ready
from the very commencement of crushing, owing to the lively
amalgamating agents introduced, and the amalgam so collected inside
the mortars presents a fine hard appearance, needing hammer and chisel
to separate it from the plates; outside, on the tables, a peculiar kind
of fine steel wire brushes are used, and acids or knives are altogether
avoided in cleaning up. This relates to the heavier portion of the gold
liberated by crushing; the other kind, known in California as " float
gold," passes away in the blue muddy water with the tailings, but it is
subsequently intercepted on other copper plates, as will be described
below.
The Screens (Gratings).—It
appears to anyone studying the reduction of the ores in California, as
if their experts could not rest satisfied with any kind of appliance,
machine, or process they operate with, but that they must vary them or
invent something fresh; the effects thereby obtained are carefully
observed, and a large portion of their otherwise unoccupied time is
given freely with that end in view. This is the result of their most
liberal code of patent laws, which induce the people to exert
themselves to invent something new, well knowing that their capitalists
are ever willing to assist and purchase new inventions if proved
valuable after trial. In this instance we know that gratings are made
here chiefly of iron plates, perforated by machinery; in California,
however, the same plates are also used, but they are made without a "
burr " like ours at one side ; secondly, they make their holes oblong
and either horizontal or diagonal. The American " screens " are
likewise made of brass and steel wire gauze ; the brass-wire gauzes are
manufactured up to No. 40; for instance, in the Empire Company's
batteries the screen frames are 4 feet long by a height of 9 inches,
and, as their screen number indicates, there are not less than 1,400
holes per square inch, and still they crush on an average 40 tons per
diem with their 20-head battery. The Californian iron-plate screens are
made of the best Russian iron, which is of a very tenacious character,
and the size of the holes and number per square inch is ascertained and
regulated by various sizes of sewing needles, which also perform the
work as punchers. The narrow slit screens are also a novelty,
possessing, however, obvious advantages over those with round holes;
raw quartz, or ore when crushed, presents oblong particles chiefly, and
thus the "slotted" screens discharge the particles with much
greater speed than those of any other description, and they are
therefore very highly esteemed. The slits are from | of an inch in
length, and the ordinary width, and as they are either horizontally or
diagonally placed, they clear themselves very rapidly. Considering the
heavy Californian stampers, which reduce their quartz very quickly,
more than we can do with our lighter stampers, these slotted screens,
placed in their frames with a "hang" forward on top, permit them to get
through as large, if not larger, quantities of ore per head, than we
can expect to do with gratings in a vertical position and a very much
less number of holes per square inch. In point of fact, they crush
finer, and therefore liberate more gold for amalgamation on their
copper plates.
In
order to do all this at the least expense of manual labor the
quartz-miller locates his machinery at an elevation which, as a rule,
is never less than 25 feet above the tailings shoots, which latter are
also calculated for a fall of from 3 inches in the foot. The floors of
the mill are arranged in terraces, in order to facilitate the passage
of the ore's under treatment from one machine to the other without too
much manual* labor.
The
Empire Company have adopted a treatment of their ore entirely different
from others, though quite as satisfactory, as proved by the results of
periodical assays made both of the ores and tljeir " wastes" The crushed
