nsion, 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 boilers, the proportions are--
heating surface 9 square feet, fire grate 70 square inches, sectional area
of tubes 10 square inches, sectional area of back uptake 12 square inches,
sectional area of front uptake 10 square inches, sectional area of chimney
7 square inches, ratio of diameter of tube to length of tube 1/28th to
1/30th, cubical content of boiler exclusive of steam chest 6.5 cubic feet,
cubical content