No. 6. 



DEPARTMENT OF AGRICULTURE. 



823 



The material, before treatment, is always fiuely ground so as to 

 facilitate the chemical action. After the treatment has been com- 

 pleted the mass is dried and ground for use. 



The materials which are chietly used as sources of phosphoric acid 

 in fertilizers are given in the following table, together with their 

 average composition : 



TABLE 7. 

 Giving the Approximate Amount of Phosphoric Acid in Fertilizing Materials. 



Apatite, . 

 Bone ash. 

 Bone 

 Bone 

 Bone 



black, 



black (dissolved) 



meal 



Bone meal (from glue factory), ... 



Bone meal (dibsolved), 



Carribean guano, 



Cuban guano 



Double super-phosphate 



Florida rock 



Florida soft phosphate 



Keystone concentrated phosphate, 



Mona Island phosphate 



Navassa phosphate, 



Orchilla guano, 



Peruvian guano . 



South Carolina rock (ground), ... 



South Carolina rock (floats) 



South Carolina rock (dissolved), .. 



Slag phosphate (American), 



Slag phosphate (German) 



Tennessee phosphate rock 



16.0 

 0.4 



10.0 



0.7 

 6.5 i 

 6.5 i 

 5.0 



0.3 



15.6 



22.4 



2.5 



4.0 



0.3 



38. 2 

 7.5 



9.2 

 14.3 



4.6 



10.5 



3.8 

 0.3 

 0.5 

 3.5 



4.9 

 27.7 

 27.5 



2.0 



38.0 j 



35.9 



28. 3 ! 



17.0 : 334 



22.5 138 



28.9 130 



17.5 300 



18.9 



17.9 



44.0 8C0 



30.0 



24.0 



47.7 770 



21.8 150 



34.3 



26.8 



13.3 168 



28.0 6 



28.0 10 



16.0 L'80 



21.0 



30.0 



35.0 



760 

 718 

 667 

 340 

 450 

 578 

 350 

 378 

 358 

 88b 

 600 

 480 

 950 

 436 

 686 

 536 

 266 

 560 

 560 

 320 

 420 

 600 

 700 



SOURCES OF SUPPLY OP PHOSPHORIC ACID. 



A study of the figures given in the preceding tables, particularly 

 those of Table 4, leave but little doubt but that there must come a 

 time with all soils, under normal conditions of cropping, when their 

 natural contents of phosphoric acid will be much reduced, if not 

 exhausted. This has been the experience of farmers the world over. 

 Happily, nature made ample provisions for supplying all require- 

 ments for this valuable and essential plant food. 



The first material used for furnishing phosphoric acid was bone, 

 .and the chief reliance was placed in this source for many years and 

 even now it is very popular and furnishes a considerable percentage 



