564 MINERALOGY 



acidified with HC1, evaporated to dryness on the bath in* a small 

 porcelain dish ; boil the residue with 2 cc. of water, cool, dilute 

 with 2 cc. alcohol and filter through a small filter ; to the filtrate 

 one drop of dilute HC1 is added and the potassium is precipi- 

 tated as K 2 PtCl 6 . 



Sodium, Na. Atomic weight 23. Fusing point, 95.6 C. 



a. Sodium compounds when heated in the O. F. yield an intense 

 yellow flame. This test is so delicate that great care and judgment 

 must be exercised in its use, before deciding that sodium is present 

 in sufficient amount to be considered as a constituent of the min- 

 eral. The flame must therefore be both strong and persistent. 



Illustration. Heat some powdered halite, NaCl, on platinum 

 wire. 



Lithium, Li. Atomic weight, 6.93. Fusing point, 186 C. 



a. Most lithium compounds when Heated in the O. F. either on 

 wire or in the forceps yield a very bright crimson flame. Stron- 

 tium is another metal that yields a crimson flame, very much like 

 that of lithium, and care must be taken not to confound the two. 

 Sodium generally occurs with lithium ; after heating for some time 

 the yellow flame of sodium may mask the lithium flame. If the 

 fused powder or fragment is momentarily removed from the flame, 

 then brought in contact with it again slowly, the pure crimson 

 flame of lithium will appear, first unmixed with yellow ; as lithium 

 salts are more volatile than sodium salts they color the flame first. 



Illustration. Heat a small fragment of lepidolite in the for- 

 ceps, in O. F., observe the crimson flame of lithium, and finally also 

 the yellow flame of sodium. 



6. Some minerals, especially silicates, do not readily yield a 

 lithium flame when heated alone ; before deciding that a mineral 

 does not contain lithium, it should be mixed with 4 parts of lithium 

 flux ; the mixture is fused on wire in the Bunsen burner flame. 



Illustration. Powdered spodumene, LiAl(Si0 3 ) 2 , is mixed to 

 a stiff paste with water and 4 parts of lithium flux and fused on 

 wire in the Bunsen burner flame. After the flux has had time to 

 decompose the silicate the crimson flame of lithium will appear. 



Rubidium, Rb. Atomic weight, 85.45. Fusing point, 28.5 C. 



Caesium, Cs. Atomic weight, 132.1. Fusing point, 26.37 C. 



Both very rare metals ; they occur in small quantities in lepidolite, 

 and some sphalerites. They may be separated from other metals 

 and silicates, as is potassium ; the precipitate is tested with the 

 spectroscope. 



