VISCOSITY 



223 



concentration of the solution and finally decreasing again. But 

 the curves of swelling and of volume of sediment were only 

 parallel at the beginning of the experiment, since the swelling 

 (which occurred at once) was followed by some of the casein 

 going into solution or into suspension. The longer the experi- 

 ment lasted the smaller the volume of the sediment became and 

 the larger the mass which went into the supernatant solution. 

 This is expressed in Fig. 63. The upper curve represents the 

 volume of the sediment after 1 hour. The suspension of 1 gm. of 



pH 1.4 L6 16 2.0 22 2.4 2.6 2.8 3.0 3.2 3.4 3.6 "3.8 4.0 4.2 



FIG. 64. Dry weight of sediment of casein chloride solutions after 1 and 22 



hours. 



casein in 100 c.c. of HC1 of different concentration had been kept 

 for 1 hour at 20, had been shaken repeatedly but not frequently, 

 and the suspension was then passed into 100 c.c. graduates and 

 allowed to settle at 20C. After 2 hours the volume of the sedi- 

 ment was measured and the volumes are the ordinates of the 

 curve marked " after 1 hour" in Fig. 63. A similar experiment 

 was made in which the suspension of casein was kept for 22 

 hours at 20C. and was allowed to settle during 6 hours also at 

 20C. The volumes are the ordinates of the second curve in 

 Fig. 63, marked " after 22 hours." The abscissae are the pH 

 of the total solution and suspension. 



The curve " after 1 hour" is clear, since it is chiefly the expres- 



