EXPANSION. 109 



Q. When, bottled ALE and PORTER is set before 

 a FIRE, why is the CORK FORCED OUT sometimes ? 



A. If the bottle be not quite full, there 

 will be air between the liquor and the 

 cork ; this air (expanded by the heat of 

 the fire) forces out the cork. 



Q. Why does ALE or PORTER FBOTH more, 

 after it has been set before the fire ? 



A. The froth of ale or porter depends 

 upon the pressure to which it is subjected j 

 and as the air (between the liquor and 

 the cork) is expanded by the heat, it 

 presses against the liquor, and increases 

 the quantity of froth. 



Q. Why is the FROTH of ale and porter 



INCREASED by PRESSURE ? 



A. Because the liquor absorbs carbo- 

 nic acid so long as it is under pressure; and 

 the moment that the pressure is removed, 

 the carbonic acid escapes in foam or froth. 



Q. When a boy makes a BALLOON, and sets 

 Jire to the cotton or sponge (which has been steeped 

 in spirits of wine), why is the balloon INFLATED, or 

 blown out ? 



A. The air inside the balloon is 

 expanded by the flame, till the whole 

 balloon is blown out without a crumple. 



