Page:Proceedings of the Royal Society of London Vol 60.djvu/230

210 The densities were determined by weighing. These numbers show that no important separation has been effected. The difference in density of the two portions may possibly be attributed to-experimental error. When the density of the heavier portion was taken the weather was damp, and we have found it difficult to obtain concordant results under such circumstances, owing doubtless to the uneven deposition of moisture on the surfaces of the bulb and its counterpoise. But as it stands, the difference is an extremely minute one, and it may, we think, be taken that any separation of argon, if effected at all, is very imperfect.

Two hundred c.c. of helium from fergusonite of density 2.13 were separated into two nearly equal portions by diffusion. The rate of diffusion was 7.14″ per millimetre as a mean of two experiments, giving 7.13″ and 7.15″ respectively. The most diffusible portion of this gas gave the rate 7.12″ per millimetre. The more diffusible half of this gas had the rate 7.48″, and the least diffusible of the remainder 7.38″, the temperature being lower. A second specimen of helium from mixed sources, samarskite, fergusonite, broggerite, &c., which showed the nitrogen spectrum strongly, gave a rate for the first portion of 8.29″. This half on rediffusion had the rate 7.64″, and the residue of 8.39″, showing that a separation was being effected. The heavier residue of the remainder from that portion which showed the rate 8.39″ was too small to make it possible to diffuse it by the usual method. A second method was therefore resorted to, and it was directly compared with hydrogen under the same circumstances. While hydrogen took 12.14″ per millimetre, the residue took 21.00″, and calculating its density from these rates, we have—

21.00″)2x 1-0082 3-02. (12-14")2

This would correspond, if it be granted that the impurity is nitrogen, to a percentage of 8.5 of that gas. This residue showed a