Page:Proceedings of the Royal Society of London Vol 60.djvu/228

208 When towards the end only a small amount of gas is available, the process may be modified by raising the reservoir I, and so diminishing the volume of A. The clip L is then closed, and the gas is allowed to diffuse as before, but the volume in A is kept constant. The rate of diffusion can be compared with that of hydrogen under precisely similar circumstances.

In all the experiments the temperature did not alter by more than a degree or two; as the object was to effect a separation, and not to make accurate determinations of the rates of diffusion of gases, careful regulation of temperature was unnecessary.

(a) Hydrogen.—The time required for the column of mercury in H to sink through 8 centimetres, starting always from the same level, was found in three experiments to be (1) 433″, (2) 420″, and (3) 437″ ; the mean is 430″. The average rate per millimetre is 5.37″.

(h) Oxygen.—The time which pure oxygen, made from permanga-