that the active constituents of manure are removed in the soil by 

 these compounds, and that the new compounds are decomposed 

 slowly for the use of the plant. In a subsequent investigation 1 , 

 he always found phosphoric acid combined with aluminum and 

 iron, and never with calcium and magnesium. He added solu- 

 tions of calcium phosphate to the pure hydroxides of aluminum 

 and iron, and to soil, and found after a few days that the filtered 

 water contained calcium but no trace of phosphoric acid. 



Deherain 2 examined a large number of soils. Some of these 

 contained phosphoric acid insoluble in water charged with carbon 

 dioxide, while others gave up phosphoric acid to this solvent. 

 Soils containing compounds insoluble in carbon dioxide water 

 gave up phosphoric acid to water containing calcium carbonate 

 ammonium carbonate. A solution of calcium carbonate in water 

 charged with carbon dioxide acted on iron phosphate producing 

 calcium phosphate. 



The role of phosphoric acid in the soil was taken up by 

 Liebig 3 in connection with his extended investigations on soil 

 absorption. He determined the solvent effect of sodium chloride, 

 sodium nitrate, and ammonium sulphate on phosphates of calcium 

 and magnesium. In all cases appreciable quantities of the phos- 

 phates were dissolved. When the solutions thus made were 

 added to soil the phosphoric acid was absorbed. Such changes 

 were thought to have a favorable influence in bringing about the 

 distribution of phosphoric acid in the soil. 



Knop 4 confirmed the observations of Thenard regarding the 

 role of iron and aluminum hydroxides in soil absorption. He 

 showed that phosphoric acid was fixed in greater amount and 

 more rapidly when these compounds were added to soils, and 

 that soils containing large quantities had greater reverting prop- 

 erties than those containing small amounts. Data were not 

 accessible. 



Peters 5 endeavored to ascertain the state in which phosphoric 

 acid is held in soils. He manured a soil with bone dust and 



1 Compt. rend., 46, 212. 



2 Ibid., 47, 47, 988. 



3 Am. Chem. Phar., 106, 185. 



4 Jahresbericht, 1865, 804. 



5 Ann. Landw., 1867, 31. 



