Electro-metallurgy

—A general term covering the application of electro-chemistry to the industries; it includes: firstly, the reduction of metals from solutions of their ores, a proce too costly for general application, but one useful in the accurate a ay of certain ores, as, for example, of copper; secondly, the copying of types, plaster casts, and metal work by cathode deposits of metal; thirdly, the covering of objects made of baser metal with a thin film of another metal, such as gold, silver, or nickel. All these operations are included under the general term of electro-metallurgy. s In 1836 De La Rue observed that in a Daniell’s cell the copper deposited out of the solution upon the copper plate which served as a pole took the exact impre of the plate, even to the scratches upon it. In 1839, Jacobi, Spencer, and Jordan independently developed out of this fact a method of obtaining, by the electrolysis of copper, impre ions (in reversed relief) of coins, stereotype plates, and ornaments. A further improvement, due to Murray, was the employment of moulds of plaster or wax, coated with a film of plumbago in order to provide a conducting surface upon which the deposit could be made.