M'arthur Democrat. (McArthur, Vinton County, Ohio) 1853-1865, 1858-05-13


salt produce cold enough to freeze
cream 7" '' '"'U'I His.
Philosophically speaking, the ex.
preston produce cold," is incorrect.
There is no such positive agency as
cold, Just as there is really no such
color as black. Black is the absence
ofcolor, and cold is the absence Of heat.
In mixing snow and salt, therefore,
what we produce is the absence Of
heat. In other words, heat is absorb-
ed in such way as to be no longer
present; or rather, no longer sensible;
so as to act upon our nerves or upon
the thermometer. Strictly speaking,
the heat is still there. Why, then, do
we not feelit9 Because it has become
latent; because it has entered into
such an inanimate combination with
the salt water resulting from the lique-
faction of the snow and salt, as to be
no longer perceptible.
And why has the heat thus entered
into the salt water9 Because it re-
quires more heat to keep a liquid in
its state of liquidity than it does to
keep a solid in its state of solidity;
therefore, whenever a solid, like ice
and salt, assumes a liquid form, itab.
sorbs from surrounding objects a con-
siderable quantity Of heat, which, be.
ing engaged in preserving the liquid
ity ofthe substance, becomes insensi-
bic or latent. This is called by chem.
lists the heat of fuidity.
Now, when cream is brought into
the immediate neighborhood of snow
and salt while it is changing from a
solid to a liquid state, heat is of course
distracted from it, and it necessarily
freezes. The heat which served to
keep it in a fluid state has gone into
the salt water, to keep it in similar
condition. Cold results from the melt
ing of all substances, but the peculiar
advantage of the ice and salt mixture
| is that it requires no heat to liquify it.
The liquefaction results from the
chemical action of the ice and salt,
which have what chemists call an
affinity for each other--a tendency to
combine. Whenever liquefaction is
thus suddenly produced, without the
application OF heat, a freezing mix
ture is the result. There are many
such mixtures, from the melting O.
which ice.cream may be manufactured
where there is no ice or snow. They
all act upon the same principle. The
heat of them, we believe, is mixture
of nitrate ofammonia with the ordina
ry washing soda. This will nearly
freeze mercnry. When Fahrenheit
made his thermometer, he knew OF n,
greater degree of cold than that whicI
results from the snow end salt mix
ture, and very unscientifcally fxeC
upon it as his Zero, or starting point
! Modern chemists, taking advantage o
the principle of which we are treating
have brought a refrigeration equal t.
| 1876 2 below Fahrenheit's zero. DR.
Kane and his companions wintered il
an atmosphere often as cold as go Q
below, and sometimes reaching 100
When liquids are converted into
vapor, the same phenomena take:
place as those that accompany the
| iiquefaction of solids. Many persons
have noticed the cold produced by the
rapid evaporation of ether or alcohol
in the palm of the hand. Wine cool
ers are made on this principle, and
water is cooled in hot climates by pro
noting evaporation from the surface
of the vessel which contains it.. 1t is
the chilliness resulting from eVapora.
ton which constitutes the danger o.
suffering wet clothes to dry upon the
person.
AS might be anticipated, when va
pors are changed to liquids, or liquids
to solids, she heat which had been alb
sorbed is given out again, and tht
temperature of surrounding objects i.
proportionably raised. If the SNOW
and salt could he soliilfied again, al
rapidly as they were melted, the hea
evolved would be as great as the colo
had been. This sudden solidifcatior
does not often take place. The slak
ing of lime is a familiar instance of it
The heat, in this case, does not pro
ceed from the lime, as many suppose
but from the water. The lime anC
water have such an affinity or attrac
ton from each other, that the latte
Immediately unites with the forme
and becomes solidifed, thus liberatin;
the heat or fnidity of the water, an,
raising the temperature. .s8 .
We have used the word heat in it
ordinary acceptation, as signifyiHi
both cause and effect. In strict chem
ical language, heat is the sensation W
experienceinitouching heated body
the cause of that sensation is propen
, termed colorzc.--ROckiagham Va
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