CHAPTER XXXIII 

 CALCIUM AND ITS COMPOUNDS 



CALCIUM belongs to a family of metallic elements which includes 

 also strontium, barium, and radium. This family resembles that 

 to which sodium and potassium belong in so far that the metals 

 are second in activity only to the two last named and that the 

 hydroxides are active bases. The chief differences are that the 

 metals of the present group are bivalent and that all the carbonates 

 and many other single compounds are insoluble. 



Compounds of calcium confer a brick-red color upon the Bunsen 

 flame. 



Calcium. The metal is made by electrolyzing melted cal- 

 cium chloride in a graphite crucible, which forms the anode. 

 The cathode is a rod of icon, one end of which clips into the fused 

 salt. The calcium, liberated at this point, adheres to the rod. 

 The latter is slowly raised, in such a way that the calcium always 

 remains in contact with the liquid. In this fashion a long " cab- 

 bage-stalk " of calcium is finally produced. 



The metal is slightly harder than lead and has a silver-white 



luster. It decomposes cold water, liberating hydrogen (p. 50). 







Calcium Carbonate CaCO 3 . The carbonate is the com- 

 monest compound of calcium. White marble is a pure variety, 

 composed of crystals compactly wedged together. Limestone 

 does not show much crystalline structure and usually contains 

 clay and other impurities. Chalk is made up of shells of minute 

 marine organisms. Shells, coral, and pearls are likewise mainly 

 calcium carbonate. Well-formed crystals (calcite, or Iceland 

 spar Fig. 93 and aragonite Fig. 94) are common. 



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