The daily phoenix. [volume] (Columbia, S.C.) 1865-1878, 1872-04-13

about two years ago, has been vigorously
carried forwald with but trifiing inter.
rnptlon, and will, it is now estimated. be
completed within year and half.
l65, 600 cubic yards Of rock were toa be
removed from the river, and of this
amount at least 49, 900 cubic yards have
already been taken out. About 24O men
are now employed in the work, nearly
all Of whom are Cornish miners of long
experience. A much larger number were
I f>rmerly employed, but the introduction
of the diamond drill and the increased
use Of machinery in all branches of the
labor has permitted great reduction OF
tue working force. A hundred of the
workmen were recently discharged.
The immense bed of rock is now per-
forated by sixteen tunnels aud seven
concentric galleries, the floor line OF
which is thirty-two feet below the level
OF the river at mean low tide. It was
originally designed to make the channel
but twenty-five feet in depth, but subse-
quently it WAS determined to render it
perfectly safe for vessels Of the largest
draught. The average height of the
tunnels and galleries is twenty-five feet,
and their width sixteenth, leaving roof
from seven to ten feet thick, supported
by Numerous pillars. The length of the
extreme gallery is 600 feet, and Of the
grand tunnel 2l2M feet. There will ul-
tlmately be twenty eight tunnel head
inge, some of which will extend 375 feet.
The work of boring is done wholly by
machinery, the laborers serving only to
trim and dress the rock after the rougher
work has been executed, and to perform
the operations connected with blasting.
OF the six drills used, two are diamond-
pointed drills and four Burleigh steel
percussion drills. Tho diamond drill is
the invention of RodoIphe Leschot,
French engineer, and was first used in
the construction of the Mont Gems tun.
mel. but is now worked by improved ma
chinery under American patents. The
two used at He'll Gate were introduced
last October, and have proved so satis-
factory that three more will be added in
few weeks. This drill consists of a
hollow disc an inch snd-a half in diane
ter, the rim of which is studded with
twelve bits of black carbon. Attached
to an iron pipe of the same thickness, it
is propelled by compressed air at pres
cuts it's way through the hardest rock
with marvellous rapidity. TIE motion
is rotary and the number of revolutions
$50 per minute. Unlike percussion
drills, it receives no wear except from
friction, and hence is constantly in work
ing order, and needs no sharpening.
Forty-four feet and four inches have
been tunneled by this drill in eight
hours, through mass of granite and
quartz. By screwing on additional
pieces OF pipe it can be propelled in one
direction to an indefinite extent, but for
blasting purposes it is seldom driven
further than fifteen feet. Occasionally,
however, through tho Intervention of
new process in blasting, it is expedient
to continue tunnel of this character
for long distance, thereby effecting q
great saving of time. Sand or clay is
then rammed into the bore until it is
nearly full, to act as IL recoil block to the
charge, and the rock is blasted section
by section.
All the blasting at He'll Cato is done
by nitro glJccrine, and has been SO care
fully managed that not an accident has
yet occurred. The nitro .glycerine is
made into cartridges from eight to fif-
teen inches in diameter, and holding
from four to eight ounces. They are
coated with n glutinous composition
which effectually protects them from
water. When blast is made, little
lube OF illuminate Is attached to the
cartridge and spark transmitted to it
through a wire connecting with an cleo.
trio battery. Though large number of
cartridges are often discharged in sue
cession with great rapidity, they arc
never fred at once, as tho vibration in
this case might seriously jar the stone
roof, opening seams for the admission of
the water.
The explosions arc OF tremendous
force, shattering the rock into fragments
OF u size convenient for removal. These
are piled on cars drawn by mules. run
ming on iron tracks, which are Ibid in
all the tunnels, and conveyed to the
shaft, where they are hoisted up by
steam derrick. The masses already
taken out form two immense cmbank-
ments on the river front
building near the mouth OF the
shaft contains three large steam boilers
and five compressors, the latter furnish
ing the motive power for tho drills. In
working the compressers, lubricating oil
is now used instead of water, thereby
avoiding tho formation of ice in the
pipes during tho cold weather. Near by
is powerful steam pump, which drains
oil the tunnels comparatively dry through