Morey (Silliman's Journal, vol. ii, p. 121.) states a singular experiment, in which nitre is used; viz: If to tallow or linseed oil, a small quantity of saltpetre be added, and the temperature raised to nearly that of the boiling point, the saltpetre appears to be dissolved by the oil; they will evaporate together, and the mixture, or the vapour, will burn, wholly excluded from the atmosphere.
Saltpetre was one of the substances employed by the alchemists. It appears from the memoir of Geoffroy, (Coll. Academ. 1722,) that the object of the alchemists was twofold; the transmutation of metals, and particularly what were denominated the baser metals into the precious, which they pretended to effect by a universal spirit, the grand elixir, the philosopher's stone, &c. and the reduction of metals to their earths. Alchemy was introduced into Europe by the crusaders, and it is remarkable, that, in the reign of Henry IV, an act was passed to make it felony to transmute metals. Mr. Boyle, aware of its absurdity, suggested the propriety of repealing that act, which was done. One of their powders was composed of nitre, cream of tartar, and sulphur.
Preparation. Although nitrate of potassa is generated in abundance, particularly in the East, yet in all countries, where the circumstances are favourable to its production, it is found. It never occurs, native, in very large masses. It is generally found in an efflorescence, on the surface of the soil, or in caverns. It never exists in the soil more than a few yards beneath the surface. We may remark, that native nitre has never been found in pure clay, or pure sand, except in the rock-ore, as it is called, of the western United States. It is often found in caverns, and fissures in calcareous rocks.
In the East Indies, the districts which furnish saltpetre, are swept at certain seasons of the year. This is repeated two or three times a week; for the saltpetre again appears in the same places, in the form of efflorescence.
It is supposed that some countries furnish saltpetre, in consequence of the drought, which continues for some time. At Lima, M. Dombay informs us, there is seldom rain; and the fields, which serve as pasturage for beasts, are so much covered with saltpetre, as to be removed with the spade. There must then be a rapid formation of nitre. M. Talbot observes, that in the meridional provinces of Spain, the earth frequented by animals, contains it, ready formed. When saltpetre became an article of importance, the rulers of Germany, &c. justified themselves in exclusively carrying away the incrustations of walls from private houses, which, when it could be used, became accessorium fundi. Accordingly this regale, as it was called, was extended every where, and was generally unpopular. In 1419, Gunther, archbishop of Magdeburgh, issued the first grant, which was the right of searching saltpetre and boiling it, during a year, in the district of Gibicherstein, for which the person, to whom it was granted, was to pay a barrel of saltpetre, and deliver to the archbishop the remainder at a certain price.
The succeeding archbishop, Frederick, let, in 1460, to a burgher of Halle, all the earth and saltpetre that could be collected in the bailiwick of Gibicherstein, for four years, at the annual rent of a given quantity of refined saltpetre. Bishop Ernest, in 1477, let, for his time, the privilege of collecting saltpetre. In 1544, saltpetre was collected, in the same manner, from the rubbish before the gates of Halle; and in the year following, the magistrates of Halle erected a powder mill, and had saltpetre works. John VI, archbishop of Triers, granted similar privileges in 1560. The saltpetre regale, was long known, and confirmed by a Brandenburgh decree in 1583.
Old walls, and the vicinity of stables, frequently exhibit saltpetre in the state of efflorescence. It was the ancient scrophula contra lapides, represented as a kind of leprosy. For the spontaneous production of nitre, animal and vegetable substances, in a state of decomposition, and the presence of dry atmospheric air are necessary. That lime, and the calcareous carbonates also promote its formation, there can be no doubt.
Notwithstanding the large quantity of saltpetre collected in the East Indies, we are told, that two-thirds of the whole are annually sent into China, and other parts of Asia, to make artificial fire-works. The pyrotechny of the Chinese is said to be very perfect; in variety and beauty, some writers assert they exceed all other nations. There is a natural nitre bed at Apulia, near Naples, which affords 40 per centum of nitre. Pelletier, (Ann. de Chim. tome xxii.) has published an analysis. The cavity of Molfetta is one hundred feet deep, containing grottos or caverns. Nitrate of potassa is found in the interior, in efflorescence or crusts, attached to compact limestone. On removing these efflorescences, others appear. The soil in this cavity is richly impregnated with nitre.
In Switzerland, the farmers extract an abundance of saltpetre from the stalls under their cattle. During the American revolution, when every expedient was resorted to, to obtain a supply of this article, the floors of tobacco houses, &c. were dug up and lixiviated. In the reign of Charles the First, certain patentees were authorised to dig up the floors of all dove-houses, stables, &c. the floors being again laid with mellow earth.
The Ukraine, Podolia, Hungary, Spain, Italy, Peru, and India, furnish more or less of this salt, which is extracted by lixiviating the earths that compose the soil. The springs, in particular districts of Hungary, contain it.
We are informed, (Ann. de Chim. xx. 298,) that, during the second and third years of the French Republic, the government required every district to send two intelligent young persons to Paris. This convocation, consisting of nearly eleven hundred persons, received regular instruction from their first chemists, partly concerning the manufacture of cannon, and partly respecting the manufacture of saltpetre and gunpowder. This body of pupils was afterwards distributed among the different establishments in proportion to their abilities, and saltpetre was soon furnished in abundance.
In the United States, we have an abundant source of saltpetre in the nitre caves of the western country. There is now no occasion for lixiviating the soil of tobacco houses, or of stables, or the refuse of old buildings, the preparation of artificial nitre beds, as adopted in France, or for any other expedient, to furnish a supply of saltpetre; these caverns, which are calcareous, producing it in great abundance. The earth of these caves does not, however, contain pure nitrate of potassa, but generally a mixture of this salt and nitrate of lime, a calcareous nitrate which constitutes the principal part. The latter is changed into nitrate of potassa, as we shall observe more particularly hereafter, by making a lixivium of the earth in the usual manner, and passing it through wood ashes. The alkali, which the latter contains, decomposes the nitrate of lime, by uniting with the nitric acid; hence the fluid, which passes through, is nitrate of potassa or saltpetre. This is evaporated, and suffered to crystallize. It is then the crude, or rough nitre, which is purified, principally by re-solution, and crystallization.
The saltpetre makers, at the caves, have found, that two bushels of ashes, made by burning the dry wood in hollow trees, afford as much alkali as eighteen bushels of ashes obtained from the oak. Notwithstanding the nitre earth contains a mixture of the nitrates of potassa and lime, nitrate of potassa, nearly pure, has been discovered. It is sometimes found in the fissures of sandstone, or among detached fragments. Some of these masses are said to weigh several hundred pounds.
Besides these caverns, which have been accurately described by Dr. Brown, in the Transactions of the American Philosophical Society, (vol. v, vi.) similar caverns have been discovered in Tennessee, and in some parts of Virginia and Maryland. At Hughes' cave near Hagerstown, in Maryland, this salt has also been made.
We are of opinion, that most of the calcareous caverns in the United States, if carefully examined, might be found to contain nitre, or at least, the calcareous nitrate, which is readily converted into nitre by lixiviation with wood ashes, or the addition of a due