POTASSIUM, RUBIDIUM, CAESIUM, AND LITHIUM 567 



soluble in cold water, which fact is taken advantage of for separating 

 lithium from potassium and sodium. This salt, Li. 2 CO 3 , is easily con- 

 verted 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 then a strong 

 galvanic current is 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 B B), and the negative pole 

 of an iron wire, on which the metal is 



. FIG. 77. Preparation of lithium by the 



deposited alter the current has passed action of a galvanic current on fused 

 ,. ,, , . , ,. ,, lithium chloride. 



the molten mass for a certain length or 



time. Chlorine is evolved at the positive pole. When a somewhat 

 considerable quantity of the metal has accumulated on the wire it is 

 withdrawn, the metal is collected from it, and the experiment is then 

 carried on as before. Lithium is the lightest of all metals, its specific 

 gravity is 0'59, owing to which it even floats 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 colour- 

 less flame. 40 



Bunsen tried to determine by means of the spectroscope whether 

 any other as yet unknown metals do not occur in different natural 

 products together with lithium, potassium, and sodium, and he soon 

 discovered two new alkali metals showing independent spectra. They 

 are named after the characteristic coloration which they impart to the 



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 sul- 

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

 ration 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. 



