Lithium (sym. Li; equiv. 7.0; sp. gr. 0.5936) is the metallic base of the alkali lithia, and derives its name from the Greek word lithos, 'a stone.' It was discovered by Arfvedson in 1817 in some Swedish minerals; but since the introduction of spectroscopic research it has been found to be widely present in many mineral waters, in the ash of plants, &c. The metal is of a white, silvery appearance, and is much harder than sodium or potassium, but softer than lead. It admits of being welded at ordinary temperatures, and of being drawn out into wire, which, however, is inferior in tenacity to leaden wire. It fuses at 356° (180° C.). It is the lightest of all known solids, its specific gravity being little more than half that of water; it decomposes water at ordinary temperatures. It burns with a brilliant light in oxygen, chlorine, and the vapours of iodine and bromine. It is easily reduced from its chloride by means of a galvanic battery. When lithium is burned in air it forms an oxide, lithia, , along with a trace of a higher oxide. This oxide, when treated with water, yields a hydrate, , having alkaline properties and resembling soda and potash. Lithia forms a series of salts (carbonate, chloride, citrate, &c.) analogous to the potash and soda salts, and all of these, when placed in the flame of a Bunsen burner and examined with the spectroscope, show characteristic red bands by which their presence can always be ascertained.
In medicine the salts of lithia hold a high place as solvents of uric acid. The carbonate and citrate are used for this purpose, and are said to be much more efficient in cases of gout and gravel than the potash salts.