_A condenser_ is an apparatus, separate from the cylinder, in which
exhaust steam is condensed by the action of cold water; _condensation_
is the act or process of reducing, _by depression of temperature or
increase of pressure_, etc., to another and denser form, as gas to the
condition of a liquid or steam to water. There is an electrical device
called “a condenser” which must not be confounded with the hydraulic
apparatus of the same name; there is also an optical instrument
designated by the same term, which belongs to still another division of
practical science.
_A vacuum_ is defined very properly as an empty space; a space in
which there is neither steam, water or air—the absolute absence of
everything. The condenser is the apparatus by which, through the
cooling of the steam by means of cold water, a vacuum is obtained.
_The steam after expelling the air from the condenser fills it with its
own volume_ which is at atmospheric pressure nearly 1700 times that of
the same weight of water.
Now when a vessel is filled with steam at atmospheric pressure, and
this steam is cooled by external application of cold water, it will
immediately give up its heat, which will pass off in the cooling water,
and _the steam will again appear in a liquid state_, occupying only
1/1700 part of its original volume.
But if the vessel be perfectly tight and none of the outside air can
enter, the space in the vessel not occupied by the water contains
nothing, as before stated. The air exerting a pressure of nearly
15 pounds to the square inch of the surface of the vessel tries to
collapse it; now if we take a cylinder fitted with a piston and connect
its closed end to this vessel by means of a pipe, the atmospheric
pressure will push this piston down. The old low pressure engines were
operated almost entirely upon this principle, the steam only served to
push the piston up and exhaust the air from the cylinder.
In Fig. 578 is exhibited the effect of jets of water from a spray
nozzle meeting a jet of steam; the latter instead of filling the space
with steam is returned to its original condition of water and the space
as shown becomes a vacuum.
Briefly stated condensation and the production of a vacuum may be used
to advantage in the following ways: