LITHIUM, a metallic element belonging to the group of alkali metals and occurring on the earth only in combination, having been first recognised as a separate element by Arfvedson in 1817, symbol Li, atomic number 3, atomic weight 6.94 (two isotopes 6 and 7). It is widely distributed, although in small proportions, in the mineral, vegetable and animal kingdoms. It is found in several characteristic minerals, e.g., lepidolite or lithia mica and in petalite. The ash of many plants contains an appreciable amount of lithium chloride (tobacco ash about 0.44%), and lithium compounds are present in every organ of the human body and especially the lungs. The term "lithia wa ter" recalls the reputation possessed by lithium salts such as the carbonate or citrate for assisting in the elimination of uric acid in gout and in rheumatoid affections, but the potency of lithium compounds in this respect is much exaggerated since the toler ated dose of lithium does not increase the solubility of uric acid in the blopd serum. Accordingly, lithium salts have been largely superseded in medicine by organic diuretics such as urotropine (hexamine).
Silicates containing lithium, when heated with calcium oxide, carbonate or sulphate, yield the corresponding soluble lithium compounds which can be extracted with water. The extract, freed from heavy metals, contains lithium and other alkali metals; these are converted into carbonates, and lithium carbonate, being only sparingly soluble, is deposited and separated. The carbonate is converted into lithium bromide and chloride ; a mixture of the former salt with 12% of the latter melts at 520° C and is used in the electrolytic production of metallic lithium. The metal has been isolated by electrolysis of a solution of lithium chloride in pyridine, and also by heating lithium hydroxide with magnesium.
Lithium is a silvery white metal tarnishing in moist air. It is harder than the other alkali metals but softer than lead, which it resembles in ductility. Its melting point is variously given 179° to r86° C. It is the lightest of those elements which are solid at the ordinary temperature and it has the highest specific heat, 0-9408, of any solid element. Its spectrum is characterised
by a bright red line (6,708 A.U.) and a fainter orange one A.U.). Lithium decomposes water at the ordinary temperature, liberating hydrogen and forming a caustic solution of lithium hydroxide (lithia). Lithium burns in air or oxygen to the white oxide, Li20, and when heated in nitrogen it furnishes the nitride, Lithium hydride, LiH, produced by direct combination of the metal with hydrogen at bright red heat, is a white, crystalline opalescent mass melting at 68o° C; it undergoes electrolytic decomposition, liberating lithium at the cathode and hydrogen at the anode. Lithium fluoride, LiF, is sparingly soluble, but the chloride, LiC1, is soluble in water and also in many organic solvents such as the alcohols, acetone and pyridine. Lithium hydroxide, LiOH, produced by adding water to the oxide, is a white crystalline mass resembling caustic soda or potash but less hygroscopic ; it dissolves readily in water and absorbs car bon dioxide to form lithium carbonate, Lithium acetyl acetone, obtained in colourless needles by the action of acetylacetone on aqueous lithium hydroxide, is soluble in wa ter or alcohol. Lithium phosphate, is very sparingly soluble in water and less so in alkaline solutions, and is sometimes employed in the estimation of lithium ; for this purpose the fluoride is also used and the solubility of lithium chloride in amyl alcohol serves to separate lithium from the other alkali metals. Lithium fluoride and fluophosphate are used in ceramics in the production of enamels. The lithium salts employed in medicine are the benzoate, bromide, carbonate, citrate, hippurate, iodide, salicylate, sulphate and hydrogen tartrate. Lithii citras effer vescens is a mixture of citric acid, lithium citrate and sodium bicarbonate. Since in large or concentrated doses lithium salts cause unpleasant symptoms, they should be freely diluted.