186 ME. MACQUOEN EiNKINE ON THE THEEMO-DYNAiHC IHEOET 
to which adding the rectangle ADEFA, the work of o.ve pound of steam k found 
to be ^ 
i?3) = «hyp.lOg^— + • (18-) 
JP2 
in which 
«=1109550 foot-pounds; 5=540*4 foot-pounds per degree of Fahee>"SEIT. 
The Mean Effective Peessure, or work per unit of volume traversed by the piston, is 
( 18 a.) 
The heat expended per pound of steam, by a diiferent mode of division from that 
given in the formulae 16, is computed as follows : 
Part of the sensible heat, SQAK=J(4~*^4) ; 
Latent heat of evaporation at the temperature KADN=H2=«--5f2 ; 
Work performed between the temperatures 5, and ABCDA = vdp as in equation 1 1 . 
The addition of those quantities gives for the whole expenditure of heat pee poind 
OF steam in foot-pounds of energy, 
^=:J(4-54)4-«-^^2+£’'^#=J(^2“^4)+a(l+hyp.logy^)-5f, . . . (19.) 
(J=772 foot-pounds per degree of Fahrenheit). 
The heat expended per unit of space traversed by the piston is equivalent to a pressme 
whose intensity is n q . i 
(19-'*' 
The efficiency of the steam is the ratio 
( 20 .) 
E=W-h?^=l, 
of the work performed by the steam on the piston to the heat expended on the steam ; 
and that ratio having been determined, the available heat of a pound of fuel may be 
computed from the indicated work per pound of fuel, or vice versd, by means of the 
equation, 
available heat 1 (‘^1 ) 
indicated work~E‘ 
In the practical use of equations 18, 18a, 19, 19a, 20, and 21, the usual data are. 
the initial pressure jpi, the ratio of expansion r, the pressure of exhaustion and the 
temperature of the feed-water t,. From p,, by the aid of equations 6, 7, 8, 9. or ot 
tables, are to be found and d,. Then 
rvi=v^\ 
and from by the aid of the same equations, or of tables, are to be found and 
and thus are completed the data for the use of equations 18 and 19. 
Let OH=po represent the pressure, and HG=^;o the volume, of a pound ot steam at 
