Mckel, a silver-white, malleable, and ductile metal, discovered by Cronstedt in 1751. It is represented by the symbol Ni; its atomic weight is 58'8, and its specific gravity is 8'279, increasing to 8.666 when forged. It is closely allied to iron and cobalt, and is associated with them in meteorites and many ores. The principal ore of nickel is the arsenide, to which the ancient miners gave the name of Kupferniclel, or false copper, because they tried in vain to extract copper from it; and it was in this mineral that Cronstedt first detected the metal. Among the other ores of nickel are the following: 1. Pentlandite, sulphuret of iron and nickel, occurring in hornblende in southern Norway, and in gneiss at Craigmuir in Argyleshire, Scotland, where it is extensively mined. It is also found in Cornwall, and was named after Mr. Pentland. 2. Nickel vitriol, a native sulphate, often found with kupfernickel in cobalt mines. It results from alteration of nickel ores, and occurs in Galicia, Spain: near Baireuth, Germany; at the Wallace mine.

Lake Huron, in crystals with pentlandite; and at Gap nickel mine, Lancaster co., Pa. 3. Nickel glance, gersdortite, or weisses Niclcelerz, sulpho-arsenide of nickel, found at Loos in Sweden; in the Albertine mine in the Hartz, with calcite, fluor spar, and quartz; in quicksilver near Ems; and with decomposed ga-lenite and blende at Phcenixville, Pa. Nickel also exists in genthite, a silicate, found at Texas, Lancaster co., Pa., containing about 35 parts of silica, 31 of nickel, and 15 of mag-nesia; at Lake Superior; and in Malaga, Spain, with chromate and talcose schist. It also occurs in emerald nickel (Nickelsmaragd), which is found in chromic iron in Lancaster co., Pa., in the Shetland islands, and in Galicia, Spain. It is a hydrated carbonate of nickel with a little carbonate of magnesia. Kupfernickel occurs in the Saxon mines of An-naberg, and in Thurginia, Hesse, and Styria; in Dauphiny, France; in Cornwall, England; in Chili and the Argentine provinces; and at Chatham, Conn., in gneiss. Nickel is obtained in Birmingham from the arsenio-sulphide and from Speiss, a deposit formed in the pots in which arsenide of cobalt and copper nickel are fused with carbonate of potassium and pounded quartz in preparing smalt.

The ore or speiss is fused with chalk and fluor spar, and the metal afterward separated by means of sulphuretted hydrogen and chloride of lime. A button of pure metal can also be obtained by heating the oxalate of nickel without further flux; and by reducing the oxide by means of hydrogen gas and fusing with borax, we can also obtain pure metal.. In the United States the metal is usually obtained by roasting the powdered ore or speiss first by itself, and then with powdered charcoal, till the garlic odor of arsenic has disappeared, mixing the residue with three parts of sulphur and one of potash, and melting in a crucible with a gentle heat. I he product is a sulphide free from arsenic, which being washed is dissolved in concentrated sulphuric acid containing a small portion of nitric acid. The addition of carbonate of soda causes a precipitate of carbonate of nickel, which may be reduced by heating with charcoal. - Nickel, according to Deville, is more tenacious than iron, and not much more fusible.

It is magnetic at ordinary temperatures, but loses this property at 250° C., recovering it on cooling; burns in oxygen gas like iron, and is converted into oxide; dissolves readily in hydrochloric and dilute sulphuric acids, with evolution of hydrogen; is also soluble in nitric acid and aqua regia; and does not readily tarnish in the air. Although nickel can be hammered into thin foil, and drawn into fine wire, it is rarely used alone except as an electro-plating. - Compounds of Nickel. The principal alloys of nickel are: German silver, composed of copper 51, zinc 30.6, and nickel 18.4 parts in 100, and also in other proportions; tiers-argent, composed of two parts of nickel and one of silver; paclc-fong, an alloy resembling German silver, brought from China nearly 200 years ago, and composed of zinc 44, copper 1G, and nickel 40 per cent.; tutenag, another Chinese alloy, containing zinc 37, copper 46, and nickel 17 per cent. Many of the copper coins of the European continent and the United States are alloys containing various proportions of nickel. Kupfernickel, Ni2As2, already mentioned as the principal ore, is a true arsenide. Sometimes a part of the arsenic is displaced by an equivalent quantity of antimony.

Arsenical nickel, NiAs2, is another native ore, which by ignition in closed vessels parts with a portion of arsenic, and becomes kupfernickel. Nickel glance, already mentioned as an ore, has the formula NiSAs. Nickelous chloride, or chloride of nickel, NiCl2, is formed by treating the oxide with hydrochloric acid, by heating nickel filings to low redness in a stream of chlorine gas, or by heating the hydrated chloride. Its solution on evaporation yields beautiful green hydrated crystals, containing nine equivalents of water. There is a double salt of chloride of nickel ammonium. There are two oxides: a protoxide, NiO, and a sesquiox-ide, Ni203, the first of which only forms salts. It may be obtained in an anhydrous state by calcining the nitrate or carbonate in a covered crucible, or by heating nickel filings with nitre. It is olive green, of specific gravity 5.75. It may be precipitated as a bulky green hydrate from its salts by caustic potash. It is soluble in acids, forming pale green salts. It forms insoluble compounds with baryta, stron-tia, and several other bases, and forms a deep blue solution with ammonia.

Three sulphides are known: a subsulphate, NiS2, formed by reducing the sulphate by charcoal or hydrogen; the protosulphide, NiS, occurring native as millerite, or formed by fusing sulphur and nickel; and the disulphide, NiS2, a steel-gray powder obtained by heating to redness sulphur with carbonates of nickel and potash, and treating the mass with water. An anhydrous carbonate, NiC03, is formed by heating chloride of nickel with alkaline carbonates in sealed tubes. It crystallizes in minute rhombohe-drons, and is not attacked by strong acids at ordinary temperatures. The hydrocarbonate, NiC02,2NiII„04, exists in the ore emerald nickel already mentioned. Its specific gravity is 2.67, hardness 3 to 3.25, color emerald-green with strong vitreous lustre; it gives off water when heated, and turns blackish. Nitrate of nickel, or nickelous nitrate, Ni2N03, 6H20, formed by dissolving the metal in nitric acid, crystallizes in emerald-green eight-sided prisms, soluble in twice their weight of cold water, and when heated forms a basic salt. An am-moniacal nitrate, Ni2N034NH3,2H20 (Laurent), is deposited in octahedral crystals from a warm concentrated solution of nickel in ammonia. When exposed to the air the crystals give off ammonia and crumble to a bluish white powder.

Sulphate of nickel, or nickelous sulphate, NiS04,7H20, may be obtained by dissolving metallic nickel or its oxide or carbonate in sulphuric acid. It crystallizes in green rhombic prisms, soluble in three parts of cold water, insoluble in alcohol. When the prismatic crystals are exposed to the light, they are converted into small regular octahedrons held together in the form of the parent crystal. When the solution crystallizes between 59° and 77° F. the octahedrons form directly with six molecules of water, having a specific gravity of 2.037. A potassic nickelous sulphate also may be formed, and other double sulphates of nickel. Each molecule of nickel sulphate in the solid form will absorb six molecules of ammoniacal gas. There are several other salts of nickel, as the fluoride, bromide, iodide, phosphide, and many oxygen salts. - The salts of nickel are generally of a delicate green, both when solid and in solution; they redden litmus slightly, have a sweet metallic astringent taste, and taken into the stomach excite vomiting. With borax before the blowpipe they form a reddish yellow bead, which becomes paler on cooling. The addition of a potassium salt colors the bead blue. In the reducing flame the bead becomes gray from particles of reduced metal.

Sulphuretted hydrogen gives no precipitate in a solution acidulated with sulphuric acid, but a nearly neutral solution of I nickel acetate may be perfectly precipitated by this reagent with the aid of a gentle heat. Hydric ammonisulphide gives a black sulphide, slightly soluble in excess of precipitant. Ammonia gives a pale green precipitate, soluble in excess of ammonia, forming a bright blue solution, from which potash in excess precipitates a green compound of nickelous oxide and potash. Caustic potash and soda throw down a pale green bulky precipitate of hydrated nickelous oxide, insoluble in excess of alkali. The carbonates of the alkaline metals give a pale apple-green precipitate of basic carbonate of nickel, which is soluble in sesquicarbonate of ammonia. Potassic ferrocyanide gives a greenish white, and the ferricyanide a yellowish green precipitate, both soluble in hydrochloric acid. - McJcel Plating. The possibility of depositing nickel by means of the battery appears to have been known to Becquerel and Jacobi as early as 1862; but it remained for Isaac Adams of Boston, Mass., to invent a method for practically accomplishing the object. Adams employs the double chloride of nickel and ammonium or sulphate of nickel and ammonium.

He says the presence of even slight traces of the fixed alkalies is injurious, as they occasion the deposition of oxide of nickel. From pure salts the layers of metals are deposited with great regularity and of sufficient thickness to admit of a fine polish. According to Jacobi, the anode should be made of pure fused nickel, and Remington prefers to suspend pieces of metal in the bath. Prof. Bottger observes that porous nickel occludes hydrogen the same as palladium. Becquerel insists that the presence of a fixed alkali, such as potassa, is not at all injurious to, and in no wise affects the deposition of nickel, since the double sulphate of nickel and potassa can be applied, as well as the double sulphate of nickel and ammonia; but if the positive electrode is not made of nickel, it is necessary to add ammonia in order to saturate the sulphuric acid which is set free. A method for plating various metals with nickel without the aid of the battery, devised by Prof. Stolba, is as follows: In the plating vessel, which may be of porcelain, though the author prefers copper, is placed a concentrated solution of zinc chloride, which is then diluted with from one to two volumes of water, and heated to boiling.

If any precipitate separates, it is to be redissolved by adding a few drops of hydrochloric acid. As much powdered zinc as can be taken on the point of a knife is thrown in, by which the vessel becomes covered internally with a coating of zinc. The nickel salt (either the chloride or sulphate may be used) is then added until the liquid is distinctly green; and the articles to be plated, previously thoroughly cleaned, are introduced, together with some zinc fragments. The boiling is continued for 15 minutes, when the coating of nickel is completed, and the process is finished. The articles are well washed with water and cleaned with chalk. If a thicker coating be desired, the operation may be repeated. Prof. Stolba found that copper vessels thus plated were scarcely tarnished after several months' use in the laboratory. Nickel plating has now become an industry of great importance in the United States. - Nickel is used for magnetic needles, for philosophical and surgical instruments, and in watch movements.