Chapter XI
GALVANISM AND ELECTRO-PLATING
Simple Electro-plating
To the average boy experimenter, electro-plating is one of the most fascinating of the uses to which electricity may be put. In scientific language the process is known as electrolysis, and involves the separation of a chemical compound into its constituent parts or elements by the action of an electric current and the proper apparatus. Electrolysis cannot take place, however, unless the liquid in the tank, commonly called the electrolyte (no relation to electric light), is a conductor.
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.
Obtain a clear plank twelve inches wide, well seasoned, and free from knots or sappy places. Cut two sides twenty inches long and two ends eight inches long. With chisel, saw, and plane shape the ends of the side planks as shown at [Fig. 2]; or if there is a mill at hand it would be well to have the ends cut with a buzz-saw, thus insuring that they will be accurate and fit snugly. Screw-holes are bored with a gimlet-bit, and countersunk, so that screws will pass freely through them and take hold in the edges of the boards. Screws and plenty of white-lead, or asphaltum varnish, should be used on these points to make them water-tight; then the lower edge of the frame is prepared for the bottom board. Turn the tank bottom up, and, with a fat steel-wire nail and a hammer, dent a groove at the middle of the edge of the planks all around, as shown in [Fig. 3]. It will not do to cut this out with a gouge-chisel, because it is intended that the wood should swell out again if necessary. The object of driving the wood down is to form a valley into which a line of cotton string-wicking, soaked in asphaltum varnish or imbedded in white-lead, may be laid. This should be done (as shown in [Fig. 4]) before the bottom is screwed on, so that afterwards (in the event of the joint leaking) the wood will swell and force the wicking out, and thus properly close the fissure.
The bottom board should be provided with holes all around the edge, not more than two inches apart, through which screws can be driven into the lower edge of the tank. Treat the wood, both in and outside, to several successive coats of asphaltum varnish, and as a result you will have a tank resembling [Fig. 1].
Two shallow grooves are to be cut in the top of each end board of the tank, for the cross-bars to fit in immovably. These bars should be about three inches apart; and the ones holding the anodes, or flat copper plates, should be close to one side, leaving plenty of room for objects of various sizes to be properly immersed.