Tricalcic or insoluble lime phosphate has the formula 3 

 P, 5 . 



Basic slag has the formula 4 Ca O, P 2 O 5 . To put this more 

 graphically, although less scientifically, the insoluble phosphate 

 would be composed thus : 

 Lime ) 



Lime [ Phosphoric acid. 

 Lime ) 

 Basic slag. 

 Lime } 



Lime f p hos phoric acid. 

 Lime | 

 Lime ) 



It is a well-known fact that the more lime there is in combina- 

 tion with phosphoric acid the more insoluble the compound is. 

 Basic slag is an exception ; it is more soluble than the tricalcic 

 phosphate in any other mineral or animal phosphate. Before we 

 explain the reason for the basic slag being more soluble, we will 

 show the formula of two other phosphates. 



Soluble or mono-calcic phosphate Ca O, 2 (H 2 O), P 2 O 5 obtained 



by treating the tricalcic phosphate with an acid thus : 3 Ca O, 



P 2 O 5 -4- 2 H 2 SO 4 = Ca O, 2 (H 2 O), P 2 O 5 -+- 2 Ca SO 4 , the soluble 



phosphate may be shown thus : 



Lime 



Water 



Water 



The other phosphate called dicalcic or precipitated phosphate 

 lime and reverted phosphates 2 Ca O, H 2 O, P 2 O 5 

 or Lime j 



Lime Phosphoric acid. 

 Water I 



The mono-calcic or soluble has 56 par s of lime for every 142 

 parts of phosphoric acid and is ihe most soluble. The dicalcic 

 phosphate has 112 parts of lime for every 142 points of phosphoric 

 acid, it is far less soluble than the mono-calcic, but more soluble than 

 the tricalcic. 



The tricalcic phosphate has 168 parts of lime for every 142 

 parts of phosphoric acid, it is the most insoluble of phosphates. 



The basic slag li;is 224 parts ( f lime for evvry 142 parts of 

 phosphoric acid. Although it has more lime th;m the tricalcic it is 

 much more soluble than and differs little Irom the dicalcic. 



The reason for this is, that the tetrabasic phosphate is a super- 

 saturated salt. It has less chemical affinity to resist decomposition 

 when brought in contact with any substance or agency that can 

 cause decomposition. 



Professor Wagner has experimented with basic slag, super- 

 phosphates and other manures, as to the amount of phosphoric acid 



> Phosphoric acid. 



) 



ed dicalcic or precipitated phosphate of 



