Potassium (K), the third element in the alkali metal group, has an atomic number of 19 and an atomic mass of 39.0983 amu. Its melting point and boiling point are 145.9°F (63.28°C) and 1,398.2°F (759°C) respectively. Davy discovered and isolated potassium in 1807, by passing electricity through molten potassium hydroxide to obtain the free metal. Potassium is nearly as abundant as sodium in the earth's crust (21,000 parts per million). Much less potassium than sodium is present in seawater, however, partly because the plant life of the world absorbs potassium in large quantities. The chief minerals of potassium are sylvite, sylvinite, and carnallite.
Almost all the potassium used industrially goes into fertilizer, although small amounts of potassium hydroxide, potassium chlorate, and potassium bromide are important, respectively, in the detergent, explosive, and photography industries. Like sodium, potassium is a vital nutrient for organisms in a variety of ways.