430 



when a diminution of the number of large particles to the equilibrium 

 value could take, place. As a, however, lies in the area between 

 M — M and M' — M' , this change does not take place, and the 

 reached condition continues to exist. 



The same thing takes place when the relation between small and 

 large particles is another than a, e.g. h or d. In these cases the 

 change must take place resp. along /; — h' and d — d' ; and when 

 consulting the figure, it is easy to see that the more water will be 

 absorbed bj the gel as there are fewer large particles present at the 

 beginning. These smaller values are found in aqueous gels. Point 

 b" can be reached, as was stated in table V and tig. 4, by heating 

 a gelatin solution with the concentration a' , and allow it to gelatinize 

 again ; transforniation of small particles into large ones taking place 

 later, at the moment that the condition is represented by b" the 

 change of concentration can take place, which then proceeds along 

 /;" — b', till the permaneut state b' has been reached. 



As the gelatin solution was already moi-e dilute before the addition 

 of the water, it has a smaller number of large particles immediately 

 after the gelatification. This implies the fact established above that 

 a gel imbibes the more water as it contained the more water 

 beforehand. 



If on cooling the limit between sol and gel is about reached, the 

 condition along the line e — e' changes on addition of water, so that 

 though a uniform distribution is attained, the condition still differs 

 from the equilibrium by a too great number of large particles. This 

 case is the same as was mentioned in table II: in the part of fig. 5 

 on the right side of the G — G limit the changes are as described 

 above for dilution of a concentrated sol. 



It has already been pointed out that dry gelatin does not "dissolve" 

 in water, but "imbibes", because there are many large particles in 

 this condition. Through a special treatment of a gelatin solution, 

 liowever, the gelatin may be made anhydrous in such a condition 

 that it consists almost entirely of small particles. This condition may 

 be represented by h in fig. 5. If so much water is added to gelatin 

 in this condition that the equilibrium of the system is brought top, 

 the change must be represented by h — h' , and a perfectly homogeneous 

 state of uniform distribution of gelatin and water must also occur 

 at 12°. 



The separation between gelatin and water must not be effected in 

 this case by drying, but by freezing. When a dilute gelatin solution 

 (V4 7o) of i 70° is suddenly reduced to a temperature below the 

 freezing-point, the gelatin very quickly gets into the temperature 



