174 SOILS AND FERTILIZERS 



used for making soap and glue ; they are then pul- 

 verized and sold as fertilizer under the name of bone 

 meal, which contains from 1.5 to 2.5 per cent, of nitro- 

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

 Steamed bone makes a more active fertilizer than raw 

 bone. 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 percent, 

 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 

 produced. On a poor soil 400 pounds of acid-phos- 

 phate per acre is an average application. It is usually 

 applied 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 



