Gold, Chlorides of

1. Monochloride. AuCl. Syn. Aurous chloride , Pro to chloride of gold . A yellowish-white ma , formed when a solution of trichloride of gold is evaporated to dryne , 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. AuCl 3 . Syn. Auric chloride , Terchloride of gold , Trichloride of gold , Auri chloridum . Prep. Gold, 1 part, di olved by aid of heat in nitro-hydrochloric acid, 8 parts, and evaporated down to near dryne , 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. Uses, . It has been employed by Duportal, Chrestien, Niel, Cullerier, Legrand, and others, as a substitute for mercury, in scrofula, bronchocele, chronic skin diseases, .; also as a caustic.— Dose , 1 ⁄ 20 gr., di olved in distilled water, or made into a pill with starch; or, in frictions on the gums, in quantities of 1 ⁄ 16 to 1 ⁄ 10 gr. Its most important use, however, is as a reagent in photography, large quantities being manufactured for use as a chief agent in toning photographic prints. To some extent it is also used for electro-gilding, and mixed with exce of bicarbonate of pota ium, it forms a good yielding solution for small articles of copper. These are to be first cleaned with dilute nitric acid, and then boiled for some time in the mixture. The above is the salt generally referred to under the name of the ‘chloride of gold,’ or in commerce occasionally as the ‘muriate of gold.’