208 



THEORY OF COLLOIDAL BEHAVIOR 



the pH (of the gelatin) on the viscosity, and the upper curve the 

 influence of the pH on the volume of the gelatin. The two curves 

 are similar. 



The valency of the anion of the acid influences the viscosity of 

 suspensions of protein in a similar way as it does the viscosity 

 of solutions. This proof is furnished in Fig. 54. Doses of 0.5 

 gm. of finely powdered gelatin (going through a sieve of mesh 



3.0 



2.5 



2.0 



1.5 



1.0 



25 



20 





"I 



.* 



pH 1.8 2JO 22 2.4 26 Z8 ao a2 3.4 a6 a8 40 42 4.4 



FIG. 53. Showing that the influence of pH on viscosity of 0.5 per cent sus- 

 pensions of powdered gelatin in water is similar to the influence of pH on vis- 

 cosity of gelatin solutions, and that the volume occupied by the particles in the 

 suspension varies in a similar way as the viscosity. Temperature 20C. 



size 100 but not through sieve of mesh size 120) of pH 7.0 were put 

 into a series of beakers containing each 100 c.c. of HC1 of different 

 pH and kept in the solution over night at a temperature of 20C. 

 Simultaneously a similar series of beakers containing each 100 c.c. 

 of H 3 PO 4 and H 2 SO 4 of different pH (instead of HO) were pre- 

 pared, each receiving also 0.5 gm. of powdered gelatin. After 

 19 hours the viscosities of all these series of suspensions were 

 determined at 20C. Figure 54 gives the result, the ordinates 

 being the values for the viscosity ratios, gelatin suspension: 

 water, and the abscissae are the pH of the gelatin particles 

 at equilibrium. The curves show that the viscosity of suspen- 

 sions of gelatin sulphate is a little less than half that of suspensions 

 of gelatin chloride and phosphate of the same pH. The curves 

 for the suspensions of gelatin chloride and gelatin phosphate are 

 alike, with the exception of part of the descending branch. 



