Gelation in Beversihle Colloidal Systems. 



105 



that when dried gelatine absorbs water heat is liberated, but when 

 gelatine saturated with water is dissolved in water heat is absorbed. 



I have verified the general form of the curve AB in a way which 

 eliminates all the errors due to the expression of the fluid phase 

 from the gel. A cylindrical column of gel 15 cm. high was 

 divided by two vertical cuts at right angles into four equal pieces. 

 Four stoppered glass vessels were taken of the same size and shape, 

 and in each one of the pieces was placed and just covered with water. 

 Two of the bottles were kept at 14° for a week, and two at 44° ; the 

 water in both was found to have dissolved some of the agar, and to 



30 



a8 



Fig. 1. 



12 3^5 d A^dr. 



B'B 



c c' 



H^O 100 99 36 97 96 93 34 



contain per 100 grammes of the solution 0*50 gramme and 0*12 gramme 

 of dry agar respectively. 



The curves AB, DC continued upwards will meet at some point 

 which marks the consolute temperature for agar and water. I have 

 attempted to fix this point by observing the changes in the intensity of 

 the beam of polarised light scattered normal to the ray when parallel 

 light is passed through a gradually cooling hydrosol. The observa- 

 tions, which are still in an initial stage, have so far failed to fix the 

 point. 



The study of ternary systems under the microscope makes it probable 

 that as the curves AB, DC are continued upward they reach a point 



