The Homogeneity of Helium and Argon. 207 



2*15, and of argon 38'62. This would place argon below potassium, 

 the atomic weight of which is 39'L However, it must t>6 acknow- 

 ledged that such refinements in calculation are far from trustworthy. 



Third, helium and argon may each consist of a mixture of two 

 or more elements. This view has been expressed with regard to 

 helium by Professors Bunge and Paschen ( Sitzungsber. d. Akad. d. 

 Wissensch.,' Berlin, 1895, pp. 639 and 759), on the ground that the 

 lines of its spectrum can be shown to belong to two distinct series. 

 The question whether argon is a mixture or not was discussed in 

 the memoir by Lord Rayleigh and one of the authors (Zoo. cit. 9 

 p. 236). It is with this possibility that the present communica- 

 tion has to deal. 



Two methods suggest themselves as suitable in order to ascertain 

 whether argon and helium are mixtures of two or more elements, 

 or are single elements. The first is fractional solution in water; 

 the second fractional diffusion. The second method is obviously 

 the better calculated to yield the desired data ; for if these gases 

 contain constituents of different density, diffusion is an infallible 

 means of separating them. 



Description of Diffusion Apparatus. 



After a number of trials, the stem of an ordinary tobacco-pipe 

 was found to yield the best results. Plaster of Paris is too porous, 

 and various forms of graphite tried did not effect so rapid a sepa- 

 ration of two known gases as unglazed clay. In fact, nothing 

 could have been more satisfactory than this apparatus. 



It consists of a reservoir for the gas, A, into which projects a 

 piece of the stem of a tobacco-pipe, B, sealed at the lower end in 

 the flame of an oxy-hydrogen blowpipe. When the stop-cock C 

 is open, and D and E shut, the gas in A must pass through the 

 pipe-clay tube on its way to the reservoir of the pump F. The fall 

 of the mercury in the tube G, read on the scale H, is timed, about 

 8 cm. fall being taken as sufficient for the purpose. The mercury 

 rises in A, and falls in the reservoir I during the diffusion. When 

 the experiment is finished, the gas is pumped out of the reservoir F, 

 and collected in tubes similar to that depicted at K, and stored in 

 a frame resembling a miniature umbrella-stand. The stop-cock D 

 is then opened, and the clip L is shut, and the less diffusible portion 

 of the gas is pumped out and collected in other tubes, and set apart. 

 The purity of the gas is ascertained by means of the vacuum tube M. 

 After all gas has been removed, the stop-cocks C and D are shut; a 

 new charge of gas is introduced at N, the stop-cock B being opened, 

 and the operation repeated. After a sufficient amount of the first 

 diffusate has been collected, it is. again introduced into the reservoir 

 A, and the process repeated. 



E 2 



