realizing the Advantages of the Air-Engine. 17 



During Ex- During Com- 



pansion. pression. 



Temperatures (ordinary scale), 650° Fahr. 150° 



Absolute temperatures, . 1111° ... 611° 



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

 pressure in pounds per square foot at 32° Fahr., 26,214 

 foot-pounds. 



Computation of the Maximum Theoretical Duty of One Pound of 

 Coal by the general law. 



Tir .i. i m ■ 65 ° - 150 500 n .- 



Maximum theoretical efficiency, — — — = U-4& 



J 1111 1111 



Duty of one pound of coal, J^. x 6,000,000 = 2,700,000 

 ft. -lb., as in Example IV. 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 tbe pressure and volume of one pound of air at the 

 temperature of 650°. 



Power developed by one pound of air during its expansion 

 at 650° Fahr. to 1J times its original volume, being also the 

 mechanical equivalent of the heat expended to produce the 

 expansion. 



59,074 x (hyp. log. 1| = 0-4054652) = 23,953 ft.-lb. 



Weight of air which is expanded to 1 J times its volume at 

 650° Fahr. by the combustion of one pound of coal. 



6,000,000 



23,953 



250-5 lb. 



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

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



VOL. I. NO. I. — JAN. 1855. B 



