640 CASEIN VISCOSITY STUDIES 



a smooth coat of iridium. A well plated electrode lasted during one 

 complete run of a single series of casein solutions titrating from the 

 acid end of the series toward the alkaline end, usually about eight 

 consecutive determinations. 



The hydrogen ion concentrations of the various solutions were 

 determined without dilution at 30°C. They were also determined 

 after equal time intervals of contact of casein and solvent (2^ hours), 

 immediately following the viscosity determination. 



Effect of the Concentration of Caseinate on the Viscosity at Constant pH. 



As previously mentioned pH 9.0 was chosen as the arbitrary reac- 

 tion to which all the solutions were adjusted for these measurements. 

 Casein R was employed and it was measured into wide mouthed 

 flasks in the quantities necessary to yield the various concentrations 

 represented on the curve in Fig. 2 as the experimental points. They 

 were soaked in water, and the required amount of m/1 NaOH was 

 then added to reach pH 9.0 (electrometric) after adjusting to final vol- 

 ume. In calculating the concentration of caseinate, allowance was 

 made for the moisture (2.10 per cent) in casein R. Fig. 2 shows 

 graphically the nature of the concentration effect. It confirms 

 Chick and Martin's results.^ 



Viscosity-pH Measurements of Casein in NaOH, NHiOH, KOH, and 



LiOH. 



The interest in the foregoing viscosity-concentration curve lies in 

 choosing the proper concentration of caseinate solutions for the exten- 

 sive viscosity measurements. By reference to Fig. 2 we find that a 

 9 to 10 per cent caseinate solution is in the region of maximum sen- 

 sibility to differences in reaction and to other factors such as salts, 

 or ion effects. It was decided, therefore, to dissolve 10 gm. of Casein 

 i? or G in 100 cc. of solvent solution in every case. As the alkali was 

 varied in each mixture the water was varied correspondingly so that 

 the total volumes of the two were always 100 cc. This gave solu- 

 tions containing approximately 9 per cent of caseinate. 



For brevity the tables of each individual set of experiments are 

 omitted and the data as far as possible are presented in Fig. 3. Only 



