238 ANALYTICAL CHEMISTRY. 



has been added. Heating facilitates complete precipitation of the 

 carbonates of the alkaline earths. 



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 while hot. 



Treatment of the precipitate formed by hydrogen sulphide in 

 warm acid solution. The precipitate is collected upon a small 

 filter, well washed with water, and then examined for its solubility 

 in ammonium sulphide. This is done by placing a portion 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., or fully soluble (metals 

 of the arsenic group), and treated according 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 fil- 



QUESTIONS. 321. State the three groups of heavy, and the three groups of 

 light metals. 322. By which two reagents may all heavy metals be precipi- 

 tated ? 323. Why is a solution acidified before the addition of hydrogen sul- 

 phide, when testing for metals? 324. Which metals are precipitated by 

 hydrochloric acid? 325. Which two groups of metals are precipitated by 

 hydrogen sulphide 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 ammonium hydroxide, before adding 

 ammonium sulphide ? 328. Which two groups of metals are precipitated by 

 ammonium sulphide, and in what forms of combination? 329. Name the 

 group-reagent for the alkaline earths. 330. Which metals may be left in solu- 

 tion after hydrogen sulphide, ammonium sulphide, and ammonium carbonate 

 have been added ? 



