VISCOSITY 



225 



The correctness of this inference is supported by the viscosity 

 curves in Fig. 65, which represent the viscosity after 1 hour and 

 after 22 hours. The experiments are the same as those referred 

 to in Figs. 63 and 64. The viscosity of the total suspension and 

 solution was measured in a straight viscosimeter with a time of 

 outflow for water of 48.4 seconds at 20C. The curve for the 

 viscosities after 1 hour is the expression chiefly of the swelling, 

 since casein chloride goes only slowly into solution at 20C. 

 The curve is almost continuous and has its maximum in the 

 region between pH 2.1 and 2.4, where also the swelling is a 



maximum. There is, however, a slight depression at pH 2.2, 

 where the solubility of the casein is a maximum. 



The curve for the viscosities, Fig. 65, after 22 hours shows, how- 

 ever, a distinct saddle at pH 2.2 where the solubility of casein 

 chloride is a maximum. This agrees with the assumption that 

 the high viscosity is due to swollen particles of casein, a certain 

 quantity of which had been dissolved at or near pH 2.2. This 

 solution of the particles capable of swelling beneath that size 

 where they no longer can occlude water must diminish the rela- 

 tive volume of the casein and cause a diminution of the viscosity. 

 Below a pH of 1.8, where the solubility of the casein is consider- 

 ably diminished, the 1-hour and the 22-hours viscosity curves 

 (Fig. 65) no longer differ materially. As a consequence of the 



15 



