The New York herald., 1876-09-20
THE GREAT MINE.
Precautions Taken to Guard
Against All Accidents.
RENDING THE ROCK.
How the Columns and the Roof Rock
viii Be Destroyed.
FLOODING THE MINE.
The Operation Performed bv
Means of a Siphon.
THE BATTERY BOMBPROOF.
Boxing the Wires Leading
Through the Headings.
OPINIONS OF ENGINEERS.
How the AstOrians Regard the Approaching
Big Blast.
THE BATTERY BOMBPROOF.
Boxing the Wires Leading
Through the Headings.
How the AStorians Regard the Approaching
Big Blast.

re destruction OF every part Of Halets Point reef
above tie Lowell Of twenty eight feet soundngs by the
simultaneous explosion Of several thousand holes filled
with heavy charges Of nitro glycerne and dynamite Is
IN undertaking that neccssates the precaution
10 guard against accidents and failure. With regard to
the provisions against the former they must be
sidercd In two casses local and general and such
they will be explained IN the present article The first
care Of tho engineers is TO protect the exploding
apparatus from injury by any parts Of the rock
that may DO projected from the reof by tho
orce OF tho explosion This they have accomplished in
he manner hereinafter described In large mass of
Mrasned rock such that OF Halles Point reef which
has been excavated with iunnos CALLER
les the effects produced by equal charges Of explosives
In all tho holes will differ very much In character It
must bo remembered that the resistance offered by
mass Of rock 10 the orco of the exposion is meas-
urod by the shortest distance from tho centre Of
bharge to the free surface and by tho cohesvcness of
Ihc atoms Of which the rock is formed. The first ia
termed the line OF least resistance, that along which
She energy Of the expanding gas generated
BY the combustion Of tho explosive finds the loas OBJ
Saclc to It's forco II hollow sphere of ron shcll
br instance with eccentric interior and exterior CIR
sumferences. Is charged with powder and fred, the
bowl shaped portion will remain unbroken. In ike
iqusly TO the plano Of It's Sides leave greater
mass OF the stono sdo Of the hole
Ihan the other, the weaker portion will be
Ihattored to pieces by the explosion Of tho
Sharge, whiie the heavier and stronger part will
be only cracked into pieces Now, II the density
or the gneiss rock Haetts Point equal through
out the entire mass 1t would be tho easiest thing pos
rble for experienced mining engineers to calculate
and, indeed, 70 regulate, tho effects that would DO pro-
luced by tho explosion. They could graduate their
shargcs both strength and regulate thom 70 To-
cation oxact accordance with tho necessities OF the
case, aud feel confident in the results being they
desired TO produce them. But with q forma-
tton variable in It's nature, and this varia-
uon being complicated by stratincation,
anc isrhcr by tho peculiar directions of galleries
snd headings with relation to tho limo Of stratncaton
the difcuity OF determining positive results
hundred fold Tho axis OF the rcef in this instance
IL coinc,dsnt with ts stratncatcnthat is projects
into The channel In the direction the align
ment Of the layers OF rock and consequently OF
tho headings have been driven right angles with this
line, aud the sratincason. While, therefore,
tho explosion will split OF tho supporting columns
into regular blocks OF the thickness OF
the several strata, tho effort Of the force
what might bo called Its grain TO mako this
lhtlo clearer, let suppose Two blocks OF wood
from the same piece and with the character Of
nbrc Now. Of these 10 simply split by the action
OF a wedge with comparatively little effort while If we
try tho other end from end tho resistance will
DO immense. In the same way the explosives Will
operate at Hallou's Point reef tho rock columns
shat support the r0oi. To overcome the differ
cnce In tho resistance Of the rock tho engineers
have made careful calculations BY which they
determined the requirements for each column scpa-
ratey. Perfect diagrams Of the made, CIV
ing its variations Of outline at several heights from tho
ground line to where It connects with tho roof Tho
stratncaton was Indicated on these, together with
the peculiar ccgrce OF cohesveness In tho
Particles OF each stratum. that reality the
graduation OF tho charge s made TO depend
local conditions, each set OF cartridges having
specified amount Of work perform u given mass
OF rock II the foresight, therefore, can So
tho best results, far the destruction OF tho
columns 10 concerned the operations at Hallos Point
promise to be eminently successful
shci oil the reef, all the varying conditions
described In the columns exist in II Also
with tho additional complication OF Its arch
like shape which makes Il almost self sustaining
Could columns be removed from under this rocky
shell the probability that would not fail TO sustain
It's weight and that OF the water In
dealing, therefore, with the roof, General Newton has
wisely limited hs prospective results to general rac
ture Of tho shell with moderate charges introduced
~ considerable Intervals These charges being fired
simultaneously with those that shatter and rcnd the
rock columns beneath intended iu break
Ing up tho roof while subsidies the debris the
columns There Is intention whatever TO blow the
roof on the columns and scatter IN small pieces
all around II Is hore that will be found
the value OF this pan as local prccaution
against accident In order that any portion Of
the shattered columns should DO thrown by tho
force Of tho explosion TO u great distance It
should first be blown through covering OF ten
feet thick Of rock which Immediately ovcrlcs IL with
force that could not DO impaired by monster rined
gun. Even though an opening large enough TO per-
alt the passage through Of such rock projcctile
Il would be met above the rock by inrush
ing column OF water many ieet deep, which
would so retard its motion rs 80 cause to rise but
:cw feet above the river surfaces In ordinary blasting
operations such those commonly witnessed In tho
work OF street grading and scwer cutting up town. It
!s usua TO cover the loaded hole before dring with a
number OF logs chained together so as TO prevent tho
stone from scattering with the shock OF the explosion
Now, tho root rock ai Halcs Point acts IN the vcry
way tho heavily loaded columns, and will pro-
vent any danger rom arising whom the latter are being
blasted
FLOODING THE woRKIxG&
inc introduction OF water INTO every part OF sne
works before nring must also DO regarded as local
rrecau'on OF two-fo!d value In the trss place u
what Is called taps the great mino in The most per-
iect manner by hlling u with powerful resistant 20
the escape OF gases before they have accomplished
thcr work Ia the absence OF tampng the line OF least
fcsistance would be along thc OF the blast hole
tscIf and therefore, instead OF bursting through the
rounding rock the or the explosion would
pass OIL through the hole docs through tue barrel
Of gun Ir loaded rife, Tor instance tho ballet
partial tamping the charge nclosing II go
rs TO concentrate the energy OF the explosion. but
The resistance offered by bullet very much lest
.han that offered by the barrel se tho line OF cass
resistance Is IN tho direction OF the bullet and along
The BARREL II the bullet was tightly wcdged In the
gun, 20 that the cxp'os'on could disodge IL
quickly, the gun would burst ike tho rock when
the charge Ii exploded Bus II will be asked.
and very naturally, how water will oncr much re-
distance the depths OF the Haetts Point mine as
Il,c rock that surrounds the cartridge Water when
incIosed Ia circuniscr bcs place and without any
Chance OF moving becomes rs inert Its pres
increases IN direct proportion to It's depth so
that at the bottom OF tho shalt say thirty feet
low high water level at the time of tho explosion
each square foot OF surface that depth would be
pressed on with weight equal TO about $50 pounds
Or u htto Than fifteen pounds per square inch,