638 CASEIN VISCOSITY STUDIES 



tions is at once appreciated and for comparative measurements of 

 such protein solutions is probably more nearly representative of their 

 true internal friction because the measurements can be made quickly 

 and with little molestation of their physical structure.^ 



The writer chose the MacMichael viscosimeter which embraces the 

 rotating disc because of its availability to those interested in checking 

 the viscosity values of casein solutions. The double brass bowl 

 furnished with the instrument was replaced by one designed espe- 

 cially for these investigations. The essential difference was the 

 provision for accurately controlling the temperature of the water 

 bath in the outer chamber so that the viscosity measurements could 

 be made at known temperatures. Fig. 1 is a cross-sectional diagram 

 of the bowl used. A represents the removable inner bowl of brass for 

 holding the solution under measurement; B, the outer bowl which is 

 made to fit on the turntable of the instrument; C, the brass supports 

 for the inner bowl; D, a small spiral of nichrome wire wound around 

 a silica tube for the heating unit, and is inclosed in a small tube of 

 pyrex glass; E, a small mercury thermoregulator. D and E are sus- 

 pended in the water bath F and held rigid; the rotation of the bowl 

 by the driving mechanism produces the stirring effect. D and E are 

 further operated through a relay with carbon lamps in series in the 

 circuits. G is the suspended disc furnished with the instrument. 

 (For further comments on the MacMichael viscosimeter seeHerschel.*) 



The values given for the viscosity of the various casein solutions 

 are those obtained by subtracting the viscosity of the solvent at the 

 temperatures measured from the total viscosity of the solution 

 expressed in the divisions marked on the dial of the instrument. 

 They are not absolute values, therefore, but only relative; the same 

 relation would doubtless hold for any type of viscosimeter. The 

 viscosity was measured at 25°C. 



Determination of pH. — In the first instances of the work the reac- 

 tion of the casein solutions was gauged by the use of the sulfoneph- 

 thalein indicators similar to the method since described by Haas.^ 

 Five drops of the casein solution were placed on the inner surface of 



7 Garret, H., Phil. Mag., 1903, vi, 374. 



8 Herschel, W. H., /. Ind. and Eng. Chem., 1920, xii, 282. 

 * Haas, A. R. C, /. Biol. Chem., 1919, xxxviii, 49. 



