WOLFRAMITE. 179 



tion filtered, and evaporated to crystallization. On 

 igniting the salt in the air, pure yellow tungstic acid is 

 left. 



Or 3 parts of the mineral, very finely powdered, may 

 be mixed with an equal quantity of carbonate of 

 potassa, or f dry carbonate of soda, the mixture 

 heated to redness for half an hour, and the tungstate 

 of potassa which is formed, may be extracted from 

 the cooled mass with water.* 



Pure tungstic acid may be obtained from this 

 solution by boiling, and adding drop by drop hydro- 

 chloric acid or nitric acid, not too dilute, until there is 

 a small excess. From the solution neutralized with 

 hydrochloric acid, tungstate of lime may be pre- 

 cipitated by chloride of calcium which may be decom- 

 posed, after washing, by boiling hydrochloric acid. 



If very finely-powdered tungsten, with an excess 

 of chloride of calcium, is kept in a state of fusion for 

 some time, and the cooled mass dissolved in water, 

 small brilliant octahedral crystals of tungstate of lime 

 are obtained. 



If tungstic acid is gently ignited in a stream- of 

 hydrogen, a blue tungstate of the oxide of tungsten is 

 formed, with a stronger heat, brown oxide, and a still 

 higher temperature, metallic tungsten ^as a gray 

 crystalline powder. 



II. For quantitative analysis, the levigated mineral 

 is digested with a mixture of 4 parts of concentrated 

 hydrochloric acid and 1 part of nitric acid, until it is 

 completely decomposed; the solution is then evapo- 

 rated to dryness, which operation should be finished on 

 the water-bath, the chloride of manganese and sesqui- 



* If the solution is green from the presence of a manganate, it 

 may be decomposed by adding a little ammonia and warming. 

 On dissolving the residual proto-sesqnioxides of iron and manga- 

 nese or. the metallic sulphides obtained as above mentioned in 

 concentrated hydrochloric acid, columbic acid remains behind. 



