402 The Economic Production of Artificial Heat. 



placed far oat in the apartments, and their flues are so arranged 

 as to traverse a considerable space before entering the chimney, 

 that the products of combustion may part with as much heat as 

 possible previous to their escape ; for, after the gaseous current 

 has ceased to be applied to heating purposes, the heat it con- 

 tains is totally lost. The whole heating power of the fuel, 

 therefore, is not obtained, unless the temperature of its gaseous 

 products is lowered to that of the atmosphere ; this is impos- 

 sible when it is burned in the ordinary way, but the nearer we 

 approximate to it the better. The heating of rooms, in very 

 cold countries, by stoves, is not only economical and convenient, 

 but productive of a pleasing temperature with great ease when 

 their management is understood. All disagreeable smell, and 

 other inconveniences — unless the heat is allowed to become 

 immoderate — are prevented, by placing on each stove a vessel 

 of water for evaporation. Stoves are, however, more suited 

 to the use of wood than of coal : the combustion of the latter 

 is not so easily regulated, and the soot which it produces is 

 more troublesome, though not so inflammable. When reasonable 

 care is taken, they are not found very liable to cause accidents by 

 fire ; nor would insurance companies, in the countries where 

 they are used, consider their absence an additional security. For 

 culinary purposes, at least with wood, they are extremely effective, 

 convenient, and economical : and, however employed, they con- 

 sume much less fuel, for a given heating power, than an open 

 fire-place. In the application of heat to the objects of the 

 manufacturer, all the discoveries which science has made with 

 regard to combustion have been brought into operation. The 

 conditions required for perfect combustion are few and simple, 

 but they are of the highest importance : a proper supply of 

 the supporter must be provided, and it must be mixed with 

 the combustible at a sufficiently high temperature. If either of 

 these is imperfectly fulfilled, a waste of fuel and the want of a 

 proper temperature will be the inevitable consequences. 



It will be useful to notice briefly the chief sources of a waste 

 of heat during combustion. Of these, not the least common is 

 the presence of hygrometric water in the fuel. This must cause 

 a loss of heat, since, as it will certainly be evaporated, its 

 amount is to be deducted from that of the water which otherwise 

 would be converted into steam ; or the heat it absorbs must be 

 considered as diminishing that which should be applied to the 

 object in view. Newly-felled wood often contains fifty per cent. 

 of water ; and so much of the heat given off by the remaining 

 fifty per cent, is consumed in evaporating it, that scarcely any 

 useful heat remains. After twelve months, wood may contain 

 twenty-five per cent, water : and, if it is kept in a dry place, ten 

 per cent, which, if expelled artificially, will be re-absorbed from 



