different kinds of Coal-gas Burners, Sfc. 215 



Tt may naturally be supposed, that if these gases are sup- 

 plied with a due proportion of air for combustion, the amount 

 of light should bo always the same ; and that, consequently, 

 when the gas is completely burned, it is of little consequence 

 in what sort of burner it is consumed. This is not, however, 

 the case. No doubt, when the gas is completely burned by a 

 due admission of air, we arrive at the greatest amount of light 

 that is to be expected, but we may err in supplying air too 

 freely; and though by this the whole of the elements are 

 united with its oxygen, and carbonic acid and water are 

 formed to the same extent as before, yet we may find that 

 much less light is afforded. Hence, also, the reverse will 

 occur, when the supply which has been too liberal is dimi- 

 nished ; the light for the same consumpt of gas is then in- 

 creased^ 



This must be accounted for on the principle established by 

 Sir H. Davy, that a gas burns with a white light when it con- 

 tains an ingredient, which is not volatilized by the heat gene- 

 rated during its combustion. The element of this nature in 

 coal-gas is carbon, which, though in union with hydrogen, may 

 be set free, and in its tmcombined state be then ignited and 

 burned, in which case it will afford white light. Unless, there- 

 fore, the gas be so consumed that it will undergo decomposi- 

 tion before it is actually burned, it will not afford much light ; 

 and it is chiefly this which causes the difference in the illumi- 

 nating power of burners differently constructed. 



From what has been said, it is evident that coal-gas may 

 be burned in two ways. In the one, it may be burned strictly 

 as a hydro-carbon ; by which, both the hydrogen and carbon 

 will at once, and as if simultaneously, unite with oxygen ; in 

 the other way, it may, during the combustion, be so far de- 

 composed, that the hydrogen will first combine with oxygen, 

 and set the carbon free, and in this free and uncombined state 

 it will then unite with oxygen : now, in the former case, it 

 will burn and not give much light, in the latter the light will 

 become intense ; and hence the necessity of attending to this 

 in consuming coal-gas for the purposes of illumination. 



That what has been said with regard to the decomposition 

 of gas really occurs, is shewn by setting fire to it, and holding 



