. Dental metallurgy, for the use of dental students and practitioners. Europe are located inEngland, Hungary and Silesia. Zinc, as a rule, does not existin the free state in nature, although it is claimed that thenative metal has been found near Melbourne, Australia. The principal ores are: sulphide, sphalerite, (ZnS); oxide,zincite or red zinc, (ZnO); carbonate smithsonite or calamine,(ZnC03); silicates willimite, (Z^SKX); calamine, (ZnOH)2,Si03; oxide franklinite or horseflesh ore, (FeMnZn) carbonate is also known as zinc blend. Blend isderived from the German, meaning to dazzle, whi
. Dental metallurgy, for the use of dental students and practitioners. Europe are located inEngland, Hungary and Silesia. Zinc, as a rule, does not existin the free state in nature, although it is claimed that thenative metal has been found near Melbourne, Australia. The principal ores are: sulphide, sphalerite, (ZnS); oxide,zincite or red zinc, (ZnO); carbonate smithsonite or calamine,(ZnC03); silicates willimite, (Z^SKX); calamine, (ZnOH)2,Si03; oxide franklinite or horseflesh ore, (FeMnZn) carbonate is also known as zinc blend. Blend isderived from the German, meaning to dazzle, which refers REDUCTION 245 to the brilliancy of the crystals, which are almost black, dueto the presence of iron sulphide. Reduction.—The ore is first roasted in a reverberatoryfurnace; then distilled, mixed with charcoal, in closedearthen or iron vessels. The roasting converts the carbonateor the sulphide into the oxide: ZnCOs 2ZnS ? - heat302 ZnO + CO22ZnO + 2SO2. The charcoal reduces the oxide and the free zinc distilsover into the receivers. ZnO + C = Zn + Fig. 57 The process varies in different countries; in Silesia,Germany, fire-clay muffles are used, this is known as theSilesian process (Fig. 57); in Belgium, earthenware tubes,Belgian process (Fig. 58); and in England, fire-clay English furnace is conical in shape, having an interiordome; six crucibles are placed within the furnace, each has ahole in the bottom, through which an iron pipe passes toconvey the zinc vapor. After placing the charge of zinc oxide 246 ZINC and coke in the crucible, the top is cemented into place andthe crucibles are heated until a bright red heat is first portions of the gas from the iron tubes are com-monly very impure, containing cadmium and arsenic and the
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