CHAPTER VII. 



PHOSPHATES. 



Phosphates are those materials that contain phosphoric acid. 

 The phosphates occur as phosphate of Hme, iron and alumina, 

 in which compounds the phosphoric acid is united with lime, 

 iron and alumina respectively. Since the phosphoric acid in fer- 

 tilizers is derived mainly from phosphate of lime we will limit 

 our treatment of the subject to the important materials compos- 

 ing this group. 



The phosphates of lime occur as organic, organic and mineral, 

 and mineral compounds. 



Bones. — The chief source of phosphoric acid from the organic 

 phosphates of hme are bones. The composition of bones is 

 variable. The bones from old mature animals are richer in phos- 

 phate of lime than bones from young animals. Dififerent bones 

 from the same animal also show a variable composition, as the 

 harder more compact bones are richer in phosphate of lime than 

 the softer, porous ones. 



Raw Bone-Meal. — This is the finely ground product derived 

 from raw bones and it contains all the constituents of thenii. 

 It carries considerable organic matter much of which is in the 

 form of fats, which makes it hard to grind and to handle on the 

 market. The presence of organic matter makes it objectionable. 

 The fatty matter, which slowly decomposes, tends to make this 

 fertilizer very slowly available for plant food and so it is called 

 a slow acting fertilizer. Raw bone-meal usually contains about 

 19 to 25 per cent, of phosphoric acid and 2 to 4 per cent, of 

 nitrogen, with an average of 22 per cent, of phosphoric acid 

 and 3.5 per cent, of nitrogen.* 



The phosphates are sold to the trade on the basis of tri- 

 calcium phosphate present. To convert tricalcium phosphate 

 to phosphoric acid, multiply by the factor 0.4576 and to get the 

 equivalent of tricalcium phosphate from a given percentage of 

 phosphoric acid multiply, by 2.185. 



Steamed Bone-Meal. — Most of the bone sold for fertilizing 



