216 



THEORY OF COLLOIDAL BEHAVIOR 



temperature at which the two opposite processes the formation 

 and the melting of micellae occur equally rapidly in a 2 per cent 

 solution of gelatin chloride of pH 2.7 lies between 25 and 35C. 



2.0 



5 10 15 20 25 30 35 40 45 50 55 60 



Time in minutes 



FIG. 58. Increase of viscosity of gelatin sulphate solution of different pH on 

 standing. The increase is most rapid at the isoclectric point, thus proving that 

 the acid retards or prevents the formation of submicroscopic solid particles of 

 jelly on standing. 



When acid is added to powdered isoelectric gelatin the time 

 required to dissolve the particles diminishes at a given tempera- 

 ture with increasing hydrogen ion concentration of the solution and 

 this tendency of the particles to dissolve with increasing hydrogen 



