PASSAGE INTO SOLUTION 



279 



The type of relation which was found to subsist between the 

 time which elapsed after the introduction of the casein and the 

 number of grams of casein dissolved in 100 cc. of solvent is shown 

 diagrammatically in the accompanying figure, in which the 

 abscissae represent minutes and the ordinates the number of 

 grams of casein dissolved in 100 cc. of solvent. It will be ob- 

 served that the rate of solution is at first very great, but that 

 it very rapidly falls off. It does not fall to zero, however, that 

 is, the curve does not appear to approach an asymptote, but 

 is rather of a parabolic form. Nor does this appear strange 

 when we observe that although, after two hours of stirring, the 



rate of solution of the casein is very small, yet the solvent is 

 still very far from being "saturated" with casein. The alkali- 

 equivalent of 1 gram of casein is, as we have seen (Chaps. V, 

 IX and X), 11.4 X 10"* equivalent gram molecules, but the 

 proportion of the casein actually dissolved to the amount of 

 base present in the solvent was always, even after two hours 

 of stirring at room temperatures, very much less than this.* 



* It might be imagined that the solutions of the caseinates which contain 

 only 11.4 X 10~* equivalents of base per gram of casein, and which are pre- 

 pared by neutralizing the excess of base which is employed to dissolve the 

 casein by the addition of a strong acid, are "supersaturated" with respect 

 to casein. Two facts speak very strongly against this view, however. The 

 first is that the electro-chemical behavior of casein in much more alkaline 

 solutions already foreshadows the fact that the least proportion of alkali 

 which will hold one gram of casein in solution is 11.4 X 10"^ equivalents (Cf. 

 Chap. X). The second is that if a 3 per cent solution of casein in 0.0043 

 N KOH (1 gram of casein to 14 X 10~^ equivalents of base) be prepared by 

 dissolving casein in excess of base and then neutralizing the excess with acid, 

 it can be kept in a sealed glass vessel, in the presence of excess of toluol for 

 6 months without any deposition of casein occurring. At the end of from 

 10 months to a year a very bulky white precipitate is deposited leaving the 



