arted to the cooling water.

d. The entrance of water into the refrigerator, due to the liquid
being not perfectly anhydrous.

e. The useless evaporation of water in the generator. With regard to
the amount of heat used, it will have been seen that the whole of that
required to vaporize the ammonia, and whatever water vapor passes off
from the generator, has to be supplied from without. Owing to the fact
that the heating takes place by means of coils, the steam passed
through may be condensed, and thus each pound can be made to give up
some 950 units of heat. With the absorption process worked by an
efficient boiler, it may be taken that 200,000 thermal units per hour
may be eliminated by the consumption of about 100 lb. of coal per
hour, with a brine temperature in the refrigerator of about 20 deg. Fahr.

_Compression Process._--In this process ammonia is used in its
anhydrous form. So far as the action of the refrigerator is concerned,
it is precisely the same as it is in the case of the absorption
apparatus, but instead of the vapor being liquefied by absorption by
water, it is drawn from the refrigerator by a pump, by means of which
it is compressed and delivered into the condenser at such pressure as
to cause its liquefaction at the temperature of the cooling water. It
must be borne in mind, however, that allowance must be made for the
rise of temperature of the water passing through the condenser, and
also for the difference in temperature necessary in order to permit
the transfer of heat from one side of the cooling surface to the
other. In a compression machine the work applied to the pump may be
accounted for as follows:

a. Friction.

b. Heat rejected during compression and discharge.

c. Heat acquired by the ammonia in passing through the pump.

d. Work expended in discharging the compressed vapor from the pump.

But against this must be set the useful mechanical work performed by
the vapor entering the pump. The heat rejected in the condenser is the
heat of vaporization taken up in the refrigerator, less the amount due
to the higher pressure at which the change in physical state occurs,
plus the heat acquired in the pump, and less the amount due to the
difference between the temperature at which the vapor is liquefied in
the condenser and that at which it entered the pump. An ammonia
compression machine, as applied to ice making, contains ice-making
tanks, in which is circulated a brine mixture, unc