The Ottawa free trader. [volume] (Ottawa, Ill.) 1843-1916, 1857-03-21

Doi.ing Water.
We live, and move, and have our being al
the bottom of an atmospheric ocean whose
lower strata are pressed upcn by all above
them. Unlike the waters Of the common
sea, the atmosphere yields considerably to
this superintendent pressure. Ii shrinks
ike compressed spring, and ike II, e1er-
cises an elastic force proportioncd 10 the
weight which It has to bear / pillar o.
air, with base Of one square inch resting
upon the surface of the sea, and reaching
to the top Of the atmosphere, weighs in
round numbers fifteen pounds; and this
therefore Is the pressure cXertcd by the
atmosphere on each square inch Of the sea 5
surface. II varies with narrow limits. ac-
cording as the pressure is that ol the warm.
light air Of the south, or Of the cool. dense
air OF the north: in the former cas-. the ba-
romcter falls, in the latter Il rises. We ha vc
heard an intelligent youth ask the following
question Suppose room containing peo-
PIE TO be shut Up, ard every chink and
Granny closed, SO that al communication
shall be cut away between the air within
and thst without. Here, although the cell
ing and ais Interpose TO shield the Deople
in the room from the pressure Of the atrnos-
paerc, still each Of them bears the same
pressure as person outside the room; and
I haroFnetrfc column will stand as high with
III the room a without il. VI hat is the rea-
son: The reason is. that the air within
theroom possesses tEc full elastic force which
tie pr' ssurc Of the 4 mosphrrc can give il /;
the spring was compressed before the room
was cio>od, and It's power Cf lifting the ba-
ronetric column is therefore the same as
that Of the free atmosphere
\ vessel Of water, with its surface ex-
posed, yields up vapor al all temperatures,
aud the water viii finally disappear; but the
elastic force Of This vapor will depend on the
temperature at "l.ich il is generated, being
greater the higher the temperature If the
heat be sufficient TO boil the water, bubbles
rise and sometimes foat for considerable
time upon the surface.
Let Us consider the casc-ot such bubble,
whcse area is one SQUARE inch. efrak;e
thing bears the atmospheric prv--rrr- vf If
teen pounds. Why, then, does not the film
burst: Simply because the elastic force OF
the steam within the bubble is exactly equal
to the elastic force Of the air without 80
that the film Is IL realty placed between two
gaseous cushions, whicl. press upon il equal.
ly, III opposite directions, and therefore ncu-
traize each other. UA,il the wafer IS hot
enough To produce steam of this tension, It
cannot boil the tendency to ebUlli,ion IS
subdaed by the atmospheric pressure. Tn
der the full atmospheric pressure Of fifteen
pounds per square inch, water toils At
temperature OF 2l2- Fahr. .n3 hence steam
generated Al this tenn -rGt-r- Is s..G 10 have
an elastic force equal TO one atmosphere
But !! Z portion Of the atmospheric pressure
be removed, water Will boil before it-rc..hcs
2l2~. Take the case oG Z bubble coating
on the surface o! water At tie top of = noun
tain. We have seen tkat the existence Of
the thin film which constitutes the bubble,
depends on the pressure against it from
within being the same as the pressure upon
il from without But TIC pressure without
the bubble on the summit Of the mountain
is less than at the surface of the sea. and
hence the elastic force OF the steam must be
less in the former position than in the latter.
This is the case; and 10 produce this feebiy
elastic steam less heat is required; or in
other words, the boiling point Of water on
tie mountain is lower than at the sea level.
At $4,000 feet, on Doukia mountain, in the
lIimalaya, DIR. Hooker found that water
boiled at 1893; so that tea, soup, and choco-
late, which require to be made with water Of
nearly temperature of 2l2I T., would be
o, very inferior quality in this mountain re-
cerd mountain TO satisfy ourselves that the
boiling point si:.!;s as tie atmospheric pres
sure is diminished. If water at 1867 be
placed under the receiver Of an air-pump,
and the air DC removed until the pressure
becomes as low as it is on Doukia, the water
viii boil. II il not even necessary 10 heat
the more volatile liquids to produce this ci-
feet. \ beaker of alcohol, placed under the
receiver of an air pump, at the ordinary tenn
pcraturc OF our climate, will boil violently
when the receiver is sufficiently exhausted.
Reversing the conditions, we can, by in
creasing the pressure upon its surface, enable
water to attain far higher temperature
than 2l2' without boiling. Thus, as is ma
tural to expect, an external force which Tc-
sists the tendency OF h,at to tear aSunder
the particles OF liquid, and convert it into
vapor, elcvatcs TIE boiling point OF the
liquid.
The boiling point depends also on tie na
ture OF the vessel in which the liquid is
placed. Anything that resists the separation
OF the particles, produces the same effect as
an increase of external pressure Water
adhcres TO certain surfaces much more
strongly than to others; thus, it c!ings 10
glass more tenaciously than to metal; So
that, to make water boil in glass vessel, re-
qures more heat than is necessary if it be
contained in a metallic vessel
In boiling their solutions in glass vessels,
chemists have to DC very careful, for the ad-
hesion between glass and liquids is over
come by jerks; Instead Of 2 amicab.c
ebulition exhibited in metallic vessel, the
solution boils by starts and this in some
times SO energetic a manner, as TO project
the solution quite out Of the glass vessel.
But the most remarkable influence upon the
boiling point of water is exercised by the
air which it holds in solution When water
is exposed to air, certain amount Of the
latter is absorbed by the liquid, the magni-
tude of the ABSORPTION being proportional to
the pressure exerted by the air on the sur
face Of the liquid. 1t is extremely difficult
to expel this air, but it may be done by con-
tinued boiling. Imagine glass tube, which
has been exhausted by the air-pump, to be
half filled with water which has been purged
Of its air by boiling, and Theoretically closed
at both ends. This water adheres so closely
to the sides Of the tube, that when the latter
is turned upside down, the liquid will not
fall dOwnwards, but will cling to the upper
portion of the tube. This experiment shows
that the adhesion between the liquid and
the glass IS enormously increased by the ex-
pulsion of the air, for no such effect could
be produced with ordinary water but it
also teaches US that the cohesion among the
particles Of the liqsid itself is very great;