VISCOSITY 



207 



at 20C., and then their time of outflow through a capillary 

 tube was ascertained at 20C. The time of outflow of water 

 through the viscometer at this temperature was 24 seconds. It 

 was essential to stir the suspension thoroughly before sucking it 

 into the viscometer since the gelatin particles sink rapidly to the 

 bottom of the dish. 



4.0 



3.5 



3.0 

 fi 



J> 2.0 



1.5 

 1.0 



lulion 



Vis 



OS 



itv 



\ 



at 2 



oc. 



pH 1.6 1.8 2.0 2.2 2.4 2.6 2.8 3.0 3.2 3.4 3.6 3.8 40 42 



FIG. 52. Difference in the viscosity of a suspension of 0.5 gm. of powdered 

 gelatin in 100 c.c. and of the solution of the suspension in the same liquid; both 

 viscosities were measured at 20C. 



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 c.c.), the volume of the gelatin was ob- 

 tained (with a considerable error). Then the gelatin was melted 

 and the pH of the melted mass of gelatin as well as of the filtrate 

 was determined potentiometrically. Figure 53 gives the result 

 of such an experiment. The lower curve shows the influence of 



