91 G COPPER 



This pyrites is composed of nearly equal proportions of sulphide of copper and sulphide 

 of iron. Richer ores, consisting of oxides and carbonates of copper, &c., are also 

 worked in. 



The earthy matters which accompanj' the pyrites are usually siliceous, though in 

 Bomo mines the mineral is mixed with either clay or fluor-spar. Along with these sub- 

 stances, tin ore and arsenical pyrites occasionally occur with the copper ; and though 

 these two minerals are not chemically combined, yet they cannot be entirely separated 

 by mechanical preparation. The constituent parts of the ore prepared for smelting are, 

 therefore, copper, iron, and sulphur, with earthy matters, and, in some cases, tin and 

 arsenic. The different ores are mixed in such proportions that the average metallic 

 contents may amount to 8 per cent. The smelting process consists in alternate 

 roastings and fusions. 



In the roasting operation the volatile substances are mostly disengaged in the 

 gaseous state, while the metals that possess a strong affinity for oxygen become 

 oxidised. In the fusion the earthy substances combine with these oxides, and form 

 glassy scoria? or slags, which float upon the surface of the melted metal. 

 The calcinations and fusions take place in the following order : 

 1. Calcination of the ore. 2. Fusion of the calcined ore. 3. Calcination of coarse- 

 metal. 4. Melting the calcined coarse-metal. 6. Calcination of fine-metal (second 

 matt). 6. Melting calcined fine-metal. 7. Roasting coarse-copper. In some smelting- 

 works, this roasting is repeated four times ; in which case a calcination and a melting 

 are omitted. In other works, however, a saving is made without increasing the 

 number of roastings. 8. Refining or toughening the copper. 



Besides these operations which constitute the treatment of copper properly speaking, 

 two others are sometimes performed, in which only the scoriae are smelted. These 

 may be designated by the letters a and b : a is the re-melting of a portion of the 

 scoriae of the second process, which contain some metallic granulations ; b is a par- 

 ticular melting of the scoriae of the fourth operation. This fusion is intended to 

 concentrate the particles of copper in the scorise, and is not practised in all smelting- 

 works. 



First Operation : Calcination of the ore. The different ores on arriving from Corn- 

 wall and other localities where they are mined, are discharged in continuous cargoes 

 at the smelting works, in such a way, that by taking out a portion from several heaps 

 at a time, a tolerably uniform mixturo is obtained; which is very essential, since 

 the ores, being different in quality and contents, act as fluxes for each other. 

 The mixed ore is transported to the works in wooden measures each holding a hun- 

 dred-weight. The workmen entrusted with the calcination convey the ore into the 

 hoppers of the calcining furnace, whence it falls into the hearth ; other workmen 

 spread it uniformly on the surface with iron rakes. The charge of a furnace is from 

 3 tons to 3 tons. Fire is applied and gradually increased, till towards the end of the 

 operation, the temperature is as high as the ore can support without melting or agglu- 

 tinating. To prevent this running together, and to aid the extrication of the sulphur, 

 the surfaces are renewed, by stirring up the ore at the end of eve'-y hour. The calcin- 

 ation is usually completed at the end of 12 hours, when the ore is raked into the arch 

 under the sole of the furnace, and when cold enough to be moved, is taken out of the 

 arch, and conveyed to the calcined heap. 



The ore in this process scarcely changes weight, having gained by oxidation nearly 

 as much as it has lost in sulphur and arsenic ; and if the roasting has been rightly 

 managed, the ore is in a black powder, owing to the oxides present. 



The utilisation of the sulphurous vapours evolved during calcination is explained, 

 p. 928. 



Second Operation: Fusion of the calcined ore. The calcined ore is likewise given 

 to the smelters in measures containing a hundred- weight. They throw it into hoppers, 

 and, after it has fallen on the hearth, spread it uniformly. They then let down the 

 door, and lute it tightly. In this fusion there are added about 2 cwt. of scoriae (' metal 

 slag ') proceeding from the melting of the calcined matt, to be afterwards described. 

 The object of this addition is not only to extract the copper that these scoriae may con- 

 tain, but also to increase the fusibility of the mixture. Sometimes, when the composi- 

 tion of the ore requires it, lime, sand, or fluor-spar is added, more particularly the latter. 

 The furnace being charged, fire is applied, and the sole care of the founder is to keep 

 up the heat so as to have a perfect fusion ; the workman then opens the door, and stirs 

 about the liquid mass to complete the separation of the 'metal' (regulus, or matt) 

 from the scorise, as well as to hinder the melted matter from sticking to the sole. 

 The furnace being ready, that is, the fusion being perfect, the founder takes out the 

 scoriae by the front door, by means of a rake. When the mass is thus freed from the 

 scoriae, a second charge of calcined ore is introduced to increase the metallic bath ; 

 which second fusion is executed like the first. New charges of roasted ore are put 



