838 



DONNAN EQUILIBRIUM AND VISCOSITY 



- 1 



and may try to calculate the value of c = 



^0 



from our observa- 



tions. Since ip is the ratio of the volume of the gelatin to the 

 volume of the solution and the latter is 100 cc, we have to multiply 



the value 



^0 



-1 



by 100 to obtain c. 



volume of gelatin 

 Table II shows the results of such a calculation. 



TABLE II. 



Considering the fact that the gelatin particles are not perfect 

 spheres, as Einstein's theory demands, and considering the further 

 fact that the measurements of the volume of gelatin are crude, it 

 is surprising that where the volume of the gelatin is small the con- 

 stant c is so near that expected on the basis of Einstein's formula, 

 namely 3.1 instead of 2.5. Larger values are found (from 4.2 to 

 6.0) when the swelling of the gelatin particles becomes too large to 

 permit the strict application of Einstein's formula. In all proba- 

 bility a second variable enters in this case, namely the large size of 

 the individual granules. We shall see in a later paper that in the 

 case of suspensions of gelatin particles the viscosity is not only a 

 function of the relative volume of the suspended particles but also 

 of their size, increasing (for the size used in our experiments) with 

 the size. This might account for the fact that in Table II the value 

 of c varies with the size of the particles. 



