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Updated: May 2, 2025
The sulphurisation of the gold gives no ocular manifestation by change of colour or perceptible increase of weight, as in the case of the formation of sulphides of silver, lead and other metals, on account of the extremely superficial action of the sulphur, and hence probably the existence of the gold sulphide escaped detection by chemists.
The operations of the Government assay office in Frankfort during the last year have developed the fact that gold, platinum, palladium, and selenium are found in old silver coins and also in ores which were formerly supposed to be nearly pure sulphides and oxides of lead and silver.
Skey also showed by very carefully conducted experiments that the metallic sulphides are not only better conductors of electricity than has hitherto been supposed, but that when paired they were capable of exhibiting strong electro-motive power.
When zinc amalgam is used, alkalies would, of course, be detrimental. When no other water than that from the mine is available, difficulties often arise owing to the impurities it contains. These are various, but among the most common are the soluble sulphates, and sometimes free sulphuric acid evolved by the oxidisation of metallic sulphides.
In the presence of this difficulty, do one of two things; either utilise or neutralise. In certain cases, I recommend the former. Sometime since I was treating, for gold extraction, material from a mine which was very complex in character, and for which I coined the term "polysynthetic." This contained about half a dozen different sulphides.
There will be old Wilson, with his diamonds and palaver, expatiating on the country and the mines; and Blaisdell, with that dignified way of his, talking of nitrates and sulphides, and so many milligrams equaling so many grains troy, and so many gramestons in so many pounds avoirdupois, and all that razzle-dazzle, and Rivers, not saying much of anything, but smiling, and calculating how many thousands he is going to put in his own pockets."
The result would be carbonates and sulphides of metals, earth, alkalies, and free quartz, but quartz and sulphides of the metals are soluble in solutions of carbonates and sulphides of the earths and alkalies, and the essential constituents of the ore might, therefore, readily be conveyed to openings in the vein where they would have been deposited on relief of pressure and diminution of temperature.
Boil the finely divided substance with about one-eighth its bulk of pure hydrochloric acid; add from time to time potassic chlorate until the solids are reduced to a straw-yellow fluid. Treat this with excess of bisulphate of sodium, then saturate with sulphuretted hydrogen until metals are thrown down as sulphides. These may be collected and tested.
Closely allied to this subject is the investigation of the mode in which certain metals are reduced from their solutions by metallic sulphides, or, in common language, the influence which the presence of such substances as mundic and galena may exercise in effecting the deposit of pure metals, such as gold, in mineral lodes.
In this process the powdered ore is allowed to fall in a shower from a considerable height, through the centre of a vertical shaft up which a flame ascends; the powdered ore in falling through the flame is heated to an oxidising temperature, and the sulphides are thus depleted of their sulphur and become oxides.
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