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MINING IN CALIFORNIA AND NEVADA.
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"where
friction necessitates the use of oil or other lubricants. The plungers
and lifts run from 12 to 20 inches in diameter on the Comstock and are
all constructed of riveted boiler plates from 3/8 inch to 1/2 inch in
thickness.
VENTILATING MACHINES, OR BLOWERS AND EXHAUSTORS.
It
is already stated above, that the remarkable occurrence and combination
of certain minerals in the deep ground evolves heat, such heat ranging
from 90 degrees to 130 degrees Fahr., and consequently it is
compulsory, on the one hand, to furnish solid ice in large quantities
to the miners during working hours, to cool their system and refresh
their bodies, but also to supply them with as good and wholesome air as
can be obtained. As regards the latter, the introduction of mining
diamond and power drills has been attended by salutary effects,
inasmuch as the compressed air used as a motor for these labor-saving
machines, in its exhaust ameliorates the atmosphere by removing the
depraved and lighter gases into the upcast shafts, or within reacn of
the exhaustors. The air compressors have already been described, and
the ventilating machines used either as forcing or exhausting-fans are
all on the same principle (Root's), which assimilates that of the
centrifugal pumps if such are driven in one direction, or the opposite
with diversifying effects. " Ice chambers " are also constructed for
the use of the miners, who reach them after a spell of but few minutes'
work in the face of their workings in quite an exhausted state, thus
explaining why these mines must be worked seven days per week, as, if
they cease operations for a few hours only, the gases would accumulate
so quickly and strongly that they could not be got rid of by any known
means at present.
Section IV.—Crushing Mills.
The
ore, as delivered by the " cars," or trucks, into the " dumps," or
paddocks, is not of a very coarse nature, and can therefore be fed into
the boxes by the circular patent ore-feeders direct, without the
intervention of stonebreakers, one young man attending to the feed of
from 40 to 50 heads during eight hours shifts. The mortars are of the
ordinary size and description ; the stampers weigh from 700 to 800
lbs. each, and have a drop of from 7 to 8 inches. The No. 40 screen, or
wire gauge, is used for the crushed ores to pass through, delivering
the same over the splash-board consecutively into several tanks, 7 feet
square by 30 inches in depth. In regular rotation, these tanks are
emptied of the sands they contain, which are then placed into a series
of pans for grinding, amalgamation, and concentration.
(a.) CONCENTRATION AND AMALGAMATION.
These
pans (Horn's) receive their charges in quantities of two tons a time,
and in these they are worked for five hours ; the pans are 60 inches in
diameter, each 32 inches deep, and the "muller" revolves 14 times per
minute. After working the "pulp "—i.e., crushed sand—for
three hours, about 400 lbs. of mercury are added, in the form of a thin
spray, to each charge, and then the remainder of the time—two hours—is
given for thorough mixing. After that the plugs at these pans are
successively opened from the top, and the pulps are run into the "settler" which is 10 feet in diameter by a depth of 3 feet, and in which the muller rotates
H
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