HARPER F. ZOLLER 637 



being certain that the reaction of the casein solution was the same in 

 all concentrations. pH 9.0 was chosen for these measurements 

 because at this point we are in the region of maximum viscosity of 

 casein in the ordinary alkalies. 



Preparation of Solutions. — Alkalies. — Sodium, potassium, and 

 lithium hydroxides were freed as far as possible from their carbonates 

 by preparing concentrated solutions and allowing the carbonates to 

 crystallize, then filtering or pouring the clear solutions from the 

 precipitate. Molar solutions were then prepared of the respective 

 compounds; m/1 solution of freshly distilled NH3 was also prepared. 



Casein. — Casein was obtained by purifying a quantity of imported 

 casein according to the method of Hammarsten as modified by 

 Robertson. 1 This was designated by the symbol R. A casein, the 

 history of which was completely known, so as to overcome the ques- 

 tion of heated casein, was prepared by precipitating the casein from 

 fresh, unpasteurized skim milk with dilute HCl according to the 

 grain curd method.^ The casein was then dissolved in ammonia and 

 reprecipitated twice in order to free it from salts and other impurities. 

 It was then dried with concentrated alcohol without the use of heat. 

 This casein was designated as G in the following studies. 



In the preparation of all casein solutions for the different studies 

 the casein was carefully weighed into a dry flask and 50 cc. of dis- 

 tilled water, which had been freshly boiled and cooled by drawing 

 C02-free air through it while immersed in running cold water, were 

 added with thorough shaking to prevent the finely divided casein 

 from forming lumps. After soaking in the water for 30 minutes the 

 requisite quantity of alkali (m/1) was added from a burette. The 

 mixtures were set in a water bath controlled at 30°C. and when all 

 the casein had dissolved (2 hours were allowed) they were made 

 up to final volume with the distilled water described above. 



Measurement of Viscosity. — Although many of the measurements 

 of viscosity of casein solutions have been conducted in the past 

 with the usual type of capillary viscosimeter the present work was 

 done ahnost entirely with a rotating disc instrument. The con- 

 venience of this latter type of instrument for the heavy casein solu- 



^ Clark, W. M., Zoller, H. F., et al., J. Ind. and Eng. Chem., 1920, xii, 1163. 



