840 



DONNAN EQUILIBRIUM AND VISCOSITY 



gelatin varied in the neighborhood of 3.0; the temperature was 20°C. 

 After 2^ hours, when the Donnan equilibrium between the par- 

 ticles and the surrounding solution was supposed to be established, 

 the viscosity of each suspension was measured at 20°C. and the vol- 

 ume occupied by the suspended particles of gelatin was ascertained 

 in the manner described. It was found that the addition of salt 

 diminished the relative volume of the gelatin particles and the vis- 

 cosity in a similar way (Fig. 6). The observed volume of the solu- 

 tions containing little or no salt was probably a little too great on 

 account of incomplete filtration. 



The measurement of the pH of the gelatin solution and the outside 

 solution showed that the addition of salt diminished the difference 

 between the two, as Donnan' s theory demands (Table III). 



TABLE III. 



SUMMARY AND CONCLUSION. 



1. Gelatin solutions have a high viscosity which in the case of 

 freshly prepared solutions varies under the influence of the hydrogen 

 ion concentration in a similar way as the swelling, the osmotic pres- 

 sure, and the electromotive forces. Solutions of crystalline egg al- 

 bumin have under the same conditions a comparatively low viscosity 

 which is practically independent of the pH (above 1 .0) . This differ- 

 ence in the viscosities of solutions of the two proteins seems to be 

 connected with the fact that solutions of gelatin have a tendency 

 to set to a jelly while solutions of crystalline egg albumin show no 

 such tendency at low temperature and pH above 1.0. 



2. The formulas for viscosity demand that the difference in the 

 order of magnitude of the viscosity of the two proteins should cor- 



