Uses, &c. It has been employed by Duportal, Chrestien, Niel, Cullerier, Legrand, and others, as a substitute for mercury, in scrofula, bronchocele, chronic skin diseases, &c.; also as a caustic.—Dose, 1⁄20 gr., dissolved 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 excess of bicarbonate of potassium, 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.’
Gold, Chloride of, and Sodium. AuCl3. NaCl. 2Aq. Syn. Aurochloride of sodium; Sodii aurochloridum. Prep. Auric chloride, 85 parts; chloride of sodium, 16 parts; dissolve in a little distilled water, evaporate until a pellicle forms, then put it aside to crystallise. It forms beautiful orange-coloured rhombic prisms.
Dose, &c. 1⁄20 to 1⁄12 gr., made into a pill with starch or lycopodium, in the same cases in which the terchloride is ordered. Mixed with 2 or 3 times its weight of orris powder, it has been used in frictions on the tongue and gums, and an ointment made with 1 gr. of the salt, mixed with 36 gr. of lard, has been applied to the skin deprived of the epidermis by a blister.
Gold, Cyanide of. AuCy3. Syn. Auric cyanide. Prep. Add a solution of pure cyanide of potassium to a solution of pure auric chloride as long as a precipitate forms, carefully avoiding any excess; wash, and dry the precipitate.
Prop., Uses, &c. The salt is a pale-yellow powder, insoluble in water, but very soluble in a solution of cyanide of potassium, forming the double cyanide of gold and potassium so largely used in the electrotype process. Cyanide of gold is employed to a certain extent in medicine.—Dose, 1⁄12 to 1⁄10 gr., made into a pill, in the usual cases in which gold is administered. The first formula is essentially similar to that of the French Codex.
Gold, Extraction of, by Sodium Amalgam. (Crookes’ Method, Patented.) In the extraction of gold by amalgamation serious difficulties are often occurring through the ‘flouring’ or ‘sickening’ of the mercury employed, and the prevention of the amalgamation by a coating of tarnish on the gold. So much is this the case that losses of from 30 to 60 per cent. of the gold are usually incurred, and, in many cases a still more serious loss of mercury.
When certain minerals, as tellurium compounds, pyrites, &c., occur in the gold ore, the mercury is apt, on trituration, to become subdivided into excessively minute globules, which, owing to their tarnished condition, refuse
to unite, and are consequently washed away, it being almost impossible to separate them from the heavier portions of the ore. This is technically called ‘flouring,’ ‘granulating,’ &c. Besides this, certain of these minerals affect the mercury in another way, that is, by ‘sickening’ it, or causing it to lose its bright surface and fluidity, and prevents its amalgamating with the gold. Besides the inconvenience and loss thus caused, a further loss of gold takes place from the inability of the ordinary mercury to touch or amalgamate tarnished gold, unless it is ground with it, for a more lengthy period than is found practicable in most cases.