(C.)—OTHER PROCESSES.
Prof. Monnier's Treatment of Sulphurets.
Having
already described the geological features observed at the New
Providence mine, Nevada City, attention is now directed to their very
extensive works in which their ore is manipulated, primarily for the
gold, and secondarily for the silver, zinc, lead, copper, and iron such
ores contain. These ores resemble somewhat those of St. Arnaud,
Percydale, and in a minor degree the Whip Reef, of Sandhurst, in which
places a great deal of difficulty has been experienced in finally
separating these constituents of a refractory or rebellious combination
of metalliferous substances.
The
ore is hand-picked and run through Cornish rollers in the proportion
of 80 per cent, of ore and of 20 per cent, sulphate of soda, until it
passes through screens with 576 holes per square inch; it is then fed
into one of Bruckner's revolving roasting furnaces, 40 feet long by 5
feet in diameter, with a fall of 6 inches for its length towards the
discharge end; the hearth is at the discharge end, and thus the flames
meet the slowly descending ores, whilst the furnace revolves but three
times a minute. The chemical reaction in this furnace is as
follows:—The oxydation of sulphur produces sulphuric acid, which
combines with the soda, forming a bisulphate of soda, and when this
substance approaches the vicinity of the hearth, or fireplace, near its
final discharge from the furnace, it is decomposed, and the bisulphate
gives up sulphuric acid, reacting on the sulphates and oxydes that may
have formed, at the same time converting into soluble sulphates silver,
copper, lead, &c, iron alone remaining an oxyde. The roasted ore is
then placed into large tanks with water for " lixiviation," or
leaching, and the liquor obtained is passed through layers of "cement
copper" (pure), in other vats, in order to precipitate a portion of the
sulphates of silver whilst the liquid retains a low temperature. The
remaining solution is then run through an evaporating pan, in order to
regain the sulphate of soda for repetitionary use, and in this manner
the process is continued until insoluble residues are obtained which
contain the gold and some silver; these are carefully ground in
arastras, and finally passed over electro-copper plates and through
mercury wells, upon and in which the more precious metals are retained
by amalgamation for subsequent retorting. According to the professor's
showing, this kind of ore produced results at the rate of from 88 to 93
per cent, on the assay for gold, 70 per cent, for silver, and the
copper is wholly extracted. The red oxyde of iron, it should be
mentioned, which is thrown aside here in the colony, after roasting and
grinding pyrites, was in California utilized as coloring matter,
possessing a good body, rendering wood fireproof and protecting iron
from rust. Another advantage for Monnier's process consists in the fact
that in other processes the miners lose the silver daring
clilorination, and that chlorination of gold takes forty-eight hours on
the average, whereas, by this manipulation, all the more valuable metals are collected, and this can be done in about half the time.
Having
now described the principal methods adopted by Californian mine
superintendents to work their lodes, and the various processes which
their amalgamators and calciners use in the reduction of their ores, it
will be conceded, I submit, that on the whole very great pains are
taken in that State with the extraction of gold or other metals. And,
for these reasons alone, these various matters should deserve the
careful consideration
