Page:Willich, A. F. M. - The Domestic Encyclopædia (Vol. 2, 1802).djvu/414

382&#93; >$2] GOL leaves that would cover a space of 1400 square inches. This precious metal is the heaviest of all known bodies, excepting ft la- tin a, its specific gravity b"ing to that of distilled water as 1,'25S1 to 1,0003 ; that is, one solid inch of gold w ighs about nineteen or twenty times heavier than one cubic inch of water. It melts in a low white heat, requiring, according to Mr. V/edgewood's calculation, 523/ degrees of Fahrenheit's, or thirty-two of his own thermome- ter; a point much higher than that required for the melting of snver or copp< r. Gold is not only the universal circulating medium for the purchase of commodities, but it is also ap- plied to various purposes j for in- stance, chains, watches, plate, the making of gold lace for liveries, Sec. As die manulaemre last mentioned frequently becomes tarnished, and totally lo^es its lustre, we shall briefly observe, that this may be easily restored, by gently rubbing the Lice w'.th a sponge dipped in warm spirit of wine. Gold is soluble in aqua-regia, by which considerable quantities of it are consumed by carvers andg'.kk i .-,, and also for the ornamenting of china, &c. It may, likewise, though imperfectly, be dissolved in the must 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 abunda. ce or scarcity of the form; r metal. In our coinage, tiie value, of fine gold is to that of fine silver, as 15 Z to 1. A similar proportion may be. con- sidered, upoa an average, as the flx< d t indard of Europe. Then are various tan thoda of de- termining the Jincatbs of gold, or GOL 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 ac- curately marked on each ; and, by rubbing the metal under examinati- on, and one or more of the needles, close to each other on a touck-stone, the diherent strokes are compared, in order to judge by the colour which bears the strongest resem- blance to that of the doubtful me- tal. 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 ac- curacy as that of ascertaining the specific gravity of different metals, yet the touch-needles give a more exacl information than might be expected from this superficial assay. Thus, an expert goldsmith will not alt oget her decide from the difference of colour, but will also be gu ded bj the concomitant effect produced on the texture of the metal, when abraded by the touch-stone, name- ly, whetherit be rough, dry, smooth, or greasy. — See Guinea. Several metallic compositions, however, yield marks or impres- sions on the. touch-stone, very near- ly resembling those of pure gold, and which can be distinguished or detected only by another more ac- curate, test. In order to guard against such impositions, it is ne- cessary to apply a drop of aqua- fortis to the suspected metallic strokes on the stone : if they do not disappear, in consequence of tiiis" application, it may be safely con-