COPPER 



slaked lime, the precipitate is dried and fused with carbonaceous matters and a little 

 Band, and metallic tin obtained ; the caustic soda-solution is evaporated to drynoss 

 and used over again. This process was proposed for the treatment of very poor copper 

 ores that are mixed with tin, or poor tin ores mixed with copper, but does not appear 

 to have been practically applied. 



Process formerly employed at Ckessy. The principal ore smelted at Chessy was the 

 azure copper, or blue carbonate, which was discovered by accident in 1812. Red 

 copper ore, also, came into operation there after 1825. The average metallic contents 

 of the richest azure ore was from 33 to 36 per cent. ; of the poorer, from 20 to 24. 

 The red ore contained from 40 to 67 parts in 100. The ore was sorted to an average 

 of 27 per cent, of metal, to which 20 per cent, of limestone was 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, was added to each charge, which consisted of 200 pounds 

 of the above mixture, and 1 50 pounds of coke. When the furnace (fourneau a mancke, 

 see the Scotch smelting hearth, under LEAD) was in good action, from 10 to 14 such 

 charges could be worked in 12 hours. When the crucible was full of metal at the end 

 of this period, during which the cinder had been frequently raked off, the blast was 

 stopped ; the matt floating over and the metal being sprinkled with water and taken 

 off, left the black copper to be treated in a similar way, and converted into rosettes. 

 The refining of this black copper was performed in a kind of reverberatory furnace. 



The cinders produced in this reduction process were either vitreous and light blue, 

 which were 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 oxide of copper into the cinders. They consisted of silicate of alumina, of lime, 

 and of protoxide of iron ; the red contained some silicate of copper. 



The copper - refining 

 J furnace at Chessy was of 



\ the kind called Splciss- 



ofen (split-hearth) by 

 the Germans. Fig. 512 

 is a section lengthwise 

 on the dotted line A B of 

 fig. 513, which is the 

 ground plan. 



The foundation-walls 

 were made of gneiss ; 

 the arch, the fire-bridge, 

 and the chimney, of fire- 

 bricks. The hearth a 

 was formed of a dense 

 mixture of coal-dust, 

 upon a bottom of well- 

 beat clay b, which re- 

 posed upon a bed of 

 brick-work c. Beneath 

 this there was a slag 

 bottom d ; e is the upper, 

 and / the under dis- 

 charge-hole. The hearth 

 was egg-shaped ; the 

 longer axis being 8 feet, 



the shorter 6^ feet; in the middle it was 10 inches deep, and furnished with the 



outlets g g, which lead to each of the split-hearths, h h, fig. 513. These outlets were 



contracted with fire-bricks i i, till the proper period of the discharge. The two hearths 



were placed in communication by a canal k ; they were each 3^ feet in diameter, 16 



inches deep ; floored with well-beat coal-ashes, and received about 27 cwts. for a charge. 



I is the grate ; m, the fire-bridge ; n, the boshes in which the tuyeres lie ; o, the 



chimney ; p, the working door, through which the slags may be drawn off. Above 



this was a small chimney, to carry off the flame and smoke whenever the door was 



opened. 



The smelting post or charge to be purified at once, consisted of 60 cwts. of black 

 copper, to which a little granular copper and copper of cementation were added ; the 

 consumption of pit-coal amounted to 36 cwts. As soon as the copper was melted, the 

 bellows were set a-going, and the surface of the metal soon became covered with a 

 moderately thick layer of cinder, which was drawn off. This was the first skimming 

 or decrassage. By-and-by, a second layer of cinder formed, which was in like manner 

 removed; and this skimming was repeated, to allow the blast to act upon fresh 



