454 Mr. J. Taylor's Lectures on MduHurgif. 



The ores being deprived of sulphur, or at least to a certain 

 degree, — for one calcination does not effect this completely, — 

 the next step in smelting is to get rid of all the earthy mixture, 

 which is done at once by the simple operation of bringing the 

 whole into a state of fusion. 



It has already been stated that some of the metallic oxides 

 combine with certain earths in fusion, and act powerfully as 

 a Jiitx, which is a term employed for substances that pro- 

 mote the fusibility of others in the fire. It is also necessary to 

 remark, that although a single earth, as silex, for instance, is 

 nearly infusible by itself in our strongest fires, yet by mixing 

 the earths together their fusibility is increased, and we obtain 

 the power of rendering them all fluid by heat. Further, that 

 some of the earths and some of the metallic oxides possess 

 this influence in a greater degree than others. Thus lime in 

 all its states, but particularly in that of fluor-spar, and oxide of 

 lead, are the most powerful assistants of the fusion of earthy 

 matter in general, or the best fluxes. 



Many salts, indeed, possess this property to a much greater 

 extent; but they are far too expensive for use in the larger ope- 

 rations of smelting, diough they are much used for trials in 

 the small way called Assays. 



Now as the ores commonly contain different mixtures in 

 different mines, and as it results from what has been said that 

 such a combination as may be thus expected is useful in pro- 

 moting the fusion of the w'hole ; the smelters find it desirable 

 to mix the ores from different veins on this account ; but as 

 even this does not always succeed sufficiently, an addition is 

 commonly made of lime, limestone or fluor-spar. 



With a mixture of these, die ores are submitted to the 

 strongest action of the fire; complete fusion of the whole mass 

 takes place; the earthy parts form a fluid impure glass, being 

 completely vitrified; the metallic parts of the ore, either quite 

 free from sulphur or in a degree combined with it, are also en- 

 tirely melted, and a perfect separation takes place, owing to 

 the great difference in the specific gravity of tlie substances ; — 

 the earthy glass in a liquicl state, which is now called slag or 

 scoria, occupying the upper place, and the metallic part by its 

 weight sulking down and forming a licjtiid stratum of melted 

 metal underneath, where also it is protected from oxidation 

 and evaporation from the intense heat a}5plied. The whole is 

 in some cases stirred, to assist the precipitation of the metallic 

 matter to the bottom of the furnace ; in other cases this is left 

 to take place of itself 



The fusion oi" copi^er ores is conducted in revcrberatory fur- 

 naces 



