1814.] On the Composition of Blende. 93 



5. The remaining 38 grain had the appearance of small grains 

 of quartz, mixed with a particle or two of undecomposed blende. 

 To remove this portion of ore the whole was digested in diluted 

 nitric acid for a day. The residue was now pure quartz sand, and 

 weighed - 3 grain. The liquid containing the OS grain of 

 blende in solution was accidentally lost. On that account, I shall 

 consider the quartz sand as amounting to 0*3S grain. 



G. The two portions of acid liquid which had been digested on 

 the ore, and which contained the greatest part of it in solution, 

 were mixed together, and almost, but not quite, saturated with 

 carbonate of soda. A considerable excess of caustic ammonia was 

 then poured in. By this alkali the oxide of iron was thrown down 

 in yellowish red flocks, while the whole of the zinc was held in 

 solution. The oxide of iron being separated by the fdter, washed, 

 dried, and heated to redness, weighed 8 - 5 grains. Now this is 

 equivalent to 5*98 grains of metallic iron. 



/. The residual liquid was now boiled in a glass retort down to 

 half its bulk, in order to drive off the ammonia and precipitate the 

 oxide of zinc. About one half of that oxide precipitates after a 

 few minutes boiling ; but it requires considerable concentration 

 before the other half falls down. From this circumstance it is not 

 improbable, that ammonia and oxide of zinc unite in two propor- 

 tions. The oxide of zinc thus obtained, being washed, dried, 

 and heated to redness, weighed 3o'*4 grains. This is equivalent to 

 29*32 grains of metallic zinc. It may be proper to mention, that 

 the oxide of zinc thus obtained was not quite white, but had a 

 slight tinge of green. I conceived that this might be owing to the 

 presence of copper; but if this metal was actually present, it was 

 in too minute a quantity to be detected by the usual tests. 



8. The liquid thus freed from iron and zinc was mixed with 

 nitric acid till it acquired a perceptibly sour taste. This was done 

 to prevent any inaccuracy from the presence of ammonia, if any 

 should still remain in the liquid. A solution of muriate of barytea, 

 was then mixed with it. The sulphate of barytcs which precipi- 

 tated, being washed, dried, and heated to redness, weighed 

 77*616 grains. Now 77*616 grains of sulphate of barytcs contain 

 26'«J Trains of sulphuric acid, or 10 - 5G grains of sulphur. 



Prom the preceding analysis it appears that blende is composed 

 of the following ingredients: 



Zinc 29-32 58'G4 



Sulphur 14*32 28*6-1 



Iron 5*98 ll*9fi 



Quartz 0*38 0*76 



50-00 



Hut a^ the quartz was only mixed with the ore i:i grains it inav 

 be abstracted. In that case brown blende is composed of 



