Mercury and gold combine very readily, and yield a white alloy, termed an amalgam, which is used in gilding. In consequence of the readiness with which these metals unite even at ordinary temperatures, mercury is used for the extraction of gold.
As a general.rule, the ductility of gold is much impaired by alloying other metals with h, while its hardness and sonorousness are increased.
Two oxides of gold are known—a protoxide, AuO, and a teroxide, Au°,. Neither of these oxides can be formed by the direct union of the elements, and both of them are reduced by heat. The protoxide is a dark-green or bluish-violet powder. It forms no definite salts. It is obtained by the decomposition of protochlo•ide of gold with a solu tion of potash. The teroxide is a brown powder, which is reduced, not only by heat and light, but by many other reducing agents. It combines. more readily with bases than with acids, and hence has been termed auric acid. We obtain it by mixing a solution of terchloride of gold with magnesia or carbonate of soda, and boiling.
Two chlorides of gold are known, corresponding to the oxides, viz., a protochloride, AuCl, and a terchloride, AuC1,. Of these, the latter is the most important• it is obtained by dissolvin gold in aqua regia, and evaporating the solution to drynues, at a temperature not exceeding 300°, when we obtain this compound, as a deliquescent yel lowish brown or reddish mass, which is soluble in water, alcohol, and ether, with which it forms o•ange-colored solutions.
The chlorides of many of the organic bases form crystallizable double salts with the terehloride of gold, and these compoiinds are often employed to determine, the combin-, iug power of the organic alkali.
Metallic gold in the form of a brown powder is thrown clown from the solution-of the terchloride by most reducing agents. This reducing power of protosulphate of iron is employed in the preparation of chemically pure gold.
bisulphide of gold is obtained in the fo•tn of a black powder by passing a current of sulphureted hydrogen through a cold solution of terchloride of gold. "If finely divided gold be heated with sulphur in contact with carbonate of potash, a double sul phide of gold and potassium is formed; it resists a red heat, and :s very soluble in water; this sulphur salt is used for gilding china, and produces the color known as Burgos luster."—Miller's "Elements of Chemistry," 2d ed., vol. ii, p. 74.
Fulminating ,gold, a compound known to the alchemists, who (Basil Valentine, for example) formed solutions of terchloride of gold, occurs as a green powder, when pre pared by immersing teroxide of gold (or antic acid) in caustic ammonia. By modifying the mode of preparation, we obtain it of a.brownish-yellow color. From Puma's anal• psis of the green powder, it seems to be represented' by the formula 2NH,An0,, the brownish-yellowish powder having a more complicated formula. These powders deto• nate when rubbed, struck, or beaten, or when an electric spark is passtd through them, with a loud sharp report and a faint light, and they yield nitrogen gas, ammonia, and water. None but professed chemists should attempt to prepare them, in consequence of their dangerous explosive character. On one occasion, drahm of fulminating gold introduced into a bottle burst it as the stopper was being turned round, in conse quence of small particles of it having adhered about the mouth, and both the operator's eyes were destroyed by the projected fragments of glass.
The Purple of Cassius is an important gold compound. It derives its name from its having been first described by Andreas Cassius in 1685. See CASSIUS, PURPLE OF.
None of the salts of the oxides of gold are of sufficient importance to require notice in this article.
For the description of Mosaic Gold, see Tug. •