342 DR T. THOMSON on the Composition of Blende. 



ret of zinc, it became necessary to examine the composition of 

 blende again with as much attention to accuracy as possible, in 

 order to ascertain whether the supposed excess of sulphur really 

 exists in it. 



An analysis of the crystals of blende, obtained from the spe- 

 cimen which Mr T. MUIR had examined, gave me the following 

 result : 



Zinc, 65.7 



Iron, ..... 0.740 

 Sulphur, .... 32.628 



99.076 



The amount of iron was exactly the same as Mr MUIR had ob- 

 tained ; but the quantity of zinc was 0.42 grains more, while the 

 sulphur was 0.736 grains less than in his analysis. My loss 

 amounted to 0.924 per cent., and was undoubtedly zinc ; for I 

 was at so much pains to obtain all the sulphur, that none of it 

 could well be lost. The real quantity of zinc, then, in 100 

 grains of the blende, was, 



'- ! ' 



66.629 gr., requiring . . 31.352 sulphur 

 0.748 gr., iron requiring 0.354 sulphur 



Total, . . 32.206 



The quantity of sulphur which I actually obtained exceeds 

 this quantity by only 0.422. Here the excess is less than one- 

 third of that in Mr MUIR'S analysis. 



I analyzed another specimen of brown blende, having the 

 diamond lustre, and a specific gravity of 3.9779. The consti- 

 tuents obtained were, 



