CALCIUM. 157 



mixture of dried calcium sulphate, starch, and charcoal until the 

 contents have lost their black color. By the deoxidizing action of 

 coal and starch the larger portion of calcium sulphate is converted 

 into sulphide. 



Analytical reactions. 

 (Calcium chloride, CaClg, may be used.) 



1. Add to solution of a calcium salt, the carbonate of either potas- 

 sium, sodium, or ammonium: a white precipitate of calcium carbon- 

 ate, CaCO 3 , is produced. 



2. Add sodium phosphate to neutral solution of calcium : a white 

 precipitate of calcium phosphate, CaHPO 4 , is produced. 



3. Add ammonium (or potassium) oxalate to a calcium solution : a 

 white precipitate of calcium oxalate, CaC 2 O 4 , is produced, which is 

 insoluble in acetic, soluble in hydrochloric acid. 



4. Sulphuric acid or soluble sulphates produce a white precipitate 

 of calcium sulphate, CaSO 4 , in concentrated, but not in dilute solu- 

 tions of calcium. 



5. Add potassium or sodium hydroxide : a white precipitate of 

 calcium hydroxide, Ca(OH) 2 , is produced in concentrated, but not in 

 diluted solutions. Ammonia water gives no precipitate. 



6. Calcium compounds impart a reddish-yellow color to the flame. 



Stontium, Sr 11 = 87.3. Found in a few localities in the minerals 

 strontianite, SrCO 3 , and celestite, SrSO 4 . Its compounds resemble 

 those of calcium and barium. The oxide, SrO, cannot be obtained 

 easily by heating the carbonate, as this is much more stable than 

 calcium carbonate. It may, however, be readily prepared by heating 

 the nitrate. The hydroxide, Sr(OH) 2 , is formed when the oxide is 

 brought in contact with water; it is more soluble than calcium 

 hydroxide. 



Strontium nitrate, Sr(NO 3 ) 2 , Strontium chloride, SrCl 2 , Strontium 

 bromide, SrBr 2 , and Strontium iodide, SrI 2 , may be obtained by dis- 

 solving the carbonate in the respective acids. The nitrate is used 

 extensively for pyrotechnic purposes, as strontium imparts a beau- 

 tiful red color to flames ; the bromide and iodide are official. 



Analytical reactions. 

 (Strontium nitrate, Sr(NO 3 ) 2 , may be used.) 



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

 phosphates are analogous to those of calcium. 



