COPPER 



925 



at the top, which is the widest part ; the interior dimension decreasing gradually 

 towards the hearth, where the width is 6 feet. 



The blast is supplied by six water-tuyers placed radially, or nearly so, at a height of 

 from 4 to 5 feet above the hearth. On one side is a dam plate over which slag flows 

 continuously whilst on the opposite side is a tapping hole through which tho matt is 

 drawn off from time to time. 



The top of the furnace is closed by a cup-and-cone, and the waste-gases are conveyed 

 to the stoves employed for heating the blast, the temperature of which is raised to 

 370 F. 



The reverberatory furnace employed in the calcination processes is in all essential 

 respects similar to that used in Wales for the roasting of the various matts produced 

 in the English method of smelting. 



The following is an outline of the routine generally employed : 



1. Boasting the schists in the open air, in large heaps, in order to drive off water, 

 bitumen, and other A'olatile matters and at the same time to induce such a state of 

 division between the particles of the ore as shall be most suitable to subsequent melt- 

 ing operations. 



2. The first melting in a cupola-furnace, the object being the separation of silica and 

 earthy matters in the form of slag and the concentration of the copper in a matt con- 

 taining 36 per cent, of that metal, together with some silver. 



3. The matt formed in the last operation is roasted in the open air in rectangular 

 'stalls,' the object being the elimination of a portion pf the sulphur and the oxidation 

 of some of the iron. 



4. The roasted matt or coarse-metal is concentrated in a reverberatory furnace in 

 order to fit it for the next process for extracting the silver by Ziervogel's method. 

 During the roasting, lead, arsenic, and zinc are to some extent eliminated and a regulus 

 produced which is rich in copper and silver ; at the conclusion of the operation this 

 is granulated by being run into a vat of water. 



5. For the extraction of the silver, the granulated matt is ground to a fine powder, 

 and roasted in a reverberatory furnace at such a temperature that as much as possible 

 of the copper shall be converted into oxide, whilst the silver remains in the form of 

 sulphate ; this is washed from the roasted material by means of hot water and the 

 silver subsequently precipitated from solution by metallic copper. 



6. Fusion for blister-copper. The residue from the lixiviation vats is made into 

 balls with about 8 per cent, of clay, which serves the double purpose of supplying 

 materials for slag and at the same time forming tho powder into lumps and preventing 

 its clogging the furnace. 



The fusion is conducted in a cupola-furnace and fluid products flow continuously from 

 it into a basin, and arrange themselves according to their specific gravities ; namely, 



518 



519 



first, metal ; second, a thin layer of rich matt ; and thirdly, slag. The latter is broken 

 and sorted, and any containing copper is, together with the matt, worked over in one 

 of the earlier operations. 



