Potassium was first isolated in 1807 by Humphry Davy, who electrolysed molten potash and watched droplets of a soft metal skitter and ignite on the surface, the first metal won by electricity. The English name comes from potash, the potassium carbonate leached from wood ashes in iron pots. The symbol K derives from the Latin kalium, itself from the Arabic al-qali, the calcined ashes, the same root that gives the word alkali. Potassium is essential to life, its ions carrying nerve impulses and regulating the water balance of cells, and the great bulk of the potash mined today, chiefly potassium chloride, is spread as fertiliser to supply this nutrient to crops. Potassium carries a small natural radioactivity: about one atom in ten thousand is the isotope potassium-40, present in every banana and in the human body itself, a fact popularised as the banana equivalent dose, a rough, informal unit sometimes used to put small radiation exposures in perspective.
Potash was also economically important early in American history: producing and exporting potash and pearl ash, refined from wood ash, was one of the young United States' first industrial exports, and in 1790 the first patent ever granted by the US government went to Samuel Hopkins for an improved method of making potash.