SEPARATION OF THE METALS OF EACH GROUP. 215 



or fully soluble (metals of the arsenic group), and treated ac- 

 cording to Table V., or it is partly soluble and partly insoluble 

 (metals of both groups). In the latter case, the total quantity 

 of the washed precipitate is to be treated with warm ammonium 

 sulphide ; upon filtering, an insoluble residue is left, which is 

 treated according to Table IV. ; to the filtrate, diluted sulphuric 

 acid is added as long as a precipitate is formed, which precipi- 

 tate contains the metals of the arsenic group as sulphides, gen- 

 erally with some sulphur from the ammonium sulphide. 



The precipitation of sulphur in the absence of metals of the 

 arsenic group, frequently leads beginners to the assumption that 

 metals of this group are present. The precipitate consisting of 

 sulphur only is white and milky, but flocculent, and more or 

 less colored in the presence of the metals of the arsenic group. 



QUESTIONS. 



331. By what tests can mercurous chloride be distinguished from the 

 chloride of silver or lead ? 



332. How can it be proved, that a precipitate produced by hydro- 

 sulphuric acid in an acid solution contains metals of the arsenic and 

 lead groups? 



333. How can mercuric sulphide be separated from the sulphides of 

 copper and bismuth ? 



334. How does ammonium hydrate act on a solution containing bis- 

 muth and copper? 



335. State the action of strong, hot hydrochloric acid on the sulphides 

 of arsenic and antimony. 



336. Suppose a solution to contain salts of iron, aluminium, zinc, and 

 manganese ; by what processes could these four metals be separated and 

 recognized ? 



337. How can barium, calcium, and strontium be recognized when 

 dissolved together? 



338. By what test is magnesium recognized ? 



339. State a method of separating potassium when mixed with other 

 metallic compounds. 



340. How are ammonium compounds recognized when in solution 

 with other metals ? 



