PHOSPHORUS 



189 



insure a small increase rather than a decrease in the future 

 years. 



More specific data concerning the use of raw rock phosphate, 

 the results of the most careful experiments, and the comparative 

 value of different forms of phosphorus are more fully discussed 

 in the following pages, after some consideration of organic matter. 



Acid phosphate. Acid phosphate is the name of a manufactured 

 product, not of a chemical' compound. 



Chemically, there are two acid phosphates of calcium, (i) the 

 monocalcium phosphate, CaH 4 (PO 4 ) 2 , and (2) the dicalcium phos- 

 phate, Ca 2 H 2 (PO 4 ) 2 . These chemical compounds, together with 

 tricalcium phosphate and tetracalcium phosphate, phosphoric acid, 

 phosphorus pentoxid, and phosphorus, itself, form a very impor- 

 tant and interesting series. For the sake of simplicity and uni- 

 formity, two atoms of phosphorus are given in each case, this being 

 necessary in some cases : 



Of these substances, tricalcium phosphate is the only one that 

 occurs in nature. The element phosphorus takes fire when exposed 

 to the air, two atoms of phosphorus uniting with five atoms of 

 oxygen to form phosphorus pentoxid, sometimes called phosphoric 

 oxid. This compound is the most powerful dehydrating agent 

 known in chemistry, having power to abstract water from many 

 other substances. It unites with water to form true phosphoric 

 acid, H 3 PO 4 , or H 6 (PO 4 ) 2 . This is one of the strong acids, and if it 

 comes in contact with calcium carbonate, for example, it takes up 

 one, two, and, finally, three bivalent atoms of calcium in place of 

 the univalent hydrogen atoms, and thus forms acid monocalcium 



