334 DR T. THOMSON on the Composition of Blende. 



crystallized blende. And his method of proceeding was as fol- 

 lows : 



1.758 grammes (27.15 grains) of pulverized blende were di- 

 gested in aqua regia, which had been previously heated till it 

 began to give out fumes of chlorine gas. When all action was 

 at an end, the undissolved portion was separated by the filter, 

 washed and dried. It weighed 0.393. Being exposed to a red 

 heat a good deal of sulphur was driven off, but a portion of un- 

 decomposed blende remained, which, being again heated with 

 aqua regia, was completely dissolved. 



The solution thus obtained was diluted with water, raised to 

 the boiling temperature, and mixed with an excess of carbonate 

 of potash. The heat being continued till all excess of carbonic 

 acid was driven off, the precipitated carbonate of zinc was col- 

 lected on the filter. After being washed, dried, and ignited, it 

 weighed 0.146. It was oxide of zinc, equivalent, according to 

 BERZELIUS'S formulas, which ARFWEDSON follows, to 0.117 parts 

 of metallic zinc. From this ARFWEDSON concludes, that the 

 0.393 parts of residue were composed of 



Zinc, 0.117 



Sulphur, 0.276 



0.393 



The sulphuric acid in the original aqua regia solution was 

 precipitated by muriate of barytes. The ignited sulphate of 

 barytes obtained weighed 2.288, equivalent, by BERZELIUS'S for- 

 mula, to 0.786 sulphuric acid, or 0.316 sulphur. 



The liquid thus freed from sulphuric acid was raised to the 

 boiling temperature, and precipitated by carbonate of potash, 

 the heat being continued till all excess of carbonic acid was 

 driven off; the oxide of zinc obtained, weighed after ignition 



