STRONTIUM. 283 



2. Add calcium sulphate solution : a white precipitate of strontium 

 sulphate, SrSO 4 , is formed after a few minutes. This test shows that 

 the sulphate is less soluble than calcium sulphate. 



3. Add dilute sulphuric acid or a solution of a sulphate : a white 

 precipitate forms at once in concentrated, after a while in dilute, 

 solutions. 



4. Add potassium chromate solution : a pale-yellow precipitate of 

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

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

 tation.) 



5. Volatile strontium compounds color the Bunsen flame crimson 

 (see remarks in test 6 for calcium.) The color appears at the moment 

 when the substance is first introduced into the flame, whereby the color 

 can be seen, even in the presence of barium. Lithium is the only 

 other metal which gives a similar flame, but strontium may be dis- 

 tinguished from it by test 3 applied in somewhat dilute solution. 



Tests 2 and 3 combined with 5 give conclusive proof of strontium 

 compounds. Insoluble compounds are treated as directed under tests 

 for calcium. 



Barium, Ba 11 = 136.4. 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, 

 and to which it imparts an alkaline reaction. 



