ongealable at any
temperature likely to be reached during the process. This brine also
circulates around coils of wrought iron pipes, in which the liquid
ammonia passing from the condenser is vaporized, the heat required for
this vaporization being obtained from the brine. A pump draws off the
ammonia vapor from the refrigerator coils, and compresses it into the
condenser, where, by means of the combined action of pressure and
cooling by water, it assumes a liquid form, and is ready to be again
passed on to the refrigerator for evaporation. The ammonia compression
process is more economical than the absorption process, and with a
good boiler and engine about 240,000 thermal units per hour can be
eliminated by the expenditure of 100 lb. of coal per hour, with a
brine temperature in the refrigerator of about 20 deg. Fahr.

GENERAL CONSIDERATIONS.

From what has been said, it will have been seen that, so far as the
mere application is concerned, there is no difference whatever between
the absorption and compression processes. The following
considerations, therefore, which chiefly relate to the application of
refrigerating apparatus, will be dealt with quite independent of
either system. The application of refrigerating apparatus may roughly
be divided into the following heads:

a. Ice making.

b. The cooling of liquids.

c. The cooling of stores and rooms.

_Ice Making._--For this purpose two methods are employed, known as the
can and cell systems respectively. In the former, moulds of tinned
sheet copper or galvanized steel of the desired size are filled with
the water to be frozen, and suspended in a tank through which brine
cooled to a low temperature in the refrigerator is circulated. As soon
as the water is completely frozen, the moulds are removed, and dipped
for a long time into warm water, which loosens the blocks of ice and
enables them to be turned out. The thickness of the blocks exercises
an important influence upon the number of moulds required for a given
output, as a block 9 in. thick will take four or five times as long to
freeze solid as one of only 3 in. In the cell system a series of
cellular walls of wrought or cast iron are placed in a tank, the
distance between each pair of walls being from 12 to 16 in., according
to the thickness of the block required. This space is filled with the
water to be frozen. Cold brine circulates through the cells, and the
ice forms on the outer surfaces, graduall