498 CALCIUM. 



rated below that temperature, it yields large hexagonal prisms 

 of hyposulphite of lime, on cooling, which are colourless. They 

 contain 5 eq. of water, and are persistent in air. 



Nitrate of lime is a highly deliquescent salt, which crystal- 

 lizes with 6 eq. of water, like the nitrates of the magnesian class. 

 Jt is soluble in alcohol. 



Phosphates of lime. When earth of bones is dissolved in hy- 

 drochloric acid, and the solution afterwards neutralised by am- 

 monia, that substance is thrown down as a light gelatinous 

 precipitate, which Berzelius has distinguished as the bone- 

 earth phosphate. It contains 8 eq. of lime, with 3 eq. of phos- 

 phoric acid. When moderately dried, it retains, I find, 4 eq. of 

 water ; and as it is a tribasic phosphate, its formula probably is 

 2 (3CaO, PO 5 ) + HO, 2CaO, PO 5 + 3HO. 



On adding chloride of calcium to the tribasic subphosphate 

 of soda, a corresponding phosphate of lime precipitates, of 

 which the formula is 3CaO, PO 5 . This phosphate occurs in 

 nature, in combination with fluoride of calcium in the form of 

 hexagonal prisms, in the minerals apatite and moroxite. The 

 formula of apatite is CaF + 3 (3 CaO, PO 5 ). The native phos- 

 phates of lead occur in the same form, with chloride of lead in 

 the place of fluoride of calcium. Hedyphan is the same mine- 

 ral, in which a portion of phosphoric acid is replaced by arsenic 

 acid. 



Another tribasic phosphate of lime is obtained on pouring the 

 solution of common phosphate of soda, drop by drop, into chlo- 

 ride of calcium ; the liquid becomes acid. This precipitate is 

 slightly crystalline. Its formula, exclusive of its water of crys- 

 tallization, is HO, 2CaO, PO 5 . Berzelius describes also a bi- 

 phosphate of lime, obtained on evaporating a solution of the 

 preceding salt in nitric acid to the point of crystallization, of 

 which the probable formula is 2 HO, CaO, PO 5 . There also 

 exist a pyrophosphate and metaphosphate of lime. The inso- 

 luble phosphates of lime are soluble in water containing car- 

 bonic acid. It is possibly in this manner that phosphate of 

 lime is dissolved by the alkaline animal fluids. 



Chloride of lime, bleaching powder. This compound is equally 

 remarkable for its valuable applications in the arts, and for the 

 discussions to which its anomalous or doubtful constitution has 

 given rise. It is generally prepared by exposing hydrate of 

 lime, from the purest lime, to chlorine gas, the latter being sup- 



