CHAPTER XI 

 HEAT 



51. Heat is a form of energy which causes all molec- 

 ular activity. It can be produced by the chemical action 

 known as oxidation. Since energy cannot exist apart 

 from matter, heat cannot be thought of except as a 

 condition of matter. The faster the molecules of a sub- 

 stance move the more heat it contains. A piece of iron 

 which is red-hot has more heat in it than when it can be 

 held in the hand. The molecules of the iron are also 

 more active when it is red-hot. 



Heat is made in our homes by burning wood, gas, or 

 coal. When coal is burned in boilers, the heat generated 

 changes water into steam. When gasoline is burned in 

 the engine of an automobile, it generates enough me- 

 chanical energy to drive the machine at high speed. 

 Heat generated by fires is used to melt ores and for the 

 forging of iron. Heat is used to prepare our meals, 

 to make our homes comfortable. It enables plants 

 and animals to grow and thus produce our food. By 

 the oxidation of the food in our bodies we are kept 

 warm and able to move about. All of us have daily 

 experiences with heat in some form. Because of this 

 close relation to daily life it is important that every one 

 should know a few facts and laws concerning heat. Every 

 one should know how to use the instruments for measur- 

 ing the degree of heat of a body and something about the 

 relative amount of heat that given substances will absorb. 



