282 METALS AND THEIR COMBINATIONS. 



should first be moistened with strong hydrochloric acid to convert 

 them to the volatile chloride before introducing into the flame. (See 

 note to test 4 for potassium.) 



Test 3, done in dilute solution, combined with tests 4 and 6, is 

 decisive for recognizing calcium compounds. The oxide, carbonate, 

 and phosphate may be dissolved by dilute hydrochloric acid for tests. 

 The phosphate solution cannot be neutralized without precipitation, 

 but if left weakly acid and considerably diluted test 3 can be applied. 



The above tests are examples of more or less complete reactions, due to the 

 formation of insoluble or sparingly soluble substances, and their removal from 

 the field of action by precipitation (see pages 116 and 193). The ionic equa- 

 tions in the tests are as follows : 



Test 1. Ca" -f 2C1' + 2Na' + CO 3 " = CaCO 3 + 2Na" + 2C1'; 

 Ca" + SO/' + 2Na' + CO 3 " = CaCO 3 + 2Na' + SO/'; 

 Ca" + 2(OH)' + 2Na- + CO 3 " - CaCO 3 + 2Na' + 2(OH)'. 



Test 2. Ca" + 2C1' + 2Na' + HPO 4 " = CaHPO 4 + 2Na- + 2C1'; 

 Test 3. Ca" + 2C1' + 2NH 4 '+ C,O 4 " = CaC 2 O 4 + 2NH 4 - -f- 2C1'. 

 The equations for sulphate and hydroxide of calcium are similar (see test 1). 

 Test 4. Ca" + 2C1' + 2H- + SO/' = CaSO 4 + 2H- 4- 2C1'; 

 Test 5. Ca" + 2C1' + 2Na + 2(OH) 7 = Ca(OH) 2 + 2Na -f- 2C1'. 



The ionic equations in the tests for strontium and barium are like those for 

 calcium. 



Strontium, Sr" = 86.94. 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. 



Tests for strontium. 



(Use about a 5 per cent, solution of strontium nitrate.) 



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

 phosphates are analogous to those of calcium. 



