Ill) Dr. R. D. Kleeman on the Kinetic 



applies also to mixtures. The resultant equation gives the 

 relation between / 3 and / 4 , these being the only quantities 

 in the equation that cannot be directly measured. 



If the concentration of one of the ingredients is small in 

 comparison with that of the other, say 3 in comparison with 

 4, the rate of diffusion of the molecules 3 is according to 

 equation (7) given by 



^"W 9 m 'di (8) 



V.N 

 In the case of a gas n 3 = — ^- 3 , where V 3 is the velocity ot! 



translation of a molecule, and the equation assumes the well- 

 known form given in the kinetic tbeory of gases. 



It will be evident from a consideration of the nature of 

 the mean free path / 3 from its definition that it is not neces- 

 sarily equal to either 1 Y or / 2 in the case of a liquid, though 

 this may approximately hold in the case of a gas. We must 

 therefore write, as before, l 3 = l^ . i|r 2 (T,/o), where ^(Ti/Oj) in 

 the case of a gas becomes a constant. 



The Superior Limit of the Average Velocity of a Molecule 

 in a Substance. 



We have seen that the number of molecules crossing a 

 cm. 2 in a substance increases at a greater rate with the 

 density of the substance than we should expect if it behaves 

 as a perfect gas. If the molecules may be regarded as points, 

 this would bo entirely due to an increase in their average 

 velocity due to molecular attraction. The velocity calcu- 

 lated on this supposition is thus the superior limit of the 

 average velocity of a molecule in a substance. Let V v 

 denote this limiting velocity, p the density of the substance, 

 and m a the absolute molecular weight. The number of 

 molecules n crossing a cm. 2 per second is then given by 



where n is given by equation (1), and hence 



v ~ p \ A /' 



The molecular velocity calculated by this equation is usually 

 for a liquid about 10 times its minimum velocity. Since the 

 value of n depends on the finite size of the molecule? as well 



