SCIENCE OF COMMON THINGS. 221 



Matter not destroyed by combustion. Heat, how originated by combustion. 



The combination of some substance with oxygen, - 

 or the act of combining with oxygen. 



1468 Js there not always an increase in weight during the combustion 

 of inflammable materials, rather than a loss f 



The products of combustion always exceed the weight 

 of the original substance burned, by an amount equal 

 to the weight of the oxygen gas absorbed during the 

 combustion. 



1469 What becomes of the oxidized products of combustion f 



They for the most part combine with oxygen to form 

 gases and vapors. We apply to these products the 

 general term smoke. 



147*0 What is an essential requisite to every process of combustion f 



That there should be a free supply of air, and that 

 the products of combustion, or the smoke, should be 

 conducted off. 



147*1 Why, when we burn a candle or a piece of wood in the air, does 

 there always seem to be a loss of matter f 



Because the results of combustion in these cases are 

 either gases or vapors, the existence of which, not being 

 apparent to common observation, requires to be made 

 known by experiment. 



Until nearly the close of the last century it was generally believed and 

 taught, that when a body was burned, something went out of it, that it 

 lost weight. Lavoisier, a celebrated French chemist, overthrew this doc- 

 trine by burning a substance in connexion with an arrangement whereby 

 all the results or products of the combustion were saved. These on 

 being weighed showed a gain rather than a loss, the amount being equal 

 to the quantity of oxygen which had been absorbed from the air during 

 the process of combustion, by the burning substance itself. 



147*3 How is heat evolved by combustion ? 



By chemical action. As latent heat is liberated, 

 when water is poured upon lime, by chemical action, 

 so latent heat is liberated in combustion by chemical 

 action also. 



147*3 What chemical action takes place in combustion f 



The elements of the fuel combine with the oxygen of 

 the air. 



147*4 What is the temperature required to induce the combination of 

 oxygen with any substance called ? 



10* 



