Potassium (K) is found in virtually all aerobic cells and is essential to life. It is the third most abundant element in the human body (after calcium and phosphorus) and the eighth most abundant element in the earth’s crust, with a mass percent of 1.8, which means that every 100 grams (g) of the earth’s crust contains 1.8 g of potassium. Potassium is a very reactive alkali metal with an atomic number of 19 and an atomic weight of 39.098 atomic mass units (amu). Its outer “4s” electron is not bound very tightly to the atom, which is therefore easily ionized to K+ (Dean 1985), and potassium reacts readily with chlorine to form the salt potassium chloride. Potassium chloride is a white crystalline solid at room temperature with alternating potassium ions and chloride ions on the lattice sites. Potassium is found primarily in seawater and in natural brines in the form of chloride salt. The minerals mica and feldspar also contain significant quantities of potassium (Dean 1985).

The Discovery of Elemental Potassium

Potassium was first isolated in 1807 by Humphry Davy (1778–1829), who electrolyzed “potash” with a newly invented battery designed to contain a series of voltaic cells, with electrodes made out of zinc and copper plates dipped in a solution of nitrous acid and alum. In Davy’s time, the term “potash” referred to any number of different compounds, including “vitriol of potash” (potassium sulfate), “caustic potash” (potassium hydroxide), and “muriate of potash” (potassium chloride as well as potassium carbonate), the last of which was formed by leaching ashes from a wood fire and evaporating the solution to near dryness in an iron pot.