Plate
VI.—The principle of these boxes is governed by the fact that fine
sands, if' dropped into deep water, will reach the bottom quicker or
slower, in accordance with their respective specific gravity, To
facilitate the process, these boxes are made with sloping sides (50
degrees) towards a centre, and each set may comprise any number, but in
succession, those, after the first box increase in size, and produce
of course residues of different values, a and b. The sizing boxes are filled with water after closing valve o, then
the residues are allowed to flow slowly into the first box, where the
first separation takes place, the metalliferous portions covering the
bottom, and the lighter portions rising and eventually flowing through Z into No. II. box at W, which is a few inches lower at its inlet than at u. Both or any of these boxes are provided with a valve r at or near the bottom, through which the heavier ores may be withdrawn by turning the handle o in the stuffing-box t. Inasmuch,
however, as this opening of the valve would effect a sudden rush of the
total contents out of the box, on account of the great weight of water
and sand combined, the launder S has been constructed with a
view of counterbalancing this pressure by forcing the slimes or sands
up to a certain height, where they discharge as class a, b, or
other less valuable resultants, as the case may be, if other boxes are
used. The latter residues are again ground in the Hendy's pans with
steam and chemicals, and those discharged at m from the sizing
boxes are passed into the "automatic sluices," which are simply a
species of "tyes," which, however, work quite satisfactorily "without" any
manual labor. They are 15 feet long, 4 feet deep, and 2 feet wide, set
at a grade of If inches per foot. At the discharge end, a door is fixed
within guides at either side of the sluice, but that door is open when
its top is below the bottom of the sluices, and the latter are
closed by the door rising to its full height of over 3 feet 6 inches.
The working of the sluices and of the door is regulated by the amount
of supply of sands at the upper end, and accomplished by means of an
intricate set of machinery, which is set in motion by a crossed belt
from the vertical spindle of the adjacent buddle, and causes this door
to rise the 3 feet 6 inches, or more, required within every twenty-four
.hours. With an extra quantity of water added, the sands fall into the
top of the sluices, and the heavier parts remain there, whilst the
lighter pass over the door at the end, and in this manner the
separation of both goes on without manual labor and very little
superintendence, in fact the panmen overlook quite a number of such
appliances. The pyrites so obtained are again passed through the sizing
boxes, and the residues ensuing therefrom are worked in concave buddies
of the ordinary description, of which there are two in each set. These
buddies ooncentrate, generally speaking, only up to a certain
percentage, the remainder being sand; to remove that sand the same
pyrites are slowly fed into the " tossing tubs," an old Cornish
invention, I believe, but very effective for the purposes intended.
These "tossing tubs" are
simply open vats constructed of sugar-pine staves and bottom ; the
staves are 2| inches thick, and the tubs generally measure 4 feet 4
inches wide at the top by 3 feet 10 inches at the bottom, inside
measurement, by a height of 2 feet 6 inches, a central and
vertical shaft passes through the bottom stuffing-box, and it is made
to revolve at the rate of fifty-three revolutions per minute. The shaft
is furnished with two projecting arms, level with the top of the tub,
which are bent down so as nearly to touch the inside periphery, and
also the bottom of the tub; a series of flat pieces of iron fixed on
edge are screwed at different heights and angles to these arms, so that
by the revolution of the spindle this
