Copper, according to Walchner, is as widely distributed in nature as iron, and occurs in all soils, and ferruginous mineral waters and ores. It has been discovered in seaweed; in the blood of certain Cephalopoda and Ascidia, and of a species of Limulus ; in straw, hay, eggs, cheese, meat, and other food-stuffs; in the liver and kidneys, and, in traces, in the blood of man and other animals; it has also been shown by Church to exist to the extent of 5 - 9 per cent, in turacin, the colouring-matter of the wing-feathers of the Tτιraco. The ores containing copper in sufficient proportion to render its extraction economically practicable are numerous. It occurs not unfrequently native, sometimes in very great masses, as on the south shores of Lake Superior, where pieces of 150 tons weight have sometimes been obtained. Native copper most frequently occurs in masses of irregular form in rocky fissures, and often crystallized. The principal ores of copper are Cuprite, Melaconite, Malachite, Chessylite, Atacamite, Chrysocolla, Chalcodte, Chalcopyrite, Erubescite, and Tetrahedrite. Cuprite, or red oxide of copper,. Cu 2 O, is a mineral which crystallizes in the cubic system, and contains 88 - 78 of metal. It occurs in most cupriferous mines, but never by, itself in large quantities. Melaconite, or black oxide of copper, CuO, contains, when pure, 79 , 85 of the metal. It was formerly largely worked in the Lake Superior region, and is abundant in some of the mines of Tennessee and the Mississippi valley. Malachite, or green carbonate of copper, CuCO 3 , Cu(HO) 2 , is a beautiful and valuable ore containing about 56 per cent, of the metal; it is obtained in very large quantities from South Australia, Siberia, and other localities. Frequently intermixed with the green carbonate is the blue carbonate of copper, chessylite or azurite, 2CuCO 3 , Cu(H0) 2 , an ore containing when pure 55*16 per cent, of the metal. It was formerly characteristic of Chessy, near Lyons. Atacamite is a hydrated oxychloride of copper, occurring chiefly in Chili and Peru; it crystallizes in the rhombic system. Chrysocolla is a hydrated silicate of copper, CuSiO 3 , 2H 2 O, containing in the pure state 30 per cent, of the metal; it is an abundant ore in Chili, Wisconsin, and Missouri. The sulphur compounds of copper are, however, the most valuable in an economical point of view. Chalcocite, redruthite, copper-glance, or vitreous copper, is a sulphide, Cu 2 S, containing very nearly 80 per cent, of copper. Copper pyrites, or chalcopyrite, a sulphide of copper and iron, CuFeS 2 , crystallizes in the pyramidal system and contains 34 ’ 6 per cent, of copper when pure; but many of the ores, such as those worked specially by wet processes on account of the presence of a large proportion of sulphide of iron, contain less than 5 per cent, of copper. Cornish ores are almost entirely pyritous; and indeed it is from such ores that by far the largest proportion of copper is extracted throughout the world. In Cornwall copper lodes usually run east and west. They occur both in the killas or clay-slate, and in the growan or granite. Erubescite, bornite, or horseflesh ore is a sulphide of copper andiron much richer in copper than the ordinary pyrites, and containing 56 or 57 or, according to the formula FeCu 2 S 3 , 62 5 per cent, of copper. Tetrahedrite, fahlerz, or grey copper, a sulphide crystallizing in the cubical system, contains from 30 to 48 per cent, of copper, with arsenic, antimony, iron, and sometimes zinc, silver, or mercury. The numerous other compounds of copper have more interest from a mineralogical than from a metallurgical point of view.

Copper is obtained from its ores by two principal methods, which may be denominated—(1) the pyro-metallurgical or dry method, and (2) the hydro-metallurgical or wet method; and a small proportion of metallic copper is procured by (3) the electro-metallurgical method.

The methods of working vary according to the nature of the ores treated and local circumstances. The dry method, or ordinary smelting, cannot be profitably practised with ores containing less than 4 per cent, of copper, for which and for still poorer ores the wet process is preferred.

Smelting. —In Great Britain ordinary copper smelting is almost entirely centred at Swansea in Wales, although it is also practised in Lancashire. The processes there employed for extracting copper are technically known as the “English method,” in contradistinction to numerous other modified processes adopted at Continental and other foreign smelting centres. The following is an outline of the English method as conducted at Swansea.

The ores are divided by the smelter into two general classes—those containing sulphur, and those having little or no sulphur. The former are subdivided according as they contain much silica, iron pyrites, tin, arsenic, &c., or a larger or smaller quantity of copper. The object of this classification of ores in the yard is to enable the operative smelter to make up a constant working mixture, having the following characters :—

1. The copper present is not under 9 nor above 14 per cent.; if under the former it would be unprofitably poor; if over the latter, the slags would have a tendency to retain copper, creating a loss.

2. After being calcined for an ordinary length of time, it will fuse easily without the necessity of adding flux, giving a clean and easily fused slag.

3. The mat or coarse metal obtained from fusion contains as nearly as possible 30 per cent of copper.

4. The mixture does not contain ores having impurities calculated to make the copper of too low a quality.

There is no definite or fixed rule to guide the smelter in these classifications, except a practised eye in distinguishing the character of ores, and the report of the assayer.

I. Calcination of the Ores.— The mixture of ores being selected according to these rules, it is carried to hoppers on the top of a large reverberatory furnace, termed the calcining furnace, and is then let down into the hearth, where, after drying a little, it is spread equally over the bottom, and covered to a depth of from 6 to 8 inches. The quantity of ore put in varies, according to the size of the furnace, from 3 tons to 4 tons. The fire of the furnace is kept low at first; after two or three hours the ore on the sur face becomes visibly red, and the heat is gradually increased to a yellow red; but this heat penetrates to the depth of only about 2 inches, consequently the ore has to be stirred and turned over by means of long iron paddles every hour, so as to expose a new surface to the action of the air and fire. The calcination lasts generally from twelve to twenty-four hours, the length of time being dependent on the proportions of silica and sulphide of iron in the charge. Calcining furnaces are now very commonly provided .with Siemens regenerators and heated with gas. The following changes take place :—the sulphur is partly burned off, forming sulphurous and sulphuric acids, and partly volatilized in the free state; arsenic is volatilized and oxidized; and part of the copper and iron lose sulphur and combine with oxygen, forming oxides.

When the ore is sufficiently calcined, it is let down into the cubs or vaults beneath, by openings in the floor. Water is added to the hot ore in the cubs to prevent dust and assist further oxidation; the ore is then removed to a yard, and there stored up, ready for the fusing furnace. The following analysis of ore, before and after calcining, will give an idea of the changes that have taken place :— [table]

IT. Fusion of Calcined Ore.— The next operation is the fusing of the calcined ore, which is done in a reverberatory furnace, termed an ore fusing furnace, fitted also with a hopner on the top for charging it. The charge consists of [table]

When the charge islet down into the furnace it is spread equally over the bottom, the doors are all closed, every airhole is stopped with clay, and the heat of the furnace increased as rapidly as possible.

After about five hours’ firing, when the furnace has reached a white heat, the door-plate is removed, and a long iron rake passed through the contents to make sure that the whole is perfectly fused. This being the case, the workman begins the operation of skimming, that is, drawing off the slag, which floats on the surface of the mat, and removing it at the front door. When the surface is skimmed, the common practice is to let down a second charge of ore, and to fuse and skim in the same manner, before tapping the furnace to let out the metal or mat, which is generally tapped into large pits of water, and so granulated. These pits are from 6 to 8 feet deep, and from 4 to 5 feet square, and into them a perforated box is lowered, which receives the charge of metal, and is raised by a crane or pulley. The metal is then removed to a yard for the next operation. This mat is termed granulated coarse metal. In many cases the coarse metal is first run into moulds and subsequently crushed for the next operation.

The average composition of good coarse metal is given by Le Play as [table]

III. Calcination of Coarse Metal.— This operation is performed in the same manner as the calcination of the ore. The charge of metal, which is about 4 tons, covers the bottom of the hearth to the depth of 4 inches or so. It is put in through the hoppers fitted upon the top of the furnace, as described for the ore. The coarse metal being easily fused, great care is required not to raise the heat of the furnace too high, otherwise the metal will cake, and by adhering to the bricks will prove prejudicial bcth to the calcination and to the furnace. When the charge is let into the furnace, it is slowly brought to a visible red, which during the next fourteen hours is gradually increased to a bright red heat. This temperature is continued until the charge has been altogether twenty-four hours in the furnace, when it is let down through the bottom into the cubs, and water is thrown upon it.

The following analyses give an average result of the changes effected in this operation :— [table]

IV. Fusion of Calcined Coarse Metal.— Tn this operation the charge for an ordinary-sized furnace of 8 feet by 13 feet is—

25 cwt of calcined metal,

5 to 7 cwt. slags from the roaster and refinery furnaces;

2 to 3 cwt. of cobbing

In this mixture the oxide of iron is in excess in relation to the silica, and it is therefore much more easily fused than the ore; but the reactions which take place are similar: the silica and oxide of iron combine to form slag, which floats upon the surface of the mat and has to be skimmed off, after which the mat is tapped out into sand-moulds. Two charges are generally fused before the metal is tapped out. This mat is termed blue metal from its being of a slate-blue colour; the scoria is termed sharp slag, from its containing an excess of oxide of iron, and being consequently used as a flux for fusing the ore in operation II.

The following is the composition of good blue metal and sharp slag :— [table]

Should there be no ores such as carbonates or oxides on hand to smelt, the blue metal, instead of being tapped into sand-beds as described, is run into pits of water in the same manner as coarse metal, and subjected to another calcination and fusion.

When oxides and carbonates, such as the Australian ores, are on hand, they are generally fused with the calcined coarse metal, by which means a double advantage is obtained; the excess of oxide of iron in the calcined metal fluxes the silica of the ore which has little iron, and the copper in the ore is converted into cupric sulphide, a condition necessary for reduction by the present method of smelting. The produce of this fusion is a mat termed pimpled or white metal, from its having small rough granules on the surface of the ingots. The average composition of this metal is— [table]

The composition of the slag from this operation is very variable; it always contains copper, and has to be remelted.

V. Roasting.— This operation has been often identified with calcining, from which, however, it is distinct. The roasting differs from the fusing furnace by having a large opening in the side for putting in the charge, and it is furnished with more air-holes in the bridge. The charge for an ordinary-sized furnace is 3 tons. When the metal is brought to fusion, the air-holes of the furnace are all opened, and a free current is allowed to pass over the surface of the fused mass: the heat of the fire is then regulated so as to keep the charge in a sort of semi-fluid state. This is continued for about twenty-four hours, during which a great portion of the sulphur is driven off, and the iron, by uniting with silica and other matters, forms scoria, which is from time to time skimmed off. When all the impurities are removed, and the mat or regulus acquires the composition of sulphide of copper, Cu 2 S, then (except when the regulus has been very rich) begins another operation termed the second roasting, or roasting proper, requiring other twenty-four hours. In this last roasting, when the air-holes are opened, a brisk effervescence ensues over the surface of the fluid mass.

The chemical reactions which give rise to this effervescence may be explained thus, The oxygen of the air combines in the first place with a portion of the sulphur. forming sulphurous acid. A portion of the copper is also oxidized, to form the sub-oxide, and instantly reacts upon another portion of the sulphide, reducing the metal. The reactions are chemically represented thus :—

2Cu 2 O + Cu 2 S = 6Cu + SO,.

The process is a very beautiful one, and exhibits a nice adaptation of principles to practice. The sponge regulus has a specific gravity of 5, the reduced copper of about 8; so that the copper sinks to the bottom, where it is protected, and a new surface of regulus becomes exposed to the action of the air.

If the ore be pure, or if no select copper be required, the operation of roasting is continued until the whole of the copper is reduced; when it is tapped out into sand-moulds, forming coarse copper, bed copper, pimpled copper, or blistered copper, according to quality. The term, coarse copper is applied occasionally to all these kinds except the blistered. If the ingot sets with contraction and exhibits a smooth hollow surface, it is termed bed, and generally indicates the presence of other metals, as tin. When the surface of the ingot is covered with pimples, it is termed pimpled copper, and indicates the presence of sulphur. When covered with large scales of oxide of copper, it is termed blistered; but this is only when the copper is good and ready for refining. The following analysis of blister copper is given by Le Play :— [table]

To make select copper, the roasting is carried on until about one-fourth of the copper in the regulus is reduced; the furnace is then tapped, and the reduced metal is obtained at the bottom of the first and second ingots, or pigs, as copper bottoms, which contain most of the metallic impurities. The regulus is collected and again roasted, which produces the purest metal the ordinary process of smelting can give; it is termed best selected.

VI. Refining.— In this operation, the remainder of the sulphur and foreign metals present in the copper is removed, and the metal is brought into a condition fit for the market. The refining furnace is similar in general form to a roasting furnace, except that the bottom inclines gradually down from all sides towards a deep part, or well, which is near the end door. It has also a large door on one side, but neither opening in the roof nor side tap-hole. Siemens’s regenerative furnace has been very generally introduced for refinery purposes. When the copper is to be finally ladled out of the furnace the deep part, or well, allows of the ladle being dipped into the metal till the last portions are quite baled out. From 6 to 8 tons of copper from the roasting furnace are put into the refining furnace, the doors and air-holes of which are closed, and the heat is raised until the metal is in fusion, when the air-holes are opened. A short roasting is generally required, which is done in the manner above described, and the scoria which collects is carefully skimmed off. The separation of impurities is facilitated by occasionally stirring the metal with a rake. Some refiners throw pieces of green wood upon the surface, under the impression that it assists the escape of sulphur. The roasting is continued until a ladleful of the metal taken out sets with contraction. If the metal be very coarse, it will set with a surface having a frothy appearance; if finer, it sets with expansion, first round the edge, then swelling towards the centre, forming a little mound or cone, and occasionally boiling over and throwing up jets of metal, forming a miniature volcano. When the setting of the metal in the ladle is favourable, the charge is ready for the operation of poling. A quantity of charcoal or anthracite coal is first thrown upon the metal to prevent oxidation by the air, and then the end of a large pole of green wood, generally of birch or oak, is inserted into the melted copper, and kept pressed down to the bottom of the metal, which spurts and boils violently. This operation, it will be at once apparent, consists in the reduction of an oxide or suboxide. Since oxide of copper dissolves in metallic copper, as a salt dissolves in water, and makes it brittle, to put pieces of wood or charcoal upon the surface would not remove the oxygen; hence the necessity of poling, in order to bring the carbonaceous matters into contact with the dissolved oxide. As the poling proceeds the refiner takes from time to time small samples called assays, which he hammers and breaks for examination. When the copper reaches the proper “pitch” the assay bends without breaking, and if cut and broken the fracture is fibrous, and presents a silky lustre. When this pitch is attained the pole is withdrawn, and a quantity of charcoal thrown upon the surface; and, if the copper is for rolling or hammering, a little lead is...

Copperas is used in dyeing and tanning, in the manufacture of ink, Prussian blue, and Nordhausen sulphuric acid or fuming oil of vitriol, in medicine as an astringent and tonic, and in analytical chemistry. In the 13th century it was in request for sheepdressing. When calcined it yields first a white salt, FeSO 4 ,H 2 O, the ferri sulphas exsiccata of pharmacy, and finally brownish-red ferric oxide or colcothar of vitriol (colcothar vitrioli, caput mortuum, or crocus Martis), employed as a paint and polishing-powder. Colcothar may also be prepared by calcining a mixture of 100 parts by weight of copperas with 42 of common salt, and washing out the resulting sodium sulphate. Jeweller's rouge or plate-powder is the washed and calcined precipitate of ferric oxide obtained by adding solution of sodium carbonate to solution of copperas.