HOW IS HEAT PRODUCED? 



105 



it gives us warmth and comfort. It means warm rooms 

 in winter ; it makes possible the cooking of raw foods ; it 

 gives us hot water, hot air, and hot foods. Today fire 

 has come to be used in hundreds of ways that the ancients 

 never dreamed of. 



PROBLEM I. HOW IS HEAT PRODUCED? 



If you are a boy or girl scout, you know how to build a 

 fire. First you get some paper or dry leaves, cover with 

 some shavings or thin kindlings, and then place larger 

 sticks at an angle over the other materials so as to make 

 a good circulation of air. When the fire has started, you 

 fan it or blow on it to keep it burning. Evidently a fire 

 must have something that will burn, a good supply of 

 air which contains oxygen, and enough heat to warm the 

 material to what is called its kindling temperature. 



Demonstration 1. Kindling Temperatures. 



Break off and discard the heads of two matches, place the sticks 

 on an asbestos mat. Two inches away from them put a piece of 

 sulphur or brimstone the size of a grain of rice. Melt about 

 20 grams of lead in an iron spoon supported on a stand as shown 

 in the diagram. Do not use 

 more heat than is needed 

 just barely to melt the lead. 

 When the lead melts, pour 

 half of it on the asbestos so 

 that it touches the sulphur, 

 and pour the rest of it so that 

 it covers the end of the sticks. 

 Does either substance take 

 fire? Remelt the lead in the 

 spoon. When it is just melted, 

 turn the gas under it low and 

 stick the end of a match stem 

 into the lead. Does it take 



fire ? Rub the end of one of the sticks in the sulphur so that some 

 of it clings to the stick, and touch it to the lead. Look closely, 

 for sulphur burns with a pale blue flame. Which has the lower 

 kindling point, the sulphur or the wood ? 



