206 Drs. W. Ramsay and J. Norman Collie. 



"The Homogeneity of Helium and of Argon." By WILLIAM 

 RAMSAY, Ph.D., F.R.S., and J. NORMAN COLLIE, Ph.D., 

 F.R.S. Received July 21, 1896. 



Preliminary. 



It was pointed out by Lord Rayleigh and one of the authors that it 

 is a legitimate conclusion to draw, from the found ratio between its 

 specific heat at constant pressure and that at constant volume, that 

 argon is a monatomic element (* Phil. Trans.,' 3895, A, p. 235). A 

 similar deduction can be drawn regarding helium (' Chem. Soc. 

 Trans.,' 1895, p. 699). And as the molecular weight of hydrogen is 

 accepted as twice its atomic weight, and as the density of helium is 

 approximately 2, and that of argon approximately 20, the molecular 

 weights of these elements are approximately 4 and 40 respectively. 

 If, however, the molecule is identical with the atom, then the atomic 

 weights must also necessarily be 4 and 40. 



Bat argon, with an atomic weight of 40, finds no place in the 

 periodic table of the elements, if, as is usual, it is contended that the 

 elements must necessarily follow each other in the numerical order of 

 their atomic weights. 



Certain suppositions may be made which would obviate this diffi- 

 culty. First, the evidence from the ratio of the specific heats may 

 lead to a false conclusion. But it is inconceivable that any struc- 

 ture, except one of the simplest kind, should transform all energy 

 communicated to it as heat, into kinetic energy of translation. 

 Still, before a final decision on this point is arrived at, it would be 

 well to a.ctually determine the specific heat of argon, and this will 

 shortly be done. It may, however, be mentioned, that preliminary 

 experiments have shown it to be much lower than that of hydrogen, 

 air, or carbon dioxide, volume for volume. 



Second, helium and argon may consist of a mixture of monatomic 

 with diatomic molecules. The perfectly normal expansion of these 

 gases appears to negative this supposition ('Phil. Tra'ns.,' loc. cit., 

 p. 239, and Roy. Soc. Proc.,' vol. 59, p. 60). Even at a tempera- 

 ture of 88 there appears to be no marked tendency towards 

 association. It is true that the ratios of the specific heats do not 

 quite reach the theoretical number I 1 66 7. That found for helium 

 was 1'652, and that for argon T659, with the most carefully purified 

 samples. Assuming (what there seems good ground to doubt) that 

 the last decimal place may be trusted, helium can be calculated to 

 contain nearly 7 per cent, of diatomic molecules, and argon rather 

 more than 3 per cent. If this calculation be permitted, the atomic 

 weight of helium would become 4'02, taking its found density at 



