LITHIUM (L). In its chemical relations this metal more nearly resembles the alkali metals, potassium and sodium, than any others; but it is a kind of connecting link between that group and tho next, or metals of the alkaline earths (barium, calcium, &c.) Ida existence was first pointed out by Arfwedson (1817), who discovered its oxide when examining a mineral in the laboratory of Berzellus. Its name is derived from Mar, a stone, it having been found in the mineral kingdom only.
The principal sources of lithium are the minerals lepidolite, triphane, and petalite. A table of their percentage composition is given under the respective names in the NAT. HIST. Div. Their formula; is thus represented in Miller's ' Elements of Chemistry :'— Lithium may be obtained in the metallic state by decomposing its chloride with an electric current generated from five or six pairs of Bunsen's nitric acid battery. It is a white metal, harder than potassium or sodium, but softer than lead. It melts at 356° Fahr., and is not volatile when heated to redness. At common temperatures two pieces may be welded together by pressure. It can be drawn into wire, but is less tenacious than lead. Its specific gravity is hence it is the lightest solid body known; it floats even on the surface of naphtha. It rapidly oxidises in the air, and if assisted by heat burns with a brilliant carmine-tinted flame. It decomposes water in a similar manner to sodium, and ignites when placed in strong nitric acid.
The equivalent of lithium is 6.53.
Lithium and oxygen form but one compound, namely :— Oxide of lithium (LO). The mineral from which it is to be extracted is reduced to an almost impalpable powder, and then ignited with twice its weight of quicklime in a silver crucible. The resulting mass is next treated with hydrochloric acid, then with sulphuric acid, and the sulphate of lithia thus formed dissolved out from sulphate of lime by washing with water ; a small quantity of oxalate of ammonia is now added to remove lime that may have been dissolved, and sulphuric acid thrown out of solution by the addition of baryta water. On evaporating the filtered liquid the lithia separates out in grains. If necessary, it may be fused in a, silver crucible, vessels of platinum being rapidly corroded by it.
Hydrate of lithia is not so soluble in water as the hydrates of potash or soda are. It has a strong caustic taste, and turns vegetable reds to blues. In the fused state it is white, transparent, has a crystalline structure, does not deliquesce in the air, and dissolves in water with disengagement of heat.
Lithium and chlorine form :— Chloride of lithium (LCI). It is readily made by dissolving the oxide in hydrochloric acid. On evaporation the solution yields cubical crystals, very soluble, exceedingly deliquescent, and containing four equivalents of water of crystallisation.
Iodide of lithium (LI +6H0) crystallises in needles, and fluoride of lithium in small opaque grains.
Sulphide of lithium is formed in the same way as sulphide of sodium, and much resembles that compound.
Sulphate of lithia (LO,80, + Aq). On evaporating the solution of this salt, obtained as described under oxide of lithium, tabular crystals of the above composition are obtained.
Carbonate of lithia is precipitated when carbonate of am monia is added to a strong solution of chloride of lithium. It may be washed with alcohol, in which it is insoluble. It is slightly soluble in water, the resulting solution having an alkaline reaction. On the application of heat to the dried salt it fuses, and solidifies on cooling to a white transparent mass of pearly lustre and crystalline fracture.
Carbonate of lithia has been recommended to be administered as a solvent for calculi in the bladder. It certainly effects the solution of uric acid most rapidly when triturated with that substance in a mortar containing a little water; but as many calculi do not contain uric acid, and as most of those that do contain it have an external coating of phosphates, it follows that the carbonate of lithia, being an alkaline substance, may do more harm than good if administered indiscriminately.
Double phosphate of lithia and soda.—When phosphate of soda is added to a solution of a lithium salt no precipitate is at first produced ; but on evaporating to dryness the above compound remains as a white powder, almost insoluble in water, and quite insoluble in dilute aqueous solutions of the alkaline phosphates. Before the blowpipe, with carbonate of soda, the double salt fuses to a clear bead, transparent when hot but opaque when cold. A fused specimen examined by Berzelius contained but generally its composition is very variable, probably on account of the two bases, lithia and soda, being capable of replacing each other.
Tests for lithium.—Salts of lithium are readily fusible in the blowpipe flame, imparting to it a carmine red colour, and attacking the platinum wire holder or other platinum vessel in a characteristic corrosive manner. Their presence is further confirmed by forming the carbonate and double phosphate in the way already mentioned.