The Forest Republican. [volume] (Tionesta, Pa.) 1869-1952, 1877-04-11

force than another and another OK
plosiop is recorded, and no one left
to tell the old story Of plenty Of water
just before she went up.
That there are a great many ex-
plosions caused by overheatiug near
the bottom Of The boiler, causing the
water to be thrown with such force as
to break the shell, think there can
be no doubt. Mr.. Rankin (see bis
manual Of the steam engine 9nd other
prime movers says of This class of ex.
plosions: There is much difference
of opinion rs to some points Of. detail
in the manner in which this phenom.
non is produced, but there can be no
doubt that its primary causss are,
first, the ovcrheating Of the plates Of
the boiler (beiDg in most cases that
portion called the crown sheet, which
is directly over the hre), SO that a
store Of heat is accumulated and
secondly, the sudden contact Of such
overheated plates with water, SO that
the heat stored up is suddenly expend-
ed in the production of a large quani-
ty of steam at high pressure. Some
engineers hold that no portion of the
plate can thus become overheated Jun
less the level Of the surface Of the wa
ter sinks so low as to leave that por-
ton of the plate above it, and uncov-
cred. Others maintain with NJ. Bou-
tigney, that when metallic surface
is heated above a certain elevated
temperature, water is prevented from
actually touching it, either by a di.
rect repulsion or a film or layer of
very dense vapor and that when this
has once taken place, the plate being
left dry, may go Oh rising in tempera-
ture for an indefinite time, until some
agitation, or the introduction Of cold
water, shall produce contact between
the water and the plate, and bring
about an explosion" Mr.. Brown, in
the eighth edition of his Treatise on
the Steam Engine, says; There can
be no doubt that the water is rrpelled
from The metal in The same manner as
it would be done if it were in the
spheriodal state and explosions have,
no doubt, had their origin in this phe.
nomona. The water appears to be
repelled rom. those parts where the
heat is greatest" Mr.. Calbourn, in
speaking of the rising Of the water be,
cause of the condensation Of the steam
above the water, says, regarding the
force Of the blow given by it: "In
this case it would not be necessary to
assume the existence Of any defect in
tie boiler; for when the water once
struck violently, the soundest iron
would probably be broken, and the
strongest workmanship destroyed"
The experiments Of the committee
Of the Franklin Institute, demonstra-
ted that the temperature of maximum
vaporization Of a clean iron surface,
like that Of a clean iron steam boiler,
is 3463 G f.. that the temperature of
perfect repulsion for the same is $50 Q
L. that the temperature Of mamimum
imum vavorization for iron high
" oxidated, hut clean, is 3S10 f.:
that Of perfect repulsiou of the
same is 433 the temperature OF
maximum vaporiZation Of polished
copper is 292 while that Of perft ct
repulsion is 315 for the same oxi-
dizod, the temperature Of maximum
vaporization is 317 o; while that Of
perfect repulsion is 336
1t is known to all who have had
any experience in tho examination OF
exploded boilers, and also in the in
spection of old boilers that have not ex.
ploded, that there are many boilers in
use that are defective in construction,
with poor safety valves on them; gauge
cocks half choked up, aud with large
accumulalions Of sediment or scale in
them, so that it is hard to understand
why they have net exploded, while in
many instances of explosion there are
10 such indications Of weakness, or o.
defective fittings. Many exploded
boilers never show evidence Of being