290 



COLLOIDS AND ELECTROLYTES 



concentrations of another acid to it, we notice a similar depression. 

 Fig. 11 gives the effect of the addition of different quantities of 

 HNO3 and of H2SO4 to 1 gm. of gelatin of pH 3.3; 0, 0.1, 0.2, 0.4, 

 0.8, 1.6, 3.2, 6.4, 12.8, and 25.6 cc. of m/4 acid were contained in 100 

 cc. of gelatin solution of pH 3.5. The outside solution contained 

 the same concentration of acid. The depressing effect of HNO3 was 

 like that of HCl, and the depressing effect of H2SO4 was greater. 

 Fig. 12 shows that the depressing influence of the addition of acid 

 is manifested in a similar way in the influence of the concentration 

 of acid upon the initial diffusion of water into the gelatin solution. 



S 



'-a 



160 



140 



120 



100 



80 



60 



40 



20 



iinririniirillll 



4000 2000 1000 500 250 125 62 31 ^^ 15 



Concentration o| acid added, 



Fig. 12. The same effect of the addition of acid upon the initial rate of diffusion 

 of water into the gelatin chloride solution. 



If we add neutral salt, e.g. KNO3 or K2SO4, to a 1 per cent gelatin 

 solution with a pH = 3.5, taking care that the pH of the solution is 

 not altered by the addition of salt, the depressing effect is about the 

 same as when we add acid. To doses of 1 gm. isoelectric gelatin of 

 pH 3.5 were added 0, 0.1, 0.2, 0.4, 0.8, 1.6, 3.2, 6.4, 12.8, and 25.6 

 cc. of m/4 KNO3 or K2SO4, and enough water was added to make 

 the volume 100 cc. The pH remained the same in all solutions. 



