HARPER r. ZOLLER 



649 



Upon another occasion the writer has shown the effect of the 

 heat treatment of milk upon the optimum temperature for acid pre- 

 cipitation of casein^^ and at the same time presented some data to 

 show that this denaturation of the casein affected its hydrophyllic 

 properties. ^'^^ Again the conduct of casein, heated and unheated, 

 toward borax solutions in the borax solubility test* emphasized that 

 casein which had been subjected to high temperatures imbibes more 

 water in solution and thereby produces greater internal friction or 

 viscosity; in many instances they gel where normal casein solutions 

 flow readily. The writer has further shown the formation of j8 casein 

 in highly heated casein solutions.^'' 



To show the effect of heat treatment of casein upon its viscosity 

 in NaOH several experiments were conducted, two of which are 

 described. Fresh skim milk was divided into two portions, A and B. 

 The casein was precipitated from A according to the normal grain 

 curd method^ without heating the milk externally above 34°C. B was 

 pasteurized at 65°C. for 45 minutes and the casein was precipitated 

 from it with the modified grain curd method described by the writer. i* 

 The two moist caseins were dried under the same conditions in an air 

 current at 40°C. The viscosities of the resulting caseins A^ and Bo 

 were measured at 25°C. in the MacMichael apparatus as modified. 

 Casein Bo contained 0.45 per cent more ash than A^. 



EXPERIMENT I. 



The other experiment mentioned above consisted in pasteurizing 

 a 6.0 per cent solution of Casein R dissolved in NaOH at 80°C. for 

 30 minutes. The solution was cooled thoroughly and its viscosity at 

 25°C. was compared to the viscosity of a similar solution that had not 

 been pasteurized. 



^* ZoUer, H. F., /. Ind. and Eng. Chetn., 1921, in press. 

 " Zoller, H. F., Chem. AhsL, 1921, xv, 401-02. 



