56 SPHALERITE. 



in this mineral. The precipitatate, after being filtered 

 off and washed, is treated as in No. 36. 



The first filtrate, which contains the zinc and gene- 

 rally a little iron, is heated to ebullition, and mixed, 

 first with some hypochlorite of soda to peroxidize the 

 iron, then with excess of ammonia, until all the oxide 

 of zinc is redissolved, and the sesquioxide of iron pre- 

 cipitated ; the latter is then washed and ignited. It 

 cannot be obtained by this method perfectly free from 

 oxide of zinc. 



From the filtrate, the zinc is precipitated by sulphide 

 of ammonium. The precipitate should not be filtered 

 off until it has separated from the liquid; it is washed 

 with water containing a little sulphide of ammonium, 

 and digested (together with the filter), while yet moist, 

 with concentrated hydrochloric acid, the solution fil- 

 tered off) and the oxide of zinc precipitated, at the 

 boiling-point, by carbonate of soda. The precipitate is 

 washed, dried, ignited, and weighed as pure oxide of 

 zinc. 



Or it may be dried as sulphide of zinc, removed 

 from the filter as much as possible, which is burned, 

 and the ashes added to the sulphide, mixed with a little 

 sulphur, placed in a weighed bulb tube, and ignited in 

 a current of hydrogen, and then weighed as sulphide 

 of zinc. 



Sesquioxide of iron may be more completely sepa- 

 rated from oxide of zinc by means of succinate of am- 

 monia, as described in No. 25, or by carbonate of 

 baryta (No. 25, III.) 



If, as has been proposed, the solution were mixed 

 with acetate of soda, so as to convert the iron and zinc 

 into acetates, and treated with sulphuretted hydrogen, 

 not only zinc, but iron also would be precipitated. 



