JACQUES LOEB 89 



was measured in a straight viscometer with a time of outflow for 

 water of 48.4 seconds at 20°C. The curve for the viscosities after 

 1 hour is the expression chiefly of the sweUing, since casein chloride 

 goes only slowly into solution at 20°C. 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 after 22 hours shows, however, 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 of 2.2. This solution 

 of the particles capable of swelling beneath that size where they 

 no longer can occlude water must diminish the relative volume of 

 the casein and cause a diminution of the viscosity. Below a pH of 

 1.8 where the solubility of the casein is considerably diminished, 

 the 1 hour and the 22 hours viscosity curves (Fig. 9) no longer differ 

 materially. As a consequence of the 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 funda- 

 mental for the theories of viscosity and of colloidal behavior in general 

 that 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. 

 In order to get a more rapid dispersion of the particles the experiment 

 was carried out at 40°C. The time of outflow of water through the 

 viscometer at 40° was 35.5 seconds. Fig. 10 gives the results. The 

 viscosity measurements were made at four different times; namely, 

 first, immediately after the powdered casein was put into the FICl; 

 then after 1,3, and 6 hours. During this time the casein chloride 

 solutions were kept at 40°C. 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 suspensions and during 



