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NILOMETER, sometimes called JWiloscope, an instrument used among the ancients to measure the height of the water in the river Nile, in its periodical overflowings. It was first set up, it has been asserted, by Joseph, during his government in Egypt. The measure of it was sixteen cubits, this being the height to which it must rise in order to insure the fruitfulness of the country. NINTH, in music, an interval, containing an octave and a tone; also a name given to the chord, consisting of a common chord, with the eighth advanced one Ilote. NIPA, in botany, a genus of the Appendix Palmae class. Natural order of Palmae or Palms. Essential character: male, spathe; corolla six-petalled : female, spathe : . corolla none; drupes angular. There is but one species, viz. N. fruticans, the young palm, is without the trunk; but in the adult state, it is some feet in height; leaves pinnate ; pinnastriated, margined and smooth; flowers male and female on the same palm; but distinct on different peduncles: males several, late. ral, inferior, on dichotomous peduncles, in spikes: females terminating, aggregate in a globular head, sessile. It is a native of Java and other islands in the East Indies, where the leaves are used for covering houses and making mats. The fruit is eaten both raw and preserved. NIPPLES, in anatomy. See MAMMAny gland. NISI PRIUS, a commission directed to the judges of assize, empowering them to try all questions of fact issuing out of the courts at Westminster, that are then ready for trial by jury. The original of which name is this: all causes commenced in the courts of Westminster-hall are, by course of the courts, appointed to be tried on a day fixed in some Easter or Michaelmas term, by a jury returned from the county where the cause of action arises; but with this proviso, nisi prius justiciarii ad assisas capiendas venerint: that is, unless, before the day prefixed, the judges of assize came into the county in ques. tion, which they always do in the vacation preceding each Easter and Michaelmas term, and there try the cause ; and then upon the return of the verdict given

by the jury to the court above, the judges there give judgment for the party for whom the verdict is found. All trials at law, in the civil courts, and at the assizes, are tried by this process, and are called trials at Nisi Prius.

NISSOLIA, in botany, so named in honour of Guill. Nissole, M.D. of Montpellier; a genus of the Diadelphia Decandria class and order. Natural order of Papilionaceae, or Leguminosae. Essential character: calyx five-toothed; capsule one-seeded, ending in a ligulate wing. There are two species, viz. N. arborea, tree nissolia; and N. fruticosa, shrubby nissolia; both natives of Carthagena, in woods and coppices. NITIDULA, in natural history, a genus of insects of the order of Coleoptera. Antennae clavate, the club solid, and nearly orbicular; shells margined ; head prominent; thorax flattened, margined. There are about forty-two species enumerated by Gmelin, separated into sections according to the form of the lip. A. Lip cylindrical. B. Lip square. N. bipustulata is oval, black; shells with a red dot. It inhabits Europe and America, and lives on carcases, meat, bacon, &c. NITRARIA, in botany, a genus of the Dodecandria Monogynia class and order. Natural order of Ficoideae, Jussieu. Essential character: calyx five-cleft; corolla five-petalled, with the petals arched at top : stamina fifteen or more; drupe oneseeded. There is but one species, viz. N. schoberi. Thick-leaved Nitraria. NITRATES, in chemistry, saltsformed of the nitric acid, and alkalies, earths, &c. They possess the following properties : , soluble in water, and capable of crystallizing by cooling; when heated to redness with combustible bodies, a violent combustion and detonation is produced : sulphuric acid disengages from them fumes which have the odour of nitric acid : when heated with muriatic acid, oxymuriatic acid is driven off; they are decomposed by heat, and yield at first oxygen gas. There are twelve nitrates, of which the most important is the nitrate of potash, or nitre : this salt, known also by the name of salt-petre, is produced naturally in considerable quantities, particularly in Egypt, and has been known from time immemorial. Roger Bacon mentions it under the name of nitre, in the thirteenth century. The importance of this substance for the purposes of war has led chemists to seek the best means of preparing it, especially as nature has not laid up large magazines of it, as she has of other salts. It is now ascertained, that nothing more is necessary for the production of nitre than a basis of lime, heat, and an open, but not too free, communication with dry atmospheric air. When these circumstances combine, the acid is first formed, and afterwards the alkali. See NITR1c acid. NITRE. See NITRATEs. Nitre is found abundantly on the surface of the earth, in India, South America, South Africa, and even in some parts of Spain. In Germany and France it is obtained by means of artificial nitre-beds. These consist of the refuse of animal and vegetable bodies, undergoing putrefaction, mixed with calcareous and other earths. It has been ascertained, that if oxygen gas be presented to azote at the instant of its disengagement, nitric acid is formed. This seems to explain the origin of the acid in these beds. The azote, disengaged from these putrefying animal substances, combines with the oxygen of the air. The potash is probably furnished, partly at least, by the vegetables and the soil. The nitre is extracted from these beds, by lixiviating the earthy matters with water. This water, when sufficiently impregnated, is evaporated, and a brown-coloured salt obtained, known by the name of crude nitre. It consists of nitre, common salt, nitrate of lime, and various other salts. The foreign salts are either separated by repeated crystallizations, or by washing the salt repeatedly with small quantities of water: for the foreign salts being more soluble, are taken up first. , Nitre, when slowly evaporated, is obtained in six-sided prisms, terminated by six-sided pyramids; but for most purposes it is preferred in an irregular mass, because in that state it contains less water. The specific gravity of nitre, as ascertained by Dr. Watson, is 1.9. Its taste is sharp, bitterish, and cooling. It is very brittle. It is soluble in seven times its weight of water, at the temperature of 60°; and in rather less than its own weight of boiling water. When exposed to a strong heat it melts, and congeals by cooling into an opaque mass, which has been called mineral crystal. Whenever it melts, it begins to disengage oxygen; and, by keeping it in a red heat, about a third of its weight of that gas may be obtained: towards the end of the process azotic gas is disengaged. If the heat be continued long enough the salt is completely decomposed, and pure potash remains behind. It deto

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nates more violently with combustiblebodies than any of the other nitrates. When mixed with one-third part of its weight of charcoal, and thrown into a red-hot crucible, or when charcoal is thrown into red-hot nitre, detonation takes place, and one of the most brilliant combustions that can be exhibited. The residuum is carbonate of potash. A still more violent detonation takes place, if phosphorus is used instead of charcoal. Nitre oxydizes all the metals at a red heat. The composition of nitre, according to Kirwan, is

Acid - - - 44

Potash - - - 51.8

Water 4.2 100.0

Nitre furnishes all the nitric acid in all its states, employed either by chemists or artists: it is obtained by decomposing it by means of the sulphuric acid. When burnt with tartar, it yields a pure carbonate of potash. In the assaying of various ores it is indispensable, and is equally necessary in the analysis of many vegetable and animal substances. But one of the most important compounds, formed by means of nitre, is gunpowder, which has completely changed the modern art of war. The discoverer of this compound, and the person who first thought of applying it to the purposes of war, are unknown. It is certain, however, that it was used in the fourteenth century.— From certain archives, quoted by Wiegleb, it appears that cannons were employed in Germany before the year 1372. No traces of it can be found in any European author, previous to the thirteenth centu#: but it seems to have been known to the Chinese long before that period.— There is reason to believe that cannons were used in the battle of Cressy, which was fought in 1346. They seem even to have been used three years earlier at the siege of Algesiras; but before this time, they must have been known in Germany, as there is a piece of ordnance at Amberg, on which is inscribed the year 1303. Roger Bacon, who died in 1292, knew the properties of gunpowder : but it does not follow that he was acquainted with its application to fire-arms. See GUNPowDER. When three parts of nitre, two parts of potash, and one part of sulphur, all previously well dried, are mixed together in a warm mortar, the resulting com

ound is known by the name of fulminating powder. If a little of this powder be

put into an iron spoon, and placed upon burning coals, or held above the flame of a candle, it gradually blackens, and at last melts. At that instant it explodes with a very violent report, and a strong impression is made upon the bottom of the spoon, as if it had been pressed down very violently. This sudden and violent combustion is occasioned by the rapid action of the sulphur on the nitre. By the application of the heat, the sulhur and potash form a sulphuret, which is combustible at a lower heat so 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 ascribed. 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 fevers as a cooling remedy, and as a diuretic in urinary affections. . It is employed also in many arts, as in dyeing ; 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 GUNPowdeh. 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

4 into oxygen and nitrogen gases. For all # practical purposes, however, the nitric

acid is obtained from nitrate of potash, WOL. IX.

o 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 pipe-clay, sifted sand and cut tow. In the tubulure 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 #. products, let a bent glass tube rom 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, leav. ing an eighth or tenth part in the retort. The acid for the last process should be condensed as much as possible, and the redistillation conducted very slowly; and if it be stopped, when half is come over, beautiful crystals of muriate of lead will be obtained on cooling the remainder, if litharge be used, as M. Steinacher informs us; who also adds, that the vessels should

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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 receiver 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 observable, 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 coiourless. 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 without great caution. It inflames volatile oils, such as those of turpentiue 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 acts very powerfully on almost all the metals: But Baume 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 dies; 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 syphilis and af. fections 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. posed to heat it decrepitates, and at length gives out its acid, which is decomposed;

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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 waters. 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 ex

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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 an 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 chrystallizes in it. When the fluid is sufficiently evaporated, it is taken out and cooled, and great part of the nitre separates in crystal; 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 mannel”. 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 degrees; but boiling water dissolves its own weight. One hundred parts of alcohol, at a heat of one

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