14S 



Fig. 1(3. Frozen nuck'iis from .salivary gland of Cliironomioi tentan.s. 

 (Original, Buck.) 



is, of curves expressing the course of tlie temperature of 

 a freezing object in terms of time. We shall analyse here 

 briefly the essential characters of freezing curves and, to 

 begin with, those of the freezing curve of water. 



1. Freezing Curve of Water. If a mass of distilled 

 water, perfectly stirred, at a temperature T (above zero), 

 is exposed to a cooling bath at a constant temperature t 

 (below zero), the temperature of the water will drop, in 

 terms of time, according to a curve of the type repre- 

 sented ill Figure 17. This composite curve consists of 

 three limbs : AB, BC, and CD, which represent the course 

 of the temperature before, during, and after freezing, 

 respectively. 



The limbs AB and CD are eooVmg curves. Under ideal 

 conditions, as has been stated in the third section of the 

 Preliminary Chapter (r/. in particular the formula 5), 

 such curves are exponential. 



AB and CD nie not, liowever, identical. The curve AB 



