ght in the South. During the last twelve years, however, nearly every
Southern town of importance has established its own factory for making
ice, and the process has become so perfect and cheap that the artificial
ice competes with the natural article shipped from the New England
States.

The cost of transportation, handling, and enormous waste by melting
serves to make "Boston ice" a costly luxury to the Southern consumer.
This has stimulated the invention of improved methods of making
artificial ice.

On his first visit to an ice factory, one who is not familiar with
ice-making machinery will be surprised to see large steam-engines and
boilers, with great piles of coal, and will wonder how the use of fire
and steam can assist in producing cold; but a little understanding of
the chemistry of the process will enable him to perceive the need of
such machinery.

All objects contain a certain amount of heat. The capacity for retaining
this heat varies in different substances. Liquids retain more than
solids, and gases more than liquids. If gases be compressed, their
heat-retaining capacity will be reduced in proportion. Nearly all of the
known gases may be compressed until they assume the liquid form. Gas
made from ammonia when subjected to a pressure of about one hundred and
fifty pounds to the square inch, becomes a liquid. Should the pressure
be now removed, the liquid ammonia will instantly rush into gas again,
and in doing so tries to absorb the heat which has been squeezed out of
it.

[Illustration: AN ICE "CAN."]

If this expansion into gas be allowed to take place in pipes sunk in
brine, it will draw all the heat out of the brine, and cause the brine
to become cold enough to freeze fresh water in cans suspended in it, and
convert the fresh water in the cans into solid ice.

In the factories which freeze the water in cans there is provided a very
large brine-chamber or vat, so deep that the cans may be immersed in it
nearly to their tops. The cans are about four feet deep, and are made of
galvanized iron. They are filled with pure water, and let down into the
brine through openings in the top of the vat. Between the rows of
water-cans are tiers of iron pipes running back and forth through the
brine, and throughout these pipes the expansion of gas takes place,
cooling the brine to ten degrees below zero. Ice soon begins to form on
the inside and bottom of the cans under the influence of this intense
cold. It