NITRITES are salts formed by the union of nitric acid with bases. Some are found in a natural mineral condition, as saltpeter and cubic niter. They are distin guished for their solubility in water. On being heated, they undergo decomposition, being converted either into free nitric acid and a base, or into oxygen and a nitrite. For potassium nitrate and sodium nitrate, see NITER, ante. In many respects, one of the most important nitrates is the nitrate of silver, or lunar caustic (q.v.); see also SILVER, ante. It is of great use n surgery and the arts. As a caustic it acts powerfully, but rather superficially, producing a white slough, which blackens soon on exposure to the light. It is used in it solid state, or in solutions of all strengths. If dissolved in pure water, it remains colorless; but the smallest particle of organic matter will cause the solution to turn dark. On this account it is employed far making marking-fluids for linen. Indelible ink is usually made by dissolving 1 part of nitrate of silver and 4 parts of gum-arabic in 4 parts of water, and adding a little India ink to give it color, so that it may be seen when the mixture is applied. The place which is to receive the impression is first moistened with a solution of carbonate of soda and dried. After the application of the ink, the writing is exposed to the sunlight. Lunar caustic markings may be readily removed by applying a few drops of tincture of iodine, and dissolving out the iodide of silver thus formed by a solution of hyposulpliite of soda, or a dilute solution of caustic potash. Nitrate of silver is used in photography (q.v.). Nitrate of ammonia, or amnionic nitrate (according to modern nomenclature. ammonium nitrate), NILO,NO.. or, according to later views, may he formed by the action of the galvanic current on a mixture of nitrogen and oxygen with an excess of hydrogen; but the common method is to add a slight excess of aqua ammonia to nitric acid. If crys tallization is conducted slowly, six-sided prisms, like those of nitrate of potash, will be formed, having a specific gravity of 1.635. It melts at 226' F., and at 482' oecomposes into water and nitrous oxide, or laughing-gas. See NITROGEN, ante. Nitrate of baryta, baryta saltpeter, is made by treating the native carbonate of baryta with nitric acid.
It crystallizes in anhydrous regular octahedrons, having a specific gravity of 3.184. 'When heated strongly it is converted into baryta, or baric oxide, with evolution of oxygen and nitrogen. Nitrate of bismuth and also sub-nitrate are important salts in the arts and medicine. See BisMuTh, ante. Nitrate of cobalt, prepared by the action of nitric acid on the oxide, crystallizes from solutions in beautiful pink-red deliquescent crystals, hav ing a specific gravity of 1.83. It is much used in the chemical laboratory, particularly es a blow-pipe reagent. With magnesium compounds,,Atields a pink color; with those of zinc, green; and with aluthinum CoMpounds ebUtiLifUraliaev'for this reason it is much used in coloring porcelain and earthenware. Nitrate of copper is made by the action of diluted nitric acid on copper turnings. Nitric oxide given off during the operation. It crystallizes from cold solutions in beautiful blue, deliquescent, rhom boidal prisms, containing four molecules of water. From solutions above 59° it crystallizes with three molecules of water in needles, having a specific gravity of 2.047, soluble in alcohol. ' Nitrate of copper is converted, by moderate heat, into an insoluble basic nitrate. By raising the heat, the acid is completely driven off, leaving only the black oxide of the metal. Nitrate of copper is sometimes useful in surgery, as an application to certain ill-conditioned ulcers. The nitrates of iron are important salts. The pro tonitrate, or ferrous nitrate, is formed by digesting iron-turnings in very dilute nitric acid. It crystallizes in pale green rhombohedrons, having the formula It is much used in dyeing. The pernitrate, or ferric nitrate, is made by dissolving iron turnings in nitric acid of sp. gr. between 1.2 and 1.3. It is used in surgery. Nitric acid forms several salts with lead, the principal of which is the common nitrate, or plumbi nitrate, It crystallizes in anhydrous regular octahedrons, usually milk-white and opaque. It dissolves in 7._, parts of cold water. It is decomposed by heat, with evolution of peroxide of nitrogen. Nitric acid Thum a greater number of salts with mercury titan with any other metal, one of which is used in medicine (see MERCURY, ante), and the other for the manufacture of corrosive sublimate.