JACQUES LOEB 835 



High temperature favors jelly formation in the case of egg albumin 

 and retards it in the case of gelatin. 



These observations corroborate the suspicion that the high order 

 of magnitude of viscosity of gelatin solutions may be in some way 

 connected with the tendency of this protein to set to a gel. 



We do not yet know how the tendency of a protein solution to form 

 a gel can account for the following two facts: first, that this ten- 

 dency is accompanied by a rise in viscosity, and second, that the 

 pH influences the viscosity in a way suggestive of the Donnan 

 equilibrium. One possible answer to this question might be that 

 the formation of a continuous gel by a protein solution may be 

 preceded by the formation of a number of submicroscopic particles 

 of gel, each occluding a considerable amount of water. This oc- 

 clusion of water would cause a considerable increase in the volume 

 of the mass of gelatin and this could account for the rise in viscosity 

 with the tendency to form a gel. The Donnan equilibrium would 

 regulate the quantity of water occluded by each particle and this 

 would account for the influence of pH. The idea of such a pos- 

 sibility gave rise to the following experiments on the viscosity of 

 suspensions of powdered gelatin in water. 



III. Influence of Volume of Powdered Gelatin on Viscosity. 



When we suspend finely powdered gelatin in water of a sufficiently 

 low temperature, and measure the viscosity of such suspensions we 

 find that they may have even a higher viscosity than gelatin solu- 

 tions of the same concentration of gelatin and that the pH influences 

 the viscosity of the suspension in the same characteristic way as that 

 expressed in the curves of Fig. 1. 



0.5 gm, of Cooper's powdered commercial gelatin of a pH of about 

 6.0 was added to 100 cc. of water containing varying amounts of 

 HCl. The particles had uniform size (going through Sieve 100 but not 

 through Sieve 120), but their shape was extremely irregular. They 

 were left in the solution several hours at 20°C., and then their time 

 of outflow through a capillary tube was ascertained at 20°C. The 

 time of outflow of water through the viscometer at this temperature 

 was 24 seconds. It was essential to stir the suspension thoroughly 



