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Electroplating

The deposition by electrolysis of a coating of metal upon a conducting surface. The simplest system makes the object to be plated the negative electrode or plate in a galvanic couple. Thus a spoon or other object may be connected by a wire to a plate of zinc. A porous cup is placed inside a battery jar. The spoon is placed in the porous cup and the zinc outside it. A solution of copper sulphate is placed in the porous cup, and water with a little sodium or zinc sulphate dissolved in it, outside. A current starts through the couple, and copper is deposited on the spoon.

A less primitive way is to use a separate battery as the source of current; to connect to the positive plate by a wire the object to be plated, and a plate of copper, silver, nickel or other metal to the other pole of the battery. On immersing both object and plate (anode) in a bath of proper solution the object will become plated.

In general the anode is of the same material as the metal to be deposited, and dissolving keeps up the strength of the bath. There are a great many points of technicality involved which cannot be given here. The surface of the immersed object must be conductive. If not a fine wire network stretched over it will gradually fill up in the bath and give a matrix. More generally the surface is made conductive by being brushed over with plumbago. This may be followed by a dusting of iron dust, followed by immersion in solution ot copper sulphate. This has the effect of depositing metallic copper over the surface as a starter for the final coat.

Attention must be paid to the perfect cleanliness of the objects, to the condition of the bath, purity of anodes and current density.

Voltaic batteries are largely used for the current as well as special low resistance dynamos. Thermo-electric batteries are also used to some extent but not generally.