glass, soaj), t'tc, llic waliT wliicli liad separated from llif 

 gelatinous mass during freezing was almost free from the 

 dissolved sn])stanc'e. After complete thawing, one could 

 still see the inhomogeneous mass to consist of clumps of the 

 jelly and of a dilute solution. 



The freezing of gelatin gels has been the object of 

 extended studies by Moran (1926) and Hardy (1926). 

 They observed three types of freezing: the compact sur- 

 face freezing, the intermittent freezing and the dis- 

 seminated freezing. 



Compact S u r face F r e e z i n g. ]\Ioran exposed 

 to sub-zero temperatures discs of gelatin gels of various 

 concentrations, measuring 3 mm. in thickness and 15 mm. 

 in diameter. With water contents higher than 34^ and 

 temperatures from - 3° to - 19°, ice formed around the 

 discs, while the inside gelatin core became more concen- 

 trated. The authors removed the ice shells and determined 

 the amount of water so frozen and the maximal gelatin 

 concentrations reached by the core. They found that these 

 concentrations varied from 54.3yr to 65.2% when the tem- 

 peratures varied from -3° to -19°. If a preparation 

 frozen at - 3° was put consecutively at lower temperatures 

 (even in liquid air) and brought back to -3°, the concen- 

 tration was 54.37^ , that is, the same as in gelatin frozen 

 at -3°. 



With very high water contents and low freezing tem- 

 peratures, for example 88% and - 11°, there were, in ad- 

 dition to the surface freezing, some centers of crystalliza- 

 tion formed inside of the gelatin core where one could find 

 places containing a "sponge of gel" (Fig. 10, A). 



Briefly, when freezing was slow, water separated from 

 the gel and came to the surface to solidify in a compact 

 mass of ice ; when freezing was rapid or when there was 

 great abundance of water, crystallization took place inside 

 the gel. 



Intermittent F r e e z i n g. ^loi-an, studying the 

 congelation at - 11° of gels containing 62''/ water, observed 

 granulations, 2 to 3 mm. in diameter, of congealed material. 



