Potassium (K) is an alkali metal with similar properties to sodium, including a very high reactivity to water and oxygen. Although once primarily (and unknowingly) used for gunpowder, it is overwhelmingly used as an agricultural fertiliser. It is named after potash, from which it was originally isolated.

Elemental potassium is a very soft, light grey metal that can be easily cut with a knife. It does not occur in nature, but rather forms salts, especially with halogens. It is found extensively in plants, from which it can be isolated.

Begin by burning some wood, preferably hardwood, to ash. Scoop this ash into a pot and add water. Boil the water away, leaving a white residue on the sides. This is potassium hydroxide. You can also buy potassium hydroxide at some hardware stores to skip the steps above.

Prepare an electrolysis setup with a heating plate, a 12v car battery, and graphite rods for electrodes (copper and steel will corrode, nickel is an acceptable substitute). The potassium metal will gather on the cathode, connected to the negative terminal of the battery. Heat the potassium hydroxide until it turns white and melts. Place the anode and cathode in the molten metal and remove the heat; the reaction will sustain itself at this point. Remove the electrodes before the molten material solidifies.

Potassium should be stored in mineral oil, as it will react with the atmosphere and with water.