The daily dispatch. [volume] (Richmond [Va.]) 1850-1884, 1870-07-30

1t j. well known that on the tops Of very
high mountains il is very difficult to cook
..gS and Potatoes in the ordinary way. The
article MAY be tImblcd about in the boiling
u,Iid during the legitimate three min
utcS." but At the end of that time the eggs
viii he far from done" a much longer
time must bc allowed, and even thou the
r-g> will not be very hard. II, now, i'll or
der to discover the catise of all this, we en-
anime the water with i thermometer we
viii ind that it is boiling, or in other words,
It Is passing Oft into steam at Il temperature
lar below 2l2 degrees. The cause of this
!, ut these great elevations the pressure OF
'hc atmosphere is much less than in the
lower regions. But this diminished pres
>ure We can produce by means of
the air-pump, and when we do so the
water gives off steam very rapidly
and becomes very cold, but it does
not freeze; for as soon us the air
has been al removed from the glass vessel
or receiver of the air-pump, the Vapor OF
water rises and fills it., the process is brought
:" Il close, and we cannot, rs Il general
thing, remove the watery vapor with sutti-
"rut rapidlty 10y means of the pHmp alone.
But il happens that some substances, such
Is very dry oat meal, and particularly oil of
Nltriol, have such II powerful attraction for
water that they remove it very rapidly from
any confined atmosphere i'll which they may
lac placed. Indeed, oil of vitriol, or, us it Is
called by chemists, sulphuric acid, has such
powerful attraction for watcry vapor that
ii condcnseS it, combines with it, and be-
comes very hot. SO powerful is this affinity,
that If We take jar of cold acid and IN
equal jar Of ice-cOld water and mix them
together, they will become boiling hot. If,
now, we place some Of This ACID In the re-
Crlvcr along With the water, as fast us the
NApor OF water rises it will be absorbed by
the acid and the water will continue to
give OF fresh vapor until its temperature
has been reduced before the yaporing
point. This point is never reached, how
ever, until the water has been frozen. III
this way il is easy TO make Ice in il warm
leCturc-room, and this was the method
pump which bears his name, proposed to
manufacture ice for sale. But the process
l. too difficult and too imperfect to allow of
IT. being used far anything but an expert
Iucnt.
Liquid carbonic acid, although il is capa-
hIc Of producing such low temperature, is
not available for practical purposes, and
consequently other liquids have been re-
sorted 10, such AZ ether, ammonia, and
some OF the products derived from the dis
'Ilation oi petroleum. w nen these liquids
are employed an air-pump is always used,
ana OF course on the large scale steam
engine Is USED to drive the air-pump. The
process Is as follows: The water to be
frozcn having been placed in vessels made
oi sheet metal, so that the heat may be
rapidly conducted away, these vessels are
surrounded with the freezing liquid, which
may be ether, ammonia, cryOgene, or any
other available fluid. The apparatus is so
arranged that while the mouths of the
freezing boxes are open to the air,
the liquid that surrounds their outer
surface is contained in an alright receiver,
and from this receiver the air and yapor are
exhausted by means of an air-pump. The
evaporation Of the liquid soon lowers the
temperature so far that the water freezes,
and ice Is thus produced. To prevent any
loss OF the freezing liquid, the apparatus is
10 arranged that the same pump that ex-
hausts ON one side condenses on the other.
me Fapor of the liquid lis therefore power
iiully compressed and reconyerted into a
liquid which, after being cooled, is again
passed into the refrigerator TO be used over
gam. We say after 1t has been cooled;
Tor. after compression 10 the liquid form
u IL very hot. Aud thus The steam.