Year: 1870

Twenty-three Tons of Powder Exploded In
San FraBciscO HarbOr-A Triumph of Eu-
RineerinR skill.


Blossom Rock was situated in the harbor of
San Francisco and has proved great annoy
ance and danger to shipping. 1t was submerged
six feet below the surface at low tide, and was
situated where the water rolled in large swells
which, being interrupted in their progress were
broken and tossed into wild eommotion. The
difficulties to be encountered in an attempt at
removing huge mass of rock so situated can
readily be imagined; yet this work was begun,
and with the utmost confidence in his ultimate
success, nearly four months ago, by Colonel
Won Schmidt, civil engineer.


PREPARING FOR ATTACK.


The first work to be done was to make care
full survey of the rock. This was carefully
done, and from it plans were drawn. The next
work was to construct q water-tight cofer-dam
on the rock and around that part of it Through
which the shaft was to be sunk. This was
found to be most difficult. The coffer-dam was
first put in its place, and then scow was built
around it. into which about two hundred and
fifty tons of stone were thrown. The dam was
lined around with bags of sand to more effectu-
ally keep out the water, and when this was COM
plete, an iron turret was placed inside
OF or 81 sunk Tins n the nro' rock Ta' e1GsadSd dssDed
of three feet and closely and thoroughly
cemented in its place. This being done, the
work of excavation, or sinking the shaft, com
meneed. A platform was erected on the rock,





width. On this an engine and a complete
hoisting apparatus were placed at one end, and
at the other shanty was erected containing six
sleeping apartments and q kitchen, which was
also used as an eating room by the workmen.
When the shaft had been sunk sufficiently to
permit the work of excavation to be extended
to either side, the work was considered fairly
begun, and from that time forward it was
pushed with all the despatch possible.


TUKNELLING THE ROCK.


rrrN do fSsa
and involved the heaviest responsibility. 1t
required the closest attention and the exercise
of more than ordinary SKILL AS the work pro-
gressed and the excavation became larger the
crust OF rock left standing would naturally
become weaker and more likely to cave in. In
order to prevent this pillars of rock were left
standing at short intervals from each other,
until the limit of six feet was everywhere
reached. Then 1t became necessary to move
those pillars away. Before this was done, up
rights of heavy timbers were set thickly around
the cavity to supply their place, and in this way
all fear of the roofing falling was obViated. All
the pillars, except the two main ones, were
removed several days ago. The cutting away
of these two was the last work done before the
powder was stored for the grand explosion.


THE CHARGE.


The amount of powder used was about twenty
three tons, which was placed in casks and boiler
tanks, very firmly made and perfectly water
proof. The barrels were placed close to the
side of the excavation, near the junction of the
arch or roof with the floor, so as to blow away
the arch from the lowest point of excavation
The boilers, containing more powder, were
placed through the centre of the chamber where
the distance from the top to the bottom OF the
excavation was the greatest. This was so ar
ranged as to equalize the force on each portion
of the rock. The most perfect arrangements
were made for exploding the charge. piece
of gas-pipe, two and half feet, was in
serted in each barrel, and q piece six feet
long in each boiler. These were filled with fine
gunpowder, and in the end of each was
placed Illuminating cartridge. All of these
were then connected together by insulated
electric wires, the ends of which passed to the
surface of the water through tube in the shaft,
and thence to vessel at anchor about 1000 feet
from the rock in a southerly direction. Here it
was connected with an electric battery in charge
of Mr.. j. S. Field, an electrician of approved
skill. The Illuminating cartridges, when reached
by the electric spark, were expected to explode,
setting fire to the powder in the tubes, and
thence communicating to the mass of powder in
the casks and boilers. When all was arranged,
the coffer-dam was removed and the water per-
mitted to fill up the excavation and act as
tamptng.


THE SUBMARINE CAVERN.


The space eXcavated measured in the clear
inside l4O by 80 feet, and it is estimated that
about 40 600 cubic feet of stone were removed in
making it. The height of the highest pillar was
20 and the lowest feet.


THE GRAND REsULT-A PERFECT SUCCESS.


The telegraph informs us of the final act ia
this great engineering project. On Saturday
afternoon last, at 2 o'clock, Blossom Rock was
blown up, and the result was all that the most
enthusiastic supporters of the plan anticipated
No accident Of any kind is reported. When the
immense amount of powder was touched off the
water, apparently 100 feet in diameter, was
thrown to the height of about 100 feet, the centre
being filled with smoke and stones, the latter
going far above the water. Between $4,000 aut
$4,000 people witnessed the explosion. The
explosion was scarcely perceptible in the city o.
san Francisco, and only deep thud acconipa
MED the blast