CHAPTER XXVIII 



SOME EFFECTS OF HEAT ON BODIES 



FROM our previous experiments we know that heat 

 aids in the evaporation of liquids. 



Have some of the pupils measure a piece of heavy iron 

 wire, a long nail, or bolt in the following way: Lay the 

 nail on a piece of pine board and make a scratch across 

 the width of the board at each end of the nail. Now place 

 the nail on a shovel on top of a glowing bed of coals in the 

 stove. Heat it till it is red hot. Now lay it on the board, 

 trying to get it exactly between the scratches. What 

 effect has the heat had upon it? Put it out of doors till it 

 is cold. Try it again on the scratched board. What is 

 the effect of cooling it? Most solids act as this piece of 

 iron did. They expand when heated and contract when 

 cooled. Think of some practical illustrations of this. 

 Why heat a tire before setting it on the wheel ? Why are 

 bolts which are to hold together two walls often heated red 

 before they are put in, and the nuts tightened as the bolts 

 cool? 



Do liquids expand when heated ? Fill a tin cup level 

 full of water, heat it slowly. What happens ? Put a piece 

 of glass tubing through a rubber stopper. Fill a glass 

 flask full of water. Put in the stopper. The water should 

 now show in the tube above the stopper. Slowly heat the 

 flask. What indication have you that water expands with 



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