VISCOSITY 



209 



Experiments on the influence of these three acids on swelling 

 (Fig. 19, Chap. V) show that the curves for the relative volume of 

 powdered gelatin in solutions of these three acids are similar to the 

 viscosity curves in Fig. 54 since the relative volume of gelatin 

 sulphate was found to be not far from one-half of that of gelatin 

 chloride or gelatin phosphate of the same pH. 



4.5 



4.0 



3.5 



2.5 



2.0 



1.5 



1.0 



*.u 



7 



Viscosity of suspen- 

 sions of 05 gm. of 

 powdered gelatin in 

 100 cc. of acid solution 





\ 



pH 16 16 2.0 2.2 2.4 2.6 2.8 3.0 3.2 3.4 3.6 3.8 4.0 4.2 44 46 



FIG. 54. Viscosity of suspensions of 0.5 gm. of powdered gelatin of grain 

 size 100 to 120. Abscissae are the pH, the ordinates the ratio of time of outflow 

 of suspension to time of outflow of water. The influence of HC1 and HsPC^ is 

 practically identical for the same pH while H2SO4 depresses the viscosity of the 

 suspensions to a little less than one-half of that for HC1. 



We have seen that the viscosity of a gelatin chloride solution, 

 e.g., of pH 3.0, is lowered when neutral salts are added and the pH 

 kept constant (Fig. 29, Chap. VI). The same is true for the 

 viscosity of suspensions of powdered gelatin. Doses of 0.5 

 gm. of powdered gelatin of pH 6.0, going through sieve 100 but 

 not through sieve 120, were put each into 100 c.c. of water con- 

 taining 6 c.c. of 0.1 N HC1, and different quantities of NaNO 3 , so 

 that the concentration of the salt varied in the different solutions 

 from M/8 to M/2,048. One solution contained no salt. The 



14 



