The Homogeneity of Helium. 



319 



6 lowered, so that the gas in J passed into 6. This stopcock was 

 then shut. The contents of 5 were then transferred in a similar 

 manner into A, and one-third of the gas was diffused into the pump. 

 It was collected as before in 6. The diffusion jar A now contained 

 as much gas as had been present in 5. The contents of 4 were next 

 added ; half of this was removed by diffusion and transferred to 5. 

 The contents of 3 were added ; half was diffused and transferred 

 to 4. The contents of 2 were added ; half was diffused and collected 

 in 3. And, lastly, the contents of 1 were added, and the half dif- 

 fused collected in 2. Stopcock D was then opened, and the mercury 

 in the diffusion jar A allowed to run up to the dotted line ; the clip 

 L was closed. All gas was pumped out of A and collected in 1 ; 

 this constituted one complete round. 



As it was not possible to empty the tube issuing from J com- 

 pletely of gas by lowering the reservoir of 1, and as, if not emptied, 

 the heavy gas would have contaminated the light gas from 6 during* 

 the next round, the following method was made use of. The gas 

 from 6 was transferred to the empty reservoir A ; and then, by 

 lowering the reservoir of 6, mercury rose in the tube issuing from J, 

 and expelled all the heavy gas in the connecting tubes into 6. The 

 clip K was then closed, and by opening the stopcocks la and 6a, so 

 that communication took place between jars 1 and 6, the small quan- 

 tity of gas in 6 was transferred to 1. The apparatus was now ready 

 for a second round. 



The Fractional Diffusion of Air. 



In order to test the working of the apparatus, a set of diffusions 

 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. A 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, pre- 

 pared by the action of solutions of ammonium chloride on sodium 

 nitrite, in presence of copper sulphate. The gas was dried and 

 passed over red-bot 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 opera- 

 tions, 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. 



