Running electricity through water breaks it apart into separate gases. In this setup, a 9-volt battery sends current through salt water via two pencil tips. Hydrogen gas collects at one pencil as tiny bubbles rise to the surface.

Hydrogen is the lightest gas, so it rises fast when freed from water by electricity. Two copper wires in a beaker of salt water carry current that splits the water, and gas bubbles form at the wires and rise into upside-down test tubes. Changing the salt amount barely affects the speed. But raising the voltage from 1.5V to 6V cuts the collection time from about 14 minutes down to under 5 minutes.

Hydrogen gas is so light that even a small amount trapped inside a soap bubble will lift and drift upward. This project fills soap bubbles with hydrogen gas from a tank, producing bubbles that range from less than 1 mm to over 18 mm across. Smaller bubbles hold so little of this lightweight gas that they produce no visible flame when ignited, while larger ones hold enough to combust visibly — and above 18 mm, combustion turns explosive.

Running electricity through salt water splits the water apart, and the hydrogen gas that forms is visible as bubbles collecting on the copper electrodes. Two copper wires sit in a beaker of salt water and connect to batteries. As current flows, hydrogen gas rises into an inverted test tube placed over one wire. More voltage pushes more current through the solution, so the gas collects faster each time you add another battery.