382 ANALYTICAL CHEMISTRY. 



35. SEPARATION OF METALS INTO DIFFERENT GROUPS. 



General remarks. The preliminary examination will, in most 

 cases, decide whether or not a metal or metals are present in the sub- 

 stance to be examined. If there be metals, the solution should be 

 treated according to Table II., page 344, in order to find the group 

 or groups to which these metals belong, and also to separate them 

 into these groups, the individual nature of the metals themselves 

 being afterward demonstrated by special methods. 



The simplest method of separating from each other the 57 metals 

 known, if all were in one solution, would be to add successively 57 

 different reagents, each of which should form an insoluble compound 

 with but one of the metals. By separating this insoluble compound 

 from the metals remaining in solution (by filtration), and by thus pre- 

 cipitating one metal after the other, they all could be easily separated. 

 We have, however, no such 57 reagents, and are, consequently, com- 

 pelled to precipitate a number of metals together, and the reagents 

 used for this purpose are known as group-reagents. 



They are : 



1. Hydrogen sulphide, added to the solution previously acidified by 

 hydrochloric acid. Precipitated are : the metals of the arsenic and 

 lead groups as sulphides. 



2. Ammonium sulphide, added after supersaturating with ammonium 

 hydroxide. Precipitated are : the metals of the iron group and of 

 the earths as sulphides or hydroxides. 



3. Ammonium carbonate. Precipitated are : the metals of the 

 alkaline earths as carbonates. 



4. In solution are left : the metals of the alkalies and magnesium. 

 The order in which these group-reagents are added cannot be 



QUESTIONS. What is analytical chemistry, and what is the object of quali- 

 tative and of quantitative analysis? What properties of a substance should 

 be noticed first in- making a qualitative analysis? By what tests may organic 

 compounds be distinguished from inorganic compounds? Explain the terms 

 decrepitation and deflagration. Mention some substances which are completely 

 volatilized by heat, some which are fusible, and some which are not changed 

 by heating them. What is meant by " hepar," and which element is indicated 

 by the formation of hepar? Mention some metals which may be liberated 

 from their compounds by heating on charcoal with potassium cyanide and car- 

 bonate. Which metallic compounds and which acids are capable of coloring a 

 non-luminous flame? Name the colors imparted. State the metals which im- 

 part characteristic colors to a borax bead. Which solvents are used for lique- 

 fying solids, and what precautions should be observed in this operation? 



