114 EFFECTS OF HEAT. 



Q. Wliy does a KETTLE sing, when the boiling 

 water begins to COOL again ? 



A. Because the upper surface cools 

 first ; and the steam (still rising from the 

 lower parts of the kettle) is again 

 entangled, and escapes fitfully. 



Q. Why does BOILING WATEB SWELL ? 



A. Water (like air) expands by heat. 

 The heat of the fire drives the particles 

 of water further apart from each other ; 

 and (as they are not packed so closely 

 together) they take up more room; or 

 (in other words) the water swells. 



Q. What is meant when it is said, " that HEAT 

 drives the PARTICLES of water further APART from 

 each other." 



A. Water is composed of little glo- 

 bules, like very small grains of sand ; the 

 heat drives these particles away from 

 each other; and (as they then require 

 more room} the water swells. 



Q. Why does BOILING WATER BUBBLE ? 



A. Water contains air ; and (as the 

 water is heated) the air is driven out, and 

 raises a bubble in that part of the water 

 which resists its escape. 



