156 



MANURES. 



VII. 



crystals of the same composition as the mineral gypsum, 

 CaSO 4 .2H 2 0. This causes the product to "set" or "dry," 

 and after this it is ground in suitable mills and screened and 

 is ready for the market. 



" Double superphosphate" is sometimes made by preparing 

 phosphoric acid by the action of excess of acid upon one por- 

 tion of the phosphate, removing the greater part of the calcium 

 sulphate, and adding the phosphoric acid to another portion of 

 the original phosphate, thus converting the tricalcium into 

 monocalcium phosphate 



Ca 8 P A + 4H 3 P0 4 - 3CaH 4 P. 2 O H . 



Such a product is very concentrated and may contain as much 

 as 40 % of phosphoric acid, nearly all in the soluble form . 



Manures similar to superphosphate are made by the action 

 of sulphuric acid upon bone-ash, bones, or guano. These 

 resemble mineral superphosphates so far as the state of 

 existence of their phosphoric acid is concerned, but may, of 

 course, contain nitrogenous constituents. 



The following table gives the amount of the most important 

 fertilising ingredients in various forms of manures of this class, 

 expressed in the usual conventional way : 



Mineral super- 

 phosphate. 



Dissolved 

 bones. 



Dissolved 



Peruvian 



guano. 



Dissolved 

 bone-ash. 



Monocalcium phosphate. . . 



= tricalcium phosphate 



rendered soluble 

 Insoluble phosphates 

 Calcium sulphate ( + 2H./)) 

 Alkaline salts ... 

 Ammonia 



1520 915 913 2029 



2432 



14 



5254 



22-5 



1424 

 16-21 

 2333 

 2-53-5 

 23-5 



1420 

 512 



1630 

 610 

 710 



3145 



16 

 4651 

 12-5 

 00-2 



A word of explanation as to the commercial methods of 

 expressing analytical results may be here given. It is the 

 custom to indicate by, say, " 24 per cent, soluble phosphates" 

 that 24 is the amount of tricalcium phosphate which contains 

 the same quantity of phosphoric acid as is present in the 

 soluble (monocalcium) phosphates contained in 100 parts of 

 manure. 



