and Laboratory Methods. 



1193 



'vv. iO.O\*v\*i\ 



add ammonium hydroxide. If the precipitate was lithium phosphate no turbidity 

 should result, while the alkaline earths are again precipitated. 



//. Addition of Atnmonium Carbonate to neutral solutions of salts of Lithium 

 causes the separation of Lithium Carbonate. 



Li2S04 + (NH4)2C03 = Li2C03 + (NH J2SO4. 



Method. To the drop of the neutral solution, which should not be too dilute 

 with respect to lithium, add a fragment of solid ammonium carbonate. After a 

 short time there will appear near the circumference of the drop, globulites, 

 bunches of needles and thin, more or less irregular plates and bristly masses 

 (Fig. 42). The general appearance of these 

 aggregates will vary somewhat with the con- 

 centration of the test drop. 



Remarks. All substances forming difficultly 

 soluble carbonates interfere. 



The reaction requires care and experience 

 in order that it can be made to always yield 

 acceptable results. 



Since the lithium carbonate separates only 

 after some little time, there are apt to appear, 

 almost simultaneously, crystals of other salts, 

 particularly if the test drop contains sulphates. 

 In such an event add to the drop a little dilute alcohol ; lithium carbonate will 

 remain undissolved for some time, while the sulphates or chlorides of the other 

 members of the first group will pass into solution. 



Exercises for Practice. 



Try the above methods for lithium first on a simple salt of this element, then 

 on mixtures of lithium and other members of its group, and lastly try mixture 

 containing ammonium and others containing calcium, magnesium, etc. 



EXAMINATION OF SUBSTANCES CONTAINING THE ELEMENTS OF 



GROUP I. 



Ammonium is tested for in a portion of the material by expelling it in the 

 manner previously given. 



The material to be tested is brought into solution by any suitable means, not 

 introducing alkalies. 



If soluble in HCl, the solution of the chlorides is evaporated to dryness, and, 

 if ammonium salts are present, the residue is ignited until all these salts have 

 been driven off. The residue is extracted with absolute alcohol or with carefully 

 purified amyl alcohol. The alcoholic extract is evaporated to dryness and the 

 residue tested for the members of Group I. 



When sulphuric acid has been employed, or if the substance contains sul- 

 phates, it is first necessary to convert the material into chlorides ; this is accom- 

 plished by treating with barium chloride in sufficient amount to precipitate all 

 the sulphuric acid and removing any excess of barium by means of ammonium 



