156 ZIRCON. 



acid is driven off by heat from the residue, which is 

 completely soluble on being digested in water, if the 

 decomposition was complete. The alumina is precipi- 

 tated by carbonate of ammonia. The filtered liquid 

 is then evaporated to dry ness, placed in a platinum 

 crucible and carefully raised to a red heat with the 

 precaution that nothing is thrown out from the crucible 

 by the decomposition of the sulphate of ammonia. A 

 small piece of carbonate of ammonia is held in the 

 crucible and allowed to evaporate slowly. The residue 

 is weighed as neutral sulphate of soda. 



86. ZIRCON. 

 Zr0 2 , Si0 2 . 



A carefully-selected specimen of zircon which has 

 been ignited, and thus deprived of color, is levigated 

 to a very fine powder, and fused, at a good heat, in a 

 platinum crucible, with 4 parts of anhydrous carbonate 

 of soda. The mass is digested with water, which dis- 

 solves the silicate of soda, and leaves a silicate of soda 

 and zirconia as a crystalline powder; this is washed 

 and decomposed by digestion with concentrated hydro- 

 chloric acid. The mass is dried up in a water-bath, 

 treated with water containing hydrochloric acid, the 

 silica filtered offj and the zirconia precipitated by 

 ammonia. 



If the zirconia contain any iron, the precipitate is 

 digested with oxalic acid, which dissolves the sesqui- 

 oxide of iron, leaving oxalate of zirconia, at least the 

 greater part, undissolved. 



Or the precipitate may be treated with sulphide 

 of ammonium, to convert the iron into sulphide, 

 the solution once more decanted, and the black 

 precipitate treated with solution of sulphurous acid, 



