78 ANNUAL OF SCIENTIFIC DISCOVERT 



tracted from the published researches of Prof. Thompson, of England, on the 

 dynamic theory of steam : 



" 1. The engine of the Fowey Consols mine was reported, in 18i5, to have 

 given 125,089,000 foot-pounds of effect for the consumption of one bushel, or 

 ninety-four pounds, of coal. Now, the average amount evaporated from Cor- 

 ftjsh boilers, by one pound of coal, is eight and a half pounds of steam ; and 

 hence, for each pound of steam evaporated, 150,556 foot-pounds of pressure 

 are produced. 



" The pressure of the saturated steam in the boiler may be taken as three 

 and a half atmospheres, and consequently the temperature of water will be 

 150. Now, by Regnault (end of Memoire x), the latent heat of a pound of 

 saturated steam, at 140 Cent., is 508, and since, to compensate for each 

 pound of steam removed from the boiler in the working of an engine, a 

 pound of water at the temperature of the condenser (which may be estimated 

 at 30) is introduced from the hot well, it follows that 618 units of heat 

 Cent, are introduced to the boiler for each pound of water evaporated. But 

 the work produced for each pound of water evaporated was found above to be 

 156,556 foot-pounds; hence, --^f^--, or 25'3 foot-pounds, is the amount of 

 work produced for each unit of heat transmitted through the Fowey Consols 

 engine. 



" 2. The best duty on record, as performed by an engine at work (not for 

 merely experimental purposes), is that of Taylor's engine, at the United 

 Mines, which, in 1840, worked regularly for several months at the rate of 

 98,000,000 foot-pounds for each bushel of coal burned; this is T 9 ^- or '784 of 

 the experimental duty reported in the Fowey Consols engine. 



" Hence, the best useful work on record is at the rate of 198'3 foot-pounds 

 for each unit of heat transmitted, and is l jf fj 3 -, or forty-five per cent, of the 

 theoretical duty, on the supposition that the boiler is at 140 and the con- 

 denser at 30. 



"3. French engineers contract (in Lille, in 1847, for example,) to make 

 engines for mill power which will produce 30,000 metre-pounds, or 98,427 

 foot-pounds, of work for each pound of steam used. If we divide this by 618, 

 we find 159 foot-pounds for the work produced by each unit of heat. This is 

 36' 1 per cent, of 440, the theoretical duty. 



" 4. English engineers have contracted to make engines and boilers which 

 will require only three and a half pounds of the best coal per horse power per 

 hour. Hence, in such engines, each pound of coal ought to produce 565,700 

 foot-pounds of work; and if seven pounds of water be evaporated by 

 each pound of coal, there would result 80,814 foot-pounds of work for each 

 pound of water evaporated. If the pressure in the boiler be three and a half 

 atmospheres (temperature 140), the amount of work for each unit of heat 

 will be found, by dividing this by 618, to be 130'7 foot-pounds, which is 

 -L3-jp^, or 29'7 per cent, of the theoretical duty. 



" 5. The actual average of work performed by good Cornish engines and 

 boilers is 55,000,000 foot-pounds for each bushel of coal, or less than half the 

 experimental performance of the Fowey Consols engine, and scarcely more 

 than half the actual duty performed by the United Mines engine in 1840; in 

 fact, about twenty -five per cent, of the theoretical duty. 



" 6. The average performance of a number of Lancashire engines and 

 boilers have been recently found to be such as to require twelve pounds of 

 Lancashire coal per horse power per hour (i. e., for performing 60 >< 33,000 

 foot-pounds), and a number of Glasgow engines such as to require fifteen 



