132 METALS AND THEIR COMBINATIONS. 



23. CALCIUM. 



Ca = 40 



General remarks regarding the metals of the alkaline earths. 

 The three metals, calcium, barium, and strontium, form the 

 second group of light metals. Similarly to the alkali-metals, 

 they decompose water at the ordinary temperature with libera- 

 tion of hydrogen ; their separation in the elementary state is 

 even more difficult than that of the alkali-metals. 



They differ from the latter by forming insoluble carbonates, 

 and phosphates (those of the alkalies are soluble), from the 

 earths by their soluble hydrates (those of the earths are insoluble), 

 and from all heavy metals by the solubility of their sulphides 

 (those of heavy metals are insoluble). The sulphates are either 

 insoluble (barium) or sparingly soluble (strontium and calcium). 

 The hydrates and carbonates are decomposed by heat, water or 

 carbon dioxide being expelled and the oxides formed. They 

 are bivalent elements. 



Occurrence in nature. Calcium is one of the most abundantly 

 occurring elements. As carbonate (CaC0 3 ) it is found in the 

 form of calc-spar, limestone, chalk, marble, shells of eggs and 

 mollusca, etc. ; or, as acid carbonate, dissolved in water. The 

 sulphate is found as gypsum or alabaster (CaS0 4 2H 2 0); the 

 phosphate (Ca 3 2P0 4 ) in the different phosphatic rocks (apatite, 

 etc.); the fluoride (CaFl 2 ) as fluorspar; the chloride (CaCl 2 ) in 

 some waters, and the silicate in many rocks. It also enters the 

 vegetable and animal system in various forms of combination, 

 chiefly, however, as phosphate and sulphate. 



Calcium oxide, Lime, Calx, CaO = 56 (Oxide of calcium, Quick- 

 lime, Burned lime), is obtained on a large scale by the common 

 process of lime-burning, which is the heating of limestone or 

 any other calcium carbonate to about 800, in the so-called lime- 

 kilns. On a small scale the decomposition may be accomplished 

 in a suitable crucible over a blowpipe flame : 



CaCO 3 = CaO + C0 2 . 



The pieces of oxide thus formed still retain the shape and 

 size of the carbonate used for decomposition. 



