hour be equivalent to an actual horse power, and 28.9 cubic inches of water
be requisite for the condensation of a cubic inch of water in the form of
steam, 28.9 cubic feet of condensing water per horse power per hour, or
13.905 cubic inches per second, will be necessary for the engine, and the
size of the injection orifice must be such that this quantity of water
flowing with the velocity of 43.15 ft. per second, or 517.8 inches per
second, will gain admission to the condenser. Dividing, therefore, 13.905,
the number of cubic inches to be injected, by 517.8, the velocity of influx
in inches per second, we get 0.02685 for the area of the orifice in square
inches; but inasmuch as it has been found by experiment that the actual
discharge of water through a hole in a thin plate is only six tenths of the
theoretical discharge on account of the contracted vein, the area of the
orifice must be increased in the proportion of such diminution of effect,
or be made 0.04475, or 1/22d of a square inch per horse power. This, it
will be remarked, is the theoretical area required per actual horse power;
but as the friction and contractions in the pipe further reduce the
discharge, the area is made 1/15th of a square inch per actual horse power,
or rather per cubic foot of water evaporated from the boiler.

335. _Q._--Cannot the condensation of the steam be accomplished by any
other means than by the admission of cold water into the condenser?

_A._--It may be accomplished by the method of external cold, as it is
called, which consists in the application of a large number of thin
metallic surfaces to the condenser, on the one side of which the steam
circulates, while on the other side there is a constant current of cold
water, and the steam is condensed by coming into contact with the cold
surfaces, without mingling with the water used for the purpose of
refrigeration. The first kind of condenser employed by Mr. Watt was
constructed after this fashion, but he found it in practice to be
inconvenient from its size, and to become furred up or incrusted when the
water was bad, whereby the conducting power of the metal was impaired. He
therefore reverted to the use of the jet of cold water, as being upon the
whole preferable. The jet entered the condenser instead of the cylinder as
was the previous practice, and this method is now the one in common use.
Some few years ago, a good number of steam vessels were fitted with Hall's
condensers,