AUROUS COMPOUNDS. 6/5 



Gold is the only metal of a yellow colour. When pure, it is 

 more malleable than any other metal, and nearly as soft as lead. 

 Its ductility appears to have scarcely a limit. A single grain of 

 gold has been drawn into a wire 500 feet in length, and this 

 metal is beaten out into leaves which have not more than 

 l-200,000dth of an inch of thickness. The coating of gold on 

 gilt silver wire is still thinner. When very thin, gold is trans- 

 parent, thin gold leaf allowing a green light to pass through it. 

 The point of fusion of this metal is 2016; it contracts con- 

 siderably upon becoming solid. The density of gold varies 

 from 19.4 to 19.65, according as it has been more or less com- 

 pressed. It does not oxidate or tarnish in air, at the usual 

 temperature, nor when strongly ignited. But this and the 

 other noble metals are dissipated and partly oxidated, when a 

 powerful electric charge is sent through them in thin, leaves. 

 Gold is oxidated in contact with vitrifiable fluxes, and communi- 

 cates to them a ruby colour. It is not dissolved by nitric, 

 hydrochloric or sulphuric acid, nor indeed by any single acid. 

 It is Beted upon by chlorine, which converts it into perchloride, 

 and by acid mixtures, such as aqua regia, which evolve chlorine. 

 It combines in two proportions with oxygen, forming the 

 two oxides Au 2 O and Au 2 O 3 , neither of which combines with 

 acids. 



Oxide of gold, Aurous oxide, Au 2 O, 2586 or 20J.21. This 

 oxide is obtained by decomposing the corresponding chloride of 

 gold, by a cold solution of potash, as a green powder. It is 

 partly dissolved by the alkali, and soon begins to undergo de- 

 composition, being resolved into the higher oxide and metallic 

 gold. The latter forms a thin film upon the sides of the vessel, 

 which is green by transmitted light, quite like gold leaf. 



Chloride of gold, Aurous chloride, Au 2 Cl, is obtained by eva- 

 porating a solution of the perchloride to dryness, and heating 

 the powder thus obtained by a sand bath, retaining it about the 

 temperature of melting tin and constantly stirring it, so long as 

 chlorine is evolved. It is a white saline mass having a tinge of 

 yellow, which is quite insoluble in water. In the dry state, it is 

 permanent, but in contact with water it gradually undergoes de- 

 composition, and is converted into gold and the perchloride. 

 This change takes place almost instantaneously at the boiling 

 temperature. 



A corresponding aurous sulphur et is formed when sulphuretted 



