330

COPPER.

The operation of refining copper is delicate, and requires, upon the part of the work-men, great skill and attention to give the metal its due ductility. Its surface ought tobe entirely covered with wood charcoal; without this precaution, the refining of themetal would go back, as the workmen say, during the long interval which elapses in themoulding; whenever this accident happens, the metal must be stirred up anew with thewooden 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 re-fining; that is, when it was dry. Its color is now of a very brilliant yellowish red,and its fracture is fibrous. When this circumstance occurs, when the refining, as theworkmen say, has gone too far, the refiner removes the charcoal from the top of themelted metal; he opens the side door, to expose the copper to the action of the air, andit then resumes its malleable condition.

Mr. Vivian, to whom we owe the above very graphic account of the processes, hasexplained, in a very happy manner, the theory of refining. He conceives, we may con-clude, that the copper in the dry state, before the refining, is combined with a small por-tion of oxygen, or, in other words, that a small portion of oxyde of copper is diffusedthrough the mass, or combined with it; and that this proportion of oxygen is expelledby the deoxydizing action of the wood and charcoal, whereby the metal becomes malle-able. 2. That when the refining process is carried too far, the copper gets combined witha little charcoal. Thus copper, like iron, is brittle when combined with oxygen andcharcoal; and becomes malleable only when freed entirely from these two substances.

It is remarkable, that copper, in the dry stale, has a very strong action upon iron ; andthat the tools employed in stirring the liquid metal become very glistening, like thoseused in a farrier’s forge. The iron of the tools consumes more rapidly at that time, thanwhen 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 seemsto indicate, as in the case of iron, the presence of oxygen.

When the proper refining point has been passed, another very remarkable circum-stance has been observed ; namely, that the surface of the copper oxydizes more difficultly,and that it is uncommonly brilliant; reflecting clearly the bricks of the furnace vault.This fact is favorable to the idea suggested above, that the metal is in that case combinedwith a small quantity of carbon ; which absorbs the oxygen of the air, and thus protectsthe metal from its action.

Copper is brought into the market in different forms, according to the purposes whichit is to serve. What is to be employed in the manufacture of brass is granylated. Inthis condition it presents more surface to the action of zinc or calamine, and combine?witli it more readily. To produce this granulation, the metal is poured into a largeladle pierced with holes, and placed above a cistern filled with water, which must b ehot or cold, according to the form wished in the grains. When it is hot, round grainsare 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 a reirregular, thin, and ramified ; constituting jfca/AeraZ shot. The bean shot is the form em-ployed in brass making. .

Copper is also made into small ingots, about 6 ounces in weight. These are intendsfor exportation to the East Indies, and are known in commerce by the name of JaP nI jcopper. Whenever these little pieces are solidified, they are thrown, while hot, into c°water. This immersion slightly oxydizes the surface of the copper, and gives it afinerecolor.

Lastly, the copper is often reduced into sheets, for the sheathing of ships, and ma n >other purposes. The Hafod works possess a powerful rolling mill, composed of iopairs of cylinders. It is moved by a steam engine, whose cylinder has 40 i nC j®*diameter. See the representation of the rolling mill of the Roval Mint, unGold. > _ * n

The cylinders for rolling copper into sheets are usually 3 feet long, and 15 inchesdiameter. They are uniform. The upper roller may be approached to the under on >by a screw, so that the cylinders are brought closer, as the sheet is to be made thinner.

The ipgots of copper are laid upon the sole of a reverberatory furnace to be *l eate ’they are placed alongside each other, and they are formed into piles in a cross-hkerangement, so that the hot air may pass freely round them all. The door of the I? 1 "is shut, and the workman looks in through a peep-hole from time to time, to see it Jhave taken the requisite temperature; namely, a dull red. The copper is now P a '•■ bebetween the cylinders; but although this metal be very malleable, the ingots cann aCreduced to sheets without being several times heated; because the copper cools, aquires, by compression, a texture which stops the progress of the lamfhation. . n t j, c

These successive heatings are given in the furnace indicated above; though,