2.\mdash ; Spectra of rhodium rays : 111 planes of diamond .
for are ( after slight correction for errors of ) .
Dividing these by 1 , 3 , 4 , 5 respectively , we obtain .
These are not exactly equal , as they might be expected to be , but increase for the larger angles and tend to a maximum .
The effect is due to reasons of geometry arising from the relatively high transparency of the diamond for -rays , and the consequent indefiniteness of the point at which reflection takes place .
The true value is the maximum to which the series tends , and may with sufficient accuracy be taken as .
In order to keep the main argument clear , the consideration of this point is omitted .
We can now find the distance between successive ( 111 ) planes .
We have The structure of the cubic crystals which have so far been ated by * Boy .
Soc. Proc vol. 88 , p. 428 .
VOL. LXXXIX.\mdash ; A. Prof. W. H. Brag and Mr. W. L. Brag .
these methods may be considered as derived from the face-centred lattice ( fig. 3 ) : that is to say , the centres which are effective in causing the reflection of the -rays are placed one at each corner and one in the middle of each face of the cubical element of volume .
This amounts to assigning FIG. 3 .
four molecules to each such cube , for in general one atom in each molecule is so much more effective than the rest that its placing determines the structure from our point of view .
There are four , because the eight atoms at the corners of the cube only count as one , each of them belonging equally to eight cubes , and the six atoms in the centres of the faces only count as three , each of them belonging equally to two cubes .
The characteristics of the reflection are then as follows:\mdash ; Let ABCDEFGH be the cubical element .
There are effective centres at all the corners and at , the middle points of the faces .
edge of the cube being denoted by , the reflecting planes which are parallel to a cube face , called generally the ( 100 ) planes , are spaced regularly , the distance from plane to plane being .
All the planes contain equal numbers of centres .
The ( 110 ) planes , of which the plane through ACGE is a type , are regularly spaced at a distance , and also are all equally strewn with effective centres .
The ( 111 ) planes , of which the planes through EDB , HCF are types , are regularly spaced at a distance , and again are all similar to each other .
In what may for the present be called the normal case , any one of these sets of planes gives a series of spectra which diminish rapidly in intensity as we proceed from lower to higher orders , as , for example , the spectra of the rhodium rays given by the ( 100 ) planes of rock-salt .
( Fig. 1 shows the spectra of the first two orders .
) The Structure of the The relative spacings of the spectra given by these three sets of planes are shown in fig. 4 .
Spectra of the 100 ) planes supposed to occur at values of proportional to 1 , 2 , 3 , , it follows from the above argument that the ( 110 ) planes will give spectra at , , and the ( 111 ) planes at The position of the first spectrum of the ( 111 ) planes ( fig. ) a peculiarity of the face-centred lattice .
If the effective centres were at the corners only FIG. 4.\mdash ; Spectra of face-centred lattice .
of a cube whose length of side was , the spacings of the three sets of planes would be , and , and the three sets of spectra would occur at1 , 2 , The cubical crystals which we have so far examined give results which resemble the diagram of fig. 4 more or less closely .
Individual cases depart so little from the type of the diagram that the face-centred lattice may be taken as the basis of their structure and the departures considered to reveal their separate divergencies from the standard .
For convenience of description we will speak of the first , second , third spectra of the ( 100 ) or ( 111 ) planes and so on , with reference to fig. 4 .
We may then , for example , describe the peculiarity of the rock-salt ( 111 ) spectrum*by saying that the first order spectrum is weak and the second strong .
The interpretation .
cit. is that the sodium atoms are to be put at the centres of the edges of the cubic element of volume , and the chlorine atoms at the corners and in the middle of each face or vice : for then the face-centred lattice ( cube edge ) is brought half to being the simple cubic lattice ( edge a ) having an effective centre at every corner .
The first ( 111 ) spectrum tends to disappear , the second to increase in importance .
In the case of potassium chloride , the atoms are all of equal weight and the change is complete : the first order spectrum of the ( 111 ) planes disappears entirely .
In zincblende or iron pyrites one atom is so much more effective than the other that the diagram of spectra is much more nearly characteristic of the face-centred See preceding paper .
Prof. W. H. Brag and Mr. W. L. Brag .
lattice : at least so far as regards the spectra of the lower orders .
We hope to deal with these cases later .
Let us now consider the case of the diamond .
The spectrum given by the ( 111 ) planes is shown in some detail in fig. 2 .
It should be stated that the ordinates represent the gross currents observed ; nothing has been subtracted for natural leak , scattered radiation , and so forth .
We first use the angular measurements to enable us to determine the number of carbon atoms in the elementary cube of side .
Lt us assume provisionally that there are four carbon atoms to each cube , making the face-centred lattice .
The density of the diamond is , and the of each atom is 12 times the weight of each hydrogen atom or 12 The volume of the cube is therefore The of each will then be The distance between consecutive ( 111 ) planes Now we have found experimentally that the right value is These two numbers are very nearly in the ratio of 1 : .
It is clear that we must put , not four , carbon atoms in the elementary cube ; we then obtain , and this close agreement with the experimental value suggests that we are proceeding in the way .
The value of is We have therefore four carbon atoms which we are to assign to the elementary cube in such a way that we do not interfere with the characteristics of the face-centred lattice .
It is here that the absence of the second order spectrum gives us help .
The interpretation of this phenomenon is that in addition to the planes spaced at a distance apart there are other like planes dividing the distances between the first set in the ratio 1 : 3 .
In here marallel aimilar planes anfig 5paced tfwaves fglancing aystem A are reflected in a second order spectrum we have 2 AB .
The planes reflect an exactly similar radiation which is just out of step with the first , for the difference of phase of waves reflected from A and is 2 , and therefore the difference of phase of waves reflected from A and is .
Consequently the four atoms which we have The Structure of the at our disposal are to make new ( 111 ) planes parallel to the old and related to them as are to ABC .
When we consider where they are to go we are helped by the fact that being four in number they should go to places which are to be found in the cubes in multiples of four .
The simplest plan is to puG them in the centres of four of the eight smaller cubes into which the main cube can be divided .
We then find that this gives the spacing because the perpendicular from each such centre on the two ( 111 ) planes which lie on either side of it are respectively and S(3 ) , where is the length of the side of one of the eight smaller cubes .
For symmetry it is necessary to place them at four centres of smaller cubes which touch each other edges only : e.g. of cubes which lie in the and corners of the large cube .
If this is done in the same way for all cubes like the one taken as unit it may be seen on examination that we arrive at a disposition of atoms which has the following characteristics:\mdash ; ( 1 ) They are similarly in parallel planes spaced alterl ) ately at distances and , or in the case of the diamond and cm .
: the sum of these being the distance which we have already arrived at .
( 2 ) The density has the right value .
( 3 ) There is no second order spectrum in the reflection from ( 111 ) planes .
It is not very easy to picture these dispositions in space .
But we have come to a point where we may readjust our methods of defining the positions of the atoms as we have now placed them , and arrive at a very simple result indeed .
Every carbon atom , as may be seen from fig. 5 , has four hbours at distances from it equal to cm .
, oriented with respect to it in directions which are parallel to the four onals of the cube .
For instance , the atom at the centre of the small cube Abcdefgh , fig. 6 , is related in this way to the four atoms which lie at corners of that cube , the atom at the centre of the face ABFE is related in the same way to the atoms at the centres of four smali cubes , and so on for every other atom .
We may take away all the structure of cubes and rectangular axes , and leave only a design into which no elements enter but one and four directions equally inclined to each other .
The characteristics of the may be realised from a consideration of the accompanying photographs ( figs. 7 and S ) of a model , taken from different points of view .
The very simplicity of the result suggests that we have come to a right conclusion .
The appearance of the model when viewed at right angles to a cube diagonal is shown in .
The ( 111 ) planes are seen on , and the Prof. W. H. Brag and Mr. W. L. Brag .
FIG. 6 .
FIG. 7.\mdash ; View perpendicular to axis .
FIG. 8.\mdash ; The ( 110 ) planes are vertical and horizontal .
The Structure of the 1 : 3 spacin is obvious .
The union of every carbon atom to four neighbours in a perfectly symmetrical way might be expected in view of the persistent tetravalency of carbon .
The linking of six carbon atoms into a ring is also an obvious feature of the structure .
But it would not be right to lay much stress on these facts at present , since other crystals which do not contain carbon atoms possess , apparently , a similar structure .
We may now proceed to test the result which we have reached by examining the spectra reflected by the other sets of planes .
One of the diamonds which we used consisted of a slip which had cleavage planes as surfaces ; its surface was about 5 mm. each way and its thickness mm. By means of a Laue photograph , to be described later , it was possible to determine the orientation of its axes and so to mount it in the -ray spectrometer as to give reflection from the ( 110 ) or the ( 100 ) planes as desired .
As regards the former there should be no special features , for the four carbon atoms which we placed at the centres of four of the eight smaller cubes all now lie in ( 110 ) planes .
The latter are equally spaced and all alike , the space distance being or .
The first glancing angle at which reflection occurs is , -therefore , .
The experimental value was .
The spectra of higher orders occurred at and .
The sines of these three angles are , and , or nearly as 1 : 2 : 3 .
Great precision was not attempted ; to attain it would have been needlessly troublesome .
The intensity of the different orders fell off in the usual way .
On the other hand , the ( 100 ) spectrum might be expected to show certain peculiarities .
By placing four atoms at the centres of the four small cubes we have , in fact , interleaved the 100 planes , as it were : and these now consist of similar planes regularly spaced at a distance or The first spectrum should therefore occur at an angle .
Using the language already explained , we may say that the first ( 100 ) spectrum has disappeared , and , indeed , all the spectra of odd order .
Spectra were actually found at and : the sines of these angles being and , the latter being naturally much less intense than the former .
A careful in the neighbourhood of showed that there was no reflection at all at that angle .
The results for all three spectra are shown rammatically in fig. 9 , -ich should be compared with fig. 4 .
It is instructive to compare the reflection effects of the diamond with those Prof. W. H. Brag and Mr. W. L. Brag .
of zincblende .
Our results seem to show that it is built up in exactlythe same way , except that the ( 111 ) planes contain alternately zinc atoms only and sulphur atoms only .
If the zinc atoms are placed at each corner of the cube and at the centre of each face , the sulphur atoms lie at four of the eight centres of the smaller cubes .
The ( 100 ) planes , like the ( 111 ) planes , contain FIG. 9.\mdash ; Spectra of diamond .
alternately zinc and sulphur atoms .
These alternations of constitution modify the forms of the various spectra , so that they lie between the forms of the space-centred lattice ( fig. 4 ) and the forms of the diamond ( tig .
9 ) .
The first spectrum is not entirely absent but is much smaller than the second , and in the same way the second ( 111 ) spectrum , though it is to be seen , is smaller even than the third .
The scheme of the zincblende spectra is shown in fig. 10 .
Their actual positions perfectly with those which FIG. 10.\mdash ; Spectra of zincblende .
can be calculated from a knowledge of the density of the crystal , the weight of the molecule , and the wave-lengths employed .
In consequence of the alternation of zinc and sulphur planes at unequal along the ( 111 ) axis , the crystal ceases to be symmetrical about a plane perpendicular to that axis .
It becomes hemihedral , and acquires polarity .
We now go on to consider the Laue photograph of diamond .
photograph taken with a section of diamond cut parallel to the cleavage plane 111 ) is shown in fig. 11 .
The experimental arrangement was similar Structure of the Diamond .
to the original arrangement of Laue , the distance from diamond to photographic plate cm .
, and the time of exposure four .
A test photograph was taken first , which made it possible to calculate the exact orientation to be given to the diamond in order that the incident X-rays might be truly parallel to a axis .
The symmetry of fig. 11 shows FIG. 11 .
that a close approximation to this orientation has been obtained .
The -ray bulb had a platinum anticathode .
In fig. 12 is given the raphic projection of this pattern .
* The spots of the photograph are represented in the by dots of corresponding magnitude , and several circles , each the spots reflected by the planes of one zone , are drawn .
The indices placed next the spots are the Millerian indices of the planes which reflect these spots , the planes being referred to three equal axes making with each other as in the case of the examples zincblende and fluorspar given in the above paper .
Imagining a See preceding paper .
Prof. W. H. Brag and Mr. W. L. Brag .
cube with one corner at the diamond and the long diagonal of the cube parallel to the incident -rays , the three cube edges would meet the photographic plate at the points marked .
The spot ( 110 ) is thus reflected in the cube face , meeting the plate along , ( 110 ) being the indices of a cube face referred to axes employed .
It will now be shown that on analysis the photograph appears to be in accordance with the structure which we have assigned to the diamond on the FIG. 1 result of the reflection experiments .
In the first place , of the three cubic space lattices it is evidently that which has ints at cube corners and at the centres of the cube faces which is most characteristic of the diffracting system .
For our purpose this space lattice is most conveniently referred to three axes which are onals of the cube faces meeting in a corner .
The co-ordinates of any point of the system may then be written where are any integers , positive or negative , and is half the diagonal of the square of edge The Structure of the Diamond .
The indices of the refiecting plane are iven for each spot of the photograph , and it will be seen that they could not possibly have a more simple form .
If referred to the cubic axes they become much more complex .
Along the axes chosen , the interval between successive points of the lattice is the smallest possible , and these axes are very important point-rows of the system .
The remarkable series of spots on the three circles in the diagram which culminate at the points ( 110 ) , ( 101 ) , ( 011 ) , are due to planes which pass through these point-rows , and this alone is evidence of the paramount importance of the cube face diagonals as axes .
It is thus clear that a simple analysis of the pattern can be made if the planes are referred to axes of the face-centred cubic lattice .
It is also evident , however , that the pattern is more complex than it should be if due to a set of identical points in this lattice , of which examples have been given in a former paper .
For instance , there are spots reflected by the planes , ( 131 ) , ( 141 ) , and , , and yet none by the plane diagram , .
In the case of zincblende and fluorspar no complications of this kind occur , although in these cases the presence of the hter atoms of sulphur and fluorine must affect somewhat the diffraction pattern given by the lattice ement of heavy atoms of zinc and calcium .
Yet here , where carbon atoms alone are present , the pattern is not as straightforward as those iven by zincblende and fluorspar .
We thus come to the conclusion that the carbon atoms are not on a single space lattice .
If the structure to diamond in the former part of this paper is correct , a simple explanation of the diffraction pattern can be arrived at .
According to this structure the carbon atoms are not arranged on a space lattice , but they may be regarded as situated at the points of two interface-centred space lattices .
These lattices are so situated in relation to each other that , calling them A and , each point of lattice is surronnded symmetrically by four points of lattice tetrahedronwise and .
This can be seen by leference to the diagram of fig. 6 .
It is now clear why the pattern must be referred to the axes of the facecentred lattice , for if the structure is to be arded as built up of points arranged on the simple cubic lattice , with three equal axes at angles , no fewer than interpenetrating lattices must be used to give all the points .
Consider lattice A referred to the cube face onals as axes .
Then all the points of that lattice have indices being any .
The relative position of lattice is arrived at if we imagine lattice A to suffer a translation along the axis which is 290 Prof W. H. Brag and Mr. W. L. Brag .
the long diagonal both of the elementary parallelepiped and of the cube , the amount of this translation being one-fourth of the long diagonal .
Reference to one of the diagrams will make this more clear than any explanation which could be given here .
The points of lattice then have co-ordinates The planes of lattice A which have Millerian indices ( lmn ) are iven by where is any integer .
The corresponding planes of lattice iven by or When the ( lmn ) planes of both lattices are considered together , three cases present themselves : ( 1 ) When is a multiple of four , the planes of lattice are coincident with those of lattice , both being given by integer x .
An example of this is found in the plane or ( 130 ) .
( 2 ) When is a multiple of two but not of four , the planes of lattice A are by Those of lattice are given by and are thus half-way between the planes of lattice A. Examples.\mdash ; Planes such as ( 110 ) and ( 121 ) .
( 3 ) When is odd , the equations of the ttVO sets of planes and , or and the planes occur in pairs , in such a way that the two planes of a pair are separated by one-fourth of the distance between the successive pairs .
Examples.\mdash ; Octahedron faces ( 100 ) , ( 010 ) , 001 ) , and ( 111 ) .
It is now clear wherein lies the difference between planes and ( 131 ) , on the one hand , and on the other .
The ( 12-1 ) planes of the one lattice alone would probably give a strong reflection of a part of the -ray spectrum in Structure of the Diamond .
which there a large amount of energy , but the presence half-way between them of the planes of the lattice annuls their effect .
On the other hand , though the and planes now occur in pairs , the reflected from them is the same as that for a single lattice .
On looking over the indices of the reflecting planes , it will be seen how .
a proportion of them have either odd or a multiple of four ; in fact , the departure of the pattern from simplicity is just that which would be expected from the nature of the point system , which differentiates the planes into these three sets .
A more complete analysis of the pattern would be of little interest here because the positions of the reflection peaks afford a much simpler method of analysing the structure .
In comparison the exarnples iven in the former paper , this is a case where the diffraction is caused by a point system as ainst a space lattice , both a translation and a rotation necessary to bring the system into self-coincidence .
This yives special interest to the photograph .
We have to thank both Prof. S. P. Thompson , F.B.S. , and Dr. Hutchinson .
of the Mineralogical Laboratory , Cambridge , for their kindness in us diamonds which were used in these experiments .
|
rspa_1913_0085 | 0950-1207 | Morphological studies in the benzene series. IV. \#x2014;The crystalline form of sulphonates in relation to their molecular structure. | 292 | 313 | 1,913 | 89 | Proceedings of the Royal Society of London. Series A, Containing Papers of a Mathematical and Physical Character | E. H. Rodd, B. Sc.|Prof. H. E. Armstrong, F. R. S. | article | 6.0.4 | http://dx.doi.org/10.1098/rspa.1913.0085 | en | rspa | 1,910 | 1,900 | 1,900 | 16 | 370 | 10,089 | http://corpora.clarin-d.uni-saarland.de/surprisal/6.0.3/?id=rspa_1913_0085 | 10.1098/rspa.1913.0085 | null | null | null | Atomic Physics | 37.508158 | Chemistry 2 | 33.646326 | Atomic Physics | [
-23.494298934936523,
-62.61905288696289
] | 292 Morphological Studies in the Benzene Series .
IV.\#151 ; The Crystalline Form of Sulphonates in Relation to their Molecular Structure .
By E. H. Rod , B.Sc. , Salters ' Company 's Research Fellow , City and Guilds College .
( Communicated by Prof. H. E. Armstrong , F.R.S. Received July 3 , 1913 .
) In Part III of these studies , in which a number of isomorphous paradi-bromobenzenesulphonates of the rare earth metals ( La , Ce , Nd , Pr , Gd , Sm ) are described crystallographically , * the conclusion was arrived at that in these salts three of the benzenesulphonic groups , together with 9 or 12 molecules of water , are disposed symmetrically in a plane around a central atom of the tervalent metal .
Molecular units presumably of this kind are packed together in a structure one dimension of which corresponds to the thickness of a single benzene complex observed in numerous substituted benzene derivatives , such as diiodobenzene , for example ; as was pointed out , the salts under consideration may be regarded , in fact , as derived from benzene merely by the pushing apart of the zigzag columns of carbon domains , depicted by Barlow and Pope as characteristic of the hydrocarbon , in such manner as to allow of the introduction of the substituting groups present in the sulphonate in addition to benzene .
In view of this result , it was desirable to determine the crystalline structure of the acid from which the salts were derived as well as of salts containing metals of other degrees of valency .
Numerous unsuccessful attempts were made to obtain measurable crystals of the paradibromo-acid ; ultimately , good crystals were secured of the corresponding dichloro-acid and of its lanthanum , neodymium and praseodymium salts .
The measurements made of these salts , together with those of several related salts , are described in the following section ; the issues are discussed under the headings :\#151 ; ( 1 ) The isomorphism of the dichloro- and dibromobenzenesulplionates .
( 2 ) The morphotropic relationship of dibromobenzenesulphonates to the unsubstituted salts .
( 3 ) The relationship of the two gadolinium ^\gt ; -dibromobenzenesulphonates * " Paradibromobenzenesulphonates ( Isomorphous ) of the ' Rare Earth ' Elements a Means of Determining the Directions of Valency in Tervalent Elements , " by H. E. Armstrong and E. H. Rod , ' Roy .
Soc. Proc. , ' 1912 , A , vol. 87 , p. 204 .
Morphological Studies in the Benzene Series .
( 7H20 and 12H20 ) with reference to the change of structure induced by changes in the degree of hydration .
Lanthanum p-dichlorobenzenesulphonate , La(C6H3Cl2S03)3.15H20.\#151 ; This hydrate is deposited at all temperatures between 10 ' and 50 ' C. from a solution of the salt .
It consists of anorthic prisms or tables which effloresce quickly on exposure to air .
The forms \amp ; { 100 } , ^{101 } and c{001 } constitute the prism faces , the other forms developed being e{010 } , y ?
{ 0lT } and occasionally The crystal faces are never very well developed , and usually give multiple reflections .
There is a distinct cleavage parallel to a.{100 } .
Water : Found 25'26 ; calculated 24'84 per cent. System : Anorthic .
Axial ratios : a:b:c \#151 ; T6193 : 1 : T6028 .
\#171 ; = 76 ' 26 ' ; \#163 ; = 113 ' 48 ' ; 7 = 68 ' 6 ' .
Angle .
No. of observations .
Limits .
M^an observed .
Calculated .
100:101 16 53 ' 12'\#151 ; 54 ' r 53 ' 44 ' 101 :001 13 56 28 \#151 ; 57 14 56 49 56 ' 47 ' 001 : 100 20 69 1\#151 ; 70 0 69 29 \#151 ; 100 :010 14 71 24\#151 ; 72 21 71 46 \#151 ; 010 :110 7 37 47 \#151 ; 38 22 38 6 \#151 ; 110:100 7 69 37\#151 ; 70 23 70 8 70 8 001 :010 7 84 5\#151 ; 84 32 84 14 84 18 010 :001 7 95 42 \#151 ; 96 2 95 49 95 42 101 :010 5 68 30 \#151 ; 68 43 68 36 \#151 ; 010 : III 1 \#151 ; 43 5 43 3 III : 101 1 68 19 68 21 001 : 110 2 70 41\#151 ; 70 56 70 49 70 59 110:101 2 36 20 \#151 ; 36 48 36 34 36 39 101:001 2 72 29 \#151 ; 72 40 72 34 72 22 Neodymium p-dichlorobenzenesulphonate , Nd(C6H3Cl2S03)3.12H20.\#151 ; This hydrate is deposited when an aqueous solution of the salt is allowed to crystallise at any temperature between the ordinary and 50 ' C. It forms rose-coloured , short , thick or flat prisms , the prism zone consisting of the forms Z{010 } , m{110 } and ?
i{120 } ; the faces upon this zone are always much striated and give multiple reflections .
The facets at the ends of the prism , consisting of the forms r{011 } and o{101 ) , are beautifully developed and give good single images ( see fig. 1 ) .
The crystals are closely isomorphous with those of the gadolinium salt , Gd(C6H3Br2S03)3.12H20 ; but the two salts differ slightly , thus : ( 1 ) whilst the gadolinium salt has a tabular habit , the neodymium salt is prismatic , being elongated in the direction of the c axis ; ( 2 ) the form { 120 } is occasionally developed in the neodymium salt but not in the gadolinium salt , in which the form { 130 } is sometimes present .
Mr. E. H. Rocld .
Water : Found 21-00 ; calculated 20'89 per cent. System : Monosymmetric .
Axial ratios : a:b:c=0*5872:1 : 0-3810 .
/ 3 = 76 ' 34 ' .
Angle .
No. of observations .
Limits .
Mean observed .
Calculated .
010:011 15 69 ' 34'\#151 ; 69 ' 45 ' 693 40 ' Oil : Oil 7 40 37 \#151 ; 40 47 40 41 40 ' 40 ' 010 : 120 8 40 31 \#151 ; 42 27 41 17 41 12 110:011 14 68 46\#151 ; 68 50 68 48\#163 ; Oil : 101 14 41 6\#151 ; 41 12 41 10^ 41 10\#163 ; 101 : 110 14 69 58 \#151 ; 70 4 70 1 010 : 101 4 89 55 \#151 ; 90 4 90 0 90 0 Praseodymium p-dichlorobenzenesulphonate , P^CbHaChjSOa ) ; } .
12HgO.\#151 ; This hydrate , like that of the corresponding neodymium salt with which it is isomorphous , is deposited at temperatures between 10 ' and 50 ' C. The crystals , which are of a pale green colour , resemble those of the neodymium salt in habit but are not so well developed .
The zone [ 010:120 :110 ] is invariably badly striated .
Water : Found 20-71 ; calculated 20-81 per cent. System : Monosymmetric .
Axial ratios : a:b:c = 0*5887 :1 : 0-3819 .
76 ' 26 ' .
Morphological Studies in the Benzene Series .
295 Angle. .
No. of observations .
Limits .
Mean observed .
Calculated .
010 : Oil 21 69 ' 24 \#151 ; 69 ' 57 ' 69 ' 38 ' 011:011 9 40 27 \#151 ; 40 53 40 43 40 ' 44 ' 110:011 10 68 24 \#151 ; 68 48 68 40 \#151 ; Oil : 101 11 41 3 \#151 ; 41 32 41 13 \#151 ; 101 : no 9 69 43 \#151 ; 70 28 70 5 70 7 010 :120 3 41 1 \#151 ; 41 30 41 14 41 9 120 :110 1 \#151 ; 19 10 19 4 no : no 3 59 25 \#151 ; 59 34 59 29 59 34 Pr(C6H3Cl2S03)3.15H20.\#151 ; When a strong , apparently supersaturated solution of praseodymium p-dichlorobenzenesulphonate was allowed to crystallise spontaneously at room temperature , on two occasions , together with the massive crystals of the dodecahydrate , a few smaller crystals were obtained in the form of hexagonal plates ; when examined these were found to be anorthic and closely isomorphous with the salt La(C6H3Cl2S03)3.15H20 they must be taken , therefore , to contain 15H20 , although they have not been obtained in sufficient quantity for analysis .
Like the crystals of the corresponding Lanthanum salt , they gradually become opaque when kept .
The crystals were so poorly developed that a complete examination could not be made .
A corresponding hydrate of the neodymium salt has not been observed .
When the crystals are allowed to remain in contact with the solution they are gradually converted into the dodecahydrate .
Gadolinium p-dibromobenzenesulphonate , Gd(CeH3Br2S03)3.7H20.\#151 ; This , hydrate was described in Part III of these studies but crystals have been obtained only recently on which the forms were developed that are necessary for the determination of the axial ratios .
These were deposited from water at 45 ' C. The heptahydrate forms very massive monosymmetric prisms ; the faces are always striated and seldom give good reflections .
The forms generally occurring are a{100 } , \#163 ; \gt ; { 110 } , r{120 } and ^{101 } .
Another form is required for the complete determination of the crystal constants ; on a few occasions e{101 } was observed and still more rarely m{122 } .
The crystals are elongated in the direction of the c axis .
There is a perfect cleavage parallel to a{100 } ( see fig. 2 ) .
System : Monosymmetric .
Axial ratios : a:b:c=1-2595 :1 : 0-6031 .
/ 3 = 89 ' 16 ' .
VOL. LXXXIX.\#151 ; A. Mr. E. H. Rod .
Angle .
No. of observations .
Limits .
Mean observed .
Calculated .
100 110 14 51 ' 17'-51 ' 55 ' 51 ' 55 CO 110 120 7 16 21\#151 ; 17 2 16 47 16 ' 48 ' 100 : : 120 8 68 12\#151 ; 68 41 68 20 68 21 120 : : 120 4 42 58 \#151 ; 43 29 43 15 43 18 100 : 101 14 63 14 \#151 ; 64 19 63 49 101 : : 101 5 50 28 \#151 ; 51 35 51 11 101 : : 100 4 64 28 \#151 ; 65 13 64 33 65 0 110 : : 101 5 74 11\#151 ; 74 33 74 22 74 5 120 : : 101 5 80 20 \#151 ; 80 58 80 44 80 38 101 : : 122 3 3t 45\#151 ; 32 6 31 54 32 24 100 : 122 3 77 42\#151 ; 77 45 77 44 77 48 Didymium benzenesulphonate , Di(C6H5S03)3.9H20.\#151 ; This hydrate has been described by Holmberg but not measured.* It is very soluble in water and generally separates from the aqueous solution as a crystalline mass ; a few measurable crystals were obtained from a mixture of aqueous alcohol and ethylic acetate in the form of very thin hexagonal shaped plates .
Water was estimated in the salt crystallised from this solution : found 2074 per cent. ; calculated for Di(C6H5S03)3.9H20 , 2090 per cent. The most prominent form on the crystals is a{100 } ; other forms developed are r{101 } , o{111 } , and more rarely p{322 } .
Measurable crystals were difficult to obtain and were always imperfect .
The cleavage is parallel to \lt ; x{ 100 } ( see fig. 3 ) .
System : Orthorhombic .
Axial ratios : = 2,0795 :1 : T9374 .
Angle .
No. of observations .
Limits .
Mean observed .
Calculated .
100:101 11 46 ' 32\#151 ; 47 ' 30 ' 47 ' 2 ' 101 :101 6 85 14 \#151 ; 86 48 85 51 85 ' 56 ' 100:111 7 66 40 \#151 ; 66 57 66 52 \#151 ; 111 till 3 46 16 \#151 ; 46 24 46 18 46 16 100 : 322 3 57 9 -57 33 57 24 57 20 101 : 111 3 54 25 \#151 ; 54 38 54 31 54 48 The Isomorphism of Dichloro- and Dibromobenzenesulphonates.\#151 ; From the measurements given above , it is obvious that praseodymium and neodymium p-dichlorobenzenesulphonate dodecahydrate are very closely isomorphous with gadolinium ^-dibromobenzenesulphonate dodecahydrate .
This relationship is of prime importance as proof that the three metals and the two halogens respectively are mutually displaceable in such salts .
The following values speak for themselves:\#151 ; * ' Zeit .
anorg .
Chem. , ' vol. 53 , p. 83 .
Morphological Studies in the Benzene Series .
297 Salt .
Axial ratios .
a : b : e \amp ; \#166 ; Equivalence parameters .
x : y : z Gd(C6H3Br2S03)3.12H20 Nd(C6H3Cl2S03)3.12H20 Pr(C6H3Cl2S03)3.12H20 0 -5952 :1 : 0 3817 0 -5872 :1 : 0 -3810 0 -5887 :1 : 0 -3819 76 ' 48 ' 76 34 76 26 6 -1415 :10 3885 : 2 -6257 6 0921 :10 -3750 : 2 6352 6 '0988 : 10 -3598 : 2 -6376 Attention may be specially directed to the fact that the z parameter has a value very closely approximating to the value 2-642 observed in p-diiodo-benzene , which is characteristic , according to the Barlow-Pope hypothesis , of the rhombohedral marshalling in benzene derivatives generally .
Fig. 3.\#151 ; Di(C6H5S03)3.9H20 .
Morphotropic Relationship of Substituted and Unsubstituted sulphonates.\#151 ; It is to be expected that didymium benzenesulphonate , which crystallises with nine molecules of water , would bear a close relationship to the corresponding neodymium salt , Nd(C6H3Br2S03)3.9H20 .
This expectation is fully realised .
The benzenesulphonate is orthorhombic , the axial ratios being a :b:c = 2-0801:1:1-9374 , whilst the neodymium ^\gt ; -dibromobenzenesulphonate is also orthorhombic a :b':c ' = 1-3990:1:0-8789 .
When the crystals of the two salts are compared , two significant facts are noticeable : firstly , that the ratio a ' : V is almost exactly two-thirds of : ; secondly , that angles on one of the corresponding zones of the two crystals are practically identical .
Thus , in the case of the didymium benzenesulphonate , we have { 100 } : { 101 } = 47 ' 2 ' , and in that of the dibromobenzene sulphonate { 100 } : { 301 } =46 ' 42 ' .
If in the benzenesulphonate { 101 } be changed to { 301 } and at the same time Mr. E. H. Rod .
the ratio a:bbe multiplied by two-thirds , the axial ratios of the salt become a :b:c = 1*3868 :1:0-8611 , i.e. almost identical with those of the neodymium p-dibromobenzene-sulphonate .
Moreover , the pseudo-trigonal character of the salt is revealed , as the ratio c : bis very nearly equal to the value 0*866 :1 , characteristic of trigonal symmetry.* The equivalence parameters of the benzenesulphonate deduced from the actual ratios thus arrived at , in comparison with those of the neodymium p-dibromobenzenesulphonate , are as follows :\#151 ; x y z Nd(C6H3Br2S03)3.9H20 ... ... ... 2*6475 : 5*6773 : 9*9796 Di(C6H3S03)3.9H20 ... ... ... .
2*6502 : 5*7327 : 9*8729 The close similarity between the structures of the two salts is immediately obvious from these figures.* !
* Relationships Consequent on Changes in the Degree of Hydration of Sulphonates.\#151 ; The relationship between the dodecahydrates of gadolinium ^-dibromobenzenesulphonate and the nonahydrate of dibromobenzene* Cf .
Part III , p. 213 .
t In calculating the equivalence parameters of the acid , it is necessary first to modify the axial ratios by multiplying a by three-quarters and c by 2 .
As objection is sometimes made to this mode of treatment by those who do not clearly appreciate the flexible character of axial ratios , it may be as well to refute these objections here .
The axial ratios of a crystal may be defined as the relative distances from the centre of the crystal at which the form which is designated ( 111 ) cuts the three axes .
In all systems but the cubic , the choice of ( 111 ) is to a certain extent arbitrary : the lower the symmetry of the system , the wider is the range of choice .
For instance , in the case of the monosymmetric sodium p-dichlorobenzenesulphonate described in this paper , there was a wide choice : a particular form was chosen as ( 111 ) and others then became ( 322 ) and ( 122 ) ; but there was no reason why either of these others should not have been made ( 111 ) ; if ( 322 ) had been called ( 111 ) , the axial ratio a : b would have had two-thirds its present value .
Moreover , we are at present entirely ignorant of the causes determining what particular forms shall develop on the crystal and there is no a priori reason why these should always be the simplest possible forms .
In view of these considerations it is not therefore surprising that in most cases , when dealing with orthorhombic and mono-symmetric crystals , some slight modification of the interpretation originally given to the measurements is necessary , in order that morphotropic relationships between different substances may be revealed in the equivalence parameters .
Without guidance from previous knowledge and a general idea of the relationship sought , it would be impossible to discover the morphotropic relationships pointed out in this paper .
Fortunately Barlow and Pope have worked out the structure of crystalline benzene on incontrovertible evidence and a relationship to benzene is first looked for .
When this is found , it is generally accompanied by other significant relationships which serve to enhance the probability of the correctness of the results obtained .
This was particularly well illustrated in the case of the acid and salt just discussed , as the very close structural relationship of acid to salt is apparent only when the x parameters of the two agree with the z parameter of rhombohedral benzene .
Morphological Studies in the Benzene Series .
299 sulphonate of several other metals was discussed in the previous communication .
The heptahydrate now described is apparently very different in form .
It crystallises in the monosymmetric system , the axial ratios being a:b:c-1-2595 :1 : 0-6031 ; / 3 = 89 ' 16 ' .
The markedly pseudo-trigonal structure , which was a feature of the nona- and dodeca-hydrates , is no longer apparent ; this is to be expected , as the number 7 , the number of molecules of water contained in the salt , is incompatible with three-fold symmetry .
When the equivalence parameters of the salt are calculated , the axial dimension b being doubled , the following values are obtained :\#151 ; x:y:z = 5-7160:9-0768:2-7373 .
The z parameter approaches closely that of crystalline benzene , 2*780 ; it therefore appears probable that this salt may be derived from the benzene structure of hexagonal marshalling ( z = 2-780 ) , and not from the alternative rhombohedral marshalling ( z = 2*64 about ) , as are the other salts .
From the general similarity of the parameters of the heptahydrate to those of the other hydrates , it is to be inferred , however , that the molecules of all these salts have very similar configurations , and differ merely in being derived from the two forms of benzene , the difference being due , therefore , only to the manner in which the successive layers of molecules are superimposed one upon another .
The Relationship in Crystalline Form of Acid and the Sulphonates of Metals .
In view of the conclusions arrived at in the previous sections and in Part III of these studies , it appears probable that the crystalline structure of the rare earth salts generally of benzenesulphonic acid and its halogen derivatives always conforms to one type , the type being one in which three sulphonic groups are symmetrically arranged around a central atom of the metal .
In the case of such salts , the arrangement must be largely determined by the metal ; in the case of the acid , the attractive tendencies of the constituent radicles are chiefly operative : as chemical methods throw but little light on such a problem , the study of crystalline form becomes of special importance , as a means of determining the directions in which the forces act in the formation of solids .
p-Dichlorobenzenesulphonic Acid , C6H3CI2SO3II.3II2O.\#151 ; Crystals are best grown from a solution containing a little sulphuric acid , which reduces the solubility of the sulphonic acid considerably .
The crystals are usually aggregates of prisms , rarely separate .
The prism zone is made up of the Mr. E. H. Rod .
forms Z{010 } , r { 110 } and a{100 } , the last being sometimes undeveloped .
The prism end is formed by the two faces of the*form p{Oil } ( see fig. 4 ) .
Fig. 4.\#151 ; C6H3C12S03H.3H20 .
System : Monosymmetric .
Axial ratios : a:b:c = 0*6255 :1 : 0*2918 .
/ 3 = 79 ' ; 36 ' .
Angle .
No. of observations .
Limits .
Mean observed .
Calculated .
010 :110 25 58 ' 12'\#151 ; 58 ' 40 ' 58 ' 24 ' 110:110 10 62 47 \#151 ; 63 25 63 13 63 ' 12 ' 110:100 9 31 24\#151 ; 31 50 31 36 31 36 010 : Oil 13 73 48\#151 ; 74 10 73 59 \#151 ; Oil : Oil 5 31 49 \#151 ; 32 10 32 0 32 2 110 : Oil 5 72 52\#151 ; 73 7 73 0 \#151 ; Oil : 110 5 106 53 \#151 ; 107 14 107 2 107 0 110:011 6 90 1\#151 ; 90 30 90 17 90 11 Oil : 110 6 89 33\#151 ; 89 55 89 43 89 49 As the y\gt ; -dibromobenzenesulphonates of La , Nd and Pr crystallise with nine molecules of water\#151 ; three molecules per acid radicle\#151 ; they are the salts with which the acid can best be compared , as noj ?
-dichlorobenzenesulphonates containing this proportion of water are known .
On contrasting the axial ratios a b c La(C\lt ; 5H3Br2S03)3.9H20 ( orthorhombic ) ... ... . .
1*3965 : 1 : 0*8753 H(C6H3Cl2S03).3H20 ( monosymmetric ) ... ... ... . .
0*6255 : 1 : 0*2918 Morphological Studies in the Benzene Series .
301 it is obvious that the ratio c:bof the salt is exactly thrice that of the acid .
This result is of special importance , inasmuch as each group in the molecule of the acid is repeated three times in that of the salt , the valency volume of the latter being therefore three times that of the acid .
When the equivalence parameters of the acid are calculated and compared with those of the salt the following values are obtained :\#151 ; W x H(C6H3C12S03).3H20 ... ... ... 50 2-6763 : 5*7050 : 3-3296 La(C6H3Br2S03)3.9H20 ... ... 150 2-6480 : 5-6885 : 9-9582 It can be seen that the dimensions of the assemblage are practically identical in two directions and that the third dimension is exactly three times as great in the salt as in the acid .
The significance of the values given under x will be obvious .
If as the crystal unit of the acid we take that of three molecules having a valency volume equal to that of the salt and calculate the equivalence parameter of the acid on this basis , values are obtained which are immediately comparable with those of the salt , viz. , x:y:z = 2-6763 : 5-7013 : 9-9880 .
In other words it appears to be legitimate to assume that the crystalline structure of the acid is pseudo-trigonal like that of the salt of a tervalent metal\#151 ; that is to say , that three molecules of acid act in conjunction .
If such be the case , the formation of the salt from the acid involves merely the displacement of three adjacent hydrogen atoms , each of unit volume , by a single atom of metal of three times the volume valency of the hydrogen atom .
The fact that the symmetry is changed from monosymmetric to orthorhombic in the passage from acid to salt is proof that the equivalence though not absolute is very close ; apparently the metal has the effect of rendering the arrangement slightly more symmetrical .
Assuming , in the case of the acid , that the molecules are disposed in groups of threes , the crystalline form is evidence of an attractive influence exerted at the moment of crystallisation , if not in the solution , which causes the sulphonic radicles to set radially , so that a mass of the acid ( or of the salt of a rare earth metal ) can Joe regarded as a mosaic of triangular groups each of which has its centre occupied by three sulphonic radicles .
Further justification of these conclusions is afforded by the following argument : The structure assigned by Barlow and Pope to the form of benzene in which the crystal units are packed together in rhombohedral marshalling is that given in fig. 5 .
Such a structure has rhombohedral symmetry , the point O , around which are grouped three small or hydrogen Mr. E. H. Rod .
spheres , being an unique point of the structure from which emerges a trigonal axis perpendicular to the plane of the paper .
For the present purpose it is sufficient to consider only the three benzene units outlined in the figure which are disposed symmetrically about the point 0 .
If the three hydrogen spheres at 0 be removed in order to make room for three sulphonic groups , the whole structure is expanded ; if the expansion take Fig. 5 .
place symmetrically , so as to make room for three sulphonic groups together with nine molecules of water , the structure would assume the appearance shown diagrammatically in fig. 6 .
This figure is drawn strictly to scale , the shaded area representing the space which would be occupied by the acid groups and the water assuming that no expansion took place in a direction perpendicular to the plane of the paper .
The heavily outlined figure therefore represents the crystal unit of the acid or of a " corresponding " salt .
It is highly probable that when such units are packed together , they are more or less compressed in one direction or another according to the nature of the radicle at 0 and that the crystal retains trigonal symmetry more or less completely according to the influences at work at each centre .
Presumably the complex would assume an approximately triangular shape through compression and its outline would be approximately such as is represented by the broken line triangle .
In constructing the diagram the figure was drawn to scale , using the x and y values of benzene in deducing the hydrocarbon areas and assigning to the shaded space an area ( the valency volume Morphological Studies in the Benzene Series .
303 divided by the vertical dimension of rhombohedral benzene , = 2*64 ) corresponding to the valency volume of the sulphonic groups , the metal and the nine molecules of water .
In drawing the triangle subsequently , the areas cut off were balanced against those included outside the figure .
It is very 0=M or Ms , Fig. 6 .
noteworthy that the length AD in the figure thus constructed is practically identical with the y value of the acid referred to three molecules ; also that the length AF is that of the 2 value .
The Influence of Monad and , Dyad Metals on the Crystalline Structure of Benzenesulphonates .
In this section measurements are given of the potassium , sodium and zinc salts of y\gt ; -dichlorobenzenesulphonic acid .
The results are discussed together with those obtained by Weibull , * who has measured a large number of benzenesulphonates and tolueneparasulphonates .
Potassium p-dichlorobenzenesulphonate , C6H3CI2SO3K.\#151 ; This salt was described by Lesimplet as crystallising with one molecular proportion of water .
I find it to be anhydrous .
It crystallises from water at temperatures from 20 ' to 37 ' C. in thin monosymmetric prisms ; as a general rule , each prism consists of two individuals twinned on a{100 } .
The twin plane is a good plane of cleavage .
The face a{100 } is always badly striated and useless for purposes of measurement but the a face obtained by cleavage * * Zeit .
Kryst .
Min. .
' vol. 15 , p. 234 .
t ' Zeit .
Chem. , ' 1868 , p. 226 .
Mr. E. H. Eodd .
gives good reflections .
The forms ^\gt ; { 110 } and r{122 } give brilliant reflections ; ^{102 } is sometimes developed , but usually as a mere line ( see fig. 7 ) .
Potassium : found 14*78 ; calculated , 14*75 per cent. System : Monosymmetric .
Axial ratios : a:b:c=1*5054:1:0*7636 .
/ 3 = 83 ' 27 .
Angle .
No. of observations .
Limits .
Mean observed .
Calculated .
no = no 19 112 ' 20'\#151 ; 112 ' CO 112 ' 28 ' no : no 18 67 25\#151 ; 67 51 67 33 67 ' 32 ' 100 : no 4 56 13\#151 ; 56 16 56 14 56 14 122:110 12 70 45\#151 ; 71 9 70 54 \#151 ; 110 :122 6 109 1\#151 ; 109 13 109 8 109 6 122 :122 9 71 9\#151 ; 71 20 . .
71 13 \#151 ; 100:122 12 73 15\#151 ; 73 48 73 33 73 37 110 : 122 6 50 5\#151 ; 50 14 50 9 50 9 122 :110 6 129 44 \#151 ; 130 0 129 49 129 51 100 :102 1 \#151 ; 69 53 69 42 Fig. 7.\#151 ; Q6H3C12S03K .
Fig. 8.\#151 ; C6H3Cl2S03Na .
H20 .
Sodium 'p-dichlorobenzenesulphoncite , CeHyCbSOsNa .
H^O.\#151 ; This monohydrate was described by Lesimple .
I have obtained another hydrate which forms massive crystals which effloresce with great rapidity in air .
Measurable crystals of the monohydrate were obtained from aqueous solutions at 37 ' C. It forms massive plates or oblique six-sided tables growing upon the form \lt ; x{ 100 } .
The other forms observed were c{001 } , Z{101 } , m{102 } , r{110 } , ^\gt ; { 122 } , ^{322 } .
There is a perfect cleavage parallel to a{100 } from which form an optic axis emerges perpendicularly .
The larger crystals appear from the analytical results to enclose water ( see fig. 8 ) .
Morphological Studies i the Benzene Series .
305 Water : found 7"25 per cent. ; C6H.3Cl2SO3Na .
H2O requires 6*75 per cent. Sodium : found , in anhydrous salt 9-21 per cent. ; CeHgChSOaNa requires 9*23 per cent. System : Monosymmetric .
Axial ratios : a:b:c \#151 ; 3'0529 :1 : 1*9583 .
/ 3 = 88 ' 46y .
Angle .
No. of observations .
Limits .
Mean observed .
Calculated .
100 : 101 15 56 ' 22 ' \#151 ; 56 ' 35 ' 56 ' 27 ' 101 : : 001 13 32 20 \#151 ; 32 32 32 26 32 ' 19 ' 100 : : 001 11 88 37 \#151 ; 88 55 88 50 88 46 001 : : 100 12 91 2 \#151 ; 91 12 91 7 91 14 001 : : 102 4 17 49 \#151 ; 18 2 17 55 17 54 102 : : 100 5 73 0 \#151 ; 73 43 73 15 73 20 100 : : 122 23 80 54 \#151 ; 81 17 81 9 122 : : 100 23 98 41 \#151 ; 99 2 98 51 98 51 100 : : 322 2 65 44 \#151 ; 66 1 65 52^ 65 54 322 : : 122 2 15 12 \#151 ; 15 16 15 14 15 15 122 : : 122 12 56 30 \#151 ; 56 54 56 43 122 : : 122 12 122 58 \#151 ; 123 27 123 17 123 17 101 : : 110 4 79 49 \#151 ; 80 10 80 0 80 6 110 : : lOl 4 99 49 \#151 ; 100 10 100 0 99 54 101 : : 122 4 62 35 \#151 ; 62 46 62 42 62 39 122 : : lOl 4 117 12 \#151 ; 117 27 117 16 117 21 100 : 110 4 - 71 42 \#151 ; 71 54 71 49 71 52 110 : : 110 2 36 19 \#151 ; 36 27 36 23 36 16 Zinc p-dichlorobenzenesulphonate , Zn(C6H3Cl2S03)2.8H20.\#151 ; This salt crystallises in groups of long prisms when a hot solution is allowed to cool or in single short prisms when a cold saturated solution is allowed to evaporate .
The crystals are always slightly distorted , opposite faces not being quite parallel .
The most prominent form developed is a{100 } , the other forms on the prism zone being ^{101 } , e{101 } , ^\gt ; { 301 } ; this zone is striated and no angles measured in the zone were used in calculating the axial ratios .
The faces forming the prism ends were beautifully developed , the forms being r{lll } , \#163 ; { 012 } , ${111 } .
No definite cleavage could be detected ( see fig. 9 ) .
Fig. 9.\#151 ; Zn(C6H3Cl2S03)2.8H20 .
Mr. E. H. Rod .
Water : found 22*42 per cent. ; ( C6H3Cl2S03)2.Zn.8H20 requires 21*77 per cent. Zinc : found 9*89 per cent. ; calculated 9*88 per cent. System : Monosymmetric .
Axial ratios : a:b:c \#151 ; 2*9985 :1 : 2*4539 .
/ 3 = 79 ' 20 ' .
Angle .
No. of observations .
Limits .
Mean observed .
Calculated .
101 111 15 59 ' 44'- -59 ' 51 ' 59 ' 47 ' 101 = 111 7 60 20- -60 29 60 26 60 ' 26 ' 001 : 012 15 50 18- -50 27 50 20 012 : 012 7 79 14- -79 23 79 19 79 20 001 : 111 12 65 30- -65 42 65 38 111 : 111 8 42 45- -43 1 42 51 42 49 111 : 001 7 71 23- -71 37 71 31 71 33 100 : 111 6 68 52- -69 0 68 57 68 56 111 : 111 4 34 40- -34 44 34 42 34 44 111 : 001 4 76 19- -76 24 76 21 76 20 101 : : 111 2 64 9- -64 12 64 lot 64 8 100 : : 101 14 44 30- -44 53 44 40 44 24 101 : : 001 11 34 33- -34 52 34 41 34 56 100 : : 001 12 79 16- -79 29 79 23 79 20 001 : : 101 3 43 28- -43 34 43 31 43 28 101 : i 301 3 33 41- -33 48 33 45 33 47 001 : : 301 12 77 14- -77 23 77 18 77 15 SOI : : 100 16 23 16- -23 25 25 1 19 23 25 Magnesium p-dicklorobenzenesulphonate , ( C6H3Cl2S03)2Mg.8H20.\#151 ; Welldeveloped crystals of this salt were obtained in the form of fairly stout plates or short prisms by allowing an aqueous solution to evaporate slowly at 25 ' C. The angular measurements of the crystals are almost identical with those of the zinc salt .
The crystals belong to the hemimorphic class of the monosymmetric system , as they are destitute of a plane of symmetry , the two ends of the prisms ( which are elongated in the direction of the b axis ) being differently developed .
The form { 212 } invariably appears on only one end of the prism , being sometimes so largely developed at that end that other forms are almost entirely suppressed .
The prisms appear to consist of two individuals imperfectly twinned on { 010 } , and to be expanded in a belt around the middle of the prism ; moreover , the faces on opposite ends of the prism are never truly parallel .
Fig. 10.\#151 ; Mg(C6H3Cl2S03)2.8H20 Morphological Studies the Benzene Series .
The forms developed are the same as those obtained in the ease of the zinc salt , together with the hemimorphic form { 212 } .
The habit is slightly different from that of the zinc salt , as a comparison of the two figures will show .
The prism zone is badlv striated parallel to the axis .
No definite cleavage was detected ( see fig. 10 ) .
Water : found 22'66 ; calculated 23*23 per cent. System : Monosymmetric hemimorphic .
Axial ratios : a :b:c=2*9970 :1 : 2*4450 .
\#163 ; = 79 ' 41\#163 ; ' .
Angle .
No. of observations .
Limits .
Mean observed .
Calculated .
101 : 111 15 59 ' 45'\#151 ; 59 ' 54 ' 59 ' 49 ' 111 : III 8 60 16 \#151 ; 60 26 60 23 60 ' 22 ' j 111 : : 111 12 51 41\#151 ; 52 19 51 57 100 : : 111 9 68 46\#151 ; 69 17 69 2 69 3 111 : : 111 16 34 31 \#151 ; 34 48 34 43 111 : : 100 11 76 5\#151 ; 76 24 76 14 76 14 001 : : 111 1 \#151 ; 65 35 65 41 111 : : 111 7 42 50 \#151 ; 43 6 42 57 42 56 111 : 001 2 71 19\#151 ; 71 29 71 24 71 23 100 : :2I2 4 67 34 \#151 ; 67 52 67 47 67 43 212 : : 012 2 \#151 ; 28 53 28 52 012 : : 100 2 83 12\#151 ; 83 22 83 17 83 25 001 : : 012 4 .
50 16 \#151 ; 50 22 50 19 50 15\#163 ; 212 : : III 4 18 2\#151 ; 18 10 18 6 18 16 The values are summarised in the following table:\#151 ; Salt .
w. Axial ratios .
a : b : c. A Fractions used .
Equivalence parameters.* x : y : z. }6H5S03)2Zn.6H20 100 3 546 : : 1 : : 1 -108 86 ' 6 ' 4 c/ 3 9 -4844 : 3 9513 : 2 -6747 36H6S03 ) 2Mn.6IL\gt ; 0 100 3-602 : : 1 : 1 -1142 86 24\#163 ; 4c 13 9-5640 : 3 -9448 : 2 -6552 J6H5S03)2Mg.6H ; 0 100 3-538 : : 1 : : 1 -1099 86 38 4c/ 3 9 -4940 : 3 -9321 : 2 -6834 36H5S03)2Cd.6H20 100 3 645 : : 1 : 1 -123 86 20i 4c/ 3 9 -6160 : 3 *9500 : 2 -6381 36H5S03)2Cu.6H20 100 3-653 : : 1 : : 1 -114 86 38 4c/ 3 9 -6547 : : 3 -9257 : 2 -6430 36H4CH3.S03)2Zn.6H20 112 4-020 : : 1 : : 1 -1081 88 26 4c/ 3 10-709 : : 3 -9266 : : 2 -6637 36H4CH3.S03)2Mn.6H.,0 112 4-078 : : 1 : 1 -1131 88 18J 4c/ 3 10 -7882 : : 3 -9261 : : 2 -6454 D6H4CH3.S03)2Mg.6H20 112 4 -035 : : 1 : : 1 -1055 88 274 4c/ 3 10-7362 : : 3 -9220 : 2 -6608 D6H3Cl2S03)2Zn.8H20 ... 108 2 -4539 : : 1 : : 2 -9985 79 20 3a/ 2 , c/ 2 9 -9770 : : 4 -0637 : : 2 -7106 36H3Cl2S03)2Mg.8H20 ... 108 2-4450 : : 1 : 2 -9970 79 414 3a/ 2 , c/ 2 9 9507 : : 4 -0658 : : 2 -7132 D6H4CH3S03)NH4 50 0 -8922 : : 1 : 1 -4505 90 0 3a/ 2 , c/ 2 5 -1030 : : 3 -6758 : : 2 -6656 C6H4CH3S03)K.H20 48 0-8650 : : 1 : 3 -2982 90 0 2a , c/ 4 3 -2285 : : 5 -5854 : : 2 -6618 06H4CH3SO3)Ag 44 1 -4329 : : 1 : : 2 -5286 87 144 c/ 3 3 -3163 : : 4 -7520 : : 2 -7957 06H3Cl2SO3 ) Na .
HoO 42 1 -9583 : : 1 : : 3 -0529 88 46 2a/ 3 , c/ 4 4 -5650 ; :3 -4965 : :2 -6563 C6H3C12S03)K 38 0 -7636 : : 1 : : 1 -5054 83 274 3a/ 2 , c/ 2 4 -0548 : : 3 *5401 : : 2 -6646 !
6H3C12S03H.3H20 50 0 -2918 : : 1 : : 0 -6255 79 36 2a , 3c/ 4 3 -3296 : : 5 -7050 : 2 *6763 or 150 0 -2918 : : 1 : : 0 -6255 79 36 2a , 3c/ 4 9 -9888 : 5 -7050 : 2 -6763 * The choice of symbols for the parameters being arbitrary , the values have been arranged so as to bring 3m into harmony and are not always in the order corresponding to the axial ratios .
Mr. E. H. Rod .
A glance at the column of equivalence parameters shows that , throughout the series , with one exception , one parameter has a practically constant value , as it varies only between 2-64 and 2*68 , the mean value being 2*658 .
This value has been met with in all the salts of tervalent metals previously discussed and must be taken to represent the distance between corresponding points in successive layers of benzene complexes in rhombohedral marshalling .
The occurrence of this value is proof that in the crystalline structure of all the salts considered , as in those of tervalent metals , the substituting groups are not intruded be the layers of benzene complexes but are included within and form part of these layers .
In view of the conclusion that the crystalline form of p-dichlorobenzene-sulphonic acid is similar to that assumed by salts of tervalent metals and that its molecules become grouped in triads , it is important to consider whether there be any evidence of such an arrangement in the case of the salts of monad metals .
In only one instance , that of potassium p-toluenesulphonate , does this appear to be immediately obvious .
The axial ratio : in this salt is 0865 :1 , a value almost identical with the ideal trigonal ratio 0866 :1 .
It will be noticed that the parameter values of this salt are very similar to those of dichlorobenzenesulphonic acid and that the two compounds have nearly the same valency volume .
It is further legitimate to assume that as the value 2*6618 represents the thickness of each layer , the value ( 3*2285 ) is that in the direction DO in fig. 6 , the y value ( 5*8855 ) being that of AD .
In silver toluene-/ \gt ; -sulphonate one parameter has the value 2*7957 , which is practically that of the z parameter of the second form of benzene , 2*780 .
It is highly probable , therefore , that the crystal structure of this compound is modelled on the hexagonal type of benzene marshalling , not the rhombohedral .
It has been pointed out already that the two modes of arrangement differ essentially only in the manner in which successive layers of benzene complexes are packed together one upon the other .
It is conceivable that the trigonal arrangement prevails also in this salt and that it differs merely in being derived from " hexagonal " rather than " rhombohedral benzene .
" Further , it may be regarded as not improbable that the remaining salts of the group are similarly constituted , though the evidence is of such a character that no definite conclusion is possible at present .
Though the equivalence parameters of the rhombohedral type of benzene are not known , they are probably numerically very close to those of ^\gt ; -diiodo-benzene .
The equivalence parameters of this substance are x:y:z = 3*1402:3*6161:2*6419 .
When one hydrogen atom is displaced by the sulphonic group , it is to be expected that a considerable elongation will be produced in one direction in Morphological Studies in the Benzene Series .
309 the crystal structure , that is to say , in the direction either of the x or of the y parameter ; it may also be anticipated that the adjustments necessary to bring the assemblage into a close-packed condition would involve a certain amount of distortion which would affect the dimension of the other parameter .
The introduction of molecules of water of crystallisation would also produce a dimensional change , probably an elongation in the same direction as that affected by the sulphonic group ; a methyl group in the ^-position might be expected to produce an elongation in the same direction .
Finally , it is to be supposed that one parameter in each of the salts would correspond more or less closely with either the x or the value of rhombohedral benzene , i.e. with 3T40 or 3-616 ; the other should be considerably greater .
It is noteworthy , therefore , that in the three salts under consideration the y parameter approaches as closely as can be expected to the y value , 3-616 , of jp-diiodobenzene , the third parameter being considerably elongated and varying according to the nature of the compound .
Equivalence parameters .
Salt C6H3Cl2S03.Na .
H20 ... ... . .
4-5650 : 3-4965 : 2-6563 C6H3C12S03.K ... ... ... ... .
4-0548 : 3-5401 : 2-6646 C6H4CH3S03.NH4 ... - ... ... . .
5 1030 : 3-6758 : 2*6656 As the argument adopted in the previous communication and also in the present has been that there is close analogy in structure between p-diiodo-benzene and the sulphonates of pseudo-trigonal form , this close correspondence between the salts of the monad metals and the diiodo-compound might be regarded as an indication that these latter salts are also of pseudo-trigonal form .
If this point of view be accepted , the y values should be trebled and , therefore , are not to be compared with those of the salts of bivalent metals .
A second possibility , however , is that in some cases the structure of the salts of monad metals is similar to that which appears to be characteristic of those of dyad metals now to be discussed , two atoms of the monad metal taking the place of the dyad .
Probably such questions as these will be settled only by the study of the optical properties of the salts or by the application of methods such as are now being developed involving the use of X-rays .
Passing to the salts of bivalent metals , the marked elongation of the x parameter is the striking feature ( see table , p. 307 ) .
It is scarcely possible to doubt that the influence of the metallic atoms is exercised from a mean position between two " lines " of benzene molecules which become thrust apart by the intrusion of the sulphonic radicles connected in pairs with the metallic atoms and the attendant molecules of water .
This mode of arrangement is represented in fig. 11 , which is drawn to scale in the manner already explained .
Mr. E. H. Rod .
On contrasting the parameter values with the dimensions of the full-line figure , which is constructed from the assumed parameter values of rbombo-hedral benzene and the valency volume of the salt , it appears that whilst slight compression is exercised in one direction ( that of there is a corresponding expansion in the direction at right angles to x. This alteration , which is shown by the broken line figure , corresponds to that involved in the case of trigonal salts in the compression of the irregular figure into the triangular form .
It may be taken to represent the orienting influence exercised at and from the centre of the metallic atom .
It appears to be a noteworthy point that whereas in the case of the salts of triad and monad metals a perfect cleavage plane exists in the plane of the layers of benzene , no such cleavage is manifest in salts of the dyad metals .
On reference to fig. 6 , it is noticeable that whereas , in the case of the triad metallic salts , the three hydrogen atoms displaced are in one plane , the two atoms displaced by the salts of the dyad metal are in different planes .
Obviously if the atoms thus displaced were those belonging to different benzene molecules in two superposed layers , the benzene layers would be tied together and it is not only conceivable but to be expected that in such a case there would be no cleavage plane .
The present inquiry has shown that in selecting for study paradibromo-benzenesulphonic acid and the rare earths a peculiarly fortunate choice was made , as attempts to use other acids and other oxides of tervalent metals have been attended with but little success .
The acids used unsuccessfully include ^-diiodobenzenesulphonic , p - bromobenzenesulphonic , 1*3 - dibromobenzene-4-sulphonic , T3-dibromobenzene-5-sulphonic , m-nitrobenzenesulphonic and m- and p-benzenedisulphonic acids .
The salts derived from p-diiodobenzene-sulphonic acid are noteworthy on account of their slight solubility in water ; they crystallise in thin flakes unsuitable for goniometric measurement .
The following figures show how much less soluble the salts of the diiodo-acid are than those of the dibromo-acid :\#151 ; Fig. 11 Morphological Studies in the Benzene Series Salt .
La(C6H3Br2S03)3.9H20 .
Nd(C6H3Br2S03)3.9H20 Nd(C6H3I2SO3)3.10H2O .
Anhydrous salt dissolved per 100 grm. water at 25'1 ' C. 4'52 grm. 6-81 " " Of the salts of the other acids used , none crystallised well from water , most of them being very soluble ; nor were better results obtained when either alcohol or ethylic acetate or mixtures of these with water were used as solvents .
In the hope of gaining information which would be of service in determining the position of the rare earths in the periodic scheme of classification , the ferric , chromium and aluminium salts of ^\gt ; -dibromobenzenesulphonic acid were studied ; unfortunately , these all crystallise with much water in masses of very fine needles and have not been obtained in measurable form .
The normal ferric salt , a white compound , is stable only in presence of an excess of acid : water readily hydrolyses it into a yellow basic salt , Fe(0H)(C6H3Br2S03)2.12II20 ; this is further decomposed by water in neutral solution and converted into a more basic salt the composition of which has not been determined .
Although it has not therefore been possible to establish any morphotropic relationship between the salts of the rare earth metals and those of other tervalent metals , yet it is extremely probable that some such relationship does exist .
In this connexion , it is interesting to note that Bodman* has shown that the nitrates of didymium and bismuth are isodimorphous and crystallise together .
The p-Dibromobenzenesulphonates of Iron , Chromium and Aluminium .
The following is a brief account of these salts , which have not hitherto been described .
In each case the salt was prepared by dissolving the hydroxide of the metal , purified by dialysis , in a solution of the sulphonic acid .
Ferric p-dibromobenzenesulphonate.\#151 ; Ferric hydroxide dissolves only to a limited extent in jp-dibromobenzenesulphonic acid .
The solution so obtained is dark yellow when hot but colourless when cold ; it deposits the normal ferric salt in the form of a mass of very fine white needles .
This salt cannot be recrystallised from water , since it is stable only in presence of excess of acid .
For analysis it was filtered from the solution , washed with cold water and dried on a porous plate ; on standing , it gradually became yellow , owing to loss of water .
The ratio of metal to acid radicle was determined by dissolving the salt in cold water , precipi- vol. lxxxix.\#151 ; A. Mr. E. H. Kodd .
ammonium y ?
-dibromobenzenesulphonate left in solution being determined by evaporating to dryness and weighing .
The mean of two determinations gave Fe : ( C6H3Br2S03 ) = 1 : 2'985 .
The results obtained for the sample analysed agreed with the formula Fe(C6H3Br2S03)3.13H20 but it is doubtful whether this be the true formula .
Fe ( C6H3Br2S03 ) H20 Calculated ... ... . .
4'53 per cent. 76'52 per cent. 18-95 per cent. Found ... ... ... ... 4-55 " 76'39 " 19-69 " The salt dissolves readily in alcohol and ether giving yellow solutions .
Basic Ferric p-dibromobenzenesulphonate.\#151 ; When the normal salt is dissolved in warm water and the solution is allowed to cool , a basic salt separates in the form of golden yellow spangles .
This salt is itself decomposed by warm water giving a brick-red coloured precipitate which has not been analysed .
The analytical figures for the yellow salt agree with the formula Fe(0H)(C6H3Br2S03)2.12H20 .
Fe H20 Calculated ... ... 6"05 per cent. 23"50 per cent. Found ... ... ... . .
6'06 " 23*92 " Chromium p-dibromobenzenesulphonate.\#151 ; This salt crystallises from aqueous solution in masses of fine bluish needles , very soluble in water , giving a dichroic solution .
It is soluble also in alcohol and ether .
The analytical results agree with the formula Cr(C6H3Br2S03)3.14H20 .
Ratio Cr :(C6H3Br2S03 ) = 1 : 2*86 .
Cr ( C6H3Br2S03 ) H20 Calculated ... ... .
4"21 per cent. 75"62 per cent. 20"17 per cent. Found ... ... ... . .
4-42 " 75-60 " 19-87 Aluminium p-dibromobenzenesulphonate.\#151 ; This salt crystallises in masses .of fine white needles from aqueous solution .
It is easily soluble in water and in alcohol and ether .
Analytical results agree with the formula Al(C6H3Br2S03)3.18H20 .
Ratio A1 : ( C6H3P\gt ; r2S03 ) found = 1 : 3'00 .
A1 ( C6H3Br2S03 ) H20 Calculated ... ... . .
2*09 per cent. 72-91 per cent. 25"0 per cent. Found ... ... ... ... .
2-10 " 73-50 " 24-0 Scandium p-dibromobenzenesulphonate.\#151 ; This salt crystallises from aqueous solution in colourless , long , thin striated plates belonging to the mono-symmetric system .
Analysis agrees with the formula Sc(C6H3Br2S03)3.14H20 .
Water : found 20"30 ; calculated 2030 per cent. Morphological Studies in the Benzene Series .
Cobaltous p-dibromobenzenesulphonate.\#151 ; The salt was obtained in an attempt to prepare the cobaltic salt by neutralising the acid with eobaltic oxide ; it crystallises in long thin pink needles .
Analysis agrees with the formula Co(C6H3Br2S03)2.9H20 .
Water : found 18*96 ; calculated 19*04 per cent. Cobalt in anhydrous salt : found 8*57 ; calculated 8*56 per cent. Summary .
The present account is an extension of the previous communication in which it was shown that the ^-dibromobenzenesulphonates of several of the tervalent rare-earth metals all crystallise in pseudo-trigonal forms .
In the light of the Barlow-Pope hypothesis these are to be regarded as so constituted that the molecules are arranged in layers in a plane at right angles to the pseudo-trigonal axis .
Each such layer appears to be of the thickness attributed to a single layer of benzene molecules in crystalline benzene or one of its halogen derivatives .
In the formation of the sulphonate the benzene structure is opened out to admit of the introduction of the sulphonic radicles , of the metallic atoms and of water molecules between the benzene molecules in such manner that the trigonal symmetry of the original structure is either preserved or at most only slightly modified .
It is now shown that similar conclusions may be drawn with reference to the structure of |\gt ; -dichlorobenzenesulphonic acid , several salts of which isomorphous with ^-dibromobenzenesulphonates are described .
The structure of sulphonates containing monad and dyad metals is also discussed .
It is argued that in the formation of the latter the molecules of benzene in contiguous rows become separated by the intervention of the sulphonic radicles ( together with water ) which are united in pairs by the metallic atom .
The structure of the salts containing monad metals appears in some cases to be pseudo-trigonal like that of the acid ; in others to resemble that of salts of dyad metals .
Diagrams to scale are given illustrating the molecular structure of the several types of crystal .
It is proposed to study the optical properties of crystals of salts such as those described , in the hope of discovering criteria significant of the several types .
2 c VOL. LXXXIX.\#151 ; A. The Energy of R Rays .
319 The tube D had been lined inside with shellac to obviate such an occurrence but it was thought that discharge might take place from the aluminium window , 1 mm. diameter , which , of course , could not be covered with shellac .
An earthed ring electrode was accordingly placed at E , so as to prevent such discharge reaching the lining of the tube A. Then the discharge tube was started , using cathode rays of given speed , and the ionisation in the long cylinder due to the Rontgen rays was measured for different voltages applied to the cylinder .
The cylinder in this experiment contained air at a pressure of 10 cm .
, so that saturation could be obtained at much lower voltages than 400 volts .
Hence any deviation from the usual form of saturation curve was to be attributed to a subsidiary discharge in the vacuum tube , due to the air insulation breaking down under the voltage applied to the tube D. Table I shows the values of the resistance P necessary to balance the electroscope when cathode rays of speed from 7 x 109 to 9 x 109 cm./ sec. were used .
P would , in the ordinary way , be proportional to the ionisation in the long cylinder per unit cathode ray current , and , if saturation were obtained , would be constant , in spite of altering the voltage applied to the long cylinder .
How , from fig. 5 we see that saturation actually is attained under these conditions .
Hence any change in P as the voltage is altered would indicate a disturbed value for the cathode ray current , due to a subsidiary discharge which might be expected to increase with the voltage applied .
From Table I we must conclude that no abnormal effect comes in till the pressure in the vacuum tube is such that cathode rays of speed 9 x 109 cm./ sec. are produced .
Table I. T 103 .
Voltage on cylinder .
| V-T-109 ... 7 .
7-5 .
8 .
8-5 .
9 .
20 27 37 51 73 400 20 27 37 51 75 350 20 27 * 37 51 75 300 20 27 37 51 70 200 20 27 37 51 70 100 20 27 37 51 69 50 20 27 37 51 63 20 Let us now review the progress that has been made in eliminating experimental errors .
We have placed the long cylinder properly in alignment , and have shown that the Rontgen rays cannot strike the curved surface of this cylinder and that they are totally absorbed by the gas inside .
We
|
rspa_1913_0086 | 0950-1207 | The energy of r\#xF6;ntgen rays. | 314 | 327 | 1,913 | 89 | Proceedings of the Royal Society of London. Series A, Containing Papers of a Mathematical and Physical Character | R. T. Beatty, M. A., D. Sc.|Prof. Sir J. J. Thomson, F. R. S. | article | 6.0.4 | http://dx.doi.org/10.1098/rspa.1913.0086 | en | rspa | 1,910 | 1,900 | 1,900 | 13 | 209 | 4,418 | http://corpora.clarin-d.uni-saarland.de/surprisal/6.0.3/?id=rspa_1913_0086 | 10.1098/rspa.1913.0086 | null | null | null | Atomic Physics | 35.665199 | Electricity | 24.100911 | Atomic Physics | [
7.893956184387207,
-75.09957885742188
] | ]\gt ; The Energy of Rontgen Rays .
* By .
T. BEATTY , 1f.A .
, D.Sc .
, Emmanuel College , Clerk Maxwell Student of the University , ( Communicated by Prof. Sir J. J. Thomson , F.RS .
Received June 10 , \mdash ; Read June 26 , 1913 .
) In this paper an account will be given of experiments which have been made to determine the amount of energy which reappears as Rontgen radiation when homogeneous cathode rays of given speed fall upon anticathodes of different materials .
The method of attack is modified from that used in a previous research on " " The Direct Production of Bontgen Badiations by Cathode Particles.\ldquo ; Fig. 1 is taken from that paper , and shows how cathode rays of given speed , which have been isolated by means of magnetic deflection , strike an anticathode situated in the tube A. The Bontgen rays so produced pass into an ionisation vessel , and the ionisation due to them is measured by an electroscope C. omogeneous FIG. 1 .
Now , in order to absorb the Rontgen rays completely , and so measure their total energy of ionisation , a long zinc cylinder was made , 150 cm .
long and 10 cm .
in diameter .
A calculation of the absorption coefficients of various substances for Rontgen rays showed that , if this cylinder were filled with air which had been saturated with the vapour of methyl iodide at room temperature , then total absorption of the ontgen rays should take place if The expenses of this research have been partly covered by a Government Grant from .
the Royal Society .
Beatty , ' Roy .
Soc. Proc , vol. 87 .
pp. 511-518 .
The Energy of Rontgen Rays .
the rays were generated by cathode rays whose velocity did .
not exceed cm .
per second .
In the next place , it was desirable that the thin window through which the Rontgen ) escape from the vacuum chamber into the ionisation chamber should be so thin that the absorption of the ontgen rays by it could be neglected .
This is an essential point , because even homogeneous cathode rays , on an anticathode , become heterogeneous as they penetl.ate into the anticathode , and so give rise to heterogeneous ontgen rays .
We know the absorption coefficients of most of the common elements for homogeneous Bontgen rays , but evidently cannot apply these values to the heterogeneous ntgen rays now under discussion .
To produce the thin window , a lead plate 1 mm. thick was pierced with a number of fine holes , each about 1/ 30 mm. diameter , the holes all lying within a circle of mm. diameter .
This was accomplished by placing the lead plate on a plate of glass and making the holes with a very fine needle ; the lead plate was then covered with aluminium leaf mm. thick , which was stuck on with shellac , and in this a window was produced , which would stand a difference of pressure of an atmosphere on the two sides , and whose maximum absorption of the rays which were used did not exceed 1 per cent. In fig. 2 the ionisation chamber is shown placed in position .
A cone of rays has been represented as starting from the illuminated portion of the anticathode , passing through the window , and diverging the chamber .
viously , the actual cone of -rays must lie inside one if the rays are to be totally absorbed without the curved surface of the cylinder .
The axis of the beam of rays was found by a photographic method , and the cylinder correspondingly aligned .
The cylinder was then waxed on to the end of the vacuum tube , as shown in fig. 2 , and air saturated with the vapour of methyl iodide was drawn into it .
Dr. R. T. Beatty .
From fig. 3 it will be seen that , on plotting the ionisation caused by the rays against the sixth power of the velocity of the cathode rays , straight lines are obtained , until the velocity of the cathode rays exceeds cm .
per second .
The abruptness of the change led me to suspect that the rays were not totally absorbed when this velocity was exceeded .
To test this , the zinc cylinder was replaced by one of brass , which was strong enough to be exhausted .
Methyl iodide was admitted at almost saturation pressure .
The curves ( fig. 4 ) now become straight lines within the limits of velocities used , showing that , as suspected , total absorption had not been obtained with the .
A number of experimental errors have , however , still to be discussed , and it will be shown that the real relation is quite different from that shown in fig. 4 .
These preliminary results having been obtained , a more detailed investigation was now made of possible experimental errors .
Elimination of Errors .
In the first place , the method of averaging a galvanometer deflection over the space of a minute is unsatisfactory with such a fluctuating current as is Tloe Energy of Rontgen Rays .
given by a discharge tube .
Frequently , out of ten attempts to take a reading , only one is obtained with a sufficiently steady reading of the galvanometer .
FIG. 4 .
This unsteadiness of the tube is , indeed , the greatest difficulty met with in work of this kind .
In a previous paper on " " The Direct Production of Characteristic Rontgen Radiations\ldquo ; .
cit a balancing method was used , in which the depended only on the ratio of two resistances and , the electroscope being used as a null instrument .
One of these resistances was composed of a mixture of copper sulphate and glycerine , the other of xylol and absolute alcohol .
It was determined to use a similar method in the present experiment , but to employ metallic resistances .
318 Dr. R. T. Beatty .
These resistances will be but briefly described here , as a complete description of them will form the subject of a separate paper .
They were made by depositing films of platinum vacuo upon quartz rods until the required conductivity was obtained .
The necessary metallic connections were sealed in the evacuated glass tube and soldered to the ends of the quartz rod .
The behaviour of these films is a function of their thickness .
They are quite unstable when the esistance lies between and ohms ; for smaller resistances they become more constant , while for resistances greater than ohms they acquire perfect stability in a few weeks ; in the resistances of this order which were finally selected for use Ohm 's Law was found to be obeyed .
A platinum resistance of this kind was now used for , its resistance was ohms ; a laboratory was used for P. In the preliminary experiments , approximate saturation of the ionisation current had been obtained with a central rod electrode when the cylinder was kept at a potential of 400 .
To obtain complete saturation more drastic methods were now found necessary .
A rectangular framework of copper gauze , 6 cm .
cm .
in cross-section and 1 metre in length , was used as electrode , and inside this a gauze strip 3 cm .
broad was tightly stretched , so that when the outer brass cylinder and the gauze strip were kept at 400 volts the potential gradient never fell below 260 Yolts centimetre anywhere in the region where ionisation took place .
Fig. 5 shows the saturation curve so obtained with different pressures of methyl iodide .
There was still a possibility that since the tube ( fig. 2 ) was at a potential of 400 volts , it might act as anode to the vacuum tube when the discharge was running , and so give a wrong value to the cathode ray current .
FIG. 5 .
The Energy of Rontgen Rays .
The tube had been lined inside with shellac to obyiate such an occulTence it was thought that discharge might t , ake place from the aluminium window , 1 mm. diameter , which , of course , could not be covered with shellac .
An earthed electrode was placed at , so as to prevent such discharge reaching the of the tube A. Then the discharge tube was started , using cathode rays of given speed , and the io.nisation in the long cylinder due to the Rontgen rays was measured for different voltages applied to the cylinder .
The cylinder in this experiment contained air at a pressure of 10 cm .
, so that saturation could be obtained at much lower voltages than 400 volts .
Hence any deviation from the usual form of saturation curve was to be attributed to a subsidiary in the vacuum tube , due to the air insulation breaking down under the voltage applied to the tube D. Table I shows the values of the resistance necessary to balance the electroscope when cathode rays of speed from to cm . .
were used .
would , in the ordinary way , be proportional to the ionisation in the cylinder per unit cathode ray current , and , if saturation were obtained , would be constant , in spite of the voltage applied to the oIJg cylinder .
Now , from fig. 5 we see that saturation actually is attained under these conditions .
Hence any change in as the voltage is altered would indicate a disturbed value for the cathode ray current , due to a subsidiary discharge which might be expected to increase with the applied .
From Table I we must conclude that no abnormal effect comes in till the pressure in the vacuum tube is such that cathode rays of speed cm . .
are produced .
Table I. Let us now review the progress that has been made in eliminating experimental errors .
We have placed the ; cylinder properly in alignment , and have shown that the Bontgen rays cannot strike the curved surface of this cylinder and that they are totally absorbed by the inside .
We Dr. R. T. Beatty .
have obtained complete saturation of the ionisation current , and we have shown that no subsidiary or false discharge occurs till the speed of the cathode rays rises to 9 cm .
The method of balancing the electroscope readings requires that the platinum resistance should keep constant and obey Ohm 's law .
Only a brief mention of its behaviour has been made in this paper , but in a later contribution it will be shown that these conditions were fulfilled in the resistances which were selected for use .
Effect of Reflected Cathode Rays .
But there is an additional possibility of error which at first sight appeared formidable .
When cathode rays strike an anticathode some of them are turned back and do not complete their path in the anticathode .
Now if a considerable amount of the energy ( not necessarily the number ) of the cathode rays is diverted in this way a correction must be made in our results .
But the whole subject of scattering of cathode rays of speeds from to .
has never been studied quantitatively .
Measurements have only been made for where in some cases 70 per cent. of the incident beam has been found to be reflected , and for cathode rays of speeds of 1000 volts or less , where no reflected rays of speed greater than 25 volts have been found .
One might , as Sir J. J. Thomson suggested to me , make the anticathode of metal leaf in the form of a Faraday cylinder so as to catch all the cathode rays .
Such a cylinder , however , would have subtended so large an angle at the window that the emergent cone of rays would have struck the wall of the ionisation cylinder before completely absorbed by the gas inside .
Evidently the Faraday cylinder must be made extremely small .
Now a surface of soot or platinum black may be considered as an aggregate of imperfectly formed Faraday cylinders and it be expected that less reflection would be obtained from such surfaces than from the polished material .
To test this point the ionisation cylinder and the window were removed and a brass tube furnished with two diaphragms and a Faraday cylinder was substituted ( fig. 6 ) .
The number of reflected cathode rays entering this cylinder was determined as a fraction of the number of primary rays incident on the * Kovarik , ' Phil. Mag Nov. 1910 , vol. 30 , pp. 849-866 .
Lenard , ' Ann. ' 1904 , vol. 15 , p. 485 ; Von Baeyer , ' Verh .
D. P. Ges 1908 , vol. 10 , pp. 96 , 953 ; Gehrts , ' Ann. .
Phys Dec. 21 , 1911 , vol. 15 , p. 995 .
term " " cathode ray of speed of volts\ldquo ; means an electron whose speed is that which would be acquired by falling through a potential difference of volts .
The Energ.of Rontgen Rays .
anticathode .
Then knowing the solid angle of the cone of reflected rays entering the Faraday cylinder we can calculate the percentage of rays reflected in all directions .
A small bar magnet was then brought close to the Faraday cylinder so that only the faster reflected rays could reach this cylinder .
FIG. 6 .
The results are shown in Table II .
Column 4 contains the numbers in Column 3 expressed as percentages of those in Column 2 .
II .
It thus appears that soot only reflects about two fifths of the fast rays compared with graphite , while from platinum black the fast rays are only 30 per cent. of those from polished platinum .
Hence these porous materials when used as anticathodes should give a closer approximation to the form of the curve for the energy of the -rays than should graphite or polishefl platinum .
The ionisation cylinder was next put in position and filled with methyl iodide vapour .
For different speeds of cathode rays the ionisation due to the Rontgen rays was determined for four anticathodes .
On comparing the curves it was found that the results for platinum and platinum black were identical , as also those for graphite and soot .
This remarkable result shows at once that the reflected cathode rays must carry only a few per cent. of the energy of the incident cathode rays , as otherwise the energies of the emitted Bont.-en rays would not be identical for the anticathodes when polished and when finely subdivided .
Dr. R. T. Beatty .
As no further source of experimental error now appeared probable the final step was taken of comparing the ionisation energy of the rays from an anticathode with the energy of the cathode rays incident upon that anticathode .
The Final Experiments .
Results have been obtained with anticathodes of rhodium , silver , and aluminium , and preliminary curves have been obtained for copper .
As the numerical results have been calculated from the curve obtained for rhodium a few remarks may be made about the behaviour of this anticathode .
It is not easily oxidised , so that one may be sure that the cathode rays are not absorbed in a film of oxide .
Again we can obtain two characteristic radiations from rhodium .
One is to be expected when the speed of the cathode rays exceeds , but it is very easily absorbed and carries but little .
The other is known to occur when the speed of the cathode rays exceeds .
This speed was not reached in the experinnents and so the second characteristic radiation did not appear .
In fig. 7 are given the relative ionisations due to the rays per unit cathode ray when cathode rays of different speeds are used .
Ths curves for silver and aluminium are the mean of four sets of ; for rhodium eight sets were taken , while the curve for copper is merely a preliminary result .
It will be seen that when characteristic radiations are not excited the energy of the Rontgen rays is proportional to the fourth power of the velocity of the parent cathode rays .
With copper the same result holds good till the rays exceed a speed of .
, then the line bends owing to the presence of the characteristic radiation .
We now proceed to calculate the absolute values .
From fig. 7 we see that when .
the balancing resistance must be 82,400 ohms for a rhodium anticathode .
Now the resistance was ohms .
Hence Ionisation current due to -ray pencil Cathode ray current The diameter of the thin window cm .
Distance of window from anticathode Therefore Solid angle -ray pencil Hence if we assume that the -rays are emitted uniformly in all directions , The Energ.of ntgen Rays .
FIG. 7 .
324 Dr. R. T. Beatty .
where fraction of speed of light .
Since the numbers for silver and aluminium are roughly as the atomic weights , and as Kaye*has found the same result to hold for a very large number of elements , we may take for a working rule where total ionisation current due to -rays per unit of cathode ray current , atomic weight of radiator .
This will only hold in cases where characteristic radiations are not being excited .
Energy of the -rays .
The next step is to find how much energy the -rays possess relatively to the energy of the primary cathode rays .
Let X be defined as above and let mean the number of pairs of ions which would be produced by the primary cathode rays .
It is , therefore , also the ratio of the ionisation current due to the cathode rays per unit of cathode ray current .
Then we shall take the fraction as that fraction of the energy of the cathode rays which reappears as -rays .
Is this assumptionjustifiable ?
If the X-rays were first transformed into cathode rays , as the case when air is ionised according to Wilson 's experiments , and if no loss of energy accompanied such a transformation , then the relative ionisations would really be a measure of the relative energies .
The author , however , has that in the ionisation of the vapours and gases , Ni , direct ionisation is produced in addition to the indirect ionisation through the intermediate production of cathode rays .
Possibly this direct effect only happens when the ionised gas has its characteristic radiation excited .
If direct ionisation is also produced in then relative ionisations are not necessarily a measure of relative energies .
Nevertheless , a consideration of other results leads to the conclusion that the proportionality holds even in such cases .
Thus KleemanS has found that direct ionisation takes place with -rays , and yet the relative number of ions produced by , and * Kaye , ' Phil. Trans , vol. 209 , pp. 123-151 .
Wilson , ' Roy .
Soc. Proc 1912 , , vol. 87 .
Bearty , ' Boy .
Soc. Proc 1911 , , vol. 85 .
S Kleeman , ' Roy .
Soc. Proc 1909 , , vol. 82 .
The Energy of Rays .
-rays keeps remarkably constant as we pass from one gas to another .
* has found a similar proportionality for cathode rays and -rays in the case of and .
Hence we may assume the same proportionality in the present experiment .
No data exist as to the total number of ions produced in by cathode rays .
We can , however , calculate the number in air , and for the present we shall assume that the same number would be produced in has found that the number of ions of one sign produced per centimetre in air by homogeneous cathode rays varies inversely as the energy of the rays , or .
( 1 ) When mass of electron , he found for air at N.T.P. Thus works out as has found that the rate of loss of energy of cathode particles in passing through air is given by ( 2 ) Hence the total number of pairs of ions equals .
( 3 ) Therefore , between ( 2 ) and ( 3 ) , and in the value of if equals velocity of cathode rays expressed as a fraction of the velocity of light .
Hence .
( 4 ) For example , if a platinum radiator be excited by cathode rays of speed cm .
, therefore is the energy of the ' independent -rays ; the characteristic -rays , * Kleeman , ' Phil. Mag Nov. , 1907 , p. 631 .
Barkla , 'Phil .
Mag Feb. 1912 , [ 6 ] , vol. 23 , pp. 317-333 .
Glasson , ' Phil. Mag Oct. , 1911 , vol. 22 , pp. S Whiddington , ' Roy .
Soc. Proc 1912 , , vol. 86 .
Beatty , ' Roy .
Soc. Proc 1912 , , vol. 87 .
The Energy of Rays .
which will be excited in this example , will increase the total energy emitted .
Previous Investigations .
Wien , 1905 , ated the question of the energy carried by X-rays .
He used an X-ray tube with a platinum anticathode , and employed a constant potential diflerence between cathode and anode of 58,700 volts .
He measured the energy of the -rays both a bolometer and thermopile .
The bolometer method ; the thermopile gave On the values which would be given by equation ( 4 ) : we have .
Therefore .
( 5 ) But the cathode rays in Wien 's experiment were heterogeneous , so that the energy of the bundle must have corresponded to a smaller potential than 58,700 volts .
The author has found that with such high potentials the main stream of cathode rays has a speed corresponding to about two-thirds of the potential as given by the spark gap .
When the cathode rays are deflected to give a manetic spectrum the band of luminosity on the willemite screen is discontinuous , the discontinuities corresponding to the oscillations in the at each break of the primary current in the coil .
Five or six such oscillations can usually be recognised by the cathode spectrum , the velocity of the rays decreasing with each successive oscillation .
From a study of the heterogeneous cathode rays , when analysed in this way , the author concludes that the number in formula ( 5 ) should be divided by six to correspond with the conditions of Wien 's experiment .
Then This is still higher than Wien 's results , but allowance for absorption of the soft rays due to the glass may bring the two values close together .
Evidently , one cannot correct for the absorption of these soft rays by finding the absorption due to a second piece of glass .
Whiddington found that the energy of the -rays from a silver anticathode varied nearly as the fourth power of the speed of the cathode rays .
He describes the experiment as follows:\mdash ; " " The first experiment was to see how the actual primary -ray ent , rgy ( Ep ) escaping through depended on the velocity of the cathode rays striking the anticathode .
To do this , the radiator was replaced by * Wien , ' Ann. .
Phys 1905 , 18 , vol. 5 , pp. 991-1007 .
Whiddington , ' Roy .
Soc. Proc 1911 , , vol. 85 , p. 328 .
stal Iolecular C the iouisation chamber I. After correcting the observed values of the ionisation currents for the variations of the absorption coefficients of the Rontgen rays with , it comes out that ( per unit cathode ray current ) is nearly proportional to In a subsequent paper , a discussion will be given of the results here described with regard to their .
upon theories of the method of transference of from the cathode ray to the -ray .
It gives me great pleasure to acknowledge the kindly attitude hich Sir J. J. Thonlson has continued to assume towards this work .
The the mmetry of the Simpler Organic Componnds and their Iolecu tstitution.\mdash ; Part II .
By WALTER , Ph. D. ( Communicated by Sir James Dewar , F.R.S. Received June 19 , \mdash ; Read June 26 , 1913 .
) In this paper the experimental results concerning the crystalline properties of the unsaturated aliphatic hydrocarbons , the simpler oxygen-and sulphurcompounds of carbon , the halogen-compounds , and the simpler aromatic given .
Bthylene.\mdash ; Ethylene , prepared from alcohol and sulphuric acid , was purified by liquefying it and distilling it twice .
It crystallises very well , prisms being formed .
Two distinct systems occur , one parallel to a prism and the other parallel to the basal plane ( or an orthodome ) .
The.doublerefraction is of middle strength ; the extinction is in some sections parallel to the prismatic cleavage , in others it is not .
The of the optical axes is large , and the optical character negative .
These optical observations show that ethylene crystallises in the monoclinic crystal system .
Acetylene.\mdash ; Acetylene which been from lcium carbide WfiS purified by passing it through a solution of chromic acid in acetic acid , and by subsequently it by cooling with liquid air .
The temperature of the solid mass was then to rise until it began to evaporate , and the first and last portions to evaporate pumped away , the middle portion only collected .
These operations -ere repeated twice .
|
rspa_1913_0087 | 0950-1207 | The relation between the crystal symmetry of the simpler organic compounds and their molecular constitution. \#x2014;Part II. | 327 | 339 | 1,913 | 89 | 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.1913.0087 | en | rspa | 1,910 | 1,900 | 1,900 | 7 | 288 | 6,073 | http://corpora.clarin-d.uni-saarland.de/surprisal/6.0.3/?id=rspa_1913_0087 | 10.1098/rspa.1913.0087 | null | null | null | Atomic Physics | 33.536465 | Chemistry 2 | 30.813316 | Atomic Physics | [
-10.417152404785156,
-46.231815338134766
] | Crystal Symmetry and Molecular Constitution .
327 the ionisation chamber I. After correcting the observed values of the ionisation currents for the variations of the absorption coefficients of the Rontgen rays with v , it comes out that E ( per unit cathode ray current ) is nearly proportional to vC ' In a subsequent paper , a discussion will be given of the results here described with regard to their bearing upon theories of the method of transference of energy from the cathode ray to the X-ray .
It gives me great pleasure to acknowledge the kindly attitude which Sir J. J. Thomson has continued to assume towards this work .
The Relation betiveen the Crystal Symmetry of the Simpler Organic Compounds and their Molecular Constitution.\#151 ; Part II .
By Walter Wahl , Ph. D. ( Communicated by Sir James Dewar , F.R.S. Received June 19 , \#151 ; Read June 26 , 1913 .
) In this paper the experimental results concerning the crystalline properties of the unsaturated aliphatic hydrocarbons , the simpler oxygen- and sulphur-compounds of carbon , the halogen-compounds , and the simpler aromatic hydrocarbons are given .
Ethylene.\#151 ; Ethylene , prepared from alcohol and sulphuric acid , was purified by liquefying it and distilling it twice .
It crystallises very well , large prisms being formed .
Two distinct cleavage systems occur , one parallel to a prism and the other parallel to the basal plane ( or an orthodome ) .
The .doublerefraction is of middle strength ; the extinction is in some sections parallel to the prismatic cleavage , in others it is not .
The angle of the optical axes is large , and the optical character negative .
These optical observations show that ethylene crystallises in the monoclinic crystal system .
Acetylene.\#151 ; Acetylene which had been prepared from calcium carbide was purified by passing it through a solution of chromic acid in acetic acid , and by subsequently solidifying it by cooling with liquid air .
The temperature of the solid mass was then allowed to rise until it began to evaporate , and the first and last portions to evaporate were pumped away , the middle portion only being collected .
These operations were repeated twice .
Dr. W. Wahl .
Relation between Acetylene cannot be liquefied at ordinary pressure , but is condensed directly in the solid state .
If condensed at not too low a temperature , it forms small isotropic crystals , which consist of cubes , the corners of which are cut off by the octahedron .
On further cooling , a transition occurs , and the small crystals become strongly double-refracting .
This transition takes place very readily and is reversible .
If the gas is condensed by rapidly cooling the crystallisation vessel with liquid air , it is condensed directly into the double-refracting modification .
This then grows in the shape of small prismatic crystals which exhibit a parallel extinction .
This second form of acetylene is therefore tetragonal , hexagonal or rhombic .
At certain temperatures both modifications are seen to form simultaneously , and the one subsequently changes rapidly into the other according as the temperature is above or below that of the transition point .
Carbon Monoxide.\#151 ; Carbon monoxide was prepared by heating a mixture of sodium formate and sulphuric acid and passing the gas through caustic potash solution .
It was then purified by condensation and fractionating .
Carbon monoxide crystallises in the regular crystal system .
The manner of growth indicates that the prevailing form is that of the rhombic dodecahedron .
Carbon Dioxide.\#151 ; Carbon dioxide has been investigated by Liversidge , * who found that it crystallises in the regular system .
Recently Behnken has described an elaborate apparatus which has been used for the investigation of carbon dioxide and some other gases.f According to the observations of Behnken carbonic acid is regular .
When pure , dry carbon dioxide is condensed in the crystallisation vessel by cooling with liquid air it condenses in the form of small cubes which are quite isotropic .
No polymorphic change was observed above \#151 ; 210 ' .
Carbon Oxychloride.\#151 ; A bottle containing a 20-per-cent , solution of phosgene in toluene ( Kahlbaum ) was connected with the condensation vessel of the apparatus used for fractionating the hydrocarbons and the other gases .
The whole apparatus was first exhausted and the condensation vessel then cooled in liquid air , and the stopcock separating the phosgene solution from the condensation vessel was then opened .
In this way sufficient phosgene was gradually pumped out of the solution and condensed in the crystallisation vessel .
It was then allowed to boil off and the higher boiling part collected over mercury .
On investigation in the crystallisation vessel , it was , however , found that the entire quantity of the liquefied gas did not crystallise simultaneously , but that small isotropic crystals were deposited on * A. Liversidge , 'Chem .
News , ' vol. 71 , p. 152 ; vol. 77 , p. 216 .
t H. E. Behnken , ' Phys. Kev .
, ' 1912 , vol. 35 , p. 66 .
Crystal Symmetry and Molecular Constitution .
329 the walls of the crystallisation vessel at a much higher temperature than that at which the principal part crystallised .
These crystals apparently belonged to carbon dioxide , and the presence of hydrochloric acid gas was , therefore , also probable , the two being the products of the action of moisture on phosgene .
It seems that these admixtures are not sufficiently removed by condensation .
The gas was , therefore , admitted to a previously evacuated glass bulb containing a small quantity of metallic sodium , and allowed to remain over this for some time .
After this treatment the phosgene was found to crystallise homogeneously .
Phosgene is liquid over a considerable range of temperature .
On cooling it becomes supercooled , and an unstable modification crystallises , as a rule , out of the supercooled melt .
If cooled rapidly , the growth of this modification may be entirely arrested and the remainder of the melt becomes quite viscous .
If the preparation is allowed to get warmer after the unstable modification has been formed a transition into the stable form very soon takes place .
When this again is partially melted , it crystallises readily on cooling .
The stable modification possesses a high double-refraction , but isotropic sections occur also .
It belongs , therefore , either to the tetragonal or hexagonal system , but it has not been possible to determine to which of the two , as the cleavage is not very distinct .
The optical character of the stable modification is positive .
The unstable modification possesses an extremely high double-refraction and shows parallel extinction .
It is probably orthorhombic .
Carbon Oxysulphide.\#151 ; Carbon oxysulphide was prepared by the action of concentrated sulphuric acid on the allyl ether of isosulphocyanic acid .
The gas was purified by passing it through wash-bottles containing potassium hydroxide solution and concentrated sulphuric acid .
It was then liquefied , and , after a part had been allowed to boil off , a fraction was collected for investigation .
Carbon oxysulphide crystallises in extremely fine needles , which grow with great rapidity .
The double-refraction of these needles is very high and they always extinguish the polarised light in the position parallel to the principal sections of the nicols .
The needles are thus either tetragonal , hexagonal or orthorhombic , but it has not been possible to find any experimental evidence from which conclusions might be drawn as to which of these crystal systems the oxysulphide belongs to .
No polymorphic change has been observed above \#151 ; 200 ' .
Carbon Bisulphide.\#151 ; Carbon bisulphide crystallises in very strongly double-refracting needles which belong to the monoclinic or triclinic system.* Methyl Chloride.\#151 ; Methyl chloride was prepared by heating trimethylamine * ' Roy .
Soc. Proc. , ' A , vol. 87 , p. 379 .
VOL. LXXXIX.\#151 ; A. Dr. W. Wahl .
Relation between hydrochloride .
The gas was purified by fractionating it .
Methyl chloride crystallises from the supercooled melt in form of a fine grainy mass .
If part of this is melted and recrystallised , long needles , rapidly growing in several directions , are formed .
They are very strongly double-refracting and show parallel extinction .
On further cooling a marked cleavage in the longitudinal direction of the needles is developed , but no polymorphic change has been observed at temperatures above \#151 ; 200 ' .
As needles of parallel extinction are seen which exhibit a different strength of double-refraction they cannot belong to the tetragonal or hexagonal system , but are either orthorhombic or monoclinic with a very small angle of extinction on the clinopinakoid .
Dichlormethane.\#151 ; Methylene chloride crystallises well , long prisms being formed which seem to be terminated by a pair of domal faces .
The doublerefraction is strong and the extinction parallel to the prism axis .
This modification of dichlormethane is orthorhombic .
At low temperature it changes enantiotropically into a mass of needles of much lower doublerefraction .
Trichlormethane.\#151 ; Chloroform crystallises well .
Large crystal fields of strong double-refraction are mostly formed , but occasionally isotropic fields are developed .
In one instance one of these grew with a remarkably regular hexagonal outline .
Chloroform is thus trigonal or hexagonal .
No polymorphic change has been noticed above \#151 ; 200 ' .
Tetrachlormethane.\#151 ; Carbon tetrachloride crystallises at \#151 ; 22 ' in isotropic grains , but when the temperature is lowered a transition into a double-refracting mass takes place at \#151 ; 47'.* Methyl Bromide.\#151 ; When cooled , methyl bromide , as a rule , becomes strongly supercooled , but at a very low temperature crystallisation takes place , the resulting product being a fine grainy mass , which shows " aggregate-polarisation .
" When the preparation is allowed to get warmer gradually , strongly double-refracting prisms of another modification grow slowly in the grainy mass , and at still higher temperature these change into a third modification which also grows in prismatic forms , but is not as strongly double-refracting as the second modification .
Very soon after this transition the crystals melt .
The second modification has also been obtained directly by crystallisation of the supercooled melt .
The transition between Form I and Form II takes place readily in both directions .
As stated , Form III on heating grows quite slowly in Form II , and if the preparation is again cooled when only part of III has changed into II , the further growth of II is arrested , but it does not change back into III .
This is probably due to a very * This transition has recently been described by V. M. Goldschmidt , 'Zeitschr .
f. Krystallographie , ' 1912 , vol. 51 , p. 26 .
Crystal Symmetry and Molecular Constitution .
331 small velocity of transition , and to the falling- off of this velocity to almost negligible value on lowering the temperature , whereby , at low temperatures , a kind of pseudo-equilibrium between the Forms II and III results .
The modification I , which is stable at the melting-point , crystallises in the monoclinic crystal-form , and is sometimes twinned according to the orthodome .
The extinction angle between the two halves is in maximum only about 12 ' , which gives an extinction angle of about 6 ' on the clinopinakoid .
The modification II possesses , as already stated , a much stronger doublerefraction .
It is orthorhombic , or , possibly , monoclinic , with a quite small extinction angle .
Of modification III nothing more definite than that it is double-refracting can be said .
It has only been observed as a very fine grainy mass .
Methyl bromide is thus trimorphic .
Dibrom-methane.\#151 ; Methylene bromide crystallises readily in long prismatic needles which belong to the orthorhombic crystal system .
At a temperature close to \#151 ; 200 ' a polymorphic transition into another double-refracting modification takes place .
Bromoform.\#151 ; Bromoform becomes easily supercooled .
At temperatures not much below the melting-point the velocity of crystallisation is , however , considerable .
Remarkably enough , the crystals are simultaneously developed and grow in two different crystal directions ; partly as long narrow laths , and partly as large crystal fields ; the former possess a very strong double-refraction and parallel extinction , the latter are isotropic , but show in convergent light the cross of a uniaxial , optically negative crystal .
The lath-shaped needles are probably crystals which grow in the direction of a lateral crystal axis , and are developed with the basal plane at right angles to the walls of the crystallisation vessel ; the isotropic fields are crystals which grow with the basal plane parallel to the walls .
Thus bromoform crystallises in thin hexagonal tablets .
When the temperature is lowered , crystal germs of a second strongly double-refracting modification are formed in great number inside the first modification , but they grow very slowly , and w'hen the temperature is further lowered they entirely cease to grow .
Bromoform exhibits thus a case of pseudo-equilibrium between two crystal modifications at low temperature .
If the temperature is very suddenly lowered , it is therefore easily possible to cool down the first modification to \#151 ; 180 ' without any noticeable amount of the second modification being formed at all .
When the temperature is then allowed to rise , and the preparation reaches a temperature interval in which crystal-nuclei of the second modification are formed and the velocity of transition attains noticeable values , the crystals I are transformed into a grainy mass of the form II .
When a still higher Dr. W. Wahl .
between ' temperature is reached , Form II again changes into Form I , which , on further increase of temperature , melts .
In consequence of the passing over of one transition on rapidly cooling , and the pseudo-stability of Form I at low temperature , a change of one form into the other and the reverse change can thus take place without the sense in which the temperature is changing being reversed .
Tetrabrom-methane.\#151 ; Tetrabrom-methane crystallises in cubic growth-structures , which at +46 ' change into a monoclinic modification .
This latter is also obtained directly by crystallisation from ether , petrol-ether , and other solvents at room temperature .
It has been measured by Zirngiebl , * who found that it very closely approaches a regular octahedron , although it is monoclinic .
No further transition has been observed at temperatures'above \#151 ; 200 ' .
Methyl Iodide.\#151 ; Methyl iodide crystallises in long prismatic needles , some showing parallel extinction , and others showing an extinction angle up to about 25 ' .
They belong to the monoclinic system .
A twinning parallel to the orthodoma is also sometimes seen .
The cleavage , according to a prism , is well developed , and also a second cleavage , parallel to the basal plane or the orthodoma .
No polymorphic transition has been observed above \#151 ; 200 ' .
Methylene Iodide.\#151 ; The diagram of state of methylene iodide has been investigated by Tammann and Hollmann , f who describe the occurrence of four modifications .
According to their measurements at high pressures , the modification which at ordinary pressure crystallises out of the molten condition at +5*7 ' , changes at \#151 ; 6'5 ' into another modification .
This change is stated to be reversible .
On investigating methylene iodide in a similar way to the other substances described in this paper , it was found that the needle-shaped crystals which are formed out of the melt at ordinary pressure are orthorhombic .
No polymorphic change has been detected at a temperature slightly below zero , and the crystals remain unchanged down to very low temperature , although they become very cracked .
At about \#151 ; 200 ' an alteration in the crystallised product takes place .
It has , however , not been possible to make out whether this depends upon a polymorphic change , which proceeds very slowly , or whether it is due to the separating out from solid solution of some decomposition product of the methylene iodide .
The difficulty of arriving at a decision arises from the fact that methylene iodide changes under the action of light sufficiently quickly to exhibit a distinct coloration from dissolved * Compare Groth , * Chemische Krystallographie , ' vol. 1 , p. 230 .
t G. Tammann and R. Hollmann in ' Krystallisieren und Schmeltzen , ' Leipzic , 1903 p. 278 .
' Crystal Symmetry and Molecular Constitution .
333 iodine after but a few minutes .
It is therefore , practically impossible to investigate the substance in a pure state .
Iodoform.\#151 ; Iodoform has been investigated cryStallographically by Ranmielsberg , Kokscharow , and Pope.* It crystallises in the hexagonal system in tablets , which are parallel to the basal plane .
Iodoform is partially decomposed when heated to the melting point , and it is therefore difficult to obtain good crystal-growth directly from the melt .
It was , however , found that it crystallises from the melt in a very similar way to bromoform , large isotropic fields and narrow double-refracting laths being formed .
This corresponds entirely to the growth in tablets which is obtained from solutions .
No polymorphic change takes place between the melting-point temperature and room temperature , but it seems that a change takes place in the crystals not far below room temperature .
However , since the iodoform is decomposed to a certain extent when melted , it has not yet been possible to make out with certainty whether it is a polymorphic change which takes place , or whether the change is due to the separating out of solid solution of some of the decomposition products .
Methane Tetraiodide.\#151 ; Methane tetraiodide crystallises , according to Gustavson , f in octahedra , which are isotropic in polarised light , and thus regular .
Mononitromethane.\#151 ; Nitromethane crystallises very readily , forming large crystal fields , which belong to the monoclinic system .
The doublerefraction is high .
The angle of the optic axes is large , and one of the axes shows a strong dispersion .
The optical character is positive .
On cooling further , a cleavage parallel to the prism , and a second , but less distinct , cleavage parallel to the basal plane , are formed .
No other modification has been observed above \#151 ; 200 ' .
Tetranitromethane.\#151 ; Tetranitromethane crystallises in the regular crystal system .
At low temperature an enantiotropic transition into another modification takes place .
The double-refraction of this modification exceeds in no sections 0-005 .
It is probably tetragonal or hexagonal .
Chloropicrin.\#151 ; Chloropicrin crystallises in the shape of long thin needles which possess a strong double-refraction and a parallel extinction .
It thus belongs to either the tetragonal , hexagonal , or orthorhombic systems , No other polymorphic modifications have been observed above \#151 ; 200 ' .
Methyl Alcohol.\#151 ; Methyl alcohol is monoclinic or triclinic.t At low temperature a polymorphic transition takes place .
* See Groth , ' Chemisehe Krystallographie , ' vol. 3 , p. 4 .
t G. Gustavson , ' Ann. der Chemie , ' vol. 172 , p. 173 .
+ See ' Roy .
Soc. Proc A , vol. 87 , p. 379 .
Dr. W. Wahl .
Relation betiveen Ethyl Alcohol.\#151 ; Ethyl alcohol does not crystallise well .
It belongs to one of the crystal systems of low symmetry.* Tertiary Butyl Alcohol.\#151 ; The original sample of trimethylcarbinol prepared by Butlerow was examined crystallographically by Pousirewsky .f He states that the alcohol in the anhydrous state crystallises in the shape of six-sided prisms terminated by the basal plane .
The angle between the prism faces was roughly measured by Pousirewsky as being 120 ' , and the angle between the prism faces and the basal plane as being 90 ' .
This would indicate that the crystals belong to the hexagonal system .
Pousirewsky , however , found that the crystals are optically bi-axial , the axial plane being parallel to the basal plane .
He therefore considered trimethylcarbinol to be orthorhombic but pseudo-hexagonal .
The alcohol was investigated in the same way as the other substances described in this paper , and it was found that , when not quite anhydrous , it crystallises in the shape of needles which grow with great rapidity , when pure crystal fields are formed .
Some of them have been found to be isotropic .
At a temperature not far below that of the melting point , and several degrees above zero , a transition takes place into another modification which is very similar to the first one .
Both modifications possess a low maximum double-refraction .
No cleavage has been observed in the first modification , and in the case of the second the cleavage developed at quite low temperature is of an irregular character .
These observations , compared with those of Pousirewsky , show that trimethylcarbinol crystallises from the molten state in hexagonal crystals which already at a temperature above zero change into a very similar but orthorhombic modification without the outer shape of the crystals being changed .
Pousirewsky 's optical determinations were evidently made at a temperature below that of the transition point , whereby he was led to draw the conclusion that the carbinol was orthorhombic , pseudohexagonal and not really hexagonal .
Dimethyl Ether.\#151 ; Dimethyl ether was prepared by the interaction of methyl iodide on sodium methylate and the gas was purified by condensation and fractionation .
Dimethyl ether crystallises in long narrow prisms which show parallel extinction and possess a very low double-refraction .
The ether is rhombic .
No other modification has been obtained above \#151 ; 200 ' .
Methyl-ethyl Ether.\#151 ; The ether was prepared by the interaction of methyl iodide and sodium ethylate , and purified by condensation and fractionation .
Methyl-ethyl ether crystallises in prismatic columns of medium high double- * ' Roy .
Soc. Proc. , ' A , vol. 87 , p. 378 .
t Butlerow , ' Liebig 's Annalen , ' vol. 162 , p. 229 .
Crystal Symmetry and Molecular Constitution .
335 refraction . .
These belong to the monoclinic or triclinic system .
No other polymorphic form has been observed above \#151 ; 200 ' .
Ethyl Ether.\#151 ; Timmermans* has recently found that two modifications of ethyl ether exist , a stable one melting at \#151 ; 116'2 ' and an unstable one melting at \#151 ; 123'3 ' .
The crystallisation of the stable modification has been described earlier , f It crystallises in the rhombic system .
If ether is very suddenly cooled , it becomes glassy , and when warmed the unstable modification usually crystallises in beautiful spheruliths showing the " Bertrand cross .
" This form is much less double-refracting than the stable form .
When the temperature rises further , crystal germs of the stable modification are formed ; it then grows rapidly inside the unstable modification , just as in the liquid phase .
It is remarkable that the growth of the stable form often starts at the centre of the spheruliths of the unstable form .
Acetone.\#151 ; Acetone crystallises in the monoclinio or triclinic system .
] ; No polymorphic transition has been observed above \#151 ; 200 ' .
Ortho-ethyl Ether of Carbonic Acid.\#151 ; When cooled by admitting liquid air to the vacuum-vessel surrounding the crystallisation-vessel the ortho-ethyl-ether of carbonic acid , as a rule , gets supercooled .
At a temperature between \#151 ; 180 ' and \#151 ; 200 ' the stiff liquid becomes glassy in character and cracks in quite a peculiar manner , giving rise to a product which is absolutely similar in appearance to the perlitic volcanic glasses .
If the exhaust on the liquid air is turned off and the preparation is allowed to warm gradually , the perlitic structure disappears as the glass of the ortho-ether warms .
If the stiff liquid is caused to crystallise by rubbing the wall of the vessel with a metal wire a very great number of crystal nuclei are formed , and grow very slowly .
The phenomenon has much the same appearance as when ammonium magnesium phosphate is precipitated from a solution by rubbing the walls of the vessel .
If the crystallisation vessel in which crystals have previously been formed is slowly cooled , a great number of isolated crystal nuclei appear ; these grow on further cooling into small growth-structures with sharp boundary lines .
They consist of small flat tetragonal bi-pyramids , the tops of which are cut off by the basal plane .
Other sections occur which have grown parallel to the basal plane , and have the appearance of square letter envelopes .
These sections are isotropic between crossed nicols .
As far as can be estimated under the microscope , the angles of these tetragonal bi-pyramids must be practically those of the regular octahedron .
The orthoether is thus tetragonal and pseudo-regular .
* J. Timmermans , 'Bull .
Soc. Chim .
Belgique , ' 1911 , vol. 25 , p. 300 .
t ' Boy .
Soc. Proc. , ' A , vol. 87 , p. 378 .
+ See ' Roy .
Soc. Proc. , ' A , vol. 87 , p. 379 .
Dr. W. Wahl .
Relation between On further cooling the liquid gets quite viscous , and the small octahedra entirely cease to grow , the liquid ultimately becoming a perlitic glass , in which the " porphyric " octahedral crystals lie embedded .
This product is very similar to the volcanic glasses containing porphyric felspars and quartz .
When this product is allowed to warm gradually the perlitic cracks in the glass at first disappear , and then a devitrification of the glass takes place .
Hereby an immense number of very minute grains are formed , which are so small that they are scarcely distinguishable from one another , and appear as a crystallised " ground mass " merely by their action on polarised light .
At higher temperatures the size of these grains gradually increases at the expense of their number , and the product finally , before melting , consists of the original , unaltered porphyric growth-structures embedded in a porphyric , " hypidiomorphic " grainy mass .
If , again , the melt in which porphyric growth-structures have already been formed is cooled very slowly during the time the crystal-germs are forming and able to grow , it is possible to obtain a product consisting entirely of the crystal growth-structures .
These crystallisation and devitrification phenomena have been described here in detail , because the resulting products are almost identical in appearance with some of the volcanic rocks rich in silica , the genesis of the structure of which has been the subject of much discussion .
Trimethylene.\#151 ; Trimethylene was prepared from trimethylene bromide in the manner described by Gustavson.* The gas was purified by passing it through bromine and subsequently condensing it and fractionating it .
Trimethylene crystallises very readily , forming large crystal fields .
On cooling further two cleavage systems are developed : the one is parallel to the planes of a rhombohedron , the other is parallel to the basal plane .
The extinction is parallel to the basal cleavage and bisects the angle of the other cleavage system .
The strength of the double-refraction is very different in different crystal directions .
The maximum double-refraction , which is about 0'012 , is shown by those sections in which the basal cleavage is most distinctly developed .
Certain sections are nearly isotropic , but exhibit a kind of undulatory extinction , and on rotating the nicols in some cases faint bluish and yellowish tints are seen , instead of a definite extinction .
An investigation of such crystal fields in convergent light shows that trimethylene is practically uniaxial , but optically anomalous .
The dispersion phenomena as seen in convergent light indicate that the interference figure is in reality that of a bi-axial crystal with an extremely small axial angle , the axial angles for red and for blue light standing at right angles to each other , as in the case of some Sanidines and in Brookite , * Gustavson , ' Journ. Prakt .
Chemie , ' vol. 36 , ( 2 ) , p. 300 .
Crystal Symmetry and Molecular Constitution .
337 and as is also sometimes seen in optically uniaxial substances which exhibit \#166 ; " optical anomalies .
" It seems that the extent to which these anomalies in trimethylene are developed depends to a certain degree upon the rapidity with which the cooling takes place ; it has , however , not been possible to find a crystal field showing a normal uniaxial interference figure .
No other polymorphic modification has been observed above \#151 ; 200 ' .
The conclusion to be drawn from these optical properties with regard to the crystal system of trimethylene is , either that it crystallises in the trigonal system but is optically anomalous , or that it crystallises in the orthorhombic system and is pseudo-trigonal .
The principal cleavage system must be interpreted as being parallel to the planes of a flat rhombohedron , but the crystals grow in the direction of the horizontal axes , and a second cleavage system parallel to the basal plane is also developed .
Judging from the cleavage we thus arrive at the conclusion that the hydrocarbon is trigonal but optically anomalous , and not orthorhombic and pseudo-trigonal ; but a quite definite proof in favour of the one or the other alternative cannot be given .
Hexamethylene.\#151 ; If rapidly cooled hexamethylene becomes a cracked glass .
Slowly cooled it can be brought to crystallise , and once crystallised it crystallises readily .
It grows in large dendrites , forming cubic gratings .
The crystal fields are absolutely isotropic .
At low temperature this cubic modification changes enantiotropically into a double-refracting modification , which grows in a peculiar way in large patches inside the cubic modification , without the general structure due to the crystallisation forms of the original cubic modification being in any way interfered with .
The maximum double-refraction of this second form is about 0'012 .
Methyl-hexametliylene.\#151 ; Methyl-cyclohexane becomes invariably glassy on -cooling , but if the wall of the crystallisation vessel is rubbed with a metal wire before the cooled liquid has become very viscous , crystallisation can be brought about .
Very slowly growing spheruliths are then developed .
If the once crystallised mass is melted in part and recrystallised by again cooling the preparation , monoclinic prisms are formed .
The cleavage is parallel to the prism and to the basal plane , the angle between the orthopinakoid and the basal plane being about 75 ' .
The extinction angle on the clinopinakoid is about 15-20 ' .
The crystals are .often simple twins according to the orthopinakoid , and each half is poly-synthetically twinned according to the basal plane , giving rise to a " herringbone structure , " similar to that of the pyroxenes in the diabasic rocks of the great Whin Sill .
No other polymorphic form has been observed above \#151 ; 200 ' , 338 Dr. W. Wahl .
Relation between Benzene.\#151 ; Benzene has been investigated crystallographically by v. Groth * It crystallises in the orthorhombic system .
Benzene was examined as to the possible occurrence of other polymorphic modifications , but no transition into some other form could be detected above \#151 ; 200 ' .
Also no " monotropic " unstable modifications have been observed .
Toluene.\#151 ; Toluene crystallises in a very similar way to benzene .
It is orthorhombic , and no further modifications have been observed above \#151 ; 200 ' .
Para-xylene.\#151 ; Para-xylene has been investigated crystallographically by Jannasch.f It is monoclinic .
No other polymorphic modification has been observed above \#151 ; 200 ' .
Mesitylene.\#151 ; From the moderately supercooled melt glass-spherulites and small strongly double-refracting needles are formed .
After the preparation has been caused partially to melt the recrystallisation takes place with great velocity , prismatic crystals of high double-refraction and parallel extinction being formed .
On further cooling a very distinct prismatic cleavage and a perhaps still better developed cleavage parallel to the basal plane are formed , but no polymorphic transition has been observed above \#151 ; 200 ' .
If the liquid , however , is strongly supercooled before crystallisation sets in , a second unstable modification of very strong double-refraction is formed .
This modification is also orthorhombic , and can be melted and recrystallised from the melt in the absence of the stable modification .
The unstable modification , however , passes slowly into the stable one , once this is formed , and grows just as crystals grow in a viscous liquid .
Both modifications of mesitylene are orthorhombic .
Hexametliyl-benzene.\#151 ; Hexamethy 1-benzene crystallises similarly to benzene in orthorhombic prisms of strong double-refraction .
No polymorphic transition has been observed above \#151 ; 200 ' , nor any unstable modifications .
Hexachloro-benzene.\#151 ; Hexachloro-benzene also crystallises in orthorhombic prisms .
Biphenyl-methane.\#151 ; Diphenyl-methane crystallises in orthorhombic needles .
Tetraphenyl-methane.\#151 ; Tetraphenyl-methane crystallises from benzene-solution in the shape of needles . !
Through the kindness of Prof. Gomberg the author has had the opportunity of examining , in polarised light , the tetraphenyl-methane prepared by him .
The crystals which are formed on solidification from the molten state are identical in character with those crystallising out of solutions .
According to their optical properties they \gt ; * v. Groth , ' Jahresberichte d. Chemie , ' 1870 , p. 2 .
t P. Jannasch , 'Ann .
d. Chemie , ' vol. 171 , p. 79 .
+ A. Gomberg , ' Ber .
Deutsch .
Chem. Ges .
, ' 1897 , vol. 30 , p. 2043 ; and 1903 , vol. 36 , p. 1090 .
Crystal Symmetry and Molecular Constitution .
339are orthorhombic .
oSTo other polymorphic modification has been observed above \#151 ; 200 ' .
Further Investigation of Trimethyl-methane.\#151 ; As it was not possible previously to obtain crystals other than such as had grown in one certain crystal direction , * the investigation of trimethyl-methane has been renewed several times , and fresh samples of the gas prepared and investigated in crystallisation vessels of different size and width .
After many vain attempts growths in several directions have been obtained by cooling very rapidly* and it has been established that the way in which the hydrocarbon crystallises is very similar to that of trimethylene , which has been described above .
Certain sections are practically dark between crossed nicols , but show in convergent light a cross which is opening slightly .
The dispersion phenomena are in this case not as pronounced as in the case of trimethylene .
The optical character of trimethyl-methane is negative .
Besides the cleavage which in the earlier stage of the investigation was regarded as being parallel to a prism , but is now considered as being parallel to the basal plane , a rhombohedral cleavage also occurs .
Trimetliyl-methane is thus either trigonal and optically anomalous , or rhombic , but pseudo-trigonal ; but more probably the former .
* See ' Roy .
Soc. Proc. , ' A , vol. 88 , p. 359 ,
|
rspa_1913_0088 | 0950-1207 | Note on electric discharge phenomena in rotating silica bulbs. | 340 | 344 | 1,913 | 89 | Proceedings of the Royal Society of London. Series A, Containing Papers of a Mathematical and Physical Character | The Hon. R. J. Strutt, M. A., Sc. D., F. R. S. | article | 6.0.4 | http://dx.doi.org/10.1098/rspa.1913.0088 | en | rspa | 1,910 | 1,900 | 1,900 | 2 | 115 | 2,316 | http://corpora.clarin-d.uni-saarland.de/surprisal/6.0.3/?id=rspa_1913_0088 | 10.1098/rspa.1913.0088 | null | null | null | Electricity | 40.936951 | Thermodynamics | 16.333769 | Electricity | [
7.267242431640625,
-56.816402435302734
] | 340 Note on Electric Discharge Phenomena in Rotating Silica Bulbs .
m the Hon. E. J. Strutt , M.A. , Sc. D. , F.R.S. , Professor of Physics , Imperial College of Science , South Kensington .
( Received July 22 , 1913 .
) The late Rev. F. J. Jervis Smith described some curious experiments on this subject before the Royal Society , * without , however , offering any interpretation of his results .
I have recently repeated most of his experiments , and have made others which have thrown light on the matter .
As the result , it does not seem that anything fundamentally new as to the mechanism of discharge is to be learnt from this line of research .
Still , the work is worthy of brief record , if only to save others the trouble of traversing the same ground .
Jervis Smith 's fundamental experiment !
is as follows : The exhausted bulb is placed near a body charged to 1,000 volts or more .
When the bulb is rotated , a luminous glow is maintained within it .
It is not difficult to foresee this result .
The rarefied gas may be regarded as a conductor .
Suppose the body negatively electrified .
Then , since the potential on the inside of the bulb is lower near the outside electrified body than elsewhere , positive electricity will flow to this neighbourhood and negative electricity to other parts of the bulb , until the electric field inside the bulb is nearly neutralised .
When the bulb is rotated , these induced charges will be carried round with it , and will have to flow through the gas to recover their equilibrium position .
In doing this they set up the ordinary luminosity of discharge .
To predict the precise direction of the stream lines would be very difficult , and it does not appear that much would be gained by success .
As regards the detailed effects of magnetic fields in various directions in deflecting the luminosity the same may be said .
I find that , just as in ordinary discharge tubes , the luminosity at low vacua is mainly that characterising the residual gas , while at high vacua the fluorescence of the silica under cathode rays predominates .
In Jervis Smith 's third paper , he describes luminosity produced by rubbing the outside of the rotating silica vessel .
I have used the dry hands as rubbers , almost enclosing the bulb in the two palms .
The luminosity is * ' Roy .
Soc. Proc. , ' 1908 , A , vol. 80 , p. 212 ; 1908 , A , vol. 81 , pp. 214 , 430 .
+ I find , however , that this experiment , and also the experiment of producing luminosity in an exhausted globe by rotating it under a rubber , were described as long ago as 1709 by F. Hawksbee , F.R.S. , ' Physico-mechanical Experiments on " Various .Subjects , ' pp. 36 , 62 .
Electric Discharge Phenomena in Rotating Silica .
341 then very bright and , under certain conditions , it survives after the rubbing is over .
The cause of luminosity is not materially different from what it was in the previous case .
Before considering it some experiments will be described :\#151 ; ( 1 ) On a favourable dry day the bulb was rubbed .
Removing the hands and having the bulb rotating at a distance from other objects , the luminosity was extinguished .
But on bringing the hand or any other earthed conductor near ( not touching ) , the luminosity was restored .
( 2 ) The rotating bulb was rubbed .
A brass cylinder a little larger was then placed co-axially over it .
No luminosity could be seen .
Displacing the cylinder to one side , still without touching , luminosity was restored .
( 3 ) The bulb was rubbed .
An earthed conductor was then adjusted near it , inducing luminosity as in ( 1 ) .
A bun sen burner was passed underneath i for a moment to discharge electrification , the top of the flame was not allowed to approach nearer than 3 or 4 inches below the bulb , and did not warm it perceptibly .
Luminosity was permanently extinguished .
( 4 ) The electrification produced on the outside of the bulb by rubbing with the hand is positive .
This was proved by lowering it into a Faraday cylinder connected with an electroscope charged with electricity of known sign .
Let us for simplicity suppose that the rubber has been removed , leaving the outer surface of the bulb uniformly electrified .
Then , if the surroundings in which the bulb rotates are symmetrical about the axis of rotation , no electric field will be created within the bulb .
But if an earthed conductor is situated on one side of it , the potential of an element of area of the inner surface will be lowered when that element passes near the conductor .
Thus , positive electricity will flow to the point in question , and negative electricity away from it to other portions of the bulb .
As before , the charges which .
have thus attached themselves to the inner walls are continually carried , round , and have to flow back through the gas to their equilibrium position .
Another of Jervis Smith 's experiments may be referred to which does not fall very well under the title of this note .
If a brush discharge from an induction coil is merely allowed to play over a highly exhausted silica bulb like that used in the rotation experiments , the bulb remains brightly luminous afterwards , sometimes for several minutes .
In repeating the experiment , I find that this luminosity shows curious flickerings , which are greatly accentuated if earthed conductors are brought near the bulb , and then removed .
If the bulb is held for a moment high above a bunsen flame , or if it is breathed upon , the luminosity ceases .
As before , the luminosity is connected with electrification of the outside surface .
This electrification is initially uneven , and , as the charge creeps over the surface , Hon. R. J. Strutt .
on Electric \#166 ; currents flow through the rarefied gas inside .
The approach of earthed conductors also upsets the uniformity of potential inside , and produces the same result .
It is certainly curious that these effects should be so persistent .
It need scarcely be said that they have merely a superficial resemblance to the afterglow phenomena due to chemical changes in the gas , which I have examined in previous papers .
Finally , it remains to consider one more of Jervis Smith 's experiments , which , indeed , first attracted me to the subject .
His description runs thus:\#151 ; " A silica glow bulb was rotated as before .
The camel-hair rubber , after being in contact with the bulb , was removed , and no glow was visible ; but , \#166 ; on establishing the magnetic field ( about 800 C.G.S. units intensity ) , the bulb instantly glowed brightly , the glow lasting in some cases eight minutes before it died out .
When pointed pole pieces were used on either side of the rotating bulb , a bright equatorial* band about 5 mm. wide of greenish glow was generated .
" Fig. 1 .
I have repeated this experiment without difficulty ( fig. 1 ) .
As before , it depends on electrification of the bulb surface .
Diselectrification by a flame .destroys the effect .
Each pole of the magnet , acting merely as an earthed conductor , lowers the potential of the inner surface of the bulb near it , so that these two portions of the surface tend to act as cathodes .
The electric force may not be enough to cause discharge ; but when the magnet is excited it produces a magnetic force parallel to the electric force , and this , as is known , f lowers the discharge potential so that discharge can occur .
At the same time a beam of " magnetic rays " J proceeds from each cathode towards the other , along the * The magnetic force is perpendicular to the axis of rotation .
The band is equatorial with reference to the latter and stretches between the pole pieces .
+ See Birkeland , 'Compt .
Rend .
, ' Feb. , 1898 , vol. 121 , p. 586 .
f It is not necessary here to enter on the difficult question of the nature of these lays .
For our purpose they are simply cathode rays modified by longitudinal magnetic force .
Discharge Phenomena in Rotating Silica Bulbs .
343 magnetic lines .
These constitute the luminous band described .
To my eyes it is blue , not green .
On the explanation given , the ends of the luminous band are each cathodes other parts of the bulb surface acting as anode .
It may be objected that the appearance of the band suggests a discharge from one end of it to the other .
The experiment indicated in fig. 2 with discharge in a stationary vessel answers this objection ; C and C are each fiat metal cathodes , and are connected together by a wire .
A is anode .
N and S are hollow pole pieces of an electromagnet .
Fig. 2 .
A Wimhurst machine is used .
At suitable rarefaction , no discharge occurs unless the magnet is excited .
When it is excited , a band of negative glow stretches across as shown , exactly like that observed in the rotating vessel .
A little positive light can be seen near the anode A , but it is inconspicuous .
Going back to the rotating vessel , these magnetic rays ought not to be seen if the bulb becomes negatively electrified by friction , for then the parts of the inner surface near the magnet poles would act as anodes , not as cathodes .
An exhausted glass bulb was heated and coated with sealing wax over a zone equatorial to the axis of rotation .
While being rubbed with silk it was luminous , but the insulation was apparently not good enough to get luminosity when the rubbing had been discontinued .
To examine the magnetic effect , rubbers were held near each of the pole pieces of the magnet .
Under these conditions the magnetic rays had been brilliant , using the quartz bulb .
With the glass one coated with sealing wax , no magnetic rays were seen ; on the contrary , when the magnetic force was strong , the luminosity ( apparently a cathode ray phosphorescence of the glass ) was concentrated in rings lying in 344 Dr. J. N. Pring .
the zone of friction , which were nearly great circles , and of nearly uniform brightness all round .
In this case the cathodic portions of the zone which is being rubbed are those distant from the magnet poles .
The cathode rays experience not a longitudinal but a transverse magnetic force , and are curled up into small circles , so as to strike the walls again near their point of origin , and produce phosphorescence there .
It is true that at any one moment only a portion of the zone is under excitation , but each portion is excited successively , and the phosphorescence lasts long enough to produce sensible uniformity of illumination .
The Origin of Thermal Ionisation from Carbon .
By J. K Pring , D.Sc .
( Communicated by Prof. E. Rutherford , F.R.S. Received July 26 , 1913 .
) It has been shown by the present writer in conjunction with A. Parker* that the ionisation which is produced by carbon at high temperatures , and in presence of gases at low pressures , is reduced to a much smaller order of magnitude by eliminating impurities from the carbon , and by exhausting to a high degree the containing vessel .
The results threw considerable doubt on the whole basis of the theory of electronic emission from incandescent solids .
According to this theory , j- the ionisation produced by elements at high temperatures is due to the escape of free electrons which pass into the surrounding space on account of the kinetic energy acquired at the high temperature .
It was shown , however , in the above work that in the case of carbon this ionisation is probably related to some chemical action or some intermediate effect exerted by the gas in contact with the solid .
Fredenhagen , \#163 ; who made measurements with sodium and potassium in a high vacuum , came to similar conclusions with regard to the validity of the above theory of electronic emission .
Harker and Kaye , S in investigating the large ionisation currents from * ' Phil. Mag. , ' 1912 , vol. 23 , pp. 199 .
t Richardson , 'Phil .
Trans. , ' 1903 , A , vol. 201 , p. 497 ; 'Phil .
Mag. , ' 1912 , vol. 24 , pp. 737-744 ; ibid. , 1913 , vol. 26 , p. 345 .
J 'Verh .
Deutsch .
Phys. Gesell .
, ' 1912 , vol. 14 , pp. 384-394 .
S ' Roy .
Soc. Proc. , ' 1912 , A , vol. 86 , pp. 379-396 ; ibid. , 1913 , A , vol. 88 , pp. 522-538 .
|
rspa_1913_0089 | 0950-1207 | The origin of thermal ionisation from carbon. | 344 | 360 | 1,913 | 89 | Proceedings of the Royal Society of London. Series A, Containing Papers of a Mathematical and Physical Character | J. N. Pring, D. Sc. |Prof. E. Rutherford, F. R. S. | article | 6.0.4 | http://dx.doi.org/10.1098/rspa.1913.0089 | en | rspa | 1,910 | 1,900 | 1,900 | 9 | 340 | 6,671 | http://corpora.clarin-d.uni-saarland.de/surprisal/6.0.3/?id=rspa_1913_0089 | 10.1098/rspa.1913.0089 | null | null | null | Thermodynamics | 56.624576 | Atomic Physics | 16.102486 | Thermodynamics | [
6.229974746704102,
-61.644569396972656
] | 344 Dr. J. N. Pring .
the zone of friction , which were nearly great circles , and of nearly uniform brightness all round .
In this case the cathodic portions of the zone which is being rubbed are those distant from the magnet poles .
The cathode rays experience not a longitudinal but a transverse magnetic force , and are curled up into small circles , so as to strike the walls again near their point of origin , and produce phosphorescence there .
It is true that at any one moment only a portion of the zone is under excitation , but each portion is excited successively , and the phosphorescence lasts long enough to produce sensible uniformity of illumination .
The Origin of Thermal Ionisation from Carbon .
By J. N. Pring , D.Sc .
( Communicated by Prof. E. Rutherford , F.R.S. Received July 26 , 1913 .
) It has been shown by the present writer in conjunction with A. Parker* that the ionisation which is produced by carbon at high temperatures , and in presence of gases at low pressures , is reduced to a much smaller order of magnitude by eliminating impurities from the carbon , and by exhausting to a high degree the containing vessel .
The results threw considerable doubt on the whole basis of the theory of electronic emission from incandescent solids .
According to this theory , f the ionisation produced by elements at high temperatures is due to the escape of free electrons which pass into the surrounding space on account of the kinetic energy acquired at the high temperature .
It was shown , however , in the above work that in the case of carbon this ionisation is probably related to some chemical action or some intermediate effect exerted by the gas in contact with the solid .
Fredenhagen , J who made measurements with sodium and potassium in a high vacuum , came to similar conclusions with regard to the validity of the above theory of electronic emission .
Harker and Kaye , S in investigating the large ionisation currents from * ' Phil. Mag. , ' 1912 , vol. 23 , pp. 199 .
t Richardson , 'Phil .
Trans. , ' 1903 , A , vol. 201 , p. 497 ; 'Phil .
Mag. , ' 1912 , vol. 24 , pp. 737-744 ; ibid. , 1913 , vol. 26 , p. 345 .
| 'Verh .
Deutsch .
Phys. Gesell .
, ' 1912 , vol. 14 , pp. 384-394 .
S ' Roy .
Soc. Proc. , ' 1912 , A , vol. 86 , pp. 379-396 ; ibid. , 1913 , A , vol. 88 , pp. 522-538 .
The Origin of Thermal Ionisation from Carbon .
345 carbon in gases at atmospheric pressure , conclude that an important part is played by the presence of impurities .
The ionisation from metals was also considered to be largely affected by the presence of occluded gases .
Richardson , * in discussing the results of Pring and Parker , admits that the ionisation originally measured by him in the case of carbon was largely influenced by the presence of impurities leading to chemical reaction .
The result of this was to lead to an abnormally high value being given to the constant A in the expression A(fie~Q28 , which was deduced to represent , on the basis of the thermionic theory , the relation between ionisation and temperature .
By revising the constants from which the values in this formula are derived , the formula was made to follow much more closely the experimental results of Pring and Parker , though it still gave values considerably higher than the latter , and did not agree with the observed influence of temperature .
It was , however , maintained that the fundamental theory put forward by Richardson , accounting for the relation between ionisation and temperature , was not disturbed .
Scope of Experiments .
The aim of the present work was to see if any direct electronic emission can be attributed to incandescent carbon , when the large ionisation effects , which were found in the earlier work to be due to chemical action , were more completely removed .
For this purpose the purification of the carbon and the exhaustion of the surrounding vessel were carried out more extensively than before , and the effect on the ionisation at definite temperatures was carefully measured .
A series of experiments was also made in which small quantities of the highly purified gases\#151 ; helium , argon , nitrogen , hydrogen , carbon monoxide , and carbon dioxide\#151 ; were admitted to the vessel at known pressures , to see if any relation could be traced between the ionisation and the relative chemical action of these gases on carbon .
Apparatus.\#151 ; The apparatus used was of the same type as that in the earlier work .
The carbon was mounted in water-cooled holders , as shown in fig. 1 .
The copper tubes ( A , A ) served for the introduction of the current used to heat the carbon .
Air-tighc connections with the side tubes of the flask were made at b , b , by means of soft wax .
The carbon used was in the form of a rod , 8 cm .
long and 0'5 cm .
diameter , and contained a hollow space in the centre , 1-5 mm. diameter .
I he sample used in the measurements was kindly presented to the writer by I)r .
J. A. Harker , and was part of some material which had been * 'Phil .
Mag. , ' 1912 , vol. 24 , p. 737 .
VOL. LXXXIX.\#151 ; A. 2 E Dr. J. N. Pring .
carefully purified before compressing in the rod form .
Further purification was carried out in this work , after mounting in the apparatus , by heating for long intervals at very low pressures .
The carbon rod had a resistance of Earth Fig. 1 .
about 0'25 ohm , and by passing a current of 80 amperes at 20 volts a temperature of 1850 ' was attained when the pressure was below 0005 mm. For the ionisation measurements , one of the terminals ( D ) was connected to earth , and a source of positive potential applied to ' the wire E , to which was connected a small disc .
This disc was placed at a distance of about 8 cm .
from the heated carbon .
Since a potential of 220 volts was applied in the case of all comparative measurements , it could be assumed that the greater part of the ions produced in the vessel would be collected .
A number of experiments were made with a vessel which was coated with silver on the inside , and the metal lining wras then used as the anode .
After heating for some time , the conductivity became very uncertain , so that this method was abandoned in favour of the disc anode .
A complete collection of the ions was not essential in these measurements , as the ionisation currents varied over such a large range under changing conditions .
It became only necessary to consider the order of magnitude in interpreting the results .
The exhaustion of the vessel was effected by means of a Gaede mercury pump connected to the apparatus at M. The higher pressure side of this pump was exhausted by a Sprengel pump .
In addition to this , the charcoal tube H , which was cooled by liquid air , was also applied for the final exhaustion of the main apparatus .
After removal of the liquid air , the charcoal was always disconnected from the main apparatus by means of the The Origin of Thermal Ionisation from Carbon .
347 tap K , and before each experiment was exhausted continuously for at least 12 hours , by means of the Sprengel pump connected to L , while the temperature was kept at about 400 ' by a surrounding electric furnace .
A Topler pump of large capacity at F was used for preliminary exhaustions and for the removal of gases which it was desired to collect .
This pump also served as a pressure gauge , by using the scale placed behind the capillary at N. The column of gas in the capillary was arrested and measured when it stood at a height of 70 cm .
above the reservoir R. The calibration showed that a column 1 cm , high corresponded to a pressure in the apparatus of ( M)03 mm. This enabled a measurement to be made within 0-0001 mm. in the absence of condensable gases .
The U-tubes ( P , P ) , which were surrounded by liquid air during the experiments , were used to condense mercury vapour in order to protect the charcoal from this metal , and also in order to condense any impurities arising from the grease of the taps .
A spectrum tube connected at S was used for the purpose of spectroscopic examination of the gases present , and to obtain an idea of the pressure when below the limits of measurement by the mercury gauge .
The degree of exhaustion obtained with this apparatus when the carbon was cold could not be measured by any of the methods available .
No trace of discharge was visible in the spectrum tube on connecting with an induction coil , which , in air , gave a 5-inch spark .
However , even after prolonged use of the apparatus , detectable quantities of gas always appeared when the temperature of the carbon was taken above about 1300 ' .
The lowest pressure obtained , when the carbon was at 1900 ' , was estimated by the mercury gauge at 0-0002 mm. , but in most cases it could not be reduced below 0'001 mm. at this temperature .
Temperature Readings.\#151 ; These were made with a Wanner optical pyrometer sighted directly on to the heated carbon .
The pyrometer was first carefully calibrated and standardised by comparing with a thermo-junction pyrometer , and at the melting points of pure platinum and iridium.* It was ascertained in some earlier measurements that the absorption of the light by the clean glass of the vessel did not cause an error exceeding 10 ' in the measurement .
On account of the possibility of error in hurried individual measurements , a large number of readings were first taken at different temperatures , and at a pressure of 0-001 cm .
, and the values were plotted ( watts against temperature ) in the form of a curve .
Since readings of the current and voltage were made in every case , this * See Pring , ' Lab .
Exercises in Phys. Chem. , ' Manch .
Univ. Press , p. 154 .
Dr. J. N. Pring .
curve was referred to in all subsequent readings , and in many cases a direct temperature reading during the actual experiment was avoided altogether .
The curve was determined after the carbon showed no further change in resistance with continued heating .
By comparing the values obtained by the different methods used for calibrating the pyrometer , and by considering the degree within which carbon radiates as a black body , * it was found that an accuracy to within 25 ' could he relied on at 1300 ' in the temperature measurements and within about 60 ' at 2000 ' .
Measurement of Ionisation .
The source of positive potential , usually 210-220 volts , which connected with the anode wire E , was first passed through a water resistance of about 1 megohm .
For the measurement of the larger ionisation currents a milli-ammeter or galvanometer was inserted in the circuit at T. For the smaller currents , a Dolezalek electrometer was used in parallel with standard capacities ranging from 0'001 to 0'3 microfarad .
The wire leading from the electrometer was encased in an insulated metal tube , which , together with a metal cylinder placed around the lower part of the glass vessel at Y , a narrow guard-ring of tin foil at X , and metal plates placed under the galvanometer and electrometer , was connected to the source of positive potential , in order to prevent any leak from the insulated anode to earth .
When using the full potential a voltmeter was connected to the circuit immediately before and after each series of measurements .
In order to ascertain the actual potential applied in the cases where larger ionisation currents were obtained , and where a fall of potential through the water resistance would result , the voltmeter was connected permanently between the earth wire and the further side of the galvanometer .
A number of additional readings were taken at a lower potential by using a source of 100 volts , and cutting down by means of the resistance .
The Dolezalek electrometer gave a scale deflection of 1 cm .
per minute when used with 0001 mf .
capacity , with a current of 3 x 10"12 ampere .
No detectable leak occurred through the apparatus when cold , and by applying an additional potential of 2 volts by means of a cell , on to the insulated electrometer wire , no appreciable leak to any of the surrounding metal guards could be observed .
Since the surface of the carbon was 13 sq .
cm .
all the ionisation values below have been divided by this figure , in order to give the current per square centimetre of surface .
* Ibid. , p. 157 .
The Origin of Thermal Ionisation from Carbon .
349 The experiments recorded in this paper were carried out after the carbon had been subjected to prolonged heating in a high vacuum , and was not capable of further purification by this treatment . .
Preparation of Gases .
Nitrogen.\#151 ; The gas was prepared by heating ammonium nitrite , storing in a gas-holder , and then after drying was passed through molten phosphorus and through a spiral cooled by liquid air , and then into a vessel containing mercury .
This gas was admitted in small quantities to the main apparatus through the tap Z ( fig. 1 ) by first filling the small space between this and a second tap connecting with the gas-holder .
The results of the ionisation measurements are given in Table I , and are plotted in the form of curves for the different temperatures ( fig. 2 ) .
The ordinates represent the logarithm of the ionisation and the abscissae the pressure .
Hydrogen.\#151 ; This was prepared by electrolysing baryta , and , after passing over heated platinised asbestos , calcium chloride , and phosphorus pentoxide , the gas was absorbed by palladium foil contained in a glass tube and warmed by an electric furnace .
One end of the tube connected directly to the main apparatus at Z ( fig. 1 ) , and when the palladium was cold , the end leading to the generator was closed by means of a tap and the tube exhausted by means of the Topler pump , and finally by the Gaede pump on the main apparatus .
By then warming the palladium and regulating the connecting taps , definite quantities of hydrogen were admitted to the reaction vessel .
The results of the ionisation measurements obtained are shown in Table II , and in fig. 3 .
Carbon Monoxide.\#151 ; This was prepared by the action of formic acid on heated sulphuric acid , and , after passing through a concentrated potassium hydrate solution , was admitted to a thoroughly exhausted vessel of 50 c.c. capacity , which was fitted with a tap and contained some phosphorus pent-oxide .
The gas was allowed to remain in this tube for 15 hours , and then admitted to the reaction vessel through the tap Z , as in the case of the nitrogen .
In all these experiments where gases were admitted to the reaction vessel , the U-tube P would remove any condensable impurity .
The results of these measurements are shown in Table III and in fig. 4 , as before .
Carbon Dioxide.\#151 ; This was obtained from a cylinder of commercial gas , and , after storing in a bulb , was admitted directly into the apparatus .
The measurements made with this are shown in Table IIIa , and also on fig. 4 .
Helium.\#151 ; This was extracted from samarskite , and , after removal of water Dr. J. N. Pring .
vapour and most of the hydrogen by admitting to charcoal cooled by liquid air , the gas was passed over heated copper oxide , and then stored in a tube .
Before admitting to the apparatus through the tube L the gas was exposed for a few minutes each in succession to the two charcoal tubes Y and H , which were cooled by liquid air .
Readings with this gas are given in Table IV and fig. 5 .
Argon.\#151 ; This was prepared by passing atmospheric nitrogen over finely powdered calcium carbide mixed with a small quantity of calcium chloride and heated in an iron pipe fitted with water-cooled jackets at the ends .
The unabsorbed gas was then passed several times over calcium in a smaller tube , over heated copper oxide , and then dried by phosphorus pentoxide .
The gas was then finally purified by exposing to an electrical discharge in a tube in which the cathode consisted of a liquid alloy of sodium and potassium ( 70 per cent , potassium ) .
The tube arranged for this had a capacity of about 100 c.c. Two right angle bends were provided , and platinum wires sealed in the walls , one at the end making connection with the liquid alloy , and the other joining on to an aluminium electrode at a distance of 8 cm .
from the lower electrode .
A trial was first made with this tube by admitting nitrogen to a pressure of 1 cm .
and connecting the tube to a small pressure gauge .
After passing the discharge for 8 minutes this gas was so completely absorbed as to stop the discharge .
The impure argon was then admitted to a pressure of about 1 cm .
, and the discharge passed for a few hours .
A quantity of this gas was then admitted to a carefully exhausted spectrum tube , and examined spectroscopically .
No nitrogen could be detected , though hydrogen lines were present , presumably arising from the electrodes .
The argon was admitted to the apparatus by connecting the tube to Z. The readings obtained with this gas are shown in Table V and in fig. 6 .
In the curves for argon and helium , the ordinates , on account of their lower value , are plotted on twice the scale used for the other gases .
The values of all the readings taken at the equilibrium stages are entered in the tables , and these have been plotted on the diagrams in every case when the value came within the range of the axes , and when the potential employed had been 210-220 .
Procedure of Experiment .
The apparatus was first evacuated as described above , and after any admission of gas containing moisture , was first allowed to stand several days in presence of phosphorus pentoxide , after carefully exhausting .
During this interval no rise of pressure could , as a rule , be observed .
The Origin of Thermal Ionisation from Carbon .
351 If the carbon was maintained at 1300 ' and the taps leading to the pumps were closed , the rise of pressure in 5 minutes was usually too small to measure , but above this temperature it became important , amounting at 1800 ' to about 0003 mm. in five minutes .
It would be expected that some of the gas arising in these cases would result from the decomposition of traces of hydrocarbons given from the wax seals used to hold the water-cooled tubes .
In the experiments which were conducted at the lowest pressures , the exhaustion of the vessel was continued throughout the measurement .
When using purified gases , a small quantity of the gas was admitted after first closing the taps leading to the pumps , adjusting the temperature of the carbon by means of rheostats , and completing all the electrical connections on the high potential circuit .
Readings of the ionisation current were then made by means of the electrometer or galvanometer , immediately after the admission of the gas , and then at definite intervals .
These were followed by readings of the pressure and temperature as described above .
Comparative experiments were conducted from time to time by exhausting the vessel , closing all taps , and noticing the increase of ionisation with time due to the increase of pressure which gradually took place at the high temperatures .
Tabulation of Results .
Table I.\#151 ; Nitrogen ( pure ) .
Temp. Pressure .
Ionisation .
Temp. Pressure .
Ionisation .
Potential Difference 210-220 volts .
o mm. amp .
per sq .
cm .
o mm. amp .
per sq .
cm .
1130 0*001 8 -5 x 10~13 1615 0-002 5 8 x 10-10 1150 0*3 3 8 x10"8 1630 0-009 3 -2 x 10-7 1200 \lt ; 0*0001 2 -3 x 10-12 1650 0-03 3 -8 x 10~5 1270 0-003 2 '4 x 10-11 1750 0 -0015 7 -7 x 10"9 1270 0-3 ( 5 -1 x 10-7 1830 0-004 4 -5 x 10-8 1280 \lt ; 0*0001 3 -1 x 10-'2 1840 0*03 2 -2 x 10-4 1280 o-ooi 3-9x10"12 1900 0*0002 1 -3 x lO-9 1325 0*0006 2-8xl0- " 1900 0 *0004 2 -4 x 10-9 1350 o-oooi 1 -9 x 10~u 1900 0 -0007 4 -8 x lO-9 1370 0 -0016 1 -4 x 10-10 1900 o-ooi 5 -4 x lO-9 1410 0*005 1 -6 x 10~9 1900 0 -0015 9 -4 x lO-9 1440 0*001 2 -4 x lO-10 2000 0*002 2 -4 x 10-8 1450 0 *0001 1 -7 x lO-10 2020 0-0015 1 -2 x 10"8 1610 0 *0008 3 -0 x lO-10 2025 0 -0008 8 -5 x lO-9 1610 0*003 1 -7 x 10-9 Potential Difference 100 volts .
1285 0*0001 1 -57 x lO-10 1630 0*0006 4 -0 x lO-9 1365 0 *0001 3 3 x 10-'* ' 1830 o-ooi 1 -5 x 10_s 1475 0*0003 9 -7 x lO-10 1900 0 -0005 2 -7 x lO-9 352 Dr. J. N. Pring .
These results , which are plotted in the form of curves in fig. 2 , show the very large part played by the pressure of the surrounding gas .
At low pressures , however , the ionisation approaches a limiting value for each temperature .
As discussed below , this is probably due to the occlusion of residual gas .
Table II.\#151 ; Hydrogen .
Potential 210-220 volts .
Temperature 1850 ' .
Temp. Pressure .
Ionisation .
Potential .
i Pressure .
Ionisation .
o mm. amp .
per sq .
cm .
volts .
mm. amp .
per sq .
cm .
1200 \lt ; 0*0001 2 -3 x l(p12 100 1-0 5 -5 x 1CP2 1200 0 *0002 3 -1 x KT12 85 1 0 1 -8 x 10-2 1200 o-ooi 6 '8 x icr12 95 1 -o 5 -0 x 10"2 1200 0*002 9 -3 x icr12 93 1 0 1 -3 x 10-2 1200 0-003 1 '2 x 1CP11 115 0*03 4 -5 x HP2 1200 0 -0075 2 -1 x 10"10 100 0-03 4 -5 x 10-2 1200 0*16 1 -5 x 10'8 75 0-03 3 5 xlO-2 1200 0*4 1 -0 x 10-8 55 0*03 2 -5 x 10-2 1340 0 *0002 l -6 x nr11 40 0*03 1 -0 x lO-2 1340 0*002 4 -4 X 10_u 1340 0*003 7 7 x 10-11 1340 0*006 l-5x KP6 These values are plotted in the form of curves in fig. 3 , where the absciss\#174 ; denote the pressures , and the ordinates the logarithm of the ionisation currents .
Table III.\#151 ; Carbon Monoxide .
Potential 210-220 volts .
Temp. Pressure .
Ionisation .
Temp. Pressure .
Ionisation .
o | mm. amp .
per sq .
cm .
o mm. amp .
per sq .
cm .
1180 \lt ; 0*0001 1 -5 x HP12 1280 0*003 1 -1 x 10-a 1180 o-ooi 3 85 x 10-*2 1315 0-002 4 -8 x 10-u 1180 0*002 1 0 x10~n 1340 0 -0012 1 -2 x IIP11 1180 0-005 2 -7 x 10-10 1410 0*002 2 -5 x 1CP10 1180 0-006 3 -0 x lO-10 1410 0-007 1 -3 x 1CP6 1180 0*08 2 -3 x 10-8 1550 0 -0015 1 -3 x 10-9 1180 0-7 1 -7 x 1CP8 1550 0*002 3 -8 x lO-9 1280 \lt ; 0*0001 2 -15 x 10-12 1550 0 *0045 1 -Ox 10-\#174 ; 1280 0-0015 1 -0 x 10- " 1720 0-002 \gt ; 4'0x 10"6 Table IIIa.\#151 ; Carbon Dioxide .
Potential 210-220 volts .
Temp. Pressure .
Ionisation .
Temp. Pressure .
Ionisation .
o mm. amp .
per sq .
cm .
0 mm. amp .
per sq.cm .
1160 0 -008 2'3xlCP8 1180 0-008 3'8x 1(P8 1180 0-004 5 -1 x 1CP10 1270 0-003 3 1 x KP ' The results with carbon monoxide and dioxide are also shown in fig. 4 .
The Origin of Thermal Ionisation from Carbon .
353 Table IY.\#151 ; Helium .
Potential 210-220 volts .
Temp. Pressure .
Ionisation .
Temp. Pressure .
Ionisation .
o mm. amp .
per sq .
cm .
o mm. amp .
per sq .
cm .
1085 \lt ; 0 0001 1 -1 X 10-'2 1425 0*0005 3 -4 x lO"11 1085 0*004 4 -3 x 10-12 1425 0-002 3 -5 x 10-n 1210 \lt ; 0*0001 2 -2 x 10-12 1425 0*004 6-9X1CT11 1210 0*004 5 -8 x 10~12 1425 0*007 1 -5 x 10- ' ' 1210 0*008 1 -9 x 10-'1 1425 o-oii 3 -2 x 1CT10 1280 \lt ; 0-0001 3 1 x 10-12 1550 0-004 1 -6 x 1CT10 1280 0 *0015 3 -4 x 10-12 1570 0*0006 1 -7 x 1CT10 1280 0 -004 1 -1 x 10-11 1570 0*011 9 -2 x lO-10 1280 0-006 2 -5 x lO-11 1780 0*004 6-9 x 10-10 1280 0*021 1 -0 x 1CT10 1790 o-ooi 6 9 x 1CT10 1425 0-00015 2 -7 x KT11 1790 0 *0075 1 -9 x 10-9 1425 0 -00025 3 2 x10- " 1830 0*004 3 -1 x 1CT9 These values are plotted in the form of curves in fig. 5 , the logarithmic scale of ordinates used being twice those taken in the preceding cases .
Table Y.\#151 ; Argon .
Potential 210-220 volts .
Temp. Pressure .
Ionisation .
Temp. Pressure .
Ionisation .
o mm. amp .
per sq .
cm .
o mm. amp .
per sq .
cm .
1270 0-009 4 -3 x 10- " 1460 0-0003 3 -4x 10-11 1270 0-012 5 1 x10-u 1460 0-009 7-8 xlO-11 1280 0*002 3 5 x 10-12 1570 0 *0003 1 -3 x 10-* ' 1290 \lt ; 0-0001 1 -7 x 10"12 1590 o-ooi 2 -0 x 10-10 1290 0*003 6 -7 x lCT12 1590 0 -002 2 -5 x 10-\gt ; ' 1340 0 *0001 1 -0 x lCT11 1590 0 009 3 -8 x lO"10 1340 0 *0003 i-0x icr11 1590 0 012 6 -15 x 10-\gt ; ' 1340 0-009 5 -9 X 10_u 1800 0 -0025 6 -7 x lO-10 1340 0-012 6-9xl0-n 1815 0*003 7 -7 x 10~ ' ' 1440 0*012 1 -5 x lO-10 1860 0*005 3 1 x Hr9 These values are represented in the form of curves in fig. 6 , the logarithmic scale of ordinates being the same as in the case of helium .
In the case of all figures given in the above tables the readings represent the results obtained when the ionisation current had become stationary After a change of pressure of gas in the vessel , an appreciable interval was usually necessary before the ionisation assumed a constant value .
This time effect is shown in experiments tabulated below .
The important result is at once clear from these tables , that whereas with the gases which are known to react with carbon , a very large effect is exerted by the pressure of the gas on the ionisation , while with the inert gases the ionisation shows comparatively very little change over a large range of pressure , and gives values of a much smaller order of magnitude than the other gases .
Dr. J. N. Pring .
In the ease of all gases , at the minimum pressures , the ionisation converges to a limiting value determined only by the temperature .
This is probably due to the influence of residual impurities retained by the carbon .
Table VI.\#151 ; Change of Ionisation after Change of Pressure of Gas .
1 .
Carbon Monoxide admitted to the evacuated vessel .
Temperature of carbon , 1180 ' .
Pressure of gas admitted , 0 *005 mm. Temperature of carbon , 1280 ' .
Pressure of gas admitted , 0 *003 mm. Time .
Ionisation .
Time .
Ionisation .
0 '25 min. 1-0 " 1- 5 " 2- 0 " 3-0 amp .
per sq .
cm .
2 -1 x 10~u 1 -5 x 10- " 1 -9 x 10-io 2 -4 x 10- ' ' 2 -8 x lCT10 0 -25 min. 0-5 " ID " 2-0 " 3 " 5 " amp .
per sq .
cm .
1 -3 x 10-u 7 D x 10-'i 6 -0 x 10- ' ' 1 -0 x lO-9 1 -5 x IQ"9 2 .
Carbon Dioxide .
Temperature , 1160 ' .
Pressure , 0 *008 mm. Temperature , 1270 ' .
Pressure , 0 '003 mm. Time .
Ionisation .
Time .
Ionisation .
30 secs .
1 min. \#166 ; 14 " 24 " 3 " amp .
per sq .
cm .
7 -0x lO"'2 7-OxlO"11 1 -5 x 10~8 2 -3 x 10-* 2-3x 10~8 * 5 secs .
15 " 1 min. 14 " 3 " 4 " 5 \#187 ; 6 amp .
per sq .
cm .
1 1 x 10-'1 3 -8 x 10"n 1 -4 x 10"10 4 -4 x 10"10 6 -5 x 10-10 2 -1 x lO-9 3 -1 x 10- ' 3 1x 10 " ' Ionisation on Reduction of Pressure in above Experiment at 1160 ' .
Time .
Pressure .
Ionisation .
mins .
mm. amp .
per sq .
cm .
0 0*008 2 -3 x 10~8 li 0*001 9 -9 x lO-9 2* 0 *0005 9 -9 x lor9 3J \lt ; 0*0001 9 -9 x IQ-9 Temperature raised to 1350 ' and lowered to 1160 ' .
\lt ; 0-0001 1 -5 x 10-12 The Origin of Thermal Ionisation from Carbon .
Nitrogen 0030mm .
0020 0015 oo:o # Hydrogen 0 005 0025 0 015 Pressure .
Fig. 3 .
Dr. J. N. Pring .
X 1720 ' Carbon Monoxide x Carbon Di-oxide \#174 ; \lt ; \#163 ; \gt ; 1160 ' 0020 0025 0-015 0010 0030 0 005 Pressure .
Fig. 4 .
Helium 0020 0-015 0-010 Pressure .
Fig. 5 .
The Origin of Thermal Ionisation from Carbon .
Discussion of Results .
A. Relation between Ionisation and Pressure .
It is seen from Table VI above that , on admitting gas at a higher pressure during an experiment , a certain interval was necessary before the maximum of ionisation was attained .
With the inert gases ( helium and argon ) , which gave the lowest ionisation , this time effect could not be observed , but with the other gases it increased in proportion to their final ionisation current .
Thus , at about 1200 ' , hydrogen gave a maximum value in about 30 seconds , carbon monoxide in about 3 minutes , and carbon dioxide not until after 5 minutes .
If equilibrium was reached at any given pressure , and the pressure was then lowered , at first only a slight decrease in the ionisation followed , and finally , in some cases , the current would suddenly fall to a lower value .
The high ionisation obtained at low pressures could also , in some cases , be suddenly lowered by momentarily interrupting the potential applied to the circuit .
In many cases , however , the reduction could only be brought about by taking the temperature considerably higher\#151 ; while the pressure was low\#151 ; and then lowering again .
This time lag or hysteresis in the ionisation has been observed by other workers , and it is quite apparent from these results that it is caused mainly by an occlusion of the gas in the carbon .
The gas is only very slowly evolved on heating , and probably it cannot be entirely eliminated .
Readings taken after a reduction of pressure during the experiments 358 Dr. J. N. Pring .
have not been entered in the above Tables ( I to V ) on account of their uncertain value .
B. Influence of Potential on Ionisation Currents .
It is seen that in the experiments conducted at low pressures , the potential difference used to collect the ionisation played a comparatively unimportant rdle .
If the fundamental ionisation arising from the carbon was largely increased by ionisation by collision in the gas , a very large change of current with potential would have been expected .
Hence the great differences observed when using different gases cannot be explained by the known differences in ionic mobilities .
C. Effect of Different Gases on the Magnitude of the Ionisation .
The results of the measurements with different gases given in Tables I-Y show that the ionisation from carbon increases in these cases in the following order:\#151 ; ' Aroon'1/ nitr'gen\gt ; hydrogen , carbon monoxide , and carbon dioxide .
This order is the same as for the known chemical activity between carbon and these gases .
While the first two are chemically inert , nitrogen reacts to a small degree to form cyanogen , * and with hydrogen to form small quantities of methane , ethylene , and acetylene , f while carbon monoxide gives a small quantity of carbon dioxide and carbon , j and carbon dioxide reacts rapidly to give carbon monoxide .
With the inert gases the increase of ionisation with pressure is seen to be very slight indeed when compared with the active gases .
It is seen from the curves ( figs. 2 to 6 ) that the ionisation does not converge to zero at the lowest pressures , but rather assumes a constant value for each temperature .
This is what would be expected in the light of the above phenomena of absorption .
At the lowest pressures the amount of gas held in the carbon would always appear to correspond to a higher pressure on the outside , and it was indeed found that the higher the temperature to which the carbon had been previously heated , while keeping the pressure constant\#151 ; and thus the more completely the occluded gas had been driven out\#151 ; the lower the final value to which the ionisation was reduced at that pressure .
By repeatedly * H. v. Wartenberg , ' Zeit .
f. Anorg .
Chem. , ' 1907 , p. 52 , pp. 299-315 ; Smith and Hutton , ' Amer .
Electroch .
Soc. Trans. , ' 1908 , vol. 13 , pp. 359-365 .
t Pring and Fairlie , 'Chem .
Soc. Trans. , ' 1912 , vol. 101 , p. 91 .
J Ithead and Wheeler , ' Chem. Soc. Trans. , ' 1910 , vol. 98 , p. 2178 .
The Origin of Thermal Ionisation from Carbon .
admitting and withdrawing one of the inert gases , the ionisation from the heated carbon was also considerably lowered , but could not be reduced beyond a certain limit , as would be expected from the impossibility of excluding completely extraneous gas when working at the high temperatures .
In fig. 7 curves are plotted to show the ionisation produced by the different gases when at a constant pressure of 0-005 mm. The ordinates are expressed in amperes multiplied by 10~12 and the abscissae represent the temperatures .
Ionisation , amps , x 10 ~12 .
( 0-005 mm. ) ^^'n_tlon^xide \lt ; o*m'n Fig. 7 .
Minimum Ionisation Fig. 8 .
lig .
8 shows , in the form of a curve , the minimum ionisation values obtained from the carbon at the lowest pressures used .
The ordinates here represent the logarithm of the ionisation and the abscissae the temperatures .
360 The Origin of Thermal Ionisation from Carbon .
The minimum current for 1 sq .
cm .
surface of carbon is seen to be 1*7 x 10-12 at 1200 ' , and 8-5 x 10~9 at 2025 ' .
These values are respectively about 107 and 10u times smaller than those originally estimated by Richardson ( loc.tit .
) , and which formed the basis of the theory of thermionic emissivity , and are about 105 times smaller than the values recalculated by Richardson { loc. tit.)after the revision of the constants of his formula .
Summary and Conclusions .
The ionisation produced by carbon at high temperatures , which hitherto has been generally held to be mainly due to direct electronic emission , was found in some earlier work to be dependent to a very high degree on the presence of gas and other impurities in contact with the carbon .
The conclusion then drawn , that the large currents hitherto observed were derived from some reaction between the carbon and the gas , has been confirmed in the present work .
It has been shown that a still further large reduction in the ionisation is brought about by eliminating further the absorbed gases from the carbon .
By admitting known amounts of different pure gases to the carbon the ionisation produced was found to be directly proportional to the known chemical activity of these gases .
The progress of absorption of the gas by the carbon and its evolution could , moreover , be traced by the ionisation currents .
It is clear from these results that the thermal ionisation ordinarily obsei'ved with carbon is to be attributed to chemical reaction between the cai'bon and the surrounding gas .
While it is difficult to prove definitely that there is no electronic emission from the heated carbon itself , it is obvious that it is exceedingly small compared with ionisation which can be attributed to ordinary chemical change .
The small residual currents which are observed in high vacua after prolonged heating are not greater than would be anticipated whexx taking into account the great difficulty of x'enxoving the last traces of gas .
I wish to thank Prof. Rutherford for the kind interest he has taken in the progress of this work .
|
rspa_1913_0090 | 0950-1207 | On the refraction and dispersion of gaseous nitrogen peroxide. | 361 | 369 | 1,913 | 89 | Proceedings of the Royal Society of London. Series A, Containing Papers of a Mathematical and Physical Character | Clive Cuthbertson|Alfred W. Porter, F. R. S. | article | 6.0.4 | http://dx.doi.org/10.1098/rspa.1913.0090 | en | rspa | 1,910 | 1,900 | 1,900 | 6 | 109 | 2,952 | http://corpora.clarin-d.uni-saarland.de/surprisal/6.0.3/?id=rspa_1913_0090 | 10.1098/rspa.1913.0090 | null | null | null | Thermodynamics | 39.82859 | Tables | 26.711767 | Thermodynamics | [
-2.973055601119995,
-36.88999938964844
] | ]\gt ; On the action and Dispersion of aseous Nitrogen By CLIVE CUTHBERTSON , Fellow of University , London , MAUDE UTHBEIiTSON .
( Communicated by Alfred W. Porter , F.R.S. Received July 29 , 1913 .
The study of the refraction and dispersion of gaseous nitrogen peroxide is specially interesting , to the opportunity it affords for observing the changes which accompany the polymerisation of the molecule .
No previous determinations are recolded in the usual books of reference .
The gas which we used was prepared by } ) lead nitrate , which had previously been ground to fine powder and heated for two hours to 15 C. to expel moisture .
It was condensed in a bulb , and quantities of about a cubic centimetre of the liquid were off in lass tubes hich were broken vacuo in a dry bulb containing .
Taps usually lubricated with metaphosphoric aci but in some cases with a lnixture of pure paraffin and vaseline , which was not appreciably attacked by the Doas .
Apparatus a For the detern } ination of refractiye indices Jamin 's refr ctometer 1 used .
The bulb containing the liquid was connected with the ictonleter tnbe by a tap .
Another tap connected a manometer , consisting of -tubes in series , the first containing oil and the seconld long capillary separated the oil from the hich led to the In a measurement of the refraction the liquid was first cooled to C. , at which temperature its pressure is ible , and the whole apparatus was evacuated with a Topler pump , ] tubes containing soda-lime and potash and , till the difference of pressure shown by the manometer corresponded with the barolnetric height .
The manometer tap was then closed and the liquid allowed to warm , while the observer counted the interference bands passed the cross-wire as the vapour flowed into the refractometer tube .
When a convenient number had passed , the tap connecting the bulb of was closed , and dry ftir was admitted into the manometer till the pressure nearly eqUalled that of the nitrogen peroxide .
The manonleter tap was then opened , and the difference between the pressure of the atmospl ) and that of the gas was read .
VOL. LXXXIX.\mdash ; A. 2 362 Mr. C. Cuthbertson and Mrs. M. Cuthbertson .
The barometric height was again taken , the temperature observed , and the number of bands noted .
The density of the gas present in the refractometer tube was determined by means of a density bulb connected with it in parallel , and immersed in the same water-bath .
Owing to the strong absorption of the vapour it was found impossible to use the mercury green line for measurements of refraction .
For this purpose we used red light obtained by means of a fixeddeviation spectroscope , fitted with an adjustable slit at the eye end , which sifted out a band of light not exceeding 10 A.U. in width .
Even with this red light the maximum number of hands which could be counted when the vapour contained 96 per cent. of was only about 80 , so that great accuracy was not attainable .
Reduction of Observations .
Our object is to compare the refractive and dispersive powers of the of and respectively , and their relation to those of nitrogen and oxygen .
It is , therefore , necessary to reduce the refractivities experimentally observed at various temperatures and pressures to the same standard conditions as those under which the refractivities of the permanent gases are usually expressed .
These are , of course , the temperature and pressure of the gas should be C. and 760 mm. But in dealing with substances which are not perfect gases , it , is desirable.to substitute for these conditions the real standard which they are meant to define , viz. , that the number of molecules of the gas present in unit volume should equal the number of molecules present in unit volume of a permanent gas , e.g. oxygen , at C. and 760 mm. pressure .
In the present case the pressure and temperature of the gas were observed , and it was assumed , for the purpose of the reduction , that each constituent ( i.e. and ) behaved as a perfect gas , and that the mixture remained of the same composition .
Upon these assumptions the reduced refractivity , which we shall denote by , is given by * where is the number of interference bands , the length of the tube , and the temperature and pressure of the experiment .
of Gaseous 363 The observed density*of the was reduced in the same manner .
If denotes the observed density ( gram1nes per litre ) and the reduced density , The standard density for each constituent was obtained fro1n the ving figures : Gramnles .
Weight of 1 litre of nitrogen at .
and 76 cm .
oxygen , , Hence , , 1 , , and , , 1 , , 4.11622 We have thus obtained a reduced refractivity and a reduced density .
The former expresses the refractivity which would be given at C. by a gaseous mixture in the proportions of molecules of were those which exist at the temperature and pressure of the experiment , and for which the density WftS such that ) number of molecules present per cubic centimetre was equal to the number present in unit volume of oxygen at C. and 760 .
latter iyes us the weight of lluit volmne of the aseous mixture under the same conditions .
ning the additive law to hold for the aseous I , it is evident that if we plot the reduced refractivities ainst the reduced densities , we should obtain a line .
The values of the reduced refractiyities which correspond with the ndnrd densities of given above will be the refractivities of and the standard conditions .
Table I ives the results of ten experinnents the refraction .
* It may be asked why we did not use the observations of E. and L. on the connection between the density , temperature pressure of ( ' Wied .
Ann vol. 24 , p. 445 , and vol. 27 , p. 606 ) .
These were mined from observations nine temperatures nearly all above C. , and at the low tempel and it was necessary for us to use in order to obtain large } ) cntage of ) discrepancies between their observations and the values calculated from Gibbs ' formula are so great that it was impossible to use them for the calculation of tho density at inte1mediate temperatures and pressures .
Schreber ( ' Zeit .
Phys. Chem 1897 , vol. 24 , p. 660 ) has analysed the tions of the brothelB Natanson , and gives a formula from which the dissociation be calculated at any temperature and pressure .
Our iirst series of expeliments was based on the use of this formula , but after three months ' work it foumd it , too , is untrustworthy at low temperatures .
In fig. 1 the values for the reduced refractivity are plotted against the corresponding values for the reduced density .
* The points fall on a straight line which cuts the ordinate whose abscissa is at the point , and the ordinate whose abscissa is at the point 1123 .
The constants , calculated by the method of least squares , the following equation to this line : is , perhaps , not obvious why we should not obtain a similar straight line by plotting the experimental values of the refractivity and density instead of the reduced , , since the latter are both derived from the former by multiplying by the same factor .
But this is not so .
In any one gaseous mixture let there be molecules of and of .
Let the refractivities of one molecule of and one molecule of be denoted by and respectively , and that of the mixture by ; and let the molecular weights of the two constituents be We have , and , assuming the perfect gas law for each constituent , also whence Multiplying by we have ' a linear equation between the reduced refractivity and reduced density .
Dispersion of Gaseous itrogen Peroxide .
365 The discrepancies between the calculated and observed values of the refractivity are all less than per cent. , except in the last two experiFIG .
1.\mdash ; Reduced refractivity of nitrogen peroxide plotted against reduced density .
ments , where they are and respectively .
This was to be expected , owing to the low pressure and high temperature of the experiments , which increases the difficulty of the density .
Hence , finally , we obtain the reduced refractivity of pure for and for pure It thus appears that the refractivity of a molecule of exceeds that of two molecules of by about per cent. In order to check this result we tried the experiment of operating with a constant density of gas at different temperatures .
The gas was admitted to the tube in the usual way , and the pressure , temperature , and hands read .
The refractometer tube was then sealed off with as short a side tube as possible , and the tubes were heated and cooled in a water-bath , while the variation of the position of the bands was observed .
The results were as follows:\mdash ; Mr. C. Cuthbertson and Mrs. M. Cuthbertson .
As the temperature was raised the proportion of molecules of increased , while the density of the gas remained constant .
The diminution of the retardation of under these circumstances , which is shown by the retrogression of the bands , proves that the refractivity per molecule of is less than that of .
The rate of diminution is rather faster than we should expect from the results of the main experiment ; but the accuracy of this subsidiary form of experiment is seriously affected by " " drift\ldquo ; or " " end effects\ldquo ; owing to the of temperature , and the to be attributed to it , as a ntitative experiment , is small .
Relation to activities of Oxygen .
We have recently shown that the refractivities of ammonia , nitric oxide and nitrous oxide are greater than the sum of the refractivities of the elements which compose them by , 3 , and per cent. respectively .
* peroxide exhibits the same phenomenon .
The additiye value for is found from Half of this is and The sum is while the experimental value is , an increase of 21 per cent. DISPERSION .
Procedure .
Measurements of the dispersion are limited , by the absorption , to the red and green , and even in this region trustworthy values would be difficult to obtain were it not for the enormous dispersive power of the molecule of .
In order to trace the shape of the dispersion curve as it passes through the absorption bands it was necessary to abandon the monochromatic sources of light which are available when a cras is transparent * ' Phil. Mag April , 1913 , p. 592 .
Refractvon and Dispersion of Gaseous ogen Peroxide .
S67 to the whole spectrum , and to do the best which is possible with a narrow section of the spectrum of white .
In this case the source was a Nernst lamp .
The fixed-deviation spectroscope was fitted with an adjustable slit at the eye end , and the two slits were till the beam which the second slit did not exceed 10 .
in breadth .
The apparatus was evacuated and the optical paths of the two beams equalised by means of the compensatol , so that no moyement was seen in the position of the interference bands as the was continuously from to .
Gas was now admitted till a nunlber of hands had passed , when the supply cut off .
The compensator was then altered till the same number of bands had passed in the opposite direction .
If the wave-length drum is now rotated any change in the position of the band is due to ) difference of dispersive powers of glass and gas .
* Three sets of experiments were made ; the first , at the lowest temperature and highest pressure which could conveniently be used , so as to obtain the greatest proportion of molecules of .
The reduced density of this mixture was about , and the proportion of molecules of present was 765 per 100 molecules .
At an intermediate temperature and pressure a single experiment made on gas containing 48 per cent. of molecules of The third set was made at the highest temperature and lowest presstlle convenient , on gas containing approximately 4 per cent. of lnolecules of and 96 per cent. of The results are raphically in fig. 2 .
In the first set of experiments , in which the proportion of was small , the curve could be traced throughout its whole as far as It is comparatively smooth , but shows clearly the characteristic rise and elative fall on passing through each region of absorption .
In is shown the curve obtained with ,52 per cent. , but the final density of the gas was so great that much light was absorbed , an * The compensator was of special design and retards light of all wave-lengths equally except so far as dispersion affects them .
It consisted of two pairs of wedge-shaped pieces of glass , with their thick ends opposed , mounted vertically in a metal with their exterior surfaces at right angles to the beam of light .
Three of the wedges are fixed .
The fourth is movable vertically by means of a screw , and is mounted so that the distance between the interior surfaces remains constant .
Each of the two beams of light passes through one pair of wedges , which are optically equivalent to a plane parallel sheet of glass .
By screwing the movable wedge up or down , the path of one of the two beams is accelerated or retarded , and all wave-lengths equally , except so far as dispersion affects them .
Mr. C. Cuthbertson and Mrs. M. Cuthbertson .
only six points on the curve could be obtained , intermediate parts.-of the spectrum being obliterated .
Fig. 2 ( 3 ) gives the curve obtained from the third set of experiments , when 96 per cent. of was present .
It shows the increased size of the humps FIG. 2.\mdash ; Dispersion of nitrogen peroxide .
on the curve due to the increased percentage of , and ives a fair idea of the position of their maxima and minima .
But farther than this the accuracy of this series cannot be trusted .
In order to obtain readings between 6000 and 5600 , it was 1lecessary to reduce the number of bands to 17 , and even to 13 , and , under these conditions , an error of 1/ 30 of an interference band was equivalent to an error of in the value of the refractivity .
In the figure the three curves have about the same inclination to the horizontal .
But , since the refractivity diminishes as we pass from ( 1 ) to ( 3 ) , the dispersive power increases in the same order and proportion .
Refraction and Disper.sion of Nitrogen Peroxide .
369 It is well known that , with sufficient dispersion , at low tennperatures , the absorption bands of are seen to consist of fine lines , which blend into a band as the temperature is raised , , no doubt , if it were possible to trace our dispersion curve from line to line , a series small maxima would be shown .
Our apparatus is not capable of these microscopic changes , but only records the general effect in passing through a of absorption .
The most interesting question raised by these observations is the cause of the incl.ease of refractivity which accompanies polymerisation , coupled with the decrease of dispersive power .
It is much to be desired that measurements of the refractivity should be supplemented by accurate observations of the position of the absorption bands the infra-red and ultra-violet for each constituent separately .
So far as we can discover , no one has attempted this .
records that the is transparent between and 238 , but this appears to be all that is known .
We are much indebted to the Boyal Society for a yrant in aid of this work .
The results given aboye be summarised as follows:\mdash ; 1 .
The l.efractivity of pure for , reduced to standard conditions by the formula is approxilnately 0 That of pure is ) , so that the effect of polymerisation is to increase the refractivity by about per cent. 2 .
The refractivity of a molecule of is greater tlJan those of the elements of which it is connposed by per cent. 3 .
The dispersive power of a molecule of in the red and reen i considerably greater than that of a molecule of * Living and Dewar , 'Roy .
Soc. Proc vol. 46 , p. 222 .
Hartley , ' Chem. Soc. Journ , vol. 39 , .
Ill. VOL. LXXXIX .
|
rspa_1914_0001 | 0950-1207 | On the diffraction of light by particles comparable with the wave-length. | 370 | 376 | 1,914 | 89 | Proceedings of the Royal Society of London. Series A, Containing Papers of a Mathematical and Physical Character | B. A. Keen, B. Sc.|Alfred W. Porter, F. R. S. | article | 6.0.4 | http://dx.doi.org/10.1098/rspa.1914.0001 | en | rspa | 1,910 | 1,900 | 1,900 | 2 | 110 | 2,505 | http://corpora.clarin-d.uni-saarland.de/surprisal/6.0.3/?id=rspa_1914_0001 | 10.1098/rspa.1914.0001 | null | null | null | Optics | 36.246942 | Tables | 22.20323 | Optics | [
17.55746841430664,
-22.422395706176758
] | ]\gt ; On the Di.action of Light by Particles Comparable with the Wave-length .
B. A. KEEN , B.Sc. , Physics Research Scholar , and ALFRED W. PORTER , F.R.S. , Fellow of Universiby , University of London .
( Received October l , \mdash ; Read November 27 , 1913 .
) This research was undertaken to investigate an effect first noticed by one of us ( A. W. P. ) when experimenti1lg with the light scattered by suspensions of finely divided sulphur .
These were obtained , in the well-known way , by depositing sulphur a solution of thiosulphate of soda by means of a weak acid .
When such a suspension is placed in the path of a beam from an arc lamp focussed on a SCl'een , the image of the carbon is usually red , of rrreater or less depth ding to the size and number of the diffracting particles .
The production of this red colour has been satisfactorily explained by Lord Rayleigh* as due to the selective blue light by particles which are small compared with the wave-length of the One of us noticed , however , that if time ) given for the particles to increase in size ( and in number also ) the solution after becoming nearly opaque transparent yain , but in this new stage an excess of blue is transrnittc , which attains at one stage a deep indigo tint , this wards changing through various blue-green reen tints , to white .
This very remarkable result is in direct variance with the current theory of the action of small particles , and presents , therefore , a problem investigation .
While making quantitative measurements upon it we found that analogous pheno.mena had been observed previously , though no ation had been undertaken to explain the effect observed .
For example Captain Abney , in connection with his preparation of a hotographic plate which would be sensitive to the infra-red region , experimented with silver bromide and attempted to get it in a different molecular condition from that generally found .
He says : ' I need not detail the different methods of preparation of this compound in collodion that were carried out .
In some cases I obtained it in a state which , when viewed by transmitted light , appeared of a sky-blue colour inclining to green , visibly abSorbing the red .
In this condition it ( the photographic plate ) was sensitive to the whole spectrlun , visible and inyisil ) \ldquo ; 'Phil .
Mag 1871 , , pp. ; 1899 , vol. 43 , pp. 376-384 .
'Phil .
Trans 1880 , Pt. II , p. ) ofLight by ticles Cwith Wave-length .
371 , Walther Bitz*gives a new method of preparing the sensitive compound , , iving superior results to those obtained by Abney .
In the course of his directions he notes:\mdash ; " " Les bromures de zinc et sont a peu pres equivalents : on peut aussi remplacer le d'alcool et d'c'ther par de l'alcool me'thylique ou de tone .
La transformation du bromure d'argent est donc d'ordre purement physique ; elle est d'ailleurs toujours d'une augmentation du diametre des grains .
Enfin l'emulsion a soumise sous pression des temp allant pendant ume heure et pendant 24 heures .
Il n'a cependant pas possible de depasser la limit donnee par Abney , le bronure devenant granuleux et se de'composant .
La couleur caract bleue de d'Abney ( par transparence ) ici imme'diatement et a froid .
These vations made by others are important ) ecause they show that the is not peculiar to sulphur .
of The research consisted of , at instants after setting free the thiosulphuric acid , the transparency of the suspension to monochromatic lights of various wave-lengths .
For this purpose a Hiifner spectrophotometer was employed , and made by Messrs. and Co. Light passing first through a fixed nicol , and then through one which can be rotated , is matched with the solution and the second nicol .
its way the is sorted into its constituent colours by means of constant deviation prism ; the match call therefore be made any desired in succession .
By trial it was found that the most suitable .
of acid and thiosulphate to use were such that the first sign of blue } appeared about two minutes after mixing , at ordinary temperatures .
The exact strengths used in the present work were lnolecule thiosulphate per litre and .
molecule of HC1 per litre .
These were approximately chemically equivalent .
It was soon found that , to obtain any concordance in the results obtained on different occasions , it was to pay particular attention to temperature and also to keep the solution continually stirred .
Stray had to be excluded as far as possible , as it seriously affected the power of the eye in matching the two halves of the beam .
It was also necessary to guard against fatigue of the eye in the course of an experiment .
The ular lass cell containing the solution was of 1 cm .
interllal meter .
This immersed in a one containing water to keep the temperature constant , ' Comptes Rendus , ' 1906 , vol. 143 , p. 16 372 Messrs. B. A. Keen and A. W. Porter .
of while between this and the source of light another water cell was placed to S act as a heat screen .
As source of light a Welsbach mantle was employed .
Various heat and screens were placed where experience indicated .
thermometer was placed in the solution .
Air was continually through to prevent the particles settling and to make their rowth as regular as possible .
The air tube was arranged so that the stream of bubbles was outside the field of view .
A very steady stream of air was obtained from a toy vertical steam engine driven " " backwards\ldquo ; by an electric motor .
To prevent any considerable evaporation a glass plate was placed over the top of the small cell .
The reaction was complete in about 30 minutes .
At the close of an experiment the cell was cleaned with a wet plug of cotton wool to remove any adhering sulphur , thoroughly washed out with distilled water , and dried by a stream of dust-free air .
Two typical \mdash ; one in the blue and the other in the red\mdash ; were elected , and the complete experiment performed with one wave-length at a time .
The final curves obtained ( fig. 1 ) are each composed of three sets of FIG. 1 .
obtained in this manner .
The readings for either wave-length do not differ among themselves by more than the experimental error involved in setting the nicol .
* It will be noticed that the initial portion of each curve is ot The experimental points have been omitted to prevent confusion .
The magnitude of the experimental error , however , is slightly less than that between the values indicated by circles in fig. 2 and the mean curve drawn through them .
Light by Particles Comparable with the .
373 iven .
There are two reasons for this omission .
In the place very little of the light is diffracted at this early stage of the reaction , consequently the of the source is too bright to permit of accurate comparison of the intensity of the two halves of beam , as considerable movements of the adjustable nicol then produce no appreciable ariation of intensity .
The second source of error is due to the rapid rate at which the intensity changes in the stages of the reaction , that is to say , immediately after the first pause during which no deposit is formed .
This obviously makes any experimental error of more importance .
Reliable readings of this initial pol.tion of the curve were obtained in separate experiments by a colour screen in the path of that portion of the beam which passes the solution .
Although this reduced the intensity of the light in an ascertainable ratio , it made the accuracy in setting the nicol much reater , as a small movement of the nicol now 5 Minubes 15 FIG. 2.\mdash ; Curve intensity of transmitted light in the early stages of the reaction .
withcolourscreenwithoutcolourscreen } Temperature 374 Messrs. B. A. Keen and A. W. Porter .
action of produced appreciable effect on the intensity .
From these readings the corresponding intensities , had the screen been absent , were easily obtained .
With the help of an assistant to read the watch , readings were taken at Hhorter intervals .
The curve obtained is shown in fig. 2 , the readings being indicated by circles .
A control experiment was made without the colour screen : , these readings are indicated by crosses .
As already mentioned , the yrowth of the particles is very sensitive to temperature changes .
In fig. shown two curves to indicate this .
The temperatures were adjusted by putting hot water or ice in the water-bath .
FIG. 3.\mdash ; Curves showing the effect of temperature upon the reaction .
Naturally the temperature could not be kept very constant by this means and these curves must be regarded as qualitative only .
The character of the curve is very different at the two temperatures , the observations at the lower temperature not indicating the dip which is the subject of this paper .
It should be observed that the data for figs. 2 and vere taken with a different experimental cell from those for fig. 1 .
The size of the particles was measured with the microscope when the intensity of the passing through was a minimum , i.e. about 10 minutes after mixing ( see fig. 1 ) .
At the end of 10 minutes a drop of the solution was placed on a slide , and further action was then stopped by neutralising the unchanged acid with ammonia .
The extreme limits of variation were from to , thus indicating that the particles at this stage were considerably Light by Particles Comparable with the -length .
375 larger than those used by Lord Rayleigh in his experiments .
* This was confirmed by repeating his experiments with solutions of the strength mentioned above .
Particles of the size used by Lord give rise to the early portion of the curve in The gradual change of the transmitted from red through blue to white is well brought out by the curves in fig. 1 .
In the first stages of the reaction the intensity of the blue light falls off more rapidly than the red .
At the end of about 8 minutes the blue has reached its minimum intensity and begins to increase , while the red light is still to its minimum .
The transmitted \mdash ; when due allowance is made for the rest of the spectrum\mdash ; becomes a purple oolour .
After the cross , blue end of the spectrum predominates , and hence the blue colour of the transmitted hich radually changes to white as the remaining rays increase in intensity .
The minimum and final intensities are the same for each wave-length .
The final intensity ( the horizontal portion of the curves ) remains constant for a considerable time and then very slowly increases , owing to the ulation and consequent settling of the sulphur particles .
Interesting information on the rate of growth of the ) articles is afforded by an examination of the curves given in fig. 1 .
If the abscissae of the curve for blue are increased in the ratio of the wave-lengths , i.e. 660/ 475 , the new points are very nearly coincident with the ctlrve for red light .
The points so obtained are indicated by crosses .
As one would expect , the agreement is not so complete in the initial portion of the curves , but ovel the greater part very reement holds .
This result shows that the transmitted intensity may be represented as a function of , where is the time .
With regard to the relation between the time and the diameter of the particles more difficulty exists .
In the through which Lord Rayleigh has extended his calculations , the intensity is a function of the diameter divided by .
This would make the diameter the particles increase proportionally to the time .
Too much mcertainby exists in to the physical cesses involved during the of the particles to devise with any confidence a theoretical value for the rate of rowth .
We may safely assume a practically instantaneous liberation of acid , which then decomposes .
If this were all , the rate of liberation of sulphur would be proportional to the undecomposed thiosulphuric acid , or , and , that itself would be a linear function of in the early stages .
But experimental evidence is in favour of the existence at first of supersaturation , ' Collected Papers , ' vol. 5 , p. 547 ; 'Roy .
Soc. Proc 1910 , , vol. 84 , p. 376 of Light by Particles Convparable with Wave-length .
hich at last gives way with a sudden deposition of sulphur particles , which .
then grow .
If we assume that the thiosulphuric acid has decomposed according to the monomolecular law throughout , and that from this stage all that is formed deposits on the particles , same equation will still hold good for the period after the sudden deposition .
But this law is too simple an account , for the process will be mainly controlled by the diffusion of supersatu.rated solution toward the formed particles .
The amount reaching the particles may be taken as proportional to area or to their mass ) and the equation becomes .
In the early stages ( for which can be treated as constant ) this leads to const .
so that the diameter would be a linear function of the time .
In the recent paper by Lord , which we have cited , interesting shown to take place in the polarisation of the as the particles increase , but here does not appear to be any indication of the phenomena with which this paper deals .
We not foumd it possible to modify the theoretical equations , so as to make the calculations manageable for the larger particles with which we seem chiefly to be concerned .
The phenomena appear to be analogous to the different order spectra obtained with an ordinary .
The results are published in the hope that the attention of mathematicians may be called to an interesting but very difficult which still requires mathematical treatment .
|
rspa_1914_0002 | 0950-1207 | On an inversion point for liquid carbon dioxide in regard to the Joule-Thomson effect. | 377 | 378 | 1,914 | 89 | Proceedings of the Royal Society of London. Series A, Containing Papers of a Mathematical and Physical Character | Alfred W. Porter, F. R. S. | article | 6.0.4 | http://dx.doi.org/10.1098/rspa.1914.0002 | en | rspa | 1,910 | 1,900 | 1,900 | 3 | 30 | 492 | http://corpora.clarin-d.uni-saarland.de/surprisal/6.0.3/?id=rspa_1914_0002 | 10.1098/rspa.1914.0002 | null | null | null | Thermodynamics | 52.244662 | Tables | 32.759778 | Thermodynamics | [
-10.210564613342285,
-31.90633201599121
] | ]\gt ; an Point for Carbon Dioxide Regard to the Joule-Tho ?
nson By ALFRED W. PORTER , F.R.S. ( Received October 6 , \mdash ; Read November 13 , 1913 .
) In a paper published recently in the ' Philosophical Transactions ' " " On the Thermal Properties of Carbonic Acid at Low Temperatures *Prof . .
Frewen Jenkin and Mr. D. B. Pie , amongst other results , those obtained from a series of measurements of the Joule-Thomson effect for liquid at various temperatures .
These results are tabulated in Table of their paper .
They of particular interest because , within the range of temperatures to which they correspond , they find an inversion point for the Joule-Thomson ect , i.e. , a temperature at which the effect over from being a cooling ( at higher temperatures ) to being a heating .
As they themselves say : experiments on the Joule-Thomson for liquid appear to have been published\ldquo ; pie , and as they admit that it is not easy to what effect the presence of a of air ( which was there ) may have ou their results , any method of them should prove of value .
Such a test can be made by utilising the values of the specific volumes of liquid which they rive in a diagram on p. 78 of paper .
Method of Test .
If the drop of pressure employed may be treated as a differential the JouleThomson effect is en by the equation The inversion point must therefore corresponld to a minimum ullt ) value of Applicat ion of Test .
I have read off from the diagram of specific volumes the values at various pressures and temperatures and calculated the ratios .
These are tabulated below:\mdash ; 'Phil .
Trans 1913 , , No. 499 .
Joule-Tho ?
nson Effect .
Liquid Carbon Dioxide . .
in . .
in . .
in .
All these three sets concur in giving a minimum value of at a temperature not much removed from C. The inyersion point actually found experimentally lies between and , and by plotting their cooling effects one finds it to be at , the high pressure being between 668 and 664 lbs. .
in .
, and the low pressure between433 and 3.60 .
The mean pressure is therefore about .
in .
Thus , the rather remarkable result that an inversion point exists near the point found is confirmed .
The result is remarkable , because it implies that liquid is in this region behaving very nearly like a perfect gas , its volume being nearly proportional to the absolute temperature .
It may be added that .
in .
is about times the critical pressure , and C. is about .
times the critical temperature ; and that these are approximately co-ordinates of an inversion point for any van der Waals liquid .
|
rspa_1914_0003 | 0950-1207 | The diurnal variation of terrestrial magnetism. | 379 | 392 | 1,914 | 89 | Proceedings of the Royal Society of London. Series A, Containing Papers of a Mathematical and Physical Character | George W. Walker, A. R. C. Sc., M. A., F. R. S. | article | 6.0.4 | http://dx.doi.org/10.1098/rspa.1914.0003 | en | rspa | 1,910 | 1,900 | 1,900 | 8 | 171 | 4,029 | http://corpora.clarin-d.uni-saarland.de/surprisal/6.0.3/?id=rspa_1914_0003 | 10.1098/rspa.1914.0003 | null | null | null | Tables | 48.768129 | Fluid Dynamics | 19.50965 | Tables | [
46.1385612487793,
3.1585495471954346
] | ]\gt ; The Diurnal Variation of lIagnetism .
By GEORGE W. WALKER , , F.B.S. , formerly Fellow of Trinity ( Received October 15 , \mdash ; Read November 13 , 1913 .
) The diurnal variation of terrestrial gnetism has been the subject experimental study for many years , and at a considelable numbel of observatories scattered all over the earth .
But the co-ordination of the results , and the theoretical ation of the se or causeh of the phenomena , have not made progress seems to bear a ) proportion to the vast amount of observational that has muLtted .
As far as I know , Dr. Arthur Schuster 's memoirs*titute the most systematic attempt to reduce this matter to scientific law order .
Although I have found it convenient to depart from the pursued by Schuster , thus of ) ocednre in no suggested by various remarks in his llemoirs .
The comparative lack of interest in the sub , ject arises , I believe , in measure from the difficulty ( commented on ) Schuster ) of the experimental data in a fornl conyenient for rational arison .
tories still continue to reduce their observations to publish .
results in a variety of ways , and , unless one ) undertake a amount of tedious ithmetical conn ) nffitiun at the very outset , it tically impossible to obtain a comprehensive of the The Advisory Committee of Eskdalennnir recommended the instruments should be arranged so to record directly the , components of netic force , the resnlts for began to take definite shape , it was , pel.haps , natural I ) old ] ) interested in comparing the results with those the unly other which at the time also recorded the components , Potsdam ( Seddin ) .
The I made in the light of conclusions , brought out points of such interest that I induced ttenlpt to collect data from other observatories ) the values the eographical components .
Following Schuster , the lata I desired to were the Fourier coefficients iu the components .
I myself to the 24-hour and the 12-hour , because I share the entertained ) many of those realise the err that arise on the ' Phil. Trana , ' 1899 , vol. 180 , and 1908 , vol. 208 .
Mr. G. W. Walker .
experimental and side , that the shorter period terms are of very donbtful accuracy .
further confined my attention to the yearly value , not because seasonal variation is } ) ortant , but because I felt that there was a .
danger of coming to rief in a multitude of facts .
The data I have been able to obtain are collected in tabular form .
If they appear somewhat meagre , 1 .
would point out that I had perforce to confine attention to atories whose results could , without very much arithmetical labour , be put in the form desired .
I hope that the information disclosed by the table will encourage others to make a contribution to it , and thus to the progress of knowledge of the phenomena .
In the table the quantities are those in the equivalent formulae and , where is the local mean time at the station and the unit of nitude is or auss .
From information very kindly supplied by the directors of the various observatories , the statement may be made : 1 .
Practically all days are used , not selected quiet days .
2 .
The curves are not smoothed , except in the case of the results for Pola .
7 ) .
The original curves gave records of and except at Eskdalemuir and Seddin , where and were directly recorded .
4 .
The hourly values are those at the exact hour , except at Seddin , where the hourly value is the estimated mean for an hour centering at the exact hour .
1 need perhaps hardly say that one could wish for data obtained in recisely the same way , and that before entering on a minute arithmetical computation , all data should refer to the same year .
It was soon obvious from my inquiries that one would have to wait several years before such data could be obtained .
, I think certain broad inferences may be drawn from the data collected in the table , and these seem to me of vital importance .
It will be convenient to review briefly the main points in Schuster 's memoirs .
If we grant the main proposition , that it is correct to represent the variations by a potential metion , the problem may be divided into two parts : The empirical determination of the potential function which represents the observations .
The Diurnal oflIacynetism .
Mr. G. W. Walker .
( 2 ) The theoretical ation of the physical causes that give the potential function so determined .
These two divisions are substantially represented in Schuster 's first and second memoirs .
But the two divisions are not entirely independent , ( 1 ) must borrow from any hint gested in ( 2 ) , and ( 2 ) must be kept within the indicated by ( 1 ) .
In the first memoir , Schuster dealt with observations from the four Pavlovsk , Greenwich , Lisbon and Bombay .
Observing that in the west component the Fourier terms depended substantially on the local time ( a feature which is in the main confirmed by our table ) , he showed how the potential could be calculated .
Since the west component is the form is the co-latitude and the longitude , it is only necessary to the proper expression for in Tesseral and then the simple integration with respect to gives , when multiplied by , the function His conclusion reached was that principal parts of the mean diurnal variation for the year could be expressed by a potential metion of the form where is the local time or the equivalent Greenwich time plus the longitude , say .
In the second memoir Schuster proposes to explain these terms as arising from electrical currents in the atmosphere , set up by the joint action of the ermanent part of the earth 's magnetic field and the mechanical oscillation of the atmosphere .
Thus the barometric variation is associated with the llagnetic diurnal variation .
Certain i.ormidable difficulties occur and are carefully noted by Schuster , but I need not comment on them .
In attempting to deal with the seasonal variation Schuster supposes that the conductivity of the air depends on the sun 's zenith distance , and , assuming a simple and tentative expression for the conductivity , investiates o potential function that arises .
The analysis is necessarily exceedingly complicated .
Let us now return to the empirical expression obtained Schuster .
A potential of the form 1nust give components to north and to wesb ; and again the form Th of zetism .
gives components , sin2 .
The following Table II facilitates the parison of the formulae just obtained with the data collected in Table Table II .
If ow we examine the data and consider only , then , allowance for the that the are not all for the same year , we have , I thinl 's expression .
Batavia is , however , bnormal .
, taking the values for only we have strong support for a formula of the type iven by Schuster .
But clearly for any one station values of and should the same constants in the formula .
is not the case .
The phase are not in agreement , and what is even more serious is fhat the amplitudes of the nolth component and all too boreat as compal.ed with the values computed from the potential function which ) resents t ) west componenlt .
The matter looks still more difficult if we compare the of with the and of W. I confess that the result was ) one could see no flaw in method , and the west values did , on the whole , depend ' on local time .
There , of course , the qibility of a higher zonal harmonic , but this did not promise much help , and I was certainly to enter on much arithmetical computation .
There remained the possibility of obtaining function which would contribute to without to .
This practically meant a term on time from some fixed meridian , as Schuster indicated .
After carefully studying Schustel.'S theory of the cause , with its complicated analysis , it to that one : process , that is to say , one may in perfectly elleral 1luine 384 Mr. G. W. Walker .
potential functions which are differentially related to opposite sides of the earth .
The process may stop as soon as we get the terms which represent the data , and then we may seek for the physical meaning of the terms .
In mathematical terms we start with the primary potential l. Any space derivative of this is also a potential .
Thus a slJace derivative fixed with to the earth gives a contribution to the fixed part of the earth 's field , while a space derivative fixed with to the sun gives a contribution to diurnal change .
In this simple way expressions were formed and it was found that the terms sought for could arise .
I think will be convenient to postpone consideration of the manner in which they were obtained and to give first the results .
For the 24-hour term the form of potential function at which I arrived may be written A , wherein is the local mean time and are the co-latitude and longitude of the station , while may .
be regarded as the lopgitude of some arbitrary meridian .
Since the data do not all refer to the same year a minute numerical analysis would be out of place .
Thus only round numbers were selected for the constants .
By trial the following form was finally selected:\mdash ; .
This gives in units of the following values for the north and west components : numerical values computed are shown in Table III .
Although the observed values are given in units of , it must be remembered that the accuracy in most cases does not exceed 1 I think it will be admitted that we have , on the whole , got a substantial representation of the data .
The better agreement that might have been obtained for the European stations had , of course , to be sacrificed somewhat to get the cnrious features exhibited by the Bombay and Batavia data .
The gnetism .
Table sion .
Helwan Tha potential function obtained must also account for values of We are at liberty to suppose that any term in arises from an external or interior source , and further that these contributions may differ in phase .
We may , therefore , introduce a division of the constants that will the correct value of at the surface and at the same time account for the observed values of .
In fact , if we could depend on the values of we have the important means of determining the external and internal proportions .
But unfortunately the obseryations of are poor and everyone who has really faced the experimental difficulties admits that the results are most unsatisfactory .
In particular I know that the Eskdalemuir results for are quite unreliable , and , from the other data , I think they must be regarded with some suspicion .
The Potsdam and De Bilt results do , however , agree very well , and so I take them as a sort of standard .
But clearly the position is a weak one , and therefore I do not feel justified in giving more than a general indication of what our formula would do .
I therefore assume that the outside and inside contl.ibutions agree in phase , and as regards the second order harmonics I adopt SchusCel.'S result that the internal contribution is one quarter of the external .
In the first order harmonic I assume that the contribution from source is nil .
We thus get the formula for The computed values , marked provisional , are entered in Table III .
The results are , on the whole , in the right direction , and might be brought closer by taking a smaller proportion from an internal source , but I do not think it worth while to force the matter until better data are available .
VOL. LXXXIX.\mdash ; A. 2 Mr. G. W. Walker .
We now consider the 12-hour terms .
The form which I found it convenient to try was The first four terms involve harmonics of order 3 but the last is of order 1 .
I finally dropped the term in , made and C. It also seemed an advantage to make Thus the empirical form adopted was so that The components to north and west thus become cos2 The computed values shown in the followin Table Table W. V. ( Provisional .
) Again , I think these numbers give substantial agreement with the data .
Turning to the data for , the numbers look more hopeful than in the case of the 24-hour terms , and the experimental errors that affect the 24-hour term are perhaps not so serious in the 12-hour term .
Thus I was tempted to push the agreement somewhat further .
The Diurnal Variation of Terrestrial qnetism .
387 The data gested that the main part for the northern stations arose from the term in , but was chiefly iu the cosine term and practically nil for the sine term .
This can be met a } ) has difference between the outside and inside contril ) utions .
Thus assumed .
Hence we have , Asin To get the results for Potsdam , we have the additional equations Hence , , which Tees with Schuster 's result thab is about 1/ 4 of A. Next the term in .
the main of the terms at Batavia , and assuming for the 1noment that the harnlonic was entirely of order 3 , I took the form Hence The values at Batavia gest taking , Hence This makes about one-fourth of A. But the harmonic was really made up of a main part of or and a minor part of order 1 , and the correction to is thus found to be sec45o where we have assumed that the first order term was entirely external .
The net result is The computed values in Table to very satisfactory agreement with the data .
I do not , of course , that Chis empirical representation of the data in Table I is unique or final , but I do think it is clear that the Schuster terms alone will not co-ordinate the data , and the form we have obtained does go a very conside1able way vards meeting the difficulties .
388 .
G. W. Walker .
We may now consider how the terms were arrived at , in such a way as to 6 provide a clue to the physical meaning without binding oneself to any special theory .
In the figure let , be rectangular axes through the earth 's centre in the directions , earth 's way , radius to the sun , and perpendicular to the plane of the ecliptic .
Let OX , , be fixed rectular axes in the , but not rotating with it , OZ the axis of rotation , and OX in the plane and OZ .
is thus the obliquity of the ecliptic and an angle expressing the time of the year .
The direction cosines of OX , OY , , referred to , are OX ; ; OZ Let be the polar co-ordinates of a point fixed on the earth , and let refer to any other point on the earth .
Suppose start with a potential and differentiate along the direction .
We get a potential function Since remains constant while the earth rotates , we simply have a contribution to permanent field of the earth , representing a doublet with its axis in the direction , ] us differentiate along .
We get where is the local time at the point of observation reckoned from midnight .
The term in contributes nothing to diurnal variation , but contributes a seasonal term to the general field .
It has a maximum in summer , minimum in winter , and vanishes at the equinoxes .
Variation of Terrestrial Jfcxgnetism .
389 The term in contributes to the variation .
The amplitude has a semi-annual seasonal variation , to its maximum value 1 at the equinoxes , and falling to its minimum value at the solstices .
Ayeraged for the year it contributes a term to the ) diurnal variation .
Such a term is indicated by the data .
We may , if we like , picture it as a uniform field in the direction of the , within ich the earth rotates .
In a similar way we may differentiate , and so a term Let us now carry the process of forming functions further by differentiating the direction .
We may write the result in the form where is Greenwich mean time , the co-ordinates of a point fixed with respect to Greenwich , and the co-ordinates of the station referred to Greenwich .
The first two terms contribute nothing to diurnal variation , but only annual seasonal terms to the , eneral field .
The remaining terms contribute to diurnal variation , the amplitude a semi-annnal seasonal variation fluctuating between 1 and .
Averaged for the year we get terms in the mean diurnal variation .
If is we have a term , where is the local time .
Similarly , a term arises by differentiating .
We thus get the Schuster terms in the 24-hour term of diurnal variation .
If , we have the term ( A ) Similarly , differentiating along , we get a term Now , in this latter form eplace by are at liberty to do .
We get ( B ) Adding ( A ) and ( B ) , we where is Greenwich mean time .
Mr. G. W. Walker .
Again , deduct from ( A ) and we get These are the terms we found it desirable to introduce .
We have thus obtained the terms required for the data , and clearly we might have taken a llore general form had it been necessary .
We seen that Schuster proposed to explain his term as arising from the permanent field and tidal oscillation .
But there are great difficuJties in the way .
Our analysis confirms the association with the permanent field , but otherwise may silIJply mean differential conductivity of the air as between midday and midnight , and as between sunrise and sunset , the difference arising from the ultra-violet radiation from the sun .
As ards the term depending on mean time , its mode of generation would appear to associate it with a magnetic axis lying in the plane of the equator .
If there is such an axis the intensity will have to be feeble if it is not to produce a very pronounced influence on the eneral field , as indicated by observations .
My main objective has been the mean diurnal variation for the year , letting the seasonal variation take care of itself .
But I anticipated that any correct method of approach would provide by extension for the seasonal appears to be the case in analysis iven .
Seasonal change is provided for , but the terms we have obtained contribute only semi-annual change , not annual change .
The latter is important , but will not of course leave an Huence on the mean yearly value .
Thus it may be expected arise in a way which differs from that we have already used .
But differentiation along supplies the kind of function wanted .
Thus where is the local time and tau The first term contributes to the permanent field .
The second term contributes to the diurnal variation at any particular time of the year .
But the phase passes a cycle in the course of the year , and so contributes when averaged for a year .
seasonal change is , however , beyond the lilnits I had prescribed myself in this paper , and I shall not pursue it further on this occasion .
So far the examination has referred to the -hour terms , but the data indicate the necessity for to the Schuster expression siu2 in the 12-hour terms also .
Our method for the The Ofnetism .
391 24-hour term suggests that we should get new 12-hour terms by a second differentiation along or .
The formulae become more complicated if we are to retain the sun 's annual variation in declination .
We therefore simplify the matter by regarding the sun as remaining in the plane of the equator .
If we thus lose sight of the seasonal variation , we gain in conciseness .
If we take the form ' i.e. , we get as a potential form which leads to The contribution to the 12-hour term is of the form co , but did not find this term of much assistance in the data .
The Schuster term arises by in , which then becomes , and then the , or of If , on the ) , we put in , which then and then form the , or of this , we arrive at 12-hour terms of the forms\mdash ; ( C ) and 3 .
In the latter replace by .
We get 3 eos ) .
( D ) Addition of ( C ) and ( D ) gives the form , while , if we subtract ( D ) from ( C ) , we get the form .
I found it conyenient to add to these forms a term ) may be regarded as a field parallel to the } ) lane of the equator rotating with the angular velocity of the earth but in the ) osite direction .
We have thus formed a simple specification of the terms which seem to fit with the data .
I have no theory to propose as to their , beyond Schuster 's view that they arise from ential conductivity of the regions of the } ) here .
If further data confirm the probable reality of Che terms , it should not be a difficult matter to } ) ress the law of conductivity which uld account for them .
As we have only had to proceed to Cond differentials with r to the sun 's direction , or the earth 's , it does not look as if the differential conductivity required is of a very complex nature .
The Diurnal Variation of Terrestrial Magnetism .
The possibility of the electric and magnetic state of the earth with its translational movement has often attracted attention , although without success .
It may not be out of place here to give a general solution of the electromagnetic equations for a body of conductivity in a straight line with velocity , where is the velocity of radiation .
The tion , which I believe is new , refers to the steady state .
If the components of electric force and magnetic force the equations are and A solution is expressed by ; where is a solution of Primary solution\mdash ; where and other solutions may be obtained by the usual process of differentiation .
|
rspa_1914_0004 | 0950-1207 | A suggestion as to the origin of black body radiation. | 393 | 398 | 1,914 | 89 | Proceedings of the Royal Society of London. Series A, Containing Papers of a Mathematical and Physical Character | George W. Walker, A. R. C. Sc., M. A., F. R. S. | article | 6.0.4 | http://dx.doi.org/10.1098/rspa.1914.0004 | en | rspa | 1,910 | 1,900 | 1,900 | 4 | 81 | 1,612 | http://corpora.clarin-d.uni-saarland.de/surprisal/6.0.3/?id=rspa_1914_0004 | 10.1098/rspa.1914.0004 | null | null | null | Tables | 48.531326 | Fluid Dynamics | 25.546403 | Tables | [
39.72852325439453,
-39.10770034790039
] | ]\gt ; A Suggestion as to the Origin of Black Body diation .
By GEORGE W. WALKEB , A.B.C.Sc .
, M.A. , F.B.S. , formerly ellow of Trinity College , ( Received October 15 , \mdash ; Read November 13 , 1913 .
) The discussion on " " Radiation\ldquo ; in Section A at the recent British Association in was one of profound interest .
Some of the remarks made then suggested the investigation which I now describe .
Planck 's formula*for the emission function is .
This formla represents bhe observations for short and ] waves at various temperatures with considerable closeness ; and , if it is the correct expression , it is held by some to prove that the classical equations of dynamics and electrodynamics at fault .
As I do not think the classical equations are in much danger if properly applied , I have endeavoured to trace the dynamical explanation of the experimental data .
There must be many formulae which will express the data as well as Planck 's form .
In searching for such an expression of dynamical , I went back to the equations for the motion of a charged sphere which I established on dynamical principles .
A clue to a solution very soon appeared , and without further remark , at present , I will state the formula that was tried .
If the emission within a range is expressed by it will be remembered that , in order to satisfy Stefan 's and Wien 's laws , the expression must be a function of the product Accordingly , I selected the formula as a function which satisfies the following conditions:\mdash ; ( 1 ) It gives Stefan 's law that the total radiation ries as , since and .
( 2 ) It gives Wien 's law that the maximum radiation at any temperature occurs when constant .
In our formula 'Theorie .
Warmestrahlung , ' 1906 , p. 157 .
'Phil .
Trans 1910 , p. 152 .
Mr. G. W. Walker .
( 3 ) It gives the condition that the maximum radiation at any temperature for this wave-length varies as .
In our formula ( 4 ) It gives Lord formula for long waves These conditions are required by the experimental work of Kurlbaum , Wien , , Lummer and Pringsheim , and Rubens .
The remaining point is therefore whether the formula will fit with the lesnlts of Paschen or Lummer and Pringsheim for short wave-lengths .
I take Lummer and data as typical .
It soon appeared that one take , and then takes the simpler form We have at once from data where the units are in microns ( 1 cm and in rade degrees absolute .
In computing the ordinates for any specified value of , it is convenient to note that for any eIlgth equal to or , the function varies as .
The are the numerical values of the function .
I take the experimental of Lummer and at temperature 1450o absolute , for which is practically 2 , and choosing the scale to give a maximunl ordinate of 73 units as shown in their diagram , the curve from our formula was calculated , and is shown in fig. 1 .
It fits the whole experimental curve excellently .
We have thus obtained a formula which fits all the data as well as , if not better than , Planck 's .
It is empirical , and there may be many others .
But Verh . .
Deutsch .
Phys. Gesell 1899 , , .
217 .
A Suggestion as to the Origin of Black Body Radiation .
395 in form it ests what we may expect from a dynamical system with very heavy damping .
The equation where ?
and for the motion of an electron , has been much used by Lorentz , to whom we hs in owe it , and by Planck .
But it is only an nate equation , although for many purposes a very good one .
I have shown*that more correct expressions for the motion are given ) the two equations where is the value at of the lnction which defines the state of the field in the aetber , 'Phil .
Trans .
cit. Mr. .
W. Walker .
The equations were obtained first for a conductor , and were afterwards shown to be vely nearly true for an insulating sphere .
Let us suppose that the restoring force is linear , so that , and we then Thus the free motion is determined by where Hence is a root of the equation If , we get of which the roots are , squares of , or where is the frequency .
would agree with a calculation by Lorentz .
But experiments are against the supposition that the intrinsic mass of an electron , is zero , and Kaufmann 's numbers suggest that is of the same order as .
For a positiye particle it is generally agreed that is small .
Hence , retaining , we get two pairs of complex roots .
The approximate values squares of are where and These equations may be arded as applicable to the behaviour of a molecule made up of a heavy , and so comparatively stationary , positive particle with a electron revolving round it .
The vibrations are of two types .
In the first , which closely rees with A Suggestion as to the of Black Body .
397 Lorentz ' result , the damping is for optical purposes small , and the reduction of amplitude in the time between two collisions of a molecule with its neighbours would be nall .
But in the second type we have very different .
The frequency is enormous and the damping so for optical purposes that the reduction of amplitude to a small fraction of its original value may be regarded as instantaneous .
Just after each encounter the amplitudes of the two types may be regarded as comparable , but before the next encounter the second type will have been suppressed by almost stantaneous radiation , while the first type will not have suffered any great reduction .
Have we not here a clue to the " " quantum\ldquo ; theory and the characteristic Bontgen radiation ?
In a detailed discussion it will be necessary to take account of the radiation the positive particle also .
Let us now consider the steady radiation from an electron in which the motion is governed by the equations and is maintained by a purely mechanical force .
The mean rate of radiation , viz. , , I find to be where Tbis result is equftlly applicable to a positive particle with appropriate values of , and .
A similar result hold when the joint action of a positive and Cive combination is considered , and ?
are a combination of the intrinsic and electric inertia ter1ns , hile would now be a linear quantity detining the radius of the orbit .
The coefficient of is , as far as or enters , simply eneralised form of and I have little doubt that it could be fitted with the data .
There are always three positive values of for which is a maximum .
These are in the vicinity of , and The corresponding maximum intensities are in the ratio nearly .
If we choose so that the first comes in the observed range of wave398 A Suggestion to the Origin of Black Body Radiation .
thso , the other two are in the ultra-violet , and if is small , they are of slight importance as compared with the first .
If , and only in so far as , Wien 's and Stefan 's laws are true , we require to suppose that varies as and varies as , and the expression is then a function of .
The reconciliation of these with each other and with the virial theorem of Clausius is a matter of difficulty , but as the experimental evidence is that either lnw is strictly true , the matter may well rest for the present .
These considerations , and the present estimates of atomic magnitudes , lead me to suspect that black body radiation is determined not by the electron , nor by the positive particle alone , but by the joint action of the two .
My conclusions are : \mdash ; ( 1 ) That the experimental data can be well represented by a formula of dynamical type , of which I yiven one .
( 2 ) That Newtonian dynamic and the electrodynamics of are capable of giving an explanation of that formula .
[ Note added October 23 .
1913.\mdash ; Plallck 's radiation function has been applied by Einstein*and by to the explanation of the variation of atomic heats with tempel.ature .
By similar reasoning I find that if the radiation function varies as the typical term in the expression for the atomic heat varies as where is some definite temperature .
The following table ives the numerical values The result is similar to that required to explain the observations of Nernst .
] I would express my rateful thanks to Sir Joseph Larmor , who haS discussed this paper with me , and by his gestions has added so mnch to the manner of presenting the lesults .
'Ann . .
Phys 1907 , vol. 22 , p. 184 .
Sitzber . .
Berl .
Akad 1911 , p. 494 .
|
rspa_1914_0005 | 0950-1207 | The mathematical representation of a light pulse. | 399 | 404 | 1,914 | 89 | 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.1914.0005 | en | rspa | 1,910 | 1,900 | 1,900 | 7 | 82 | 1,566 | http://corpora.clarin-d.uni-saarland.de/surprisal/6.0.3/?id=rspa_1914_0005 | 10.1098/rspa.1914.0005 | null | null | null | Fluid Dynamics | 47.845845 | Tables | 27.295205 | Fluid Dynamics | [
40.113136291503906,
-40.10997772216797
] | ]\gt ; The of Light Pulse .
By B. A. HOUSTOUN , , Ph. D. , ) , Lecturer on Physical Optics in the University of Glasgow .
icated by Prof. A. Gray , F.R.S. Received October 22 , \mdash ; Read November 27 , 1913 .
In recent years , to the work of , Schuster , and others , our views as to the nature of white light have undergone a change , and it is now universally accepted that white crht consists of irregular pulses which are transformed into trains of sine vaves by their a prism .
the method of this tion is not clearly understood , as the reasoning on the subject is unfortunately somewhat general , the only concrete case well known the pulse represented Had the nature of f ) .
] pulse been better understood , there possibly never have been any talk of the " " Light Quantum\ldquo ; or unit theory of The object of this note is to call attention to a new class of expressions representing the initial form and dispersion of a pulse .
They are both simple and elegant , and one of them gives the ergy distribution required by Wien 's law for black body radiation .
They have been ested by one of Kelvin 's hydrodynamical papers .
* do not depend on the Fourier analysis and this is an , for we never know how much of the latter is subjective .
Consider the equation .
( 1 ) If we substitute , we find that the equation represents the yation of waves in a mediunr in the velocity is directly proportional to the period .
This is the law of deep.sea waves ; it is obeyed by no medium for light waves although it gives the variation with the period in the right direction .
After the necessary corrections have been made the distribution of the energy in the spectrum of an incandescent solid is independent of the prism producing the spectrum .
Results obtained therefore for a hypothetical medium the aboye can easily be transferred to any other medium .
Equation ( 1 ) can be written .
" " Initiation of Deep-Sea Waves , etc ' Proc. .
Soc. Edin 1906 , , p. 399 .
Dr. R. A. Houstoun .
This is formally the same as the equation for the one-dimensional conduction of heat , namely , Kelvin 's instantaneous-plane-source solution for the latter is By analogy , is a solution of ( 1 ) .
Disregard the plus in the index and add a constant to .
The expression still satisfies ( 1 ) and becomes .
( 2 ) Since ( 1 ) is linear , we can differentiate ( 2 ) times with to and the result , , ( 3 ) is still a solution .
To find the initial form of this solution put in ( 3 ) and then differentiate times with respect to .
The result is Write , disregard the constant factor , and this becomes We take the first part of this expression as the initial form , i.e. we choose the real part of ( 3 ) .
In .
( 1 ) the initial form of the disturbance is represented on the same scale , 2 , 3 , 4 , and 5 .
FIG. 1 .
Representation of Light Pulse .
Kelvin has already ( loc. cit. ) treated the case of a deep-sea wave having the first of the aboye initial forms , and has shown how the disturbance spreads ithin a distance of a few wave-lengths from the origin .
But it is here necessary to proceed quite otherwise , since in optics observer is always at a much reater distance than this from the source .
The quantity is a constant for the .
Let fi it by ) that a harmonic wave of cm .
medinm with a velocity of cm . .
Ic has been the velocity of snch a wave is ) obtain or ttely , in sec. .
The initial disturbance is ) iven 1 ) hence its value at the is .
If be the of the point for which it has half its maximm value , , can be taken as a measure the the initial We shall examine the its -xinnum has travelled out ia distance of cm .
from the :$hall ) sulall in with 2 .
Then ill eneral is sIuall .
A for which vould .
to travel ont 2 cm .
, and ular disturbance will take he order .
While the disturbance is passing a oint 2 .
out , ] ) approxi1nately The fact that so ) things very ) only terlu to be retained .
in is easily seen to be [ t-siu ) .
VOL. LXXXIX.\mdash ; A. 2 I Dr. R. A. Houstoun .
Since is small compared with , we may write for for , and 1 for .
Hence , making this substitution , taking the real part and omitting the in the denominator , we obtain where .
Since is of the order of , the first term in the argument of the cosine varies very much more rapidly than the second .
Disregard the second , therefore , and we obtain finally or Acos .
( 4 ) We shall now find the manner in which the energy is distributed over the different wave-lengths for a given value of .
The at is given by ; i.e. or It thus increases as the square of the distance from the .
The in a distance is proportional to .
The change of wave-length in this distance is given by The energy per wave-length is therefore Substitute ; then the per is Wien 's law for black body radiation is stated as If is put , the two expressions .
Hence the second of our initial pulses must be of exactly the same nature as that emitted by a black body .
What is more , our symbol varies inversely as , the absolute temperature of the black body .
The unexpected simplicity of the ] ation seems to prom se well for the future of this way of regarding black body radiation .
The Representation of Light Pulse .
As a check upon the analysis we can calculate the energy in the initial pulse .
It is given in the general case by ; therefore , .
Also , .
On substitution the integral becomes If , this varies as the inverse fourth power of or the direct fourth power of T. We have thus arrived at Stefan 's law of black body radiation .
Let us now definitely make ?
and examine the shape of the pulse when its aximum has travelled 2 cm .
from the igiu .
For the maximu1n 1 which gives .
We see incidentally that the group velocity is .
Write 2 for in this expression for and substitute the result in ( 4 ) , at the same time putting .
If we omit the constant factor , 4 ) then becomes .
This expression gives the disturbance as a ulction of , and it is represented in .
To make the clear has been yiven the very value of It will be seen from fig. 2 that the initial pulse has been dispersed by the medium into a train of ways all comprised between 1 and 5 cm .
, the long waves coming first and the wave-length gradually decreasing as we get to the rear of the train .
There is , of course , a similar train travelling the other way at the same distance on the other side of the origin .
The wavelength at the point of maximum amplitude , i.e. the dominant wave-length , is obtained by combining and .
It is therefore and is always the same , i.e. the same wave-length .always rides on the crest of the group .
In the case represented in fig 2 , the The Mathematical of a Light Pulse .
dominant wave-length is cm .
, a very long heat wave .
If it were green , at that distance out there should be roughly 3500 times as many lengths in the train , but , of course , the number always increases the further the group goes .
The period of a wave iven by i.e. or Hence the wave-velocity , , is the same value as was obtained by substitution in equation ( i ) .
The dispersive power of a medium is usually specified by In our hypothetical medium the velocity varies as lihe , and the velocity for is cm . .
Consequently is not far from 1 , and it seems more reasonable to measure the dispersive power simply by , which has the value For flint glass the value and for air the value hence the dispersive power of our hypothetical medium is roughly 14 times that of flint glass and times that of air .
I am indebted to Dr. Green for gesting that Kelvin 's hydrodynamical solutions might be applied to optics ; also for showing me an original derivation of Rayleigh 's energy law by the application of group velocity .
|
rspa_1914_0006 | 0950-1207 | Note on the colour of zircons, and its radioactive origin. | 405 | 407 | 1,914 | 89 | Proceedings of the Royal Society of London. Series A, Containing Papers of a Mathematical and Physical Character | the Hon. R. J. Strutt, M. A., Sc. D., F. R. S. | article | 6.0.4 | http://dx.doi.org/10.1098/rspa.1914.0006 | en | rspa | 1,910 | 1,900 | 1,900 | 2 | 60 | 1,491 | http://corpora.clarin-d.uni-saarland.de/surprisal/6.0.3/?id=rspa_1914_0006 | 10.1098/rspa.1914.0006 | null | null | null | Optics | 32.135374 | Geography | 18.746133 | Optics | [
-9.347346305847168,
-0.16337153315544128
] | 405 Note on the Colour of Zircons , and its Radioactive Origin .
By the Hon. R. J. Strutt , M.A. , Sc. D. , F.R.S. , Professor of Physics , Imperial College , South Kensington .
( Received November 11 , \#151 ; Read November 27 , 1913 .
) Crystals of the mineral zircon are found in a variety of different colours .
What I have to communicate refers to the brown kinds .
Of these , two may be ' distinguished : the common opaque brown variety , easily obtained in large quantity from the South of Norway and from North Carolina , and the transparent reddish brown kinds known as hyacinth , and obtained , for instance , from Expailly in Auvergne , from Unkel , on the Rhine , and from Campbell Island , New Zealand .
It is remarkable that the opaque kinds occur in plutonic rocks , such as syenites , and the transparent ( when their matrix can be traced ) only in basalts and other lavas .
Their outline is rounded , even when found , as at Unkel , embedded in perfectly fresh basalt .
For this reason it has been supposed ( and I have no doubt correctly ) that such zircons have been derived from the melting down of plutonic rocks which originally contained them .
Zircon , from its extreme resistance to chemical attack , would survive almost all other minerals .
Incipient chemical attack would account for the rounded shape , which is in extreme contrast to the sharp crystal outline of the zircons in their original home in plutopic rocks .
Hyacinths lose their reddish brown colour completely when heated to a temperature of about 300 ' C. , and this fact , considered in relation to their occurrence embedded in a solidified lava , presents at first sight no small difficulty .
How is it that they were not decolorised by the heat of the molten rock ?
Or , if they were decolorised , how has the colour been recovered ?
For it will hardly be suggested that transparent crystals of a material so resistant have been coloured by any action of percolating water Another somewhat similar difficulty is raised by the fact that these transparent zircons are thermoluminescent .
The crystals , when moderately heated , give out a phosphorescent glow , at the same time that they lose their colour .
But this glow does not recur on a second heating of the specimen , and the question presses for answer , How has the capacity to glow been recovered ?
\#151 ; for presumably it was not present in the crystals when they first cooled down in their matrix of molten lava .
It is known that the crystals decolorised by heat have their colour restored by exposure to radium .
One day 's exposure to a few milligrams of radium produces a distinct effect in restoring the colour .
Exposure to radium also restores the property of thermoluminescence .
406 Note on the Colour of Zircons , and its Radioactive Origin .
Now , as I showed some years ago , * zircon is a distinctly radioactive mineral , containing hundred of times as much radioactive matter as ordinary rock masses .
It is suggested , therefore , that the zircons found in lavas have had their colour and thermoluminescence restored by the slow action , during prolonged ages , of the radium they themselves contain .
On this view , it might appear that the depth of colour , taken with the amount of radioactive material present , and the observed rate of coloration by radium would give a means of estimating the time which had elapsed since the lava matrix became cool .
Unfortunately , however , the colour of the zircons is saturated , that is to say , further exposure to radioactive matter does not deepen it .
To test this point , two transparent brownish-red hyacinths from Expailly were ground down to slices about 075 mm. thick .
These were examined under a low microscopic power , as their area was somewhat small for naked eye comparison , and the depth of tint which they each showed by transmitted light was found to be as nearly as possible the same .
One slice was exposed on the surface of 5 mgrm .
of radium bromide with a very thin layer of mica interposed .
After the lapse of a month , the tint was scarcely , if at all , deeper than that of the other , which had been reserved for comparison .
The specimen was then decolorised by heat and again exposed to the radium .
In four days it had recovered the original tint and did not get any darker with further exposure.^ We cannot , therefore , determine from the depth of colour what time has elapsed since the specimen cooled .
It should be possible to find an inferior limit to it , and this might be of interest in connection with the general question of geological time , for the hyacinths of Expailly ( for instance ) occur in basalt which is overlain by strata containing extinct mammalian remains .
J The chief difficulty in finding such a limit is this : The a-rays are probably the chief agent concerned in the colouring process , and as these only penetrate distances of the order of mm. , it would be necessary in determining experimentally the rate of coloration by strong radioactive preparations , to use slices of decolourised zircon of some such thickness as this .
Unfortunately the colour producible in such thin layers is much too faint for measurement , and it would be necessary to superpose many of them .
This would greatly complicate the experiment .
The opaque brown zircons mentioned at the beginning of this note seem to he in a different state from the transparent hyacinths .
For , as originally * ' Roy .
Soc. Proc. , ' 1906 , A , vol. 78 , p. 152 .
t Decolorising by heat and recolouring by radium can be repeated indefinitely .
J See Scrope , ' Geology of Central France .
' Intermittent Vision .
found , they are not thermoluminescent , nor can they be made so by exposure to radium .
Moreover they are not decolorised by moderate heating .
As already explained , there is reason to believe that hyacinths are formed from these opaque zircons by the action of a bath of molten basalt .
It was attempted , and with partial success , to imitate this experimentally .
Basalt was kept melted in a platinum crucible over a gas furnace , and some opaque zircons immersed in it for 24 hours .
After this they were extracted , and found to be quite white , though not transparent .
On exposure to radium they now took on the redder colour of hyacinths and became , like them thermoluminescent .
The only outstanding point is the transparency of natural hyacinths .
This may result in some way from the gently increasing , very prolonged action of the molten basalt under geological conditions , which cannot be artificially imitated .
Intermittent Vision .
By A. Mallock , F.R.S. ( Received November 11 , \#151 ; Read December 11 , 1913 .
) It is a matter of fairly common observation that the spokes of the wheels of passing motor cars often appear momentarily stationary , and sometimes even seem to be turning in the direction opposite to their actual motion .
It was pointed out to me by the Hon. T. F. Fremantle that these appearances , which last only for a small fraction of a second , coincide with the steps of the observer , and are only noticeable when the speed of the vehicle lies between certain limits .
On the one hand the motion must be too quick for the eye to follow the individual spokes , and on the other it must not exceed a certain limit , which is apparently slightly different for different individuals .
To examine the phenomena more closely and conveniently a 4-inch disc of black paper was prepared , on which 12 equally spaced radial white lines were superposed , and the disc was mounted on a heavy top , running on ball bearings , and which when spun lost its speed slowly .
An electric contact on the top in conjunction with a recording chronograph gave the angular speed at each instant , while another pen worked by the observer allowed signals to be marked on the chronograph paper , indicating according to a code the nature of the appearance of the disc in various circumstances .
It was found that the lines on the spinning disc appeared stationary not
|
rspa_1914_0007 | 0950-1207 | Intermittent vision. | 407 | 410 | 1,914 | 89 | 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.1914.0007 | en | rspa | 1,910 | 1,900 | 1,900 | 5 | 47 | 1,384 | http://corpora.clarin-d.uni-saarland.de/surprisal/6.0.3/?id=rspa_1914_0007 | 10.1098/rspa.1914.0007 | null | null | null | Optics | 26.729664 | Measurement | 25.304501 | Optics | [
-9.180933952331543,
-0.07771798223257065
] | Intermittent Vision .
found , they are not thermoluminescent , nor can they be made so by exposure to radium .
Moreover they are not decolorised by moderate heating .
As already explained , there is reason to believe that hyacinths are formed from these opaque zircons by the action of a bath of molten basalt .
It was attempted , and with partial success , to imitate this experimentally .
Basalt was kept melted in a platinum crucible over a gas furnace , and some opaque zircons immersed in it for 24 hours .
After this they were extracted , and found to be quite white , though not transparent .
On exposure to radium they now took on the redder colour of hyacinths and became , like them thermoluminescent .
The only outstanding point is the transparency of natural hyacinths .
This may result in some way from the gently increasing , very prolonged action of the molten basalt under geological conditions , which cannot be artificially imitated .
Intermittent Vision .
By A. Mallock , F.R.S. ( Received November 11 , \#151 ; Read December 11 , 1913 .
) It is a matter of fairly common observation that the spokes of the wheels of passing motor cars often appear momentarily stationary , and sometimes even seem to be turning in the direction opposite to their actual motion .
It was pointed out to me by the Hon. T. F. Fremantle that these appearances , which last only for a small fraction of a second , coincide with the steps of the observer , and are only noticeable when the speed of the vehicle lies between certain limits .
On the one hand the motion must be too quick for the eye to follow the individual spokes , and on the other it must not exceed a certain limit , which is apparently slightly different for different individuals .
To examine the phenomena more closely and conveniently a 4-inch disc of black paper was prepared , on which 12 equally spaced radial white lines were superposed , and the disc was mounted on a heavy top , running on ball bearings , and which when spun lost its speed slowly .
An electric contact on the top in conjunction with a recording chronograph gave the angular speed at each instant , while another pen worked by the observer allowed signals to be marked on the chronograph paper , indicating according to a code the nature of the appearance of the disc in various circumstances .
It was found that the lines on the spinning disc appeared stationary not Mr. A. Mallock .
only at each step , but that any slight mechanical shock , such as is given by gently tapping the head or body , or by working the jaws or by winking , was equally efficacious .
When the speed was so low that only 9 or 10 lines passed a fixed point in a second , the appearance was merely that of ordinary " flicker " and when 80 or more lines passed in the same time the surface looked uniformly grey , and in both cases mechanical shock had no apparent effect .
Figs. 1-6 give an idea of the impression received at various speeds of rotation .
4 5 6 Figs. 1-6 .
The first thing noticeable after the angular velocity drops to about six revolutions per second ( i.e.about 70 lines per second ) is that at each shock the uniform grey surface seems to break into a number of radial lines ; it is difficult to estimate their number , but a guess would put it between 40 and 50 .
This is the conventional way in which rapid rotation is suggested in drawings .
When the speed has dropped to about 4'5 revolutions per second , the lines appear equal]y spaced ( i.e. at intervals of 15 ' ) , fig. 6 .
At three revolutions per second the appearance is that of fig. 4 , the lines being separated by their natural intervals of 30 ' .
Above and below this speed the lines again are grouped in pairs ( figs. 3 and 5 ) , and at 1*5 revolutions , the spacing becomes uniform at 15 ' , see fig. 2 , rather better defined than in the corresponding fig. 6 .
Intermittent Vision .
At a lower speed still the lines again appear in pairs ( fig. 1 ) , but now dickering tends to obscure the effect .
The intensity of the light has a good deal of influence on the result .
In .a feeble light very little can be seen of stationary images , and when the light is very strong flickering interferes before the stage shown in fig. 2 is reached .
An explanation of the above-mentioned phenomena can be given on the assumption that a slight mechanical shock of any kind produces a periodic but rapidly extinguished paralysis of the perception of light .
( I have reason to believe that something of the same kind happens as regards sound but the .observations in this case are not so easily made .
) Fig. 7 .
Suppose that the nerves on which " seeing " depends cannot bear more than a certain amount of mechanical acceleration without loss of sensibility , and let the curve A , fig. 7 , represent the mechanical acceleration consequent on a shock or blow of any kind .
Let B and C be two lines giving the limits of acceleration which does not produce loss of sensation .
Then the effect of the shock will be to extinguish the image of a bright object for the times indicated by the length of the shaded parts of diagram .
The first recurrence of the image after the shock will last for a short time only , and thus if the object is in motion a fairly defined image of it will be seen at a distance from the first disappearance equal to its travel in the time DE .
As the vibration consequent on the shock dies out the time of visibility increases , the next eclipse being represented by FG , and so on .
For the class of shocks which are considered here only two or at most three secondary images can be made out .
More severe shocks cause a displacement of the directions of the eye 410 Intermittent Vision .
which displaces the image on the retina , and it is difficult to say what is seen ; but mechanical displacement of the image on the retina without loss of sensibility does not explain the observed facts .
For , in this case , only those lines would be affected which were considerably inclined to the direction of vibration ; and although the direction of the vibration ( .the application of the shock to the top or sides of the head ) has some effect on the pattern of the stationary lines , the differences are not large , and any shock makes all the radial lines visible , though in a slightly different degree .
If the explanation suggested in this paper is correct it will be seen from fig. 7 that there are two intervals of eclipse to each complete vibration , and that since , when the disc makes three revolutions per second , the lines have turned through their natural interval of 30 ' before sensibility is restored , the period is 18 per second .
The chief interest of this intermittent vision lies in the definite period involved .
What determines the period , however , is not clear ; it may be merely the mechanical period of the head on its elastic supports , or on the other hand it may be a period belonging to the brain or nerves .
That such a slight shock as that caused by opening the eyelids is effective , rather suggests the latter origin , whilst the fact that when the shock is caused by tapping the head or body the effect increases with the strength of the blow , is more consistent with a vibration of the head as a whole .
|
rspa_1914_0008 | 0950-1207 | A method of measuring the pressure produced in the detonation of high explosives or by the impact of bullets. | 411 | 413 | 1,914 | 89 | Proceedings of the Royal Society of London. Series A, Containing Papers of a Mathematical and Physical Character | Bertram Hopkinson, F. R. S. | abstract | 6.0.4 | http://dx.doi.org/10.1098/rspa.1914.0008 | en | rspa | 1,910 | 1,900 | 1,900 | 1 | 52 | 1,467 | http://corpora.clarin-d.uni-saarland.de/surprisal/6.0.3/?id=rspa_1914_0008 | 10.1098/rspa.1914.0008 | null | null | null | Measurement | 43.482001 | Fluid Dynamics | 27.627031 | Measurement | [
38.67892837524414,
-20.693449020385742
] | 411 A Method of Measuring the Pressure Produced in the Detonation of High Explosives or by the Impact of Bullets .
By Bertram Hopkinson , F.R.S. ( Received October 17 , \#151 ; Read November 27 , 1913 .
) ( Abstract .
) If a rifle bullet be fired against the end of a cylindrical steel rod , or some gun-cotton be detonated in its neighbourhood , a wave of pressure is transmitted along the rod with the velocity of sound .
If the pressure in different sections of the rod be plotted at any instant of time , the abscissae being distances along the rod , then at a later time the same curve shifted through a distance proportional to the time will represent the then distribution of pressure .
Also the same curve represents the relation between f the pressure across any section of the rod and the time , the scale of time being approximately 2 inches for 10-5 seconds .
In particular it represents the relation between the total pressure applied to the end of the rod and the time , and the length of the curve represents the total duration of the blow .
If the rod be divided at a point a few inches from the far end , the opposed surfaces of the cut being in firm contact and carefully faced , the wave of pressure travels practically unchanged through the joint .
At the free end it is reflected as a wave of tension , and the pressure at any section is then to be obtained by adding the effects of the pressure wave and the tension wave .
At the joint the pressure continues to act until the head of the reflected tension wave arrives there .
If the tail of the pressure wave has then passed the joint the end-piece flies off , having trapped within it the whole of the momentum of the blow , and the rest of the rod is left completely at rest .
The length of end-piece which is just sufficient completely to stop the rod is half the length of the pressure wave , and the duration of the blow is twice the time taken by the pressure wave to travel the length of the end-piece .
Further , it is easy to see , as is proved in detail in the paper , that the momentum trapped in quite short end-pieces will be equal to the maximum pressure multiplied by twice the time taken by the wave in traversing the end-piece .
Thus by experimenting with different lengths of end-pieces and determining the momentum with which each flies off the rod as- the result of the blow it is possible to measure both the duration of the blow and the maximum pressure developed by it .
This is the basis of the experimental method described in the paper .
A steel rod is hung up as a ballistic pendulum , and the piece is held on to the end by magnetic attraction .
412 Mr. B. Hopkinson .
Pressure Produced the A bullet is fired at the other end , and the end-piece is caught in a ballistic pendulum and its momentum measured .
The momentum of the rod is also measured .
Most of the experiments described in the paper were made with lead bullets with the object of checking the accuracy of the method .
On the assumption that a lead bullet behaves on impact as a fluid the time taken completely to stop it , which is the duration of the blow , is equal to the time which it takes to travel its own length , and the maximum pressure is equal to the mass per unit of length in the section of greatest area multiplied by the square of the velocity .
The experiments showed good agreement between the observed and calculated values of the maximum pressure as is shown in the following table :\#151 ; Velocity of bullet .
1 Maximum pressure .
Calculated .
Observed .
ft./ sec. lb. , K 2000 43,500 42,600 1240 15,700 16,70i\gt ; 700 5,450 5,320 The observed duration of the blow is in the case of the highest velocity about 6 per cent , greater than the time taken by the bullet to travel its own length .
This discrepancy is to be accounted for partly by the fact that the bullet is really not absolutely fluid , but is also in part due to the non-fulfilment of some of the conditions postulated in the simple theory ol the method .
It seems probable that the principal source of error of the latter kind is that the pressure applied by the bullet is not uniformly distributed over the end .
Experiments with rods of different diameter show that the larger ones give larger estimates of the duration of the impact .
Having established by experiments on lead bullets that the method of experiment is capable of giving within a few per cent , both the maximum pressure and the duration of very violent blows , experiments were next made on the detonation of gun-cotton .
Cylinders of dry gun-cotton l^inch x lj inch and weighing about 1 oz. were detonated with fulminate at a distance of about f- inch from the end of the steel rod .
The results may be expressed by saying that the average value of the pressure during a period of 10~5 seconds in the neighbourhood of the maximum is about thirty tons per square inch .
The absolute maximum is of course considerably higher .
The pressure has practically disappeared in 1/ 50,000 second , Detonation of High Explosives .
4IS that is at least 80 per cent , of the impulse of the blow has been delivered !
within that time .
Experiments were also made with gun-cotton in contact with the rod , but owing to the permanent deformation of the steel , which would have the effect of deadening the blow , the results in this case cannot claim to be precise .
They lead , however , to the conclusion that the maximum pressure at the surface of contact is at least double what it is when an airspace | inch thick is interposed .
The results obtained for gun-cotton , though lacking in precision , throw some light on the nature of the fracture which is produced by the detonation !
of this explosive in contact with a mild steel plate .
They show that the* pressure of the gun-cotton may be regarded as an impulsive force in the-sense that only very small displacement of the steel occurs during its action .
Its effect is to give velocity to the parts of the plate with which it is in .
contact , the remainder being left at rest .
In a plate 1 inch thick the velocity given by a slab of gun-cotton of about the same thickness is roughly 200 feet per second .
The resulting strain depends upon the ratio of this velocity to the velocity of propagation of waves of stress into the material , , and , assuming perfect elasticity , shearing stresses of the order of 100 tons per square inch may be produced in a plate of this thickness .
In static tests on mild steel the metal flows when the shearing stress is of the order of 10 tons per square inch , and no materially greater stress can exist .
But if the rate of straining is sufficient , the viscosity of the flowing metal becomes important , and the shearing stress may approximate to the value corresponding to perfect elasticity .
The shearing stress is accompanied by tension , which under such circumstances may be sufficient to break down the-forces of cohesion .
Thus the steel is cracked in spite of its ductility , just as pitch may be cracked by the blow of a hammer .
From the measured duration of the pressure produced by gun-cotton it may be inferred that the velocity of shear required to crack mild steel is of the order of 1000 radians-per second .
The shattering of the plate by the gun-cotton probably occurs during the time that the pressure is acting\#151 ; that is within two or three hundred-thousandths of a second\#151 ; and before the plate has had time to be sensibly deformed .
The bending of the broken pieces , which is always found when mild steel is broken in this way , occurs subsequently , and is due to the relative velocities which remain in the different parts of each piece of the-plate after the plate has been broken and the pressure has ceased to act .
|
rspa_1914_0009 | 0950-1207 | The selective absorption of ketones. | 414 | 418 | 1,914 | 89 | Proceedings of the Royal Society of London. Series A, Containing Papers of a Mathematical and Physical Character | Prof. George Gerald Henderson, D. Sc., LL. D.|Isidor Morris Heilbron, Ph. D.|Dr. G. T. Beilby, F. R. S. | article | 6.0.4 | http://dx.doi.org/10.1098/rspa.1914.0009 | en | rspa | 1,910 | 1,900 | 1,900 | 5 | 78 | 2,196 | http://corpora.clarin-d.uni-saarland.de/surprisal/6.0.3/?id=rspa_1914_0009 | 10.1098/rspa.1914.0009 | null | null | null | Atomic Physics | 44.74664 | Biochemistry | 23.545784 | Atomic Physics | [
9.28345775604248,
-35.88535690307617
] | 414 The Selective Absorption of Ketones .
By Prof. George Gerald Henderson , D.Sc .
, LL. D. , and Isidor MorrisHeilbron , Ph. D. ( Communicated by Dr. G. T. Beilby , F.R.S. Received October 23 , \#151 ; Read December 11 , 1913 .
) The absorption of light by carbon compounds is either continuous or selective , although not infrequently both kinds of absorption are found to occur together .
In the visible and ultra-violet portions of the spectrum the absorption is decidedly a constitutive property of the compound ; apparently the only additive relation is the effect of increasing the mass of the molecule , as , for instance , in homologous series , when displacement of the absorption band towards the red accompanies increase in the molecular weights .
Hartley 's pioneer work on absorption led him to recognise clearly the dynamic nature of this property , and to arrive at the conclusion that it is caused by the vibrations of sub-molecular particles synchronising with those of the incident waves of light .
Support is lent to this conclusion by the observation that the absorption and emission spectra of simple substances are identical .
As regards the nature of the particles to whose vibrations selective absorption is due , Hartley originally expressed the view that these must be atoms , or groups of atoms .
More recent investigations confirm this opinion so far as the infra-red region is concerned ; but , on the other hand , according to Drude 's work on the electronic theory of dispersion and absorption , the particles whose oscillations cause selective absorption in the visible and ultra-violet regions are sub-atomic and probably correspond to .
the valency electrons .
If this be so , the relations between the absorption and the constitution of carbon compounds must be sought in the dynamic state of the valencies of the absorbing group of atoms .
As a general rule carbon compounds which exhibit selective absorption belong to the cyclic class , whilst aliphatic compounds show merely a weak general absorption .
This rule , however , is not without exceptions , for it is now known that many aliphatic ketones , as well as their derivatives , which contain the \#151 ; CH2\#151 ; CO\#151 ; or the \#151 ; CO\#151 ; CO\#151 ; group absorb selectively in the visible or the ultra-violet region .
Some at least of these compounds are capable of existing in tautomeric modifications , namely a keto form R.CH2.CO .
R ' and an enol form R.CH : C(OH).R ' , and it has been suggested that the absorption of these compounds is due to some intramolecular vibration which occurs when one tautomeric form changes into the other .
The Selective Absorption of Ketones .
It is highly improbable that the oscillation of the labile hydrogen atom between the carbon and the oxygen atoms , R.CH2.CO .
R ' ^ R.CH : C(OH).R ' , is the immediate cause of the vibration , because the oscillation frequency of the absorption band is not materially changed when that hydrogen atom is replaced by a metallic atom of very much greater mass .
According to the electronic theory the linkage between the atoms of a compound is formed by the migration of an electron , or a group of electrons , from one atom to the other , and a change of linkage must be accompanied by a movement of these valency electrons .
Hence it is concluded that the absorption of such ketones must be due to the electronic disturbance which results from the change of one tautomeric form to the other .
The authors have studied the absorption spectra of a number of compounds containing the \#151 ; CH2\#151 ; CO\#151 ; or the \#151 ; CO\#151 ; CO\#151 ; group , as well as of such derivatives as their semicarbazones , and are unable , for several reasons , to accept the view that the electronic disturbances which , doubtless , are the primary cause of absorption are the result of any tautomeric change .
Thus the aliphatic ketones of the type R.CO .
R ' exhibit selective absorption , and yet it has been shown by a strictly chemical method that these compounds are entirely ketonic in structure , no trace of an enol form being perceptible even in presence of alkali .
Again , ethyl acetoacetate exists in a keto form , CH3.C0.CH2.C02Rt , and an enol form , CH3.C(0H):CH .
C02Et ; neither form of itself exhibits selective absorption , but addition of alkali to each has the effect of producing a banded spectrum ; yet it has been proved that the characteristic absorption band is entirely independent of tautomeric keto-enol oscillation .
Again , the authors ' results show that the oscillations which cause the selective absorption exhibited by the aliphatic ketones must be of the same type in each of these compounds , since each gives the same band , and consequently the suggested relationship between selective absorption and the activity of the carbonyl group in ketones induced by a keto-enol change cannot exist .
The view has been advanced that in ketones the intramolecular vibration takes place primarily within the carbonyl group , which is to be regarded as the oscillation centre of those compounds .
We hold that this is a correct view , and that if the residual valency of the carbonyl group is taken into account it is possible to form a conception of a type of intramolecular oscillation which may be the cause of the selective absorption exhibited by ketones and their derivatives .
Gebhardt 's theory of valency postulates for each atom a maximum affinity , which may or may not be fully called into play when atomic linkage takes place .
Hence , since the total affinity of each atom remains constant , if for Prof. G. G. Henderson and Dr. I. M. Heilbron .
any reason the bond between linked atoms is weakened residual affinity must appear on each as a free partial or " ionised " valency .
Such free partial valencies , which are capable of acting as subsidiary affinity forces , are most likely to appear on atoms linked by a double bond ; for example , the atoms of the carbonyl group ( \gt ; 0=0 ) ; or else may first be called into existence by other influences .
Accepting these ideas in modified form , we suggest , firstly , that selective absorption in ketones is caused by intramolecular vibrations , due to the alternate formation and breaking down of unstable ring systems , and , secondly , that the momentary formation of those ring systems is effected through the agency of free partial valencies , which , under certain conditions , make their appearance on the atoms of the compound .
In order to illustrate this suggestion , the case of acetone , CH3.CO .
CH3 , may be considered .
According to our view , it is possible for free partial valencies to appear on the carbon and the oxygen atom of the carbonyl group of this compound , because the bond between those atoms will be weakened by the attractive influence of a hydrogen atom on the oxygen atom .
The momentary linkage , through a partial valency , of this hydrogen atom to the oxygen atom will weaken the bond between the former and the carbon atom to which it is linked , and a free partial valency will appear on this carbon atom also .
Fig. 1 , in which , as in the other figures , partial valencies are indicated by dotted lines , represents this phase\#151 ; CH3\#151 ; C-----CH2 CH3\#151 ; Ch^CH2 0 ... .H OH Fig. 1 .
Fig. 2 .
The free partial valencies on the carbon atoms will tend to unite , but , we suppose , can only do so by drawing upon the affinity of the oxygen and hydrogen atoms , with the result that the partial linkage between them will be broken down and the phase represented in fig. 2 will be formed .
This phase also will only have a momentary existence , because wdienever the free partial valencies on the carbon atoms have neutralised each other , the first phase will be reproduced .
In short , there will be an intramolecular oscillation between the two phases , and it is to the electronic disturbances which accompany this oscillation that , we believe , the selective absorption of acetone is to be attributed .
According to this view precisely similar oscillations should take place The Selective Absorption of Ketones .
within the molecules of the homologues of acetone , and therefore each of these ketones should exhibit essentially the same absorption curve as acetone .
Our experiments prove that this is actually the case .
Moreover , we have found that the semicarbazones of acetone and its homologues , ^3\gt ; C=dST .
NH.CO .
NH2 , exhibit only general absorption , and this result CH3 also is indicated by our hypothesis , for although in these compounds there is a double linkage between a carbon and a nitrogen atom , yet the attraction between hydrogen and nitrogen is not sufficiently strong to cause the appearance of free partial valencies , hence the resulting intramolecular vibrations do not occur .
The idea of intramolecular oscillations arising from momentary ring formation can be extended to other groups of ketones , of which diacetyl , CH3.CO .
CO.CH3 , and acetyl acetone , CH3.CO .
CH2.CO .
CH3 , may be taken as examples .
The former exhibits an absorption band similar in kind to that of acetone , but considerably displaced towards the red end of the spectrum .
In this case we suppose that a double oscillation of the same type as that of acetone occurs ( figs. 3 and 4)\#151 ; h2c- -c 0- .ch2 H2C ^ .
C C CH H 6 0 Fig. 3 .
H H- ... b 6- Fig. 4 .
.H while , considering the position of the band , it is also possible that an additional oscillation arising from the union and disruption of the free partial valencies of the carbon atoms of the carbonyl groups may also take place ( figs. 4 and 5)\#151 ; h2c\#151 ; c\#151 ; c\#151 ; ch2 h2c----C^IC\#151 ; ch2 H ... .6 0 ... .H H 0 0 H .Fig .
4 .
Fig. 5 .
The absorption band of acetyl acetone is produced in quite different concentration from that of any of the simple ketones , and therefore in all probability must be caused by a somewhat different type of intramolecular vibration .
Bearing in mind that acetyl acetone exists chiefly in the enol VOL. LXXXIX.\#151 ; A. 2 K Dr. Laurie and Messrs. McLintock and Miles .
form , and that there is evidence that the intramolecular vibrations are not due to tautomeric change , we suppose that , whilst the oscillations are in this case also due to the ultimate formation and breaking down of an unstable intramolecular ring system , the ring is different in type from that assumed to be found in the simple ketones , and that the oscillations take place between the phases represented in figs. 6 and 7 .
o H ^-c\ .** .C-CH , CH-C 3 3 C-CH .
.* .
H K **H Fig. 6 .
Fig. 7 .
The examples quoted will , we hope , serve to make our suggestions regarding the cause of selective absorption in ketones sufficiently clear .
It remains to be added that further work is in progress which is intended to test the validity of these suggestions .
Egyptian Blue .
By A. P. Laurie , D.Sc .
, F.R.S.E. , W. F. P. McLintock , B.Sc. , and F. D. Miles , B.Sc. , A.B.C.S. ( Communicated by Sir A. H. Church , K.C.Y.O. , F.R.S. Received October 29 , \#151 ; Read December 4 , 1913 .
) The artificial blue pigment used in Egypt from the IVth Dynasty and also used widely during the time of the Roman Empire has been investigated by many chemists , including Sir Humphry Davy , * Vauquelin , f H. de Fontenay , * Darcet , F. Fouqu6 , S and Dr. W. J. Russell , F.R.S. , but the exact nature of the compound and the manner of its formation do not yet seem to have been finally decided .
According to Vitruvius , the blue was made by heating together a mixture of copper filings , sand , and soda in a furnace .
A great deal of information * " On Colours in Use by the Ancients , " ' Phil. Trans. , " 1815 .
t ' Passalacqua 's Catalogue,5 p. 239 .
t ' Annals de Chimie,5 serie 5 , vol. 2 , p. 193 .
S ' Bull .
Soc. des Mines de France , vol. 12 , p. 36 .
|
rspa_1914_0010 | 0950-1207 | Egyptian blue. | 418 | 429 | 1,914 | 89 | Proceedings of the Royal Society of London. Series A, Containing Papers of a Mathematical and Physical Character | A. P. Laurie, D. Sc., F. R. S. E.|W. F. P. McLintock, B. Sc.|F. D. Miles, B. Sc., A. R. C. S. |Sir A. H. Church, K. C. V. O., F. R. S. | article | 6.0.4 | http://dx.doi.org/10.1098/rspa.1914.0010 | en | rspa | 1,910 | 1,900 | 1,900 | 7 | 191 | 5,735 | http://corpora.clarin-d.uni-saarland.de/surprisal/6.0.3/?id=rspa_1914_0010 | 10.1098/rspa.1914.0010 | null | null | null | Chemistry 2 | 49.269438 | Thermodynamics | 14.895695 | Chemistry | [
8.934401512145996,
-36.11531448364258
] | 418 Dr. Laurie and Messrs. McLintock and Miles .
form , and that there is evidence that the intramolecular vibrations are not due to tautomeric change , we suppose that , whilst the oscillations are in this case also due to the ultimate formation and breaking down of an unstable intramolecular ring system , the ring is different in type from that assumed to be found in the simple ketones , and that the oscillations take place between the phases represented in figs. 6 and 7 .
o H ^-c\ .** .C-CH , CH-C 3 3 C-CH .
.* .
H K **H Fig. 6 .
Fig. 7 .
The examples quoted will , we hope , serve to make our suggestions regarding the cause of selective absorption in ketones sufficiently clear .
It remains to be added that further work is in progress which is intended to test the validity of these suggestions .
Egyptian Blue .
By A. P. Laurie , D.Sc .
, F.R.S.E. , W. F. P. McLintock , B.Sc. , and F. D. Miles , B.Sc. , A.B.C.S. ( Communicated by Sir A. H. Church , K.C.Y.O. , F.R.S. Received October 29 , \#151 ; Read December 4 , 1913 .
) The artificial blue pigment used in Egypt from the IVth Dynasty and also used widely during the time of the Roman Empire has been investigated by many chemists , including Sir Humphry Davy , * Vauquelin , f H. de Fontenay , * Darcet , F. Fouqu6 , S and Dr. W. J. Russell , F.R.S. , but the exact nature of the compound and the manner of its formation do not yet seem to have been finally decided .
According to Vitruvius , the blue was made by heating together a mixture of copper filings , sand , and soda in a furnace .
A great deal of information * " On Colours in Use by the Ancients , " ' Phil. Trans. , " 1815 .
t ' Passalacqua 's Catalogue,5 p. 239 .
t ' Annals de Chimie,5 serie 5 , vol. 2 , p. 193 .
S ' Bull .
Soc. des Mines de France , vol. 12 , p. 36 .
Egyptian Blue .
has been obtained as to the actual furnaces used and the methods of heating which will be found in " Notes on Egyptian Colours " by F. C. J. Spurrell , reprinted from the 'Archaeological Journal , ' September , 1895 .
The temperature of the furnace was never sufficiently high to result in fusion , a mass of semi-fused frit being obtained which was easily powdered , and there is evidence that this frit was powdered and reheated more than once in order to develop the blue .
Modern chemists have analysed samples of this blue , and have also made experiments on its reproduction .
We do not propose to give an account of all these , but simply the summing up of the main facts which have led to the necessity for a further investigation .
Fouque* experimented upon samples of real Egyptian blue , and gives an analysis , from which he comes to the conclusion that the blue was a double silicate of copper and calcium , for which he gives the formula Ca0 , Cu0,4Si02 , and states that the samples he examined were entirely free from soda and potash .
He then proceeds to state that this double silicate is a definite crystalline compound , of which the following are the characteristics:\#151 ; " The specific gravity is 3*04 .
" It is a crystalline substance , belonging to the quadratic system .
It appears in the form of scales flattened parallel to the base of the prism , and often jagged at the edges , sometimes , however , ending in clear rectangular outlines .
The diameter of these scales does not exceed 2 mm. , their thickness rarely exceeds 0'5 mm. They are of a beautiful azure blue .
" Seen in parallel light between crossed nicols they remain tinted in all directions .
In convergent polarised light they display the cross and ring characteristic of uniaxial minerals .
With a quarter-wave-length mica plate it is easy to determine the negative sign of the mineral .
These scales , seen under the microscope on their edge , with interposition of a nicol , offer a very remarkable pleochroism .
With the rays vibrating parallel to the axis , they are of a pale rose colour ; with vibrations in a direction perpendicular to the axis they are of an intense blue .
" The double refraction is O031 .
" Shortly after this paper by Fouque , Dr. W. J. Russell took up the question of the nature of Egyptian blue , and , after examination of samples supplied to him by Prof. Flinders Petrie , proceeded to make a series of elaborate experiments on its reproduction .
He has given an account of these in a paper printed in Prof. Petrie 's volume on Medum , and also in a lecture read before the Royal Institution ( 1893 ) .
He states that he succeeded in making the blue from mixtures of copper carbonate , calcium carbonate , quartz sand , and fusion mixtures .
He made a large number of experiments on mixtures * ' Comptes Rendus , ' vol. 108 , p. 325 .
2 k 2 420 Dr. Laurie and Messrs. McLintock and Miles .
in which calcium carbonate was an ingredient , and on several from which the calcium carbonate was left out .
It is not quite clear whether he regarded the calcium carbonate as an essential constituent , and whether he considered that the sodium and potassium carbonates had also entered into the combination of the blue itself , or were merely there as fluxes .
It is evident , on examining his notebooks , that Dr. Russell had Fouque 's paper before him , because more than once he mentions trying Fouque 's receipt , in which potassium sulphate replaces the potassium and sodium carbonates , but he in no case refers to the crystalline properties , or indicates that he has examined his samples between crossed nicols , so it would appear that he regarded Fouque 's conclusions as of no importance .
In the account given by Mr. Spurred already referred to , after an elaborate description of the actual processes of manufacture as rediscovered in Egypt from the examination of remains of .
furnaces and of lumps of Egyptian blue that have been found , he proceeds to reject Fouqu6 's results , stating that his products could not be the Egyptian blue at all without soda as a necessary ingredient .
A careful study of Fouque 's paper reveals the fact that he has made several contradictory statements as to the method of preparation of the blue , and it is impossible to derive from his paper any clear conception of how the blue was made .
Our attention was directed to the matter from the fact that having got some samples of real Egyptian blue we proceeded to examine them between crossed nicols , and at once the crystalline character of the blue was revealed .
The crystals were mixed with quartz and very often with a little lime , which may have been present from the beginning or may have been added as part of the mixture when the blue was used for painting .
This directed our attention to Fouque 's paper , and on making a more careful examination we found that the description given by him of the crystalline character of the blue was absolutely correct .
We examined samples from the lid of a coffin of the Xlth Dynasty and from a piece of Roman fresco on the Palatine Hill , a piece of the crude frit obtained from the Manchester Museum , a piece of crude frit occurring among Dr. Russell 's samples , two samples from Viriconium in Shropshire , a sample obtained in Syria , and another sample formerly in the possession of Dr. Russell , from Gurob and of the XVIIIth Dynasty .
In every case these samples , obtained from so many different sources and extending over such large periods of time , prove to have exactly the same crystalline character .
We have also obtained a sample from Knossos , which is typical Egyptian blue .
Egyptian Blue .
It is evident then that Fouque 's description of the nature of this compound is correct , and it became of interest to examine the samples actually prepared by Dr. Eussell to see whether they consisted simply of a semifused copper glass or of the properly constituted blue .
Fortunately Dr. Scott was able to supply us with a large number of these samples , and also to lend us the late Dr. Russell 's notebooks , by which we were able to trace his methods of preparation .
These methods can be roughly divided into two groups : cases in which the blue was prepared from copper carbonate , quartz , and fusion mixture alone ; and from copper carbonate , calcium carbonate , quartz , and fusion mixture .
The samples we obtained were all numbered and dated , so that it was possible to trace in the notebooks the processes through which they had been put .
In the case of the samples containing calcium carbonate we found that in every instance they had been ground and reheated sometimes several times before the blue was properly developed , the sample after the first heating very often being black , the blue gradually improving with each new heating .
In the case of the blue made without calcium carbonate the one heating seems to have been sufficient .
In all we examined some 13 specimens of the blue prepared by Dr. Russell .
Of these eight were prepared with calcium carbonate and five with sodium-potassium carbonate alone .
The eight specimens prepared with calcium carbonate were all genuine examples of the Egyptian blue , consisting simply of quartz grains and of the blue crystals , as far as could be detected under the microscope .
Of the five samples made with sodium-potassium carbonate alone , two contained a few very minute crystals of the right formation , probably due to traces of lime , the rest consisting simply of blue glass , and therefore proving not to be Egyptian blue at all .
The enquiry up to this point had definitely established two facts .
In the first place the Egyptian blue is correctly described by Fouque as a definite crystalline silicate of copper , with the properties that have already been enumerated .
In the second place Dr. Russell succeeded in reproducing this copper silicate by repeatedly grinding and heating at a temperature below fusion , a mixture of quartz , copper carbonate , calcium carbonate , and fusion mixture , but in the absence of calcium carbonate the blue was not found , with the exception of the occasional minute traces mentioned above .
At the same time it was evident that the exact conditions under which this crystalline compound was formed had not been established , and therefore the following experiments were instituted .
For these experiments , the following mixture was taken : Fine sand , 36 grin .
; fusion mixture , 4 grm. ; copper carbonate , 8'6 grm. ; calcium carbonate , 7'2 grm. The copper 422 Dr. Laurie and Messrs. McLintock and Miles .
carbonate and the calcium carbonate are in the proportions given by Fouque s formula .
The amount of fusion mixture and of sand in this receipt is taken from one of Dr. Russell 's , with the exception that the amount of copper carbonate has been slightly reduced .
The experiments were carried out in a Heraeus electric resistance furnace , with a platinum-iridium junction introduced , with a view to measuring the temperature .
A few grammes of the mixture were introduced into a small Battersea parting cup , which was about half full .
As soon as the mixture had been heated sufficiently long to begin to set , a little piece of broken crucible was laid on the top , and the rest of the crucible packed with asbestos .
The thermal junction , which was placed in a double quartz tube , but with the end of the junction bare , was buried in the asbestos , the other junction being kept at about 20 ' .
The temperatures were read on one of Paul 's thermo-galvanometers .
The sample was kept at a uniform temperature from 16 to 20 hours .
The first batch inserted was kept at a temperature of 760 ' .
On examining the product on the removal from the crucible , it was -seen that the greater part of the mixture was still upcombined , but at the same time the quartz had been slightly attacked , being covered partly with a bluish-green glass .
The next batch was kept at a temperature of 800 ' .
On examining the resultant mass a considerable quantity of an olive-green glass was seen to have been formed .
There was still a certain amount of white uncombined material , and a considerable quantity of black copper oxide .
The next batch was run at a temperature of 830 ' .
On examining the product under the microscope , it contained , as would be expected , a considerable quantity of uncombined and unfused quartz , and a certain amount of black , uncombined copper oxide , the olive-green glass already described , and large quantities of the blue crystals , agreeing exactly in their optical properties with those found in the Egyptian blue in the correct samples prepared by Dr. Bussell .
On cutting a section through the mass , and mounting in Canada balsam , it was quite easy to see the colourless pieces of unattacked quartz , with occasional particles of black copper oxide , and the blue crystals surrounded by a magma of the olive-green glass which was still present .
Having arrived at the temperature at which the blue was formed a gas muffle was adjusted to the same temperature , and in this larger batches were made .
In the case of these batches Dr. Bussell 's plan of regrinding and reheating was adopted .
By doing this two or three times the green glass completely disappears , and only occasional traces of black copper oxide are left , the resultant mass consisting of the blue crystals and uncomEgyptian Blue .
bined quartz , and corresponding therefore to the lump samples of frit from the Egyptian furnaces , but much richer in the crystalline blue .
The next sample was run in the same way in the electric furnace at a temperature of 905 ' .
This sample , on examination , proved to contain quartz , black copper oxide , and olive-green glass , but no blue crystals at all .
Evidently , therefore , the temperature at which these blue crystals are formed lies between 800 ' and 900 ' , and is somewhere about 830 ' .
In order to confirm still further the limiting temperature of about 900 ' another batch was run at 890 ' .
The product was found to consist almost entirely of green glass , with a few blue crystals at the bottom of the crucible .
It is evident then from these experiments that 900 ' may be taken as the limiting tefnperature .
In a further experiment a little more of the blue frit which had been formed in the muffle furnace was taken and raised to a temperature of 1150 ' .
It seemed to consist of quartz and bottle-green glass with no indication of the formation of cuprous oxide , as mentioned by Fouque .
When heated at the lower temperature it at once recovered its blue colour , showing the reformation of the crystalline copper silicate .
Another portion was put into a wind furnace and raised to a temperature of about 1400 ' , and then heated in an electric furnace at about 850 ' , when the blue was restored .
The matter was pressed still further by taking a small portion of the blue frit from the muffle furnace and fusing it before an oxyhydrogen blowpipe .
This sample proved to contain some cuprous oxide when examined under the microscope , thus agreeing with Fouque 's description .
The button was then run for 48 hours at 850 ' , and the result was a brilliant blue mass which , on examination under the microscope , proved to contain Egyptian blue .
These experiments , then , seem to settle conclusively the conditions as to temperature for the formation of the blue , showing that , even after raising the mass to the temperature of the oxyhydrogen blowpipe , the Egyptian blue crystallises out at a temperature of 850 ' .
These experiments show that the regrinding and reheating , which must have been the Egyptian practice , and which was also done by Dr. Russell , is not necessary for the formation of the blue , though it seems to be necessary in order to get the whole of the green glass converted into the blue crystalline compound .
The main point of interest , however , revealed by these experiments is the formation of a crystalline silicate under conditions which , the authors believe , have not been formerly recorded .
In the first place , the mass is far below the fusion point of the whole .
If 424 Dr. Laurie and Messrs. McLintock and Miles .
the temperature is high enough , the ultimate result is to i'use the whole mass with the formation of a complex silicate , but at the temperature of 850 ' the quartz is attacked far below its fusing point , and this crystalline double silicate is formed , the mass merely becoming pasty in the process , never reaching true fusion , and forming when cold a frit , which can easily be crushed in a mortar , like the lumps of frit found in the Egyptian furnaces .
The next point revealed , which seems of considerable interest , is the narrow range of temperature within which this crystalline body is formed .
On both sides of the region of temperature the result of the process is merely the formation of an olive-green glass , but within the right range the blue crystals are formed in the olive-green glass magma , disappearing again when the temperature is slightly raised .
The next point to be investigated was the bearing of the proportion of fusion mixture on the result .
The original proportion of fusion mixture given in the formula at the beginning of the paper was taken directly from Dr. Russell 's notebooks , and had been arrived at by him as the result of many experiments .
Our first experiments were made with a view to finding what the effect of the increase of the amount of fusion mixture would be , and therefore a mixture was made up containing : fine sand , 15 ; calcium carbonate , 3'6 ; copper carbonate , 4*3 ; and fusion mixture 6 grm. instead of 2 grm. This was run for some 20 hours at 850 ' , the result being complete fusion into a deep green glass , the quartz practically completely dissolving in the mass .
An intermediate mixture wTas then taken , in which the mass of fusion mixture was reduced to 4 grm. This mixture did not fuse completely at 850 ' into a glass , but was heavily fritted and contained some traces of blue .
It is evident from these experiments that if the amount of fusion mixture is increased much beyond the limits described by Dr. Russell , the copper-lime silicate does not crystallise out of the mass , but remains in solution as a green glass .
The next experiment was in the opposite direction , the mixture being made up in the usual proportions , but containing no fusion mixture at all .
This was run for some hours at 850 ' , the result being that there were indications of a slight attack upon the quartz particles , but the whole mass had refused to frit .
It was then kept for a considerable time at a temperature of 1050 ' , the result being that , after'20 hours at this temperature , the mass was partially fritted , but contained large quantities both of cupric and cuprous oxide , and a certain amount of a yellowish-green glass .
On the top of the crucible a few crystals of Egyptian blue were found .
The mass was then returned to the furnace , and kept at 850 ' for about 48 hours .
On Egyptian Blue .
425 examining it , a certain amount of Egyptian blue was found throughout the mass .
It is evident from this experiment that Egyptian blue can be formed as stated by Eouqu^ without the intervention of soda or potash , and is therefore evidently a compound into which neither soda nor potash enters as an essential ingredient .
A mixture was now prepared in which the amount of fusion mixture was reduced to 1 grm. After heating for 16 hours at 850 ' , the mass was found to be very slightly fritted , and although the quartz particles showed slight signs of being attacked , no blue had been formed .
It was therefore run for some 20 hours at 1000 ' , the result being that the whole mass was flitted , but contained no Egyptian blue .
This mass was then run for 48 hours at 850 ' , the result being the formation of large quantities of blue .
It is therefore evident from these experiments that the formation of the blue does not necessarily depend on the presence of soda or potash salts , but without their presence the mass is so infusible that it is difficult to get the copper , lime , and silica to enter freely into combination .
When the amount of fusion mixture is only 1 grm. , the temperature of 850 ' is not sufficient to cause proper fritting of the mass and the solution of the lime and copper , but by raising the temperature to 1000 ' , the small amount of soda present is compensated for by the additional temperature , with the result that on again heating at 850 ' Egyptian blue is freely formed .
If the amount of fusion mixture is raised to 2 grm. the best conditions are obtained , the temperature of fusion being sufficiently low to enable the mass to be fritted at 850 ' , while at the same time the fusion mixture is not present in sufficient excess to keep the copper-lime silicate in solution , so that it crystallises freely through the mass .
If the amount of fusion mixture is increased much above this , the copper-lime silicate is kept in solution in a fused mass , and no blue is formed .
These experiments then , with those already described dealing with the conditions of temperature , define the -conditions for the formation of the Egyptian blue .
As the Egyptians themselves had no pure soda to use , it seemed of interest to prepare a sample with a soda of the same composition as the Trona which comes from the Egyptian desert .
A sample of soda was therefore made up containing the required impurities in the right proportions .
Dr. Laurie and Messrs. McLintock and Miles .
Analysis of Trona ( probably from Wady Atrun ) .
Given by Klaproth.* Sod .
sesquicarb ... ... . .
32'6 grin .
Water and insoluble omitted .
Sod .
sulphate ... ... ... .
208 " Insoluble not specified in Sod .
chloride ... ... ... .
15-0 " analysis .
The above mixture was introduced in place of the fusion mixture without altering the proportions of the other ingredients .
On running this for about 40 hours at a temperature of 850-860 ' , large quantities of the Egyptian blue were successfully formed .
We have also successfully prepared the blue with potassium sulphate as the flux .
Eor the purpose of analysis , some of the blue frit was taken which had been made in a muffle furnace , and had been re-ground and re-heated two or three times ; 40 grm. were crushed , passed through a 120-mesh sieve , and then more finely ground .
The finely-ground mass was then heated for three hours with aqua regia in order to dissolve out the copper oxide , and washed with water .
After stirring it was found that a good deal of bluish material remained for a long time in suspension .
On examination this proved to contain none of the Egyptian blue , and was therefore rejected .
The dry material , after this rough separation with water , was then mixed with bromoform of specific gravity 2'88 , and treated in a centrifugal machine , After rotation , blue is found at the bottom , and a cake of lighter material at the top , which contains very little of the , blue crystals in spite of a fairly deep colour .
An examination of the heavy residue shows that it consists mainly of blue crystals , with a little isotropic , almost colourless glass .
This glass is found in large quantities in the light material .
To remove the last traces of glass the process was repeated , using a mixture of methylene iodide , and benzene of specific gravity 2'948 .
The material thus separated , on examination under the microscope , proved to be almost perfectly pure .
It contained occasional crystals of blue , which were still united to fragments of quartz , but no glass .
This material was therefore taken for analysis , and two analyses were made by fusion in the usual way with soda .
The figures obtained compare as follows with those given by Fouque .
Fouque states that the substance is a copper-calcium silicate containing no alkali .
This statement we have been able to confirm to the extent that we find it quite possible to prepare the Egyptian blue crystals without the addition of alkali at all .
At the same time , it does not follow that when alkali is present some of the copper , or calcium , is not replaced by the alkali metals within the crystal .
* Lunge , ' Sulphuric Acid and Alkali , ' 1895 , vol. 2 , p. 61 .
Egyptian Blue .
Fouque 's analysis is as follows :\#151 ; Si02 63-7 CaO 14-3 CuO 21-3 Fe203 0-6 99-9 This analysis is , we think , somewhat open to criticism , as it is difficult to understand how , dealing with pure materials , he obtained such a large quantity of iron , especially as we found that there is no iron present at all in the blue that we have made .
The following are the results of two determinations of the silica , copper oxide , and calcium oxide :\#151 ; Si02 ... ... ... 63-4 63*4 CaO ... ... ... ... .
14-38 14*35 CuO ... ... ... . .
19-48 19-58 It will be noted that the figures for silica and calcium oxide agree very closely with those obtained by Fouque , but the percentage of copper is slightly lower .
A fresh portion of the separated sample already described was treated with hydrofluoric acid , with a view to making an estimation of the alkali metals , if they proved to be present , and the results obtained are as follows :\#151 ; K20 ... ... ... . .
1-19 Xa20 ... ... ... .
0-93 The results add up to a total of 99*38 for our first analysis , and 99*45 for the second .
These figures seem to us to make it highly probable that , in the presence of an alkali , some of the copper or calcium is replaced by the alkali metals , and that therefore it is not correct to state that Egyptian blue consists always and entirely of copper , calcium , and silica , but this may be taken as an approximate statement of its composition , which also approximately agrees with the formula given by Fouque\#151 ; Ca0 , Cu0,4Si02 .
In addition , we have determined the two refractive indices of the crystals .
The refractive index of the extraordinary ray is practically the same as that of cassia oil , T605(3 ) , whilst the refractive index of the ordinary ray , determined in a mixture of monobromonaphthalene and quinoline , is 1-635(4 ) .
This gives for the double refraction \amp ; \gt ; \#151 ; e = 0*031 , agreeing exactly with the figure obtained by Fouque .
Dr. Laurie and Messrs. McLintock and Miles .
Thanks to the kindness of Dr. J. J. H. Teall , F.R.S. , we were enabled to examine a sample of the blue made by Fouque , and we found that it was optically identical with our material .
It is , perhaps , of some interest to speculate as to how this blue came to be discovered by the Egyptians , and we think the explanation is to be found in their method of glazing , which has been described by Mr. Burton in his paper on Egyptian Ceramics.* According to Mr. Burton , their copper glaze was somewhat infusible and not suitable for running on earthenware , and it was therefore their custom to carve out of sandstone various beads and other ornamental objects , and then glaze these with a copper glaze which ran easily when in contact with a siliceous body .
As has been shown by these experiments , at the lowest temperature such a glaze would be bluish green , and at a higher temperature olive green , but there would also be a certain intermediate temperature between the two olive greens in which the blue crystals of the silicate would be formed .
It is therefore almost inevitable that in the process of glazing these objects carved out of sandstone , they would occasionally hit upon the temperature at which they got a deep crystalline blue , and this would very naturally lead to the attempt to prepare such a blue as a pigment by replacing the siliceous body by sand .
In fact , one may say that the only change between their method of glazing on carved sandstone objects and the preparation of the blue itself was in replacing the lump of sandstone by sand , and in carefully arriving at the temperature at which crystalline blue would be formed .
It is therefore easy to understand how other races who have developed the art of coloured glazing on earthenware itself have never discovered this double crystalline silicate , and how it was discovered by the Egyptians owing to the peculiar method of glazing on sandstone itself , which they seem to have been familiar with from the earliest times .
The special conditions under which this crystalline silicate has been formed seem to us to contain certain elements of novelty .
They are doubtless similar to those obtaining in the devitrification which takes place when a glass is kept at a temperature below fusion for a considerable length of time , and also to the conditions present in forming Portland cement .
Although it is evident that the mass contains at the temperature of 850 ' a certain amount of glass in a state of fusion , yet the whole mass is never fused and is therefore not disturbed in the coarse relationship of its various parts , while the process by which the blue is formed seems to be due to the fused glass acting as a carrier , dissolving the lime , copper oxide , and quartz , enabling * ' Journ. Soc. Arts , ' 3rd May , 1912 , No. 3102 .
Egyptian Blue .
429 them to combine and crystallise out , and then proceeding to dissolve further portions of these constituents .
If the mass is reground and reheated several times , the amount of glass that can be discovered in the finished product becomes very small , the green glass completely disappearing , and it is conceivable that if a sufficient length of time had been given to the process , a very minute quantity of glass would be sufficient to act as a solvent and a carrier , and so produce ultimately a large quantity of crystalline silicate throughout the mass , while this glass itself might possibly devitrify at a lower temperature .
The final result , therefore , would be that the arrangement in bulk of the mass of material would remain the same , that the temperature would never have been raised beyond the moderate heat necessary to fuse the low fusion glass , that a large amount of crystalline silicates would result , and that the amount of glass necessary to produce this would be very small in quantity .
These special conditions , therefore , for forming crystalline silicate seem to us worthy of further investigation , as they possibly have some bearing on the conditions which have occurred in Nature in certain cases .
In conclusion , we have thought these results worth publishing , not only because of their archaeological interest , but because it is highly probable that there are many other crystalline silicates which can be formed in presence of excess of unfused quartz at comparatively low temperatures under these special conditions .
# I
|
rspa_1914_0011 | 0950-1207 | The influence of the constituents of the crystal on the form of the spectrum in the X-ray spectrometer. | 430 | 438 | 1,914 | 89 | Proceedings of the Royal Society of London. Series A, Containing Papers of a Mathematical and Physical Character | W. H. Bragg, M. A., F. R. S. | article | 6.0.4 | http://dx.doi.org/10.1098/rspa.1914.0011 | en | rspa | 1,910 | 1,900 | 1,900 | 4 | 148 | 3,971 | http://corpora.clarin-d.uni-saarland.de/surprisal/6.0.3/?id=rspa_1914_0011 | 10.1098/rspa.1914.0011 | null | null | null | Atomic Physics | 63.611032 | Optics | 15.778693 | Atomic Physics | [
12.054898262023926,
-79.62760925292969
] | 430 The Influence of the Constituents of the Crystal on the Form of the Spectrum in the X-ray Spectrometer .
By W. H. Brag , M.A. , F.R.S. , Cavendish Professor of Physics in the University of Leeds .
( Received November 12 , \#151 ; Read November 27 , 1913 .
) The construction and use of the X-ray spectrometer have been described in previous papers.* It is found that the relative intensities of the various parts of a spectrum may be greatly altered by changing the crystal which is used in the spectrometer .
The present paper contains an account of experiments made to determine the origin of this effect .
It is shown that it may be ascribed to well known discontinuities in the relations between the atomic weight of an absorbing screen and its power of absorbing X-rays of given quality .
This cause operates through the absorbing action of the atoms of which the crystal is composed .
It is convenient , in the first place , to describe briefly the form of the spectra emitted by anti-cathodes made of various materials .
In the adjoining figure A.W = l9l Os rays A.W =193 Ir rays B Pt rays A.W. =19 5 i i_____________i______________t_____________[ '----- , - ^ i 15 15 20 25 30 35 -40 Fig. 1 .
are shown the spectra of osmium , j- iridium , and platinum , as given by the ( 111 ) plane of the diamond .
The three allied metals here show certain common characteristics .
Each spectrum contains , in the first place , a quantity of * ' Roy .
Soc. Proc. , ' A , vol. 88 , p. 428 ; vol. 89 , pp. 246 and 276 .
t Note added November 27.\#151 ; A closer examination of the rays issuing from the osmium bulb shows that there are five similar triplets , the head of each being identical with one of the five platinum lines .
Specti'um in the X-ray Spectrometer .
431 general radiation ; radiation , that is to say , which varies continuously in wave-length over a certain somewhat indefinite range .
It is clear that there is a considerable amount of such radiation for all angles of setting of the ionisation chamber which are less than about 25 ' .
Possibly this general radiation may eventually be found to consist in part at least of bands of homogeneous rays , but the resolving powers of the spectrometer are hardly sufficient as yet to determine the point .
It may be remembered that Moseley and Darwin * using an apparatus of high resolving power , did not succeed in separating it into definite constituents .
It is not , however , with this general radiation that I propose to deal at present .
Each metal emits certain groups of characteristic homogeneous rays .
The characteristic rays of platinum divide themselves obviously into three groups which in the original paperf were called A , B , and C ; the latter two are really double , as subsequent experiments have shown .
Moseley and Darwin determined their spacings with great precision .
Osmium also has three groups placed in the same way as those of platinum , but , as might perhaps be expected from its lower atomic weight , they extend somewhat further into the longer wave-lengths .
The iridium spectrum again contains three groups , placed in a somewhat similar fashion to those of its companion metals , but they are not very strongly marked .
Attention may be directed to the very strong peak in the osmium spectrum at 17*8 ' .
If the spectrum had been given by rock salt ( 100 ) , the angle would have been 13 ' .
In fig. 2 are shown the spectra of palladium and rhodium .
Their remarkable simplicity and strong similarity to each other are very noticeable .
The crystal used is rock salt ( 100 ) .
The angles at which the lines occur are , in the case of palladium , 104 ' and 1T8 ' ; in the case of rhodium , ll-0 ' and 12*6 ' .
The wave-length of the more intense palladium line is 0576 x 10~8 , and of the more intense rhodium line 0'603 x 10~8 .
As has already been explained , the precision of these lines and their remarkable intensity in comparison with the general radiation makes the rhodium and palladium bulbs of great service in the investigation of crystal structure .
Fig. 3 shows the spectra of nickel and copper .
Here , again , there are two noticeable lines in each .
They are of nearly equal intensity , but their relative spacings , strange to say , resemble closely those of the palladium and rhodium rays .
The two copper lines are at 28 6 ' and 32'0 ' ; the nickel lines at 31-2 ' and 34-6 ' .
If the spectra of the last four metals are compared it is seen that the wave-length increases as the atomic weight diminishes .
The frequency is not quite proportional to the square of the atomic weight .
* 'Phil .
Mag. , ' June , 1913 .
+ ' Roy .
Soc. Proc. , ' A , vol. 88 , p. 428 .
Prof. W. H. Brag .
Form of Possibly an exact relation of this kind might have been anticipated , as Whiddington has shown that the energy of the cathode ray required to excite an X-ray of given quality is proportional to the square of the atomic Pd rays NaCl(iOO ) Rh rays NaCl(IOO ) Fig. 2 .
Cu rays ; Na Cl ( ioo ) Ni rays : Na Cl ( 100 ) weight of the metal which emits that quality , and the quantum epergy of the X-ray would he proportional to the frequency .
Spectra of silver and tungsten have also been obtained , but no very remarkable characteristic effects have yet been observed , except the existence of a small peak in the tungsten spectrum at 25'8.* It should be mentioned that the form of the spectrum is influenced not only by the nature of the radiator and the nature of the crystal but also by the circumstances of its production .
Characteristic rays always occur in exactly the same place , but their relative intensities with respect to one another and with respect to the general radiation are modified by such causes as the nature and thickness of the glass wall of the X-ray bulb , by the width of the slits , narrower slits giving higher resolving power , and no doubt also by the general form of the X-ray bulb , its state of exhaustion , the nature of the coil , and so forth .
The spectra which are shown above are therefore examples made under circumstances which need special definition before they can be fully interpreted .
It is only the positions of the various peaks representing the wave-lengths of the characteristic rays which are invariable .
The spectrometer furnishes us with an arrangement of radiations in the order of the magnitude of their wave-lengths , and we are therefore able to make measurements on the relation between the wave-length and the absorbing powers of various screens .
* ' Roy .
Soc. Proc. , ' vol. 89 , p. 247 .
Spectrum in the X-ray Spectrometer .
433 From the work of Bark la we can anticipate the broad results of such measurements .
In papers published at various times Barkla has shown that each metal emits characteristic homogeneous rays , and that the rays characteristic of any one metal can only be excited by rays characteristic of metals of higher atomic weight than its own .
This is at least true as long as we deal with waves of one series as defined by Barkla .
He has also shown that homogeneous X-rays are strongly absorbed by any substance in which they can excite the rays characteristic of that substance .
If , for example , we consider the absorption of rays by a nickel screen we find that the absorption coefficient diminishes as the rays which we are considering are characteristic of chromium , iron , cobalt and nickel successively .
Nickel itself is peculiarly transparent to its own rays .
None of these substances are able to excite the characteristic X-rays of nickel ; but if we pass on now to consider the absorption coefficient of nickel for the rays emitted by zinc , we find a sudden and very large increase .
From this point onwards the absorption coefficient is of a higher order altogether , and though it again declines as the atomic weight of the radiator increases , it is evident that the coefficient has at a certain critical stage mounted to a much higher range of values .
These facts are perhaps more easily expressed in terms of the results of the X-ray spectrometer , and it will be shown in a moment that the new experiments quite confirm them .
Let us for example suppose that we had an X-ray spectrum in which the energy was so distributed among the various wave-lengths that the form of the spectrum was the straight line AB in fig. 4 .
Now let us imagine Fig. 4 .
ourselves placing in turn various absorbing screens in the path of the rays and remeasuring the spectrum in each case throughout its entire length .
The abscissae in this figure are the angles of the ionisation chamber for rock-salt ( 100 ) .
The spectrum obtained after the insertion of a copper screen would be something of the form of the line marked " Cu " in the figure ; for whereas copper rays are themselves ( see fig. 3 ) emitted at angles 28*6 ' and VOL. LXXXIX.\#151 ; A. 2 L Prof. W. H. Brag .
Form of 32 ' , these we know from Barkla 's work must belong to the region of wavelengths which are transmitted with particular ease , inasmuch as they cannot excite the characteristic radiations of copper , but for wave-lengths somewhat smaller than this we should expect a very marked increase in the absorption coefficient of copper , and this would be indicated by the sharp drop of the curve in the figure .
The subsequent slow rise as the wave-length further diminishes is meant to represent the fact that after this stage has been passed the absorption coefficient once more diminishes with the wave-length .
Let us now proceed to consider actual experimental results .
We cannot obtain a spectrum of the simple form of fig. 4 , but we may use , for example , an osmium spectrum in which are represented waves of a large range of wave-length , though they may not all be represented to the same extent .
In fig. 5 are shown the spectrum over a range between 25 ' and 30 ' , when Os rays Zn screen Cu screen Fe screen Fig. 5 .
Pt rays .
A 20 25 30 20 25 30 Fig. 6 .
Pd rays Na Cl ( tool Pd screen/ IO 15 Fig. 7 .
zinc , copper , iron screens are successively placed in the path of the osmium rays .
Zinc is transparent in the higher order to practically all the wavelengths within these limits .
Copper is transparent in the higher order only to waves past 27*5 ' .
The insertion of the copper screen has removed an important radiation at about 27 ' , transmitting easily the radiation of 28-5 ' .
Iron is not transparent in the higher order to any wave-length within this radiation .
The peak marked a appears in all three , but this is as it should be , for it is the second order spectrum of the strong osmium band at 13 ' and Spectrum in the X-ray Spectrometer .
possesses the penetrating power of that band .
The penetrating power of the band at 13 ' is high because the wave-length is small .
Though it lies on the wrong side of the critical points of the zinc , copper , and iron curves of fig. 5 , it is far distant from those points .
The same effect may be shown by the use of the rays from a platinum bulb .
The platinum rays have a strong peak at 27 ' , which I have termed A on previous occasions .
The figure ( fig. 6 ) shows the spectrum of platinum between 20 ' and 30 ' , first when no screen is placed iu the path of the rays , secondly when a zinc screen is placed in the path of the rays , thirdly when a copper screen is interposed .
The figure shows that the zinc is relatively opaque to all rays at smaller angles than 27 ' , but transmits easily the strong radiation at that angle .
Copper , however , is opaque to ^ays at 27 ' also .
Thus the division between relative transparency and opacity is sharply marked ; an atom of weight 65 transmits rays at 27 ' , and an atom of weight 63 does not .
The same effect is illustrated again in fig. 7 , which shows the effect of placing a palladium screen in front of the rays from a palladium bulb .
It will be observed that , while the palladium rays themselves are transmitted in considerable quantity , all the rays to the left of the 10 ' are very largely absorbed .
Let us now pass on to consider what happens when the atoms in the crystal itself are such as to be relatively opaque to portions of the incident radiations .
Fig. 8 ( c ) shows the spectrum of platinum rays reflected by a crystal of zinc blende .
If we compare this with the form of the spectrum as given by rock salt ( fig. 8 , a ) , we observe that the peak A is very largely increased relatively to the peaks at B and C. From what has preceded a very simple explanation is at once forthcoming .
The rays at 27 ' ( in NaCI , or 24 ' in ZnS ) which constitute the A peak penetrate the zinc with comparative ease ; the rays at 23 ' and 19 ' ( about 20 ' and 17 ' in ZnS ) are very quickly absorbed by the zinc ; consequently there is little opportunity for their energy to be scattered or reflected , since the great bulk of it is quickly taken up in other ways .
These other ways we know from previous experiments to be wholly or at least in great part the conversion of X-ray energy into cathode ray energy .
When the quality of the X-ray is such as to be able to excite the .characteristic radiation in a substance on which it falls , there is at the 2 l 2 436 Prof. W. H. Brag .
Form of same time an unusually large expenditure of energy in the production of cathode rays .
An experiment such as that shown in fig. 8 ( c ) above may be taken to indicate therefore that the scattering which is the basis of the reflection of X-rays does not display the same marked change as the absorption coefficient does on passing through the critical value .
Zinc blende gives a very large reflection of the peak A because the zinc is relatively transparent to the rays at 27 ' .
In this region of the spectrum much less energy is spent in making cathode rays and there is much more available for reflection .
There is no evidence as yet that the magnitude of the A peak as given by zinc blende is due to any special response of the zinc to the rays at that point ; the effect is simply explained as a consequence of the peculiar absorption laws .
We may test this hypothesis further in the following way .
If we take crystals which contain an atom whose weight is somewhat larger than that of zinc we ought to find that the line of division between relatively high transparency and absorption has moved towards the left into the radiation of smaller wave-lengths .
In fig. 8 ( ) is shown the spectrum of the platinum rays given by a crystal of sodium arsenate .
Here it will be seen that both the peaks A and B are now strongly represented , but C remains still very small .
The reason is that arsenic absorbs strongly all rays to the left of about 22 ' when the spectrum is given by XaCl ( 100 ) ; this is equivalent to about 21 ' in sodium arsenate .
A crystal containing bromine , such as potassium bromide , allows rays to pass through which are short enough to include all the three groups of platinum or osmium .
In the figure ( fig. 9 ) is shown the spectrum of the osmium rays given by potassium Os rays K Br ( 100 ) Fig. 9 .
bromide and the three groups are now shown more nearly in their proper proportions .
There should be a strong peak at lO'b0 , namely , that which occurs in the rock salt ( 100 ) spectrum at 13 ' , as has been mentioned already .
This is almost completely destroyed in the present spectrum , for bromine is relatively opaque to the rays of that quality .
The main result of these experiments is to show the influence of the Spectrum in the X-ray Spectrometer .
437 weight of the atom in the crystal on the form of the spectrum .
Within a region of atomic weight from 40 upwards , certain remarkable discontinuities of absorption occur in the manner explained above .
When such atoms are present therefore in the crystal and the radiations divide themselves between those which lie on the one side of a critical point and those which lie on the other side , the spectrum will also show a sharp division at that point , being far stronger relatively on the one side than on the other .
As to the influence of the weights of the atoms in a crystal when they are smaller than 40 , we have still to take into account the very remarkable change in their absorption coefficients to all X-rays which occur when we pass from atoms of carbon and oxygen and so forth to atoms of aluminium or chlorine .
Barkla has shown that aluminium absorbs all X-rays nine times as much as carbon , weight for weight .
If the scattering power does not vary in the same abnormal way , then we should expect that a crystal of small atomic weight would be an exceptionally good reflector , on the same principle as before , that the less energy spent in absorption , the more there is available for scattering .
We should expect , therefore , the diamond to give strong reflections apart from other reasons .
This is well known to be the case .
The diamond , moreover , gives reflections at far larger angles than other crystals .
It must go a long way to explain this , that the spacings of the planes in the diamond are small , and therefore the spectra are thrown to wider angles , and also , that in a case where so much energy is spent in reflection , second-order spectra will be more obvious .
It is quite possible that thermal agitation may have less influence on reflection intensity in the case of the diamond than in the case of other crystals , but these experiments show that good reasons for the peculiarities of the diamond reflection are already to be found in other directions .
It is very important to know the exact nature of the law connecting the atomic weight with the amount of scattering .
The above experiments show that there are not the same abnormal variations in the amount of scattering as we proceed from lower to higher atomic weights as there are in the case of the absorption coefficients .
Certain experiments which have been made by my son and myself indicate that the law is one of simple proportionality ; that is to say , the amplitude of the scattered wave is proportional to the weight of the scattering atom .
At any rate , certain results , to which I will now refer briefly , are very simply explained on this hypothesis .
A structure of the diamond , founded on measurements made with the X-ray spectrometer , has been explained in a recent paper.* It was pointed out that the second-order spectrum given by the ( 111 ) plane disappeared in * ' Roy .
Soc. Proe .
, ' A , vol. 89 , p. 277 .
438 Form of Spectrum in the X-ray Spectrometer consequence of the peculiar spacing of the planes .
Zinc blende has the same construction as the diamond , except that the two interpenetrating lattices are composed of zinc and sulphur atoms respectively , and are therefore of different weight , while the two lattices of the diamond are both composed of carbon atoms , and are therefore of equal weight .
The disappearance of the second-order spectrum referred to may be considered as due to an interference between the effects of the two lattices .
When these two lattices are no longer of equal weight , the interference is incomplete , and accordingly the ( 111 ) spectrum of zinc blende gives a small second-order spectrum .
In the case of fluorspar , the first order spectrum of the ( 100 ) planes and the second order spectrum of the ( 111 ) planes have again disappeared , or very nearly so .
In this case there are three lattices .
The two fluorine lattices can be derived from the calcium lattice by equal simple translations in opposite directions along a cube diagonal ; the amount of translation being a quarter of the length of the diagonal .
The result is that the ( 100 ) planes contain calcium atoms and fluorine atoms alternately .
There are two fluorine atoms to one calcium atom and therefore the weights in the planes are approximately equal , as in the case pf the diamond .
The disappearance of the first .order spectrum indicates , therefore , that the conditions for mutual interference are satisfied when the weights are nearly equal , independently of the fact that in the one case the weight is due to calcium atoms and in the other to twice as many fluorine atoms .
Weight alone and not atomic nature has determined the amount of scattering .
The disappearance of the second order ( 111 ) spectrum is explained in the same way .
Other illustrations of the proportionality between scattering power and atomic weight are to be found in a comparison of the spectra of the various members of the calcite series .
This point , with its bearing on the analysis of crystal structure , is more fully considered in a separate paper by W. L. Brag .
Mr. W. L. Brag and Mr. S. E. Pierce have kindly helped me to make some of the measurements referred to in this paper .
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rspa_1914_0012 | 0950-1207 | A simple form of micro-balance for determining the densities of small quantities of gases. | 439 | 446 | 1,914 | 89 | 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.| Prof. Sir J. J. Thomson, O. M., F. R. S. | article | 6.0.4 | http://dx.doi.org/10.1098/rspa.1914.0012 | en | rspa | 1,910 | 1,900 | 1,900 | 1 | 138 | 3,878 | http://corpora.clarin-d.uni-saarland.de/surprisal/6.0.3/?id=rspa_1914_0012 | 10.1098/rspa.1914.0012 | null | null | null | Measurement | 44.391604 | Thermodynamics | 43.60153 | Measurement | [
4.183351516723633,
-25.48872947692871
] | 439 A Simple Form of Micro-Balance for Determining the Densities of Small Quantities of Gases .
By F. W. Aston , B.A. , B.Sc. , A.I.C. , Trinity College , Cambridge .
( Communicated by Prof. Sir J. J. Thomson , O.M. , F.R.S. Received November 13 , \#151 ; Read December 11 , 1913 .
) In some work on the homogeneity of atmospheric neon it was desirable to adopt a method of determining gaseous densities which could be easily and quickly performed with a very small volume of gas without risk of loss or contamination , and which in addition would yield results reliable to about OT per cent. The standard method of weighing a known volume of the gas on an ordinary balance yields results of the highest accuracy so long as that volume is large enough .
As OOl mgrm .
may be regarded as the ordinary limit of accuracy of the chemical balance at least 10 mgrm .
of the gas would be required , and even it this quantity ( rather more than 10 c.c. at atmospheric pressure in the case of neon ) had been available , the elaborate precautions necessary to obtain OT per cent , accuracy would put the method out of court on the consideration of time alone .
On the other hand the ingenious method devised by Schloesing* could hardly be expected to give results of this accuracy , and is also open to objection on the score of contamination .
Inasmuch as the accuracy of determination of the density of a very small quantity of gas must ultimately be limited by the sensitivity of the balance employed , it seemed to me that the most hopeful solution of the problem was offered by the quartz micro-balance first described by Steel and Gfrantf and subsequently used with such notable results by Gray and Ramsay J in their determination of the density of radium emanation .
This instrument , which can be made of a sensibility of 10~9 grm. , was made with a small quartz bulb fixed to one end of the beam , the weighings being done by altering the pressure of the air in the balance case .
By knowing the buoyancy of the bulb and observing the pressure necessary to bring the beam to zero , the weight at the other end of the beam could be calculated .
If , however , we alter this procedure and balance the bulb by a fixed counterpoise , the pressure necessary to bring the beam to zero will be a * 'Comptes Rendus , ' 1898 , vol. 126,.p .
220 and 476 .
+ ' Roy .
Soc. Proc. , ' 1909 , A , voi .
82 , p. 580 .
+ ' Roy .
Soc. Proc. , ' 1910 , A , vol. 84 , p. 536 .
440 Mr. F. W. Aston .
Simple Form of Micro-Balance for measure of the density of the gas in the balance case .
This is the principle of the method here described .
It will be seen at the outset that the balance is used as a truly null instrument , all the forces on the beam , with the single exception of surface pressure , being identically the same whenever a reading is taken , so that the most sweeping simplifications may be made in its construction .
The general arrangement of the instrument can be seen in the accompanying diagram , which shows it in plan and elevation .
View and Plan of Balance and Case , about half actual size .
The qioving part of the balance is made entirely of fused quartz ( shown black ) .
It turns upon a single knife-edge cut on a piece of quartz rod about 0'5 mm. thick .
The one on the balance at present in use was ground for me by Messrs. Hilger , but very satisfactory ones can be made by the method given by Steel and Grant ( loc. cit. ) .
To this rod , a few millimetres above the knife-edge , are fused two others of about the same thickness forming the arms of the beam .
To the end of one arm is fused a quartz bulb and to the other a counterpoise made of a piece of rod about 2 mm. thick .
The quartz rods and bulb " were supplied by the Silica Syndicate , Ltd. , the latter had a volume of about 0'3 c.c. , and as the density of air is negligible compared to that of quartz , it was sealed up without exhaustion .
The assembling of the beam was done by means of a small oxy-coal-gas flame , and proved a surprisingly easy operation , the one in use at present being made and roughly adjusted in a quarter of an hour .
It has a total length of about 5 cm .
, and weighs under 0'2 grm. Adjustment of the Balance .
This is done in two stages , the first consists in bending the arms and adding or subtracting small quantities of quartz to or from the counterpoise until the whole swings evenly when supported on the knife-edge in the open air , and has a fairly long period of swing .
This operation is also much easier than would appear at first sight , for fused silica lends itself particularly well to this kind of work .
Determining the Densities of Small Quantities of Gases .
441 The fine adjustment is , however , a much more troublesome operation , as in this the balance can only be tested at about the pressure at which it is required to work .
It is obvious that , given sufficient sensitivity , the smaller the working pressure in the balance case the less the quantity of gas required for a measurement .
On the other hand , as an accuracy of OT per cent , was desired , it was decided to employ a pressure which could be measured to that degree without elaborate apparatus , in practice about 100 mm. of mercury .
For this adjustment a rough balance case was made of a piece of glass tube closed at one end by an accurately fitting rubber stopper , which could be easily removed to admit the balance .
Inside the tube was a piece of plane quartz mounted horizontally on a piece of sealing-wax to support the knife-edge .
The other end of the tube was connected to a mercury manometer and , by means of a three-way tap , either to the atmosphere or to a reservoir kept exhausted by means of a filter-pump .
The procedure was quite simple .
The roughly adjusted beam was taken , and a small excess of quartz added to the counterpoise ; it was then placed in the tube and the latter exhausted , and the pressure at which the balance turned over observed .
If this was too high , the end of the counterpoise was drawn out into a thin tail ; if too low , the end of this tail was allowed to fuse up into a knob .
The latter adjustment was invariably the final one , as by this process , if the time of immersion in the flame is judged with care , the C.G. of the balance can be moved towards the bulb with the greatest possible delicacy .
In general , the sensitivity of a balance can be conveniently judged by observing its period of swing , but , in this one , so large is the surface of the bulb in relation to the whole moving mass that the latter is nearly perfectly dead beat , so that its sensitivity is best measured by observing , by means of a microscope , the movement of the tail corresponding to a definite small change of pressure .
The actual adjustment for sensitivity is carried out by adding or subtracting minute quantities of quartz to or from the top of the rod carrying the knife-edge , which is left projecting for that purpose .
After every trial air must be admitted , and the balance taken out and readjusted , and as the greatest care must be observed not to damage the knife-edge during so many manipulations this " vacuum " adjustment puts a somewhat severe tax on one 's patience .
It can usually be completed in an hour or so , after which the balance is thoroughly annealed and cleaned by the methods recommended by Steel and Grant ( .
cit. ) .
442 Mr. F. W. Aston .
Simple Form of Micro-Balance for The Balance Case .
This is made of pieces of glass cemented together with sealing-wax as indicated in the figure .
In order that the quantity of gas used might be as small as possible , the narrow part of the balance , i.e. all but the bulb , is contained in a cell about 3 mm. wide , made of thick plate glass , and in order to cut down the volume still further a portion of the upper side is cut away , as indicated , to make room for the highest central part of the beam .
The bulb is housed in a glass tube , which in its turn is closed by a glass plug with a flat face pushed in as far as possible without actually touching the bulb itself .
The plane upon which the knife-edge rests is a small piece cut off a parallel quartz plate ( ground by Messrs. Hilger ) and cemented on to a glass support which rests on the bottom of the cell .
Owing to its very small dimensions , a few square millimetres , the adjustment of this plane to an accurately horizontal position appeared , at first sight , to present some difficulty .
This , however , was easily surmounted by the following very simple device:\#151 ; Two small plumb-bobs were suspended by pieces of white thread behind the balance case at such a distance apart that they subtended about a right angle at the quartz plane .
The thread of one of the bobs was then observed together with its mirror image in the quartz plane from a point a few inches above and in front of the latter , and the whole balance case tilted until the two lay exactly in one straight line .
This was repeated with the other bob , and when both satisfied this condition the balance was permanently fixed in position .
It is clear that , subject to the sides of the cell being optically good , the plane must now be truly horizontal .
The balance case is connected by a short piece of capillary tube , as a precaution against an accidental destructive inrush of gas , through one stopcock to the gas-admission apparatus and pump , and through another to the short limb of the manometer .
This is of the simple U-form , the two limbs being made of tube of identical diameter ( about 1 cm .
) .
The longer limb is exhausted as highly as possible and sealed off .
The level of the mercury in the U is accurately controlled by the pinchcock and squeezer device described by Lord Rayleigh.* I he reading of the difference of level is done by means of brass sleeves , as in the ordinary barometer , the one carrying a scale and the other a vernier reading to 0 05 mm. When the balance is not in use the case is kept completely exhausted , the * 'Phil .
Trans. , ' A , vol. 196 , p. 211 .
Determining the Densities of Small Quantities of Gases .
443 uptilted tail lying in the upper of the two small quartz forks fixed inside the case , in the position shown in the diagram .
As a precaution against draughts or other exterior disturbance , the whole balance case is surrounded with a lead box , which also contains a thermometer reading to 0T ' C. The balance case , the manometer , and the tubes through which the gas was admitted had a total volume of only a few cubic centimetres , so that the quantity of gas necessary to make a determination amounted to 0-45 c.c. in the case of oxygen .
Method of Taking Measurements .
About the right volume of gas , generally known from previous experience , is admitted into the balance case and manometer , and the mercury level in the latter slowly raised ( increasing the pressure in the balance case ) until the bulb rises and the knob at the extremity of the counterpoise appears on the field of a fixed reading microscope .
The pressure is then carefully adjusted , by means of the squeezer , until the knob reaches some definite arbitrary zero point , and shows no tendency to move .
The pressure is then read off .
The gas is now pumped out and the operation repeated with a gas of known density , the ratio of the densities being clearly the inverse of the pressures read .
Behaviour of the Balance Practice .
The instrument was primarily designed to compare the densities of specimens of neon .
The bulb has a buoyancy corresponding to 03 c.c. This volume of neon at a pressure of 100 mm. weighs about 004 mgrm .
; hence to give an accuracy of OT per cent , the balance must be sensitive to 0'00004 mgrm .
There is , however , not the least difficulty in obtaining ten times this sensitivity .
The distance from the knife-edge to the knob at the end of the counterpoise is about 3 cms .
The reading microscope has an eyepiece scale of 40 wide divisions to the millimetre .
In the case of oxygen the knob of the balance now in use moves 30 microscope divisions for a change of pressure of 1 mm. in the manometer .
So excellent is the definition that a change of position corresponding to 0'05 division could easily be detected , this implies a sensitivity of 10-6 mgrm .
, about the same as that attained by Steel and Grant .
A\hen the gas is let into the evacuated balance case , the tail generally tends to stick in the fork ; the pressure must then be raised rather above that which should be sufficient and the floor of the room lightly tapped with the foot .
This is the only form of release as yet found necessary .
The damping due to the volume of the bulb has already been mentioned , it 444 Mr. F. W. Aston .
Simple Form Micro-Balance for is quite marked in the open and is increased very greatly by the close-fitting walls of the balance case .
This constitutes one of the greatest virtues of the instrument , as not only does it mean that the tail follows change of pressure with admirable fidelity , making the setting rapid and easy , but since it is literally impossible to make the beam move rapidly enough to do itself an injury it will suffer the most incredible ill usage , and in addition give accurate results under very unfavourable conditions as regards vibration .
Thus the one at present set up on an ordinary laboratory table will give quite satisfactory readings even while two liquid air machines and a large gas engine , etc. , are running in the next room .
The only serious fault of the balance is the tendency of the zero to alter .
When the first one was set up this was so pronounced as to render the instrument quite useless , as it was out of all proportion to the sensitivity .
New beams , planes , and knife-edges were tried and radioactive matter introduced to eliminate electrostatic effects with little or no result , and , in despair , the thing was left to itself ( in an evacuated state ) for several days .
On trying it again the disturbances had almost disappeared , and a week or so later the zero could be trusted to remain constant for a reasonable time .
This effect has not yet been satisfactorily explained , but I am inclined to put it down to actual distortion of the beam due to insufficient annealing , the effects being much more serious than those noticed by Steel and Grant on account of the more rigid construction of their beam .
The Influence of Temperature .
In the measurement of density by the ordinary method , temperature and its exact measurement play an important part .
The density globe must remain for a long time in a bath of known temperature before it is detached from the manometer , and should hang , for hours if the highest accuracy is desired , in the balance case before its weight is determined .
By the present method these delays are entirely eliminated , for so minute is the quantity ( about ( M)005 grin .
) of gas employed that when this is compressed inside the massive walls of the balance case thermal equilibrium is almost instantaneous .
The whole operation of determining the density of a gas to OT per cent , can be completed in 10 minutes ( this time including that necessary for admission and subsequent exhaustion of the gas ) .
Such speed makes the temperature correction for zero quite unnecessary , as it is safer to take a reading with the standard gas either before or after a set of measurements is made , during which the temperature of the balance-case never alters enough to affect the fourth place in the results .
This check also eliminates any error due to the creeping of the zero already alluded to .
Determining the Densities of Small Quantities of Gases .
445 Oxygen derived from potassium permanganate and purified over potash and phosphorus pentoxide was adopted as the most convenient gas for standardising purposes .
Pure dry air also was used , comparisons between the two serving to show how reliably the balance was working .
In some cases , however , such as the comparison of the densities of several samples of the same gas for purity , the standard gas is not required , as for this purpose the readings of pressure are themselves quite sufficient .
The following are a few typical readings for oxygen and air , together with the density of the latter derived from them if 0 = 16 :\#151 ; Oxygen . .
... .
65-20 75-65 76-00 76-35 Air ... .
72-00 ... !
14-49 83-45 83-90 84-35 Density . .
14-50 14-49 14-48 The density from the accepted values , after proper corrections have been made , works out at 14"482 .
As the working pressure is low , correction must be made in order to obtain the weight of a standard litre at N.T.P. ; but , on the other hand , the molecular weight is given directly by comparison with the result for oxygen .
Thus the following figures were obtained at the same time as were those in the last column given above , they are the pressure readings for seven different fractions of very highly purified atmospheric neon :\#151 ; 121-05 , 120-25 , 121-05 , 120-90 , 121-00 , 121-05 , 121-05 .
The mean is 12 P00 .
This , compared with 76 '35 as above , gives a density of 10-096 ( O = 16 ) , and therefore a molecular weight of 20*19 , which agrees to practical identity with the accepted value of 20-200 obtained by Watson.* It is as well to note here that the only theoretical correction necessary to apply to the instrument is the one described by Lord Eayleigh for change of buoyancy of the bulb with change of pressure .
Here the maximum change is some 50 mm. , and , as the bulb is enormously more massive for its dimensions than the ordinary glass density globe , this correction could not possibly affect the fourth place in the result .
The results quoted above show that , used in the work for which it was designed , the apparatus is entirely satisfactory , and it seems likely that , by further refinements in construction , its efficiency could be considerably extended .
Thus there is , theoretically at least , no definite limit imposed upon the quantity of gas necessary to " float " the bulb .
This indeed bears no obvious relation at all to the quantity required to fill it\#151 ; one of the great advantages obtained by weighing by displacement\#151 ; so that by shaping the * 'Chem .
Soc. Journ. , ' 1910 , Trans. , vol. 50 , p. 810 .
446 Micro-Balance for Determining the Densities of Gases .
balance case more closely to the balance , the necessary quantity of gas could be still further diminished .
Again , clearly , if larger quantities of gas are at disposal , the instrument could , with much greater ease in its construction , be arranged to work at atmospheric pressure , the accuracy being thus at once extended to the fifth place .
In addition , it seems likely that it may be turned with profit to another problem , viz. , the measurement of pressure in gases of known density , Readings with the present instrument show that it has an even scale over comparatively large displacements , so that it could easily be adjusted to read pressures of , e.g.,0 to 2 mm. with an accuracy of about O'Ol mm. There is nothing in its construction which precludes its being made entirely of quartz and glass , so that it offers a hopeful solution to the problem of observing the phenomena of electrical discharge at low pressures in gases , such as the halogens , which debar the use of mercury manometers .
As in this case the volume would not have to be curtailed , a larger bulb might be employed , and the reading microscope replaced with advantage by a mirror and scale .
In conclusion , I may state that the instrument herein described may be assembled in a comparatively short time by any skilled glass-worker , and , thanks to the very small quantity of material used , at a cost of a few shillings .
Summary .
1 .
A simple micro-balance is described , by which the densities of gases may be determined relative to some standard gas , using a null method .
2 .
About half a cubic centimetre only of the gas is required .
3 .
The determination can be performed in a few minutes , with an accuracy of OT per cent. 4 .
Possibilities of its use in other fields of research are indicated .
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