V. 

 CURIOSITIES OF VOLATILE LIQUIDS. 



i. Freezing produced by Boiling. 



IN a previous section we saw that the 

 quantity of heat required for vaporisation is 

 so great that hot water kept boiling at low 

 pressure, without fire or flame to help it, used 

 up so much heat of its own in boiling, that it 

 was rapidly cooled to a moderate temperature. 

 We have only to continue the process, keep- 

 ing the pressure over the water low enough, 

 and it will boil itself into ice. This has been 

 frequently done ; but to keep the pressure low 

 enough for the formation of ice requires strong 

 sulphuric acid and a good vacuum pump. 



It is easier to get the freezing of water by 

 the boiling of another liquid more volatile than 

 itself, such as carbon bisulphide or ether. 

 Carbon bisulphide is another thing whose 

 presence in the house will be objected to by 

 the powers that be, its odour being such that 

 the exhaust from a motor-car seems in com- 

 parison to resemble the spicy breezes which 

 blow soft o'er Ceylon's isle. We will therefore 

 choose ether, though the smell of ether, too, 

 will be anything but welcome in the house, and, 



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