*Project Gutenberg*. Public domain.

273. *Q.*—But are 33 cubic feet of
steam expended per minute equivalent to a cubic foot
of water expended in the hour?

*A.*.—Not precisely, but nearly so.
A cubic foot of water produces 1669 cubic feet of
steam of the atmospheric density of 15 lbs. per square
inch, whereas a consumption of 33 cubic feet of steam
in the minute is 1980 cubic feet in the hour.
In Watt’s engines about one tenth was reckoned
as loss in filling the waste spaces at the top and
bottom of the cylinder, making 1872 cubic feet as
the quantity consumed per hour without this waste;
and in modern engines the waste at the ends of the
cylinder is inconsiderable.

274. *Q.*—What power was generated
by a cubic foot of water in the case of the Albion
Mill engines when working without expansion?

*A.*—In the Albion Mill engines when
working without expansion, it was found that 1 lb.
of water in the shape of steam raised 28,489 lbs. 1
foot high. A cubic foot of water, therefore,
or 62-1/2 lbs., if consumed in the hour, would raise
1780562.5 lbs. one foot high in the hour, or would
raise 29,676 lbs. one foot high in a minute; and if
to this we add one tenth for waste at the ends of
the cylinder, a waste which hardly exists in modern
engines, we have 32,643 lbs. raised one foot high in
the minute, or a horse power very nearly. In
some cases the approximation appears still nearer.
Thus, in a 40 horse engine working without expansion,
Watt found that .674 feet of water were evaporated
from the boiler per minute, which is just a cubic
foot per horse power per hour; but it is not certain
in this case that the nominal and actual power were
precisely identical. It will be quite safe, however,
to reckon an actual horse power as producible by the
evaporation of a cubic foot of water in the hour in
the case of engines working without expansion; and
for boiling off this quantity in flue or wagon boilers,
about 8 lbs. of coal will be required and 9 square
feet of flue surface.

MODERN MARINE AND LOCOMOTIVE BOILERS.

275. *Q.*—These proportions appear
chiefly to refer to old boilers. I wish you to
state what are the proportions of modern flue and tubular
marine boilers.

*A.*—In modern marine boilers the
area of fire grate is less than in Mr. Watt’s
original boilers, where it was one square foot to nine
square feet of heating surface. The heat in the
furnace is consequently more intense, and a somewhat
less amount of surface suffices to evaporate a cubic
foot of water. In Boulton and Watt’s modern
flue boilers they allow for the evaporation of a cubic
foot of water 8 square feet of heating surface, 70
square inches of fire grate, 13 square inches sectional
area of flues, 6 square inches sectional area of chimney,
14 square inches area over furnace bridges, ratio
of area of flue to area of fire grate 1 to 5.4.
To evaporate a cubic foot of water per hour in tubular