JACQUES LOEB 



837 



These experiments prove, first, that a suspension of powdered gel- 

 atin in water shows the same variation in viscosity with the variation 

 of the hydrogen ion concentration as does a solution of freshly pre- 

 pared gelatin; and, second, that the relative volume of the suspended 

 particles varies in a similar way as the viscosity (Fig. 5). In this 

 case there is little doubt that the variations in the volvune of the 

 suspended particles of gelatin under the influence of the pH are due 

 to the existence of a Donnan equilibrium between the particles and 

 the surrounding water, since we have already shown in a former 

 publication that there exists a difference in the pH of the solid par- 

 ticles of powdered gelatin and the supernatant water and this fact 

 was further corroborated in these experiments (Table I). 



TABLE I. 



Donnan Equilibrium Between Suspended Particles of Gelatin and Supernatant 



Water After 20 Hours. 



0.5 gm. of Gelatin Suspension in 100 cc. H^O Containing Various Amounts of 

 HCl at Temperature of 20°C. 



pH of gelatin 



particles , 



pH of supernatant 



water 



4.79 

 4.74 



4.62 

 4.30 



4.33 

 3.95 



4.17 

 3.76 



3.93 

 3.55 



3.60 

 3.21 



3.26 

 2.95 



3.02 



2.77 



2.68 

 2.56 



2.39 

 2.31 



2.16 

 2.10 



2.07 

 2.02 



1.80 

 1.75 



The point which is of importance is the question of the applica- 

 bility of Einstein's formula to these experiments 



= \-\-2.S<P 



The fact that the shape of the suspended particles of gelatin is very 

 irregular and that the average size of the individual particles plays 

 also a role must warn us not to expect too strict an applicability of 

 the formula in our case; and we may expect to obtain slightly differ- 



ent values than 2.5 for the constant. Since we can measure - as 



Vo 



well as <p directly in our experiments, we may write Einstein's equa- 

 tion in the form 



V 



■Oq 



— l=C<p 



