BARIUM, STRONTIUM, AND CALCIUM, 233 



posed of chlorine and oxygen. Perhaps the reason that 

 the old name chloride of lime is retained is that it is diffi- 

 cult to fix upon a proper name for this mixture of two 

 salts. 



Chloride of lime is made by exposing slaked lime, slightly 

 moistened, to chlorine gas ; this is eagerly absorbed by the 

 lime, forming calcium hypochlorite and calcium chloride, 

 while some of the calcium hydrate remains unchanged. 

 The bleaching powder thus prepared is very uncertain as 

 to the amount of its bleaching properties, and these are 

 very liable to be impaired by exposure to air and other 

 circumstances. As offered in the market it varies much in 

 its value according to its age, care in keeping it, and also 

 care in its original preparation. 



324. Calcium Phosphate, Ca 3 (PO 4 ) 2 . While carbonate of 

 lime is the mineral out of which all shells are made, the 

 phosphate of calcium, mixed with very small quantities of 

 the carbonate and sulphate and fluoride, forms the mineral 

 portion of bones. It is estimated that the amount of phos- 

 phorus contained in this salt in the bones of a full-grown 

 man is from 500 to 800 grammes. Phosphorus is obtained 

 from bones, and the process is described in 253. As phos- 

 phate of lime exists so largely in animals, it is necessary 

 that it be provided for them in the food that they eat. 

 Accordingly it is present in all cereal grains, in leguminous 

 plants, and many other vegetables, the soil of course fur- 

 nishing it to them. It is not only, then, the animal sub- 

 stance in bones, the gelatine, that makes them a good ma- 

 nure ; but the mineral part is of essential service, to some 

 crops especially, if the soil be at all deficient in phosphate 

 of lime. 



Calcium phosphate occurs abundantly also in the min- 

 eral kingdom, as you will learn more particularly in the 

 study of Mineralogy, Part III. 



