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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.
Determination of the Ratios of Diffusion of Gases of known Purity.
(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-
