268 



THEORY OF COLLOIDAL BEHAVIOR 



2.0 of the outside solution, and with a further increase in the 

 concentration of the acid the swelling becomes less again. 



Figure 79 gives the measurements of the same particles after 

 24 hours. At this time all the particles in the region of greatest 

 solubility for HC1 and for H 3 PO 4 , i.e., between pH of the outside 



Swelling of casein 

 in different acids 

 at 24 C in 1 hour 



Concentration of acids 



FIG. 78. Influence of different acids on the swelling of casein. 



solution of 1.8 and 2.9, had completely dissolved and could no 

 longer be measured. 



Figure 79 shows another fact; namely, that the rate of swelling 

 is not the same in different acids. It is about the same inHCl 

 and H 3 PO 4 (for the same pH) but decidedly less in HNO 3 and 

 still less in H 2 SO 4 and trichloracetic acid. It was found that the 

 rate of solution of casein in these different acids followed closely 



