Electricity & Magnetism

Liquid Litmus

This exhibit is a glass tank containing a salt solution and some special dyes. On either side of the tank are electrodes that cause electrically charged particles in the solution, called ions, to move towards the electrodes, depending on whether they carry a negative or positive charge. Bubbles can be observed being released on the surface of the electrodes. The electricity is breaking water apart and releasing hydrogen and oxygen. The dyes change color depending on whether the solution is acidic or basic. Near the positively charged electrode, the liquid becomes acidic and makes the dyes turn yellow. Near negatively charged electrode, the liquid becomes basic (or alkaline), so it turns purple. A magnet held on the surface of the glass near where yellow and purple are mixing causes the fluid to begin to swirl, because when electrically charged particles move in a magnetic field, they move in curved paths.