FERTILIZERS 23 



SOURCES OF PHOSPHORIC ACID. 



33. Phosphoric acid, or phosphorus, in fertil- 

 izers, is always found in combination with other 

 elements. Usually it is obtained from bone or phos- 

 phate rocks. As rock it cannot become readily 

 available without treatment with sulphuric acid. 

 As bone, unacidulated, it must be very finely ground 

 to be available, and when thus ground is undoubt- 

 edly the best form for citrus culture, as it is all 

 equally available and its ability to rot or ferment 

 has not been destroyed by the acid. (40) 



ACIDULATED PHOSPHATES. 



34. These are made by treating bone or phos- 

 phate rock with sulphuric acid. Their value may 

 vary according to the amount of acid used by the 

 manufacturer, and the phosphorus content of the 

 mother rock. If 800 pounds of acid were used with 

 1200 pounds of bone or rock, it would be a 40>o 

 acidulation, as 800 is 40% of 2000. 



In acidulated goods whether rock or bone, there 

 are always three forms of phosphoric acid a soluble 

 form, a "reverted" form, and an insoluble form. The 

 last is of least "commercial" value, but may have 

 very great agricultural value under proper soil con- 

 ditions. The "reverted" is of doubtful value, as it 

 has to first undergo a chemical change before becom- 

 ing available. An insoluble portion is necessary in 

 order to obtain the soluble, but does not add value 

 to the fertilizer. State laws allow the reverted to 

 be estimated as available with the water soluble, so 

 that the soluble and reverted forms constitute the 

 commercial or "available" phosphoric value of a fer- 



