Fire and Heat 113 



changes in your own locality? In the Pacific Northwest? In the 

 Mississippi valley region? 7. What do you imagine would be the 

 effect upon agriculture in these regions? 8. You may shape a piece 

 of clear ice like a reading glass and the sun's rays passing through it 

 will heat one's hand very noticeably before the ice shows much sign 

 of melting. Explain. 



V. PRODUCTS AND MATERIALS OF COMBUSTION 



44. Oxygen in all products of combustion. It has been 

 learned that when such metals as lead and iron or such sub- 

 stances as phosphorus and sulfur are burned or oxidized, new 

 substances called compounds are produced. Because of the 

 presence of oxygen in these compounds or products of combus- 

 tion, they are called oxids, such as iron oxid, lead oxid, sulfur 

 dioxid and so on. You will find this to be true of any product 

 of combustion, that is, it is an oxid or contains oxygen no 

 matter what the other elements may be. We have now to 

 try to capture the products of burning some common substances 

 and learn from them what they are and from what substances 

 besides oxygen they are produced. 



We may take the candle as a typical instance of burning 

 materials, a kind of miniature gas plant. A candle is composed 

 of cotton wick and some combustible material, such as tallow, 

 paraffin, or the like. Heat melts the substance which then 

 gathers in a cup-like depression around the wick and passes up 

 through the wick in a stream. Near the top the liquid is 

 changed by heat to a gas which burns. Flame is always a 

 burning gas. If the material be wood or coal, it must none 

 the less be changed into gas to produce a flame. If you watch 

 burning wood or coals, you may see jets of gas pouring out, 

 which finally ignite and burn as flame. When all the gas burns 

 off, or, as we say, when the wood or coal burns to " coals/' 

 there is no more flame, just a glowing mass of coals. 



Extinguish the flame of a candle and observe that the melted 

 substance around the wick becomes solid just as it was before 



