realizing the Advantages of the Air-Engine. 13 



In Boiler. In Condenser. 



Temperatures (ordinary scale), 270° Fahr. 140° 



Absolute temperatures, . 731° 601° 



Pressures, lb. lb. 



Per square inch, , . . 41-93 2*89 



Per square foot, . . . 6038- 415'7 



Cubic feet. 



Volume of one pound of steam in the boiler, 9*852 



Latent heat of evaporation of one pound of 



ft.-lb. 

 steam (mechanical equivalent), . . 715,800 



Computation of the Maximum Theoretical Duty of one pound of 

 Coal by the General Law. 



mu" V i • ffi • 270°- 140° 130° ni# __ 

 Theoretical maximum efficiency, WoTo — = ^ — 0'178 



130 

 Duty of one pound of Coal, 1 =— r x 6,000,000 = 1,067,000 as in 



7 ol 



Example I. of the table in article 10. 



■Computation of the Maximum Theoretical Duty of one pound of 

 Coal, introducing the changes of pressure and volume undergone 

 by the Steam. 



Water evaporated by one lb. of coal, 

 available heat of combustion 6,000,000 



8-382 lb. 



latent heat of one lb. of steam 715,800 

 Ratio of expansion required to enable the steam to produce its 

 maximum effect, 10*774. 



The detailed computation of this ratio is too tedious to be 

 inserted here. The method pursued is fully explained in the 

 Philosophical Transactions for 1854, Part I. 



per lb. of water. 



per lb. of coal, 

 cubic feet. 



82*579 

 888-82 



cubic feet. 



Space filled by steam at full pressure, 9*852 

 at the end of the expansion, . 106*04 



as space traversed by the piston. 



ft.-lb. 13Q ft.-lb. 



Effect of one pound of steam, 715,800 x ^ = 127,297.* 



* This quantity consists of the total action of the entering and expanding 

 steam, on one side of the piston, diminished by the action of the steam which 



