A common metallic element of the alkali group, in nature
   always occuring combined, as in common salt, in albite, etc. It is
   isolated as a soft, waxy, white, unstable metal, so readily oxidized
   that it combines violently with water, and to be preserved must be kept
   under petroleum or some similar liquid. Sodium is used combined in many
   salts, in the free state as a reducer, and as a means of obtaining
   other metals (as magnesium and aluminium) is an important commercial
   product. Symbol Na (Natrium). Atomic weight 23. Specific gravity 0.97.