284 PHYSICAL PROPERTIES 



be observed that this ratio, for any of the given periods of time, 

 is very nearly constant.* 



The temperature-coefficient of the velocity of solution is very 

 small. The difference between the amounts of casein dissolved, 

 after a given time, at 18-20 degrees and at 26 degrees are only 

 slightly greater than or equal to the possible error of the deter- 

 minations. So far as the accuracy of the method employed 

 enables us to decide, the temperature-coefficient of the rate of 

 solution, between the temperatures of 20 and 36 degrees, is prac- 

 tically zero.f At higher temperatures the rate of solution in 

 solutions of the hydroxides of the alkalies is increased and the 

 rate of solution in solutions of the hydroxides of the alkaline 

 earths is very materially diminished. At these temperatures, 

 also, solutions of the caseinates of the alkaline earths, which are 

 neutral to phenolphthalein, become alkaline to phenolphthalein, 

 while solutions of the caseinates of the alkalies which are neutral 

 to phenolphthalein do not (63). I have sought to account for 

 these facts by supposing that temperatures above 36 degrees 

 lead to a polymerization of the protein moiety of the caseinates 

 of the alkaline earths (83). 



The low temperature-coefficient would in itself lead us to 

 suspect that the process which determines the rate of solution 

 of casein in solutions of bases is not chemical in nature. 



That the rate of solution of the casein is not determined by 

 the velocity of a chemical reaction occurring exclusively in the 

 liquid phase is also shown by the fact that the rate of solution 

 of the casein is dependent upon the mass of casein initially in- 

 troduced into the mixture. Were the rate of solution of the 

 casein dependent solely upon the velocity of a reaction between 

 casein and the alkali, taking place in the liquid phase, then since, 

 in the presence of undissolved casein, the liquid would always 

 be saturated with casein, the rate of solution should be inde- 

 pendent of the mass of undissolved casein. We are led to con- 

 clude, therefore, that the processes which determine the velocity 

 of solution occur, in part at all events, either within or at the 

 surfaces of the suspended particles of undissolved casein. 



* At "saturation" of the alkali with casein the numerical value of this 

 ratio would be 91. 



t It was for this reason, of course, that no special effort was made to main- 

 tain a constant temperature during the progress of the experiments. 



