230 ANNUAL OF SCIENTIFIC DISCOVERY. 



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that the average quantity of coal which we expend in realizing a given 

 effect by means of the steam-engines is about thirty times greater than 

 would be requisite with an absolutely perfect heat-engine. 



" The causes which render the application of heat so uneconomic in 

 the steam-engine have been brought to, light by the discovery of the 

 dynamical theory of heat ; and it now remains for mechanicians, guided 

 by the light they have thus received, to devise improved practical meth- 

 ods of converting the heat of combustion into available power. 



~" I have hitherto spoken of coal only as a source of mechanical power, 

 but it is also extensively used for the kindred purpose of relaxing 

 those cohesive forces which resist our efforts to give new forms and 

 conditions to solid substances. In these applications, which are gener- 

 ally of a metallurgical nature, the same wasteful expenditure of fuel is 

 everywhere observable. In an ordinary furnace employed to fuse or 

 soften any solid substance, it is the excess of the heat of combustion 

 over that of the body heated which alone is rendered available for the 

 purpose intended. The rest of the heat, which in many instances con- 

 stitutes by far the greater proportion of the whole, is allowed to escape 

 uselessly into the chimney. The combustion also in common furnaces 

 is so imperfect that clouds of powdered carbon, in the form of smoke, 

 envelope our manufacturing towns, and gases which ought to be com- 

 pletely oxygenized in the fire pass into the air with twO'thirds of their 

 heating power undeveloped." 



" Some remedy for this state of things, we may hope, is at hand, in the 

 gas regenerative furnaces recently introduced by Mr. Siemens. In 

 these furnaces the rejected heat is arrested by a so-called " regenera- 

 tor," as in Stirling's air-engine, and is communicated to the new fuel 

 before it enters the furnace. The fuel, however, is not solid coal, but 

 gas previously -evolved from coal. A stream of this gas, raised to a 

 high temperature by the rejected heat of combustion, is admitted into 

 the furnace, and there meets a stream of atmospheric air also raised to 

 a high temperature by the same agency. In the combination which 

 then ensues, the heat evolved by the combustion is superadded to the 

 heat previously acquired by the gases. Thus, in addition to the ad- 

 vantage of economy, a greater intensity of heat is attained than by the 

 combustion of unheated fuel. In fact, as the heat evolved in the fur- 

 nace, or so much of it as is not communicated to the bodies exposed to 

 its action, continually returns to augment the effect of the new fuel, 

 there appears to be no limit to the temperature attainable, except the 

 powers of resistance in the. materials of which the furnace is composed. 



" With regard to smoke, which is at once a waste and a nuisance, I 

 can state with perfect confidence that, so far as the raising of steam is 

 concerned, the production of smoke is unnecessary and inexcusable. 

 The experiments to which I refer proved beyond a doubt, that, by an 

 easy method of firing, combined with a due admission of air and a 

 proper arrangement of firegrate, not involving any complexity, the 

 emission of smoke might be perfectly avoided, and that the prevention 

 of the smoke increased the economic value of the fuel and the evapora- 

 tive power of the boiler. As a rule, there is more smoke evolved from 

 the fires of steam-engines than from any others, and it is in these fires 

 that it may be most easily prevented. But in the furnaces used for 

 most manufacturing operations the prevention of smoke is much more 



