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CHEMICAL NEWS, THE Commercial Classification of Refined Copper. 73 this oxide is not soluble in the molten copper it will float CHEMICAL NEWS. to the surface, where it may be removed by skimming. As copper stands high among metals in the order of nobility the metallic impurities with the exception of the precious metals may be readily removed in theory. In practice while elimination proceeds rapidly while considerable quantities of impurities are present, the rate diminishes until traces are reached which cannot be slagged off with any reasonable amount of scorifying. Therefore furnace refining is limited in its application to relatively pure crude copper unless a low grade refined copper is contemplated. Less than 10 dols. worth of silver and gold per ton will justify electrolytic refining. The Returning to the bath of molten copper which has been skimmed clean, it is necessary to reduce the excess cuprous oxide dissolved, and no better way has yet been devised than the old Welsh process of covering the bath with a protecting layer of charcoal or low sulphur coke, and then forcing the butts of green trees or poles of hard wood beneath the surface by means of suitable tackle. cuprous oxide is reduced in this way until a normal amount corresponding to an oxygen content of from 0.04 to 0 07 per cent is left when the copper develops its best physical characteristics, the condition of the copper being followed by the appearance of the fracture of small buttons cast in a spoon or "say ladle" which is a sort of ductility test, and by the swell or depression of the surface of an ingot as it cools, which indicates the gas content. The copper is then cast by means of one of the several types of ladling machines which have been very successfully developed in recent years. When the copper is to be electrolytically refined it is first given a rough furnace refining and cast into anode plates, which are then electrolysed in a strongly acid solution of copper sulphate. The same order of nobility applies, but the great preponderance of copper over the impurities is now an aid as it assists the selective action of the current in depositing only copper at the cathode. Silver and gold are also saved as they are insoluble in the electrolyte chosen, and fall to the bottom of the tank as anode mud or slimes to be separately refined and parted. It is quite evident that copper entering an electrolytic refinery must entirely lose its identity, and that the purity of the resulting cathode copper will depend upon the conditions under which electrolysis is carried out rather than upon the momentary quality of the day's anodes. Therefore it is not necessary to consider whether the input be converter bar, black copper, or Lake mineral when buying electrolytic, but simply whether the product meets the accepted standards of quality for electrolytic copper. The world's copper supply comes from four main sources, sulphide ores, oxidised ores, native ores, and scrap. Perhaps the chief chemical characteristic of copper is its affinity for sulphur, and the largest deposits of copper ores consist of more or less complex sulphides. Near the surface these ores are frequently altered to oxides and carbonates by atmospheric influence, and there are also large deposits entirely free from sulphur. Native copper ores where the copper exists as free metal occur in various parts of the world in small quantities, but notably in the enormous deposits in the northern peninsula of Michigan, where they form the source of the so-called Lake Copper. Metallurgically there are three typical processes for producing crude or unrefined copper from the ore, based on the general principles of oxidising sulphides and reducing oxides, (a) roasting, smelting, and converting, (b) alternate oxidation and reduction, and (c) direct reduction of oxidised ores. (a), which is a strongly oxidising process by which the great majority of the American production is made from sulphide ores, results in the almost complete elimination of impurities which have volatile oxides, in cluding some of the worst enemies of refined copper, such as arsenic. Converter bar nearly always runs 99 per cent copper plus silver, and is not likely to carry more than a few hundredths of a per cent of any impurity but nickel. (b) is the old Welsh process, still used to some extent abroad, based upon the reaction between copper oxides and sulphides to eliminate sulphur as sulphur dioxide gas, and carried out in a long series of roasts and fusions in reverberatory furnaces. The removal of impurities is here Electrolytic cathodes should be very pure. They imperfect, although they may be to a certain extent generally run about 99.95 per cent copper, much of the segregated in a portion of the product, when the origin of missing 005 per cent probably being hydrogen. The the "best selected" copper of Great Britain. When the metallic impurities generally total about 0.02 per cent. ores are wholly oxidised the copper may be recovered by Except for the fact that individual cathodes may vary more direct reduction in a blast furnace (c), and as this is or lese in impurity content they are ideal material for brass a strictly reducing process the resulting black copper making. Copper producers, however, have never seldom runs over 96 per cent, due to iron and other im-couraged the sale of cathodes, as there is apt to be some purities reduced. Except in the case of "best selected" | and similar English coppers all of the products from the foregoing processes are given a further treatment or refining which may be broadly divided into furnace or fire refining and electrolytic refining. Fire refining is based upon the scorifying effect of cuprous oxide upon base metals contained in a bath of molten copper. The crude copper is melted in a reverberatory furnace, and air blown into the bath. Cuprous oxide rapidly forms and dissolves in the bath, the blowing being stopped at or before the saturation point. In this way oxygen is carried to all parts of the molten bath, and when there are any metals present which are more easily oxidised than copper, cuprous oxide is reduced back to copper, and the oxide of the impurity is formed. If Paper presented at the Annual Meeting of the American Institute of Metals, Sept. 7 to 11, 1914, at Chicago, Ill. From the Chemical Engineer, xx., No. 5. en shrinkage in weight during shipment owing to the comparative ease with which nodules or small pieces can be detached either accidentally or intentionally. Also cathode shipments unbalance the work in a refinery in proportion to their magnitude, as melting cathodes into market shapes is a distinct part of the process. This melting is done in a reverberatory furnace, and originally was an exact duplication of the fire refining already described. As the cathode copper is already pure, a simple melting is all that should be required, but molten copper is so susceptible to contamination that until recently the gases from combustion, iron in the rabbles, &c., were absorbed to a sufficient extent to require actual refining. At the present time large quantities of cathodes are being added to the molten charge during ladling and earlier, basic furnaces are being substituted for acid ones, thereby suppressing slag formation, and attention is being paid to keeping coal ashes from blowing over from the |