VV2 



crystallization velocity was slig-litly increased by the sub- 

 stances dissolved. 



Callow (1925) stndied the action of various concentra- 

 tions of gelatin on the growth of ice crystals in gels of that 

 substance. He found that 1% gelatin reduces the rate of 

 crystallization of water to about half its value, IV/c renders 

 the velocity 45 times lowei-, and 3% renders it 350 times 

 lower. 



The velocity of crystallization in biological material is 

 entirely unknown. 



B. THE PHASE SEPARATION 



1. Solutiojis and Sii.speusions. It is \\q\\ known that, in 

 the freezing of a solution, w^ater separates from the solute 

 and freezes alone, while the solution becomes more con- 

 centrated. Some biologists have attempted to observe this 

 separation under the microscope. Molisch (1897) says 

 that, by mounting drops of 10 /'r solutions of sodium 

 chloride, potassium nitrate, magnesium sulfate, cobalt 

 chloride, etc., on microscope slides and exposing them to 

 low temperatures, he could see the water freeze out in 

 several crystallization centers and form ice masses which 

 wedged betw^een them the concentrated salt solution; the 

 latter, in its turn, crystallized in a different form of crystal. 

 This separation of w^ater w^as seen in the same manner in 

 solutions of dyes. 



According to Goeppert (1830), when plants which con- 

 tain a milky sap, for example, RJius, Euphorbia, Papaver, 

 Ficus, are frozen, the sap solidifies into transparent ice. 

 However, the yellow^ sap of Chelidonium gave yellow ice. 



]\Iolisch (1897) reported that, wOien he put to freeze at 

 a temperature of - 6°, on the stage of the microscope, the 

 milky sap of the fig tree, Ficus elastica (a substance which 

 consists of an aqueous solution and of droplets of rubber), 

 he could see the w'ater freeze out into ice crystals wiiich 

 separated row's of particles of rubber. On thawing, the 

 two phases mixed again. Similar experiments were made 

 with suspensions of carmine, indigo and gum and the same 



