THE STABILITY OF PROTEIN SOLUTIONS 



263 



This was a quantity of alcohol in excess 

 of that required to bring the solution 

 to the critical point. After cooling to 

 room temperature, the 50c.c. of alcohol- 

 water solution of 1 per cent originally 

 isoelectric gelatin were titrated with a 

 2>^ M NaCl or 2J^ M CaCl 2 solution 

 until permanent flocculation occurred. 

 The number of cubic centimeters of 2^ 

 M NaCl and CaCl 2 required varied with 

 the pH of the original gelatin solution as 

 Table L indicates. The pH in the table 

 are those which the solution of gelatin 

 would have had if it had been diluted 

 with 40 c.c. of water instead of with 

 alcohol. We do not know the actual pH 

 in the alcoholic solutions except that it 

 should be less than without alcohol. 



Near the isoelectric point and in fact 

 up to about pH 4.0 or 3.8 of the pH 

 which would have been found had the 

 solution contained no alcohol, the 

 gelatin was not completely dissolved 

 even when no salt was added, and the 

 same was true when the pH (in our 

 arbitrary standard) fell below 1.6. 

 From pH 3.8 to pH 2.4 the cubic 

 centimeters of 2J^ M NaCl required 

 for flocculation increased from 0.03 c.c. 

 atpH 3.8 to 1.3 c.c. at pH 2.4; from 

 then on it diminished again. Since 

 the pH in the alcoholic solution was 

 probably less than it would have been 

 in a solution free from alcohol, the 

 maximal stability of the gelatin in an 

 alcohol-water mixture was at a pH 

 greater than 2.4. These results are 

 difficult to explain on any other basis 

 than the Donnan equilibrium. 



P=H 



