The impurities found with the product of the stamp mill are principally the *vein) rock, from which, owing to the intimate mixture of the copper and rock, the separation of the former has been incomplete, and incidental impurities, such as iron, sulphur, arsenic, with traces of nickel and of some of the rarer ele ments. The function of the smelter is to remove the impurities and to leave the copper in a condition best fitted for the different uses to which it is to be put. These are principally: (1) For electrical purposes, as wire, where great conductivity is required; (2) for rolling into plates, where great tensile strength may be desired; and (3) for mixing with other metals to form alloys. The forms in which it leaves the smelter are indicative of these uses. They are respectively bars, cakes and ingots. When it is known that .07 of 1 per cent of arsenic in copper will reduce the conductivity of the latter to 75, and that arsenic is almost always present in copper ores, and to some extent also in native copper, the necessity of careful refining will be realized. Copper derived from copper ores generally contains enough impurities to render it unfit for electrical purposes unless it is refined electrolytically. For this purpose it is cast into plates called anodes. In the Lake Superior region the copper derived from the higher or younger formations of the copper bearing series has generally been found to be pure enough on leaving the smelter to be used for wire (99.9 per cent fine and upwards), but the copper from the lower or older beds usually carries enough arsenic to render such a use impossible without further refinement. This copper, on the other hand, with the proper percentage of arsenic, is tougher and more desirable for some uses than the purer grade.
The mineral is treated first in a melting or reverberatory furnace, the flame passing from the fire-box over the copper under a low arched roof with a stream of air brought in from be low. This is an oxidizing process and the slag that separates from the copper and is drawn off from the surface of the latter contains from 8 to 14 per cent of the metal, largely in the form of oxides, mixed with a large amount of the impurities. After the removal of the slag, charcoal is thrown on top of the melted copper and the liquid mass of the latter is agitated by the insertion of green poles of hardwood (apoling”, the ignition of which and of the charcoal produces the carbon that takes up the oxygen in the copper, thus changing the action of the furnace from an oxidizing to a reducing process. This is often preceded by blowing
a charge of air through the molten copper. By dipping small buttons of the metal in a trial ladle from time to time, if the copper sets with a level surface the process of °poling') is com plete. If the reduction is overdone, the charge must be reoxidized and again reduced. There upon the copper is ladled or run out into moulds. The tendency of modern practice has been to increase the size of the melting furnace contingent upon the ability to keep the heat throughout of an even temperature. Some modern furnaces can take a charge of 100 tons at a heat. It has also been found advantageous instead of doing the refining in these large melting furnaces to run the copper from them into special refining furnaces. The fuel used in the melting furnace is soft coal.
The slag derived from the reverberatory furnace is broken up and eventually taken to a blast furnace, otherwise called a cupola, where the action is reducing, and here the slag is re melted. This process is substantially the same as the process in the reverberatory furnace ex cept that the copper being mixed with a large amount of slag, other substances such as lime stone, iron or silica are added to form a proper mixture for fusing and for the proper separa tion of the copper. The relative amounts of the several materials are ascertained in advance by analysis. All of the ingredients are mixed with anthracite coal, with or without coke, and to stimulate ignition a cold blast of air under compression is driven upwards through the mass. The copper falls out and is drawn off at the bottom of the furnace, containing even then a larger amount of impunties than the product of the first process; this copper should be refined separately. In practice the slag-copper is poured into ingots or ingot-bars, but never into wire bars. It is sometimes specially branded.
The slag that is finally rejected contains about .7 of 1 per cent of copper and is usually discharged into a stream of water which gran ulates it and carries it away in launders.
Lucius L. HUBBARD, General Manager of Champion Copper Com pany, Painesdale, Mich.