JACQUES LOEB 829 



Hatschek,^ Smoluchowski,^ Hess/ and Arrhenius^ have modified 

 Einstein's formula so as to make it valid for any concentration. 

 Arrhenius replaces the linear by a logarithmic formula 



Log ■n - Log 7?(, = d<p (2) 



where (p is again the fraction of volume occupied by the solute in the 

 solution and d a constant, while r? and 770 have the same significance 

 as in Einstein's formula. 



All the formulae agree in one point, namely that the fraction of 

 the volume occupied by the solute in the solution is the main variable 

 upon which the relative viscosity of a solution depends. It has been 

 pointed out by Oden^ and others that in addition to the relative 

 volume occupied by suspended particles the average size of the in- 

 dividual granules in a suspension plays also a role in viscosity. Ac- 

 cording to these theories of viscosity, it should be possible to corre- 

 late the characteristic influence of the hydrogen ion concentration 

 upon the viscosity of gelatin solutions with a variation in the relative 

 volume or the average size of the gelatin particles in solution, since 

 the mass of gelatin in solution remains the same in these experiments. 



The measurement of the viscosity is in our experiments the time 

 of outflow of the solution through a capillary tube and the method 

 of the experiments (already described in a previous paper) was briefly 

 as follows. To 50 cc. of a 2 per cent solution of isoelectric gelatin 

 is added the desired acid, e.g., HCl, in sufficient quantity and then 

 the volume is raised to 100 cc. by the addition of enough distilled 

 water. This 1 per cent solution of originally isoelectric .gelatin is 

 rapidly heated to 45°C., kept at that temperature for 1 minute, 

 and then rapidly cooled to 24°C. (or any other desired tempera- 

 ture). The viscosity is measured immediately after the solution 

 was cooled to 24°C., since on standing the viscosity increases un- 

 equally at different pH. The measurements were all made by deter- 

 mining the time of outflow through a capillary tube. The time of 



5 Hatschek, E., Kolloid Z., 1913, xii, 238; 1920, xxvii, 163. 

 ^ Smoluchowski, M. v., Kolloid Z., 1916, xviii, 190. 

 7 Hess, W. R., Kolloid Z., 1920, xxvii, 1, 154. 



^Arrhenius, S., Meddelanden from K. Vetenskapsakademiens Nobelinstitut, 

 1917, iii, No. 21. 



^ Oden, S., Nova acta regiae Societatis Scienliarum Upsaliensis, 1913, iii, No. 4. 



