248 



THEORY OF COLLOIDAL BEHAVIOR 



This conclusion is supported by an investigation of the influence 

 of the pH on the solubility of gelatin. 



We have seen that addition of little acid to isoelectric gelatin 

 increases the osmotic pressure, viscosity, P.D., and swelling, 

 while beyond a certain pH the addition of more acid has a depress- 



gelatin chloride pH 3.3 

 at 35 C. 



Concentration of salts 



FIG. 74. Influence of salt on solution time of 0.8 gm. of powdered gelatin 

 chloride of pH 3.3 in 100 c.c. salt solution at pH 3.3. The gelatin is no longer 

 soluble beyond 1M NaCl. 



ing effect. It was of interest to find out whether such a maximum 

 followed by a drop existed in the influence of acid on the solu- 

 bility of gelatin. This is not the case at least between pH 4.7 

 and 1.0, since the solubility increases steadily with increasing 

 hydrogen ion concentration, as was proven by measurements of 



