96 Professors Kirchhoff and Bunsen on Chemical 



wire, freed from every trace of sodium salt by ignition, shows the 

 reaction most visibly on allowing it to stand for a few hours in 

 the air. In the same way the dust which settles from the air 

 in a room, shows the bright line Na a : to render this evident 

 it is only necessary to knock a dusty book, for instance, at a 

 distance of some feet from the flame, when a wonderfully bright 

 flash of the yellow band is seen. 



Lithium. 



The luminous ignited vapour of the lithium compounds gives 

 two sharply defined lines, the one a very weak yellow line, Li /3, 

 and the other a bright red line, Li a. This reaction exceeds in 

 certainty and delicacy all methods hitherto known in analytical 

 chemistry. It is, however, not quite so sensitive as the sodium 

 reaction, only, perhaps, because the eye is more adapted to 

 distinguish yellow than red rays. When 9 milligrammes of 

 carbonate of lithium mixed with excess of milk-sugar was burnt, 

 the reaction was visible in a room of 60 cubic metre capacity. 

 Hence, according to the method already explained, we find that 

 the eye is capable of distinguishing with absolute certainty a 

 quantity of carbonate of lithium less than 10 ~ 000 of a milli- 

 gramme in weight : 0'05 grm. of carbonate of lithium salt, burnt 

 in the same room, was sufficient to enable the ignited air to show 

 the red line Li a for an hour after the combustion had taken 

 place. 



The compounds of lithium with oxygen, iodine, bromine, and 

 chlorine are the most suitable for this peculiar reaction ; still 

 the carbonate, sulphate, and even the phosphate give almost as 

 distinct a reaction. Minerals containing lithium, such as tri- 

 phylline, triphane, petalite, lepidolite, require only to be held in 

 the flame in order to obtain the bright line Li a in the most 

 satisfactory manner. In this way the presence of lithium in 

 many felspars can be directly detected, as, for instance, in the 

 orthoclase from Baveno. The line is only seen for a few mo- 

 ments, directly after the mineral is brought into the flame. In 

 the same way the mica from Altenberg and Penig was found to 

 contain lithium, whereas micas from Miask, Ashaffenburg, 

 Modum, Bengal, Pennsylvania, &c, were found to be free from 

 this metal. In natural silicates which contain only small traces 

 of lithium, this metal is not observed so readily. The examina- 

 tion is then best conducted as follows : — A small portion of the 

 substance is digested and evaporated with hydrofluoric acid or 

 fluoride of ammonium, the residue moistened with sulphuric acid 

 and heated, the dry mass being dissolved in absolute alcohol. 

 The alcoholic extract is then evaporated, the dry mass again dis- 

 solved in alcohol, and the extract allowed to evaporate on a shal- 



