Page:Proceedings of the Royal Society of London Vol 60.djvu/231

Rh strong nitrogen spectrum ; 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, ‘ Roy. Soc. Proc.,’ vol. 59, p. 265.) The rate was again measured against that of hydrogen under precisely similar conditions, and it was found that while hydrogen took 2000" for diffusion, this specimen of helium took 28.28″. And calculation 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 diffusate 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 hydrogen 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 0°.............. 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..................... 162.843 c.c. Pressure at filling................. 668.5 mm. Temperature........................ 19.20° W eight................................. 0.2450 gram Density.................... ............. 2.049