RS oe 


a 
te 
MECHANICAL ACTION OF HEAT. 179 
we obtain for the value of the expansive action of unity of weight of steam, 
1 
Ss, o 8, a 
d8.P=P.V 25 (1- (=) ) 
Sy, bye Ma py 2 <5) 
as “) 
s being used to denote = or the ratio of the volumes occupied by steam at the 
1 
end and at the beginning of the expansion respectively. 
A table to facilitate the computation is given in the Appendix. 
The gross mechanical action of unity of weight of steam on one side of the 
piston is found by adding to the above quantity the action of the steam before it 
begins to expand, or P, V,, and is therefore 
1 
1 Gane 
1B Wa (5-r5° ‘) . . . (46.) 
The values of the coefficients and exponent being 
1 1 
las wie thy 6 
For initial pressures between 
1 and 4 atmospheres, . : : : 7 6 -2 
4and 8 atmospheres, . : j F 6 5 2 
(24.) The following deductions have to be made from the gross action, in 
order to obtain the action effective in overcoming resistance. 
First, For loss of power owing to a portion of the steam being employed in 
filling steam-passages, and the space called the clearance of the cylinder at one 
end. Let the bulk of steam so employed be the fraction ¢S, of the space filled 
by steam at the end of the expansion ; then the loss of power from this cause is 
P,cS,=csP, V,. 
Secondly, For the pressure on the opposite side of the piston, of the steam 
which escapes into the condenser, or into the atmosphere, as the case may be. 
Let P, be the pressure of this steam; the deduction to be made for its action is 
P, 8, (1—c)=P, V, (l—e)s. 
These deductions having been made, there is obtained for the effect of unity 
of weight of water evaporated, 
1 162 
ae (5-125 ee —cs) -P,d-os}. 2 7) 
(25.) The effect of the engine in unity of time is found by multiplying the 
VOL. XX. PART I. 3B 
