On the Relative Rates of Effusion of tome Gases. 423 



had no potential-difference against the metal, i. e. it would be 



P in the equation (2), 



1 C Pi 

 0= —I v dp. 



neJ F 



The constant P in Nernst's equation (1) would also represent 

 it if the gas law is applicable between the pressures p l and P. 

 When the value of P in this logarithmic formula, however, 

 comes out so immense as, for instance, it does in the case of 

 zinc (10 19 atm.), it seems reasonable to put down the discre- 

 pancy to the failure of the gas law over the necessarily great 

 range between p± and P. In these cases the P of Nernst's 

 formula could not be considered as more than a constant, 

 having a meaning which is made evident by a comparison of 

 equations (1) and (2). The gas law may be taken to apply 

 between unit pressure and p x in (2); hence P is such that 

 RT log P represents \v dp of the ions in the solution between 

 unit pressure and the actual electrolytic solution pressure of 

 the metal. 

 Owens College, Manchester. 



XL [. The Relative Rates of Effusion of Argon, Helium, and 

 some other Gases. By F. G. Donnan, M.A., Ph.D., 

 Junior Fellow, Royal University of Ireland *. 



Introduction. 



WHILE investigating argon and helium, Prof. Ramsay 

 and Dr. Collie f have found that these gases diffuse 

 through a porous plug into a vacuum with velocities which 

 are higher, when compared with a standard gas such as 

 oxygen, than those calculated according to the law of the 

 inverse square root of the density. The object of the present 

 investigation is to ascertain the relative rates of flow of these 

 gases through a small hole in a thin-walled partition, i. e. their 

 relative rates of effusion. 



The subject of the efflux of fluids was investigated by 

 D. .Bernouilli J. Since that time the subject has been inves- 

 tigated both theoretically and experimentally by numerous 

 writers. In the present case we have only to deal with the 

 efflux of gases. So long ago as 1804 Leslie § suggested the 

 determination of relative densities by this means, and in fact 



* Communicated by the Physical Society : read March 2, 1900. 



t Proc. Roy. Soc. vol. lx. p. 200. 



\ Hydrodynamica, 1738, Sec. 10, pr. 34, p. 124. 

 '•'§' Experimental luquiiy into the Nature and Propagation of Heat,' 

 p. 534. 



