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

tuOe, except the cOneSi0n between the llquiC
particles themselves. Now here we have
forcc which tends to resist the separation o.
the particles; how will it effect the boiling
point Of the liguid? Most remarkably
2" ater thus purged of its air may be heated
to tempcra ure of 2750 Fahr. without boil
ing; and when it does boil, it is not with the
gentle ebuliition of ordinary water. The
PARTICLES snap suddenly asunder ike broken
spring, and eGUllition is converted into ex-
p!usion
II is possible that this property of water
may sometimes act dsastrousIy in the case
of steam boilers. For If the water in Z
boiler be deprived Of It's air by long boiling,
II may assume the condition described, and
become heated TO a degree far beyond that
which corresponds to the pressure upon its
surface, as indicated by the guage. Explo-
slons very often occur at the precise moment
Il when the engineer turns on the steam an
act which would be calculated to rupture the
cohesion of a mass OF water in the state re-
terred to, and 10 cause it instantly to apply
ITS excess OF heat to the generation Of steam,
0: enormous tension. No man practically
acquainted with experimental! investigation,
and the numberlcss chances that arise to
modify and defeat the most probable con-
lectures, Will te inclined to express himself
But one thing is certain, that We ought 10
know whether this cause, or the other causes
with which conjecture alone now deals, can
practically affect the questions Of boil.r-ex-
plcsons. We know nothing; but We ought
to know a great deal, for the whole s,.biec:
Is clearly within the range Of experimental
investigation. Instead OF being reduced TO
vague Surniscs, certain experimental results
ought to Be before US as the basis Oh which
70 found rai!ona! opinion. But such re-
suits are wanting, not on account or the in
superable difficulty o. the subject, but sim
ply because there IS no person with sufficient
cash, leisure, ability, and inclination 10 IN
! dcrtglie the invest CATION.
We now turn to the examination or an
ether interesting point connected with the
( boiling water. To l. person unacqu2nted
with the facts Of the case, nothing can ap-
pear more MAJ ilcs:iy true than the state
meat that the hottie. a vessel IS into which
water j. poured, the sooner the liquid Will
/ boil. But this statement is diamcI.jcally
opposed 10 fact. Let silver basin be heated
10 reinesS, and ,e; small quantity Of water
be poured into it. The water instead of
flashing .a,o steam, Is might be expected,
VII. gather itself into gloJulc, and roll
upon the hO; surface SIS drop OF mercury
upon a table, 'r IS rain-trop upon cab
bage-,eaL The LIQUID Is in q stctc Of iQccs-
SAINT motion: sometimes II e!uagatcs itsc!.
into al oval in one direction; thea, drawing
itself up. It becomes elongated in direction
perpendicular TO the former; and these
changes take place 50 rapidly that 4 star
shaped figure IS oitcu the result. Some
times ros,t'cs Of surprising beauty are thus
formed. " bile the drop i in this sph roi-
dal condition, as it i called, .et the lamp
which heats It be witLdFaw the basin
gradually cogis. ana -,ter a short time the
drop loses lis spharCida. share, spreads out
on the surface Of the basin, AID IS inStaats-
neousiy thrown into violent ebuliition.-
, Throughout the Continent, this is known as
the experiment. OF Leidenfrost, who described
the phenomenon in u worh. published TO
wards the close Of the last century.
Mate. 10 not the only liquid " hicil is ca
pablo o exhibiting his effect: it is obtained
more easi : with alcohol and s.il more east
ly with ether. In fact, the mere volatile
the liquid, the more readily i; assumes the
sphero.Ia. condition. In the place Of a me
tai'ic basin, water near lis boiling point may
be made use OF 10 support drop 0. ether.
Instead Of mixing with the hot Eatcr, the
ether gatIcr Itself ~ into a globule. and
rolls about upon the surface Q: the other
liquid.
Here follows an experiment, illustrated
by diagram, which, without the wood-cUI
would be uuintc!ligible, and IS therefore
omitted. The experiment demonstrates that
tie electric current is cut of between the
heated surface and the globulc of water,
showing that the TWO therefore canno; be in
contact
Tbs experiment, however, beautiful as It
is, has not been deemed quite convincing:
il has Sii.l been doubted whether an interval
really exists between the liquid and the
heated surface and as ocular demonstration
appeared TO be the only one calculated to re-
move sccPtic;srn, an experiment which fur
nishcs this has been devised. 4 silver basin
is turned upside down, and its convex sur
face fceb.y ipdented, so rs to enable it to
supper, Z drop. Placed above = lamp, the
basin IS rendered red-ho,, and a drop Of
Opaque ink, into which little alcohol has
been introduced, is placed upon the basin.
Behind the latter is stretched fine platinum
wire, brought 10 . state OF incandesceEce by
sending q current OF electricity through it.
When the eye Of the observer is brought to
level with the bottom OF the drop, the
glowing platinum wire viii be distinctly
seen through ;he interval between the ink
and the basin. Drops, fully half an inch in
diameter, have been examined in this way /;
and it has been found that ct no point do
they touch the surface of the red-hct metal.
This experiment leaves 10 doubt upon the
mind that an interval exists between the
spheroidal drop and the heated surface; to
what, then, is this interval due? At an
early period Of railway history it was pro-
posed by that original genius, George Ste
phenson, 10 substitute for ordinary steel
springs, in the cas-. of locomotives, springs
of elastic staam. 1t was proposed to con-
vey the steam into cylinders. in which pis
tons should move steam-tig ght; these pistons
supported by the steam beneath them, were
TO bear the weight of the locomotive. Now,
what the great engineer proposed for the To-
comotivc, the sphcrodial drop effects for it
selt--it is borne upon 4 cushion O! its own
steam. The surface must be hot enough TO
generate steam of sufficient tension to lift
the drop. The body which bears the drop
must be of such a nature as to yield up rea-
Oily supply Of heat; for the drop cyapo
rates and becomes gradually smaller, and to
make good the heat absorbed by the vapour,
the substance on which the drop rests must
yield heat freely-in other words, it must be
good conductor of heat This is why a
silver basin was recommended for the ex-
pertinent, for silver stands at the head OF
conductors. Again, a cushion of vapour
being required, the liquid must be of such
a nature as 10 furnish this. Hence it is that
the most volatile liquids-those which are
most readily converted into vapour-show
the phenomenon most readily.-It is to the
escape of steam in regular pulses from be- !
meath the drop that the beautiful figures
which it sometimes exhibits are to be refer
red. BY using very fiat basin, over which |
the spherodial drop spreads itself widely, |
we render it difficult for the vapour to es-
cape from the centre to the edges OF the |