222 



THEORY OF COLLOIDAL BEHAVIOR 



particles in the casein chloride solution is indicated by the 

 opacity of the solution. 



The material used in our experiments was a fine dry powder of 

 nearly isoelectric casein prepared after Van Slyke and Baker. 

 Particles of equal size of grain (between mesh 100 and 120) were 

 sifted out and 1 gm. of such powder was put into 100 c.c. each 

 of solutions of HC1 of different concentration to bring the casein 

 to varying pH. A microscopic examination of the granules 



22 



8 E0 



S 18 



.-> 



g 16 



.9 14 



1 



I 



10 

 8 

 6 

 4 



Volune ofscdimen 



incc. 



pH 1.4 1.6 1.6 20 2.2 2.4 2.6 28 3.0 32 3.4 3.6 3.8 4.0 4.2 



FIG. 63. Swelling and solution of casein chloride in 1 and 22 hours at 20C. 



showed that they underwent a swelling which was a minimum 

 at the isoelectric point, which increased with increasing hydrogen 

 ion concentration until it reached a maximum, and which then 

 diminished again with a further increase in the hydrogen ion 

 concentration (see Chap. XV). Hence, the volume of the 

 casein particles suspended in the HC1 varied in a similar way 

 with the pH as the volume of suspended particles of gelatin. 



This swelling could also be observed when the suspension was 

 put into 100 c.c. graduates and the suspended particles were 

 allowed to settle. . The volume of the sediment was a minimum 

 at the isoelectric point increasing with increasing hydrogen ion 



