Note 3 — THE GATHERER.
Reading edition
Footnote 3
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The theory of this artificial formation of saltpetre is detailed by Chaptal, in Annales de Chimie, tom. xx.—The bulk of saltpetre used in this country is brought from the East Indies, where, at certain seasons of the year, it is found deposited on the surface of the soil. It is swept off once or twice a week, and as often renewed. At Apulia, near Naples, there is a bed containing 40 per cent. of it; and in Switzerland the farmers extract it in abundance from the earth under the stalls of the cattle. In the reign of Charles I. great attention was paid to the making of saltpetre in England. Certain patentees were authorized by royal proclamation to dig up the floors of all dove-houses, stables, &c. In France, the plaster of old walls is washed to separate the nitrate of lime, which is a soluble salt, and this, by means of potash, or muriate of potash, is afterwards converted into nitre. Mr. Bowles, in his Introduction to the Natural History of Spain, assures us there is enough saltpetre in that country to supply all Europe for ever.