Europe is supplied with gold chiefly from Chili and Peru, in South America; though a small-quantity is likewise imported from China, and the coast of Africa. This metal is also found in the sands of several large rivers which do not spring from mountains, but contain veins of gold: mines of it exist in various parts of Europe, and a very promising one has lately been discovered in the county of Wicklow, in Ireland.
Gold is obtained in a pure or native state more frequently than any other metal; it is in general mixed with a stony matter, from which it is extracted by amalgamation. It is more ductile than lead, or tin, but less elastic than either iron or copper. Gold becomes hard and brittle, by continued hammering, but resumes its ductility when slowly heated. Being the toughest, and at the same time the most malleable of all metals, one grain of it may be hammered leaves that would cover a space of 1400 square inches.
This precious metal is the heaviest of all known bodies, excepting pla-tina; its specific gravity bring to that of distilled water as 19,2581 to 1,0000; that is, one solid inch of gold weighs about nineteen or twenty times heavier than one cubic inch of water. It melts in a low white heat, requiring, according to Mr. WedgewoOd's calculation, 523/ degrees of Fahrenheit's, or thirty-two of his own thermometer; a point much higher than that required for the melting of silver or copper.
Gold is not only the universal circulating medium for the purchase of commodities, but it is also applied to various purposes ; for instance, chains, watches, plate, the making of gold lace for liveries, etc. As the manufacture last mentioned frequently becomes tarnished, and totally loses its lustre, we shall briefly observe, that this may be easily restored, by gently rubbing the lace with a sponge dipped In warm spirit of wine.
Gold is soluble in aqua-regia, by which considerable quantities of it are consumed by carvers and gilders, and also for the ornamenting of china, etc. It may, likewise, though imperfectly, be dissolved in the most concentrated aqua-fortis.
The relative value of gold to-that of silver, was anciently as twelve to one. This proportion, however, varies according to the abundance or scarcity of the former metal. In our coinage, the value of fine gold is to that of fine silver, as 15 1/2 to 1. A similar proportion may be considered, upon an average, as the fixed standard of Europe.
There are various methods of determining the fineness of gold, or the proportion of alloy which it contains. For this purpose, touch-needles are generally employed, by which the respective quality of gold! can be ascertained with tolerable exactness. These needles are small bars made of compound metals, in different proportions, which are ae-curately marked on each ; and, by rubbing the metal under examination, and one or more of the needles, close to each other on a touch-stone, the different strokes are compared, in order to judge' by the colour which bears the strongest resemblance to that of the doubtful metal. The most usual stones for this test are black basaltes, though either flint, or potter's ware of a black colour, may be employed with equal advantage. And though such a criterion cannot be relied upon with the same degree of accuracy as that of ascertaining the specific gravity of different metals, yet the touch-needles give a more exact information than might be expected from this superficial assay. Thus, an expert goldsmith will not altogether decide from the d ifference of colour, but will also be guided by the concomitant effect produced on the texture of the metal, when abraded by the touch-stone, namely, whether it be rough, dry, smooth, or greasy. - See Guinea.
Several metallic compositions, however, yield marks or impressions on the touch-stone, very nearly resembling those of pure gold, and which can be distinguished or detected onlv by another more accurate test. In order to guard against such impositions, it is necessary to apply a drop of aquafortis to the suspected metallic strokes on the stone : if they do not disappear, in consequence of this application, it may be safely conConcluded that the gold is ge-nuine; as, in the contrary case, it will be evident that it is a base or adulterated metal.