646 CASEIN VISCOSITY STUDIES 



Many of these salts are employed in casein water-resisting glues 

 to combine with the excess of calcium oxide used as solvent for the 

 casein. Certain ones will effect the setting time of the glues, thereby 

 regulating the smoothness of the product. The above data on vis- 

 cosity influence of these salts should indicate the choice of correct 

 solvents for particular purposes. 



The peculiar behavior and place of borax among these curves 

 should not be passed without remarking that the phenomenon may 

 possibly be traced to the influence of polyhydroxyl groups upon the 

 dissociation of boric acid. Glycerol, mannitol, and various sugars 

 are known to cause increased dissociation of boric acid which permits 

 of the determination of boric acid by titration. The presence of 

 tyrosine in casein suggests that casein may contain free hydroxyl 

 groups, and these have indeed been demonstrated by the preparation 

 of acylated products. It is possible that casein will act similarly 

 toward boric acid thus effecting the displacement of the maximum 

 viscosity. 



///. Alkaline Hydrolysis of Casein as Influencing Its Viscosity. 



Section I of this series . showed that when casein is dissolved in 

 alkalies other than NH4OH the viscosity of the solutions containing 

 the same concentration of casein increases as the pH increases up to 

 9.2 after which the viscosity sharply drops to the region of pH 10.5 

 after the viscosity remains fairly constant. In case of NH3 solutions 

 of casein there is not such a drop after reaching the maximum vis- 

 cosity (temperature of solutions 25°C). The odor of all casein 

 solutions, the pH of which are pH 10.0 or more, is distinctly ammo- 

 niacal. Moist litmus paper becomes blue when held above these 

 solutions, while strong HCl evolves dense white fumes when brought 

 in their vicinity. 



Dakin and Dudley^^ have prepared what they term racemized casein 

 by treating casein with 2 per cent NaOH for several hours, or until 

 the specific rotation has decreased to zero. They observe that 

 ammonia is evolved, that the racemized casein contains a low con- 

 tent of phosphorus, and describes the process of decrease in rotation 



12 Dakin, H. D., and Dudley, H. W., /. Biol. Chem., 1913, xv, 263. 



