806 ANNUAL REPORT OF THE Off. Doc. 



PHOSPHATES. 



PHOSPHATIC OR PHOSPHORIC ACID FERTILIZERS. 



THE DIFFERENT SOURCES AND FORMS OF PHOSPHORIC ACID USED IN 

 AGRICULTURE, AND THEIR METHODS OF PREPARATION AND 



APPLICATION. 



Bv H. J. Pattekson. 

 Director arid Chernsit of Maryland Agricultnral Experiment Station. 



INTRODUCTION. 



Phosphates possess considerable interest to the agriculturist 

 beyond their great importance in the every-day practical considera- 

 tion of the means for maintaining and increasing the productive 

 capacity of the land. 



The foundation of the present system of agricultural chemistry 

 was laid in connection with the study of the use of phosphates. 

 The growth of agricultural chemistry, with the research based upon 

 it, has brought about the development of the other sciences as re- 

 lated to agriculture and so produced all that may be encompassed 

 by the term "Modern Scientific Agriculture." And phosphates may 

 be said to be the initial of all that which may be hoped for as a 

 result of the vast and world-wide efforts now being put forth in 

 all classes of agricultural research. 



HISTORICAL. 



There is no definite record as to the time when the use of phos- 

 phates first came into existence, but as far as can be judged from 

 the early records and writings upon agricultural topics, there seems 

 to be but little doubt that the first commercial fertilizers ever used 

 were chiefly phosphatic in their nature, and the good results which 

 attended their application was mainly due to phosphoric acid. 



From some notes of Varro it might appear that phosphates may 

 have been used to some extent even B. C. but it is very sure, that 

 even if such were the case,it w^as not until comparatively recent times 

 that the value and need of phosphoric acid was actually recognized. 

 Writers record that upon the first invasion of Britain by the Romans, 



