192 



SOLUTION AND PRECIPITATION OF PROTEINS 



Figs. 1 and 2 show another fact; namely, that the rate of swelling 

 is not the same in different acids. It is about the same in HCl and 

 H3PO4 (for the same pH) but decidedly less in HNO3 and still less in 

 H2SO4 and trichloracetic acid. It was found that the rate of solution 



p 



s 



0) 

 to 



s 



B 



CO 



•T-l 



CD 



e 



I 



1000 500 



^ N M 

 200 lUO 50 



20 



10 



H 

 4 



2 



IM 2M 



Concentration of acids 



Fig. 1. Relative swelling of isoelectric granules of casein when put into acids 

 of different concentrations, at 24°, after 1 hour. The hydrogen ion concentration 

 of the casein particles is less than that of the outside solution on account of the 

 Donnan equilibrium. The latter concentrations are plotted as abscissae. The 

 ordinates are the relative average diameters of the granules. 



of casein in these different acids followed closely the rate of swelling. 

 It took longer to dissolve casein in HNO3 than it did in HCl (at 20*C.) ; 

 and the casein was practically insoluble in H2SO4 and trichloracetic 

 acid in 24 hours. 



