238 ELECTROCHEMISTRY 



will be f, that of the third f, etc. But if, to solutions which 

 contain the same amount of a base we add varying amounts 

 of casein, the osmotic pressures of all of these solutions, as indi- 

 cated by their freezing-points are the same. Evidently, therefore, 

 a given quantity of base always gives rise to the same number 

 of protein ions, whether the base is combined with more or with 

 less protein. This obviously corresponds with the view that 

 each equivalent of base opens up a given number of — COH.N — 

 groups, and not at all with the view that it neutralizes terminal 

 -COOH groups. 



The experimental data which were obtained by Robertson 

 and Burnett are enumerated in Tables I and II in Chap. XIII 

 (p. 333). On referring to the results which are therein cited 

 it will be observed that the depression of the freezing-point which 

 is brought about by the dissolved caseinate of the alkalies is in 

 every case very nearly that which would be observed in a solu- 

 tion of the same molecular concentration as that of the alkali 

 which is neutralized by the casein. Now these solutions are 

 quite extensively (over 80 per cent, Cf. Tables, section 1) dissoci- 

 ated and it therefore follows that each molecule of alkali gives rise 

 to one ion of caseinate. That the same is true for the alkaline 

 earths is readily seen when allowance is made for their compara- 

 tively slight degree of dissociation (Cf. Tables VI, VII and VIII). 

 Now in the formation of a salt by the splitting of a single 

 — COH.N— bond each molecule of neutralized base would give 

 rise to two ions of caseinate, while in the formation of a salt by 

 the splitting of a double —COH.N— bond one molecule of 

 neutralized base might give rise to only one ion of caseinate. 

 This will be clear from the following equations: 



H 



++ I 



-COH.N- + NaOH = -CONa + ^N- 



I 

 OH 



H OH 



++ \/ 

 ^ COH.N ^ /CONa "^N. 



Rf ^R + 2NaOH = Rf ++ + ^R 



^ COH.N / ^CONa ^N^ 



/ \ 

 H OH 



