VISCOSITY 205 



increase of viscosity during coagulation of aluminium oxide that 

 the coagulating particles occupy a volume 400 to 500 times as 

 great as that occupied by the dry material itself. 1 This apparent 

 increase of volume he explains through the aggregation of needle- 

 shaped particles, water being occluded between these particles. 

 Smoluchowski apparently did not associate this occlusion of 

 water with the Donnan equilibrium. 



If we adopt this idea for the explanation of the high order of 

 viscosity of gelatin solutions as compared with solutions of egg 

 albumin we reach, the conclusion that the gelatin solutions contain 

 submicroscopic particles of solid jelly , i.e., micellae which occlude 

 relatively large quantities of water, whereby the relative volume 

 occupied by the gelatin in solution is increased, and that such par- 

 ticles are lacking or scarce in the case of solutions of egg albumin. 

 These particles of solid jelly are the precursors of the continuous 

 jelly to which the gelatin solution has a tendency to set. The fact 

 that these particles are lacking or scarce in the case of solutions of 

 egg albumin is connected with the fact that the latter solutions 

 have no tendency to set to a jelly at ordinary temperature and a 

 pH above 1.0. When the pH is below 1.0 and the temperature 

 higher the solutions of crystalline egg albumin set to a jelly and 

 in that case their viscosity becomes of the same high order of 

 magnitude as that of gelatin solutions. 



This assumption would also explain why the pH causes a 

 similar variation in the viscosity of gelatin solutions as in their 

 osmotic pressure, while the viscosity of solutions of crystalline 

 egg albumin shows no such influence of the pH. There must 

 arise a Donnan equilibrium between these submicroscopic 

 particles of solid jelly and the surrounding solution, and this 

 Donnan equilibrium must regulate the amount of water occluded 

 by the submicroscopic particles of solid jelly, floating in the 

 gelatin solution. Since the low order of magnitude of the vis- 

 cosity of albumin solutions excludes the existence of a consider- 

 able number of such submicroscopic solid particles in the solution, 

 it becomes obvious that the Donnan equilibrium cannot manifest 

 itself to any large extent in the viscosity of solutions of this 



1 Quoted from ZSIGMONDY. The paper of SMOLUCHOWSKI is inaccessible 

 to the writer since the number of the journal in which it appeared failed 

 to reach the Institute during and since the war. 



