We stood upon one occasion beside a furnace, when the charge was in the act of being withdrawn; but we took especial care never to do the like again. The sensation resembled what one might expect to feel on holding a lighted lucifer-match under each nostril. It is surprising how the workmen stand it. For the greater part of their lives, these poor Welshmen exist habitually in an atmosphere so charged with the above-mentioned abominable gases, that it is difficult to understand from whence their lungs receive the necessary supply of pure oxygen.[6] Sulphurous acid, we may add, is the predominant smell in a copper-work; but arsenic acid, hydrofluoric acid, and even arseniuretted hydrogen, are not at all unfrequent.
2. Melting the Calcined Ore.—This is a totally different operation from the last: in place of roasting, it is one of fusion. The calcined ore is put into the furnace much in the same manner as before; a quantity of the slag from a subsequent process is added to assist in the fusion, and the heat is increased till the whole mass becomes liquid. The object is to separate the earthy matter, which, from being specifically lighter, rises to the surface of the liquid mass in the form of slag, and is drawn off. After two or three charges, the furnace becomes quite filled, and an aperture is then opened in it, through which the red-hot liquid flows into an adjoining pit filled with water. It is by this means granulated, and is now termed 'coarse metal,' or 'regulus;' and is, in fact, an admixture of the sulphurets of iron and copper, containing about 30 per cent. of the latter.
But it is to the earthy impurities here given off that we especially wish to direct attention. This slag, as it is termed, when drawn from the furnace, is run into oblong sand-moulds, from which, when cold, it is taken outside to the 'slag-bank,' as it is called—'slag-mountain,' we prefer saying; and an ugly mountain it is!—where it is broken into small pieces, examined to see whether it still contains metal, and if not, is left to accumulate. It consists essentially of silicon, oxygen, iron; or, to speak more correctly, it is a silicate of the protoxide of iron. It is, in fact, a true igneous rock. Portions of quartz and silica still remaining unfused, are often contained in the masses, which give to them, when broken, a true porphyritic appearance, while, from the great preponderance of the protoxide of iron, it is invariably black.
So hard, solid, and indurated do these slags, in process of time, become, that a very tall chimney, the most conspicuous object in the works, is built on the top of a slag-bank. And this beautiful commodity is not without its use in the arts. Part of it is occasionally cast into iron moulds, shaped like old Gothic arches, only uglier; and the casts are applied in great quantity as coping-stones to the walls and fences in the regions of the copper-works. Although not a very tasteful, it is yet a very useful, and, at the same time, a very characteristic application. We may add here, that the aggregate produce of the substance of the different Swansea works may be estimated at about 260,000 tons a year. Our readers may judge for themselves of the ultimate change this is calculated to bring about in the Carboniferous System, and of the learned controversies that are likely to arise among future geologists with respect to the character and constitution of these carefully disintegrated rocks!
To return to the smelting process. The last product—the regulus—is again calcined, with the view of bringing the iron to the state of an oxide. It is again melted, slagged, and run into pigs. In this last operation, the whole iron is driven out in the slag, and the remainder—'white metal,' as it is called—is almost a pure sulphuret of copper. The sulphur, having all along preserved its combination with the copper—a fine illustration of the theory of chemical attraction—must now at length be expelled. This is effected by the last process of roasting. When in a state of fusion in the furnace, the charge is exposed to a stream of air, in which case a double action ensues. Part of the oxygen enters into combination with the sulphur, producing sulphurous acid, which is expelled in the form of vapour, and part of it combines with the copper remaining in the furnace; this is again run out into the form of pigs, and in this state it is termed 'blistered copper.' To produce the finer kind of copper, another process has yet to be gone through; but for ordinary tough copper, it is at once transferred to what we may describe as the last stage, and that is—
3. Refining.—We quote Mr Vivian:—'The pigs from the roasters are filled into the furnace through a large door in the side: the heat is at first moderate, so as to complete the roasting or oxidising process; after the charge is run down, and there is a good heat on the furnace, the front door is taken down, and the slags skimmed off. An assay is then taken out by the refiner with a small ladle, and broken in the vice; and from the general appearance of the metal in and out of the furnace, the state of the fire, &c., he judges whether the toughening process may be proceeded with, and can form some opinion as to the quantity of poles and charcoal that will be required to render it malleable, or, as it is termed, to bring it to the proper pitch. The copper in this state is what is termed dry: it is brittle, of a deep-red colour, inclining to purple, an open grain, and crystalline structure. In the process of toughening, the surface of the metal in the furnace is first well covered with charcoal; a pole, commonly of birch, is then held into the liquid metal, which causes considerable ebullition, owing to the evolution of gaseous matter; and this operation of poling is continued, until, from the assays which the refiner from time to time takes, he perceives that the grain, which gradually becomes finer, is perfectly closed.' After some further manipulation of a similar kind, the refiner is at length satisfied of its malleability, and that the copper is now in its proper place, as he terms it. It is then poured out by means of iron ladles, coated with clay, into ingots or moulds of the different sizes required by the manufacturer.
'This process of refining or toughening copper, is a delicate operation, requiring great care and attention on the part of the refiner to keep the metal in the malleable state.' It is also, beyond comparison, the most beautiful sight in the copper-works. At one particular stage of the process, we saw the mass of molten copper in the furnace—some five or six tons—assume the most beautiful and resplendent appearance it was possible to imagine. It was like a sea of 'burnished gold;' and, indeed, were it not for the intense heat, the red-hot ladles of the workmen, and other little circumstances of the kind, the stranger would have some difficulty in believing that he did not look upon a beautifully polished mirror.
We have now come to the end of the smelting process; and have left ourselves no room to describe the transformation into sheets, bars, bolts, and boilerplates which the metal undergoes in the next department of the works. These, however, are a better understood series of operations, consisting, as they do, of the usual and ordinary processes of rolling the hot metal between powerful iron rollers. Nor have we space to allude even to the vastly numerous and varied applications of the metal; although we may take the opportunity of briefly adverting to the recently discovered process of smelting copper by electricity, and of inquiring into the probability of its ever becoming an economical application.
It will be seen, in the first place, that the present mode of smelting copper, though simple in theory, appears in practice extremely complex. For this reason, within the last twenty-five years there have, we believe, been as many patents taken out to simplify and hasten the operation. Without exception, these have been proved to be altogether inapplicable. Let us see how this is explained.
Out of these numerous improvements, we select two that appear peculiarly attractive. The first is the method of precipitating the copper, in our second process, from the fused silicates containing it, by the action of the electric current—the negative pole of the battery terminating in an iron plate, which replaces the copper in the liquid mass. The second method is an improvement on this. From some experiments made at the School of Mines in Paris, it was shewn that metallic iron alone, without the aid of the battery, was capable of precipitating copper from the silicates in a state of fusion, just as it does in saline solutions at ordinary temperatures. But in applying this last method to practice—for the electricity was obviously rendered unnecessary by the discovery—it was found that the expenditure of iron was so great, that it could not be profitably applied except as a means of assisting the reduction.