HEAT 



131 



causes the body as a whole to become larger, or we say 

 expansion has taken place. 



Many materials expand irregularly when heated, but 

 rubber is the only material which contracts when heated. 



Experiment 32. The ball and ring ex- 

 periment is a classical one (Figure 113). Given 

 an iron ring and an iron ball that will just pass 

 through it at ordinary temperature. Heat the 

 ball and see if it will now pass through the 

 ring. In what direction has the ball ex- 

 panded? Now heat the ring and see if the 

 ball will pass through. Cubical expansion is 

 expansion in every direction. Linear expan- 

 sion means simply an increase in length. 



Experiment 33. Arrange an iron rod as 

 shown in Figure 114 so that one end rests on 

 an ordinary knitting needle attached to a 

 pointer. As the rod is heated it increases in length. This expan- 

 sion is shown by the movement of the pointer. 



FIG. 113. The Ball 

 and Ring Experiment. 



FIG. 114. Expansion of Solids. 

 As the rod expands or contracts the pointer moves correspondingly. 



Expansion of Liquids. Liquids expand as we have 

 already seen in the mercury and alcohol thermometers. 



Experiment 34. Take a flask and fit it with a two-hole rubber 

 stopper. Pass a glass tube about sixteen inches long through one 

 hole of the stopper and a thermometer through the other hole. 

 Fill the flask with water and place the stopper in the flask so that the 

 water rises a fraction of an inch above the base of the stopper. 

 Now heat the water slowly, noting temperatures and heights of the 

 water in the tube. A scale may be improvised from an ordinary 

 meter bar as shown in Figure 115. Draw a curve of the expan- 



