14 W. J. M. Rankine on the Means of 



ft.-lb. 



Effect of one pound of coal, 127,297x8-382 = 1,067,000 as 



before. 



Mean effective pressure during the whole action of the steam, 



effect 127,297 1,067,000 19nndftl , f , 



= =- 1non , = — tt oo on = 1200*46 lb. per square toot = 



space 106-04 888'82 r ^ 



8*34 lb. per square inch. 



Coal per horse-power per hour, 



iVifi7 > nnn =: ^ ^ ^*' as * n ^ ie ^ exam P^ e °f the table in 

 article 10. 



B. 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 270° and 140° of 

 Fahrenheit. 



(The object of the following computation is not to exemplify 

 the mode of working of any existing or proposed air-engine, 

 but simply to illustrate the fact, that the maximum theoretical 

 efficiency of thermo-dynamic engines is the same when the 

 limits of temperature are the same, of what nature soever the 

 working substance may be. 



It is also to be observed, that the maximum theoretical duty 

 of one pound of coal in an air-engine is independent of the 

 rate of expansion of the air, and of its density and pressure. 

 The rate of expansion affects the weight of air which must be 

 employed to perform a given duty, and the densities and pres- 

 sures affect the size of the receivers and cylinders required to 

 contain that weight of air. 



If definite values, therefore, are assumed for those quan- 

 tities in the following calculations, it is only for the sake of 

 fixing the ideas, and giving numbers instead of algebraical 

 symbols.) 



Data. 



Mechanical equivalent of the whole available heat obtained 



is being condensed on the other side, and also by the power consumed in pro- 

 ducing, by the forcible compression of part of the steam into the liquid state, 

 a quantity of heat sufficient to raise the temperature of the water from 140° to 

 270° Fahrenheit. 



