SMELTING. 



jHf, or eakineitton, the ufes of which operation are to ex- 

 pel the volatile, ufelefs, or noxious fubftances, as water, 

 vitriohc acid, fulphiir, and arfenic ; to render the ore 

 more friable and fitter for the fubfequent contufion and 

 fufion ; and, laftly, to calcine and deftroy the viler metals ; 

 for inftance, the iron copper-ores, by means of the fire, and 

 of the fulphur and arfenic. Stones, as quartz and flints, 

 coutainiiig metallic veins or particles, are frequently made 

 red-hot, and then extinguilTied in cold water, that they may 

 be rendered fufficiently friable and pulverable, to allow the 

 reparation of the metallic particles. 



Roafting is unnecefTary for native metals ; for fome of the 

 richer gold and filver-ores ; for fome lead-ores, the fulphur 

 of which may be feparated during the fufion ; and for many 

 calciform ores, as theie do not generally contain any fulphur 

 and arfenic. 



In the roafting of ores, the following attentions muft be 

 given : i. To reduce the mineral previoufly into fmall lump?, 

 that the furface may be increafed ; but they muft not be fo 

 fmall, nor placed lo compaftly, as to prevent the paffage 

 of the air and flame. 2. The larger pieces muft be placed 

 at the bottom of the pile, where the greatelt heat is. 

 3. The heat muft be gradually applied, that the fulphur 

 may not be melted, which would greatly retard its expul- 

 ilon ; and that the fpars, fluors, and ftones, intermixed with 

 the ore, may not crack, fly, and be difperfed. 4. The ores 

 not thoroughly roafted by one operation muft be expofed to 

 a fecond. j. The fire may be increafed towards the end, 

 that the noxious matters more ftrongly adhering may be 

 expelled. 6. Fuel which yields much flame, as wood and 

 foffile coals free from fulphur, is faid to be preferable to 

 charcoal or coaks. Sometimes cold water is thrown on the 

 calcined ore at the end of the operation, while the ore is yet 

 hot, to render it more friable. 



No general rule can be given concerning the duration or 

 degree of the fire, thefe being very various according to the 

 difference of the ores. A roafting during a few hours or 

 days is fuffieient for many ores ; while fome, fuch as the 

 ore of Rammelftjerg, require that it ftiould be continued 

 during feveral months. 



Schlatter enumerates five methods of roafting ores. i. By 

 conftrufting a pile of ores and fuel placed in alternate ftrata, 

 in the open air, without any furnace. 2. By confining fuch 

 a pile within walls, but without a roof. 3. By placing the 

 pile under a roof, without lateral walls. 4. By placing the 

 pile in a furnace confifting of walls and a roof. 5. By 

 roalting the ore in a reverberatory furnace, in which it muft 

 be continually ftirred with an iron rod. 



Several kinds of ftifions of ores may be diftinguiflied. 

 I. When a fulphureous ore is mixed with much earthy mat- 

 ter, from which it cannot be eafily feparated, by mechanical 

 operation?, it is frequently melted, in order to difengage it 

 from thefe earthy matters, and to concentrate its metallic 

 contents. By this fufion, fome of the fulphur is diffipated, 

 and the ore ic. reduced to a ftate intermediate betwixt that 

 of ore and of metal. It is then called a mitt (lapis ful- 

 phureo-metallieus), and is to be afterwards treated like a 

 pure ore by the fecond kind of fufion, which is properly the 

 (melting, or extraftioii of metal by fufion. 2. By this 

 fufion or fmelting, the metal is extrafted from the ore 

 previoufly prepared by the above operations, if thefe be 

 neceflary. 



The ores of fome very fufible metals, as of bifmuth, may 

 be fmelted by applying a heat fuffieient only to melt the 

 metals, which are thereby feparated from the adhering ex- 

 traneous matters. This feparation of metals by fufion, 

 without the vitrification of extraneous matters, may be 



called eUquatlon. Generally, a complete fuGon of the ore 

 and vitrification of the earthy matters are neceflary for the 

 perfeft feparation of the contained metals. By this me- 

 thod, metals are obtained from their ores, fometimes pure, 

 and fometimes mixed with other metallic fubftances, from 

 which they muft be afterwards feparated. To procure this 

 feparation of metals from ores, thefe muft be fo thinly 

 liquefied, that the fmall metallic particles may difengage 

 themfelves from the fcoria ; but it muft not be fo thin as to 

 allow the metal to precipitate before it be perfeAly difen- 

 gaged from any adhering extraneous matter, or to pervade 

 and deftroy the containing veflels and furnace. Some ores 

 are fufficiently fufible ; but others require certain additions, 

 called ^a.vf J, to promote their fufion, and the vitrification 

 of their unmetallic parts ; and alfo to render the fcoria 

 fufficiently thin to allow of the feparation of the metallic 

 particles. 



Different fluxes are fuitable to different ores, according 

 to the quality of the ore, and of the matrix, or ftone ad- 

 herent to it. 



The matrixes of two different ores of the fame metal 

 frequently ferve as fluxes to each other ; as, for inftance, 

 an argillaceous matrix with one that is calcareous ; thefe 

 two earths being difpofed to vitrification when mixed, 

 though each of them is fingly inlufible. For this rcafon, 

 two or more diffiereiit ores to be fmelted are frequently 

 mixed together. 



The ores alfo of different metals require different fluxes. 

 Thus, calcareous earth is found to be beft fuited to iron 

 ores, and fpars and fcoria to fufible ores of copper. 



The fluxes moft frequently employed in the fmelting of 

 ores, are calcareous earth, fluors or vitreous fpars, quartz, 

 and fand, fufible ftones, as flates, bafaltes, the feveral kinds 

 of fcoria, and pyrites. 



Calcareous earth is ufed to facilitate the fufion of ores of 

 iron, and of fome of the poorer ores of copper, and, in 

 general, of ores mixed with argillaceous earths, or with fel- 

 fpar. This earth has been fometimes added with a view of 

 feparating the fulphur, to which it very readily unites : but 

 by this union, the fulphur is detained, and a hepar is formed, 

 which readily diflblves iron and other metal?, and fo firmly 

 adheres to them, that they cannot be feparated without 

 more difficulty than they could from the original ore. This 

 addition is therefore not to be made till the fulphur be pre- 

 vioufly well expelled. 



Fluors, or fufible fpars, facilitate the fufion of moft 

 metallic minerals, and alfo of calcareous and argillaceous 

 earths, of fteatites, afbeftus, and of fome other infufible 

 ftones, but not of filiceous earths without a mixture of cal- 

 careous earth. 



Quartz is fometimes added in the fufion of ferruginous 

 copper ores, the ufe of which is faid chiefly to be, to enable 

 the ore to receive greater heat, and to give a more perfeft 

 vitrification to the ferruginous fcoria. 



The fufible ftones, or flates, bafaltes, are fo tenacious 

 and thick when fufed, that they cannot be confidered pro- 

 perly as fluxes, but as matters added to leflen the too great 

 liquidity of fome very fufible miner.jls. 



The fcoria obtained in the fufion of an ore is frequently 

 ufeful to facilitate the fufion of an ore of the fame metal, 

 and fometimes even of the ores of other metals. 



Sulphurated pyrites greatly promotes the fufibility of the 

 fcoria of metals, from the fulphur it contains. It is chiefly 

 added to difficultly fufible copper ores, to form the ful- 

 phureous compounds called matts, that the ores thus brought 

 into fufion, may be feparated from the adhering earthy mat- 

 ters, and tliat the ferruginous matter contained in them may 



be 



