358 



NATURE 



[February io, 1898 



SOCIETIES AND ACADEMIES. 

 London. 



Royal Society, January 20. — "The Homogeneity of 

 Helium." By William Ramsay, Ph.D., LL.D., Sc.D., F.R.S., 

 and Morris W. Travers, B.Sc. 



About a year ago, a paper by Dr. Norman Collie and one of 

 the authors (W. R.) was published, bearing the title "The 

 Homogeneity of Helium and of Argon." In that paper 

 (Nature, 1896, p. 546) various reasons were adduced to 

 show why an attempt to determine whether or no argon and 

 helium are homogeneous was worth making. The results of 

 the experiments at that time indicated that while it did not 

 appear possible to separate argon into two portions of different 

 densities, the case was different with helium. Samples were 

 obtained after repeated diffusion which possessed respectively 

 diffusion rates corresponding to the densities 2'I33 and 1*874. 

 It was there pointed out that these densities are not correct 

 (although their ratio is probably not wrong), owing to the 

 curious fact that the rate of diffusion of helium is too rapid 

 for its density, i.e. it does not follow Graham's law of the inverse 

 square root of the densities. These samples of gas also differed 

 in refractivity, and the difference was approximately proportional 

 to the difference in density. 



Towards the end of the paper, the conjecture was hazarded 

 that it was not beyond the bounds of possibility that the 

 systematic diffusion of what we are accustomed to regard as a 

 homogeneous gas, for example, nitrogen, might conceivably sift 

 light molecules from heavy molecules. It is true that the fine- 

 ness of the lines of the spectrum would offer an argument in 

 favour of the uniformity of molecular weight ; but still it is 

 never advisable to assume any physical theory without submit- 

 ting it to rigorous proof. And it was thought possible that the 

 fractional diffusion to which helium had been subjected might 

 have had the result of effecting such a separation ; a separation, 

 not of chemical species, but of molecular magnitude. The other 

 and more ordinary explanation of the splitting of helium into 

 fractions of different density is that helium must be regarded as 

 a mixture of two gases, one lighter than the other. 



Since the publication of the paper mentioned. Dr. A. Hagen- 

 bach has confirmed the possibility of separating helium into por- 

 tions of two densities by diffusion ; and the diflerences in density 

 were practically the same as those observed in the laboratory of 

 University College, London. 



These experiments were made with somewhat over 200 c.c. of 

 gas ; but it was decided to make experiments of a similar kind, 

 on a much larger quantity of helium. 



An apparatus was therefore constructed, similar in principle 

 to the one previously employed, but on a much larger scale. 

 The Fractional Diffusion of Air. 



In order to test the working of the apparatus, a set of diffu- 

 sions was carried out with air. After four rounds, comprising 

 twenty-four diffusions, the light portion contained 17 '37 per 

 cent, of oxygen and the heavy portion 22*03. -^ fairly rapid 

 separation was thus being effected considering the closeness of 

 the densities of nitrogen and oxygen. 



The Fractional Diffusion of Nitrogen. 



A similar set of experiments was carried out with nitrogen, 

 prepared by the action of solutions of ammonium chloride on 

 sodium nitrite, in presence of copper sulphate. The gas 

 was dried and passed over red-hot iron prepared by reduction of 

 ferric oxide in order to remove any oxygen or to decompose any 

 oxides of nitrogen which might be present. After thirty rounds, 

 involving 180 operations, the "light" portion of the nitrogen, 

 after purification by circulation over copper oxide, had not 

 altered in density. It must therefore be concluded that nitrogen 

 is homogeneous as regards the relative density of its individual 

 molecules. 



The Fractional Diffusion of Helium. 



The first sample of helium employed was prepared from 

 samarskite and cleveite. After seventeen rounds, involving 102 

 operations, the diffusion rates of the lighter and heavier portions 

 were measured. 



A fresh quantity of gas from cleveite was similarly treated. 



The light gas from the first set of diffusions was then mixed 

 with the light gas from the second set of diffusions and the mix- 

 ture was re-diffused fifteen times, involving ninety operations. 

 The density of the lightest portion of this helium was deter- 

 mined by weighing and found to be i "988. The helium had, 



NO. 1476, VOL. 57] 



therefore, not been made sensibly lighter by re-diffusion. The 

 mean of the two determinations may be taken as the true den- 

 sity of pure helium ; it is i '98. The refractivity of this sample 

 measured against hydrogen and multiplied by the ratio between 

 hydrogen and air, viz. 0'4564, gives o'i238. This specimen of 

 light helium of density i '988 was placed in one of the refractivity 

 tubes, and the lightest helium of the former preparation (density 

 = I "979) in the other. They had the same refractivity (1000 to 

 1004). The contents of No. i, obtained from the mixture of 

 light gases, had the density 2-030, showing that only a little 

 heavier material had been withdrawn. 



The lighter fractions of helium were then sealed up in glass 

 reservoirs and stored. The heavier portions were placed in the 

 diffusion apparatus and submitted to methodical diffusion. 



After fifteen rounds (ninety operations) the heaviest fraction 

 had density 2 '275, the lightest 2-08. The refractivity of the 

 heaviest gas was next determined and found to be o'i327. This 

 gas examined in a Plucker's tube showed brilliantly pure helium 

 lines, but along with these the reds and green groups of argon. 

 Calculating from the density of this gas it should contain i -63 

 percent, ofargon according to the equation ig6lx+2qy = 2-2y^. 

 Calculating from the refractivity the percentage of argon should 

 be I 05, from the equation f245.r-fo"95967= 13-33. ^ mix- 

 ture of 99 per cent, of the purest helium and i per cent, of 

 argon was made, and it showed the argon spectrum with about 

 the same or with somewhat less intensity than the heaviest gas. 

 Finally, the heavy gas was diffused to the last dregs, so that 

 only about 0*5 c.c. remained undiffused ; and this small residue, 

 transferred to a Pliicker tube, showed the argon spectrum with 

 only a trace of the spectrum of helium. The yellow line and 

 the bright green line were visible, but feeble. This spec- 

 trum was compared with that of a mixture ofargon with a trace 

 of helium, and nearly the same appearance was to be seen. 

 With the jar in parallel and a spark gap interposed the blue 

 spectrum ofargon was equally distinct in both tubes ; and, more 

 iniporlant still, there was no trace of any unknoivn line. It 

 appears, therefore, that helium contains no unknown gas, nor is 

 it possible to separate it by diffusion into any two kinds of gas ; 

 all that can be said is that most minerals which evolve helium on 

 heating also evolve argon in small quantity. This accounts for 

 the difference in density observed in different samples of helium ; 

 and in one instance, viz. malacone, the amount of argon evolved 

 on heating the mineral, though small, was much in excess of the 

 helium, so far as could be judged by the spectrum. 



We are disappointed in the result of this long research, be- 

 cause we had thought it not improbable that an element of 

 density 10 and atomic weight 20 might prove to be the cause of 

 the fact that different samples of helium possess different densi- 

 ties, according to the mineral from which they are extracted, 

 and also of the separation of helium into portions of different 

 densities by diffusion. We still regard it as by no means im- 

 probable that further research will lead to the discovery of the 

 " missing " element. 



Addendum. Since this paper was written. Profs. Runge and 

 Paschen, in a communication to the British Association in 

 August of last year, have withdrawn their contention that 

 helium is a mixture, or, perhaps more correctly stated, they now 

 ascribe to helium the same complexity as that of oxygen, the 

 spectrum of which may also be arranged in two series, each con- 

 sisting of three sets of lines. As oxygen has not yet proved to 

 be complex, the surmise that helium is complex therefore falls to 

 the ground. 



Chemical Society, January 20. — Prof Dewar, President, in 

 the chair.— A ballot for the election of Foreign Members was 

 held and Profs. S. Arrhenius, P. Curtius, A. P. N. Franchimont, 

 W. Korner, W. Markownikoff, N. A. Menschutkin, H. 

 Moissan, W. Ostwald, F. M. Raoult, I. Remsen, W. Spring, 

 L. J. Troost, P. Waage and J. D. van der Waals were subse- 

 quently declared duly elected.— The following papers were 

 read :— The preparation of pure iodine, by B. Lean and W. H. 

 Whatmough. Pure iodine is conveniently prepared by heating 

 cuprous iodide in a stream of dry air at 220-240° ; it melts at 

 112-5-114°. — Derivatives of bromtolylhydrazine, by J. T. 

 Hewitt and F. G. Pope. — Researches on the terpenes. (i) On 

 the oxidation of fenchene, by J. A. Gardner and G. B. Cock- 

 burn. On oxidising fenchene with dilute nitric acid, cis-campho- 

 pyric acid and its anhydride are formed. Turpentine hydror 

 chloride, when oxidised with nitric acid, yields camphoric and 

 camphopyric acids. — The action of alkalis on amides, by J. B. 

 Cohen and C. E. Brittain. The authors have succeeded in pre- 



