74 FIRST YEAR COURSE IN GENERAL SCIENCE 



reason alcohol thermometers are used in cold climates. 

 Because alcohol is cheaper than mercury, colored alcohol 

 is much used in ordinary thermometers. (LABORATORY 

 MANUAL, Exercise X.) 



76. Conduction. Whenever the temperature of a body 

 is higher than that of its surroundings, it gives out some of 

 its heat. There are three methods by which heat is dis- 

 tributed: conduction, convection, and radiation. 



If two bodies of different temperatures are in contact, 

 after a time the temperature of the colder body will rise 



FIG. 31. CONDUCTION OF HEAT 



Phosphorus takes fire at a low temperature. 1. If a piece of phosphorus 

 is placed on a strip of metal and the metal is heated at a distance from it, 

 the phosphorus soon burns. Why? 2. Why in Fig. 31 do not both 

 pieces ignite at once? 



and that of the warmer will fall. If one end of a cold 

 iron rod is heated in a fire, the end in the fire will soon 

 become red-hot and the other end warm. The end 

 farther from the fire is heated by conduction. Heat has 

 passed from molecule to molecule until the one farthest 

 from the source of heat has received it. After the source of 

 heat is removed, the distribution continues until all parts 

 of the bar are of the same temperature. The iron is said to 

 be a conductor. All the metals are heat conductors. 



