COLLOIDAL SUBSTANCES 



281 



alcohol, while the viscosity had risen considerably when the 

 solution contained less than 80 per cent alcohol. 



The opalescence of the alcoholic solutions indicates the pres- 

 ence of aggregates of gelatin, but since the relative viscosity of 

 these alcoholic solutions is low as compared with the viscosity of 

 solutions of gelatin in pure water, and since the alcoholic solutions 

 no longer set to a jelly, the micellae in the watery solution and in 

 the alcohol-water mixture, containing 80 per cent alcohol or 

 more, must be different. The fact that the viscosity ratio is 

 low in the opalescent gelatin-alcohol solutions (which no longer 

 can set to a jelly) indicates that the micellae in this solution 



TABLE LIV. VISCOSITY AT 15C. AFTER THE SOLUTION HAD BEEN KEPT 

 AT 9C. FOR 2 DAYS 



occlude less water than the micellae formed in the solutions of 

 gelatin in water (or in water with not too much alcohol) . 



This is in harmony with the assumption (made in Chap. 

 XIV) that the forces which hold gelatin in solution in pure 

 water or in water with little alcohol, are different from those 

 which hold the gelatin in solution when the critical limit for 

 alcohol has been exceeded. In aqueous solutions or in solutions 

 with much water and little alcohol where setting of gelatin to a 

 jelly is possible, the molecules or ions of jelly are distributed 

 evenly in the solvent probably on account of the strong forces 

 of residual valency between solute and solvent. The large 

 gelatin molecules can adhere to each other only through those 



