SOME EFFECTS OF HEAT ON BODIES 243 



cup level full of melted paraffin? Will a piece of solid 

 paraffin dropped into a cup of liquid paraffin sink or swim ? 

 Why? 



Do all substances contract as they solidify? If the 

 weather is freezing cold, set a tin cup level full of water in 

 a saucer and set both out of doors overnight. Has the 

 water contracted or expanded as it cooled and solidified? 

 Why will freezing water break a pitcher or glass ? Which 

 is heavier, ice or water ? Put a piece of ice into a cup of 

 water. Does it sink or float ? 



Water then differs from the other substances studied 

 in that it expands when it solidifies or freezes. But we 

 found by means of a previous experiment that water ex- 

 pands when heated, and contracts when cooled. There 

 must,, therefore, be a certain temperature at which water 

 reaches its greatest weight or density. This temperature 

 is 4 Centigrade or 39.2 Fahrenheit. If then water is 

 heated above 39.2, what does it do? If it is cooled below 

 this temperature what does it do? If you had a cupful 

 of water whose temperature was 70 F. and you heated the 

 water, would it expand or contract ? What if you cooled 

 it? At what temperature would it stop contracting and 

 begin to expand again? 



All liquids do not act as water does, but continue to 

 contract until they are solidified. Can you think of any 

 practical use that is made of this fact ? The thermometer 

 is constructed upon this principle. It is a small tube filled 

 with mercury or alcohol. When the temperature is warm 

 what does the mercury do ? When the temperature is cool 

 what does it do ? By the expansion and contraction of the 

 mercury we are able to measure temperature. 



