1902 Encyclopedia > Lithium

Lithium




LITHIUM, one of the rarer metallic elements, intermediate in its character between sodium and barium. It was discovered in 1817 by Arfvedson in the course of an analysis of petalite in Berzelius's laboratory. He recognized the presence in this mineral of a new kind of alkali, which his master subsequently named "lithia," to denote its mineral origin. Lithia, though widely disseminated throughout the mineral world - traces of it being found in almost all alkaliferous silicates, in the soils derived from these, and in many mineral waters - nowhere occurs in any abundance, except in the immense masses of lithia-mica (lepidolite) known to exist in Bohemia. Of other lithia-minerals (all rare) we may name petalite and spodumene (both silicates of alumina and alkalies) and triphylline, a mixed phosphate of ferrous, manganous, and lithium oxides. Only lepidolite comes into consideration as a raw material for the preparation of lithia and its salts. But the extraction from it of pure lithia in any form is difficult. The first step is the disintegration of the finely powdered mineral, which may be effected by means of vitriol and hydrofluoric acid (or vitriol and fluorspar) ; the silicon goes off as gaseous fluoride, the bases remain as sulphates. Or else we may mix the mineral intimately with quicklime, and by very intense heating of the mixture produce a more highly basic silicate, which is readily disintegrable by acids. In either case it is easy to unite all the bases (A1.,03, Fe203, CaO, MgO, Li20, 1i20, Na,0) into a solution of chlorides or sulphates. From it we precipitate successively and remove by filtration (1) the bases not alkalies or Lip by means of excess of milk of lime, and (2) the lime introduced by operation (1) by means of carbonate of ammonia. There results a mixed solution of potash, soda, lithia, and ammonia salt, from which the last-named component is easily removed by evaporation to dryness and ignition. For these very tedious operations Troost has substituted an elegant process which, though admittedly imperfect in the analytic sense, lends itself admirably to manufacturing purposes. He mixes ten parts of the finely powdered mineral with ten parts of carbonate of baryta, five parts of sulphate of baryta, and three parts of sulphate of potash, and melts down the mixture in a powerful wind-furnace. There results a mass which separates spontaneously into a lower layer forming a transparent glass, and an upper one consisting of the sulphates of barium, potassium (sodium), and lithium, the latter representing about three-fourths of the lithia contained in the mineral. By treatment with water the sulphate of baryta is easily removed as an insoluble residue ; the mixed alkaline sulphates are converted into chlorides by decomposition with chloride of barium, and from the dry mixed chlorides approximately pure chloride of lithium is obtained by lixiviation with ether-alcohol, which solvent dissolves only very small proportions of the other chlorides. To purify the crude chloride it is dissolved in water and, by double decomposition with carbonate of soda, converted into a precipitate of carbonate of lithia, Li,CO3, which must be washed with small instalments of water, as it is very appreciably soluble in water. This carbonate of lithia is still contaminated with soda, To purify it fully dissolve it in water with the help of carbonic acid, filter, and evaporate slowly on a water-bath ; the added carbonic acid goes off, and pure cl•bonate of lithia separates out in crystalline crusts (Troost). One litre of pure water dissolves 12 grammes; 1 litre of water kept saturated with carbonic acid dissolves 52.5 grammes of the carbonate. The dry salt fuses at a red heat, but before doing so loses part of its carbonic acid, which, after cooling, it shows no tendency to take up again from the atmosphere. Perfectly acid-free lithia, Li20, can be obtained by heating a mixture of the carbonate and pure charcoal in a platinum crucible, or by heating the nitrate for a long time in a silver one. If the preparation, ultimately, of the hydrate Li201120 = 2LiOH is contemplated, the latter operation may be very materially shortened by addition of metallic copper, which reduces the nitric acid. The anhydrous oxide, when treated with water, dissolves without much evolution of heat as hydrate, LiOH, which, by evaporation (in silver) is easily obtained in the solid form. It melts at a dull red heat, but at even higher temperatures loses no water. It dissolves in water (far less abundantly than soda), with formation of a strongly-alkaline solution, which neutralizes all acids, with formation of salts. Like baryta, it refuses to form acid sulphates or carbonates (the bodies HLiSO, and HLiCO3 exist only in solution), and forms insoluble or almost insoluble salts with carbonic and phosphoric acids (formula; Li2CO3 and Li3PO4); and, last not least, it is not reducible to metal by charcoal at any temperature. Add to this that the highly deliquescent chloride LiC1, when dehydrated by heating, always loses part of its chlorine as HO, and we feel tempted to conclude that in the case of lithium, as in that of barium or magnesium, two equivalents are united into one atom Ti = Li2 = 11. But the specific heat of the metal demands the lesser number.' Metallic Lithium, although long before known to exist, was successfully prepared for the first time in 1855, by Bunsen. He obtained it by fusing the pure chloride in a porcelain crucible, and decomposing the fused salt by a battery of four or six "Bunsens," using a rod of retort charcoal as a positive and a knitting wire as a negative pole. The metal separates out in about pea-sized globules, which stick to the wire, and, thanks to the protecting action of the fused chloride, can be lifted out and collected without reoxidation, under rock-oil. Lithium is a silver-white metal, of only '58 specific gravity (it floats on rock-oil), somewhat softer than lead, and like it susceptible of being pressed into wire. It tarnishes in air, though far less readily than sodium. When thrown upon water it gradually dissolves as hydrate, with evolution of hydrogen, but without fusing. The metal melts at 180°0., and at a somewhat higher temperature takes fire and burns into oxide with a brilliant white flame. Hence the characteristic intensely red colour which a colourless gas flame assumes when a lithium salt is volatilized in it must be a property of something else than the metal itself; perhaps it is the hydroxide LiOH that emits it. The red lithium flame forms a spectrum consisting chiefly of one brilliant red and a somewhat faint orange line.

Lithia-salt solutions behave to general reagents pretty much like those of potash or soda, from which, however, they differ in the following points ; - (1) concentrated solutions are precipitated by carbonate of potash or soda ; (2) even dilute solutions when mixed with phosphate of soda and caustic soda, in the heat more readily, give precipitates of the phosphate PO4Li3, soluble in 2530 parts of plain, and in 3900 parts of ammonia water, more largely in solutions of ammonia salts ; (3) unlike potassium salts, they give no precipitate with chloride of platinum. (W. D.)








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