SOLUBILITY AND COMBINING CAPACITY 249 



of equivalents of protein salt to which one equivalent of base 

 gives rise. Hence: 



X = xi — X = fjLm — 96.43 p (m + ») m. 



When m = 0, therefore, that is, when the quantity of base 

 is insufl&cient to combine with the given mass of casein, X must 

 be 0. Hence the value of 6i when \ = is a true measure of the 

 minimum combining capacity of casein. 



For 1.5 per cent solutions of casein in calcium hydrate solutions 

 we found that 



X X 10-5 = 30,830 6i - 488,000 6i2 - 53.4; 



putting X = and estimating 6i we find that 



6i = 0.001782; 



dividing this by 1.5, the percentage of casein, we find that X = 

 when the equivalence between the casein and the calcium hydrate 



^^ 1 gram = 11.9 X 10-^ equivalents; 



a value so near that (11.4 X 10-^) obtained for the alkalies that 

 they may be regarded as being, within the experimental error, 

 identical. 



In the previous (German) edition of this work I stated that 

 we were justified in the light of these results in tentatively 

 assuming, pending more direct evidence, that the various bases 

 dissolve casein in equivalent-molecular proportions. Since then 

 Van Slyke and Bosworth have shown (25), by direct analytical 

 determinations, employing dialysis to remove the chloride formed 

 on neutralizing the excess of base with hydrochloric acid, that 

 the minimal proportion of a diacid base which will dissolve casein 

 is about 23 X 10~^ equivalents but that an insoluble compound 

 is formed containing 11.3 equivalents of the base. In other 

 words the minimal equivalent combining capacity of casein for 

 bases is the same for diacid as monacid bases. 



We have seen (1) that each — COH.N— bond of casein which 

 is opened up by the entrance of a KOH molecule reacts with 

 the base in accordance with the equation : 



H 



-COH.N- +KOH = COK + '^N- 



I 

 OH 



