EOX EXPERIMEXTS WITH PHOSPHORIC ACID 

 EROM DIFEEREXT SOURCES. 



L. H. Merrill. 



Eor several years a series of experiments have been in progress 

 at mis Station designed to show the relative availabilit}" of phos- 

 phoric acid as supplied in several common forms, and also the 

 var}-ing abilit}^ of some of our common crops to obtain phos- 

 phoric acid from the same source. The results obtained up to 

 the close of 1B95 were published in the report of this Station for 

 that year, and also in Bulletin 34. While the work cannot be 

 considered complete, yet as it is necessary to leave it for a time, 

 it seems desirable to bring together all the results thus far 

 obtained, including those previously published. In order to 

 make the report complete in itself much of the explanatory mat- 

 ter is also reprinted. 



COMMERCIAL PHOSPHATES. 



Phosphate of Lime. — Xearh* all the phosphoric acid found in 

 our markets and used for fertilizing purposes is in combination 

 with lime as phosphate of hme. Three forms are in common 

 use,, viz. : 



1. Insoluble phosphate of lime. This is the form in which 

 nearly all the phosphates exist in nature and from which the 

 second and third forms described below are derived. Bones are 

 made up largely of this substance and are accordingly extensively 

 used in the preparation of commercial phosphates ; but the chief 

 source of the insoluble phosphate now used in this countr}- is 

 rock phosphate, large deposits of which are found in South 

 Carolina and Florida. It is insoluble in water and, unless finely 

 ground, its phosphoric acid is given up ver}- slowly to the plant. 

 This is the tricalcic phosphate of chemists. 



2. Soluble phosphate of lime. When the insoluble phosphate 

 is treated with dilute sulphuric acid a large part of the lime 



