(English, soda; Medieval Latin, sodanum, headache remedy) Long recognized in compounds,sodium was first isolated by Davy in 1807 by electrolysis of caustic soda.

Sodium is present in fair abundance in the sun and stars. The D lines of sodium areamong the most prominent in the solar spectrum. Sodium is the fourth most abundant elementon earth, comprising about 2.6% of the earth's crust; it is the most abundant of thealkali group of metals.

It is now obtained commercially by the electrolysis of absolutely dry fused sodiumchloride. This method is much cheaper than that of electrolyzing sodium hydroxide, as wasused several years ago.