SPHALERITE. 55 



weight obtained is calculated upon the whole quantity 

 of sulphide of copper. 



Or the filter with its contents may be allowed to dry 

 in the funnel, the precipitate detached, and thrown 

 into a beaker ; the filter is then completely incinerated, 

 the ash added to the sulphide of copper, and the latter 

 oxidized with agua-regia till the sulphur separates of 

 a pure yellow color. From the filtered solution, the 

 protoxide of copper, as in No. 29, is precipitated at a 

 boiling heat by caustic potassa, ignited and weighed. 



The solution filtered from the sulphide of copper, 

 containing the iron in the form of protoxide, is heated 

 nearly to boiling, in a flask, concentrated if necessary 

 by evaporation, and treated at the same time with 

 chlorate of potassa in small portions, until all the prot- 

 oxide of iron is converted into sexquioxide, which is 

 then precipitated by ammonia, washed, dried, and 

 ignited. 



Notwithstanding the solubility of oxide of copper in 

 caustic ammonia, this reagent will not effect its com- 

 plete separation from sesquioxide of iron, since the 

 latter carries down with it a considerable quantity ~of 

 oxide of copper which cannot be extracted by ammonia. 



31. SPHALERITE, OR BLENDE. 



ZnS. 



The solution is effected just as in the case of chalco- 

 pyrite. -The mineral must be very finely powdered, 

 and very concentrated acid must be employed. 



After the sulphuric acid which is produced has been 

 precipitated by chloride of barium, and the excess of 

 baryta has been removed, the solution is saturated with 

 sulphuretted hydrogen, in order to precipitate any cop- 

 per and cadmium which often occur in small quantities 



