
OF SINGLE-ACTING EXPANSIVE STEAM-ENGINES. 203 
Fuel for 6000 lb. of steam at 0-01d., : : . £0°2500 
Interest on £0:432, at 5 per cent... : : : 0:0216 
Estimating the cost of the engine at £250 per square foot of piston, we find 
k= 5 per cent. per annum on £250 = £12°5, 
h hin. 
and =| = 0-0217 ; ea 144 
1 
P 10 
The point C is taken on this line, at — = 5144 divisions of the axis of 
1 
abscissee to the left of O Y. 
The tangent CT being drawn, is found to touch the locus of Z at 2°800 divi- 
sions to the right of O Y. 
Then s=2°800 is the ratio of expansion sought, corresponding to the greatest 
economy. 
If we make c=0°05 as in Mr WicksTEED’s engine, then the fraction of the stroke 
_ to be performed at full pressure is 
The line BOA, then, is to be drawn so that its ordinates are Piya ess. 
1 
LV 
7 =0°323 
being nearly the same as in experiment F. 
The mean resistance of the useful load per square foot of piston is 
lve 2 P, —F=1713°6 lb. 
The duty of one square foot of piston per hour,— 
Rin = 8,225,300 foot-lb. 
And one horse-power being 1,980,000 foot-lb. per hour, the real horse-power 
of the engine is 
4-154 per square foot of piston. 
The duty of one pound of steam is 
RV,s = 97,154 foot-lb. 
To give an example of a special case, let the duty to be performed be 198,000,000 
foot-pounds per hour, being equal to 100 real horse-power, for 6000 hours per 
annum. This being called E, we find from the above data that the area of piston 
required is 
E . 
A Rin = 24:072 square feet. 
The consumption of steam per hour is 
E 
iS Eis = 2038 lb. 
which requires 2038 x 0:016=32°608 tons of boilers. 
VOL. XX. PART II. 3H 
