BONE FERTILIZERS 1 83 



gen and from 22 to 29 per cent, of phosphoric acid. 

 Steamed bones make a more active fertilizer than raw 

 bones. Occasionally, well-prepared bone meal is used 

 for feeding pigs and fattening stock in the same way 

 that flesh meal is used. 



224. Dissolved Bone. — When bones are treated 

 with sulphuric acid as in the manufacture of super- 

 phosphates the product is called dissolved bone. The 

 tricalcium phosphate undergoes a change to more 

 available forms, as described, and the nitrogen is ren- 

 dered more available. Dissolved bone contains from 

 2 to 3 per cent, of nitrogen and from 15 to 17 per 

 cent, of phosphoric acid. 



225. Bone-black. — When bones are distilled bone- 

 black is obtained. It is extensively employed for re- 

 fining sugar, and after it has been used and lost its 

 power of decolorizing solutions, it is sold as fertilizer. 

 It contains about 30 per cent, phosphoric acid and is a 

 concentrated phosphate fertilizer. 



226. Use of Phosphate Fertilizers. — The amount 

 of phosphoric acid advisable to apply to crops, varies 

 with the nature of the soil and the kind of crop to be pro- 

 duced. On a poor soil 400 pounds of superphosphate 

 per acre is an average application. It is usually ap- 

 plied as a top dressing just before seeding, and may be 

 placed near the hills of corn or potatoes, but not in 

 contact with the seed. It is not advisable to make 

 heavy applications of superphosphates at long inter- 



