824 ANNUAL. REPORT OF THE Off. Doc. 



of the amount used. But very soon it was determined that phos- 

 phoric acid was the chiefly valuable ingredient in bone and that 

 phosphates were so essential for plant growth and development, it 

 was pointed out by Professor Henslow, in 1845, in a lecture before 

 the British Association, describing the Suffolk Coprolites, that these 

 deposits of mineral i)hosphates could be of immense value for 

 application in agriculture. 



Even at this time large workable deposits of mineral phosphates 

 were known to exist, they having been almost simultaneously dis- 

 covered in several countries, notably those discovered by Buckland, 

 in England, Berthier in France and Holmes in America (Ashley 

 River, S. C, 1837), and since that time numerous other large deposits 

 have been discovered in almost every part of the world, but those 

 w^hich are of special interest in the United States are those deposits 

 of Florida, Tennessee and Virginia. 



The mode of occurrence of the best-known deposits of phosphates 

 of lime are quite erratic. They have been found in rocks of all 

 ages and of nearly every texture. Sometimes they are very pure, 

 sometimes their constituents are extremely variable. Sometimes 

 they are found in veins, sometimes in pockets and again in stratified 

 layers or beds, in connection v^'ith fossilized remains of all kinds de- 

 posited by ancient seas. 



The supply of phosphates available for agricultural purposes may 

 be divided, from a chemical standpoint, into two principal classes: 

 1st. Phosphates of lime or calcium phosphates. 

 2d. Phosphates of iron and alumina. 



(1) PHOSPHATES OF LIME OR CALCIUM PHOSPHATES. 



For the manufacture of fertilizers and for agriculture purposes, 

 phosphates of lime are generally preferred. This preference by the 

 manufacturer is due to the physical characteristics of the compounds 

 formed when treated with acid, and the preference on the part of 

 the farmer no doubt has been moulded in a measure by the prefer- 

 ences of the manufacturers, yet, to a large extent, is probably due 

 to the fact that bones are phosphates of lime, and they learned early 

 to appreciate the good etfects of bone and also in many sections 

 recognized the great A^alue of lime as a soil improver. 



In this connection, there has been given a detailed description of 

 the various sources of lime phosphates, and for their chemical dis- 

 tinctions, see under "Forms of Phosphoric Acid," on page 18. 



