METHOD OP OBTAINING COPPER.

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merely in vitrification. Liquid ammonia cause* it to oxidatequickly when air is admitted. It decomposes muriate of am-monia and red sulphurated oxid of mercury by heat. It ispoisonous to the human constitution.

METHOD OF OBTAINING COPPER.

Copper is procured from its ores by different processes accord-ing to the nature of those ores. If they contain much sulphur,after being pounded and washed, they are roasted in the open airto dispel the sulphur. The ore is afterwards roasted once ortwice more, and is melted in an open fire into a mass, called amat of copper. In this state it still contains a large quantity ofsulphur, which the workmen continue to expel by repeated roast-ings and fusion, till the metal acquires a certain degree of purity,and is called black copper, which is somewhat malleable, butstill contains sulphur, iron, and in general some other impuri-ties. In order to get entirely rid of these, the copper is hastilyfused with three times its weight of lead. The lead unites withthe copper and expels the iron; and the rest of the metals whichhappen to be mixed with the copper are thus expelled. Thecopper is afterwards refined by keeping it heated in cruciblesfor a considerable time, so that it may throw up all the fo-reign substances it still contains in the form of scoriae. It isexamined from time to time by immersing iron rods into it,which become coloured with a small quantity of copper, and itspurity is judged of by the brilliant redness of these specimens.