ANALYSES OF FERTILIZERS 

 FALL SEASON, 1915: SPRING SEASON. 1916 



By B. W. Kir,c;oRE. 

 W. G. Haywoui). J. Q. Jackson, E. S. Df:war. E. B. Hart and F. C. Wiggins. 



Tlic analyses presented in this Bulletin are of samples collected by 

 the fertilizer inspectors of the Department, under the direction of the 

 rommissionor of Agriculture, durinjz; fall months of 1915 and the 

 spring months of 1916. They should receive the careful study of every 

 farmer in the State who uses fertilizers, as by comparing the analyses 

 in the Bulletin with the claims made for the fertilizers actunll.v 

 ii-t(i. the farmer can know by or before the time fertilizers are put in 

 the ground whether or not they contain the fertilizing con.stituents in 

 the amounts they were claimed to be prosont. 



TKRMS USED IN ANALYSES 



Water-sol able Phosphoric Acid. — Phosphate rock, as dug from the 

 mines, mainly in South Carolina, Florida, and Tennessee, is the chief 

 source of phosphoric acid in fertilizers. 



In its raw, or natural, state the phosjjhate has three parts of lime 

 united to the phosphoric acid (called by chemists tricalcium plios- 

 jihate). This is very insoluble in water and is not in condition to be 

 taken up readily by plants. In order to render it soluble in water and 

 fit for plant food, the rock is finely ground and treated with sulphuric 

 acid, which acts upon it in such a way as to take from the three-lime 

 phosphate two parts of its lime, thus leaving only one part of the lime 

 united to the phosphoric acid. This one-lime phosphate is wliat is 

 known as water-soluble phosphoric acid. 



Reverted PhospJioric Acid. — On long standing some of this water- 

 soluble phosphoric acid has a tendency to take lime from other sub- 

 stances in contact with it, and to become .somewhat less soluble. This 

 latter is known as reverted or gone-back phosphoric acid. This is 

 thought to contain two parts of lime in combination with the ])hosphoric 

 acid, and is thus an intermediate product between water-soluble and the 

 original rock. 



Water-soluble phosphoric acid is considered somewhat more valuable 

 than reverted, because it becomes better distributed in the soil as a con- 

 sequence of its solubility in Avator. 



Araihible Phosphoric Acid is made up of the water-soluble and re- 

 verted ; it is the sum of these two. 



