The name of sal─ammoniac was acquired by this substance from its having been found by the ancients in great abundance amongst sand near the temple of Jupiter Ammon, in Africa. It is at present found in Persia; and, accompanying sulphur, amongst volcanic matter near Mount Vesuvius. This salt was formerly imported from Egypt in the form of conical loaves, or of round cakes, which were convex on one side and concave on the other; but it is now made in Europe, by burning at the same time soot, bones, oil, and salt. The deposit formed by the vapour consists of sal─ammoniac, in conjunction with other substances, which are separated from it by a subsequent process. When good, it is white, transparent, and dry within; and externally of yellowish grey, or blackish colour. Sal─ammoniac is applied to many useful purposes. Occasionally it is used in medicine. A considerable portion of it is consumed by dyers, to give brightness to some of their colours. It is also employed in the assay of metals, to discover the presence of iron; and having the property of rendering lead brittle, is sometimes used in the manufacture of shot. By coppersmiths and tinners it is used for cleansing the surface of the metals which they are about to cover with tin. In certain manufactories sal─ammoniac is mixed with tobacco, to give that article, or the snuff that is made from it, additional stimulant properties. Sal─ammoniac dissolved in nitric acid (30) forms the fluid named _aqua─regia_, which is employed in the solution of gold. ──────────────────────────────────────────────────────────────────────── ORDER II.—METALLIC SALTS. SALTS OF IRON. 208. _GREEN VITRIOL, IRON VITRIOL, or COPPERAS, is a mineral salt formed on a decomposition of pyrites (236) by the moisture of the atmosphere. It is also called SULPHAT OF IRON._ _Its colour is bright green, and its taste very astringent; a solution of it in water dropped on oak bark instantly produces a black spot._ Although copperas is occasionally found in grottoes, caverns, the galleries of mines, and other places; yet, being much in request by dyers, tanners, and the manufacturers of ink, it is artificially prepared from pyrites. This mineral being moistened and exposed to the air, a crust is formed upon it, which is afterwards dissolved in water; and from this the crystals of vitriol are obtained by evaporation. The principal use of vitriol is in dyeing woollen articles, hats, and other manufactures, black. It is the basis of ink, and is used in the manufacture of Prussian blue. If it be reduced to powder by the action of fire in a crucible, and mixed with powder of galls, it forms a dry portable ink. Sulphuric acid (24) may be obtained from this kind of vitriol by distillation. The residue, after the process is completed, is used as a red paint; and when washed, is employed for the polishing of steel. SALTS OF COPPER.