_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.