The Economic Production of Artificial Heat. 407 



increased. This principle, in a modified form, has been applied 

 to the consumption of smoke : for which purpose a small quantity 

 of steam is thrown into the forepart of the furnace, above the 

 fuel, by a fan-shaped distributor, having* a few small apertures; 

 and the instant the steam is turned on through the name and 

 smoke, the latter disappears. The cause of this extraordinary 

 effect is not certainly known. Some consider that the steam 

 merely carries the air mechanically to the fuel ; others, that the 

 steam is decomposed by the carbonaceous matter of the smoke 

 at a high temperature, carbonic oxide and hydrogen being pro- 

 duced • and that the combustion of these augments the amount 

 of heat evolved. The latter supposition is apparently confirmed, 

 by the fact that more water is sometimes evaporated than can 

 well be ascribed to the fuel : in which case, it would seem rea- 

 sonable to attribute some of the effect to combustion of the 

 hydrogen ; but whatever heat is given out by the burning 

 hydrogen must have been first obtained from the fuel itself, 

 since exactly the same amount of heat is required to decompose 

 water, as is afterwards evolved during the recomposition of its 

 elements. The steam increases the draught to such a degree, 

 that its force must be diminished by side openings in the chim- 

 ney, or other means • and hence, supplying air for combustion 

 by tubes passing down through the chimney ceases to be injuri- 

 ous ; and the chimney may be made smaller and lower. Since 

 with this contrivance no air passes through the ash-pit, com- 

 bustion takes place altogether on the surface of the fuel ; and 

 the absence of smoke causes the heat to be radiated more 

 directly, and, therefore, more effectually, on the bottom of the 

 boiler. 



We have now briefly alluded to the best modes of using the 

 more ordinary kinds of fuel; and, from the great difference 

 between the amount of heat obtained in practice and that 

 which theory would lead us to expect, it can easily be imagined 

 how much yet remains to be done in this department of practical 

 science. The separate condensation of steam, invented by 

 Watt, and the application of the principle of expansion, by 

 Woolf and Hornblower, greatly augmented the dynamical value 

 of fuel; and yet the mechanical effect obtained from even the 

 best condensing expansive engine is many times less than it 

 would be if, according to the received " mechanical equivalent 

 of heat," the whole heat were changed into work. The locomo- 

 tive, from its peculiar position, is, perhaps, least favourably 

 circumstanced, so far as relates to the economy of fuel ; yet, 

 with all the sources of waste to which it is exposed, it will do as 

 much work with one pound of coke as a good non-expansive 

 condensing engine with a pound of coal, and more than twice 

 as much as a good high-pressure stationary engine with the 



