i6 



Florida and Tennessee rock and bone are the common sources of 

 supply ; they contain from 60 to 80 per cent of tri-calcic phosphate and 

 when untreated are not ordinarily used for fertilizer because of their 

 insolubility. When treated with sulphuric acid, however, they fur- 

 nish the soluble and available phosphoric acid usually found in 

 commercial fertilizers. 



Soluble phosphoric acid. Mono-calcic or one-lime phosphate is a 

 product resulting from treating the insoluble phosphates with oil of 

 vitriol or sulphuric acid. In the process the sulphuric acid combines 

 with two parts of lime forming gypsum or sulphate of lime, and a 

 compound results having one lime, two water and one phosphoric 

 acid. This form of phosphoric acid is easily soluble in water. 



In the treatment of a phosphate with oil of vitriol, it is not economy 

 to add sufficient acid to act upon all of the insoluble phosphate ; 

 the insoluble phosphate remaining will be acted upon, more or less, 

 by the soluble phosphoric acid produced and rcTerted (di-calcic) or 

 two-lime phosphate will result. This compound is not soluble in 

 water but is gradually dissolved by soil water and thus becomes 

 available to plants. 



The term ^'•ai'ailaldc phosphoric acid''' is the sum of the water sol- 

 uble and reverted phosphoric acid and designates that portion of the 

 total phosphoric acid which laboratory methods show as being soluble 

 in water and neutral citrate of ammonia of a certain strength. 

 Soluble phosphoric acid is considered to have the same value whether 

 its source is from acid phosphate, dissolved bone black, or dissolved 

 bone ; the same may be said of reverted phosphoric acid. The fol- 

 lowing table gives a list of the more common sources of phosphoric 

 acid with their average composition. 



Tennessee phospliate, 



.So. Carolina rock pho.sphate,. . . 



Florida phosphate, 



Bone ash, 



15one meal,* 



Dissolved bone, 



Dissolved bone black, 



Acid phosphate,! 



Basic slag, 



♦Analyses variable. .Steamed bone ordinarily contains le.ss nitrogen and more phos- 

 phoric acid than raw bone meal. 



tTwo grades are offered, the low grades vary from 12 to 15 per cent and the better grades 

 from 15 to 19 per cent phosphoric acid. 



+By Wagner's method. 



