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MINING IN CALIFORNIA AND NEVADA.
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use
of superheated steam has been proved exceptionally beneficial, as it
accelerates amalgamation, through vaporizing the mercury and keeping it
always bright and susceptible for gold absorption. The " mullers" in
these pans revolve but ten to twelve times per minute, and the steam is
introduced every three to four hours, when the blanketings, or what
remains of them, have been ground fine enough. Besides the action of
the steam, the pair of pans in each set are opened twice every day, and
the following substances, mixed, are added to the " pulp," viz., one
part of Sal Ammonia, three parts of saltpetre, weighing about £ lb. the
lot; 1 lb. of quicklime is also given at the same time, by means of
which a chemical reaction is produced, which results in the rapid
extraction of the free gold. The remaining pulps pass into the
principal launder for future treatment.
The
expense for grinding and treating blanketings amounts to one dollar per
diem each pan, and the daily duty of the eight pans employed amounts to
9,600 lbs., or 1,200 lbs. each of the eight pans employed. It is
possible to grind these blanketings and sands so as to deprive them by
mechanical means of nearly all the gold they may be charged with; but
this has been found both too expensive and not nearly so effectual as
if these residues were finally disposed of, after calcination, by the
chlorination process. Eetuming now to the second portion of the crushed
ore which passed over the blankets into the shoots, it should be
mentioned that the strakes have a "grade" of 1-1/2 inches per foot, and
the ripple table 1 inch per foot.
Hunter's Rubbers.—These
machines receive the above—viz., crushed ore passed over blankets—which
are still impregnated with a good percentage of very light or "float
gold," both from the strakes direct and from the grinding pans as
already described, but neither steam nor chemicals are used in their
manipulation. This Hunter's rubber (Plate V.,) is rather a complicated
machine, combining, like most other American gold-saving appliances,
two or three different actions, viz., grinding, amalgamation, and
concentration. It has a similar appearance, it will be seen, as the old
shaking tables, and its motion is also similar; but in detail it
differs materially from the former. From the frame-work a well
stayed, depend two bearers (1), by means of four bars of round iron (2,
2), and these are rocked fifty times a minute by two excentrjcs (3),
and pulleys (4), with a stroke from 5 to 7 inches. Six pieces of pine
wood (5.5.5.5.5.5.) are bolted to the bearers longitudinally, their
tops being round and the bottom square, where they are armed at the
bottom with the same number of shoes ($.6.6.6.6.6.), all these being
the really movable parts of the machine. In a strong cast-iron box a
false bottom is laid by means of alternate strips of wood and cast-iron
dies, in the same longitudinal fashion, bo that
the shoes rub upon the dies and thereby grind the ores. At the same
time the tops of the wooden strips (5) are covered with electro-copper
plates, and as they are immersed, any, in fact nearly all the float
gold liberated by the grinding is collected at the apex of each
cylindrical copper plate, 'and the pyrites are also concentrated in
this box. This is a very valuable machine, as it collects from 10 to 12
per cent, of gold that would otherwise float away with the blue slimy
water, which it is well known is allowed to escape elsewhere.
At
each operation residues escape, and they find their way from the rubber
into the chief launder, where they join those left over from the
blanketings treated as detailed. All these residues then pass into the
distributor at the head of the "Hungarian sizing boxes"
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