158 METALS AND THEIR COMBINATIONS. 



2. Add calcium sulphate : a white precipitate of strontium sul- 

 phate, SrSO 4 , is formed after a few minutes. 



3. Add sulphuric acid or a soluble sulphate : a white precipitate 

 forms at once in concentrated, after a while in dilute solutions. 



4. Add potassium chromate; a pale-yellow precipitate of stron- 

 tium chromate, SrCrO 4 , is formed, which is soluble in acetic acid 

 and in hydrochloric acid. (Potassium dichromate causes no precipi- 

 tation.) 



5. Strontium compounds color the flame beautifully red. 

 Barium, Ba u = 136.9. Occurs in nature chiefly as sulphate in 



barite or heavy spar, BaSO 4 , but also as carbonate in witherite, BaCO 3 . 

 Barium and its compounds resemble closely those of calcium and 

 strontium. 



Barium chloride, BaCl 2 + 2H 2 O, is prepared by dissolving the 

 carbonate in hydrochloric acid. It crystallizes in prismatic plates, 

 and is used as a valuable reagent. 



Barium dioxide or peroxide, BaO 2 , is made by heating the oxide to 

 a dark -red heat in the air or in oxygen. When heated above the tem- 

 perature at which it is formed, decomposition into oxide and oxygen 

 takes place. This power to absorb oxygen from air and to give it up 

 again at a higher temperature has been used as a method of preparing 

 oxygen on the large scale. Unfortunately, the barium oxide cannot 

 be used for an unlimited number of operations, as it loses the power 

 to absorb oxygen after it has been heated several times. The use 

 made of barium dioxide in preparing hydrogen dioxide has been 

 mentioned before. 



Barium dioxide is a heavy, grayish-white, amorphous powder, 

 almost insoluble in water, with which, however, it forms a hydroxide r 

 and to which it imparts an alkaline reaction. 



Barium oxide, BaO, is made by heating barium nitrate, Ba(lS"O 3 ) 2 ,, 

 which itself is made by dissolving barium carbonate in nitric acid. 



Barium salts are poisonous ; antidotes are sodium and magnesium 

 sulphate. 



Analytical reactions. 

 (Barium chloride, BaCl 2 , may be used.) 



1. The reactions of strontium with soluble carbonates, oxalates, 

 and phosphates are analogous to those of calcium solutions. 



2. Add sulphuric acid or soluble sulphates : a white precipitate of 

 barium sulphate, BaSo 4 , is produced immediately, even in dilute 

 solutions. The precipitate is insoluble in all diluted acids. 



