186 



B"B' 



Fig. 28. SulK-ooling curvo of a liquid under ideal conditions. Abscissae: 

 time; ordinates: teni])eraturi'. 



tiiiiies its course, past the line of the freezing point BB', 

 down to the suhcooling point C. It then rises abruptly 

 to the freezini*' point B'. The subcoolino' curve consists of 

 2 limbs AC and CB'. The temperature interval CB" is 

 the degree of suhcooling. 



AC is an ordinary exponential cooling curve. 



Concerning the curve (/B' we shall discuss briefly two 

 questions : that of the maximum reached by the curve and 

 that of the calculation of the freezing-curve-areas (see 

 above, under "Freezing Curves") in cases in whicli there 

 is some sub-cooling. 



The problem of the maximum reached by the rising tem- 

 perature can be treated as follows. Three factors influ- 

 ence the temijerature, one of which tends to raise the 

 maximum whik' the other two tend to lower it. These 

 three factors are: 1. The amount of heat Qi liberated by 

 freezing, during the time B"B' ; 2. The amount of heat Q- 

 withdrawn by the cooling bath, during the same time. 3. 

 The amount of heat Q-, used for bringing up the tempera- 

 ture of the material from the suhcooling point. Qi is 

 either equal to the sum Q- - Q:., or it is smaller or larger 



