Potassium, a silvery-white, metallic chemical element. Chemically, it is classed as an alkali metal, along with sodium, lithium, rubidium, and cesium. Potassium is one of the lightest metals, and at room temperature is so soft that it can be cut with a knife. It is extremely active chemically and is similar, in many respects, to sodium. When placed in water, potassium reacts violently, producing potassium hydroxide and hydrogen. The chemical reaction generates enough heat to ignite the hydrogen produced. If exposed to the halogen elements, such as fluorine, potassium explodes. In chemical laboratories, potassium is kept covered with a layer of kerosene, in glass bottles.

Potassium is the seventh most abundant element on earth, accounting for about 2.6 per cent of the earth's crust. Because of its extreme reactivity, however, potassium is never found free in nature. It is found in a variety of minerals. The two leading commercial sources of potassium are the minerals sylvite and carnallite, both of which contain potassium chloride. Potassium is also present in sea water and in brines. Potassium is necessary to living cells and is found in all plants and animals.

The major producers of potassium are Canada, Belarus, Germany, France, and the United States. Together, they produce about 90 per cent of the world's output of potassium salts.

Potassium is prepared from potassium chloride. The chloride is melted and fed into an exchange column. As the melted potassium chloride flows down the column, sodium vapor is allowed to rise from the bottom of the column. The sodium combines with the chlorine, forming sodium chloride and releasing pure metallic potassium. Metallic potassium is used in the preparation of potassium peroxide.

Metallic potassium was first prepared, in 1807, by Humphry Davy. He isolated it from potassium hydroxide by using an electric current.

Potassium Compounds

Potassium is used primarily in its various compounds. Potash is a term loosely applied to potassium when it is combined in several of its compounds. The most important potassium compound is potassium chloride. It is used primarily in fertilizers, and is sometimes called muriate of potash. Potassium hydroxide, or caustic potash, is a type of lye. It is used in making various other potassium compounds, in soap production, and as a bleaching agent.

Potassium nitrate, or saltpeter, is used in fireworks, in explosives, and as an oxidizer in rocket propellants. Potassium carbonate is used in shampoos, certain types of glass, and ceramics, and for dyeing and bleaching textiles. Potassium peroxide is used in gas masks to remove harmful substances and to generate oxygen.

Symbol: K (from the Latin name kalium). Atomic number: 19. Atomic weight: 39.0983. Specific gravity: .86. Hardness: .5. Melting point: 146.66 F. (63.7 C.). Boiling point: 1,425 F. (774 C.). Potassium has two stable isotopes: K-39 and K-41. Potassium belongs to Group IA of the Periodic Table and has a valence of + 1.