644 CASEIN VISCOSITY STUDIES 



to stand for 30 hours, but the relative values remained the same; 

 that is, the maximum viscosity occurred when the casein had com- 

 bined with 90 — 100 X 10~^ gram equivalents of base. When 180 

 X 10~^ gram equivalents of alkali were added to 1 gm. of casein in 

 the writer's studies, the viscosity had fallen to a minimum, or on the 

 flat part of the curve, and the pH was greater than 10.5. This 

 would indicate that hydrolysis is taking place at this combining 

 capacity, or at least it is in the first stages. 



II. Anion Influence on the Viscosity of Casein Solutions. 



The anions studied in this connection were those resulting from the 

 ionization of the following salts: Na3P04, NaF, Na2S03, Na2B407, 

 NaoCOs, Na3As04, and Na2Si03. Casein is readily soluble in solu- 

 tions of the above salts. It is also readily soluble in solutions of the 

 neutralized acids (neutral sodium salts) , such as citric, oxalic, tartaric, 

 etc., but these viscosity data are not presented. 



The method used in preparing the casein solutions was essentially 

 the same as that for the pure alkalies described in Section I. The 

 casein was first soaked in 50 cc. of water and the solvent then meas- 

 ured into each quantity; they were then made up to volume. After 

 the regular time interval (2| hours), the viscosity and hydrogen ion 

 concentration were measured exactly as in Section I. Fig. 4 shows 

 the viscosity curves plotted from the experimental data. 



The curve for sodium carbonate is necessarily similar to the NaOH 

 curve. Naturally, if the curves represented the data for viscosity 

 plotted against concentration of salt solution instead of pH we would 

 observe wide variations in the gradient of the various curves corre- 

 sponding to the differences in the dissociation of the solvents. Since 

 the degree of internal friction varies more pronouncedly with the 

 pH than with the concentration of molecules of the solvent, we are 

 correct in representing the values as given in Fig. 4. It was impos- 

 sible to use the hydrogen electrode in the sodium sulfite solutions for 

 the determination of pH, because of fluctuating potentials probably 

 resulting from sulfur dioxide which permeates the solutions. The 

 dissociation constant of sulfurous acid is less than that of casein and 

 this accounts for the formation of SO2 in the solutions. The pH was 

 determined roughly by the spot test with sulfonephthalein indicators. 



