Some of the simplest experiments in chemistry use common household chemicals. The generation of hydrogen gas and oxygen gas by the electrolysis of water requires no special chemicals or apparatus. Water breaks down into the two types of atoms that make up the compound water. By applying a battery voltage to salt water, the electrical force breaks down water into hydrogen and oxygen.
Mix a quart of water with enough salt to make a saturated solution. Stir constantly until no more salt will dissolve and pour the solution into a reservoir. Fill both test tubes with this solution also. The salt water will be the source of water for the experiment. The salt added is so that the solution is conductive, because the conductivity of pure water is extremely low.
Connect the wires to the terminals of the battery, one to each terminal. Make sure they don't touch each other or they will short out the battery. Turn the test tubes upside down in the reservoir and secure them with the holders. Make sure that there is no air trapped in the test tubes as you turn them over.
Position the wires such that one wire is beneath the edge of each test tube and stick up into the tube by a few centimeters.
Observe as bubbles start to form on the wires under each test tube. Also note that as the bubbles continue to form and float to the top, the gas in the top of the tube forces the water out of the bottom of the test tube. Hydrogen generation occurs under the tube that has the wire connected to the negative pole of the battery. Oxygen generation occurs under the tube that has a wire connected to the positive side of the battery. Given enough time to form a measurable amount of gas, you will note that there is twice the amount of hydrogen generated than oxygen. This is because there are two atoms of hydrogen for every atom of oxygen in water.