Mineralogy of South America. 5 



Silver, iron, nickel, and cobalt were also specially examined for, 

 but not found present in the mineral. 



42*01 grs. of the mineral in fine powder were now examined 

 for tellurium by the same process as is described in the case of 

 native bismuth. No tellurium, however, was found present. The 

 analysis will therefore stand as follows : — 



Bismuth . . . 16*20 or 80*93 per cent. 

 Sulphur . . . 3*92 „ 19*61 „ 



20*12 100*54 



Considering the atomic equivalent of bismuth as 106, and that 

 of sulphur as 16, the formula Bi 2 S 3 would require the following 

 percentage composition : — 



Bismuth, 2 atoms . . . 212 or percentage 81*53 

 Sulphur, 3 atoms . . . j£8 „ 18-4 7 



260 100*00 



Mispickel. — This mineral only occurs crystallized in the San 

 Baldomero mine when in small drusic cavities or close to the 

 walls of the vein, where the crystals are frequently found protru- 

 ding from the surface of the massive mineral and imbedded in 

 carbonate of lime, or, as before stated, in the bismuthine. All 

 the crystals I have observed belong to the trimetric system, and 

 are rhombic octahedrons more or less modified, most generally 

 as twin crystals. Perfect octahedrons are occasionally found, 

 but only when imbedded in the soft bismuthine. No cleavage- 

 planes could be observed. Colour : silver- white to grey- white ; 

 but fresh surfaces tarnish quickly, becoming of a brassy colour 

 on exposure. 



The specific gravity was found to be 6*255 at 60° Fahr. When 

 heated alone, the mineral first evolves sulphide of arsenic and 

 then metallic arsenic, and leaves sulphide of iron containing a 

 trace of cobalt and nickel. 



The chemical analysis was conducted as follows : — 



23*42 grs. in finest powder were intimately mixed with 60 

 grs. pure nitrate of potash previously mixed with 60 grs. pure 

 anhydrous carbonate of soda, and fused in a silver crucible ; the 

 mass deflagrated very gently, but a strong smell of arsenic was 

 observed; it did not flow; the whole on cooling was digested 

 with water, and, after filtration and washing, the filtrate was 

 acidified by hydrochloric acid, and the sulphuric acid precipitated 

 by addition of a solution of chloride of barium. The sulphate of 

 barytes collected amounted to 33*16 grs., equal to 4*575 grs. 

 sulphur, or 19*534 per cent, in the mineral. 



The insoluble oxides were now dissolved in hydrochloric acid, 

 neutralized by ammonia, and the iron separated from the cobalt, 



