POTASSIUM, EUBIDIUM, CESIUM, AND LITHIUM 575 



and potassium ; but the carbonate is sparingly soluble in cold water, 

 which fact is taken advantage of for separating lithium from potassium 

 and sodium. This salt, Li 2 CO 5 , is easily converted into the other 

 compounds of lithium. Thus, for instance, the lithium hydroxide, 

 LiHO, is obtained in exactly the same way as caustic soda, by the 

 action of lime on the carbonate, and it is soluble in water and 

 crystallises (from its solution in alcohol) as LiHO,H 2 O. Metallic 

 lithium is obtained by the action of a galvanic current on fused 

 lithium chloride ; for this purpose a cast-iron crucible, furnished 

 with a stout cover, is filled with lithium chloride, heated until the 

 latter fuses, and a strong galvanic current is then passed through the 

 molten mass. The positive pole (fig. 77) 

 consists of a dense carbon rod C (sur- 

 rounded by a porcelain tube P fixed in an 

 iron tube BB), and the negative pole of 

 an iron wire, on which the metal is 

 deposited after the current has passed 

 through the molten mass for a certain 

 length of time. Chlorine is evolved at the 

 positive pole. When a somewhat consider- 

 able quantity of the metal has accumulated 



., . ... ..IT xi i i FIG. 77. Preparation of lithium by the 



On the Wire it IS Withdrawn, the metal IS action of a galvanic current on fused 



collected from it, and the experiment is 



then carried on as before. 39 bis Lithium is the lightest of all metals, its 

 specific gravity is 0*59, owing to which it floats even on naphtha ; it 

 melts at 180, but does not volatilise at a red heat. Its appearance 

 recalls that of sodium, and, like it, it has a yellow tint. At 200 

 it burns in air with a very bright flame, forming lithium oxide. In 

 decomposing water it does not ignite the hydrogen. The characteristic 

 test for lithium compounds is the red coloration which they impart to 

 a colourless flame. 40 



Bunsen in 1860 tried to determine by means of the spectroscope 



59 bb Guntz (1898) recommends adding KC1 to the LiCl in preparing Ll by this 

 method, and to act with a current of 10 amperes at 20 volts, and not to heat above 450, 

 BO as to avoid the formation of Li 2 Cl. 



40 In determining the presence of lithium in a given compound, it is best to treat the 

 material under investigation with acid (in the case of mineral silicon compounds hydro- 

 fluoric acid must be taken), and to treat the residue with sulphuric acid, evaporate to 

 dryness, and extract with alcohol, which dissolves a certain amount of the lithium 

 sulphate. It is easy to discover lithium in such an alcoholic solution by means of the 

 coloration imparted to the flame on burning it, and in case of doubt by investigating its 

 light in a spectroscope, because lithium gives a red line, which is very characteristic and 

 is found as a dark line in the solar spectrum. Lithium was first discovered in 1817 in 

 petolite by Arfvedson. 



