332

COPPER.

than in the roasting furnace. The long axis of the oval hearth is 14 feet; its short axis10 feet; its mean height 2 feet.

300 *

The principal ore smelted at Chessy isthe azure copper, which was discoveredby accident in 1812. Red copper ore, also,has come into operation there since 1825.The average metallic contents of the richestazure ore are from 33 to 36 per cent.; ofthe poorer, from 20 to 24. The red orecontains from 40 to 67 parts in 100. Theore is sorted, so that the mean contents ofmetal may be 27 per cent., to which 20per cent, of limestone are added; whencethe cinder will amount to 50 per cent, ofthe ore. A few per cents, of red copperslag, with some quicklime-and gahrslag, areadded to each charge, which consists of200 pounds of the above mixture, and150 pounds of coke. When the furnace(fourneau a manche , see the Scotch smelting hearth, under Lead) is in good action,from 10 to 14 such charges are worked in 12 hours. When the crucible is full of metalat the end of this period, during which the cinder has been frequently raked oflj the blastis stopped, and the matte floating over the metal being sprinkled with water and takenoff, leaves the black copper to be treated in a similar way, and converted into rosettes.The refining of this black copper is performed in a kind of reverberatory furnace.

The cinders produced in this reduction process are either vitreous and light blue,which are most abundant; cellular, black, imperfectly fftsed from excess of lime; or.lastly, red, dense, blistery, from defect of lime, from too much heat, and the passage ofprotoxyde into the cinders. They consist of silicate of alumina, of lime, protoxyde ofiron ; the red contain some silicate of copper. •

307

The copper-refining fur-nace at Chessy, near Ly-ons, is of the kind calledSpleiss-ofen (split hearths)by the Germans . Fig. 307is a section lengthwise inthe dotted line a n of fig*308, which is the groundplan.

The foundation-walls aremade of gneiss; the arch,the fire-bridge, and th echimney, of fire-bricks. Thehearth, u, is formed of adense mixture of coal-dust,upon a bottom of well-beatclay, 5, which reposes upona bed of brickwork c. ® e 'nealh this there is a slogbottom d; e is the upper?and f the under dischargehole. The hearth is egg'shaped ; the longer axis be-ing 8 feet, the shorter b«feet; in the middle it * s

10

inches deep, and furnished with the outlets g g, which lead to each of the Spleiss-hearthsh h 3 Jig. 308. These outlets are contracted with fire-bricks i i, till the proper periodthe discharge. The two hearths are placed in communication by a canal 1c: they arefeet in diameter, 16 inches deep; are floored with well-beat coal ashes, and receive abou27 cwt. for a charge. ,

l is the grate; m , the fire-bridge; n, the boshes in which the tuyeres lie; o 9 t ®chimney; p> the working door through which the slags may be drawn oif. -A- b0this is a small chimney, to carry off the flame and smoke whenever the dooropened. ^ i.

The smelting post or charge, to be purified at once, consists of 60 cwt. oicopper, to which a little granular copper and copper of cementation is added 1

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