the county of Wicklow, in Ireland, are so impregnated with sulphate of copper, that one of the workmen having accidentally left a shovel in this water, found it some weeks after so incrusted with copper, that he imagined it was changed into copper. The proprietors of the mines, in pursuance of this hint, made proper receptacles for the water, and now find these streams of as much interest to them as the mines. When miners wish to know whether an ore contains copper, they drop a little nitric acid upon it; after a short time they dip a feather into the acid, and then wipe it over the polished blade of a knife; and if there be the smallest quantity of copper in it, the copper will be precipitated on the knife.[109] A mass of _native_ copper has been found in a valley in the Brazils, containing 2,666 pounds weight. The description of it in the Memoirs of the Royal Academy of Sciences at Lisbon is said to be very interesting, as the largest specimen ever found before this weighs only ten pounds. In the museum of the Academy of Sciences at St. Petersburgh, is a piece of native malleable copper of extraordinary magnitude, found on the copper island lying to the east of Kamschatka.[110] The Romans were acquainted with this metal; for the only money used by that people, till the 485th year of their city, was made of it, when silver began to be coined. In Sweden, houses are covered with copper.[111] _Iron_ is of a livid blueish color, and one of the hardest and most elastic of all metals. When dissolved, it has a nauseous styptic taste, and being strongly rubbed emits a peculiar smell. It is attracted by the magnet, and has the property of becoming itself magnetic. It is fused with great difficulty, but gives fire by collision with flint. An iron wire only one-tenth of an inch in diameter, will carry a weight of 450 pounds without breaking; and a wire of tempered steel, of the same size, will carry one of about 900 pounds. Iron becomes softer by heat, and has capability of being welded to another piece of the same metal so as to form one entire mass; and this may be done without melting either of the pieces. No other metal, except platina, possesses this singular properly, which renders it most suitable for every common purpose. Its specific gravity varies from 7.6 to 7.8.