MICROCHEMICAL REACTIONS OF THE COMMON ELEMENTS 297 



heating with hydrochloric acid, in which strontium sulphate is 

 soluble, while the barium compound remains undissolved and 

 can then be recrystallized by heating with sulphuric acid. Even 

 in mixtures, however, it is almost invariably possible to find 

 characteristic forms of both barium and strontium, providing the 

 analyst has a little patience and carefully examines the entire 

 preparation. 



Any lead sulphate which may be present will appear, first, in 

 crystals very suggestive of strontium sulphate, then, in a short 

 time, in larger crystallites which may at times be mistaken for 

 barium sulphate. Treatment with hydrochloric acid, or, better, 

 with sodium hydroxide, will remove the lead, leaving the barium 

 salt unacted upon. 



Precautions. 



It is sometimes desirable to apply other tests to the precipitated 

 sulphate in order to confirm the presence of barium. In such an 

 event, transfer the washed precipitate to platinum foil or to a 

 platinum cup and fuse with potassium carbonate. The fused 

 mass is then extracted with water and the residue of barium 

 carbonate dissolved in hydrochloric acid. This solution can 

 then be tested for barium by any of the tests given below. 



Since chlorides of the trivalent metals sometimes interfere 

 with the formation of characteristic crystals of barium sulphate, 

 it is advisable to decant the supernatant liquor after the addi- 

 tion of the reagent and before heating with an excess of the acid. 

 When dealing with unknown mixtures it is always best to pro- 

 ceed in this manner. 



EXPERIMENTS. 



a. Try above method on a simple salt of Ba. 



b. Make a mixture of salts of Ca and Ba, recrystallize at once without remov- 

 ing the Ca. From another portion remove the Ca with hot water and recrystal- 

 lize the residue. 



c. Try a mixture of Sr and Ba. Remove the Sr by treating with HC1 and re- 

 crystallize the residue. 



d. Try a mixture of Ca, Sr and Ba, recrystallizing at once, then removing in 

 turn the Ca with hot water and the Sr with HC1. 



e. After having tried the other reactions for Ba fuse some BaSO 4 with K 2 CO 3 

 and proceed as directed above. 



