THE STABILITY OF PROTEIN SOLUTIONS 



247 



and M/256, on the time required to dissolve 0.8 gm. of powdered 

 isoelectric gelatin at 35C. The salt solutions had a pH of 4.7. 

 It is obvious from the table that the dissolving power of the 

 chlorides increases with the valency of the cation while the dissolv- 

 ing power of the Na salts increases with the valency of the anion. 



TABLE XLVo. TIME IN MINUTES REQUIRED TO DISSOLVE 0.8 GM. OF 

 POWDERED ISOELECTRIC GELATIN AT 35C. 



While isoelectric gelatin is only sparingly soluble, gelatin 

 salts are highly soluble. Doses of 0.8 gm. of powdered gelatin 

 of pH of about 3.3 dissolve very rapidly in 100 c.c. HC1 of the 

 same pH at 35C. The addition of NaCl or CaCl2 no longer 

 increases the solubility, except for CaCU in concentrations above 

 M/16. Na2SC>4 or (NH^SC^ abruptly diminishes the solubility 

 at a concentration above M/4; and NaCl does so above a con- 

 centration of 1 M (Fig. 74). 



Figure 75 shows the influence of the three salts on the solution 

 time of Na gelatinate of pH 10.5. Na 2 SO4 diminishes the solu- 

 bility abruptly at a concentration above M/8 while both NaCl 

 and CaCU increase the solubility of Na gelatinate, NaCl in 

 concentrations above M/2, and CaCl2 in concentrations above 



M/16. 



In all three cases, therefore, is the solubility of gelatin dim- 

 inished by sulphates, but only exceptionally by chlorides. This 

 explains the results contained in Table XLV. The solubility 

 of gelatin in water does not depend on the Donnan equilibrium. 



