140 Mr. D. Forbes's Researches on the ' 



Before the blowpipe it afforded only the reactions due to pure 

 oxide of tin. 



Cassiterite, brownish. — In addition to the blowpipe reactions 

 for oxide of tin, the yellow colour of the borax globule, whilst 

 warm, indicated the presence of iron, whilst the insoluble white 

 matter in the phosphate-of-soda bead showed silica to be present. 

 A trace of manganese was also indicated on treating the mineral 

 with nitrate of potash on platinum- foil. 



The chemical examination was conducted as follows : — 



20*52 grs. in impalpable powder were intimately mixed with 

 130 grs. of a mixture of anhydrous carbonate of soda and sul- 

 phur in equal parts, and fused in a Berlin porcelain crucible for 

 some time; on cooling, the mass was dissolved out in water, 

 to which a little sulphide of ammonium was added. An insoluble 

 residue remained amounting to 3*70 grs., which was fused as be- 

 fore, with 24 grs. of the same mixture of sulphur with carbonate of 

 soda, and dissolved in water ; a very small quantity still remained 

 insoluble, from which sulphuric acid with a few drops of nitric 

 acid extracted some alumina and oxide of iron, which were sepa- 

 rated by potash and determined as usual. The oxide of iron 

 contained a little manganese, which, however, was not separately 

 determined. 



From the solution of the sulphide of tin in sulphide of sodium, 

 the former was precipitated by hydrochloric acid, and after being 

 collected on a filter, washed, and dried with the usual precau- 

 tions, was converted by prolonged ignition into binoxide of tin. 

 The results thus obtained will, when tabulated, stand as fol- 

 lows : — 



In 100. 



Binoxide of tin 18-84 91*81 



Sesquioxide of iron (with manganese) 0*21 1*02 



Alumina 0*15 0*73 



Silica and insoluble ..... 1*33 6*48 



20*53 100*04 



Cassiterite, black. — The specific gravity of the deep-black 

 variety of Cassiterite, taken on 187*40 grs. at temperature of 60° 

 Fahr., proved to be 7*021. Before the blowpipe, the only differ- 

 ence in behaviour from the last-mentioned specimen was in the 

 much stronger reaction of iron and manganese. 



In the examination of this specimen 20*11 grs. in impalpable 

 powder were added by degrees to 300 grs. caustic potash, already 

 in fusion in a gold crucible, and kept in the liquid state for 

 some time. On digestion with water, a residue, apparently of 

 undecomposed mineral, was left, amounting on determination to 

 1*89 gr., which was again treated as before with potash in fusion. 

 An insoluble residue (1*11 gr.), apparently only undecomposed 



