180 WOLFRAMITE. 



chloride of iron dissolved out, the tungstic acid filtered 

 off, washed with alcohol, dissolved in ammonia, sepa- 

 rated by filtration from the columbic acid, the solution 

 evaporated, the residual ammonia-salt ignited with ac- 

 cess of air, and the tungstic acid weighed. 



The filtrate, containing alcohol, is evaporated to 

 expel the latter, diluted with water, and the oxides of 

 manganese and iron separate as in No. 25. They 

 usually contain a little lime. 



Or the levigated mineral is ignited in a platinum 

 crucible, with 3 parts of carbonate of potassa, the 

 mass dissolved in water, the residual oxides thoroughly 

 washed, the solution neutralized with nitric acid, and 

 the tungstic acid precipitated by nitrate of suboxide 

 of mercury, the free nitric acid being afterwards 

 neutralized with a few drops of ammonia, so that a 

 black precipitate begins to appear. The precipitate is 

 thoroughly washed, a very dilute solution of nitrate of 

 suboxide of mercury being used at last, since other- 

 wise, the precipitate is liable to pass through the filter ; 

 it is then dried and ignited, when pure tungstic acid 

 is left. 



Or the solution of alkaline tungstates is neutralized 

 with nitric acid, the tungstic acid precipitated by 

 acetate of lead, with addition of a few drops of ammo- 

 nia. The washed precipitate is decomposed by diges- 

 tion with sulphide of ammonium, which dissolves all 

 the tungsten as a sulphide. The filtrate from the 

 sulphide of lead is evaporated to dryness, the mass 

 carefully oxidized with nitric acid, and again evapo- 

 rated to dryness and ignited. 



The mixture of the oxides of iron and manganese is 

 dissolved in concentrated hydrochloric acid, which 

 usually leaves undissolved a small quantity of tungstic, 

 columbic, and silicic acids. The two oxides are then 

 separated as in No. 25. 



