CALCIUM. 281 



evolves chlorine, of which it should contain not less than 30 per cent, 

 in available form. The action of hydrochloric acid takes place thus: 



Ca(ClO), -f 2HC1 = CaCl 2 + 2HC1O; 

 2HC10 -f 2HC1 = 2H 2 O + 4C1. 



Bleaching-powder is a powerful disinfecting and bleaching agent. 



Sulphurated lime, Calx sulphurata, is a mixture of calcium sulphide and 

 sulphate, obtained by heating to redness in a crucible a mixture of dried cal- 

 cium sulphate, starch, and charcoal until the contents have lost their black 

 color. By the deoxidizing action of the coal and starch the larger portion of 

 the calcium sulphate is converted into sulphide. 



Calcium carbide, C. 2 Ca, is manufactured on a large scale by heating in 

 an electric furnace a mixture of lime and coal, or coal-tar. The combined 

 action of the high temperature and of the electric current causes this decompo* 

 sition to take place : 



CaO + 30 = CaC 2 + CO. 



Calcium carbide thus made is not pure; it forms gray or brown masses of 

 extreme hardness ; it is used extensively for generating acetylene gas, C 2 H 8 , which 

 is evolved when calcium carbide acts on water : 



C 2 Ca + H 2 O = C 2 H 2 -f- CaO. 



Tests for calcium. 

 (The reagent solution of calcium chloride, CaCl^ 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. Try the test also on solution of calcium 

 sulphate and lime-water. 



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

 white precipitate of calcium phosphate, CaHPO 4 , is produced. 



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

 salt : a white precipitate of calcium oxalate, CaC 2 O 4 , is produced, 

 which is insoluble in acetic, soluble in hydrochloric acid. Try the test 

 also on solution of calcium sulphate and lime-water. 



4. Sulphuric acid or soluble sulphates produce a white precipitate 

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

 tions of a calcium salt. Try the test also on lime-water. 



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. (See Remarks 

 on Tests, page 274.) 



6. Volatile compounds of calcium impart a reddish-yellow color to 

 the Bunsen flame. Non-volatile compounds, as the oxide, carbonate, 

 phosphate, etc., have scarcely any effect on the flame. (Try it.) These 



