tip too much room ; but I may say that any ordinary intelligent " roaster " will soon understand the work.
The
so thoroughly roasted ore is cooled gradually and placed in wooden
vats, holding about three tons each charge, in which they are
moistened, and the lids are after a time screwed down, and the joints
hermetically closed by means of a dough of flour. There are false
bottoms in these vats, which are either kept apart by means of a layer
of quartz-gravel or they are a fixture, and then are simply perforated
so as to admit, either way, the chlorine gas, conveyed through a leaden
pipe at the bottom of these vats, and as soon as about one-fourth of
the roasted pyrites have been placed in the latter, the remaining
portions of the charge are then quickly filled in to within a couple of
inches of the top of these vessels, and then, after putting down the
covers, the chlorine gas is allowed to permeate the charges for about
eight hours—each charge of 2,000 lbs. (American) having been reduced by
calcination to about 1,440 lbs. only. The manufacture of chlorine gas
is effected for each charge of, say, three tons of ore in each vat from
the following ingredients, viz.:—30 lbs. sulphuric acid, 20 lbs. salt,
and 18 lbs. of manganese ; these substances are slowly and carefully
heated in a leaden vessel placed in a sand bath so as to ensure the
non-melting of the gas originator, and the gas so obtained is conveyed
thereupon to the vats for action. As soon as the proper time has
elapsed for the gas to act, the vats are opened and pure spring or "rain water' added
until the solution thus obtained and collected in a much larger vat
close by exhibits no trace of that greenish tint, which color denotes
the presence of the ter-chloride of gold. An indiarabber hose conveys
the solution into the large vat in such a way as to produce a rotary
motion of such fluid, which facilitates the precipitation and
deposition of the gold by the addition of sulphate of iron, at the
bottom of the vessels in the form of a brown powder; this is very
carefully collected, after removing the fluid parts by a spyhon, and
smelted with borax, so as to separate any impurities it may then be
associated with.
The
charges for " chloriding," as it is termed in California, were as
follows :—If three or more tons, 20 dollars per ton; one ton or less,
25 dollars each ton.
It
having been demonstrated in the above description that this
chlori-nation process is much superior to our common manipulation with
inclined furnaces, which are doing about only one-third of the work of
the drop furnaces, and that the collection of gold in grinding pans
with mercury is certainly not so effective as if the gold was dissolved
by chemical action and precipitated in a simple manner without
mechanical power, the strong recommendation of the delegate for its
general adoption will, it is hoped, obtain the support of mine owners
here.
The
only objection that has been urged against the chlorination process, as
carried out in California, has been to the effect that the coarse gold
remains undissolved during the time stipulated, and is consequently
lost in the waste. It is only by comparing the gold in the matrices
here and in California that we can arrive at the results that make up
facts in this and other matters ; the gold in the Californian lodes is
frequently very fine, but it is also very coarse, so that there is,
after all, not so much difference as fancied by us. And, even if this
coarse gold remained undissolved, it is certainly very pure after the
process and eminently susceptible for collection upon the
electro-copper plates over which all wastes are afterwards passed in
California, without any additional expense or loss of time.
