Phosphates 



no appreciable results — sometimes no results at all ; 

 so that some soils naturally rich in mineral phos- 

 phates will still respond to soluble phosphates. 

 Simply ground they are still frequently used for 

 the adulteration of other manures, principally com- 

 pound manures, also guano, superphosphates, and 

 basic slag, and in this way they have done bad 

 service. 



Good samples of mineral phosphates should 

 contain from 50 to 75 per cent, tribasic phosphate, 

 which corresponds to 23 to 34 per cent, phosphoric 

 anhydride, P2O5 (anhydric phosphoric acid). 



Assimilable Phosphates. 



Phosphates to be assimilable, ought to be 

 soluble in water, as is the case with superphosphates, 

 or soluble in weak acids — as is the case with reverted 

 superphosphate and basic slag, or capable of being 

 rendered soluble in the soil, as may occur with 

 tricalcic phosphates. 



Trials which have given contradictory results 

 have been made on the strength of comparative 

 experiments, offering solutions of a problem which 

 has not been discussed in the right light : for 

 example, a trial in acid earth by means of super- 

 phosphate and tricalcic phosphate. 



Generally speaking, by using superphosphate in 

 neutral soil and in alkaline soil needing no lime, or 

 even in a light acid soil, when we want to obtain a 

 rapid action, good results will be obtained. Mmeral 

 phosphates should not be employed in such cases. 

 As a rule basic slag should be used in soils requiring 

 lime, in neutral or acid soils, and in soils that 



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