Lightning flask experiment. Footage of a high-voltage generator (right) being used to generate plasma discharges from a metal plate (lower left) to a round-bottomed flask (left) containing an electrolyte (salt) solution. The metal plate is placed under the flask and covered with a sheet of white paper. Electric arcs are visible with the lights on, and then in close-up with the lights off. The purple glow is due to ionisation of air molecules to form a plasma.