THE ACTION OF NEUTRAL SALTS 



93 



the increase of the viscosity by the H ions stops as soon as the 

 pH of the solution reaches about 3.0 for the reason stated. 



When the same experiment is repeated with a gelatin solution 

 of pH 3.0, the addition of NaCl immediately causes a drop also 



8 



I 



4 

 2.3 

 2.2 

 2.1 

 20 

 1.9 

 1.8 

 1.7 

 1.6 

 1.5 

 1.4 



1.2 

 1.1 

 1.0 



Concentration 



FIG. 28. When the gelatin solution has a pH of 2.5, HC1 and NaCl depress the 

 relative viscosity of the gelatin solution to the same degree. 



(Fig. 27) while the addition of HC1 no longer causes a rise but 

 the drop commences a little later than in the case of NaCl. 



When, however, the same experiment is made with a gelatin 

 solution of pH 2.5 (Fig. 28), an immediate drop is noticed upon 

 the addition of HC1 as well as in the case of the addition of NaCl, 



M 



