THE STABILITY OF PROTEIN SOLUTIONS 



269 



the rate of swelling. It took longer to dissolve casein in HNO 3 

 than it did in HC1 (at 20C.); and the casein was practically 

 insoluble in H 2 SC>4 and trichloracetic acid in 24 hours. 



The rate of swelling is a function apparently not only of the 

 osmotic pressure inside the particle caused by the Donnan equilib- 



2.5 



N H H H 

 lOOD 500 200 100 



Concentration of acids 



Fio. 79. Connection between swelling and solution of casein particles. 



rium, but also of the force of cohesion between the particles. 

 Procter and Wilson have suggested that the rapid increase of 

 swelling of solid gelatin with a rise in temperature is due to a 

 corresponding diminution of cohesion between the molecules of 

 gelatin with rising temperature. The influence of the anionof 

 gelatin-acid salts on the cohesion of the particles of a solid gel is 

 apparently much smaller than the influence of the anion on the 



