
OF SINGLE-ACTING EXPANSIVE STEAM-ENGINES. 199 
The data respecting the dimensions and load of the engine, which are constant 
throughout the experiments, are the following :— 
Area of piston, : 7 . A=34-854 square feet. 
Stroke, . : y ; ; Z =10 feet. 
Cubic space traversed by piston during one down stroke, = A /=348:54 cubic feet. 
Clearance and valve-boxes, 5 é : ; : 4 18-00 

Sum, F 366°54 
Therefore, c=0:05 
R=useful load of piston, . . : =1597: Ib. per square foot. 
F= additional resistance, . é : = 2666 bas ws 
R+F= total mean pressure on piston, = 1863-6 
The mode of calculation is the following :— 
Mr WicksTEeEp states the fraction J of the stroke performed at full pressure in 
each experiment. From this the ratio of expansion s is computed by equation 
(0), giving in this case 
1 _ 9.95" 40-05 
s L : 
The value of Z corresponding to s is then found by means of the third column 
of Table second ; that column being selected because the initial pressures were all 
below four atmospheres. This affords the means of determining the initial pressure 
of the steam by equation (59), viz. :— 
P,=7 (R+F)=18636 5 
By using Table first according to the directions prefixed to it, the volume of 
one pound of steam at the pressure P,, in cubic feet, is calculated, and thence, by 
equation (60), the weight of steam per stroke, according to theory, which is com- 
pared with the weight as ascertained by experiment. 
Further to illustrate the subject, the useful effect, or duty of a pound of steam, 
is computed according to the theory and the experiments respectively, and the 
results compared. 
The following Table exhibits the results. 
VOL. XX. PART II. og 
