to leaves by hammering it between thin animal membrane. Its preparation constitutes the trade of the goldbeater. These leaves are only 1⁄28200 of an inch in thickness. Gilt silver is hammered in the same way, but the leaves are thicker. The latter is called party gold. Both are used by artists and gilders, and by druggists to gild pills, &c.
Gold, Powdered. Syn. Divided gold, Gilding powder, Gold bronze, Gold colour; Auri pulvis. Prep. Gold, 1 part; mercury, 7 parts; form an amalgam, and expose it to heat until all the mercury is volatilised; or the mercury may be dissolved out with hot nitric acid. In either case the residuum is to be powdered, washed, and dried. If the quantity operated on is considerable, the process should be so conducted as to save the mercury.
From gold leaf and honey ground together, as the last, by means of a stone and muller. This is the plan commonly adopted in the small way by artists.
From a solution of gold in aqua regia precipitated by protosulphate of iron, the resulting powder being washed, dried, and gently heated, This gives pure gold.
Uses, &c. Powdered gold is employed in gilding by japanners and by artists. It is either sold in powder (gold in powder), or made up into shells (gold in shells). Its use in medicine has been already noticed.
Gold, Standard. The standard gold of this country is an alloy of pure gold, 11 parts, with pure copper, 1 part. Formerly the alloy consisted partly of silver, as found in some of the older coins now in circulation. It is often spoken of as 22 carats fine.
Gold, Chlorides of:
1. Monochloride. AuCl. Syn. Aurous chloride, Protochloride of gold. A yellowish-white mass, formed when a solution of trichloride of gold is evaporated to dryness, and the residuum is exposed to a heat of about 440° Fahr., until fumes of chlorine cease to be evolved. It is insoluble in water, which decomposes it, slowly when cold, but rapidly by the aid of heat, into metallic gold and the trichloride.
2. Trichloride. AuCl3. Syn. Auric chloride, Terchloride of gold, Trichloride of gold, Auri chloridum. Prep. Gold, 1 part, dissolved by aid of heat in nitro-hydrochloric acid, 8 parts, and evaporated down to near dryness, and allowed to crystallise.
Prop. Orange-red crystalline needles, or ruby-red prismatic crystals; deliquescent; soluble in water, ether, and alcohol, forming a deep-yellow solution; at the heat of 500° Fahr. it suffers decomposition, chlorine being given off and pure gold left behind. It is reduced by ferrous sulphate, oxalic, sulphurous, formic and phosphorous acids, as well as by most of the metals, to metallic gold. It combines with several of the metallic chlorides, forming a series of double salts, which are mostly yellow when in crystals, and red when deprived of water.