by
a similar height, and they weigh each about 3,000 lbs. The usual "lip "
is cast on to the under part of the feed-hole to prevent the
back-splash; the opposite opening or discharge, as intended for the
gratings, extends, in order to increase the capabilities of these
boxes, for the whole length of same, and the gratings form one piece
only, without the usual central dead division, as with us ; besides
that, the gratings on the top lines overhang their base lines,
in order to their still further freeing the passage of the fine ore by
means of the then more effective splash. Outside the mortars a
splash-board is screwed on to the lower part of the discharge rim, in
order to deliver the regularly distributed crushed ore on to the
blankets or into the launders, which convey it into the "pans." The
false bottoms are set inside the mortars on a layer of quartz gravel,
and the octagonal form of their bottom renders their removal, on
cleaning up, by means of chisels a very easy matter. Those
proprietaries which crush their ore with quicksilver in the
mortars—there are others who prefer not doing so—have found it most
advantageous to adopt means by which a much larger percentage of the free gold is arrested inside the mortars (Plate III.), and I very soon became convinced that this new method of " lining "
of boxes or mortars with properly prepared copper plates needed but
explanation on my part to lead up to its general adoption in Victoria.
There are two ways of fixing these copper plates in such a position as
would bring them into constant contact with the crushed ore and the
thereby liberated particles of gold.
Firstly
the mortars are cast purposely to receive, on proper shelves, this
copper-plate lining; and, secondly, the old boxes may be at once
adapted for the same purpose until a renewal is necessary, when the
first-named should be obtained and no other. It may be mentioned in
passing that those mortars prevent any possibility of peculation of
amalgam.
The first-named kind of mortars {see Plate
III.) are cast to a pattern, so as to introduce beneath the rim for the
gratings (inside the mortars) a kind of sloping shelf 4 inches wide for
the whole length of its front discharge, at an angle of from 30 to 35
degrees towards the false bottoms. Into this shelf four holes e are
drilled, or recesses cast half an inch in diameter and 1-1/2 inches
deep, which are plugged with dry and soft wood. A copper plate of the
exact size of this shelf, 1/8 inch thick, is then laid on a strip of
blanketings equal in size, and then four copper screws are inserted
through corresponding holes | inch diameter, and the copper-plate
blanketing into the wooden plugs, which, on getting wet, will swell,
and thus the plates are securely screwed down until the next
cleaning-off, when they are unscrewed and so forth. Both the upper and
lower edges of the plates should receive a batter, in order to make a
good joint, and to prevent the fine-crushed ore getting behind same.
Any subsequent repairs should be made with copper rivets, and, in fact,
the more battered these plates become, the better are they for the
interception of gold.
The
other method does not necessitate the immediate change in the pattern
of the boxes in use until they are unfit for use, and the adaptation of
old boxes for these copper plates does not, so far as I could judge,
interfere with their efficacy. The ordinary frame g, which holds the gratings, is not quite so high, in order that a piece of soft wood d (Plate IV) may be screwed on to its lower part at d; it is 3-1/4 inches high and If inches wide; and at the same time lug c is
made higher by broad strips of boiler-iron, so as to catch both the
wooden insertion and the gratings frame properly. At the inner side of
the piece of wooden insertion d a triangular strip of soft wood e is screwed on, which has the prepared copper plate f fixed
