This Acid may be separated from the Copper which it hath dissolved by distillation only: but the operation requires a fire of the utmost violence. The Copper remaining after it must be fused with the black flux, to make it appear in its natural form; not only because it still retains a portion of the Acid, but also because it hath lost part of its phlogiston by being dissolved therein. The black flux is very well adapted both to absorb the Acid that remains united with the Copper, and to restore the phlogiston which the metal hath lost. The most usual method of separating Copper from the Vitriolic Acid is by presenting to that Acid a metal with which it hath a greater affinity than with Copper. Iron being so qualified is consequently very fit to bring about this separation. When therefore plates of Iron well cleaned are laid in a solution of Blue Vitriol, the Acid soon begins to act upon them, and by degrees, as it dissolves them, deposites on their surfaces a quantity of Copper in proportion to the quantity of Iron it takes up. The Copper thus precipitated hath the appearance of small leaves or scales, exceeding thin, and of a beautiful copper-colour. Care must be taken to shake the Iron-plates now and then, to make the scales of Copper fall off, which will otherwise cover them entirely, hinder the Vitriolic Acid from attacking the Iron, and so put a stop to the precipitation of the remaining Copper. When these scales of Copper cease to settle on the clean Iron plates, you may be sure all the Copper that was in the liquor is precipitated, and that this liquor, which was a solution of Copper before the precipitation, is a solution of Iron after it. So that here two operations are performed at one and the same time; to wit, the precipitation of the Copper, and the dissolution of the Iron. The Copper thus precipitated requires only to be separated from the liquor by filtration, and melted with a little black flux, to become very fine malleable Copper. The Copper may also be precipitated out of a solution of Blue Vitriol by the interposition of a Fixed Alkali. This precipitate is of a greenish blue colour, and requires a much greater quantity of the black flux to reduce it. Copper dissolves in the Nitrous Acid, in the Marine Acid, and in _Aqua regis_; from all of which it may be separated by the same methods as are here ordered with regard to the Vitriolic Acid. CHAP. IV. _Of_ IRON. PROCESS I. _To separate Iron from its Ore._ Pound into a coarse powder the martial stones or earths out of which you design to extract the Iron: roast this powder in a test under the muffle for some minutes, and let your fire be brisk. Then let it cool, beat it very fine, and roast it a second time, keeping it under the muffle till it emit no more smell.