66 MANUFACTURE OF FERTILIZING MATERIALS 



tions e.g., ammonium citrate solution than is the 

 natural phosphate, Cas(PO4)2, and is reckoned as 

 possessing a certain manurial value. These points 

 have to be taken into consideration in the analyti- 

 cal examination of superphosphate. 



When a mineral phosphate will not pay for con- 

 version into superphosphate it may be used for the 

 production of precipitated phosphate, which con- 

 sists mainly of "dicalcium phosphate/ ' CaHP04. 

 The preparation is conducted by dissolving the 

 phosphate in hydrochloric acid, sufficiently diluted 

 to leave siliceous matter and much of the oxides 

 of iron and aluminium undissolved. The solution 

 is neutralized by lime or chalk, when the precipi- 

 tated phosphate is thrown down. It has been 

 proposed to utilize waste calcium sulphide for 

 this precipitation, the point of neutrality' being 

 discernible by the formation of FeS; the EbS 

 evolved is collected for use as a source of sulphur. 

 As already stated, this form of calcium phosphate 

 is more vluable than Ca3(P04)2, and, being pre- 

 cipitated, is very finely divided; it contains up to 

 40 per cent of P20s, and is much used abroad. 



