ZINKENITE. 83 



heat, and the sulphate of copper extracted from the 

 mass by water. The sulphate of lead is washed, dried, 

 and ignited. The oxide of copper is precipitated from 

 the solution by caustic potassa, at a boiling heat. 



This method is not quite accurate, since a little sul- 

 phide of copper dissolves in the sulphide of ammonium 

 together with the tersulphide of antimony; sulphate 

 of lead, moreover, is not quite insoluble. The deter- 

 mination of the lead is more accurate if all free sul- 

 phuric acid be expelled by heat before the sulphate of 

 copper is extracted with water. 



A more exact method for the analysis of this mineral 

 is that with chlorine, described in the article upon 

 Tetrahedrite. 



57. ZINKENITE.* 

 PbS, Sb 2 S 3 . 



The amount of sulphur present may be inferred from 

 the loss which the compound suffers when heated in a 

 bulb-tube, through which a stream of hydrogen is 

 passed, when all the sulphur is evolved as sulphuretted 

 hydrogen, and PbSb remains behind. 



The relative proportions of lead and antimony are 

 determined as in No. 55. 



For the direct estimation of the sulphur, the finely- 

 divided compound is mixed with 3 parts of chlorate of 

 potassa, and 3 parts of carbonate of soda, and heated 

 in a porcelain crucible, at first gently, and ultimately 

 to redness, until the chlorate of potassa is completely 

 decomposed. The salts are then extracted from the 



* Plagionite jamesonite, and feather-ore, are similar combinations. 

 Zinkenite may be easily prepared artificially by fusing together 7* 

 parts of sulphide of lead, with 11 parts of black tersulphide of 

 antimony iu a glass tube. 



