208 



Drs. W. Eamsay and J. Norman Collie, 



When towards the end only a small amount of gas is available, 

 the process may be modified by raising the reservoir I, and so dimi- 

 nishing 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". 



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



