198 



THEORY OF COLLOIDAL BEHAVIOR 



the limits of 5.0 and 1.16 had no measurable influence on the 

 viscosity of the solution. G. Hedestrand 1 found in Euler's 

 laboratory a slight variation in the viscosity of 2 N glycocoll 

 solutions upon the addition of acid or alkali; the minimum was 

 found at pH 6.4 where the viscosity was about 1.36, while at 



"5 3.5 

 B 3.0 



2.5 



8 



2.0 



1.5 



1.0 



gelatin 



pH 1.4 1.6 15 2.0 2.2 2.4 26 28 3.0 3.2 3.4 3.6 3.8 40 4.2 4.4 4.6 



FIG. 48. Influence of pH on viscosity of freshly prepared gelatin chloride 



solutions. 



pH 3.0 it was 1.38. This is an influence of pH of a much lower 

 order of magnitude than the one found in the case of gelatin solu- 

 tions or casein solutions. These results cast a serious doubt on 

 the assumption that the variations in the curve of the viscosity 

 of gelatin, as expressed in Fig. 48, were caused by variations in 

 the hydration of the individual gelatin ions. 



This doubt was increased by experiments on the influence of pH 

 on the viscosity of crystalline egg albumin which indicated only a 

 slight, almost negligible influence of the pH on the viscosity. Fig- 

 ure 49 gives such an experiment with 3 per cent originally iso- 

 electric albumin brought to different pH through the addition 

 of HC1. The ordinates are the viscosity ratios of albumin solu- 

 tion over water, drawn on a larger scale than those in Fig. 48, and 

 the abscissae are the pH of the solution. It is obvious that if com- 

 pared with the gelatin curves the pH has only a very slight 



1 HEDESTRAND G., Arkiv Kemi, Min. och Geol., vol. 8, p. 1, 1921. 



