WHAT ARE THE CHARACTERISTICS OF HEAT? 113 





8o1 



7o 



<5C> 



50* 



30 



do" 



-10 



-17.751 



2oo f water 



1 180 

 170' ' 

 160 



1150 



140 



130* 



120 

 .110 



|-l. lT7ormal 

 90 

 [So' 



of ice. A tub of water on 



a cold night gives up heat 



to the air. Fruits and 



vegetables do not freeze 



until the temperature is 



as low as 28 F. ; and 



so tubs of water placed 



in farmers' cellars have 



many times kept fruits 



and vegetables from freez- 

 ing. In changing water 



to steam at 212 F. a large 



amount of heat is stored 



in the molecules of steam. 



This energy may be used 



in cooking, in heating, 



and in the production 



of mechanical energy by 



means of the steam en- 

 gine. When steam con- 

 denses to a liquid, all 



this stored heat is given 



off. That is why a burn 



by steam is so much 



worse than a burn by 



boiling water. Both are 



the same temperature, 



but the steam has more 



heat in it. 

 Freezing and Boiling Temperatures. Water freezes 



and ice melts at 32 F. It seems strange at first to 



think of water and 

 ice at the same 

 temperature. But 



How are clinical thermometers used ? when just enough 



H. & w. sci. i 9 



room 

 temperature 



poiTZ.1, 



of water 



I lo 







If butter melts at 93 F. it will melt at what 

 temperature Centigrade ? 



