88 Dilute Acids and Phoq)liorus Compounds in the Soil 



curve, on which was based the evidence for simple dissolution of a simple 

 phosphate. 



Table II. Amounts of P^^^ extracted hy dilute nitric acid of varying 

 concentration from soil {Barnfield Subsoil) in 24 hours at room 

 temperature ; 100 gms. of soil to 1000 c.c. of acid. 



The effect of time on the process. This is shown both in the Tables 

 and the Curves. Nitric acid gives the most remarkable result of all. 

 The shorter the time of extraction the more P2O5 is dissolved : in a 

 few seconds more is brought out than in 20 minutes, and considerably 

 more than after 24 hours. This holds for all strengths of acids up to 

 N/5, and beyond with poor soil, though with the richer Hoos 2C soil 

 the curves cross at N/8 (Fig. 2 e). The result can only mean that P2O5 

 is being taken back from the solution by the soil. 



Hydrochloric acid shows the same behaviour up to N/10, but at 

 greater concentrations the curves cross ; at N/5 the 24 hour curve lies 



