72 HEAT AND ENERGY 



81. Changes of Volume. When, without more matter 

 being added, a body grows larger, it is said to expand ; 

 when, without losing any of its particles, a body grows 

 smaller, it is said to contract. As a general rule, masses 

 expand when they are heated arid contract when cooled. 



Experiment 63. Secure a hollow metal ball which exactly fits 

 into a ring (Fig. 56). Heat the ball, and see if it can be forced 

 through the ring. Heat both ring and ball and try them again ; 

 they should fit. Cool the ball and heat 

 the ring. How do they fit now? 



Carefully measure a long iron nail. 

 Heat it thoroughly and measure again. 

 Is it longer or shorter? 



Experiment 64. Fill a test tube with 

 water and fit a stopper lightly into its 

 mouth. Heat the water and note the re- 

 sult. Explain this. (Do not crowd the 

 stopper or heat the water too highly.) 



Fill a long narrow tube with hot water ; 

 FIG 56 let it cool to an ordinary temperature and 



note any change in volume. 



Experiment 65 Arrange a tube so as to run through the 



stopper of a flask or bottle, into a vessel of water, as in Fig. 57. 

 Heat the flask and explain what you observe. What is in the 

 flask? What change does it undergo? 



Now remove the heat, watching the tube carefully. As the 

 flask cools, what change takes place in its contents? Try to 

 account for what you notice. 



82. Uses of Expansion and Contraction. From these 

 experiments we see that liquids and gases may expand 

 and contract as well as solids. The value of this will 

 be seen when we study convection ( 91). In the 

 case of solids this principle is commonly used to good 



