Iowa voter. [volume] (Knoxville, Iowa) 1867-1874, 1871-07-27

TEE fact that thlre now exist several
-nschines " aics through the consumption
# coal pr 5uce ice. is ore quite inexpii-
cable 10 many /: and perhsps while We are
enjoying oar iced drinks, so grateful IL
The hot weather suddenly come upon us,
an explanation IT this apparent paradox
Dsy not b. unacceptable. That heat should
directly or indir- ctiy pr ducs cold seems,
II FIR thought So impo<s!oli'iy never
b lgss, in the iabor5tory OF nature this IL
40 operation Constantly going on; and Il
is In this wise:
When ver body changes from 8 solid
10 8 liquid state, or from LIQUID
70 3 yzpurous c n3ition, large amoul Is
u sensible heat disanpear Either
The temperature g. nsibie hsst) Of
The body Itself falls very much
lo~e than II was b fore it's cnange Of
state, or pes stole heat is abs'ractcd from
surrounding Dodies n maintain the ex-
pandng substance If IT'S former tempe
rature Thu heat distracted and stored
up in the body, 80 that it no longer pro-
duoes the effects popularity included in the
term hea ing" has been called latent
heat It's amount varies greatly in diff
ierent solids, liquid a d vapors.
Now there are two ways in which bodies
may be- expanded, namely: By aiding to
their heat-sensible or latent, or both-0r
ny removing the pressure their surfaces
sustain. Or we may, if we choose, both
impart heat and remove pressure stimuli
taneously.
Thus she gas chlorine, when submitted
T. pressure of about four atmOspheres,
becomes q liquid, and will remain 50 as
long a. the pressure is continued During
the act of compression, il gives off Ger
tain amount Of neat, which is the exact
equivalent of the mechanical power en-
ployed in reducing its volume. When the
pressure is removed, il expands to its orig
inaI bulk as gas, and in so doing takes
the same amount OF heat, from other
bodies, IA it lost when compressed. Air,
when compressed. gives off heat, and alb
serbs the same amount again when it ex-
pands. In reducing the volume Of bod es,
we may not only use compr ssion, but We
may also abstract heat by bringing them
into contact with colder bodies, thus pow
ertully aiding the mechanical power ia
bringing about the desired result.
But IN, chanical power ia only another
name for heat, the source of all terrestrial
power Ii we employ water wheel to
generate our po Aer, we find this possible
only because h, at has raised the water for
us. If we use wind as a motor, it is heat
that puts the air In motion and if we en-
ploy steam, we must do the same thing.
II we use an electrOmeter we tind 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
pa4es 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 repeats dly
until ice is produced
Tnus we see that heat indirectly pro-
duc,s colo, and this is only an expression
of general law. Nothing IAN gain heat
without loss OF heat in something else,
and though the gain or loss may be latent
an not app ar in the temp nature, yet we
may be sure that the sum total Ii always
the same, Scientific American