CALCIUM. 133 



Lime is a white, odorless, amorphous, infusible substance, of 

 alkaline taste and reaction; exposed to the air it gradually ab- 

 sorbs moisture and carbon dioxide, the mixture thus formed 

 being known as air-slaked lime. 



Lime occupies among bases a position similar to that of 

 sulphuric acid among acids, and is used directly or indirectly 

 in many branches of chemical manufacture. 



Calcium hydrate, Ca2HO (Slaked lime). When water is sprinkled 

 upon pieces of calcium oxide, the two substances combine chemi- 

 cally, liberating much heat; the pieces swell up, and are gradu- 

 ally converted into a dry, white powder, which is the slaked 

 lime. When this is mixed with water, the so-called milk of lime 

 is formed. 



Lime-water, Liquor calcis. This is a saturated solution of cal- 

 cium hydrate in water; 10,000 parts of the latter dissolving 

 about 15 parts of calcium hydrate. In making lime-water, 1 

 part of calcium oxide is slaked and stirred for about half an 

 hour with 30 parts of water. The mixture is then allowed to 

 settle, and the liquid, containing besides calcium hydrate the 

 salts of the alkali-metals which may have been present in the 

 lime, is decanted and thrown away. To the calcium hydrate 

 left, and thus purified, 300 parts of water are added and occa- 

 sionally shaken in a well-stoppered bottle, from which the clear 

 liquid may be poured off for use. 



Lime-water is a colorless, odorless liquid, having a feebly 

 caustic taste, and an alkaline reaction. When heated to boiling 

 it becomes turbid by precipitation of calcium hydrate (or perhaps 

 dioxide). Carbon dioxide causes a precipitation of calcium 

 carbonate. 



Calcium carbonate, Calcii carbonas prsecipitatus, CaC0 3 = 100 

 (Carbonate of calcium). Precipitated carbonate of calcium is ob- 

 tained as a white, tasteless, neutral, impalpable powder by 

 mixing solutions of calcium chloride and sodium carbonate : 



Cad 2 -f Na 2 CO 3 = 2NaCl + CaCO 3 . 



Calcium sulphate, CaS0 4 = 136 (Sulphate of calcium, Plaster of 

 Paris). It has been mentioned above, that the mineral gypsum 



