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 (Liebig). M. Ilinski and G. v. Knorre (Ber., 1885, 18, p. 169) separate the metals by adding nitroso--naphthol in the presence of 50% acetic acid, a precipitate of cobalti nitroso--naphthol, [C10H6O(NO)]3Co, insoluble in hydrochloric acid, being formed, whilst the corresponding nickel compound dissolves in hydrochloric acid. E. Pinerua separates the metals by taking advantage of the fact that cobalt chloride is soluble in ether which has been saturated with hydrochloric acid gas at low temperature. For an examination of the above and other methods see E. Hintz, ''Zeit. anal. Chem.'', 1891, 30, p. 227.

Nickel fluoride, NiF2, obtained by the action of hydrofluoric acid on nickel chloride, crystallizes in yellowish green prisms which volatilise above 1000° C. It is difficultly soluble in water, and combines with the alkaline fluorides to form double salts. Nickel chloride, NiCl2, is obtained in the anhydrous condition by heating the hydrated salt to 140° C., or by gently heating the finely divided metal in a current of chlorine. It readily sublimes when heated in a current of chlorine, forming golden yellow scales. It is easily reduced when heated in hydrogen. It forms crystalline compounds with ammonia and the organic bases. It is soluble in alcohol and in water. Three hydrated forms are known, viz. a mono-, di-, and hexa-hydrate; the latter being the form usually obtained by the solution of the oxide or carbonate in hydrochloric acid. Nickel chloride ammonia, NiCl2·6NH3, is obtained as a white powder when anhydrous nickel chloride is exposed to the action of ammonia gas (H. Rose, Pogg. Ann., 1830, 96, p. 155), or in the form of blue octahedra by evaporating a solution of nickel chloride in aqueous ammonia. When heated to 100° C. it loses four molecules of ammonia. Two hydrated forms have been described, one containing three molecules of water and the other half a molecule. Numerous double chlorides of nickel and other metals are known. The bromide and iodide of nickel resemble the chloride and are prepared in a similar fashion.

Several sulphides of the element have been obtained. A subsulphide, Ni2S(?), results when the sulphate is heated with sulphur or when the precipitated monosulphide is heated in a current of hydrogen. It forms a light yellow amorphous mass which is almost insoluble in acids. The monosulphide, NiS, is obtained by heating nickel with sulphur, by heating the monoxide with sulphuretted hydrogen to a red heat, and by heating potassium sulphide with nickel chloride to 160-180° C. When prepared by dry methods it is an exceedingly stable, yellowish, somewhat crystalline mass. When prepared by the precipitation of nickel salts with alkaline sulphide in neutral solution it is a greyish black amorphous compound which readily oxidizes in moist air, forming a basic nickel sulphate. The freshly precipitated sulphide is soluble in sulphurous acid and somewhat soluble in hydrochloric acid and yellow ammonium sulphide (see H. Baubigny, Comptes rendus, 1882, 94, pp. 961, 1183; 95, p. 34). Nickel sulphate, NiSO4, is obtained anhydrous as a yellow powder when any of its hydrates are heated. When heated with carbon it is reduced to the metal. It forms hydrates containing one, two, five, six and seven molecules of water. The heptahydrate is obtained by dissolving the metal or its oxide, hydroxide or carbonate in dilute sulphuric acid (preferably in the presence of a small quantity of nitric acid), and allowing the solution to crystallize between 15° and 20° C. It crystallizes in emerald-green rhombic prisms and is moderately soluble in water. It effloresces gradually on exposure to air and passes into the hexahydrate. It loses four molecules of water of crystallization when heated to 100° C. and becomes anhydrous at about 300° C. The hexahydrate is dimorphous, a tetragonal form being obtained by crystallization of a solution of the heptahydrate between 20° and 30° C., and a monoclinic form between 50° and 70° C. Nickel sulphate combines with many metallic sulphates to form double salts, and also forms addition compounds with ammonia aniline and hydroxylamine. The nitrate, Ni(NO3)2·6H2O, is obtained by dissolving the metal in dilute nitric acid and concentrating the solution between 40° and 50° C. It crystallizes in green prisms which deliquesce rapidly on exposure to moist air.

Nickel carbonyl, Ni(CO)4, is obtained as a colourless mobile liquid by passing carbon monoxide over reduced nickel at a temperature of about 60° C. (L. Mond, Langer and Quincke, Jour. Chem. Soc., 1890, 57, p. 749). It boils at 43° C. (751 mm.), and sets at −25° C. to a mass of crystalline needles. It is readily soluble in hydrocarbon solvents, in chloroform and in alcohol. Its critical pressure is 30 atmospheres and its critical temperature is in the neighbourhood of 195° C. (J. Dewar, Proc. Roy. Soc., 1903, 71, p. 427). It decomposes with explosive violence when heated rapidly. Dewar and Jones (Journ. Chem. Soc., 1904, p. 203) have made an exhaustive study of its reactions, and find that it is decomposed by the halogens (dissolved in carbon tetrachloride) with liberation of carbon monoxide and formation of a nickel halide. Cyanogen iodide and iodine mono- and tri-chloride effect similar decompositions with simultaneous liberation of iodine; sulphuric acid reacts slowly, forming nickel sulphate and liberating hydrogen and carbon monoxide. Hydrochloric and hydrobromic acids are without action; hydriodic acid only reacts slowly. With aromatic hydrocarbons in the presence of anhydrous aluminium chloride, in the cold, there is a large evolution of hydrochloric acid gas, and an aldehyde is formed; at 100° C., on the other hand, anthracene derivatives are produced. Thus by using benzene, benzaldehyde and anthracene are obtained. Dewar and Jones suggest that in the latter reaction it is the metallic nickel which is probably the reducing agent effecting the change, since it is only dissolved in any quantity when the anthracene hydrocarbon is produced. When mesitylene is used, the reaction does not proceed beyond the aldehyde stage since hydrocarbon formation is prevented by the presence of a methyl group in the ortho-position to the -CHO group. Acids and alkalis are in general without action on nickel carbonyl. The vapour of nickel carbonyl burns with a luminous flame, a cold surface depressed in the flame being covered with a black deposit of nickel. It is an extremely powerful poison. Mond and his assistants have discovered several other carbonyls. For example cobalt gives CO(CO)4, as orange crystals which melt at 51°, decomposing at a higher temperature, giving CO(CO)3 and CO at 60°; CO(CO)3 forms jet black crystals. For iron carbonyls see ; also L. Mond, H. Hirtz and M. D. Cowap, ''Jour. Chem. Soc.'', 1910, 97, p. 798. Nickel carbonate, NiCO3, is obtained in the anhydrous state by heating nickel chloride with calcium carbonate in a sealed tube to 150° C. (H. de Sénarmont, Ann. Chim. Phys., 1850 [3], 30, 138). It crystallizes in microscopic rhombohedra insoluble in cold acids. By precipitation of nickel salts with solutions of the alkaline carbonates, basic carbonates of variable composition are obtained.

Numerous determinations of the atomic weight of nickel have been published, the values obtained varying from 58·0 to approximately 59·5. The more recent work of T. W. Richards and Cushman (Chem. News, 1899, 79, 163, 174, 185) gives for the atomic weight of the metal the values 58·69 and 58·70.

NICKNAME, a name given to a person in addition to his personal names, Christian and surname, either as a playful or familiar form of address or as a mark of ridicule, contempt or hatred. The Middle English form of the word, nekename, shows that it is a corruption of “an ekename” (i.e. “added” name; eke, earlier eche, from the root seen in Lat. augere, Gr.  ), and is therefore equivalent to the Lat. agnomen.

There is an interesting list of national nicknames in Notes and Queries, 9th series, 4, 212-214.

 NICOBAR ISLANDS, a British group of twelve inhabited and seven uninhabited islands in the Bay of Bengal, between Sumatra and the Andaman Islands, to which latter they are administratively appended. They have an aggregate area of about 635 sq. m., Great Nicobar (Loöng), the largest and southernmost of any size, covering 333 sq. m. Six others range in area from about 20 sq. m. to 62 sq. m.; the rest are mere islets. A careful census of the natives, taken by Mr E. H. Man in 1901, gave a total population of some 6700, at about which figure the estimates of the number of inhabitants have always stood. Car Nicobar (Pu), the most northerly island, with an area of 49 sq. m., was by far the most densely populated, and had 3500 inhabitants, Great Nicobar containing only 450. The marine surveys of these islands are still meagre and unsatisfactory, but the whole of the Nicobars and outlying islands were surveyed topographically by the Indian Survey Department in 1886–1887, when a number of maps on the scale of 2 in. to the mile were produced, giving an accurate coast-line. Some of the islands have mere flat, coral-covered surfaces; others, again, are hilly, the Great Nicobar rising to 2105 ft. On that island there are considerable and beautiful streams, but the others generally are badly off for fresh surface water. There is one good harbour, a magnificent land-locked shelter called Nancowry Harbour, formed by the islands of Camorta and Nancowry (both known to natives as Nankauri).

Geology.—The Nicobars form part of a great submarine chain, of which the Andamans are a continuation. Elaborate geological reports were issued by a Danish scientific expedition in 1846 and an Austrian expedition in 1858. Dr Rink of the former found no trace of true volcanic rocks, though the chain as a whole is known for its volcanic activity, but features were not wanting to indicate considerable upheavals in the most recent periods. He considered that the islands belonged to the Tertiary age. Von Hochstetter of the Austrian expedition classified the most important formations thus: eruptive, serpentine and gabbro; marine deposits, probably late Tertiary, consisting of sandstones, slates, clay, marls, and plastic clay; recent corals. He considered the whole group connected geologically with the great islands of the Malay Archipelago farther south. The vexed question of the presence of coal and tin in the Nicobars has so far received no decided scientific support. The white clay marls of Camorta and Nancowry have become famous as being true polycistinan marls like those of Barbados. Earthquakes of great violence were recorded in 1847 and 1881 (with tidal wave), and mild shocks were experienced in December 1899.

Meteorology.—It has always been held to be important to maintain a meteorological station on the Nicobars, for the purpose of