No. 7. DEPARTMENT OF AGRICULTURE. 137 



and in addition to this greatly retards the decomposition of the bone 

 in the soil. Raw bone is usually treated under pressure with steam 

 to effect the removal of the ossein or nitrogenous material and fat. 

 While the ossein contains nitrogen and its removal thus diminishes 

 the amount of nitrogen in the bone, the gelatinous material is more 

 valuable for the making of gelatine and glue. The fat is utilized 

 for making soap. Steamed bone contains from 28 to 30 per cent, of 

 phosphoric acid and about 2 per cent, of nitrogen. Its composition 

 will of course vary with the extent of steaming. The greater the 

 amount of gelatinous material removed the less nitrogen and more 

 phosphoric acid it will contain and vice versa. Bone ash is the name 

 applied to bones which have been burned in the open air. Bone black, 

 more often spoken of as animal charcoal, represents bones which 

 have been charred in vessels from which the air has been excluded. 

 The moisture fat and nitrogenous materials are thus driven off, the 

 residue consisting chiefly of insoluble tri-calcium phosphate and 

 charcoal. The presence of the latter renders the phosphoric acid 

 quite unavoidable and although bone black contains ordinarily over 

 thirty per cent, of phosphoric acid, it is not valuable in this form as 

 a fertilizer. 



Dissolved hone Hack is made from bone black by treatment with 

 sulphuric acid in the same manner that dissolved rock is manufac- 

 tured from rock phosphate and contains from 15 to 17 per cent, of 

 available phosphoric acid. 



Guanos: The natural guanos consist chiefly of the deposits of sea 

 fowls deposited in rainless regions. Chief among these may be men- 

 tioned Peruvian Guano. It is to the nitrogen compounds that guanos 

 of this class owe their chief value, although the phosphoric acid 

 they contain, 12 to 15 p^r cent., is also of very considerable value. 

 The supply of nitrogenous guano is practically exhausted so that 

 what appears on the market under this name now is mostly of an in- 

 ferior quality or is what is known as Rectified Guano. 



Phosphatic Guano: There are certain islands in the Pacific Ocean 

 and elsewhere exposed to abundant rains where the dung of sea 

 fowls has accumulated under such conditions that all the readily 

 soluble matter has been washed away, phosphate of lime remaining. 

 The supply of the best of these phosphate guanos has, however, also 

 been practically exhausted. 



BectiHed Phosphate, is the name used to designate some of the in- 

 ferior forms of guano which have been treated with sulphic acid to 

 render the phosphates soluble and have had nitrogen added in the 

 form of sulphate of ammonia. 



Basic Slag: Odorless phosphate or slag phosphate are names com- 

 monly applied to this material. It is a by-product from the manu- 

 facture of iron and steel by a process invented by Jacob Reese, of 

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