388 



ANALYTICAL CHEMISTRY. 



trate, diluted sulphuric acid is added as long as a precipitate is 

 formed, which precipitate contains the metals of the arsenic group as 

 sulphides, generally with some sulphur from the ammonium sulphide. 



TABLE IV. Treatment of that portion of the hydrogen sulphide 

 precipitate which is insoluble in ammonium sulphide. 



The precipitate may contain the sulphides of lead, copper, mercury, 

 bismuth, and cadmium. Heat the well-washed precipitate with nitric acid in 

 a test-tube, and filter. 



TABLE V. Treatment of the hydrogen sulphide precipitate which is 

 soluble in ammonium sulphide. 



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

 and 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 consists 

 of arsenous sulphide 



The residue is dissolved by boiling 

 with hydrochloric acid and a little 

 potassium chlorate, and the solu- 

 tion examined by Fleitmann's 

 test. 



A dark-colored residue may indi- 

 cate gold or platinum, for which 

 use special tests. 



The solution may contain the chlorides of 

 antimony and tin. 



The solution is introduced into Marsh's appara- 

 tus when all antimony is gradually evolved 

 as antimoniuretted hydrogen, while tin re 

 mains with the undissolved zinc as a black 

 metallic powder, which may be collected, 

 washed, dissolved in hydrochloric acid, and 

 the solution tested by the special tests for 

 tin. 



