WULFENITE. 181 



97. SCHEELITE. 

 CaO, W0 3 . 



The mineral, very finely powdered, is digested with 

 concentrated nitric acid, the mass evaporated nearly to 

 dry ness, mixed with alcohol, and filtered. The resi- 

 dual yellow tungstic acid is washed with alcohol, 

 ignited and weighed. The alcohol is expelled from 

 the solution by evaporation, the latter neutralized with 

 ammonia, and the lime precipitated by oxalate of am- 

 monia. 



98. WULFENITE (MOLYBDATE OF LEAD). 

 PbO, Mo0 3 . 



Several methods are employed for obtaining the 

 molybdic acid from this mineral. 



I. In order to remove the carbonates of zinc and of 

 protoxide of iron, the finely-powdered ore is treated 

 for some time, and frequently agitated, with dilute 

 hydrochloric acid; it is afterwards washed by decan- 

 tation, and decomposed by boiling concentrated hydro- 

 chloric acid. The mixture is then evaporated to 

 dryness, the residue powdered, and digested with am- 

 monia. Insoluble basic chloride of lead and molybdate 

 of ammonia are thus formed; the solution containing 

 the latter is filtered off, and evaporated to crystallization. 

 The mother-liquor from the crystals, or even the entire 

 solution, may be mixed with nitric acid, evaporated to 

 dryness, and the residue extracted with water, when 

 the mol3 T bdic acid is left. 



II. The powdered ore is fused with an equal weight 

 of dry carbonate of soda, the fused mass poured out, 

 taking care to separate it as far as possible from the 

 oxide of lead which has settled at the bottom, and dis- 



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