The Bulletin * 21 



been particularly noted, and this point is, to my mind, a vital one. I should 

 add that it fully explains the beneficial facts your bulletin calls attention to. 



Illustrating what I mean, I am handing you a copy of an analysis of the 

 N. P. Pratt Laboratory, in which I have taken pains to have determined 

 the actual amount of free phosphoric acid in a representative sample 

 of acid phosphate thirty days old. Of course, you will recognize 

 that this free phosphoric acid, which is always present, shows in all 

 official analyses as "water-soluble" phosphoric acid, and no distinction 

 is drawn between the free phosphoric acid and the monocalcium phosphate, 

 both of which are soluble in water. Whenever free phosphoric acid is ap- 

 plied to the soil, it will immediately combine with the iron and aluminum 

 in that soil, and lose its solubility In water; but if it is brought into com- 

 bination, in process of manufacture, with ground limestone, it will combine 

 to form dicalcium phosphate, which is not only soluble in the ammonium 

 citrate solutions of the analytical methods, but it is most readily soluble 

 in the soil solution and much more available to the plant than the phosphates 

 of iron and alumina which would otherwise be presented in the soil to 

 the plant. 



Prom the manufacturer's side of the case free phosphoric acid, which 

 absolutely and undoubtedly exists to a large extent in all acid phosphates, 

 is a nuisance from every point of view. It gums up his fertilizer machin- 

 ery; it destroys his bags, and it absolutely prevents him from safely mixing, 

 in his fertilizer formulas, the useful nitrate of soda without danger of its 

 decomposition and loss through its reaction with the free phosphoric acid 

 in acid phosphate. 



We are learning something in America, and our practical Commissioners 

 of Agriculture can immensely aid to spi-e^d this information if they will go 

 after it like you are doing. Our people, both the manufacturers and the 

 farmers, have so long traveled in the beaten track of 10-2-2, or 9-2-3, 

 or 8-2-2, etc., in their fertilizer formulas, that the fertlizer manufacturer 

 and the farmer do not appear to understand the real composition and ap- 

 plicability of their goods. It is, therefore, certainly time that practical men 

 like yourself in official position should begin to spread useful information 

 for the benefit both of the manufacturer and the consumer. 



We cannot suppose that any well posted agricultural chemist could main- 

 tain that the phosphates of iron and alumina are as desirable a plant food 

 as dicalcium phosphate is, notwithstanding some of these forms of phosphoric 

 acid are soluble in the ammonium citrate solution of the analytical methods; 

 and as commercial acid phosphate through its free phosphoric acid (and, 

 also, though more slowly, through its m'onocalcium phosphate) will readily 

 form, with the soil, phosphates of iron and alumina, I have reached the 

 conviction that the laws of the States ought, by preference, to require the 

 manufacturer to convert the free phosphoric acid, which is now so rampant 

 in his acid phosphates, into dicalcium phosphate by the use of lime car- 

 bonate, in order to forestall and prevent the quick formation in the soil of 

 the phosphates of iron and alumina. 



Some of these days these facts will become so well recognized by well 

 informed agriculturists that we will wonder why we have so long shut our 

 eyes to patent chemical and plant- food facts; and as your Department is 

 the first, to my knowledge, in the Southern States to begin to see things 

 in the way they ought to be presented, I trust you will pardon this long 

 letter congratulating you upon the movement you inaugurated in North 

 Carolina. 



With assurances of my high esteem, I remain, 



Yours very truly, 



(Signed) N. P. Pratt. 



