HARPER F. ZOLLER 643 



The viscosity drops precipitously following the maximum with 

 each alkali except NH4OH. In this case there is a slight fall but it 

 continues to remain high even in great concentrations of ammonia 

 (50 cc. of m/1 to 10 gm. of casein). At pH 10.5 with NaOH, KOH, 

 and LiOH there is an evolution of NH3 from the solutions, shown by 

 white fumes with concentrated HCl and by turning methyl red to 

 yellow (methyl red paper was held above the solution). Following 

 pH 10.5 the viscosity is constant and about parallel to the ammonium 

 hydroxide curve. This serves to show that in these concentrations 

 of alkali the casein is furnishing NH3 to the solutions so that they 

 simulate the influence of the pure ammonium curves. Hence the 

 flattening could be attributed to the accumulation of NH3. This 

 will be dealt with further in Section III. 



Robertson calls attention to the relation between the ionization of 

 protein solutions and their viscosity. ^ The viscosity increases with 

 the electrolytic dissociation of the proteins; of course as ionization is 

 conceived to be zero (or in electrochemical equilibrium) at the iso- 

 electric point, we find simultaneously with the isoelectric condition a 

 minimum viscosity. Hence Robertson points out^ that at the point 

 of maximum base-binding capacity, or saturation with base, there 

 should be a maximum viscosity. If we note the quantity of NaOH 

 that is necessary to cause the casein to attain its maximum viscosity 

 at pH 9.2 we find that for each gram of moisture-free casein 0.98 cc, 

 of normal NaOH was required (average of eight determinations). 

 At this point 1 gm. of casein had combined with 98 X 10 "^ gram 

 equivalents of alkali. This value is slightly greater than one-half 

 the value obtained by Robertson (180 X 10~^) using the gas chain 

 method. ^^ The writer employed very concentrated solutions (8 to 10 

 per cent) of casein, while Robertson worked with very dilute solutions 

 and this may be responsible for the difference in observations. In 

 two instances, the writer allowed the concentrated casein solutions 



11 Robertson, T. B., /. Physical Chem., 1910, xiv, 528. 



The high concentrations of casein used by the writer have given values for 

 the pH of the maximum viscosity, considerably different from those observed 

 by Loeb in working with dilute solutions. (Loeb, J., /. Gen. Physiol., 1921, iii, 

 357.) The interval between the preparation of the casein solution and the 

 determinations of the pH seemed ample for the equilibrium. 



