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Oreide

An alloy supposed to be of French origin; it is used as a substitute for "ormolu" in the manufacture of cheap jewelry, excelling the latter alloy very much in its gold-like character. First, melt copper 100, then add and stir well in magnesia 6, sal-ammoniac 3.6, quicklime 9.12, tartar of commerce 9, and zinc or tin 17, in the order as given. This must be kept fusing about three quarters of an hour before it is used.

Copper 80, zinc 13.5, nickel 6.5 is recommended as equal to the former as an oreide mixture. See ORMOLU; MOSAIC GOLD; MOCK GOLD; GOLD; TOMBAC. Ores are the mineral bodies from which metals are extracted, the latter being found therein sometimes in a metallic state, and so nearly pure as to be called native metals. But it is generally in a state of ore that metal occurs, that is, in combination with its mineralizing substance. When metals combine in the metallic state they are termed alloys; combined with acids, they form carbonates, bromides, phosphates, chlorides, etc., and are then designated metallic salts. With sulphur they form sulphurets and sulphides; and, again, combined with oxygen they form the numerous oxides. The soil and rocks consist of metallic oxides, but the chief metals are not so widely disseminated. They are found in various places and at different depths below the surface, in the form of seams, beds, or mineral veins, and sometimes as lodes (See LODE). The treatment of ores for obtaining the metal is mechanical and chemical, the more valuable ores requiring considerable care in their management; but the operations vary considerably, according to the kind of ore under treatment.

The ores of lead and tin when brought to the surface are at once sorted, and the purest lumps set aside for treatment in the smelting-furnace; what is left, after being subjected to a crushing or hammering process, is again sorted. What remains is then crushed in revolving cylinders and passes through sieves, the finer residue being agitated in water by a process termed jigging. The crushing is completed in the stamping-mill, where the ore is repeatedly pounded and washed, and the powdered ores settle in layers, according to their specific gravity.

The chemical treatment of ores is invariably twofold--roasting or calcining, and reducing. (See CALCINATION.) If they contain volatile products, as sulphur and arsenic, which may be removed by oxidation or heat, they are first roasted. This is accomplished in a kind of reverberatory furnace, where the fuel is served at one end and the flame and heated gases are reverberated or thrown down from the arched roof of the furnace upon the ore, which is distributed over its bed. In this way ores are oxidized. Should the ore contain sulphur, it is burned off and passes away as sulphurous acid, while arsenic escapes in the form of arsenious acid. Sometimes lead is at once procured by the operation of roasting, or it is changed to the state of oxide, which necessitates another process to set it free.

Reduction of ores means the chemical process of deoxidation, or smelting. It is effected by heating them to a high temperature in contact with substances which take the oxygen from the metal by superior affinity. Carbon is the chief among deoxidizing agents, and removes the oxygen in the form of carbonic oxide and carbonic acid. For the removal of the numerous earthy impurities, substances are employed which are called fluxes; these readily combine with them in a molten condition and flow off as a slag. See CAST IRON; REDUCTION OF ORES.

Organ-pipes are usually made from a composition of tin 9, lead 1, subject to slight variations. See ALLOYS; WHITE ALLOYS; TIN; LEAD.