GALENITE. 61 



filter, is dissolved in hydrochloric acid with a little 

 chlorate of potash, the solution saturated with potassa, 

 and then hydrocyanic acid added until the precipitate 

 is again dissolved. From this solution of the double 

 cyanides the cadmium may be precipitated by sulphu- 

 retted hydrogen, and the copper will remain. The sul- 

 phide of cadmium is treated as in No. 35. The solu- 

 tion of copper is boiled with aqua regia, and while hot 

 the copper precipitated by caustic potassa. 



The copper maybe separated from cadmium as from 

 zinc, by sulphocyanide of potassium, as in No. 33. 



37. GALENITE. 

 PbS. 



The finely-powdered mineral, placed in a capacious 

 dish, is gradually moistened with fuming nitric acid 

 until it is entirely converted into white sulphate of 

 lead ; a few drops of sulphuric acid are added, to 

 insure complete conversion, the mass ignited and 

 weighed. 



If the residue, previously to ignition, be treated 

 with water, and filtered, only traces of lead are found 

 in the solution. If the galena contain copper, iron, or 

 silver, they will be detected in the solution, the first 

 two by ammonia, and the silver by hydrochloric acid. 



If the galena be oxidized with more diluted nitric 

 acid, the residue consists of a mixture of sulphate of 

 lead and sulphur, while the solution contains nitrate 

 of lead, from which the lead may be precipitated by 

 sulphuric acid, or, more completely, by oxalate of am- 

 monia, after neutralization. By igniting the dried 

 residue, the sulphur is volatilized, and sulphate of lead 

 remains. 



When boiled with a solution of carbonate of soda, 

 6 



