TETRAHEDRITE. 



91 



mixture of 3 parts of carbonate of soda and 1 part of 

 cyanide of potassium, and heated in a covered porce- 

 lain crucible until all the arsenic is driven off'. On 

 treating the residue with water, the tin would be left 

 behind in the metallic state. Or the mixture could 

 be heated in a long glass tube, in a slow current of 

 carbonic acid gas, and thus the arsenic obtained as a 

 sublimate in the tube. In order to secure a more 

 complete condensation, a weighed coil of fine sheet 

 copper could be introduced into the tube, and heated 

 to ignition at one place for the purpose of forming 

 arsenide of copper. 



63. TETRAHEDRITE. 



4 (Cu, Ag, Fe, Zn, Hg), + (Sb 3 , As, Bi) 2 S s . 



Every specimen of tetrahedrite does not contain all 

 these constituents; some of them may be entirely 



Fig. 12. 



