Nitrates, salts formed by the combination of nitric acid with bases. Some of these are natural products, as the nitrates of potash, soda, lime, and magnesia; and others are artificially formed, as the nitrates of the metals. Several of both kinds are sufficiently important to require particular mention. None of these salts possess acid reaction; they are distinguished for their solubility in water, and hence, the acid not forming a precipitate with any base, its presence, free or combined, can be determined only by other methods, several of which are described in works on chemistry. At a high heat the nitrates undergo decomposition, sometimes being converted into free nitric acid and the oxidized base, and sometimes into oxygen, which escapes, and nitrous acid, which remains in combination with the base, forming a nitrite. - 1. Nitrate of Potash, Nitre, or Saltpetre. First in importance among these salts is the nitrate of potash, or potassic nitrate, represented by the formula KN03. It is an anhydrous, dimorphous white salt, having a specific gravity of 2.07, crystallizing in long six-sided prisms with dihedral summits, belonging to the rhombic system, and also in rhombohedral forms resembling ordinary calc spar.

Frankenheim observed that when a solution of saltpetre is left to evaporate under the microscope, both kinds of crystals make their appearance together. When the evaporation takes place slowly, the crystals are almost all rhonibohedrons; but if these are touched with a prismatic crystal, the solution becomes turbid with formation of prismatic crystals. These prismatic crystals may be again converted into rhorabohedrons by heating to near the fusing point. Nitrate of potash dissolves in 3½ parts of water at 64° F., and in one third its weight of boiling water. It is insoluble in absolute alcohol, is not subject to deliquesce, has a sharp biting taste, and is without action on vegetable colors. It fuses without decomposition at 674-4°, and when cast into moulds solidifies to a white fibrous radiated mass known as sal prunelle. At a red heat it decomposes with formation of nitrite and evolution of oxygen, and at a higher heat the nitrite is also decomposed, with evolution of oxygen and nitrogen and formation of potassic oxide and peroxide. In large crystals it is apt to contain water mechanically held, which retains in solution some of the foreign salts derived from the mother liquor, as sulphate of soda and the chlorides of potassium and sodium.

Smaller crystals are commonly purer; but common salt is almost always present to some extent, and is particularly injurious to saltpetre designed for the manufacture of gunpowder. A mixture of saltpetre with carbonaceous matters is explosive when highly heated; and when this mixture is intimately made, the product is gunpowder; sulphur, winch is commonly introduced, not being essential for this property. (See Gunpowder.) Saltpetre is obtained both as a natural and artificial product. It is generated wherever nitrogenous animal and vegetable matters undergo decomposition in the presence of moist calcareous earth containing potash, the temperature being generally above 60° F. Ammonia is produced, which is decomposed, its nitrogen forming with oxygen nitric acid, which combines with the alkaline earths present. Nitre forms naturally upon the walls of cellars and of caves as an efflorescence. On the surface of some soils in warm countries it also appears in this form after the rainy season, and in sufficient quantity to render its collection profitable.

In Hindostan it is thus produced so abundantly and cheaply, that our own market is largely supplied from Calcutta. To separate the nitre from the earth which contains it, this is lixiviated with water, which dissolves out the soluble salts; and in the large vats into which the liquid is conveyed the salts crystallize as the water is evaporated by solar or artificial heat, The first crystals that form are crude saltpetre; nitrates of lime and magnesia mostly remain in the mother liquor, and are either thrown away with it, or in some cases are decomposed by treatment with car-bonate of potash, and their nitric acid is thus recovered in new quantities of nitre. Natural saltpetre beds are also worked in Hungary, Egypt, Spain, and in various warm countries. In hot countries it does not appear that the immediate presence of decomposing animal matters is essential to the production of saltpetre; but ammonia thus derived and existing in the atmosphere is no doubt brought to the potash. In temperate climates the salt is artificially produced in what are called in Europe saltpetre plantations. These are compost heaps of animal and vegetable matters intermixed with earth, and with potash, lime, and magnesia, presented in porous form, as in ashes, marl, chalk, and old mortar.

The heaps are exposed to the air, but it is better to protect them from the rain. Gutters are excavated around them, and in these are kept liquids from the cattle stalls and other similar fluids rich in nitrogen, with which the materials are occasionally moistened. In Sweden, the heaps are worked over once a week in summer and once a month in winter, and twigs are introduced to keep them open. The work is generally continued three years, until the product of saltpetre amounts to about 5 oz. in 1,000 cubic inches. For an annual product of 10 cwt. it is necessary to work over full 120 cubic fathoms of earth, of which one third becomes ripe each year, and is removed from time to time from the outermost layers to be lixiviated. The crude product obtained is afterward purified by repeated solutions and crystallizations. Saltpetre is now extensively manufactured by the double decomposition of the nitrate of soda from Chili and the chloride of potassium from the salt mines of Stassfurt, Germany. Besides its use for making gunpowder, nitre is employed in the manufacture of nitric acid.

It is also a useful oxidizing flux in metallurgical operations, and in medicine is much used for its cooling properties in inflammatory affections, and also as a promoter of perspiration and the secretions of the liver. In acute rheumatism it is sometimes administered in doses, largely diluted with water, to the extent of from one to two ounces, though half an ounce in concentrated solution causes heat and pain in the stomach, which may be followed by convulsions and death. When taken in poisonous quantities there is no antidote known, and the only relief is by the use of the stomach pump, laudanum to allay the pain, and mucilaginous drinks and cordials. Nitre is also a powerful antiseptic, and is used in the preservation of meats, as for curing hams. - 2. Nitrate of Soda. Another variety of nitre, called cubic nitre, is the salt nitrate of soda or sodic nitrate (Na N03). It crystallizes in obtuse rhombohedrons of specific gravity 2.26. It is deliquescent, soluble in about twice its weight of cold water, and has a cooling saline taste. It fuses at 591°, and is decomposed at a higher temperature. It is found in beds among the hills in the province of Tarapaca which skirt the coast of Peru, and at their base on the W. side of the pampa over an extent of not less than 150 m.

Under the nitrate of soda is marl impregnated with saline matter and mixed with fragments of shells. The nitrate of soda, as quarried, is very variable in quality, some yielding not 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 sometimes 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 L)r. 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 reported to occur in large quantities in Pernam-buco, west of Ipu, the formation extending 15 to 20 m. - 3. Nitrate of Silver, or Lunar Caustic. Among other nitrates the most important is the nitrate of silver, or argentic nitrate (Ag N03). It may be prepared by dissolving pure silver in nitric acid, evaporating to dryness, and fusing to expel nitrous acid, and to destroy 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, having a specific gravity of 4.336. At 426° it fuses, and may then be cast into the crystalline sticks which pass under the names of lunar caustic and lapis infernal is, and are employed 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 nitrate 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 organic 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 compounds, 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 substances 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 adding 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 written 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, and dissolving this by a solution of hyposulphite of soda, or a dilute solution of caustic potash. A hair dye is also prepared with nitrate 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 Amnionic Nitrate (nitrum flammans, N03NH4, or according to the old formula NH40,N05). 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 dilute 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 considerable disappearance of heat, and it is often used in frigorific mixtures. It melts at 226° F., and at 482° is completely decomposed, with conversion into nitrous oxide or laughing gas and water (N03NH4-=N20 + 2H20). It is the material universally used for the production of laughing gas. (See Nitrous Oxide.) - 5. Nitrate of Barium, Baric Nitrate, or Baryta Saltpetre (Ba2N03), is commonly' produced by treating a solution of sulphide of barium, 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 expelled, with evolution of oxygen and nitrogen, the residue being pure baric oxide, or barytes. (See Sulphate of Barium, under Sulphates.) - 6. Nitrate of Bismuth, or Bismuthous Nitrate (Bi 3N03, 5H20; 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 insoluble baric subnitrate (Bi203,21IN03) falls, called by the older writers magistery of bismuth. Another basic nitrate (Bi203,HN03) 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, absorbent, 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 spasmodic diseases, and in dysentery and diarrhoea. Rayer employed it with advantage in diarrhoea of phthisis and typhus. M, Monneret recommends it as a drying application. Dr. W. R. Hamilton of St. Augustine, III. ("American Journal of Medical Sciences," Oct. 1, 18(35), recommends it to prevent pitting in smallpox. - 7. Nitrate of Cobalt, or Golaltous Nitrate (Co2NOs,6HaO), is prepared by dissolving the oxide in nitric acid. It forms pinkish red, prismatic, deliquescent crystals of specific gravity 1.83. It is often employed as a reagent for the blowpipe, magnesium compounds yielding a pink-colored mass, those of zinc green, and those of aluminum blue. Adding a concentrated solution of potassic nitrate to a solution of cobaltous nitrate, acidulated with nitric or acetic acid, throws down a beautiful orange-yellow precipitate, consisting of microscopic four-sided prisms, with pyramidal summits. Cobalt in nickel may he discovered by its means. - 8. Nitrate of Copper, or Cupric Nitrate (Cu2NO3.6H2O), is made by dissolving copper in slightly diluted nitric acid.

During the operation nitric oxide gas (NO) is copiously given off, 3Cu + 8HN03, yielding 3(Cu2N03) + 2NO+4H20. Concentrated acid yields peroxide of nitrogen ( NO2). Cupric nitrate is a beautiful blue, highly deliquescent salt, crystallizing in rhomboidal prisms. At temperatures above 59 F., it crystallizes with 3H20 in needles of specific gravity 2.047, which are very soluble in alcohol. Moderate heat converts it into insoluble basic nitrate, Cu2No3,3CuH202. A further heat expels all the acid, leaving black oxide. Cupric nitrate is used in medicine as an application to sloughing ulcers. If the crystals are folded in tin foil, they will act so powerfully upon the metal as to emit sparks, the tin being converted into stannic oxide. - 9. Nitrates of Iron. These are commonly known as the protonitrate and the pernitrate; in the new nomenclature they are known respectively as ferrous nitrate and ferric nitrate. The ferrous nitrate may be formed by digesting iron turnings in very dilute nitric acid, and also by dissolving protosulphide of iron in cold dilute nitric acid of specific gravity less than 1.12. It crystallizes in pale green rhombohedrons, having the formula Fe2NO3,6H2O. This salt is used in dyeing.

The pernitrate or ferric nitrate is prepared by digesting metallic iron in nitric acid of specific gravity from 1.12 to 1.3. A solution of it is used as an astringent and tonic in medicine, and as a lotion in surgery, under the name.of liquor ferri nitratis (United States Pharmacopoeia). - 10. Nitrates of Lead. Lead forms several salts with nitric acid, the principal of which are plumbic nitrate (Pb2N03) and dibasic plumbic nitrate (Pb2N03,PbII202). The first is formed by dissolving metallic lead or plumbic oxide (litharge, PbO) in an excess of slightly diluted nitric acid. It crystallizes in regular anhydrous octa-hedra, generally opaque. A dull red heat reduces it to protoxide, with evolution of oxygen and nitric peroxide. Caustic ammonia added to excess of the nitrate forms the dibasic salt, The nitrate of lead is used in chemistry in preparing other lead compounds, as for instance the iodide, which is done by the double decomposition of this salt with iodide of potassium. It is also used as a reagent in the laboratory. In medicine it is employed as an application to excoriated surfaces, and its solution forms Ledoyen's disinfecting fluid. - 11. Nitrates of Mercury. Mercury forms a greater number of nitrates than any other metal.

Among them are the normal subnitrate, or mercurous nitrate, and the normal mercuric nitrate, the latter of which is used in medicine. The liquor hydrargyri nitratis is extensively used in the London hospitals for cutaneous diseases, and it has been employed as an application in boils, carbuncles, acne, lupus, and sloughing ulcers. In treating boils a full-sized drop of the liquor is applied to the apex of the furuncle. The unguentum hydrargyri nitratis forms the citrine ointment of the pharmacopoeias, and is used as a stimulant and alterative application in various cutaneous affections, particularly of the scalp. - All the other inorganic as well as organic nitrates of importance will be found under the heads of their bases. - 12. Alcoholic Nitrates, or Nitric Ethers. When nitric acid is heated with alcohol, part of the alcohol is oxidized, and the nitric acid is reduced to nitrous acid, which acting on the remainder of the alcohol produces nitrous ether and other bodies; but if urea is added to the liquid, it immediately decomposes the nitrous acid, and nitrate of ethyl is formed. The other alcohol radicles may also be transformed by the action of nitric acid in the presence of urea into corresponding nitric ethers, as amyl nitric ether, methyl nitric ether, etc.

They have some resemblance to the nitrous ethers. (See Nitrites).