MR. MACQUORN RANKINE ON THERMO-DYNAMFCS. 
165 
Temperature in Centigrade Degrees : — 
At upper limit At lower limit 
of Actual Heat. 
Above melting ice (T) 
140° 
o 
O 
TF 
Above zero of gaseous tension (r) . . 
414-6 
314-6 
Above absolute cold (r—z) 
412-5 
312-5 
Pressure in pounds per square foot ( P) 
. 7 557 
153-34 
,, „ per square inch .... 
52*5 
1-065 
Initial Volume of saturated steam, V B = u', = . 
8'004 cubic feet per pound 
Latent Heat of Evaporation : — 
In degrees, applied to one pound of liquid water 509 o- l Centigrade. 
In foot-pounds (LJ 707,445-36. 
From these data are deduced the following results: — 
Absolute Maximum Efficiency ; — 0~2424. 
Duty of one pound of water ; being the area 
of the diagram ABCD 171,484-75 ft. lb. 
V olume at which the compression must com- 
mence ; calculated as in art. (41.) . . V u = 49*1 cubic feet per pound. 
Volume to which the Expansion must be car- 
ried ; calculated by equation (72.) . . V c =258*1 cubic feet per pound. 
Ratio of Expansion =y^=|^j^=32*25. 
(45.) Liquefaction of Vapour by Expansion under Pressure. 
In fig. 22, let the abscissae of the curve BFR indicate the volumes corresponding 
to complete evaporation at the pressures denoted by its ordinates. For most known 
fluids, a curve of no transmission BCN, drawn from any point B of the curve of com- 
plete evaporation in the direction of X, falls within that curve; so that by expansion 
of saturated vapour under pressure, a portion in most cases will be liquefied. 
To ascertain whether this will take place in any particular case, and to what extent, 
equation (60.), which gives the volume of unity of weight of saturated vapour at the 
temperature r 2 , is to be compared with equation (72.), which gives the volume at the 
same temperature of unity of weight of an aggregate of liquid and vapour, which has 
expanded under pressure from a state of complete evaporation at the temperature t x . 
The difference between the volumes given by these equations is as follows (neglecting, 
as usual, the expansibility in the liquid state) : — 
