PRINCIPLES OF COMBUSTION. 131 



coal, than by allowing the whole body of gas to escape into the 

 atmosphere. 



Let us bear in mind, that smoke is always the same, whether 

 it may be generated in a common fire-place, in a furnace, or in a 

 retort; and that, strictly speaking, it is not inflammable, as by 

 itself it can neither produce flame nor permit the continuance 

 of flame in other bodies, as is proved from the fact that a lighted 

 taper being introduced into a jar of coal gas, (or smoke,) is 

 instantly extinguished. 



How, then, is it to be consumed or prevented, and rendered 

 available for the production of heat ? The answer is, solely by 

 effecting a chemical union, not with the air merely, as is the 

 dangerous notion, but with the oxygen of the air, the "sup- 

 porter" of flame, the heat-giving constituent of the air, in given 

 quantities, and at a given temperature. 



This at once opens the main question, What are these quan- 

 tities, and what is this temperature ? and, are there any other 

 conditions requisite for effecting the chemical union of the 

 oxygen of the air with the inflammable gas, to the best 

 advantage ? 



Effective combustion, for practical purposes, is, in truth, a 

 question more as regards the air and the gas ; and the former, 

 as referable to our object, would appear better entitled to the 

 term combustible than the latter, inasmuch as the heat is in- 

 creased in proportion to the quantity of air we are enabled to 

 use advantageously. Besides that, we have no control over the 

 gas after having thrown the fuel on the furnace, but we can 

 exercise a control over the air, as we shall show, in all the 

 essentials of perfect combustion. It is this which has done so 

 much for the perfection of the lamp, and may be rendered 

 equally available for the furnace. 



Now, although this control, and the management arising out 

 of it, influences the question of perfect or imperfect combustion, 

 and, therefore, affects that of economy, yet, strange to- say, in an 

 age when chemical science is so advanced, and in a matter so 

 purely chemical, this is precisely what is attended to in practice. 

 The how, the when, and the where, this controlling influence 

 over the admission and the action of the air is to be exercised, 

 12 



