116 



GENERAL SCIENCE 



is also true of water which becomes colder than 39. Hence, in deep 



lakes the water will seldom reach a temperature below or above 



39 F. at the bottom. 



It will be easily seen by the diagram that water at 34 F. and 



water at 44 F. have the same weight. What other degrees have 



corresponding weights ? Water when 

 freezing expands so rapidly that a cubic 

 foot of water at freezing point 32 F., 

 changing from water into ice at 32 F., 

 changes weight from 62.416 pounds to 

 57.5 pounds per cubic foot. That is, 

 ice weighs about 5 pounds less per cubic 

 foot than water. 



If this expansion did not occur, ice 

 would not float, but would sink to the bot- 

 tom of our lakes and rivers, freezing solid 

 all bodies of fresh water. It would be 

 impossible to get heat enough even in the 



hottest parts of the earth to thaw out the lakes during the summer. 

 Expansion of Metals and Solids. With few exceptions nearly 



all metals and solids expand with heat. Telephone and telegraph 



FIG. 90. When all the water 

 in the lake reaches the 

 temperature of 39.2 F., it 

 is as heavy as it will become 

 by lossof heat. As the water 

 near the surface continues 

 to lose its heat, it grows 

 lighter and remains at the 

 surface until changed into 

 ice. 



FIG. 91. Why has 

 the top of the bottle 

 been forced out? 



FIG. 92 



wires sag more during a hot day than during a cold day because of 

 the extra length caused by expansion. A mile of copper wire will 

 be 100 inches longer on a hot day in summer than on a cold day in 

 winter, and a mile of aluminum wire will expand 200 inches. The 



