Steam-Engine. 429 



powerful pressure, while they admit of being heated, as it were, 

 red hot; whereby steam would be obtained of an excessively 

 high temperature, and which, developing itself by its expansive 

 force in the great cylinder would possess even after its dilata- 

 tion an elastic force sufficiently energetic. A similar arrange- 

 ment was likewise attempted formerly, in order to furnish steam 

 for Savary's engine ; but it does not appear to have been found 

 profitable enough to be continued in use ; and after the calcula- 

 tions we have made on the expenditure of heat employed in the 

 formation of steam at every temperature, it seems improbable 

 that a sufficient saving can be made in such engines to compen- 

 sate for their inconveniences. Advantages of a different kind 

 might be realized, if we could succeed in employing, without loss, 

 some liquid different from water, having a much greater elastic 

 force at the same temperature. 



One inevitable consequence of employing high temperatures 

 is, that the loss of heat by radiation is much greater, and this 

 makes an important item in calculating the results. To form 

 an idea of the diminution of effect arising from these different 

 circumstances we are to remember that according to Lavoisier 

 and Laplace, 1 gramme or 15,444 grains Troy of charcoal, deve- 

 lopes in burning 13038 degrees of heat by Fahrenheit's scale, or 

 about 92 pn Wedgewood's. Now 15,444 grains of water at the 

 temperature of 212, by being converted into steam absorb 

 1020,6 by Fahrenheat; then 15,444 grains of charcoal would 

 reduce to steam 200 grains of water, on the supposition that no heat 

 is lost, and that the water is already brought to the temperature 

 of 212. But after a great number of experiments made upon the 

 most perfect engines and the best constructed furnaces, Mr Clem- 

 ent found that 1544,4 grains of charcoal does not produce more 

 than 6 or 7 times as much steam, and 1544,4 grains of the best 

 fossil coal never produces more than 6 times as much steam ; 

 whence it will be seen that nearly half the heat is lost by radia- 

 tion, and the conducting power of the boiler and the surrounding 

 bodies. The loss is without doubt still more considerable in 

 engines of a high pressure. 



526. When we know the elastic force of the steam introduced 

 under the surface of the piston, it is easy to estimate the whole 

 pressure resulting from it ; but in this estimate it is necessary to 



