Eighth operation. Refining or toughening

—The pigs of copper intended for refining are put upon the sole of the refining furnace through the door in the side. A slight heat is first given, to finish the roasting or oxidation, in case this operation has not already been pushed far enough. The fire is to be increased by slow degrees, so that, by the end of 6 hours, the copper may begin to flow. When all the metal is melted, and when the heat is considerable, the workman lifts up the door in the front, and withdraws with a rake the few scoriæ which may cover the copper bath. They are red, lamellated, very heavy, and closely resemble protoxide of copper. The refiner takes then an a ay with a small ladle, and when it cools, breaks it in a vice, to see the state of the copper. From the appearance of the a ay, the aspect of the bath, the state of the fire, ., he judges if he may proceed to the toughening, and what quantity of wooden spars and wood charcoal he must add to render the metal malleable, or, in the language of the smelters, bring it to the proper pitch. When the operation of refining begins, the copper is brittle or dry, and of a deep red colour approaching to purple. Its grain is coarse, open, and somewhat crystalline. To execute the refining, the surface of the metal is covered over with wood charcoal, and stirred about with a spar or rod of birch wood. The gases which escape from the wood, occasion a brisk effervescence. More wood charcoal is added from time to time, so that the surface of the metal may be always covered with it, and the stirring is continued with the rods, till the operation of refining be finished; a circumstance indicated by the a ays taken in succe ion. The grain of the copper becomes finer and finer, and its colour gradually brightens. When the grain is extremely fine, or closed , when the trial pieces half cut through and then broken, present a silky fracture, and when the copper is of a fine light red, the refiner considers the operation to be completed; but he verifies still further the purity of the copper, by trying its malleability. For this purpose, he takes out a sample in his small ladle, and pours it into a mould. When the copper is solidified, but still red-hot, he forges it. If it is soft under the hammer, if it does not crack on the edges, the refiner is satisfied with its ductility, and he pronounces it to be in its proper state . He orders the workmen to mould it; who then lift the copper out of the furnace in large iron ladles lined with clay, and pour it into moulds of the size suitable to the demands of commerce. The ordinary dimensions of the ingots or pigs are 12 inches broad, 18 long, and from 2 to 2 1 ⁄ 2 thick. The period of the refining proce is 20 hours. In the first six, the metal heats, and suffers a kind of roasting; at the end of this time it melts. It takes four hours to reach the point at which the refining, properly speaking, begins; and this last part of the proce lasts about 4 hours. Finally, 6 hours are required to arrange the moulds, cast the ingots, and let the furnace cool. The charge of copper in the refining proce depends upon the dimensions of the furnace. In the Hafod works, one of the most important in England, the charge varies from 3 to 5 tons; and the quantity of pure copper manufactured in a week is from 40 to 50 tons. The consumption of fuel is from 15 to 18 parts of coal, for one part of refined copper in pigs. When the copper offers difficulties in the refining, a few pounds of lead are added to it. This metal, by the facility with which it scorifies, acts as a purifier, aiding the oxidation of the iron and other metals that may be present in the copper. The lead ought to be added immediately after removing the door to skim the surface. The copper should be constantly stirred up, to expose the greatest po ible surface to the action of the air, and to produce the complete oxidation of the lead; for the smallest quantity of this metal alloyed in copper, is difficult to clear up in the lamination; that is to say, the scale of oxide does not come cleanly from the surface of the sheets. The operation of refining copper is delicate, and requires, upon the part of the workmen, great skill and attention to give the metal its due ductility. Its surface ought to be entirely covered with wood charcoal; without this precaution, the refining of the metal would go back , as the workmen say, during the long interval which elapses in the moulding; whenever this accident happens, the metal must be stirred up anew with the wooden pole. Too long employment of the wooden rod gives birth to another remarkable accident, for the copper becomes more brittle than it was prior to the commencement of the refining; that is, when it was dry . Its colour is now of a very brilliant yellowish red, and its fracture is fibrous. When this circumstance occurs, when the refining, as the workmen say, has gone too far , the refiner removes the charcoal from the top of the melted metal; he opens the side door, to expose the copper to the action of the air, and it then resumes its malleable condition. Mr. Vivian, to whom we owe the above very graphic account of the proce es, has explained, in a very happy manner, the theory of refining. He conceives, we may conclude, that the copper in the dry state , before the refining, is combined with a small portion of oxygen, or, in other words, that a small portion of oxide of copper is diffused through the ma , or combined with it; and that this proportion of oxygen is expelled by the deoxidizing action of the wood and charcoal, whereby the metal becomes malleable. 2. That when the refining proce is carried too far, the copper gets combined with a little charcoal. Thus copper, like iron, is brittle when combined with oxygen and charcoal; and becomes malleable only when freed entirely from these two substances. It is remarkable, that copper, in the dry state , has a very strong action upon iron; and that the tools employed in stirring the liquid metal become very glistening, like those used in a farrier’s forge. The iron of the tools consumes more rapidly at that time, than when the copper has acquired its malleable state. The metal requires, also, when dry , more time to become solid, or to cool, than when it is refined; a circumstance depending, probably, upon the difference in fusibility of the copper in the two states, and which seems to indicate, as in the case of iron, the presence of oxygen. When the proper refining point has been pa ed, another very remarkable circumstance has been observed; namely, that the surface of the copper oxidizes more difficultly, and that it is uncommonly brilliant; reflecting clearly the bricks of the furnace vault. This fact is favourable to the idea suggested above, that the metal is in that case combined with a small quantity of carbon; which absorbs the oxygen of the air, and thus protects the metal from its action. Copper is brought into the market in different forms, according to the purposes which it is to serve. What is to be employed in the manufacture of bra is granulated. In this condition it presents more surface to the action of zinc or calamine, and combines with it more readily. To produce this granulation, the metal is poured into a large ladle, pierced with holes, and placed above a cistern filled with water, which must be hot or cold, according to the form wished in the grains. When it is hot, round grains are obtained analogous to lead shot; and the copper in this state is called bean shot . When the melted copper falls into cold water perpetually renewed, the granulations are irregular, thin, and ramified; constituting feathered shot . The bean shot is the form employed in bra making. Copper is also made into small ingots, about 6 ounces in weight. These are intended for exportation to the East Indies, and are known in commerce by the name of Japan copper. Whenever these little pieces are solidified, they are thrown, while hot, into cold water. This immersion slightly oxidizes the surface of the copper, and gives it a fine red colour. Lastly, the copper is often reduced into sheets, for the sheathing of ships, and many other purposes. The Hafod works po e a powerful rolling mill, composed of four pairs of cylinders. It is moved by a steam engine, whose cylinder has 40 inches diameter. See the representation of the rolling mill of the Royal Mint, under Gold . The cylinders for rolling copper into sheets are usually 3 feet long, and 15 inches in diameter. They are uniform. The upper roller may be approached to the under one, by a screw, so that the cylinders are brought closer, as the sheet is to be made thinner. The ingots of copper are laid upon the sole of a reverberatory furnace to be heated; they are placed alongside each other, and they are formed into piles in a cro -like arrangement, so that the hot air may pa freely round them all. The door of the furnace is shut, and the workman looks in through a peep-hole from time to time, to see if they have taken the requisite temperature; namely, a dull red. The copper is now pa ed between the cylinders; but although this metal be very malleable, the ingots cannot be reduced to sheets without being several times heated; because the copper cools, and acquires, by compre ion, a texture which stops the progre of the lamination. These succe ive heatings are given in the furnace indicated above; though, when the sheets are to have a very great size, furnaces somewhat different are had recourse to. They are from 12 to 15 feet long, and 5 wide. See Bra . The copper, by succe ive heating and lamination, gets covered with a coat of oxide, which is removed by steeping the sheets for a few days in a pit filled with urine; they are then put upon the sole of the heating furnace. Ammonia is formed, which acts on the copper oxide, and lays bare the metallic surface. The sheets are next rubbed with a piece of wood, then plunged, while still hot, into water, to make the oxide scale off; and lastly, they are pa ed cold through the rolling pre to smooth them. They are now cut square, and packed up for home sale or exportation. The following estimate has been given by MM. Dufrénoy and Elie de Beaumont of the expense of manufacturing a ton of copper in South Wales. | £ | s. | d. | | 121⁄2 tons of ore, yielding 81⁄2 per cent. of copper | 55 | 0 | 0 | | 20 tons of coals | 8 | 0 | 0 | | Workmen’s wages, rent, repairs, . | 13 | 0 | 0 | | 76 | 0 | 0 | The exhalations from the copper smelting works are very detrimental to both vegetable and animal life. They consist of sulphurous acid, sulphuric acid, arsenic and arsenious acids, various gases and fluoric vapours, with solid particles mechanically swept away into the air, besides the coal smoke. Mr. Vivian has invented a very ingenious method of pa ing the exhalations from the calcining ores and matts along horizontal flues or rather galleries of great dimensions, with many cro ings and windings of the current, and exposure during the greater part of the circuit to copious showers of cold water. By this simple and powerful system of condensation, the arsenic is deposited in the bottoms of the flues, the sulphurous acid is in a great measure absorbed, and the nuisance is remarkably abated. The following figures represent certain modifications of the copper calcining and smelting copper furnaces of Swansea. IMG:4147767755307473660_illo0325a.png:Swansea copper furnaces Fig. 304. is the section of the roasting furnace lengthwise; fig. 303. the ground plan; in which a is the fire-door; b the grate; c the fore-bridge; d the chimney; e e working apertures on each of the long sides of the furnace, through which the ore is introduced, spread, and turned over; f f cast-iron hoppers; g g openings in the vaulted roof; h the hearth-sole; i i holes in this; k a vaulted space under the hearth. The hearth has a suitable oval shape, and is covered with a flat arch. Its length is 16 feet, breadth 13 1 ⁄ 2 , mean height 2 feet. IMG:4147767755307473660_illo0325b.png:Melting furnace Fig. 305. is a longitudinal section of the melting furnace; fig. 306. the ground plan in which a is the fire door; b the grate; c the fire bridge; d the chimney; e the side openings; f the working doors; g the raking-out hole; h iron spouts, which conduct the melted metal into pits filled with water. The melting furnace is altogether smaller; but its firing hearth is considerably larger than in the roasting furnace. The long axis of the oval hearth is 14 feet; its short axis 10 feet; its mean height 2 feet. The principal ore smelted at Che y is the azure copper, which was discovered by accident in 1812. Red copper ore, also, has come into operation there since 1825. The average metallic contents of the richest azure ore are from 33 to 36 per cent.; of the poorer, from 20 to 24. The red ore contains from 40 to 67 parts in 100. The ore is sorted, so that the mean contents of metal may be 27 per cent., to which 20 per cent. of limestone are 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 , are added to each charge, which consists of 200 pounds of the above mixture, and 150 pounds of coke. When the furnace ( fourneau à manche , see the Scotch smelting hearth , under Lead ), is in good action, from 10 to 14 such charges are worked in 12 hours. When the crucible is full of metal at the end of this period, during which the cinder has been frequently raked off, the blast is stopped, and the matt floating over the metal being sprinkled with water and taken off, leaves the black copper to be treated in a similar way, and converted into rosettes . The refining of this black copper is performed in a kind of reverberatory furnace. The cinders produced in this reduction proce are either vitreous and light blue, which are most abundant; cellular, black, imperfectly fused from exce of lime; or, lastly, red, dense, blistery, from defect of lime, from too much heat, and the pa age of protoxide into the cinders. They consist of silicate of alumina, of lime, protoxide of iron; the red contain some silicate of copper. IMG:4147767755307473660_illo0326.png:Split hearth The copper-refining furnace at Che y, near Lyons, is of the kind called Splei -ofen (split hearths) by the Germans. Fig. 307. is a section lengthwise in the dotted line A B of fig. 308. , which is the ground plan. IMG:4147767755307473660_illo0327a.png:Split hearth The foundation-walls are made of gnei ; the arch, the fire-bridge, and the chimney, of fire-bricks. The hearth, a , is formed of a dense mixture of coal-dust, upon a bottom of well-beat clay b , which reposes upon a bed of brickwork c . Beneath this there is a slag bottom d ; e is the upper, and f the under discharge hole. The hearth is egg-shaped; the longer axis being 8 feet, the shorter 6 1 ⁄ 2 feet: in the middle it is 10 inches deep, and furnished with the outlets g g , which lead to each of the Splei -hearths h h , fig. 308. These outlets are contracted with fire-bricks i i , till the proper period of the discharge. The two hearths are placed in communication by a canal h ; they are 3 1 ⁄ 2 feet in diameter, 16 inches deep; are floored with well-beat coal ashes, and receive about 27 cwt. for a charge. l is the grate; m , the fire-bridge; n , the boshes in which the tuyères lie; o , the chimney; p , the working door through which the slags may be drawn off. Above this is a small chimney, to carry off the flame and smoke whenever the door is opened. The smelting post or charge, to be purified at once, consists of 60 cwt. of black copper, to which a little granular copper and copper of cementation is added; the consumption of pit-coal amounts to 36 cwt. As soon as the copper is melted, the bellows are set a-going, and the surface of the metal gets soon covered with a moderately thick layer of cinder, which is drawn off. This is the first skimming or decra age . By and by, a second layer of cinder forms, which is in like manner removed; and this skimming is repeated, to allow the blast to act upon fresh metallic surfaces. After 4 or 5 hours, no more slag appears, and then the fire is increased. The melted ma now begins to boil or work ( travailler ), and continues so to do, for about 3 ⁄ 4 of an hour, or an hour, after which the motion ceases, though the fire be kept up. The gahrproof is now taken; but the metal is seldom fine in le than 3 ⁄ 4 of an hour after the boil is over. Whenever the metal is run off by the tap-hole into the two basins i i , called SPLIT-HEARTHS , a reddish vapour or mist rises from its surface, composed of an infinite number of minute globules, which revolve with astonishing velocity upon their axes, constituting what the Germans called spratzen (crackling) of the copper. They are composed of a nucleus of metal, covered with a film of protoxide, and are used as sand for strewing upon manuscript. The copper is separated, as usual, by sprinkling water upon the surface of the melted metal, in the state of rosettes , which are immediately immersed in a stream of water. This refining proce lasts about 16 or 17 hours; the skimmings weigh about 50 cwt.; the refuse is from 15 to 17 per cent.; the lo from 2 to 3 per cent. The gahrslag amounts to 11 cwt. IMG:4147767755307473660_illo0327b.png:Kupfergahrheerd The refining of the eliquated copper (called darrlinge ) from which the silver has been sweated out by the intervention of lead, can be performed only in small hearths. The following is the representation of such a furnace, called, in German, Kupfergahrheerd . Fig. 309. is the section lengthwise; fig. 310. is the section acro ; and fig. 311. is the ground plan, in which a is the hearth-hollow; b , a ma ive wall; c , the ma out of which the hearth is formed; d , cast-iron plates covering the hearth; e , opening for running off the liquid slag; f , a small wall; g , iron curb for keeping the coals together. The hearth being heated with a bed of charcoal, 3 ⁄ 4 cwt. of darrlinge are laid over it, and covered with more fuel: whenever this charge is melted, another layer of the coal and darrlinge is introduced, and thus in succe ion till the hearth become full, or contain from 2 1 ⁄ 4 to 2 1 ⁄ 2 cwt. In Neustadt 7 1 ⁄ 2 cwt. of darrlinge have been refined in one furnace, from which 5 cwt. of gahrcopper has been obtained. The blast oxidizes the foreign metals, namely, the lead, nickel, cobalt, and iron, with a little copper, forming the gahrslag ; which is, at first, rich in lead oxide, and poor in copper oxide; but, at the end, this order is reversed. The slag, at first blackish, a umes progre ively a copper red tint. The slag flows off spontaneously along the channel e , from the surface of the hearth. The gahre is tested by means of a proof rod of iron, called gahr-eisen , thrust through the tuyère into the melted copper, then drawn out and plunged in cold water. As soon as the gahrspan (scale of copper) appears brownish red on the outside, and copper red within, so thin that it seems like a net-work, and so deficient in tenacity that it cannot be bent without breaking, the refining is finished. The blast is then stopped; the coals covering the surface, as also the cinders must be raked off the copper, after being left to cool a little; the surface is now cooled by sprinkling water upon it, and the thick cake of congealed metal ( rondelle ) is lifted off with tongs, a proce called schlei en (slicing), or she i ben reis sen (shaving), which is continued till the last convex cake at the bottom of the furnace, styled the kings piece , is withdrawn. These rondelles are immediately immersed in cold water, to prevent the oxidation of the copper; whereupon the metal becomes of a cochineal red colour, and gets covered with a thin film of protoxide. Its under surface is studded over with points and hooks, the result of tearing the congealed disc from the liquid metal. Such cakes are called rosette copper. When the metal is very pure and free from protoxide, these cakes may be obtained very thin, one 24th of an inch for example. The refining of two cwts. and a half of darrlinge takes three quarters of an hour, and yields one cwt. and a half of gahr copper in 36 rosettes, as also some gahrslag . Gahr copper generally contains from 1 1 ⁄ 2 to 2 1 ⁄ 2 per cent. of lead, along with a little nickel, silver, iron, and aluminum.