
MECHANICAL ACTION OF HEAT. 183 
Consequently to give the maximum useful effect, 
P,=P,+/ = 648 ]b. per square foot. 
Total pressure of the steam when first admitted, P,=7200 Ib. 
Volume of 1 Ib. of steam V, =8°7825 cubic feet. 
Therefore P, V, =63234 the: raised one foot. 

Pp — 648 and consequently, 
2 
Expansion to produce the maximum useful effect s= Ge 
6 
yi =7877 
Space traversed by the piston during the action of one pound of steam, 
=V, (1—c) s=65'886 cubic feet. 
Gross effect of one pound of steam, in pounds raised one foot high, 
9 
1 
apie (765-8 —57) Pryde oy. a ago04 
Deduct for resistance of engine when unloaded fV,(1—c)s = 4744 
Effect of one pound of steam in nan resistance ores 107260 
on useful load, : 
This being multiplied by 624, gives for ae effect of one cui foot 
of water evaporated, in pounds raised one foot, : : : : 6,703,750 
It is here necessary to observe, that M. pr Pamsour distinguishes the useful 
resistance into two parts, the resistance of the useful load independently of the 
engine, and the increase in the resistance of the engine, arising from the former 
resistance, and found by multiplying it by a constant fraction which he calls 6. 
In calculating the net useful effect, he takes into account the former portion of the 
resistance only ; consequently, 
Net useful effect as defined by M. DE PAMBOUR = ass net a Gea) . (54) 
The value of 6, for double acting steam-engines generally, is considered by 
M. DE Pameour to be ?; consequently, to reduce the effect of one cubic foot of 
water as calculated - to that which corresponds with his definition, we must 
deduct ,, which leaves, 

5,865,781 lb. raised one foot: 
M. pz Pamsour’s own calculation gives, 
6,277,560 
being too large by about one-fifteenth. 
(32.) In order to shew the limit of the effect which may be expected from the 
expenditure of a given quantity of heat in evaporating water, and also to verify 
the approximate method employed in calculating the expansive action of the 
steam, I shall now investigate the maximum gross effect, including resistance of 
all kinds, producible by evaporating unity of weight of water at a higher tem- 
perature and liquefying it at a lower, and compare, in two examples, the power 
produced, with the heat which disappears during the action of the steam, as 
calculated directly. 
VOL. XX. PART I. 3¢ 
