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 vege table 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, disen gaged from these putrifying animal sub stances, 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 sufficient ly 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 crystalliza tions, 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 eva porated, 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 crys tal. Whenever it melts, it begins to dis engage oxygen ; and, by keeping it in a red beat, about a third of its weight of that gas may be obtained : towards the end of the process azotic gas is disengag ed. If the heat be continued long enough; the salt is completely decomposed, and pure potash remains behind. It deto nates more violently with combustible bo dies than any of the other nitrates. When mixed with one-third part of its weight of charcoal, and thrown into a red-hot cru cible, 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 car bonate 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 compo sition 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 carbon ate of potash. In the assaying of various ores it is indispensable, and is equally ne cessary 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 ap plying it to the purposes of war, are un known. It is certain, however, that it was used in the fourteenth century. From certain archives, quoted by Wieg leb, it appears that cannons were employ ed in Germany before the year 1372. No traces of it can be found in any European author, previous to the thirteenth centu ry ; 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 hate been known in Germany, us there is a piece of ordnance at Amberg, on which is inscribed the year 1303. Ro ger Bacon, who (lied in 1292, knew the properties of gunpowder ; but it does not follow that he was acquainted with its application to fire-arms. See Guxrow nEn. When three parts of nitre, two parts of potash, and one part of sulphur, all previously well dried, are mixed toge ther in a warm mortar, the resulting com pound is known by the name of fulminat ing powder. if a little of this powder be pot 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 bad 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 sul phur and potash form a sulphuret, which is combustible at a lower heat probably than even sulphur. Sulphurated hydro gen gas, azotic gas, and perhaps also sul phurous acid gas, are disengaged almost instantaneously. It is to the sudden ac tion 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 mix ture of equal parts of tartar and nitre, deflagrated in a crucible, is known by the name of white flux. It is merely a mix ture of carbonate of potash, with some pure potash. When two parts of tartar, and one of nitre, are defiagrated 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 diu retic in urinary affections. It is employ ed 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 Niamons acid; also GIINPOSSilali.