Progress of Foreign Scieme. 



159 



poration to dryness, which renders the silica insoluble. If any 

 copper be associated with the nickel, in the potash precipitate, 

 it may be separated from an acid solution by sulphuretted hy- 

 drogen, which does not act on the latter metal. 



The water in which the acid vapours have been condensed, 

 contains arsenic and sulphur. But if the mineral contained, at 

 the same time, bismuth, zinc, antimony, or tin, the muriates 

 of these metals would be also found in the liquid. This last 

 circumstance would render the analysis extremely complicated. 

 M. Berzelius, for this reason, passes over it in silence. The 

 bottle H I must be furnished with a ground stopper. The inte- 

 rior of the tube I K being washed, we cork the bottle, and 

 leave it in a warm place, till the greater part of the precipitated 

 sulphur be acidified. If there remains any part of it, we open 

 the bottle, and make the liquid boil ; the sulphur is aggluti- 

 nated, and may then be conveniently washed, dried, and 

 weighed. 



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To be certain that the acid liquor contains neither iron, 

 carried along by an ill-conducted operation, or other 

 metals, whose chlorides are volatile, we saturate it as exactly 

 as possible with caustic potash. Tf a precipitate fall, we col- 

 lect and examine it; then we render the liquid acidulous again, 

 and precipitate the sulphuric acid by muriate of barytes. We 

 next pour into the residuary liquid a solution of a known quan- 

 tity of metallic iron in nitric acid, and precipitate the oxide of 

 iron and arsenic acid by ammonia in excess. If this operation 



