EXAMINATION OF COMMERCIAL FERTILIZERS 127 



Phosphoric Acid. The phraseology regarding 

 the phosphoric acid in fertilizers is often confus- 

 ing. As may have been inferred, three forms 

 of phosphoric acid are recognized in fertilizers, viz. : 



1. That readily soluble in water, consist- 

 ing presumably of calcium "superphosphate" 

 (CaH 4 (P0 4 )2). 



2. That not readily soluble in water, but 

 soluble in certain organic solutions, presumably 

 consisting of CaH(PO 4 ) or acid ferric and 

 aluminic phosphates. 



3. That insoluble both in water and in the 

 solvents for No. 2, remaining presumably in 

 the condition in which it originally existed in 

 the phosphate rock. 



Notwithstanding the fact of there being 

 numerous possible combinations between phos- 

 phoric acid and lime in a fertilizer, it is often 

 required that a report shall show the amount 

 of "bone-phosphate," to which any given per- 

 centage of phosphoric acid is equivalent. The 

 percentage of phosphoric acid multiplied by the 

 factor 2.1831 will give the desired figure. 



No. 1 is called "soluble phosphoric acid" or 

 "water-soluble phosphoric acid." 



No. 2 has been called " reverted, inverted, 

 reduced," etc., phosphoric acid, or, because it 

 is usually determined by washing it out with 

 a solution of ammonium citrate, it has been 

 called " citrate soluble." 



The sum of Nos. 1 and 2 is usually meant 



