THE COLLOIDAL PROPERTIES OF SOIL 



59 



similar manner and the peculiarities disappeared. The direct 

 action of dilute acids on soil phosphates, therefore, appears to 

 be a simple chemical reaction of the ordinary kind. 



The reverse action was investigated by swamping the 

 direct action by adding sodium phosphate to the solution : it was 



sC 



O IO 20 JO 4O SO 



P a 6 mgs. per 1000 ccs C 



FIG. 20. Showing that the experimental points obtained in the action of dilute 

 acid on soils lie on adsorption curves. 



found that P 2 O 5 was absorbed from the solution notwith- 

 standing the presence of acid, and the phenomenon was of 

 the ordinary type fitted by the equation given on page 149. 

 Absorption was not confined to phosphoric acid : it also 



