COPPER 917 



in till the matt collected on the hearth rises to a level -with the door-way, which hap- 

 pens commonly after the third charge. The tap-hole is now opened, and the matt 

 flows out into a pit filled with water, where it is granulated and collects in the pan 

 placed at the bottom. The granulated matt is next conveyed into the matt warehouse. 

 The oxidation with which the grains get covered by the action of water does not allow 

 the proper shade of the matt or coarse-metal to be distinguished ; but in the bits which 

 stick in the gutter it is seen to be of a steel-grey colour. Its fracture is compact, and 

 its lustre metallic. The scoriae, known as ore-furnace slag, often contain metallic 

 grains ; they are broken and picked with care. All the portions which include metallic 

 particles are re-melted in an accessory process. 



In this operation the copper is concentrated by the separation of a great part of the 

 matters with which it was combined. The granulated matt produced contains in 

 general 33 per cent, of copper ; it is therefore four times richer than the ore ; and its 

 mass is consequently diminished in that proportion. Its constituents are principally 

 copper, iron, and sulphur. It is termed coarse-metal. 



The most important point in the fusion just described, is to make a fusible mixttire 

 of the earths and oxides, so that the matt of copper may, on account of its greater 

 specific gravity, sink below and separate exactly from the slag. This is attained by 

 means of metallic oxides contained in the scoriae of the fourth operation, of which 2 cwt. 

 were added to the charge. These consist almost entirely of oxide of iron. When the 

 ores are very difficult to melt, about half a hundred-weight of fluor-spar is added ; but 

 this must be done with precaution, for fear of too much increasing the scoriae. 



The work proceeds day and night. Five charges are commonly put through in the 

 course of 24 hours ; but when all circumstances are favourable, that is to say, when 

 the ore is fusible, when the fuel is of the first quality, and the furnace in good condition, 

 even six charges a day have been despatched. 



The charge is a ton and a half of calcined ore, so that a smelting furnace nearly 

 corresponds to a calcining furnace ; the latter turning out 7 tons of calcined ore in 24 

 hours. The workmen are paid by the ton. 



Third Operation: Calcination of coarse-metal. The object of this operation is 

 principally to oxidise the iron, which is more easily accomplished than in the first 

 calcining, because the metal is now disengaged from the earthy^ substances, which 

 screened it from the action of the air. 



This calcination is executed in the furnace already represented in Jigs. 505, 506, 507, 

 page 915, exactly in the same way as the ore was calcined. The metal must be. per- 

 petually stirred, to expose all its surfaces to the action of the hot air, and to hinder 

 clotting together. The operation lasts 24 hours ; during the first six, the fire should bo 

 very moderate, and gradually increased to the end of the calcination. The charge is, 

 like that of the first, 3^ tons. 



Fourth Operation : Melting the calcined coarse-metal. In the fusion of this 

 first calcined matt, some scoriae of the latter operations must be added, which are 

 very rich in oxide of copper, and some crusts from the hearth, which are likewise 

 impregnated with it. Addition may also be made of richer crude ores, such as oxides 

 and carbonates. The proportion of these substances varies according to the quality 

 of the calcined matt. 



In this second fusion, the oxide of copper contained in the scoriae is reduced by the 

 affinity of the sulphur, one portion of which passes to the state of sulphurous acid, 

 while the other forms a subsulphido with the free copper. The matt commonly 

 contains a sufficient quantity of sulphur to reduce the oxide of copper completely ; 

 but if not, which may happen if the calcination of the matt has been pushed too far, 

 a small quantity of uncalcined matt must be introduced, which, by furnishing sulphur, 

 diminishes the richness of the scoriae, and facilitates the fusion. 



The scorise are taken out by the front door by means of a rake. They have a great 

 specific gravity ; are brilliant with a metallic lustre, very crystalline, and present, in 

 the cavities, crystals like those of pyroxene ; they break easily into very sharp-edged 

 fragments, and contain no granulated metal in the interior ; but it sometimes occurs, 

 on account of the small thickness of the stratum of scoriae, that these carry off with 

 them, when withdrawn, some metallic particles. 



These scoriae, as we have already stated (under Fusion of the roasted Ore}, are in 

 general melted with it. In some cases, however, a special melting is assigned to them. 



The matt obtained in this second fusion is either run out into water like the first, or 

 moulded into pigs (ingote), according to the mode of treatment which it is to undergo. 

 This matt, termed by the smelters fine-metal when it is granulated, and blue-metal when 

 it is in pigs, is of a light grey colour, compact, and bluish at the surface, and contains 

 about 60 per cent, of copper. 



(ft.) Particular Fusion of the Scoria of the fourth Operation. In re-melting these 

 scoriae, the object is to procure the copper which they contain. To effect this fusion, 



