648 CASEIN VISCOSITY STUDIES 



with increasing pH. All casein solutions at pH 10.0 to 10.5 and 

 higher pH responded to the copper reaction; if dilute acid is added to 

 the casein solutions, which contain copper, and give the violet color, 

 a dark color is formed owing to the formation of peptized copper 

 sulfide. 



The protein body which is precipitated from the alkaline hydrol- 

 ysate of casein by the addition of dilute acids is, as described by 

 both Dakin and Maynard, very gelatinous. It forms a clear trans- 

 parent gel of high viscosity. The formation of this hydrolytic 

 product from casein in the presence of the liberated NH3 is believed 

 to be responsible for the flattening of the viscosity curve at pH greater 

 than 10.0. 



The quantity of nitrogen split off from casein by the alkaline 

 hydrolysis was found to be nearly ^ the lysine nitrogen of the original 

 casein and designated as free amino nitrogen by Van Slyke and 

 Birchard.^^ 



It can be stated with a sense of security that in solutions originally 

 containing casein of which the pH are greater than 10.0, we are no 

 longer dealing with casein but with protein-cleaved products. The 

 flattening of the viscosity curve is coincident with the alkaline hydrol- 

 ysis of the casein. 



Furthermore the glues and adhesives formed from casein are ulti- 

 mately a mixture of these cleaved products. It seems necessary 

 now to determine the relative adhesive power of pure caseinate and 

 the protein body which constitutes the larger bulk of the casein 

 alkaline hydrolysate. 



IV. Temperature as Effecting the Viscosity of Casein Solutions. 



If we heat solutions of casein in alkalies (NaOrl) to the boiling 

 point and allow the solutions to cool spontaneously the resulting 

 viscosities as measured at 25°C. are very little different from the vis- 

 cosities of the unheated solutions at equivalent pH. Upon the other 

 hand if the casein is precipitated from its solutions, after they have 

 been heated, by acid and is then dried the resulting casein again dis- 

 solves in alkalies to furnish solutions of much higher viscosity. 



" Van Slyke, D. D., and Birchard, F. J., /. Biol. Chem., 1913, xvi, 539. 



