344 DR T. THOMSON on the Composition of Blende. 



fluous to state them. The sulphur rather exceeded the theore- 

 tical quantity ; but the excess was exceedingly small. 



These analyses seem to me to leave no doubt, that the zinc 

 in blende is combined with 1 atom of sulphur only. Blende is 

 a simple sulphuret of zinc, but never entirely free from an ad- 

 mixture of bisulphuret of iron ; but the proportion of this last 

 substance is so small and so variable, that it cannot be considered 

 as a chemical constituent of blende, but rather as a mechanical 

 mixture. In the second of my analyses the blende contains the 

 greatest proportion of iron-pyrites of any of the varieties which 

 I subjected to analysis. It consists of about 



52 atoms sulphuret of zinc, 

 1 atom bisulphuret of iron. 



While, in the first variety analyzed, the constituents are nearly 



74 atoms sulphuret of zinc, 

 1 atom bisulphuret of iron. 



These variations are inconsistent with chemical combination. 



