The Portland daily press., 1872-11-28
TERMS $500 PER ANNUM In ADVANCE

10 move heavy masses, splitting but not shat
lerlng them the latter are purely agents of
destruction, shattering and pulverizing what
ever reSlsts them. In firearms the object is to
set the projectile i'll motion; if the proiectile
is light, as in arifle, there is little inertia to be
overcome, and therefore the gunpowdsr used
Is Is nne-gralned and burns quickly; if the pro-
Jeetlle Is heavy, as in a fifteen-inch gun,
thr mere Is great inertia to be overcome, and
ene.elore the powder used is very coarse
eiaihea, The larger pieces of powder being the
, PIC vi an egg, so that the combustion NAV be
nole Sraauai and the force of the powder
e;a, Gu 20 roy ueveioped until the projectile is
iairiy IN motion, otherwise the gun would
burst from too sudden a tieyelonment Of tbs
force of the powder, as in the BURSTING of tbe
''big gun" ON the princeton" when onr Gov
ernment first began to make big guns. So al
so in blasting at the quarries, coarse powder il
used to split the rock and avoid all unnecessa-
ry shattering of the rock split out. For these
reasons a combustive powder is used in the
military and civil arts where gradual pressure
low initial pressure is a requisite. But where
a crushing, shattering and destructive effect
is sought, ''powder" of great initial pressure,
is used; for example, in blasting tunnel like
the Hoosac tunnel, blasting out ores, removing
distractions from navigable water,-in q
word, where the solid condition of the object
blasted is OF no consequence, such powders
as dynamite, ntro-glycerne, dualin, guii-cot-
ton, illuminate of mercury are used. With
this distinction fairly in mind let US consider
the question of the use of powder in level
ling buildings in the path of confgration like
that which swept over us week ago. Sup
pose a building to be ''minedo with ordinary
blasting-power, placed in the cellar; when
the powder is fired the force is continually in
creasing; one floor after another is
lifted, the windows blown out, uu-
4 oil hA =
then the maximum pressure is brought to
bear from the inside OF the buildings against
the top of the walls, so that the walls are top
pied outwards into the street. If an insult
ficient quantity of powder was used, the
force might be only sufficient to blow out the
windows, as sometimes happened when tie
gas escaping from broken pipe is suddenly
ignited. But suppose that the building was
mined with some explosive powder of high
initial pressure, like duain, the maximum ef-
feet would be felt at once; the shock would
be against the base of the buildng,no against
the top of the walls, the building would be
shattered and shaken down vertically as If by
an earthquake; cut off at It's base, its sup
ports knocked out from beneath SO that it
must collapse upon the ground it stands
upon, and not topple over into the street, as
when destroyed by powder.
Thus, then, we see the difference between
combustive powder of low initial pressure,
like gunpowder, and explosive powder of high
initial pressure, like dualin the former gen.
crates force which may be described as an
inverted cone, its apex resting on the mine,
the maximum power being at distance from
the powder at its apex; whereas the latter
may be likened to sphere, in the centre of
which the mine is situated as in bombshell,
crushing, shattering, and destroying in its ex-
plosion everything about it.
As an illustration of this crushing force Of
an explosive powder of great initial pressure,
F! some two years ago neghboring town was
| building new road where the contractor
| came across some unstratified trap rock
which was as tough as a blacksmith's anvil !;
! holes had been drilled for blasting and powder
used, but no damagedone to tie rock. Finally
dualin was used; some two pounds were
! heaped on the top of the rock, which was
| cubic in shape, about four feet high,-the
| dualin covered with newspaper upon which
| couple of shoveliuls of sand was placed and
| the charge fired by fuse. Of course no one
| ever saw the sand or newspaper, but the rock
was so completely shattered and crushed that
| the fragments were used for matchmaking
the road without breaking.
| Now ifin like manner dualin was heap
1 ed up against the base of a wall aud
fired, the base would be shattered and
| destroyed, and the superstructure would
drop down. So much for the action of ex-
plosiye powder of great initial pressure upon
masonry buildings.
With regard to wooden frame buildings,
there is sufficient elasticity in the material
used to allow severe shaking without de-
struction. In fact, in earthquake countries,
wooden frame buildings and trees are rarely
destroyed, though the most sold masonry
crumbles like dust. For the blowing up OF
such buildings it may be questioned whether
powder of low initial pressure is not more eff
ficient than such agents as dualin; because
the gradually increasing force of the former
would draw the lemons out of the mortises
and separate the outer covering of boards
from the frame and thus produce more COM
plete destruction than the sudden shatteiina
| shock produced by dualin.
With regard to both classes of these de-
structive agents, it should be remembered
that not only do they differ in the time occu-
pied in developing their force, but in the
amount of force produced. Thus nitro-glycer-
inc has about seven times the powerof ordi-
nary gunpowder, and is able to shatter
wrought iron, which cannot be done with
gunpowder; this is probably the result of the
suddenness of the shock, which does not al
low the fibres of wrought iron sufficient time
to stretch, an important consideration in the
destruction of buildings which have more OF
less wrought iron used in their construction.
In conclusion it is to be hoped that the city
authorities Will avail OF the present Opportlt
nifty, when there are so many walls and mass
es of masonry to be levelled in the burned dis.
trict.to inaugurate thorough set of expert
ments in this branch of engineering, the rec
ords of which, if properly made and preserv
ed, may prove of incalcuabe value in similar
calamities, whether occurring in Boston OF
elsewhere, and furnish accurate data for ap-
plication in arrestiDg future con1agrations by
the destruction of the building in the path Of
the fire. FL. N +.