The
roasting is conducted at a low temperature in some form of
reverberatory furnace. Salt is added in the roasting to convert all the
metals present, except iron, into chlorides. The auric chloride is,
however, decomposed at the elevated temperature into finely-divided
metallic gold, which is then readily attacked by the chlorine gas. The
roasted mineral, slight moistened, is next introduced into a wooden
vat, pitched inside, and furnished with a double bottom, as is shown in
fig. 8. Chlorine is led from a suitable generator beneath the false
bottom, and rises through the moistened ore, resting on a bed of broken
quartz below the false bottom, converting the gold into a soluble
chloride, which' is afterwards removed by washing with water. The
precious metal is then precipitated as metallic gold by sulphate of
iron. The process has been greatly improved in America by Kustel,
Deetken, and Hoffmann; with proper care it is a very perfect one, and
yields 97 per cent of the gold originally present in the ore. It is
stated not to cost more in California than 50s. a ton Any silver
originally present in the ore is of course converted into chloride of
silver and remains with the residue, from which it may be extracted by
the solvent action of brine or by amalgamation.
GOLD IN CEYLON. (From the Ceylon Observer, April 8, 1881.)
Extracts
from a Paper read at the Royal Asiatic Society, Ceylon Branch, by Mr.
A. C. Dixon, on Gold in Ceylon. The following are the main facts:—
There
is a great similarity between the hill regions of Ceylon and the S. E.
Wynaad district at the N. W. base of the Nilgiris, which has recently
become so prominent an account of its auriferous reefs. As to the
probable age of these districts we are uncertain, but there can be no
doubt that the two regions are contemporaneous, consisting of granitoid
schists or gneissoid rocks—that they are highly metamorphosed, and that quartz reefs form a conspicuous feature.
The reefs are often white, occasionally somewhat brecciated and not un-frequently bound together by haematite or limonite.
Although
the strike of the rock is peculiar in the Nilgiris, E. N. E., yet the
auriferous reefs run N. N. W. corresponding with the gneiss a little
further to the north. The general run of the rocks is N. to N. W. As on
the Wynaad we have an absence of intrusive rock. No dykes, porphyritic
masses or basalts. It has been observed that the auriferous belts are
richest where micaceous and chloratic rocks occur. Strange to say in
the cuttings of the railway into our hill district and the various
cuttings on the public roads no prominent reefs have been crossed;
probably one or more may be met with in the extension of the railway
from Nawalapitiya to Nanuoya. In several parts, the country is
traversed by large persistent reefs of quartz with numerous narrow
seams and veins diverging from them and often traceable into
decomposed lithomargic earth. Some good examples of these are to be
found in the Balangoda, 1'ussellawa, Ramboda and Dolosbage districts.
The
character of the vegetation in prospecting for gold is of great
assistance in Australia, where each formation is characterized by
distinct forms of vegetation, but in Ceylon we have no guidance, at the
mountainous zone, is but one formation. Gold occurs in three chief
forms. I, As scattered grains or nuggets on alluvial deposits, having
beSn set free by natural causes from its matrix. 2, In grains and
leaves on numerous veins, chiefly quartz. Still in the matrix but not
with other metals : this is called free gold. 3, Associated
(but not chemically combined) with numerous other metallic compounds,
tuch as arsenides, sulphides, &c, generally classed under the term pyrites, found on veins of quartz and other rocks.
In
the first form I have met with it in the alluvium of the Deduruoya
beyond Kurunegala. The particles were exceedingly small and other
metallic
