92 On the Composition of Blende. [Aug. 



blende contained more than 12 per cent. Hence I think there can 

 be no doubt that the yellow blende is the purest. Probably some 

 of the transparent and crystallized specimens of it may be alto- 

 gether free from iron ; though none such have yet fallen into my 

 hands. 



As my method of analysis was always the same, I consider it as 

 unnecessary to detail any more than one experiment ; and I shall 

 make choice of the one with the exactness of which I was myself 

 most satisfied. The specimen was from Huel Anne in Cornwall, 

 and was picked up by myself on the spot. It was not crystallized ; 

 but I made choice of it as in appearance quite free from all ad- 

 mixture of earthy or foreign matter of any kind. 



Its colour was blackish brown. The lustre splendent and semi- 

 metallic. The fracture foliated ; but the six fold cleavage, which 

 usually characterizes blende, could not be recognized in it, owing 

 to its being composed of granular concretions. It was opaque. 

 The streak was yellowish brown. It possessed the usual degree of 

 hardness of blende. Its specific gravity was 4*0-19. 



1. Fifty grains of this zinc were reduced to a fine powder,* 

 and digested in a flask for two days with diluted nitric acid. At 

 first the action was pretty violent, and nitrous gas was discharged 

 copiously ; but after some hours it ceased entirely. The ore was 

 then floating upon the surface of the liquid, and appeared coated 

 over with sulphur. The whole was thrown upon a filter, and the 

 undissolved residuum being well washed and dried in the open air, 

 was exposed for 24 hours upon an iron of the temperature of rather 

 more than 110°. Thus dried, it weighed 2(! grains. 



2. These 26 grains were put upon a watch glass and exposed to 

 the heat of a lamp. The matter underwent an incipient fusion, 

 emitted a white smoke, and at last took fire and burnt with a blue 

 flame, giving out a strong odour of sulphur. When all appear- 

 ance of combustion and smoke was at an end, the glass was allowed 

 to cool. The matter, being now weighed, was found to amount to 

 22 - 4 grains. The 36 grains of loss were considered as sulphur 

 dissipated bv the heat. 



3. The 2:2-4 grains of residue, which had now assumed the ap- 

 pearance of the original blende, were put into a flask and digested 

 two days with diluted nitric acid. The second day, as all action 

 was over, and the whole very nearly dissolved, the flask was exposed 

 for some hours to a heat of about 130°. The whole was then 

 thrown upon a filter. The undissolved portion was well washed 

 and dried. It weighed 0.5-1 grain. 



4. This small residue was put upon a watch glass and exposed to 

 the heat of a lamp. It emitted a visible smoke having the odour 

 of sulphur. When cold its weight was reduced to 0*38 grain. 

 The 016 grain of loss was, considered as sulphur dissipated by the 

 heat. 



* I founil in the preceding analyse"!, thai unless the blende be reduced to 

 powder, the experiments are li;.!)ie ■<• considerable loss. 





