86 THE ADDRESSES, LECTURES, ETC., OF 



WHAT is FUEL ? 



Some of you may have already said within yourselves that it is 

 but wasted time to enlarge upon such a theme, since all know that 

 fuel is coal drawn from the earth, from deposits, with which this 

 country especially has been bountifully supplied ; why disturb our 

 plain understanding by scientific definitions which will neither 

 reduce the cost of coal, nor make it last longer on our domestic 

 hearth ? 



Yet I must claim your patience for a little, lest, if we do not 

 first agree upon the essential nature of fuel, we may afterwards be 

 at variance in discussing its origin and its uses, the latter at any 

 rate being of practical interest, and a subject worthy of your most 

 attentive consideration. 



Fuel, then, in the ordinary acceptation of the term is carbona- 

 ceous matter, which may be in the solid, the liquid, or in the 

 gaseous condition, and which, in combining with oxygen, gives 

 rise to the phenomenon of heat. Commonly speaking, this 

 development of heat is accompanied by flame, because the sub- 

 stance produced in combustion is gaseous. In burning coal, for 

 instance, on a fire-grate, the oxygen of the atmosphere enters into 

 combination with the solid carbon of the coal and produces car- 

 bonic acid, a gas which enters the atmosphere, of which it forms a 

 necessary constituent, since without it, the growth of trees and 

 other plants would be impossible. But combustion is not neces- 

 sarily accompanied by flame, or even by a display of intense heat. 

 The metal magnesium burns with a great display of light and 

 heat, but without flame, because the product of combustion is not 

 a gas but a solid, viz. oxide of magnesium. Again, metallic iron, 

 if in a finely divided state, ignites when exposed to the atmos- 

 phere, giving rise to the phenomena of heat and light without 

 flame, because the result of combustion is iron oxide or rust ; but 

 the same iron, if presented to the atmosphere more especially to 

 a damp atmosphere in a solid condition, does not ignite, but is 

 nevertheless gradually converted into metallic oxide or rust as 

 before. 



Here, then, we have combination without the phenomena either 

 of flame or light ; but by careful experiment we should find that 



