Page:The American Cyclopædia (1879) Volume XII.djvu/477

 NITRATES 463 more than 25 per cent, and some three times as much of the genuine salt. It is mostly worked with the pick and shovel, but is some- times so compact that the beds have to be blasted. Portions of the salt are pure white like loaf sugar, and others are colored reddish brown, lemon yellow, and gray. Its average composition was found by Dr. A. A. Hayes to be as follows : nitrate of soda, 64*98 ; sulphate of soda, 3-00; chloride of sodium, 28*69; iodic salts, 0-63 ; shells and marl, 2*60 ; total, 99*90. The extraction and refining of the salt afford employment to a large part of the inhabitants of the province. It is taken to Iquique for shipment to all parts of the world. It is used in the manufacture of nitric acid, of saltpetre, and of iodine, but its tendency to deliquesce renders it unfit for that of gunpowder ; it is, however, a valuable fertilizer. The salt is re- ported to occur in large quantities in Pernam- buco, west of Ipu, the formation extending 15 to 20 m. 3. Nitrate of Silver, or Lunar Caus- tic. Among other nitrates the most important is the nitrate of silver, or argentic nitrate (Ag NO 3 ). It may be prepared by dissolving pure silver in nitric acid, evaporating to dryness, and fusing to expel nitrous acid, and to de- stroy impurities which may have been received during the operation, dissolving in water, and crystallizing. The salt crystallizes in square tables, which are colorless and anhydrous, hav- ing a specific gravity of 4*336. At 426 it fuses, and may then be cast into the crystal- line sticks which pass under the names of lunar caustic and lapis wfernalis, and are em- ployed in surgery. At higher temperatures it is reduced to a metallic state. Nitrate of silver acts powerfully but superficially as a caustic, giving rise to a white slough, which blackens on exposure to the light. It may be used in solutions of all strengths, and also solid. In the latter form it is sometimes diluted with alum or sulphate of copper. The sticks of ni- trate of silver are occasionally made to contain chloride of silver in order to render them less brittle. Its solution in pure water remains colorless ; but if the smallest quantity of organ- ic matter be present, it is soon discolored when exposed to the light. It is thus a delicate test of the presence of organic matter. With albumen and fibrine it forms insoluble com- pounds, and may be employed to remove them from solution. The property of the solution to turn black by the reduction of the oxide of the silver, when the fluid is applied to organic sub- stances and exposed to the light, renders it of important use for marking linen. The so-called indelible ink is prepared for this purpose by dissolving one part of the salt and four parts of gum arabic in four parts of water, and add- ing a small quantity of India ink. The spot to be marked is first wetted with a solution of carbonate of soda and dried, and when writ- ten upon it is exposed to the sunlight. The spots may be removed by converting the silver with a few drops of iodine into the iodide, 607" VOL. xn. 30 and dissolving this by a solution of hyposul- phite of soda, or a dilute solution of caustic potash. A hair dye is also prepared with ni- trate of silver by dissolving it in ether. The nitrate is extensively used in photography on account of the action of light upon it. (See PHOTOGRAPHY.) 4. Nitrate of Ammonium, or Ammonic Nitrate (nitrum flammans, N0 3 NH 4, or according to the old formula NH 4 O,NO 5 ). Nitrate of ammonium is formed by the action of the electric current on a mixture of nitrogen and oxygen with an excess of hydrogen ; also by passing sulphuretted hydrogen gas through di- lute nitric acid ; but the common method is to add a slight excess of aqua ammonia to nitric acid. It ordinarily crystallizes in long flexible needles, or deposits as an amorphous mass; but if the crystallization takes place slowly, six- sided prisms like those of nitrate of potash may be obtained, of specific gravity 1*635. When this salt is dissolved in water, there is a consid- erable disappearance of heat, and it is often used in f rigorific mixtures. It melts at 226 F., and at 482 is completely decomposed, with conversion into nitrous oxide or laughing gas and water (N0 3 NH 4 =N 2 + 2H 2 0). It is the material universally used for the production of laughing gas. (See NITKOUS OXIDE.) 5. Nitrate of Barium, Baric Nitrate, or Ba- ryta Saltpetre (Ba2NO 3 ), is commonly pro- duced by treating a solution of sulphide of ba- rium, or of the carbonate of barium, which is found native as a mineral, with nitric acid. It crystallizes in anhydrous regular octahedral crystals, of specific gravity 3*184 (Karsten). Unless the solution is dilute, nitric acid will cause precipitation without evaporation. When heated it decrepitates strongly, then fuses, and at a high temperature all the acid is ex- pelled, with evolution of oxygen and nitrogen, the residue being pure baric oxide, or barytes. (See SULPHATE OF BAEIUM, under SULPHATES.) 6. Nitrate of Bismuth, or Bismuthous Ni- trate (Bi 3NO 3, 5H 2 O ; sp. gr. 2*376), is easily formed by dissolving the metal or the oxide or carbonate in nitric acid of moderate strength. The concentrated solution must be filtered through asbestus, as it corrodes paper from its readiness to part with a portion of its acid. When the salt is largely diluted with water, an acid salt remains in solution, while an insolu- ble basic subnitrate (Bi 2 O 3 ,2HN0 3 ) falls, called by the older writers magistery of bismuth. Another basic nitrate (Bi 2 O 3 ,HN0 3 ) is known, which like the other loses acid by washing. The subnitrate is a heavy white powder of faintly sour taste, and reddens litmus paper. It is used in medicine as an antispasmodic, ab- sorbent, sedative, and astringent. When long used it produces scorbutic symptoms, a proof that it is absorbed. It is principally employed in painful affections of the stomach, in spas- modic diseases, and in dysentery and diarrjioaa. Rayer employed it with advantage in diarrhoea of phthisis and typhus. M. Monneret recom- mends it as a drying application. Dr. W. E.