137 



tlic gel was now occuijied by a large iinmbcr of clear sijlieri- 

 eal spaces each about 3 micra in diameter and arranged in 

 rows." {Cf. Fig. 10, D). 



Hardy called this kind of freezing "disseminated freez- 

 ing. ' ' The spherical masses that he observed had a diam- 

 eter as large as 20 micra. He showed, furthermore, that 

 the spheres consisted of pure ice. To explain their forma- 

 tion, he suggested that they had started as crystallization 

 centers, but that, owing to the rapid cooling, the viscosity 

 of the material was soon high enough to prevent their 

 further grow^th. 



As it was said above, with high w^ater contents and very 

 slow freezing, some centers of crystallization are formed 

 within the gelatin gel and there result irregularly dis- 

 tributed crystalline spots wdthin the remaining non-crystal- 

 line gelatin. It seems that this type of freezing differs 

 from the one just described under the name of disseminated 

 freezing only by the shape of the crystals, w^hich were 

 prismatic in the first instance and spherical in the second. 

 In both cases, the crystals are of pure ice, by opposition to 

 what happens in the case of intermittent crystallization. 

 So, w^e shall distinguish two types of disseminated freezing 

 according to the shape of the crystals, and we shall call 

 "Granular disseminated" the type in which the crystals 

 are spherical and "Irregular disseminated" the other. 



The researches of ^loran and Hardy can then be sum- 

 marized in the following points : 1. The irregular dis- 

 seminated freezing was observed mostly in gels of high 

 water content (88^^ w^ater) but also wdth more concen- 

 trated gels if freezing was moderately rapid ; 2. The gran- 

 ular disseminated freezing occurred with very rapid cool- 

 ing (in liquid air and at -19°) ; 3. Surface freezing took 

 place over a large range of w^ater contents but it required a 

 slow cooling; 4. Intermittent freezing extended also over 

 a large range of water content and it occurred at intermedi- 

 ate cooling velocities (with an external temperature from 

 -6° to -13.5°). 



]\[oran pointed out another important fact, namely, that 



