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cyanide with a compound of mercury soluble therein, and, if desired, crystallizing it. The material thus obtained is employed in conjunction with caustic alkali, or, what yields better results, with a solution of alkaline cyanide. If the process be performed at the mines without the assistance of the compound previously prepared, the solutions may be formed in the vat itself and in the presence of the ore. Thus, if to an ore lying in a solution of alkaline cyanide a mercury or lead-salt soluble in such solution be added, the gold will pass into solution, displacing the baser metal; or the material may be made directly at the mines by dissolving a mercury or lead compound in alkaline cyanide just as required, employing about two ounces or more of a mercury salt for each ounce of gold. To employ any of the above-described solvent solutions the ore is ground in the usual fashion and placed inside tanks of wood, or if the tanks be of metal the inside and all the metallic connections are coated with paint, or varnished, or otherwise protected, so as to prevent the mercury salt acting upon them, and the mass of ore is washed to free it from acid bodies which would precipitate the mercury ; or the washing may be done simultaneously with the grinding. The alkalinesolvent solution is poured over the ore and allowed to run through. It is again poured over the ore and allowed to rest for several hours, and it is essential that the solution should still be alkaline as it runs from the ore. The ore is next washed, and the solutions and washings are treated in either of the following methods:— The auriferous solution is acidified with sulphuric or other acid and run over iron filings or finely-divided iron, which precipitates the gold ; or, without acidifying, I employ the highly active galvanic couple devised by the chemists Gladstone and Tribe, known as the copper-zinc couple, which may be prepared according to the methods described by them either as a wet or dry couple. The latter I prefer, as it is more suitable for export, and is made by agitating and gently heating a mixture of finely-divided copper with zinc. This highly-reducing agent plays a double office when brought into contact with the auriferous solution, as it not only reduces the gold to the metallic state, but also any excess of mercury that may be in. the solution. The zinc-copper couple acts well even in an acid solution. In the practical working of the process two rules are to be observed : Firstly, the solution is to be alkaline until the gold has displaced the baser metal and the solution has been run off the ore ; and, secondly, the alkalinity during the precipitation by the zinc-copper couple must not be so great as to prevent the precipitations taking place freely. The alkalinity may be regulated in the ordinary way by the addition of a sufficient quantity of an alkali, such as caustic soda, or by practically neutralising by acid. The above process is applicable to ores where the gold is in a metallic state, as well as to those in which it is in chemical composition with other substances. Here I would remark that by the terms " base metal " and " baser metal " I mean to denote mercury, lead, and such other metals as are displaced by metallic gold from their solutions in alkaline cyanide. If and so far as the gold is in the form of a sulphide in the ore the use of metallic salt is not required, as the sulphide of gold will pass into solution in an alkaline cyanide without any other metallic salt being present. Ido not therefore claim the above method, as applied to the purpose of the extraction of gold, when in the form of a sulphide of gold, which may be extracted or got rid of in any way desired, but only so far as the gold is in the shape of metallic gold or compound other than the sulphide; but, subject to the above limitation, I would have it understood that what I claim is,— 1. In the extraction of precious metals from their ores, the employment of a substance formed by the action of a solution of an alkaline cyanide upon a salt or compound of a baser metal soluble therein, so as to produce a displacement of the baser metal by the precious metal, which thereby passes into solution. 2. In the extraction of precious metals from their ores, the employment of a salt or compound of a baser metal in a solution of an alkaline cyanide in which it is soluble, so as to produce a displacement of the baser metal by the precious metal, which thereby passes into solution. 3. In the extraction of precious metals from their ores, dissolving precious metals by means of a solution containing both a cyanide of potassium or sodium and a salt or compound of a baser metal in solution therein, so as to produce a displacement of the baser metal by the precious metal, which thereby passes into solution. 4. The preparation for use in the extraction of precious metals from their ores or solvents, substantially as described. 5. In the extraction of precious metals from their ores, the use of a zinc-copper couple for the precipitation of precious metals from solution. Dated this 24th day of December, 1894. John James Hood. Impeovembnts in Electrolytic Apparatus foe decomposing Chloride op Sodium ob Potassium in Solution, and foe leading away the Pboducts of Decomposition. I, Trevenen James Holland, of Mount Ephraim House, Tunbridge Wells, England, Colonel, C.8., Retired List, Her Majesty ! s Army, do hereby declare the nature of my invention for " Improvements in Electrolytic Apparatus for decomposing Chloride of Sodium or Potassium in Solution, and for leading away the Products of Decomposition," and in what manner the same is to be performed, to be particularly described and ascertained in and by the following statement: — This invention relates to apparatus for decomposing solution of chloride of sodium or chloride of potassium by electrolysis, the object of the invention being directed mainly to rendering the said apparatus continuous in its action. The apparatus to which my present invention is applied consists of a tank of slate or other material suitable for electrolytic purposes, divided transversely into cells or compartments by