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GOLD. —Metallurgical Operations.

The general arrangement of chlorination works isshown in plan and elevation by Fig. 3, Plate I. ABruckner’s cylinder, in which the ore undergoes apreliminary roasting to remove precipitating agents,such as sulphur, antimony, and arsenic, is shown atI. The leaching vats are at A, the precipitating vatsat B, trucks to remove spent ore at C, the gas-gener-ator at d, and the waste tub, where the water runsthrough sawdust, at e.

Many other methods are adopted for extracting theprecious metal from the tailings, &c., but the readerrequiring further information must be referred to thelarger treatises, such as “ The Mining and Metallurgyof Gold and Silver, ” by Mr. J. A. Phillip, the“ United States Statistics of Mines and Mining,” &c.

Calverts Chlorination Process .—The following pro-cess of extracting gold by means of nascent chlorinewas devised by Crace Calvert, and is closelyanalogous to that of Plattner just described :—Hefound that if 2-2 parts of fine gold be added to 100parts of pure sand, and placed in a bottle with asaturated solution of chlorine gas for twenty-fourhours, only 0'5 part of gold is dissolved. If, insteadof chlorine water, a mixture of chlorine water andhydrochloric acid be used, 0 - 6 is dissolved. If themixture consist of sand, reduced gold, peroxide ofmanganese, and hydrochloric acid, T4 part gold isdissolved. It was thus abundantly proved that thefact of the chlorine being in its nascent state materi-ally aided the solution of the gold, although eventhen there remained 08 part undissolved. Aftermany experiments, he decided that the following isthe best method for extracting on a commercialscale:—The finely-reduced auriferous quartz shouldbe intimately mixed with about 1 per cent, of per-oxide of manganese; and if common salt be used(which, together with sulphuric acid, may be substi-tuted for the hydrochloric acid), this material shouldbe added at the same time as the manganese, in theproportion of 3 parts of salt to 2 of manganese. Thewhole should then be introduced into closed vats,having false bottoms, upon which are laid smallbranches covered with straw, so as to prevent thereduced quartz from filling the holes in the falsebottom. Hydrochloric (or sulphuric) acid is thenadded, and after standing for twelve hours, watershould be poured in in sufficient quantity to fill thewhole empty space below the false bottom. Thisliquid, after being pumped up several times, andallowed to percolate through the entire mass, is runoff into vats, the gold being separated by means of aconcentrated solution of protosulphate of iron. Incases where silver also is present, it is desirable toemploy common salt and sulphuric acid, as by thismeans the chloride of silver formed is retained insolution by the excess of common salt. The silveris separated before proceeding to extract the goldand copper.

METALLURGICAL OPERATIONS.—Fusion.—When the gold is received from the gold-washer , inthe shape of gold-dust, or when it has been separatedfrom its ores by amalgamation or otherwise, it hasnow to be subjected to a series of metallurgical |

operations to obtain it in a state of perfect purity.The first of these is that of fusion with borax, andcasting the metal into ingots, by which it is obtainedin a convenient form, and freed at the same timefrom earthy and other impurities. For this purposethe gold dust from the washings, or the spongy goldobtained by amalgamation, is mixed with a littledried borax, and is introduced into a black-leadcrucible, previously heated in a common meltingfurnace. After .the fusion of the metal, a slag,consisting of the grosser impurities, accumulates onthe surface ; this must be thickened by the additionof a little bone-ash, and then skimmed off. Themetal is now cast into ingots, by being pouredinto iron ingot-moulds, previously warmed and oiledby wiping the internal surface with a piece of towdipped in sweet oil. It is an old practice, nowdiscarded by some metallurgists as useless, to addto the metal, when thoroughly melted in the cru-cible, a small quantity of corrosive sublimate; thecontents are then well stirred, and, in consequenceof the volatilization of the sublimate, effervescencetakes place. That this is attended with no injuriouseffect seems to have been fully established by along experience; and that it may even be pro-ductive of benefit is probable, by bringing to thesurface any extraneous matter which might bedetached from the interior of the crucible, and sopermitting its removal along with the slag. Thecrucibles which have been used in a series of suchoperations retain a portion of gold, which renders itimportant to preserve them, with a view to the subse-quent extraction of the precious metal by smelting.

Smelting of Gold Ores. —Although the readiestmethod of extracting the gold from rich alluvialsands is by repeated washings, in the manner alreadydescribed, and in the treatment of quartz rock,iron pyrites, and other auriferous minerals, themethod involving the tedious operations of pounding,washing, and amalgamation is usually adopted; yetin the latter case the same object may be accom-plished by direct smelting —a term technically appliedto a process, or series of processes, by which a metalis extracted, by the agency of fire, from the sub-stances with which it may be combined or mixed innature. It is well known that by this method ironis extracted from its ore in the blast furnace, andsome years ago aRussian gentleman, named Anossow,even proposed to smelt in this manner the auriferoussand of the Ural, alleging that a much larger quantityof gold could be so obtained than by the most skil-fully conducted process of washing. His methodconsisted in smelting the sand with iron, the latterbeing employed simply as a vehicle to collect thegold, or to perform, in its melted state, the samepart as mercury in the processes already described.When the gold was obtained in this state of com-bination, the mass was exposed to the action of sul-phuric acid, by which the iron was dissolved and thegold remained in the insoluble residue. From someexperiments which were made at the Museum ofPractical Geology in London , it was found that, if itwere advantageous on the score of economy, cast-iron