Wyandot County Republican. [volume] (Upper Sandusky, Ohio) 1869-1903, 1871-07-20
Miscellany.
How Bodies May be Frozen by Heat.

IHE 1acb that there now exist several
machines which through the consumption
of coal produce ice, is one quite inexpi-
cable to many; and perhaps while we are
enjoying our iced drinks, SO grateful in
the hot weather suddenly corle upon US,
an explanation OF this apparent paradox
may not be unacceptable. That heat should
directly or indirectly produce cold seems,
at first thought, an impossibility; never
theless, in the laboratory of nature this is
an operation constantly going on; and it
is in this wise:
Whenever body changes from solid
to liquid state, or from liquid
to ,yapofous condition, large amounts
of sensible heat disappear Either
the temperature sensible heat) of
the body itself falls very much
lower than it was before its change of
state, or sensible heat is distracted from
surrounding bodies to maintain the ex-
panding substance of its former tempe.
rature The heat distracted and stored
up in the body, so that it no longer pro-
duces the effects popularity included in the
term "healing," has been called latent
heat. It's amount varies greatly in diff
ierent solids, liquids, and vapors.
Now there are two ways in which bodies
may be expanded, namely: by adding to
buOlk uC1b-SGliSlOlSU VI lGtCub, VI UOtll-UT
by removing the pressure their surfaces
sustain. Or we may, if we choose, both
impart heat and remove pressure sinul-
taneously.
Thus the gas chlorine, when submitted
to a pressure of about four atmospheres,
becomes liquid, and will remain SO as
long as the pressure is continued. During
the act OF compression, it gives OFF GER
tain amount of heat, which is the exact
equivalent of the mechanical power en-
ployed in reducing its volume. When the
pressure is removed, it expands to its orig
inal bulk as gas, and in so doing takes
the same amount OF heat, from other
bodies, as it lost when compressed. Air,
when compressed, gives off heat and ab.
serbs the same amount again when it ex-
pands In reducing the volume Of bodies,
we may not only use compre ssion, but we
may also abstract heat by bringing them
into contact with colder bodies, thus pow
erfully aiding the mechanical power in
bringing about the desired result.
But mechanical power is only another
name for heat, the sourca of all terrestrial
power If we employ a water wheel to
generate our power, we find this possible
only because heat has raised the water fol
us. Ii we use wind as motor, it is heat
that puts the air in motion and if we en-
ploy steam, we must do the same thing
If we use an electrometer we find our ma
terials prepared for us through the same
agency.
The various ice machines employ vola.
tile materials such as expand into gas at
ordinary temperatures, or at least do SO
when atmospheric pressure is removed
from their surfaces. In thus expanding
they abstract heat from water placed in
suitable vessels, brought in contact with
the absorbing bodies The expanded
gases are next compressed, the heat given
off during the compression being absorbed
by some other body-most generally
water. The condensed and cooled mate
rails are then allowed to expand in con
tact with the vessels containing the water
to be frozen again, and so on repeatedly
until ice is produced =
Thus we see that heat indirectly pro
duces cold, and this is only an expression
Of a general law. Nothing can gain heat
without loss OF heat in something else
and though the gain Or loss may be Iatent
AMI not app, ar in the temp erature, yet we
may be sure that the sum total is alwayl
the same. .-Scientifc american.