Elements of Mineralogy. 



fulphur, a finall proportion of copper, and 

 the remainder tin. Mem. Stock. 1781, p. 

 328. 



15. To efiay tin ores in the liquid 11^7 has 

 hitherto been thought imprafticable ; how- 

 ever, Mr. Bergman has devifed the following 

 method, which is generally fuccefsful. Let 

 the tin ore, well feparated from its ftony 

 matrix by wafhing, and reduced to the moil 

 fubtile powder, be digefted in concentrated 

 oil of vitriol in a ftrong heat for feveral 

 hours, then when cool add a fmall quantity 

 of concentrated marine acid, and fuffer it to 

 ftand for one or two hours ; then add water, 

 and when the folution is clear pour it off, 

 and precipitate it by fixed mineral alkali. 

 131 gr. of this precipitate wafhed and dried 

 are equivalent to 100 of tin in its reguline 

 ftate, if the precipitate confifts of pure tin ; 

 but if it contains copper or iron, it ihould be 

 calcined for one hour in a red heat, and then 

 digefted in nitrous acid, which will take up 

 the copper, and afterwards in marine acid, 

 which will feparate the iron. 



1 6. In the dry ivay^ thefe ores, after pul- 

 verization and feparation of the ftony matter 

 by wafhing, are to be melted with a mixture 

 of double their weight of a flux, confifting of 

 equal parts of pitch and calcined borax, in a 



crucible 



