LIQUID AIR.
Air, like water, assumes the liquid form at a certain temperature. Water
boils and vaporizes at 212 degrees Fahrenheit above zero, while liquid
air boils and vaporizes at 312 degrees below zero.
Heat and cold are practically relative terms, although scientists talk
about an "absolute zero" (the point of no heat), and Professor Dewar
fixes this point at 461 degrees Fahrenheit below zero. Others have
estimated that the force of the moon during its long night of half a
month, is reduced in temperature to six or seven hundred degrees below,
which is far lower than Professor Dewar's absolute zero. However this
may be, to an animal that is designed to live in a temperature of 70 or
80 degrees Fahrenheit, any temperature below zero would seem very cold.
If, however, we were adapted to a climate where the normal temperature
was 312 degrees Fahrenheit below zero, we should be severely burned if
we should sit down upon a cake of ice. Such a climate would be
impossible for animal existence, for the reason that there would be no
air to breathe, since it would all liquefy.
Liquid air is not a natural product. There is no place on our earth cold
enough to produce it. If the moon had an atmosphere (which it probably
has not) it would liquefy during the long lunar night, for heat radiates
very rapidly from a planet when the sun's rays are withdrawn from it.
As you have already surmised, liquid air is a product of intense cold.
Any method that will reduce the temperature of the air to 312 degrees
Fahrenheit below zero will liquefy it. Great pressure will not do this,
for we may compress air in a strong vessel until the pressure on every
square inch of the vessel is 12,000 pounds, or six tons, and still it
will not liquefy unless the temperature is brought down to the required
degree of coldness. If this is done it will change from a gas to a
liquid, but will occupy as much space as before, if it is condensed to a
pressure of six tons to the square inch.
Until twenty years ago it was supposed that oxygen and atmospheric air
(the latter a mixture of oxygen and nitrogen) were fixed gases and could
not be liquefied. In 1877, it is said that Raoul Pictet obtained the
first liquid oxygen, but only a few drops. About fifteen years later
Professor Dewar of the Royal Institution, London, succeeded in
liquefying not only oxygen but atmospheric air. And besides liquefying
the air he made ice of it.
In 1892 I visited London, where I met Professor Dewar, who invited me to
witness an exhibition of the manufacture of liquid oxygen--and
incidentally liquid air--at the Royal Institution. To me it was a most
wonderfully interesting event. I saw air, taken from the room, gradually
liquefy in a small glass test tube open at the top. When the tube was
withdrawn from the refrigerating chamber it boiled by the heat of the
room, and rapidly evaporated. We lighted a splinter of wood and blew it
out, leaving a live spark on the end of it, and held it over the mouth
of the tube, knowing that if anything like pure oxygen were evaporating
the splinter would relight and blaze (an old experiment with oxygen
gas). At first the splinter would not relight, because the evaporating
gases were a mixture of oxygen and nitrogen in the proportions to form
air. But owing to the fact that nitrogen evaporates sooner than oxygen,
a second trial was successful, for the splinter immediately began to
blaze, showing that the gas evaporating then was pure, or nearly pure,
oxygen.
When the liquid oxygen was poured into a saucer and brought into
proximity with the poles of a powerful magnet the liquid immediately
rushed out of the saucer and clung to the magnet poles; showing that
oxygen is magnetic.
Since that time other experimenters have succeeded in making liquid air
on a comparatively large scale, and the process is simple when we
consider some of the old methods.
Mr. Tripler of New York, who has made liquid air in great quantities,
does it substantially as follows: First, he compresses air to about 2500
pounds to the square inch. Of course the air is very hot when it is
first compressed because all the air in the tank has been reduced in
bulk about 166 times, and all the heat that was in the whole bulk of air
is concentrated into one-166th of the space it occupied before it was
compressed. It is 166 times hotter. There are two sets of pipes running
from the compressor to a long upright tank called the liquefier. These
pipes pass through running water, so that the compressed air is quickly
cooled down to the temperature of the water (about 50 degrees
Fahrenheit). The pipes--at least one set of them--run the whole length
of the liquefier, and most likely are coiled. This set of pipes contains
the air to be liquefied. A second set of pipes runs to the bottom of the
liquefier, where there is a valve. By opening this valve a jet of
compressed air is allowed to play on the other set of pipes, when
intense cold is produced by the sudden expansion of the air. This cold
air rushes up around the pipe containing the air to be liquefied and
escapes at the top, thus absorbing the heat until the temperature is
reduced to 312 degrees below zero. Then the air liquefies and runs into
a receptacle, where it may be drawn off at pleasure.
It will be seen that a large part of the compressed air is wasted in
cooling the remainder sufficiently to liquefy.
The use to which liquid air may be put, advantageously, is an unsolved
problem; but no doubt it will have a place in time. All great
discoveries do. Electricity had to wait a long time for recognition; but
what a part it plays now in the everyday life of the whole civilized
world!
Curious effects are produced by this intense cold. Meat may be frozen so
hard that it will give off a musical tone when struck. Here is a pointer
for the seeker of novelties in the line of musical instruments.
Liquid air furnishes a beautiful illustration of the fact that a burning
gas jet is continually forming water as well as giving out heat and
light. If we put liquid air into a tea kettle and hold it over a gas
jet, ice will form on the bottom from the water created by the flame,
and it will freeze so hard that the flame will make no impression upon
it, other than to make the ice cake grow larger.
Although liquid air is not found in nature, and is therefore called an
artificial product, it is produced by taking advantage of natural law.
Without the intellect of man it never would have been seen upon this
earth; and the same may be said concerning many things in our world,
both animate and inanimate. The genius of man is God-like. He lifts the
veil that shrouds the mysteries of nature, and here he comes in very
touch with the mind of the Infinite. Man interprets this thought through
the medium of natural law, and lo, a new product!
How much life would have been robbed of its charm and interest if all
these things had been worked out for us from the beginning! For there is
no interest so absorbing and no pleasure so keen as that of pursuit when
the pursuer is reaching out after the hidden things that are locked up
in Nature's great storehouse. From time to time she yields up her
secrets, little by little, to encourage those who love her and are
willing to work, not only for the pleasure of the getting, but for the
highest and best good of their fellows.
WATER.