The Princeton union. [volume] (Princeton, Minn.) 1876-1976, 1911-11-16
OF: air. ! I

It May Readily Turn the Their
mometer Into a Fibber.
THE BOILING WATER POINT.
Degrees, but Under Certain Condi-
tions 1t May Be Several Hundred
Degrees-The Critical Temperature.
On an ordinary Fahrenheit thermom-
eter there is written opposite PIP de-
grees Boiling point Of water" and OPP
posite 80 degrees Freezing point of
water Neither Of these is correct ex-
cept for a certain condition Of the at
mosphere, and that is when it gives on
the barometer about thirty inches, or
fifteen pounds pressure to the square
inch. This is the ordinary pressure at
what is known as sea level, and to this
all thermometers are elaborated. In a
mountainous region the pressure is
hardly ever so much as fifteen pounds.
and water boils at sometimes as low as
200 degrees.
If water is boiled in a diving bell,
where the pressure is forty or fifty
pounds a square inch, it's temperature
will be several hundred degrees in
stead of PIP. If water is boiling in
near vacuum the temperature is so
small that the hand thrust into the
water would actually feel cold.
What has been said about the boiling
point applies to some extent to the
freezing point, but here it differs for
different materials, whereas the re-
marks about the boiling point of water
apply to the boiling points of all
liquids
Some substances when they freeze
become larger, while others become
smaller. On this depends the freezing
point at different pressures Of atmos-
phere. Water expands on freezing; so
do type metal and some other things.
All other substances become smaller
on freezing. Water pipes burst when
the water freezes. Coins of gold and
silver are stamped instead of being
nodded, for the metals grow smaller on
freezing or solidifying, and consequent
~ the coin would be wabbly.
1t has been found that the things
that expand on solidifying, as water,
freeze at lower temperature when
the pressure is increased, while the
others freeze at higher. When a
substance that expands freezes under
higher pressure than usual it has to
exert more force to shove the pressure
away, and consequently has to use up
more of its heat energy, thus losing
more heat and becoming colder.
Take the substance that contracts
when it solidifies. The pressure will
help it to get smaller, and consequent
~ the greater the pressure the less
heat it has to lose On attaining the
solid state. so it will freeze at higher
temperature. If the pressure is great
enough it may freeze or solidify at
thousand degrees temperature, which
is high enough to change most sub
mospheric pressure.
This is one Of the reasons advanced
to prove that the interior Of the earth
is solid. for the assumption is that the
core is made up Of substances that
contract when freezing, and there is,
Of course, an enormous pressure a few
hundreds of miles below the surface.
In regard to the boiling points of
liquids. there is an upper limit to the
point at which thing boils-that is,
changes to the state of vapor. 1t is
called the critical temperature. No
matter how great a pressure exists on
a substance, if it is at temperature
greater than it's critical it will change
to vapor anyhow.
The ignorance of this point held
back the making of liquefied gases
such as air, carbon dio1ide. etc.-for
many years. The experimenters tried
to iquefy gases at ordinary temporal
lures by enormous pressures. whereas
if they had just cooled the gases be-
low their critical temperatures before
applying the pressure iquefaction
would have ensued Immediately.
This is the method employed today
in making liquid air. The air is COM
pressed at first and then allowed to
issue from a small orifce, thus ex-
panding and cooling, is then pumped
back and compressed by the pump,
allowed to go through the orifce
again, thus cooling still more, until at
last it is below the critical tempera-
ture. when the compression caused by
the pump liquefes it. - Lawrence
Hodges in Chicago Record-Herald.