[Fig. 305.] is a longitudinal section of the melting furnace; [fig. 306.] the ground plan in which a is the fire door; b the grate; c the fire bridge; d the chimney; e the side openings; f the working doors; g the raking-out hole; h iron spouts, which conduct the melted metal into pits filled with water.
The melting furnace is altogether smaller; but its firing hearth is considerably larger than in the roasting furnace. The long axis of the oval hearth is 14 feet; its short axis 10 feet; its mean height 2 feet.
The principal ore smelted at Chessy is the azure copper, which was discovered by accident in 1812. Red copper ore, also, has come into operation there since 1825. The average metallic contents of the richest azure ore are from 33 to 36 per cent.; of the poorer, from 20 to 24. The red ore contains from 40 to 67 parts in 100. The ore is sorted, so that the mean contents of metal may be 27 per cent., to which 20 per cent. of limestone are added; whence the cinder will amount to 50 per cent. of the ore. A few per cents. of red copper slag, with some quicklime and gahrslag, are added to each charge, which consists of 200 pounds of the above mixture, and 150 pounds of coke. When the furnace (fourneau à 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 metal at the end of this period, during which the cinder has been frequently raked off, the blast is stopped, and the matt floating over the metal being sprinkled with water and taken off, 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 fused from excess of lime; or, lastly, red, dense, blistery, from defect of lime, from too much heat, and the passage of protoxide into the cinders. They consist of silicate of alumina, of lime, protoxide of iron; the red contain some silicate of copper.
The copper-refining furnace at Chessy, near Lyons, is of the kind called Spleiss-ofen (split hearths) by the Germans. [Fig. 307.] is a section lengthwise in the dotted line A B of [fig. 308.], which is the ground plan.