190 
w = weight of water in boiler at the commencement of 
the experiment. 
w' = weight of water in boiler at the close of the experi- 
ment. 
q = weight of wood used for lighting the fire. 
1 = co-efficient of latent heat of steam = 965.7. 
t = quantity of heat necessary to raise the water in tanks 
from its mean temperature to that at which it is evaporated. 
t' = quantity of heat necessary to raise the water in the 
boiler from the initial to the final temperature. 
t" = quantity of heat necessary to raise water at the tem- 
perature of the tanks to the final temperature of the boiler. 
P == weight of coal consumed during experiment. 
E = the co-efficient of evaporative power of wood. 
E' = co-efficient of the evaporative power of coal. 
Then 
(W — E g -f w — w') 1 -j- ( W -f w — wQ t + wt' -f- (w' — w) t" ^ 
p-j — .L. 
The relative value of the different fuels, as shown by 
these experiments, need not be here enumerated. The 
average result of thirty experiments on coal and patent fuel 
gave 8.69 as the number of lbs. of water converted into 
steam by 1 lb. of coal. This quantity, it may be remarked, 
is far below the theoretical result. There are at present 
no authentic experiments on other species of fuels, with 
which these may be compared. I have, however, taken an 
average of the theoretical value of various fuels, as obtained 
from the litharge experiments, which will be sufficient to 
exhibit their relative economic importance. 
For different kinds of wood, lbs. of lead reduced 
by 1 lb. of dried wood 13.4 
Do. do. do., wood containing 90 p. c. of Ho 13.9 
No. of lbs. of lead reduced by 1 lb. of wood char- 
coal 30.9 
Ditto varieties of peat (foreign) 14.7 
