Lond. Nitras Potassae, Edin. Dub. Nitrate of Potassa. Nitre.

Sgn. Nitre, Nitrate de Potasse (F.), Salpetersaures kali (G.), Salpeter (Dutch, Dan. Swed.), Saletra (Polish), Nitro (I. S. Port.), Salitre (S.), Selitra (Russ.), Pottle Ooppoo (Tarn.), Shora (Pers.), Sandaiva (Malay), Ubkir (Arab.), Wedie looneo (Cyng.), Shora (H.), Yavac Shora (San.).

This salt is well known in commerce under the name of saltpetre or nitre. It may be regarded both as a natural and artificial production: being found effloresced on the surface of the soil in Hungary2 and some parts of Europe3, South America, Africa4, and very abundantly in India5, whence this country is chiefly supplied; while in some countries, as in Germany and France, it is artificially produced. Nitre is prepared by art by the same means as nature employs, the artificial composts being imitations only of the natural soils where it is most abundantly formed; by giving, therefore, an account of the former mode, both will be better understood. Glauber first suggested the formation of what are termed nitre-beds. In France they consist of a compost of putrefying animal and vegetable matters, such as blood, offal, excrementitious matters, and decaying leaves, with street-sweepings, old mortar, chalk, and other calcareous matter; which are mixed in casual proportions, and lightly spread in long beds, covered with roofs to protect them from the weather. These are turned up occasionally, frequently moistened with putrid water or urine; and at the end of two years, or less, are supposed to be fit to yield the nitre by lixiviation.

The theory of this process, which is not yet completely elucidated, was not at all understood till the experiments of Thouvenal, and the discovery of the composition of nitric acid by Mr. Cavendish, removed much of the obscurity in which it was involved: the following is the explanation. The spontaneous decomposition of the animal and vegetable matter evolves nitrogen, oxygen, hydrogen, and carbon, which reuniting by the operation of new affinities, new compounds are formed; and among these nitric acid, by the union of the nitrogen from the animal substances with the oxygen from the vegetable matter. The acid thus formed is attracted partly by the calcareous earth of the beds, and partly by a portion of potassa, either contained in them ready formed, or, as some have supposed, formed during the process. The presence of animal matter, although it aid the formation of nitre, yet is not essential; for Dr. J. Davy found a rich impregnation of nitre in a nitre-cave near Mensoora, in the district of Doom-bera, in Ceylon, in a decomposing rock consisting of calcspar, felspar, quartz, mica, and talc, in a humid state, exposed to the air, and perfectly free from any animal matter.1 The presence of a certain degree of heat and humidity, of atmospheric air, of lime and some alkaline mineral, is absolutely necessary; for besides fixing the nitric acid when formed, the affinities lime exerts to oxygen and nitrogen favour very much their combination, and consequently the formation of the acid.

1 Amer. Journ. of Med. Scien. vol. xv. p. 362.

2 Beudant's Travels in Hungary.

3 A great repository of native nitre in Europe is the Pulo of Molfelta, in the province of Puglia, in the kingdom of Naples. It is a deep cavity formed by the falling in of several caverns. The Abbe Fortis first drew public attention to this place, at which time it was lined with a crust of nitre an inch thick, which on being scraped off was successively renewed in a few days.

4 Near the city of Tlemsan, in the kingdom of Algiers, six ounces of nitre are extracted, by simple lixiviation, from one quintal of the common mould.-Shaw's Travels, p. 228.

5 The presidency of Calcutta exports annually upwards of 8000 tons of nitre.

The compost, when ready to be lixiviated, is first mixed with wood-ashes, or with pulverized impure potassa, to decompose the nitrate of lime. It is then put into a cask furnished with a cock at the bottom, and an inner, false, perforated bottom; a quantity of river water is now poured over it, and after some hours the cock is turned, and the liquor drained off, which is used instead of water for a second portion of earth; and this is successively repeated, till it is supposed to be sufficiently impregnated with the soluble matter of the compost. The lixivium, which contains chiefly nitrate of potassa, and the hydrochlorates of potassa and of soda, is now boiled and clarified with bullocks' blood or a solution of glue; and the boiling continued, the hydrochlorates as they form being withdrawn by perforated ladles, till the liquor is so concentrated that a few drops poured on cold iron immediately crystallize. It is then, when nearly cold, poured into separate crystallizing dishes, in which after some days the salt is found deposited in a confused mass of opaque, dirty white, imperfect crystals, which, after being broken to pieces and drained, are known under the name of rough or crude nitre, or crude saltpetre.

1 Davy's Account of the Interior of Ceylon, 4to. p. 32. Lond. 1821.

Nitre is brought from Bengal in an impure state, but crystallized, put up in bags, each containing two bazar maunds, or 164 lbs. weight.1 The crystallized state of this impure nitre arises from the lixivium of the soil having been slowly evaporated in shaded, shallow pits. To purify crude nitre, it is repeatedly washed with cold water, which dissolves the deliquescent hydrochlorates: and then is boiled with half its weight of water, until a pellicle forms on the surface; after which the solution is poured into leaden coolers, and stirred till it is quite cold, by which means the salt is deposited in acicular crystals.2 Different processes are employed in different places.

Qualities.-Pure nitrate of potassa is inodorous; and has a bitterish, sharp taste, occasioning a sensation of cold both in the mouth and stomach. It is generally in white, pellucid, brittle, sixsided prisms, terminated by two-sided summits, the specific gravity of which is 1.933. These crystals are soluble in seven parts of water at 60°, producing cold during their solution; but boiling water takes up its own weight of them. They are perfectly insoluble in strong alcohol. They are permanent in the air, melt when exposed to a moderate heat, and when cast into moulds form Sal Prunelle. They contain no water of crystallization, but water is generally entangled in them. In a strong heat it undergoes the igneous fusion; oxygen gas is disengaged at first, and afterwards nitrogen gas; and, in a continued intense heat, the acid is completely expelled and decomposed, leaving behind pure potassa.

1 Each Bengal ship of 800 tons generally brings home in a period of war about 5000 bags of nitre.

2 Nitre was unknown to the ancients; and Beckmann thinks that it was not discovered till the 13th century. The term sal petrosum is first mentioned in the work of Albertus Magnus "De Mirabilibus Mundi" in a prescription of Marcus Graecus for making the Greek fire: but it is probable, as Beckmann conjectures, that this salt was known long before this period in India, where he believes gunpowder also was invented, and brought by the Saracens from Africa to Europe. -History of Inventions, vol. iv.

Nitre when mixed with inflammable substances detonates in a strong heat; and if charcoal be used, a pure carbonate of potassa remains behind. It is likewise decomposed by the sulphuric acid, alum, sulphate of magnesia, and the sulphates of zinc, copper, and iron, when aided by heat; and in the cold by baryta. According to the analysis of Berard, 100 parts of nitrate of potassa contain 51.36 nitric acid, and 48.64 potassa1, or 1 eq. of potassa=47.15+ 1 of nitric acid= 54.15= 101.3.

Nitrate of potassa sometimes contains hydrochlorate and sulphate of soda, and sulphate of potassa. The hydrochlorate is discovered by nitrate of silver, throwing down a precipitate, every 100 grains of which denote 42 1/2 of hydrochlorate of soda. The sulphates are detected by nitrate of barytes.2

Medical properties and uses. - Nitrate of potassa is refrigerant, excitant, and diuretic; and, when externally applied in solution, it is cooling and detergent. If taken in repeated small doses, it increases the secretion of urine, in which, and in the alvine dejections, the salt may be detected, unchanged, by chymical tests. It is efficaciously given in active haemorrhages, particularly haemoptysis, in which it may be administered in doses of a drachm, without exciting griping or any action in the bowels. It is also useful in herpetic eruptions. Although diuretic, yet it is of little use in dropsies, and is contra-indicated in typhus and hectic fever: in the latter of which, as Dr. Percival has justly observed, it lowers the pulse at first, but afterwards raises it higher than before. A small portion of it, allowed to dissolve slowly in the mouth, often removes incipient inflammatory sore-throat; and thence its utility in gargles in that complaint.

It is most advantageously given dissolved in mucilaginous fluids, as almond emulsion, in moderate doses not exceeding grs. xv. frequently repeated: but the dose may be carried to 3 ij. with safety. In larger doses it excites nausea, a lively sensation of cold at the epigastric region, and sometimes colic; and in very large doses, from 3 iv. to j. for instance, which have sometimes been taken by mistake for sulphate of soda, it causes vomiting, hypercatharsis, bloody stools, convulsions, and sometimes death. Opium and aromatics are the best antidotes.

Officinal preparations. - Acidum Nitricum, L. E. D. Potassae Sulphas, L. E. D. Potassae Bisulphas, L. Sulphas Potassae cum Sulphure, E. Trochisci Nitratis Potassae, E.

1 Ann. de Chim. t. lxxi. p. 69.

2 Henry's Elements of Experimental Chymistry, 7th ed vol. ii, p. 464.