282 PHYSICAL PROPERTIES 



quantity of solvent employed was 100 cc. and the number of 

 grams of casein initially added to it was 5. For a reason which 

 will shortly appear no especial effort was made to maintain a 

 constant temperature during the progress of an experiment, but 

 at the head of each table are given the temperatures of the mix- 

 ture at the beginning and at the end of the experiment. The 

 temperature at the beginning of the experiment is placed first. 

 In the column headed " calculated" are given the values of x 

 calculated from the above formula, the constants K and m being 

 determined from all of the observations by the method of least 

 squares, employing for this purpose the form: 



logio x = m logio t + logio K. 



The possible experimental error in the determination of the 

 concentration of a casein solution by means of its refractive 

 index is always 0.07 gram per 100 cc. It will be seen that the 

 differences (= A) between the observed and calculated values of 

 x are usually considerably less than the possible error in the 

 determination of the concentration of the casein in the filtrates. 



Equally concentrated solutions of KOH, NaOH, and NH 4 OH 

 dissolve casein with about equal rapidity, while solutions of the 

 hydroxides of the alkaline earths dissolve casein much more 

 slowly, Sr(OH) 2 dissolving the casein most rapidly, Ca(OH) 2 

 more slowly and Ba(OH) 2 more slowly still. As I have pointed 

 out in Chaps. X and XI this fact is of significance when viewed 

 in the light of the facts that solutions of the caseinates of the 

 alkaline earths become opalescent on heating, while those of the 

 caseinates of the alkalies and ammonium do not (63), that the 

 caseinates of the alkaline earths will not pass through the pores 

 of a clay filter, while those of the alkalies and ammonium readily 

 do so (63), and that in these and in other ways the caseinates 

 of the alkaline earths give evidence of being present, in their 

 solutions, in the form of more bulky molecules than those of 

 the caseinates of the alkalies and of ammonium under equivalent 

 conditions. It appears probable that when casein is suspended 

 in solutions of the hydroxides of the alkaline earths the soluble 

 caseinate is just as readily formed as it is in solutions of the 

 alkalies, but that it is hindered in passing out of the casein par- 

 ticles, through their capillary pores, into the solution, just as it 

 is hindered in passing through the pores of a clay filter. We 



