The rate of diffusion of the gas of density 2*057 was determined finally, so as to afford a check on its density. It took 657*9" for a quantity to diffuse; while the same volume of hydrogen under precisely similar circumstances took 492*3". Reducing these numbers to density, if hydrogen be taken as T0082, the helium possesses the density 1*801, which compares very favourably with the number already found, T826.
As a final check on these results, a sample of helium from an entirely different source, samarskite, was so diffused, that first ninetenths were removed by diffusion; from the residue nine-tenths was again removed, and the process was repeated a third time. The more diffusible portion was tested as regards rate; while hydrogen took 492*3" to diffuse, this sample took 652*6". Stated as density, the number is 1*771.
The actual density was next determined, with the following result:— Volume of globe............. .... 162*843 c.c. Pressure at filling.......... ... 691*6 mm. Temperature................. .... 19*85° W eight........................... Densitv ......................... .... 2*080
This number closely coincides with the density of the previous specimen, freed from argon by diffusion; and in this case it must be remembered, no systematic process for separating two possible constituents was carried out, but the heavier portion only was removed. The heavier gas separated by diffusion was examined for argon, and it was possible to see the green group of five lines, but not the red lines. And with a jar and spark-gap, argon could just be detected.
The rate of diffusion of this gas, which, stated as density, gives the number 1*8, differs from the density determined by weighing, viz., 2 08, or thereabouts. This might be caused (1) by a lighter portion passing over first during diffusion, leaving a heavier portion behind; or (2) by the hypothesis that the rate of diffusion of helium is abnormal; and helium has already shown such very remarkable properties in relation to refractivity for light, and conductivity for electricity, that the hypothesis is not unwarrantable. The first supposition, however, is the more probable, and was put to the test in the following manner.
A smaller apparatus was made for measuring the rate of diffusion of 10 to 20 c.c. of gas; and the rates of the sample of density 2*08, and of the less diffusible residues from this sample were determined, both the hydrogen and the helium were carefully measured and diffused under precisely similar conditions. While the hydrogen took 181″ to diffuse, the helium of density 2.08 took 246.6″, implying a
