SEPARATION OF THE METALS OF EACH GROUP. 217 



TABLE V. Treatment of the hydro sulphuric acid precipitate which is 

 soluble in ammonium sulphide. 



The precipitate may contain the sulphides of arsenic, antimony, tin, 

 and of a few of those metals which are but rarely met with in qualitative 

 analysis, such as gold, platinum, molybdenum, and others, which latter 

 metals, if suspected, may be detected by special tests. 



Boil the washed precipitate with strong hydrochloric acid. 



An insoluble yellow residue con- 

 sists of arsenious sulphide. 



The residue is dissolved by boil- 

 ing with hydrochloric acid and a 

 little potassium chlorate, and the 

 solution examined by Marsh's test. 



The solution may contain the chlorides 

 of antimony and tin. 



The solution is introduced into Marsh's 

 apparatus when all antimony is gradually 

 evolved as antimoniuretted hydrogen, while 

 tin remains with the undissolved zinc as a 

 black metallic powder, which may be col- 

 lected, washed, dissolved in hydrochloric 

 acid, and the solution tested by the special 

 tests for tin. 



