Water, or water with mixtures of chemicals, such as sulphate of copper, sulphate of zinc, chloride of nickel, cyanide and nitrate of silver, or uranium and other metallic salts, are good conductors. Oil is a non-conductor, and a current will not pass through it, no matter what the pressure may be. The simplest electro-plating outfit, and the one that a boy should start with, is the sulphate of copper bath, such as is commonly employed by makers of electrotypes, and which is in extensive use by refiners of copper for high-grade electrical use. More than half of the total output of copper in the world is used for electrical work--conductors, switches, and all sorts of parts--and since any impurity in the copper interferes with its conducting powers, it is most important that it should be free from any traces of carbon or arsenic. The electrolytic refining of copper is now a very important process in connection with electric work, and about half a million tons of copper are treated annually to free it from all impurities. Moreover, the gold, silver, and other valuable metals which may be found in copper-ore are thus recovered. The electro-plating, electrotyping, and refining operations are one and the same thing; but in the first instance the object to be plated is left in the solution only a short time or until a blush of copper has been applied. In the second process the wax mold is left in long enough for a thin shell of copper to be deposited; and in the third, the kathodes are immersed until they are heavily coated with copper. To carry on any of these operations it will be necessary to have a small tank or glass jar to hold the plating-bath or electrolyte. Preferably it should be of a square or oblong shape. But a serviceable tank may be constructed from white-wood, pine, or cypress, if proper care is taken in making and water-proofing (Fig. 1). For experimental purposes a tank eighteen inches long, ten inches wide, and twelve inches deep will be quite large enough to use as a copper bath. For silver, nickel, or gold, smaller tanks should be employed, as they contain less liquid, or electrolyte, which in the more valuable metals is expensive.