86 Fertilizers 



phates vary in their content of soluble phosphoric acid, 

 due both to the variation in the content of the phosphoric 

 acid in the phosphates used as raw materials, and to the 

 excellence of the method of manufacture. In other words, 

 the superphosphates, while practically identical in so far 

 as the form of phosphoric acid is concerned, vary in their 

 total content of soluble phosphoric acid. For example, 

 superphosphates made from the animal phosphates, as 

 bone-black, bone-ash and the like, are usually richer in 

 soluble phosphoric acid than those made from animal bone, 

 or from many of the mineral phosphates, because these 

 phosphates are of such a character as to enable the manu- 

 facturer to convert all the phosphoric acid present into a 

 soluble form, and at the same time to secure a fine, dry 

 product, that may be readily handled an important 

 consideration in making superphosphates. 



Mineral phosphates, both because of their hardness and 

 of the presence of other minerals, which are attacked by 

 the acid, are less easily dissolved, and require more acid in 

 proportion to the phosphate present than those from 

 organic sources. They are also less absorbent, preventing 

 the acid from permeating the mass of the material, and 

 hence it is more difficult to secure good condition when 

 sufficient acid is used to dissolve the phosphate. In 

 making superphosphates from these materials, less acid is 

 used than is required to completely dissolve the phos- 

 phates, and there is, therefore, always present in them 

 more or less of the insoluble phosphoric acid. 



In the case of animal bone, too, less sulfuric acid is used 

 than is required to completely dissolve the phosphoric 

 acid. Otherwise, a gummy, sticky product would result, 

 due largely to the organic matter in the bone. The insolu- 

 ble phosphoric acid in bone, bone-black and bone-ash 



