Page:The American Cyclopædia (1879) Volume XII.djvu/447

 NICKEL 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, Ni2NOs,6H2O, 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, Ni2N0 3 4NH s ,2H a O (Lau- rent), is deposited in octahedral crystals from a warm concentrated solution of nickel in am- monia. When exposed to the air the crystals give off ammonia and crumble to a bluish white powder. Sulphate of nickel, or nickel- ous sulphate, NiSO^THaO, may be obtained by dissolving metallic nickel or its oxide or car- bonate 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 grav- ity 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 re- duced metal. Sulphuretted hydrogen gives no precipitate in a solution acidulated with sul- phuric acid, but a nearly neutral solution of nickel acetate may be perfectly precipitated by this reagent with the aid of a gentle heat. Hydric ammoriisulphide gives a black sulphide, slightly soluble in excess of precipitant. Am- monia gives a pale green precipitate, soluble in excess of ammonia, forming a bright blue solution, from which potash in excess precipi- tates a green compound of nickelous oxide and potash. Caustic potash and soda throw down a pale green bulky precipitate of hydrated nick- elous 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 f errocyanide gives a green - ish white, and the ferricyanide a yellowish green precipitate, both soluble in hydrochloric acid. Nickel Plating. The possibility of de- positing nickel by means of the battery ap- pears to have been known to Becquerel and Jacobi as early as 1862 ; but it remained for Isaac Adams of Boston, Mass., to invent a NICOBAR ISLANDS 433 method for practically accomplishing the ob- ject. 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 suffi- cient thickness to admit of a fine polish. Ac- cording 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 am- monia in order to saturate the sulphuric acid which is set free. A method for plating va- rious metals with nickel without the aid of the battery, devised by Prof. Stolba, is as follows : In the plating vessel, which may be of por- celain, 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 coat- ing of zinc. The nickel salt (either the chlo- ride 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 com- pleted, and the process is finished. The arti- cles 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 be- come an industry of great importance in the United States. Nickel is used for magnetic needles, for philosophical and surgical instru- ments, and in watch movements. MCOBAR ISLMDS, a cluster in the Indian ocean, S. of the Andaman group and N. of Sumatra, between lat. 6 45' and 9 15' N., and Ion. 92 45' and 94 E. ; pop. about 6,000. It includes nine islands of considerable size, and several smaller ones. The most important are Great and Little Nicobar, Katchall, Kamorta, Teressa, Tillanchong, and Car-Nicobar. The largest and southernmost is Great Nicobar, abput 30 by 12 m., separated by a channel 6 m. wide from Little Nicobar, the next in size, which is 14 m. in length and 12 m. in width. The surface of all the islands is generally hilly