PASSAGE INTO SOLUTION 289 



creases. In mixtures containing concentrations of alcohol lying 

 between 4.5 and 7 mol. inclusive, the character of the relation- 

 ship is indeterminate. These relationships are illustrated by 

 the accompanying figure in which the broken lines indicate the 

 calculated continuation of the continuous lines drawn through 

 the experimentally determined points, the formula used for the 

 calculated exterpolations being: 



KMi - KM = ac-{- /3c2, 



in which KiM^ — KM represents the decrease in the coefficient 

 of penetration, c represents the concentration of alcohol, a is a 

 constant which is positive when c lies below 4.5 mol. and nega- 

 tive when c lies above 8 mol., and /S is a constant which is nega- 

 tive when c lies below 4.5 mol. and positive when c lies above 

 8 mol. 



The only explanation of these curious phenomena which offers 

 itself lies in the fact that alcohol is a coagulant of proteins, and 

 therefore brings about dehydration and consequent polymeri- 

 zation of protein molecules. At low concentrations of alcohol 

 we have to deal with the rate of solution of ''single" molecules 

 of sodium caseinate, at higher concentrations with the rate of 

 solution of polymerized molecules which we may for the sake of 

 brevity term "double" molecules, while at intermediate con- 

 centrations we have to deal with a rate of solution which is com- 

 pounded of the separate rates of solution of the two types of 

 molecules. With increasing concentration of alcohol the rate of 

 solution of the single molecules is progressively diminished, but 

 that of the double molecules is increased, owing to the fact that 

 the proportion of double to single molecules coming off from the 

 internal surfaces of the casein particles is being increased suffi- 

 ciently rapidly to more than compensate for the retardation of 

 the total rate of solution by the alcohol. At 8 mol. concentra- 

 tion, so large a proportion of the molecules coming off are of the 

 double type that thereafter the retarding effects of increasing 

 concentration of alcohol upon the total rate of solution or pene- 

 tration more than compensates for any further increase in the 

 proportion of double molecules. 



At intermediate concentrations the quantity of casein dis- 

 solved at first increases and thereafter diminishes with time, 

 casein which is initially dissolved being later reprecipitated. 



