COMBUSTION. 



139 



such a blowing forth of gas, and sec no flame, you can at 

 once produce a flame by applying a burning match to the 

 crevice, just as you do by applying it to the opened orifice 

 of a common gas-burner. 



176. Nature of Flame. To understand the cause of flame 

 we must remember that it is produced by burning gases 

 only ; solid bodies, heated ever so intensely, emit light and 

 may burn, but they can not make flame if they are incapable 

 of being converted into vapor. Thus a piece of iron or sil- 

 ver may be heated hot enough to give out light, but can not 

 burn with a flame. So with carbon, which burns without 

 flame when alone. 



In the examples mentioned the flame is caused by the 

 combustion of the gaseous hydrocarbons. 



177. Combustion of Coal. In the combustion of anthracite 

 coal when fully ignited there is no flame, for it contains no 

 hydrogen, but is nearly pure carbon. Its combustion is 

 like that of wood-coals, or charcoal. The reason that an- 

 thracite contains no hydrogen is that in its formation all 

 volatile matters were driven off by heat. There is a blue 

 flame given off by anthracite coal when it is kindling, and 

 especially w r hen a hot fire is freshly fed with coal, arising 

 from the generation of carbonic oxide, noticed in 112 ; but 

 when the coal is fairly ignited it 



burns without flame. Bituminous 

 coal, on the other hand, burns with 

 a flame because it contains hydro- 

 gen as well as carbon. 



178. Manufacture of Gas. If you 

 place some shavings in a test-tube, 

 Fig. 57, with a cork in its mouth 

 having a tube fixed into it, and ap- 

 ply heat, illuminating gas will pass 



out through the tube, and you can Fig. si. 



