106 HOW WE USE HEAT 



Kindling Temperature. This shows that different sub- 

 stances take fire at different intensities of heat. The 

 intensity or degree of heat is called temperature. In 

 making matches, the match head contains a compound 

 of phosphorus which ignites at a very low temperature, 

 and a compound that gives off oxygen easily, also pow- 

 dered glass or sand, and glue. By rubbing the match head 

 against a rough surface, enough heat is developed to ignite 

 the phosphorus. In the safety match, the head is made of 

 a substance which burns at a low temperature, while red 

 phosphorus mixed with sand or powdered glass is placed 

 on the box to give it a rubbing surface. The head of the 

 match will not ignite unless it is helped by the phosphorus 

 on the box. 



What Causes Fire ? Many substances like phosphorus, 

 sulphur, and wood when heated to their respective kindling 

 temperatures in the presence of air or oxygen will burn 

 and produce fire. Such materials if burned to give useful 

 heat are called fuels. As we shall see later, gas, coal, oil, 



and wood are fuels. When 

 fuels burn, heat is produced 

 by oxidation. In order to 

 keep a fire burning, we must 

 have oxygen and keep the 

 temperature at or above the 

 kindling temperature. You 



can easily show the effect of 



cooling below the kindling temperature. Copper is a 

 good conductor of heat. Wind a piece of copper wire into 

 a spiral coil ^ of an inch in height, making it large enough 

 to slip easily over the wick of a candle. Light the candle 

 and bring the cold wire down on the wick, the light will 

 go out. But if you light the candle again, then heat the 

 copper coil to red heat and bring it down over the wick, 

 the candle will continue to burn. This shows us that to 



