246 



THEORY OF COLLOIDAL BEHAVIOR 



as the concentration of Na 2 SO 4 is below M/32 it increases the 

 solubility of gelatin, and the more so the higher the concentration. 

 When, however, the concentration of Na 2 SO 4 is above M/32, a 

 further increase in the concentration of Na 2 SO4 diminishes the 

 solubility of gelatin and the more so the higher the concentration 

 of Na 2 S0 4 . (NH 4 ) 2 SO 4 acts like Na 2 SO 4 . We now understand 



I 



130 

 120 



no 



100 

 90 

 80 

 70 

 60 

 50 

 40 

 30 

 20 

 10 



* f f 



Concentration of salts 



FIG. 73. Influence of salts on the time required for the solution of 0.8 gm. 

 of powdered isoelectric gelatin in 100 c.c. salt solution at 35C. and pH 4.7. 

 Notice difference of curve for Na2$O4 and for CaCh and Nad. 



why we cannot precipitate solutions of isoelectric gelatin with 

 KC1 or MgCl 2 in concentrations up to 3 M (see Table XLV) while 

 we can precipitate such solutions with sulphates but only at 

 concentrations above M/2. 



It may be of interest to supplement these observations by the 

 results given in Table XLVa, on the influence of salt solutions 

 of three different molar concentrations, namely, M/1,024, M/512, 



