On the periodic table, potassium is the element Humphry Davy first isolated in 1807. Davy used electrolysis of molten potash, separating potassium from oxygen-containing compounds and obtaining the previously unknown metal. The experiment made potassium the first metal isolated by electrolysis.
Potassium is an alkali metal with atomic number 19 and symbol K. It is soft, silvery, and extremely reactive. In air it can tarnish quickly, and in water it reacts vigorously, producing potassium hydroxide and hydrogen; the heat can ignite the hydrogen. For safety, potassium is stored under mineral oil or an inert atmosphere.
Davy later used electrolysis to isolate several other elements, including sodium, calcium, strontium, barium, and magnesium, although the history of some discoveries involved earlier or competing observations. Potassium should not be confused with sodium, which Davy isolated shortly afterward in 1807. Their similar chemistry reflects their shared position in group 1, but potassium has the higher atomic number and is generally more reactive.