NICKEL (symbol Ni, atomic number 28, atomic weight 58.69, isototes 58 and 6o), a greyish-white metallic element of con siderable malleability and ductility. It has been known from the earliest times, being employed by the Chinese in the form of an alloy called pakfong. It was first isolated in an impure condition in 1751 by A. F. Cronstedt from nicolite, and his results were afterwards confirmed by T. 0. Bergman in 1775 (De niccolo, opusc. 2, p. ; 3, P. 459; 4, P• 3 74). It occurs in the uncombined condition and alloyed with iron in meteorites ; as sulphide in millerite and nickel blonde, as arsenide in kupfernickel, and fre quently in combination with arsenic and antimony in the form of complex sulphides. It is found in considerable quantities in New Caledonia in the form of a hydrated silicate of nickel and mag nesia approximating to the constitution (NiO, and in Canada in the form of nickeliferous pyrrhotines, which consist of sulphides of iron associated with sulphides of nickel and copper, embedded in a matrix of gneiss; these form the chief sources of nickel. When the former is used it is roasted with calcium sulphate or alkali waste to form a matte which is then blown in a Bessemer converter or heated in a reverberatory fur nace with a siliceous flux with the object of forming a rich nickel sulphide. This sulphide is then by further heating converted into the oxide and finally reduced to the state of metal by ignition with carbon in clay crucibles. The process adopted for the Canadian ores, which are poor in copper and nickel, consists in a prelimi nary roasting in heaps and smelting in a blast furnace in order to obtain a matte, which is then further smelted with a siliceous flux for a rich matte. This matte is then mixed with coke and salt-cake and melted down in an open hearth furnace, or in a Bessemer converter with a silicate lining.
In the Mond process, this refined matte, which contains copper, nickel and iron sulphides, is roasted to remove the sulphur, and extracted by sulphuric acid, whereby the iron and copper contents are diminished and the nickel content is relatively increased. Re duction by "water-gas" at 300° C. then leaves nickel and copper as metals and iron oxide unaffected ; at the same time, the water gas is largely deprived of its hydrogen and becomes relatively richer in carbon monoxide, the content of which is raised to 8o% by passage through a retort of hot coke. This enriched gas is
then passed over the metallic mixture at about 8o° C., whereby the nickel is "volatilised" as the carbonyl Ni(C0),; the product is passed through towers at 18o-200° C., where it decomposes and is deposited (often on pellets of pure nickel ), the resulting carbon monoxide being used again. The nickel so obtained is of a high degree of purity.
The following tables show the output of nickel from Canada and the shipments of nickel ore from New Caledonia in recent years as metric tons :— Canada. New Caledonia The metal may also be obtained on the small scale by the re duction of the oxide by hydrogen or by carbon, by ignition of the oxalate or of nickel ammonium oxalate by reduction of the chlo ride in a current of hydrogen (E. Peligot), by electrolysis of nickel ammonium sulphate, as in the process of nickel plating.
Its specific gravity varies according to the method employed for its preparation, being about 8.8. It melts at 1,452° C. Its specific heat increases with rise of temperature, the mean value from to ioo° C. being 0.1084. It is magnetic, but loses its magnet ism when heated, the loss being complete at about 340-350° C. Nickel occludes hydrogen readily, is attacked by the halogen ele ments, and oxidizes easily when heated in air. In the massive state it is unacted upon by dry air, but if moistened with acidified water, oxidation takes place slowly. When obtained by reduction processes at as low a temperature as possible the finely divided metal so formed is pyrophoric, i.e., it may ignite spontaneously in the air. It decomposes water at a red heat. Sheet nickel is passive to fairly concentrated nitric acid, and the metal remains passive even when heated to redness in a current of hydrogen. Nickel is largely used as a catalyst for the reduction of organic compounds by hydrogen—a process first used by P. Sabatier and J. B. Senderens (see HYDROGEN and HYDROGENATION) .