92 DONNAN EQUILIBRIUM AND VISCOSITY 



colloid chemistry, which assumes that proteins form no true solutions 

 but suspensions or emulsions. According to our view protein salts 

 form, as a rule, true solutions consisting of isolated protein ions and 

 molecules, which, however, may contain in addition solid fragments 

 occluding comparatively large quantities of water. These latter 

 particles of solid material are responsible for both the comparatively 

 high viscosity of solutions of certain proteins, and for the influence 

 of electrolytes on viscosity. 



6. It is of interest to see whether or not Arrhenius's formula can 

 account for the influence of electrolytes on the viscosity of casein 

 suspensions. If this were the case, the curves representing Log 



— should run parallel to curves representing the relative volume 

 occupied by the casein in the solution. We get the values of Log — ' 



from our observations of the relative viscosity which give us — , and 



we can calculate the volume from the measured volume of the sediment 

 plus the calculated volume of the casein in the supernatant liquid. 

 The latter value we obtain by deducting the dry weight of the sediment 

 from the (known) dry weight of the whole mass of casein put into 

 the water (1 gm. powdered casein, dry weight = 0.87 gm.) , and assuming 

 that the casein in the supernatant liquid consists exclusively of sus- 

 pended particles. This is approximately correct for a 1 hour experi- 

 ment at 20°. The ordinates in Fig. 1 1 represent the values for vol- 



ume thus corrected and the values for log ~ while the abscissae are 



the pH of the suspensions. The two curves are almost parallel. 



It should be stated that these corrected volumes of casein include 

 a certain amount of water between the granules. We are, however, 

 in this case not concerned with the absolute but the relative volume 

 occupied by the casein. 



When we add NaCl in different concentrations to a casein chloride 

 solution we notice that the viscosity is diminished as it is in the case 

 of solutions of gelatin chloride. R. F. Loeb found by microscopic 

 observation that this diminution of viscosity was accompanied by a 

 diminution in the degree of swelling of the individual particles of 

 casein which ran parallel to the depression of the viscosity. 



