CHEMICAL MANURES. 97 



acid and lime. Phosphoric acid itself is formed from phosphorus 

 and oxygen : 



Phosphorus ......................................................... 31 



Oxygen .............................................................. 40 



71 



Of the phosphates, phosphoric acid is the active part. Chemists 

 are accustomed to represent phosphoric acid by the symbol, 



Ph0 5 . 



Now, PhO 5 , or 71 phosphoric acid, being a fixed term, we know 

 the principal kinds of phosphates of lime : 



Pho S Ca 



Ph 5 { 2HO, 

 which in hundreds is 



Phosphoric acid ................................................ 60.68 



Lime(CaO) ..................................................... 23.93 



Water (HO)..., ............................................... 15.39 



10(KOO 



This product has received the name of acid phosphate of lime. It 

 is prepared by treating bones or phosphates of mineral origin with 

 sulphuric acid. The acid phosphate is then mixed with sulphate of 

 lime. Under this form it receives the name of superphosphate of lime. 

 It contains from 15 to 18 per cent, of phosphoric acid, and is sold 

 at $3.04 the 200 Ibs. 



The second phosphate is expressed by the symbol, 



s HO, 

 or in hundreds 



Phosphoric acid ................................................ 52.20 



Lime ............................................................. 41.18 



Water ............................................................ 6\G2 



fOG.OO 



It differs from the first in the proportion of lime, which is greater. 

 This phosphate is not found in commerce. It has remarkable proper- 

 ties, of which it is useless to speak, since Ave cannot procure it. 

 The symbol of the last phosphate is, 



PhO 5 3CaO. 

 Its composition in 100 parts is 



Phosphoric acid ................................................ 45.81 



Lime ............................................................. 54.19 



100.00 



You see the proportion of phosphoric acid in the phosphates is 

 expressed by 



1st ................................................................. 60.68 



2d.. .............................................................. 52.20 



3d ................................................................. 45.80 



The last, which is least rich in phosphoric acid, is the phosphate 

 of bones ; it is found in nature in the form of nodules. 



7 



