421 



with one of Ihe light intensity. It is therefore possible to consider 

 an increase of the viscosity as a proof that large particles are formed, 

 whereas disappearance of large particles will always manifest itself 

 by a decrease of the viscosity. 



Hitherto experiments have been discussed,' in which the concen- 

 tration was kept constant. I will now proceed to examine the relation 



=f{T,c.) for constant temperature. In contrast with the 



preceding ones these experiments have all been made with a solution 

 of gelatin in water without any addition. Beforehand the gelatin 

 used was freed from all salts etc. in water, and dried over H^SO^ 

 in vacuo. 



The simplest case that we meet with is the dilution of a gelatin 

 solution which is a sol. We started from a 72 "/o solution, which 

 was nicide at 70°, and was then kept at 20° for live days. During 

 this time a considerable increase of the viscosity was found, from 

 which it might be inferred that the number of large particles increased. 

 This solution was diluted at the same temperature with an equal 

 amount of water to V4Vo> ^^^ then the change of its viscosity was 

 determined from time to time. It appeared that a decrease took 

 place. This may be represented in the following way. In fig. 2 the 

 viscosity is indicated on the ordinate, and the concentration on the 

 abscissa. N — N is the equilibrium line, which lias been drawn so 



c>[cCAi^/ru. 



S^ U'C^fcV. 



Fig. 2. Influence of the dilution of a gelatin solution 



on the viscosity. 

 N N is the equilibrium line, 

 the arrows indicate in which direction a change 



takes place. 



