GOLD.— Chlorination Process.

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to contract, and thus retain mercury: several hours’exposure to a low temperature is far more effectivein driving off the last traces of mercury than a shortertime with a high temperature.

When the distillation is concluded, which is knownby the cessation of any further accumulation ofquicksilver in the condenser, this distilled mercury iscollected to be used for future amalgamations. Thegold which remains in the retort, a, is now com-paratively pure; but still contains a mixture ofsilver, copper, or other metals, in greater or lessproportion, according to the sources or localitiesfrom which it has been procured. The separationof these, with a view to the obtaining of the gold ina state of absolute purity, will form the subject ofthe next portion of this article.

In the meantime it may be repeated that theamalgamating process is chiefly applied in the work-ing of auriferous veins, or gold-mining properly socalled, in contradistinction to the much more com-mon method of extracting the gold from drift-bedsor stream-mines, by the mere operation of washing.In the former case the gold, generally in very minuteparticles, is mingled with various other minerals androcks, as pyrites, zinc-blende, quartz, &c., and canonly be extracted after the whole has been reducedby stamping to a very small size—in which state thegold, often so minute as to be invisible, would bealmost entirely carried away by a stream of water.It is here therefore that amalgamation offers peculiaradvantages, as the mercury seizes on the gold, how-ever finely reduced, provided that the metallic par-ticles be not coated with a protective covering; andif the precaution has been taken not to pulverize orstamp the ore too fine when about to be submittedto those preliminary washings which precede theamalgamation, the amount of the precious metal lostmay be reduced to a minimum. When about to bebrought into actual contact with the mercury, theore or schlich cannot be reduced too small; andhence the importance of actually pounding it, ifpossible, under the surface of the mercury.

From these considerations it will be readily seenthat the process of amalgamation is not only appliedwith advantage in the working of auriferous veins orlodes, but that it may also be employed to procure aprofitable return from the re-working of the tailings orrefuse of the Australian or Californian gold-diggers.

To give an idea of what may be done with poorores, when system and skill are brought to bear, itmay be sufficient to state the average produce obtainedfrom the stamped ores at Schenmitz, in Hungary , in1842—recollecting that these had to be broken fromthe solid lodes at depths extending to 200 fathoms.The total quantity stamped in that year was above10,000 tons, and the average of the useful metalsextracted from 50 tons w’as . gold, 8 ounces; aurifer-ous silver, derived from the separating processes, bybuddies or tyes, &c., 8f pounds; lead, similarly ob-tained, 8jcwts.; the ratio of gold to the other materialsbeing in this case as 1 part to 500,000. In the case°f a particular mine, called Siglisberg, not producinglead with the stamped ores, the ratio of gold was only

as 1 part to 700,000; of auriferous silver, 1 to24,000. Now, it is interesting and instructive tocompare with this economical extraction of minutequantities from poor ores by the process of amalga-mation the produce of the manipulation by washingat the Siberian workings, where a common averageof the sands worked to profit is half an ounce in 1cwt., or fully double the amount last mentioned, andyet even the poorer ones of Hungary yield a remuner-ative return by amalgamation. It follows, that bythe same process many auriferous sands in Siberia ,as well as in other countries, which are at presentneglected as being too poor for washing, might beadvantageously worked.

Separation of Gold from Arsenical Pyrites .—Anillustration of the importance of scientific knowledgein the working of gold mines is furnished by theapplication of Tlattner’s method for the separationof gold from arsenical pyrites, in consequence ofwhich the mines of Keichenstein, in Silesia, which,as already stated, had been abandoned for more thanfive centuries, w T ere reopened with advantage.

This process is now largely practised in California under the name of the “Chlorination” process, andconsists in treating the roasted sulphurets with nascentchlorine, whereby all the precious metal is dissolved,and water having been added, the gold is subsequentlydeposited from this solution by means of protosul-phate of iron. The headings from the buddle, afterbeing tossed, &c., are introduced into a commonfurnace, and roasted in order to oxidize all the sulphurpresent in the ore. This roasting causes a consider-able decrease in weight, a ton of crude sulphuretsyielding about 1450 lbs. of roasted ore. This isintroduced into impregnation vats formed of wood,and having an inside coating of pitch and tar; theyare provided with false bottoms, generally of quartzpebbles, above which is laid a perforated earthenwareplate. The ore, slightly damp, having been placed inthese vats, the lids are fitted closely on and chlorinegas introduced under the false bottoms; this gas beingproduced in a leaden generator by the action of dilutesulphuric acid on a mixture of binoxide of manganeseand common salt. This generator is represented inFig. 5, Plate I. It contains an agitator of hardwood, and is closed by a cover resting in a water-joint, the whole being placed on a sand-bath. Priorto passing into the leaching vats any hydrochloricacid which may be present is removed by passingthe gas through water. After remaining in the gas forforty hours the lids of the vats are removed, wateris poured on the surface of the ore in order to dissolveout the gold chloride, and this is run finally, as ayellow solution, into the precipitating vats, which,in construction, are very similar to those used forimpregnating. The gold is here deposited by the aidof a solution of protosulpliate of iron, and after beingallowed to settle over night the supernatant liquid isdrawn off, and the gold treated with sulphuric acidand common salt in order to remove oxides and basiciron salts. The precipitate is finally filtered, driedin cast-iron retorts, and melted into ingots usuallyabout 900 fine.