16 



W. J . M. Rankine on the Means of 



Pressures. Volumes. 



lb. per lb. per cubic feet cubic feet 

 sq. inch. sq. foot. per lb. air. per lb. coal. 



At the beginning of the 

 expansion, 



At the end of the ex- 

 pansion, 



120 17,280 

 80 11,520 



2-2494 856-358 

 3-3741 1284-537 



Space through which the air expands, 

 = space traversed by the piston. 



Mean Pressures. 



1-1247 428-179 



Power = Mean Pressure 



lb. per 

 sq. inch. 



lb. per 



sq. feet. 



in ft.-pounds. 

 per lb. air. per lb. coal. 



Mean pressure and \ 



power during the \ 97*3 



expansion, . J 

 Deduct mean pres- "i 



sure and power 



during the com- 



601 

 pression, = — 



of the above, . 



Effective mean pres-' 

 sure and power, 

 130 

 731 



14012-88 15,760 6,000,000 



80-0 11520-85 12,957 4,933,000 



17*3 2492-03 2,803 1,067,000 



The calculations A and B illustrate the fact, that the maxi- 

 mum theoretical effect of one pound of coal between a given 

 pair of temperatures is the same, whether the working sub- 

 stance be air or steam. 



C. Example of the Computation of the Power produced by the 

 Combustion of One Pound of Coal in a theoretically perfect 

 Air-Engine, working between the temperatures of 650° and 150° 

 of Fahrenheit. 



Data. 

 Mechanical equivalent of the whole available heat obtained 

 by the combustion of one pound of coal (as before), 6,000,000 

 foot-pounds. 



Ratio of expansion of air, 1 : 1 J. 



