If two test tubes are filled with acidulated water and then inverted over the wires, the tubes will collect the gas. In a few minutes it will be noticed twice as much hydrogen as oxygen has been generated. If copper or brass electrodes &re used the acid will attack the positive one and a chemical action will take place which will prevent the liberation of any appreciable amount of oxygen, unless an excessive amount of current is passed through. ELECTROPLATING. Electroplating consists of coating bodies with metal by means of an electric current. The proper chemicals, a small tank and a suitable source of current are the only apparatus required. The process may be outlined as follows: Thoroughly clean the article to be electroplated so as to remove all grease and dirt. Attach it to the negative pole of the battery and suspend it in an electrolyte composed of some chemical salt of the metal to be deposited. In order to maintain the strength of the solution, a piece of metal of the kind to be deposited is attached to the positive electrode. A tank for plating small articles such as keys, rings, knives, etc., may be made out of a square glass battery jar by providing it with a wooden moulding fitted around the top edge to support the conductor rods. The rods are made of brass or copper and are threaded at one end so as to be provided with binding posts. The centre rod is the one from which the articles to be plated are suspended. They should be attached to it by means of a thin copper wire. The two outside rods support the anodes. The anodes are sheets of metal of the kind to be deposited which, in the case of copper plating, would be copper, in a case of silver plating silver, nickel for nickel plating, etc. [Illustration: FIG. 186.—Electroplating Tank.] Objects which are to be plated must be free from all traces of dirt or grease or the plating will not be uniform because it will not stick to the dirty spots. Articles made of plaster, wax, etc., which are not conductors of electricity can be plated by first covering with powdered graphite. Articles of iron, steel, zinc and tin cannot be silver or gold plated unless first covered with a thin coating of copper. A single storage cell is an excellent source of current for electroplating. A rheostat should be placed in the circuit so that the current can be regulated. The negative pole should be connected to the centre rod from which the articles are suspended. The positive pole is connected to the rods supporting the anodes. The tank should be filled with electrolyte to within about an inch of the top. The articles to be plated and also the anodes should be completely submerged. The electrolyte used for copper plating is simply a solution of copper sulphate in water. The electrolyte for nickel plating is composed of one part of nickel sulphate dissolved in twenty parts of water to which one part of sodium bisulphate is added.