832 DONNAN EQUILIBRIUM AND VISCOSITY 



ratio, protein solution: water, is considerably smaller in the case of 

 albumin solutions than in the case of gelatin solutions. 



The method of the experiments was as follows. 50 cc. of a 6 per 

 cent solution of isoelectric crystalline egg albumin were mixed with 

 50 cc. of HCl solution of different concentration and the pH measured. 

 The solution was rapidly brought to a temperature of 24°C. and the 

 viscosity was measured immediately at that temperature. 



The question then arises, why do amino-acids and at least one 

 protein, namely crystalHne egg albumin, behave so differently from 

 gelatin in regard to the influence of the pH on the viscosity? 

 As long as we assume that the influence of the hydrogen ion concen- 

 tration on the viscosity of gelatin-acid salt solution is due to the hydra- 

 tion of the individual protein ions this difference is incomprehensible 

 since the amino-acids as well as crystalline egg albumin should in 

 this case show the same influence of ionization on hydration as the 

 gelatin. 



The puzzle becomes still greater if we take into consideration the 

 fact that the osmotic pressure of solutions of crystalline egg albumin 

 is affected in the same way by the hydrogen ion concentration as is 

 the osmotic pressure of gelatin solutions. Why then do these two 

 proteins behave so differently as regards the influence of the pH 

 on their viscosity? 



To answer this question we are forced to the conclusion that 

 gelatin in solution must possess a way of increasing its volume which 

 is lacking in the case of solutions of crystalline egg albumin (at least 

 at ordinary temperature and at a pH above 1.0). This difference 

 seems to be connected with a difference in the ability to form a 

 gel. Solutions of isoelectric crystalline egg albumin of a high 

 concentration can be kept for many months at a temperature just 

 above the freezing point without setting to a jelly or without 

 even showing an increase in viscosity; while solutions of isoelectric 

 gelatin of even a low concentration show a rapid increase in viscosity 

 and may set to a jelly under the same conditions of temperature and 

 pH which do not alter the viscosity of egg albumin. Moreover, 

 crystalline egg albumin has a very low viscosity compared with that 

 of the same mass of gelatin in solution. 



