DISSOCIATION OF STRONG ELECTROLYTES 117 



in the state of ionization are accompanied by changes in color, 

 BjeiTum concluded that in the case of the chromium salts the state of 

 dissociation did not change with dilution, in contradiction to the 

 results apparently indicated by the molecular lowering of the freezing 

 point. Of the possibilities of regarding chromium salts either as 

 always undissociated or as always completely dissociated he chose 

 the latter. It is the more probable assumption, because on the 

 basis of our present day knowledge of the electric conductivity of 

 salts, the former possibility is not acceptable, and because it agrees 

 much better with the results deduced from the lowering of the freez- 

 ing point methods. 



This hypothesis aids us to orient ourselves, at least in a preliminary 

 way, concerning the concentration of the ions in solutions of strong 

 electrolytes. The problem still before us is to obtain quantitative 

 relations also of conductivity, osmotic pressure and the active mass. 



31. The influence of ionic charge on the conductivity 



As long ago as 1912 Hertz^ investigated the effect of the interionic 

 electric forces upon the conductivity of the ions, and his results 

 indicated that with increasing concentration the conductivity of 

 the ions must decrease, even when no change in the degree of dissocia- 

 tion takes place. Since quantitative values which are not accurately 

 known entered into his calculations, such as the mean free path of the 

 ions, it must remain for future investigations to test his calculations. 

 But in any case, quahtatively. Hertz's assertion is incontrovertible 

 that in a mixture of positive and negative ions present in higher con- 

 centrations the total conductivity is not simply the algebraic sum of 

 the conductivities of the separate ionic species, as it is in the case of 

 the most dilute solutions. Consequently it is doubtlessly also 

 incorrect to interpret the A:A^ ratio as the "degree of dissociation." 



I. Chandra Ghosh^ has recently proposed a promising way of 

 calculating the conductivity of strong electrolytes. His point of 

 departure was to the effect that the interionic potential occurring in 

 electrolyte solutions does not disappear (see following section). 

 Let A denote the "autopotential" per mol of the electrostatic re- 



■> J. Hertz, Ann. d. Physik (4) 37, 1 (1912). 



8 I. Chandra Ghosh, Transact. Chem. Soc. London, 113, 449, 627, 707, 790 

 (1918); Zeitschr. f. physikal. Chem. 28, 211 (1921); see also: H. Kallmann, 

 Zeitschr. f. physikal. Chem. 98, 433 (1921). 



