COMMON COAL F1KE. 



and, in fine, the white brilliant flame which most commonly 

 issues from the fissures of the coal, are severally explained and 

 accounted for. 



25. It has been shown that in combustion 6 parts, by weight, 

 of carbon combine with 16 of oxygen, or, what is the same, 1 part 

 with 2$. It has also been demonstrated, that in the combustion 

 of hydrogen, 1 part by weight of that gas combines with 8 of 

 oxygen. Now by these simple numerical data may be easily 

 explained the effects of a common coal-fire upon the air which 

 feeds and sustains it. 



26. It is thus found, that in burning 10 Ib. of coal the oxygen 

 contained in 1551 cubic feet of air is altogether absorbed. 



To keep the atmosphere of a room in which a fire of such coal 

 is burned fresh and pure, it would be, therefore, necessary to 

 supply fresh air at the rate of 155 cubic feet for every pound of 

 coal which is burned.* 



27. Wood is a combustible generally used for the production of 

 artificial heat in countries where coal is not so cheap and abun- 

 dant as in England. This fuel, like coal, consists principally of 

 carbon and hydrogen in various proportions, according to the sort 

 of wood. All kinds of wood contain also a proportion of oxygen, 

 as a constituent, much greater than is found in coal. 



"Wood, when green, contains a considerable proportion of water. 

 In the combustion of such wood, a large proportion of the heat 

 developed is absorbed in the evaporation of this water, and is, 

 therefore, lost for heating purposes. Wood used as fuel should, 

 therefore, be kept until this water, or the chief part of it, has 

 been evaporated. For the same reason wood kept for fuel should 

 be as little exposed to moisture or damp as possible. 



28. All fatty, oily, and waxy substances are combustible, 

 whether in the liquid or solid state. They consist of the same 

 constituents as coal and wood, but combined somewhat differently, 

 and in different proportions. Most of this class, burning with 

 flame of more or less brilliancy, are used for the purposes of 

 artificial illumination. 



Whale, sperm, olive, and cocoa-nut oils, wax, spermaceti, and 

 tallow are examples of this class of combustibles. 



29. Whatever be the sort of combustible, or whatever be the 

 purpose to which it is applied, whether for heating or lighting, it 

 will be evident from the explanations which have been here given, 

 that the combustion cannot be maintained with the necessary 



* In the preceding explanation we have omitted to take into account the 

 effect of a small proportion of oxygen which enters into the composition of 

 coal. This, however, is so insignificant, that it would be needless to 

 complicate the calculation by introducing it. 



201 



