METALLURGY. 



63 



alloy is afterwards mixed with it, and after a similar 

 operation, the remaining quantity is added, and the mix- 

 ture kept fused for about three hours, during which it 

 is frequently stirred. It is then, when the surface has 

 become quite white, poured into cones greased in the 

 h^A When it is solid, it is found to nave separated 

 into distinct parts, the upper is sulphuret of silver, the 

 lower is a metallic button composed of gold and silver. 

 If the former contain gold, it is exposed to heat in an 

 open crucible, by which part of the sulphur is dissipated, 

 and the silver set free, unites with the gold, and col- 

 lects at the bottom of the vessel as the matter cools. 

 The metal thus obtained, is repeatedly subjected to the 

 tame process, till the alloy procured contain a Urge 

 enough quantity of gold to admit of its separation 

 from the silver, by the process of parting already des- 

 cribed. 



Gold is occasionally deprived of the baser metals by 

 the use of sulphuret of antimony, sulphur having a 

 stronger attraction for the other metals than for anti- 

 mony, while it does not combine with gold. To pu- 

 rify gold by this means, it is nscsssery to employ cru- 

 cibles, which are not porous. To render them so, they 

 am soaked in oil, and then bismrarsil in the inside with 

 pounded borax. The gold alloy is fused in these, and 

 about twice its weight of sulphuret of antimony is 

 added in successive portions, taking care that the mix- 

 ture does not swell and flow out of the crucible. If 

 the quantity of gold be very small, the sulphoret most 

 be previously fused, with an additional quantity of 

 sulphur, so that too much sntimoni may not be need. 

 When the whose of the mixture is m a state of fusion, 

 and when it sparkle*, it U poured into 

 which mast be struck gentry as the 

 to cause the geld to faU to the b 

 the gold is found united with the antimony, and also 

 with a little of the alloying metals ; it must, therefore, 

 be subjected to the same process, with an additional 

 quantity of SMSpharst, a second and a third time, by 

 which the whole of these are removed. The next part 

 oftheptweeas is to separata the gold and antimony. 

 For this purpose the alloy, reduced to fragments, M 

 with one fourth of its weight of sulphur, in a 

 by which the greater part of the an- 

 and unites with the ; "* 1 *-"~ff- 



into 



risthenpoared 



I still retaining a little 



timony quits the gold, 

 blebody. The fused i 

 cones ; and when cold, the gold erf 

 st^imony, is collected at the bottom. To free it from 

 this, it most be fused, and a stream of air made to pass 

 over it, by which the antimony is oxidated, and dissi- 

 pated by the beat, and the gold U left. If not quite 

 purified by this proem, it must be fused with s little 

 nitre, which will oxidate the antimony, and leave the 

 gold pure. The talphum of antimony formed by the 

 feton of die alloy and sulphur, contains a small quan- 

 tity of gold. To obtain this from it. it must be fused 

 with about one-fifth of its weight of iron filing*, which 

 will unite with the sulphur ; the antimony will com- 

 bine with the gold, and may be separated by the me- 



The process of purifying gold by rtmmtitio*, is still 

 pfiiiliisil in some particular cases. It consist* in beating 

 the alloy to thin plates, and placing these in alternate 

 layers, with a cement cismpoaiii did nitre, 8 of cal- 

 cined green vitriol, and 2 of pounded tiles, made into a 

 paste with urine, taking care that there be cement at the 

 top and bottom of the vessels. These are placed in a fur- 

 nace, and kept at a heat, below the melting point of 



gold, for 24 hours. The gold is then removed, and Metallur- 

 boiled, first in water, and afterwards in nitric acid, by _ft-_ 

 which the foreign matter is washed off. The plates are ^ f ~i~ t ~ ' 

 repeatedly subjected to a similar operation ; and in this 

 way a great deal of the alloying metals are removed by 

 the nitric acid, set at liberty from the nitre, by the ac- 

 tion of the acid of the salt of iron on it. The superiori- 

 ty of this process depends on the nitric acid, at the 

 temperature to which it is exposed, acting on silver 

 and copper, though in small quantity, which is not 

 the case when the liquid acid is boiled on the alloy ; it 

 does not, however, afford the gold pure, it is therefore 

 practised only when this metal is not required very 

 fine, as in the formation of trinkets. 



Attay of Gold Oret. As gold ores contain in general Assay 01 

 but few ingredients, their assay is easily performed. For gold ores, 

 this purpose the ore is reduced to powder, and mixed 

 with 1 of fused borax, and 4 of sub-carbonate of potassa, 

 and subjected to heat in a crucible. When fused, it is 

 poured out, and if any remain in the vessel, it must be 

 removed by muriatic acid. This, with the fused matter 

 reduced to powder, is digested in muriatic acid, to which 

 from time to time a little nitric acid is ail.u.l. When 

 the action ctases, the solution is poured off, and the re- 

 sidue is well washed with water, the washings being 

 mixed with the solution. To the solution, neutralised 

 by a fixed alkali, green sulphate of iron U added, as 

 long as it causes any precipitation ; the precipitate, after 

 beany; washed, U fused in a crucible with a little nitre ; 

 and afibrds gold in a state of purity. If the part of the 

 ore not acted on by the acid become black by expo- 

 sure to light, it contains silver. To procure this, it 

 must be fused with about thrice its weight of sub-car- 

 bonate of potassa, by which the silver is reduced and 

 is mixed with the earthy matter. By washing the 

 product in muriatic acid, the latter is separated, and 

 the silver is left. 



Iron pyrites containing gold U analysed by digest- 

 ing the ore in muriatic acid, to which a little nitric 

 acid is sdded. What is left must be roasted to drive 

 off the sulphur, and again digested in acid. The solu- 

 tions obtained must be nciitr.ili.-td by potassa, and pro- 

 to-nitrate of mercury is added. The precipitate thrown 

 down, is then fu*ed with nitre, by which the gold is 

 procured. If silver be also contained in the ore, it is 

 obtained by treating that part of it not acted on by the 

 acid, with tub-carbonate of potassa and muriatic acid, 

 as above described. Galena, containing gold, is ana- 

 lysed by digesting it in nitro-muriatic acid, evaporat- 

 ing the solution, snd afterwards adding proto-nitrate 

 ofmercury. The insoluble part, when treated as above, 

 will yield the silver if any exist in the ore. 



The assay of gold, as performed on its alloys, will be 

 given when trusting of assay of silver. 



Silver. 



Silver is obtained not only from the proper ores of 

 silver, but likewise from some of the ores which sre 

 wrought to yield other metals. Of these the principal 

 are the ores of lead. 



Reduction of Oret. 



Two methods are practised for procuring silver, the , 

 one is by amalgamation, the other is byjution. The of otssT 

 former is followed when the ore is rich in silver, the 

 latter when it contains little of the precious metal. 



Amalgamation. The ores which are subjected to the 

 process of amalgamation, contain in general, besides 



