4 6 



CONCLUSIONS 



Summarizing briefly, the writer thinks that the following 

 conclusions are supported by the foregoing work. 



i . Lime increases considerably the solubility of precipitated 

 ferric phosphate in i per cent citric acid solution. The nature 

 of the calcium phosphate formed depends on the relative amount 

 of lime added. The reaction takes place with moderate rapidity. 

 The solubility of dufrenite is increased by the addition of lime, 

 though not to a very marked degree. 



II. Reverted phosphate of iron, formed when phosphoric 

 acid is absorbed by ferric hydroxide, is not identical with normal 

 ferric phosphate. It is much less soluble in i per cent citric 

 acid. The addition of lime to reverted phosphate of lime in- 

 creases its solubility in i per cent citric acid. The solubility in 



hydrochloric acid is increased only to a slight extent. The 

 200 



solubility in neutral ammonium citrate solution is not increased. 

 Reverted phosphate of iron appears to be a highly basic compound. 



III. Lime applied in moderate amounts to the soils used, 

 increased the solubility of the phosphoric acid, in i per cent citric 



acid, though the increase was small. The solubilitv in 



200 



hydrochloric acid was affected to a less degree, and in one of the 

 solis used no action occurred. The latter reagent, as a solvent 

 for the available phosphoric acid in soils, is of doubtful utility. 



IV. The phosphoric acid originally present in soils is 

 much less susceptible to the action of chemical agents than re- 

 verted phosphate of iron. The latter probably becomes more 

 resistant with age. 



