Harper's Electricity Book for Boys

by Joseph H. Adams

Various forms of batteries may be used for this work, and they will be described in detail. For the copper-plating bath it will be necessary to have the anodes of soft, cast, or sheet, copper sufficiently heavy so as not to waste away too quickly. These should be of the proper size to fit within the bath, and either one large one or several small ones may be employed. Stout copper bands should be riveted to the top of the plates, by means of which they may be hung on the bar and so suspended in the solution ([Fig. 10]). The contact-points should be kept clean and bright, so that the current will not meet with any resistance in passing from the rod to the plates.

In [Fig. 9] a complete outfit is shown for any plating process, the difference being only in the solution and anodes. For silver-plating a silver solution and silver anodes are required, while for gold the gold solution and gold anodes will be necessary. In this illustration, A represents the tank, B the battery, C C the anodes, D D D the kathodes, or articles to be plated, E the positive rod, F the negative, and G, H the leading-in and leading-out wires.

There is often a doubt in a boy’s mind as to how the battery is to be connected up to the bath and the articles suspended in it. But there will be no difficulty about it once that the principle of the process is thoroughly understood.

It is well to remember that the electro-plating bath is just the reverse of a battery in its action. The process carried on in a battery is the generation of electricity by the action of the acid on the positive metal, accompanied by the formation of a salt on one of the elements; while in the plating-bath the current from an external source (the battery or dynamo) breaks up the salts in solution and deposits the metal on one of the elements (the kathode).

The remaining element in the solution attacks the salts, in chemical lumps or granular form, and dissolves them to take the place of the exhausted salts; or it attacks the metal anode from which these salts were originally made, and eats off the portion necessary to replace the loss caused by the action of the current in depositing the fruits of this robbery in metallic form upon the article to be plated (the kathode). There should be no confusion in the matter of properly connecting the poles if one remembers that the current is flowing through the battery as well as through the wires and the solution in the tank.

Get clearly in your mind that the current originates in the battery of zinc and carbon or zinc and copper. The zinc is electro-positive to carbon or copper, and at a higher electric level the current flows from the zinc plate inside the cell to the carbon or copper; therefore, the zinc is the positive pole. Now the current, having flowed through the battery from zinc to carbon, or the negative plate, is bound to flow out of the battery from the carbon through the apparatus and back again to the zinc in the battery. Therefore, the wire (G) attached to the carbon of the battery leads a positive or + current, although the carbon is negative; in the battery, and the wire (H) leading out is negative, or -, although it returns the current to the positive pole of the battery.

This is the simple explanation of the circulation of current; but to cut it down still more, always remember to attach the wire from the anode rod to the carbon, or copper, of the battery, and the kathode rod to the zinc of the battery.

In copper-plating this is easy to determine without any regard to wires, because if the wires are misconnected there will be no deposit, and the kathode will turn a dark color. If everything is all right a slight rose-colored blush of copper will appear at once on the kathode. Too little current will make the process a long and tedious one, while too much current will deposit a brown mud on the kathode, which will have to be washed off or removed and the article thoroughly cleansed before a new action is allowed to take place.

With a series of cells it is an easy matter to properly govern the current by cutting out some of the cells or by using resistance-coils (see [chapter vii.] on Electrical Resistance).