the rapid action of the sulphur on the nitre. By the application of the heat, the sulphur and potash form a sulphuret, which is combustible at a lower heat probably than even sulphur. Sulphurated hydrogen gas, azotic gas, and perhaps also sulphurous acid gas, are disengaged almost instantaneously. It is to the sudden action of these on the surrounding air that the report is to be as cribed. Its loudness evidently depends upon the combustion of the whole powder at the same instant, which is secured by the previous fusion that it undergoes; whereas the grains of gunpowder burn in succession. A mixture of equal parts of tartar and nitre, deflagrated in a crucible, is known by the name of white flux. It is merely a mixture of carbonate of potash, with some pure potash. When two parts of tartar, and one of nitre, are deflagrated in this manner, the residuum is called black flux from its colour. It is merely a mixture of charcoal and carbonate of potash. Nitre is much used in medicine, in fe vers, as a cooling remedy, and as a diuretic, in urinary affections. It is employed also in many arts, as in dying; and in domestic economy, for the preservation of animal substances used for food. To these substances it imparts a red colour. See NiTROUS acid; also GUNPOWDER. NITRIC acid. The two principal constituent parts of our atmosphere, when in certain proportions, are capable, under particular circumstances, of combining chemically, into one of the most powerful acids, the nitric, which consists, according to Mr. Davy, of 70.5 of oxygen, and 29,5 of azote, or nitrogen. If these gases be mixed in this proportion in a glass tube, about a line in diameter, over mercury, and a series of electric shocks be passed through them for some hours, they will form nitric acid; or, if a solution of potash be present with them, nitrate of potash will be obtained. The constitution of this acid may be further proved, analytically, by driving it through a red-hot porcelain tube, as thus it will be decomposed into oxygen and nitrogen gases. For all practical purposes, however, the nitric acid is obtained from nitrate of potash, from which it is expelled by sulphuric acid. Four parts of pure nitrate of potash, coarsely powdered, are to be put into a glass retort, and three parts of concentrated sulphuric acid cautiously added, taking care to avoid the fumes that arise, which is best done by standing in a current of air to convey them up the chimney. Join to the retort a tubulated receiver of large capacity, with an adopter interposed, and lute the junctures with a mixture of pipeclay, sifted sand, and cut tow. In the tu bulure fix with fat lute a glass tube terminating in another large receiver, in which is a small quantity of water; and, if you wish to collect the gaseous products, let a bent glass tube from this receiver communicate with a pneumatic trough. Apply heat to the receiver by means of a sand bath. The first product that passes into the receiver is generally red and fuming; but the appearances gradually diminish, till the acid comes over pale, and even colourless, if the materials used were clean. After this it again becomes more and more red and fuming, till the end of the operation; and the whole mingled together will be of a yellow or orange colour. In the large way, and for the purposes of the arts, extremely thick cast iron or earthen retorts are usually employed, to which an earthen head is adapted, and connected with a range of proper condensers. The strength of the acid too is varied, by putting more or less water in the receivers. The nitric acid thus made generally contains sulphuric acid, and also muriatic from the impurity of the nitrate employed. If the former, a solution of nitrate of barytes will occasion a white precipitate: if the latter, nitrate of silver will render it milky. The sulphuric acid may be separated by a second distillation from very pure nitre, equal in weight to an eighth of that originally employed; or by precipitating with nitrate of barytes, decanting the clear liquid, and distilling it. The muriatic acid may be separated by proceeding in the same way with nitrate of silver, or with litharge, decanting the clear liquor, and redistilling it, leaving an eighth or tenth part in the retort. The acid for the last process should be condensed as much as possible, and the redis. tillation conducted very slowly; and if it be stopped when half is come over, beautiful crystals of muriate of lead will be ob tained on cooling the remainder, if litharge be used, as M. Steinacher informs us; who also adds, that the vessels should be made to fit tight by grinding, as any lute is liable to contaminate the product. As this acid still holds in solution more or less nitrous gas, it is not, in fact, nitric acid, but a kind of nitrous; it is therefore necessary to put it into a retort, to which a re ceiver is added, the two vessels not being luted, but merely joined by paper; and to apply a very gentle heat for several hours, changing the receiver as soon as it is filled with red vapours. The nitrous gas will thus be expelled, and the nitric acid will remain in the retort, as limpid and colourless as water. It should be kept in a bottle secluded from the light, otherwise it will lose part of its oxygen. The strongest acid that Mr. Kirwan could procure at 60° was 1.5543, which by his calculation contained .7354 of real acid; but Rouelle professes to have obtained it of 1.583. It is obseryable, that, on comparing the tables of Kirwan and Davy, the aeriform acid appears to contain a considerable portion of water more than that which is combined with soda to form the nitrate. Nitric acid should be of the specific gravity of 1,5, or a little more, and colourless. It boils at 248', and may be distilled without any essential alteration. Exposed to the air it absorbs moisture. If two parts be suddenly diluted with one of water, the temperature will rise to about 112°; but the addition of more water to this diluted acid will lower its temperature. It retains its oxygen with little force, so that it is decomposed by all combustible bodies, Brought into contact with hydrogen gas at a high temperature, a violent detonation ensues, so that this must not be done with out great caution. It inflames volatile oils, such as those of turpentine and cloves, when suddenly poured on them: but, to perform this experiment with safety, the acid must be poured out of a bottle tied to the end of a long stick, otherwise the operator's face and eyes will be greatly endangered. If it be poured on perfectly dry charcoal powder, it excites combustion, with the emission of copious fumes. By boiling it with sulphur it is decomposed, and its oxygen, uniting with the sulphur, forms sulphuric acid, Chemists in general agree, that it ácts very powerfully on almost all the metals: but Baumé has asserted, that it will not dissolve tin; and Dr. Woodhouse of Pennsylvania affirms, that in a highly concentrated and pure state it acts not at all on silver, copper, or tin, though with the addition of a little water its action on them is very powerful. He does not mention the specific gravity of this acid: he only says, that it was prepared by first expelling the water of crystallization from nitre by heat, and then decomposing this nitre by means of strong sulphuric acid, The nitric acid is of considerable use in the arts. It is employed for etching on copper; as a solvent of tin to form with that metal a mordant for some of the finest dyes; in metallurgy and assaying; in various chemical processes, on account of the facility with which it parts with oxygen and dissolves metals; in medicine as a tonic, and as a substitute for mercurial preparations in siphylis and affections of the liver; as also in the form of vapour to destroy contagion. For the purposes of the arts it is commonly used in a diluted state, and contaminated with the sulphuric and muriatic acids, by the name of aqua fortis. This is generally prepared by mixing common nitre with an equal weight of sulphate of iron, and half its weight of the same sulphate calcined, and distilling the mixture : or by mixing nitre with twice its weight of dry powdered clay, and distilling in a reverberatory furnace. Two kinds are found in the shops, one called double aqua fortis, which is about half the strength of nitric acid; the other simply aqua fortis, which is half the strength of the double. A compound made by mixing two parts of the nitric acid with one of muriatic, known formerly by the name of aqua regia, and now by that of nitro-muriatic acid, has the property of dissolving gold and platina. On mixing the two acids, heat is given out, an effervescence takes place, oxygenated muriatic acid gas is evolved, and the mixture acquires an orange colour. This is likewise made by adding gradually to an ounce of powdered muriate of ammonia, four ounces of double aqua fortis, and keeping the mixture in a sand heat till the salt is dissolved; taking care to avoid the fumes, as the vessel must be left open: or by distilling nitric acid with an equal weight, or rather more, of common salt. With the different bases the nitric acid forms nitrates. The nitrate of barytes, when perfectly pure, is in regular octaedral crystals, though it is sometimes obtained in small shining scales. It may be prepared by uniting barytes directly with nitric acid, or by decomposing the carbonate of sulphuret of barytes with this acid. Exposed to heat it decrepitates, and at length gives out its acid, which is decomposed; but if the heat be urged too far, the barytes is apt to vitrify with the earth of the crucible. It is soluble in 12 parts of cold, and 3 or 4 of boiling water. It is said to exist in some mineral watera, The nitrate of potash is the salt well known by the name of nitre, or saltpetre. It is found ready formed in the East Indies, in Spain, in the kingdom of Naples, and elsewhere, in considerable quantities; but nitrate of lime is still more abundant. Far the greater part of the nitrate made use of is produced by a combination of circumstances which tend to compose and condense nitric acid. This acid appears to be produced in all situations, where animal matters are completely decomposed with access of air, and of proper substances with which it can readily combine. Grounds frequently trodden by cattle, and impregnated with their excrements, or the walls of inhabited places where putrid animal vapours abound, such as slaughter houses, drains, or the like, afford nitre by long exposure to the air. Artificial nitre beds are made by an attention to the circumstances in which this salt is produced by nature. Dry ditches are dug, and covered with sheds, open at the sides, to keep off the rain; these are filled with animal substances, such as dung, or other excrements, with the remains of vegetables, and old mortar, or other loose calcareous earth; this substance being found to be the best and most convenient receptacle for the acid to combine with. Occasional watering, and turning up from time to time, are necessary, to accelerate the process, and increase the surfaces to which the air may apply; but too much moisture is hurtful. When a certain portion of nitrate is formed, the process appears to go on more quickly; but a certain quantity stops it altogether, and after this cessation the materials will go on to furnish more, if what is formed be extracted by lixiviation. After a succession of many months, more or less, according to the management of the operation, in which the action of a regular current of fresh air is of the greatest importance, nitre is found in the mass. If the beds contained much vegetable matter, considerable portion of the nitrous salt will be common saltpetre; but, if otherwise, the acid will, for the most part, be combined with the calcareous earth. a To extract the saltpetre from the mass of earthy matter, a number of large casks are prepared, with a cock at the bottom of each, and a quantity of straw within, to prevent its being stopped up. Into these the matter is put, together with wood-ashes either strewed at top, or added during the filling. Boiling water is then poured on, and suffered to stand for some time; after which it is drawn off, and other water added in the same manner, as long as any saline matter can be thus extracted. The weak brine is heated, and passed through other tubs, until it becomes of considerable strength. It is then carried to, the boiler, and contains nitre and other salts; the chief of which is common culinary salt, and sometimes muriate of magnesia. It is the property of nitre to be much more soluble in hot than cold water; but common salt is very nearly as soluble in cold as in hot water. Whenever, therefore, the evaporation is carried by boiling to a certain point, much of the common salt will fall to the bottom, for want of water to hold it in solution, though the nitre will remain suspended by virtue of the heat. The common salt thus separated is taken out with a perforated ladle, and a small quantity of the fluid is cooled, from time to time, that its concentration may be known by the nitre which crystallizes in it. When the fluid is sufficiently evaporated, it is taken out and cooled, and great part of the nitre separates in crystals; while the remaining common salt continues dissolved, because equally soluble in cold and in hot water. Subsequent evaporation of the residue will separate more nitre in the same manner. This nitre, which is called nitre of the first boiling, contains some common salt; from which it may be purified by solution in a small quantity of water, and subsequent evaporation for the crystals thus obtained are much less contaminated with common salt than before; because the proportion of water is so much larger with respect to the small quantity contained by the nitre, that very little of it will crystallize. For nice purposes, the solution and crystallization of nitre are repeated four times. The crystals of nitre are usually of the form of six-sided flattened prisms, with diedral summits. Its taste is penetrating; but the cold produced, by placing the salt to dissolve in the mouth, is such as to predominate over the real taste at first. Seven parts of water dissolve two of nitre, at the temperature of sixty de grees: but boiling water dissolves its own weight. One hundred parts of alcohol, at a heat of one hundred and seventy-six degrees, dissolve only 2.9. On being exposed to a gentle heat, nitre fuses; and in this state being poured into moulds, so as to form little round cakes, or balls, it is called sal prunella, or crystal miuera!. This at least is the way in which this salt is now usually prepared, conform ably to the directions of Boerhaave; though in most dispensatories a twenty-fourth part of sulphur was directed to be deflagrated on the nitre, before it was poured out. This salt should not be left on the fire after it has entered into fusion, otherwise it will be converted into a nitrite of potash. If the heat be increased to redness, the acid itself is decomposed, and a considerable quantity of tolerably pure oxygen gas is evolved, succeeded by nitrogen. This salt powerfully promotes the combustion of inflammable substances. Two or three parts mixed with one of charcoal, and set on fire, burn rapidly; azote and carbonic acid gas are given out, and a small portion of the latter is retained by the alkaline residuum, which was formerly called clyssus of nitre. Three parts of nitre, two of subcarbonate of potash, and one of sul phur, mixed together in a warm mortar, form the fulminating powder; a small quantity of which, laid on a fire shovel, and held over the fire till it begins to melt, explodes with a loud sharp noise. Mixed with sulphur and charcoal it forms gunpowder. See GUNPOWDer. Three parts of nitre, one of sulphur, and one of fine saw-dust, well mixed, constitute what is called the powder of fusion. If a bit of base copper be folded up and covered with this powder in a walnut shell, and the powder be set on fire with a lighted paper, it will detonate rapidly, and fuse the metal into a globule of sulphuret, with out burning the shell. If nitrate of potash be heated in a retort, with half its weight of solid phosphoric or boracic acid, as soon as this acid begins to enter into fusion it combines with the potash, and the nitric acid is expelled, accompanied with a small portion of oxygen gas and nitric oxide. Silex, alumine, and barytes, decompose this salt in a high temperature by uniting with its base, as was observed when speak ing of aqua fortis. The alumine will effect this even after it has been made into pottery. The uses of nitre are varions. Beside those already indicated, it enters into the composition of fluxes, and is extensively employed in metallurgy: it serves to promote the combustion of sulphur in fabricating its acid; it is used in the art of dying; it is added to common salt for preserving meat, to which it gives a red hue; it is an ingredient in some frigorific mixtures; and it is prescribed in medicine, as cooling, febrifuge, and diuretic, and some have recommended it mixed with vinegar as very powerful remedy for the sea scurvy. Nitrate of soda, formerly called cubic or quadrangular nitre, approaches in its properties the nitrate of potash; but differs from it in being somewhat more soluble in cold water, though less in hot, which takes up little more than its own weight; in being inclined to attract moisture from the atmosphere; and in crystallizing in rhombs, or rhomboidal prisms. It may be prepared by saturating soda with the nitric acid, by precipitating nitric solutions of the metals, or of the earths, except barytes, by soda: by lixiviating and crystallizing the residuum of common salt distilled with three-fourths its weight of nitric acid; or by saturating the mother waters of nitre with soda instead of potash. This salt has been considered as useless; but professor Proust says, that five parts of it, with one of charcoal and one of sulphur, will burn three times as long as common powder, so as to form an economical composition for fire works. Nitrate of strontian may be obtained in the same manner as that of barytes, with which it agrees in the shape of its crystals, and most of its properties. It is much more soluble, however, requiring but four or five parts of water according to Vauquclin, and only an equal weight according to Mr. Henry. Boiling water dissolves nearly twice as much as cold. Applied to the wick of a candle, or added to burning alcohol, it gives a deep red colour to the flame. On this account it might be useful, perhaps, in the art of pyrotechny. Nitrate of lime, the calcareous nitre of older writers, abounds in the mortar of old buildings, particularly those that have been much exposed to animal effluvia, or processes in which azote is set free. Hence it abounds in nitre beds, as was observed when treating of the nitrate of potash. It may also be prepared artificially by pour ing dilute nitric acid on carbonate of lime. If the solution be boiled down to a syrupy consistence, and exposed in a cool place, it crystallizes in long prisms, resembling bundles of needles diverging from a centre. These are soluble, according to Henry, in an equal weight of boiling water, and twice their weight of cold; soon deliquesce on exposure to the air; and are decomposed at a red heat. Fourcroy says, that cold water dissolves four times its weight, and that its own water of crystallization is sufficient to dissolve it at a boiling heat. It is likewise soluble in less than its weight of alcohol. By evaporating the aqueous solution to dryness, continuing the heat till the nitrate fuses, keeping it in this state five or ten minutes, and then pouring it into an iron pot previously heated, we obtain Baldwin's phosphorus. This, which is, perhaps, more properly nitrite of lime, being broken to pieces, and kept in a phial closely stopped, will emit a beautiful white light in the dark, after having been exposed some time to the rays of the sun, At pre. sent no use is made of this salt, except for drying some of the gases by attracting their moisture; but it might be employed instead of the nitrate of potash for manufacturing aqua fortis. The nitrate of ammonia possesses the pro All these are completely deliquescent, but they differ a little in solubility. Alcohol at 176° dissolves nearly 90.9 of its own weight. The chief use of this salt is for affording nitrous oxide on being decomposed by heat. See nitrous oxide, under the art. GAS. Nitrate of magnesia, magnesian nitre, crystallizes in four-sided rhomboidal prisms, with oblique or truncated summits, and sometimes in bundles of small needles. Its taste is bitter, and very similar to that of nitrate of lime, but less pungent. It is fusible, and decomposable by heat, giving out first a little oxygen gas, then nitrous oxide, and lastly nitric acid. It deliquesces slow ly. It is soluble in an equal weight of cold water, and in but little more hot, so that it is scarcely crystallizable but by spontaneous evaporation. The two preceding species are capable of combining into a triple salt, an ammoniaco-magnesian nitrate, either by uniting the two in solution, or by a partial decomposition of either by means of the base of the other. This is slightly inflammable when suddenly heated: and by a lower heat is decomposed, giving out oxygen, azote, more water than it contained, nitrous oxide, and nitric acid. The residuum is pure magnesia. It is disposed to attract moisture from the air, but is much less deliquescent than either of the salts that compose it; and requires eleven parts of water at 60° to dissolve it. Boiling water takes up perty of exploding, and being totally decomposed, at the temperature of 600°; whence it acquired the name of nitrum flammans. The readiest mode of preparing it, is by adding carbonate of ammonia to dilute nitric acid till saturation takes place. If this solution be evaporated in a heat between 70° and 100°, and the evaporation not carried too far, it crystallizes in hexaëdral prisms terminating in very acute pyramids; if the heat rise to 212°, it will afford, on cooling, long fibrous silky crystals: if the evaporation be carried so far as for the salt to concrete immediately on a glass rod by cooling, it will form a compact mass. According to Mr. Davy, these differ but little from each other, except in the water they contain, their component parts being as follows: more, so that it will crystallize by cooling, It consists of 78 parts of nitrate of magnesia and 22 of nitrate of ammonia. From the activity of the nitric acid as a solvent of earths in analyzation, the nitrate of glucine is better known than any other of the salts of this new earth. Its form is either pulverulent, or a tenacious or ductile mass. Its taste is at first saccharine, and afterward astringent. It grows soft by exposure to heat, soon melts, its acid is decomposed into oxygen and azote, and its base alone is left behind. It is very solu ble and very deliquescent. Nitrate, or rather supernitrate, of alumine, crystallizes, though with difficulty, in thin, soft, pliable flakes. It is of an austere aud acid taste, and reddens blue vegetable colours. It may be formed by dissolving in diluted nitric acid, with the assistance of heat, fresh precipitated alumine, well wash. ed but not dried. It is deliquescent, and soluble in a very small portion of water. Alcohol dissolves its own weight. It is easily decomposed by heat. Nitrate of zircone was first discovered" by Klaproth, and has since been examined by Guyton-Morveau and Vauquelin. Its crystals are small, capillary, silky needles. Its taste is astringent. It is easily decomposed by fire, very soluble in water, and deliquescent. It may be prepared by dissolving zircone in strong nitric acid; but like the preceding species, the acid is always in excess, |