214 ANALYTICAL CHEMISTRY. 



QUESTIONS. 



321. State the 3 groups of heavy, arid the 3 groups of light metals. 



322. By which two reagents may all heavy metals be precipitated ? 



323. Why is a solution acidified before the addition of hydrosulphuric 

 acid, when testing for metals? 



324. Which metals are precipitated by hydrochloric acid ? 



325. Which two groups of metals are precipitated by hydrosulphuric 

 acid in acid solution ? 



326. How are the sulphides of the arsenic group separated from those 

 of the lead group? 



327. Why is an acid solution neutralized or supersaturated by am- 

 monium hydrate, before adding the ammonium sulphide ? 



328. Which two groups of metals are precipitated by ammonium sul- 

 phide, and in what forms of combination ? 



329. Name the group-reagent for the alkaline earths. 



330. Which metals may be left in solution after hydrosulphuric acid, 

 ammonium sulphide, and ammonium carbonate have been added ? 



34. SEPARATION OF THE METALS OF EACH GROUP. 

 TABLE III. Treatment of the precipitate formed by hydrochloric acid. 



The precipitate may contain silver, mercurous, and lead chlorides. Boil 

 the washed precipitate with much water, and filter. 



Treatment of the precipitate formed by hydrosulphuric acid in 

 warm acid solution. The precipitate is collected upon a small 

 filter, well washed with water, and then examined for its solu- 

 bility in ammonium sulphide. This is done by placing a por- 

 tion of the washed precipitate in a test-tube, adding ammonium 

 sulphide', and warming gently. It is either wholly insoluble 

 (metals of the lead group), and treated according to Table IV, 



