Analysis of Minerals. 173 



will be more apparent after describing in greater detail the 

 various experiments which I have made. 



Quantitative analysis of Tin-ore from Cornwall. 



Two samples of roasted so-called black-tin were pow- 

 dered to an exceedingly fine powder and submitted to the 

 process sketched out above. Black-tin is the technical term 

 applied to tin-ore which has been concentrated by washing 

 away the lighter mineral impurities, drying, and afterwards 

 roasting to free it from sulphur, arsenic, and antimony. 



I took o - 5 gram of the sample, mixed it carefully with 

 sufficient powdered charcoal, and added the mixture care- 

 fully to the melted hot caustic alkali (soda was used in most 

 cases) in the silver crucible. Heat was then gently applied 

 with an ordinary Bunsen-burner, and the mass heated until 

 no further evolution of burning gas was observed, generally, 

 thirty minutes heating being sufficient. The crucible and 

 its contents were then placed in a porcelain basin, and the 

 contents dissolved out with distilled water, and filtered from 

 the insoluble oxides, undecomposed carbon, &c. I always 

 submitted the residue to a second fusion, and found in most 

 cases that every trace of mineral was completely decomposed 

 after the second fusion. In the solution were silicate of 

 sodium, aluminate of sodium, and stannate of sodium,whilst in 

 the insoluble residue were silica, bismuthic oxide, cupric 

 oxide, ferric oxide, calcium carbonate, and manganese di- 

 oxide. The details of the method of analysis of the insoluble 

 residue it will be unnecessary for me to enter into here, 

 whilst the analysis of the soluble portion simply resolved 

 itself into the elimination of the silica from the solution 

 (previously treated with hydrochloric acid in excess) in the 

 usual manner, the precipitation of the tin as sulphide, and 

 its subsequent conversion into stannic oxide, in which form 

 it was weighed. 



The analyses resulted as follows, viz. : — 



