JACQUES LOEB 91 



to be of the order of magnitude of about 12,000 a solid gel of 1 per 

 cent originally isoelectric gelatin contains over 60,000 molecules 

 of water to 1 molecule of gelatin. It is out of the question that 

 such masses of water could be held by the secondary valency forces 

 of the gelatin and water molecules. Swelling casein particles occlude 

 much less water and for this reason the viscosity of casein chloride 

 solutions never becomes as high as that of gelatin solutions, containing 

 equal masses of protein per 100 cc. of solution. 



It is well known (and we have made use of the fact earlier in this 

 paper) that the viscosity of a gelatin solution that had been heated 

 to 45°C. and is allowed to stand at 20° increases steadily even if the 

 concentration is not high enough to permit the setting of the solution 

 to a jelly. This increase in viscosity on standing seems to be caused 

 by the gradual increase in the number of solid particles of jelly due to 

 the collision of gelatin molecules or ions, these solid particles occluding 

 water and thus increasing the apparent volume occupied by the gelatin 

 in the' solution. The gradual formation of solid particles of jelly 

 from isolated molecules is most rapid at the isoelectric point and is 

 retarded by the addition of acid; while the addition of acid increases 

 the swelling of those particles of jelly which already exist in the 

 solution. It is well to keep in mind that the addition of acid to a 

 solution of isoelectric gelatin has thus two opposite effects on the 

 viscosity of gelatin solutions. 



According to Zsigmondy* Smoluchowski has explained (in a paper 

 which has not been accessible to the writer) the increase in the 

 viscosity through coagulation of a solution of aluminium oxide 

 by the assumption of an occlusion of liquid between the particles. 

 Smoluchowski calculates from the increase of viscosity during coagula- 

 tion of aluminium oxide that the coagulating particles occupy a volume 

 400 to 500 times as great as that occupied by the dry material itself. 

 This apparent increase of volume he explained through the aggregation 

 of needleshaped particles. It would be of interest to test whether 

 or not the volume of these particles and the viscosity of the suspension 

 of aluminium oxide is also controlled by the Donnan equilibrium. 



We are therefore led to a conception of the nature of protein solutions 

 which is somewhat different from that current in the literature of 



^ Zsigmondy, R., Kolloidchemie, Lcipsig, 2nd ed., 1918, 98. 



