LAWS OF ELECTROLYTIC DISSOCIATION 49 



of the acid ions to the total amount of acid radicals, irrespective of 

 the form in which they may happen to occur. The degree of disso- 

 ciation of acetic acid in a mixture of acetic acid and its Na-salt is, 

 therefore, represented by the ratio of the acetate anions to the 

 total amount of acetate radicals in the free acid as well as in the 

 Na-salt. The dissociation residue^'- is represented by the ratio of 

 the undissociated (acetic) acid radicals to the total amount of 

 (acetic) acid radicals present. These two conceptions will be re- 

 peatedly utilized in our further discussions. With such applications 

 in mind, the question arises: What is the relation of the degree of 

 dissociation and of the dissociation-residue to the hydrion concen- 

 tration? The degree of dissociation (as well as the residue) is con- 

 sidered as a function of [H+], and thus, contrary to the foregoing 

 procedure, the [H+] is treated as an independent variable. Since 

 in the acid-salt mixtures we have found the ready means of obtain- 

 ing any desired [H+] for any practical purpose, the assumption of 

 [H+] being an independent variable may now appear as quite con- 

 ceivable. 



According to the above definition, the degree of dissociation a 

 may be expressed as 



[Si 



(X = 



[A] 



where S~ as previously represents the acid anions and A the total 

 acid in whatever form present. Let us now recall the equation on 

 page 43. 



rg-1 

 According to the definition the degree of dissociation a = ttt 



and [A] = [HS] + [Si 

 Therefore, 



[Si 



a = 



[HS] + [Si 



32 L. Michaelis, Biochem. Zeitschr. 33, 182 (1911). 



