Sample of pure potassium in a sealed glass tube, c 1810.

UNITED KINGDOM - MAY 24: Pure potassium is a soft, silvery-white metal. It does not occur on its own in nature, because it combines so readily with other substances to form compounds. One is potash (potassium carbonate (K2CO3)), which is found in the ashes of burned plants. In 1807 English chemist Humphry Davy (1778-1829) became the first to make pure potassium by electrolysis. He passed a large current through molten potash in a metal pot, and pure potassium collected around the negative contact. He named the new substance potassium after its source. It is highly reactive, and burns with a lilac flame on contact with water. It is however an essential mineral in the human body as it plays a vital role in the transmission of impulses by nerve cells. (Photo by SSPL/Getty Images)