oh GUN-METAL. I05

The copper met with in commerce is generally designed ofthree qualities, viz. sure, common , and impure , as in somemines the metal will not defray the expence of purifying it.For some years past the merchants have imported copperfrom Germany, Savoy, and Japan, which is very wellpurified: that procured from Aost and Sweben is harderand less malleable; but the copper brought from Mexicois of a very inferior quality, being crude and totally unfit forwire-drawing.

18. Pure copper is red, tenacious, ductile and malleable;it is drawn into very small wire, as the strings of musicalinstruments; and beat into very thin vessels without breakingor splitting : this is a certain method of proving its purity.This copper requires a very strong and long continued heatto melt it. If it be fused without being in contact with anyphlogistic body, and the fire be stronger than is necessary tokeep it in fusion, small particles will be seen successively tocalcine; and if the same force of fire be continued, thesecalcinations will appear in the form of scoriæ floating onthe surface of the melted metal. If the scoriæ be scummedoff, pounded and mixed with a quantity of charcoal, theywill when exposed in the furnace to a strong blast revivifyand resume the metallic form. (Philos. Instit. 91, 116.)

The flame that breaks out at the fusion of pure copperwith charcoal,- is of a fine green colour; when dissolved bybil of vitriol, it exhibits a blue flame.

19. Common copper is that in which the heterogeneoussubstances are in small quantity, and do not much affect itstenacity and ductility; so that though it cannot be drawninto very fine wire, kitchen utensils are made of it.

The copper of the third kind is of an inferior quality;less tenacious and ductile: if brittle under the hammer,or when offered to the wire-drawer, it is a proof thatit contains many ferruginous or arsenical particles. Ifthere be much arsenic, the copper fuses easily; and if therebe any antimony it accelerates the fusion : but then the flameinstead of being of a greenish is of a whitish cast, and is loadedwith smoke. If the flame at the solution of copper by oil ofvitriol be yellow, it is a sign that the ore contains iron ; andif the colour become green, the iron is in great quantity.Impure copper ought never to be admitted into founderiesfor cannon, as the bronze made of it is short and brittle.

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