96 TETRAHEDRTTE. 



been dried and weighed. After being washed with 

 sulphuretted- hydrogen water, the precipitate is removed 

 from the filter, taking care not to damage the latter ; 

 it is washed off as well as possible, and a concentrated 

 solution of sulphide of ammonium poured upon it, with 

 which it is digested in a closed vessel until the whole 

 of the sulphides of arsenic and antimony are dissolved, 

 and the sulphide of mercury has assumed a pure black 

 color. When completely cold, it is again collected on 

 the filter previously used, washed first with dilute sul- 

 phide of ammonium, and towards the end with pure 

 water, dried and weighed. 



From the solution in sulphide of ammonium, the 

 sulphides of arsenic and antimony are precipitated by 

 an excess of dilute sulphuric acid, and separated and 

 determined as in No. 61. 



From the liquid which has been filtered off from 

 the precipitate by sulphuretted hydrogen, the iron can 

 only be separated by sulphide of ammonium after 

 neutralizing with ammonia, on account of the presence 

 of tartaric acid. When the sulphide of iron is com- 

 pletely separated by digestion at a gentle heat, it is 

 filtered off) and washed with sulphuretted hydrogen- 

 water; the filter is then put into a beaker, and digested 

 with hydrochloric acid until all the sulphide of iron 

 is dissolved. The solution is then filtered off from the 

 paper, the latter washed, the liquid heated with chlo- 

 rate of potassa, and the sesqui oxide of iron precipitated 

 by ammonia. 



Or the sulphide of iron is dried, removed from the 

 filter, which is burned, and the ashes added to the pre- 

 cipitate, with a small piece of sulphur, and strongly 

 ignited in a stream of dry hydrogen. It is weighed 

 as Fe S sulphide of iron. 



If the amount of sulphide of iron be but small, the 

 filter is ignited with the precipitate, the air having 



