Water can be split into its constituent elements, hydrogen and oxygen, by passing a current through it. This process is called ‘Electrolysis’. Water molecules naturally dissociated into H+ and OH-ions, which are attracted toward the cathode and anode respectively. At the cathode two H+ ions pickup electrons and form Hydrogen gas. At the anode four OH- ions combine and released Oxygen gas, molecular water and four electrons. Press the switch once to start the electrolysis process. The gasses produced, bubble their way to the surface, where they get collected inside the glass tube. This builds up pressure and pushes the water column down. Observe that the volume of Oxygen collected at the anode arm of the glass apparatus is exactly half of that of Hydrogen collected at the cathode arm. This experiment proves that the water is made up of two parts Hydrogen and one part Oxygen.