Magnesium, a silvery metallic element. It is very light, weighing only two-thirds as much as aluminum. Magnesium is an abundant element of the earth's crust and is always found combined with other elements. Magnesium is malleable and has a relatively high tensile strength. It will dissolve in acids but is insoluble in water. When heated in air, filaments or particles of magnesium will burn readily, giving off an intense white light. Small amounts of magnesium are essential for plant and animal life.

Magnesium is produced commercially from brines and seawater, and from dolomite and other minerals. Brines and sea-water are treated with lime and hydrochloric acid to produce magnesium chloride. Pure magnesium is obtained from the chloride by electrolysis. Dolomite is treated by a silico-thermic process; the dolomite is vaporized in the presence of silicon. Crystals of pure magnesium are formed from the vapor. The United States is the leading producer of magnesium, usually accounting for about 40 per cent of the world's output.

Because of its light weight, magnesium is alloyed with other metals (primarily aluminum, zinc, or manganese) for use in airplane parts, automobile parts, portable tools, luggage, and photographic equipment. Alloys of magnesium are easy to machine and take a good finish.

Magnesium is used as a reducing agent in the refining of titanium, uranium, and other metals. Because magnesium burns brightly, it is used in flares, flashbulbs, and fireworks. Magnesium is also used in some dry-cell batteries and photoengravings.

Among the important compounds of magnesium are its oxide (magnesia), its sulfate (epsom salts), its chloride, and its carbonate (magnesite). Magnesium compounds are used in fertilizers, insulation, medicines, and refractory materials. They are also used in textile processing and papermaking.

Magnesium was first recognized as a separate element by the Scottish chemist Joseph Black in 1755. It was isolated by Humphry Davy, an English chemist, in 1808 and first obtained in pure metallic form in 1831 by Antoine Bussy of France.

Symbol: Mg. Atomic number: 12. Atomic weight: 24.305. Specific gravity: 1.74. Hardness: 2.0. Melting point: 1,200 F. (649 C). Boiling point: 1,994 F. (1,090 C). Magnesium has three natural isotopes, Mg-24, Mg-25, and Mg-26. Magnesium belongs to Group II-A of the Periodic Table and has a valence of +2.