MAGNESIUM

(Mg), chemical element, one of the alkaline-earth metals of main Group IIa of the periodic table, the lightest structural metal. Known originally through compounds such as Epsom salts (the sulfate), magnesia (the oxide), and magnesia alba (the carbonate), the silvery white element itself does not occur free. It was first isolated in 1808 by Sir Humphry Davy, who evaporated the mercury from a magnesium amalgam made by electrolyzing a mixture of moist magnesia and mercuric oxide. A brief treatment of magnesium follows. For full treatment, see Chemical Elements: Alkaline-earth metals. For treatment of the refining and recovery of magnesium, see Industries, Extraction and Processing: Magnesium.