836 



DONNAN EQUILIBRIUM AND VISCOSITY 



before sucking it into the viscometer since the gelatin particles 

 sink rapidly to the bottom of the dish. • 



After the viscosity measurements were taken, the suspension was 

 put on a filter of cotton wool and the supernatant water allowed to 

 drain off. By measuring the volume of the filtrate and deducting 

 this from the original volume of the suspension (which was in all 

 cases 100 cc), the volume of the gelatin (with some error) 

 was obtained. Then the gelatin was melted, and the pH of the melted 

 mass of gelatin as well as of the filtrate was determined potentio- 

 metrically. Fig. 5 gives the result of such an experiment. The lower 



o 



t 

 § 



25 



20 



15 



10 





pH 1.8 2.0 22. 24 2.6 2.8 3.0 3.2 3.4 3.6 3.6 4.0 42 4.4 



Fig. 5. Showing that the influence of pH on viscosity of 0.5 per cent suspensions 

 of powdered gelatin in water is similar to the influence of pH on viscosity of gelatin 

 solutions, and that the volume occupied by the particles in the suspension varies 

 in a similar way as the viscosity. Temperature 20°C. 



curve shows the influence of 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. 



Moreover, the viscosity values for the suspensions of 0.5 gm. of 

 powdered particles in water are greater than the viscosity values 

 of a 0.5 per cent solution of freshly liquefied gelatin for equal pH." 

 The highest viscosity ratio of the 0.5 per cent gelatin solution was 

 about 1.75 while the highest viscosity ratio for the 0.5 per cent sus- 

 pension of gelatin was about 2.4 (Fig. 5). 



'* The viscosity of the solution increases on standing. 



