DR T. THOMSON on the Composition of Blende. 387 



opaque. But the powder was light brown. The specific gra- 

 vity was 4.076. The blende, previously reduced to powder, 

 was digested in aqua regia till a complete solution was obtained. 

 The sulphuric acid was thrown down by muriate of bary tes ; the 

 peroxide of iron, by benzoate of ammonia ; and the oxide of zinc, 

 by adding an excess of carbonate of soda, and evaporating the 

 mixture to dryness. The residual matter was digested in water, 

 and the carbonate of zinc was collected on the filter. The result 

 of the analysis was as follows : 



Zinc, 65.280 



Iron, 0.748 



Sulphur, 33.364 



99.392 



65.28 zinc requires 30.837 sulphur, 

 0.748 iron requires 0.854, to form bisulphuret. 



31.691 



Thus, there is an excess of sulphur in the blende analyzed by 

 Mr T. MUIR amounting to 1.673 per cent. But there is a loss 

 in Mr Mum's analysis, amounting to .608 per cent., and this loss 

 was undoubtedly zinc. If we add it, the quantity of zinc in the 

 blende will be 65.888, which will require 31.123 sulphur. This 

 would reduce the excess of sulphur to 1.387 per cent. This is 

 less than in ARFWEDSON'S analysis, in which the excess of sul- 

 phur amounts to 1.986 per cent. 



Mr MUIR'S analysis serving to confirm the accuracy of ARF- 

 WEDSON'S, I was naturally led to consider it as established that 

 blende contains an excess of sulphur, amounting to about 1^ 

 per cent. Now, such an excess can only exist on the supposition 

 that zinc is capable of combining with sulphur in various pro- 

 portions. For example, if we were to consider blende as a com- 



