618 TUNGSTEN. 



A compound of tungstic oxide and soda, Na + O2WO 2 , of a 

 very singular nature, was discovered by Wohler. It is obtained 

 by adding to fused tungstate of soda as much tungstic acid as 

 it will take up, and exposing the mass at a red heat to hydrogen 

 gas. After dissolving out the neutral undecomposed tungstate 

 by water, the new compound remains in golden yellow scales 

 and regular cubes, possessing the metallic lustre and a striking 

 resemblance to gold. This compound is not decomposed by 

 aqua regia, sulphuric or nitric acid, nor by alkaline solutions, 

 but yields to hydrofluoric acid. It cannot be prepared by 

 uniting soda directly with tungstic oxide. 



Tungstic acid) WO 3 ; 1483 or 118.8 is most conveniently 

 obtained by decomposing the native tungstate of lime, finely 

 pulverised, by hydrochloric acid ; chloride of calcium is dis- 

 solved, and tungstic acid precipitates. Dissolved in ammonia 

 and precipitated again by acids, tungstic acid always forms a 

 compound with the acid employed. It may be obtained in a 

 separate state by heating the tungstate of ammonia to redness. 

 It is an orange yellow powder, which becomes dull green when 

 strongly heated. Its density is 6.12. It is quite insoluble in 

 water or in acids, but dissolves in alkaline solutions. 



Tungstic acid forms both neutral and acid salts with the 

 alkalies. The tungstate of potash is a very soluble salt, which 

 may be obtained in small crystals by the evaporation of its 

 solution. When a little acid is added to the solution, an acid 

 salt precipitates, which is very slightly soluble in water. The 

 tungstate of soda is also very soluble, but may be obtained in 

 good crystals, which contain a large quantity of water of crys- 

 tallization. The acid tungstate of soda is very crystallizable, 

 and soluble in eight parts of water. A combination of tungstic 

 acid with tungstic oxide, WO 2 , WO 3 , is obtained as a fine blue 

 powder when the tungstate of ammonia is heated to redness in 

 a retort, and is also produced in other circumstances. Malaguti 

 is disposed to consider this compound as a distinct acid of 

 tungsten, W 2 O 5 (An. de Ch. et de Ph. Ix. 271.) 



Sulphurets of tungsten. The bisulphuret is prepared by 

 mixing one part of tungsten with six parts of cinnabar, and 

 exposing the mixture, covered with charcoal in a crucible, to a 

 white heat. The tersulphuret is formed by dissolving tungstic 

 acid in an alkaline sulphur et, and precipitating by an acid. It 

 is of a liver-brown colour, and becomes nearly black on drying. 



