Chapter XI. 

 Other Properties of Electrolytic Solutions. 



1. The Diffusion of Electrolytes. If a concentration gradient exists in 

 an electrolytic solution, diffusion will take place. The rate of diffusion 

 of an ion is the greater the greater its mobility. However, in view of 

 the fact that the ions of an electrolyte are oppositely charged, the dif- 

 fusion of these ions will not be independent of one another. Nernst 1 

 has derived an expression for the diffusion coefficient in dilute solutions 

 of electrolytes. The diffusion coefficient is thus given by the equation: 



(80) 



D = 



2UV 



u + v 



XRT, 



in which U and V are the ionic mobilities. If the electrolyte is not 

 completely ionized, the neutral molecules also will diffuse, and their rate 

 of diffusion will, in general, differ from that of the ions. The diffusion 

 coefficient of various electrolytes has been measured by Arrhenius and 

 more extended measurements are due to Oholm. 2 In Table CX are given 

 values for the diffusion coefficients of different electrolytes in water at 18. 



TABLE CX. 



DIFFUSION COEFFICIENTS OF ELECTROLYTES IN WATER AT 18. 



Nernst, Ztschr. f. phi/a. Chem. 2, 613 (1888). 



Oholm, Ztachr. }. phya. Chem. 50, 309 "(1905); Meddel. Vet.-Akad's. Nobelinstitut, 

 Vol. , No. 22 (1911). 



280 



