LAWS OF ELECTROLYTIC DISSOCIATION 79 



these in solution is entirely conditioned by the mass law relationship 

 of concentrations, in the following manner: 



[Acid anions] X [H+] 

 _ jj 



[Undissociated acid] 



k is in this case the dissociation constant of the acid. Since the 

 concentration of the undissociated acid is equal to the "partial 

 solubility" of the acid, X, therefore, it follows that 



[Acid anions] = 



[Hm 



The "total solubility" of the acid, A, is therefore 



k • X [H+]+k 



^ = ' + W] - ' ~wr 



or, by substituting the values given in (3) on page 52. 



X 



A = - 



P 



The total solubility. A, is, therefore, dependent upon the [H+] 

 of the solution, while X, the partial solubility, remains constant 

 (for a given temperature). This calculation is based upon the 

 assumption that the undissociated salt of the acid is not present in 

 solution. In such cases where this condition is not fulfilled a cor- 

 rection may be applied, but we need not consider this point in this 

 general discussion at present. 



These relations may be also conceived in other ways. It has 

 been shown that certain solid salts (e.g., silver salts) at higher 

 temperatures conduct the electric current not as metals but as 

 electrolyte solutions to a small but noticeable extent and display 

 material transport of ions. It must be assumed then that at least 

 a very small part of a solid electrolyte dissociates, i.e., it consists of 

 transportable ions."*- Thus in a saturated solution of benzoic acid 



*- The present day conception of a crystalline electrolyte consisting onlj' of 

 ions arranged in a space lattice ("Raumgitter") has nothing to do with the 

 above discussion. For the ions arranged in the space lattice are not in free 

 motion; they are ions only insofar as they have the same intra-atomic struc- 

 ture as the ions of a solution in Faraday's sense; but they are not ions insofar 

 as they are not freely movable. 



