226 



THEORY OF COLLOIDAL BEHAVIOR 



saddle the maximum of the viscosity curve after 22 hours now 

 lies at pH 2.6. 



Since the point at issue, namely, the diminution of the viscosity 

 when solid submicroscopic particles, capable of swelling, are 

 dissolved into particles so small that they no longer can occlude 

 water, is so fundamental for the theories of viscosity and of 

 colloidal behavior in general, it seemed necessary to look for a 

 more striking proof than that given in the experiment quoted. 

 For this purpose measurements were made on 1 per cent casein 

 chloride solutions prepared from very finely powdered casein 

 particles sifted through a 200-mesh sieve. In order to get a 



1.0 



pHl4 1.6 1.8 2.0 2.2 2.4 2.6 2.8 3.0 3.2 3.4 3.6 3.8 4.0 4.2 



FIG. 



66. Diminution of viscosity through solution of solid particles of casein 



chloride. 



more rapid solution of the particles the experiment was carried 

 out at 40C. The time of outflow of water through the visco- 

 meter at 40 was 35.5 seconds. Figure 66 gives the results. 

 The viscosity measurements were made at four different times, 

 namely: first, immediately after the powdered casein was put 

 into the HC1; then after 1J^, 3, and 6 hours. During this time 

 the casein chloride solutions were kept at 40C. The viscosity 

 curve taken immediately after the suspensions were prepared is 

 continuous and is the expression of the swelling which occurred 

 in the few minutes which elapsed in the preparation of the suspen- 

 sions and during which the casein was at 40C. The maximum 

 swelling occurred at about pH 2.3. At this time the amount of 



