168 
MR. MACQUORN RANKINE ON THERMO-DYNAMICS. 
The power developed consists of, — 
Foot-pounds. 
The area ABCD, as in article (44.) 171, 48475 
The area ADE, as in article (41.) 13,980"00 
Total power developed, per lb. of water . . 185,46475 
™ . 185,48475 
Efficiency, 847i245 . 36 = 
Absolute maximum efficiency, as in art. (44.) .... 
Loss of efficiency by omitting the heating by compression 
0*2189 
0-2424 
00235 
or about one-tenth part of the absolute maximum. 
(47.) Efficiency of a Vapour-Engine with incomplete expansion. 
It is in general impossible in practice to continue the expansion of the vapour down 
to the temperature of final liquefaction ; and from this cause a further loss of efficiency 
is incurred. 
Let it be supposed, for example, that while the pressure of evaporation F, corresponds 
to the line AB in fig. 23, and the pressure of liquefaction, P 3 , to the line EDC, the 
Fig. 23. 
A. Cx B 
pressure at which the expansion terminates, P 2 , corresponds to an intermediate line 
HLG. Let vA, t>'jB, as before, be the ordinates corresponding to complete liquefac- 
tion, and to complete evaporation, at the pressure P,. 
Draw, as before, the curves of no transmission AM, BN, cutting HLG in L and G, 
and EDC in D and C ; draw also the ordinate V g KG, cutting EDC in K. 
Then the expansion terminates at the volume V G , and ABGKE is the indicator- 
diagram of the engine. 
To find the power represented by this diagram, the area ALH is to be found as in 
article (40.), the area ABGL as in article (43.), and the rectangle HGKE by mul- 
tiplying its breadth V G — v (found as in article (43.)) by its height HE, which is the 
excess of the pressure at the end of the expansion, P 2 , above the pressure of final lique- 
faction, P 3 . 
