UNEQUAL EXPANSION 



47 



expands the more, brass or iron? Let the bars cool and 

 see if they are straight, as at first. 



b. Put the bars in salt and ice and let them become 

 cool. Which way do they bend? A metal which, when 

 heated, expands faster than another metal, also contracts 

 faster when cooled. The unequal expansion of metals 

 is made use of for practical purposes. The illustration 



shows a strip of two metals which 



are joined together their entire 



length, and then bent into the 



shape of a shepherd's crook. As 



the metals become warmer, due to 



the increased warmth of a room, 



the metal on the right expands 



more than the other metal and 



causes them both to bend to the 



left. This bending brings together 



the double metal and a screw 



which act like an electric push 



button. Instead of ringing a bell, 



however, the electricity changes 



the dampers of the furnace so 



that the air of the room will not 



be so warm. When the room 



cools off, the metals bend the 



other way and cause the electric- 

 ity to open the dampers again. 



The machine is called a heat 



regulator because it regulates 



the amount of heat which a 



room receives. 



Cut supplied by the Jewell Heat Regulator Co. 



