See TELEGRAPH.

ELECTROTYPE, ELECTRO-METALLURGY, ELECTRO-PLATING, the art of taking exact copies of any object in copper, silver, gold, or other metal, or of covering objects with metallic surfaces, through the energy of voltaic electricity. This beautiful process now so extensively used in the arts for gilding, plating, multiplying plates for engraving, and forming solid articles in gold, silver, and other metals, appears to have been first put in operation by Mr Bessemer of Camden Town, London, to deposit copper on lead castings so as to produce antique heads in relief for mantel-piece ornaments. Mr Jordan, however, in this country, and Professor Jacobi simultaneously on the continent, appear to have been the first to have made the details of the process known to the public. The process itself is a very simple one. The cast, piece of plate, or other object wished to be covered with a metallic coating, after being properly prepared, is immersed in a solution of the metal we wish to be deposited on it, and is connected with the positive or zinc pole of the galvanic battery; the other pole of the battery terminating in a plate of the metal which is in solution, and also immersed in the metallic solution. The galvanic action decomposes the metallic solution; the metal is deposited in an equal layer all over the prepared cast or object, and the acid or agent which held the metal in solution being thus set free, reacts on the plate of metal at the negative pole, dissolving it, and thus keeping up the strength of the solution. Cyanide of potassium has been found by the Messrs Elkington to be the best agent for producing solution of the oxides of silver and of gold.

When the object to be plated or gilded is of metal it requires only to be extremely clean, which is done by boiling it in caustic potash, and then dipping it in aquafortis solution. If, however, it consist of a cast of plaster of Paris, of wood, of wax, &c., its surface must be rendered a conductor of electricity to render it susceptible of the deposition of the metal on it. It is therefore carefully but completely blackened by means of plumbago; but it has been found that dipping the object in a solution of phosphorus has the same effect. For further information see VOLTAIC ELECTRICITY.