realizing the Advantages of the Air-Engine. 15 



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

 foot-pounds. 



Ratio of expansion of air, . . 1 : 1J 



The air is alternately expanded and compressed in this 

 ratio. 



During During 



Expansion. Compression. 



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



Absolute temperatures, . 731 ... 601 



Product of the volume of one pound of air in cubic feet by 



its pressure in pounds on the square foot at 32° Fahr., 



26,214 ft.-lb. 



Computation of the Maximum Theoretical Duty of one Pound of 

 Coal by the general law. 



270° - 140° 130 n -„„ 

 Theoretical maximum efficiency, =— = ^-^r =U"17o 



Duty of one pound of coal, *|° x 6,000,000 ft.-lb. = 



1,067,000 ft.-lb., as in 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 of the 

 Air. 



Product of the pressure and volume of one pound of air at the 



temperature of 270°, 26,214 x ~ * 461 = 26 > 214 x ^3 = 

 38,869 ft. -lbs. 



Power developed by one pound of air during its expansion 

 at 270° Fahr. to one and a half times its original volume, 

 being also the mechanical equivalent of the heat expended to 

 produce that expansion. 



38,869 x (hyp. log. 1| = 0-4054652) = 15,760 ft.-lb. 



Weight of air which is expanded to one and a half times its 



volume at 270° Fahr. by the combustion of one pound of coal, 



6,000,000 



15,760 



= 380-705 lb. 



Pressures and volumes of the air at different periods, sup- 

 posing the greatest pressure to be 120 lb. per square inch. 



