636 CASEIN VISCOSITY STUDIES 



mum of internal friction outcrops in all industries where casein is 

 used in the form of its solutions; e.g., paper coating, sizings, paints, 

 adhesives, nutritive preparations, dentrifrices, etc. 



Two features are brought out in the viscosity curves which deserve 

 separate treatment. On the one hand, as above mentioned, when 

 casein is dissolved in sodium borate the maximum viscosity is attained 

 at about pH 8.1 instead of pH 9.2 as is true for NaOH, KOH, and 

 LiOH. Therefore a study of the anion effect is reported in Section 

 II of these studies. Upon the other hand we observe a characteristic 

 decline in the viscosity following the maximum and this decline is 

 followed by a broad flattening of the curve. This effect has been 

 correlated with the alkaline hydrolysis of the casein, whence numer- 

 ous cleaved bodies are thrown into solution, such as ammonia, sul- 

 fides, phosphates, albumoses, etc. With the production of ammonia 

 there is a flattening of the curve which has further significance when 

 it is pointed out that solutions of casein in ammonia show a maximum 

 viscosity, but this maximum, once attained at pH 9.2, continues 

 without the characteristic decline. Thus, it will be appreciated that 

 solutions of casein in ammonia generally maintain a higher viscosity. 

 In Section III, therefore, the effect of alkaline hydrolysis upon the 

 viscosity of casein will be dealt with separately. 



Section IV will treat very briefly of the influence of high tempera- 

 tures upon the viscousness of casein solutions, inasmuch as the author 

 has treated of this factor somewhat more in detail in connection with 

 the revision of the borax solubility test for caseins.'* 



I. Relation Between pH and Viscosity of Solutions of Casein in Alkalies. 



Since the earlier investigators in dealing with casein solutions made 

 no attempt to study the effect of hydrogen ion concentration upon 

 their viscosity it was found expedient to redetermine the viscosity 

 curves of casein in alkalies using the hydrogen electrode as a check 

 upon the reaction of the solutions. Chick and Martin^ measured the 

 effect of concentration of casein upon the viscosity but did not indi- 

 cate whether or not the reaction of the solutions was held at constant 

 pH. Consequently the writer has repeated these measurements, 



5 Chick, H., and Martin, C. J., Kolloid. Z., 1912, xi, 102. 



