Part 3 out of 3
Moulds for 225 different characters are contained in this frame.]
Cold, of course, is but the absence of heat, and so refrigerating
machinery is designed to extract the heat from whatever substance it is
desired to cool. The refrigerating agent used to extract the heat from
the cold chamber must in turn have the heat extracted from it, and so
the process must be continuous.
Water, when it boils and turns into steam or vapour, is heated by or
extracts heat from the fire, but water vapourises at a high temperature
and so cannot be used to produce cold. Other fluids are much more
volatile and evaporate much more easily. Alcohol when spilt on the hand
dries almost instantly and leaves a feeling of cold--the warmth of the
hand boils the alcohol and turns it into vapour, and in doing so
extracts the heat from the skin, making it cold; now, if the evaporated
alcohol could be caught and compressed into its liquid form again you
would have a refrigerating machine.
Alcohol is expensive and inflammable, and many other volatile substances
have been discarded for the one or the other reason. Of all the fluids
that have been tried, ammonia has been found to work most
satisfactorily; it evaporates at a low temperature, is non-inflammable,
and is comparatively cheap.
The hold of the supply-ship mentioned at the head of this chapter was a
vast refrigerator, but no ice was used except that produced mechanically
by the power in the ship. To produce the cold in the hold of the ship it
was necessary to extract the heat in it; to accomplish this, coils ran
round the space filled with cold brine, which, as it grew warm, drew the
heat from the air. The brine in turn circulated through a tank
containing pipes filled with ammonia vapour which extracted the heat
from it; the brine then was ready to circulate through the coils in the
hold again and extract more heat. The heat-extracting or cooling power
of the ammonia is exerted continually by the process described below.
Ammonia requires heat to expand and turn into vapour, and this heat it
extracts from the substance surrounding it. In this marine refrigerating
machine the ammonia got the heat from the brine in the tank, then it was
drawn by a pump from the pipes in the tank, compressed by a power
compressor, and forced into a second coil. The second coil is called a
condenser because the vapour was there condensed into a fluid again.
Over the pipes of the condenser cool water dripped constantly and
carried off the heat in the ammonia vapour inside the coils and so
condensed it into a fluid again--just as cold condenses steam into
water. The compressor-pump then forced the fluid, ammonia through a
small pipe from the condenser coils to the cooling coils in the tank of
brine. The pipes of the cooling coils are much larger than those of the
condenser, and as the fluid ammonia is forced in a fine spray into these
large pipes and the pressure is relieved it expands or boils into the
larger volume of vapour and in so doing extracts heat from the brine.
The pump draws the heated vapour out, the compressor makes it dense, and
the coils over which the cool water flows condenses it into fluid again,
and so the circuit continues--through cooler, pump, compressor, and
condenser, back into the cooling-tank.
In the meantime, the cold brine is being pumped through the pipes in the
hold of the ship, where it extracts the heat from the air and the rows
of sides of beef and then returns to the cooling-tank. In the
refrigerating plant, then, of the supply-ship, there were two
heat-extracting circuits, one of ammonia and the other of brine. Brine
is used because it freezes at a very low temperature and continues to
flow when unsalted water would be frozen solid. The ammonia is not used
direct in the pipes in a big space like the hold of a ship, because so
much of it would be required, and then there is always danger of the
exposed pipes being broken and the dangerous fumes released.
Opposite as it may seem, heat is required to produce cold--for steam is
necessary to drive the compressor and pump of a refrigerating plant, and
fire of some sort is necessary to make steam.
The first artificial refrigerating machines produced cold by compressing
and expanding air, the compressed air containing the heat being cooled
by jets of cool water spirted into the cylinder containing it, then the
compressed air was released or expanded into a larger chamber and
thereby extracted the heat from brine or whatever substance surrounded
It is in the making of ice, however, that refrigerating machinery
accomplishes its most surprising results. It was said in the writer's
hearing recently that natural ice costs about as much when it was
delivered at the docks or freight-yards of the large cities of the North
as the product of the ice-machine. Of course, the manufactured ice is
produced near the spot where it is consumed, and there is little loss
through melting while it is being stored or transported, as in the case
of the natural product.
There are two ways of making ice--or, rather, two methods using the same
In the can system, a series of galvanized-iron cans about three and a
half feet deep, eight inches wide, by two and a half feet long are
suspended or rested in great tanks of brine connecting with the
cooling-tank through which the pipes containing the ammonia vapour
circulates. The vapour draws the heat from the brine, and the brine,
which is kept moving constantly, in turn extracts the heat from the
distilled water in the cans. While this method produces ice quickly, it
is difficult to get ice of perfect clearness and purity, because the
water in the can freezes on the sides, gradually getting thicker,
retaining and concentrating in the centre any impurities that may be in
the water. The finished cake, therefore, almost always has a white or
cloudy appearance in the centre, and is frequently discolored.
In an ice-plant operated on the can system a great many blocks are
freezing at once--in fact, the whole floor of a great room is
honeycombed with trap-doors, a door for each can. The freezing is done
in rotation, so that one group of cans is being emptied of their blocks
of ice while others are still in process of congealing, while still
others are being filled with fresh water. When the freezing is complete,
jets of steam or quick immersion of the can in hot water releases the
cake and the can is ready for another charge.
The plate system of artificial ice-making does away with the
discoloration and the cloudiness, because the water containing the
impurities or the air-bubbles is not frozen, but is drawn off and
In the plate system, great permanent tanks six feet deep and eight to
twelve feet wide and of varying lengths are used. These tanks contain
the clean, fresh water that is to be frozen into great slabs of ice.
Into the tanks are sunk flat coils of pipe covered with smooth, metal
plates on either side, and it is through these pipes that the ammonia
vapour flows. The plates with the coils of pipe between them fit in the
tank transversely, partitioning it off into narrow cells six feet deep,
about twenty-two inches wide, and eight or ten feet long. In operation,
the ammonia vapour flows through the pipes, chilling the plates and
freezing the water so that a gradually thickening film of ice adheres to
each side of each set of plates. As the ice gets thicker the unfrozen
water between the slabs containing the impurities and air-bubbles gets
narrower. When the ice on the plates is eight or ten inches thick very
little of the unfrozen water remains between the great cakes, but it
contains practically all the impurities. When the ice on the plates is
thick enough, the ammonia vapour is turned off and steam forced through
the pipes so the cakes come off readily, or else plates, cakes, and all
are hoisted out of the tank and the ice melted off. The ice, clear and
perfect, is then sawed into convenient sizes and shipped to consumers or
stored for future use. Sometimes the plates or partitions are permanent,
and, with the coils of pipes between them, cold brine is circulated, but
in either case the two surfaces of ice do not come together, there being
always a film of water between.
Still another method produces ice by forcing the clean water in
extremely fine spray into a reservoir from which the air has been
exhausted--into a vacuum, in other words; the spray condenses in the
form of tiny particles of ice, which are attached to the walls of the
reservoir. The ice grows thicker as a carpet of snow increases, one
particle falling on and freezing to the others until the coating has
reached the required thickness, when it is loosened and cut up in cakes
of convenient size. The vacuum ice is of marble-like whiteness and
appearance, but is perfectly pure, and it is said to be quite as hard.
More and more artificial ice is being used, even in localities where ice
is formed naturally during parts of the year.
Many of the modern hotels are equipped with refrigerating plants where
they make their own ice, cool their own storage-rooms, freeze the water
in glass carafes for the use of their guests, and even cool the air that
is circulated through the ventilating system in hot weather. In many
large apartment-houses the refrigerators built in the various separate
suites are kept at a freezing temperature by pipes leading to a
refrigerating plant in the cellar. The convenience and neatness of this
plan over the method of carrying dripping cakes from floor to floor in a
dumb-waiter is evident.
Another use of refrigerating plants that is greatly appreciated is the
making of artificial ice for skating-rinks. An artificial ice
skating-rink is simply an ice machine on a grand scale--the ice being
made in a great, thin, flat cake. Through the shallow tanks containing
the fresh water coils of pipe through which flows the ammonia vapour or
the cold brine are run from end to end or from side to side so that the
whole bottom of the tank is gridironed with pipes, the water covering
the pipes is speedily frozen, and a smooth surface formed. When the
skaters cut up the surface it is flooded and frozen over again.
So efficient and common have refrigerating plants become that
artificially cooled water is on tap in many public places in the great
cities. Theatres are cooled during hot weather by a portion of the same
machinery that supplies the heat in winter, and it is not improbable
that every large establishment, private, or public, will in the near
future have its own refrigerating plant.
Inventors are now at work on cold-air stoves that draw in warm air,
extract the heat from it, and deliver it purified and cooled by many
Even the people of this generation, therefore, may expect to see their
furnaces turned into cooling machines in summer. Then the ice-man will
cease from troubling and the ice-cart be at rest.