52 Dr Fvfe on the Pi'ecentlon of Smoke, c^t*. 



as it is calculated can be done by carbon itself, provided the 

 whole of the heat evolved by its combustion were taken up by 

 the water. Now, it is well known that in practice this is 

 never done, owing to the abstraction of part of the heat by 

 the building, and from a considerable part passing up the 

 chimney. 



Now, allowing that the available heat in practice is that 

 evolved by the combustion of the carbon of the coke, and con- 

 sequently that that which is evolved by the gaseous elements 

 is lost, an important question arises, Can we by any means 

 increase the evaporative power beyond that occasioned by the 

 fixed carbon \ in other words, Can we make available any of 

 the heat which is, or which ought to be given forth by the 

 volatile matter ? 



In carrying on the combustion of coal all the fixed carbon 

 is consumed, Avith the exception of that which falls into the 

 ash-pit ; because, before any part of it escapes as a gaseous pro- 

 duct, it must combine with oxygen ; but this is not the case 

 with the gaseous hydro-carbons. It is well known that a con- 

 siderable part of these often escapes unconsumed as hydro- 

 carbon, while another part, being decomposed, allows the 

 combustion of the hydrogen, while a portion of the carbon is 

 set free and not consumed ; and hence smoke, more or less 

 dense, according to the escape. This is occasioned by the 

 want of due admission of air to the inflammable gases, at that 

 part of the furnace where, when mixed with them, it would 

 be exposed to the temperature requisite for their combustion. 

 It is evident, then, that the more freely air is admitted, up to 

 a certain extent, at the proper place, the more perfect will 

 be the combustion of the gases. Hence the numerous contri- 

 vances for the admission of air, both cold and heated, at dif- 

 ferent parts of the furnace, by which smoke is so far prevented. 

 Allowing, however, that this is done, and that, by these pro- 

 cesses, the escape of any part of the gaseous elements uncon- 

 .sumed is also prevented, the question still remains to be an- 

 swered, Whether the practical evaporative power is increased 

 beyond that which is pointed out by the fixed carbon of the 

 coal 1 Of course I now allude to bituminous coal in general 

 use for steam-engine furnaces. 



