Aurous sulphide

Aurous sulphide, Au2S.—The pure sulphide can be prepared7 by saturation of a solution of potassium aurocyanide with hydrogen sulphide, and precipitation of the salt by acidifying the solution with hydrochloric acid. It is not produced by the action of hydrogen sulphide on a hot solution of auric chloride, as supposed by Berzelius.8 The moist substance has- a steel-grey colour when dried, it becomes brownish black. When freshly prepared, the sulphide dissolves in water to a colloidal solution, from which it is reprecipitated by addition of hydrochloric acid. The sulphide is unaffected by dilute acids, but is decomposed by powerful oxidizers such as aqua regia and chlorine. It is readily dissolved by solutions of polysulphides,0 and less readily by those of monosulphides. It also dissolves in a solution of potassium... 

Atoioioltv of gold, 174 AurioaiuiTdi 174 ohloridok 174 H iodide, 174 oid, 174 sulphide, 174 Aurous ohlorids, 174 iodi 174 oxide, 174 sulphide, 174 Compounds of gold, 174 Fotassioeotsie, 174 fltaiu, 34. 

Aurous cyanide forms yellow, microscopic laminae, very slightly soluble in Water. It is more stable than aurous iodide, but at red heat is decomposed into gold and cyanogen. Its insolubility renders it immune to the action of dilute acids and hydrogen sulphide, but solutions of ammonia, potassium hydroxide, ammonium sulphide, and sodium thiosulphate dissolve it, probably forming complex derivatives. In aurous cyanide the tendency to form complex compounds is much more marked than in the corresponding chloride, bromide, and iodide.3 Its interaction with potassium ferrocyanide has been studied by Beutel.4... 

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