The composition of acid phosphate varies according to the grade ; 

 the low grade superphosphate runs from 12 1015 per cent total 

 phosphoric acid; the better grades run from 15 to 19 per cent total 

 phosphoric acid, mostly in available form if properly manufactured. 



Dissolved Bone Black. The bone black from which this material 

 is made, is a by-product from sugar refining establishments where 

 the charred bone has been used for decolorizing sugar solutions. 

 After it has thus served its usefulness, it is treated with sulphuric 

 acid and furnishes a superior source of available phosphoric acid. 

 The average of 38 analyses made at this laboratory shows 17.56 per 

 cent of total phosphoric acid, of which 16.38 per cent was available. 

 The expression "available phosphoric acid" means the sum of the 

 water soluble and citrate soluble phosphoric acid. 



Thomas Fhosphatic Slag. This material is obtained as a by- 

 product in the manufacture of phosphorous free metallic iron from 

 phosphorous containing iron ores ; it is a valuable source of phos- 

 phoric acid and has been used for many years in Germany and 

 other European countries. Its use in this country dates back to 

 1888. Dr. C. A. Goessmann was one of the first in the United 

 States to study this material and recognized its worth as a source 

 of phosphoric acid for general farm crops. The average of 15 

 analyses made at this laboratory gives a total phosphoric acid con- 

 tent of 18.63 percent; the slag also contains an average lime con- 

 tent of 45.50 per cent of which 6 to 7 is in the form of free cal- 

 cium oxide. The phosphoric acid in slag meal is present probably 

 in combination with the lime as tetra-calcium phosphate. 



The trade values in the following table show the 

 Trade Values, average cost per pound, at retail, of the various 



forms of nitrogen, phosphoric acid and potash as 

 they were found and quoted in raw materials and chemicals in the 

 markets in New England, New York and New Jersey during the six 

 months preceding March i. 1907. 



