UNEQUAL EXPANSION 



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 

 pre 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. 



