water through 1 degree, or 14 lbs. of water through 1000 degrees, supposing
the whole heat generated to be absorbed by the water. Now, if the water be
raised into steam from a temperature of 60°, then 1118.9° of heat will have
to be imparted to it to convert it into steam of 15 lbs. pressure per
square inch. 14,000 / 1118.9 = 12.512 Lbs. will be the number of pounds of
water, therefore, which a pound of carbon can raise into steam of 15 lbs.
pressure from a temperature of 60°. This, however, is a considerably larger
result than can be expected in practice.

145. _Q._--Then what is the result that may be expected in practice?

_A._--The evaporative powers of different coals appear to be nearly
proportional to the quantity of carbon in them; and bituminous coal is,
therefore, less efficacious than coal consisting chiefly of pure carbon. A
pound of the best Welsh or anthracite coal is capable of raising from 9-1/2
to 10 lbs. of water from 212° into steam, whereas a pound of the best
Newcastle is not capable of raising more than about 8-1/2 lbs. of water
from 212° into steam; and inferior coals will not raise more than 6-1/2
lbs. of water into steam. In America it has been found that 1 lb. of the
best coal is equal to 2-1/2 lbs. of pine wood, or, in some cases to 3 lbs.;
and a pound of pine wood will not usually evaporate more than about 2 1/2
lbs. of water, though, by careful management, it may be made to evaporate 4
1/2 lbs. Turf will generate rather more steam than wood. Coke is equal or
somewhat superior to the best coal in evaporative effect.

146. _Q._--How much water will a pound of coal raise into steam in ordinary
boilers?

_A._--From 6 to 8 lbs. of water in the generality of land boilers of medium
quality, the difference depending on the kind of boiler, the kind of coal,