Mineralogy of South America. 3 



The precipitated sulphate of baryta weighed 0*26 gr., equivalent 

 to 007 per cent, sulphur in the bismuth. 



The tellurium present was determined by dissolving a fresh 

 portion of bismuth, weighing 45*55 grs., in nitric acid, neutrali- 

 zing with ammonia, then adding sulphide of ammonium in excess, 

 with which it was allowed to stand, being shaken occasionally, for 

 some five days. The insoluble sulphide of bismuth was filtered 

 off and washed with water containing sulphide of ammonium. 

 The filtrate was now treated with an excess of hydrochloric acid, 

 throwing down the sulphide of tellurium along with free sulphur 

 and a little sulphide of arsenic ; these were digested with nitric 

 acid until the sulphur was quite pure, filtered, and the solution, 

 previously strongly acidified and heated with hydrochloric acid 

 to reduce all telluric acid present, was treated with a stream of 

 sulphurous acid passed through it until all tellurium present had 

 been thrown down, allowed to stand in an atmosphere of sulphu- 

 rous acid, and then the precipitate was washed with sulphurous 

 acid and dried with proper precautions. The tellurium thus 

 obtained weighed 2*425 grs., equivalent to 5*09 per cent, in 

 the metallic bismuth. 



In order to see if any silver was present in the mineral, three 

 several portions, respectively weighing 40*50, 50*0, and 92*0 

 grs., were cupelled; in no case was any visible trace of silver 

 found, but a faint trace of gold was distinctly observed. 



According to the above examination, the analysis of the native 

 bismuth will now stand as follows : — 



Bismuth . . 



. . 94*46 



Tellurium . 



. , 5*09 



Gold . . . 



. . trace 



Arsenic 



. . 0*38 



Sulphur 



. . 0*07 



100*00 



From observations on the specific gravity of other specimens 

 of bismuth from this mine, I think it most probable that the 

 percentage of tellurium may vary greatly in different specimens, 

 which is confirmed by the analysis of another specimen from the 

 same mine*, sent some years back to the United States, and 

 which was a portion of the largest piece before mentioned. The 

 analysis is by Mr. F. A Genth, and the results as follows : — 



Bismuth .... 99*914 



Iron trace 



Tellurium .... 0*042 



99*956 

 * American Journal of Science and Arts, 2nd series, vol. xxvii. p. 247. 



B2 



