113 



Fig. 4. Formation of crystallization nuclei in a film of gelatin solution 

 enclosed between two thin glass plates and immersed in a bath at - 25°. The 

 lower left-hand corner was the first j)art of each of the two preparations to be 

 immersed in the bath. (Original, Luyet and Gehenio.) 



type represented in Figure 5. Unfortunately, little is 

 known of the course of such curves for water, aqueous 

 solutions and aqueous colloids. 



Some physical chemists consider the congelation of 

 water not as the crystallization of a liquid but as the pre- 

 cipitation of a solute from a saturated solution. What we 

 ordinarily call water would be a solution of ice (a trihydrol 



40 



20 



Fig. 5. Xumber of crystallization nuclei formed in piperine at various sub- 

 cooling temperatures. (Curve drawn from Tammann's data, 1925.) Abscis- 

 sae: temperatures (the melting point of piperine, 135°, being the origin) ; or- 

 dinates : number of nuclei. 



