JOURNAL 



k 



OF THE 



Elislia Mitchell Scientific Society 



ON THE DETERMINATION OF AVAILABLE PHOS- 

 PHORIC ACID IN FERTILIZERS CONTAINING 



COTTON SEED MEAL. 



BY F. B. DANCY, A. B. 



The term available phosphoric acid is used to denote the dif- 

 ference between the total phosphoric acid in a fertilizer and the 

 insoluble. The total phosphoric acid is the entire amount of 

 phosphoric acid, of whatever kind, that the fertilizer contains. 

 The insoluble phosphoric acid is, as generally accepted, that phos- 

 phoric acid which is left after two grams of the fertilizer, ground 

 to pass a sieve of approximately twenty meshes to the linear 

 inch, have had the soluble phosphoric acid extracted with cold 

 water and then been digested for thirty minutes, with agitation 

 every five minutes, at 65° C, with one hundred cubic centime- 

 ters of a strictly neutral solution of ammonium citrate of a spe- 

 cific gravity of 1'09, immediately after which digestion they 

 have been thoroughly washed with cold water. 



The available, then, being the difference between the total and 

 the insoluble^ it follows that insolubles being equal, the available 

 varies exactly and directly as the total; and totals being equal, 

 the available varies exactly, though inversely, as the insoluble. 



The total is a definite and fixed quantity, and there should, 

 therefore, be no material variation in its determination between 

 the work of accurate analysts. Not so with the others. The 



