8 



FIG. 51. 



Metal Ball and 

 Ring. 



CHAPTER IV 



HEAT 



61. Heat and Matter. It is a familiar fact that most 

 bodies increase in volume as they grow hot, and shrink as 

 they grow cold. Thus, a brass ball (Fig. 51) 

 which just goes through a brass ring when cold 

 will not go through it when hot. If, however, 

 the ring, as well as the ball, is heated, then the 

 ball will go through it. A liquid, like water or 

 mercury, which just fills a flask at the tem- 

 perature of the room, overflows when heated, 

 but does not fill the flask when cooled. A gas 

 behaves in the same way. Thus, if a flask of 

 air is heated (Fig. 52), some of the air escapes; but the 

 volume of the air contracts when the flask is cooled. 



How can we explain 

 these changes of volume? 

 It is hard to see how the 

 volume of a body can 

 change unless the matter 

 of the body is broken up 

 into particles, with spaces 

 between them. Then, 

 if the volume becomes 

 smaller, as is the case 

 when a body is cooled, we 



Heating expands air'cooling makes it shrink. Can explain the shrinkage 



59 



FIG. 52. 



