KETARDATION OF SOLIDIFICATION. 787 



765), and it remains stationary at that point until the 

 ice is completely melted. If a vessel containing water 

 is placed in a cold space, or, in warm weather is cooled 

 by means of a freezing mixture (see page 831), its tem- 

 perature sinks to and remains constant at that point 

 until it is completely frozen. 



The following small table contains the melting points 

 of a few substances ; up to that of lead they may be 

 determined with a common thermometer, but those 

 that are higher can only be found by difficult experi- 

 ments, which cannot be described here. 



Table of Melting Points. 



330 

 321 



' 256 



230 



111 



65 



-39 



A solid body cannot be heated beyond its melting 

 point for example, ice cannot be heated beyond 

 without undergoing liquefaction. But the converse 

 does not hold strictly in the case of liquids, for under 

 particular circumstances liquids may be cooled below 

 their freezing point, that is, below the melting point of 

 the corresponding solid body, without solidifying. This 

 exceptional phenomenon of the c retardation of solidifi- 

 cation/ can only take place if the liquid is cooled very 

 slowly and is at the same time protected from all me- 

 chanical disturbance. On a severe frosty morning in the 

 winter a glass of water may be found liquid in a room 

 of which the temperature has slowly fallen during the 



3 E 2 



