208 ELECTROCHEMISTRY 



tendency to hydrolysis of a salt of the type R.COOK must be 

 exceptionally great, yet potassium caseinate does not reveal 

 this tendency, and the conclusion is forced upon us that potas- 

 sium caseinate is not formed in accordance with an equation of 

 the above type. 



Reverting, now, to the hypothesis which I have advanced 

 regarding the mode of formation of protein salts, we shall see 

 that in the equation : 



H 



I ++ 



-N.HOC- +KOH<=>N-^- +KOC- 



I 

 OH 



no water is involved, and, consequently, the composition of the salt 

 must be dependent only upon the relative concentrations of protein 

 and base and not upon the total dilution. Similarly in the forma- 

 tion of salts with acids: 



H 



I ++ 



-N.HOC- + HCli=^ -N-^+ HOC- 



I 

 CI 



no water enters into the reaction. Hence both the dependence 

 of the composition of the salt upon the excess of acid or base 

 and its non-dependence upon dilution receive a simple interpre- 

 tation in the light of this hypothesis. 



It will I think be clear from the foregoing discussion, that the 

 non-dependence of the composition of protein salts upon their 

 dilution is one of the most emphatic proofs we possess of the 

 fact that terminal — COOH and — NH2 groups are not respon- 

 sible for their formation. 



An experiment which demonstrates in a very striking manner the 

 fact that protein salts do not undergo an appreciable amount of 

 hydrolytic dissociation in solution in water, nor split off the inor- 

 ganic radical as an ion, is the following. It will be recollected that 

 casein, deprived of its combined base or acid, is insoluble, and that 

 if, to a solution of a caseinate of a base, exactly enough free acid 

 be added (e.g., HCl) to completely neutralize the combined base 

 the free casein is entirely precipitated. Now one gram of ovo- 

 mucoid (60) combines with 45 X 10~^ equivalents of HCl to form 



