The Homogeneity of Helium and Argon. 211 



strong nitrogen spectrnm ; and the nitrogen was removed by sparking 

 with oxygen in presence of soda, until the spectrum attested its 

 absence. (It will be remembered that 0*01 per cent, of nitrogen is still 

 visible under moderate pressures, * Eoy. Soc. Proc.,' vol. 59, p. 265.) 

 The rate was again measured against that of hydrogen under pre- 

 cisely similar conditions, and it was found that while hydrogen took 

 20*00" for diffusion, this specimen of helium took 28*28". And calcu- 

 lation shows its density to be now 2*015. 



These experiments were sufficient to show, we think, that while it is 

 possible to separate nitrogen from helium, even although the former 

 is present in only small amount, we had not succeeded in separating 

 helium itself into two portions of different densities. If, then, 

 helium were a mixture, its constitutents must possess nearly the same 

 density. In no case was any alteration of the spectrum to be 

 noticed ; the diff usate and the residue were similar, and showed all 

 the well known lines of helium with the usual intensity. 



But it was deemed advisable, in view of the importance of the matter, 

 to undertake a much more elaborate set of experiments. The helium 

 was carefully purified from hydrogen and nitrogen by circulation 

 over magnesium, copper oxide, phosphorus pentoxide, and soda lime, 

 until a small quantity admitted into a vacuum tube in connection 

 with the circulating apparatus showed no spectrum either of hydro- 

 gen or nitrogen, even at a comparatively high pressure, when these 

 gases are more easily detected. The helium was then fractionated in 

 a manner exactly similar to that shown in the graphic scheme for 

 argon (p. 210). The rates of diffusion of the two samples of gas 

 were then measured. 



More diffusible portion 



Time of diffusion reduced to 662*5" 



Hydrogen 492*3" 



Density, calculated from rate ....,,.. 1*826 

 Less diffusible portion 



Time of diffusion 654'9" 



Hydrogen, at same temperature 484*4" 



Density, calculated from rate 1*842 



The density of hydrogen was taken as 1*0082, on the standard, 

 oxygen = 16. 



These samples were next weighed. 



More diffusible portion 



Volume of globe 16*2*843 c.c. 



Pressure at filling 668*5 mm. 



Temperature 19*20 



Weight 0*02450 gram 



Density 2'049 



