304 PRINCIPLES OF AGRICULTURAL CHEMISTRY 



phosphate. Bat guano and guano ash also contain phosphoric 

 acid. 



Raw bones consist of mineral matter, which is chiefly phos- 

 phate of lime, and organic matter, which is partly fat and partly 

 ossein, a nitrogenous body. The ossein decomposes in the soil, 

 and increases the availability of the phosphoric acid of the bone. 

 Bone contains 18 to 25 per cent, phosphoric acid and 3 to 5 per 

 cent, nitrogen. 



Raw bone meal is crushed or ground bone and its value depends 

 largely upon its fineness of division. The more finely it is 

 ground, the more rapid its action. Bone meal is a good fer- 

 tilizer, but acts slowly. 



Steamed bone meal is made from bone which has been steamed 

 to remove the fat and the nitrogenous matter, the latter being 

 made into glue or gelatine. The steaming makes the bone soft 

 and crumbly, and the phosphoric acid is more quickly available 

 than in raw bone. ' Steamed bone meal contains 22 to 29 per cent, 

 phosphoric acid and 1.5 to 2.5 per cent, nitrogen. 



Bone black is made by distilling or charring bones out of con- 

 tact with air. It consists chiefly of phosphate of lime and char- 

 coal, and is used for removing the coloring matter in the refining 

 of sugar. It contains 32 to 36 per cent, phosphoric acid. Spent 

 bone black is treated with sulphuric acid like phosphate rock. 



Rock Phosphates. Rock phosphates such as are used for 

 manufacture of acid phosphate consist chiefly of calcium phos- 

 phate, though they contain a small amount of iron and alumina. 

 They are found in South Carolina and Florida as nodules, 

 pebbles, or boulders, and in Tennessee in veins and pockets. 

 These rock phosphates range from 25 to 40 per cent, in phos- 

 phoric acid. 



Rock phosphates containing excessive amounts of carbonate of 

 lime or of oxides of iron or alumina, are not suitable for the 

 manufacture of acid phosphates, though they may be used for 

 direct application to the soil. The carbonate of lime consumes 

 sulphuric acid, while the oxide of iron and alumina react with 

 soluble phosphates, causing them to revert. 



