PHYSICAL PARADOXES. 



to sweep away bodily the whole mass of air sur- 

 rounding the liquid, and the saturating vapour 

 with it, so that the liquid is enclosed in a fresh 

 quantity of air with abundance of empty spaces 

 into which its molecules can move with as much 

 greater facility as we can into a 'bus or a train 

 when it is not already full. 



In this way the artificial blast blown into 

 the ether so facilitates and hastens its volatilisa- 

 tion that the process may be considered equiva- 

 lent to boiling, and the heat used up in it 

 and derived from the ether itself is so great 

 that before the thimble is empty it has be- 

 come cold enough to freeze the water beneath 

 it, so that the ice cements the thimble to the 

 board. 



It has been mentioned that the difficulty in 

 getting water to boil itself into ice is the neces- 

 sity of using a vacuum pump and apparatus 

 for keeping strong sulphuric acid stirred in a 

 vacuum. But the system introduced by 

 a well-known firm of supplying siphons and 

 capsules for aerating liquids at home, provides 

 a very convenient apparatus for showing this 

 effect with another liquid. 



If there is no such siphon in the house, 

 and it is not desired to have one, the head 

 alone (fitted with pricker and rubber washer 

 for piercing, but without the glass tube and 

 its connections) can be had from many 

 chemists for less than a shilling, and a box 



1 68 



