GOLD. —Smelting oe Gold Ores.

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might really be so applied; and that when it is meltedwith gold, an alloy seems to be formed, from whichthe greater part, if not the whole, of the gold may beextracted by again melting the alloy in contact withlead. With regard to Anossow’s process, experi-ments were reported to have been made on thelarge scale, which had perfectly succeeded; but astrong proof of its want of success is the fact that ithas never been practically adopted.

Prom the well-known infusibility of quartz, it isevident that the smelting of gold-quartz could not beeffected by merely exposing it to the strongest heatof a blast-furnace, without the addition of a flux;for although the gold would be melted, it wouldremain in the quartz, and no separation of theprecious metal would take place. Even supposingthe quartz to be first reduced to .powder, the gold ispresent in too small quantity to separate from theinfusible mass, and sink to the bottom. It is there-fore necessary to add some substance which, at ahigh temperature, shall combine with the quartz, andproduce a fusible compound, in which case the gold,more especially if combined with some other heavymetal, will, in virtue of its high specific gravity, fallto the bottom of the vessel.

The best flux for silica is carbonate of soda, butthis is too expensive to be employed on the largoscale. Lime, therefore, aided by the addition ofoxide of iron, is usually employed for this purpose.Lime alone, or lime and clay in certain proportions,will combine with quartz at a high temperature, andproduce a fusible slag. Oxide of iron will alsosuffice. When practicable, it is desirable to obtainthe oxide of iron by roasting auriferous pyrites, suchas that found in California or the Tyrol, for then theproportion of gold is increased by that contained inthe pyrites. Whatever flux be employed, it is neces-sary, in the first place, to reduce the quartz to acomparatively fine state of division, otherwise a con-siderable loss of time and waste of fuel would beincurred in effecting the perfect combination necessaryto insure the complete separation of the gold. Evenin smelting, therefore, the crushing or pulverizingprocess is not dispensed with. Assuming that limeand oxide of iron are the fluxes employed, and sup-posing the pulverized ore to have been partly con-centrated by washing, these substances are mixed inabout equal proportions, and raised to a white heatin a blast or reverberatory furnace. When oxide ofiron is employed as the flux, the reverberatory furnaceis to be preferred, because in the blast-furnace aconsiderable portion of the oxide would be reduced,and a corresponding quantity of metallic iron liber-ated, long before the mixture attained the degree ofheat requisite for the combination of the silica withthe oxide.

The product of the combination is a fusible slag orglassy substance, through which the gold, also in amelted state, tends to sink to the bottom of thefurnace. But as the portion of this metal presenteven in a large quantity of ore is very small, com-pared with the bulk of the materials through whichit is diffused, it would be difficult to collect it perVOL. II.

se, without very serious loss, in a crucible, and stillmore so in a furnace, whether reverberatory orblast. The operation is therefore materially assistedby adding another metal which shall alloy withand absorb the whole of the gold, and from whichthe latter can afterwards bo easily separated—somemetal, in short, which shall serve the same purposeat a high heat as mercury serves at the ordinarytemperature. Of all metals, lead is found to be thebest adapted for this purpose, not only on account ofits readily combining with the gold in a melted state,but also as offering peculiar facilities for its subse-quent separation from that metal. Lead has, there-fore, been uniformly employed in the processeshitherto adopted on a large scale for smelting goldores. The lead may be added to the mixture of oreand flux, either in the metallic state, or in one or otherof its combinations, from which the metal may be setfree. The materials most commonly employed tofurnish the lead are litharge and galena—the formerthe protoxide, and the latter the native sulphide ofthat metal—although the rich slags obtained bothfrom the smelting furnace and ore-hearth are alsooccasionally used. When litharge is chosen as themedium for the introduction of lead, it must bemixed with charcoal, small coal, or coke-dust, inorder to determine the reduction of the necessaryquantity of lead to the metallic state; but whengalena is used, it is mixed with scrap-iron, whichcombines with the sulphur, setting the lead free.The lead-slag which comes from the ore-hearth orthe reverberatory furnace is generally the most con-venient and least expensive material, as it containsa considerable percentage of lead, and is readilyprepared for use by grinding to powder under theedge-roll, and mixing with charcoal or other carbon-aceous matter. In this case, also, it is importantto add some scrap-iron to combine with any sulphurwhich may be present in the slag. Whichever ofthese substances be employed, the lead evolved,under the conditions mentioned, percolates throughthe mass, and subsiding by virtue of its high specificgravity to the bottom of the furnace, carries alongwith it any particles of the precious metal it maymeet with in its course. The lead is afterwardsseparated by cupellatiou —a process to be explainedshortly.

Smelting with Iron Pyrites .—Instead of directlyemploying lead as the means of concentrating thegold ores, a method has been practised in Hungary in which iron pyrites, generally itself containing asmall quantity of gold, is used with economical effectfor the same purpose. When this mineral is heatedto a certain temperature without access of air, itloses half of its sulphur, and becomes convertedinto a fusible sulphide of iron, such as is pro-duced by bringing a roll of sulphur in contact witha bar of iron raised to a white heat. Let it beassumed, therefore, that this ore consists of amixture of auriferous iron pyrites and quartz, andis mixed with the appropriate flux for the quartz,as already described, and exposed to the requisiteheat; a slag will be formed, and the sulphide of iron12