n submitted to a pressure of about 95 pounds.
During the process of liquefaction the ammonia gives up a large amount
of heat, which if absorbed or radiated while the ammonia is in the
liquid condition, the gas when allowed to expand will absorb from its
surroundings an amount of heat equal to that radiated, producing a
very great lowering of temperature. It is this principle that is
utilized in refrigeration and ice making. In the absorption system,
where aqua ammonia is used, the liquor is contained in a retort to
which heat is applied by means of a steam coil, and a great part of
the gas which was held in solution by the water is expelled, and
carries with it a small amount of water or vapor. This passes into a
separator in the top of a condenser, from which the water returns
again to the retort, the ammonia gas, under considerable pressure,
passing into the coolers. These are large receptacles in which the gas
is permitted to expand. By such expansion heat is absorbed and the
temperature of the surroundings is lowered. From the coolers the gas
returns to the absorber, from which it is pumped, in liquid form, into
the retort, to be again heated, the gas expelled and the process
repeated. As the gas passes through the different processes, being
heated under pressure, cooled, expanded again, more or less
decomposition takes place, presumably from a combination of a small
portion of the nitrogen with vegetable, animal, or mineral matter that
finds its way into the system. Such decomposition, with the loss of
nitrogen, leaves a small portion of free hydrogen, which is the gas
that can be drawn from the top of the absorber, ignited and burned.
The presence of hydrogen gas in the absorber is not necessarily
detrimental to the effectiveness of the system, but as hydrogen does
not possess the qualities of absorbing heat in the same way and to the
same extent as ammonia, the presence of hydrogen makes the operation
of the apparatus somewhat less efficient.--_Stationary Engineer._

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The refrigerating apparatus illustrated and described in the
SCIENTIFIC AMERICAN SUPPLEMENT of June 25, No. 812, is substantially
that patented by Messrs. Erny, Subers & Hoos, of Philadelphia. The
illustration was copied from their patents of November and February
last.

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