CASEIN VISCOSITY STUDIES.* 



By harper F. ZOLLER. 



(From the Research Laboratories of the Dairy Division, Bureau of Animal Industry, 

 United States Department of Agriculture, Washington.) 



(Received for publication, February 25, 1921.) 

 INTRODUCTION. 



Robertson^ has shown that when casein is dissolved in dilute acids 

 or alkalies (HCl or KOH) , the viscosity of the solution increases with 

 the increase in the concentration of the solvent. A similar set of 

 results were obtained by Sackur.^ That a maximum viscosity occurs 

 in solutions of casein in alkalies has been pointed out by the writer 

 upon another occasion.^ Detailed publication of these results has 

 been delayed because it was subsequently found that borax caused 

 a displacement of this maximum viscosity* and it was very desirable 

 to repeat with care the determination of the viscosity curves in order 

 to be sure that no error in observation had been committed in the 

 earlier experiments. 



The viscosity-pH curves of casein in alkaline solutions only are 

 considered in this paper. Viscosity-pH curves of pure casein in 

 acids have been observed by the writer, but they are lacking in the 

 practical significances manifested by the alkaline solutions. It may 

 not be remarkable that all the commercial casein glues examined 

 yielded mixtures, the pH values of which showed that the maximum 

 viscosity had been widely overstepped, and that the viscosities of 

 the mixtures lay on the alkaline flat part of the curve. The practical 

 importance of knowing at what pH casein solutions show their maxi- 



* Published by permission of the Secretary of Agriculture. 



^ Robertson, T. B., The physical chemistry of the proteins, Washington, 1918, 

 320-328. 



2 Sackur, 0., Z. physikal. Chem., 1902, xli, 672. 



3 ZoUer, H. F., Science, 1919, 1, 49. 



* ZoUer, H. F., /. Ind. and Eng. Chem., 1920, xii, 1171. 



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